Chondromalacia patellae (CMP) results from damage to the cartilage which covers the posterior aspect (back) of the patella (knee cap). This is known as articular cartilage and acts to allow smooth movement and shock absorbtion between the patella and the groove through which it runs (formed by the Femur and Tibia).
The cause of this damage can be either acute or due to a long-standing overuse injury. Acute injuries normally occur when the front of the knee cap suffers an impact, such as falling directly onto it, or being hit from the front. This results is small tears or roughening of the cartilage.
In overuse cases, the cause of the damage is usually repetitive rubbing of part of the cartilage against the underlying bone. In a healthy knee the movement of the Patella across the knee is a gliding, smooth movement. In individuals with CMP, the knee cap rubs against the part of the joint behind it, resulting in inflammation, degeneration and pain. The can be for a number of reasons, but is usually due to the position of the patella itself.
The most common feature of condromalacia patellae is patella mal-tracking. The patella most commonly runs too laterally (to the outside) in the groove. This problem is most regularly caused by muscle imbalances, where the lateral quadriceps muscles and other tissues such as the retinaculum are too tight and the vastus medialis oblique muscle is weak.Other structural problems include Patella alta, which refers to a high patella and patella baja which refers to a low patella.
Chondromalacia patellae is common in young athletes who are often otherwise injury free. Its incidence is also highest in females due to their on average higher Q angle. CMP is also more common in those who have experienced previous traumatic knee injuries such as fractures and dislocations.
CMP is often confused with PatelloFemoral Pain Syndrome (PFPS) as CMP is regularly a result of PFPS. However, they can both occur in isolation.
What are the symptoms of Chondromalacia Patellae?
- A grinding or clicking feeling when straightening the knee (known as crepitus).
- Pain at the front of the knee.
- Pain which is often worse when walking downstairs.
- Pressing down on the knee cap when the knee is straight may be painful.
- Pain when standing after extended periods of sitting (movie-goers knee).