Ankle fractures are typically rotational injuries with underlying osseoligamentous disruptions ^, The ankle joint is also encircled by numerous tendons that confer dynamic stability and in rare situations and unique fractures patterns these tendons can also get injured.

Traumatic dislocation of the posterior tibialis tendon (PTT) in the context of an ankle fracture is rare given its secure posteromedial seat within the medial malleolar groove and coverage by the flexor retinaculum and deltoid ligament complex roof. ^, Nevertheless, PTT dislocation has been reported in various types of ankle fractures where the displaced or trapped tendon is an impediment to anatomic reduction. The site of tendon entrapment appears to correlate with the deforming injury forces, with common location being the tibiofibular space in pronation-type, Weber C injury patterns. ^{,,,,,,,,,,,,,,,} The other common subluxation occurs medially when the tendon is displaced due to a medial malleolus fracture. ^,,,,,,

We present an unusual case of posterior tibialis tendon dislocation associated with an isolated distal fibula fracture. Given the rarity of PTT dislocation in ankle fractures- and particularly in the setting of this atypical injury pattern- this case highlights the importance of maintaining a high index of suspicion for PTT malposition in ankle trauma and recognizing the associated clinical and radiological features.

A 25-year-old male motorcyclist sustained a closed injury to his left ankle following a self-skid accident. The patient was unable to recall the exact position of the ankle at the time of impact. On clinical examination, the left ankle demonstrated marked swelling over both the medial and lateral aspects, along with a superficial anteromedial abrasion. Distal neurovascular examination was normal, and no other significant associated injuries were identified.

Initial radiographs revealed an ankle fracture-subluxation with a transverse fracture of the distal fibula ( Fig. 1 ). The ankle was immobilized in a splint, and initial management consisted of limb elevation and analgesia. A computed tomography (CT) scan confirmed the absence of associated medial or posterior malleolar fractures ( Fig. 1 ). Once soft-tissue swelling had adequately subsided, operative fixation of the lateral malleolus was planned, with consideration for deltoid ligament repair depending on intraoperative stability.

Plain radiographs demonstrate an ankle fracture–subluxation with a transverse fracture of the distal fibula (a). Computed tomography (CT) confirms the distal fibula fracture and absence of medial or posterior malleolar fractures.

Surgery was performed on post-admission day four under general anaesthesia with the patient in the supine position. Following induction, repeat clinical assessment revealed a localized, tubular swelling over the medial malleolus, raising intraoperative suspicion of PTT dislocation. A standard lateral approach to the fibula was performed first, and the distal fibular fracture was stabilized using a distal fibula locking plate construct. Given the strong suspicion of PTT displacement, a direct medial approach over the medial malleolus was subsequently undertaken. Intraoperative exploration confirmed that the PTT was lying superficial to the medial malleolus, with associated rupture of the flexor retinaculum as well as disruption of both the superficial and deep components of the deltoid ligament complex ( Fig. 2 ).

Intraoperative images showing PTT subluxation superficial to the medial malleolus with associated medial ligamentous disruption (a), torn anterior deep deltoid ligament (b), and final repair with retromalleolar tendon relocation and two row suture anchor repair (c).

The posterior tibialis tendon was reduced back into its retro malleolar grove. Two 3.5-mm SwiveLock anchors (Arthrex Inc., Naples, FL, USA) were inserted into the medial malleolus to repair the anterior deep deltoid ligament. This was followed by repair of the remnants of the superficial deltoid ligament and flexor retinaculum complex, which were extensively disrupted and could not be clearly delineated. An additional 3.5-mm SwiveLock anchor was placed a proximal row to reinforce the construct and provide supplementary tension to the repair ( Fig. 2 ). Following repair, PTT was noted be stable and demonstrated smooth gliding with passive ankle motion Fig. 3 .

Postoperative anteroposterior (a) , mortise (b) , and lateral (c) radiographs demonstrating stable fixation of the distal fibula and restoration of ankle mortise.

The postoperative course was uneventful. Protected weight-bearing was initiated at six weeks postoperatively, progressing to unprotected full weight-bearing at twelve weeks. At final follow-up, the patient had regained baseline ankle joint motion and successfully returned to his pre-injury level of physical activity.

A total of 26 published reports with 29 cases of PTT dislocation or entrapment associated with ankle fractures were identified in the literature between 1936 and 2023, including the present case. ^{,,,,,,,,,,,,,,,,,,,,,,,,}

Weber C fracture patterns, including two Maisonneuve fractures, ^, accounted for 18 cases (62%), representing the predominant fracture configuration associated with PTT displacement. ^{,,,,,,,,,,,,,,,} The tibiofibular interosseous space and syndesmotic complex was the most common site of PTT displacement, identified in 20 cases (69%). ^{,,,,,,,,,,,,,,,,,} Medial sided PTT subluxation associated with a medial malleolus fracture were reported in 9 cases (31%), including current case. ^,,,,,,

A missed diagnosis at the index procedure was documented in 12 cases with all missed cases involved PTT entrapment within the tibiofibular interosseous space, resulting in persistent irreducibility and need for revision surgery . ^,,,,,,,,,,,

Posterior tibialis tendon is a key medial ankle element that traverses the ankle, subtalar, and Chopart joints, with a critical role in both motion and stability of the ankle and foot. In the foot it serves as a primary dynamic stabilizer of the medial longitudinal arch and functions as a powerful inverter, contributing to propulsion during the push-off phase of gait. At the ankle, PTT forms an integral component of the medial stabilizing complex, with close anatomical and functional relationships to the deltoid ligament. Given these biomechanical roles, restoration of PTT integrity and anatomic positioning is essential for restoring post injury ankle and foot function.

PTT dislocation or entrapment in the setting of ankle fractures is a rare but well-recognized barrier to anatomic reduction. Given that the tendon normally courses within the retromalleolar groove and is securely restrained by the flexor retinaculum, displacement of the tendon typically follows a high-energy pronation-type rotational mechanism with syndesmotic disruption. ^,, In such cases, the PTT may traverse an aberrant, circuitous course into the distal tibiofibular interval or interosseous space, and at times extend into the ankle joint itself. ^,, These dislocations are frequently missed at the time of index surgery, often necessitating revision procedures for persistent malreduction. ^,,,,,,,,,,, Neglected cases may present with progressive deformity and, in some instances, require salvage arthrodesis. ^, Another reported site of PTT subluxation is with an medial malleolar fracture, however, in this scenario the displacement is typically less concealed and often directly visualized during surgical exposure and reduction of the medial malleolus. ^,,,,,,

Preoperative advanced imaging can aid diagnosis in the presence of suspicious clinical features. High-energy trauma, a Weber C fibular fracture pattern, distal tibiofibular dislocation, lateral talar translation, widening of the medial clear space, or associated medial malleolar fractures are features in which PTT subluxation should be suspected, thereby warranting a lower threshold for advanced imaging. Although MRI has been used for preoperative evaluation, ^, CT scan is the more commonly reported modality for confirming PTT dislocation in the acute trauma setting. ^,,, Tendon entrapment may be overlooked on standard bone windows, therefore, use of soft-tissue window settings is recommended, particularly when satisfactory fracture reduction cannot be achieved.

In the current case, PTT dislocation occurred without an associated medial or posterior malleolar fracture, but instead with an isolated transverse distal fibula fracture. Pattern suggests a medial-to-lateral translational force across the ankle, entering below the medial malleolus and avulsing the medial soft-tissue stabilizers, before exiting laterally through the distal fibula to produce the transverse fracture. Because the tendon was not incarcerated within the fracture site, fibular reduction resulted in a congruent-appearing joint despite persistent PTT subluxation, emphasizing the potential for missed diagnosis.

This case highlights that PTT dislocation though rare, is not confined to rotational Weber C fracture-dislocations or medial malleolus fracture entrapment but may occur across a wider range of fracture patterns. Given the critical role of PTT to both foot and ankle stability and function, failure to recognize and address PTT injury can risk malreduction, persistent dysfunction, and long-term sequelae of progressive deformity. Hence, PTT position should be assessed in all complex ankle fractures with judicious use of advanced imaging suspected cases.