The achievement of skeletal maturity with functional utility and anatomic alignment of the bone is the primary goal of treating CPT (3, 4). Among various surgical techniques that have been developed to optimize the outcomes in treating CPT, the Ilizarov technique has been proved to be valuable in promoting high rate of union through compression, dealing with limb length discrepancy via diaphyseal transfer and addressing angular deformities concomitantly. However, the prevalence of refracture after removal of the fixator is the main concern. Treating with the Ilizarov frame alone is also challenged by tissue intervention due to pins and K-wires passing through muscle compartments and discomfort led by prolonged frame wearing (22, 26–28).
IM fixation was the primary choice in union achievement and protection against refracture, with sufficient biomechanical stability provided (15, 29). The combination of the Ilizarov technique and intramedullary fixation provides adequate fixation after surgery and significantly cuts the days of frame wearing, which help to avoid the drawbacks and discomfort brought about when utilizing the external frame alone (3). In a series of 15 cases who received IM nailing combined with Ilizarov fixation, Agashe et al. reported that 14 patients (93.3%) achieved union, with primary union in 6 patients and 8 patients achieved union after secondary procedures. During the 4.2-year follow-up period, only 1 patient (6.7%) developed refracture (7). Dobbs et al. reported that trans-ankle Williams rod stabilization showed satisfactory long-term outcomes, with initial consolidation occurred in 18 (85.7%) of 21 patients (15). In a retrospective study performed by Shah et al., all 11 patients showed union after treatment with retrograde intramedullary rodding, with only 5 cases of refracture (14).
For a long period, due to the high rate of refracture, pediatric surgeons were compelled to focus on successful osteosynthesis rather than the sequelae of CPT, such as joint stiffness and arthritic change led by trans-ankle fixation; metaphyseal irritation and growth failure led by metaphyseal intrusion; and even failure of IM fixation due to inadequate space for nail interlocking in pediatric patients (7, 14, 16, 30, 31). The disadvantages of the commonly used IM rods mentioned above encouraged us to make changes in our treatment. In our study, two prebent TENs were positioned in an “Eiffel Tower” shape in the medullary canal of the affected tibia, with their respective convexities facing each other. Obviously, this elastic deformation within the medullary canal creates a bending moment within the long bone that is not rigid but stable enough to provide effective support for preventing further refracture and promoting solid union. As shown in Fig. 1a, the “Eiffel Tower” shaped elastic internal frame ensures flexural, translational, rotational and axial stability under external forces. In addition, extensive bone formation that ensures stability after removal of the external fixator was also reported to occur along the tract of the intramedullary nails (18).
The combination of IM rodding, circular external fixation and iliac bone grafting have been generally accepted as an effective procedure in protecting against refracture, promoting alignment control with high fusion rate and contributing to early removal of external fixator (7, 9, 11, 25, 32). Since 2013, we applied prebent TENs instead of using conventional IM rod for internal fixation. Our study has shown favorable results, with primary union obtained in 86.7% patients. An average number of 1.3 (1 to 2) surgeries were performed to achieve solid union for each patient, which is in line with that reported previously (11). Refracture occurred in only 2 (13.3%) of 15 patients. All obtained union of the refracture site after additional surgery. Most other studies show similar or higher refracture rates for various methods (3). 12 refractures (23.2%) occurred in 21 patients treated by a Williams rod (15). Refracture occurred in 13 (23.2%) of 56 patients treated with combined surgery including pseudarthrosis resection, intramedullary Williams rodding, autogenous iliac bone grafting and Ilizarov’s fixator in the Zhu et al. study (9). In a recent study using combined techniques of hamartoma resection, periosteal grafting, circular external fixator application, and intramedullary rodding, 5 (29.4%) of 17 CPT cases were complicated by refractures (10). As additional refractures may occur before patients reach skeletal, final outcomes should be assessed after all the patients have reached this milestone. Dobbs et al. noted that the frequency of refracture was higher when a fibular pseudarthrosis was not treated (15). Cho et al. reported a higher risk of refracture when the fibula remained ununited (26). Agashe et al. concluded that undue stress led by the persistent malalignment of the tibia and fibula, loss of intramedullary fixation and non-compliance with external bracing regimen are three major causes of refracture (7). Although we followed these suggestions carefully, two cases of refracture still occurred. In one patient (case 2), the occurrence of refracture was probably because of persistent ankle valgus deformity and fibular pseudoarthrosis. In another patient (case 14), the patient did not wear the brace and refracture occurred after major trauma.
Paley defined the success probability as:
Success probability = Union rate × [1 − Mean refracture rate]
He reported that on average, success probability was 40% in intramedullary rodding, 57% in the Ilizarov method and 58% in intramedullary rodding combined with the Ilizarov method (2). In our study, the success probability was 69.3%.
To prevent refracture, an intramedullary rod was suggested to be maintained in situ until skeletal maturity (7, 15). With longitudinal growth of lower extremity, the distal part of the tibia, the ankle, and the foot migrate distally while the rod remains in place. Thus, reoperations are usually required to push the rod across the ankle joint (16, 33). Telescopic rods, such as Bailey-Dubow and Sheffield expandable rods, can elongate as the child grows, which helps to decrease the number of reoperations required for these children. However, knee and ankle arthrotomies are still required for a tibial insertion of 2 telescoping components (31, 34). The subsequently developed Fassier-Duval Rod managed to further decrease the reoperation rate and complication rate by making the insertion with a single proximal entry (16, 35). Unfortunately, due to the lack of longitudinal and rotational stability, the sole use of Fassier-Duval rod fixation in patients with severe underlying bone pathology of CPT end up with discouraging nonunion, collapse (“negative telescoping”) and consecutive joint intrusion (16). The high cost also limits its wide acceptance in the developing area, such as mainland China, where public health care is rudimentary. On the contrary, entry points of the TENs were set distal to the proximal physis and were relatively less invasive during further nail changing as the removal and insertion of the nails did not require ankle arthrotomies.
In order to decrease the prevalence of ankle stiffness, Dobbs et al. used the solid two-part Williams intramedullary rod (the rod assembly consists of an indwelling rod and an insertion rod) and recommended surgically advancing the rod out of the ankle joint soon after the pseudarthrosis has healed (15). However, metaphyseal irritation and arthritic change of ankle joint, which results in restricted joint mobility and growth failure, remains as the rod is advanced antegrade across the ankle joint and out through the heel pad during insertion. The ankle joint was usually immobilized by rod transfixation for nearly two years after rod insertion (14, 15, 29, 36). Migration passage of the IM nail through the growth plate may lead to the formation of fibrous bridge (30). Thus, techniques that require the rod positioned across the ankle and subtalar joint are less desirable. Custom interlocking intramedullary nails may decrease the prevalence of ankle stiffness as it does not transfix the ankle joint. However, it is too large for younger patients and it is not suitable for patients in whom the segment distal to the pseudarthrosis is not long enough to accommodate adequate fixation (29). Agashe et al. used the antegrade method of intramedullary nailing which started from the proximal tibia and passed through the “fracture” till the level of the ankle. Ankle motion and achievement of union was satisfied in most of the CPT patients. However, the direction of nailing is relatively dependent on the location of the CPT, since the extremely distal location of the pseudarthrosis, may still require a transplantar nail and end up with poor ankle function (7). In our study, entry points of the elastic nails were set distal to the proximal physis and the ends of the nails were at the level of 1 cm distal to the metaphysis of tibia, which protects the ankle joints from being jeopardized by classical rodding through the ankle. Range of motion in tibiotalar and subtalar joints was optimal in 12 (80%) patients. Only 3 patients in our study developed subtalar and tibiotalar stiffness, probably due to multiple operations for attainment of union (case 6 and case 8), retrograde intramedullary rodding in the previous failed surgery (case 8 and case 15) and relatively distal location of pseudoarthrosis (case 15).
Similar to previous reports, ankle valgus deformities remained to be the most common residual deformities in our study, which occurred in 3 of 15 patients (20%) and all of them had received surgeries on fibular lesions. There seems to be a trend toward an increased rate of ankle valgus deformity post-operatively in the patients who had a fibular pseudarthrosis, which may due to a high position of the fibular distal epiphysis and an asymmetric growth of the distal tibial physis that grows more medially than laterally (29, 32). In addition, proximal migration of the distal fibula causes the talus to move follow the fibula, which contributes to ankle valgus and lateral subluxation of the ankle joint. The resultant instability of the ankle increases the risk of refracture (2, 7, 15, 37). Thus, re-establishment of the integrity of the fibula is essential for CPT treatment. The distal tibiofibular synostosis is useful in fibular healing, deformity control and refracture treatment, as described by Thabet et al (5). According to our clinical experience, hemi-epiphysiodesis is the easiest method to correct ankle valgus in CPT children with enough growth potential, as hemi-epiphysiodesis is less invasive and can reduce the risk of nonunion brought by corrective osteotomy. In our study, timely and additional procedures such as medial distal hemi-epiphysiodesis, tibiofibular synostosis and supramalleolar osteotomy with external fixation showed good outcomes in addressing ankle valgus deformity over 5°, which is also reported in previous reports (2, 5, 8). At the last follow-up, all three patients did not report any clinical symptoms such as pain or limping. Agashe et al. reported that under the treatment of Ilizarov technique combined with intramedullary rodding, the mean AOFAS score increased from 40 to 64 during a mean follow-up time of 4.5 years (7). Our study presents relatively favorable results, with the average AOFAS increased from 40.3 to 76.1. Although a relatively longer follow up period in our study (6.5 years) may lead to a slightly higher AOFAS score at the final follow up, it is still obvious that the ankle function improved greatly during the follow-up period. Only two cases developed equinus deformity. For cases whose intramedullary nailing was in the tibia, passive and active ankle dorsiflexion may help to prevent equinus deformity.
Length discrepancy is a common challenge resulting from inhibited growth of distal physis, surgical resection and bone resorption at pseudarthrosis (2). Pollon et.al reported that motorised intramedullary-lengthening nail (Fitbone®, Wittenstein, Igersheim, Germany) successfully addressed 5.5 cm of lower limb shortening in an 18-year-old CPT patient who had already obtained bone union by Masquelet induced-membrane technique and internal fixation (33). However, due to the high cost, it has not yet been established as a routine device. In developing countries where the telescopic rod or intramedullary-lengthening nail is not available, typic methods such as lengthening the shorter leg, arresting the growth of the contralateral leg and a combination of the two procedures are the indispensable methods to equalize limb length discrepancy. Choi et al. and Zhu et al. both suggested that LLD of 3 cm was the threshold for limb lengthening as functional sequelae and limping gait might occur when the residual LLD was > 3 cm (9, 22). Later, Zhu et al. presented the clinical experience that the indication and time window of proximal tibia lengthening in children was more than 4 cm and two years after the initial union of pseudarthrosis (38). We agree with the treatment threshold of 4 cm LLD suggested by Zhu et al. However, it should be noted that proximal tibial lengthening in CPT patients is characterized by a high frequency of poor bone regeneration with abnormal callus at the distraction site (21, 38). Postponing the limb lengthening will lead to more limb length discrepancy to be corrected, prolonged fixator wearing, increased HI index and a higher risk of poor bone regeneration. Thus, we performed proximal tibia lengthening in patients with limb length discrepancy of over 3 cm. Otherwise, a shoe-lift was applied according to the patients’ willingness.
Choi et al. performed 27 proximal tibial lengthening in 22 patients, some of whom had repeated lengthening. The average healing index was 89 d/cm (range, 22–280 d/cm). Proximal tibia dysplasia and repeated lengthening were identified as the risk factors of poor regenerate bone formation. For patients with the signs of proximal tibia dysplasia (trumpet-shaped narrowing, anterior inclination of the proximal physis, and anterior cortex concavity), they recommend the physeal distraction technique. However, they also pointed out that the physeal distraction technique has potential risks of secondary joint infection and premature physeal arrest (21). In our study, we performed tibia lengthening and compression of the pseudarthrosis concomitantly with TENs retained in the medullary cavity for avoiding implanting a second fixator and protection of the pseudarthrosis site. Zhu et al. introduced their experience of concomitant proximal tibial lengthening carried out in 56 patients. At the final follow-up (mean 5.2 years, range, 3 to 6.7 years), 16 (28.6%) patients had an average 2.2 cm LLD (range, 1.5–4.2 cm). In their later study, they performed proximal tibia lengthening 2 years after initial union of pseudarthrosis and suggested that proximal tibial lengthening at this point would have no side effect on the pseudarthrosis. The average HI was 63.1 d/cm (range, 47–77 d/cm). 8 of 11 cases developed proximal tibial dysplasia, with an average HI of 67 d/cm. None of the cases had refracture or nonunion of the distraction gap. The average HI in our study was 65.1 d/cm (range, 57.3 to 77.8 d/cm), which is comparable with the results presented in earlier studies. One stage lengthening may affect the healing process at the pseudarthrosis site while postponing tibial lengthening may cause larger LLD and a prolonged period of external fixation (38). Due to the retrospective nature of the study and the heterogeneous degree of limb discrepancy, the value of TENs technique in limb lengthening still cannot be confirmed directly from our study. The question therefore arises as to at what time window the proximal tibia lengthening procedure together with different intramedullary nailing techniques would yield the most favorable outcomes in terms of fewer complications, shorter duration of external fixation, a higher rate of union and lower chance of refracture.
The small number of patients is the limitation of this study. As CPT is a rare disease, more multicenter studies with larger numbers of patients included should be carried out for more meaningful conclusions. Follow-up period is not long enough to document the outcomes of these younger patients until skeletal maturity. The true success of treating CPT in a growing child can be confirmed only by following the children until maturity. In all, a well-designed prospective study is required in the future to fully investigate the advantages and drawbacks of the titanium elastic nailing technique.
In conclusion, this study demonstrated that the application of prebent titanium elastic nails (TENs), combined with bone grafting and application of circular external fixator, is a viable option for CPT in achieving and maintaining union. The advantages of the present surgical procedure lie in providing good stability and protection against refracture. The readily availability is another factor that makes it an alternative first-line surgical option for young children in the developing world. Moreover, compared with other rodding techniques, the TENs technique poses less injury to ankle joint and metaphysis, which effectively avoids ankle stiffness and reduces negative impact on tibia growth. It is necessary to follow up more patients until skeletal maturity and to evaluate its long-term outcome.