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Combined Peroneal and Tibial Nerve Lesions after Knee Dislocation
Chandan G. Reddy, MD; Kimberly K. Amrami; Robert J. Spinner
Mayo Clinic, Rochester, MN, USA
Introduction: Knee dislocations are often accompanied by stretch injuries to the peroneal nerve. A small subset of these also affects the tibial nerve. The mechanism of this combined pattern could be a longitudinal stretch injury of the peroneal nerve extending to the sciatic nerve (and tibial division); or separate injuries to both the peroneal and tibial nerves at the soleal sling or at the knee joint. We reviewed MRIs in groups of patients with knee dislocations and peroneal nerve injuries to determine the localization of the combined injury and the prevalence of subclinical injury to the tibial nerve.
Methods: We reviewed three groups of patients. Group 1 consisted of knee dislocations with clinical evidence of nerve injury (n=28), 19 of whom had complete peroneal nerve injury. Group 2 consisted of knee dislocation without nerve injury (n=19) and Group 3 consisted of patients with minor knee trauma but without knee dislocation (n=14). All patients had an MRI of the knee performed within 3 months of injury. MRI appearance of the tibial and peroneal nerve injury was scored by an independent radiologist in three zones (zone I: sciatic bifurcation; zone II: knee joint; zone III: soleal sling and fibular head) on a scale of 1 to 4 in terms of severity. Injury signal was also scored as diffuse or focal for each nerve in each of the three zones.
Results: Nearly all of the nerves visualized in Groups 1 and 2 demonstrated some degree of injury on MRI (98%). Diffuse injury was more common than focal injury. In Group 1, focal injuries of the tibial nerve were found in both zones I and II, while the peroneal nerve demonstrated focal injury in all three zones. In Group 2, there was evidence of significant tibial and peroneal nerve injury (mean MRI injury scores of 1.26 and 1.65 respectively) compared to Group 3 (0.10 for both tibial and peroneal nerve, p<0.05). In Group 1 compared to Group 2, the peroneal nerve had a significantly higher injury score (2.75, p<0.05), whereas the tibial nerve did not (1.35, p=0.51). Those patients with complete peroneal nerve injury had significantly higher injury scores (3.19) than those with partial peroneal nerve injury (1.82).
Conclusion: Subclinical neural injury following knee dislocation is relatively common. Diffuse neural injury was more commonly observed than focal injury on MRI. When present, however, focal neural injury may occur in all three zones.
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