Management Of Bone Loss In Revision Hip Biology Essay

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Total hip replacement is one of the most successful surgical procedures. With aging of the population the demand for the procedure is increasing steadily worldwide. Over 270 000 hip replacements are performed annually in the United States alone and the annual volume of hip joint replacement is projected to double over the next decade (Sedrakyan 2011). Although very successful procedure, significant percentage of patients undergoing total hip arthroplasty require revision within 10 years after the surgery because of implant failure due to infection, dislocation, periprosthetic fracture, wear and loosening of the prosthesis, pain or other reasons for failure. Improvements in implant design and surgical technique have improved the mid-term outcomes after primary total hip arthroplasty, however, the prevalence of revision hip surgery did not decrease. A steady trend of increase of revisions is observed and it is predicted to continue into the future. As a consequence the rate of revision hip arthroplasty is increasing as well (Bozic KJ 2009). The high rate and costs of revision procedures imposes high demands on both surgeon and healthcare system. Moreover, the cost of hip replacement is expected to triple in just five years (Bozic KJ 2011). Advanced treatment approaches, implant designs and surgical techniques aim at improving clinical outcomes after these complex surgeries.

...

In 2009, Bozic et al reviewed the most common causes for revision hip arthroplasty (). Instability, aseptic loosening and infection were reported as the main indications for revision surgery. This study underlined the need for a complex approach to evaluation and management of patients with implant failure after hip replacement. Such approach will guarantee precise diagnosis, proper selection of revision implant and surgical approach, uncomplicated surgery, and optimal clinical outcome.

Bone loss is the major challenge in revision setting

Patient evaluation

There is a wide spectrum of signs and complains that can occur in the setting of a failed hip prosthesis. Pain is the most common complain associated with failed prosthesis. Painful hip arthroplasty represents a common complication in about 00% of patients after total hip arthroplasty. Most of this painful hips require revision.

Groin pain can be referred to implant failure easily whereas occasional hip pain, pain in the buttock, knee pain or migrating pain can have different etiology. Other diseases and conditions such as disk disease, radiculopathy, inguinal or femoral hernia, pelvic infections, tumors, and trauma may have manifestations similar to that of failed prosthesis.

The differential diagnosis of hip pain requires a careful history and examination. In simple cases the reason could be identified with clinical examinations and standard radiographs only. Thorough examination elicits the underlying cause of hip complains such as infection, neurological injury, referred pain, wear, aseptic loosening or instability. In many cases the diagnosis is a challenge to the surgeon. In addition to clinical history and physical examination, radiographic examination and advanced imaging techniques could help establish exact location of pain, and its possible connection with the implant. Additional radiographic examinations as well as an algorithmic approach with special diagnostic imaging and tests helps to establish precise diagnosis. Roe - AP pelvis radiographs, Lat, frog-leg lateral view

CT and 3-D computed tomography are often helpful in establishing periprosthetic osteolysis and its severity.

The information obtained in this studies help assess stability of the implant, possible mechanisms for failure, extent of osteolysis, and thus guide treatment approach.

Angiography Taylor

Algorithm

Guidelines and algorithms for evaluation of painful hip arthroplasty have been published in the literature and implemented in practice (). Certain approach helps eliminate infection of the failed hip that would change treatment approach and could exclude one-stage revision ().

Classification systems for bone defects Taylor

It is important to have a practical, relatively simple classification system of bone defects associated with loose hip implants. The use of a radiographic classification system helps to establish the severity and localization of bone defects, and to guide treatment decisions. It should allows the surgeon to be prepared for the possible intraoperative findings and to plan adequate treatment approach. Various classification systems have been described in the literature (acet - D'Antonio 1989, Paprosky 1994, Gross 1998, fem - )

the classification system

(Paprosky WG 1994, ).

AAOS Classification

The American Academy of Orthopaedic Surgeons (AAOS) classification system of bone defects, described by D'Antonio et al identifies the pattern and localization of osteolysis but does not quantify the bone loss (D'Antonio 1989, 1992, fem ...).

It is the most widely used classification system in the literature.

Paproski Classification

Perhaps the second most widely used classification system, the Paprosky Classification (Paprosky WG 1994, ...) was developed to establish bone defect type, size, and localization in order to allow selection of appropriate cementless reconstructive option for a given bone loss pattern. The key advantage of the classification is assessment the host bone ability to provide initial stability of a cementless implant until bone ingrowth occurs. The bone defects are usually classified on the basis of plain radiographs. However, final assessment is made intaroperatively, after removal of the failed implant and thorough debridement of the host bone. Intraoperative assessment of implant stability is made with help of trial components. The remaining host bone determines the stability of the implant and the type of the defect.

bone grafts available Gross

Hip center Chen 2000

Preoperative planning

The principle aims in revision hip arthroplasty are to achieve stable bone bed, secure implant fixation and to restore hip center and joint kinematics. The type and severity of host bone loss determines the method of reconstruction. Careful preopertive planning improves effectiveness during surgery, and helps distinguish more complex alternatives for reconstruction if needed.

Thorough clinical and radiographic examination is essential for determining the extent and severity of bone loss, quality of the host bone, exclusion of infection, additional deformities, and potentially confounding factors. Computed tomography may be needed in the presence of massive bone loss. In case of medial migration of the failed components angiography with contrast medium should be considered. Preoperative planning is critical for the assessment of the need of graft, tools for implant removal, and selection of proper components available at the time of surgery. Appropriate surgical exposure should be planned with extensile approach often necessary. Classification system of bone defects based on radiographs that assesses the severity of bone loss according to the type of fixation for a given bone loss pattern is beneficial. In our practice, we prefer the Paproski classification system. Any attempt should be made to identify the failed implant. The implant manufacturer should be contacted for implant-specific extraction devices if available. In case of isolated partial revision it is advisable to have an option for partial (liner or head) exchange.

Surgical approaches in revision arthroplasty

Revision hip arthroplasty may require a variety of approaches in different revision situations for adequate exposure of the femur and acetabulum. Usually arthroplasty surgeons are familiar and most comfortable with a certain approach and use it in most surgeries. However, in order to obtain reproducible results after revision of most difficult cases, surgeons should be familiar with all approaches to the hip joint. Next to standard approaches used in primary total hip arthroplasty, extensile approaches were developed in order to minimize damage to the host bone, safely remove the loose implant and provide good visualization for correct insertion of the revision components.

The aims of revision surgery are to extract the failed prosthesis with minimal soft tissue and bone damage, to restore bone loss, and to implant prosthesis with stable and durable fixation. Ultimate goals are long-lasting and painless joint function.

Revising failed prosthesis is a technically demanding procedure complicated by usually compromised host bone and the need to remove the failed implant.

Contained defects can be reconstructed through any conventional approach. For uncontained defects we prefer to have wide access and, therefore, we use transtrochanteric approach or trochanteric slide with preserved insertion of vastus lateralis. If greater exposure is needed extended trochanteric osteotomy is advisable.

Posterolateral approach Issack

Extended trochanteric osteotomy

The extended trochanteric osteotomy is one of the significant achievement in revision surgery. It is safe and straightforward, saving time and minimizing risk of fracture during cement and failed implant removal. It can be combined with cementless stem with distal fixation with favorable clinical results published in the literature (Miner TM 2001).

(Fig ETO)

The phenomenon of varus remodeling occurs in 20% to 30% of loose stems (Barrack R 2003). With an extended trochanteric osteotomy the femur is modeled around the stem. This allows for the stem to be implanted in optimal orientation. The bone has great potential for remodeling and can obtain different shapes, so it usually heals without complications.

- advantages and limitations: in the light of bone quality, soft tissue healing, hardware removal, expected type of fixation of the revision implant, osteolytic defects management and bone grafting.

Surgical revision options

Majority of hip revisions could be performed using cementing technique. However, patients with severe bone loss and poor bone quality require complex alternative for revision.

Options for Femoral revision

Cemented fixation

Various studies publish the outcomes after cemented femoral revision (Amstutz 1982, Callaghan JJ 1985, Pellicci pm 1982). Utilization of the primary cementing technique produced disappointing results (Amstutz 1982, Hunter GA 1979). Gaining more extensive experience yielded acceptable short- to mid-term results (Callaghan JJ 1985, Pellicci pm 1982, Kavanagh 1985). Re-revision rates ranging from 4.3% to 6.0% and radiographic loosening ranging from 12% to 44% after mid-term follow-up of 3.4 to 4.5 years were reported (Table 1). However, long-term studies showed suboptimal outcomes after revision with early cementing technique. At 8.1-year follow-up of the initial group of cemented revisions Pellicci et al found more than doubled incidence of re-revision and radiographic loosening ranging from 5.4% to 19% and from 13.6% to 29%, respectively (Pellicci PM, Wilson Jr 1985). Similar results were published by Kavanagh et al at 10-year follow-up (Kavanagh BF 1993). Sixty-four per cent of the stems had been revised or were radiographically loose. The incidence of revision had more than doubled from 18% at 3 years to 39% at final follow-up.

Table

results of cemented revision Katz

The main reason for suboptimal results with early cemented revisions was difficulty in obtaining stable and long-lasting fixation in compromised host bone stock where the rate of re-revision was very high (Kershaw et al 1991). In early studies, the reactive sclerotic bone between the fibrous membrane and the native cancellous bone was not removed (Callaghan Bono). Poor fixation of the revision femoral component compared to that in the primary setting may be due to inadequate excision of residual fibrous membrane, incomplete drying of bone, suboptimal cement filling technique, or insufficient cement-bone interlock on the smooth sclerotic bone surface. In such setting, even long cemented stems, are generally difficult to be inserted with adequate primary and long lasting stability.

Femoral revision using so-called modern cementing techniques may yield promising results. (Fig Modern cementing tech) Different studies have demonstrated that modern cementing techniques have improved implant survival and clinical outcome compared with the mid-term results after revision with use of so-called first-generation (Rubash HE 1988, Kinov, Mulroy 1996, Raut 1995, Iorio 2008).

(Fig. Cemented revision)

Cemented femoral revision has several advantages in elderly patients. It allows early mobilization, a shorter operating time, and possibly less risk of a peroperative fracture. Use of modern cementing techiques seems to improve fixation of the femoral components and clinical outcomes and justifies its use. Whenever possible the failed arthroplasty should be revised before occurrence of severe bone loss and femoral enlargement.

Cement-within-cement fixation

Removal of the well-fixed cement mantle around the stem can be extremely difficult, time consuming, and risky procedure. A solution to the problem, cement-within-cement revision was first proposed by Eftekhar who advised on preserving the existing well cemented mantle and re-cementing the new stem into it (). In a biomechanical study, Greenwald et al. demonstrated that the shear strength was 94% that of a single block when the existing cement mantle was properly prepared (). The technique requires that the old cement surface be dried and roughened in order to provide contact area for fixation of the new cement. The cement should be injected in the early liquid phase to prevent lamination and to promote polymerization within the existing cement mantle.

This technique have been questioned by other authors (Li 1996), but further biomechanical and clinical studies have supported its use in properly selected cases (Lieberman JR 1993, Duncan WW 2009, Holt 2010). In a cadaver study, Rosenstein at al demonstrated cement-cement shear strength was greater than the cement bone interface strength (). However, the shear strength of cement bone interface was 30% weaker when cement was placed against a revised bone surface.

Impaction grafting

Femoral impaction grafting with a cemented stem was first performed in Exeter in 1987 (Holt 2010) (Fig. 00). The rationale behind this simple concept is to rebuild femoral bone stock and to provide secure fixation to the femoral stem. The biologic approach of bone restoration during revision hip arthroplasty is a highly appealing solution for restoring host bone stock a difficult procedure with usually deficient femurs. Following the initial report of highly successful results after 56 revisions with follow-up of 18-49 months (Gie 1993) the technique received wide attention and spread rapidly (Schreurs BW 2005, Wraighte PJ 2008, Ornstein E 2009, Halliday BR 2003). Further studies confirmed the favorable outcomes and it became evident that the technique allowed for restoration of femoral bone loss as the impacted allograft was incorporated and remodeled (Holt 2010, Wraighte PJ 2008).

The technique of impaction grafting appeared to be reliable, reproducible, can be learned rapidly, and produced a predictably favorable outcomes. In a series of 226 revisions, Halliday et al. reported the initial experience with femoral impaction grafting performed at Exeter with a minimum follow-up of five years (Halliday BR 2003). The overall rate of mechanical failure was 7% (16/221). Ten to 11 years survival with femoral revision for any reason as the end point was 90.5% and survival with revision for aseptic loosening as the end point was 99.1%. In 2006, Schreurs et al. published their results with femoral impaction grafting with a cemented polished tapered stem at a mean 10.4 years follow-up (Schreurs BW 2006). The average subsidence of the stem within the cement mantle was 3 mm and seven stems migrated 5 mm. No stem was revised for aseptic loosening. Three periprosthetic fractures at the tip of the stem were treated with plate fixation and all femoral implants were retained. Ornstein et al. published results of 1305 femoral revisions with impaction grafting from the Swedish arthroplasty registry (). Survivorship at 15 years for aseptic loosening was 99.1%, for infection 98.6%, for subsidence 99.0%, and for fracture 98.7%.

However, other authors reported higher percentage of intaoperative complications, mainly femoral fractures and suboptimal cementing technique (Knight JL 2000, Kinov 2007, Pekkarinen J 2000). An incidence of up to 20% peroperative femoral fractures have been reported (Schreurs 2006, Meding JB 1997, Masterson EL 1997). Stem subsidence of greater than 5 mm is a typical complication with this technique with a prevalence of up to 22% in some series (Knight JL 2000, Franzén H 1995, Eldridge JD 1997, Masterson EL 1997). Impaction grafting is prone to femoral fractures, has a steep learning curve, and shows highly variable outcomes, probably related to the surgical technique. The causes of early subsidence of the stem might be insufficient impaction of the allograft, suboptimal cement penetration and interdigitation, use of synthetic graft substitutes, or other graft additives, loss of primary fixation of the allograft-cement composite due to soft tissue infiltration and substitution of the allograft in the process of remodeling and revascularization, unrecognized femoral fracture, or fracture of the cement-allograft composite. However, in a studies on saw femurs, Flannery et al. and Cummins et al. were unable to find correlation between threshold force needed to achieve stable construct in impaction bone grafting without fracture and bone mineral density, cortex-to-canal ratio, or cortical thickness (Flannery OM 2010, Cummins 2011). According to Gokhale et al. four variables (age, femoral canal diameter, stem design, and density of the graft at the tip of the stem) affected the subsidence of the stem (Gokhale S 2005).

The original technique of impaction grafting utilized the Exeter stem (Gie 1993). The impacted graft is subjected to continuous loading and deformation. Thus the use of double-tapered polished stem appears suitable option as the stem could achieve secondary stability after subsidence. Arguing that the technique is more important than the type of prosthesis other authors have used different implant designs from those of Exeter wedge shaped prosthesis (Franzen 1995, Karholm 1999, Piccaluga 2002). Uncemented technique was also used with equally good outcome at mid-term follow-up (Masterson S 2012).

Femoral impaction bone grafting is a suitable indication for cases with severe bone deficiency. The technique is expensive, prone to complications, hast steep learning curve, and results depend on surgical skills. It may be a viable revision option for young patients with severe bone loss.

Proximal femoral allografts

Severe bone loss in femoral revision is increasing problem as the number of patients with multiple previous revision increases. These complex cases are further increasing as the age of patients undergoing hip replacement is diminishing.

A stable initial fixation is hardly obtainable in complex cases with circumferential loss of host bone >5 cm in length. Severe bone loss makes femoral revision using conventional techniques difficult. Alternatives include distal fixation of the stem or use of a proximal femoral allograft. Distal fixation requires the use of a proximally replacement prosthesis or megaprosthesis. This has some disadvantages such as: instability due to poor soft tissue attachment (Parvizi 2007, Haentjens P 1996), early loosening of the distally fixed stem (Fink B 2007), stress shielding (Bruns J 2007, Fink B 2011, Nadaud MC 2005), intraoperative fractures (Nadaud MC 2005) or difficulty with fixation in an ectatic femur. Various studies of revisions using megaprosthesis /proximal femoral replacement prosthesis/ reported survival rate within the range 58% to 84% at five to ten year follow-up (Parvizi 2007, Zehr RJ, Malkani 1993).

The revision technique using proximal femoral allograft consists of a long-stem prosthesis cemented to the allograft but not to the host bone (Gross AE 1995) (Fig. technique). Uncemented fixation of the allograft prosthesis construct would not result in long lasting stability of the prosthesis as neither in-growth nor on-growth could be expected at the allograft-implant interface. The importance of the allograft-host bone contact is a key factor for achieving stability of the construct and ensuring long-term stability of the implant (Safir).

The key to successful revision using proximal femoral allograft-prosthesis construct

Skills

Individual studies published encouraging results after use of proximal femoral allograft-prosthesis construct in large segmental defects of the proximal femur. In a series of 44 revisions with a mean follow-up of 7.15 years Vastel et al. observed two deep infections, two aseptic loosening and two fractures bellow the tip of the prosthesis (). The final prosthesis survival rate with no further surgery was 82.4% at 14 years of follow-up. The major complication was nonunion of the greater trochanter, which occurred in 25 cases. In a another series of 30 hips who underwent revision total hip replacement with an allograft prosthetic composite Sternheim et al. observed favorable long-term outcome (). The survivorship at ten, 15 and 20 years was 93%, 75.5% and 75.5%, respectively. Encouraging results were published by Blackley et al. with 78% successful results for an average of eleven years follow-up (). The allograft-prosthesis construct survivorship at five years was 90% and at ten years was 86%. A recent systematic review of 498 with a mean follow-up of 8.1 years reported survival rate of 82% (Rogers BA). The major complications were aseptic loosening observed in 13.7% of patients followed by dislocation in 12.8%.

The use of a proximal femoral allograft-prosthesis construct has some inherited disadvantages typical for complex surgery.

Allograft resorption eventually leading to failure of the revision is of major concern with longer follow-up (). Usually, it occurred after several years of follow-up and did not progress (Vastel L 2007, Blackley 2001). Authors that utilize uncemented distal fixation support the concept of direct loading of the host-allograft junction and argue that it minimizes allograft resorption (Gross AE, Blackley). On the other hand, cementing the prosthesis to the distal femur and thus stress shielding the allograft may explain the high rate of alograft resorption (Haddad 2000). Dislocation is a frequent complication after revision with proximal femoral allograft with incidence ranging from to 7.3% to 16.7% (Chandler 1994, Vastel L 2007, Rogers 2011, Haddad 2000). The risk of dislocation may be minimized by proper reconstruction of length, version and offset of the prosthesis-allograft construct and by maintaining the bone-soft tissue attachment to the host femur (Rogers). The infection rates after revision with allograft-prosthesis construct are higher than that reported after primary hip arthroplasty. Rates of infection ranging from 0 to 10.9% were reported (Langlais F 2003, Vastel, Chandler, Safir, Roque 2010). However, considering the high complexity of the technique these levels of infection are not unacceptable.

Nonunion of the allograft-host junction (Blackley 2001) or the greater trochanter (Vastel L 2007, Haddad 2000) are of major concern with the technique. A step-cut osteotomy may provide rotational stability while an oblique osteotomy may provide greater surface area for bone healing compared to a transverse osteotomy.

Femoral revision using proximal femoral allograft cemented to a long stem prosthesis is appealing option for revision. The current data from the literature support the use of the technique as a durable solution, with available evidence reporting a survivorship of 82%. It is of a particular interest in the young patients because of its potential to improve bone stock and provide substrate for subsequent revision. The development and refinement of this technique should be encouraged.

Cementless fixation of the femoral component

Obtaining stable and long lasting fixation in femoral revision in patients with severe bone deficiency is a difficult task. Long-term results after cemented revision have not been optimal (Kershaw et al 1991, Pellicci 1985, ...). High failure rates ranging between 12% to 44% at mid-term follow-up have been reported (Pellicci 1985, Kershaw 1991, Kavanagh 1985, Amstutz HC 1982). The main reason was difficulty in obtaining stable and long-lasting fixation in severe bone loss. Cementless fixation proved a promising alternative and was soon introduced in practice. However, for fears of stress shielding the ingrowth surface of first generation designs was confined to the proximal part of the stem. Although highly successful in primary arthroplasty, the limited amount of porous coating with proximal fixation led to less favorable results in revision surgery (Table 2). Failure rates of 4% to 9.5% were reported at short- to mid-term follow-up of 1 to 4 years. These results were slightly better than those obtained with early cementing technique. The technique yielded acceptable results in less severe deformities (Iorio 2008). Retrieval studies have demonstrated that less bone ingrowth occurs in revision stems compared to primary ones (Cook SD 1991). Porous surface extending to the diaphysis is needed to ensure stable primary fixation. In support of this, various authors have reported promising long-term results after revision with use of extensively coated uncemented stems (Paprosky W G, Greidanus N V 1999, Amanatullah DF 2011, Engh Jr 2004, Krishnamurthy AB 1997).

Proximal femoral deficiency results from osteolysis, infection, fracture or bone damage during implant extraction. In such cases with severe bone loss, distal fixation with cylindrical, tapered or fluted stem designs is a viable option (Engh Jr 2004, Barrack R 2003, Cameron 2003). The technique requires accurate preparation of 4 cm to 7 cm of diaphyseal bone (Engh Jr 2004, Lakstein D 2010, McAuley JP 2004). It is adaptable and can be used in situations with different severity of bone loss. Moreover, it can be used in periprosthetic fractures and is adjustable with extended trochanteric osteotomy. Distal stem fixation is the most successful strategy in terms of primary and secondary mechanical stability, bone osteointegration, and most importantly clinical results (Barrack R 2003). The main reason for its success is the fact that the implant is in contact with viable bone. Success rates of 90% to 95% have been reported with extensively coated monoblock stems over 10-year follow-up (Paprosky W G, Greidanus N V 1999, Moreland JR 2001, Weeden SH, Paprosky WG 2002). However, issues, such as thigh pain and proximal stress shielding, were reported frequently.

The principles of the Wagner stem are utilized in the tapered stems (Wagner H 2000). The cone prosthesis achieves good contact between the supportive distal diaphysis and the middle or distal third of the stem. The conical shape and the longitudinal splines promotes primary axial and rotational stability, which are prerequisites for osteointegration and long-lasting endurance of the cementless implant. The concept of modularity was introduced with the advantages of versatile proximal fill and distal fit (Kang 2008). By modularity the sizes and shapes of the prosthesis can be increased by varying the diameter and shape of the proximal and distal part of the stem and locking them in different way. Modularity offers potential advantages such as adjustment and restoration of leg length, offset, version, proximal fill, as well as compatibility with extended trochanteric osteotomy (Lakstein 2010, Barrack R 2003). The potential problem of thigh pain was not associated with tapered stem design (Wagner H 2000). Disadvantages of modular taper stem designs include complexity, risk of stem fracture, fretting and corrosion of the junction, increased inventory, and higher cost.

Various studies have reported favorable outcomes of various uncemented tapered distal fixation stems with high survival of more than 95% at 5 to 10-year follow-up (Engh Jr 2004, Krishnamurthy AB 1997, McAuley JP 2004).

The technique of cementless revision with distal fixation of the stem has been shown to be a reliable and straightforward. It ads no additional risks or complications. It can be used in all but the most severe segmental defects (Engh Jr 2004, McAuley JP 2004, Cameron 2003, Barrack R 2003). When the simple principles of the method are followed it provides stable and durable fixation of the revision implant. However, distal fixation does not restores host bone, thus making further revision surgery more difficult.

Options for Acetabular revision

The goals of revision arthroplasty are to relieve pain and to improve function. In order to obtain these goals stable and durable fixation of the revision components must be achieved with restoration of hip center. Acetabular revision is the most difficult part of hip revision. Unfortunately, there is no single surgical technique to solve the problem of fixation. The achievement of stable initial and long-lasting fixation is challenged by the severity of different acetabular defects and soft tissue damage.

The main acetabular reconstruction option is cementless pres-fit fixation of the cup with or without allograft (Civinini, Issack). When severe combined segmental and cavitary bone deficiencies, poor bone quality and viability or pelvic discontinuity are identified, other more complex options for acetabular reconstruction are required. These include trabecular metal cups, modular metallic augments, reconstruction cages, reinforcement rings, cup-cages, and structural or morselized allografts that can be used to support the reconstruction. Structural allografts or posterior column plating are usually used in cases with pelvic disruption.

Cemented fixation

In cases with no or moderate bone loss revision could be performed with simple cemented exchange of the implant. Historically, early revisions were performed with the same technique that had been used for primary arthroplasty. However, difficulties in achieving consistent long-term results had prevented use of this technique. Failure to achieve adequate cement interdigitation explained poor results reported with early cementing techniques. Key factors for good cementing technique are optimal exposure of cancellous bone, adequate containment of the cup, and a clean and dry socket (Ritter 2004). Sutherland and colleagues demonstrated that preservation of the subchondral bone can increase stiffness and stress concentration at the bone-cement junction (). Callaghan et al (Callaghan JJ 1985) reported 4.3% revisions and 34% radiographic loosening at 3.6 years follow-up of cemented revisions. Similar high rates of loosening were reported by Pellicci et al at 3.4 years follow-up (Pellicci 1982). The long-term results after cemented revision were considerably worse (Pellicci 1985). Even with improvement of the cementing technology, the cemented acetabular fixation has not improved (Table). At longer follow-up, using modern cementing techniques failure rates ranging from 35% to 65% were reported (Nelson CL 2002, Katz RP 1997). Ten-year survivorship of the acetabular component with radiographical loosening as the endpoint event was 72% (Katz RP 1997). Consequently, cement fixation of the acetabular component has become less popular among orthopedic surgeons. In contrast, hemispherous porous-coated cups with bone ingrowth potential were developed and demonstrated consistently better results.

Cementless fixation

The approach to each individual case depends on the severity and localization of host bone loss. Results after cementless revision of the acetabular component have outperformed cemented fixation (Etienne 2004, Della Valle CJ 2004, 2005). With supportive and viable host bone and a reliable ingrowth surface a hemispheric metal shell supported with screws is a straightforward solution for acetabular reconstruction. In minor or contained defects, hemispherical cup with/without grafting produced excellent results (Etienne 2004, Della Valle CJ 2004, 2005). Cementless fixation is suitable for patients with Paprosky types 1, 2A and 2B defects: without hip center migration or pelvic discontinuity. As a general rule, at least 50% of the host bone is needed to be in contact with the implant in order to support a hemispherical cup. Transfixational screws are usually used to support ingrowth of the press-fit cup. Morcelized allografts could be used to fill the cavitary defects. In deficient acetabulum with major bone loss such as Paprosky type 3 defects a hemispherical cup could be placed against the intact supportive roof ("high hip center"). Sometimes extra large (jumbo cup) or oblong cups can bypass severe bone defects and provide stable initial fixation for bone ingrowth. Cementless fixation results in a standard hip center or in a high hip center (Dearborn and Harris 2000).

High hip center

The failed acetabular components migrate in the direction of joint reaction forces creating deficient acetabular defect with greater superoinferior dimension compared to the anteroposterior dimension. In such revision setting implantation of the cementless hemispheric press-fit cup in the anatomical hip center is not possible. A straightforward decision for treatment of such defects is to place a small hemispherical press-fit cup against the supportive bone at the roof of the acetabular defect - the so-called high hip center (Figure). Most authors consider arbitrary the hip center high if it proximal greater that 35 mm to the inter-teardrop line (Dearborn and Harris 1999).

Results after cementless press-fit fixation of the acetabular component inserted with screws outperformed cemented revision. With use of this approach, despite extensive acetabular bone loss excellent implant fixation was consistently reported (Table). The durability of cementless acetabular fixation was proved in long-term studies, too. In the study of Templeton et al, none of the cementless cups have been revised for aseptic loosening at 12.9 years follow-up and only 3 cups have migrated (Templeton 2001). In a study with minimum follow-up of 20 years, Park et al demonstrated 95% survivorship with revision of the cup for aseptic loosening or radiographic evidence of loosening as the end point (). However, with longer follow-up the problem of polyethylene wear and osteolysis emerged. In the series of Park et al (2009), reoperations for wear and osteolysis were first seen at approximately twelve years postoperatively. At the time of the last follow-up 20 years after revision, the reoperation rate for polyethylene wear and/or osteolysis had increased.

The technique saves costs, time, and eliminates the use of structural allografts or cement. However, high rate of complications was reported (Jamali 2004, Dearborn and Harris 1999). This might reflect the complexity of the procedure.

Certain disadvantage of the technique is restoration of limb-length discrepancy on the femoral side whereas the defect is on the acetabular side. This would result in abnormal hip biomechanics. Increased hip joint reactive forces with high hip center and impingement might partially explain the relatively higher rate of dislocation with this technique (Wysocki 2009, Park 2009).

Considering the excellent results reported with porous coated press-fit acetabular components in terms of implant fixation, we believe that the use of press-fit cups should be considered in every revision setting if there is sufficient host bone stock to support the cup.

Jumbo cups

Extra-large cups offer certain advantages in maximizing the contact area between the cup and host when revising deficient acetabulum. There is no universally-accepted definition of the jumbo cup. Extra-large cups are arbitrary defined compared to the size of the pelvis, the hip joint, and the previous implant. Whaley et al defined jumbo cups as having a minimum outside diameter of 66 mm (men) or 62 mm (women) (). This definition was based on the fact that the revision cups used at their institution were 10 mm larger than the mean implant diameters used for primary hip arthroplasty.

The method has certain advantages (Pulido 2011): the acetabulum is prepared straightforward by reaming to a large hemispere; the large implant fills in the deficiencies and bone grafting is usually unnecessary; the center of rotation is transferred inferiorly and to some extent laterally restoring hip biomechanics; the large implant provides greater contact area and greater lever arm.

Whaley et al reported the Mayo clinic experience on 89 acetabular revisions using extra-large hemispherical components (). The probability of survival of the acetabular component at eight years was 93% with removal for any reason as the end point, and 95% with radiographic evidence of loosening or revision for aseptic loosening as the end point. Wedemeyer et al, Obenaus et al, and Dearborn and Harris published similar results with cup survivorship with end point aseptic loosening higher than 94% at mid-term follow-up (Wedemeyer C 2008, Dearborn JT, Harris WH 2000, Obenaus et al).

Disadvantage of the technique are the limitations in restoring bone stock. Moreover, most of the defects are oblong with greater superoinferior dimension than anteroposterior dimension. Converting an oblong defect to a hemispherical with extensive reaming may disrupt posterior wall or column which are critical for cup stability (Whaley et al). This risk of host bone compromise may result in superior placement of the cup.

The technique saves costs, time, and eliminates the use of structural allografts or cement. However, the rate of complications reported was rather high. This might reflect the complexity of the procedures. In the series of Park et al, the most common reason for revision in 11.6% of 138 hips was infection and dislocation (). Similar high rates of revision were reported by Dearborn and Harris (2000) and ... (). The

Oblong cups

As described earlier, large oval contained defects cannot be filled-in superoinferiorly without producing hemisphere by excessive reaming of the anterior or posterior column of the acetabulum or high placement of the cup. Suitable option in such cases are oblong cups. Oblong cup has smaller anteroposterior and mediolateral dimensions compared to the superiorinferior dimension. By accomodating the implant to the defect oblong cups can restore hip center and increase implant contact with host bone. Advantages of the technique are: lack of increased reaming of the anterior or posterior columns or medialization of the cup; increased contact between the device and the host bone; restoration of hip center (); and, avoidance of structural allografts (Berry DJ 2000). Disadvantages include higher cost, difficulties in cases with insufficient contact (Chen WM 2000), possible component malpositioning, failure to restore bone (Berry DJ 2000), and excessive bone removal in order to achieve press-fit (Pulido 2011).

In a multicenter study on 38 hips revised with oblong press-fit cups, Berry et al published good results at mean 3 years after surgery (Berry DJ 2000). There was only one failure for acetabular loosening that required re-revision. Mean Harris Hip Score (HHS) increased from 50 points preoperatively to 90 points after revision. The hip center was 37 mm above the inter-teardrop line before the operation and was corrected to 25 mm above the inter-teardrop line. Similar good results were reported by DeBoer and Christie on 18 hips revised with oblong press-fit cups (DeBoer DK). At latest follow-up 4.5 years after revision no component was loose and the mean HHS increased from 41 points preoperatively to 91 points after revision. The authors reported near anatomic restoration of the hip center to 17 mm above the inter-teardrop line after revision. Chen and Engh reported less favorable results in 37 revisions (29 with massive type 3 defects) followed-up for an average of 41 months (Chen WM 2000). Eight percent of the hips were probably loose and 16% were unstable. Eight of the 14 hips that had more than two centimeters of superior migration of the component and disruption of Koehler's line on preoperative radiographs failed (Chen WM 2000). The authors found a correlation between loosening and average distance from the inferior edge of the cup and the interteardrop line. Five of the six unstable components initially had not extended to the level of the radiographic teardrop or distal to it (Chen WM 2000).

In their early series, Sutherland (1996) reported a 50% failure rate (3 of 6) after revision with oblong cup of type 3 defects. Discouraging mid-term results were published by Babis et al using a cementless oblong cup for revision of Paproski 3A defects (Babis et al). After a mean follow-up of 60.5 months 18 hips (29.0%) were revised and a further four hips (6.4%) were loose and awaited revision. On the other hand, Civinini et al published good mid-term results after revising with oblong cup Paprosky type 2 and 3 acetabular defects (). In a series of 55 hips followed-up for an average of 7.2 years only one cup was revised for loosening.

Oblong cups are an alternative for acetabular revision, especially when the surgeon wants to correct an elevated hip center (Chen WM 2000, Moskal 2008). The technique is suitable for Paproski type 2A, 2B and 3A defects where the acetabular defect is oval. Obtaining initial stability and supplementary fixation by screws are mandatory for the stability of the implant are key factors for long-term success of the reconstruction. However, the medial wall should be intact and the failed component should not been migrated more than two centimeters. Pelvic discontinuity is also a contraindication for this technique. An alternative techniques such as structural allograft or cages should be considered in such revision settings.

Acetabullar impaction grafting

Cemented acetabular revision yielded unacceptably high rate of loosening (Callaghan, Kavanagh). Possible reason is the deficient, weaken and sclerotic acetabular bone frequently found at revision. An attractive alternative for cup fixation in massive contained defects is impaction grafting where the cup is cemented on a premoulded bed of impacted morsellized cancellous bone. In such revision setting the contact with host bone is very limited if not absent. The morsellized bone has osteoinductive and osteocunductive properties and is used as a filler scaffold of contained defects. The technique of impaction bone grafting and cemented fixation of the cup was first described in 1984 by Slooff et al (Slooff 1984 Scand, ), and later standardized by the same authors with minor modifications and technique-specific instrumentation (Busch 2011, Schreurs 2004). Morsellized graft could be used with a cementless hemispherous cup if more than 50% of the cup is in contact with viable host bone (Gross 2006). Transfixing screws should be used for additional stabilization of the cup. In cases with less than 50% contact between the cup and viable host bone the cemented cup into impacted cancellous bone should be used (Sloof TJ).

The technique can provide stable and durable reconstruction of the hip joint. Initial mechanical stability of the morscellized allograft-cemented cup composite is a prerequisite for a successful biological reconstruction. Subsequent remodeling and incorporation of grafts, provides long-term stability.

In contrast to cementless revision, this technique could restore bone loss. The modern technique consists of reconstruction of segmental and rim defects with use of a metal mesh or a solid graft (Fig. 00). The sclerotic areas are perforated with multiple 2-mm drill-holes and fresh-frozen morselized bone chips are impacted layer by layer into the acetabulum.

The clinical success of the of impaction grafting depends on the surgical technique and on the biological and mechanical properties of the morselized bone graft. Various factors connected with the graft such as graft type (cancellous, cortical-cancellous, chemical composites, additives), graft processing (fresh frozen, freeze-dried, irradiated), graft particle size and grade influence clinical result. The originators of the technique use fresh frozen allografts (Schreurs 1998, Busch 2011, Schreurs 2004).

The technique of acetabular impaction grafting is well established an various authors demonstrated reproducible results (Comba et al 2006, Garcia-Cimbrelo 2010, van Egmond 2011, Schreurs 1998). Schreurs et al reported good results after acetabular revision with impaction allografting at 15 to 20 years follow-up (Schreurs 2004). Cup survival with revision for aseptic loosening as the endpoint was 84% at 15 years. In a 20 to 28 years follow-up study, Busch et al from the same study group evaluated 42 patients with impaction grafting younger than 50 years of age (Busch 2011). With revision for aseptic loosening as the end point, survival was 85% after twenty years and 77% after twenty-five years. for signs of loosening on radiographs, survival was 71% at twenty years and 62% at twenty-five years. Results declined over time, but the authors concluded that the technique is useful for younger patients with major bone defects (Busch 2011).

Acetabular revision using impaction grafting is an attractive alternative for biologic restoration of hip joint mechanics. The procedure is technically demanding and exacting. Results comparable to those after revision with cementless hemispheric cups were obtained after use of correct surgical technique.

Reconstruction cages and antiprotrusio rings

Reconstruction cages and antiprotrusio rings are an established method of treatment for severe acetabular bone loss if contact with 50% host bone could not be established (Gross AE 2006). They have the advantage of fixation into viable host bone of the ileum and ischium with flanges while protecting allograft. Reinforcement rings or reconstruction cages can provide adequate support for the reconstruction with massive allografts in Paproski type 3 defects. Because of the poor results foolowing use of unsupported structural allograft use of reconstruction cages has been advised (Sporer 2005). Failure rates higher than 60% at an average of 2.9 years have been reported in cases with massive allografts not supported by cages (Paproski 1994). These results were supported by various studies (Hooten 1994, Garbuz 1996, Pollock 1992, Morsi 1996). Recently, this treatment approach has been questioned as TM implants provide more favorable conditions for graft incorporation and bone ingrowth (Sporer 2005).

The reconstruction cages and antiprotrusio rings have definite advantages: the cage and ring allow for restoration of hip center; they provide uniform load to the allograft stimulating bone remodeling and incorporation into host bone (Issack part 2); allow use of cement allows use of local antibiotic protection; allow correct placement of the cemented cup independent of the cage or ring. The cage protects either the morsellized or structural allograft while it remodels, and if the cage fails cementless revision can be done (Goodman 2004, Gross?).

Disadvantages include higher cost, need for wide surgical exposure of the superolateral part of the ilium. The later may risk injury of the superior gluteal nerve and limping. The major concern with standard nonporous cages and rings is that they do not allow bone ingrowth. Finally they loosen and break. However, this inability of bone ingrowth is compensated by the mechanical stability and incorporation of the graft reducing the risk of fatigue fracture of the cage. Close fit between the cage and the allograft as well as adequate fixation of the cage are a prerequisites for successful reconstruction. Cement augmentation of screws is recommended in cases with severe osteolysis or osteoporosis.

The limits of using antiprotrusio rings were demonstrated by Haentjens et al and Zehntner and Ganz (Haentjens P 1993, Zehntner MK, Ganz R 1994). High rate of migration up to 44% (12/27) at mid-term follow-up of 7.2 years was reported (Zehntner MK, Ganz R 1994). Previous designs of reconstruction cages did not allow bone ingrowth and a failure rate of 16.4% due to loosening was reported on average 4.6 years after surgery (Goodman 2004). Sporer et al reported a 2- to 8-year follow-up of 45 hips where a cage was used for a type III defects (Sporer 2005). Nine hips were revised for aseptic loosening, and an additional 9 hips were radiographically loose.

In contrast, Winter et reported no loosening or revision in 38 hips followed-up at mean 7.3 years after revision with cage (Winter 2004). In a long-term study, 18 acetabular revisions for pelvic discontinuity have been reported on average 13.5 years after surgery (Regis 2012). Two cages were revised for aseptic loosening and another two allografts showed signs of severe osteolysis. Survivorship of the acetabular component at 16.6 years with end points revision for any reason, loosening or nonunion of the allograft was 72%.

The increased rate of loosening and revision is probably multifactorial and reflexes the increased case load. Frequent indication for use of reconstruction cages is pelvic discontinuity. However, designs without bone ingrowth do not have potential for biologic fixation and rely solely on mechanical fixation.

Antiprotrusio cages and rings are an effective techique for treatment of severe bone defects. However, in recent years, newer implant designs have gained popularity. In cases with more than 50% host bone support cementless cup transfixed with screws is the treatment method of choice. Trabecular metal implants, porous augments, and triflanged acetabular components are an attractive alternative for complex acetabular reconstructions, (Gross AE 2006, Sporer 2005, Dennis DA 2003). TM cups have been proposed if contact with viable host bone is 30% to 50%. If contact with viable host bone is less than 30% a cup-cage construct was suggested (Gross AE 2006). Longer follow-up studies are needed to support the clinical use of these new implants.

Structural acetabullar allografts

One of the most difficult scenarios in revision surgery is reconstruction of a massive acetabular bone loss. Structural acetabullar allografts are a suitable revision option for uncontained bone defects (Paprosky type 2B, 3A and 3B). The size of the allograft may range from a femoral head in superolateral uncontained defects to total acetabular allograft in the case of massive uncontained defects or pelvic discontinuity.

Advantages of the technique include restoration of hip center and restoration of bone stock for future revisions (Garbuz 1996, Hooten 1994, Kwong 1993, Pollock ). However, actual restoration of viable and mechanically competent bone is questionable. Moreover, results are unpredictable, the technique is demanding and associated with various complications.

Results after revision with structural allografts have been largely controversal. Harris initially reported successful results after reconstruction of severe acetabular defects with structural allografts (Russotti GM, Harris WH 1986). However, the encouraging period of initial good functioning for 5 to 10 years was followed by later failures. In 1993, Kwong et al reported 47% failures in 30 hips with a mean follow-up period of 10 years (). And in 1997, the senior author reported total rate of revision or loosening 60% at an average of 16.5 years (Shinar 1997). High hip center for placement of the cup was suggested in cases with severe acetabular bone loss (Russotti GM, Harris WH 1986).

In a series of 33 hips followed-up on average 7 years after revision with a structural allograft Garbuz et al reported 55% success rate (1996). Fifteen hips were revised: 7 hips because of failure of the prosthesis and 8 hips because of failure of both the alograft and the prosthesis. Gross et al reported on 107 hips reconstructed with bulk allograft (1998). Thirty hips (28%) were revised and in 15.9% of cases (17 hips) the indication was aseptic loosening. The authors reported 76% successful results in the 33 hips with minimum duration of follow-up of 5 years (average, 7.1 years) after the revision. However, 8 hips needs additional reoperation because of failure of the graft and another 6 hips were revised for loosening. Hooten et al reported on a series of 31 revisions with structural allograft and cementless cup followed-up on average 46 months after surgery (Hooten 1994). Twelve (44%) cups were radiographically loose and 5 of these hips were revised.

In contrast, Paprosky et al reported a failure rate of 19 per cent (6/31) at an average follow-up of 5.7 years after revision with use of a structural allograft (Paproski 1994). The only failures in that series were in hips in which the allograft supported more than 50 per cent of the cup. In another study, Morsi et al found a success rate of 86% (25/29) at mean follow-up of 7.1 years (1996). They used a minor bulk allograft that supported less than 50% of the cup.

According to Morsi et al and Pollock and Whiteside a repeat revision does not mean failure of the reconstruction (). This complex reconstruction can be considered successful if bone stock is restored for future revisions.

Although results after revision with structural allograft are controversial, most authors agree that than the rate of success increases if more than 50% of the cup is in contact with viable host bone (Paproski 1994, Hooten 1994, Garbuz 1996).

Revision with structural allograft is a suitable option for restoration of hip center. The role of the allograft is to support the cementless cup with partial stability until adequate ingrowth occurs. The success after the procedure is technically-related. In order to optimize result after revision with structural allograft a number of principles should be followed. Structural allografts combined with antiprotrusio cages and a cemented cup should be considered only in cases with insufficient host bone to provide a stable fixation for a press-fit cup (Dearborn and harris 2000).

For optimal result, an appropriate allograft must be selected to match the mechanical requirements of the desired reconstruction. The method of processing of the bone allografts is important for the clinical result. Greater success rate with fresh frozen bone allografts was obtained compared to freeze-dried allografts (Gross?, Young 1991?). The trabecullae of the allograft should be in the direction of load for optimal stress transfer. After trimming of the allograft in order to obtain maximal contact with the host bone the allograft is fixed with 6.5 mm parallel screws in the direction of load. In case of pelvic discontinuity the column should be fixed with a plate before fixating the allograft. Use of reinforcement cages improves results after reconstruction with structural allograft (Garbuz 1996, Saleh KJ 2000).

Sporer - decision making

Custom triflanged implants

Custom triflanged prostheses have been proposed for treatment of massive acetabular defects and pelvic discontinuity, but the experience is limited and the rate of complications is high (Joshi 2002, Taylor 2012). The implant is manufactured from 3-D CT data reconstruction of the degree and localization of bone loss as well as its spatial orientation.

In 2007, DeBoer et al evaluated the outcome of revision with a custom-designed porous-coated triflanged acetabular implant in 20 hips at an average follow-up of 10 years (DeBoer DK). A definite healing of the pelvic discontinuity was found in 18 hips (90%). The remaining two implants were radiographically stable and did not migrate even when discontinuity persisted. However, the overall dislocation rate in the series was 25%. Christie et al followed-up retrospectivly 67 complex revisions with custom-made triflanged implant (Christie MJ 2001). Two discontinuities persisted but both were asymptomatic and to implant was revised. Six (7.8%) hips were revised for recurrent dislocation. Using custom triflanged acetabular components Dennis reported three failures in 24 revisions with mid-term follow-up of 4 years (Dennis 2003). He questions the value of the technique in pelvic discontinuity unless supplemented with additional column plating.

The technique has high cost, it is time consuming, requires extensile exposure, and lacks modularity. It could not be used in urgent clinical situation where it is not possible to wait for manufacturing the product. With complex implant and technically challenging surgery custom-designed triflanged prosthesis should be reserved for cases where less costly and less technically demanding options could not be used. Many surgeons consider it a salvage procedure for cases where the bone loss is catastrophic.

Trabecular metal cups

Trabecular metal (TM) cups can be used in massive contained or uncontained defects. As tantalum provides favorable environment for biological fixation TM cups have been suggested for revision of Paproski 3 defects (Sporer 2005, Gross 2006).

Early results with use of TM implants have been encouraging (Nehme 2004). TM has decreased the need for at least 50% contact of the implant with viable host bone. In Paproski 3A an 3B defects, because cages do not provide biologic fixation, Gross suggested use of a cup-cage construct when less than 30% contact can be made with viable host bone (Gross AE 2006). Instead of an allograft-cage construct a TM cup-cage construct can be used. The rationale behind the technique is that load will be taken off the cage, once bone ingrowth occurs into the trabecular metal cup. So early and mid-term failures of the cages will be prevented.

Sporer et al reported on 13 hips with pelvic discontinuity revised with tantalum cups with or without augments (2006). At mean 2.6 years after revision 12 of the 13 cups were radiographically stable. Lakstein et al reported on 53 revisions of contained defects with 50% or less contact with native bone using TM cups (Lakstein 2009). Two cups (4%) were revised and two additional cups (4%) had radiographical evidence of probable loosening at a mean 45 months follow-up. The fact that some of the TM cups lacked contact with a viable host bone is impressive. Four hips (8%) dislocated and one (2%) sciatic nerve palsy was observed. In a large multicenter study, 263 revisions with tantalum TM cups were followed-up at an average 7 years after surgery. At the most recent follow-up, all cups were radiographically stable and none required revision for loosening. Eight dislocations (3%) in the series were successfully treated with closed reduction and one schiatic palsy partially resolved at last follow-up. Kosashvili et al reported on 26 revisions of pelvic discontinuities using cages combined with trabecular metal components and morsellized bone (the so-called cup-cage technique) (2009). At mean follow-up of 45 months 23 hips (88.5%) were radiographically stable.

Promising midterm results have been demonstrated after revision with use of these new techniques. Currently, the preference is to biological fixation whenever possible, and to alternative options when initial stability could not be obtained.

Porous metal augments

Modular metal augments are used to decrease defect size and to restore bone defect to contained capable of supporting a revision cup. The size and placement of augments is highly dependable on the bone loss pattern. Augments are secured with multiple screws to host bone and remaining defects are filled in with morsellized bone. The hemispherical cup is impacted into the defect with the interface between the shell and the metal augment cemented.

Conclusion

From polyethylene wear, osteolysis and loosening, to catastrophic scenarios such as pelvic discontinuity, there is a spectrum of reconstruction options available for successful reconstruction. Prerequisite for a successful and durable revision include viable host bone, adequate surgical technique, and stable and endurable implant. Current improvements in surgical techniques, implant designs, as well as biomaterials and bearing surfaces are a significant contribution for obtaining favorable outcome after revision hip arthroplasty. Further research and well-designed clinical studies are needed in order to provide optimal treatment to the increasing number of patients requiring revision surgery in the future.

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