Validation of a novel smartphone accelerometer-based knee goniometer.

Area of Science:

• Orthopedics
• Biomedical Engineering
• Sports Medicine

Background:

• Loss of full knee extension post-anterior cruciate ligament (ACL) surgery significantly impairs knee function.
• Accurate and reproducible measurement of fixed knee flexion is challenging with conventional methods.

Purpose of the Study:

• To evaluate the interobserver and intraobserver reliability of a novel smartphone accelerometer-based knee goniometer.
• To compare the smartphone goniometer's performance against a conventional long-armed goniometer for assessing fixed knee flexion deformity.

Main Methods:

• Five healthy male volunteers participated in the study.
• Knee flexion angles were measured using both a conventional telescopic-armed goniometer and a smartphone (iPhone 3GS) knee goniometer employing a trigonometric technique based on tibial inclination.
• Bland-Altman analysis and Pearson's correlation were used to assess validity and reliability.

Main Results:

• The smartphone goniometer demonstrated superior reliability: interobserver correlation (r=0.994) and intraobserver correlation (r=0.982) significantly exceeded those of the conventional goniometer (r=0.952 and r=0.927, respectively).
• The smartphone goniometer exhibited higher precision with interobserver reliability of +/- 2.7 degrees and intraobserver reliability of +/- 4.6 degrees, compared to the conventional goniometer's +/- 8.4 and +/- 9.6 degrees.
• Data from both instruments correlated closely (r=0.947) with a minimal mean difference of -0.4 degrees.

Conclusions:

• The smartphone accelerometer-based knee goniometer is a highly reliable tool for measuring subtle knee flexion in a clinical setting.
• This novel device offers a more accurate and reproducible alternative to conventional goniometers for assessing knee flexion deformities, particularly post-ACL surgery.