VALIDATION OF TECHNIQUES IN THE MEASUREMENT OF RANGE OF MOTION AFTER TOTAL KNEE ARTHROPLASTY: ROUGH ESTIMATE OR RELIABLE OUTCOME MEASURE?

Introduction: Range of motion is an invariable outcome -measure in studies on total knee arthroplasty (TKA) and other knee surgery. Concluding that a certain change in motion equals a corresponding change in outcome may be invalid if true accuracy of current measuring techniques is unknown. This is integral to many studies. Surprisingly little has been done to validate these techniques. Methods: Maximum extension and flexion were measured in 32 TKAs by four independent observers using three common techniques: visual estimate (VE), pocket and universal goniometers (PG and UG). Lateral radiographs in reproducible positions were measured using computer analysis, providing a gold standard for comparison with clinical measurements. The correlation coefficients and coefficients of reliability were calculated. Results: There were no significant differences between observers using any method. Significant differences were found between each technique and radiographic measure (paired t-test, p Conclusions: Clinical measurements of range of motion vary significantly from radiographic measurement, with the computer assisted radiographic measurement providing high reliability as the gold standard. UG is most accurate, followed by PG and VE. However, coefficients of repeatability were surprisingly large, indicating the degree of accuracy of each measurement technique and the necessary magnitude of difference for this to be outside measurement error. This has relevance for all outcome studies and everyday clinical practice.