Computer-assisted navigation for the assessment of fixed flexion in knee arthroplasty.

BACKGROUND

Correction of a fixed flexion deformity is an important goal when performing total knee arthroplasty. The purpose of this study was to assess the accuracy of clinical assessment compared with imageless computer navigation in determining the degree of fixed flexion.

METHODS

We performed navigation anatomy registration using 14 cadaver knees.The knees were held in various degrees of flexion with 2 crossed pins. The degree of flexion was first recorded on the computer and then on lateral radiographs. The cadaver knees were draped as they would be for a total knee arthroplasty, and 9 examiners were asked to clinically assess by visual observation the amount of fixed flexion.Three examiners repeated the process 1 week later.

RESULTS

The mean error from the radiographs in the navigation group was 2.18 degrees (95% confidence interval [CI] 1.23 degrees -3.01 degrees) compared with 5.57 degrees (95% CI 4.86 degrees -6.29 degrees) in the observer group. The navigation was more consistent, with a range of error of -5 degrees to +5.5 degrees compared with -18.5 degrees to +17.5 degrees in the observer group. The observers tended to underestimate the amount of knee flexion (median error -4 degrees), whereas the navigation group was more evenly distributed (median error 0). The highest concordance coefficient was found between navigation and radiography (0.96). The concordance coefficient was 0.88 for the 3 surgeons who repeated the measurements 1 week later (mean error 3.5 degrees , range 15 degrees ).

CONCLUSION

The use of computer navigation appears to be a more accurate method for assessing the degree of knee flexion, with a reduced range of error compared with clinical assessment. The use of computer-assisted surgery may therefore provide surgeons with the information required to more consistently restore full extension during total knee arthroplasty.