INTRODUCTION: Range of motion following TKA is a commonly assessed and important outcome parameter. The reported knee ROM is often measured using manual goniometers. The accuracy of goniometer in measuring ROM of the knee is not known. We compared the knee ROM measured with a manual goniometer and compared that to measurements obtained from computer assisted navigation system.

METHODS: This prospective ongoing study has so far recruited 60 patients (71 knees) undergoing TKA by a single surgeon. Measurements of the ROM were performed intraoperatively using a 14 inch 360° Nexgen Baseline® goniometer, validated by physical therapists, and the Stryker knee navigation system^™. Consistent anatomical landmarks were used to obtain flexion and extension measurements. Each goniometer and navigation measurement was performed twice by the same reader.

RESULTS: Goniometer was more inaccurate in measuring the knee ROM than the navigation. There was a 5.07° difference between two measurements obtained with the goniometer compared to a mean discrepancy of 1.15° using the navigation system. Further, the ROM measured by navigation was on average 13.9° larger than that measured by the goniometer. BMI affected the ROM recording obtained by both the goniometer and the navigation system.

DISCUSSION AND CONCLUSION: This study indicates that goniometer is not an accurate tool for measurements of knee ROM as there is a marked discrepancy between two goniometer readings. The navigation system seemed to produce more consistent, but markedly higher, readings than a manual goniometer. Reported results on knee ROM in the literature need to be interpreted with caution and scrutinized for potential inaccuracy of the measuring tool.