David A. Spiegel, Om Prasad Shrestha, and James J. McCarthy
DEFINITION
The equinovarus deformity involves hindfoot equinus and varus and results from imbalance between inversion (tibialis posterior, tibialis anterior, or both) and eversion of the foot.
The deformity is most common in spastic hemiplegia but may also be seen in patients with diplegic and quadriplegic involvement.
The deformity may interfere with ambulation, orthotic wear, or both.
ANATOMY
The tibialis posterior muscle originates from the posterolateral aspect of the tibia, the interosseous membrane, and the medial fibula.
Although the main insertion is into the tuberosity of the navicular, fibers also insert onto the cuneiforms, the second through fourth metatarsals, the cuboid, and the sustentaculum tali.
The gastrocnemius muscle originates from the posterior surface of the distal femur, and its tendon blends with the tendon of the soleus muscle to form the Achilles tendon, which then inserts on the posterior tuberosity of the calcaneus.
The soleus muscle takes origin from the posterior portion of the upper third of the fibula, the fibrous arch between the tibia and the fibula, and the posterior aspect of the tibia.
The broad tendinous portion along the posterior aspect of the muscle joins with the gastrocnemius tendon to form the Achilles tendon.
PATHOGENESIS
The deformity results from muscle imbalance between plantarflexion–inversion (strong) and dorsiflexion–eversion (weak).
Spasticity of the tibialis posterior, the tibialis anterior, or both may be responsible for the imbalance.
NATURAL HISTORY
The deformity is initially dynamic, with a full range of motion on physical examination.
A myostatic contracture often develops over time, evidenced by the inability to achieve a full passive range of motion.
Tethering of growth may subsequently result in structural bony deformities such as hindfoot varus.
The equinovarus deformity may result in pathologic changes in both the stance and swing phases of gait, including impaired clearance during swing phase, the inability to preposition the foot in terminal swing, and loss of stability during stance phase.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients present with progressive gait disturbance, with or without pain, and may have difficulty wearing orthotics.
Pain is due to the abnormal stress distribution on the plantar surface of the foot and is commonly experienced over the distal fifth metatarsal and the lateral border of the foot. Calluses may be observed laterally.
Recurrent ankle sprains may occur as the hindfoot rolls into varus.
In addition to a comprehensive examination of the spine and both extremities, the physical examination focuses on observational gait analysis, the presence of and degree of spasticity in the individual muscle groups, the range of motion (active and passive) of the foot and ankle, and the selectivity of motor control.
Observational gait analysis focuses on the alignment of the foot and ankle during both the swing and stance phases of gait.
During swing phase, the foot is inverted and plantarflexed, which impairs clearance.
The inability to maintain the foot in neutral plantarflexion–dorsiflexion during mid-swing may be due to muscle weakness (tibialis anterior), muscle spasticity (tibialis anterior or posterior, gastrocsoleus), or a fixed equinovarus deformity.
There is inadequate prepositioning of the foot for weight acceptance during terminal swing.
Initial contact often occurs over the lateral forefoot (no heel contact), or over the lateral border of the foot, and the foot rolls into varus, which interferes with stability during stance phase.
The equinovarus deformity may also contribute to in-toeing (internal foot progression angle).
The presence and degree of spasticity should be documented.
The most common system for grading is the modified Ashworth scale. Each muscle is tested by gentle stretch; for example, spasticity of the tibialis posterior is assessed by everting the foot, while the gastrocsoleus complex is assessed by dorsiflexion.
The strength of individual muscle groups should be graded if possible.
Testing the passive range of motion determines whether the deformity is dynamic (full passive range of motion) or whether there is a myostatic component (restriction of passive range of motion).
While bench examination provides a useful estimate of motion, an examination under anesthesia provides the most accurate evaluation, as spasticity is eliminated. Such an examination is always performed at the time of surgery to finalize the treatment plan.
For patients with an equinovarus deformity, the examination focuses on the degree of passive eversion and dorsiflexion. Equinus contracture is often limited to the gastrocnemius muscle but may also involve the soleus muscle.
The Silfverskiöld test evaluates the contribution of each component of the gastrocsoleus complex to an equinus contracture, and the amount (in degrees) of passive dorsiflexion is quantified with the knee both flexed and extended. The degree of passive dorsiflexion with the knee extended indicates the absolute magnitude of contracture from the gastrocnemius and soleus. Flexion of the knee relaxes the gastrocnemius muscle and allows the contribution of the soleus to be quantified.
Selectivity of motor control is commonly impaired in children with cerebral palsy, and the distal motor groups are more involved than the proximal groups.
Selectivity is tested by asking the patient to contract an isolated muscle group against resistance.
If the patient can isolate the muscle and no “overflow” movement is observed in other muscle groups of the same limb, then adequate selectivity is present.
Most commonly, movements of more than one muscle group, or the entire limb, are elicited when testing individual muscle groups.
IMAGING AND OTHER DIAGNOSTIC STUDIES
While imaging studies are not routinely obtained, plain radiographs of the foot may be helpful in the presence of a fixed deformity.
Weight-bearing anteroposterior (AP) and lateral views are reviewed, and a Harris heel view may be considered to evaluate the degree of hindfoot varus in the weight-bearing position.
Instrumented motion analysis (gait analysis) is used in many centers to assist with surgical decision making.
Slow-motion video is an important component of the assessment and supplements the findings on observational gait analysis.
Dynamic electromyelography (EMG) monitors the electrical activity of the tibialis posterior and tibialis anterior throughout the gait cycle, determining whether individual muscles act out of phase or whether they are continuously active throughout the gait cycle (most common).
While a surface electrode may be used to assess the tibialis anterior, monitoring of the tibialis posterior requires insertion of a fine-needle electrode.
A recent study determined that the deformity was due to the tibialis posterior in 33%, the tibialis anterior in 34%, or both (31%).9
The hindfoot varus usually occurs in both the stance and swing phases of gait.
Findings on pedobarography include increased pressure across the lateral midfoot, decreased pressure on the heel at the time of initial contact, and increased pressure on the lateral border of the foot throughout stance phase.
NONOPERATIVE MANAGEMENT
Specific aspects within a comprehensive physical therapy program include stretching exercises to maintain or improve range of motion and strengthening exercises to reduce dynamic muscle imbalance.
An ankle–foot orthosis is often required to maintain alignment of the ankle and hindfoot during ambulation.
The orthotic facilitates clearance during swing phase by maintaining the foot in a neutral position, prepositions the foot for initial contact with the ground, and promotes stability during stance phase.
Night splinting may help to prevent myostatic contracture.
Injection of botulinum toxin A (Botox or Dysport) into the tibialis posterior, the gastrocsoleus, or both results in a reversible chemical denervation that decreases spasticity for about 3 to 6 months.
In addition to reducing dynamic muscle imbalance, a temporary reduction in spasticity may facilitate stretching exercises, improve bracing tolerance, and delay the need for surgical intervention.
SURGICAL MANAGEMENT
Surgical treatment of the spastic equinovarus foot is offered when the deformity impairs ambulation, interferes with bracing, or both.
Recent evidence suggests that the recurrence rate may be higher if the procedure is performed before 8 years of age, so it may be beneficial to delay split tendon transfer beyond this age if possible.2
Lengthening of the tibialis posterior muscle may be adequate for mild deformities.
Techniques include a distal Z-lengthening of the tendon and an intramuscular recession proximally.
The goal of tendon transfer is to balance the muscle forces across the hindfoot to maintain a neutral position during the swing and stance phases of gait.
A split tendon transfer is preferred as transfer of the entire tendon is associated with a significant risk of overcorrection. A normal passive range of motion is a prerequisite.
In the presence of fixed soft tissue or bony deformity, concomitant muscle lengthening, with or without osteotomy, may be required to restore motion and alignment.
Options for split tendon transfer include both the tibialis anterior and the tibialis posterior.
Dynamic EMG can help to determine whether one or both muscles are contributing to the deformity.
A split tibialis anterior tendon transfer, with or without concomitant intramuscular lengthening of the tibialis posterior, may be required in a subset of patients with an equinovarus deformity.
Several techniques have been described for split tibialis posterior transfer.
The most common involves transferring the split tendon (posterior to the tibia and fibula) to the peroneus brevis, either at its insertion or just behind the lateral malleolus. This approach focuses on balancing inversion–eversion but does not address dorsiflexion weakness (FIG 1).
An alternate technique, which may be considered when there is inadequate active dorsiflexion, involves anterior transfer of the split tendon through the interosseous membrane to the peroneus brevis (FIG 2A,B) or the lateral cuneiform (FIG 2C).
Biomechanical investigations using cadaveric specimens have studied the technical aspects of the split tendon transfer.
Moran et al10 found that all routing variations reduce the ability of the tibialis posterior to invert the hindfoot, that there was no difference between attaching the tendon proximally or distally into the peroneus brevis, and that transfer through the interosseous membrane reduced the ability to plantarflex the foot. Calculation of muscle moment arms across the subtalar joint suggested that adequate results could be achieved over a wide range of tensioning.
FIG 1 • In the technique described by Kaufer,5 the split tendon is routed behind the tibia and fibula (A) and inserted into the peroneus brevis tendon (B). C. Alternatively, the split tendon can be woven into the peroneus brevis just behind the lateral malleolus. This approach is easier and works as well when the tendon is not long enough.
FIG 2 • In the technique described by Muller et al,11 the split tendon is passed through the interosseous membrane (A) and through a subcutaneous tunnel to insert into the peroneus brevis tendon (B). C. Saji et al16 transferred the split tendon through the interosseous membrane into the lateral cuneiform.
Other procedures are commonly performed in concert with a split tibialis posterior tendon transfer.
Lengthening of the tendo Achilles (gastrocnemius with or without the soleus) is required in most cases of spastic equinovarus deformity. Depending on the degree of myostatic contracture, this can be achieved with either a recession technique (Vulpius, Baker) or a tendinous lengthening (open Z-plasty, percutaneous or open sliding lengthening).
Fixed varus deformity of the hindfoot requires a calcaneal osteotomy, either a lateral closing wedge osteotomy (Dwyer) or a sliding lateral displacement osteotomy of the calcaneus. Options for fixation include a staple, a Steinmann pin, or a screw.
Older patients with a severe fixed equinovarus deformity may require a triple arthrodesis.
A subset of patients may also have tibial torsion of a degree that warrants surgery. Consideration should be given to staging the procedures, as one study suggested that tibial derotational osteotomy should not be performed at the time of tendon transfer because of the increased risk of failure of the tendon transfer.
Preoperative Planning
The indications for surgery are based on the physical examination, with or without an instrumented motion analysis study.
An examination under anesthesia (eliminates spasticity) is performed to assess the range of motion and helps to finalize the surgical plan with respect to the type of soft tissue lengthening procedure.
The findings will solidify the operative plan with respect to the need for muscle lengthening, the technique employed for lengthening (Z-lengthening versus recession), and whether any supplementary bony procedures are required.
Positioning
The patient is placed supine.
Approach
Either three or four incisions are employed for split tibialis posterior tendon transfer.
The tendon must be released from its insertion, tunneled either anteriorly (through the interosseous membrane) or posteriorly behind the tibia and fibula, and then attached to either the peroneus brevis or lateral cuneiform.
TECHNIQUES
SPLIT TIBIALIS TENDON TRANSFER TO PERONEUS BREVIS (AFTER KAUFER)
A longitudinal incision is made over the insertion of the tibialis posterior on the navicular, and the sheath is opened (TECH FIG 1A).
The plantar half of the tendon is released, and the tendon is split longitudinally (TECH FIG 1B,C).
A second incision is made just posterior to the medial malleolus, extending proximally for 4 cm (TECH FIG 1D,E).
The sheath of the tibialis posterior is split longitudinally, and the free end of the tendon is delivered into this wound.
The longitudinal split in the tendon is extended proximally to the musculotendinous junction.
The third longitudinal incision is made about 2 cm proximal to the tip of the lateral malleolus, and extends proximally (TECH FIG 1F,G).
The peroneal tendon sheath is incised longitudinally.
The split tendon is then passed posterior to the tibia and fibula, and anterior to the neurovascular bundle, into the third incision. The split tibialis posterior tendon can be sutured into the peroneus brevis tendon at this level (see Fig 1C) or can be transferred distally, which requires a fourth incision.
The fourth longitudinal incision is made distal to the lateral malleolus, overlying the insertion of the peroneus brevis into the fifth metatarsal base (TECH FIG 1H).
TECH FIG 1 • A. A longitudinal incision is made over the insertion of the tibialis posterior. B. The tibialis posterior tendon is then dissected free at its insertion, and half of the tendon is released, most often from the plantar surface. C. The distal end of the tendon is tagged with a running, locked suture, and the division in the tendon is developed proximally as far as possible. D. A second incision is made just posterior to the medial border of the tibia, proximal to the medial malleolus. The fascia is divided longitudinally, and the tibialis posterior muscle is identified. E. The suture ends are delivered from distal to proximal through the tendon sheath, and the split tendon is brought out from the second incision. F. A short longitudinal incision is then made over the lateral side of the leg, posterior to the fibula, across from the medial incision. G. The split tendon is then passed from medial to lateral along the posterior border of the tibia and the fibula, anterior to the neurovascular bundle. The tendon is delivered through the lateral wound. H. The fourth incision is distal, and just behind the fibular malleolus. The peroneal sheath is incised longitudinally. I. The split tendon is brought through the sheath from the more proximal incision through this distal incision. J,K. The tibialis posterior tendon is then woven through small longitudinal splits in the peroneus brevis and anchored with nonabsorbable suture.
The split tibialis posterior tendon is then passed through the sheath, along the peroneus brevis, into the distal incision (TECH FIG 1I).
The tendon is woven through the peroneus brevis and secured with nonabsorbable sutures (TECH FIG 1J,K).
The foot is held in a neutral position.
A long-leg cast with the knee extended and the foot at neutral (weight bearing as tolerated) is worn for 4 weeks, and then a short-leg cast is worn for 4 additional weeks.
No bracing is required if the patient is able to actively dorsiflex the foot to neutral. If not, an ankle–foot orthosis is recommended.
SPLIT TIBIALIS TENDON TRANSFER THROUGH THE INTEROSSEOUS MEMBRANE TO THE LATERAL CUNEIFORM (AFTER SAJI)
A medial approach extends from 5 cm proximal to the medial malleolus to the insertion of the tibialis posterior tendon on the navicular.
The anterior (dorsal) half of the tendon is released and split up to the musculotendinous junction, preserving the retinaculum.
A 2-cm incision is made anteriorly, and a window is made in the interosseous membrane just proximal to the syndesmotic ligament.
The split tendon is passed anteriorly through the interosseous membrane.
A 2-cm incision is made over the lateral cuneiform, and the split tendon is delivered subcutaneously and then passed through a drill hole in the lateral cuneiform.
The tendon is secured over a button on the plantar surface of the foot, with the foot held in a neutral position.
The patient is placed in a below-knee cast with the foot in slight valgus and neutral dorsiflexion–plantarflexion.
Weight bearing is allowed after 3 weeks, and a brace is worn for 6 to 12 months.
SPLIT TIBIALIS TENDON TRANSFER THROUGH THE INTEROSSEOUS MEMBRANE TO THE PERONEUS BREVIS (AFTER MULLER)
A longitudinal incision is made at the insertion of the tibialis posterior, and the plantar half of the tendon is released from the navicular. The muscle is split longitudinally as described previously.
A second incision is made proximally, and the tendon is delivered through this incision and split up to the musculotendinous junction.
The third incision is made anteriorly, and the tendon is delivered through a window in the interosseous membrane (just above the anterior inferior syndesmotic ligament).
The fourth incision is made over the distal insertion of the peroneus brevis tendon, and the tibialis posterior is passed through a subcutaneous tunnel and woven into the distal peroneus brevis with nonabsorbable suture.
A long-leg cast is used for 3 weeks and then a short-leg cast (weight bearing as tolerated) for an additional 3 weeks.
POSTOPERATIVE CARE
Casting is recommended for 6 to 8 weeks, and options include a long-leg cast for 3 to 4 weeks, followed by a short-leg cast (weight bearing as tolerated) for 3 to 4 weeks,3,11 versus a short-leg cast for 6 weeks.16 The hindfoot is kept in neutral to slight valgus.
Physical therapy is advised when the cast is removed.
Weight bearing is typically delayed for 6 weeks, and an ankle–foot orthosis is worn after the cast is removed. Therapy focuses on range of motion and strengthening.
An ankle–foot orthosis is commonly recommended for up to 6 months after removal of the cast and may be required over the long term to facilitate clearance if active dorsiflexion is inadequate.
OUTCOMES
Several authors have reported shortto mid-term results after transfer behind the tibia and fibula to the peroneus brevis.3–8
The long-term results after this procedure have been the subject of a single study involving 88 feet.2
Twenty-five percent developed recurrent equinus, and treatment failure was observed in 44% (14 with more than 10 degrees varus, 25 with more than 10 degrees valgus).
Poor results were most common in diplegics and quadriplegics, patients less than 8 years of age, and those who had not achieved a community level of ambulation. A host of variables, including persistent spasticity, may result in progressive deformity through growth and development, especially in children with more profound degrees of neuromuscular involvement.
The technique involving split tibialis posterior transfer through the interosseous membrane has been the subject of two reports, in which 44 patients were studied at shortto mid-term follow-up.11,16
Forty-one of these had an excellent or good result, and the three poor results were due to overcorrection (one) and undercorrection (two).
The transfer helped to restore active dorsiflexion in most of the patients, eliminating the need for orthotics.
COMPLICATIONS
While immediate complications are uncommon (wound infection, pull-out of the transferred tendon, undercorrection or overcorrection), late complications are more common and relate to the effects of many variables in a growing child with spasticity and persistent neuromuscular imbalance.
Recurrent deformity results from persistent muscle imbalance, pull-out of the tibialis posterior from the peroneus brevis, insufficient tension when suturing the tibialis posterior tendon, or other variables associated with growth.
Overcorrection into valgus is most common in younger children and in patients treated by concurrent tibial derotational osteotomy.
REFERENCES
· Barto PS, Supinski RS, Skinner SR. Dynamic EMG findings in varus hindfoot deformity and spastic cerebral palsy. Dev Med Child Neurol 1984;26:88–93.
· Chang CH, Albarracin JP, Lipton GE, et al. Long-term followup of surgery for equinovarus foot deformity in children with cerebral palsy. J Pediatr Orthop 2002;22:792–799.
· Green NE, Griffin PP, Shiavi R. Split posterior tibial-tendon transfer is spastic cerebral palsy. J Bone Joint Surg Am 1983;65A:748–754.
· Kagaya H, Yamada S, Nagasawa T, et al. Split posterior tibial tendon transfer for varus deformity of hindfoot. Clin Orthop Relat Res 1996;323:254–260.
· Kaufer H. Split tendon transfer. Orthop Trans 1977;191:1.
· Kling TF, Kaufer H, Hensinger RN. Split posterior tibial tendon transfers in children with spastic cerebral paralysis and equinovarus deformity. J Bone Joint Surg Am 1985;67A:186–194.
· Liggio FJ, Kruse R. Tibialis posterior tendon transfer with concomitant distal tibial derotational osteotomy in children with cerebral palsy. J Pediatr Orthop 2001;21:95–101.
· Medina PA, Karpman RR, Yeong AT. Split posterior tibial tendon transfer for spastic equinovarus foot deformity. Foot Ankle 1989;10:65–67.
· Michlitsch MG, Rethlefsen SA, Kay RM. The contributions of anterior and posterior tibialis dysfunction to varus foot deformity in patients with cerebral palsy. J Bone Joint Surg Am 2006;88A:1764–1768.
· Moran MF, Sanders JO, Sharkey N, et al. Effect of attachment site and routing variations in split tendon transfer of the tibialis posterior. J Pediatr Orthop 2004;24:298–303.
· Muller T, Moens P, Molenaers G, et al. Split posterior tibial tendon transfer through the interosseous membrane in spastic equinovarus deformity. Foot Ankle Int 1995;16:754–759.
· O'Byrne JM, Kennedy A, Jenkinson A, et al. Split tibialis posterior tendon transfer in the treatment of spastic equinovarus foot. J Pediatr Orthop 1997;17:481–485.
· Perry J, Hoffer MM. Preoperative and postoperative dynamic electromyography as an aid in planning tendon transfers in children with cerebral palsy. J Bone Joint Surg Am 1977;59A:531–537.
· Piazza SJ, Adamson RL, Sanders JO, et al. Changes in muscle moment arms following split tendon transfer of tibialis anterior and tibialis posterior. Gait Posture 2001;14:271–278.
· Piazza SJ, Adamson RL, Moran MF, et al. Effects of tensioning errors in split transfers of tibialis anterior and posterior tendons. J Bone Joint Surg Am 2003;85A:858–865.
· Saji MJ, Upadhyay SS, Hsu LCS, et al. Split tibialis posterior transfer for equinovarus deformity in cerebral palsy. J Bone Joint Surg Br 1993;75B:489–501.
· Synder M, Kumar SJ, Stecyk MD. Split tibialis posterior tendon transfer and tendo-achilles lengthening for spastic equinovarus feet. J Pediatr Orthop 1993;13:20–23.