Liberation of an incarcerated tibialis posterior tendon following a posterior malleolar ankle fracture: a case report

The tibialis posterior tendon (TPT) wraps posteriorly around the medial malleolus within the retromalleolar groove of the distal tibia, beneath the medial flexor retinaculum.¹ This anatomy permits the TPT to act as a powerful supinator and flexor of the ankle while supporting the medial plantar arch. Ankle fractures can be complicated by TPT injuries. Numerous case reports exist detailing acute post-traumatic incarceration of the TPT in the tibiofibular space or within fracture fragments; however, delayed entrapment secondary to osseous changes is much less commonly reported.^2–4 We identified only two other case reports describing the delayed post-traumatic formation of an osseous tunnel or groove causing entrapment and irritation of the TPT at 1 year and 10 years post-injury respectively.^5,6 Both cases had injuries initially managed with open reduction and internal fixation (ORIF), although neither case used a posteromedial approach, which appears to be unique to our case.

Case report

A 39-year-old female presented at 3 months post-operatively with clinical symptoms of TPT irritation including posteromedial ankle pain, swelling and weakness of inversion. She had undergone an ORIF of a closed Maisonneuve-type fracture-dislocation injury with a comminuted posterior malleolar fragment and high fibula fracture, sustained after a skateboard fall in October 2024. Initial fixation on day 1 post-injury used a modified posteromedial approach exploiting the interval between flexor hallucis longus and the tibial nerve. Medial and lateral posterior tibial plates were applied with additional syndesmotic fixation. The patient was kept non–weight bearing for 6 weeks, transitioning from cast to moon boot at 2 weeks to allow early motion.

Subsequent imaging (ultrasound, computed tomography and magnetic resonance imaging) demonstrated TPT entrapment in a tight osseous tunnel, measuring 8mm by 10mm in width and 27mm in length, at the original posterior malleolar fracture site, with associated tendinopathy.

View Figure 1–3.

At 6 months post-surgery, the patient then proceeded to undergo removal of metalware and liberation of the incarcerated TPT using a novel technique to prevent recurrent entrapment. Using the prior posteromedial approach, the osseous tunnel and entrapped tendon were directly visualised. The tendon was mobilised, minor tears were repaired and surrounding bony surfaces were prepared. A fibula allograft, shaped to fill the defect, was placed and fixed with Acutrak screws. Upon seating of the screws, the graft split; however, it remained well fixed and was therefore accepted. Demineralised bone matrix putty was placed around the graft. Bony prominences were burred and a GENTA-FOIL resorb collagen wrap was secured around the tendon. The TPT was visualised to be gliding freely prior to closure. The patient was casted for wound healing initially, with early range of motion encouraged from 2 weeks post-operatively to prevent adhesions.

Follow-up ultrasounds at 2 and 3 months have shown improving dynamic gliding of the TPT with progressive graft integration. Clinically, reported patient symptoms include improved pain, tendon excursion and function, although some residual posteromedial swelling remains.

Conclusion

This rare case report emphasises the importance of considering delayed soft tissue complications secondary to posteromedial ankle fractures despite initial reassurance from direct visualisation of soft tissues at the time of open reduction. In this instance, multiple imaging modalities proved helpful to identify the development of an osseous tunnel with incarceration of the TPT. The intact TPT was able to be liberated and the osseous deformity corrected to prevent further future complications.