TREATMENT OF POSTERIOR TIBIAL TENDON DYSFUNCTION WITH FLEXOR DIGITORUM LONGUS TENDON TRANSFER AND CALCANEAL OSTEOTOMY
March 20th, 1996
Mark S. Myerson, MD, and John Corrigan, FRCS
We treated 32 patients with stage-II posterior tibial tendon dysfunction with calcaneal osteotomy and flexor digitorum longus tendon transfer. These 32 patients (29 women, 3 men) had an average age of 58 years (range, 46 to 73 years) and had been symptomatic for an average of 2.5 years (range, 1 to 8 years) before surgical correction. The indication for surgery was the presence of medial foot pain refractory to nonoperative treatments, including shoewear modifications, orthoses, and bracing. All patients were examined at a mean of 20 months (range, 14 to 48 months) after surgery. Functional and radiographic examinations were performed for each patient and the American Orthopedic Foot and Ankle Society Foot (AOFAS) Rating scale was used. Of the 32 patients, 30 were satisfied with the outcome of surgery, had improved function, and exhibited radiographic correction of the foot deformity. The AOFAS score improved from a preoperative mean of 48 points (range, 23 to 76) to a postoperative mean of 84 points (range, 68 to 92). In one patient, treatment failed, necessitating a triple arthrodesis for worsening deformity. The short-term results of this procedure are encouraging. Most patients (94%) experienced pain relief, had improvement in the arch of the foot, and were able to wear regular shoes without orthotic support. The addition of a medial translational calcaneal osteotomy to transfer of the flexor digitorum longus tendon for management of stage-II posterior tibial tendon dysfunction corrected the deformity and provided substantial relief of foot pain and dysfunction.
Dysfunction of the posterior tibial tendon (PTT) produces the clinical condition of the adult flatfoot, characterized by heel valgus, flattening of the medial longitudinal arch, abduction of the forefoot, and the "too many toes" sign as described by Johnson and Strom.1 The patient is unable to effectively raise the heel during single limb stance. The condition is associated with pain, commencing medially at the level of the medial malleolus, followed by pain under the medial longitudinal arch. In the final stages of dysfunction, lateral foot pain is experienced due to impingement of the calcaneus against the peroneal tendons and lower end of fibula or to abutment of the lateral process of the talus against the calcaneus.
During the early stages of this attritional process, the foot deformity is passively correctable; however, fixed contracture eventually develops, producing heel valgus and forefoot supination. In 1989, Johnson and Strom1 described the clinical stages of PTT dysfunction. Stage I is characterized by pain associated with swelling on the medial aspect of the foot and ankle. The tendon is normal in length, and tendinitis is present associated with mild degeneration. Mild weakness and minimal deformity are present. In stage II, the tendon is torn, the limb is weak, and the patient is unable to stand on tiptoe on the affected foot. Secondary deformity is present as the midfoot pronates and the forefoot abducts across the transverse tarsal joint. The subtalar joint, however, remains flexible. In stage III, degeneration of the tendon is present, the deformity is more severe, and the hindfoot is rigid. Although any clinical staging system of PTT dysfunction is somewhat arbitrary and perhaps simplistic, it is useful to better present treatment alternatives in a logical and perhaps algorithmic fashion; we have used this classification for purposes of clarity here.
Attempts to restore function of the PTT by direct repair have not been satisfactory. Motor substitution for the posterior tendon by means of tendon transfer has therefore been recommended.2,3 Although the use of the flexor digitorum longus (FDL) generally produces symptomatic improvement, and is limited to surgical treatment of stage-II dysfunction, it does not correct the flatfoot deformity. Once the PTT tears, there is usually progressively worsening dysfunction, ultimately resulting in severe deformity in the hindfoot and forefoot. Fixed deformity (stage III) is generally therefore treated by arthrodesis.
No treatment has yet been shown to alter the natural history of tendon degeneration. Therefore, treatment must be directed in the earlier stages toward relief of symptomatology and prevention of fixed deformity. The treatment for the passively correctable adult acquired flatfoot (stage II) should address the underlying deforming forces in an effort to alter the natural history of progressive deterioration and development of fixed deformity. We and others have noted that with the flexor digitorum tendon transfer alone, the foot deformity remains uncorrected.1-4 Therefore, we sought an alternative treatment for the management of stage-II PTT dysfunction. Calcaneal osteotomy was first described by Gleich in 18935 in an attempt to displace the posterior calcaneal tuberosity both medially and inferiorly and to restore the calcaneal pitch angle. Subsequently, other authors have reported on treatment of flatfoot with calcaneal osteotomy, performed with a variety of techniques.6-9
We present the results of treating PTT dysfunction and the associated flatfoot deformity with FDL tendon transfer and medial displacement osteotomy of the calcaneus.
Materials and Methods
Over a 2-year period (1991 to 1993), we treated 146 patients with PTT dysfunction. Of this group, there were initially 49 patients with stage-II PTT dysfunction, 32 of whom failed conservative care and were treated with a medial translational calcaneal osteotomy and FDL transfer. These 32 patients (29 women, 3 men) had an average age of 58 years (range, 46 to 73 years). They had been symptomatic for an average of 2.5 years (range, 1 to 8 years) before surgical correction.
At initial presentation, treatment for each of these 32 patients began with a variety of shoewear and orthotic modifications, nonsteroidal antiinflammatory medication, and activity modification. A 0.25 inch medial heel and sole wedge was used in 18 patients, a rigid orthotic support in 16, a firm accommodative orthotic support in 6, and a hinged polypropylene ankle-foot orthosis in 8. Although these treatments were moderately successful in 24 of the 32 patients, symptoms persisted to some extent in all patients. Five patients treated with the ankle-foot orthosis were markedly improved; however, once the use of the brace was discontinued, symptoms returned, and they would not accept the use of the brace indefinitely.
Surgery was indicated in this group of 32 patients specifically for and limited to patients with stage-II PTT dysfunction who had failed nonoperative treatments. Although we previously stated that stage-II PTT dysfunction in an obese patient should not be treated with a tendon transfer and that an arthrodesis would be likely,3 we placed no weight restriction on the patients in the current study, believing that the addition of the calcaneal osteotomy would be protective of the tendon transfer.
The calcaneal osteotomy is performed first with the patient positioned in the lateral decubitus position on a bean bag. The incision is made inferior and parallel to the peroneal tendons, and posterior and inferior to the path of the sural nerve. The incision extends from the upper border of the calcaneus anterior to the retrocalcaneal space, to the inferior border of the calcaneus deep to the plantar fascia. The dissection is continued down to the periosteum, which is reflected at the proposed osteotomy site, and a transverse osteotomy is made in line with the skin incision with an oscillating saw blade. The cut is made at right angles to the lateral border of the calcaneus and is inclined posteriorly at an angle of approximately 45o to the plane of the foot. No wedge is removed from the calcaneus, and the tuberosity is not shifted into varus. A toothless lamina spreader is placed in the osteotomy site and spread to relax the medial soft-tissue attachments to the calcaneus. The lamina spreader is withdrawn, and the posterior calcaneal tuberosity is then translated 10 mm medially and secured with a 6.8-mm cannulated self-drilling self-tapping screw (Orthopedic Biosystems, Phoenix, AZ). Care is taken to keep the posterior tuberosity from sliding proximally. To ensure rigid fixation and avoid inserting the screw into the posterior facet of the subtalar joint, the screw is inserted from posterior, medial, and inferior to anterior, lateral, and superior, ie directed toward the sinus tarsi. The lateral incision is then closed, the bean bag deflated, and the patient is turned supine to perform the tendon transfer.
A posteromedial incision is made in the line with the PTT, the flexor retinaculum and the sheath of the PTT are divided, and the ruptured PTT is inspected. Generally, the tendon is cut distally, leaving a 1-cm stump at the attachment to the navicular, and then cut again proximally immediately behind the medial malleolus. The proximal cut end of the tendon is either left free or sutured to the FDL tendon as a side-to-side tenodesis. This tenodesis is performed once the FDL transfer is complete. If no functional excursion of the musculotendinous unit occurs when pulling on the proximal tendon remnant (indicating scarring of the proximal tendon in its sheath), the transected end is left free behind the medial malleolus.
The tendon sheath of the FDL is then opened and exposed beneath the arch of the foot where it crosses superficial to the flexor hallucis longus tendon. A tenodesis of the stump of the FDL to the flexor hallucis longus tendon is not routinely performed as these two tendons are usually conjoined at the knot of Henry. A 4.5-mm drill hole is made in the navicular 1 cm lateral to its medial border, and the tendon is passed through the drill hole from plantar to dorsal. Before suturing the tendon transfer, a vertical ellipse approximately 6 to 8 mm in diameter is excised from the talonavicular joint, extending from its dorsal surface inferiorly to the spring ligament. The foot is then held inverted and slightly plantarflexed, and the capsule of the talonavicular joint is then repaired by plicating the ends under tension. The FDL tendon is then secured in this position to adjacent periosteum and back on to itself if the tendon stump is long enough. The tension on the FDL tendon is set halfway between its position at rest and maximum excursion, with the foot held in maximum inversion and slight plantarflexion.
The strength of the tendon transfer is then tested while the foot is taken through a full range of motion in dorsiflexion and plantarflexion. The wound is then closed in layers, and a posterior plaster splint is applied with the foot positioned in equinus and slight varus. Since no tourniquet is used, hemostasis is obtained during the operative procedure, and no drain is used.
The foot is immobilized in equinus and varus for 4 weeks, and then a more plantigrade position is assumed in the cast over the subsequent 4 weeks. During the latter part of this study, patients were allowed to commence early range-of-motion exercises, using a posterior splint for immobilization when not exercising. At 6 weeks, weight-bearing was commenced in a short leg cast (10 patients) or removable walking boot (22 patients) for 4 additional weeks. Once out of the cast or brace, patients wore an Aircast (Aircast Co., Summit, NJ) for 4 to 6 weeks, followed by strengthening exercises either supervised in a formal physical therapy program or at home. In the latter part of the study, patients were allowed to commence range-of-motion exercises at 2 weeks after surgery. Patients were taught inversion strengthening using elastic sheeting and commenced this inversion as well as plantarflexion strengthening at 10 weeks after surgery. Patients were instructed to hold on to a rail or counter for support and rise up slowly on both feet, performing three sets of 10 repetitions. Once they were able to accomplish this exercise comfortably, they commenced repetitive single-limb heel rises in a similar fashion, initially on a flat surface and then, if possible, on a step with the heel of the foot suspended over the back of the step or stair. Walking for exercise and cycling was commenced at 4 months, and other sports activities were permitted by 6 months, provided the patients were able to perform repetitive heel rises without pain. Patients were examined routinely at 2, 6, and 10 weeks and at 6, 12, and 24 months postoperatively.
All patients were examined at a mean of 20 months (range, 14 to 48 months) after surgery. Each patient was examined in a systematic manner, and objective and subjective criteria were used for determining the success of treatment. The AOFAS foot and ankle score10 was used to evaluate hindfoot function.
Radiographic assessment was performed pre- and postoperatively using standardized weight-bearing dorsoplantar and lateral radiographs (Fig. 1). On the anteroposterior view, the parameters studied were talar-first metatarsal angle and talonavicular coverage angle. On the lateral radiograph, the talar-first metatarsal angle and the height of the plantar cortex of the medial cuneiform to the floor were measured.
Functional, Subjective, and Radiographic Outcome
Of the 32 patients, 30 were satisfied with the result of their treatment, and indicated they would undergo a similar procedure again. Two patients were not satisfied. Twenty-eight patients experienced no pain with prolonged walking and activities, three had mild pain, and one patient was unable to walk comfortably without pain. Twenty-four patients felt that the appearance of their foot had improved considerably, five patients felt that there had been some improvement, two saw no improvement, and one believed that the foot was worse in appearance. One dissatisfied patient continued to experience pain and began to demonstrate increasing deformity with lateral foot pain 2 years after surgery. This patient recently underwent a triple arthrodesis for correction of pain and deformity refractory to the use of a hinged ankle foot orthosis. The second patient who was not satisfied with the outcome of surgery believed that the appearance of the foot was worse, despite radiographic and apparent functional improvement. Although this was a retrospective study, preoperative clinical function was assessed and documented, and the AOFAS foot score was used to evaluate the results. The AOFAS score improved from a preoperative mean of 48 points (range, 23 to 76) to a postoperative mean of 84 points (range, 68 to 92). We paid particular attention to the patient's ability to stand unsupported on one foot and repetitively perform a single heel rise. By 6 months, 22/32 patients (78%) were able to perform repetitive single heel rises; by 12 months, 28/32 patients (88%) were able to do so. Two patients were each able to perform a single heel rise without repetition, and two patients were unable to perform any single heel rise.
Twenty-three patients were able to wear dress shoes without any support, five patients felt more comfortable in stiff soled or running shoes, and three patients preferred a more rigid shoe. One patient was not comfortable in any shoe, wore a hinged ankle foot orthosis for support, and was eventually treated with a triple arthrodesis. Six patients found that a firm supportive accommodative orthotic support was beneficial, and four patients used a more rigid functional orthotic support. There was no correlation between the use of the orthotic support and the length of time since surgery.
Although this patient population was generally sedentary, there were many who enjoyed regular exercise, including walking, and three patients were competitive runners before the onset of PTT dysfunction. Before surgery, no patient was able to comfortably walk for more than 30 minutes without resting, and 26 patients were unable to perform activities of daily living, including grocery shopping, without pain. After surgery, the three patients who had enjoyed running returned to this sport between 6 and 8 months and, although their times for distances over 5 and 10 km had decreased, they were able to continue with recreational running on a regular basis. Postoperatively, 31 patients were able to function without pain, not only with activities of daily living, but also in regular walking.
Although the current study evaluated patients only over a short period of time, we did not identify any deterioration in activity level, strength, or shoe and orthotic preference in those patients examined 4 years after surgery, compared with the group of patients with a shorter length of follow-up.
A substantial majority of the patients demonstrated radiographic improvement in the parameters measured postoperatively. On the anteroposterior projection, there was a substantial improvement in the talonavicular coverage and the talometatarsal angles. The anteroposterior talometatarsal angle improved from a preoperative mean value of 26o (range, 0 to 47o) to a postoperative mean value of 6o (range, -10 to 30o), a mean improvement of 20o. The mean anteroposterior talonavicular coverage angle was 37o preoperatively (range, 7 to 57o); it improved to a mean value of 15o postoperatively (range, 0 to 42o). On the lateral projection, the mean talus-first metatarsal angle of -28o preoperatively (range, -45 to -10o) improved to a mean value of -13o (range -32 to 0o) postoperatively, a mean improvement of 13o. The height of the medial cuneiform to the floor increased from a mean preoperative value of 8 mm (range, 0 to 18 mm) to a mean postoperative value of 18.5 mm (range, 12 to 28 mm). On an individual basis, the value that showed a consistent improvement after surgery was the height of the medial arch as judged from the distance of the medial cuneiform to the floor. Two patients, whose preoperative deformities were the most severe in the study group, showed no improvement in the medial cuneiform to floor distance and had maximum deformity preoperatively at the naviculocuneiform joint.
The surgical procedure failed in one patient (5'4", 190 pounds), who experienced increasing pain and deformity; 3 years after surgery, she underwent a triple arthrodesis. This patient had more radiographic deformity preoperatively than the mean of the rest of the group, but there were no additional identifying features preoperatively to indicate why the procedure failed, and there was no time interval during which she was asymptomatic postoperatively.
One patient developed pain and hyperesthesias in the distribution of the sural nerve. A positive percussion test was present over the nerve corresponding to the inferior aspect of the lateral incision. This was treated with local desensitization therapy modalities, which were successful in alleviating the sensitivity; however, numbness persisted.
Two patients experienced numbness (one transient, one permanent) in the distribution of the medial plantar nerve. Two patients, who initially felt that the foot was overcorrected into varus, experienced lateral foot pain under the fifth metatarsal base and cuboid. In both these patients, however, these symptoms abated 9 to 12 months after surgery.
There were no wound complications in this group of patients.
The concept of treating the valgus heel with a calcaneal osteotomy appears to be well understood. The medial shift of the calcaneus alters the biomechanical axis of the lower limb, reducing the valgus thrust on the hindfoot. This medial shift redirects the pull of the gastrocnemius-soleus muscle group slightly medial to the axis of the subtalar joint, which places the Achilles tendon slightly medially, increasing its varus pull on the hindfoot. However, the exact mechanism of action by which this medial shift of the calcaneus functions to improve the arch is not completely understood. Although we assume that it results from the medial displacement of the Achilles tendon and the changes in the resultant forces on the subtalar joint, this has not been scientifically verified. One other potential source for this biomechanical change in the arch structure is the effect of the osteotomy on the plantar fascia, producing an improvement of the arch by tightening the windlass mechanism. However, a recent biomechanical study showed that a calcaneal osteotomy (either by medial translation or lateral lengthening) reduced rather than tightened the tension on the plantar fascia [Horton GA, Myerson MS, Parks BG, Park Y-W. The results of calcaneal osteotomy and lateral column lengthening on the plantar fascia. A biomechanical investigation. Presented at the Annual Winter Meeting of the American Orthopaedic Foot and Ankle Society, Atlanta (GA), February, 1996]. Therefore, the effect of the calcaneal osteotomy cannot be explained on the basis of the plantar fascia and subsequent tightening of the windlass mechanism.
During the phase of foot flat, the PTT functions as a dynamic stabilizer of the medial arch of the foot. With heel raise, there the tibia externally rotates relative to the fixed foot with forefoot adduction and heel inversion. This maneuver locks the transverse tarsal joints (talonavicular and calcaneocuboid joints) and converts the foot into a more rigid system, allowing the gastrocnemius soleus muscle group to produce plantarflexion of the ankle. The flexible flatfoot is more dependent on the PTT than the cavus type foot. The medial arch is intrinsically stable when the first metatarsal and navicular are in direct line with the axis of the talus or varus to this position. With increasing valgus alignment of the navicular with respect to the talar axis, the arch becomes mechanically unstable and requires dynamic support from the PTT. The more forefoot abduction there is, the greater is the reliance on the PTT.
The flexible flatfoot has an inherent mechanical disadvantage, and increased loading caused by obesity only aggravates the mechanical deformity. Loading occurs when the foot is flat on the ground but, once the heel rises, the stress is compounded as the arch is no longer supported at both ends. To produce a heel rise, a rigid lever must be produced. In the normal foot, the PTT initiates heel rise by acting as a prime mover to produce forefoot adduction and heel inversion, which has the effect of bringing the axes of the subtalar and transverse tarsal articulations more vertically. In the absence of heel inversion and forefoot adduction, the axes of the hindfoot articulations remain horizontal, and attempted heel rise causes a break or collapse in the hindfoot through the axes of the subtalar and transverse tarsal joints.
Restoration of medial dynamic support by tendon transfer has been shown to reduce symptomatology but has not been shown to correct the deformity.1,2,4 Without correction of the deformity, the abnormal mechanics can persist, and progression of deformity with time can be anticipated. The FDL tendon is approximately one-third the size of the PTT, and substitution with the FDL tendon alone seems inadequate. Ideally, the medial arch should be corrected to provide dynamic stability to the tendon transfer. We have shown this to be possible by improving the alignment of the talonavicular joint with a simple medial shift of the calcaneus. Other methods of restoring this dynamic balance to the medial foot include the use of lateral column lengthening either through the calcaneus or by interposition of a bone block graft into the calcaneocuboid joint. Currently, the use of tendon transfer for correcting PTT dysfunction is limited to early stages of deformity when the joints of the hindfoot and midfoot are still mobile and passively correctable. In those feet that are not passively correctable and that have an element of fixed deformity, clinicians have advocated various methods of hindfoot arthrodesis, including talonavicular fusion,11,12 subtalar fusion,13,14 talonavicular and calcaneal cuboid joint fusion,12 and triple arthrodesis.15,16 For those patients with more advanced deformity but with flexibility of the hindfoot maintained, the surgical treatment remains controversial. Arthrodesis is an option; however, the stresses on adjacent joints (particularly the ankle) often lead to secondary degenerative changes.8,16
In conclusion, it is therefore important to identify a procedure that may obviate the need for more extensive arthrodesis and permit the simultaneous restoration of the medial arch. We have demonstrated that a medial translational osteotomy of the calcaneus reduces the deforming valgus thrust at heel strike. By medially shifting the Achilles, its action is converted from a deforming force to a synergist working with the FDL on the tarsal kinematic chain to aid tarsal inversion. Surgical correction of PTT dysfunction should attempt to maintain flexibility of the foot, restoring motor function, reducing the deforming forces, and improving the structure of the foot. The combined procedure of FDL transfer and medial translational osteotomy of the calcaneus may well achieve these objectives.
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Fig. 1. This patient is a 53-year-old woman with stage-II PTT dysfunction. Presented are the preoperative and postoperative weight-bearing radiographs. Note the improvement in the talonavicular coverage and the talometatarsal angle on the anteroposterior view, and the height of the medial cuneiform to the floor and the talometatarsal angle on the lateral view. The axial view of the hindfoot demonstrates the medial shift of the calcaneus.