Isolated Rupture of the Plantaris Tendon in a High School Track Athlete

Abstract

P lantaris muscle or tendon injuries, although rare, have been discussed for over a century. The plantaris is a rudimentary muscle located in the superficial posterior compartment of the leg and varies in its size and development. It originates at the inferior aspect of the lateral supracondylar line of the femur and consists of a small fusiform fleshy muscle belly with a long, slender tendon that crosses obliquely between the gastrocnemius and soleus before inserting into the medial posterior calcaneus, sometimes via the Achilles tendon or occasionally fusing with the flexor retinaculum or leg fascia. Reports of isolated ruptures of the plantaris muscle or tendon are rare, but this is probably related more to misdiagnosis as Achilles tendon pathology, and that they heal quickly, than the paucity of the injury. Plantaris tendon ruptures rarely are isolated, often involving the gastrocnemius or the Achilles tendon. The term coup de fouet, or snap of the whip, was coined in 1597 to describe an Achilles tendon rupture; some authors have used the term, inappropriately, to describe plantaris tendon ruptures. Tennis leg was used to describe plantaris tendon and muscle ruptures, causing more confusion and debate. Few cases of isolated plantaris tendon rupture have been reported. These ruptures occurred at the insertion on the calcaneus or at the proximal musculotendinous junction. To our knowledge, no case has been reported regarding the rupture of the mid-plantaris tendon in isolation, making our patient’s case unique. CASE REPORT A 16-year-old male high school track athlete (6’3’’, 158 lbs) presented to the office complaining of pain in the right Achilles tendon region. He was in his mid-season training, performing modest speed work twice weekly coupled with distance running of roughly 30–40 miles weekly; he performed no plyometric training. On the previous day (weather was sunny, approximately 501F), while performing an afternoon speed workout, he was nearing the end of his fourth 200-meter sprint and felt a ‘‘pop’’ in his right posterior lower-leg region, causing him to fall. He was able to walk, stiffly, afterwards, but incurred mild swelling and pain that evening. The patient denied numbness, tingling, weakness, joint pain, and previous injuries and was otherwise in excellent health, with no allergies and no present or recent medication or supplement use. Standing exam revealed normal foot structure. Strong, equal pulses were palpated bilaterally at his distal lower extremities and capillary refill was less than 2 seconds. No motor or sensory deficits were identified, and excellent plantar