Posterior Tibialis Tendon Injury in the Athlete

Introduction

The tibialis posterior muscle and its tendon (PTT) play a vital role in most athletic activities. The tibialis posterior is the strongest inverter of the foot, it locks the triple joint during gait progression facilitating a rigid lever of push-off, and provides both power for acceleration and control for deceleration. Due to these important and repetitive roles, acute and chronic injury to the PTT are commonplace in athletes. A knowledge of disease progression, risk factors, and treatment measures is vital for treating physicians.

Acute posterior tibialis tendon injury in the athlete is rare but must always be considered in the differential diagnosis when an athlete presents primarily with tenderness, swelling, and pain over the medial ankle or plantar medial midfoot. Antecedent to the acute presentation, there often is a history of less severe prodromal symptoms more consistent with a chronic tendinopathy or tendinosis. In most cases, there are identifiable mechanical or physiologic risk factors that contribute to this development. The chronic picture is seen more often in the middle-aged to elderly athlete. While most of the literature on the topic focuses on chronic PTT dysfunction, it is important to identify acute injuries and understand them in the context of the individual athlete.

Anatomy and Biomechanics

The tibialis posterior muscle occupies the deep posterior compartment of the leg, originating along the proximal one third of the tibia and intraosseous membrane. Distally, its tendon travels posterior, then inferior, through the medial malleolar groove, changing direction abruptly almost 90 degrees. The stout retinaculum of the long flexors prevents the tendon from subluxing over the medial malleolus. Because the posterior tibialis tendon lacks a mesotenon, there is an area of relative hypovascularity from this acute turn at the medial malleolus to the medial navicular insertion. These factors of hypovascularity and the mechanical stress of a relatively acute turn of the tendon as part of a strong, weight-bearing leg muscle (second only to the gastrocnemius), make the tendon predisposed to acute and overuse injury in this area.

Because the posterior tibial tendon travels posterior to the axis of the ankle and medial to the axis of the subtalar joint, it functions as a strong ankle plantarflexor and foot invertor via the transverse tarsal joint (talonavicular and calcaneocuboid joints). The tendon also has multiple slip attachments to the capsule of the naviculocuneiform joint, all three of the cuneiforms, the cuboid, and their respective metatarsal bases in the plantar arch. The posterior tibialis tendon therefore is primarily a midfoot invertor and dynamically supports and elevates the medial longitudinal arch. It also indirectly supports the hindfoot because of its medial malleolar pulley action and intimate relationship to the deep deltoid ligament, plantar medial talonavicular joint capsule, and spring ligament (calcaneonavicular ligament). The dynamic role of the PTT places it at risk of elongation and degenerative tearing or even rupture.

The resulting loss of dynamic function can lead to progressive loss of static support structures, such as the ligaments and plantar capsules of the midfoot joints, and ultimately a pes planovalgus deformity ( Fig. 10.1 ). As the deformity progresses over time, other structures are affected, including the talonavicular joint capsule, deltoid ligament, and spring ligament. The stretching out or even frank rupture of these structures eventually leads to a more severe valgus inclination of the hindfoot and external rotation of the calcaneus, also associated with contracture of the triceps surae as it transitions into a hindfoot everter ( Fig. 10.2 ). Clinically, this may result in impinging pain and swelling in the subfibular or sinus tarsi area as the calcaneus abuts against the lateral malleolus. In very severe or neglected cases, a valgus tilt of the ankle may be seen as the deltoid ligament becomes incompetent, and asymmetric valgus arthritis can result.

Diagnosis

Usually, a detailed history, careful physical examination, and weight-bearing radiographs will establish the diagnosis of a posterior tibialis tendon injury. Additional imaging can help to further elucidate the structures involved and extent of disease, but is usually not necessary to reach a diagnosis and classification.