Patient-Specific Instrument Guided Double Chevron-Cut Distal Femur Osteotomy

Abstract

The risk of non-union and prolonged periods of protected weight-bearing still remain unsolved issues after distal femur osteotomy (DFO). To improve the stability, we developed the double chevron-cut technique, which is a modified medial closing-wedge DFO guided by a patient-specific instrument. The purpose of this study was to investigate the feasibility and outcome of this operative approach. Twenty-five knees in twenty-three consecutive patients with genu valgum and lateral compartment osteoarthritis that received double chevron-cut DFO were included. The target of correction was 50% on the weight-bearing line (WBL) ratio. Patient-reported outcomes included the Oxford Knee Score (OKS) and the 2011 Knee Society Score (KSS). The mean of the WBL ratio was corrected from 78.7% ± 12.0% to 48.7% ± 2.9% postoperatively. The mean time to full weight bearing was 3.7 ± 1.4 weeks. Union of the osteotomy was achieved at 11.3 ± 2.8 weeks. At a mean follow-up of 17 months, the OKS improved from a mean of 27.6 ± 11.7 to 39.1 ± 7.5 (p = 0.03), and the KSS from a mean of 92.1 ± 13.0 to 143.9 ± 10.2 (p < 0.001). Three patients developed complications, including one case of peri-implant fracture, one of loss of fixation, and one of non-union. The double chevron-cut DFO followed by immediate weight-bearing as tolerated is effective in treating genu valgum deformity and associated lateral compartment osteoarthritis.

Keywords: 3D-printed; cutting-guide; femoral; osteotomy; patient-specific.

Figure 1

Digital Preoperative Planning. (A) The full-length weight-bearing AP radiograph of a 67-year-old female with valgus deformity of the right knee. The femorotibial angle, MPTA, and LDFA were measured automatically in the software. (B) A 2D simulation of the osteotomy, setting the target of correction at 50% on the WBL ratio. The correction angle, wedge height, and LDFA after correction were simulated by the software. (C) The full-length weight-bearing AP radiograph of the same patient one year after DFO. The WBL ratio was corrected to 50.8%.

Figure 2

Digital 3D Model Simulation of double chevron-cut DFO. (A) The virtual 3D model of the patient in Figure 1. The osteotomy and correction after closing-wedge DFO were simulated. (B) A 3D simulation of the 3D-printed cutting jig. The wedge thickness, correction angle, and depth of bone cut were calculated based on the virtual 3D model and printed on the guide as a reminder during the surgery.

Figure 3

The surgical approach and the intraoperative radiographs. (A) A standard medial approach to the distal femur was used, utilizing the plane between the vastus medialis and adductors (distal is to the right and proximal is to the left). (B) The periosteum was elevated from the target femoral surface. The posterior femoral structure was retracted with a Bennett retractor in protection of the neurovascular bundle. (C) The customized cutting jig was placed onto the medial cortex, identifying the ideal spot with an anatomical fit of the guide. Two orientation K-wires were then inserted through the K-wire holes at the apexes of the chevron cut. (D) Positioning of the orientation K-wires was confirmed with a C-arm. (E) Four K-wires were inserted, fixing the guide onto the bone. Osteotomy was performed with a graduated oscillating saw. (F) The cutting guide and the wedge were removed after the osteotomy. (G) The osteotomy was then closed with gentle manual bending and fixed with the associated locking plate system. (H) The final position of the plate was confirmed with a C-arm. An alignment rod was not used.

Figure 4

The scatter plot of HKA and WBL ratios of all patients measured preoperatively, 2 days postoperatively, and at the final follow-up. Only one knee (4%) at 2 days postoperatively, and in the final radiographs, fell in the defined range (WBL 50% ± 10%) of outliers of correction.

Figure 5

A comparison of DFO techniques. (A) Uniplanar technique. (B) The “three-cut” biplanar technique. (C) The “four-cut” double chevron-cut technique. Note that the distal-most possible site of the biplanar is farther than in the uniplanar technique, since it avoids the femoral trochlea. The double chevron-cut technique may be performed even more distally, since it also avoids the posterior condyle of the femur.