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Journal of Pediatric Orthopaedics B:
doi: 10.1097/BPB.0b013e32834de542
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Surgical management of long bone pseudarthrosis with severe limb length discrepancy in osteogenesis imperfecta

To, Michael; Gupta, Vikas; Chow, Wang

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Department of Orthopaedics & Traumatology, The Duchess of Kent Children’s Hospital, The University of Hong Kong, Hong Kong

Correspondence to Dr Wang Chow, MD, Department of Orthopaedics & Traumatology, Duchess of Kent Children Hospital, 12 Sandy Bay Road, Pokfulam, Hong Kong Tel: +852 29 740 283; fax: +852 29 740 621; e-mail: wchowa@hku.hk

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Abstract

We report a three-stage approach in managing an 18-year-old boy with osteogenesis imperfecta who had pseudarthrosis of the left femur with 150° anterior angulation and 9.5 cm shortening. Severe long bone deformity and pseudarthrosis in osteogenesis imperfecta are difficult to manage because of the relative shortening of the surrounding soft tissue and bone fragility. Our staged approach included excision of the pseudarthrosis, gradual soft tissue lengthening by external fixator, and a modified Sofield–Millar operation, to achieve union, deformity, and limb length correction without compromising much of the bone length. The patient was able to walk with support within 3 months and independently at 1 year. In this report, the management of the nonunion in osteogenesis imperfecta is discussed, with a focus on its difficulties and the management principles.

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Introduction

Osteogenesis imperfecta is a genetic disorder in which there is a defect in the production of type I collagen, resulting in bone fragility. Patients usually have repeated fractures since childhood and have multiple deformities in the limbs as well as in the spine. The disease could be very debilitating to the patients because of the bone fragility and deformity. The advances in medicine have largely transformed the management of osteogenesis imperfecta these days and patients can now live more independently. The use of bisphosphonates has been shown to improve the bone mineral density 1 and also reduce the chances of fractures 2. With improved surgical techniques 3 and better implant design, for example, telescoping rods 4,5, the long bone deformities can be better corrected and maintained in a growing child.

The incidence of osteogenesis imperfecta is uncertain. The population frequency was estimated to be about 2.35–4.7 per 100 000 6. Because of bone fragility, fracture is very common in childhood. However, the occurrence of fracture tends to decrease with age. It is believed that most of the fractures will heal if adequate treatment is provided and nonunion is rare. Gamble et al. 7 identified 12 nonunions in 10 patients from a population of 52 osteogenesis imperfecta patients in a 10-year review. Although the number of nonunion seemed to be quite high, the actual incidence of nonunion should be much less when the total number of fractures that occurred in these patients were considered. However, when nonunion develops, it can be difficult to manage, especially in gap nonunions 8. We present this case report to discuss the treatment principles of long bone fracture nonunion with concomitant complicated deformity and shortening.

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Case report

We report on an 18-year-old boy with osteogenesis imperfecta who had a history of repeated limb fracture since early childhood. According to his caretakers, he had multiple long bone fractures involving the bilateral femurs, tibia, and humeri in the first decade of life. All the fractures were treated by traditional medicine and plywood splints. They all united, except for the left femoral fracture, which developed into pseudarthrosis. The left femoral fracture occurred at the age of eight. However, it failed to unite and, since then, he has been walking with a stick. The boy resides in the rural area of Mainland China and has to walk a long distance everyday to school. He noticed increased instability in the left lower limb and discomfort after walking long distances.

Apart from the characteristic facial features of osteogenesis imperfecta, he was relatively short for his age. The boy had an anterior bowing in the left thigh with marked shortening (Fig. 1). He also walked with a left tiptoeing gait. The anterior bump over the left proximal thigh was mobile during walking. There was no local tenderness at the bump and there was marked leg length discrepancy, with the left lower limb being shorter. The discrepancy was 9.5 cm on standing and 7.5 cm when lying down, mainly caused by femoral shortening. There was a 20° left hip fixed flexion contracture. Both active and passive left hip flexions were up to 110°. The corresponding knee movement was from 30° recurvatum to 100° of flexion. The left ankle was plantigrade, with the knee extended.

Fig. 1
Fig. 1
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The radiographs of the left femur showed a pseudarthrosis at the proximal third of the left femur with 150° of anterior angular deformity (Fig. 2). There was an associated bowing over the distal third of the femur, along with mild anterior bowing of the left tibia.

Fig. 2
Fig. 2
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The limb length discrepancy was mainly caused by the pseudarthrosis as well as the deformity of the left femur. On comparing the bone length of the left and right femurs, the discrepancy was less than 2 cm. Hence, the limb length inequality could be theoretically improved by correcting the deformity alone. However, with his long-standing deformity in the left femur, the neurovascular structures as well as the surrounding soft tissue were significantly shortened and contracted. Hence, any acute lengthening of the soft tissue would place these structures under significant tension. To overcome this, a large wedge excision of the femur at the deformity is needed in order to realign the bone without causing tension to the surrounding neurovascular structure. The disadvantage of this approach is that there may be further shortening of the bone and limb length discrepancy that cannot be corrected. The pseudarthrosis also caused significant difficulty in correction of the deformity. Although pseudarthrosis was slightly mobile, it was filled with fibrous tissue. Such marked anterior angulation produced by the pseudarthrosis could not possibly be straightened out by distraction alone. Finally, bone fragility is also an important consideration that needs to be dealt with in deformity correction. Stable and rigid fixation is not easily achieved in osteogenesis imperfecta because of bone fragility. The canal size is also very narrow at the pseudarthrosis. All these will limit the choice of implants for the fixation.

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Multiple-staged surgery

The surgical intervention was divided into three parts. In the first stage, soft tissue release at the proximal thigh and excision of the pseudarthrosis were achieved. The pseudarthrosis of the left femur was exposed through the lateral approach and about 1 cm of bone was excised till healthy bleeding was achieved (Fig. 3a). The excision of the pseudarthrosis also helped to correct the 150° anterior angular deformity in the femur. The left hip adductor and tensor fascia lata were very tight due to long-standing deformity and they were released to improve the mobility of the proximal segment of the left femur in order to reduce the tension during distraction. An Ilizarov external fixator was applied with proximal pins in the ilium and at the greater trochanter and distally at the supracondylar area of the femur (Fig. 3b). The iliotibial band was released to facilitate subsequent distraction of the soft tissue in the thigh.

Fig. 3
Fig. 3
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In the second stage, the soft tissue in the thigh was gradually lengthened using an external fixator. The distraction started on day 1 after the operation at a rate of 1.5 mm/day. After 6 weeks, the thigh length had largely improved and the bone segments were better aligned. The distal fixation of the Ilizarov fixator was advanced to the proximal tibia to provide a crossed knee external fixation construct about 1 week before the subsequent femoral osteotomy. This allowed the pin tract at the distal femur to heal completely before the subsequent surgery. This helped to reduce infection related to the pin tract. While waiting for the pin tract to heal, the thigh was further distracted. However, we had stop before full correction of the limb length could be achieved because he started to complain of numbness at the dorsal aspect of the first web space of the foot (area of the deep peroneal nerve). The leg length discrepancy was reduced from 7.5 (predistraction) to 2.5 cm (postdistraction) when measured in a supine position.

In the final stage, the Ilizarov external fixator was removed and a modified Sofield–Millar operation was performed according to Li et al. 3 (Fig. 4a). The number of osteotomies was kept minimal and the periosteum was carefully preserved. This helped improve the bone healing and reduced bone resorption. Apart from the osteotomy site for the excision of the pseudarthrosis, three additional osteotomies were needed at the proximal, middle, and distal parts of the femur to correct the anterior bowing. There was considerable difficulty in passing the Rush pin into the femur, especially at the site of the pseudarthrosis, due to the very limited canal size. A drill was used to open up the canal before a Rush pin could be inserted. The femur was stabilized with one 4.7 mm Rush pin. The limb was protected in a hip spica for 6 weeks (Fig. 4b and c).

Fig. 4
Fig. 4
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After 6 weeks of immobilization in hip spica, radiographs showed satisfactory healing at the osteotomy sites. The hip spica was removed and radiographs confirmed union of the osteotomies (Fig. 5a). There was a residual shortening of 2.5 cm in the left femur. The patient was mobilized on a long leg brace with toe touch walking and shoe raise at the initial phase of the rehabilitation. He could walk with one elbow crutch at 3 months postoperatively. At the 1-year postoperative follow-up, the radiograph showed good bone union without resorption (Fig. 5b). He could stand and walk without support. There was no fixed flexion contracture at the left hip and both active and passive flexion could reach 120°. The range of motion of the left knee was 10° recurvatum – 130° flexion and the left ankle remained plantegrade with the knee in extension (Fig. 6).

Fig. 5
Fig. 5
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Fig. 6
Fig. 6
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Discussion

Osteogenesis imperfecta is one of the most common inherited connective tissue disorders. It is characterized by increased bone fragility, resulting in multiple fractures of the long bones, often uniting in marked deformity. Sillence published his classification in 1978 9 and it is still used commonly nowadays. The classification is based on the multiple clinical, genetic, and radiologic features. Our patient likely has Type IV osteogenesis imperfecta because of a long history of repeated bone fractures since childhood, short stature, and long bone deformities. Type IV is quite variable in the severity of fractures. It varies from relatively few fractures like in Type I to more severe forms like in Type III. However, most children with Type IV osteogenesis imperfecta will have a short stature as in the case of our patient.

Our patient has had multiple fractures since early childhood but all of them healed uneventfully, except for the left femoral fracture. Gamble et al. 7 reported 12 nonunions in 10 patients in their study of 52 children with osteogenesis imperfecta. Most of their nonunions were associated with repeated fractures at a progressively deforming site. Agarwal and Joseph 8 reported nine nonunions in eight patients, of which four occurred following osteotomy and intramedullary rodding. Not all the nonunions could achieve union after a surgical intervention, and the authors commented that gap nonunions are very difficult to treat in osteogenesis imperfecta.

The main objectives in managing our patient were to (a) correct the marked deformity, (b) improve limb length inequality, and (c) achieve union at the pseudarthrosis in the bone with severe fragility. The long bone bowing is induced by repeated fractures, coupled with deforming muscular forces in the fragile skeleton. The bowing deformity per se can also result in repeated fractures. We believe that by simply managing the nonunion without correcting the deformity, the malalignment will still place the femur under tremendous stress at the deformity. Even if union is achieved, refracture is very likely once the patient starts to walk. Therefore, it was important in our patient to correct the malalignment of the femur, achieve union at the pseudarthrosis, and equalize the limb length discrepancy.

Our preoperative assessment has shown that correcting the deformity alone could minimize the limb length discrepancy. Hence, there is no need to perform bone lengthening to correct the limb length. Because of his long-standing deformities, the surrounding soft tissue could not possibly tolerate acute lengthening of 7.5 cm. We chose gradual lengthening of the thigh after excising the pseudarthrosis to minimize the potential complication of neurovascular structures. We wished to provide adequate time for the neurovascular structures as well as the surrounding soft tissue to adapt to the new length.

Ilizarov external fixations have been successfully used in correcting the long bone deformity in young adults with osteogenesis imperfecta 10,11. For our patient, the Ilizarov external fixator was used for soft tissue distraction after the excision of the pseudarthrosis and surrounding soft tissue release. This helps to offset the shortening from 7.5 to 2.5 cm. The rate of distraction was set to 1.5 mm/day because it was only used for soft tissue distraction. The gradual distraction also helps to realign the long bone between the proximal and the distal segments and facilitates the subsequent osteotomies and nail insertion. However, there is always a risk of infection after conversion of external fixation to intramedullary nailing when the external fixators have been applied for more than 2 weeks 12,13. We do worry about pin tract infection that can potentially complicate the subsequent surgery. Therefore, the distal fixation of the Ilizarov fixator is moved distal to the proximal tibia and the pin tracts in the distal femur are allowed to heal completely before the modified Sofield–Millar operation. For the entire multistaged procedure, we only administered prophylactic antibiotics (1 g intravenous cefazolin) when we excised the pseudarthrosis and applied the external fixator; transferred the distal fixation of the Ilizarov fixator to the proximal tibia; and performed a modified Sofield–Millar operation. We did not administer any routine antibiotics after the surgery prophylactically. Pin tract infection is common in patients treated by external fixators 14. The infection rate can be quite variable depending on the types of external fixation used, and ring fixators were found to have lower infection rates than unilateral fixators and hybrid fixators 15. Our patient developed only very mild pin tract infection, which was adequately treated by dressing and antibiotics.

Gamble et al. 7 and Agarwal et al. 8 used bone graft to treat the nonunion in osteogenesis imperfecta patients. However, we did not place any bone graft at the site of the pseudarthrosis after its excision. We believe that, in our case, the pseudarthrosis was caused by mechanical instability and severe malalignment. Therefore, with adequate stability provided after the excision of the pseudarthrosis and deformity correction, the osteotomy sites united uneventfully.

Complications related to limb lengthening include muscle contractures, joint instability, deformities, neurovascular injuries, and infection 14,16,17. Antoci et al. 18 showed that these complications and pitfalls correlated well with the lengthening percentage that is, the distraction regenerate length divided by the prelengthening bone segment length multiplied by 100%. Although in our patient the bone length of the femur remained unchanged during the distraction, the thigh including the neurovascular structures was lengthened. Our patient developed numbness of the left foot along the deep peroneal nerve distribution when the length gain was over 40% of the prelengthened thigh. In retrospect, it may be possible to avoid this by reducing the distraction rate when the lengthening has reached over 30%.

The classical Sofield–Millar operation in correcting the long bone deformities involves multiple osteotomies and extensive periosteum stripping. This will devascularize the intercalary bone fragment. Li et al. 3 and Abulsaad 19 performed a modified Sofield–Millar operation to address this problem. In the modified approach, the osteotomies are carried out at the most appropriate site as confirmed by the image intensifier. The number of osteotomies is kept minimal and the periosteum is preserved as much as possible to facilitate healing of the bone. This is shown to be better than the classical Sofield–Millar operation in bone healing and in preventing bone resorption. An intramedullary rod is preferred over plating in the fixation of the osteotomies because of its load-sharing property. Bone plating in patients with osteogenesis imperfecta has been studied and it was shown to result in several complications due to metal failure and re-fracture 20. An intramedullary rod is considered to be the treatment of choice in patients with osteogenesis imperfecta.

The drawback of this case report is that the follow-up time was only 1 year. However, in managing pseudarthrosis of the femur, the primary objective is to achieve solid union at the pseudarthrosis so that the patient is able to walk normally. Using this multistaged approach, solid union at the pseudarthrosis and normal walking were achieved within 1 year with relatively minimal complications. We believe that it is an effective and safe method in managing patients with marked limb deformity, limb length inequality, and pseudarthrosis. To manage osteogenesis imperfecta, we should select patients with relatively good bone quality in order to minimize complications like failure of the external fixators. We should also prepare the patients psychologically for this lengthy multistaged procedure. Furthermore, proper protective bracing and rehabilitation should be tailor-made for patients with osteogenesis imperfecta to prevent fractures because of bone fragility, especially after prolonged immobilization.

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Conclusion

It is difficult to manage fracture nonunion in patients with osteogenesis imperfecta in particular those with significant deformity and shortening. We advocate the use of staged surgery to correct the deformities, minimize limb length discrepancy, and achieve union at the pseudarthrosis. Stress fracture at the site of the deformity is common in osteogenesis imperfecta. Hence, deformity correction is considered essential to achieve union and in preventing re-fracture. In order to prevent delayed union or nonunion of the osteotomies, a modified Sofield–Millar operation should be used to minimize the number of osteotomies and to preserve the periosteum. Finally, an intramedullary rod is considered more superior than bone plating to provide stable fixation and fewer complications.

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Acknowledgements
Conflicts of interest

No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the patients of this article.

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References

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Keywords:

femur; limb length discrepancy; osteogenesis imperfecta; pseudarthrosis

© 2013 Lippincott Williams & Wilkins, Inc.

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