Torn Meniscus Symptoms And Causes

Introduction 

The meniscus (pronounced: <muh-nis-kuhs>) is a C-shaped piece of cartilage situated in the knee joint. There are two menisci (plural form, pronounced <muh-nis-kay> or <muh-nis-kee>) in each knee. They help to improve the fit between the thigh bone (femur) and the shin bone (tibia) at the knee joint and act as shock absorbers. 

The menisci can be torn through traumatic injury, often involving a twisting action of the knee, creating a shearing force. Tears can also occur without excessive forces being involved due to degenerative changes to the meniscal tissue. 

A torn meniscus is the most common type of knee injury.¹ These injuries are sometimes referred to as ‘knee cartilage tears’. 

Symptoms of a meniscus tear include knee joint pain, swelling, catching, locking, clicking, giving way and restriction of full movement. 

Meniscus anatomy

There are two menisci in each knee, a ‘medial’ one on the inside of the joint and a ‘lateral’ one on the outside. Both are C-shaped but are not identical to each other, differing in shape, size, and attachments to the other structures of the joint. 

The menisci are wedge-shaped when viewed in cross-section, with a thicker outside border, tapering to a thin inner edge. They are made of tough, rubbery tissue.²

The peripheries of the meniscus have a blood supply; this area is called the ‘red zone’, whilst the inner section has no blood supply and is called the ‘white zone’.³

The menisci play an important role in the biomechanics of the knee joint, improving the fit of the joint surfaces, distributing load, improving stability, and absorbing shock. They also contribute to proprioception (the awareness of where parts of the body are in space) and provide lubrication and nutrition to the joint.²

Types of torn meniscus

Meniscal tears can be classified in different ways depending on their location, shape, orientation, severity, and whether they are displaced or not (when a piece of meniscus has detached or an edge has flipped over). 

Configuration of a tear

Names are given to different tears depending on their shape, orientation, and location. Examples are radial tears (a tear starting from the inside edge of the meniscus, progressing across the short axis towards the outer edge)⁴ and bucket-handle tears (a tear that creates a gap in the centre of the meniscus with a shape resembling a bucket handle).⁵

Location of tear

Both medial and lateral menisci can be torn, but the medial is more commonly damaged than the lateral.¹ The posterior (back) ‘horn’ or section of the meniscus is more commonly torn than the anterior (front).⁶

Blood supply to the area of the tear

Tears can occur in both the ‘red’ zones at the peripheral edges of the menisci, which have a blood supply, and in the ‘white’ zones at the centre, which have no blood supply. ‘Red’ zone tears are more likely to heal than ‘white’ zone tears³ due to the critical role that blood plays in the healing process.⁷

Meniscal tear symptoms

The following knee joint symptoms are common following a meniscus tear: 

• Pain/tenderness
• Swelling 
• Locking, clicking, catching 
• Inability to fully straighten the knee
• Giving way³

Pain/tenderness

Pain in the knee joint may be brought on or increased by fully straightening or bending the knee and by squatting. Tenderness is common along the joint line at the front of the knee.³

Swelling

Swelling may come on gradually over the 24 hours following a traumatic incident when there is an isolated meniscal tear without damage to other knee ligaments. 

Immediate swelling of the knee following a traumatic incident, particularly when combined with a ‘pop’ sound at the time of injury, may indicate a meniscal tear combined with an Anterior Cruciate Ligament (ACL) tear. 

Swelling can also come on slowly over several days without an obvious traumatic cause.³

Locking of the knee

True locking of the knee joint (where the knee is fully locked in place and cannot be moved) may be indicative of part of the torn meniscus being dislodged and becoming caught in the joint.⁸

Meniscal tear causes

Meniscus tears are caused by trauma and by degeneration. Acute, traumatic tears occur from excessive forces being applied to a normal meniscus. Degenerative tears occur due to repetitive normal forces being applied to a worn meniscus.⁹

Traumatic tears are more likely in young, active people involved in sports. Degenerative tears are more common in older people.¹ Meniscal tears are uncommon in children under 10, although they are sometimes seen in this age group due to anatomical variations.³

All meniscal tears are more common in people assigned male at birth (AMAB) than those assigned female at birth (AFAB).⁶

Acute meniscal tear due to knee trauma

Acute, traumatic meniscal tears most commonly occur from an action of rotation at the knee, creating an excessive shearing force. The meniscus is particularly vulnerable during a twisting action of the knee whilst it is partly bent, with weight being placed through the leg and the foot fixed on the ground. 

Activities that typically cause these forces include kneeling, squatting, carrying heavy weights, rapid acceleration/deceleration, rapid changes of direction/cutting movements, and jumping. These actions are involved in sports such as football, rugby, basketball, baseball, skiing and wrestling. Meniscal tears are, therefore common sports injuries, as well as being associated with certain occupations.³

Trauma, which results in a meniscal tear, can often damage other structures of the knee at the same time. Tears of both the meniscus and ACL of the knee concomitantly are common sports injuries.⁸

Degenerative meniscal tear

Changes in meniscal tissue structure due to wear and tear can leave it more susceptible to damage and so reduce the force required to cause a tear.³ 

Common daily activities can be enough to cause a tear in a meniscus that is worn and weakened. As such, patients with this injury may not be able to identify a specific causative event.⁹

Several factors are thought to increase the risk of developing degenerative changes in the meniscus. These include ageing, being AMAB, and involvement in activities of repeated kneeling, squatting, and stair-climbing.¹⁰

​​Consequences of torn meniscus

A meniscal tear can significantly alter the biomechanics of the knee joint, affecting the alignment, stability, and load distribution. This can increase the risk of degenerative changes in the knee, including the development of osteoarthritis (OA).²

In addition, treatment of a tear through surgical removal of the full meniscus or the damaged part (meniscectomy) may reduce the contact area of the knee, putting a greater load on certain sections of the joint surfaces. This can increase wear and tear on these structures, also leading to degenerative changes.⁶

Removal of tissue through meniscus surgery was previously a common treatment for meniscus tears. However, preservation of the meniscus is now a key aim of treatment,⁸ and repair is usually favoured over removal.⁶ A number of different treatment options are available,¹ including stem cell therapy.¹¹

Further information on meniscal tears

Information on torn meniscus diagnosis and treatment options, can be found on the Mayo Clinic website and the American Academy of Orthopedic Surgeons website.

FAQs

How common is meniscus tear?

Meniscal tears are the most common type of knee injury.¹ A 2019 study showed that 6% of acute, traumatic knee injuries resulted in a meniscal tear.⁸

Meniscal tears can be caused by trauma or by degenerative changes. Traumatic tears are more common in young, sporty populations. Degenerative tears are more common in older populations.¹ Both types of meniscal tear are more common in people AMAB than in those AFAB.⁶

When should I seek medical help for a meniscal tear?

The common symptoms of a meniscal tear are pain and swelling of the knee, sensations of catching, clicking, locking or giving way, and a loss of full range of movement of the joint. If you experience any of these symptoms, particularly following a traumatic injury involving twisting of the knee, consult a Healthcare Professional for further advice. 

Summary

The menisci are two C-shaped pieces of rubbery cartilage located in each knee, which play an important role in the biomechanics of the joint.

Tears in the meniscus are common orthopaedic injuries. They can be caused by acute traumatic injuries, often involving an action of twisting at the knee. Tears can also occur from activities involving less force but applied to degenerative meniscal tissue, as is commonly found in older populations. 

Symptoms of meniscal tears include knee pain, swelling, locking, sensations of catching and clicking, reduced range of movement and giving way of the joint.