Biomechanical Aspects of the Elbow: Joint Forces Related to Prosthesis Design

Total elbow arthroplasty in rheumatoid arthritis: a population-based study from the Finnish Arthroplasty Register

BACKGROUND AND PURPOSE

Although total elbow arthroplasty (TEA) is a recognized procedure for the treatment of the painful arthritic elbow, the choice of implant is still obscure. We evaluated the survival of different TEA designs and factors associated with survival using data from a nationwide arthroplasty register.

METHODS

1,457 primary TEAs for rheumatoid elbow destruction were performed during 1982 to 2006 in one hospital specialized in the treatment of rheumatoid arthritis (n = 776) and in 19 other hospitals (n = 681). The mean age of the patients was 59 years and 87% of the TEAs were performed in women. We selected different contemporary TEA designs, each used in more than 40 operations including the Souter-Strathclyde (n = 912), i.B.P./Kudo (n = 218), Coonrad-Morrey (n = 164), and NESimplavit/Norway (n = 63) to assess their individual survival rates. Kaplan-Meier analysis and the Cox regression model were used for survival analysis.

RESULTS

The most frequent reason for revision was aseptic loosening (47%). We found no differences in survival rates between different TEA designs. We did, however, find a 1.5-fold (95% CI: 1.1-2.1) elevated risk of revision in unspecialized hospitals as compared to the one hospital specialized in treatment of rheumatoid arthritis. In the Souter-Strathclyde subgroup, there was a reduced risk of revision (RR 0.6, p = 0.001) in TEAs implanted over 1994-2006 as compared to those implanted earlier (1982-1993). The 10-year survivorship for the whole TEA cohort was 83% (95% CI: 81-86), which agrees with earlier reports.

INTERPRETATION

The influence of implant choice on the survival of TEA is minor compared to hip and knee arthroplasties. Inferior survival rates of the TEAs performed in the unspecialized hospitals demonstrates the importance of proper indications, surgical technique, and postoperative follow-up, and endorses the need for centralization of these operations at specialized units.

Radial head fractures--advanced techniques in surgical management and rehabilitation

Radial head fractures are the most common fractures in the elbow, and the treatment of nondisplaced fractures is often straightforward. However, radial head fractures with concurrent injury to the elbow stabilizers may require complex treatment and therapy that are targeted at specifically restoring elbow stability. This treatment of complex radial head fractures has recently improved because of long-term follow-up studies, increased biomechanical research on elbow stability, and improved surgical techniques. With an open line of communication between the surgeon and the therapist, an appropriate therapy plan can be initiated to protect both simple and complex injuries. The therapist should have knowledge of specific tissue healing and treatment techniques, and the patient must be educated in possible outcomes, safe arcs of motions, positioning, and proper splint use. This article summarizes current advanced techniques in the surgical management and rehabilitation of radial head fractures. Comprehensive protocols for decision making and treatment are introduced for both simple and complex radial head fractures.

Total elbow arthroplasty with the Coonrad/Coonrad-Morrey prosthesis

There have been few reports in the literature of total elbow arthroplasty extending beyond 10 to 15 years. We reviewed 40 patients (41 elbows) with a mean age of 56 years (19 to 83) who had undergone a Coonrad/Coonrad-Morrey elbow arthroplasty by one surgeon for various diagnoses between 1974 and 1994. Surgical selection excluded patients with previous elbow infection or who refused to accept a sedentary level of elbow activity postoperatively. Objective data were collected from charts, radiographs, clinical photographs and supplemented by the referring orthopaedic surgeons’ records and radiographs if health or distance prevented a patient from returning for final review. Subjective outcome was defined by patient satisfaction.

Of the 41 elbows, 21 were functional between 10 and 14 years after operation, ten between 15 and 19 years and ten between 20 and 31 years. There were 14 complications and 13 revisions, but no cases of acute infection, or permanent removal of any implant.

Kinematics and stability of the fractured and implant-reconstructed radial head

Controversy exists as to the optimal management of radial head fractures. Biomechanical studies have been conducted to quantify elbow stability for simulated wedge fractures, head excision, and head replacement, with and without the integrity of the collateral ligaments. Our in vitro studies have demonstrated that in the ligamentously intact elbow, kinematics and stability are slightly altered with simulated depressed wedge fractures up to 120 degrees of the radial head, markedly altered with head resection, and improved after radial head replacement. Radial head excision decreases elbow stability in the ligament-deficient elbow, and radial head replacement improves stability similar to that of the native radial head. The ligaments have the most marked influence on stability, particularly when the upper limb is positioned such that valgus and varus gravity loads are applied to the elbow. Whereas the radial head acts as a secondary stabilizer to the collateral ligaments with the arm in these positions, its relative role is greater when the arm is in the dependent position and elbow flexion is simulated, particularly in extension. Further studies are needed to elucidate the complex interaction of the radial head with the capitellum, the ulnohumeral joint, and the ligamentous structures for different activities of daily living.

Management of comminuted radial head fractures with replacement arthroplasty

Radial head arthroplasty is indicated for displaced comminuted radial head fractures that cannot be managed reliably with open reduction and internal fixation and that have an associated elbow dislocation. Replacement also is indicated in patients with comminuted radial head fractures that have or are likely to have a disruption of the medial col-lateral, lateral collateral, or interosseous ligaments. Biomechanical studies have demonstrated that metallic implants restore elbow stability similar to the native radial head. The early and midterm clinical experience with metallic radial head arthroplasty has been encouraging relative to earlier reports with silicone devices. Newer modular designs incorporate improved sizing to better reproduce the anatomy of the proximal radius and are easier to insert intraoperatively.

Modeling and finite element analysis of a new revision implant for the elbow

Failed total elbow arthroplasties often are associated with significant bone loss, especially at the level of both humeral condyles. Regular implants might not be ideal for those revision cases and either custom-made implants or complex bone reconstruction procedures with grafts are needed. The goal of the current study was to develop a new revision implant, based on an existing total elbow system (GSB III). The new revision humeral component, with an anterior flange instead of condylar flanges, was designed in a computer-aided design program and virtually implanted in a modeled humerus from a cadaver and subsequently was tested in a finite element model under different loading conditions. The overall distribution of the von Mises stress, as a generalized stress intensity factor, did not differ significantly between the GSB III and the new revision component. There was a tendency that the anterior flange, compared with the condylar flanges, protected the implant-cement-bone interface in the critical region of the distal stem. The finite element analysis suggests that the revision concept for failed total elbow arthroplasties, to rely on existing anterior humerus cortex instead of reconstruction of the condylar bone, seems to have no disadvantage in terms of stress distribution on the implant.

Total elbow replacement in the treatment of rheumatoid disease

Improvements in total elbow arthroplasty during the last 20 years have resulted in clinical outcomes which now are comparable with the results of hip arthroplasty. The main types of prostheses used are unlinked prostheses or semiconstrained hinged prostheses. The unlinked prostheses require the preservation of bone stock and the ability to reconstruct the collateral ligaments to achieve stability. Semiconstrained, hinged prostheses have inherent stability but humeral loosening was initially a problem. Stress transfer through the humeral stem can be reduced by using a prostheses with anterior flanges (Coonrad-Morrey or GSB3). Survivorship analyses beyond 10 years now are becoming available for these prostheses. There has been no universal agreement as to which outcome measure should be used for total elbow replacements. Future developments will include an evolution of principles as understanding of elbow biomechanics progresses. Operative technique is likely to be modified by the development of alignment aids and jigs.

Late complications with the Pritchard Mark II elbow prosthesis

Twenty-three consecutive patients with rheumatoid arthritis who had 26 Pritchord Mark II elbow prostheses were followed prospectively with a mean follow-up of 75 months (range 52 to 101 months). Two patients with three elbow prostheses have died, leaving 21 patients with 23 elbow prostheses for review. At the latest follow-up all the nonrevised elbows had achieved good or excellent results concerning pain relief and elbow motion. According to the data analyzed by a survivorship function-a Kaplan-Meier curve-the early results were promising with 92% of the prostheses surviving the first 5 years; however, only 43% of the prostheses have survived 8 years. Seven prostheses have been revised; the reasons for revision include one infection, one humeral fracture, one loosening of the humeral component, and four disconnections of the hinge. The number with disconnection of the hinge is increasing. Of 16 prostheses still not revised, the x-ray film reveals migration of the pin axle in six. Radiographic signs of component loosening or migration of the axle are not reflected in pain, function, or total score of the elbow.

Treatment of posttraumatic elbows with a new hinge-distractor

A simple design of elbow hinge distractor for the restoration of joint function in contractures, ankyloses, persistent dislocations, and nonunions is presented. Soft tissue releases and reshaping of joint surfaces is carried out surgically as required. Obtaining motion and stability is achieved with side plates attached to external fixation pins, one of which passes through the axis of rotation of the joint and about which flexion takes place. Distraction is obtained by a screw that separates the ulnar side plates from the humeral side plates. To aid in accurately placing the axis of rotation pin at surgery, a study was done to determine the best fit axis of rotation and how it relates to boney landmarks. One case of an ankylosed elbow is presented in detail, including the surgical technique. This and other previous cases have shown that good clinical results can be achieved in these otherwise poorly functioning elbows. Key index words: Elbow, Biomechanics.