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. If it does, direct your attention to the capsule of the metatarsophalangeal joint. One should perform a capsulotomy. If the deformity is only in the sagittal direction, then perform a full medial dorsal and lateral capsulotomy. In cases of a crossover deformity with a medial or lateral deviation as well, the surgeon should release the medial or lateral capsule respectively along with the dorsal capsule. Again at this time, one should load the foot to determine if the deformity has been reduced. If not, release the plantar plate from its adherence to the metatarsal head by using a McGlamry elevator. Do this carefully in order to avoid injuring the cartilage of the metatarsal head or the plantar plate itself. In some cases, if there is still a contracture present, the surgeon may need to perform a metatarsal osteotomy to release the pressure from the MPJ. A Few Thoughts On The End-To-End Fusion At this time, direct your attention to the PIPJ to prepare the joint. I prefer a fusion of the PIPJ in these severe types of deformities, especially when it comes to deformities of the second digit. The fusion can be of an end-to-end type or a peg-in-hole fusion when shortening is needed. For an end-to-end fusion, use a rongeur to help resect the cartilage surface of the head of the proximal phalanx but leave the length of the metatarsal intact. Then use a rotary burr to shape the head of the proximal phalanx. Reduce the medial and lateral condyles. It is important to reduce the size of the medial and lateral condyles in order to reduce the prominence they create postoperatively. The surgeon should reduce the end of the phalanx through its subchondral bone or more, depending on the amount of shortening that is needed and whether the end of the phalanx needs to be shaped square or round. Using a rotary burr, reduce the cartilage of the base of the middle phalanx through the subchondral bone. One should facilitate the shape that was created on the head of the proximal phalanx in order to achieve the best surface contact. Surgeons should also address any angular deformity in the proximal phalanx head or the base. Step-By-Step Pointers On Performing The Flexor Tendon Transfer At this time, the surgeon can prepare for the flexor tendon transfer. Visualize the flexor tendons through the space between the proximal and middle phalanges. Using a curved hemostat, perform delicate dissection to separate the long flexor from the short flexor. Identify the flexor digitorum longus tendon deep to the digitorum brevis at the level of the proximal phalanx region. Use the curved tip of the hemostat to grasp the flexor digitorum longus (FDL) transversely. Pull the long flexor to identify plantarflexion of the distal phalanx. Doing so helps ensure you are releasing the proper tendon. With the tendon on tension, perform transaction of the tendon distal to the hemostat at its most distal point. With the tendon in view, use a scissor to split the tendon along its course and place hemostats on the split ends. Pass the medial slip of tendon plantar to the flexor digitorum brevis (FDB) and medial to it. There should now be one-half of the tendon on either side of the proximal phalanx. Pull the tendons proximally along the phalanx shaft to the base of the digit. It is essential to tighten the tendon at the base of the toe for the best correction of plantar plate laxity. Then cross the tendons medially and laterally over the dorsum of the phalynx base with slight plantar force, bringing the phalanx into more congruency with the MPJ. If there is a transverse deformity, one can apply the tension of the tendon more medially or more laterally to reduce the deformity. When you are satisfied that you have harvested enough tendon and that the tendon slips are freely moving over the hood apparatus, direct your attention to the placement of the Kirschner wire. Place the K-wire in the center of the medullary canal of the proximal phalanx and drill toward the head of the proximal phalanx. Drive the K-wire through the base of the middle and distal phalanx and out through the end of the digit. Then retrograde the pin through the head of the proximal phalanx and just out through the base of the proximal phalanx without crossing the MPJ at this time. Then an assistant positions the tendon slips with the attached hemostats over the dorsal surface of the proximal phalanx with the proper amount of plantarflexion and medial or lateral tension. Once you are satisfied that the digit is in good position at the MPJ, use a 4.0 vicryl suture on a non-cutting needle to suture together the tendon slips at the point where they cross and grab the periosteum on the dorsal surface of the phalanx. If you have harvested enough of the tendon, there should be excess tendon on each end. If additional transverse plane correction reinforcement is necessary, the surgeon can also suture the appropriate end of the tendon to the lateral or medial capsule of the MPJ just distal to the MPJ. When the tendon transfer is secure, drive the K-wire across the MPJ into the metatarsal head in a slightly plantarflexed position to facilitate mild correction for any transverse deformity. Check the position of the wire and the final correction of the digit under intraoperative fluorography. Should You Consider The Alternative Option Of A Single Tendon Transfer? An alternate means of transfer is performing a single tendon transfer through a drill hole in the base of the proximal phalanx. This procedure allows for excellent positioning of the tendon in a sagittal plane but does not allow for much transverse correction of the toe. Transfer fixation was not easy in the past but the advent of interference screw fixation has added rigid fixation and much better short- and long-term stability. Harvest the tendon in the proximal phalynx joint of the associated toe. One may harvest the entire tendon through a small incision in the plantar aspect of the base of the proximal phalanx. Then wrap the tendon in a cross-stitch pattern with suture material of your choice. Use a drill to make a single hole in the base of the proximal phalanx. Exercise caution with the placement of the drill hole. Place a guide wire and check the position under fluoroscopy prior to drilling the hole. One can use a cannulated drill bit to make the hole. Consider making a drill hole of approximately 3 mm. Once you have made the drill hole, harvest the tendon with a tendon passer and pull it dorsally under tension. Insert an interference screw for rigid fixation. Note that it is not possible to place a K-wire across the MPJ in such cases and one can only stabilize the fixation of the proximal phalangeal joint with a K-wire to the level of the interference screw. After you have stabilized the toe in ideal position, proceed to repair the freed structures. Reattach the extensor tendon. Then coapt the subcutaneous tissues and the skin. With the tourniquet released, dress the digit with a gauze and a compressive dressing. The foot and the digit with the wire should be well protected during the postoperative period of recovery. One can allow the patient limited weightbearing for up to six weeks, depending on radiographic and clinical fusion of the MPJ. Remove the K-wire between four and six weeks postoperatively and no longer than seven weeks due to the fact that it has crossed the MPJ. Physical therapy is critical for reducing edema to the digit and returning range of motion to the MPJ. Recognizing The Benefits Of Flexor Tendon Transfers A flexor tendon transfer will greatly add to the correction of the deformity in many ways. It brings added stability to the MPJ. It can also act as an internal “splint” to the digit to heal a plantar plate disruption. It can aid in correcting the sagittal and transverse deformities at the MPJ. It will also reduce the occurrence of a clawtoe deformity from weakness of the extensor tendons after a hammertoe correction. In regard to flexor tendon transfers of the digit, a key point to remember is that the flexor tendon is actually a deforming force in digital deformities and causes an extensive portion of the deformity in hammertoes. With digital fusion procedures, which we consider to be the ideal treatment for hammertoes, there is the issue of possible mallet toe formation with preservation of the flexor tendon in its original position. With the flexor tendon transfer, the flexor tendon is no longer a deforming force and this negates the potential for mallet deformity. The second and far more important use of flexor tendon transfers is the consistent and reproducible repositioning of a digit in cases of plantar plate disruption. We have tried primary and secondary repair of plantar plate tears as well as plantar plate release and stabilization to allow fibrosis and metatarsal osteotomy reduction of plantar plate stress. We find no procedure has allowed for a more reproducible correction and decrease in pain in the lesser digits than the flexor tendon transfer. Although the surgeon may not fully reduce severe crossover deformity with a flexor tendon transfer, one can reduce a majority of the deformity with the tendon transfer. Indeed, surgeons can often perform full correction with collateral ligament reconstruction, flexor transfer and possible shortening metatarsal osteotomy in association with fusion of the proximal phalanx for hammertoe correction. When One May Consider A Split Tendon Transfer We have found no difference in the split tendon transfer versus central tendon transfer through a drill hole. There are benefits and weaknesses to each procedure. The benefit of a split tendon transfer is that it is a more simple procedure without the need for a second plantar incision. A split tendon transfer will also allow for better medial and lateral correction of the digit at the MPJ. The drawback of a split transfer is that the fixation is through suture use and the surgeon must place a K-wire across the MPJ for stability. The single best reason for doing a central transfer through a drill hole is early range of motion with a rigid internal interference screw. However, the drill hole placement is quite difficult and fracture can occur. A second plantar incision for tendon harvest is required and medial/lateral deviation correction is far more difficult. Our choice of tendon transfer is dependent on our needs. In a mildly deviated toe with plantar plate tear, we often will use a drill hole with interference fixation in association with hammertoe fusion and possible osteotomy of the metatarsal head. This allows for rapid motion and weightbearing. If the medial/lateral deformity is severe and long-term fixation is required, we prefer a split tendon transfer. Final Notes In order to have a good outcome for digital correction, it is essential to consider a flexor tendon transfer a small part of the treatment of the digit. Fusion of the hammertoe deformity, collateral ligament repair, metatarsal protrusion correction and capsular release are all essential in the overall treatment. With proper patient selection and procedure selection, long-term outcomes with digital realignment and stabilization can be excellent, resulting in happy patients and pain-free feet. Dr. Baravarian is the Co-Director of the Foot and Ankle Institute of Santa Monica. He is an Associate Professor at UCLA Medical Center and is the Chief of Podiatric Surgery at the Santa Monica/UCLA Medical Center. Dr. Baravarian may be reached at bbaravarian@mednet.ucla.edu. Editor’s note: For related articles, check out the archives at www.podiatrytoday.com.

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