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The two most commonly used and described approaches to Total Hip Arthroplasty (THA) are the anterolateral and the posterior. The anterolateral or modified Hardinge approach involves a skin incision over the greater trochanter, over or parallel with the shaft of femur. The incision is often curved posteriorly at its proximal end. Dissection is then undertaken to take advantage of the intramuscular plane between the tensor fascia lata and the gluteus medius. In the direct lateral or Hardinge approach, the acetabulum is exposed by a partial or total release of the abductor muscles (gluteus medius and minimus). This was originally achieved by a trochanteric osteotomy or detachment at their greater trochanter insertion3 described by Watson-Jones 4 and then subsequently modified by Charnley.5 The anterolateral or modified Hardinge approach, as used in Tayside, involves detaching the anterior third of the gluteus medius and minimus. This minimises the risk to the superior gluteal nerve and limits damage to the abductors.6 This modification from the original technique was described by Harris7, and Muller.8 The posterior approach involves a skin incision over the posterior aspect of the greater trochanter, proximally following inline with the gluteus maximus and distally the lateral shaft of the femur. A blunt dissection of the gluteus maximus follows emerging posterior to the abductor muscles. The external rotators (piriformis, superior and inferior gemelli and obturator internus) are then detached at the femoral insertion and reflected exposing the capsule and acetabulum.3 It was originally described by Langenbeck, and subsequently Kocher9 and finally Gibson.10
There have been numerous studies but there is still professional disagreement about which approach is the most effective for primary total hip arthroplasty. Many of the studies that have been undertaken over recent years have been considered to be deficient in both quality of study design and quantity of patients in the study sample. The Cochrane review considered four studies sufficient but only one of these included functional outcomes with the Harris Hip score.11 The study in the Cochrane review was done by Barber et al, it was limited in size, 49 patients, with a relatively short follow-up.12 Dislocation rates between these approaches have been looked at in some depth. Many studies have found a difference, while others haven’t. The difference is often considered minimal if good tissue repair is used in the posterior approach.13,14,15 Where this is the case, the implant has been shown to have half the amount of internal rotation (anteversion) when placed using anterolateral approach as opposed to the posterior approach.16
This is a retrospective study aiming to use large sample groups to answer the null hypothesis that there is no difference between an anterolateral approach and a posterior approach with regards to functional outcome scores (Harris Hip Score and Trendelenburg Test for primary total hip replacement surgery). It also aims to answer the null hypothesis that there is no difference functionally in patients that suffer post-operative dislocations. To do this it will look at the pre-operative scores and post-operative scores comparing any gain or loss in function for each patient. The reasoning behind using Harris Hip Score and Trendelenburg Test is that these are commonly used, meaning any conclusions can be easily related to clinical practice. Dislocation rates between the two approaches will also be compared.
Materials and Methods:
The data used within this project was collected under the Tayside Arthroplasty Audit Group (TAAG) database. The objective of the TAAG database is ‘to evaluate the clinical performance of all hip arthroplasties or hip resurfacings in Tayside’. Initially there were 8153 cases with data for primary hip arthroplasties (resurfacings were not included), of these 6350 cases had undergone either an anterolateral or a posterior approach to the surgery. For this data the aim was to look at pre-operative Harris Hip score results and Trendelenburg tests and again at 1-year post-operatively. Due to this, the data was further screened to ensure that each patient had a complete set of data for these tests. Some cases didn’t have data correctly collected or alternatively were not followed up at 1-year post-operatively. The resulting number of cases was 3416 with 1001 having suffered a complication within the 1-year period after surgery. These complications were medical and surgical. Not all of these complications had a direct effect on the function or rehabilitation of the joint.
The choice of Harris Hip score and Trendelenburg Testing to test functional ability has been shown to be clinically relevant as a reference tool for assessment of improvement or deterioration of the hip joint, particularly pre-operatively and at 1-year.17,18 The Harris Hip score assesses pain, ability to complete basic tasks, deformity of the joint, and range of movement out of 100. The functional score removes the subjective areas of the full score looking specifically at functional ability out of 47. Trendelenburg’s test is specifically looking at abductor deficit, although it has its recognised disadvantages.19 The need for experienced interpretation of the Trendelenburg’s test is its main disadvantage, otherwise you can get false-negatives and false-positives very easily. It was considered only relevant to look at results post-operatively at 1-year, as from a patient’s perspective this is often the expectation of relative normality. From a surgical point of view, secondary complications such as loosening of the prosthesis and deep infection are less likely to be apparent at 1 year but will have presented at 5 years.20
The TAAG database is a rolling audit of all elective hip arthroplasties or resurfacings done in Tayside. Any patient who is undergoing either of these procedures will be considered for inclusion. Exclusion criteria for audit enrolment are a previous total or cemented/uncemented hemi-arthroplasty of the affected hip or inability/unwillingness to participate in the follow up programme. If a patient consents for involvement they will be assessed pre-operatively and post-operatively, this includes radiography to assess prosthesis positioning. Data for Harris Hip Scores and Trendelenburg Test are collected at each assessment. Post-operative follow-up is at 1, 3, 5, 7 and 10 years and then every 2 years thereafter until the prosthesis fails. Operative procedures, local practices, technique used, antibiotic coverage, theatre type, and any other regimes are all recorded. If a patient suffers a complication, details of it, management, and final outcome are all recorded. All data is collected in the same format, if any clinical issues for a patient are found that patient will be referred back to the supervising consultant for review. The data available had a large range of implants used and was also unspecific for consultant surgeon who undertook each procedure.
Positive (2)On comparing the difference between pre-operative testing to post-operative testing the groups four possible results were seen. As the outcome for Trendelenburg is categorical, each result was given a value, the pre-operative result was simply added to the post-operative, as is shown in Table 2, giving an option of 1-4. For a negative to negative (1) result the anterolateral group was 59.89% and the posterior group was 51.38%. For a positive to negative result (2) the anterolateral group was 34.39% and the posterior group was 46.40%. This shows the posterior approach corrected a Trendelenburg’s positive test in 12.01% more cases than the anterolateral approach. For a negative to positive (3) result the anterolateral group was 3.52% and the posterior group was 0.55%. This shows that the anterolateral approach caused a Trendelenburg’s positive test in 2.97% more cases than the posterior approach. For a positive to positive (4) result the anterolateral group was 2.18% and the posterior group was 1.65%. When comparing the two groups as a whole, a statistical significance was found (p=<0.0001). This showed that a Trendelenburg’s positive test had a higher incidence with the anterolateral approach.
The dislocation rates in the first year were 1.7% for anterolateral group and 6.9% for posterior group. For the anterolateral group the mean Harris hip score was 46.48 and Harris Hip function score was 26.38 pre-operatively. For the posterior group the mean Harris Hip score was 48.04 and Harris Hip function score was 23.32 pre-operatively. On comparison there was no statistical significance for Harris Hip score (p=0.6164) or Harris Hip function score (p=0.5775).
Post-operatively, the anterolateral group had a mean Harris Hip score of 85.53 and a Harris Hip function score of 35.29. The posterior group had a mean Harris Hip score of 84.23 and Harris Hip function score of 35.12. On comparison there was no statistical difference for Harris Hip score (p=0.6931) and Harris Hip function score (p=0.7024).
When comparing the difference between pre-operative testing and post-operative testing the mean increase in Harris Hip score were 41.15 and Harris Hip function score 10.90 for the anterolateral group. For the posterior group the increase in Harris Hip score was 36.18 and Harris Hip function score 11.80. On comparison there was no statistical difference for Harris Hip score (p=0.1981) and Harris Hip function score (p=0.6843).
Trendelenburg test for the two dislocation groups showed that pre-operatively the anterolateral group had an incidence of 38.09% and the posterior 40%. Post-operatively the incidence in the anterolateral group was 11.9% and the posterior group was 8%. On comparison between the pre-operative groups and post-operative groups there was no significant statistical difference (p=0.8795).
The issue of which surgical approach is best for total hip replacement is still hotly debated amongst specialists and often falls to personal preference of the consultant surgeon. In today’s modern medicine, for such a decision to be based on personal preference is highly unusual. As professionals we constantly look for evidence to support our clinical day-to-day decisions. The advantages and disadvantages of each approach have been greatly studied and documented. This study uses Harris Hip scores, Trendelenburg’s test and dislocation rates to measure the success of each surgical approach.
There are some limitations to this study that need to be highlighted to give fairness to the results when compared to other studies. The first and possibly most important limitation is that this is a multicentre retrospective study that has included data from many different surgeons over a long period. It has been shown that quality can be maintained even with junior surgeons operating.21 It is therefore not always possible to account for variation in technique or clinical practice. Another limitation is the use of different implants. This could have a large impact on dislocation rate and possibly functional ability, with large diameter femoral heads being less likely to dislocate.22 Specific nerve damage has not been measured in any of these patients except for looking at abductor weakness, often from superior gluteal nerve damage (often not clinically detectable), caused during the anterolateral approach.23 Equivalently the posterior approach has been shown to cause sciatic nerve damage but this was also not measured.24 To maintain integrity of the data results, nerve deficit was an excluded complication.25 As a study, although these limitations could have impacted on the results. The hope is that by looking only at primary total hip arthroplasties in patients with osteoarthritis and excluding only complications likely to impact functional ability, the sample groups are large enough to provide a good statistical stand point to draw conclusions from.26
The anterolateral approach offers a good view of the acetabulum, which has been shown to increase the accuracy of prosthesis positioning.27 Functionally this attributes to a lower dislocation rate although some studies have shown there is no difference between the two approaches. There is an increased risk of damage to the superior gluteal nerve and the gluteus medius, which attributes to an increased likelihood of post-operative Trendelenburg gait due to abductor weakness.28 The posterior approach is considered easier to perform, and is generally a quicker procedure, limiting operative complications such as blood loss and anaesthetic issues. The abductor muscles are not disturbed so there is generally no gait abnormality but the acetabulum is more difficult to see and can make prosthesis positioning difficult, causing an increased dislocation rate.29 The sciatic nerve is at slightly more risk of being damaged as well.30
The data from this study shows some relatively important features. It supports studies that show Trendelenburg’s gait, caused by abductor weakness, has a higher incidence when using an anterolateral approach. Importantly in both full and functional Harris Hip scores the posterior approach showed an improvement over the anterolateral approach when looking at the increase from pre-operative results to post-operative results. Other studies have suggested trochanteric osteotomy as the cause of a lower Harris Hip score, due to increased pain at 1 year,31 however it would not account for the Harris Hip function score, which does not include pain as part of the scoring but was still showing a significant gain in this study.
When looking at dislocation rate use of the posterior approach shows a higher incidence, as is mentioned in much of the literature. However despite the increased dislocation rate in the posterior group, which is comparatively small, the patients who dislocate were found to do as well functionally as those who dislocated in the anterolateral group. It was also interesting to see that the mean loss in Harris hip score was approximately 5 points after dislocation and with the function score only 3 points, when compared with non-dislocating patients. Patients who dislocated were still achieving acceptable gains of greater than 20 points at 1 year, with no increased incidence of an abnormal gait. It is generally considered that a hip arthroplasty is successful if there is an increase in 20 points on the full Harris Hip score, radiographic stability of the implant and no need for femoral reconstruction (last two were excluded if they suffered these problems).17,18
In conclusion the results would seemingly favour a posterior approach to total hip replacement. Taking into account the limitations of this study it is difficult to recommend this approach, as the best for clinical use, without further research. The issue of further research is a difficult one; the main conclusion to be drawn from this study is that a large study addressing all the variables, specifically to look at functional outcomes, using a clinically popular scoring system needs to be undertaken. The difficulties of this are apparent, as it would involve a small number of surgeons working over a long period of time. If similar results could be drawn from such a study the posterior approach would certainly be a better choice for a consultant surgeon to use in primary hip arthroplasties. The slightly increased risk of hip dislocation against a possible functional improvement overall is certainly an important factor to consider. The relative risk of dislocation (4.05%) is actually less than the relative risk of an abductor weakness and the resulting Trendelenburg gait (6.4%) in this study. The functional gain is for most patients, particularly those with osteoarthritis, the reason for surgery and why hip arthroplasty is considered one of the most successful medical interventions. As such maximising this gain should be foremost in any clinicians mind.
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