Ulnar Head Replacement Research Articles

Effect of simulated muscle activity on distal radioulnar joint loading in vitro

This study investigated the relationship between simulated forearm muscle loads and the joint reaction force in the distal radioulnar joint using an in vitro model. Seven fresh frozen cadaveric specimens were mounted in an upper extremity joint simulator capable of applying pneumatic loads to various (muscle) tendons while restraining the forearm in the three positions of pronation, supination, and neutral rotation. Loads were applied to model four forearm muscles (biceps, pronator teres, pronator quadratus, and supinator) in 10 N increments ranging from 10 N to 80 N for the biceps and pronator teres and in 10 N increments from 10 N to 50 N for the pronator quadratus and the supinator. Distal ulnar arthroplasty was performed on each specimen with a custom instrumented ulnar head replacement implant that quantified loads (via strain gauge instrumentation). The relationship between increasing muscle load and joint load was found to be positive and quasilinear in most cases. The biceps had the greatest influence on the distal radioulnar joint reaction force with a joint force in the range of 8% to 33% of the applied muscle load. The pronator teres, supinator, and pronator quadratus were less influential with a joint reaction force ranging between 6% to 19%, 4% to 9% and 2% to 10% of the applied muscle load, respectively.

Design and implementation of an instrumented ulnar head prosthesis to measure loads in vitro

The development of a novel instrumented implant for ulnar head replacement is presented in this study. This implant was instrumented with strain gauges to quantify bending moments about the anatomic axes of the distal ulna, and subsequently the distal radioulnar joint (DRUJ) reaction force magnitude. The implant was surgically inserted in seven cadaveric upper extremities, which were subsequently mounted in a custom joint simulator. Simulated active unresisted pronation and supination motion trials were conducted using computer-controlled pneumatic actuators to simulate forearm musculature. Passive (unloaded) trials were also conducted. The reaction force across the DRUJ ranged from 2 to 10 N in magnitude during this unresisted motion. Increased bending moment magnitudes were measured when the forearm was positioned in supination compared to pronation. The magnitude of joint bending moments showed a consistent pattern with forearm position, regardless of simulated active or passive rotation, or supination and pronation motion trials. This result illustrates that the primary influence on joint load is likely the position and contact with the radial articulation. This study of DRUJ loading should be useful for biomechanical modeling, implant design considerations and improved knowledge of articular mechanics.

Kinematics of ulnar head arthroplasty

This in vitro study evaluated the performance of an ulnar head replacement. A joint simulator was employed that produced active forearm rotation in cadaveric specimens, with motion measured using an electromagnetic tracking system. The kinematics of the intact forearm were compared with a partial ulnar head replacement and a full replacement (with and without soft-tissue reconstruction) and a full excision of the ulnar head. There were no differences between intact kinematics and those following prosthetic reconstruction. However, ulnar head excision produced distal radioulnar joint instability in the form of radioulnar convergence and increased anteroposterior translations.

Biomechanical analysis of two ulnar head prostheses.

The biomechanical effectiveness of 2 ulnar head prostheses was evaluated in 5 fresh-frozen cadaver arms. By using electromagnetic sensors, the amount of forearm rotation, diastasis, and dorsal/palmar subluxation of the radius at the level of the sigmoid notch was measured with the forearm in neutral rotation, pronation, and supination with and without dorsal/palmar loading. Testing was done in the intact specimens and after insertion of 2 types of ulnar head prostheses. Dynamic forearm rotation was also achieved by applying loads in the line of action of the appropriate pronator or supinator muscles to obtain a centroidal path of the radius relative to the ulna. Overall after ulnar head replacement forearm rotation lessened in pronation, diastasis decreased in most forearm positions, and subluxation increased in supination compared with the intact specimen. Despite these changes, both prostheses maintained near-normal biomechanics of the distal radioulnar joint when compared with the irregular behavior occurring after distal ulna resection. Therefore these prostheses are suggested for restoration of distal radioulnar joint function.

A critical analysis of Swanson ulnar head replacement arthroplasty: Rheumatoid versus nonrhematoid

Clinical and radiographic assessment of the results of 40 Swanson silicone ulnar head prosthesis implants in three different patient groups is presented. Twenty-eight were done for treatment of rheumatoid arthritis, eight for ulnoradial impingement after the Darrach procedure, and four for ulnocarpal impingement resulting from malunited Colles' fractures. Patients were reviewed 12 to 48 months after operation (mean, 29 months). Seventy-eight percent of patients reported relief of pain and improved function. Radiologic examination showed that all patients exhibited resorption of the distal ulna (mean 4.4 mm) and that resorption was worst in the group with rheumatoid arthritis. Bone resorption about the implant predisposed the cap to both side-to-side tilt and pistoning of the prosthesis on supination and pronation. There was a 10% revision rate because of silicone synovitis. Although clinical results remain satisfactory for patients with rheumatoid arthritis and ulnocarpal impingement, the radiologic results suggest that Swanson ulnar head replacement should be restricted to elderly patients with rheumatoid arthritis.