Exploring New Advances In Digital Arthrodesis

By Gerard V. Yu, DPM, Andrew Vincent, DPM, and Wissam Khoury, DPM

Over the years, a multitude of techniques have been described and employed for digital arthrodesis, ranging from arthroplasty and arthrodesis to flexor tendon transfer and lesser digital implants. Each procedure has a place in surgical correction of digital deformities. Digital arthrodesis, in particular, provides permanent and reliable correction of deformities and is considered by the senior author to be a favored technique, especially when it comes to managing digital deformities of a biomechanical etiology. Two fundamental techniques, the end-to-end arthrodesis and the peg-in-hole arthrodesis, are commonly employed in digital deformity correction. Various modifications to these procedures have been described over the years (see “A Review Of Modifications In Digital Arthrodesis” below). The end-to-end arthrodesis essentially involves resection of the cartilaginous surfaces of the head of the proximal phalanx and the corresponding base of the middle phalanx. Fixation with a Kirschner wire (K-wire) is commonly employed for a period of five to eight weeks. Surgical correction involves extensive soft tissue dissection about the metatarsophalangeal joint (MPJ) to correct for subluxation or luxation and then crossing the K-wire fixation into the metatarsal segment in some cases. In other cases, fixation to the base of the proximal phalanx has proven to be sufficient and effective. A peg-in-hole arthrodesis is a more sophisticated and technically more demanding approach to a fusion of the toe. It involves creating a peg or spike and inserting it into the base of the middle phalanx. This creates a secure, stable point of fixation in and of itself. Unfortunately, using K-wire fixation for the stabilization of either arthrodesis does not maintain or provide any compression to the fusion site. While this is certainly not necessary, it may be desirable when you are treating patients who have a higher risk for bone-healing complications. Fortunately, clinical experience has proven that clinical arthrodesis does not necessarily correlate with radiographic arthrodesis. However, both are certainly desirable. While the peg-in-hole arthrodesis consistently provides a more reliable and predictable shortening and radiographic fusion as well as clinical arthrodesis, it is a more complex procedure requiring a higher level of surgical proficiency and skill. End-to-end arthrodesis remains the more common technique but clearly has a higher incidence of radiographic nonunion, which may or may not correlate to clinical fusion. Choosing The Correct Procedure The selection of the most appropriate procedure for correction of digital deformities is based upon a thorough understanding of the biomechanics and etiology of such deformities. While techniques of resection arthroplasty of the proximal interphalangeal joint (PIPJ) are indicated for static deformities, arthrodesis of the PIPJ is more commonly preferred when an underlying dynamic etiology of the deformity is identified. Potential etiologies include flexor stabilization, flexor substitution and extensor substitution. In addition, varieties of neuromuscular disorders are associated with dynamic imbalance and thus also require a fusion for correction of the deformities. In some situations, the flexor digitorum longus and/or flexor digitorum brevis tendon transfer techniques may be more beneficial especially in patients with muscle tendon imbalance or when significant compromise of the plantar plate exists. Tendon transfers can be used alone or in conjunction with other techniques of digital arthrodesis. While some patients will benefit from techniques of flexor tendon transfers, others may require transfer of the extensor tendons to the metatarsal bases or lesser tarsus (i.e. Hibbs suspension procedure). There are situations in which a shortening osteotomy with or without alterations of the sagittal plane alignment is necessary and appropriate for the correction of digital deformities. This is particularly true when one has a structurally elongated second metatarsal segment, which is believed to contribute to the deformity of the second toe in the presence or absence of a concomitant hallux valgus deformity. The need for osteotomy of the third, fourth and fifth metatarsals for the correction of the deformities decreases as one progresses more laterally. Where New Technologies May Come Into Play Advances in the area of biomaterials and engineering have led to a number of new internal fixation devices that one may consider in arthrodesis of the lesser digits. We have used most of these on a limited basis to gain some experience and insight into their efficacy and ease of application. One may employ absorbable cortical bone pins for digital fusions that are confined to the medullary canals of the proximal and middle phalanges. A similar technique involves using larger diameter pins such as Steinmann pins that are also confined to the medullary canals. Other absorbable pins are also available but we have not used them for this purpose. We do have concern about the rigidity of these devices as well as the potential for foreign body type of reactions that may result in significant edema of the toe and potentially sterile abscess formation. In regard to other advances in digital arthrodesis, you may consider the Weil-Carver™ Hammertoe Implant (Biomet®, Inc.) and the Stayfuse™ Inter-Digital Fusion System (Pioneer Surgical Technology). The Stayfuse is a two-component titanium device that recently garnered FDA approval for digital arthrodesis. The design of the device allows for a relatively simple insertional technique, although it is more difficult and time-consuming than the standard techniques utilizing K-wires. It also comes in several sizes and one would use templates to determine the appropriate size of the device based on the patient’s preoperative radiographs. The Weil-Carver Hammertoe Implant is FDA-approved for proximal interphalangeal joint arthrodesis of the digits. It is composed of amorphous non-crystalline co-polymer, Lactosorb®, which is synthesized from 82% L-lactic acid and 18% glycolic acid. Lactosorb® retains most of its strength for approximately six to eight weeks, which is an adequate time frame for biological consolidation to occur at the arthrodesis site. Lactosorb® completely loses its strength and degrades in approximately 12 months. The implant, which is approximately 25 mm in length, is manufactured in only one size. Both devices offer several advantages over conventional fixation when performing digital arthrodesis. There is no external postoperative implant exposure so there is no risk of pin tract infections. In addition, they are constructed of biocompatible materials, are relatively easy to use and have high patient acceptance. One distinct advantage of the Weil-Carver implant over the Stayfuse device is its biodegradability over time. An advantage of the Stayfuse device is its different sizes accommodate different anatomic sizes of the phalanges. These devices also possess similar disadvantages. There is a potential for excessive postoperative swelling due to the increased manipulation, operating time and surgical trauma. Fractures of the proximal or middle phalanges during the procedure, mechanical failure, rejection potential or other foreign body reactions can also occur. In addition, the cost of the devices is significant in contrast to the traditional K-wire. One cannot use these devices to stabilize the MPJ, which may be necessary when treating a significant deformity. When stabilization of the MPJ is an important consideration for correction of the deformity, conventional K-wires for stabilization of the fusion site and the MPJ are recommended. Finally, the Weil-Carver implant is only available in one size and may not be suitable for all patients, especially those with larger bones. Key Incision Insights And Tips On Joint Exposure Before we discuss the particular procedures for using these implants, there are several key steps and considerations one must address before executing the arthrodesis procedure. We typically employ a standard dorsal longitudinal linear incision that is centered over the PIPJ. The proximal extent of the incision will vary depending upon the severity of the deformity and the need to release soft tissues around the MPJ. In cases of significant subluxation or dislocation, we’ll typically extend the incision proximally to the level of the metatarsal neck. While some authors recommend curving the incision (via a Lazy “S” or a z-plasty approach) as you cross the lesser MPJ, we have not found that to be more beneficial than a straight linear incision if you employ plastic surgery closure techniques. Be aware that scar contracture contributing to a recurrent digital deformity can occur. However, when re-deformity occurs, it is unlikely to be caused solely by the skin itself but rather some other soft tissue or osseous component or factor. One should use electrocautery to achieve hemostasis. You will typically see numerous small venules crossing transversely and connecting the adjacent neurovascular bundles at the dorsal aspect of the toe. Proceed to perform anatomic dissection technique to the level of the extensor hood and deep fascia. Using this technique facilitates the ready separation of the skin and subcutaneous tissues as a single unit from the underlying deep fascia, which envelopes the entire MPJ and proximal phalanx, with little concern for vascular embarrassment postoperatively. You can disarticulate the PIPJ in a number of different ways, which may reflect your personal experiences and preferences. We currently recommend a simple transverse tenotomy and capsulotomy at the level of the PIPJ, followed by release of the medial and lateral collateral ligaments to expose the proximal phalangeal head. While the lead author has had extensive experience with a z-plasty lengthening of the tendon at the level of the PIPJ, this approach has been abandoned for the last several years in lieu of an alternative technique which is less cumbersome and appears to be equally as efficient and effective. When the approach described above is employed, it may be difficult to anastomose and suture the extensor tendons end to end following the completion of the procedure. Our preference has been simply to suture the distal end of the extensor tendon to the dorsal periosteum of the phalanx at the level of the fusion site. Then one would suture the proximal stump of the extensor tendon to the base or shaft area of the proximal phalanx under desired tension. From a functional standpoint, the outcomes have been equally effective. However, the execution of the procedure is simplified. Essential Pearls For Restoring MPJ Alignment Before proceeding with the osseous work to accomplish fusion, you should perform a complete soft tissue release to ensure the elimination of neutralization of the deforming forces causing contracture at the lesser MPJ. The typical sequence is to perform an extensor hood recession from distal to proximal, allowing for complete release of both the long and short extensor tendons. It is important to ensure the release of both tendons as failure to release the short extensor tendon will contribute significantly to a postoperative recurrence. Load the foot to simulate weightbearing and to ensure the proximal phalanx sits in a desired position. If necessary, perform further dissection to release the MPJ. The second step is a capsulotomy of the lesser MPJ. When there is a primary contracture in the sagittal plane (i.e., dorsiflexion without transverse plane deviation), one should perform a complete dorsal, medial and lateral capsulotomy to allow relaxation of the periarticular structures and subsequent relocation of the toe. You should modify the extent of the release in cases where transverse plane deformity is present. If significant medial deviation is present with concomitant dorsiflexion at the MPJ, completely release the dorsal and medial capsules but leave the plantar lateral capsular tissues intact. If it is released, you can perform a capsulorraphy later with heavy gauge absorbable or non-absorbable suture to assist in correcting the transverse plane deformity. A third step in the sequence is to release the plantar plate, which may be adhered to the underside of the metatarsal head. You can accomplish this with a McGlamry elevator or a mastoid gouge. Release the entire plantar plate from the underside of the metatarsal head, allowing for complete relaxation of the plantar soft tissue structures. Again, you would mechanically load the foot to determine whether you have achieved full correction and release. In the cases of severe dislocation, a shortening osteotomy or partial joint resection may be necessary to achieve complete relocation and relaxation of the toe. Once you have achieved satisfactory release and restoration of MPJ alignment, you can shift your attention to the PIPJ for execution of the arthrodesis procedure. How To Use The Stayfuse Device When using the Stayfuse device, you should perform anatomic dissection of the digit and prepare the fusion surfaces as if you are preparing the joint for an end-to-end arthrodesis. Once you have prepared the joint, drill a pilot hole perpendicular to the resected portions of the proximal phalanx and middle phalanx. When drilling the middle phalanx, it is important to drill slightly dorsal to the center point in order to accommodate for the inferior concave shape of the middle phalanx and avoid disruption or violation of the plantar cortex. Then insert the “PROX” component of the device into the proximal phalanx. Manually stabilize the proximal phalanx to prevent rotation of the phalanx while you are inserting the screw. The insertion is complete when the Hex Driver spins off the hex component of the implant, indicating the implant is flush with the bone surface. Use the same technique to insert the “MID” component into the middle phalanx. However, be aware that the Hex Driver will not spin off the hex portion of the “MID” component. Therefore, one should carefully insert the “MID” component flush with the base of the middle phalanx to allow for a solid fusion site and apposition of the osseous surfaces. Align the two components to ensure inline insertion. Remove any interposed soft tissue and insert the “MID” component into the “PROX” component. By applying moderate pressure, you’ll see the implant rotate slightly in opposite directions until the two components engage. You should feel or hear three distinct snaps to ensure interlocking of the two components. If you fail to achieve adequate approximation of the two components, the Stayfuse system may not lock and diastasis or separation may occur at the fusion site prior to osseous fusion. Inspect the fusion site carefully to verify apposition prior to wound closure. Intraoperative radiographs are helpful and recommended for ensuring proper seating and alignment. When You May Have To Remove The Implant There are some situations or scenarios that may necessitate implant removal. These include, but are not limited to: postoperative infection; failure of the surgery; bone-healing complications such as a nonunion, over or under correction and malalignment; as well as persistent pain and excessive edema which could not be otherwise explained. In these cases, one may create a cortical window over the dorsal aspect of the middle phalanx. Then you may remove the implant by elevating the tip of the device with a small elevator or curette. Grasp the tip of the device and turn it counterclockwise. This will allow you to remove both components of the implant as one unit. Fortunately, we have no experience with removal. It would seemingly be difficult and should be considered a significant disadvantage of this type of fixation. How To Use The Weil-Carver Hammertoe Implant If you decide to use the Weil-Carver hammertoe implant, perform anatomic dissection of the digit and prepare the bone for fusion by removing the articular surface of the head of the proximal phalanx and the corresponding middle phalangeal base as described above. Use a 2 mm Steinmann pin to drill the central medullary canal of both the proximal and middle phalanx. It’s important to ensure the holes are equally distant from the corresponding dorsal cortex of the bone. It is our preference to align the digit with a 0.045-inch to 0.062-inch K-wire before drilling with a 2.0-mm Steinmann pin. Doing so helps one visualize proper positioning and direction of the pilot holes and proper apposition of the fusion surfaces. In essence, one would fixate the toe with the K-wire in a normal traditional manner. Then remove the K-wire and use the holes created by the K-wire as a pilot hole for the 2.0 Steinmann pin. Proceed to introduce a 2.5 mm tap into the proximal phalanx. You should tap the proximal phalanx approximately 13 mm in depth, which corresponds to the length of the proximal segment of the implant. Then load the implant onto the manual driver and thread it into the proximal phalanx, leaving only the barbed distal portion of the implant accessible for insertion into the middle phalanx. If the portion of the implant in the proximal phalanx should piston during the insertion of the distal portion into the middle phalanx, we recommend inserting a 0.045-inch K-wire perpendicular to the shaft of the proximal phalanx and just proximal to the implant. Doing so can help prevent proximal migration during the seating of the middle phalanx. At this time, manipulate the digit to initiate proper seating of the barbed distal portion of the implant into the middle phalanx. Apply counter pressure to both the proximal and middle phalanx to achieve seating. If you used a K-wire in the proximal phalanx, remove it after you have achieved adequate apposition of the fusion interfaces. What You Should Know About The Distal Barbed Portion Of The Implant In certain cases, the distal barbed portion of the implant may be too long, making it almost impossible to seat it into the middle phalanx. It may be necessary in such cases to reduce the length of the distal barbed portion of the implant, which you can do with a power saw, power burr or bone-cutting forceps. After achieving fixation and confirming seating and apposition of the fusion surfaces, proceed to close. One can suture the collateral ligaments of the PIPJ to provide further stabilization to the fusion site if you feel it is necessary. Then perform standard anatomic closure. A Guide To Postoperative Management The postoperative management of patients undergoing digital arthrodesis will depend on the type of fixation you use. When employing K-wires, particularly those that cross the lesser MPJ, you will need to focus on protecting the pins in order to prevent bending, migration or rotation. Unprotected weightbearing will allow a bending moment across the lesser MPJ, which is likely to result in fatigue failure of the pins as well as a loss of correction. Further migration of the pins can present a complicated problem. Weightbearing is not problematic when the pins are driven only to the base of the proximal phalanx. Whenever the pins cross the lesser MPJ, it is our preference to emphasize non-weightbearing until the pin is either retrograded beyond the MPJ or removed altogether. This may not always be possible in some patient populations. One modification to the surgical shoe, which helps to maintain corrective alignment, is adding at least 1/4 or preferably 1/2 inch of firm felt from the heel to just proximal to the lesser metatarsal heads. When the lesser toes have been pinned only to the phalangeal base, the pressure on the metatarsals will help encourage plantarflexion, thus resisting the re-deformation of the toes. This modification assimilates the windlass mechanism in the foot. In cases where the K-wires have crossed the MPJs, the felt buildup will eliminate or minimize bending movements across the joint. The toes will be suspended to avoid contact with the shoe and thus minimize breakage or failure of the pins at the MPJ level. Of course, this is not an issue with the Stayfuse device and the Weil-Carver hammertoe implant. Again, we must emphasize that non-weightbearing is preferable when fixation crosses the lesser MPJ. Regardless of the device you use, take serial X-rays to confirm osseous consolidation at the fusion sites, especially with end-to-end arthrodesis. As we noted above, peg-in-hole arthrodesis procedures, when they are performed properly, have a uniformly high rate of radiographic and clinical fusion. When employing the K-wire fixation for end-to-end arthrodesis or peg-in-hole arthrodesis, one can also remove the pins between five to seven weeks following radiographic confirmation of osseous union. In a limited number of cases, it will become obvious that an osseous union has not occurred. In such cases, you may leave the pins in place for an additional one to three weeks. However, you should not leave them across the MPJ for longer than six to seven weeks as this may lead to permanent or excessive stiffness. The patient may wear a variety of digital sleeves to help reduce edema in the toe and avoid “sausage toe” formation. Digital splints are routinely employed for several months after the surgery to maintain corrected alignment. Emphasizing a removable metatarsal pad is helpful when the patient has to wear shoe gear for one or two isolated toes. During sleep, the patient can wear a splint to maintain correct alignment of all the lesser toes. One should employ physical therapy to help resolve edema and soften the postsurgical fibrosis and scar tissue formation. Emphasizing active manipulatation of the MPJs with an emphasis on the direction of plantarflexion prevents dorsal migration and dorsiflexion of the toes. We typically instruct patients about home exercise programs they can use to maintain plantarflexion at the MPJ and dorsiflexion at the DIPJ, which helps to reduce the rate of mallet toe contractures. A Few Thoughts About Second Digit Deformities Many digital deformities involve contractures with or without subluxation or dislocation at the MPJ level. Most notable are deformities of the second digit, especially the crossover second digit deformity or severe hammertoe deformity, which occurs as a result of or in conjunction with concomitant hallux valgus deformity. Successful treatment of such deformities requires an extensive soft tissue release to ensure the removal or elimination of deforming forces. Even after complete release at the level of the MPJ, stabilization across the MPJ may be required to ensure adequate correction. In more severe cases, especially those with significant length deformity, an osteotomy may be required. Final Notes Lastly, the senior author recommends that surgeons emphasize to patients that sagittal plane deformities are far more predictably corrected than transverse plane digital deformities. In cases of severe deformity, patients must have realistic expectations regarding the desired outcome. A fully normal-appearing toe with normal function is not realistic and rarely attained when correcting severe end-stage deformity. The goal of digital procedures should be to significantly reduce pain and improve function while providing a cosmetically acceptable appearance of the toes. Dr. Yu is the Director of Podiatric Medical Education and Residency Training and is the Chief of the Section of Podiatry, Division of Orthopaedic Surgery at St. Vincent Charity Hospital in Cleveland. He is the Chief of Podiatry at Huron Hospital in East Cleveland, Ohio. Dr. Yu is a Diplomate of the American Board of Podiatric Surgery and a Fellow of the American College of Foot and Ankle Surgeons. He is also the Director of Program Development and a faculty member of the Podiatry Institute in Tucker, Ga. Dr. Vincent is a recent graduate of St. Vincent Charity Hospital and completed three years of residency training. He is currently in private practice in Winchester, Va. Dr. Khoury is a third-year podiatric surgical resident at St. Vincent Charity Hospital in Cleveland.



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