Other Tendon Disorders

The peroneus brevis and longus muscles, innervated by the superficial peroneal nerve, have their origin off the fibula in the lateral compartment of the leg with the origin of the peroneus longus generally being more proximal.

The tendons pass through a sheath as they course around the fibula; at the level of the ankle, the peroneus brevis is generally anterior and sometimes medial to the peroneus longus.

The peroneus brevis inserts at the base of the 5th metatarsal, whereas the peroneus longus courses medial under the cuboid through the cuboid tunnel to attach to the plantar base of the 1st metatarsal/medial cuneiform.

The peroneus brevis is the primary muscle that provides eversion at the subtalar joint, while the peroneus longus secondarily everts by plantarflexing the 1st ray.

The primary antagonist of the peroneus brevis is the posterior tibial tendon, while the primary antagonist of the peroneus longus is the ATT.

The peroneal tendons, and especially the peroneus brevis, are critical for optimal ankle stability. Indeed, rehabilitation from an ankle sprain has a large focus on regaining and maintaining eversion strength.

As previously stated, these tendons can undergo degeneration, which can lead to split tears in the tendon. As a generalization, peroneus brevis issues tend to occur at the distal fibula, whereas peroneus longus issues tend to occur at the cuboid tunnel. This generalization is certainly not universally true but is often the case. A large peroneal tubercle can occasionally cause injury or irritation of the tendons.

At the distal fibula, a host of potential pathologies can be encountered, which can involve either the tendon itself or something external to the tendon.

• The tendon can have a single (or multiple) split tear(s). When multiple split tears are present, the structural integrity of the tendon is often compromised such that it is not terribly functional.

• Generally speaking, the muscle belly of the peroneal tendons should end prior to the sheath through which the tendons travel around the fibula. If this is not the case, this distal muscle belly can cause pain and impair function of the tendons. Also, some patients will have a peroneus quartus or an aberrant "extra" tendon that runs through the sheath around the fibula.

In the cuboid tunnel, an os peroneum (an accessory ossicle within the tendon) can potentially cause pain or fracture.

Predisposing factors to peroneal tendon pathology include a cavovarus foot and multiple ankle sprains, factors which are clearly related.

Peroneal tendon subluxation/dislocation can occur with a forceful dorsiflexion and eversion mechanism, which can cause the superior peroneal retinaculum (SPR) to fail, leading to the tendons sliding out from behind the fibula. This subluxation can lead to direct injury to the tendons in addition to causing pain and disability in and of itself.

A history of trauma will often be recalled by the patient, although it is not absolutely necessary for tendon pathology. However, ankle trauma is common, and it will sometimes be difficult to draw a direct line between the trauma and the tendon pathology.

Peroneal pathology should be actively sought in patients with recurrent ankle instability.

The station of the foot should be checked with the arch height checked. The subtle cavus foot as noted by the "peek-a-boo" heel sign should be sought.

Swelling will often be noted about the posterior distal fibula &/or along the posterolateral hindfoot.

Palpation along the course of the tendons will often elicit pain.

Pain can also occur with resisted eversion and sometimes with resisted inversion as well.

Peroneal subluxation can be elicited with dorsiflexion/eversion.

MR is most useful for evaluating the peroneal tendons, although they may be subject to the magic angle phenomenon, whereby it is difficult to achieve adequate visualization of the tendons in the region of the distal fibula.

Ultrasound can be beneficial as well, especially in its ability to provide a dynamic assessment.

These tears are not tendon tears in the traditional sense that Achilles tendon tears, for example, are. These tears are often longitudinal split tears of the tendon. While the tendons can rupture outright, meaning a discontinuity in the longitudinal course of the tendon, it is not common.

The surgical options have traditionally been tied to the degree of tendon abnormality. If a single split exists in the tendon, then the split part can be excised. Tendon repair can be attempted, although the tendon has a limited healing capacity. More commonly, surgeons will attempt to tubularize the tendon.

If multiple splits tears are present with an area of the tendon that is markedly degenerative, then excision of the degenerative segment can be performed with subsequent brevis to longus tenodesis, whereby the peroneus brevis is sutured to the longus proximally and distally.

More recently, some authors have noted success with allograft tendon repair. Instead of performing tenodesis, surgeons will resect the degenerative tendon segment and suture in a tendon allograft, which substitutes for the degenerative segment.

If both the peroneus brevis and longus are tendonotic and degenerative, a FHL transfer to the base of the 5th metatarsal can be performed to regain some eversion strength.

Generally speaking, surgeons will sacrifice peroneus longus function in order to maintain peroneus brevis function in its role as the sole everter of the foot.

These injuries often result from a failure of the soft tissue restraints that keep the tendons on the posterior border of the fibula, namely the SPR.

The morphology of the posterior fibula in terms of its relative concavity or lack thereof can certainly play a role in this pathology.

Treatment is centered on creating a space in the posterior fibula in which the tendons can reside and repairing the soft tissue restraints.

Some authors have described intrasheath subluxation of the peroneal tendons. In this pathology, there is no injury to the SPR; the tendons switch their positions, causing a painful click. Groove deepening has been found to be effective in these patients for pain relief.