Giant cell tumour of tendon sheath with simultaneous two tendon involvement of the foot treated with excision of the tumour and reconstruction of the flexor retinaculum using tibialis posterior tendon in a paediatric patient: A rare case report

•A case of giant cell tumour of the tendon sheath (GCT-TS) in a paediatric patient.•GCT-TS of the foot tendons, as seen in this case, is relatively rare.•Unique case in which the giant cell tumour was seen to be involving the tendon sheaths of tibialis posterior as well as flexor digitorum tendons, and also was extending into the ankle joint.•Novel technique of reconstruction of flexor retinaculum in GCT-TS.

Giant cell tumour of tendon sheath is a benign soft tissue tumour arising from the tendon sheath. The involvement of foot and ankle by such tumours is relatively rare. Children are not commonly afflicted by this condition. All such tumours are reported to arise either from a single tendon sheath or one joint. We report a case of giant cell tumour of tendon sheath in a 12-year-old child, arising simultaneously from the tendon sheaths of tibialis posterior and flexor digitorum longus tendons, as well as extending into the ankle joint. It was treated by complete excision of the mass along with the tendon sheaths with reconstruction of the flexor retinaculum. The location of the tumour, age of the patient, diffuse nature of the tumour and novel technique of reconstruction of the flexor retinaculum make this case extremely rare and the first to be reported in literature.