The Effect of Sagittal Knee Deformity on Preoperative Measurement of Coronal Mechanical Alignment during Total Knee Arthroplasty.

PURPOSE: The purpose of this prospective study was to determine correlation between coronal mechanical alignment measured on preoperative standing full-length radiographs and navigation during total knee arthroplasty (TKA) in the presence of an associated sagittal deformity (hyperextension and flexion deformity). MATERIALS AND METHODS: Coronal mechanical alignment measured on preoperative, standing, full-length, hip-to-ankle anteroposterior radiographs was compared with intraoperative measurements recorded with computer navigation in 200 primary navigated TKAs. RESULTS: The mean difference in mechanical alignment between the two techniques was significantly greater (p=0.001) in patients with an associated flexion deformity >10° when compared to knees with associated flexion deformity ≤10°; 48% of knees with a flexion deformity >10° had a difference of ≥3° between the full-length radiograph and navigation alignment measurements. There was a strong correlation between the radiographic and navigation measurement techniques. CONCLUSIONS: The mean difference in coronal mechanical alignment between the two techniques was significantly higher in patients with an associated flexion deformity >10°. Hence, surgeons should take caution when relying on preoperative full-length radiographs for determining coronal mechanical alignment in patients with an associated flexion deformity >10° where using navigation may be more reliable.