Modern surgery techniques for anterior cruciate ligament injuries are considered successful, as anterior stability is restored and athletes are able to return to sports. However, even though anterior stability is successfully restored in the majority, rotatory instability remains after reconstruction in some patients. This may cause limitations for regular daily activities as well as the ability to participate in sports. The rotatory instability is a likely reason why there are still athletes who are not able to return to their pre-injury activity level, or experience limited performance due to the remaining instability. It is therefore important to develop better reconstruction procedures to restore rotatory stability as well as anterior stability.
Rotatory instability is commonly examined by pivot-shift test in a clinical setting. The pivot-shift test has been shown to be superior to anterior stability tests such as Lachman and KT-1000 measurement when it comes to predicting patient-reported instability, poor subjective and objective outcome scores, as well as osteoarthritis after ACL reconstruction. Despite the clinical value of the pivot-shift test, it is evaluated based on clinician’s subjective impression. This subjective grading has been shown to have low inter-observer reliability. Moreover, there is no world-wide consensus on the grading criteria.
Although some objective measurements have been used in clinical practice to quantitatively evaluate the pivot-shift test, such as electromagnetic device, open magnetic resonance imaging system, and navigation system, several problems remain regarding their accuracy, cost, and invasiveness. Among them, navigation system seems to be the most accurate. However, due to its invasiveness it can be used only during surgery which means that we can not compare the motion of the injured knee with healthy subjects or contralateral knee.
A model-based image-matching (MBIM) technique has been developed to extract joint kinematics from video recordings using one or more uncalibrated cameras. This technique allows six degrees of freedom for knee motions, and is easily applied to a clinical setting. Although it has been validated in knee and hip motions in running and cutting maneuvers, estimates for internal/external rotation were less precise than flexion/extension and ad-/abduction. Moreover, estimates for anterior translation have not been validated. However, using pre-calibrated, non-moving cameras positioned close to the moving segments, it is likely that also internal/external rotations can be measured with higher accuracy.
The objective of this study is to validate the MBIM technique for measuring six degree-of-freedom knee joint kinematics in pivot-shift motions using 3D skin marker motion analysis as the gold standard.
One examiner will perform the pivot shift test on each leg. The pivot shift motion will be analyzed by both MBIM technique and skin marker-based motion tracking system, and the skin marker-based analysis will be served as the gold standard for knee joint motion. Tibial anterior translation and tibial internal rotation angle will be measured in the both methods, and the estimates from the both methods will be compared.
If this technique is successfully validated, we will evaluate ACL injured patients before and after operation to find out how pivot-shift phenomenon affects patients’ outcome scores in the future study, so we will be able to improve operative technique.