Paget's disease is a localized disorder marked by increased bone turnover.10 It usually is associated with deformities of the affected bone and degeneration (osteoarthrosis) in adjacent joints.4,7 Patients with severe osteoarthrosis may be candidates for arthroplasty.3,12,13 However, the complexity of the deformity sometimes makes insertion of a prosthesis difficult, and component malpositioning may lead to early prosthetic failure.3,11-13 Therefore, deformity correction before joint arthroplasty is advantageous for treatment of osteoarthrosis.
Corrective osteotomy is a good alternative to long-bone reconstruction, leading to possible prosthetic insertion and restoration of physiologic alignment of the lower limb. However, patients with Paget's disease sometimes have a limb-length discrepancy because of a deformed and shortened bone. Distraction osteogenesis has been advocated by some authors,1,5 because it enables simultaneous correction of the deformity and shortening.
We present the case of a patient with Paget's disease in which the deformity and the limb-length discrepancy were treated by distraction osteogenesis.
A 57-year-old woman was diagnosed with Paget's disease by bone biopsy done when she was 54 years old. She had severe deformities with shortening of her right femur. Her serum alkaline phosphatase level was elevated and she had diabetes mellitus. The patient took bisphosphonate orally. Deformity in the distal femur and limb-length discrepancy gradually developed (Fig 1). The patient limped and experienced pain in the adjacent knee and lower back. At the time of surgery, she had a 3-cm limb-length discrepancy. She also had a diaphyseal deformity that was 10° varus, 47° procurvatum, and 85° external rotation, with mechanical axis deviation 0.5 cm medial to the center of the knee (Fig 1A-B).
We applied a Taylor Spatial Frame (Smith & Nephew, Memphis, TN) to the femur and performed a percutaneous osteotomy with a 2-cm skin incision approximately 20 cm proximal to the physis. The frame was constructed using two rings (a 205-mm ⅔ proximal ring and a 180-mm full distal ring) and six struts. The proximal ring was fixed with three half-screws (6 mm diameter) and one smooth Ilizarov wire (1.8 mm diameter) as a half-wire. The distalring was fixed with three half-screws (6 mm diameter) and four smooth Ilizarov wires (1.8-mm diameter; one wire was used as a transfixation wire and three wires were used as half-wires). We performed the percutaneous osteotomy using a previously described method.14 The total operation time was 146 minutes and total blood loss during the operation was 100 cc. After 7 days, frame adjustments were started and performed daily, which resulted in improvement of the deformity (10° in the coronal plane, 47° in the sagittal plane, and 25° in the axial plane) and limb-length discrepancy (Fig 2) based on the total residual program. The sizes of several struts were changed during the program. Just after completion of the lengthening procedure of 51 days, two supplemental straight rods were added between the two rings (one in the anterior and the other in the posterior portion) and weightbearing was permitted. Thirty days later, the two rods were removed. Bone union was evaluated based on the radiographic findings showing enough consolidation on the anteroposterior (AP) and lateral views. Bone union was achieved after a fixation period of 132 days (Fig 3A-B). The radiographs showed a formation of normal bone in the distraction gap. No orthosis was applied. The amount of lengthening was 3.5 cm at the anterior portion of the distraction gap. Pin-tract infections sometimes occurred during distraction, and the patient had a 10°-decrease in knee flexion, but no other complications were apparent. The patient continued to take bisphosphonate orally throughout the treatment period. At the final followup 9 months after surgery, the patient reported feeling more comfortable when walking than before surgery because of improvement of the limb-length discrepancy (Fig 3C). Her low back pain was relieved, but she reported persistent mild pain in the right knee.
Using distraction osteogenesis, we reconstructed a complex and severe deformity with shortening of the affected femur anticipating a future arthroplasty in the adjacent joint. After surgery, her discomfort with gait decreased. The pain in her joint also was less, but not eliminated. If this patient becomes a candidate for an arthroplasty in the future, correction of the deformity will make it easier to insert an intramedullary guide, possibly preventing prosthetic malposition and early prosthetic failure. Additionally, the limb-length discrepancy was normalized by distraction osteogenesis, leading to improvement of gait disturbance and low back pain.
One of the interesting findings shown in the current case is that lengthening callus formed in the distraction gap looked like normal regenerate bone, although lengthening was performed at the pathologic bone. Such a finding suggests the possibility of treating this disease by distraction osetogenesis. A similar phenomenon was reported in a patient with Ollier's disease.6
The degree of the deformity of our patient (47° in the sagittal plane) was much more severe than any in the reported cases of patients with Paget's disease.8,11 Our patient had a complex deformity that we corrected using a Taylor Spatial Frame. Distraction callus was visible at the end of the lengthening period, and consolidation of the callus was achieved within a reasonable time. Blood loss was less and operation time was shorter than those in the previous report.11 Pin-tract infection was a major complication experienced by our patient during the distraction period. This complication may have originated from or been exacerbated by the patient's preexisting diabetes mellitus. Fortunately, no other complications were apparent throughout the treatment period. Loosening and migration of the half-pins or wires that were inserted into the pathologic bone were not observed. However, an increased incidence of complications in patients with underlying bone disorders who have lengthening has been reported.9
Many deformities in patients with Paget's disease are complex. Conventional correction using internal fixation is limited in degree and accuracy. A recently developed external fixator, the Taylor Spatial Frame, is a modified version of the Ilizarov external fixator.2 The mechanism of deformity correction of the device is computer based, which enables the surgeon to perform an easy correction procedure for complex deformities. The device may be a powerful tool for treatment of long-bone deformities in patients with Paget's disease.
Our results suggest distraction osteogenesis may be considered for treating patients with Paget's disease who have severe, complex deformities requiring correction.
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