Femoral deformity in tibia vara.

BACKGROUND

Previous studies have suggested that compensatory valgus deformity of the femur is common in patients with tibia vara, or Blount disease. The availability and routine use of standing long-cassette radiographs of the lower extremities to assess angular deformities has allowed quantitative evaluation of this hypothesis.

METHODS

The cases of all patients with tibia vara, two years of age or older, seen at our institution prior to treatment, over a thirteen-year period, were reviewed. Seventy-three patients with a total of 109 involved lower limbs were identified and were classified as having either infantile tibia vara (thirty-seven patients with fifty-six involved limbs) or late-onset tibia vara (thirty-six patients with fifty-three involved limbs). Standardized standing radiographs of the lower extremity were examined to assess the deformity at the distal part of the femur and the proximal part of the tibia by measuring the lateral distal femoral angle and the medial proximal tibial angle.

RESULTS

The distal part of the femur in the children with infantile tibia vara either was normal or had mild varus deformity, with a mean lateral distal femoral angle of 97 degrees (range, 82 degrees to 129 degrees). The mean medial proximal tibial angle in these children was 72 degrees (range, 32 degrees to 84 degrees). Older children with infantile tibia vara were noted to have little distal femoral deformity, with no more than 4 degrees of valgus compared with either normal values or the contralateral, normal limb. Children with late-onset tibia vara had a mean lateral distal femoral angle of 93 degrees (range, 82 degrees to 110 degrees) and a mean medial proximal tibial angle of 73 degrees (range, 52 degrees to 84 degrees). On the average, the varus deformity of the distal part of the femur constituted 30% (6 degrees of 20 degrees) of the genu varum deformity in these patients.

CONCLUSIONS

Patients with infantile tibia vara most commonly had normal alignment of the distal parts of the femora; substantial valgus deformity was not observed. Distal femoral varus constituted a substantial portion of the genu varum in children with late-onset disease. When correction of late-onset tibia vara is planned, the surgeon should be aware of the possibility that distal femoral varus is a substantial component of the deformity.