2015 ISAKOS Biennial Congress ePoster #1120

Validation of a Simplified Skin Pointer Device for Knee Rotation Measurement: A Cadaveric Study Using a Rotation-Meter

Ken-Lee Puah, MBBS(S'pore), MRCSEd, MMed(Orth), Singapore SINGAPORE
Andy Yew, PhD, Singapore SINGAPORE
Denny T. T. Lie, MBBS, FRCS, FAMS, Singapore SINGAPORE

Department of Orthopaedic Surgery, Singapore General Hospital, Singapore, SINGAPORE

FDA Status Not Applicable

Summary: A skin pointer combined with a knee rotation jig can be a reliable and simple means of quantifying knee rotation in the cadaveric knee with potential application in vivo.

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Abstract:

Background

With double-bundle and anatomically placed single-bundle anterior cruciate ligament reconstruction to aid in restoration of rotational knee kinematics, the need for objective measurement of knee rotational laxity in the clinical setting arises. The evaluation of knee rotation remains a challenge with intra-observer variability in the use of the pivot shift test. The aim of our study is to validate a simplified non-invasive skin pointer used in combination with a previously described knee rotation jig in cadaveric knees against that of a skeletally mounted bone marker.

Method

Six pairs of cadaveric legs were mounted individually on a knee rotation jig. One Kirscher wire was driven into the apex of the tibial tubercle as a bone marker and a skin pointer was attached above the tibial tubercle using a Velcro strap. Each knee was pretensioned prior to taking taking the first measurment. A rotational force of 3, 6 and 9 Nm was then applied using a torque limiting wrench attached to the rotation jig at 0°, 30°, 45°, 60° and 90° of knee flexion. This was repeated for both internal and external rotation for each specimen. The respective readings of the bone marker and skin pointer were then analysed using the Pearson correlation coefficient.

Result

The readings for total rotation obtained with the skin pointer significantly correlated with that of the bone marker at 3 Nm at 0° (skin pointer 23.9±26.0° vs. bone marker 16.3±17.3°, p=0.0), 30° (41.7±15.5° vs. 33.1±14.7°, p=0.037), 45° (49.0±17.0° vs. 40.3±11.2°, p=0.002), 60° (45.7±17.5° vs. 34.7±9.5°, p=0.001) and 90° (29.2±10.9° vs. 21.2±6.8°, p=0.019) of knee flexion and 6 Nm at 0° (51.1±37.7° vs. 38.6±30.1°, p=0.0), 30° (64.6±21.6° vs. 54.3±15.1°, p=0.011), 45° (67.7±20.6° vs. 55.5±9.5°, p=0.029), 60° (62.9±22.4° vs. 45.8±13.1°, p=0.031) and 90° (43.6±17.6° vs. 31.0±6.3°, p=0.043) of knee flexion and at 9 Nm at 0° (69.7±40.0° vs. 55.6±30.6°, p=0.001) and 60° (74.5±27.6° vs. 57.1±11.5°, p=0.006). With 9 Nm of torque, there was no statistically significant correlation at 30° (79.2±25.1° vs. 66.9±15.4°, p=0.055), 45° (80.7±24.7° vs. 65.5±11.2°, p=0.11) and 90° (54.7±21.1° vs. 39.4±8.2°, p=0.079) of knee flexion. The skin pointer exaggerated the amount of rotation compared to the bone marker at all torques and angles of knee flexion. We recognize that 9 Nm of torque may be not tolerated in live human subjects due to pain.

Conclusion

The skin pointer combined with a knee rotation jig can be a reliable and simple means of quantifying knee rotation in the cadaveric knee with potential application in vivo as a non-invasive means of measuring knee rotation in the office setting.