CHAPTER 7 Meniscal Repair
In 1885, Thomas Annandale performed the first meniscal repair.1 Because of the lack of understanding regarding the role of the meniscus, this discovery went unheralded for many years. Over time, the major role that the menisci play in load distribution, shock absorption, secondary stabilization of the knee joint, and proprioception was better understood. The menisci transmit at least 50% of a compressive load with the knee in extension.2 This increases to 85% in 90 degrees of flexion. Following a meniscectomy, the contact area is decreased by 50%, which increases the load per unit area and leads to subsequent degenerative changes in the knee. Removal of 15% to 34% of a meniscus can increase contact pressure more than 350%, so even partial meniscectomy can significantly alter joint biomechanics.3
As our knowledge of the essential role that the meniscus plays in proper knee function increased, preserving its function became increasingly important. Arthroscopic inside-out repair techniques gained popularity in the early 1980s.4 Following that, outside-in procedures were developed to decrease the chance of neurovascular injury. Recently, all-inside methods are increasingly being performed because of ease of application, decreased operative times, and even lower risk to the neurovascular structures. These techniques have led to healing rates from 60% to 80% for isolated repairs and up to 90% with concomitant anterior cruciate ligament (ACL) reconstruction.5
ANATOMY
The menisci are semilunar fibrocartilaginous structures that cover 50% of the medial and 70% of the lateral tibial plateaus.6 In cross section, their superior surface is concave and the inferior surface is convex to facilitate congruency with the femoral and tibial articular surfaces. The medial meniscus is shaped like a “C” whereas the lateral meniscus more closely resembles an incomplete “O” that is open medially. The coronary ligaments anchor both menisci to the tibia. Additionally, the medial meniscus has extensive peripheral attachments to the capsule and deep medial collateral ligament (MCL). Because of fewer capsular attachments, the popliteal hiatus, and no link to the neighboring collateral ligament, the lateral meniscus is more mobile and can displace up to 1 cm with knee range of motion.7 Its major connections to the posterior femur are through the ligaments of Humphrey and Wrisberg.
The solid microstructure of the menisci is 75% composed of collagen, with a 90% predominance of type I. The collagen is arranged in various patterns, but most of the fibers are aligned circumferentially.8 The orientation of these fibers permits absorption of the hoop stresses generated during natural movement. Radially oriented fibers provide a link between the circumferential bundles and add strength to the overall construct.9 Longitudinal or bucket handle meniscal tears disrupt these radial links between the circumferential collagen fibers. Repairing these tears may restore the biomechanical function of the native meniscus. Vertical mattress stitch configuration, which mimics the path of the radially oriented fibers, may secure more of the circumferential fibers and lead to greater repair strength more than other suture techniques.10
Thorough understanding of the meniscal microvasculature is necessary when considering repair of a tear because it plays a role in the potential for healing. Vessels from the superior and inferior branches of the medial and lateral genicular arteries perforate the menisci at the capsular attachments.11 In the area of the popliteal hiatus, the lateral meniscus lacks this peripheral supply and is an area of relative avascularity. The entire meniscus has a blood supply at birth but by 9 months, the inner third is avascular.12 By age 10, the menisci resemble those of an adult, with the outer 10% to 30% of the medial rim and 10% to 25% of the lateral rim vascularized. For clinical purposes, the menisci are often considered to have three zones, with the peripheral 3 mm considered vascular (red-red), more than 5 mm from the meniscocapsular junction, avascular (white-white), and between 3 and 5 mm, variable (red-white).13
PATIENT EVALUATION
History and Physical Examination
The diagnosis of a meniscal tear begins with a thorough initial evaluation in the office. Combining the patient’s history, physical examination, and plain radiographs can lead to a sensitivity of 88% to 95%, specificity of 72% to 92%, and positive predictive value of 58% to 85% for meniscal injuries.14 Meniscal tears in younger patients typically occur after an acute traumatic event, which often involves a twisting or hyperflexion mechanism. In the fourth decade and beyond, degenerative changes in the menisci often play a role in tears, so that less dramatic events, or even none at all, can results in a tear. Patients typically report pain, swelling, locking, catching, and giving out.
There are several tests described that focus directly on meniscal injuries. Unfortunately, no single physical examination finding can reliably predict the presence of a tear. A recent meta-analysis found a pooled sensitivity and specificity of 70% and 71% for McMurray’s test, 60% and 70% for Apley’s test, and 63% and 77% for joint line tenderness, respectively.15 Despite these findings, the authors concluded that none of the tests could accurately diagnose a tear based on the heterogeneity of study results. They could not explain the wide variation seen between each individual study’s results. Nevertheless, these tests are valuable to perform and help discern what is going on with the patient’s knee.
Diagnostic Imaging
Magnetic resonance imaging (MRI) has become the gold standard for meniscal imaging, although one must take into account that up to 13% of asymptomatic patients younger than 45 and 39% older than 45 years may have a “positive” scan.16 Benefits of MRI include providing additional information regarding associated injuries inside the knee, as well as tear location and configuration. A retrospective review following surgery for bucket handle meniscal tears has shown that whether a lesion was reparable or not could be accurately predicted 93% (26/28) of the time.17 The criteria created for this study included rim width less than 4 mm, tear length more than 1 cm, and isosignals of the peripheral rim and inner fragment with the normal contralateral meniscus in the same knee, indicating a nondegenerative process. Typically, contrast is not necessary to image the menisci properly, but should be used in cases involving a prior repair or if more than 25% of the meniscus has previously been resected to evaluate for a re-tear.18
TREATMENT
Indications and Contraindications
Once a patient has been diagnosed with a symptomatic tear of the meniscus and surgery is indicated, a number of factors play a role when considering whether the tear in this particular patient can and should be repaired. We typically explain to patients that much like real estate, location is the most important factor in addressing reparability. Adequate vascularity is a requirement for healing, so tears in the peripheral red-red zone have the best chance of healing. Tear configuration is the second most important factor, because longitudinal and vertical tears have a higher rate of healing than radial, horizontal cleavage, or degenerative tears. The third factor is size, or length, of the tear. Usually, a tear must be at least 1 cm long to be considered for repair, because smaller tears may be inherently stable and heal without surgery or be asymptomatic.19 Many of these factors are best judged arthroscopically. Acute tears also have a higher rate of healing than chronic injuries.20
Stability of the knee is another factor to consider when contemplating meniscal repair. Healing rates are less than 30% in an ACL-deficient knee that remains unreconstructed.5 It has been shown in several studies that simultaneous ACL reconstruction enhances the success of meniscal healing.21,22
In general, many surgeons consider patients younger than 40 years for meniscal repair. Although some studies have shown that older patients can heal following repairs,22 one has to weigh the risks and benefits versus a partial meniscectomy. Subjecting older patients to the risk of a possible second surgery if the tear doesn’t heal, as well as the difficulties of rehabilitation, may be unnecessary, considering that they might do just as well with a meniscectomy. In addition, older people are more likely to have articular cartilage changes and tissues with poorer healing qualities, which can jeopardize the success of a repair.
Conservative Management
Nonsurgical treatment may be considered for a select group of tears. Partial or small (less than 5 mm) complete tears located in the peripheral third may heal without operative intervention. This should only be considered for acute traumatic tears. Chronic and degenerative lesions are less likely to improve without surgery. In addition, meniscal tears generally do not heal in ligamentously unstable knees and nonoperative management is typically avoided.
