Application of a Constrained External Fixator Frame for Treatment of a Fixed Equinus Contracture Robert W. Mendicino, DPM, FACFAS, 1 Lara J. Murphy, DPM, 2 Michael P. Maskill, DPM, 3 Alan R. Catanzariti, DPM, FACFAS, 4 and Harry Penny, DPM 5 Ankle equinus can result from congenital, traumatic, neurological, and pathological etiologies. Corrective methods have been described in the literature using a combination of soft tissue releases or osseous procedures with reported complications. We present a case report of a patient with a post-traumatic fixed equinus deformity of 28 at maximum dorsiflexion, treated successfully through gradual correction using a modified constrained external fixator. The patient maintained a rectus foot and was able to perform all daily activities at the final follow-up. Fixed equinus deformities can be difficult to manage. Gradual correction with an external fixator is a reasonable treatment option. Level of Clinical Evidence: 4 (The Journal of Foot & Ankle Surgery 47(5):468 475, 2008) Key Words: ankle equinus, external fixation, post-traumatic Equinus contractures develop from a number of different etiologies including congenital, traumatic, neurological, and pathological (1 3). Acquired equinus contractures, which evolve over a period of time, can advance into a fixed deformity because of soft tissue contraction and bony adaptation. Scar contracture and neurological damage are often seen in post-traumatic cases. Acquired equinus can be encountered as a single deformity, however it is often accompanied with other forefoot and/or hindfoot misalignments including pes equinovarus (4). Osteotomies and acute soft tissue releases have been described for the treatment of complex foot and ankle deformities (5, 6). Complications relating to neurovascular structures and skin may develop with acute reduction of severe deformities (7). The Ilizarov apparatus was designed and modified to correct deformities in all 3 orthogonal Address correspondence to: Robert W. Mendicino, DPM, FACFAS, Vice Chair, Department of Surgery, Chief of Foot and Ankle Surgery, The Western Pennsylvania Hospital, 4800 Friendship Avenue North Tower First Floor, Pittsburgh, PA 15224. E-mail: rmendicino@faiwp.com. 1 Attending Surgeon and Vice Chair of Department of Surgery, The Western Pennsylvania Hospital, Pittsburgh, PA. 2 Second Year Resident, The Western Pennsylvania Hospital, Pittsburgh, PA. 3 Third Year Resident, The Western Pennsylvania Hospital, Pittsburgh, PA. 4 Attending Surgeon and Director of Residency Training Program, The Western Pennsylvania Hospital, Pittsburgh, PA. 5 Private Practice, Altoona, PA. Financial Disclosure: None reported. Conflict of Interest: None reported. Copyright 2008 by the American College of Foot and Ankle Surgeons 1067-2516/08/4705-0016$34.00/0 doi:10.1053/j.jfas.2008.05.011 planes using gradual correction (1, 4, 6 8). Herzenberg and Paley (6) described the use of the Ilizarov application for soft tissue deformity correction. Acquired cases of contraction after skeletal maturity could be realigned without the need for an osteotomy (6). An external fixator can be used as a constrained or unconstrained hinge system. A constrained hinge system uses the center of rotation of a joint as the location for the placement of the hinges. The external fixator is then manipulated or adjusted daily to rotate around the joint axis in a calculated manner. This is usually used for large joints with identifiable centers of rotation. Unconstrained systems use a distraction technique to rotate around the center of the joint. This technique uses the natural rotation of the joint and is usually used with smaller joints or deformities with multiple joint axes. Melvin and Dahners (5) described the use of a dynamic tension system with an unconstrained Ilizarov frame for correction of equinus with various etiologies. The constrained hinged method has been described to have a high level of technical difficulty for the patient and physician and has proven to be unreliable in obtaining accurate correction around the ankle joint axis (5). This manuscript describes a patient with a traumatically induced fixed equinus deformity with residual peroneal motor and sensory neuropathy. A detailed description on the application and use of a modified constrained rotating hinged frame is presented. Challenges included a retained prograded tibial rod from previous surgery for a tibial shaft fracture as well as postsurgical scar formation. The modification of the frame for creation of an appropriate ankle joint axis and motor are discussed. The use of adjunctive procedures including peroneal and tarsal tunnel release along with a gastrocnemius recession is also discussed. 468 THE JOURNAL OF FOOT & ANKLE SURGERY
FIGURE 1 (A, B, C) Pre-operative photographs of a post-traumatic fixed equinus deformity with a maximum dorsiflexion of 28 in a plantarflexed position. Case Report A 35-year-old female patient was referred to the Foot and Ankle Institute of Western Pennsylvania in October 2005 with complaints of a painful fixed equinus contracture of her left lower extremity. The patient had been involved in a severe motor vehicle accident in February 2005 resulting in a lacerated spleen, liver, and kidney along with a left-sided pelvic VOLUME 47, NUMBER 5, SEPTEMBER/OCTOBER 2008 469
FIGURE 2 (A, B, C) Pre-operative radiographs demonstrating the fixed equinus deformity and retained tibial intramedullary rod. fracture, tibial fracture, and peroneal and tibial nerve injury. The patient had a residual fixed equinus deformity with maximum dorsiflexion of 28 in a plantarflexed position and a retained tibial intramedullary rod from her previous surgery (Figures 1 and 2). Pre-operative evaluation and work-up consisted of magnetic resonance imaging (MRI), noninvasive lower extremity studies, scintigraphy to rule out underlying osteomyelitis, and electrodiagnostic studies to evaluate the extent of nerve damage. All of the pre-operative tests were unremarkable except the electrodiagnostic studies, which demonstrated left common peroneal motor neuropathy and left superficial peroneal and sural nerve sensory neuropathy. There was no evidence of acute denervation, myopathy, or myositis of bilateral lower extremity musculature. 470 THE JOURNAL OF FOOT & ANKLE SURGERY
FIGURE 3 Due to a retained tibial rod from previous surgery, 2 tibial rings were mounted using a modified technique of wire placement and application of a half pin required placement distal to the retained hardware. FIGURE 4 The footplate was mounted parallel to the foot and attached to the distal tibial ring via a constrained hinge system that used Inman s axis for accurate placement. The patient underwent surgical intervention, which included application of a multiplanar circular external fixator, gastrocnemius recession, and common peroneal nerve and tarsal tunnel release. Significant fibrosis and scarring were noted surrounding the common peroneal and posterior tibial nerves. Minimal improvement of the equinus contracture was noted with the gastrocnemius lengthening. An external fixator was then applied. Initially, 2 tibial rings were placed circumferentially around the lower extremity with the tibia located centrally. Because of the residual tibial intramedullary rod, the 2 proximal olive wires and the distal wire were angulated to pass through the cortex of the tibia rather than centrally through the bone to avoid contacting the intramedullary rod. This was performed under fluoroscopy. These wires were placed within 45 of the frontal plane in a standard crossing fashion. The distal ring was stabilized with 1 olive wire running medial to lateral and a 5-mm half pin. Because of the length of the retained tibial rod, an extension cube was placed from the tibial ring distally to allow placement of the half pin in the tibia distal to the rod (Figure 3). The olive wires were then tensioned and alignment of all components was noted to be at right angles to the tibia. This was confirmed using image intensification. A footplate was then mounted parallel to the axis of the foot. Counter-posted olive wires were placed through the metatarsal shafts and midfoot to maintain the integrity of the forefoot joints. An olive wire and smooth wire were then crossed through the calcaneus. The ankle joint axis was then evaluated for placement of the universal hinges. The ankle joint axis was determined by using Inman s axis, which runs through the distal aspects of the medial and lateral malleoli. This axis runs from anterior-medial-dorsal to posteriorlateral-plantar. This axis can be verified with the use of fluoroscopy and a Kirschner wire. A wire is run through the talus, across the distal aspects of the malleoli, creating the ankle joint axis. The ankle joint is then manipulated through its range of motion under image intensification. The pin should not rotate or translate. The connecting rods with the aligned hinges were then placed medial and lateral connecting the tibial component to the foot plate (Figure 4). The ankle joint was then distracted to prevent crushing of the talus during the correction of the equinus. A cut olive wire was placed percutaneously across the joint to prevent dislocation of the talonavicular joint. Two long rods were connected from the proximal tibial ring to the anterior foot plate to be used as the motor for the equinus correction. Two 3-hole posts were stacked obliquely to allow for a flat surface area with complete apposition of screw components on the proximal ring (Figure 5, A). This also provided proper alignment of the anterior rods and prevented improper angulation and therefore residual angular deformities following correction. Kirschner wires were placed across all the digits and the metatarsophalangeal joints to prevent digital contractures and maintain stabilization of the forefoot. The patient was admitted for 24 hours for pain management. Physical therapy was consulted for gait training. The patient was discharged home on 14 days of low molecular weight heparin for deep vein throm- VOLUME 47, NUMBER 5, SEPTEMBER/OCTOBER 2008 471
the office, providing the initial correction of the equinus deformity 1 week status post-surgery. Gradual correction was initiated 2 weeks status post-surgery. The gradual correction rate was determined by the patient s pain tolerance, the presence of posterior tibial nerve compression symptoms, and tissue elasticity. The patient was instructed to shorten the anterior rods by turning the nuts one-half turn 4 times per day. The use of conical washers aided in maintaining the angulated position of the nuts to prevent bending of the rods when locking after corrections are completed (Figure 5, B). Radiographs were taken showing 8 of plantarflexion remaining at 3 weeks status post-surgery. All joints were evaluated and showed proper alignment without any signs of dislocation. The decision was made to increase the rate of correction by a multiple of 8 (double the correction). The patient was advised to continue with this rate of correction until she was unable to tolerate the pain or until her next visit. This was continued until her seventh post-operative week at which time radiographs demonstrated a measured overcorrection of 18 dorsiflexion (Figure 6). This equaled a total correction of 46. Overcorrection was maintained for an additional 7 weeks. Generally, for contracture deformities, the external fixator is maintained for a total of twice the amount of time it takes to correct the deformity or at least a minimum of 6 additional weeks (7, 9). The patient had the fixator removed 4 months status post application. The patient was placed in a removable cast and instructed to be partial weight bearing with crutches. The patient was then placed in a molded anterior clamshell ankle-foot orthoses with a plantarflexory stop. The patient experienced minimal pain and on physical exam demonstrated passive dorsiflexion of 10. The patient was then prescribed aggressive physical therapy including range of motion exercises for the left lower extremity as well as posterior muscle group stretching and strengthening. The patient had a rectus foot and demonstrated return of function of the anterior muscle group at the 1-year follow-up examination (Figure 7). The patient was released to participate in normal daily activities and advised to remain in the ankle foot orthoses at night for the next 6 months. FIGURE 5 (A) Two long rods connected at the footplate and proximal tibial ring were used as the motor for gradual correction. Two 3-hole posts were placed in an oblique manner on the tibial ring to provide a flat surface area for connection of the rods and proper angulation for the correction. (B) A focused view shows the conical washers used to maintain the angulated position of the nuts to prevent the bending of the rods when locking after corrections are completed. bophlebitis prophylaxis and instructed to remain completely non weight bearing on the affected extremity over the course of the treatment. Shortening of 4 mm of the anterior rods was performed in Discussion Post-traumatic lower extremity deformities are challenging cases. The hinged constrained fixator method has been described as a surgical tool for correction of complex deformities in gradual settings. However, there has been no specific recommendation for its use in treating traumatic uniplanar ankle deformities. Tsuchiya et al (7) in 2003 evaluated the difference in correction between 2 different hinged groups for equinus contracture correction. They found little clinical difference between these 2 groups with mean correction of 32.9 12.9 in the natural hinge group and 36.1 10.5 in the rotating hinge group. Tsuchiya et al 472 THE JOURNAL OF FOOT & ANKLE SURGERY
FIGURE 6 (A and B) Photographs of the patient 7 weeks post-operative demonstrates a measured 18 of dorsiflexion. (C and D) Radiographic evaluation 7 weeks post-operatively demonstrates correction of the deformity with proper alignment of all lower extremity joints. VOLUME 47, NUMBER 5, SEPTEMBER/OCTOBER 2008 473
FIGURE 7 (A, B, C) Photographs of the patient at final follow-up shows the foot in a rectus position with no residual equinus. 474 THE JOURNAL OF FOOT & ANKLE SURGERY
(7) did note differences however in complications including digital flexor contractures with the rotating hinged group and anterior subluxation of the talus in the natural hinged group. These complications were avoided in this case by fixating the talonavicular, metatarsophalangeal, and digital joints. Other reported complications include tarsal tunnel syndrome, valgus drift, pin site infections, and recurrence of deformity (1, 4, 5, 8, 9). Lamm et al (10) in 2007 found that acute corrections of greater than 10 may benefit from prophylactic tarsal tunnel release. They also felt that gradual correction is much less likely to cause nerve entrapment and recommended prophylactic decompression of the posterior tibial nerve. Initiation of a secondary surgical decompression or a decrease or cessation in the rate of correction should be considered if posterior tibial nerve compressive symptoms were to occur (10). Complications also arising from improper placement or inadequate support of the external fixator can occur. Huang (11) noted the importance of distraction and proper hinge placement of the external fixator to prevent crushing of the articular surfaces. We used intraoperative pinning and consistent radiographic follow-up to monitor and prevent crushing of the talus and dislocation of the tarsal joints. Kocaoglu et al (4) in 2002 recommended prevention of toe contractures through rubber slings or Kirschner wire fixation of the distal and proximal interphalangeal joints as well as the metatarsophalangeal joints. Paley (12) in 1993 described the use of a Kirschner wire across the phalangeal bases without incorporating the metatarsals for prevention of contractures with the use of the Ilizarov device. We found operative pinning of all 5 digits across the metatarsophalangeal joints satisfactory in maintaining appropriate alignment of the forefoot without residual contractures or complications within the metatarsophalangeal joints. Recurrence of any soft tissue deformity is a concern and a well-documented complication. Huang (11) in 1996 described the use of the Ilizarov frame for correction of knee and ankle joint contractures with a recurrence rate of 11 out of 26 contractures within 3 years. Gradual correction was used to obtain an overcorrected position of 18 dorsiflexion in our case study. This correction was maintained for a calculated additional amount of time to decrease the chance of recurrence. Long-term bracing of 6 to 12 months and physical therapy are also helpful after removal of fixation to maintain soft tissue correction. Treatment of post-traumatic fixed equinus can be difficult with some potential complications including recurrence. We have provided a description of the use of a constrained hinged external fixator in conjunction with a comprehensive treatment plan in order to obtain a successful outcome. References 1. Carmichael K, Maxwell S, Calhoun J. Recurrence rates of burn contracture ankle equinus and other foot deformities in children treated with Ilizarov fixation. J Pediatr Orthop 254:523 528, 2005. 2. Hahn S, Park H, Park H, Kang H, Cho J. Treatment of severe equinus deformity associated with extensive scarring of the leg. Clin Orthop Relat Res 393:250 257, 2001. 3. Hsu K, Kuo K, Hsu R. Correction of foot deformity by the Ilizarov method in a patient with segawa disease. Clin Orthop Relat Res 314:199 202, 1995. 4. Kocaoglu M, Eralp L, Atalar A, Bilen F. Correction of complex foot deformities using the Ilizarov external fixator. J Foot Ankle Surg 411:30 39, 2002. 5. Melvin J, Dahners L. A technique for correction of equinus contracture using a wire fixator and elastic tension. J Orthop Trauma 202:138 142, 2006. 6. Herzenberg J, Paley D. Ilizarov applications in foot and ankle surgery. Advances in Orthopaedic Surgery 163:162 174, 1992. 7. Tsuchiya H, Sakurakichi K, Uehara K, Yamashiro T, Tomita K. Gradual closed correction of equinus contracture using the ilizarov apparatus. J Orthop Sci 8:802 806, 2003. 8. Elomrani N, Kasis A, Tis J, Saleh M. Outcome after foot and ankle deformity correction using circular external fixation. Foot Ankle Int 2612:1027 1032, 2005. 9. Calhoun JH, Evans EB, Herndon DN. Techniques for the management of burn contractures with the ilizarov fixator. Clin Orthop Rel Res 280:117 124, 1992. 10. Lamm B, Paley D, Testani M, Herzenberg J. Tarsal tunnel decompression in leg lengthening and deformity correction of the foot and ankle. J Foot Ankle Surg 463:201 206, 2007. 11. Huang S. Soft tissue contractures of the knee or ankle treated by the ilizarov technique. Acta Orthop Scand 675:443 449, 1996. 12. Paley D. The correction of complex foot deformities using Ilizarov s distraction osteotomies. Clin Orthop 293:97 111, 1993. VOLUME 47, NUMBER 5, SEPTEMBER/OCTOBER 2008 475