Intrasynovial flexor tendon repair - An experimental study comparing low and high levels of in vivo force during rehabilitation in canines

Background: Rehabilitation methods that generate increased tendon force and motion have been advocated to improve results following intrasynovial flex or tendon repair. However, the effects of rehabilitation force and motion o n tendon-healing may be masked by the high stiffness produced by newer sutu re methods. Our objective was to determine whether the biomechanical proper ties of tendons repaired by one of two multistrand suture methods were sens itive to an increased level of applied rehabilitation force. Methods: Two hundred and fourteen flexor digitorum profundus tendons from 1 07 adult dogs were transected and repaired. Dogs were assigned to one of fo ur groups based on the rehabilitation method (low force [<5 N] or high forc e [17 N]) and the repair technique (four-strand or eight-strand core suture ) and were killed between five and forty-two days after the procedure. Repa ir-site structural properties were determined by tensile testing, and digit al range of motion was assessed with use of a motion-analysis system. Results: Tensile properties did not differ between the low and high-force r ehabilitation groups, regardless of the repair technique (p > 0.05). In con trast, tensile properties were strongly affected by the repair technique, w ith tendons in the eight-strand group having an approximately 35% increase in ultimate force and rigidity compared with those in the four-strand group (p < 0.05). Ultimate force did not change significantly with time during t he first twenty-one days (p > 0.05); there was no evidence of softening in either of the repair or rehabilitation groups. Force increased significantl y from twenty-one to forty-two days, while rigidity increased throughout th e forty-two-day period (p < 0.05). Conclusions: Increasing the level of force applied during postoperative reh abilitation from 5 to 17 N did not accelerate the time-dependent accrual of stiffness or strength. Suture technique was of primary importance in provi ding a stiff and strong repair throughout the early healing interval. Clinical Relevance: Our findings suggest that there be a reexamination of t he concept that increases in force produced by more vigorous mobilization p rotocols are beneficial to tendon-healing. While more vigorous rehabilitati on may help to improve hand function, we found no evidence that it enhances tissue-healing or strength in the context of a modern suture repair.