Metaplastic Synovial Cyst: A Reaction to Multiplanar Shear Forces?—A Case Report on a Novel Anatomic Location and Differential Diagnosis

Synovial metaplasia was described in animal studies since the 1950s and was assumed to be a reaction to tissue disruption and theoretically related to the embryological formation of diarthrodial joints in utero. Since the description of the phenomenon in the cutaneous layer in a small case series in 1987, the prevalence has increased gradually with case reports and series published on many variations of its presentations and inciting events. We present a case of a hypertensive, otherwise physically fit 38-year-old female with a one-year history of coxalgia unresponsive to oral analgesia and discuss the possibility that the cutaneous metaplastic synovial cyst is an adaptive response to multiplanar shear forces and forms part of a spectrum of potential clinical presentations based on location.