Background: atraumatic flexor carpi radialis (FCR) rupture is rare in the absence of direct trauma. In the majority of reported cases, the patient typically complains of pre-existing volar or radial sided wrist pain and swelling, followed by an acute ‘giving way’ sensation, with either loss of wrist flexion strength or an increase in regional wrist tenderness. Atraumatic FCR rupture occurs primarily in patients who have rheumatoid arthritis and secondary carpal collapse or severe degenerative joint disease, secondary to corticosteroid injections in the FCR tendon sheath and due to osteoarthritis (OA) of the scaphoid-trapezium-trapezoid (STT) joint. Atraumatic flexor carpi radialis rupture is a rare phenomenon and should be distinguished from other pathology. A review of the literature revealed only 15 case reports published since 1959 investigating this cause of radial sided wrist pain. Case Presentation: MC, a 57 year old Caucasian female, presented to her GP after the sudden onset of pain in the right forearm while cooking. Examination revealed significant pain and swelling over the distal FCR tendon. Wrist flexion was greatly diminished in strength. Ultrasound revealed a full thickness tear of the FCR tendon at the myotendinous junction, with 31mm of retraction. The patient had an ultrasound some months earlier which revealed mild OA and synovitis in the 1st carpometacarpal joint (CMCJ), along with tenosynovitis of the FCR. The patient had been experiencing discomfort in the radial side of the right wrist, so a steroid injection of the FCR tendon was organised, with the aim of pain relief. At the time of injection, the radiologist proceeded with a base of thumb injection with a combination of Celestone and 0.75% Naropin, which was tolerated well. Three weeks after this injection, MC presented to the doctor with the symptoms described above, leading to a repeat ultrasound, which confirmed complete FCR rupture. Conclusions: intra-sheath steroid injections are a known risk factor for all tendon ruptures, and this has been reported in the literature for the FCR previously. However, FCR tendon rupture incited by an adjacent joint injection appears to be a novel event.