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Acute on chronic thromboembolism of the popliteal artery
0%
2/779
Chronic exertional compartment syndrome
33%
254/779
Entrapment of an intraseptal superficial peroneal nerve
1%
11/779
Herniation of a variant flexor digitorum accessorius longus
3%
22/779
Popliteal artery entrapment syndrome (PAES)
62%
482/779
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The patient has imaging findings of an accessory slip of the medial head of the gastrocnemius (Illustration A) and clinical signs of symptoms of popliteal artery entrapment syndrome (PAES).Popliteal artery entrapment syndrome (PAES) represents a form of exercise-induced leg pain characterized by an activity-related claudication syndrome that causes pain and cramping in the posterior leg compartment and may cause dysesthesia in the sural nerve distribution. There are a number of possible popliteal fossa aberrancies that can contribute to PAES, but the presence of an accessory slip of the medial head of the gastrocnemius muscle is a known cause of arterial compression. Diagnosis can be made with physical exam maneuvers that tension the posterior compartment musculature, including passive dorsiflexion and active, resisted isometric plantarflexion. Importantly, PAES can be mistaken for chronic exertional compartment syndrome, the latter of which more frequently involves the anterior and/or lateral leg compartments more than the posterior compartments and is seen with superficial peroneal nerve variations and fascial herniations that can cause nerve rather than arterial entrapment. Miller et al. review popliteal artery entrapment syndrome, noting that it represents a diagnostic and treatment enigma for orthopaedic surgeons. The authors state that PAES represents an uncommon condition that causes recurrent posterior leg pain and foot paresthesia in running athletes, with the most common etiology being due to an accessory or abnormal medial head of the gastrocnemius muscle. They conclude that non-surgical treatment with physical therapy and stretching of the gastrocnemius complex should be done as the first line of treatment; however, when conservative treatments are ineffective, referral to a vascular specialist for surgical intervention with a muscular band excision or transection, vascular bypass, or arterial reconstruction may be necessary.Valisena et al. provide an anatomic study of the intraseptal course of the superficial peroneal nerve. The authors note that anatomic and clinical studies have shown many variants of the superficial peroneal nerve (SPN) course and branching within the compartments and at the suprafascial layer, with the intraseptal SPN variant occurring in 6.6% to 13.6% of patients affected by SPN entrapment syndrome. In their study, the SPN was located in the anterior compartment in 2 cases and in the lateral in 13, with an intraseptal tunnel present in 10 legs (66%), at a mean distance of 10.67 cm from the lateral malleolus. They concluded that a higher rate than expected of intraseptal SPN variants was found, with further studies being needed to evaluate the effective prevalence of an intraseptal tunnel, independently from the SPN entrapment syndrome, and how to avoid associated iatrogenic complications during operative dissection.Figure A is an axial T1-weighted MRI slice showing an accessory head of the medial gastrocnemius muscles displacing the popliteal artery. Figure B is an axial MRI demonstrating the same anomaly with the structures labeled: M (medial head), 3 (third-head, or accessory head), L (lateral head). Incorrect Answers: Answer 1: Acute on chronic thromboembolism of the popliteal artery may cause claudication symptoms, but the image demonstrates an accessory head of the gastrocnemius that is the more likely cause of the patient's symptoms. Answer 2: Chronic exertional compartment syndrome is less likely in the described scenario, as described in detail above. Answer 3: Entrapment of an intraseptal superficial peroneal nerve may cause symptoms of chronic exertional compartment syndrome rather than the symptoms described in the clinical vignette. Answer 4: Herniation of a variant flexor digitorum accessorius longus is associated with tarsal tunnel syndrome, which occurs at the level of the ankle (not the posterior knee).
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