Working Diagnosis:
The working diagnosis was lateral synovial plica syndrome.

Treatment:
Using ultrasound guidance, the patient received a lateral patellofemoral joint injection into the area of thickened tissue with 2 cc of 1 percent lidocaine and 1 cc of Celestone soluspan.
The patient returned 2 months later and reported being symptom-free for 2-3 weeks until "something popped again." She was then referred to an an orthopedic surgeon for consultation.
The surgeon performed a right knee arthroscopy and reported that the medial gutter was notable for a large medial plical shelf with reciprocal changes on the femoral condyle. The lateral compartment had a distal plical shelf which made contact with the distal lateral femur. A shaving chondroplasty of the patella and synovectomy of the medial and lateral gutters was ultimately performed.

Outcome:
The patient participated in physical therapy following the surgery and continues to do well without complaints.

Author's Comments:
There is little known about lateral synovial plica syndrome as it is quite rare. One study performed arthroscopy on 400 knees and found the lateral plica to be present in only 1.3% (reference 1). Of the 1.3% of people with a lateral plica, even fewer become symptomatic as a result of this structure. Since this is a rare syndrome, the best method to diagnose and treat is not known, however, a previous case report (reference 2) had a successful outcome after synovectomy, and this patient has also done well after surgical resection.

Editor's Comments:
Although the most common knee condition presenting to a sports medicine office is patellofemoral syndrome, there is a significant need to consider PFS a diagnosis of exclusion given the large number of conditions causing similar symptoms. This rare case of a lateral synovial plica is one example.

References:
1.) S.-J. Kim and W.-S. Choe. Arthroscopic Finding of the Synovial Plica of the Knee. Arthroscopy: The Journal of Arthrooscopic and Related Surgery. Vol 13, No 1 (February), 1997: pp 33-41.
2.) Kurosaka et al. Lateral synovial plicae syndrom: A case report. Am J Sports Med. Vol 20, No 1, 1992: pp 92-94.

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