Diagnosis of the anterior cruciate ligament (ACL) injury is made by manual tests which are usually the Lachman Test, the Anterior Drawing Test (ADT), the Pivot Shift Test (PST). However, in these tests, the sensitivity is not always high. One of reason for the low sensitivity of manual testing in ACL rupture is re-attachment of ACL remnant which may change the knee stability.
The purpose of this study was to evaluate the relationship between the knee stability and Crain classification in ACL injury. Hypothesis was that Crain type ?, in which the remnant attach to near the native insertion, will cause the knee stability at the ACL injured knee.
Between 2017 and 2018, 40 consecutive patients undergoing ACL reconstructions were studied. (21 male and 19 female) Preoperatively, all patients had ACL deficiency with side-to-side difference of at least 3 mm using knee arthrometer (the Kneelax3: Monitored Rehab Systems, Haarlem, the Netherlands). There were no associated collateral ligament injuries and no meniscal tear in all knees. The contralateral knee was normal in all patients. ACL reconstruction was performed an average of 6 weeks after the injury (range, 3 to 15 weeks).
Before the operation, the Lachman Test, ADT, PST, Kneelax3 were evaluated.
Before the ACL reconstruction, an arthroscopic evaluation was performed. The configuration of the ACL remnant and its attachments to the femur and tibia were characterized based on the Crain classification of ACL remnant.
In the positive endpoint group with the Lachman Test, the type?,?and ? of Crain classification include 17 knees and the type ? of Crain classification include 13 knees. On the other hand, in the negative endpoint group with the Lachman Test, the type?,?or ? of Crain classification include 10 knees and no type ?.
In all knees with Crain type?,?, and ?, ADT were positive. However, in a half of knees with Crain type?, ADT were negative. In addition, the grade of PST in Crain ? is lower than the grade of PST in Crain ?,? and ?
In the knee with Lachman test 2B, the value of Kneelax3 was significantly large compared with the knee with Lachman test 2A.
Nagai K et al reported that the remnant, which attach to the medial wall of lateral femoral condyle, contribute to the knee stability, however, the non-anatomical re-attachment of ACL remnant is no relationship to the knee instability. Our results showed that the knee stability after ACL injury had the relationship with the type of Crain classification, and the pattern of the knee stability had the similar tendency to this report. The type ? of Crain classification may produce the knee stability because of the re-attachment to the medial wall of lateral femoral condyle. Therefore, it is so important to take this result into consideration for the diagnosis of ACL injury.