Introduction:Distal femoral osteotomy (DFO) has been performed to treat patients with knee OA. Although bi-plane technique has become popular in DFO, it is technically demanding, especially in creation of the anterior flange. To create anterior flange properly, direction of cutting and thickness of the anterior flange appear to be important. However, morphological characteristics of distal femurs considering surgical reference for DFO have never been reported. The purpose of this to examine morphological characteristic of distal femur based on the cortical shape for surgical reference in DFO.
Methods:Computed tomography images of 50 valgus knees in 49 patients and 50 varus knees in 48 patients who underwent DFO or total knee arthroplasty were analyzed. The axial slice 65 mm proximal to the joint line, which corresponds to the average starting level of the transverse osteotomy in DFO previously performed in our hospital, was chosen. First, a tangential line to the outside of the posterior cortex was drawn (Line 1). Second, a tangential line to the anterior cortex and parallel to the line 1 was drawn (Line 2). Third, tangential lines to the medial cortex (Line 3) and to the lateral cortex (Line 4) were drawn. The angle between Line 1 and Line 3 was defined as the medial cortex line angle (MCLA) and between Line 1 and Line 4 as the lateral cortex line angle (LCLA). The height of the medial and lateral side was measured as follow. The tangential lines to the inside of the posterior cortex line (Line 6) and the anterior cortex (Line 7) were drawn. The inner crossing points of the Line 7 at the medial side (point M) and the lateral side (point L) were determined. The vertical distance between Line 6 and Point M was defined as the medial cortex height (MCH) and between Line 7 and Point L was defined as the lateral cortex height (LCH). Statistical comparisons were formed between medial and lateral, and between valgus and varus knees.
Results:In valgus knees, the mean MCLA and LCLA were 68.1 ± 8.5° and 78.4 ± 4.3°, and MCH and LCH were 21.3 ± 3.5 mm and 27.3 ± 3.8 mm respectively. In varus knees, the mean MCLA and LCLA were 74.8 ± 5.9° and 80.4 ± 4.7°, and MCH and LCH were 24.7 ± 3.1 mm and 30.3 ± 3.3 mm respectively. The mean MCLA was significantly smaller than LCLA, and the mean MCH was lower than LCH in both valgus and varus knees (All, P < 0.01). The mean MCLA and LCLA in valgus knees were smaller than those in varus knees, and the mean MCH and LCH in valgus knees were lower than those in varus knees (All, P < 0.02).
Discussion:The medial cortical angle and height was shallower and lower than those of the lateral cortex at the osteotomy site, particularly in patients with valgus knee. Therefore, surgeons should be cautious when creating anterior flange during medial closing wedge DFO to avoid creating too thick anterior flange.