Preoperative and postoperative comparisons of navigation and radiologic limb alignment measurements after high tibial osteotomy.

PURPOSE

To determine whether navigation-assisted intraoperative lower limb alignment in open wedge high tibial osteotomy (HTO) correlates with preoperative and postoperative radiographic alignment.

METHODS

This prospective study involved 35 patients (39 knees) who underwent navigation HTO for primary medial osteoarthritis. The mechanical axis (MA) and weight-bearing line (WBL) ratio were calculated from preoperative radiographs, intraoperative navigation, and postoperative (6 months) radiographs. Reliability between navigation and radiographic alignment was analyzed by use of intraclass correlation coefficients (ICCs) with thresholds as follows: good, greater than 0.75; fair, 0.4 to 0.75; and poor, less than 0.4. The surgical target for the MA was a final valgus overcorrection of 2° to 8°, and the WBL ratio target was between 50% and 70%. Outliers for differences between intraoperative navigation and postoperative radiographic results were defined as greater than ±3° for the MA and greater than ±10% for the WBL ratio.

RESULTS

The MA target was achieved in 33 of 39 knees (84.6%), and the WBL ratio target was achieved in 30 of 39 knees (74.4%). ICCs for navigational reliability were good for preoperative MA and WBL ratio and fair for postoperative MA and WBL ratio. The ICCs for the MA were better than those for the WBL ratio for both preoperative and postoperative measurements. The differences between the number of outliers between the navigation and radiographic MA and WBL were greater postoperatively than preoperatively. In addition, the postoperative differences in the extent of the outliers between navigation and radiographic measurements were greater for WBL ratios than the MA (P = .023).

CONCLUSIONS

This study found that use of a navigation system achieved the target value for MA lower limb correction in over 80% of open wedge HTO cases, using radiographic data as the gold standard for alignment. Because the navigational measurements of lower limbs during open wedge HTO did not correlate with postoperative radiographic alignment, corrections should not be based solely on navigational results. In assessing the reliability of navigational open wedge HTO for correction of lower limb alignment, the MA is a better radiologic parameter than the WBL ratio.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.