Bursit-mess: a Review of the 12 Bursae of the Knee

Case Diagnosis: Semimembranosus Bursitis

Case Description or Program Description: A 54-year-old woman currently undergoing treatment for plantar fasciitis presented with left knee pain of 1 month’s duration. The pain was located in the posterior knee and spread to the distal thigh and proximal calf. It was exacerbated by transitional movements (sit to stand and stand to sit), walking, and going downstairs; and improved with rest and ibuprofen. Physical exam was significant for an antalgic gait with decreased stance phase on the left. There was tenderness to palpation along the medial hamstring tendons distally and medial joint line. Resisted knee flexion was notable for mild weakness and caused posteromedial knee pain.

Setting: Outpatient sports medicine clinic

Assessment/Results: Point of care ultrasound (POCUS) of the knee revealed a large joint effusion, and a fluid collection medial/adjacent to the distal semimembranosus tendon. MRI revealed a fluid collection at the posteromedial knee, forming a U-shape around the semimembranosus tendon adjacent to the medial collateral ligament (MCL). The patient was counseled on oral anti-inflammatory use and prescribed physical therapy with a focus on lower extremity strengthening (quadriceps, hamstrings, and pelvic stabilizers). She will follow up in 6-8 weeks.

Discussion (relevance): Knee pain is one of the most common complaints. The physiatrist’s differential for intra articular knee pain focuses on the bony structures, ligaments, and commonly affected bursae (prepatellar, suprapatellar, infrapatellar, pes anserine, and iliotibial bursa). However, there are 7 other less common bursae in the knee. Pathology to these bursae can be hard to localize on history and physical exam alone. This case highlights the role of POCUS and MRI in identifying less common knee pathologies.

Conclusions: This case illustrates the importance of including the less common bursae of the knee on the differential for knee pain and will serve to review those bursae.