Reachout Orthopedics - Issue 1

FLEXOR CARPI RADIALIS BREVIS: A RARE ACCESSORY MUSCLE PRESENTING AS AN INTERSECTION SYNDROME OF THE WRIST Patcharee Hongsmatip 1,2 , Edward Smitaman 2 , Gonzalo Delgado 3 , Donald L. Resnick 2 1  Queen Savang Vadhana Memorial Hospital, 290 Jermjomphol Road Sriracha, Chonburi 20110, Thailand patchareeh@gmail.com 2  Department of Radiology, University of California San Diego, 408 Dickinson Street, Mail code 8226, San Diego, CA 92103, USA 3  Clinica MEDS, Av Bernardo Larrain Cotapoz 12654 Lo Barnechea, 7701224 Santiago, Chile The flexor carpi radialis brevis (FCRB) is a rare accessory muscle of the forearm and wrist. It is typically asymptomatic, but has been discovered either incidentally during cadaveric studies or at the time of surgery in patients with distal forearm injury. Rarely, the FCRB muscle is associated with pain. A ccessory muscles are ana- tomic variants that have been described in the anatomic, surgical, and radiologic lit- erature [1–7]. The majority of such muscles do not lead to clinical mani- festations and are found incidentally during cadaveric dissection, surgical exploration, or imaging examinations. In some cases, however, these accessory muscles may be ac- companied by pain (e.g., when compressing a nearby nerve, vessel, or tendon) or swelling or a mass, simulating a tumor. The FCRB is a rare accessory muscle of the forearm and wrist. It was first described by Fano in 1851 [8] and, since then, has also been referred to as the flexor carpi radialis brevis vel profundus muscle [1] and short radiocarpal flexor muscle [3]. The prevalence of the FCRB muscle has been reported to be 2–8% [3, 9, 10], although the true frequency of this muscle may be higher, often encountered as an incidental intraoperative finding during volar plating of distal radial fractures [10–12]. Symptomatic FCRB muscles or tendons are rare, with only five previously reported cases [13–17]. Further, to our knowledge, our case report is only the second to describe an intersection syndrome between the tendons of the FCRB and FCR muscles, which in our patient was accompanied by tenosynovitis and a split tear of the FCR tendon as confirmed by MRI. Case Report A 51-year-old right-hand-dominant woman presented with a 3-month history of pain and swelling localized to the voloradial aspect of the left wrist; she worked as an administrative assistant and, although her symptoms were intermittent, they interfered with both her work and the activities of daily living. On physical examination, there was ill-defined soft tissue swelling and tenderness at the 18