TREATMENT OF ADOLESCENT BLOUNT'S DISEASE USING THE ILIZAROV TECHNIQUE

DEBORAH F. BELL, MD

The cause of adolescent Blount's disease is obscure, but the disorder is often associated with obesity. The treatment of the resultant varus deformity of the limb may also involve equalization of limb lengths as well as addressing any existing femoral deformity. The Ilizarov technique is ideally suited for correction of deformity as well as lengthening if required. It allows adjustment of limb alignment in the postoperative period, if necessary, to achieve a perfect mechanical axis. Fixation of the tibia is achieved through four proximal and four distal wires affixed to rings and tensioned. Half pin modifications may also be used. Our series of Blount's corrections in 14 limbs achieved restoration of length and alignment in all cases with an average treatment time of 10 weeks. As opposed to reports of other techniques, there were no nerve palsies or compartment syndromes in these patients. The only complications were pin site infection and repeat osteotomy due to premature healing in one patient. KEY WORDS: tibia vara, Blount's disease, deformity

Blount's disease, or tibia vara, is an uncommon devel- opmental condition characterized by genu varum. In- fantile and adolescent forms of the disease are recog- nized, with the former having its onset between the ages of 1 and 5 and the latter after ages 6 to 8. Erlacher is credited with the initial clinical description of a patient with this condition. 1 BIount published the first large se- ries and was the first to recognize the adolescent form in 25% of his original patients. 2 Significant controversy ex- ists as to the epidemiology and cause of the adolescent form of the disease. Nevertheless, review of the litera- ture has yielded a certain consensus.

Patients are frequently obese. Dietz noticed marked obesity in over two thirds of reported patients who were studied. 3 Additionally, a high incidence in blacks has been noted regardless of geographic origin. Langenski- old noted some hereditary and familial factors. Gross pathology demonstrates fissures and clefts within the physeal cartilage. An epiphyseal-metaphyseal osseous bar has been observed in some patients. The absence of such a bar may represent a different stage of the same disease. Beaking of the medial tibial metaphysis is usu- ally observed, but is not as prominent as in the infantile form. Histopathology of the adolescent forms shows ar- eas of fibrovascular and cartilaginous repair with disor- dered cartilage columns and large cartilaginous masses extending into the surrounding bone. 3"4

In contrast to the infantile form, little has been written about the pathogenesis of adolescent Blount's disease. Most reported patients exhibit physiologic varus that sub- sequently improves and later develops into recurrent

From the Department of Orthopaedic Surgery, Children's Hospital of Michigan, Detroit, MI.

Address reprint requests to Deborah F. Bell, MD, Department of Orthopaedic Surgery, Children's Hospital of Michigan, 3901 Beau- bien Blvd, Detroit, MI 48201.

Copyright �9 1993 by W. B. Saunders Company 1048-6666/93/0302-0008505.00/0

varus, either unilaterally or bilaterally, s Wenger et al postulated that increased weight combined with varus alignment led to a cycle of medial physeal growth sup- pression, increased varus, and further growth inhibi- tion. 6 A mechanical pathogenesis is also supported by Beskin and Thompson, 7"9 who suggested that restoration of the mechanical axis would solve the problem defini- tively."

The adolescent form has been reported as unilateral in as many as 90% of cases. Thompson's series reported bilaterality in 46%, particularly in female patients. 8 Varus deformity is often less than 20 ~ and relative short- ening of the leg may be as much as 4 cm. Medial tibial torsion is often absent. The natural history of adoles- cent Blount's disease is typically much less severe than the infantile form because of the limited remaining skel- etal growth. Surgery is indicated for progressive de- formity or for intractable patient discomfort. Operative intervention is also indicated to prevent subsequent de- generative changes of the medial knee compartment. Reports of surgical treatment include analysis of a variety of osteotomies of the proximal tibia. The need for over- correction at the time of surgery is controversial but is related to the severity of the medial tibial physeal involve- ment as well as the remaining skeletal growth. Com- mon to all reported series is a surprisingly low percentage (average 56%; range 44% to 65%) of good results by Schoenecker's criteria. 1~ Schoenecker's grading system defines a good result as a pain-free patient with less than 5 ~ difference in tibial/femoral angle. A fair result has the same radiographic criteria, but the patient experiences occasional knee pain. A poor result is characterized by restricting pain, more than a 5 ~ difference in tibial femoral angle and joint space incongruity or degeneration. The complications of residual limb length inequality, averag- ing 2.5 cm (range 1 to 4 cm), residual varus deformity, peroneal nerve palsy, and compartment syndrome are common to previous reports of conventional tibial oste- otomyfl 1A2

Operative Techniques in Orthopaedics, Vol 3, No 2 (April), 1993: pp 149-155 149

The Ilizarov technique of circular external fixation pro- vides the ability to simultaneously correct angular defor- mity, length inequality, and rotation where necessary and is an appealing alternative to conventional osteotomy in the treatment of Blount's disease. The Ilizarov tech- nique further allows the surgeon to adjust the degree of valgus correction once the patient is ambulatory and weight bearing in order to avoid the potential of under- correction or overcorrection. Once correction of the de- formity has occurred, additional lengthening and rotation correction can be performed.

TECHNIQUE

Proper preoperative planning is essential to the accurate application of this technique. The patient must be care- fully examined to assess ligamentous stability both in full- knee extension and in flexion. The patient should be examined in a prone thigh-foot angle to assess clinical rotation. The most common pitfall is misleading radio- graphs. A standing orthoroentgenogram should be ob- tained with the patient's pelvis level, using a lift under- neath the short limb if necessary. The patellae, not the feet, should point forward to allow for measurement of the true angular deformity in the proximal tibia and the distal femur. 13 Commonly, obese patients are unable to approximate their thighs in a stance (Fig 1). This factor, in addition to severe varus deformity, causes them to externally rotate the hip and minimize the radiographic appearance of varus of the proximal tibia. This is often compounded by the presence of internal rotation defor- mity. A lateral radiograph should be obtained to assure the presence or absence of the normal sagittal contour of the proximal tibia.

The patient should be measured in the outpatient set- ting for the appropriate ring size. The large size of some of these patients may necessitate special ring sizes. Allow for a minimum of two to three finger breadths between the inner aspect of the leg and the largest mid- calf circumference. Initially the proximal ring construct will be oriented parallel to the knee joint and thus will not be perpendicular to the limb. It is prudent to err on the side of the next larger ring rather than the smaller ring size to accommodate for deformity and postoperative swelling.

Once adequate radiographs have been obtained and the ring size selected, the apparatus may be constructed preoperatively. Two blocks of fixation are necessary: one must be as proximal as possible but distal to the tibial physis and usually consists of a single ring or two rings that are closely spaced. The second fixation point is a two-ring construct, separated by threaded rods, and linked together to create the distal block of fixation. Each "block" of fixation will be fixed to the bone by either four 1.8-mm wires or by a combination of wires and half pins.

The ideal technique for correction of angular deformity requires correction at the apex of the true deformity. In Blount's disease, as with other physeal derangements such as skeletal dysplasias and metabolic bone disease, correction at the apex of deformity would require four

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Fig 1. Patient's obesity plus medial tibial rotation results in externally rotated stance that will lead to misleading radio- graphs. Note laterally directed patellae.

pins in the epiphysis and physeal distraction (chondrodi- atasis). This technique has lost popularity for two rea- sons: (1) it has resulted in premature physeal closure, and (2) pins are close to or actually intra-articular and are a source of potential joint sepsis. In order to avoid these complications, the deformity is corrected by placing the pins distal to the growth plate with a planned osteotomy distal to the pin fixation. By constructing an apparatus with a hinge placement at the level of the physis (ie, above the most proximal ring) (Fig 2), the distal osteoto- my will result in accurate correction by causing medial translation of the distal fragment and restoration of the mechanical axis of the limb.

The entire frame can be constructed preoperatively with the hinges locked into position in order to minimize the intraoperative time devoted to the apparatus. Min- imal adjustments are needed during surgery. The pa- tient is positioned supine on a radiolucent operating table with the feet at the end of the table. This will allow placement of the image intensifier at the foot of the op- erating room table and patient access to the medial and lateral side of the leg without interference from the image intensifier (Fig 3).

The "traditional" Ilizarov wire configuration consists of four 1.5- or 1.8-ram wires attached to each block of fixa- tion. The wire diameter is dependent on patient size,

150 DEBORAH F. BELL

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Fig 2. (A) Preconstructed apparatus based on ra- diograph in (B). Note the fact that the apparatus "mimics" the tibial defor- mity, and that the hinge placement is proximal to the top ring.

Fig 3. The patient must be positioned at the end of the ra- diolucent table with the patella pointing up.

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Fig 4. The first wire is placed parallel to the joint line.

BLOUNT'S DISEASE TREATMENT BY THE ILIZAROV TECHNIQUE 151

Fig 5. The preconstructed apparatus is then slipped over the leg and the first wire is tensioned and affixed to the frame,

the larger diameter providing more stability. Two wires placed proximally and distally are stopper wires that are used as a fulcrum for angular correction. After the limb is prepared and draped, an osteotomy of the fibula is performed, and this incision is closed. A stopper wire is placed transversely in the coronal plane of the proximal tibia from medial to lateral parallel with the joint line or lateral physis (Fig 4). The preconstructed apparatus is slipped over the leg, and the wire is affixed to the ring and tensioned to 130 kg (Fig 5). The second wire is also a stopper wire placed transversely from medial to lateral on the most distal ring. It is positioned proximal to the distal tibial growth plate and is perpendicular to the distal tibial shaft. The next two wires are stopper wires placed transversely from lateral to medial. One is affixed to the proximal construct 0.5 to 1.0 cm distal to the first wire, and the other wire is attached to the proximal ring of the distal "block." The next four wires are plain wires. Tibial/fibular wires are inserted proximally and distally to transfix both the fibula and tibia and are inserted from the lateral side. The final two wires are inserted parallel to the medial face of the tibia from anterolateral to postero- medial and are then tensioned and tightened to their re- spective rings.

Half pin alternatives function well if one chooses to eliminate several wires and uses half pins in their place. The tibial/fibular wires could be replaced by a half pin predrilled over a wire in a retrograde fashion. The me- dial face wires can be replaced as well by anteroposterior (AP) directed half pins (Fig 6).

After secure bone fixation has been achieved, the con- necting bolts and distraction rod are removed. A 1.5- to 2-cm longitudinal incision is made over the proximal tib- ial crest just distal to the most distal of the proximal wires or pins. The approach requires minimal periosteal dis-

Fig 6. Completed apparatus shown in Fig 2. Note anteropos- terior half pins on the most proximal and distal map,

Fig 7. Radiographic confirmation of completed osteotomy.

section and a V2-in osteotome to broach the anterior tibia cortex. Thereafter, a Va-in osteotome is used to transect the medial and lateral cortices as far as possible. The osteotomy is completed by externally rotating the distal fragment relative to the proximal fragment. This is con- firmed by image intensification, and the wound is closed (Fig 7). The hinges and distraction apparatus are then reconnected to the fixator.

152 DEBORAH F. BELL

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Fig 8. (A) Preoperative pho to and (B) rad io- graphs of an obese black 14-year-old boy with ado- lescent tibia vara. Note the compensatory distal femoral valgus deformi- ty. (C) Weight bearing ra- diograph following acute correction of the distal femoral deformity using an Orthofix external fix- ator and gradual correc- tion of the tibial deformi- ty. (D) Final radiograph and (E) photo following apparatus removal.

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BLOUNT'S DISEASE TREATMENT BY THE ILIZAROV TECHNIQUE 153

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Fig 9. (A) Photo and (B) radiograph of morbidly obese white boy with a 30 = proximal tibial varus. (C) Appearance before gradual deformity correc- t ion. Note the ear l ie r hinge construct distal to the top ring. (D) Radio- graph demonstrating res- toration of the knee joint parallel to the floor. Note, however, the mild medial translation of the tibial di- aphysis due to the hinge placement at the osteoto- my level rather than at the apex of the deformity. (E) Final appearance.

154 DEBORAH F. BELL

POSTOPERATIVE MANAGEMENT

Distraction is initiated 3 days postoperat ively in pat ients requit ing only angular correction and 5 days postopera- tively in those unde rgo ing s imul taneous lengthening. Distraction shou ld proceed at no more than 1 mm daily on the medial " o p e n i n g " cortex. Conventional ly, this is done in four increments daily. Use of the Autogenesis autodistractor (Anchorage, Alaska) allows compute r ized distraction at u p to 1,440 increments daily.

Weight bear ing as tolerated is encouraged at all times. Once the pat ient is ambulatory, t rea tment cont inues as an outpat ient wi th office visits every 2 to 3 weeks dur ing the distraction phase and every 4 to 6 weeks dur ing the consolidat ion per iod. Repeat s tanding weight-bear ing o r thoroen tgenograms confirm restorat ion of the mechan- ical axis. W h e n correction is achieved, all rings should be parallel to one another . If addit ional lengthening is required, straight rods can be placed, and lengthening can be cont inued. Rotational correction should be ob- tained gradual ly as the last stage of correction.

Healing is sugges ted by visible cortices on three of four bone surfaces on the AP and lateral radiographs. Once radiographic consolidat ion appears solid, one can loosen the nuts and have the patient walk in the office to deter- mine if pain deve lops with weight beating. The nuts are re t ightened, and appara tus removal can be scheduled.

RESULTS

The Ilizarov technique has been appl ied to 14 limbs in eight male a nd two female pa t ien ts wi th ado lescen t Blount's disease f rom 1988 to 1991. The average age at surgery was 12, wi th a range of 9 to 17 years. All but two patients were black, and all but one were obese. Preoperat ive deformi ty ranged from 14 ~ to 55 ~ of tibial anatomic varus. Two patients also exhibited distal fem- oral valgus deformit ies that were corrected at the t ime of surgery (Fig 8). Complete correction of deformity was achieved in all pat ients with restorat ion of the mechanical axis. In the au thor ' s early experience, it was not appre- ciated that a s imple metaphyseal opening correction re- suited in "lateral izat ion" of the tibial shaft with a slight disturbance in the mechanical axis (Fig 9). The use of juxta-articular hinges has solved this problem and allows more accurate correction of deformity. The average t ime in the fixator was 10 weeks (range, 7 to 16 weeks) includ- ing the dis tract ion and consol idat ion period. There were no nerve palsies or compar tmen t syndromes . The only complicat ions were pin site infections requiring oral antibiotics and the need for a repeat os teo tomy in one patient due to p remature consolidation.

CONCLUSION

The Ilizarov technique of circular external fixation wi th either t ransosseous wires and/or half pin fixation affords excellent gradual correction of all deformities associated with Blount 's disease. Despi te the inconvenience of an external fixator, it can be appl ied to a limb of virtually any size thus eliminating the potential problems of internal fixation and casts in obese patients. It is stable with full weight bearing and allows bo th knee and ankle mot ion dur ing t reatment as well as shower ing and pool use. The additional ability to adjust the am oun t of correct ion once the patient is fully weight bearing avoids significant overcorrec t ion or unde rco r r ec t ion of deformi ty . The gradual incremental distract ion rather than acute correc- tion of deformity may be an impor tan t factor in avoiding peroneal nerve palsy and compar tmen t syndrome . In conclusion this technique is an excellent alternative to convent ional os teo tomy for the t reatment of adolescent Blount 's disease.

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15. Loder RT, Schaffer JJ, Bardenstein MB: Late onset tibia vara. J Pe- diatr Orthop 11:162-167, 1991

BLOUNT'S DISEASE TREATMENT BY THE ILIZAROV TECHNIQUE 155