CMP is referred to as anterior knee pain due to physical and biomechanical changes[1]. It manifests as 'softening, swelling, fraying, and erosion of the hyaline cartilage underlying the patella and sclerosis of underlying bone[2]’. Simplified, it means that the articular cartilage of the posterior surface of the patella is going though softening and degenerative changes[3]. 

The etiology of CMP is poorly understood, although most authorities believe that the causes of chondromalacia are injury, generalized constitutional disturbance and patellofemoral contact, or a result of trauma to the chondrocytes in the articular cartilage. Some authorities believe that chondromalacia is caused by instability or maltracking of the patella that softens the articular cartilage. Chondromalacia patella is usually described as an overload injury (overuse, misuse), caused by malalignment of the femur to the patella and the tibia. 

Sometimes, a muscular imbalance between the VL en VM lies underneath. Weakness of the VM causes the patella to be pulled too far laterally. The patella will grind onto the condylus lateralis, which causes the degenerative disease. 

Degenerative changes of the articular cartilage can be caused by:

Trauma: instability caused by a previous trauma or misuse during recovery

Repetitive microtrauma and inflammatory conditions

Postural distortion: causes malposition or dislocation of the patella in the trochlear groove

Some authors will use the term “patellar pain syndrome” instead of “chondromalacia” in order to describe “anterior knee pain”.

Stages of disease
In an early stage, chondromalacia shows areas of high sensitivity on fluid sequences. This can be associated with the increased thickness of the cartilage and may also cause oedema. In a later stage, there will be a more irregular surface with focal thinning that can expand to and expose the subchondral bone. 

Your physiotherapist can help!

Reference: http://www.physio-pedia.com/Chondromalacia_Patellae

Picture: Google images