A 32-year-old male architect was referred to the orthopaedic service with right PAIS. He described an injury to his right ankle several years ago as he went to kick the ball when playing football. He did not seek immediate medical attention, and the initial symptoms settled. He then went on to develop pain and medial-sided ankle swelling when he tried to carry out vigorous sporting activities some years later. On examination, there was a bony swelling behind his medial malleolus, and pain was exacerbated with plantar flexion and inversion of the ankle/foot demonstrating signs of PAIS. The MRI scans demonstrated a bony fragment with surrounding oedema associated with the medial talar tubercle. The fragment was between FDL and FHL tendons representing an "unusually located os trigonum," and there was also associated FHL tenosynovitis (see Figure 3). Interestingly lateral X-rays did not show any abnormality as this patient did not have a conventional os trigonum. He underwent operative intervention with an open excision of the bony fragment (see Figure 4). The FHL tendon was found to have a split, and this was also repaired. The postoperative course was complicated with superficial wound infection which was successfully treated with a course of oral antibiotics. At the 6-week follow-up, the patient was pleased and described that their PAIS symptoms were improving.