Frederick W Werner — Page 2

PubMed2002

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.

Biomechanical Phenomena↗

PubMed2002

Biomechanical evaluation of ligamentous stabilizers of the scaphoid and lunate.

This study evaluated the effects of sectioning the scapholunate interosseous ligament, radioscaphocapitate ligament, and scaphotrapezial ligament on the kinematics of the scaphoid and lunate. Eight cadaver upper extremities were placed in a wrist joint simulator and moved in continuous cycles of flexion-extension and radial-ulnar deviation. Positional data of the scaphoid and lunate were obtained in the intact state, after the scapholunate ligament was cut; after the scapholunate and scaphotrapezial ligaments were cut; after the scapholunate, scaphotrapezial, and radioscaphocapitate ligaments were cut; and after all 3 ligaments were cut and the specimen was placed through an additional 1,000 cycles of flexion-extension. Cutting the scapholunate ligament caused changes in scaphoid and lunate motion during flexion-extension, but not radial-ulnar deviation. Additional sectioning of the scaphotrapezial ligament followed by the radioscaphocapitate ligament caused further kinematic changes in these carpal bones. One thousand cycles of motion after all 3 ligaments were sectioned caused additional kinematic changes in the scaphoid and lunate. The scapholunate ligament appears to be the primary stabilizer between the scaphoid and lunate. The radioscaphocapitate and scaphotrapezial ligaments are secondary restraints. Repetitive cyclic motion after ligament sectioning appears to have additional deleterious effects on carpal kinematics.

Aged↗