bubble_chart Overview

On the tibial articular surface, there are medial and lateral crescent-shaped bones called menisci. The peripheral edges are thicker and tightly connected to the joint capsule, while the central portions are thinner and free. The medial meniscus is C-shaped, with its anterior horn attached in front of the anterior cruciate ligament insertion and its posterior horn attached between the tibial intercondylar eminence and the posterior cruciate ligament insertion. The middle portion of its outer edge is tightly connected to the medial collateral ligament. The lateral meniscus is O-shaped, with its anterior horn attached in front of the anterior cruciate ligament insertion and its posterior horn attached in front of the posterior horn of the medial meniscus. Its outer edge is not connected to the lateral collateral ligament, and it has greater mobility than the medial meniscus. The menisci can move to some extent with knee joint motion, moving forward during knee extension and backward during flexion. Composed of fibrocartilage, the menisci lack their own blood supply and primarily derive nutrients from synovial fluid. Only the peripheral portions connected to the joint capsule receive some blood supply from the synovial membrane. Therefore, except for injuries to the peripheral edges that can heal on their own, meniscal tears cannot self-repair. After meniscectomy, the synovial membrane can regenerate a thin and narrow fibrocartilaginous meniscus. Normal menisci deepen the tibial condylar concavity and cushion the medial and lateral femoral condyles, enhancing joint stability and absorbing shock.

bubble_chart Etiology

It is mostly caused by torsional external force. When one leg bears weight and the lower leg is fixed in a semi-flexed, abducted position, the body and thigh suddenly rotate inward. The medial meniscus is subjected to rotational pressure between the femoral condyle and the tibia, leading to a meniscus tear. For example, the greater the degree of knee flexion during a sprain, the more posterior the tear location. The mechanism of lateral meniscus injury is the same, but the direction of the force is antagonistic. If the torn meniscus partially slips into the joint space, it can cause mechanical obstruction of joint movement, hindering flexion and extension activities, resulting in "locking."

In severe traumatic cases, the meniscus, cruciate ligaments, and collateral ligaments may be injured simultaneously.

The site of meniscus injury can occur at the anterior horn, posterior horn, middle, or edge of the meniscus. The shape of the injury can be transverse, longitudinal, horizontal, or irregular, and may even fragment into free bodies within the joint.

bubble_chart Clinical Manifestations

Most cases have a clear history of trauma. In the acute phase, the knee joint exhibits significant pain, swelling, and effusion, with restricted flexion and extension. After the acute phase, the swelling and effusion may subside on their own, but pain persists during movement, especially when climbing stairs, walking on slopes, squatting, running, or jumping. In severe cases, limping or functional impairment in flexion and extension may occur. Some patients experience "locking" or a clicking sound during knee flexion and extension.

1. **Tenderness Location** The tender area usually corresponds to the site of the lesion, which is crucial for diagnosing meniscus injury and identifying its location. With the knee in a semi-flexed position, press along the upper edge of the tibial condyle (the margin of the meniscus) from front to back with the thumb. Fixed tenderness indicates meniscus injury. Passive flexion-extension or internal/external rotation of the lower leg during palpation may exacerbate the pain, and sometimes abnormal meniscus movement can be felt.

2. **McMurray Test (Rotational Compression Test)** The patient lies supine. The examiner holds the ankle with one hand and supports the knee with the other, flexing the hip and knee maximally. The lower leg is then abducted and externally rotated, or adducted and internally rotated, while gradually extending the knee. Pain or a clicking sound indicates a positive result, with the location of pain or sound determining the injury site.

3. **Forced Hyperextension or Hyperflexion Test** Passive forced hyperextension or hyperflexion of the knee joint is performed. Pain during hyperextension suggests anterior meniscus injury, while pain during hyperflexion indicates posterior meniscus injury.

4. **Lateral Compression Test** With the knee extended, forceful passive adduction or abduction of the knee is performed. Pain at the affected joint space due to compression suggests meniscus injury.

5. **Single-Leg Squat Test** The patient stands on one leg and gradually squats, then stands up. While the unaffected side is normal, the affected side may experience pain at a certain point during squatting or standing due to compression of the injured meniscus, possibly preventing full squatting or standing.

6. **Gravity Test** The patient lies on their side and actively flexes and extends the knee while lifting the lower leg. Pain occurs when the affected joint space faces downward due to compression of the injured meniscus. No pain occurs when the affected joint space faces upward.

7. **Grinding Test** The patient lies prone with the knee flexed. The examiner holds the ankle and presses the lower leg downward while performing internal and external rotation. Pain indicates meniscus injury due to compression and grinding. No pain occurs if the lower leg is lifted and rotated.

**X-ray Examination:** Although X-rays (anteroposterior and lateral views) cannot reveal meniscus injury, they help exclude other bone and joint disorders. Knee arthrography has limited diagnostic value and may cause discomfort, so it is not recommended.

**Knee Arthroscopy:** Arthroscopy allows direct visualization of the meniscus injury's location, type, and other intra-articular structures, aiding in the diagnosis of challenging cases.

In summary, the diagnosis of meniscus injury primarily relies on medical history and clinical examination. Most patients have a trauma history and fixed tenderness at the affected joint space. Comprehensive analysis of various tests usually leads to an accurate diagnosis. For severe trauma cases, concurrent injuries to collateral ligaments and cruciate ligaments should be assessed. In advanced cases, secondary traumatic arthritis should also be considered.

A discoid meniscus, which is thicker and disc-shaped, is more prone to injury and is often bilateral. The main symptom is a distinct, crisp clicking sound during joint movement. A palpable mass with tenderness may be felt at the lateral meniscus. Mucoid degeneration after meniscus injury can lead to a meniscal cyst, with symptoms similar to meniscus injury, including a noticeable local mass that becomes more prominent during knee extension.

bubble_chart Diagnosis

Most patients have a clear history of knee sprain. After the injury, the knee joint experiences severe pain, cannot straighten automatically, and the joint swells. Tenderness at the knee joint space is an important basis for meniscus injury.

bubble_chart Treatment Measures

1. Acute phase: If there is significant effusion (or hemarthrosis) in the joint, the fluid should be aspirated under strict aseptic technique. If the joint is "locked," manual reduction should be performed to release the "lock," followed by application of a long-leg cast extending from the upper third of the thigh to above the ankle to immobilize the knee in extension for 4 weeks. The cast should be properly molded, and the patient can ambulate with the cast. During immobilization and after its removal, active quadriceps exercises should be performed to prevent muscle atrophy.

2. Chronic phase: If conservative treatment fails and symptoms and signs are significant with a clear diagnosis, early surgical removal of the injured meniscus should be performed to prevent traumatic arthritis. Postoperatively, the knee should be immobilized in extension with a compressive bandage. Quadriceps isometric exercises should begin the next day, followed by straight leg raises after 2–3 days to prevent quadriceps atrophy. Weight-bearing ambulation can begin after 2 weeks, and normal function usually recovers within 2–3 months postoperatively.

3. Application of arthroscopy: Arthroscopy can be used for the treatment of meniscus injury. Suturing can be performed for peripheral meniscal tears, while partial meniscectomy is typically done to preserve the uninjured portion. Emergency arthroscopy can be performed for early suspected meniscus injury to enable early management, shorten the treatment course, improve outcomes, and reduce the incidence of traumatic arthritis. Arthroscopic surgery is minimally invasive and allows for rapid recovery. {|102|}