by Jonathan T. Deland, MD
Progressive flatfoot deformity resulting from insufficiency of the posterior tibial tendon (PTTI, also called adult acquired flatfoot deformity from failure of this tendon) is a difficult entity to treat. This is particularly true as the deformity progresses. In the past 15 years, treatment has advanced from tendon transfer in mild to moderate deformities to a tendon transfer with osteotomies or selective hindfoot fusions in more severe cases.1-4 In patients with deformity, the tendon transfer alone is insufficient and a medial calcaneal slide osteotomy is a helpful adjunct.4 However, the calcaneal slide corrects deformity only to a certain extent, whereas the aim of treatment is to make the foot as normal as possible. As the deformity progresses past the point where a medial slide can correct the deformity, procedures such as lateral column lengthening or fusions are being used.5 These procedures either cause stiffness in the foot or increase the risk of arthritis.
Before discussing whether better treatments can be developed for PTTI, it is appropriate to discuss what the best treatments are now. Multiple treatments are in use, including some that can be used at different stages of the disease. Clinical circumstances sometimes require a practitioner to weigh the benefits of procedures indicated at different stages. My study comparing four different treatments was presented at the 1999 meeting of the American Orthopaedic Foot and Ankle Society. The same independent observer (not the surgeon) assessed the patients’ results for all procedures: triple arthrodesis, lateral column lengthening with a calcaneocuboid distraction arthrodesis (CCDA), a lateral column lengthening Evans procedure (which was combined with MS osteotomy in four out of five patients), and a medial slide (MS) calcaneal osteotomy.
The triple arthrodesis incorporates fusion of the talonavicular, calcaneocuboid and subtalar joints, while the CCDA involves fusion of just the calcaneocuboid joint but with a lengthening of that joint to correct deformity. The Evans procedure uses a lengthening in the calcaneus next to the calcaneocuboid joint. The medial slide calcaneal osteotomy corrects deformity not by lengthening or arthrodesis but by sliding the posterior aspect of the calcaneus medially. The last three procedures were performed with a flexor digitorum longus tendon transfer.
There were five patients in each group. This study was not randomized, as patients were selected for each procedure according to the amount of deformity. Patients with heel valgus but minimal abduction of the midfoot had an MS osteotomy. Patients with moderate abduction had a CCDA or combined Evans/MS procedure; patients enrolled earlier in the study had the CCDA. Lastly, those patients with significant limitation of inversion were inappropriate for procedures used with a tendon transfer; these patients had a triple arthrodesis. All procedures were done by the same surgeon.
In addition to applying the AOFAS hindfoot scale (see page 36), other questions were asked to assess the functional results.6 Patients often ask about limitations in everyday walking and exercising on the affected foot; therefore, questions on these topics were added, as well as whether the surgery overall improved the patient’s ability to walk and whether he or she would decide to have the surgery again, given the choice.
All patients felt that the surgery improved their pain significantly and all except one believed their surgery improved their ability to walk and would repeat the surgery. The one exception was a patient in the CCDA group whose lateral pain was not relieved postoperatively. Although a more final and complete review of this study will be published in the orthopedic literature, the preliminary results show substantial differences between the patients who had the fusions and those who had just the osteotomies. The AOFAS hindfoot score was in the 80s for both of the osteotomy groups and in the 60s for those groups with the fusions. Answers to the questions concerning functional limitations and the ability to get enough exercise all had considerable differences when the osteotomy groups were compared with the fusion groups. Motion in the triple-joint complex was similar between the CCDA and osteotomy groups (both types of lateral column lengthening). The functional results were different. Patients with the MS osteotomy and patients with the Evans procedure had less discomfort.
From this initial review it certainly appears that the patients who were treated with osteotomies had better functional results than those who were treated with hindfoot fusions (CCDA or a triple arthrodesis). If patients have stiffness and deformities that require such fusions, the functional results are not likely to be as good. Subtalar arthrodesis, which was not included in this study, had AOFAS outcome scores in the 80s in a previous study by Mann.7 Future studies should include compare the results of subtalar arthrodesis with other procedures in the same study to make a valid comparison.
Once the patient has more deformity than can be corrected by a medial slide calcaneal osteotomy along with a tendon transfer, surgeons vary in their choice of procedure. The preliminary results of this comparative study showed that a calcaneocuboid distraction arthrodesis did not do as well as an Evans procedure. I prefer the latter lateral procedure when a lateral column lengthening is necessary. However, it does have the disadvantage of leaving the patient with increased pressure on the calcaneocuboid joint and the long-term risk of arthritis in that joint. My preference is to treat the patient before a lateral column lengthening or hindfoot fusion procedure becomes necessary. When more is required, it would be better to have a more anatomic procedure (i.e., actual repair or reconstruction of the failed ligament rather than a procedure that simply restricts motion). However, attempts at using the calcaneal osteotomy with plication of the spring ligament, where the tissue is often degenerated, have not shown that the procedure on the spring ligament improves the results.4
Whether better treatments can be devised depends on the location and extent of the ligamentous insufficiency in patients with adult acquired flatfoot. Although at surgery the extent of pathology in the posterior tibial tendon is readily apparent, the location and extent of ligament damage is not as easily seen. Often at surgery, laxity in or tears of the medial portion of the talonavicular capsule, which incorporates the superomedial portion of the spring ligament, can be seen if the surgeon looks carefully. Adult acquired flatfoot deformity requires a degree of failure on the part of ligaments that support the arch. These include the plantar fascia, the long and short plantar ligaments, the talocalcaneal interosseous ligament, and portions of the deltoid ligament as well as the spring ligament. Even if these ligaments cannot be reconstructed, knowing the precise extent of their involvement increases our understanding of the disease, available treatments, and the types of treatment that may be possible in the future.
To determine the extent of ligamentous involvement in adult acquired flatfoot, 30 patients with a surgically confirmed adult acquired flatfoot secondary to PTTI were studied. Preoperatively, the patients had moderately high resolution MRI scans with a technique that allowed good visualization of the ligaments. This included a slice thickness of 3.5 mm with no gap and a small pixel size for increased resolution (field of view 14 cm). Sagittal images were performed with a fast spin-echo technique. A grading system from another study, which correlated ligament involvement in the foot with MRI findings, was used.8 In grade I, abnormal signal (degeneration) was present in less than 50% of the ligament; in grade II, more than 50% of the ligament. In grade III, a partial tear (abnormal gross morphology) was present in less than 50% of the ligament (i.e., the tear extended less than halfway across the ligament) and in grade IV more than 50% of the ligament had abnormal morphology on the scan, indicating a very dysfunctional ligament.
In this study, 26 patients had a grade II or higher involvement of the superomedial portion of the spring ligament. The spring ligaments of almost all the patients, therefore, were at least 50% degenerated. Twenty-three had similar involvement in the plantar portion of the spring ligament. The next most frequently involved ligaments were the talocalcaneal interosseous ligament, which was involved in approximately half the patients, and the anterior deltoid, which was involved in approximately one-third of the patients. Interestingly, the plantar fascia and the long and short plantar ligaments were not significantly involved. The study group was compared to an age-matched control population. Significant differences were found between the two groups, suggesting that the ligament changes were part of the adult acquired flatfoot. For example, although more than half the PTTI patients had a partial or complete tear of the spring ligament (grade III or IV), none of the patients in the control group did. More than a third of the study patients had a partial or complete tear in the plantar portion of the spring ligament, while in the control group there were no corresponding tears.
If there is a ligament to reconstruct, it is the spring ligament complex. There is at this time no study of a series of patients with successful reconstructions of this ligament. Yet such reconstruction is not impossible; I have performed this procedure in a small series of patients. The results have shown good correction of deformity without a lateral column lengthening at or near the calcaneocuboid joint with minimum one year follow-up.
Spring ligament reconstruction would not be indicated in all patients with flexible deformities, as other ligaments may offer better opportunities for improvement. However, this type of anatomic approach is certainly possible in many patients with more than a mild deformity. This could incorporate not only reconstruction of the tendon but also reconstruction of the ligament, along with realignment of the foot via osteotomies. Reconstruction of such ligaments with nondegenerated tissue would be necessary. Such treatment would directly address the tendon and ligament involvement without a lateral column lengthening near the CC joint or even a limited fusion. This goal has not been fully realized yet, but with this study our understanding of the disorder is improving and a better treatment is possible.
Jonathan T. Deland, MD, is co-director of foot and ankle service at the Hospital for Special Surgery in New York City.
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