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Emerging Techniques In Peroneal Tendon Repair
Noting the complexities and variable outcomes that can occur with surgical repair of peroneal tendon pathology, this author emphasizes appropriate staging and discusses evidence from the literature to outline optimal treatment pathways.
Lateral ankle instability and peroneal pathology often occur simultaneously. We typically see increased lateral ankle pathology in cavus foot deformity with increased stress and demand placed on the lateral ankle. One should make all attempts at non-operative care to first strengthen the lateral ankle and decrease strain and recurrent instability. However, conservative care often fails. Accordingly, let us take a closer look at surgical concepts for more severe peroneal tendon injuries that have not responded to previous conservative care attempts and even some surgical interventions.
Although I am going to focus on repair options for these types of injuries, it is important to also consider other issues commonly associated with these patients, including the patient’s age, comorbidities, cavus foot type, equinus deformity and any overriding proximal limb deformity. It is essential to have a good understanding of the patient’s long-term expectations with regard to function and activity. In any case exhibiting muscle weakness, we must also make sure to evaluate for any underlying neuromuscular diseases. Accordingly, we typically inspect the contralateral limb for any demonstration of weakness, obtain contralateral X-rays and, in some cases, may perform pre-operative electromyogram/nerve conduction testing. In extreme circumstances, a neurology consultation is necessary.
Let’s consider our general preoperative goals for any surgical correction. We want to restore anatomic function, assist in active plantarflexion, prevent recurrent injury and restore osseous alignment. In order to do this, we must know the extent of the injury. Is there simple tenosynovitis, a mild (less than 50 percent) single peroneal tear, a significant (greater than 50 percent) single peroneal tear or a case in which both tendons are unusable? Accordingly, let us break down each stage and take a closer look at emerging trends or recent literature related to each stage.
Stage 1: When Both Peroneal Tendons Are Grossly Intact
Before we dive into the more complex pathology, it is important to look at milder peroneal tendon injuries. Consider a situation in which both the peroneus longus and peroneus brevis are grossly intact. While there are very few published studies on peroneal tendoscopy within the last 10 years, it can be useful in cases in which advanced imaging has not definitively diagnosed the pathology at hand.1
In 2012, Lui described endoscopic management of recalcitrant retrofibular pain.2 This author described using tendoscopy for this condition with and without the presence of a peroneal tendon tear, and also utilized the procedure for cases without any preoperative identifiable cause
for pain. In regard to the technique, Lui utilized a 4.0 mm, 30-degree arthroscope to perform an endoscopic synovectomy and subsequently deepened the retromalleolar groove with an acromionizer.1,2 It is important to recognize that this case series of four patients treated with tendoscopy did not involve subluxation of the peroneal tendons. In cases with peroneal subluxation, Lui recommended open repair. Although there are many benefits to a minimally-invasive approach with tendoscopy, one has to question how much visualization surgeons are able to obtain without an open approach.
In a 2018 article published in Foot and Ankle International, Hull and team looked at visualized tendon length in peroneal tendoscopy.3 When discussing tendoscopy, one describes the peroneal tendons in three zones. Zone 1 includes the peroneus brevis and longus tendons from the musculotendinous junction to the peroneal tubercle as the two tendons share a tendon sheath in this region. Zone 2 tendons at the peroneal tubercle and to the level of the base of the fifth metatarsal have separate tendon sheaths. Zone 3 includes the tendon sheath of the peroneus longus tendon in the sole of the foot.4 Using cadavers to measure visualization, Hull and colleagues found that peroneus longus visualization was entirely possible through zones 1 and 2, and up to 9.7 mm from its insertion onto the base of the first metatarsal in zone 3.3
With magnetic resonance imaging (MRI) diagnosis of mild (less than 50 percent) peroneal tendon injuries or tears, we still resort to direct repair. Krause and Brodsky suggested a treatment algorithm that depends on the amount of viable tendon (50 percent rule).5 One typically reserves primary repair of peroneal tendons for injuries that have less than 50 percent tendon involvement and when the peroneus brevis and peroneus longus tendons are grossly intact.
Studies demonstrate good to excellent outcomes with direct repair of peroneal tendons in the presence of mild injuries.6-9 Researchers have shown American Orthopaedic Foot and Ankle Society (AOFAS) scores of 82 to 91 in this patient population with minimal complications and no reoperation rate at six years.6-9 If both tendons are grossly intact, then it is wise to excise the longitudinal split and tubularize the tendon.
Stage 2: When One Tendon Is Torn And The Other Is ‘Usable’
In stage 2 injuries that involve greater than 50 percent injury to one tendon while the other tendon appears to be “usable” or functional, a tenodesis is appropriate. Typically, a side to side tenodesis or anastomosis will allow the intact tendon to compensate for the injured tendon. However, how effective is a peroneal tenodesis in replicating physiologic tension?
In a cadaver study, Pellegrini and colleagues compared both allograft reconstruction and peroneal tenodesis under loading conditions for “irreparable” peroneus brevis tears.10 They found that allograft reconstruction restored distal tension when loaded to 50 and 100 percent of physiologic load. In comparison, the authors noted that tenodesis of the peroneus brevis to the peroneus longus did not effectively restore peroneus brevis tension.
It is important to reevaluate each patient for any underlying biomechanical etiologies predisposing him or her to increased lateral ankle strain/sprain. Often, the concomitant osseous pathology is obvious in stage 3 but can be more subtle in stage 2. If one proceeds with peroneal tendon repair without addressing the underlying pathology, the patient will continue to have excess lateral load/ force on the surgical repair site. During the workup and physical examination, it is paramount to delineate the type of varus deformity present. While this is above and beyond the scope of this article, the presence of varus deformity is certainly intertwined with peroneal tendon repair. Performing calcaneal and medial column osteotomies during tendon repair is prudent.
Stage 3: When Both Tendons Are Torn And ‘Unusable’
Continued peroneal injury with failed previous surgical intervention are the most complicated cases that we see and our options tend to become limited at this point. These patients typically present with continued lateral ankle pain, may or may not have had previous peroneal surgery, and may have a significant anterior drawer finding, ankle swelling, lateral heel pain and demonstrated weakness along the peroneal tendons. These findings lead us to consider salvage types of procedures. These may be cases of traumatic ruptures or peroneal tenodesis failure, and essentially exhibit non-functioning peroneal tendons.
If both tendons are torn and “unusable,” we have to consider more extensive reconstructive options. Redfern and Myerson divided stage 3 injuries into two categories: no excursion of proximal muscle and excursion of proximal muscle.6 Excursion is literally how much myotendinous excursion or pull the tendon has in its sheath. To test this, one pulls the tendon distally with a clamp. If you can pull the tendon over one to two cm, there is appropriate muscle excursion and therefore function. If this is not the case, the myotendinous unit is non-functional.
If there is no muscle excursion, then an allograft is unlikely to be successful and a tendon transfer is indicated. A single or two-staged approach is possible. A single stage approach would involve debridement of the non-functional tendon and transfer of a tendon into the base of the fifth metatarsal. Jockel and Brodsky have noted no significant functional difference between flexor digitorum longus and flexor hallucis longus transfers.11 When harvesting flexor hallucis longus for peroneal reconstruction, it is important to obtain as much length as possible with two incisions, one at the knot of Henry and then distally at the hallux interphalangeal joint. The surgeon then reroutes the tendon posteromedially between the Achilles tendon and the medial malleolus, being careful to protect the neurovascular structures. One then passes the tendon from medial to lateral before anchoring it into the fifth metatarsal base.
Goss and coworkers in 2019 looked at minimally invasive methods for harvesting the flexor hallucis longus.12 Though this was a cadaver study, they performed an incision at the hallux interphalangeal joint plantarly and subsequently made a lateral-based incision for peroneal tendon repair through which they retrieved the long hallux flexor tendon. The authors emphasized caution when approaching the sustentaculum with the tendon harvester as graft amputation can occur with the bony endpoint. Seybold and colleagues looked at a five-year follow-up on eight patients who had lateral transfer of the flexor hallucis longus or flexor digitorum longus, and found AOFAS scores improving from 64 to 86 with all patients being able to return to preoperative activity.13
The alternative option is a staged procedure.14,15 Wapner and colleagues looked at long-term follow-up (five years) of a staged flexor hallucis longus transfer using a Hunter rod.14 This procedure utilizes a silicone rod placement in order to promote a pseudo-tendon sheath, which would provide for a more “normal” tendon with later transfer. Recommending at least six weeks between stages in order to allow for pseudo-sheath formation, the study authors reported excellent to good results in five out six patients.
If there is muscle excursion present, then one may utilize an allograft. Most studies recommend using a hamstring allograft tendon.16-18 Rapley and colleagues recommended a Pulvertaft weave for incorporation of allograft to the proximal tendon stump.19 Most of the evidence-based medicine are level 4 or 5 case series. However, allograft reconstruction
does decrease the risk of donor site morbidity associated with autograft or even flexor hallucis longus/flexor digitorum longus tendon transfers. The use of acellular dermal matrix may augment repairs in tendons with greater than 50 percent involvement. Again, these are small case series but Rapley and coworkers did note good to excellent results.19
Case Study: When A Patient Presents With Chronic Pain In The Lateral Ankle And Foot
A 56-year-old male presented with a chief complaint of long-standing pain along the left lateral ankle and foot with subjective weakness and pain. He also complained about wearing out the lateral aspect of his left shoe. The patient could not recall any significant history of a single traumatic injury. He previously experienced some relief with bracing but upon presentation, the patient cited irritation with bracing and less relief of pain.
A physical examination elicited pain along the left lateral ankle and the peroneal tendons. With significant eversion, the patient also had weakness against resistance. Manual muscle testing of his flexor hallucis longus was 5/5 without any weakness. The patient had hyperkeratotic lesions under the fifth metatarsal base and head. When the patient was in weightbearing stance, it was clear he had a high arch with a calcaneal varus deformity that was not reducible with a Coleman block test bilaterally. Although his right foot was structurally similar to his left foot, he was asymptomatic on the right side.
The radiographic workup included a weightbearing radiographic evaluation of both the foot and ankle as well as calcaneal axial views. It is important to not only evaluate the foot but alignment of the ankle joint as well. While the patient had a congruent, neutral ankle joint, the calcaneal axial view demonstrated varus deformity of the heel with weightbearing foot radiographs confirming a midfoot cavus deformity. Further advanced imaging and MRI evaluation revealed longitudinal tearing of both the peroneus longus tendon as well as the peroneus brevis tendon.
The preoperative discussion must include all possible outcomes in this case. In this scenario, I discussed thoroughly with the patient the possibility of primary repair versus peroneal tendon transfer and flexor hallucis longus transfer. Heading into the case, I knew based on the MRI findings that both tendons were partially injured. However, I have learned that MRIs can fool us both ways (over- and underestimating disease pathology) so I plan for this. I also educate the patient on the biomechanics that lead to this pathology and address the calcaneal varus.
Intraoperatively, I first performed a Dwyer calcaneal osteotomy. Of note, it is important to plan out both incisions in order to avoid a narrow skin bridge as this could pose potential for wound complications. After performing the calcaneal osteotomy, I directed my attention to the peroneal tendons. Both tendons demonstrated severe longitudinal tearing greater than 50 percent and were non-salvageable. Accordingly, I ruled out the possibility of a primary repair. Now the key is determining whether to perform a repair with allograft or a tendon transfer.
In order to make this determination, I tested the patient’s muscle excursion. There was little to no muscle excursion demonstrable in either myotendinous unit. Therefore, an allograft would likely fail. I decided to proceed with a flexor hallucis longus tendon transfer in a single-stage approach by harvesting the flexor hallucis longus tendon distally at the master knot of Henry. Making the second incision at the posterior medial malleolus allowed me to bring the flexor hallucis longus tendon from the foot to the ankle.
I then rerouted the tendon posterior to the tibia and neurovascular bundle, and into the peroneal tendon sheath prior to anchoring the tendon into the fifth metatarsal base with the foot in dorsiflexion. Harvesting the tendon with a two-incision medial approach usually yields adequate length for a transfer into the base of the fifth metatarsal without going to the hallux. Surgeons may also perform a calcaneal osteotomy in a minimally invasive fashion if they are trained to do so to avoid incisional issues.
Postoperatively, this patient was non-weightbearing for a total of six weeks. Typically, patients are in a splint for two weeks until suture removal with subsequent transition to a cast for the remainder of the non-weightbearing period. I tend to be more conservative with patients who have an osteotomy and a tendon transfer. The patient transitioned to protected weightbearing in a boot for four additional weeks and began physical therapy.
In Conclusion
Peroneal pathology requires prudent workup and advanced imaging. For a reproducible outcome, staging the tendinopathy can assist with treatment protocols. Emerging treatments and treatment pathways have allowed us to treat stage 1 with tendoscopy and stage 3 complex revisions with predictable tendon transfers. As always, we strive to continue researching peroneal tendon repair outcomes for improved patient function.
Dr. Pirozzi is a Fellow of the American College of Foot and Ankle Surgeons (ACFAS) and serves as Vice President for ACFAS Region 2. She is currently in private practice in Phoenix, Ariz.
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