by James D. Michelson, MD
James D. Michelson, MD, is associate professor of orthopaedic surgery, co-director, foot and ankle service, vice chairman, department of orthopaedic surgery, Johns Hopkins School of Medicine.
In my approach to the ruptured posterior tibial tendon, I find it helpful to keep in mind the specific goals of surgery. In order of importance, these would be pain relief, achievement of more normal shoe wear, and restoration of normal foot appearance. Of these, pain relief is the most critical. The sources of the pain include joint instability, stress on the degenerated tendon, lateral calcaneal impingement, and degenerative changes in the hindfoot articulations. I would consider the last source of pain an absolute contraindication to tendon reconstruction, since it will not address the underlying pathology.
The first three sources of pain derive directly from the biomechanical disruption involved in this condition. Therefore, surgery should focus on correcting the biomechanical deficiency. While a reconstruction of the posterior tibial tendon using the flexor digitorum longus does potentially preserve some hindfoot motion, the average size of the flexor digitorum longus is only one-third that of the posterior tibial tendon. The ability of the flexor digitorum longus to provide the strength or stability of the native posterior tibial tendon therefore cannot be taken for granted. Furthermore, it is certainly possible that the pathological conditions in the posterior tibial tendon that caused its degeneration may also be present in the flexor digitorum longus. Since such degenerative changes may be intramural in character and not apparent at the time of surgery, this can be a worrisome proposition.
The results of reconstruction of the posterior tibial tendon have been variable in the literature. The newer method of lengthening the lateral column to buttress the medial soft tissue reconstruction is theoretically interesting but has not yet withstood the test of time. There is no evidence that a congenitally short lateral column is a significant factor in patients having posterior tibial tendon ruptures. Therefore, such surgery actually introduces an anatomic deformity which results in a locked Chopart joint that puts the forefoot in a supinated position.
On the other hand, the triple arthrodesis directly addresses the issues of biomechanical instability of the hindfoot by providing immediate stability for those joints which are affected. The recuperation from such surgery is more predictable and quicker than after tendon reconstruction. Once the fusion has healed (roughly three months), no further rehabilitation or special bracing or supports are necessary. This is in contradistinction to tendon reconstruction procedures, in which up to a year of some orthotic support may be required. In general, patients report satisfaction following triple arthrodesis within a few months after healing. In contrast, one of my mentors used to relate to me that his secretary could tell who had a tendon reconstruction, since they were the least happy patients in his office for the longest time.
Obviously, the primary trade-off in a triple arthrodesis is the loss of hindfoot inversion/eversion. There has been some concern on the part of many foot and ankle surgeons that the transfer of stress from the arthrodesed joints to either the ankle or the midfoot predisposes the latter joints to premature degenerative changes. While in patients with neuromuscular diseases, triple arthrodesis may be associated with subsequent progressive deformities and ankle arthritis, this is predominantly a consequence of the underlying progressive neuromuscular imbalance.
The study by Mann stands out as the only examination of the longer-term consequences of triple arthrodesis on both midfoot and ankle arthritis. Although it is frequently said that his study demonstrated a high rate of secondary ankle arthritis following triple arthrodesis, his data indicates that, in fact, only 10 percent (1 of 10) of patients who had isolated posterior tibial tendon ruptures and underwent triple arthrodesis subsequently had clinically significant ankle arthritis. The other patients who developed ankle arthritis all had either rheumatoid arthritis or a neuromuscular disease. Interestingly, no patients in any group had clinically apparent midfoot arthritis develop over the course of the study.
While I would agree that a triple arthrodesis for a ruptured posterior tibial tendon in a 56-year old active female does not yield a normal foot, I do not think that any procedure for posterior tibial tendon rupture will yield a normal lower extremity. In balancing the risks and benefits of the two approaches, it seems to me that the predictability and known long-term results of triple arthrodesis outweighs the prolonged recuperation and uncertain ultimate outcome of a tendon reconstruction.
by Keith L. Wapner, MD
Keith L. Wapner, MD, is professor, orthopaedic surgery, and director, division of foot and ankle surgery, department of orthopaedic surgery, Medical College of Pennsylvania and Hahnemann University.
This case involves an active 56-year old female with no medical problems and no history of trauma. Her main complaint is a painful acquired flat foot deformity that has developed spontaneously over the last year. On physical examination she is five feet, seven inches tall, and weighs 165 pounds. She has 0 degrees of ankle dorsiflexion and 30 degrees of plantar flexion at the ankle, 10 degrees of inversion and 20 degrees of eversion of the subtalar joint, 10 degrees of abduction and five degrees of adduction of the transverse tarsal joint. With her heel held in neutral she has 10 degrees of forefoot varus. On standing she has 20 degrees of heel valgus, demonstrates a "too many toes signs" viewed from behind and cannot single-heel rise. Radiographs demonstrate loss of the longitudinal arch with sag at the talonavicular joint on lateral and abduction on the AP with uncovering of the dome of the talus.
Posterior tibial dysfunction is the most common cause of the acquired flat foot deformity in the adult. It does represent a spectrum of disease and ranges from mild tendinitis to complete rupture of the posterior tibial tendon and collapse of the medial longitudinal arch of the foot. Advanced stages produce significant hindfoot valgus and excessive forefoot abduction. Clinically, this appears as the "too many toes sign" when viewed from behind. Radiographically, this has been described by Hansen as representing peritalar subluxation where the calcaneus and navicular sublux around the inferior and anterior aspects of the talus.
Historically, there have been multiple techniques described to reconstruct the ruptured posterior tibial tendon. Mann has popularized the transfer of the flexor digitorum longus and this has gained wide acceptance in the orthopaedic community. This technique preserves toe function by anastomosing the distal aspect of the flexor digitorum to the flexor hallucis longus. In that the majority of patients cannot wiggle their lesser toes independent of the great toe because of normal tendinous interconnections between these two tendons, there is generally no perceived donor deficit. Mann has shown that this works best in a flexible foot where there is no fixed forefoot varus. It is essential to assess forefoot varus in the proper fashion by sitting in front of the patient with their leg hanging over the table. The heel is then placed in a neutral position, and the forefoot is observed. When the heel is brought out of valgus into neutral, if the Spring ligament complex and talonavicular capsule have become incompetent, the forefoot will remain in varus. In some patients this is a fixed deformity and in other patients, this can be passively corrected.
In reviewing the results of flexor digitorum longus transfer, Mann reported good relief of pain. However, he recognizes that this technique does not recreate the arch. In addition, the indications for this technique are limited to that portion of the disease spectrum where there is no fixed forefoot varus. Attempting to use this technique beyond the limitations defined by Mann have led to unsatisfactory results.
Myerson has recently introduced the concept of medial calcaneal osteotomy to help correct the longitudinal arch in conjunction with tendon reconstruction. Hansen and Sangeorzan have proposed lateral column lengthening by placing a wedge-shaped tricortical interposition iliac crest bone graft into the calcaneocuboid joint. This rotates the calcaneus out of its valgus position back under the talus and also rotates that navicular back over the head of the talus, thus correcting the peritalar subluxation. This has expanded the indications for reconstruction to include those patients with forefoot varus whose foot is supple. It is also recognized that some of these patients also have Achilles tendon constrictions and percutaneous tendo Achilles lengthening should be added to the technique. Dr. Hansen has further expanded this technique by performing a corrective fusion of the first metatarsal cuneiform joint in instances where he feels that it is required to further correct the forefoot deformity.
In this patient in question, I feel that she would be a good candidate for a flexor digitorum longus transfer with lateral column lengthening and tendo Achilles lengthening. This technique has the advantages of maintaining approximately 70 percent of hindfoot inversion and eversion. The motion lost is mostly in eversion that decreases the load on the posterior tibial tendon by assisting and maintaining the longitudinal arch.
Yet, maintenance of the hindfoot motion does allow a more normal gait pattern and assists in maintaining the normal function of the hindfoot complex in dissipating forces of contact in gait. It is hypothesized that this will reduce the probability of developing secondary arthritic changes in other joints of the foot such as the ankle which has been demonstrated in long-term studies following a triple arthrodesis. In addition, it has the advantage of cosmetically reconstructing the arch which patients often feel is very important.