Paper 05: Clinical Outcomes and Accuracy of Patient-Specific Instrumentation for Corrective High Tibial and Distal Femoral Osteotomy

Objectives: High tibial osteotomies (HTO) and distal femoral osteotomies (DFO) may be used for a variety of knee pathologies including unicompartmental cartilage disorders and ligamentous instability. A novel instrumentation system for osteotomies utilizing three-dimensional patient-specific instrumentation (3D-PSI) cutting guides has been recently described, however there is limited reporting on the clinical outcomes and accuracy of this system. The purpose of this study was to evaluate the clinical outcomes and accuracy of correction of a 3D-PSI osteotomy system for HTO’s and DFO’s. It was hypothesized that patients would have significant improvements in patient-reported outcome (PRO) scores and that at least 90% of patients would have coronal alignment within 10% of the planned correction. Methods: A prospectively maintained database of patients who underwent opening wedge (oW) or closing wedge (cW) HTO or DFO utilizing a 3D-PSI system (Fine Osteotomy, Bodycad, Canada) from October 2020 to January 2022 was reviewed.Preoperatively and postoperatively, PROs were collected, including the International Knee Documentation Committee Subjective Knee Form (IKDC), San Francisco 12 physical component score and mental component scores (SF-12 PCS and MCS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) including the stiffness (WOMAC-stiff), pain (WOMAC-pain), physical function (WOMAC-PF) and total (WOMAC-total) scores, the Lysholm score, Tegner activity scale, and subjective satisfaction (1-10 scale, with 10 indicating maximum satisfaction). A paired t-test was used to evaluate for differences in PRO’s from pre- to postoperatively. To assess coronal and mechanical alignment, mechanical medial tibial width ratio (mMTWr), defined as the distance from the medial aspect of the tibia to the point on the tibia where the mechanical axis intersects the tibial plateau divided by the entire width of the tibial plateau, was measured on standing whole-leg radiographs ( Figure 1 ). Radiographic measurements were performed by two blinded independent raters. Intra-class correlation coefficients (ICC) were calculated to determine inter-observer reliability for radiographic measurements between raters and reliability between the raters and the Bodycad software’s pre-operative measurements. To analyze correction accuracy, the differences between the planned final mMTWR based on the preoperative plan and actual measured mMTWr ( Figure 2 ) as well as the percentage of patients within 10% of the planned mMTWR were calculated. This 10% threshold was based on prior studies and corresponds to approximately 2 degrees of tibiofemoral angle. Results: Complete data sets were obtained for 23 cases (16 oW-HTO, 4 oW-DFO, 2 cW-DFO, 1 combined cW-HTO + oW-DFO) at mean follow-up of 2.6 years. Demographics for the cohort are shown in Table 1 . Using a Bonferroni-corrected P value (p<0.006), there were significant improvements from pre- to post-operatively in IKDC, Lysholm, WOMAC-pain, WOMAC-stiffness, WOMAC-physical function, and WOMAC-total scores ( Table 2 ). The ICC’s for pre- and post-operative mMTWR measurements were 0.996 and 0.982, respectively, indicating near perfect agreement. The ICC between the raters pre-operative measurements of mMTWr on whole-leg standing radiographs and the Bodycad measurements of mMTWr based on the 3D CT was 0.985. 89% of patients were within 10% of the planned final mMTWR, and the median difference between the planned and actual correction was 3.7% (95% CI, 2.8 – 8.4). Excluding patients who underwent removal of hardware, 22% (5/23) of patients had at least one related reoperation. Survivorship, defined as patients who did not undergo revision osteotomy or arthroplasty, was 21/23 knees (91%). Conclusions: This study found that patients who underwent corrective HTO or DFO using PSI had significant improvements in PRO’s, and there was good accuracy, 89%, of coronal correction. These findings demonstrate that osteotomy utilizing 3D-PSI can lead to clinically meaningful improvements in patient function with high accuracy of planned correction. While the median difference of 3.7% between the planned and actual correction is less than 1 degree, the presence of outliers emphasizes the importance of meticulous surgical technique and abiding by osteotomy principles even when utilizing 3D PSI. This study adds to a growing body of literature that corrective osteotomies can significantly improve patients’ quality of life and knee function in the treatment of chondral and meniscal pathologies and provides early data on the accuracy and outcomes of a newly released 3D PSI osteotomy system for HTO’s and DFO’s.

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