Anatomy of the knee
Bony Anatomy:The knee joint is the point where three bones meet. The thigh bone (femur), leg bone (tibia) and knee cap or patella. The thigh and leg bone glide over each other facilitating loading of the knee (bearing weight) and movement of the knee joint. The knee cap (patella) is convex on the part that glides over a groove (concave portion) on the thigh bone called the trochlea.
Muscular Anatomy:The knee cap has the thigh muscles (quadriceps mechanism) attached to it on its upper aspect and a rope like structure(tendon) that attaches it to the leg bone. This mechanism acts as a lever and facilitates movement of the knee joint. The effort being the quadriceps muscle, the patella the fulcrum and the patellar tendon bearing the load which is the movement of the leg bone over the thigh bone during bending of the knee.
Soft Tissue Anatomy: All three bony surfaces are covered with a 1cm thick layer of polish called cartilage. This facilitates very little friction during movement. Apart from this there are two ‘C’ shaped cushions between the thigh and leg bone, one on the inside of the knee and the other on the outside. These act as shock absorbers reducing the load that is directly transmitted to the cartilage and bone, much like shock absorbers in a bike. To keep both the thigh bone and leg bone together facilitating them to be stable are four ropes called ligaments.
Ligaments: One on the inside: medial collateral ligament (MCL)
One on the outside: lateral collateral ligament
Two in the centre crossing each other: Anterior and posterior cruciate ligaments
These can be broadly classified into:
2. Soft Tissue
Bony Injuries: These refer to fractures of the femur, tibia or patella. Bones break either into two pieces (simple fractures) or multiple pieces (comminuted fractures). They may be associated with a wound of varying size that communicates with the fracture making it an open fracture. If not they are called closed fractures. Bone may break at points where ligaments or tendons are attached to them, these injures are called avulsion injuries. If the pieces have not moved much from their original location, the fractures are called minimally displaced/undisplaced , if they have moved away from their original location they are called displaced fractures. Fractures that communicate with the joint are called intra articular fractures and those that do not extra articular fractures
Diagnosis: The patient typically will have an antecedent injury followed by pain inability to move the limb, swelling and deformity. Diagnosis is confirmed by doing x rays of the part including the joint above and below the injury. Sometimes fractures may not be visible on an Xray clearly, eg: an undisplaced crack fracture. Then doing a CT scan helps.
Treatment: Treatment largely involves the nature of the fracture, location and displacement.
Soft Tissue Injuries
ACL/PCL Tear: The anterior cruciate ligament prevents the leg bone from moving forward on the thigh bone. It has a tendancy to get injured when the knee goes into hyperextension or twists during a sporting activity/ two wheeler accident. The ligament can tear off its attachment on the thigh bone, through its middle or through its attachment on the leg bone.
Treatment: Low key persons can be treated conservatively with rehabilitation. However if there is an associated meniscus tear or the individual wants to lead a sporting/active lifestyle, the ligament needs to be repaired/ reconstructed.
This is done by keyhole (arthroscopic) surgery. Spare tendons in the body like the patellar tendon/hamstring tendons are harvested and prepared into new ligaments. These are placed into the knee by drilling tunnels into the thigh and leg bone. The new ligament is fixed with a button on the thigh bone and a screw (plastic) on the leg bone.
Sometimes if the ligaments is avulsed from the thigh or leg bone, it can be fixed back using arthroscopic techniques.
MCL/LCL Tear: these ligaments lie external to the knee joint, preventing the knee from moving sideways. They can be injured by excessive sideward movement of the leg bone that causes these ligaments to break. They can break through their mid substance and attachments at either ends.
Treatment: Ligament injuries through the substance or attachments through the thigh bone have a better tendancy to heal without surgery. However persistent instability warrants repair/ reconstruction of the same. When associated with another ligament injury meniscus injury operative treatment is imperative.
The meniscus have a tendancy to tear in isolation or in association with ligament tears.
Sometimes they spontaneously tear (degenerate) as the patient ages.
Treatment: Injury related tears can be treated by either partially removing the meniscus or repairing it via keyhole (arthroscopic) techniques. Degenerative tears are usually treated without surgery unless they produce mechanical symptoms like something is getting stuck in the knee /locked.