Meniscus Tears: Diagnosis, Repair Techniques, and Clinical Outcomes

Candidates

Candidates for meniscal repair are active patients younger than 60 years, including skeletally immature children and adolescents. Trauma during sports activities involving sudden twisting and turning is one of the most common etiologies of meniscus tears. Many meniscus tears that occur during ACL injuries extend into the middle third avascular region and are amendable to a meticulous inside-out suture repair. Magnetic resonance imaging (MRI) provides important information regarding the type of meniscus tear and potential for repair to preserve function. In knees in which repair is deemed possible, it is important to restrict strenuous activities and athletics until surgery to avoid further damage to the joint and meniscus.

Degenerative meniscus tears are much less frequently repaired because the meniscus tissue is poor in quality and often fragmented into multiple pieces. Occasionally, MRI will indicate that a repair may be possible, such as in cases of large horizontal tears. Frequently, the symptoms of tibiofemoral pain will diminish over 6 to 12 weeks in degenerative tears in older patients, allowing a conservative approach. In other knees, symptoms of locking episodes and joint swelling are more persistent or severe and require arthroscopic intervention.

Meniscus repair is frequently performed with concurrent operative procedures such as knee ligament reconstruction. Patients with lower extremity varus or valgus malalignment and associated meniscus tears are especially considered for meniscus repair. The malalignment produces high medial or lateral tibiofemoral compartment loads, and a functional meniscus is required to prevent articular cartilage deterioration. Unfortunately, many meniscus tears in varus- or valgus-aligned limbs are degenerative in nature and not repairable.

Candidates for meniscus repair must be compliant and willing to follow the postoperative program of rehabilitation, including crutch support for 4 weeks. Those in whom complex tears are repaired must agree to avoid strenuous activities and deep knee flexion for 4 to 6 months; otherwise, the repair site may be disrupted and fail.

Meniscus Tear Classification

Meniscus tears are classified according to location, type of tear, and integrity and damage to meniscal tissue and the meniscus attachment sites. This classification, along with meticulous arthroscopic inspection of the tear site, allows the surgeon to determine whether a tear is repairable. The meniscus body is divided into anterior, mid body, and posterior thirds. In addition, Anderson and associates recommended a classification system of zone 1 (rim width <3 mm), zone 2 (rim width 3-4 mm), and zone 3 (rim width >5 mm). Tears located at the peripheral attachment sites (meniscofemoral and meniscotibial), or zone 1, are referred to as outer third or red-red (R/R) tears. Single longitudinal tears are usually located in this region ( Fig. 23-1 ). These tears are classified as R/R because both portions have an internal blood supply and are repaired in all cases with high success rates expected.

Tears located in the middle third region (zone 2) are classified as red-white (R/W), and tears located in the inner third (zone 3) are termed white-white (W/W). R/W tears occur at the junction between the outer and middle third regions, approximately 4 mm from the meniscal attachment, with a vascular supply present predominately in the outer third of the tear. White-white tears are located in the region in which no blood supply exists to either portion of the tear. When a repair is performed for these tears, the sutures may provide access to the vascular supply. In addition, rasping of the meniscus-synovial border provides a vascular supply to the repair site from synovial migration of cells on the surface of the meniscus. It should also be noted that the vascular supply to the meniscus, particularly in younger patients, still requires study and may extend greater than 5 mm in depth into the central zone.

Repairs of complex tears and tears that extend into the middle third region are evaluated on an individual basis. Tear patterns in this region include single longitudinal, double longitudinal, triple longitudinal, horizontal, radial, and flap. The rationale for repair of these tears is that removal results in essentially a total meniscectomy because a substantial amount of meniscal tissue is resected ( Fig. 23-2 ). This is especially concerning in younger patients in their second to fourth decades of life and all athletically active individuals. These tears are often repairable with reasonable success rates, as described later in this chapter.

Single meniscal tears occur in a single plane, regardless of location. These include longitudinal, radial, and horizontal tears. These tears are most commonly found in the posterior horn and are usually repairable. Complex tears occur in more than one plane or direction. These include tears in the vertical plane (double or triple longitudinal), in the vertical and horizontal planes, or in the vertical and radial planes (flap tears). Each component of the tear is identified and may or may not be repairable.

The decision for repair is based on the qualitative evaluation of the meniscus tissue's integrity and absence of traumatic or degenerative changes. The meniscus tissue should appear nearly normal, with no secondary tears or fragmentation that would affect its projected function. The meniscus rim should be trimmed of tear fragments. A horizontal tear into the meniscus rim is a negative variable because it is difficult with sutures to fully restore the tear site owing to inner gaps between the horizontal tear arms. This is one indication in which a fibrin clot may provide a benefit. A large flap tear may be reduced and approximated, and if the tissue has adequate integrity, repair is considered in active patients. A meniscus that has been displaced in the notch may shorten and contract within 3 to 4 weeks, preventing reduction, and accordingly, early arthroscopy and repair are indicated. More specific recommendations of repair indications and techniques are provided for specific tears later in this chapter. The role of incorporating a fibrin clot or platelet-rich plasma to aid the healing process remains poorly understood. Clinical studies are lacking at present; the surgeon's judgment is therefore required on a case-by-case basis.

Meniscus Function

The menisci provide several vital mechanical functions in the knee joint. They act as a spacer between the femoral condyle and tibial plateau and, when there are no compressive weight-bearing loads across the joint, limit contact between the articular surfaces. The amount of joint narrowing due strictly to the physical absence of the menisci is in the range of 1 to 2 mm.

Under static-loading conditions, the menisci assume a significant load-bearing function in the tibiofemoral articulation. At least 50% of the compressive load of the knee joint is transmitted through the menisci in 0 degrees of extension, and approximately 85% of the load is transmitted at 90 degrees of flexion. The presence of the menisci increases the contact area to 2.5 times the size compared with a meniscectomized joint. The larger contact area provided by the menisci reduces the average contact stress (force/unit area) acting between the joint surfaces. Removal of as little as 15% to 34% of a meniscus increases contact pressures by more than 300%. After total meniscectomy, the tibiofemoral contact area decreases by approximately 50%, and the contact forces increase twofold to threefold.

Lee and colleagues evaluated the effects of serial meniscectomies in the posterior segment of the medial meniscus. Compared with the intact state, the medial contact area decreased from 20% (after removal of 50% of the posterior segment of the medial meniscus) to 54% (total meniscectomy). Medial contact stress increased from 24% (50% meniscectomy) to 134% (total meniscectomy). Medial peak contact stress increased from 43% (50% meniscectomy) to 136% (total meniscectomy). The peripheral portion of the medial meniscus provides a greater contribution to increasing contact area and decreasing contact stresses compared with the central portion. Muriuki and associates created 15- to 20-mm single longitudinal tears in the R/W portion of the posterior horn of the medial meniscus in cadaver knees and reported significant increases in maximum contact pressure and reductions in contact area that were similar to those associated with total meniscectomy.

The menisci remain in constant congruity to the tibial and femoral articular surfaces throughout knee flexion and extension and contribute to stability of the knee joint. Medial meniscectomy performed after sectioning of the ACL results in increased anterior tibial translation at 20 to 30 degrees of knee flexion during a Lachman test compared with that measured in knees with an intact ACL. Thus the loss of the medial meniscus after an ACL rupture is problematic, especially in varus-angulated knees. Spang and associates reported significant increases in ACL strain measured with a variable reluctance transducer in cadaver knees following medial meniscectomy at 60 and 90 degrees of knee flexion ( P < .05). Increases in meniscal strain have also been reported following ACL transection in the laboratory. In knees with posterior cruciate ligament (PCL) ruptures, the increase in posterior tibial translation allows a change in tibiofemoral contact in which the menisci posterior horns have a reduced weight-bearing function. This is sometimes referred to as a PCL meniscectomy . The effect is greater for the medial compartment in which the middle and anterior thirds of the medial meniscus have less weight-bearing function than the lateral meniscus.

The lateral meniscus provides concavity to the lateral tibiofemoral joint owing to the normal posterior convexity of the lateral tibial condyle, allowing the stabilizing effect of joint weight-bearing forces to reduce lateral compartment anterior and posterior translations. Lateral meniscectomy performed after sectioning of the ACL results in increased anterior tibial translation at 30 degrees of knee flexion during a pivot shift test compared with that measured in knees with an intact ACL. Recent studies indicate that the lateral meniscus may be a more important restraint than the medial meniscus to anterior tibial translation during the combined loads applied during the pivot shift test. Partial lateral meniscectomy has been estimated to increase contact pressures by 50% during the stance phase of gait. Total lateral meniscectomy results in a 45% to 50% decrease in total contact area and a 235% to 335% increase in peak local contact pressure.

Loss of the medial meniscus results in a smaller, more medial displacement of the center of pressure. Load is subsequently transmitted through the articular cartilage and subchondral bone to the underlying cancellous bone through this more central route, thus stress-shielding the proximal aspects of the medial tibial cortex. The deleterious effects of meniscectomy on tibiofemoral compartment articular cartilage have been demonstrated in multiple experimental studies. For these reasons, it is paramount to preserve meniscal function, if possible, in knees with varus osseous malalignment.

In addition, the menisci provide specific load-bearing functions to the knee joint during walking and are theorized to assist in overall lubrication of the articular surfaces. Even partial meniscectomy affects knee joint kinetics by reducing range of knee motion and increasing knee adduction moments during stance.

Meniscus Suture Repair Biomechanics

Historically, biomechanical investigations have compared properties of suture techniques with those of rigid all-inside meniscus fixation devices. * Problems with devices such as meniscal arrows, screws, and darts have been well-documented experimentally and clinically. In addition, several studies concluded vertical sutures were superior to both horizontal sutures and meniscus arrows in mean load-to-failure and maximum tensile strength values. ^†

* References .

† References .

More recently, suture repair techniques, suture materials, and all-inside devices have been tested experimentally to determine initial fixation strength and performance under cyclic loading with varying results ( Table 23-1 ). The majority of studies published to date have been performed in porcine knee models rather than human models. Ultra-high-molecular-weight polyethylene-based (UHMWPE) sutures used in all-inside techniques are now available with newer all-inside repair devices, such as NovoStitch (Ceterix), Hi-Fi (Conmed Linvatec), and FiberWire (Arthrex). Further studies are required to determine the biomechanical properties of these sutures and devices as used for meniscus repair. The lack of both experimental and clinical data precludes definitive recommendations for any one of the currently available all-inside devices over the others. In addition, the reported load-to-failure rates for most of these devices that use one or two sutures is low, justifying consideration for inside-out repairs with multiple sutures to be described. In addition, the low load-to-failure rates and creep properties identify the need for slower postoperative rehabilitation in regard to resumption of full weight bearing, especially for complex meniscus repairs and root repairs. At present, there is little scientific justification regarding when it is safe to resume full weight bearing or return to sports after these types of repairs, although it is appreciated that peripheral longitudinal tears at the R/R junction demonstrate adequate healing within the first 4 to 6 weeks after surgery. The postoperative rehabilitation recommendations are provided in Chapter 25 , with empirical rules build in to protect the meniscus repair.

Meniscus Repair Healing

There are few published experimental studies on the strength of a healing meniscus suture repair (without cell-based therapy or growth factors) subjected to tensile loads or assessed for residual defects and complications. In 1995, Miller and associates reported acceptable healing rates of single longitudinal meniscus tears repaired in the periphery in a goat model. More recently, Miller and colleagues found unacceptably high rates of chondral damage 6 months after implantation of Meniscal Fastners (Mitek, Westwood, MA), BioStingers (Linvatec), and Clearfix Screws (Mitek) in this same animal model. The authors cautioned against the use of these rigid all-inside devices in humans. In 2009, Hospodar and coworkers reported superior healing of meniscus repairs done with an inside-out suture technique compared with the all-inside FasT-Fix device in goats. The FasT-Fix group had longer residual full-thickness defects ( P = .01) and longer residual partial-thickness defects ( P < .001) 6 months postoperatively.