What is a lateral meniscus tear?

A lateral meniscus tear is an injury characterized by tearing of cartilage tissue within the knee joint located at the outer aspect of the knee, typically resulting in pain in this region.

The knee joint comprises of the union of two bones: the long bone of the thigh (femur) and the shin bone (tibia) (figure 1). Between the bone ends are 2 round discs made of cartilage called the medial (inner) and lateral (outer) meniscus (figure 1).

Each meniscus acts as a shock absorber cushioning the impact of the femur on the tibia during weight-bearing activity. Normally the surface of the meniscus is very smooth allowing easy movement of the femur on the tibia. Occasionally due to excessive weight bearing or twisting forces, the meniscus can be torn or damaged so that the surface is no longer smooth. When this occurs to the lateral meniscus, it is known as a lateral meniscus tear.

Injuries to the lateral meniscus are less common than medial meniscus injuries. Occasionally a lateral meniscus tear may occur in combination with injuries to other structures of the knee, such as the cruciate ligaments, the collateral ligaments, or the medial meniscus.

Causes of a lateral meniscus tear

Lateral meniscus tears often occur traumatically due to excessive weight bearing and twisting forces. This typically occurs in sports that require sudden changes of direction and twisting movements (sometimes in combination with excessive straightening or bending of the knee). These sports may include football, soccer, basketball, netball and snow skiing. Lateral meniscal tears frequently take place when the foot is fixed on the ground and a twisting force is applied to the knee (e.g. when another player's body falls across the leg, or when a player is tackled) or following a forceful jump or landing.

Lateral meniscal tears may also occur over time through gradual wear and tear associated with overuse. This typically occurs in association with repetitive or prolonged weight bearing or twisting forces that are beyond what the meniscus can withstand (e.g. excessive distance running). Overuse meniscal injuries may also be associated with degenerative changes to the knee joint. In older patients where degenerative changes are present, injury to the lateral meniscus may occur with a relatively trivial movement.

Signs and symptoms of a lateral meniscus tear

Patients with a lateral meniscal tear often experience a sudden, sharp pain at the outer aspect, front or back of the knee at the time of injury. Some patients may also report that they heard an audible sound at the time of injury or experienced a tearing sensation. There is usually pain with weight bearing activity and twisting movements of the knee. Patients may also experience pain when climbing stairs, attempting to kneel or when squatting. Swelling is often present and may occur a few hours after injury or, more commonly, in the following days. Tenderness may also be experienced on firmly touching the knee joint at the outer aspect of the knee. The knee may also feel weak or unstable and may click, lock or give way during certain movements.

In minor cases of lateral meniscus tears there may be little or no immediate symptoms. In these cases, symptoms may develop gradually over the coming days, typically with an increase in weight bearing or twisting activity. In more severe cases there may be severe pain and significant restriction in knee range of movement. Intermittent locking, clicking sensations, and episodes of giving way or collapsing may be present. The patient may also walk with a limp or, be unable to weight bear due to pain.

Diagnosis of a lateral meniscus tear

A thorough subjective and objective examination from a physiotherapist is usually sufficient to diagnose a lateral meniscus tear. Investigations such as X-ray and MRI are sometimes used to confirm diagnosis and exclude the presence of other injuries to the knee. In rare cases, where an MRI has proven inconclusive, an investigative arthroscope may be performed to assist diagnosis.

Surgery for a lateral meniscus tear

Despite appropriate physiotherapy management, a small percentage of minor meniscal tears fail to improve and subsequently require surgery in order to get back to full activity. The majority of large meniscal tears also require surgery. This is particularly true in those cases where the knee is 'locked'. Surgery for lateral meniscus tears is minimally invasive. The procedure is called a knee arthroscopyand involves a surgeon cutting away the torn part of the cartilage via 2 small incisions so that the meniscal surface is smooth once again. The aim of surgery is to preserve as much of the meniscus as possible in attempt to maintain shock absorption capacity of the knee and to prevent future degeneration. The treating physiotherapist and doctor will refer to a specialist if surgery is indicated. Physiotherapy and rehabilitation is then required following surgery to ensure an optimal outcome and enable a safe return to sport or activity. This should ideally commence before surgery to hasten recovery.

Prognosis of a lateral meniscus tear

Those patients with minor lateral meniscus tears that are managed conservatively can usually expect to return to sport or activity in approximately 2 - 4 weeks. For moderate tears that are managed conservatively return to sport or activity may take 4 - 6 weeks or longer.

Minor lateral meniscus tears that are managed surgically can sometimes return to sport or activity within 4 – 6 weeks, although most surgical repairs (especially when the meniscus tear is moderate to severe) will usually require a rehabilitation period of 6 - 8 weeks or longer. If there is damage to other structures in the knee, such as the anterior cruciate ligament, rehabilitation may require an extended period. It is important that lateral meniscus injuries are managed appropriately, as inappropriate treatment may lead to the development of early knee osteoarthritis.

Contributing factors to the development of a lateral meniscus tear

There are several factors which can predispose patients to developing this condition. These need to be assessed and corrected with direction from a physiotherapist. Some of these factors include:

• muscle weakness (particularly of the quadriceps, hamstrings or gluteals)
• muscle tightness (particularly of the quadriceps, hamstrings or calf)
• inappropriate or excessive training
• inadequate warm up
• joint stiffness (especially the knee, hip or ankle)
• poor biomechanics
• postural issues
• inadequate rehabilitation following a previous knee injury
• decreased fitness
• fatigue
• poor pelvic and core stability

Physiotherapy for a lateral meniscus tear

Physiotherapy treatment is vital to hasten the healing process and ensure an optimal outcome in all patients with lateral meniscus tears regardless of whether they have surgery.Physiotherapy treatment may comprise:

• soft tissue massage
• electrotherapy
• taping or bracing to support the knee
• the use of crutches
• mobilization
• dry needling
• hydrotherapy
• ice or heat treatment
• progressive exercises to improve flexibility, balance and strength (especially the VMO muscle)
• activity modification advice
• education
• biomechanical correction
• anti-inflammatory advice
• weight loss advice where appropriate
• the use of Real-Time Ultrasound to assess and retrain the VMO muscle
• a gradual return to activity program

For those patients who are undergoing surgery to repair the torn meniscus, physiotherapy and rehabilitation should commence prior to surgery. This may include treatment to reduce pain and swelling, electrotherapy, strengthening and range of movement exercises, the use of a compression bandage, and the use of crutches etc. Following surgery, physiotherapy and rehabilitation is essential to assist the healing process and ensure an optimal outcome.

In the final stages of rehabilitation for all lateral meniscus tears the physiotherapist can devise an appropriate return to sport or activity plan. Returning to activity too soon or without adequate rehabilitation will often lead to knee swelling and re-injury to the meniscus.

Other intervention for a lateral meniscus tear

Despite appropriate physiotherapy management, some patients with lateral meniscus tears fail to improve either conservatively or following surgery. When this occurs the treating physiotherapist or doctor can advise on the best course of management. This may include further investigations, pharmaceutical intervention, corticosteroid injection, or further surgery.

Exercises for a lateral meniscus tear

The following exercises are commonly prescribed to patients with a lateral meniscus tear. You should discuss the suitability of these exercises with your physiotherapist prior to beginning them. Generally, they should be performed 3 times daily and only provided they do not cause or increase symptoms.

Your physiotherapist can advise when it is appropriate to begin the initial exercises and eventually progress to the intermediate and advanced exercises. As a general rule, addition of exercises should take place provided there is no increase in symptoms.

Initial Exercises

Knee Bend to Straighten

Bend and straighten your knee as far as possible and comfortable without increasing your pain (figure 2). Repeat 10 - 20 times provided there is no increase in symptoms.

Figure 2 – Knee Bend to Straighten (right leg)

Static Quadriceps Contraction

Tighten the muscle at the front of your thigh (quadriceps) by pushing your knee down into a towel (figure 3). Put your fingers on your inner quadriceps to feel the muscle tighten during contraction. Hold for 5 seconds and repeat 10 times as hard as possible without increasing your symptoms.

Figure 3 – Static quadriceps contraction (left leg)