Soft tissue injuries of the knee
The knee joint is a hinge type synovial joint that mainly allows for flexion and extension along 150 degrees, with a small degree of medial and lateral rotation. It is formed by the articulations between the patella, femur and tibia. The articular surfaces are the medial and lateral condyles of the femur, the tibial condyles and the inferior aspect of the patella with the anterior aspect of the distal femur. Blood supply is through genicular anastomosis while nerves are the femoral, tibial and common fibular nerves. The joint has medial and lateral menisci that act to increase the stability of the joint and act as shock absorbers. There are four bursae around the knee, the suprapatellar bursa, prepatellar bursa, infrapatellar bursae and semimembranosus bursa. There are four planes of movement:
- Extension - produced by quadriceps femoris
- Flexion - produced by hamstrings, gracilis, sartorius and popliteus
- Lateral rotation - produced by biceps femoris
- Medial rotation - produced by semimembranous, semitendinosus, gracilis, sartorius and popliteus
The major ligaments of the knee are:
- Anterior cruciate ligament
- Prevents anterior translation of the tibia relative to femur
- Well innervated by tibial nerve
- Posterior cruciate ligament
- Prevents posterior translation of tibia relative to femur
- Lateral collateral ligament
- Resists varus angulation and restrains axial rotation
- Popliteal Femoral ligament/posterior lateral corner
- Works with the posterior cruciate to control external rotation
- Medial collateral ligament
- Resists valgus angulation
The knee relies on these ligaments for stability and damage to these ligaments takes a long time to heal, if they ever do. Below we consider some of the main soft tissue injuries of the knee.
Anterior cruciate rupture
This is a trauma commonly caused in sport by a sharp twisting movement, or where a tackle has pushed the upper part of the tibia forwards. Rupture of the ACL is one of the most common causes of acute haemarthrosis (80%), patients will often describe the process of feeling something ‘go’ in the knee, often with an audible snapping
noise. The knee is unable to sustain almost any weight and the knee will swell rapidly with bleeding into the joint, within 15 minutes there will be swelling and protective muscle spasm.