Review Question - QID 220018

A defect of > 50mm (5cm) between peripheral nerve ends dictates the need for nerve autograft in order to ensure a tension-free repair.

Nerve-grafting after peripheral nerve injury is guided by a set of principles with the goals of ensuring complete scar removal from nerve ends and creating a tension-free repair by using a graft that is at least 10% longer than the gap. Surgical options include direct repair, conduits, vein grafts, nerve allografts, nerve autografts, and nerve transfer. Conduits made of type I collagen can be used for defects up to 20mm in length, as they rely on the formation of a fibrin clot to serve as a scaffold for host Schwann cells to build upon. The gold-standard for defects > 5cm, however, is nerve autografting, which can be accomplished using a host of donor sites including the medial and lateral antebrachial cutaneous and posterior interosseous nerve terminal branches, however, these are better used for nerve defects in the distal zone. For palm-level defects, the gold standard remains sural nerve autografting, though there is literature to suggest that processed nerve allograft may be effective for gaps up to 7cm (see Safa et al.)

Grinsell et al. provide a review of clinical and experimental therapies for peripheral nerve reconstruction after injury. The authors note that less than half of patients who undergo nerve repair after injury regain good to excellent motor or sensory function and that current surgical techniques are similar to those described by Sunderland more than 60 years ago. They conclude that recent surgical options including nerve transfers demonstrate promise in improving outcomes for proximal nerve injuries and experimental molecular and bioengineering strategies are being developed to overcome biological roadblocks limiting patient recovery.

Namazi et al. performed a cadaveric study to assess donor nerve grafts for covering thumb nerve defects. The authors looked at five cadaver thumbs from palm to interphalangeal joint, dividing this length into three segments corresponding to the metacarpal, the proximal phalanx, and the distal phalanx. They concluded that in the palm and metacarpal zones, respectively, the sural and lateral antebrachial cutaneous nerves were the best match in both domains.

Safa et al. performed a large multi-center study of peripheral nerve repair throughout the body with processed nerve allografts (PNA). The authors included 385 subjects and 624 nerve repairs and found an overall 82% meaningful recovery (MR) was achieved across sensory, mixed, and motor nerve repairs up to gaps of 70 mm. They concluded that clinical evidence supports the continued use of PNA up to 70 mm in sensory, mixed and motor nerve repair throughout the body and across a broad patient population.

Figure A is a clinical photograph of a hand with a primary laceration over volar zone II of the palm with an evident flexor tendon injury to the middle finger given its resting extended position.

Incorrect Answers:
Answers 1-4: The gold standard for nerve gaps > 5cm remains sural nerve autografting.