What is the Patellofemoral Joint?
The knee joint consists of two main joints, the tibiofemoral and patellofemoral joints. There is a third lesser important joint called the proximal tibiofibular joint which is a fibrous joint between the top of the shinbone and fibula.
The patella (kneecap) is a bone that is contained within the quadriceps tendon. Bones contained within tendons are called sesamoids and the patella is the biggest sesamoid in the body. The function of the patella is to increase the lever-arm of the quadriceps mechanism, by moving it away from the trochlear grove. This increases the strength of the quadriceps. In people who have the patella removed surgically (patellectomy) for various reasons, the power of the quadriceps decreases by 30%, which is why patellectomy should be avoided.
The patella arbitrarily divides the quadriceps tendon into what is known as the patellar tendon below the patella and the quadriceps tendon above the patella. The patella moves against the trochlea groove at the end of the femur. As the patella forms part of the joint it is also covered by articular cartilage.
The patellofemoral joint has to tolerate some of the largest body weight forces in the body and can have to withstand up to 8 to 9 times of body weight with activities such as jumping, running, and stair climbing. It is therefore not surprising that the patellar has the thickest articular cartilage of any joint in the body.
Patello-femoral disorders can be roughly broken down into:
– Patello-femoral pain
– Patello-femoral instability
– Patello-femoral pain and instability
– Other Conditions
This is also known as anterior knee pain because the pain is felt at the front of the knee. Anterior knee pain can be a difficult problem to diagnose & treat and can be challenging from both the orthopaedic surgeon’s point of view and the patient’s. It is also known as anterior knee pain syndrome with the term syndrome implying that there are a number of different causes that can lead to anterior knee pain and this is in fact entirely true.
Classically, anterior or patellofemoral knee pain is pain that is felt at the front of the knee. It is commonly worse with prolonged sitting, going up and down stairs, or activities that involve bending the knee, such as kneeling and squatting. It is commonly made worse with sports. It can be associated with clicking and grinding of the knee as well as swelling within the knee. The syndrome arises due to damage or irritation to the lining surface cartilage (articular) of the patella causing softening, fibrillation, and breakdown of the articular cartilage. Anterior knee pain has in the past also been inappropriately termed chondromalacia patellae (inappropriately because the original definition of chondromalacia patellae was painless softening of the articular cartilage of the patella).
The actual cause of patella pain is not clearly understood. It is indirectly related to irritation and stimulation of nerve fibre endings but it is the cause of the irritation of these nerves that can be difficult to define. Damage to the lining surface of the patella and chronic alteration in the biomechanics of the patella tracking and movement mechanism can lead to irritation, overuse, and stimulation of the nerves, causing pain.
There are a number of factors that are known to contribute or potentially predispose to anterior knee pain and these include factors such as:
– Flat feet
– Rotational abnormalities of the femur
– Knocked knees (genu-valgum)
The basic premise of all of these is a biomechanical abnormality in that there is an increased force pulling the kneecap outwards which can lead to increased pressure against the outer part of the kneecap joint causing thinning and damage to the lining surface, leading to pain. This is also known as patella malalignment. Abnormal pressures can be directed through a normal joint but in an excessive amount in activities that lead to repeated overloading of the knee such as jogging, jumping, and so forth.