616 - Snapping Pes Syndrome: An Atypical Presentation of Pes Anserine Bursitis

Case Diagnosis: Snapping Pes Syndrome with Pes Anserine Bursitis

Case Description: A 68-year-old female presented with medial right knee pain and a snapping sensation with minimal relief from prior bracing, analgesics, corticosteroid injections, and physical therapy. Physical examination revealed medial joint line and pes anserinus tenderness with visible subluxation of the medial hamstring tendons over the medial femoral condyle during knee flexion and extension. Initial knee radiographs demonstrated small tri-compartmental marginal osteophytes and chondrocalcinosis. MRI of the right knee revealed a large pes anserine bursal effusion, mild tri-compartmental degenerative disease, and posterior lateral and possible posterior medial meniscal tears. The patient underwent ultrasound-guided bursal steroid injection, which led to gradual symptomatic improvement. After several weeks of physical therapy, she underwent a repeat injection with added bursal aspiration. If symptoms do not improve, an orthopedic referral for surgical management may be considered at the next visit.

Discussions: Snapping pes syndrome causes palpable medial knee snapping from pes anserine tendon subluxation over an adjacent structure, typically the medial femoral condyle. This is an important cause of extra-articular snapping, which should be differentiated from intra-articular sources such as plicae and the menisci. Dynamic ultrasound has been noted as useful in characterizing snapping pes syndrome in real-time. As in the described case, larger pes anserine bursal effusions may present a nidus for hamstring tendon subluxation. To the authors’ knowledge, there have not been any other reports specifically describing these two pathologies occurring concurrently.

Conclusions: This case highlights the consideration of snapping pes syndrome as a cause of knee pain and snapping, which may present in conjunction with bursitis. A multifaceted treatment plan is necessary for these patients including physical rehabilitation and corticosteroid injections.