KNEE ANATOMY & FUNCTION

The Knee Joint is made of :

  • Bones - Femur, Tibia, Patella & Fibula
  • Ligaments connecting the bones
  • Articular Cartilage which is a coating on the bone like the paint on the wall
  • Menisci - shock absorbers between two bones (femur and tibia) to minimize friction
  • Capsule - covering or encapsulating the joint such that it is a watertight structure
  • Muscles outside this capsule which make the joint move

Bones

The Knee Joint is made of the thigh bone (femur) which sits on the leg bone (tibia). In front of both is a knee cap (patella). A thin bone adjacent to the tibia provides structural support.
The Knee thus comprises of three compartments :

  • Medial Tibiofemoral - the space between the femur and tibia towards the inner side (adjacent to the other leg).
  • Lateral Tibiofemoral - the space between the femur and tibia towards the outer side (away from the other leg)
  • Patellofemoral - the space between the femur and the knee cap

Arthritis typically reduces the medial tibiofemoral space to start with. It gradually affects other compartments. Severe arthritis is thus termed tricompartmental i.e. involving all three compartments.

LIGAMENTS
Ligaments are strands of soft tissue which connect two bones. They cannot contract or expand and thus are a constant length. They provide stability to the knee. The chief ligaments of clinical importance in Knee injuries are:

The Anterior Cruciate Ligament - at the front of the knee. This is one of the most common ligament ruptured following injuries in sports or road traffic accidents. Major advancements over the last 15 years have enabled us to understand these injuries better and treat them by advanced arthroscopic techniques.

The Posterior Cruciate Ligament - at the back of the knee. This is a very strong ligament preventing the tibia from moving excessively backwards beneath the femur. Traditionally, this ligament was left to heal by itself. However, results were suboptimal in quite a few cases. Over the last decade techniques (which require a high degree of skill) have evolved in successfully reconstructing this ligament in a subset of patients which would otherwise not do well.

The Lateral Collateral Ligament (Posterolateral Complex : PLC) - on the outer side i.e. away from the opposite leg. This ligament complex was unrecognized until a few years ago!! Cruciate ligament reconstructions are liable to fail if this injury goes unrecognized. Reconstruction of this ligament complex is one of the most recent advancements in knee ligament reconstructions.

The Medial Collateral Ligament - on the inner side i.e. towards the other leg. Sprains of this ligament are very common. Complete tears do pose a treatment dilemma especially when they are associated with other ligament injuries.

The Patellofemoral Ligament - This ligament connects the knee cap to the femur. Reccurent knee cap dislocations (especially after an injury) cause it to rupture. Reconstruction of this ligament is a part of some patellofemoral stabilizations.

ARTICULAR CARTILAGE This is the smooth coat of white tissue over the femur, tibia and patella which reduces friction between apposing bones. Erosion of this coating results in irregular surfaces rubbing against each other - Arthritis.

This phenomenon might affect very small areas in the young athletic adult. Such defects are called Osteochondral Defects and are amenable to Articular Cartilage Restoration procedures.

Erosion of articular cartilage might affect just one compartment of the knee. Such knees respond well to Joint Realignment procedures or Limited Replacements.

Wide erosion of cartilage results in severe arthritis. Such knees respond well to Total Knee Replacements.

MENISCUS
Besides the articular cartilage, there are two shock absorbers which prevent the femur from rubbing against the underlying tibia. They withstand the impact of the forces across this weight bearing joint. These structures might tear as a result of an injury or as a result of degeneration consequent to arthritis.
Since most of the meniscus (except the outer most portion) has no nourishment from blood vessels, tears do not heal. Peripheral tears in the outer most portion can be stitched by skilled arthroscopic techniques. Other tears need to be excised.

The biomechanics of a meniscus is such that removal of the torn portion restores its weight bearing properties.

CAPSULE
The knee is in a polythene bag - The Capsule. This structure renders the knee water tight.
A contraction of the capsule limits motion. This is generally seen after injury especially when the knee has been immobilized for long periods. It is thus important to follow supervised rehabilitation regimes.

Knees with limited range of motion consequent to contracted capsules are dealt with by arthroscopic releases followed by immediate aggressive physiotherapy.

MUSCLES
The two chief muscle groups are the Quadriceps in the front of the knee and The Hamstrings at the back.

Grafts to reconstruct ligaments are taken from portions of these muscles.
A well coordinated contraction of these muscle groups is important in proper knee motion. Physiotherapists spend most of their time achieving the right balance, flexibility and strength in these muscle groups.