Supraspinatus tendon repair into a bony trough in the rabbit: Mechanical restoration and correlative imaging

Abstract

Recurrence of tears is a common complication after rotator cuff surgery. Retearing seems to occur early after surgery and may be attributed to too early or too vigorous exercises. We found no experimental data correlating the strength of the rotator cuff early after surgery and imaging. Our objectives were to measure the peak load to failure of rabbit supraspinatus tendon-bone constructs at early times postoperatively, to determine their mode of failure, and to determine whether computed tomography (CT) can predict their strength. We divided one supraspinatus tendon of 40 adult female white New Zealand rabbits and, after resection of the enthesis, sutured the tendon into a bony trough. Ten rabbits were killed immediately and 10 each at 1, 2, and 6 weeks postoperatively. The explanted tendons of both shoulders were imaged on CT and tested to failure. Compared to normal tendons (mean 210 +/- 42 N), the mean strength was very low at 0 weeks (57 +/- 21 N) and 1 week (86 +/- 33 N) (both p < 0.05); it had recovered by 6 weeks (324 +/- 66 N). Early on, suture pullout was the most common mode of failure, whereas at 6 weeks, mid-substance tears predominated (p < 0.05). Hypoattenuation on CT was associated with increased strength of the tendon-bone construct (p < 0.05). The strength of the surgical construct is very low in the early postoperative period. Therefore, the shoulder should be submitted only to loads not interfering with healing.