Failure of the biceps superior labral complex: a cadaveric biomechanical investigation comparing the late cocking and early deceleration positions of throwing.
OBJECTIVE
The goal of the study was to determine which position of the throwing motion, late-cocking or early deceleration, was more likely to produce lesions of the biceps superior labral complex.


METHODS
Cadaveric biomechanical model.


METHODS
Ten paired cadaver shoulders were prepared and mounted on a custom testing apparatus in 60 degrees glenohumeral abduction with the humerus in the plane of the scapula. All specimens were loaded with 100 cycles of subfailure external rotation torque (7.9 N-m) with 22 N applied to the rotator cuff tendons and long head of the biceps tendon. One of each pair of specimens was randomly tested in a late cocking position for throwing (>125 degrees external rotation, 60 degrees glenohumeral abduction, in the plane of the scapula). The other was tested in a position of early deceleration (80 degrees external rotation, 60 degrees glenohumeral abduction, 16 degrees horizontal adduction). The biceps was loaded to failure with the shoulder fixed in these positions. The specimens were then examined by 2 experienced shoulder surgeons, blinded to the test protocol, to assess for the presence of a type II SLAP lesion.


RESULTS
Failure of the biceps superior labral complex occurred at the superior glenoid in 9 of 10 specimens in the late cocking position and in 2 of 10 specimens in the early deceleration position (P =.055). Five specimens developed type II SLAP lesions, with more in the late cocking position (4 of 10) than in the early deceleration position (1 of 10; P =.12). Load to failure was significantly less for the late cocking position (289 +/- 39 N) than for the early deceleration position (346 +/- 40 N; P =.004).


CONCLUSIONS
These results suggest that the late cocking position may contribute to biceps-superolabral complex injuries in the thrower's shoulder.
Kuhn
John E
JE
University of Michigan Shoulder Group, Orthopaedic Research Laboratories, Department of Orthopaedic Surgery, the University of Michigan, Ann Arbor, Michigan, USA. jekuhn@umich.edu
Lindholm
Stephen R
SR
Huston
Laura J
LJ
Soslowsky
Louis J
LJ
Blasier
Ralph B
RB
D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D002358:Cartilage, Articular / Q000503:physiopathology*; D005260:Female; D006801:Humans; D006811:Humerus; D008297:Male; D008875:Middle Aged; D009068:Movement; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011187:Posture; D016059:Range of Motion, Articular; D012399:Rotation; D017006:Rotator Cuff / Q000503:physiopathology; D012540:Scapula; D012785:Shoulder Joint / Q000503:physiopathology*; D013710:Tendons / Q000503:physiopathology*