Anatomic and biomechanical analysis of the short and long head components of the distal biceps tendon.

HYPOTHESIS: The short head bundle of the distal biceps tendon is more efficient at elbow flexion, and the long head is more efficient at forearm supination. METHODS: The short and long head bundles of the distal biceps tendon were separated to the bicipital tuberosity in 6 cadavers. The area and centroid of each bundle insertion were computed from surface points measured within each footprint. Each bundle was individually loaded. The supination torque and flexion load generated were recorded at 90° of elbow flexion. The slope of the torque generated versus biceps load was used to define the supination moment arm. The ratio of the flexion load generated to biceps load applied was used to define the relative flexion efficiency. RESULTS: The short head insertion was positioned distal and anterior relative to the long head and typically included the apex of the tuberosity. The areas of the long and short heads were 59 ± 15 and 94 ± 44 mm(2) (P = .07), respectively. The long head moment arm was significantly higher in supination. The short head had a significantly higher moment arm in neutral and pronation. The ratio of the flexion load to biceps load was 15% higher for the short head. CONCLUSION: The short and long heads of the biceps have distinct insertions. The short head's insertion allows it to be relatively more efficient at elbow flexion at 90°. In the neutral and pronated forearm, the short head is the relatively more efficient supinator. In the supinated forearm, the long head becomes relatively more efficient at supination.

Arthroscopic repair of the scapholunate interosseous ligament.

Scapholunate injuries are the most frequent of the intercarpal ligament injuries in the wrist. Current repair methods generally involve an open approach the dorsal capsule of the wrist. Arthroscopic repair of the dorsal portion of the scapholunate interosseus ligament would carry the advantages of less stiffness and would preserve the important dorsal capsular stabilizers. In the development of this technique, we first sought to determine the anatomic location and accessibility of the dorsal scapholunate ligament and the site in which a suture anchor would be placed. Ten fresh-frozen cadaver limbs were used. With the arthroscope in the 4 to 5 portal, the most dorsal portion of the SLIL was visualized in each specimen. K-wires were inserted through the 3 to 4 portal into the scaphoid adjacent to most distal portion of the dSLIL visualized. All limbs were dissected and the location of the wires relative to the prominence on the scaphoid directly adjacent to the central portion of the dSLIL was measured. The location of the prominence relative to the dSLIL was studied through magnified photography of a stained section of a cadaveric scaphoid. The mean distance of these wires distal to the center of the dSLIL is presented. Then the technique of arthroscopic repair of the dSLIL was developed using additional cadaveric wrist specimens. The technique is described.