Review Question - QID 218933

The distal innervation of the common peroneal nerve would be most likely to be injured following a knee dislocation. The Extensor hallucis longus (EHL) is a distal innervation of the common peroneal nerve.

Knee dislocations are high energy traumatic injuries characterized by a high rate of neurovascular injury. Diagnosis is made clinically with careful assessment of limb neurovascular status. If there is an associated nerve injury, the common peroneal nerve is most commonly involved (25% incidence); tibial nerve injury is less common. Radiographs should be obtained to document reduction. Treatment is generally emergent reduction and stabilization with assessment of limb perfusion followed by delayed ligamentous reconstruction.

Natsuhara et al. reviewed the frequency of vascular injury in knee dislocations across year of diagnosis, age, sex, and US geographic region and the proportion of these injuries requiring surgical repair. They reported that there is a lower frequency of vascular injury associated with knee dislocation and a lower proportion of vascular injuries undergoing surgical treatment than previously reported, supporting a more selective angiography protocol to screen for vascular injury. They concluded that future large-scale and prospective studies should analyze factors that may predispose to vascular injuries after knee dislocation and determine which patients should be screened for vascular injury after knee dislocation.

Weinberg et al. reviewed which patient factors are predictors of vascular injury after knee dislocation and what are the diagnostic utilities of palpable dorsalis pedis or posterior tibial pulses, and the presence of an ankle-brachial index (ABI) of 0.9 or greater. They reported that increased BMI and the presence of open dislocation are associated with a greater risk for vascular injury after knee dislocation. They concluded that the combination of a palpable dorsalis pedis and posterior tibial pulse combined with an ABI of 0.9 or greater was 100% sensitive for the detection of vascular injury based on clinical follow-up at 6 months.

Poage et al. reviewed peroneal nerve palsies including workup and treatment options. They discuss the nerve anatomy as it branches from the sciatic nerve in the proximal popliteal fossa, then crosses posterior to the lateral gastrocnemius muscle, and finally curves around the head of the fibula. They state the most common etiology of peroneal nerve palsies are compressive in nature, however, traumatic etiology has the worst prognosis overall.

Figure A depicts a radiograph of a posterior knee dislocation. Illustration A depicts the innervations of the tibial and common peroneal divisions of the sciatic nerve.

Incorrect Answers:
Answer 1: The biceps femoris short head is innervated by the common peroneal division of the sciatic nerve, however this innervation occurs proximal to the knee. It would be less likely to be involved than distal innervations of the common peroneal nerve such as the EHL.
Answer 2,4,&5: These are innervated by the tibial nerve branch of the sciatic nerve. The common peroneal nerve is much more commonly injured following a knee dislocation.