Pressure between the humeral head and the subscapularis tendon after the modified Boytchev procedure.

The pressure between the humeral head and the subscapularis tendon was determined in 32 patients who had recurrent anterior shoulder dislocations. These patients' pressures were measured during a modified Boytchev procedure both before and after transposition of the conjoined tendon, and they were remeasured at the time of screw removal, performed at a mean of 13 months after the initial surgery. The mean clinical follow-up period was 31 months. A micro-tip catheter transducer was inserted into the glenohumeral joint between the humeral head and the subscapularis tendon. Pressures were measured at particular degrees of motion for two positions: passive external rotation of the arm at the side at 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees and passive external rotation at the 90 degrees abducted position at 0 degrees, 30 degrees, 60 degrees, and 90 degrees. The pressures were statistically significantly higher after the conjoined tendon transfer at all measured degrees of motion in the two positions. The pressures at the time of screw removal were not statistically significantly different from those seen after the tendon transfer during external rotation at 90 degrees of abduction. The modified Boytchev procedure increases the pressure between the humeral head and the subscapularis tendon. We suspect that this increased pressure increases proprioceptive stimuli in the subscapularis tendon and thus accelerates the protective reflex needed to prevent shoulder dislocation.