Meniscal Tears in ACL-Deficient Knees

Abstract & Commentary

Synopsis: An analysis of meniscal tears in almost 500 patients with ACL-deficient knees demonstrated that tears of the medial meniscus were slightly more common than lateral meniscal tears. The most common tear pattern was a peripheral posterior horn tear.

Source: Smith JP III, Barrett GR. Am J Sports Med. 2001;29(4):415-419.

Meniscal tears occur commonly in patients with ACL injury. The incidence has been reported as high as 96% in chronic ACL-deficient knees. Lateral meniscal tears have been reported to be slightly more common than medial meniscal tears in the acute ACL-injured knee.1 Smith and Barrett prospectively evaluated 1065 knees in 1021 patients. Approximately three fourths of these patients had ACL reconstruction within 6 weeks of injury, and the other one fourth had ACL reconstruction chronically. Meniscal tears were present in 45% of the knees. The study group included 303 males and 173 females. The average patient age was 25.4 years (range, 9-57). The tears were classified into zones based upon the system described by Cooper and colleagues.2 Medial meniscal tears were present in 53% of cases, and lateral meniscal tears occurred in 47% of cases with meniscal tears. Peripheral tears were present in approximately three fourths of the medial meniscal tears but in slightly less than half of the lateral meniscal tears.

Comment by Mark D. Miller, MD

This is an interesting study of meniscal tear location in ACL-deficient knees. Smith and Barrett state that it is prospective, but there is no way to verify this statement. This paper does not challenge the commonly held tenant that lateral meniscal tears are more common in acute ACL-injured knees, because approximately one fourth of the study group had chronic ACL deficiency and the acute group is not stratified to allow us to address this issue. What I found most interesting, and it agrees with what I see clinically, is the high incidence of peripheral meniscal tears. This is important because most (if not all) of these tears should be repaired. Repair of peripheral meniscal tears, especially with concurrent ACL reconstruction, represents the best opportunity for successful meniscal healing. Smith and Barrett attempt (unsuccessfully in my opinion) to explain their findings based upon a theory originally proposed by Hughston. This theory suggests that the semimembranosus muscle plays a role in peripheral medial meniscal tears. Another theory Smith and Barrett cite is based upon the role of the posterior horn of the medial meniscus serving as a "bumper" in the ACL-deficient knee. This theory makes more sense, as it is known to serve as a secondary stabilizer to anterior displacement of the tibia, and the extra force it must resist in the ACL-deficient knee may result in injury. Neither theory can be proven in this study, however, and the important thing to recognize is the high incidence of peripheral tears, not how they occur.

References

1. Bellabarba C, et al. Am J Orthop. 1997;26:18-23.

2. Cooper DE, et al. Clin Sports Med. 1991;10:529-548.