Abstract
Introduction
Patient matched instrumentation (PMI) have been proposed the accuracy of bone cuts through custom cutting blocks and provide the proper alignment of total knee arthroplasty (TKA). On the other hand, there are some reports that the introduction of PMI for guiding bone cuts could increase the incidence of malalignment in primary TKA. Recent comparisons between patient-specific cutting guides and quantitative assessments of postoperative alignment have revealed the presence of outliers with respect to coronal alignment. The purpose of this study was to assess the implanted component alignment post-operatively between one type of MRI based PMI (Visionaire; Smith & Nephew, Inc, Memphis, Tenn) and conventional surgical instrumentation (CI) using radiographs and CT scan.
Methods
32 knees in 32 patients (25 women) with medial type knee osteoarthritis were underwent cruciate retaining TKA between September 2013 and May 2015, and were included in this study. Preoperative MRI scanning of the hip, knee, and ankle was performed for PMI group (n=12) and CT scanning was performed for CI group (n=20) 6 weeks before surgery according to a standard scanning protocol to determine the surgical epicondylar axis (SEA). Postoperatively, we compared operation time, blood loss, and mechanical alignment of two groups. Post-surgical mechanical alignments such as hip-knee-ankle angle (HKA), frontal femoral component angle (FFC), and frontal tibial component angle (FTC) were determined using long leg radiographs (Fig. 1). CT scans were used to assess the condylar twist angle (CTA) made by SEA and posterior condylar axis (Fig. 2). Each measurement was performed by two, blinded independent observers, and interclass correlation for each measurement was calculated. A student's two-tailed t test was used to compare the two cohorts, with statistical significance set at a p-value of <0.05.
Results
There was no significant difference between the two groups regarding preoperative age, body mass index, degree of mechanical deformity, mean operation time or mean blood loss. Mean pre / postoperative HKA in the PMI group was 166.8 ± 6.4°/ 176.7 ±1.9° and 168.3 ±8.3° / 178.8 ±2.1°in the CI group. There was no significant difference between two groups, but there were fewer ± 3° HKA outliers with CI group (20%) than with PMI group (50%). Postoperative FFC was 89.1 ± 0.6° in PMI group and 88.1 ± 1.2° in CI group. FTC was 87.8 ± 1.4° in PMI group and 89.3 ± 1.6° in CI group. CTA was −0.8 ± 0.6 ° in PMI group and −1.2 ± 1.1° in CI group. There was no significant difference between PMI and CI group in postoperative mechanical alignment, but there were higher ± 3° FTC outliers in PMI group (50%) compared to CI group (10%)(p=0.01). (Fig.3)
Discussion and Conclusion
Although the overall mean mechanical alignment for PMI group was similar to CI group, these results suggest that PMI did not significantly improve alignment. It should be recommended to use only for the femoral component.
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