A 7-year-old boy presented with both of his thumbs flexed (Figure 1), the inability to perform the ‘thumbs-up’ gesture, and difficulties in opposing thumbs and fingers in activities such as holding a pencil during writing, pincer movements, and picking up small objects. His mother only observed the deformity for one month after the boy complained of difficulty in writing during class. He had no prior history of trauma to the thumbs or pain and swelling in other joints. There were no other birth anomalies noticed by his parents. Upon examination, the boy had flexion deformities of the interphalangeal joint (IPJ) on both of the thumbs. Passive range of motion of the IPJ was not possible and both were fixed at 60° of flexion. Power of both thumbs could not be assessed as there was no motion of the joint. The range of motion of the metacarpophalengeal joints (MCPJ) of both thumbs and all other finger joints was normal. A 0.5cm x 0.5cm subcutaneous nodule was palpable at the volar crease of the MCPJ bilaterally. The nodule was tender on palpation; however, no overlying skin changes were evident.

Locked knee is an orthopaedic condition requiring urgent treatment. Although the condition can be diagnosed via history, physical examination and imaging studies, the cause of the mechanical obstruction may only be apparent during arthroscopic examination of the knee joint. It is known that imaging plays a role in evaluating the integrity of intra-articular structures, however in some atypical cases, imaging cannot identify the definitive cause of locked knee. Here we report on two cases of locked knee, due to uncommon conditions which were unobservable via normal imaging studies.