Patellofemoral disorders are a range of problems that affect the patellofemoral joint, located at the front of the knee, formed by the femur and kneecap. They can be caused either by an injury or a long-term condition.
In the first part of this guide, Mr Bilal M. Barkatali, an expert specialist knee surgeon, will aim to discuss and describe what exactly is a patellofemoral joint and the possible problems that can affect the function of this complex part of your leg.
What is the patellofemoral joint?
The patellofemoral joint is a very complex joint consisting of two bones at the front of the knee. The two bones are the patella (kneecap) and the front of the distal femur (thigh bone just deep to the kneecap).
The patella joins with the front of the femur in the area called the trochlea. This joint is made up of complex boney and soft tissue anatomy, and having problems with any of these can cause pain and instability around the patellofemoral joint.
What is the main function of the patella?
The function of the patella is multifaceted. Its primary purpose is to serve as a mechanical pulley for the muscles at the front of the thigh while the patella changes direction during knee movements. This helps to increase moment arm around the centre of rotation of the knee, and also to reduce the joint reaction forces between the patella and the trochlea and between the tibia and femur. It’s an evolutionary advantage in terms of joint forces and biomechanics and makes the patella essential to healthy knee joint function.
What problems can affect the patellofemoral joint?
The patellofemoral joint can cause pain for several reasons and is a very common complaint seen by physiotherapists and knee surgeons.
The three main categories are:
- Cartilage injury
- Chondromalacia, which is a softening of the articular cartilage.
Patellofemoral instability is a debilitating condition and can affect anybody at any age. The two most common presentations are teenage girls, who have developmental instability around the joint, or adult male and female athletes who have injuries to their knees resulting in instability.
It essentially means a feeling of giving way of the patella or a dislocation of the joint where the patella comes out laterally and dislocates from the front of the knee. This is very painful and usually requires relocation with some form of anaesthetic either in the ambulance or the A&E department.
Instability can be differentiated into developmental or traumatic causes. This means that if it's due to developmental causes then it is usually an abnormality with the joint ie. a shallow trochlea or high riding patella. If it's traumatic it means the anatomy is fine but due to the trauma, there has been some damage caused to the joint - usually a rupture to the MPFL (medial patella-femoral ligament).
Cartilage injury can occur to the patellofemoral joint due to the high forces going through it. Due to the small surface area at the front of the patella, the joint forces have been calculated in various studies. They have demonstrated forces of:
- 1.3x body weight during walking on flat surfaces
- 3-4x body weight when climbing stairs
- 6x body weight during running
- up to 8x body weight during a deep knee squat
These calculations demonstrate how incredible the patellofemoral joint is to withstand such high forces during different types of activities. Due to these incredibly high forces, the cartilage behind the knee cap or the front of the trochlea can become damaged and painful.
Sometimes cartilage damage is due to recurrent and repetitive instability of the knee cap either from gliding laterally or due to complete dislocation of the joint. Once the injury to the cartilage has started, this turns into a degenerative process, causing debilitating pain in the front of the knee.
Chondromalacia is a condition that affects a significant proportion of the population and a common complaint seen by a physiotherapist.
This is usually called anterior knee pain and is a diagnosis of exclusion. This means that we must check all other problems before we decide that chondromalacia is the cause of the pain.
Chondromalacia is essentially a softening of the cartilage and it is unable to resist the high levels of forces going through the joint. There is no surgical treatment for this and no surgery should be attempted to treat it. The main treatment is physiotherapy and strengthening of the muscles around the joint to offload the patellofemoral softened cartilage.
Read Mr Bilal M. Barkatali’s second part to this guide in which he discusses the various treatment options available for patellofemoral disorders.
If you are experiencing any problems with your knees, visit Mr Barkatali’s Top Doctors profile and book a consultation.