Abstract
Introduction
The shuck test was widely used to assess the overall soft-tissue tension around the hip joint during surgery. There have been few attempts to standardize how one evaluates soft tissue tension in total hip arthroplasty. The aim of this study was to ask how reliable the shuck test was as a measure of soft tissue tension in total hip arthroplasty.
Methods
First, we assessed the intra- and inter-examiner variability of the force generated in the shuck test. Next, we asked how the strength of traction forces and joint position on the distance of displacement of the prosthetic head at surgery. Twenty-one hip surgeons, consisting of seven experienced hip surgeons, seven junior hip surgeons, and seven surgeons in training were included in the first study. Test subjects were instructed to pull a traction gauge with their customary range of force. Each subject performed two sets of the shuck test in one week interval. Eighteen patients who had cementless THA through postero-lateral approach using 3D-CT based navigation system were enrolled in the second study. After implantation of components, the leg was pull caudally using our original device [Fig. 1]. The strength of applied traction force was 20 %, 30 %, 40 % and 50 % of body weight of each patient. The distance of displacement of a prosthetic head during traction was recorded at flexion angles of 0, 15, 30 and 45 degrees using the navigation system. Internal or external rotation of legs was controlled within 5 degrees.
Results
There was a significant difference among examiners in the range of force generated in shuck test. The mean force was 24.1 kg (SD; 6.4, range; 11 to 35). There was no significant difference in the range of force among experienced, junior surgeons and surgeons in training (p=0.11). Intra-class correlation between the tests and re-tests was 0.8. The distance of displacement of prosthetic heads during traction increased with traction forces significantly (p=0.001). There were significant differences in the distance of displacement of prosthetic heads during traction among flexion angles (p=0.001). The femoral head displaced most at the flexion angle of 15 degrees.
Conclusion
There were considerable inter-examiner differences in the range of forces generated by the shuck test. The strength of traction forces and flexion angles influenced significantly the distance of displacement of prosthetic heads. It is necessary to standardize the strength of traction forces and flexion angles in order to make the shuck test reliable.
