Foot ulcers are the major risk factor for amputation among people with diabetes. Fifteen percent of people with diabetes will experience a foot ulcer. In this particular patient population, 14 to 24 percent will require lower extremity amputation.1 Loss of protective sensation and repetitive mechanical trauma (high foot pressures) are the major causes of diabetic foot ulceration.2,3 As per the ADA consensus report, the plantar forefoot is the most common location for foot ulcers.1 The underlying source of forefoot ulceration is increased forefoot pressure that results from pathologic gait patterns and structural deformity.4,5 So when it comes to prophylaxis of foot complications in the non-ulcerated neuropathic foot and for the cure in the ulcerated foot that cannot be appropriately accommodated externally by shoes and or braces, the goal is to control the foot deformity internally via reconstruction or amputation and accommodation. The trend in recent years for any elective or non-elective foot surgery has been to focus upon osseous structures in order to maintain the correction. It is well known that soft tissue correction, such as tendon lengthening or transfer as an isolated procedure, will have a high rate of failure due to progressive contracture postoperatively. While osseous procedures are generally required for rigid deformity, it is also true that isolated osseous procedures that do not address soft tissue contractures in diabetic foot surgery will also lead to overall failure.5 While there are tendon balancing procedures that are recommended for the neurologically intact foot as well as the insensate foot, it’s important to have a strong understanding of the role of muscle imbalances as they relate to diabetic foot pathology. How Muscle Imbalances Come Into Play Diabetic polyneuropathy is a frequently encountered complication in the lower extremities.6 Polyneuropathy has sensory, autonomic and motor components. Anterior leg weakness and intrinsic muscle atrophy of the foot are the result of motor neuropathy. When peroneal nerve atrophy is present, be aware that is a contributing factor in allowing the posterior muscle groups to gain a mechanical advantage over the weak anterior muscles.7 You may also attribute gait and balance disturbances to the degradation of muscle proprioception.8 Van Gils, et. al., offer an in-depth discussion of the pathological biomechanics associated with the diabetic foot.7 Non-enzymatic glycosylation of soft tissues has also been implicated in diabetic complications, although this was not necessarily limited to the lower extremity.9-11 When researchers examined collagen fibers under electron microscopy, they found that the fibers had increased packing density, decreased diameter of fibers and abnormal morphology of fibrils in the Achilles tendons of diabetics who had concomitant gastroc-soleus equinus. These factors all contribute to tightening and contracture of the Achilles tendon.12 Glycosylation of the flexor tendons of the foot was reported by Ramirez, et. al.13 Cheiroarthropathy, a syndrome of limited joint mobility associated with diabetes, has been observed as a frequent and early complication of diabetes.7 This condition, which is more common in the upper extremities, has been described in the lower extremities as well.14-16 This syndrome has been associated with the other well-known complications of diabetes, including cardiovascular disease, retinopathy and nephropathy.17 Long-term glycemic control, as measured by hemoglobin A1C (HbA1C), demonstrates close correlation with limited joint syndrome. The risk of cheiroarthropathy increases by 250 percent for each 1 percent increase in HbA1C over 8 percent.18 While complications in the diabetic foot may be attributed to different tendinous and bony pathology, equinus and equinovarus foot position are two of the most important and commonly encountered pre- and post-surgical foot deformities. (See “Understanding The Impact Of Equinus And Equinovarus Deformities” on page 66) What About Tendon Balancing In The Intact And Ulcerated Diabetic Foot? There are several different indications for tendon balancing in diabetic patients who are not undergoing amputation.26 Non-neuropathic patients may also require Achilles tendon lengthening if they have an equinus deformity or painful forefoot lesion. You may also consider this procedure for patients who currently have a neuropathic forefoot ulceration or a history of forefoot ulceration. In a gait laboratory study, Armstrong, et. al., evaluated patients before and after isolated Achilles tendon lengthening procedures.27 The mean peak pressure in the forefoot decreased significantly (by 27 percent) during the postoperative period from 86 (+/- 9.4) newtons per square centimeter preoperatively to 63 (+/- 13.2) newtons postoperatively. The mean dorsiflexion significantly increased from 0 (+/- 3.1) degrees to 9 (+/- 2.3) degrees. This study demonstrates that Achilles tendon lengthening is a worthwhile procedure you can consider as an adjunct to wound healing or for prophylaxis. Other clinical studies have suggested that Achilles tendon lengthening can reduce healing time of people with forefoot ulcers.28 Employing Tendon Balancing In Amputation Procedures Rarely do digital amputations and ray resections require tendon balancing. The types of procedures that do require attention are: distal and proximal transmetatarsal amputation (TMA), Lisfranc amputation, Chopart’s amputation and Syme’s amputation. With the exception of the Syme’s amputation, as the level of amputation proceeds proximally, the likelihood of developing an equinovarus foot deformity increases.29TMA. This procedure was first described by McKittrick, et. al., in 1949.30 The original procedure was performed by transecting the metatarsal just proximal to the head, leaving a long residual stump. Stuck, et. al., described the procedure as an amputation through the proximal metaphysis of the metatarsal shafts.25 They advocated Achilles tendon lengthening as well as transferring the tibialis anterior tendon in order to balance the expected late development of an equinovarus foot. Often, the decision on metatarsal length is now made intra-operatively based upon osseous destruction and tissue viability. The distal TMA is preferred to the proximal TMA as long as you perform an adjunctive tendon procedure at the time of surgery. When you have ensured appropriate tendon balancing, the distal TMA presents the patient with a stable, functional limb.31Lisfranc amputation. Sanders describes the Lisfranc amputation level as the “most proximal level that allows satisfactory function of the foot.” 31 The Lisfranc amputation is a disarticulation through the tarsometatarsal joint. Be sure to leave the second metatarsal base as a keystone between the medial and lateral cuneiforms, and leave the fifth metatarsal base intact. Doing so allows for foot eversion by the pull of the peroneus tertius and peroneus brevis. Achilles tendon lengthening and a split tibialis anterior tendon transfer (STATT) have been recommended as adjuncts to this procedure. We generally do not favor using the STATT in this population for reasons we will discuss below. Chopart’s amputation. You would perform this amputation through the talonavicular and calcaneocuboid joints. With the obvious exception of the Achilles tendon insertion to the calcaneal tuberosity and the partial attachment of the tibialis posterior tendon to the sustentaculum tali, all other tendinous insertions have been removed. Reyzelman, et. al., proposed that more distal amputations were more likely to fail than Chopart’s.29 Lieberman, et. al., reported success when they performed Achilles tendon lengthening (TAL) at the same time as a Chopart amputation.32 While this amputation level does not allow for propulsive gait, you are able to preserve limb length, as compared to the Syme’s amputation. You’ll find that generally, the lateral plantar lesions are much less common with this procedure when compared to Lisfranc and proximal TMA procedures. Appropriate tendon procedures would be Achilles tendon lengthening and possible transfer of the tibialis anterior, extensor digitorum longus or peroneals. Generally, for reasons already discussed, the Chopart amputation is preferred over proximal TMAs and Lisfranc procedures for proximal midfoot amputation. Syme’s amputation. Sir James Syme of Edinburgh described amputation of the foot in the mid-19th century. Syme’s amputation provides a long extremity (albeit not full-length) to transmit the body weight to the ground. Patients psychologically have responded well to this amputation due to the feeling that their legs have not been taken. This level of amputation is also advantageous from the standpoint of energy conservation as compared to more proximal lower extremity amputations. While tendon balancing in the traditional sense is not often thought of with this amputation, the tenodesis of the Achilles tendon to the posterior aspect of the tibia can prevent heel pad migration and future complications.33 Key Insights On Performing An Achillies Tendon Lengthening Achilles tendon lengthening (TAL). Eliminating equinus and increased forefoot pressure is of the utmost importance in preventing diabetic foot complications. In 1996, Nyska, et. al., examined the plantar pressure patterns of individuals wearing high-heeled shoes versus low-heeled shoes.34 The results indicated a significant increase in total maximal plantar pressure for those who wore high-heeled shoes. Among these patients, there was less pressure imparted on the rearfoot. While this study did not directly involve people with diabetes, the data can be extrapolated. Wearing high-heeled shoes essentially recreates the effect of equinus upon foot biomechanics. Indeed, several authors have linked significant forefoot pressures and presence of neuropathic ulceration.27,35,36 As previously mentioned, this link necessitates the lengthening of the Achilles tendon by manipulative and surgical means. Physical therapy may be a useful treatment for patients with early diabetes and no complications. However, for patients with long-standing diabetes and poor glycemic control, it is difficult to resolve the glycosylation of the Achilles tendon without surgical intervention. In our opinion, Achilles tendon lengthening is the most important tendon balancing procedure in the diabetic foot. We prefer the triple hemi-section of the Achilles tendon as described by Sanders.37 This is a modification of the original triple hemi-section described by Hoke.38 You would begin the procedure by making three small stab incisions to the midline of the Achilles tendon. Make the distal incision approximately 1 cm to 3 cm proximal to the insertion on the calcaneus. Then make the other two incisions proximally at intervals of 2.5 cm to 4 cm. Insert the blade parallel to the long axis of the tendon, in the midline from posterior to anterior. Once the blade has penetrated the substance of the tendon, rotate it 90 degrees so it is perpendicular to the tendon. With a dorsiflexory force applied to the foot, carefully use the blade to transect the tendon. Place two of the three sections medially and one laterally. After sectioning, the person applying dorsiflexory force to the foot should feel a give or snap. You may cover the resulting wounds with a butterfly type closure or suture as per your preference. You should then maintain the extremity in a dorsiflexed position in a posterior splint, short leg cast or removable cast walker. You should modify the device so it is irremovable for a period of six weeks. Pertinent Pearls On Other Tendon Balancing Procedures For The Diabetic Foot Anterior tendon balancing is dependent upon any significant structural foot deformity prior to undertaking this procedure. Traditionally, transfer of the tibialis anterior tendon and long extensor tendons has been advocated to treat a range of pathology, including equinovarus, weak dorsiflexion, cavovarus, clubfoot and as an adjunct to transmetatarsal amputation.39 In-phase transfers are generally preferred to out-of-phase transfers. Performing a traditional tibialis anterior tendon transfer involves the complete removal of the tendon from its insertion and subsequently transferring it to the lateral aspect of the foot, generally the lateral cuneiform. At the High-Risk Diabetic Foot Clinics at the Southern Arizona VA Healthcare System, we frequently use this procedure as an adjunct to Chopart amputations. In our experience, performing a TAL alone in more active individuals does not adequately address tendon concerns at this level. We advocate detaching the tibialis anterior tendon and reattaching it to the talar neck. You may transfer the tendon to the talus via slinging, drill holes or bone anchors. When the tibialis anterior tendon is not available, you may consider the long extensor tendons or peroneal tendons as viable alternatives in a similar fashion. When performing a split tibialis anterior tendon transfer (STATT), you would transfer the lateral half of the tibialis tendon to the lateral column of the foot via three incisions. You would proceed to reinsert the tendon onto the cuboid, lateral cuneiform or anastomose it with the peroneus tertius tendon. The functional goal of this procedure is to increase dorsiflexory strength and decrease inversion. STATT has been advocated as an adjunct in transmetatarsal and other midfoot amputations in order to help prevent or treat varus deformity. We generally will not perform this procedure in most patients as we favor transferring an entire, robust tendon in a mature adult to only part of one while leaving the other part as a potentially deforming force. Hibbs originally described the Hibbs Procedure for its usefulness in treating clawfoot.40 Since that time, podiatrists have also used this procedure to treat anterior equinus and flexible cavus deformity as well as an adjunct in some foot amputations. This procedure is similar to the tibialis tendon transfer in that the reinsertion site usually is the lateral cuneiform or third metatarsal base. You would pass the long extensor tendons through a drill hole in the midfoot, proceed to pass them through the plantar aspect of the foot and hold them in place with a button or other device. This procedure also increases foot dorsiflexion and reduces forefoot deformity and plantar forefoot pressure. In Conclusion All too often in the course of treating the diabetic foot, we, as a profession, fail to address through the continuum of care. The satisfaction of healing a chronic foot ulcer is typically followed by the disappointing realization that the ulcer will likely recur or has recurred, possibly with infection, necessitating amputation if the mechanical etiology of the malady is not addressed either extrinsically or intrinsically. We can greatly reduce the complication rates in the diabetic foot if we keep the reality of our patients’ ambulatory needs in mind. We should constantly ask ourselves what would happen if the patient ambulates. As patient empowerment often fails, we need to maintain our focus on intensive monitoring and thoughtful prevention in order to keep the high-risk foot intact. Within the team approach to diabetes care, we need to continuously strive to improve podiatric outcomes. Modern preventive and curative diabetic foot care is obviously multifaceted. However, the more we can do to address the underlying structural and biomechanical causes of foot complications, such as tendon length and position, the better our chances may be in reducing or halting the progression of lower extremity complications. Dr. Armstrong is the Director of Research and Education within the Department of Surgery, Podiatry Section at the Southern Arizona Veterans Affairs Medical Center in Tuscon, Ariz. Dr. Armstrong is also a member of the Board of Directors for the American Diabetes Association. Dr. Claxton is a third-year resident at the aforementioned institution. Editor’s Note: For a related article, see “Preserving The Diabetic Foot,” written by Jonathan E. Moore, DPM, Lawrence Harkless, DPM, and George Liu, DPM, in the December 2001 issue of Podiatry Today. For more information, check out the archives at www.podiatrytoday.com. CE Exam #106 Addressing Tendon Balancing Concerns In Diabetic Patients Choose the single best response to each question listed below: 1. Which of the following have been proposed as the etiology of equinus in persons with diabetes mellitus? a) Non-enzymatic glycosylation b) Cheiroarthropathy c) Motor neuropathy d) All of the above e) None of the above 2. The prevalence of equinus in people with diabetes mellitus is believed to be: a) Negligible b) Less than 20 percent c) 45 percent d) 70 percent e) Greater than 90 percent 3. The tibialis posterior tendon inserts to which of the following plantar structures? a) Medial cuneiform b) Intermediate cuneiform c) Lateral cuneiform d) Cuboid e) All of the above 4. Although controversial, the Chopart amputation level with appropriate tendon balancing is advocated because: a) Propulsion is preserved b) Several of the common sites for ulceration after other midfoot amputations are eliminated c) Limb length is preserved d) a and b e) b and c 5. In addition to Achilles tendon lengthening, which of the following tendon transfers should be performed at the same time as a Chopart’s amputation? a) Tibialis anterior b) STATT c) Hibbs d) Jones e) Young 6. The split tibialis anterior tendon transfer (STATT) is advocated in which of the following amputations? a) Syme’s b) Chopart c) Transmetatarsal d) Lisfranc e) c and d 7. The Hibbs procedure is: a) Transfer of the tibialis anterior tendon to the cuboid b) Transfer of the extensor hallucis longus to the first metatarsal c) Tenotomy of the Achilles tendon d) Transfer of the long extensor tendons into the lateral cuneiform or third metatarsal base. 8. Peak plantar pressure of the forefoot _________ after Achilles tendon lengthening. a) Increases b) Decreases c) Remains the same d) None of the above 9. The most common location for diabetic foot ulcers is: a) Posterior heel b) Inferior heel c) Fifth metatarsal tuberosity d) Navicular tuberosity e) Plantar forefoot 10. Mechanical advantage of the posterior muscle groups over the anterior muscle groups is due to: a) Plantaris tendon rupture b) Autonomic neuropathy c) Peroneal nerve atrophy d) Guarding e) Loss of proprioception Instructions for Submitting Exams Fill out the postage-paid card that appears on the following page or log on to www.podiatrytoday.com and respond electronically. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam. Responses will be accepted up to 12 months from the publication date.
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Clin Pod Med Surg 14(4):741-761, 1997. 38. Hatt RN, Lamphier TA. Triple hemisection: A simplified procedure for lengthening the Achilles tendon. N Engl J Med 236:166-169, 1947. 39. Miller SJ. Principles of muscle-tendon surgery and tendon transfers. In: Comprehensive Textbook of Foot Surgery, 2nd ed., Vol. 1, pp1297-1333. McGlamry ED, Banks AS, Downey MS, ed. Williams and Wilkins, Baltimore, 1992. 40. Hibbs RA. An operation for “clawfoot.” J Amer Med Assoc 73:1583, 1919.