Knee bones & ligaments

Medial Collateral Ligament (MCL) & Posterior Cruciate Ligament (PCL) Tears & Sprains

Knee ligament injuries are common, especially medial collateral ligament (MCL) tears / ‘sprains’.

These injuries and the much less frequent posterior cruciate ligament (PCL) tears rarely require surgery although early diagnosis and (where necessary) bracing can avoid more serious problems later.

More uncommon but sometimes devastating injuries are those involving more than one ligament. These are often high-energy injuries requiring a combination of surgery, bracing and rehabilitation and their long-term outcomes (prognoses) are less predictable.

Medial Collateral Ligament (MCL) Injuries

The medial collateral ligament (MCL) is a broad ligament which sits on the inner aspect of the knee, connecting the femur to the tibia.

The role of the MCL is to help stabilise the bones of the knee joint. It prevents excessive movement of the tibia moving outwards relative to the femur (valgus direction).

MCL injury is the commonest of the knee ligament injuries. It may occur in isolation, or in combination with ACL rupture, meniscal tears, complex ligament injury, or fracture.

MCL tears occur with a wrenching or twisting injury; eg. a “valgus” contact injury. It is painful when it happens. A tearing sensation may be felt. Swelling and pain is only felt on the inner aspect of the knee. If the whole knee swells up rapidly, it is probably more than just an MCL injury.

Torn Medial Collateral Ligament diagram


Examination will usually show tenderness on the inner aspect of the knee at the point where the MCL is torn. It can tear in the middle, or it can pull off the bone at either end.

Early accurate diagnosis is important to enable optimum treatment outcome.

MCL tears are graded into three groups.

Grade 1: partial tear or sprain, when some fibres are torn but it is not really stretched. Examination will reveal pain and tenderness, but no laxity.

Grade 2: partial tear with definite stretching, and will feel lax when examined.

Grade 3: a complete rupture with dramatic opening up. This is more likely to have an associated ACL tear.

Grade 2 and 3 are distinguished by special examinations.


X-ray of a right knee MCL Rupture

X-rays might be normal, unless a fragment of bone is pulled off. Sometimes an excessive gap between the bones on the inner aspect will be apparent.

MCL Injury - Calcification x-ray of right MCL Injury

A Pellegrini-stieda lesion is seen as calcification at the top of the ligament in some chronic cases.


MCL Injury - MRI scan of right knee - normal & ruptured MCL

MRI scans will show up MCL tears, as will ultrasound scans, but they are not always necessary.

ACL knee brace non-surgical treatment


An isolated MCL tear will heal very well without the need for surgery.

Grade 1 injuries are treated according to symptoms. No brace is required. Crutches can be used early on until it is comfortable enough to walk without them. Rest, ice, compression, elevation and physiotherapy are all beneficial. Full recovery is at least six weeks.

Grade 2 and grade 3 injuries are usually treated with a brace for six weeks, to prevent the MCL stretching up while it is trying to heal. Although it is possible to do well without bracing, most surgeons feel it is beneficial to the outcome. For that reason early accurate diagnosis is important, to avoid missing the boat with bracing treatment. It can take up to 3 months for full recovery.

Surgery is rarely required. Repair might be considered urgently where there is a complex ligament injury e.g. knee dislocation.

In chronic laxity, especially with other ligament tears, reconstruction with the patient’s own hamstring tendon, or artificial graft material, is occasionally undertaken.

In summary, most patients with MCL tears do very well without surgery, with no long-term issues.

Posterior Cruciate Ligament (PCL) Injuries

PCL injuries occur less frequently than anterior cruciate injuries and are commonly due to an impact to the front of the leg, or more specifically, the top of the tibia at the front.

The commonest causes of injury are sports injuries (falling heavily onto the front of the knee in flexion – rugby; or collisions with goalposts – football) and car accidents where the top of the shin strikes the dashboard.

There is initially pain and swelling within the joint and a sense of insecurity but these injuries rarely cause true instability unless they are combined with damage to another ligament [see complex ligament injuries].

PCL Injuries -PCL MRI scan of a normal & PCL tear injury

Treatment of isolated posterior cruciate ligament injuries is usually conservative [non-surgical] involving physiotherapy. If the diagnosis is made within a week or so, a special brace (PCL brace) might be used, to hold the tibia forwards while some healing occurs.

The prognosis following these injuries is good but some patients do develop pain behind the patella over many years, because of increased load on that joint. Nevertheless, many people with this injury return to full activities including high-level sport.

PCL injuries combined with other ligament damage, however, usually produce instability problems and usually require surgical reconstruction.

Complex Ligament Injuries

A complex ligament (or ‘multi-ligament) injury of the knee implies that more than one of the major knee ligaments have been damaged.

The major knee ligaments are the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).

The LCL has important associated structures grouped together, which are referred to as the postero-lateral corner.

In order to sustain a complex ligament injury of the knee the patient will usually have experienced a major accident or high-energy twisting injury. In such cases both the treatment and rehabilitation can be difficult and prolonged.

Presentation Of Complex Knee Ligament Injury

These injuries can present as obviously dislocated knees requiring immediate manipulation to simply restore the shape of the leg (and reduce pressure on important blood vessels) or may initially appear to be a minor injury but with increased pain and/or swelling.

Some present much later with instability (giving-way) problems. In order to damage more than one ligament the knee will have dislocated at the moment of injury even if it immediately pops back into place.

Pain is usually more severe than with simple injuries and sometimes the injury can involve the blood vessels supplying the lower leg (an emergency) or a vital nerve (‘common peroneal’) leading to temporary or permanent ‘foot drop’.

Complex Knee Ligament Injury Knee Dislocation
Complex Knee Ligament Injuries - MRI scan of a normal LCK & an LCL tear

Diagnosis & Investigation Of Complex Knee Ligament Injury

Urgent assessment by a specialist is critical for these injuries as surgery is usually required and for some injuries should ideally take place within 2-3 weeks (except ACL/MCL combination – see MRI scan image).

Clinical examination is combined with imaging (x-rays, MRI and sometimes additional blood vessel investigations) in order to plan treatment.

Treatment Of Complex Knee Ligament Injuries

Complex ligament injuries of the knee are quite rare and treatment is, by definition, more difficult. It usually involves multiple ligament reconstruction and a long period of rehabilitation.

Where early surgery is required this often takes place after a week or two (to allow swelling to reduce) and is normally followed by a period of time with the knee in a brace using crutches.

ACL/MCL injuries are probably the most common combination and are usually best treated by allowing the MCL to heal with the knee protected in a hinged knee brace for a few weeks followed later by ACL reconstruction.

Sometimes if there is severe stretching of the outer ligaments of the knee, where patients present later, an osteotomy may be required to try and improve the alignment of the knee.

Results of surgery for complex knee ligament injury depend on the specific injury pattern and are much less predictable than for simple anterior cruciate ligament ACL reconstruction.

When these injuries are combined with nerve and/or blood vessel damage the chances of returning to active sport is substantially reduced.

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