To date, however, translations of this magnitude have not been demonstrated in vivo. In the shoulders of patients with isolated ruptures of the LHB, when compared with their contralateral healthy shoulders, average superior position differences of the humeral head of 2.2 mm (maxi- mum difference of 6 mm) at 45°, 90°, and 120° of abduction were measured by Warner and McMahon using serial, static radiographs. The authors theorized this amount of superior translation could contribute to an iatrogenic impingement syndrome. However, in the clinical literature, the stabilizing role of the LHB has not been as evident. For instance, the distance between the acromion and the humeral head in static radiographs was not altered after tenotomy. Similarly, Boileau et al4 have further questioned the stabilizing role of the LHB, showing no clinical evidence of instability or proximal humeral migration in patients who were treated with tenodesis compared with those treated by superior labral anterior posterior (SLAP) repair. Moreover, significantly more patients were able to return to their previous level of sports participation when compared with SLAP repair in this study.
Clearly, surgeons still face a confusing and contradictory body of evidence surrounding the biomechanical function of the LHB. While cadaveric studies show a stabilizing effect of the LHB, clinical data suggest that there is no clinically demonstrable increased humeral head motion after LHB tenodesis or tenotomy. Therefore, the purpose of this study was to investigate the effects of the LHB on glenohumeral kinematics in vivo using highly sensitive and accurate 3-dimensional imaging. To do this, we used a biplane fluoroscopy system to compare shoulders in patients who had undergone an isolated LHB tenodesis with their healthy contralateral shoulder during abduction, a simulated late cocking phase of a throw, and a simulated lifting task (loaded forward flexion). Our hypothesis was that there would be no differences in glenohumeral translations greater than 1.0 mm between the shoulders.