Achondroplasia (ACH) is the most common skeletal dysplasia characterized by rhizomelic shortening of the limbs, characteristic facies with frontal bossing and midface hypoplasia, increased lumbar lordosis, and trident hand. The average height of adult patients with ACH ranges from 124 to 131 cm. For the treatment of short stature in ACH, growth hormone (GH) has been administered in some limited countries, but the response to GH is moderate, and the long-term effect remains controversial 1. For the patients who hope to increase their height, the limb lengthening has been used to improve not only the psychological and emotional state but also the quality of life of the patients. However, increasing the magnitude of lengthening is associated with increase in complications, such as premature physeal closure, adjacent joint contractures, and regenerate fractures 2–4.
Equinus contracture of the ankle joint is a frequently encountered complication during extensive tibial lengthening in ACH, in spite of aggressive physiotherapy for range of motion (ROM) exercise or use of customized splint to maintain ROM 5. Belthur et al. 6 described that the tibial lengthening beyond the tolerance of the gastrocnemius–soleus–Achilles tendon complex to stretch leads to increasing tension and pulling the heel into the equinus position. Theoretically, extensive tibial lengthening can lead to flexion contracture of the knee because of the function of the gastrocnemius as a biarticular muscle. The effect of extensive tibial lengthening on the ROM of the hip joint, however, has not been examined previously. Moreover, temporal changes in the ROM of the lower limb joints throughout the treatment period have not been fully investigated.
In the present study, we repeatedly measured the ROM of the hip extension, knee extension, and ankle dorsiflexion at every 1 cm of length gained during the distraction period, and at monthly intervals after the completion of distraction in patients with ACH who had undergone extensive tibial lengthening. Interestingly, joint contractures were observed in the hip in addition to the knee and ankle in some patients.
Patients and methods
Seven consecutive patients with ACH who had undergone bilateral tibial lengthenings using monolateral external fixators (DynaFix rail system; EBI LP, Parsippany, New Jersey, USA) at our institution between 2012 and 2014 were recruited in this study. We defined ‘extensive lengthening’ as the bones that gained the length of 40% or more of the original bone. One patient was excluded from the current study because he could not gain sufficient length owing to extremely poor regenerates. Overall, 12 limbs of six patients (two male and four female) with an average age at surgery of 10.8±0.9 years were examined.
All operations and postoperative management were performed by or under the direct supervision of the senior author (H.K.). Two centimeter at the junction of the distal and middle third of fibular diaphysis was resected, followed by stabilization of the distal part of the fibula with a cannulated screw to prevent lateral malleolus proximal migration. We never fixed the proximal tibiofibular joint to allow the caudal descent of the fibular head during the distraction in this specific disease. Then, the monolateral fixator was placed on the anteromedical aspect of the tibia with 5–6 cortical screws, and the proximal diaphyseal osteotomy was subcutaneously performed by multiple drill holes followed by an osteotome (Fig. 1a). The physiotherapy regimen was standardized in all patients. Passive ROM exercises and isometric strengthening exercises were commenced on the first postoperative day and weight-bearing with crutches was encouraged, depending on patient tolerance. After an initial delay of 14 days, gradual distraction of 0.5 mm twice daily was commenced. The rate of distraction was individually adjusted considering the callus formation on the radiographs and the ROM of adjacent joints. Paying attention to premature consolidation, we usually slowed the distraction rate during the late phase of distraction to minimize the deterioration of contracture. During distraction, patients who had deteriorated ankle dorsiflexion of 0° or less were encouraged to use night splint (ankle foot orthosis) until the contracture recovered (Fig. 2). Patients who showed toe walking owing to equinus contracture were recommended to wear customized high-heel shoes not only to assist walking but also to provide mechanical strength to new bone regenerates (Fig. 3). Termination of lengthening for patients with ACH who hoped to gain maximum length, was determined based on either bone-related (poor regenerates) or joint-related (contracture) problems. As none showed remarkable bone-related problems to terminate the lengthening in this series, the senior author (H.K.) determined the termination of distraction when the patient showed remarkable crouch gait even with the high-heel shoes and became difficult to walk with crutches. The cannulated screw used for distal fibular fixation was removed soon after the completion of distraction (Fig. 1b). The devise was loosened to allow dynamization of the regenerates as it matured. The decision to remove the fixator was made based on the radiographic appearance of the regenerated bones (Fig. 1c).
Measurements of the ROM in individual joints were performed by the physiotherapists using a classic goniometer (Muranaka Medical Instruments Co. Ltd., Osaka, Japan). Hip extension was measured with the patients’ buttocks at the end of the rehabilitation platform with knees flexed to the chest. One leg was stabilized in this position, whereas the limb of interest was allowed to maximum extension by the physiotherapist. Extension measurements represented the position of the extended limb relative to the horizontal. For measurements of knee extension, the patient lay supine on a platform and a towel was rolled up and placed underneath the ankle of the test limb to allow the knee to extend as much as possible. The center of the goniometer was aligned with the lateral femoral condyle, the movable arm with the lateral malleolus, and the immovable arm with the greater trochanter. The patient’s knee joint of interest was passively extended by the physiotherapist and the angle of the goniometer was measured. For measurements of ankle dorsiflexion, patients were lying in a supine position with the knee flexed, and the physiotherapist manually verified a subtalar neutral position and placed the ankle in full dorsiflexion. Ankle dorsiflexion was measured as the angle between the lateral midline of the lower leg (a line from the fibula head to the tip of the lateral malleolus) and the lateral border of the foot. The ROM of hip extension, knee extension and ankle dorsiflexion was measured before distraction, at every 1-cm length gained during distraction period, and at monthly intervals after the termination of distraction (during consolidation period) until the frame removal. The same physiotherapist continuously measured the ROM for an individual patient.
The average amount of lengthening was 9.2±1.2 cm (7.8–10.7 cm), corresponding to an average proportional lengthening of 52.8±6.8% (44–62%) of the original bone length (Table 1). The average healing index was 34.1±11.0 days/cm (28.0–68.1 days/cm). The left tibia of case 4 needed prolonged lengthening time (357 days) owing to its poor regenerates; thus, the overall average period of lengthening reached to 140.3±70.2 days (97–357 days). Rates of distraction ranged from 0.5 to 1.5 mm/day, depending on an individual patient. During the treatment period, superficial pin track infection was commonly seen in all patients, but it was successfully treated with oral antibiotics without developing deep infection such as osteomyelitis. Only one regenerate fracture occurred while the pins were in situ after removal of the frame, which was treated successfully with further fixation using the frame.
The ROM of the ankle dorsiflexion, knee extension, and hip extension is shown in Figs 4–6, correspondingly. Restriction in ankle dorsiflexion appeared before distraction and deteriorated as the distraction progressed (Fig. 4a), but it improved gradually after the termination of distraction (Fig. 4b). Knee extension was obviously limited after the lengthening of 4 cm or more, but recovered within a month after the termination of distraction (Fig. 5a and b). Interestingly, limited range of hip extension was observed after the lengthening of 6 cm or more, despite being not an adjacent joint in tibial lengthening (Fig. 6a). The ROM of hip extension was synchronically ameliorated with the improvement of knee flexion contracture (Fig. 6b). All cases recovered the ROM of the lower limbs to the preoperative level within 12 months after the removal of the pins.
The average follow-up period was 39.2 months (31–49 months) after removal of the pins. At the end of tibial lengthening, genu varum deformity remained in six limbs of four patients. These deformities were intentionally corrected during subsequent femoral lengthening in three cases. One patient did not undergo femoral lengthening because of her social problem. At the latest follow-up, four patients showed full activity of daily living including sports activities, one patient needed all-day bracing owing to progressive kyphoscoliosis, and the other patient is scheduled for decompression surgery owing to cervical myelopathy.
In the current study, the ROM in ankle dorsiflexion was restricted before distraction. During the surgical procedure, great care should be taken to avoid tethering extensor (tibialis anterior, extensor digitorum longus, and extensor hallucis longus) or flexor (triceps surae, tibialis posterior, flexor digitorum longus, and fibularis longus) muscles of the ankle joint with screws 6. In our series, it is unlikely that the tibial screws caused tethering as they were inserted from anteromedial aspect of the tibia without penetrating any muscles. On the contrary, it is recommended to prevent proximal migration of the fibula using a distal tibiofibular syndesmotic screw during tibial lengthening 7. The fibula, however, rotates around its vertical axis and affects tibiofibular syndesmosis when the ankle is plantar flexed and dorsiflexed. Norkus and Floyd 8 stated lateral fibular rotation of ~3°–5° to accommodate the talus with dorsiflexion. The distal tibiofibular syndesmotic screw may affect the range of ankle dorsiflexion through prevention of rotational movement of the fibula during dorsiflexion. Insertion of the syndesmotic screw with a maximal dorsiflexed position during surgery may be beneficial to prevent the early loss of ankle dorsiflexion.
Adjacent joint contractures are common complications in limb lengthening procedures 9,10, but to our knowledge, there were no reports describing flexion contracture of the hip joint in tibial lengthening. In the current study, the contracture tended to appear first in the ankle, then in the knee, and finally in the hip joint as the distraction progressed. During the early phase of distraction, tibial lengthening beyond the tolerance of the gastrocnemius–soleus–Achilles tendon complex to stretch leads to increased tension in this complex, and pulling the heel into the equinus position. We then used a customized ankle foot orthosis in a maximal dorsiflexed position during night-time to prevent further deterioration of contracture. Night splint treatment may have provided beneficial effects on maintenance of ankle ROM in our study. Instead, increased tension to the gastrocnemius–soleus–Achilles tendon complex during subsequent distraction may have caused knee flexion contracture, resulting in the crouch gait pattern. Hip flexion contracture observed in the late phase of distraction may have resulted from a compensatory mechanism for the knee flexion contracture and ankle equinus during crouch gait in children with ACH.
As patients with ACH show increased ligament and joint laxity, their muscle length should exceed bone length before lengthening, thereby facilitating the lengthening process. Kim et al. 11 reported that patients with ACH tolerated larger amount of lengthening with fewer complications than those with other etiologies. However, increasing the magnitude of lengthening had significant risks of complications including a decreased ROM of adjacent joints even in ACH children 12. Venkatesh et al. 13 demonstrated that patients with ACH who gained the length of more than 50% of their initial length were associated with an increased incidence of stiffness in adjacent joints in femoral lengthening. Irrespective of extensive lengthening in the current study, all of the contracture developed during the distraction phase finally resolved with conservative treatment after the completion of distraction. Various reasons can be considered for this favorable result, including aggressive physiotherapy with muscle stretching exercises, application of customized splint and shoes, slower distraction rate, and relatively younger age. Timing to terminate the distraction is another important issue for patients with ACH who hope to gain length as long as possible. We could prevent irreversible contracture by stopping further distraction at the time when difficulty in walking with crutches became apparent.
The main limitation of the current study was its small sample size and its resulting lack of statistical power. Second, only children with ACH aged 9–12 years were examined; therefore, our results cannot be extended to older patients. Adolescent or adult patients with ACH who undergo tibial lengthening could show different results owing to their different extensibility of muscles and tendons from those of children. Third, the percentage of lengthening and the rate of distraction, which could affect soft-tissue tolerability against distraction, varied among each individual.
Conflicts of interest
There are no conflicts of interest.
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