Elbow is a hinge joint which connects the forearm and the upper arm. It also plays an important part in the functioning of the wrist. Hence it is very important to have a proper functioning elbow. And when an elbow is damaged there arise a need for a replacement. Arthritis is one of the main reasons for elbow joint replacement. The elbow joint can also be damaged due to injury or fracture and as it is difficult for the fractured bone to heal itself particularly in aged patients; joint replacement provides an alternative option.
Anatomy of the elbow joint:
The elbow consists of bones, joints, ligaments, tendons, muscles, nerves and blood vessels .
The bones in the elbow consists of the upper arm bone called as humerus, lower arm bones ulna which is the larger bone of the forearm and radius which is the smaller bone of the forearm. Radial bone is the one which is on the side of the thumb. Figure 1 shows the schematically the arrangement of bones in the elbow joint .
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Figure 1: anatomy of elbow, bones.  Figure 2: anatomy of elbow, cartilage. 
Figure 2 shows the articular cartilage. In the elbow it exists between humerus ulna and radial bone. Articular cartilage lines the bones at the joints. It can as thick as "quarter of an inch"  for large weight bearing joints. But since the elbow joint is a lighter joint it is slightly thinner. Articular cartilage can be described as "white, shiny and has got a rubbery consistency" . It has a slippery nature which allows the bones to perform their natural movements without causing any damage to the bone. It also reduces the effects of sudden jolts.
Another very important element of elbow joint is ligaments and tendons. Ligaments are number of soft tissues present in a joint which connects the bones with each other. There are two important types of ligaments in the elbow joint know as medical collateral (inside edge of the elbow) and lateral collateral ligament (outside edge of the elbow). The main function of these ligaments is to hold the elbow joint tight while performing its natural movements, damage to the ligament will cause a permanent loosing of the elbow joint. The band tissues which connect muscles to bones are known as tendons. Tendons play a very important role in the elbow joint as it helps in connecting muscles such as biceps and triceps muscles to the elbow joint. As it allows the muscles to have a bond with the bones, it leads to the strengthening of the joint. The important muscles in the elbow joints are the biceps, triceps, wrist extensors, wrist flexors.
Figure 3: General anatomy of elbow joint. 
Nerves are another important element in the elbow joint. The main function of nerves is to carry the signals from the brain to the joints which facilitate the movement of the joint and also carry back information such as temperature, pain and touch to the brain. The radial nerve, the ulnar nerve, and the median nerve control the movement of the elbow joint . The elbow joint also contains blood vessels which are responsible for the blood flow in and out of the joint.
Latitude Elbow prosthesis:
Why do we need prosthesis? Elbow plays an important part in the movement of the arm as well as the wrist. Hence we need a fully functioning elbow. As we know that the damaged elbow causes a lot of pain during movement, it becomes essential to replace the joint with an artificial elbow joint. The artificial joint comprises of metal and plastic which are perfectly designed to fit together and perform the natural movement of the elbow joint without causing any pain.
There are many reasons for an elbow to get damaged. Most common of all is arthritis. The two major types of arthritis which are responsible for the damaged elbow are degenerative and systemic degenerative arthritis. There are various types of elbow joints (prosthesis) available today, but the most common type among all is the hinge type.
Tornier latitude elbow joint:
The Tornier latitude elbow is the "first third generation total elbow prosthesis" . Developed in United States of America, at the prestigious centers in collaboration with highly renowned elbow surgeons. It was launched in 2001.
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The Tornier elbow prosthesis is a three part system which consists of the humeral stem, ulnar stem and floating radial cup. They are basically of two types, unlinked configuration and linked configuration as shown in figure 4 and 5. The examination of the surrounding soft tissues in done and the result of which determines the use of linked or unlinked mode in the implant.
Figure 4: linked configuration . Figure 5: unlinked configuration .
Humeral stem and spool:
Humeral stem is the component that is inserted into the humerus during arthroplasty of elbow. It has got medial and lateral fins which prevent intra medullar rotations. The posterior aspect of the flange has a textured surface which enhances bone growth and thus prevents posterior migration. Figure 4 shows the posterior aspect of the flange. The spool is secured to the stem with the cannulated screw which allows for the passage of sutures to attach soft tissue for the initial stabilization . Humeral spool has been designed with a "concave barrel shaped trochlea to preserve linear contact throughout 70 of valgus/varus movement with ulnar component" . It comes in three sizes of stem and 4 sizes of spool that is small, medium, large and large+ .
Figure 6: posterior aspect of the flange .
Ulnar stem is the part in the prosthesis that is inserted in ulna bone. Ulnar stem comes in two versions short and standard. Notches have been provided to improve cement fixation. It also has fins which prevent the rotation of the stem. The ulnar cap allows pre or post-operative locking. The geometry of the standard stem has been designed in such a way that it reduces the stresses acting on the cortical wall by replicating the natural curve of the ulna. The implant is converted into a linked semi-constrained device by the action of ulnar cap which is designed to capture the humeral component [3, 4]. Figure 7 shows the standard ulnar stem. "The ulnar component comes in three sizes of stem and two lengths, which are standard and short" .
Figure 7: standard ulnar stem .
Radial head is the key anatomical structure in the elbow. The majority of the compressive load which is acting on the elbow is transferred across the radio humeral joint. The absence of radio humeral joint increases the load on the ulno- humeral joint, which results in increase of risk of instability and a premature wear. The radial head is available in "four sizes of head diameter 18, 20, 22 and 24 mm and stems of diameters 5mm and 6.5mm" .
Materials used in the latitude elbow prosthesis:
The main material which is used in manufacturing of latitude elbow prosthesis is cobalt chrome the other materials used is stainless steel and UHMWPE (ultra-high molecular weight polyethylene). The humeral stem is made using cobalt chrome alloy. The humeral spool is made using chrome alloy along with a PEEK-OPTIMA polymer. Stainless steel is used to make humeral screw. All the radial components in the elbow joint prosthesis are made using cobalt chrome alloy along with UHMWPE. There is a stem component in the ulnar which is made of cobalt chrome and the bushing made of UHMWPE.
The selection all the above bio materials are very important in manufacturing the elbow joint prosthesis. We need to check the bio compatibility (behaviour of bio material in various context) of all the materials used in manufacturing any prosthesis. The cobalt chromium alloy which is used in manufacturing the above prosthesis has been used for decades for the manufacturing of surgical implants which are in contact in blood, soft tissues and bone . As cobalt chrome alloy provides the property of excellent corrosion resistance and wear properties, they are as a metal component in total joint replacement. UHMWPE is a plastic with good bearing characteristics that is low coefficient of friction. Thus it is used as a concave compound in the total joint systems in which it is implanted with other metal components such as cobalt chrome . UHMWPE "surface on the ulnar component have been designed to facilitate an anatomic distribution of joint reactive forces" . Use of UHMWPE to articulate cobalt chrome alloy parts reduces tissue sensitisation which is caused due to the release metal particles in this case cobalt and chrome from the prosthesis due to friction at the joints .
Forces on the elbow joint:
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Figure 8: forces acting on the elbow during flexion .
Biomechanics of elbow joint plan an important role in the design of elbow joint prosthesis. Muscle actions which produce an interaction between the limbs and the surrounding during day to day activity are mostly responsible for the forces acting on the upper arm. When the flexion is initiated the force generated in the elbow joint is greatest. At 900 of flexion it has been show that there is increase in flexion strength and decrease in elbow forces, which is because of the "improved mechanical advantages of the elbow flexors secondary to lengthening of the flexion moment arm" . The force generated at the elbow has been shown to be about three times the body weight during certain activities . Studies have shown that during dressing and normal activities the joint reaction forces were 300N, rising from the required about 1700N and pulling a table caused a force of 1900N, almost three times of body weight . Studies conducted have shown that females have 55% of flexion strength of males .
It has been put forth that the artificial joint will be loosened due to the combination of acting tensile and torsion forces on to it. The tensile force acting on the artificial elbow joint may be discounted at the elbow, provided there is now sudden jerk on the joint. Sudden jerk of the arm can produce a pull through of the radial head which normally does not occur while lifting a weight .
While designing an elbow prosthesis is necessary to understand the forces acting on the diseased elbow. Studies have shown that elbows infected with rheumatoid arthritis, which is the largely responsible for elbow joint replacement will have flexion strength of about 45% of normal . Forces as high as 2.4kN have been determined to be acting on a rheumatoid arthritis infected elbow .
Hand force (N)
Humero-coronoid Force (KN)
Force on distal humerus (KN)
Table 1: Elbow joint forces during flexion for male RA patients .
Hand force (N)
Humero-coronoid Force (KN)
Force on distal humerus (KN)
Table 2: Elbow joint forces during extension for male RA patients .
Quality control issues related to prosthesis design:
Quality control of components is paramount to ensure safety and longevity of the product. And when it comes to medical parts and equipment's it is even more important to ensure a good quality in the product as failure or malfunctioning could cost the patient his life.
Most common testing standards are European, British, International and American standards. Tornier elbow implants have satisfy BS EN ISO 14630: 1998 general requirements for non-active surgical implants.
But it is not easy to test medical components like prosthesis as it is difficult to replicate all the motion and movements of that of the natural joint. Moreover the prosthesis is supposed to last lifelong it is difficult to test the prototype for such a long period of time. It is also difficult to replicate the surrounding environment of the joint in the test rig as there will be a need to provide alternate lubricating fluid as synovial fluid used by the human body is difficult to obtain.
Clinical test results for Tornier latitude elbow implants:
As the implant design for Tornier elbow prosthesis is relatively new, till date no clinical data is available .
Comparison with other elbow implants:
Most of the elbow implants available have similar design features. Though some of the designs have different silent features, not much information exists to clearly show its advantages over the others.
Coonard- Morrey elbow joint is made of titanium alloy as compared to that of Tornier which is of cobalt chrome alloy. The humeral component of Coonard- Morrey is designed in such a way that it can be used in both the right as well as the left elbow that is the component is interchangeable. Additionally the humeral component comes with an option of extended flange to facilitate use when distal humeral bone stock is missing. The ulnar component has a plasma sprayed porous coating which facilitates bone growth .
Discovery elbow prosthesis also uses titanium alloy and has roughened surface finish in areas that do not have porous coating. This uneven surface finish aids bone growth and prevent the prosthesis from dislodging. The polyethylene bearing surface comes attached to the ulnar component but it can be detached and replaced in case of bearing wear. The humeral and the ulnar component are connected using a cobalt chrome condyles. This is a noncritical linkage as it does not need assembly until the components are fully inserted .
Huene bi-axial elbow prosthesis, as its name suggests has a two axial system. Single axial system like the Tornier cannot completely provide the translocation of the axis of rotation during normal articulation of the elbow. The bi-axial system manages to accurately replicate the anterior translocation of the ulna. This feature gives the Huene bi-axial elbow prosthesis 16 degree of varus-valgus laxity and 10 degree of rotational laxity as compared to Tornier's 7 degree of varus-valgus laxity. The feature not only provides exceptional motion but also reduces implant loosening, component fracture, and wearing of the bearings .
Benefits and drawback of Tornier prosthesis:
Tornier latitude elbow provides relief for patients suffering from arthritis. And by replicating the anatomy of the elbow it restores the natural kinematics of the joint.
It provided the option to use the implant in linked or unlinked mode. In case the implanted is to be converted from unlinked to linked, it can be easily done without removing the implant. .
The spool is designed in such a way that it allows for a better anatomic distribution of joint reactive force and also provides 7 degrees of varus-valgus laxity .
The humeral spool has been provided with a concave barrel shaped trochlea which keeps line contact throughout 7 degree of varus-valgus movement with the ulnar component .
The humeral stem has been designed with fins to prevent intramedullary rotation.
The anterior flange facilitates bone grafts which help prevent posterior migration.
The stem of the ulna component has been provided with the natural bow of the ulna bone which helps in reducing stresses on the cortical wall .
However good the prosthesis might be but it won't be able to provide the full mobility of the natural arm.
Most of the patients undergoing elbow joint replacement will be having the problem of weak bones mostly due to arthritis and by the removal of bone for the placement of the joint further weakens the bone strength.
It has a single axis design which cannot completely account for the translocation of the axis of rotation that accounts during normal articulation .
Bearing wear cannot be completely eliminated.
The wear particles are also a cause of concern as it may get mixed with the tissues and may become difficult to separate.
There are chances of the prosthesis coming loose due to excessive stresses especially in younger patients who tend to have more activities.
Scope for improvements:
Tornier elbow prosthesis is a semi-constrained prosthesis, hence it cannot fully replicate the natural movement of the elbow joint. The bi-axial system developed by Huene could be considered to give more degrees of movement. The role of bearing geometry on polyethylene wear is poorly understood . Further work can be done in this regard to reduce wear. Tornier prosthesis uses bone cement as bonding agent, option like increased bone growth into the prosthesis can be looked in to further strength the prosthesis and or eliminate cement usage. Options to use bio materials in the prosthesis can be looked into to increase the bio compatibility of the prosthesis.
Total elbow joint replacement is a relatively new procedure, hence there is not much clinical data available to compare between different types of elbow prosthesis. Tornier elbow prosthesis replicates the kinematics of the natural elbow to a higher extent. It provides an option for linked and unlinked prosthesis. It is good option for people needing elbow replacement though there is not much to distinguish it from other elbow prosthesis.