Essential Insights On Flexor Tendon Transfers

Author(s): 
By Babak Baravarian, DPM

It would be safe to say that among foot deformities, lesser digital deformities are one of the most common and one of the most complicated problems. The etiology and mechanism of action of the deformities have been well established. In order to best fix the deformity, the surgeon must have a good knowledge of the specific anatomy as well as the intricate biomechanics within the digits. The mechanism of action for the development of hammertoes, mallet toes and clawtoes has been established in the literature. It is beyond the scope of this article to expound on the anatomy and the etiology of digital deformities. Instead, we will address complicated digital deformities most commonly involving the second metatarsophalangeal joint (MPJ) and digit that benefit from a flexor tendon transfer. It is simple enough to reduce a digital deformity in the short term. The difficulty is keeping the recurrence rate to a minimum and maintaining functionality of the MPJ whenever possible. Stabilization of the MPJ is just as essential in correction as getting the phalanges in a rectus position. Although one may identify instability of the MPJ in any of the lesser digits, it is most prevalent at the second. This can be in the form of a predislocation syndrome, crossover deformity and other variations of a plantar plate disruption. The fact that the plantar plate of the second MPJ lies directly underneath the second metatarsal head may lead to the increased incidence of instability in the second MPJ. When the MPJ is unstable, the surgeon must identify if there is a deformity purely in the sagittal plane or if there is any medial or lateral deviation as well. One would test this with the foot in a loaded position, and it is best to evaluate this with the patient in a full weightbearing position. If there is medial or lateral crossover, there is usually a defect in the collateral ligaments or the suspensory ligaments. A pure dorsally dislocated digit is associated with a plantar plate disruption or tear. A combination of the two may also be present. In the case of crossover deformities, due to the dorsal and medial deviation, there is commonly a loss of the collateral and plantar plate apparatus. The main decision making process for digital deformity is through clinical examination. During the clinical evaluation, one should manipulate the digit in order to identify the degree of the defect in the plantar plate. Clinicians can do this by grasping the digit between the thumb and the lateral aspect of the index finger, and applying a dorsiflexory force at the base of the proximal phalanx over the metatarsal head. I have found that if there is a dorsal excursion of more than 4 mm, a disruption in the plantar plate is highly probable. In cases of attenuation, partial tear or complete tear of the plantar plate, the surgeon may perform a direct repair. This is often difficult and often does not allow for stable and reproducible deformity correction. I prefer to utilize a flexor tendon transfer to augment the digital deformity repair and decrease the chance of recurrence. Inside Insights On Hammertoe Repair When repairing a hammertoe, it has been well established that one should employ a stepwise approach to correction. Make a dorsal incision from just distal to the proximal interphalangeal joint (PIPJ) to just proximal to the metatarsal head. Some will choose a lazy S-type incision. After achieving hemostasis, carry dissection down to the level of the extensor tendons, the extensor apparatus and deep fascia. Using blunt dissection, separate the skin and deep tissues from the deep fascia and the capsular tissues, retracting medially and laterally to avoid neurovascular embarrassment. Make a transverse incision through the extensor tendon and the capsule of the PIPJ just proximal to the end of the cartilaginous surface of the head of the proximal phalanx. Follow this by releasing the medial and lateral collateral ligaments of the PIPJ. Use the blade along the medial and lateral aspects of the phalanx down to bone in order to release the extensor tendons from the dorsal surface of the proximal phalanx, extending proximal to the joint capsule of the MPJ. At the same time, one should release the extensor hood apparatus. Then clamp the end of the tendon with a hemostat and wrap it in gauze to keep it hydrated. Proceed to load the foot in order to determine if the deformity still exists.

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