Reachout Orthopedics - Issue 1

voloradial aspect of the wrist. Her pain was aggravated by resisted palmar flexion, but the results of both Tinel and Phalen’s tests of the median nerve were negative. Magnetic resonance imaging of the wrist (Fig. 1) demonstrated an accessory muscle at the voloradial aspect of the distal radius, situated between the pronator quadratus (PQ) muscle and the FCR tendon. The tendon of the accessory muscle coursed along the deep aspect of the FCR tendon, then crossed over the FCR tendon in an ulnar to radial direction within the FCR tunnel, and inserted into the trapezium. Portions of this tendon distally were U-shaped. There was also a longitudinal split tear of the FCR tendon, and tendinosis and extensive tenosynovitis of the FCR and FCRB tendons centered at their intersection. The clinical and imaging findings were consistent with an intersection syndrome related to the tendons of the FCRB and FCR muscles. The patient was treated with physical therapy and non-steroidal anti-inflammatory drugs for 3 weeks with marked improvement in pain, and she was able to return to work and had no difficulties with activities of daily living. Discussion The FCRB is a rare accessory muscle of the forearm and wrist. It originates from the voloradial aspect of the distal third of the radius, distal to the origin of the flexor pollicis longus muscle and proximal to the origin of the PQ muscle [3]. The FCRB is composed of a fusiformmuscle belly that passes superficial to the PQ muscle proximally and deep to the FCR muscle and flexor retinaculum distally [5, 6]. At the level of radiocarpal joint, it forms a relatively short tendon [3, 10] that parallels and lies radial to the FCR tendon within the FCR fibro-osseous tunnel [5, 10, 16, 18, 19]. The tendon of the FCRB muscle may insert into the second, third, or fourth metacarpal bases; the radial aspect of a carpal bone, such as the trapezium or capitate; or retinacular septum within the FCR fibro- osseous tunnel (Fig. 2) [1, 2, 6, 10, 16, 20, 21]. The FCRB muscle is innervated by the anterior interosseous nerve and is supplied by a branch of the anterior interosseous artery [2–4]. Its function has been reported to be radial wrist flexion without thumb or finger flexion by tension application [5, 10, 22]. A symptomatic FCRB is rare; there was only one other case report in which the tendon of the FCRB muscle was associated with symptoms and signs consistent with a tendon intersection syndrome [16]. Although surgical exploration was not performed in our patient, the imaging findings are akin to those of the patient described by Peers et al . [16], who had involvement of the FCRB and FCR tendons and accompanying tenosynovitis. Another case report, by Smith and Kakar [14], describes a patient with wrist pain associated with FCRB tenosynovitis and a complete tear Fig. 1: Tendon intersection syndrome between the tendons of the FCRB and the FCR muscles. Axial ( a [proximal] through d [more distal]) fluid-sensitive fat-suppressed sequences demonstrate tendinosis of the FCRB tendon ( closed arrows ) as it crosses over the FCR tendon ( arrowheads ) in an ulnar to radial direction with associated tenosynovitis within the FCR tunnel and an accompanying longitudinal split tear of the FCR tendon ( open arrow ). Symptomatic FCRB muscles or tendons are rare, with only five previously reported case. 19