Given the subtle nature of peroneal tendon subluxation or instability, these authors discuss the pathoanatomy of the condition, keys to diagnosis and emerging insights on surgical management.
Diagnosing peroneal tendon subluxation can be challenging as the majority of cases are subtle in their presentation and clinicians commonly misdiagnose the condition as a lateral ankle sprain. Prompt diagnosis and timely intervention are key to preventing chronic peroneal dislocation, instability and tears.
Of course, in order to recognize and treat peroneal tendon subluxation, one must have a firm grasp of the pathoanatomy and biomechanics associated with this condition. The lateral compartment of the lower leg is comprised of the peroneus longus and brevis muscles. They both travel posterior to the fibula within the fibular groove and at this level are in the same sheath with the peroneus brevis anteromedial to the peroneus longus. In the inframalleolar region, the peroneus longus and brevis muscles form separate sheaths around the peroneal tubercle, which can have various sizes and shapes.1 Inferiorly, the peroneal tendons are bound by the calcaneofibular ligament and the inferior peroneal retinaculum. The pathoanatomy of this condition lies within the integrity of the superior peroneal retinaculum, its contents and the ability to maintain those contents within the retromalleolar groove.
The superior peroneal retinaculum has a lateral, non-osseous roof and a floor comprised of an anterior osseous (retromalleolar groove) and medial non-osseous (posterior intermuscular septum of the leg) portions.2 As Standring described, the superior peroneal tunnel fibers extend superiorly, posteriorly and medially approximately 3.5 cm from the distal tip of the fibula and merge with the deep transverse fascia of the leg.3 Researchers have shown via cadaver dissection that the superior peroneal retinaculum, a static structure, has an impact on anterior ankle subluxation along with its dynamic, housed components: the peroneal tendons.4
The posterolateral portion of the distal fibula is bound by a retromalleolar ridge and superomedially by a retromalleolar tubercle. Multiple anatomic studies of the retromalleolar groove have detailed the shape to be most commonly concave. Edwards found an incidence of a concave groove in 82 percent of 178 specimens and 11 percent had flat surfaces.5 Athavale dissected 60 fibulas and 33 had concave surfaces, 21 were concave with a central ridge, two were flat and four were irregular.2
Interestingly, these authors discuss the pathoanatomy of this injury to be related not to the groove itself but to the fibular rotation.2,5 An externally rotated fibula would inherently relax the superior peroneal retinaculum and allow for peroneal subluxation. The internal rotation of the fibula would tend to tighten or stretch the superior peroneal retinaculum, impinging the peroneus brevis tendon against the retromalleolar tubercle, which would cause longitudinal tears. Adachi and coworkers also confirmed through magnetic resonance imaging (MRI) evaluation of 39 ankles that there was no significant difference in the morphological shape of the retromalleolar groove between patients with and without peroneal subluxation.6 Nonetheless, a normal fibular retromalleolar surface is made of smooth fibrocartilage and allows for tendons to glide freely.