Surgical treatment of the varus knee caused by vitamin D-resistant rickets. Report of two cases and review of the literature

Abstract

Introduction: Hypophosphatemic rickets is a rare X-linked genetic disorder clinically characterized by bone deformities, especially localized in the lower limbs, such as varus and valgus knees. Diagnosis is based on clinical observation and biochemical parameters. Treatment is pharmacological, however, if the skeletal deformities are severe, it is necessary a surgical correction.

Presentation of cases: We report two patients with hypophosphatemic rickets and severe varus knee. Both patients were surgically treated by bilateral femoral and tibial osteotomy, and stabilized with a uniplanar external fixator. No complications occurred in the post-operative period. The patients were clinically and radiographically checked thereafter over time. At last follow-up, 2 and 19 years after surgery, both patients were asymptomatic without recurrence of the deformity.

Discussion: In case of severe bone deformities caused by hypophosphatemic rickets, surgical approach is mandatory. Most authors agree that the ideal time to perform the operation is close to the end of bone maturity, to avoid the risk of recurrence of the deformities. However, in some young patients, with severe and progressive deformity, it is necessary to plan an early surgical correction in two or more stages, and multiple osteotomies should be planned.

Conclusion: According to our results, we believe that surgical treatment should ideally be performed close to skeletal maturity, but in one of our cases with serious deformities of both lower limbs, an early surgical correction was necessary despite the young age.

Keywords: Deformity correction; Hypophosphatemic rickets; Varus knee; Vitamin D resistant rickets.

Fig. 1

A. Weight-bearing radiographic examination of the pelvis and lower limbs of a 5-year-old girl affected by hypophosphatemic rickets with severe varus deformity of the lower limbs. The deformity is most evident at the level of the femurs, however it also appears present at the level of the tibias. B. Radiographic examination after simultaneous corrective osteotomy of both femurs. The osteotomy was performed at the diaphyseal level and was stabilized using a uniplanar external fixator. C. Radiographic examination after simultaneous corrective osteotomy of both tibias. The osteotomy was performed at the diaphyseal level and was stabilized using a uniplanar external fixator.

Fig. 2

A. Weight-bearing radiographic examination of the pelvis and lower limbs of a 13-year-old boy affected by hypophosphatemic rickets with severe varus deformity of the lower limbs. The deformity is most evident at the level of the femurs, however it also appears present at the level of the tibias. B. Radiographic examination after simultaneous corrective osteotomy of both femurs. The osteotomy was performed at the diaphyseal level and was stabilized using a uniplanar external fixator. C. Radiographic examination two months after corrective osteotomy of the right tibia. The osteotomy was performed at the proximal metaphyseal level and was stabilized using a uniplanar external fixator. A modest lower limb discrepancy of the operated skeletal segment is present. D. Radiographic examination after corrective osteotomy of the left tibia. The osteotomy was performed at the diaphyseal level and was stabilized using a uniplanar external fixator. A slight overcorrection is present.

Fig. 3

A. Clinical aspect of the same patient as in Fig. 2 at the final follow-up, 19 years later. A good alignment of the left lower limb was present while the right lower limb presented a mild varus deformity associated to a mild overlength. The patient was completely asymptomatic and was satisfied with the result. B. Radiographic examination, 19 years after surgery showed lower limbs good alignment. The femorotibial angle measured 0° on the right side and −4° on the left. Two cm of lower limb discrepancy is present.