We describe a novel surgical technique to prevent equinus from occurring during tibial lengthening with an intramedullary self-lengthening telescopic nail. We developed this technique after experiencing difficulties with equinus in some of our earlier cohorts of patients. Based on our clinical experience, we have been satisfied with this technique and our results support its success. However, we also were compelled to conduct an anatomic investigation of potential structures at risk by using a cadaver model.
Our clinical study had several limitations. First, the number of patients was relatively small (14 limbs in 10 patients) and might not have been large enough to reveal a small percentage of complications that might be associated with this method. Second, our measurements of ankle range of motion were purely clinical and might be subject to error [26
]. Third, it is unknown how applicable this technique would be to the general orthopaedic community. Our center specializes in limb lengthening, and we have developed considerable expertise and experience in all aspects of limb lengthening, including identifying risk factors preoperatively and addressing postoperative complications.
External fixation to lengthen the tibia is a well-established technique [1
]. Ankle equinus contracture during tibial lengthening is a frequently reported complication [9
]. The reported incidence in the literature ranges from 1% to 7% [9
]. Joint contracture during lengthening occurs because of the tension generated in the muscle during distraction osteogenesis [21
]. This affects biarticular muscles most because they tend to have fibers of various lengths, as opposed to uniarticular muscles, which have fibers of fixed length [21
]. In biarticular muscles, inadequate adaptation of the perimuscular connective tissue during distraction osteogenesis results in the muscles becoming relatively short compared with the bone, resulting in joint contractures [8
]. During tibial lengthening, the gastrocnemius-soleus-Achilles tendon complex is at risk. Tibial lengthening beyond the tolerance of the muscle to stretch will place this complex under increasing tension, pulling the heel into the equinus position. The tolerance of the muscle complex to stretch depends on many factors: the rate of lengthening, the diagnosis and associated diseases of the patient (ie, higher incidence of complications in congenital, neuromuscular, and skeletal dysplasia cases), amount of lengthening (ie, more than 20% of the bone segment length), unifocal or bifocal lengthening, status of the gastrocnemius-soleus-Achilles tendon complex (eg, previous surgery, scarring), and the technique of pin insertion [18
A number of options are available for preventing and managing ankle equinus contracture during lengthening [18
]. The problem can be dealt with preoperatively, intraoperatively, and/or postoperatively. Before surgery, the physiotherapist can teach patients a gastrocnemius-soleus-Achilles tendon complex stretching program and show them what to expect with splinting. During the surgical procedure, great care should be taken to avoid tethering the gastrocnemius-soleus-Achilles tendon complex with pins. The use of an atlas is recommended. If pins are inserted through this complex, they must be inserted properly by positioning the muscle group at its maximal stretch, with the ankle in full dorsiflexion. In high-risk cases (eg, lengthening more than 20% of bone segment length, scarred gastrocnemius complex, associated diseases [eg, congenital conditions, neuromuscular conditions, skeletal dysplasia], unstable ankle, when the patient is too young to cooperate with physical therapy), either prophylactic pinning of the foot or spanning the ankle with an external fixator is recommended. The ankle usually is spanned during the lengthening phase, and the foot component of the external fixator is removed during the consolidation phase. If prophylactic pinning of the foot and spanning of the ankle are not performed, a number of options are available to prevent ankle equinus contracture postoperatively. These options include passive stretching, positioning, and static and dynamic splinting of joints. The goal is to keep the muscle at its maximum stretch for as long as possible. However, especially in high-risk cases, it is difficult to prevent and correct equinus contractures with stretching, positioning, and splinting alone, unless the ankle can be maintained in the corrected position for at least 6 hours per day and the patient is compliant [27
]. For high-risk cases, it might become necessary for the foot to be included in an external fixator secondarily to hold the ankle in dorsiflexion. Dorsiflexion can be achieved very easily with an external fixator.
Tibial lengthening with the ISKD has been developed to reduce the complication rates associated with external fixation and to improve patient comfort [5
]. However, the ISKD does not allow for precise control of the rate of distraction during lengthening and it is impossible to span the ankle to prevent equinus contracture.
] first described a permanent extraarticular ankle fusion in 1923 to treat the flail ankle with equinus deformity. He used an onlay bone graft from the calcaneus to the tibia to achieve fusion and correct the equinus deformity. A temporary extraarticular ankle arthrodesis with a screw has not been previously described in the literature. The senior author (DP) first used this technique in 2003. Since then, we have selectively used a temporary EAAS screw to prevent ankle equinus contracture from developing during tibial lengthening with the ISKD in patients at high risk for developing ankle equinus contracture. The indications for stabilizing the ankle in our series included lengthening more than 5 cm, unstable ankle, congenital or neuromuscular condition, skeletal dysplasia, and preexisting ankle equinus contracture.
The extraarticular calcaneotibial screw has been successful in preventing equinus contracture from developing during tibial lengthening with the ISKD. The preoperative ankle range of motion was regained within 6 months after screw removal. In this series, no complications associated with the insertion of this screw occurred. Specifically, we did not observe any mechanical failures (fractures of the screws) or any fractures caused by the screws. Our protocol of limiting weight bearing probably prevents this. Another potential complication is inadvertent ankle/subtalar joint compression. This is unlikely to occur because we always use a fully threaded implant, thus avoiding compression. Since this study was closed, we have had a recent case, still under treatment, in which a serious complication was observed. That patient developed a deep posterior compartment syndrome and tarsal tunnel syndrome from hemorrhage that seemed to result from the EAAS screw. It is unclear which vessel was damaged. The posterior tibialis artery was intact as assessed by Doppler ultrasonography, but a large hematoma was discovered at the time of surgical decompression.
The cadaveric study showed the potential anatomic structures at risk during insertion of the EAAS screw. The flexor hallucis longus muscle belly is most at risk, but unnamed branches of the posterior tibial artery and vein could also be at risk. The screw should be inserted in a slightly oblique fashion from the upper edge of the calcaneus, slightly lateral to the center, and should be aimed slightly lateral in the tibia to avoid injury to the flexor hallucis longus muscle.