RADIOLOGICAL ANALYSIS OF THE KNEE IN CONGENITAL LONGITUDINAL DEFORMITIES

Abstract

Introduction: The knee joint in congenital longitudinal deformities of the lower extremity shows a large variety of pathological findings. Valgus deformity is found in most cases and is described as being juxta- articular. To describe the true anatomic pathology we performed a radiographic analysis of the knee joint in congenital longitudinal deformities.

Patients and Method: Between 1985 and 2001 we treated 102 patients presenting with congenital longitudinal deformities. Inclusion criteria for this study were diagnoses of fibular hemimelia (FBH) and/or congenital femoral deficiency (CFD), an age between 5 and 16 years, unilateral affection and availability of long standing X-rays, whereas bilateral affection or previous operations on the lower extremities were defined as exclusion criteria. Twenty-four parameters were defined on the femur and tibia respectively and a nomenclature was created. The mean values including standard deviation were calculated and we statistically compared the parameters of the affected to those of the non-affected knee. Furthermore, MRI scans of the knee joint of 20 of these patients were evaluated.

Results: Thirty- nine patients (19 female, 20 male) met the inclusion criteria. The average age at the time of evaluation was 8.87 years (3.1 SD). A combined deficiency of femur and tibia was found in 35 patients. The predominant diagnosis was CFD in 13, fibular hemime-lia in 13 and fibular aplasia in 9 cases. The anatomic lateral distal femoral angle (ALDFA) measured 75.4° (2.5 SD) on the affected, and 81.6° (1.6 SD) on the non-affected knee. The lateral distal femoral metaphyseal angle of the affected side and of the non-affected side showed no significant difference. The distal lateral femoral epiphyseal width (DLFEW) was decreased in the affected limb compared to the non affected limb, whereas the distal medial femoral epiphyseal width (DMFEW) of the affected and non-affected side showed only a minor difference. In the tibia we found no significant difference between the variables for the medial proximal tibial angle (MPTA) and for the medial proximal tibial metaphyseal angle (MPTMA) of the affected and the non-affected limb. A significant difference was found between the proximal lateral tibial epiphyseal width of the affected and the non-affected side. Analysis of the MRI scans revealed aplasia of the anterior cruciate ligament in 18 cases and aplasia of the posterior cruciate ligament in 8 of the 20 cases. The defect of ossification of the lateral tibial epiphysis as seen in plain X-rays is visible in the MRI scans as cartilage anlage. (Only the most important findings are summarized)

Conclusions: In our patient population only four patients had FBH or CFD but 35 cases presented combined defects; we assume that the femur is affected to some extent in almost all cases of FBH. The hypoplasia was only found in the lateral aspects of femur and tibia and was primarily located within the femoral epiphysis. The metaphysis was not or only minimally affected in the evaluated longitudinal deficiencies. Awareness of sagittal instability, due to ACL and/or PCL aplasia, is necessary to avoid subluxation or dislocation when lengthening procedures are performed.