Key Insights On Surgical Treatment Of Degenerative Peroneal Tendon Dysfunction

These authors present pearls on treating a 59-year-old with a rupture to the peroneus brevis tendon and advanced peroneus longus tendinopathy.

Peroneal tendon injuries are common, particularly among athletic individuals. However, there have been a growing number of attritional peroneal injuries among older, non-athletic patient populations. Often, these injuries tend to coincide with repetitive ankle sprains secondary to lateral ankle instability. Attrition of the peroneals secondary to repetitive microtrauma derived from a varus subtalar joint may also contribute to dysfunction and biomechanical forces.^1,2 When this goes undiagnosed, degenerative peroneal tendon dysfunction occurs, resulting in a varus deformity with pathologic biomechanical implications if left untreated.

The peroneus brevis originates in the lateral compartment from the distal two-thirds of the fibula and intermuscular septum, and carries distally and posteriorly to the fibula before inserting into the base of the fifth metatarsal at the level of the styloid process.^2-4 Likewise, the peroneus longus originates in the lateral compartment intermuscular septum and proximal two-thirds of the fibula, and courses distally and posterior to the peroneus brevis tendon.^2-4 At approximately 4 cm proximal to the distal aspect of the lateral malleolus, the peroneus brevis and longus tendons enter the common peroneal synovial sheath, and subsequently enter a fibrous canal that the superior peroneal retinaculum stabilizes.^2-5

The literature often describes the mechanism for an acute peroneal tendon subluxation with concomitant tearing as a result of rapid dorsiflexion with peroneal musculature contraction. However, in chronic conditions, other etiologies may be present. Examples include overcrowding within the peroneal groove due to the presence of a low-lying peroneal muscle belly, accessory peroneal muscle or a shallow peroneal groove along the posterior aspect of the fibula. Over time, anomalies can result in superior peroneal retinaculum insufficiency and subluxation of the peroneus brevis tendon. As this occurs, the peroneus brevis tendon splits due to mechanical forces along the lateral fibular ridge and the peroneus longus tendon becomes anteriorly positioned in between the peroneus brevis split.^4,5 In this state, repetitive microtrauma of the peroneal tendons occurs, causing fibroblastic proliferation and ultimately progressing to pathologic degeneration of the peroneal tendons.^4,5

Pedal architecture can also contribute to superior peroneal retinaculum and peroneal tendon overload. For example, in subtle cavus deformity, a predominant heel varus will result in pathologic peroneal strain and over time, attrition of the peroneal tendons will occur.⁶ When this degenerative peroneal tendon injury progresses unrecognized, lateral ankle instability ensues.

In 2004, Redfern and Myerson found that when patients present with peroneal tendon tears, 43 percent are likely to have some degree of instability while 66 percent will also present with an increased varus tilt when stressed.⁷ Likewise, DiGiovanni and colleagues in 2000 found patients with chronic lateral ankle instability presented with peroneal synovitis, retinacular attenuation and longitudinal peroneus brevis tears 77 percent, 54 percent and 25 percent of the time respectively.⁸

In this chronic dysfunctional state, the peroneal tendon muscle belly becomes scarred and atrophic. Subsequent unopposed overpowering of the deep flexors leads to subtalar and midfoot varus instability.^2,4,5,7,9,10 In this chronic presentation with varus instability, simple repair of the isolated tendinous injuries is inadequate and necessitates a lateral flexor tendon transfer in order to restore biomechanical eversion and plantarflexion forces. With this in mind, we present a case and surgical technique when performing a lateral flexor digitorum longus tendon transfer due to degenerative peroneal tendon dysfunction.

A Closer Look At The Patient Presentation

A 59-year-old female with a significant past medical history of thyroid disorder presented with pain to the anterolateral aspect of her left foot lasting for approximately 10 months. Initially, she sought medical care but received no presumptive diagnosis. Upon further examination, the patient demonstrated a rupture of the peroneus brevis tendon at the area of the peroneal tubercle as well as advanced peroneus longus tendinopathy with a high-grade tear inferior to the level of the cuboid, resulting in a significant flexible adductovarus deformity with lateral instability of the left foot and ankle.

With loss of her peroneal muscle function and with unopposed deep flexor compensation, we deemed a lateral transfer of the flexor digitorum longus tendon necessary to restore proper biomechanical eversion and plantarflexion (see photo above at left). In addition, weakening of the antagonist tibialis posterior muscle through a myotendinous lengthening may be necessary as an adjunctive procedure. In regard to the patient’s heel varus position, we planned to perform a Dwyer calcaneal osteotomy with consideration for a subtalar arthrodesis to correct the heel varus state should the Dwyer and lateral flexor digitorum longus tendon transfer provide inadequate correction intraoperatively.

What You Should Know About The Surgical Technique

With the patient under mild sedation, we ensured the patient was in supine position on the operating table. Following general anesthesia, we rotated the patient into a lateral position and placed a pneumatic thigh tourniquet on the patient’s left lower extremity. After scrubbing, prepping and draping the left lower extremity in the usual aseptic manner, we used an esmarch to exsanguinate the left foot and inflated the tourniquet to 350 mmHg.

We directed our attention to the lateral aspect of the left foot and made a linear longitudinal incision along the posterolateral aspect of the calcaneus. At this time, we identified all neurovascular structures and retracted the structures as necessary. Using a sagittal saw, we made an incision along the lateral posterior wall of the calcaneus and subsequently employed a mallet and osteotome to complete the repair. Subsequently, we performed lateral closure of the posterior calcaneus with a sagittal saw feathering technique until we noted correction to the heel varus deformity. Fixation consisted of two parallel 4.5 mm x 15 mm partially threaded cannulated screws via a standard AO technique (see photo at right).

We proceeded to make a lateral curvilinear incision along the peroneal tendons, taking care to identify and retract all vital neurovascular structures. After incising the peroneal sheath, we noted the peroneus brevis and peroneus longus tendons were dystrophic with bulbous longitudinal tears and attenuation of peroneal musculature that were visible intraoperatively (see photo at left). The peroneus longus and brevis tendons were nonviable. This required resection of the peroneus longus distally at the level of the lateral cuboid as well as proximal resection just superior to the lateral malleolus. The distal aspect of the peroneus brevis tendon was viable and we left it intact for augmentation of the flexor digitorum longus tendon.

At this time, we performed a lateral transfer of the flexor digitorum longus tendon. Through a small incision, we identified the flexor digitorum longus tendon along the medial aspect of the foot at the level of the master knot of Henry (see photo at right). Under tension, we transected the flexor digitorum longus tendon distally to ensure the adequate length required for transfer. Then after measuring 9 cm proximal to the distal aspect of the medial malleolus, we made another small incision in order to mobilize the flexor digitorum longus tendon (see photo below at left), subsequently passing the tendon laterally and posteriorly to the tibial nerve and fibula before coursing distally along the fibular groove.

We then reapproximated the flexor digitorum longus to the remaining peroneus brevis tendon under maximum tension utilizing the Pulvertaft technique and secured it using 4-0 Mersilene (Ethicon) (see right photo). Then we repaired the peroneal sheath over the flexor digitorum longus tendon. In addition to the flexor digitorum longus tendon transfer, we noted the plantar fascia had excessive tension intraoperatively and performed a percutaneous plantar fasciotomy. Correction of the adductovarus foot type was visible intraoperatively without the need for a subtalar joint arthrodesis or myotendinous lengthening of the tibialis posterior.

The patient remained non-weightbearing for six weeks postoperatively until evidence of healing across the Dwyer osteotomy surgical site was evident radiographically with noted correction of the ankle mortise (see left photo). After six weeks postoperatively, the patient received a controlled ankle motion (CAM) boot and ASO Ankle Brace (Medical Specialties) to wear with full weightbearing activity. The patient may begin participating in physical therapy at eight weeks following surgery. At 10 weeks, the patient should begin transitioning out of the CAM boot and into a supportive shoe. At the last follow-up visit, the patient was ambulating pain-free in a supportive shoe with correction of the previous flexible adductovarus deformity evident.

What The Literature Reveals About Peroneal Tendon Injuries

Peroneal tendon injuries are a common, yet frequently underreported, source of chronic lateral ankle pain. In 2003, Dombek and coworkers evaluated 40 patients with chronic lateral ankle pain by way of surgical intervention and confirmed the presence of peroneus longus and/or brevis tendon tears. The study reported that approximately 58 percent of the patient population had a history of trauma, most commonly lateral ankle sprain.¹

Despite this, a vast number of patients report that they cannot recall one precipitating event leading to their ankle pain. In a study performed by Krause and coworkers, 45 percent of the patients were unable to relay a history of trauma to the affected ankle.¹¹ This large population of patients with unrecognized traumatic causes lends to the difficulty in correctly diagnosing this injury upon the first clinical presentation. On average, patients presenting to the clinic for the first time had already received 3.3 incorrect diagnoses.¹ In this setting, attrition of the peroneal tendons secondary to varus deformity is likely to be contributory to the degenerative peroneal tendon dysfunction and overall ankle and subtalar instability.

Subtalar and midfoot varus instability remain problematic with degenerative peroneal tendon dysfunction. When undiagnosed, progression to an adductovarus and degenerative peroneus deformity occurs. These abnormal biomechanical forces result in peroneal tenosynovitis and degenerative lengthening secondary to functional subluxation of the peroneus brevis and attrition within the peroneal groove. As this process continues, the peroneal retinaculum becomes attritional, resulting in longitudinal peroneus brevis tendon splitting.⁷ The long-term sequelae of chronic lateral ankle, subtalar and midfoot instability results in attrition and scarring within the peroneal groove and subsequent atrophy of the muscle belly, leading to peroneal dysfunction. When left unrecognized, midfoot adduction occurs, increasing strain along the peroneus longus tendon within the cuboid groove.^2,4,5,7,10

Previous studies have demonstrated good results with lateral flexor digitorum longus tendon transfer when surgically treating chronic degenerative peroneal tendon dysfunction. In 1998, Borton and colleagues proposed performing a flexor digitorum longus tendon transfer in order to accommodate chronic peroneal dysfunction, and demonstrated good results and alleviation of ankle pain at six- and eight-year follow-up visits.¹²

Recently, authors have discussed using the flexor hallucis longus tendon rather than the flexor digitorum longus tendon for surgical correction of degenerative peroneal tendon dysfunction. Silver and colleagues compared lower extremity muscle strength, noting the flexor hallucis longus demonstrated twice the muscle strength in comparison to the flexor digitorum longus.¹³ Seybold and coworkers in 2013 compared flexor digitorum longus and flexor hallucis longus lateral tendon transfers in nine cadaver specimens. They noted visual compression of the tibial nerve when surgeons performed the flexor digitorum longus transfer, predisposing patients to possible tibial neuritis symptoms.⁹

However, in a 2013 review of eight patients, Jockel and Brodsky utilized a flexor hallucis longus or flexor digitorum longus tendon transfer when both peroneal tendon tears were beyond surgical reconstruction. They noted improved American Orthopedic Foot and Ankle (AOFAS) scores from 64 to 86 and a decrease in the Visual Analog Scale from 4.2 to 0.7 with 87.5 percent of patients returning to preoperative activity levels.¹⁴ Likewise, Seybold and colleagues in 2016 compared lateral transfer of the flexor digitorum longus and flexor hallucis longus in nine patients over an eight-year period, noting no statistically significant differences between groups.¹⁰

In Conclusion

Peroneal tendon pathology often goes unrecognized in patients who present with lateral ankle pain. Degenerative peroneal tendon dysfunction can progress with loss of attrition and muscle function resulting in cavovarus deformity of the ankle, subtalar, and midfoot. In this condition, surgical intervention is recommended. Lateral transfer of the flexor digitorum longus tendon into the peroneus brevis using the Pulvertaft technique may establish a rectus foot in a flexible cavovarus deformity secondary to degenerative peroneal tendon dysfunction.

Dr. Visser is the Director of the Foot and Ankle Surgery Residency program at SSM Health DePaul Hospital in St. Louis. He is a Fellow of the American College of Foot and Ankle Surgeons.

Dr. Wolfe is a first-year resident at SSM Health DePaul Hospital.

Dr. Maestas is a first-year resident at SSM Health DePaul Hospital.

References

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