A twenty-three-year-old female national champion ice skater presented with pain on the lateral aspect of the right foot and ankle of eighteen months’ duration. The pain had begun insidiously with no preceding trauma. She had no previous history of ankle sprains or injury to the lower leg or foot. She did not have any paresthesias, weakness of the lower extremity, low back pain, or any sensation of instability. She had been evaluated previously by a trainer and was thought to have a mild lateral ankle sprain; she subsequently wore an ankle brace and took nonsteroidal anti-inflammatory medications. She did not receive any corticosteroid injections. She could still participate in skating but continued to have pain, which led to a progressive decline in her skating performance.
Fifteen months after the initial evaluation, the patient felt a sudden increase in pain while skating, with a sense of instability on the lateral side of the ankle. She reported that she was pushing off at the moment of injury and did not have an inversion twist to her ankle. Because of the pain, she was unable to continue skating; she also had difficulty walking and exercising.
On presentation to our clinic, the patient reported localized pain behind and below the lateral malleolus. Physical examination revealed no swelling or deformity in the foot or ankle. The neurological evaluation, including strength and sensation testing, was normal. She had tenderness anterior and inferior to the lateral malleolus; the area of the calcaneal tubercle was the most tender (Fig. 1). Stress testing in dorsiflexion and eversion also revealed pain at the same area without evidence of peroneal tendon subluxation. There was no evidence of ankle instability. She had no signs of reflex sympathetic dystrophy, and the vascular examination was normal. She did not have a prominent calcaneal tubercle or any apparent foot deformity.
Radiographs of the foot and ankle were normal with no avulsion fractures of the distal part of the fibula noted. Inversion stress radiographs of the ankle did not demonstrate any substantial differences from the contralateral ankle. A computed tomography (CT) scan of the ankle was normal and did not demonstrate any tendon subluxation or fracture. Magnetic resonance imaging (MRI) demonstrated increased signal at the level of the calcaneal tubercle but did not demonstrate any peroneal tendon abnormalities. Dynamic ultrasound scans were obtained with use of a linear array transducer with a frequency of 9 to 13 MHz (LOGIQ 9; General Electric, Milwaukee, Wisconsin) and standard acoustic coupling gel. Ultrasonography with the foot and ankle in the resting position showed the peroneal tendons in their normal position; however, with active eversion and dorsiflexion, dislocation of the peroneus longus tendon over the calcaneal tubercle was seen (Fig. 2). This activity reproduced the patient’s symptoms, and a diagnosis of peroneus longus tendon dislocation over the calcaneal tubercle was made.
The treatment options were discussed with the patient; operative intervention was elected to first confirm the diagnosis and then repair the torn retinaculum. Surgery was performed eighteen months after the first symptoms began and three months after the onset of severe pain and disability. The patient was placed in the lateral decubitus position; because she declined regional anesthesia, general anesthesia was administered. A 5 to 6-cm incision was centered over the peroneal tendons. A complete dislocation of the peroneus longus tendon over the calcaneal tubercle was found. The inferior portion of the inferior peroneal retinaculum was completely absent (Figs. 3-A and 3-B). However, the superior portion of the inferior peroneal retinaculum, which restrains the peroneus brevis, was intact and remained inserted on the calcaneal tubercle. The peroneus longus tendon was not fixed in position and could be easily reduced back to its anatomic position below the calcaneal tubercle. The peroneus longus tendon had no fissures or partial tear, and the calcaneal tubercle was not prominent. Because of the complete absence of the retinaculum over the peroneus longus tendon, direct retinacular repair or reinsertion was not possible; the inferior portion of the inferior peroneal retinaculum was reconstructed with part of its superior portion. The proximal half of the superior portion of the inferior peroneal retinaculum was released from its attachment to the extensor retinaculum and hinged at its calcaneal tubercle attachment. This portion of the retinaculum was moved distally and sutured into the periosteum on the lateral side of the calcaneus (Figs. 4-A and 4-B). There was no subluxation of the peroneal tendons once the reconstruction was completed.
After surgery, the ankle was placed in a non-weight-bearing short leg cast for six weeks. After the cast was removed, physical therapy was started. At twelve weeks, the patient began athletic activity. She progressively returned to full activity and subsequently returned to competitive ice skating without symptoms. Three years after surgery, she had a full range of motion of the ankle with no evidence of tendon subluxation. She had no pain or sensations of ankle instability.
The anatomy, pathology, and treatment of dislocation of the peroneal tendons over the lateral malleolus after injury of the superior peroneal retinaculum have been well described in the literature7-12. Klos et al.6 recently reported a case of isolated dislocation of the peroneus longus tendon in a twenty-three-year-old man while playing soccer. The trauma was sustained with the foot in plantar flexion, abduction, and eversion. The diagnosis was made primarily by physical examination four weeks after the injury. An MRI scan did not demonstrate any abnormalities; ultrasonography was not performed. Because conservative management was unsuccessful, the patient eventually underwent surgery. After identification of the calcaneal tubercle and torn inferior peroneal retinaculum, the retinaculum was reconstructed with use of a dorsolaterally based periosteal flap. The groove at the fulcrum was deepened with a gouge. After reduction of the tendon into its groove, the periosteal flap was placed over the reduced tendon and held in place with titanium suture anchors and absorbable suture. Our case represents another report of a dislocation of the peroneus longus tendon associated with a partial tear of the inferior peroneal retinaculum.
There are several important differences between our case and the typical case of subluxation of the peroneal tendons over the lateral malleolus. The major difference is the mechanism of injury in our patient. In most patients, there is a history of acute trauma with forced dorsiflexion and eversion of the foot at the ankle, which is associated with a forceful contraction of the peroneal muscles8,13,14. Our patient’s history suggests that chronic stress was a contributing factor to the failure of the inferior peroneal retinaculum.
The diagnosis of subluxating peroneal tendons over the lateral malleolus can be made with the patient’s history and physical examination12,15. A painful snapping sensation over the lateral aspect of the ankle is the classic indicator of peroneal tendon subluxation. Having the patient dorsiflex and plantar flex the foot at the ankle can allow the examiner to visualize or even feel the peroneal tendons move over the lateral malleolus. Stress testing can also be performed. During this testing, the foot will be plantar flexed at the ankle and everted against resistance, a maneuver that should demonstrate the tendon subluxation and cause pain. Our patient presented with pain on the lateral aspect of the foot and ankle without snapping. Physical examination revealed localized tenderness over the calcaneal tubercle on palpation. Stress testing in eversion and plantar flexion revealed pain in the same area without subluxation of the tendon.
Other causes of pain over the lateral aspect of the ankle may include stenosing tenosynovitis of the peroneal tendons, hypertrophy of the calcaneal tubercle, tear of one or both of the peroneal tendons, or an anatomical variant such as bifurcation of a peroneal tendon. None of these abnormalities was identified in our patient during surgical exploration.
Imaging of patients who may have subluxation of the peroneal tendons over the lateral malleolus should begin with radiographs. An avulsion fracture of the fibula at the point where the superior peroneal retinaculum attaches can occur in up to 16% of patients with subluxating peroneal tendons9. CT was utilized in our patient to evaluate other potential sources of pain, such as calcaneal fracture or subtalar injury. MRI can be of benefit when evaluating patients with subluxation of the peroneal tendons2,16 as the tendons can be frankly subluxated or dislocated anterolaterally relative to the fibular groove. Our patient did not have any of these findings on MRI.
The use of diagnostic ultrasonography to evaluate tendons around the foot has been described previously5,17,18. Neustadter et al.17 studied thirteen patients who had dislocation of the peroneal tendon over the lateral malleolus. They found that ultrasonography had a 100% positive predictive value for revealing peroneal tendon subluxation, and they considered it to be the primary choice for imaging of peroneal tendon subluxation.
Our case demonstrates the complexity of the anatomy of the restraints of the peroneal tendons as they course from the distal aspect of the leg to the foot (Fig. 1). The superior peroneal retinaculum, originating from the posterolateral aspect of the fibula and inserting onto the calcaneus, is the more frequently injured structure in patients with subluxating peroneal tendons. In their study of seventy-three patients with dislocations of the peroneal tendons, Eckert and Davis9 found that the superior peroneal retinaculum was torn. They speculated that the intact inferior peroneal retinaculum played an important role in peroneal tendon stability. The inferior peroneal retinaculum is continuous anteriorly with the fibers of the extensor retinaculum and is attached posteriorly to the lateral aspect of the calcaneus. Some retinacular fibers attach to the calcaneal tubercle, forming a septum that creates separate individual compartments for the peroneus longus and peroneal brevis tendons. In our patient, the portion of the inferior peroneal retinaculum that stabilized the peroneus longus tendon was torn, but the portion that stabilized the peroneus brevis was intact.
There have been several methods described to treat tears of the superior peroneal retinaculum. These options include primary repair, deepening of the peroneal groove in the fibula, or reconstruction of the retinaculum with local tissue, autografts, or allografts10,13,15,19-21. In our patient, we were able to reconstruct the torn portion of the inferior peroneal retinaculum with local tissue, but another option would have been to reconstruct it with a free tissue transfer.
In summary, we present an unusual case of isolated dislocation of the peroneal longus tendon caused by a tear of a portion of the inferior peroneal retinaculum. The history and physical examination did not result in an accurate diagnosis; ultrasonography of the peroneal tendons led to the correct diagnosis. Reconstruction of the inferior peroneal retinaculum allowed the patient to return to sports with no limitations. This diagnosis should be included in the differential diagnosis of patients with suspected peroneal tendon injury or dislocation.