709 - Sudden Lower Extremity Swelling Secondary to Plantaris Rupture: A Case Report

Plantaris muscle rupture


Case Description:

A 72-year-old female with right patellofemoral joint arthroplasty in 2017 was referred to an outpatient musculoskeletal clinic for ultrasound-guided right popliteal cyst aspiration and corticosteroid injection. She has a history of previous right knee palpation-guided corticosteroid injections at an outside facility. The aspiration was completed without adverse events, and she reported improvement of pain and swelling immediately and at 3 week follow up. Several weeks subsequent, she developed sudden right posterior knee pain, hardening of the lower extremity, and audible “popping” sensation while walking over uneven surfaces.

Discussions:

The differential diagnosis for sudden lower extremity pain and swelling includes deep venous thrombosis (DVT), infection, and compartment syndrome. Notably, the patient had patellofemoral arthroplasty, raising concern for hardware infection. The patient denied fevers, chills, dyspnea, erythema, lower extremity numbness or paresthesias, or regional drainage. Given the rapidity and severity of swelling, she was recommended emergent evaluation for potential compartment syndrome. Workup, including laboratory evaluation and ultrasound, was negative for DVT and showed complex fluid in the popliteal region. Outpatient magnetic resonance imaging (MRI) of the right knee revealed complete plantaris muscle rupture with hematoma, with an intact distal plantaris tendon.

She was recommended elevation of the leg, manual therapy, modalities including ice/heat, activity modification, and physical therapy for lower extremity strengthening with eventual complete resolution of symptoms.

Conclusions:

Sudden onset lower extremity swelling should be evaluated for possible infection or DVT, and compartment syndrome should be considered. Plantaris muscle rupture is a rare cause of sudden lower extremity swelling.