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Published on: May 11, 2011
MRI-measured tendon retraction distance is associated with EMG-confirmed neurotrauma in proximal hamstring avulsion
David Wood1, Miloš Spasojevic1,2, Sofie French3
1North Sydney Orthopaedic and Sports Medicine Centre Sydney New South Wales Australia.
Purpose:
Complete proximal hamstring avulsion injuries are anatomically complex because of their proximity to the sciatic nerve. This study characterises neurological abnormalities following injury and surgical repair. Although denervation has been described, its severity, pattern and diagnostic thresholds in relation to magnetic resonance imaging (MRI) findings, anatomical innervation and tendon retraction distance remain poorly defined.
Methods:
In this prospective longitudinal cohort study, 18 patients undergoing surgical repair of MRI-confirmed complete proximal hamstring avulsion were evaluated using serial electromyography (EMG) and MRI performed preoperatively and postoperatively over 12 months. Tendon retraction distance, muscle and sciatic nerve MRI characteristics and EMG evidence of denervation were recorded. EMG findings were used to distinguish traumatic from postoperative nerve injury. Receiver operating characteristic analysis and Youden's J-statistic were applied to determine a tendon retraction threshold associated with neurotrauma.
Results:
Among the 18 patients, 5 (28%) had preoperative nerve injuries. Of the 13 patients without denervation preoperatively, 3 (23%) experienced iatrogenic injuries postsurgery. SHORE scores and MRI did not differ significantly between normal and abnormal EMG cohorts, although neurological symptoms were numerically more frequent in the abnormal group. Increased tendon retraction was significantly associated with more severe EMG abnormalities in the hamstring muscles, with a 5-cm threshold demonstrating good discrimination.
Conclusion:
Proximal hamstring avulsion injuries exhibit varying degrees of neuropathology and recovery. MRI-measured retraction, not MRI signal changes, may predict neurotrauma. EMG is required to confirm denervation. Retraction distance over > 5 cm (nerve at risk distance, NARD) is associated with a substantially increased risk of neurotrauma, but the long-term clinical consequences of underlying nerve injury, especially in the athlete, require further investigation.
Level Of Evidence:
Level II, prospective longitudinal cohort study.
