Orthopedics and Orthopedics Surgery

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Meniscal Injuries
Michael D’Amato, MD, and Bernard R. Bach, Jr., MD

Clinical Background
The importance of the menisci in preserving the health and function of the knee has been well established. Most of the functions performed by the menisci relate to protecting the underlying articular cartilage.

By increasing the effective contact area between the femur and the tibia, the menisci lower the load–per–unit area borne by the articular surfaces. Total meniscectomy results in a 50% reduction in contact area.

The menisci transmit central compressive loads out toward the periphery, further decreasing the contact pressures on the articular cartilage.

Half of the compressive load in the knee passes through the menisci with the knee in full extension and 85% of the load passes through the knee with the knee in 90 degrees of flexion.

Meniscectomy has been shown to reduce the shock absorption capacity of the knee by 20%.

Meniscal Movement
The lateral meniscus has been shown to be more mobile than the medial meniscus. In each meniscus, the anterior horn has greater mobility than the posterior horn. The reduced mobility of the posterior medial meniscus may result in greater stresses in this area, leading to increased vulnerability to injury. This would explain the higher rate of meniscal tears that occur in the posterior medial meniscus.

Weight-bearing has been shown to effect few changes in the movement of the menisci, although it has been suggested that meniscal loading may lead to distraction of radial tears. ROM of the knee, especially increasing rotation and flexion of the knee past 60 degrees, results in significant changes in the AP position of the menisci. Clinically, second-look arthroscopy has shown that extension of the knee maintains a posterior horn meniscal tear in a reduced position, and knee flexion results in displacement of the tear.

Meniscal Healing
King, in 1936, first noted that communication with the peripheral blood supply was critical for meniscal healing. Arnoczky and Warren, in 1982, described the microvasculature of the menisci. In children, the peripheral blood vessels permeate the full thickness of the meniscus. With age, the penetration of the blood vessels decreases. In adults, the blood supply is limited to only the outer 6 mm or about a third of the width of the meniscus. It is in this vascular region that the healing potential of a meniscal tear is greatest (Fig. 4–42). This potential drops off dramatically as the tear progresses away from the periphery.
Meniscal healing is also influenced by the pattern of the tear (Fig. 4–43).

Longitudinal tears have a more favorable healing potential compared with radial tears. Simple tear patterns are more likely to heal than complex tears. Traumatic tears have higher healing rates than degenerative tears, and acute tears more so than chronic tears.
Rehabilitation Considerations

Weight-bearing and Motion
Although weight-bearing has little effect on displacement patterns of the meniscus and may be beneficial in approximating longitudinal tears, weight-bearing may place a displacing force across radial tears. Several studies have confirmed the benefits of early motion by demonstrating meniscal atrophy and decreased collagen content in menisci after immobilization. ROM of the knee before 60 degrees of flexion has little effect on meniscal displacement, but flexion angles greater than 60 degrees translate the menisci posteriorly. This increased translation may place detrimental stresses across a healing meniscus. As knee flexion increases, compressive loads across the meniscus also increase. The combination of weight-bearing and increasing knee flexion must be carefully balanced in the development of a rehabilitation protocol.

Axial Limb Alignment
Varus malalignment tends to overload the medial compartment of the knee, with increased stress placed on the meniscus, and valgus malalignment has the same effect on the lateral compartment and lateral meniscus. These increased stresses may interfere or disrupt meniscal healing after repair. Patients with limb malalignment tend to have more degenerative meniscal tears, which have been suggested to have an inherently poorer healing capacity. The use of an “unloader” brace has been recommended to help protect the healing meniscus, although no scientific data exist to support this approach.

Rehabilitation after Meniscectomy
Because there is no anatomic structure that must be protected during a healing phase, rehabilitation may progress aggressively. The goals are early control of pain and swelling, immediate weight-bearing, obtaining and maintaining a full ROM, and regaining quadriceps strength.

Rehabilitation after Meniscal Repair
Current studies support the use of unmodified accelerated ACL rehabilitation protocols after combined ACL reconstruction and meniscal repair. In tears with decreased healing potential (such as white-white tears, radial tears, or complex pattern tears), limiting weight-bearing and limiting flexion to 60 degrees for the first 4 weeks have been suggested to better protect the repair and increase the healing potential of these difficult tears. However, we are unaware of any published studies that support these measures.

Rehabilitation after isolated meniscal repair remains controversial. The healing environment clearly is inferior to that with concomitant ACL reconstruction, but good results have been obtained with accelerated rehabilitation protocols after isolated meniscal repairs.

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