Correction of coronal plane deformities around the knee using a tension band plate in children younger than 10 years.

BACKGROUND: Guided growth through temporary hemiepiphysiodesis has gained acceptance as the preferred primary treatment in treating pediatric lower limb deformities as it is minimally invasive with a lesser morbidity than the traditional osteotomy. The tension band plate is the most recent development in implants used for temporary hemiepiphysiodesis. Our aim was to determine its safety and efficacy in correcting coronal plane deformities around the knee in children younger than 10 years.
MATERIALS AND METHODS: A total of 24 children under the age of 10 were operated for coronal plane deformities around the knee with a single extra periosteal tension band plate and two nonlocking screws. All the children had a pathological deformity for which a detailed preoperative work-up was carried out to ascertain the cause of the deformity and rule out physiological ones. The average age at hemiepiphysiodesis was 5 years 3 months (range: 2 years to 9 years 1 month).
RESULTS: The plates were inserted for an average of 15.625 months (range: 7 months to 29 months). All the patients showed improvement in the mechanical axis. Two patients showed partial correction. Two cases of screw loosening were observed. In the genu valgum group, the tibiofemoral angle improved from a preoperative mean of 19.89° valgus (range: 10° valgus to 40° valgus) to 5.72° valgus (range: 2° varus to 10° valgus). In patients with genu varum the tibiofemoral angle improved from a mean of 28.27° varus (range: 13° varus to 41° varus) to 1.59° valgus (range: 0-8° valgus).
CONCLUSION: Temporary hemiepiphysiodesis through the application of the tension band plate is an effective method to correct coronal plane deformities around the knee with minimal complications. Its ease and accuracy of insertion has extended the indication of temporary hemiepiphysiodesis to patients younger than 10 years and across a wide variety of diagnosis including pathological physis, which were traditionally out of the purview of guided growth.

INTRODUCTION

Pediatric deformity correction has been at the core of the foundation of Orthopedics since the publication of L’Orthopedia by Andry in 1741. Identifying these pathologic deformities and their subsequent management forms an integral part of pediatric orthopedic surgery.

Presence of angular deformities around the knee in children is a common finding including genu valgum and genu varum.1 However, a majority of these deformities are physiologic in nature corresponding to the normal physiologic changes in the alignment of mechanical axis from birth to adolescence.23 Differentiating between these physiologic deformities from pathologic conditions such as Rickets, skeletal dysplasias, etc., is of paramount importance as the majority of the physiological ones correct themselves by adolescence requiring no treatment.4 However, some of these physiologic deformities may persist beyond adolescence warranting orthopedic management. Thus, correct patient selection is important.

Osteotomies have traditionally been the mainstay of treating deformities not only in adults but also in children. These involve extensive soft-tissue dissection, complications of wound closure, infection, delayed union, malunion and prolonged immobilization which increases the morbidity of the patients.567 Guided growth harnesses the plastic nature of the physis to bring about the desired correction required. Being minimally invasive technique with a lesser morbidity than osteotomy,89 Guided growth is an alluring option and has gained acceptance as the preferred primary treatment in pediatric lower limb deformities. Conventionally, temporary hemiepiphysiodesis has been carried out after the physiologic remodeling of the knee has ended. However, neglecting the pathologic deformities at a younger age could worsen the deformity, lead to gait disturbances and affection of the surrounding joints in due course of growth. Early guided growth in pathologic knee deformities brings about a qualitative improvement in the physis of not only the knees but the hips and ankle as well.10 Use of staples have a fear of permanent iatrogenic physeal arrest111213 preventing their use in under the age of eight by most authors.14 Mielke and Stevens in 1996 reported good results with the use of staples in the under 10 age group with no report of a permanent physeal arrest.14 Though several studies have reported application of the tension band plate in a few young patients, none have shown results exclusively in this age group.

We present outcome of the patients who underwent deformity correction through temporary hemiepiphysiodesis employing the tension band principle.

MATERIALS AND METHODS

With prior institutional board review, 29 patients under the age of 10 with a coronal plane deformity around the knee were operated upon from July 2007 to August 2012 at our institute. Twenty four of them were completed plate removal with a followup of at least 1 year after plate removal. The results of three of these children were still pending at the time of data collection and thus were excluded from our study. Two of them had inadequate followup data also warranting exclusion from this study.

All the children were operated with an extra periosteal tension band plate and two nonlocking screws and each deformity was treated with a single plate per physis. Patient selection was done meticulously to confirm the pathology and rule out physiological deformities based on the clinical history, metabolic work-up and radiographic assessment. Full length anterior posterior (AP) weight bearing radiographs of both limbs with the patella facing forwards were taken with a lateral view of the knees as well (preoperatively as well as on followups). Patients were examined for limb length discrepancies, ligamentous laxity and patellar tracking. Detailed visual gait analysis was performed. All the patients were ambulatory. None of the patients had patellar subluxation or dislocation.

We had seven cases of nutritional Rickets, five cases of vitamin D resistant Rickets, four cases of metaphyseal chondrodysplasia, two cases of posttraumatic tibia valga and one each of congenital short femur syndrome, idiopathic genu valgum, achondroplasia, distal femur valgus secondary to proximal tibia chronic osteomyelitis, arthrogryposis with bilateral genu valgum and developmental dysplasia of the hip (DDH) with a unilateral left genu valgum [Table 1].

Table 1

Patient demographics and results

After confirming the pathological nature of the deformity and ruling out a physiological deformity, the parents were counseled regarding the nature of the disease, its progression and the consequence of the deformity on the surrounding joints, ambulation, gait and further development. All these patients had a significant clinical deformity and after a written informed consent, surgical intervention was carried out. Counseling the parents regarding the gradual nature of deformity correction that temporary hemiephysiodesis employs is very important especially amongst the rural population.

Operative procedure

A single plate was applied per physis. Under general anesthesia, tourniquet was applied and a 2 cm incision taken centering over the physis located under a C-arm. A 1.2 mm K wire now passed into the physis under fluoroscopic guidance. Care should be taken to avoid any damage to the physis. The tension band plate (2-hole 4.5 mm titanium plate) now placed extra periosteally and 1.6 mm guide wires introduced into the metaphyseal and the epiphyseal region with care to avoid damaging the periosteum. The plate placed flush to the bone and fixed with 4.5 mm fully threaded self-tapping cannulated screws over the guide wires into the metaphysis and the epiphysis after drilling with a 3.2 mm cannulated drill bit. A gap between the bone and the plate has been known to cause screw breakage.15 The final placement of the plate and the screws is confirmed under the C-arm in AP and lateral views with the plate being in the center on the lateral view to avoid any iatrogenic sagittal plane deformities. Skin was sutured with nonabsorbable sutures.

Though many centers perform surgery on outpatient department basis, we advise admission to our patients for 1-2 days postoperatively for early ambulation and physiotherapy. On the postoperative day 1, mobilization of the knee was started. Early ambulation was encouraged with weight bearing and the child discharged after satisfactory physiotherapy. Full activity is usually gained in 3-4 weeks. These patients were followed every 3 monthly with full length standing AP and lateral radiographs. The radiographs were evaluated by measuring the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), mechanical axis deviation and the tibio-femoral angle. The mechanical axis ratio (MAR) was obtained by measuring the distance of the mechanical axis from the midpoint of the proximal tibial epiphysis and dividing it by the width of the proximal tibial epiphysis.1416 The MAR would eliminate any discrepancy of magnification on radiographs and aid in standardizing the result. Implant removal was carried out when there was no clinically visible deformity and the mechanical axis corrected to zone 1 or with mild overcorrection.141718 Statistical analysis employing the paired t-test was carried out to assess the MAR and the tibiofemoral angles. P < 0.01 was considered to be significant.

The response of the physis varies with age, the nature of the disease, nutrition and is unpredictable. Following implant removal recurrence of the deformity as a result of the rebound phenomenon is very common and many studies do advocate a mild overcorrection into the opposite zone 1 to compensate for the impending rebound.91114161920212223 After removing the plate, 3 monthly followups were carried out until 1 year followed by annual followups. If a rebound was detected, 3 months followups were continued until a decision of resurgery taken. We intend to followup these patients until maturity to determine the incidences of premature physeal closure, limb length discrepancy, rebound phenomenon and other complications.

RESULTS

In all, a total of 24 patients were included in our study. Of which, 11 patients were males and 13 were females. Thirteen of them suffered from genu valgum while the remaining 11 had a genu varum deformity. Sixteen of the children had a bilateral presentation. In all, there were 63 deformities (Femur-34, Tibia-29) in 40 limbs that were operated upon.

The 12 children with Rickets were treated with prior bracing. All of them were given appropriate medical treatment for Rickets, which was continued after surgery. Of the four children with metaphyseal chondrodysplasia, one had undergone bilateral tibial osteotomy. The two cases of posttraumatic tibia valga had received treatment for the fracture in the form of closed reduction and casting. The patient with arthrogryposis had undergone bilateral supracondylar femoral osteotomies for knee fixed flexion deformity and a lateral closing wedge osteotomy for cavus foot. Open reduction of the hip was done for the child with DDH followed by Salter's innominate osteotomy. One patient with a congenital short femur syndrome had undergone lengthening of the femur over an Ilizarov construct 5 years prior.

The average age at surgery was 5 years 3 months (range: 2 years to 9 years 1 month) [Figure 1]. The postimplant removal followup of these patients ranged from 1 to 4 years (mean 21 months). Total followup ranged from 1 year 7 months to 5 years 8 months. The plates were removed after a mean of 15.625 months (range 7-29 months) [Figure 2]. In the genu valgum group, the anatomical tibiofemoral angle improved from a preoperative mean of 19.89° valgus (range 10°-40° valgus) to 5.72° valgus (range 2°-10° valgus) at plate removal. In patients with genu varum the anatomical tibiofemoral angle improved from a mean of 28.27° varus (range 13°-41° varus) to 1.59° valgus (range 0-8° valgus). The MAR improved from a preoperative mean of 0.902-0.177. In the genu valgum group, the MAR improved from 0.753 (range 0.35-1.67) to 0.14 (range 0.01-0.33), while in the genu varum group it changed from 1.02 (range 0.7-1.45) to 0.211 (range 0.05-0.72) both of which were highly significant with P < 0.001 [Tables 2 and 3]. Overall rate of correction was 1.53°/month (below 5 years of age - 1.67°/month, above 5 years of age - 1.39°/month).

Figure 1

Distribution of age at surgery

Figure 2

Duration of implantation of the plate to achieve a neutral mechanical axis, mean being 15.6 months

Table 2

Measurements-mechanical axis ratio and tibiofemoral angle

Table 3

Statistical analysis

All the patients showed improvement in the mechanical axis [Figures 3 and 4]. Twenty one of these patients showed complete correction with the mechanical axis returning into zone 1 or with slight over correction into the opposite zone 1 after a mean of 15.625 months. One case of nutritional Rickets, aged 3 years with a bilateral genu valgum deformity showed over correction to opposite zone 2 in both limbs 15 months after surgery. The preoperative tibiofemoral angle was 22° and 21° for the right and left limbs respectively which progressed to a varus of 2° in both limbs after 15 months. This child had good followup initially but missed followups after 9 months. He reported 6 months later with over correction. The child had no symptoms with a mild clinical varus deformity and did not require further management.

Figure 3

(a) Preoperative radiograph of a 4 year 3 months old case of nutritional rickets and bilateral genu valgum. (b) Postoperative radiograph with plates inserted in bilateral femur and tibia. (c) Neutral mechanical axis 7 months after insertion. (d) Clinical appearance before surgery. (e) Clinical appearance at 7 months after surgery

Figure 4

(a) A 4 year 10 months old boy with a posttraumatic tibia valga with mechanical axis in lateral zone 3. (b) Radiograph at 4 months after plate insertion shows the mechanical axis in lateral zone 2. (c) Radiograph at 12 months after plate insertion showing a neutral mechanical axis. (d) Clinical appearance before surgery. (e) Clinical appearance 12 months after surgery following which the plate was removed

Two patients showed partial correction. Patient no. 2 was a case of nutritional Rickets with bilateral genu valgum with the mechanical axis progressing to zone 2 bilaterally after a followup of 29 months. The other child, a case of vitamin D resistant Rickets and bilateral Genu varum showed partial correction at 12 months followup with the mechanical axis returning to zone 2 in both limbs with no correction seen in last 2 followups. Both these patients improved to normal values of LDFA and MPTA with the deformity at the knee corrected but with a residual bowing of the tibia and femur respectively, subsequently requiring osteotomies.

Two cases of screw loosening were observed. One of them developed loosening at the fifth followup at 15 months but had completed the desired correction and did not require further revision. The other child, a 4-year-old boy with vitamin D resistant Rickets and a unilateral valgus deformity developed loosening of the metaphyseal screw with backing out of the plate 9 months after plate insertion. This was revised with longer screws and the deformity corrected completely 8 months later.

No cases of limb length discrepancy were noted. One case of chronic osteomyelitis of the proximal tibia had developed a compensatory valgus deformity at the distal femur with the femoral physis being intact. The distal femur valgus was corrected by tension band plate application. We also carried out simultaneous lengthening and varus correction of the proximal tibia over an Ilizarov construct. The case of congenital short femur had a preoperative shortening of 3 cm which remained unchanged for 21 months after plate removal.

No cases of screw breakage were seen. None of the cases had any signs of infection postoperatively. During the followup, none of the physis suffered from permanent damage or premature physeal arrest (longest total followup being 68 months). All the cases resumed growth after implant removal. Two patients (1 Rickets + 1 metaphyseal dysplasia) developed a rebound phenomenon and scheduled for resurgery. Mean time for the rebound was found to be 16.33 months after plate removal. However, a longer followup is required to ascertain the actual incidence of this recurrence. None of the 24 patients developed a sagittal plane deformity until last followup.

DISCUSSION

From birth to adolescence, there is a continuous change in the tibiofemoral angle at the knee as part of the physiological evolution of limb alignment. A newborn present with a genu varum of up to 15° followed by a neutral mechanical axis by the age of 12-18 months. By the age of 3-4 years, a maximum genu valgum of up to 12° develops, which gradually settles to a 4-7° of valgus during adolescence corresponding to the adult values.2 However, throughout childhood the mechanical axis remains in the central half of the knee joint (zones +1 and −1 around the midline) in normal subjects despite the above mentioned variations.24 This evolution in limb alignment should always be borne in mind especially while treating deformities in the younger age group to prevent any inadvertent surgery on physiological deformities. Thus, patient selection should be carefully done during the physiologic remodeling phase and a physiologic deformity should be ruled out before a decision for surgery is taken. However, one should keep in mind the possibility of overlap of deformities due to the underlying pathology and the normal physiologic process.

As the deformities around the knee progress, gait disturbances arise which are noticed as soon as the child starts walking. A genu valgum of >10°, leads to a circumducting gait and anterior knee pain.25 A genu varum would cause a lateral thrust, ligamentous laxity and a waddling gait.26 These deformities around the knee have been known to cause precocious osteoarthritis often requiring surgery.27

Apart from the clinical signs and symptoms, it is important to note the effect of these deformities on the malleable physis. Heuter and Volkmann independently studied the effect of compression and tension forces on the physis and the consequent bone remodeling and growth.282930 Excessive and sustained forces on the epiphysis, exert pressure on the mechanotransducer chondrocytes, inhibiting the growth of the physis. Thus, a deformity would undergo progression until the eccentric loading of weight exists on the physis further exacerbating the gait disturbance, pain and ultimately leading to functional disability. Going by the Heuter-Volkmann principle one should be correcting these deformities at the earliest.

However, traditionally, most authors advocate delaying surgery, i.e., temporary hemiepiphysiodesis until 8-10 years of age due to concerns of permanent physeal damage.11121314203132 The factors supporting this thought are a young malleable physis, a pathologically compromised physis and the implants used in hemiepiphysiodesis.

Patients with a pathologic physis (also known as sick physis) including conditions such as Rickets, skeletal dysplasias etc., were also until recently excluded from the purview of temporary hemiepiphysiodesis. The governing ideology was the already compromised physis may not tolerate direct surgical manipulation with the likelihood of a permanent physeal arrest and irreversible damage.20 In the year 2008 Stevens and Klatt published a retrospective review of 14 patients with a pathological physis undergoing temporary hemiepiphysiodesis.20 They showed improvement in not only the limb alignment but also the pathological state of the physis. The explanation being, by eliminating the eccentric loading of the already compromised physis, the recovery occurs faster. They advocated that in due course of time, the pathology at the knees and the malaligned limbs would affect the hips and ankles as well. These patients would later need surgery for the consequent deformities at the ankle and hips as well.33 As the mechanical axis corrected, there was an improvement in appearance and width of not only the physis at the knees but at the hip and ankle as well. Thus, the current trend is to perform a temporary hemiepiphysiodesis at an early age to prevent deterioration of not only the knees but the surrounding joints as well. Studies by Novais and Stevens and Boero et al. show safe implementation of temporary hemiepiphysiodesis in pathologic physis with the preferred implant being a tension band plate and screw construct.2634 However, the rate of correction seen in a pathologic physis would be slower than an idiopathic deformity owing to the slower growth rate in these physis.26 Our cases corrected at an average rate of 1.53°/month.

Staples have been a popular implant in performing temporary hemiepiphysiodesis around the knee since their introduction by Blount and Clarke in 1949.11133536373839404142 Staples work by introducing a rigid fulcrum within the physis. This rigid fulcrum brings about compression of the physis and retards growth in that portion of the physis. Prolonged presence of such a rigid implant around the physis carried the concern of bringing about permanent physeal closure.211121331 In order to avoid such a permanent damage to the physis, temporary hemiepiphysiodesis was not advocated in preadolescent children.

Studies regarding the mechanical and biological responses of the physis to compression, have shown chondrogenesis and provisional calcification to come to a standstill following staple insertion.4344454647 Biopsy specimens have shown disorganized cell columns and metaphyseal tongues of disorganized cartilage and biochemical alteration by radioimmunoassay in presence of staples.34 However all these changes caused by stapling seem to be reversible in nature.1243454647 And most studies advocate removal of these staples within 24 months to resume growth of the physis.143944 Prolonged retention of these staples beyond the stipulated time would raise the chances of physeal damage.

In an article in 1996, Mielke and Stevens have reported a series of 25 patients younger than 10 years who underwent temporary hemiepiphysiodesis.14 The mean age at time of surgery was 6 years and 4 months (ranging from 3 years 6 months to 9 years 11 months). They showed improvement in every case with no instances of a permanent physeal closure or a limb length discrepancy. One staple backed out and one broke while implant removal. However, staples though effective have a number of complications including breakage, extrusion, migration and malposition.203548 There have been reports of inadvertent permanent hemiepiphysiodesis.4950 Migration of these staples increase the frequency of repeat surgery especially in younger patients.19 The prongs of the staples being smooth allow easy extrusion and migration in a predominantly unossified bone in younger patients. In 1998, Métaizeau et al. introduced transphyseal screws to retard growth on one side of the physis.9 This method however has concern of irreversible and complete growth arrest as the transphyseal screws traverse the physis.51

The concept of the tension band plate with two nonlocking screws to bring about temporary hemiepiphysiodesis was introduced by Stevens in 2007 in lieu of the complications of staples. These plates have their center of rotation outside the physis and as the physis grows the screws toggle in the plate and pivot in the bone bringing about gradual correction.1931 Thus, unlike the staples which bracket the physis this system of plate and screws does not compress the physis52 reducing the concern of permanent physeal damage.142034 Stevens stated that this system brought about a more rapid correction than staples.19 Stevens and Klatt in 2008 reported a lower complication rate than with staples.20 Several studies have shown a favorable result with the use of this technique.192031525354

In contrast, several comparative studies between hemiepiphyseal stapling and tension band plate hemiepiphysiodesis have shown no significant difference in the rate of deformity correction.52555657 The complication rates too have been reported to be the same.5257 A recent randomized clinical trial by Gottliebsen et al. also found no difference in treatment times in patients inserted with either the tension band plate or the staple.58 With regards to surgery time, Jelinek et al. noted that the time required for either insertion or removal of the tension band plate to be significantly shorter than staples.57 Furthermore, the insertion of the tension band plate is far more precise and controlled preventing any accidental insertion of the screws in the physis.52 This scenario is important in cases of skeletal dysplasias due to the altered anatomy in the epiphysiometaphyseal region. Several studies now advocate using this system safely in younger patients with a pathological physis.263134 In our study, we applied the tension band plate to patients as young as 2 years with no cases of a permanent physeal closure or limb length discrepancy with improvement in every case. We had a success rate of 91.66%, similar to that of other studies.19203152

One concern of these plates is the breakage of the metaphyseal screw. Burghardt et al. reviewed 65 patients with a mechanical failure of this system.15 In all these cases, the screws had broken and not the plate. Nearly 93% of these patients were either obese, overweight or morbidly obese (according to NIH). Schroerlucke et al. in their study have reported breakage of the metaphyseal screws in 8 of the 31 patients operated upon all of which suffered from Blounts disease.54 Until date, implant failure has only been reported in patients of Blounts which is rare in India.5 None of the patients we operated upon were obese and none of them suffered from screw breakage or implant failure. We propose that this system is well suited for the Indian children. In cases of obesity, it is suggested to use two parallel such tension band plates with solid screws to minimize breakage.15

Cases of staple migration have been reported in the past but none for the tension band plate until Oda and Thacker in 2011 reported a case in which a tension band plate applied to the anterior distal tibia was pulled through the physis leading to the creation of an anterior physeal bar in a 9-year-old female.48 However, this is an isolated case and no such other cases have been reported. Placing the screws equidistant from the physis would prevent such an occurrence.

Ambiguity still persists regarding the timing of implant removal. Early removal would lead to undercorrection while delaying it would cause overcorrection. One should also bear in mind the rebound phenomenon seen following plate removal. Thus, most studies advocate an overcorrection of 5° to take into account the rebound phenomenon. Two of our patients suffered the rebound phenomenon after an average of 16.33 months and required repeat surgery. Thus, the response of the physis may be unpredictable at times and with the possibility of under correction and rebound phenomenon, one may have to repeat this procedure multiple times to maintain a neutral mechanical axis in the growing child. Temporary hemiepiphysiodesis being minimally invasive, it is the least morbid option in correcting angular deformities around the knees and can be repeated as required. It has thus become safer to guide growth in younger preadolescent patients with the advent of the tension band plate [Figure 5].

Figure 5

Guide to guided growth - flow chart depicting the guidelines for temporary hemiepiphysiodesis

Finally, an important aspect is counseling of the parents. Compliance may be a problem as no immediate result is obtained following surgery. Parents should be counseled regarding the gradual nature of deformity correction and that it may take as long as 1.5-2 years for the deformity to correct. Followup at regular intervals, preferably every 3 months is advised to prevent overcorrection and early detection of any complication.

CONCLUSION

Temporary hemiepiphysiodesis through application of the tension band plate is an effective method to correct coronal plane deformities around the knee with minimal complications. Its ease and accuracy of insertion has extended the indication of temporary hemiepiphysiodesis to patients younger than 10 years and across a wide variety of diagnosis including pathological physis which were traditionally out of purview of guided growth. It carries a reduced risk of physeal damage when compared to other implants and the procedure can safely be repeated in cases of rebound with minimal morbidity.