Knee collateral ligaments

What important role do the collateral ligaments play in the knee joint?

The knee joint has two collateral ligaments, namely an inner (medial collateral ligament) and an outer (lateral collateral ligament), which run along the side of the knee. They are attached to the thigh bone and run down to the corresponding lower leg bone. The lateral ligaments prevent the knee joint from bending sideways.

The inner ligament prevents the knee joint from bending inwards when it is extended. The outer ligament prevents the knee joint from bending outwards. The collateral ligaments provide the knee joint with important stability. The inner ligament, a flat, wide ligament with a length of approx. 7 cm, is closely connected to the knee joint capsule and the inner meniscus. The much thinner outer ligament, on the other hand, is not connected to the knee joint capsule and the outer meniscus. It runs as an independent ligament from the femur to the fibula. This makes the outer meniscus more flexible and therefore less prone to tearing than the inner meniscus.

How does an injury to the collateral ligaments occur?

The most common injury to the collateral ligament is caused by sports accidents. A lateral force applied to the knee joint can either tear the collateral ligament completely (total rupture) or only partially (partial rupture) or only be strained or overstretched. Injury to the medial collateral ligament is significantly more common than injury to the lateral collateral ligament.

What are the symptoms of a torn collateral ligament?

When a collateral ligament is injured, patients complain of unsteadiness (instability) of the knee joint during movement and weight-bearing. They also complain of pain at the corresponding site of the injured collateral ligament, which intensifies when the knee joint is loaded and moved. If parts of the collateral ligament are torn, a haematoma forms at this site.

How is a collateral ligament tear examined?

In addition to the exact mechanism of the accident, clarification includes a thorough clinical examination with a test of the stability of the collateral ligaments in extension and slight flexion (30°). The instability, i.e. the ability to open, is categorised in degrees of severity:

• Grade I: < 5 mm slight instability
• Grade II: 5-10 mm moderate instability
• Grade III: > 10 mm severe instability

This is followed by an imaging examination. The radiological examination serves to rule out a bony avulsion. An MRI scan shows the extent of the collateral ligament injury as well as other possible additional injuries to the knee joint such as a meniscus tear, cartilage injury or cruciate ligament tear. The findings are then discussed in detail and possible forms of treatment are explained.

How is a torn collateral ligament in the knee treated?

Most collateral ligament injuries are treated conservatively. These are strains and overstretching or partial tears of the collateral ligament. The therapy includes

• Cooling and rest
• Anti-inflammatory medication
• Knee brace/splint for 4 to 6 weeks
• Partial weight-bearing of the knee joint with the help of walking sticks
• Physiotherapy

If conservative therapies do not help or if there are additional concomitant injuries such as a torn meniscus, cartilage damage or torn cruciate ligaments, the knee must be surgically stabilised. Surgery is more likely to be required for external ligament injuries than internal ligament injuries.

The following surgical techniques are available and must be used individually depending on the findings:

• Suture: The torn ligament can be sutured directly or reattached to the bone with special anchors.
• Bony avulsion: The torn piece of bone is reattached to the bone with a screw.
• Reinforcement: If the collateral ligament is too weak after suturing, it can be reinforced with an artificial ligament. The artificial ligament is attached to the bone with screws.
• Reconstruction: The torn collateral ligament is replaced using the body's own tendons. These are attached with anchors to the origin of the defective collateral ligament and to the corresponding attachment.

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