Partial nerve lesions with a varying degree of retained function and often a painful neuroma pose a dilemma for the clinician. Surgical treatment of partial nerve lesion is perilous because of possible damage to intact axons and subsequent loss of retained function. We present a new rat model of a partial nerve lesion, allowing further study to improve treatment for this condition. A partial (50%) lesion of the tibial portion of the rat sciatic nerve was created and compared to standard crush and neurectomy control lesions. The extent of lost function and the progress of postoperative recovery following the three lesions were compared using serial walking track analyses and end-point muscle weight ratios for atrophy as outcome measures. All groups had tibial functional indices (TFI) significantly different from one another after 1 week. TFIs for the crush group returned to normal by 4 weeks, whereas the neurectomy group showed no recovery. The partial lesion group gradually improved, reaching a plateau of 44% by 7 weeks. Gastrocnemius muscle weight ratios for the partial, crush, and neurectomy lesions at 9 weeks were 0.63, 0.87, and 0.32, respectively. There was a strong correlation between the TFI and muscle weight ratios (r(2) = 0.89; P < 0.001) suggesting that these outcome measures are highly predictive of function. In conclusion, the partial lesion showed a gradual but incomplete functional recovery with a complementary degree of muscle atrophy. The model may prove useful in the evaluation of proposed treatments for partial nerve lesions and the associated painful state.

Standard treatment for a neuroma-in-continuity with partial retained function is neurolysis with or without grafting. The present study tests the outcome of a novel partial nerve lesion bypassed with an end-to-side bridge graft, intended to increase the number of axons crossing the defect while not disturbing intact axons. An 8-mm portion of tibial nerve was resected in 20 rats. Three weeks later, half had the defect repaired with an end-to-side bridge allograft and perineurial windows; controls had only neurolysis. Recovery was evaluated using walking-track analysis, allodynia testing, muscle weight ratios, and histology at 8 weeks. No significant differences in motor or sensory functional recovery were noted between the two groups. Histology showed good axonal regeneration through the defect in all specimens. The experimental group also had regenerated axons in the bridge graft, but their maturity was less advanced, presumably due to delays in regeneration.

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A partial nerve lesion and associated neuroma can be either left alone or repaired with a graft. A by-pass graft around the undisturbed lesion with end-to-side attachments might be a good alternative. This study in rats examines these strategies using walking-track analysis, muscle weights, and histology. After a tibial nerve partial lesion (3 mm) and a 21-day delay, the reexposed lesion was either not repaired, repaired with an interposed allograft, or a by-pass allograft. Functional results showed that all three groups had a steady improvement over the 8-week period, but without significant group differences. Gastrocnemius muscle ratios reflected intermediate atrophy. Axons regenerating through the lesion were more advanced than those which regenerated through the grafts and a neuroma was absent. The partial lesion can regenerate to an intermediate level without any intervention, including a by-pass graft, although the delayed repair strategy may have counteracted any potential benefits.