The patellofemoral joint is the front of the knee joint where the kneecap is. It is composed of the patella (kneecap) and the femur (thigh bone), which are both covered with joint lining cartilage and contained within the knee joint capsule. The quadriceps tendon (from the thigh muscle) inserts into the patella at the top and the patella tendon runs from the bottom of the patella to the tibia (shin bone). The patella moves in a groove in the femur called the femoral groove. The patella improves the biomechanical efficiency of the quadriceps muscle to move the tibia to help with activities such as stair climbing, squatting, rowing or standing from a chair. These activities press the patella against the femur and will cause pain if the patellofemoral joint is damaged. Pain from the patellofemoral joint is a very common cause of knee pain in all ages. It can occur for no apparent reason or can result from a specific injury such as a direct blow or twisting injury. The most common cause of anterior knee pain across all ages is the presence of tight hamstrings. This puts extra pressure on the kneecap and cause softening of the articular cartilage and pressure within the bone. This is often called chondromalacia patellae and create the sensation described as patella migraine. Some types of pain can be resistant to all forms of treatment and can recur many years following initial presentation.
Particular problems include…
- The patella slipping out of joint (dislocation).
- Partially slipping out of joint (subluxation).
- Maltracking – meaning it does not move in the groove as it should. This leads to abnormal stresses and results in pain in the area.
- Fracture (breaking the bone).
- Arthritis.
- Patella tendonitis – this is inflammation of the tendon beneath the patella.
Symptoms include…
- Anterior (front) knee pain usually worse going up and down stairs or prolonged periods of sitting, or squatting.
- Clicking or grinding within the knee.
- Locking or the feeling that the knee cannot move.
- Giving way.
- Swelling.
Patellofemoral Crepitus or Crunching
You may have a feeling of roughness or noisy crunching when you bend and straighten your knee. If the crunching is not painful then treatment may not be needed. Crunchig that is associated with pain or swelling usually indicates that the joint lining is breaking down and will eventually lead to arthritis. Softening of the cartilage as a young adults usually a combination of genetics, tight hamstrings, abnormal tracking of the kneecap and excessive loading with exercise. This may develop into a wear and tear process as you get older and become an arthritic process slowly developing in the knee
Maltracking
The kneecap does not always move in the groove as it should. Abnormal sliding is known as maltracking and this can cause pain. This can often be the result of a high or small patella, abnormal alignment of the leg, tight structures on the outer aspect of the knee or weak structures on the inner aspect. The surrounding muscles are vital to the normal tracking of the patella and weakness in one or overtightening of another can lead to abnormal tracking. Physiotherapy plays a vital role in the treatment of this disorder and surgery is a last resort. Surgery can vary from an arthroscopic lateral release (cutting the tight internal structures on the outside of the knee using keyhole access only) to a tibial tubercle realignment where the bone is cut and placed in a different position to change the direction the kneecap moves. A MPFL (Medial Patello Femoral Ligament) reconstruction can be required if the bones are normal but the structure keeping the kneecap in place has torn.
Fat Pad
The fat pad does not usually cause symptoms and is therefore often missed as a cause of anterior knee pain. Minor trauma to the area, torn menisci, chondral injuries and any inflammatory process of the knee can cause irritation of the fat pad. As with most causes of anterior knee pain this usually settles with time and physiotherapy. If the problem becomes chronic with a thickened and scarred fat pad then an arthroscopy may be required to ‘debulk’ the area to allow the knee to lock out straight and allow normal walking and lifting of the leg.
Plica
A plica is a normal fold of tissue found in the knee. It forms part of the soft tissue lining which seals the fluid into the joint. A painful plica usually creates medial joint (inside of the knee) pain and can mimic a meniscal tear. In some cases the pain is felt more at the front of the knee. When a plica is pathological, damage to the adjacent joint lining cartilage is seen at arthroscopy. They can become inflamed or rub on the cartilage lining excessively after an injury with heavy loading of the joint as described above.
Is based on history and examination and assisted by investigations. Examination includes looking at the overall alignment of the limb, assessing tracking and position of the patella, feeling for areas of tenderness, tightness of soft tissue structures and strength of muscles.
Always start with plain X-rays which include a skyline patella view. Usually MRI or CT scans with special views are required. These can help look for any maltracking and damage to the joint surfaces. One of the important distances to measure is the TT-TG distance (Tibial Tubercle to Trochlear Groove) which helps predict whether a soft tissue or bone procedure will be more successful.
Mostly treatment is non operative and is based around re-establishing the normal tracking of the patella within its groove.
Physiotherapy plays a vital role in this assisting with…
- Relief of acute pain.
- Muscle strengthening exercises (especially the quadricep muscles).
- Hamstring and Iliotibial band stretching.
- Taping.
Occasionally surgery can be helpful if conservative management has failed. It is especially useful if there is mechanical catching or locking within the knee.
Surgery
Surgical options include…
- Arthroscopy to debride any cartilage flaps.
- Lateral release which releases tight structures on the outer aspect of the patella to help with tracking. This is done arthroscopically.
- Extensive realignment procedure which involves a larger incision and redirecting muscle and ligaments to improve the tracking of the patella.
- Patellofemoral replacement.
These procedures have a reasonable chance of success in the right patient but should only be attempted after months of conservative treatment has failed
Results are not as predictable as with other procedures on the knee and surgery may not be successful in some cases.