Have you ever experienced knee pain when you’re walking up or down stairs? Or when you’re squatting or doing lunges at the gym?
Introduction
Well, this pain in the front of the knee may be caused by what is colloquially known as ‘Runners’ Knee’. Condromalacia patella or CMP is another term used to describe this phenomenon. You certainly don’t have to be a runner to experience this particular pain. The front of the knee is made up of our patella (aka knee cap) as well as the groove of our femur. These two surfaces are lined by soft cartilage which makes movement there smooth and painless. Contact pressures at this patella-femoral surface increases when we bend our knees. Due to a variety of reason, the cartilage wearing out and high pressures cause us to feel pain and crepitus (grinding sounds) in the front of our knee when we go about our daily lives.
The patella usually moves upwards and downwards during normal knee flexion and extension. Sideway movements are not ideal but happens to many of us.
Medical History and examination
When I meet patients in clinic, they often give a history of painful, grinding sounds coming from their knee when they are using the stairs, picking up children from the floor or exercising in the gym. Their level of pain and disability may be varied but they all describe a loss of function and slowing down of their general physical activities. Most describe some frustration that they are not as active as before.
After a thorough medical examination, I usually organise some x-rays of their knee to document the general alignment and bony architecture of their knees. This includes a weight bearing or standing x-ray of both knees, a side view and a skyline view from the top of the knee. An MRI is also useful to assess the true damage to their cartilage and other soft tissues such as their meniscus and ligaments.
This particular x-ray view is called a ‘skyline’ view. It shows how the patella interacts with the femur groove. The left patella is clearly tracking out of the groove and is not centered.
These MRI scans of the knee show wearing out of the patella cartilage with cysts and arthritis of the patella-femoral joint.
Causes of patella-femoral pain
Patients often ask why their knees hurt so much and they’re only in their 40’s or 50’s. They’re not old! Well, there are many reasons for this to happen:
- Genetics: the general alignment of our knee and the quality or robustness of our cartilage is strongly influenced by our genes.
- General knee alignment and patella tracking. We are also born with a certain anatomy which influence how our patella tracks in the femur groove.
The Q-angle is a measurement which helps to determine if your patella tracks well in the femur groove of your knee. It is influenced by how wide our hips are, whether your knee alignment is neutral, varus or valgus. The wider your hips and the more valgus your knees, the greater will be the Q-angle. The larger this angle, the poorer is your patella tracking and this may cause the knee pain to deteriorate faster.
- Dysplasia of the knee. This describes the lack of normal anatomy in the femur groove. A flat or dysplastic femur groove is not able to contain the patella when the knee is flexed. The patella tends to move laterally towards the outside border of the knee, rather than up and down. This abnormal lateral movement wears out the patella-femoral joint faster.
- Nature of physical activities. Twisting and pivoting sports place a high level of stress and strain around the knees. It may lead to patella dislocations, shearing forces around the patella surfaces and increases the risk of dislocations and ligament injuries.
Treatment options
This will depend on the underlying cause of your patella-femoral pain. The first thing to do is to manage pain and swelling around the knee with the usual advice:
- Rest and refrain from exacerbating physical activities
- Ice
- Compression
- Elevation
Simple analgesics such as Paracetamol and Arcoxia (NSAID) may be helpful in reducing pain and inflammation. Stronger medications may be required for some.
A simple knee brace is useful as a form of compression. This helps prevent excessive swelling in the knee as well as help improve patella tracking during knee flexion. Patients are also sent for physiotherapy to improve the strength of their quadriceps or thigh muscles to improve the patella tracking. The physiotherapists will also stretch out their calves and hamstrings to improve the general function of their knee.
Non-surgical treatment for patella-femoral pain revolves around intra-articular injections into the knee. Hyaluronic acid is a form of lubrication which may help reduce the friction and grittiness of the knee joint. This injection is administered under local anaesthetic.
Surgical Treatment of patella-femoral arthritis
Knee preservation techniques to repair the cartilage and improve the patella tracking around the knee may be done by a variety of techniques. Arthroscopic or key-hole techniques may be adopted for cartilage microfracture or regenerative techniques. An arthroscopic lateral release may help the patella to be better centered in the femoral trochlear to improve its tracking.
For patients with poor Q-angles as described above, a tibial tuberosity osteotomy and transfer may be performed to medialise and anteriorise the tibial tuberosity. This reduces both the patella-femoral pressures as well as the Q-angle. Both these factors are effective in managing patella-femoral pain and arthritis.
Knee replacements may be performed for patients with end-stage patella-femoral arthritis or knee arthritis in general.
