Knee Anatomy

The knee joint consists of the weight-bearing articulation between the tibia and femur and the articulation between the patella and femur, which allows the pull of the quads to be directed anteriorly over the knee to the tibia without wearing the tendon.

Menisci

The articular surfaces include the two femoral condyles and the superior aspect of the tibial condyles. Two fibrocartilaginous menisci sit on the tibia and wrap around the outside to form C-shapes.  They improve congruency between the femoral and tibial condyles during jhoint movements where the femoral surface changes from a small, curved surface in flexion to a large flat surface in extension. The medial meniscus is attached to the margin of the capsule and the MCL whereas the lateral meniscus is unattached to the capsule making it more mobile. The menisci area interconnected anteriorly by the transverse ligament and the lateral meniscus is also connected to the popliteus tendon.

Ligaments

Patellar Ligament – continuation of the quads. It is attached above to the margins and apex of the patella and below the tibial tuberosity.

Lateral Collateral Ligament – a cord-like ligament that is attached to the lateral femoral epicondyle (just above the groove for the popliteus tendon) and the lateral fibular head. It is separated from the fibrous membrane by a bursa.

Medial Collateral Ligament – a broad and flat ligament that is attached by much of its deep surface to the underlying fibrous membrane. It is attached to the medial femoral epicondyle just inferior to the adductor tubercle and the medial surface of the tibia above and behind the attachments of Sartorius, gracilis and semitendinosus.

Transverse Ligament – Connect the anterior external regions of the lateral and medial menisci within the knee joint, sitting behind the infrapatellar fat pad.

Anterior Cruciate Ligament – attaches to a facet on the anterior intercondylar area of the tibia and a facet at the posterior lateral wall of the intercondylar femoral fossa. It prevents anterior displacement of the tibia relative to the femur.

Posterior Cruciate Ligament – attaches to the posterior intercondylar area of the tibia and medial wall of the intercondylar femoral fossa. It restricts posterior displacement.

The ACL crosses the PCL laterally as they pass through the intercondylar region.

Tibiofibular Joint

This is a synovial joint between the tibia and fibular that allows very little movement. The capsule is supported by anterior and posterior tibiofibular ligaments.

Locking Mechanism

In order to reduce the amount of work required to stand, the knee joint is ‘locked’. The change in shape and size of the femoral surfaces facilitates this. In flexion, the surfaces are curved on the posterior aspect of the femoral condyles. In extension, the surfaces move anteriorly to the flat areas on the inferior aspect of the femoral condyles. Therefore the joint becomes more stable in extension due to an increase in the surface area. Additionally the femur rotates medially on the tibia leading to the associated ligaments tightening. Furthermore, in standing an individual’s centre of gravity falls anteriorly to the knee joint further reducing the work required to stand.

Strains

Sprains or strains often present with an acute onset of symptoms. Eccentric exercise is likely to cause injury at the musculotendinous junction, making the mechanism of injury an important assessment point. Pain is often present, although complete ruptures present with no/minimal pain. The amount of swelling depends partly on the severity and time since injury, alongside with the area damaged. It can take up to 24 hours for the full extent of the swelling to become apparent. In a muscle strain bleeding is common. For an intramuscular haematoma, bleeding is contained within the sheath resulting in pain and localised swelling. Whereas in extramuscular haematoma, bleeding spreads throughout the intermuscular spaces resulting is less pain but with more diffuse swelling.

More severe strains can be indicated by the symptoms lasting more than a few days. ROM is primarily limited during the acute phase; therefore if limited range of motion remains after the pain and swelling decreases a grade III strain is more likely. Additionally, weakness is also more common during the acute phase due to painful inhibition of contraction. A ‘pop’ sound can also suggest a grade III strain.

Grading Strains

Grade 1

Less than 5% of the fibres are damaged and the fascia remains intact. Therefore the bleeding is contained and minimal. Pain is localised with minimal loss of function. Recovery takes 1-4 weeks.

Treatment includes PRICE, gentle stretching, active movement and return to function.

Grade 2

Many fibres are damaged although the fascia remains intact. The bleeding is considerable but remains contained. Pain is significant enough to reduce contraction. Recovery takes 3-6 weeks.

Treatment includes PRICE, stretches at 24 hours and active movement.

Grade 3

Severe number of fibres are damaged and the fascia is disrupted. There is considerable bleeding that may diffuse, resulting in a significant loss of function. Recovery takes 4-8 weeks.

Treatment includes PRICE and stretching after 5-7 days.

Grade 4

Complete rupture of the muscle with extensive bleeding and swelling. Contracture of muscle ends begins with complete loss of active contraction and function. Recovery takes 3 months.

Treatment includes PRICE and possible surgical management.

Treatment

In the first 24-48 hours PRICE, gentle mobilisation and analgesics (inc. NSAIDs for rapid return to work or competitive sports) is indicated. Physiotherapy and early mobilisation can be started after 2-3 days of rest. Patients should be reviewed after one week to assess for improvement, as those with worsening pain and no functional improvement may have a grade III rupture. Complete ruptures presenting in the first 24-48 hours should undergo surgical repair followed by physiotherapy.

PRICE
Protection - Prevents worsening of injury
Rest - Avoids pain from movement. Complete immobilisation is not indicated to prevent significant loss of ROM. Even for grade III injuries a functional splintage is strongly suggested.
Ice - Reduces pain. Application of ice should be for 10-30 minutes wrapped in cloth to avoid cold injury. Repetition can be as frequent as required, providing the affected part is fully warmed back to body temperature.
Compression - Provides comfort by limiting movement and reducing swelling, although should be applied so as to not reduce blood flow. 
Elevation - Helps to reduce swelling, especially with the affected part above heart level.

Medications
Paracetamol is the first choice for minor injuries and when taken regularly (every 6 hours) is highly effective. NSAIDs are also effective, but the adverse effects are greater. They may reduce healing time and therefore are effective for people who need to return to work or sport. A topical NSAID is rarely indicated. Paracetamol and NSAIDs can be used, however a combination of 2 NSAIDs is contraindicated.

Early Mobilisation
Prevents stiffness and maintains ROM.

Therapeutic Ultrasonography
Little evidence to support that ultrasound has significant benefit and is no longer recommended.

Short Wave Diathermy
Although commonly used, there is little evidence to support use for swelling, pain and ROM improvements.

Surgery
Is not indicated within the first 24 hours due to the implications of swelling on repair.