Partial ACL Tears

Abstract & commentary

Synopsis: Partial ACL ruptures involving less than 50% of the ligament have a good prognosis over the long term.

Source: Messner K, Maletius W. Eighteen- to twenty-five-year follow-up after acute partial anterior cruciate ligament rupture. Am J Sports Med 1999;27:455-459.

Partial anterior cruciate ligament (acl) tears occur less frequently than complete ruptures, and there is uncertainty surrounding their long-term significance. As one would expect, the amount of instability that develops appears proportional to the degree of initial injury. However, little is written concerning the natural history of partial ACL tears over the long term.

Messner and Maletius have followed a group of 22 consecutive patients with a partial ACL tear for a mean of 20 years (range, 18-25). All patients but one, who died, were available for evaluation, which is truly remarkable after such a long period. In each case the diagnosis of a partial ACL tear was made by arthroscopy and an examination under anesthesia within 10 days of injury. No patient had greater than 1+ anterior laxity or greater than 50% damage to the ligament.

Three patients had suture repair of the partially torn portion of the ACL, while all other partial ACL injuries were treated nonoperatively. Nine patients with greater than 2+ valgus laxity underwent primary repair of the medial collateral ligament (MCL), a procedure commonly performed 25 years ago. All patients had concomitant acute injuries in the knee. The period of initial immobilization of the knee depended on these concomitant injuries rather than the ACL and ranged from one to six weeks.

Patients were evaluated at 12 and again at 20 years post-injury by physical exam, instrumented arthrometry, weight-bearing X-rays, Tegner score for activity level, and Lysholm score for knee function. At the latest follow-up, quadriceps strength was assessed and quality-of-life issues were measured by SF-36 health survey.

During the entire follow-up period, no patient underwent ACL reconstruction. Two patients had arthroscopy for meniscal tears and one patient had a late MCL injury. At the latest follow-up, 17 of 21 patients had Lysholm scores in the excellent range, and quality-of-life scores were generally better than those of a reference sample in the general population. Although only 13 of 22 patients were able to initially return to their preinjury activity level, the Tegner scores did not deteriorate between the 12- and 20-year time points.

At 20 years, 10 knees had a 1+ Lachman exam, two knees a 2+ Lachman, and one knee a positive pivot shift. Instrumented laxity measurements were less than 3 mm, which is considered normal, for 20 of 21 knees. About half the knees developed mild arthritis by X-ray, with little progression between 12 and 20 years. Four patients had more advanced changes.

Comment by David R. Diduch, MS, MD

From this excellent longitudinal prospective study by Messner and Maletius, we can conclude that partial ACL ruptures involving less than 50% of the ligament have a good prognosis over the long term. No patient underwent late ACL reconstruction over a 20-year follow-up period. However, because these were major knee injuries with concomitant damage to other structures in every case, few patients returned to the same level of preinjury sports activities. Given that the vast majority of patients developed only mild ACL laxity by exam or arthrometry, we might conclude that these other injuries were more significant over the long run.

Therefore, we can advise our patients with partial ACL injuries involving less than 50% of the ligament to not develop progressive laxity and to remain reasonably active. The difficulty clinically can be in determining whether the ACL is truly only partially torn with less than 50% ligament involvement. Magnetic resonance imaging (MRI) can be helpful in this regard and can be confirmed by instrumented laxity measurements. Arthroscopy, together with an exam under anesthesia, can be added when the diagnosis and treatment are in doubt. Some objective information is encouraged because patient guarding during the physical exam can confuse the picture and underestimate the degree of laxity. Of course, even partial tears by MRI that demonstrate clinical laxity by history and exam are functionally complete tears and should be treated as such.

Thus, this paper, despite the small numbers of patients, is an important addition to the ACL literature given the extremely long follow-up in nearly all patients. True partial ACL tears do well over the long term. The major limiting factor appears to be associated injuries. Just as with complete ACL tears, preserving the meniscus appeared to have the greatest influence on late arthritic changes. These findings will be helpful in the future as we counsel patients regarding optional treatment.