Meniscal tears and cartilage injuries are common issues in the knee of a female athlete. As female athletes are significantly more likely to suffer anterior cruciate ligament (ACL), tears they are also prone to associated injuries to their meniscus and articular cartilage. The incidence of high-grade chondral injuries ranges from 5% to 10% in patients over 40 years old, , and cartilage lesions may be even higher in athletes. Additionally, the incidence of chondral lesions in patients with recurrent patellofemoral instability may be as high as 63.2%–96%. , Meniscal tears are also more common in female athletes in gender-comparable sports. Making an accurate diagnosis of these injuries in the primary care setting can be crucial to patient care, as untreated meniscal and articular cartilage injuries can lead to progressive degenerative changes, pain, and functional limitation. This chapter will review the anatomy, clinical and radiographic presentation, and treatment of meniscal tears and cartilage pathology in the female athlete.
Meniscus Structure and Function
The gross shape of the meniscus can be divided into two parts: the medial meniscus and the lateral meniscus. The medial meniscus is C-shaped with a triangular cross section, whereas the lateral meniscus is more circular and covers more of the articular cartilage surface area. The medial and lateral menisci are connected by the transverse (intermeniscal) ligament anteriorly. While there are variants of the meniscal bony attachments, the menisci are connected to the tibia peripherally by the coronary ligaments and posteriorly to the femur by the meniscofemoral ligaments. The anterior meniscofemoral ligament is often referred to as the ligament of Humphrey and runs from the posterior horn of the lateral meniscus anterior to the posterior cruciate ligament (PCL) and inserts on the femur. The posterior meniscofemoral ligament is referred to as the ligament of Wrisberg. This ligament attaches to the posterior aspect of the lateral meniscus and crosses the PCL superiorly and medially to insert onto the medial femoral condyle.
The anatomy of the meniscus allows it to perform its two primary roles: modulating force transmission and acting as a secondary knee stabilizer. Owing to the elastic nature of the meniscus, it allows for more shock absorption than articular cartilage alone. The shape of the meniscus allows for increased contact area with the femoral condyles, thus increasing the congruency at the interface of the femur, meniscus, and tibia. Additionally, the shape of meniscus allows it to functionally deepen the tibial surface, which provides stability. The posterior horn of the medial meniscus acts as the main secondary stabilizer to anterior translation. The lateral meniscus is more mobile. Therefore it confers less stability than the medial meniscus, but in the setting of an ACL-deficient knee, the menisci become the primary knee stabilizers.
The meniscus is composed of fibroelastic cartilage, which contains collagen, proteoglycans, glycoproteins, and cells. Water comprises 65%–75% of the total meniscal contents and collagen constitutes the majority (60%–70%) of the dry weight of the meniscus. The majority of collagen in the meniscus is type I collagen. The meniscus also contains cells called fibrochondrocytes, which help synthesize the fibrocartilaginous matrix. An important point regarding the composition and structure of the meniscus is the orientation of its fibers. The meniscus contains both radially and longitudinally oriented fibers, which allow the meniscus to expand under compression and this is important for its functions of increasing contact area and providing shock absorption.
Blood supply and healing potential
The blood supply to the meniscus is by the middle genicular artery, which supplies the posterior horns; the medial inferior genicular artery, which supplies the peripheral 10%–30% of the medial meniscus; and the lateral inferior genicular artery, which supplies the peripheral 10%–25% of the lateral meniscus. In general, the innate healing potential of the meniscus is limited, largely because of its limited blood supply. Peripheral meniscal tears are considered to have healing potential because of their proximity to the vascular supply. It is believed that tears in the peripheral 25% of the meniscus can heal via fibrocartilage formation but that tears in the central 75% of the meniscus likely have limited to no intrinsic healing ability. Therefore identifying the location of meniscal tears is crucial, as the location of the tear is very important in determining the treatment plan.
Types of Injury
Meniscal tears are very common and are one of the most frequent causes of knee pain in active patients. The mean annual incidence of meniscal tears is approximately 60 per 100,000. , The majority of meniscal tears affect the medial meniscus in the posterior horn, and meniscal tears are most common in the third, fourth, and fifth decades of life. Meniscal tears are more common in males than in females in a ratio of 3:1 and are commonly associated with ACL injuries. Isolated medial meniscal tears in females younger than 30 years and with stable knees are uncommon. Injuries that are often concomitant with meniscal tears and should therefore raise the index of suspicion for a meniscal injury include tibial plateau fractures, femoral shaft fractures, and the presence of a hemarthrosis. ,
Classification/types of meniscal injury
There are several methods for classifying meniscal tears. Important factors to consider when evaluating meniscal tears include chronicity, location, pattern, and size of the tear. Chronicity (acute vs. degenerative) can be determined from a combination of clinical history and imaging and is a very important factor in determining the treatment plan. Location of the meniscal tear is also important for decision-making regarding management. The “red-red zone” of the meniscus is often referred to as the outer third, which is considered to be the region of the meniscus that has adequate blood supply and more intrinsic healing potential. The “red-white zone” refers to the middle third of the meniscus, and the “white-white zone” refers to the inner third of the meniscus. These areas do not have a direct blood supply and therefore their healing potential is limited. The pattern of meniscal tears is also variable and may include vertical/longitudinal, bucket handle, oblique/parrot beak, radial, horizontal, complex, and/or root tears ( Fig. 6.1 ). Finally, the size of the tear may be difficult to quantify, but it is also important in determining treatment. While no strict guidelines exist, understanding the percentage of the meniscus involved in the tear can be crucial to determine whether the patient needs a meniscectomy (partial removal of the torn meniscal segment) or a meniscal repair.
Meniscal cysts are also common and represent 1%–10% of meniscal pathology. While patients may present with an isolated meniscal cyst, meniscal cysts are very commonly associated with meniscal tears. Patients may present with symptoms similar to those found with meniscal tears or meniscal cysts may be encountered incidentally on a magnetic resonance imaging (MRI). Meniscal cysts can be perimeniscal (within the meniscus itself) or parameniscal (extruded fluid outside the meniscus). Typically, cysts form because the meniscal tear functions as a one-way valve, and synovial fluid is extruded and forms a discrete collection. Symptomatic cysts are more common laterally.
A discoid meniscus is a congenital abnormality in which the meniscus does not have its typical anatomic shape. The incidence of discoid meniscus is 3.5%–5% of the general population. It typically involves the lateral meniscus and can be bilateral in 25% of cases. Although not always symptomatic, the presence of a discoid meniscus often presents in adolescence with symptoms including pain, clicking, and mechanical locking. In a retrospective review of adolescent patients undergoing arthroscopy for isolated lateral meniscal pathology, 75% had a discoid meniscus. However, if patients are not symptomatic and the presence of a discoid meniscus is found only incidentally, surgical intervention is not recommended.
Clinical Presentation and Workup
The clinical presentation of patients with isolated meniscal tears may be variable. If the tear is isolated to the medial or lateral aspect of the meniscus, there may be pain, which localizes to the medial or lateral aspect of the knee. A careful history should be taken to elicit this. Additionally, patients should be asked whether or not they have mechanical symptoms, such as locking, catching, or clicking. They may also report delayed or intermittent knee swelling. Patients may or may not report a history of acute injury, but patients should always be asked if there were any inciting events that they can identify, as well as the mechanism of the injury. Typically, acute meniscal tears occur due to a twisting or hyperflexion injury and may present with acute pain and swelling subsequently. Degenerative tears, on the other hand, may occur in older patients who may report an atraumatic history of chronic pain and joint swelling.
A careful and thorough physical examination should be performed for any patient presenting with knee pain. To begin with, general alignment and gait should be observed and documented. Any swelling or joint effusion should be noted, and range of motion should be tested. It should be noted if there are mechanical blocks to motion at this time. Thorough palpation should be performed, and joint line tenderness is the single most sensitive physical examination finding for a meniscal tear.
There are several provocative tests that can be used to help identify a meniscal injury on physical examination. The McMurray test consists of flexing the knee, placing one hand on the joint line and the other holding the foot. The leg should be rotated as it is brought from flexion to extension. A palpable click with associated pain is considered a positive test result. The Thessaly test consists of having the patient stand with the knee at 20 degrees of flexion and twisting the knee into internal and external rotation. Any clicking or discomfort elicited is considered a positive test result. Lastly, the Apley compression test involves having the patient lie prone with the knee flexed. The examiner then applies an axial load and internally and externally rotates the tibia, again in an attempt to elicit any discomfort or a click in the knee. Although these tests may be helpful, they each have low sensitivity, specificity, and diagnostic accuracy, and therefore, advanced imaging is still recommended if the clinical suspicion for a meniscal tear is high. Finally, additional ligamentous testing and a thorough neurovascular examination should be performed to rule out any concomitant injury. Other diagnoses that may be confused with a meniscal tear include symptomatic plica, fat pad impingement, chondral lesions, and synovitis.
Plain radiographs should be obtained in patients presenting with knee pain, especially in the traumatic setting, to rule out fracture or gross abnormalities. Standard knee series should include anteroposterior, true lateral, and Merchant views. In addition to ruling out acute fractures and gross abnormalities, plain radiographs can help in evaluating overall alignment, degenerative changes, abnormal widening of the lateral compartment or squaring of the femoral condyles (commonly seen in the setting of a discoid meniscus), and meniscal calcifications (may be present in the setting of crystalline arthropathy). Thus other helpful views may include a posteroanterior flexion weight-bearing view to evaluate early joint space wear involving the posterior femoral condyles and standing hip-to-ankle images to evaluate overall alignment.
Although plain radiographs may be helpful in ruling out additional pathology, the mainstay imaging modality of choice for evaluating meniscal tears is MRI. If there is no acute pathology on plain radiographs and the patient continues to complain of symptoms consistent with a meniscal injury, an MRI should be considered ( Fig. 6.2 ). Although MRI is the most sensitive test for identifying meniscal pathology, there are also high false-positive rates, so results should be interpreted with caution. Other important findings to identify on MRI are a “double PCL” sign or a “double anterior horn” sign that can represent a bucket handle meniscus tear and often requires surgical intervention.
After a thorough evaluation is performed as described earlier, treatment of the meniscal tear can be determined. Nonoperative treatment is typically indicated for physiologically older patients with degenerative tears and for patients without the presence of mechanical symptoms. Nonoperative treatment can consist of a combination of activity modification, antiinflammatory agents, and physical therapy as first-line treatment. Occasionally, intra-articular injection may be offered in the setting of a chronic meniscal tear refractory to the aforementioned nonoperative measures for symptomatic relief.
Surgery may be indicated for patients with mechanical symptoms and/or patients who have had acute tears. Surgical options for meniscal tears include partial meniscectomy, meniscal repair, and, in limited cases, meniscal substitution or transplantation. Overall, indications for surgical intervention are highly patient- and surgeon-dependent, but they typically include a combination of symptoms that affect activities of daily living, work, or sports; positive physical examination findings consistent with a meniscal tear; failure to respond to conservative measures; and an absence of other causes of knee pain.
Partial meniscectomy is typically indicated for patients who have complex or degenerative tears that are not amenable to repair. Meniscal repair is best utilized for patients with tears in the “red-red zone”; those with vertical, longitudinal, or bucket handle tears; and those with root tears. Often the decision of whether to perform a partial meniscectomy or a meniscal repair is made intraoperatively after a more complete assessment of the tear pattern and tissue quality can be made under direct visualization. The decision to perform partial meniscectomy versus meniscal repair can be complex. Only approximately 20% of meniscal tears are considered reparable. Indications for meniscal repair are widely variable but may include a combination of the following: a complete vertical longitudinal tear >10 mm long, a tear in the peripheral 10%–30% of the meniscus, a tear that is unstable, a tear without secondary degeneration, a tear in an active patient, or a tear associated with concurrent ligamentous injury. In younger patients with borderline tear patterns, a concerted effort is typically made to save the meniscus and perform a meniscus repair, particularly when it is a lateral meniscal tear.
Meniscus allograft transplantation (MAT) is an advanced procedure that has become more commonly practiced over the last decade. MAT is typically utilized for young, symptomatic patients who have undergone a near-total meniscectomy previously. These patients typically have limited alternative surgical options and are at risk for developing early degenerative changes over the course of their lifetime without the stabilizing and shock-absorbing properties present of the meniscus. Although MAT is not considered a definitive treatment option for these patients, it may help prevent rapid progression of degenerative changes. In addition, on the medial side, medial MAT may be a useful adjunct to stabilize a knee undergoing ACL reconstruction in the setting of medial meniscus deficiency, particularly in the young patient population. There are some contraindications to perform MAT, which include inflammatory arthritis, ligamentous instability, obesity, grade III-IV chondral wear, diffuse arthritis, and malalignment. Results at a minimum of 10-year postoperative follow-up have demonstrated survivorship rates of 73.5% at 10 years and 60.3% at 15 years, with improved functional outcomes compared to preoperative scores.
Articular Cartilage Injuries
Structure and Function
Types of cartilage
Articular (hyaline) cartilage is a specific type of cartilage that lines joint surfaces. Other types of cartilage in the human body include fibroelastic cartilage, fibrocartilage, elastic cartilage, and physeal cartilage. While articular cartilage injuries may occur on any articular surface, this chapter will focus on the articular cartilage injuries in the knee.
Articular cartilage is composed primarily of water, which accounts for approximately 75% of its overall mass. The remainder of articular cartilage consists of collagen (of which 90% is type II), proteoglycans, noncollagenous proteins, and cells. The cells within articular cartilage are primarily chondrocytes, which help produce collagen, proteoglycans, and enzymes. The composition of articular cartilage is essential to its function, as its high water content and structural organization help decrease friction and evenly distribute force.
Layers of articular cartilage
Normal articular cartilage is composed of several layers, which also inform its function. There are three distinct zones that have been identified based on chondrocyte cell morphology and type II collagen fiber orientation. The superficial zone is composed of type II collagen fibrils, which are oriented parallel to the joint line. This zone has the highest concentration of collagen and the highest cellular density. It contains flattened chondrocytes and sparse proteoglycans and is responsible for resisting shear forces. The next zone is the intermediate or transitional zone. This zone consists of type II collagen fibrils, which are oriented in an oblique and less organized fashion. This is the thickest layer within the articular cartilage, and this layer contains round chondrocytes and abundant proteoglycans. The final zone is the deep or basal layer. This layer is composed of type II collagen fibrils, which are oriented perpendicular to the joint. This layer contains round chondrocytes arranged in columns, has the highest concentration of proteoglycans, and is responsible for resisting compressive forces. Deep to the basal layer is the tidemark, which separates the true articular cartilage from the deep, calcified cartilage.
Stress response and injury
Articular cartilage is able to respond to various forms of stress and injury over time. Physiologic stress can stimulate matrix synthesis and inhibit chondrolysis; however, excess stress on articular cartilage can suppress matrix synthesis and promote chondrolysis. It has been proposed that primary chondrocyte cilia act as mechanosensory organelles, which can help modulate the adaptive signaling mechanisms in response to various levels and durations of mechanical loads.
Injury to articular cartilage can arise acutely as a result of a single mechanical load or multiple repetitive loads over time. Injury types can be categorized into microdamage (which typically results from repetitive blunt trauma with no gross disruption of the articular cartilage), chondral fractures (which consist of articular cartilage disruption ranging from surface disruption to lesions that reach the tidemark), and osteochondral fractures (which involve lesions that penetrate through the subchondral bone).
Innate repair and healing potential
Owing to its avascular nature, articular cartilage has limited healing potential, which makes management of articular cartilage injuries particularly challenging. With very limited inherent blood supply, articular cartilage relies primarily on synovial fluid for oxygen and nutrients. Superficial cartilage lesions (those that do not pass through the tidemark) do not typically result in true “healing,” as mature articular cartilage chondrocytes have limited proliferative potential. In contrast, deep cartilage lesions (those that do pass through the tidemark) can result in fibrocartilage healing. A deep laceration that penetrates the subchondral bone allows for hematoma formation and mesenchymal stem cell migration. However, the resultant fibrocartilage has distinct characteristics from native hyaline cartilage. In general, fibrocartilage has poor wear characteristics compared with normal hyaline articular cartilage.
Types of Injury
The spectrum of cartilage injuries is wide, ranging from acute focal defects to more chronic, diffuse injuries. Overall, the incidence of true articular cartilage injuries is unclear, but it is estimated that the incidence of high-grade chondral injuries ranges from 5% to 10% in people over 40 years old. , However, this likely underestimates the true incidence of articular cartilage injuries, as these estimates were obtained from arthroscopic studies and therefore likely more accurately reflect the incidence of symptomatic articular cartilage injuries. The incidence of asymptomatic articular cartilage injuries may be as high as 14%–59% in athletes.
The first step of classification for articular cartilage injuries should be descriptive and should focus on the location of the lesion. For the knee in particular, the location is essential, especially with regard to whether or not the lesion is in a weight-bearing region of the knee, as this is important for management. Lesions located in the femoral condyles afford the widest variety of treatment options, whereas lesions located in the patella and trochlea can be more difficult to treat, in large part due to the variable topography of these regions. Tibial cartilage defects can also be challenging to manage, given the relatively thin cartilage in this area and the difficulty in accessing the mid-tibia to posterior tibia through arthroscopic techniques.
Defect size is also pivotal in determining the treatment plan for patients with articular cartilage injuries. While the absolute size of a lesion is often referenced when making surgical decisions, it is important to remember that the lesion size relative to the size of patient’s bony anatomy is likely more clinically relevant. In general, small symptomatic lesions can be treated with a variety of procedures, whereas the options for the treatment of larger, more extensive articular cartilage defects are more limited.
There are two main classification systems commonly utilized to describe the severity of an articular cartilage lesion. The Outerbridge grading system was developed for arthroscopic evaluation of articular cartilage and includes ranges from grade 0 to grade IV. Grade 0 represents normal cartilage, grade I represents cartilage softening and swelling, grade II represents superficial fissures, grade III represents deep fissures without exposed bone, and grade IV represents exposed subchondral bone. The International Cartilage Repair Society (ICRS) also developed a grading system that consists of five different grades, ranging from 0 to 4. Grade 0 is normal cartilage. Grade 1 is nearly normal cartilage with only superficial lesions. Grade 2 is abnormal cartilage with lesions that extend to <50% of the cartilage depth. Grade 3 is severely abnormal cartilage with lesions that extend to >50% of the cartilage depth. Grade 4 is severely abnormal cartilage that has lesions that extend through the subchondral bone ( Fig. 6.3 ).