Anatomic variants within the superior peroneal retinaculum may predispose a patient to recurrent or chronic instability and pain. The thinking is that a low-lying muscle belly causes instability through an “overcrowding” phenomenon although studies show it is the most common additional component within the tunnel and therefore is most likely a normal finding.7 Other anatomic variants include the muscle or tendon of the peroneus quartus, a ruptured peroneus brevis and even an accessory peroneal nerve.8-14 These all may contribute to peroneal pathology and instability in some form, and are often associated with subluxation.
What To Expect From The Patient Presentation And Diagnostic Imaging
Most clinical presentations of peroneal subluxation, dislocation or instability are subtle in nature and rely on an appropriate patient history and examination. Physicians can frequently misdiagnose these as lateral ankle sprains and a specialist must thoroughly evaluate these injuries.15 Monteggia first described this injury in ballet dancers in 1803.16 Two centuries later, athletes are still more inclined to sustain these injuries, especially in sports such as skiing, ice skating, soccer, basketball, gymnastics and rugby.17-21
The mechanism of these acute injuries is commonly a dorsiflexed foot and sudden or heavy contraction of the peroneal muscles. Acute symptoms of snapping or popping with pain and feelings of instability are common. Posterolateral ankle ecchymosis, edema and tenderness occur as well while forced eversion or activation of the peroneal tendons will incite pain.
If left untreated, these patients subsequently have chronic peroneal dislocation, instability and tears. Patients may be able to actively dislocate a peroneal tendon with or without pain. The pain is most commonly retromalleolar and associated with fullness or edema in this region from a peroneal split tear and tenosynovitis. Patients will also complain of instability and “giving way.”
A prudent diagnostician will also evaluate the patient’s lateral ankle ligament complex with an anterior drawer and talar tilt examination, comparing it to the contralateral limb. This complex also plays a role in the pathogenesis of peroneal instability. One should also evaluate appropriate hindfoot alignment and gait for fixed or functional varus.
Ankle and hindfoot radiographs are helpful in diagnosing varus malalignment, avulsion fractures, osteochondral lesions and osteophytes. Advanced imaging may assist in the diagnosis of osseous abnormalities associated with the retromalleolar groove and distal fibula. Szczukowski and colleagues utilized computed tomography (CT) in the diagnosis of suspected peroneal subluxation with good success.22
Magnetic resonance imaging is another non-dynamic imaging modality clinicians use heavily for foot and ankle pathology. When discussing MRI and peroneal tendons, one must be aware of the magic angle phenomenon. This common finding causes increased signal intensity within a normal tendon when the tendon fibers and magnetic vector form an angle of 55 degrees. Imaging the foot and ankle in slight plantarflexion (approximately 20 degrees) can decrease this effect.23 The MRI aids in the diagnosis of associated conditions such as lateral ankle ligament attenuation, peroneal tears and tenosynovitis, and hypertrophied peroneal tubercles.24