Summary

Quantitative evaluation of knee movements during Lachman and Pivot-shift test was performed in ninety ACL injured knees using an electromagnetic system, and their positive rates were compared. Each knee had a different combination of the anterior and/or rotatory knee laxities. Both tests are clinically important to extract different features of the joint laxity in the ACL injured knees.

Abstract

Objective

Lachman test (LT) and pivot-shift test (PST) are gold standard for knee joint laxity evaluation in the anterior cruciate ligament (ACL) injured knees. Those two manual tests are known to assess different knee laxity, i.e. anterior laxity and rotatory knee laxity. The detailed knee movement analysis during the manual tests is currently possible by using an electromagnetic system and might characterize the different knee laxities in the ACL injured knees. Therefore, the purpose of this study was to quantitatively evaluate the knee movements during LT and PST using an electromagnetic system sensor and to compare them in terms of positive rate in the ACL injured knees.

Method

Ninety ACL injured knees were enrolled. The knee movement during the LT and the PST was evaluated by an electromagnetic measurement system (JIMI kobe, Arthrex Japan). The anterior tibial translation (ATT-LT, mm) was provided as a parameter for the LT assessment, and the anterior tibial translation (ATT-PST, mm) and the acceleration (ACC-PST, m/sec2) of the pivot-shift were calculated for the PST assessment. More than 2mm of the ATT-LT and the ATT-PST was considered as abnormal, so was more than 0.5 m/sec2 of the ACC-PST. Positive rate of those three values in the ACL injured knees, i.e. percentage of cases which had abnormal values, were compared using the Chi-square test, and significance was set at p <0.05.
Result:
The overall positive rate of all three values, i.e. abnormal in at least one of the three, was 83% (75/90 cases). ATT-LT was abnormal in 62 cases (69%), whereas abnormal ATT-PST was found in 35 cases (39%). ACC-PST increases over 0.5 m/sec2 in 40 cases (45%). Lower positive rate in PST than LT was observed for both ATT and ACC (p <0.01). Out of 51 knees which were abnormal in PST, 13 knees (25%) demonstrated normal LT. Conversely, there were 13/28 cases (46%) of abnormal LT that showed normal PST.

Discussion

Different positive rate was demonstrated by the two gold standard tests for the ACL injured knees based on the quantitative measurements of those manual tests.
It is widely known that LT is known to have better sensitivity to detect the ACL deficiency, while PST has greater specificity. LT and PST are different not only for the testing accuracy but also for the evaluation target, i.e. anterior laxity and rotatory knee laxity. Each ACL injured knee could have an individually different laxity in combination of anterior and rotatory knee laxity depending on its original joint laxity, magnitude of the ACL injury and concomitant soft tissue injuries.
Both LT and PST are clinically important to have different features to assess the joint laxity in the ACL injured knees. Further studies are wanted to identify the factors affecting each laxity in the ACL injured knees.