Plantar first metatarsal head ulcerations can be challenging to treat. Ulcerations under the first metatarsal head reportedly represent the most common cause of lower limb amputations in patients with diabetes in the United States.1 Providers typically utilize non-surgical treatments first to try to heal the ulceration and these treatments include local wound care, immobilization and offloading. When these measures fail, surgical intervention may be necessary before the ulceration progresses to infection or osteomyelitis.
It is essential for podiatrists to first assess the overall foot structure and potential biomechanical cause of the plantar first metatarsal head ulceration. Overlooked causes are peroneal overdrive and the subtle cavus foot. Accordingly, let us take a closer look at the anatomy of the peroneus longus, the clinical examination involved in working up peroneal overdrive and employing tendon transfers to treat this condition.
Essential Anatomical Insights
The peroneus longus tendon arises from the proximal two-thirds of the lateral fibula, intermuscular septum and the lateral condyle of the tibia.2 The peroneus longus tendon is innervated by the superficial peroneal nerve. The peroneus longus tendon lies posterior to that of the peroneus brevis. Both the peroneus longus and brevis tendons are found within the retromalleolar groove bound by the superior peroneal retinaculum, posterior talofibular ligament, calcaneofibular ligament and posterior inferior tibiofibular ligament.2 Below the retromalleolar groove, the two tendons separate into their own distinct synovial sheaths. The peroneal longus tendon passes below the peroneal tubercle, courses obliquely through the cuboid tunnel and eventually attaches to the plantar proximal portion of the medial cuneiform and first metatarsal base. The peroneus longus is both a plantarflexor of the first ray and an everter of the foot.2
What To Look For In The Clinical Examination
First one must assess the overall foot structure. If the patient has a cavus foot type, the Coleman block test is important to perform. With the patient on a one to two inch solid surface, such as a wooden block, the podiatrist should place the first metatarsal off the surface to allow it to drop. If the heel becomes neutral, the rearfoot varus is driven by the first metatarsal and potentially peroneal overdrive. If the heel remains in varus, the deformity is rearfoot-driven.
The subtle cavus foot is non-neurologic in etiology. It results from first metatarsal position and hyperactivity of the peroneus longus muscle.3 A plantarflexed forefoot creates a functional forefoot equinus, which also affects ankle dorsiflexion. The weightbearing plane of the foot is more plantarflexed with the first metatarsal head lower than the heel. When the ankle is plantarflexed, the peroneus longus muscle gains a mechanical advantage, allowing it to overpower the tibialis anterior muscle.3 Additionally, the peroneus longus can overpull as a result of recruitment of the muscle to assist a weak Achilles tendon.4 These two theories explain the presence of a plantar first metatarsal ulcer in the absence of a fixed deformity.
The only way to diagnose peroneal longus overdrive is by physical examination. To assess for peroneal overdrive, the physician places one thumb on the plantar aspect of the second through fifth metatarsal heads and the other thumb under the first metatarsal/seamoid complex. The patient then plantarflexes his or her ankle. Overactivity of the peroneal longus is demonstrated when the first ray goes into a stronger plantarflexion than the remaining lesser metatarsals. Employing the Silfverskoid test should also allow physicians to determine if equinus contributes to the deformity. It is not uncommon for patients with diabetes to have an underlying equinus contracture contributing to increased forefoot pressures as well as pathologic peroneus longus overdrive.4
Key Aspects Of The Peroneus Longus To Peroneus Brevis Tendon Transfer
After ensuring supine positioning of the patient, one may use a thigh tourniquet, set at 300 mgHg, to provide hemostasis. After anesthesia administration, the surgeon preps and drapes the lower extremity above the knee and distal.
If the Silfverskioid test revealed a contributing equinus deformity, one addresses this first with the appropriate lengthening procedure. The surgeon proceeds to direct his or her attention to the dorsal lateral aspect of the foot and ankle. One makes an approximately four cm incision to the cuboid along the peroneal tendons. While deepening the incision, the surgeon should take care to identify and not damage the sural nerve.
Proceed to isolate the peroneal tendons. Follow the peroneal longus tendon as far distal as possible and transect it. The proximal stump of the peroneus longus tendon is then ready for transfer to the peroneus brevis tendon. I choose to use a Pulvertaft weave technique. One would perform this transfer under physiologic tension with an assistant holding the ankle and foot in neutral position.
After achieving a secure transfer, the surgeon can close subcutaneous tissues and skin. I apply a standard postoperative dressing and place the patient in a posterior splint with the ankle locked in neutral and out of equinus. I keep the patient non-weightbearing for four weeks. After four weeks, the patient may transfer to a walking boot and initiate physical therapy.
When a patient presents with a non-healing ulceration plantar to the first metatarsal head despite appropriate wound care, offloading and immobilization, he or she may require surgery to help heal the ulceration and subsequently prevent infection and amputation. Be sure to fully assess the biomechanical reason(s) for the ulceration. Do not forget about peroneal longus overdrive as a potential cause. If this is the case, the peroneus longus to peroneus brevis transfer is a powerful tool to help heal these ulcerations.
Dr. Butto is board-certified by the American Board of Foot and Ankle Surgery, and is a Fellow of the American College of Foot and Ankle Surgeons. She is in private practice in Avon, Ct.
1. Dayer R, Assal N. Chronic diabetic ulcers under the first metatarsal head treated by staged balancing. J Bone Joint Surg Br. 2009;91-B(4):487-493.
2. Davda K, Malhotra K, O’Donnell P, Singh D, Cullen N. Peroneal tendon disorders. EFORT Open Rev. 2017;2(6):281-292.
3. Visser HJ, Ansari A, Thompson S. Assessing and treating subtle cavus foot deformity. Podiatry Today. 2015;28(6):56-60.
4. DiDomenico LA, AbdelFattah SR, Hassan MK. Emerging concepts with tendon transfers. Podiatry Today. 2018;31(2):26-32.