Short-term immobilization after combined flexor tendon and digital nerve repair has traditionally been considered to protect the early nerve repair from rupture. Unfortunately, this can result in complications related to loss of motion in the digit as a result of the delay in performing tendon rehabilitation. The authors designed this study to evaluate the resistance to rupture of freshly repaired digital nerves in a cadaver model, with increasing gap lengths and tensions, and with nerve grafts. Both protected and unprotected early motion protocols were simulated to determine the benefit of splinting in preventing rupture. 100 digital nerves in 10 fresh cadavers were studied. Gap lengths of 0-10 mm, in increments of 2.5 mm, were created. Bruner incisions, microscopic dissection, and standardized 3-point 10-0 nylon epineural repairs were used. Gaps were created at the level of the PIP joint in the fingers and the proximal phalanx in the thumb. Following repair, each digit was closed and a modified Duran early mobilization protocol was performed on the digit, first in an extension blocking splint. After mobilization of each gap length in the splinted group was performed, the skin was reopened and the repair inspected. If gapping or rupture had not occurred, the mobilization was repeated without splint protection to 60 degrees of hyperextension at the MCP joint. When rupture occurred, or if a 10 mm gap length was reached without failure, a nerve graft was inserted with the same gap length and testing was repeated. There were no significant differences in gap length producing rupture within each splint protocol. However, there was a significant difference between splinting and non-splinting protocols with rupture occurring at 9.7 +/- 0.8 mm vs. 7.3 +/- 1.9 mm, respectively. The percentages of nerves remaining intact dropped off precipitously in the splinted group at 10 mm vs. 5 mm for the unsplinted group. Grafting prevented ruptures in all groups.
The deleterious effects of digital nerve repairs on functional results after flexor tendon repair have been well-documented. This study attempts to provide some objective criteria for allowing early passive motion after combined digital nerve/flexor tendon repairs based on the gap length of the nerve defect. In the cadaver model, a defect of up to 10 mm appears to be tolerated without rupture in a carefully controlled protocol with dorsal blocking splint protection. Longer gaps bridged with nerve grafts allow early motion with or without splint protection. The authors acknowledge the potential differences that may exist between nerve repairs in cadaver fingers and those in live subjects, including the effects of tissue elasticity, scar tension, and vascular changes in early wounds. However, their results do offer encouraging incentive and some guidelines for instituting early protected motion protocols in combined digital nerve/flexor tendon repairs. Protective splinting during early motion and the liberal use of nerve grafts appear to minimize the risk of nerve rupture during this critical period.