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Three of the four quadriceps muscles originate on the femur, so their angle of pull is parallel with the angle of the femur. This means these muscles will be pulling in a slight diagonal. Consequently, the patella is also pulled in a slight lateral direction (Image 3). This uneven pull makes the patella susceptible to a lateral tracking disorder. The medial side of the quadriceps group offsets the pull of the patella in a lateral direction. The distal end of the vastus medialis has a group of fibers angled in an oblique direction and are thus called the vastus medialis obliquus (VMO). A primary function of the VMO fibers is to offset the tendency of the patella to be pulled laterally. DESCRIPTION OF PATHOLOGY Chondromalacia literally means "softening of the cartilage." However, this problem involves much more than just the cartilage. The cartilage may initially soften, but repeated compressive irritation of the cartilage surface causes cracking, chipping, and degeneration. The continual compressive load on the cartilage can wear away segments of the joint surface and lead to permanent damage. Activity levels play a big role in the likelihood of developing chondromalacia, simply due to the repeated flexion and extension movements of the knee. The condition is also more likely to occur in certain populations. Young people may be more prone to chondromalacia because growth spurts may cause an imbalance between muscle and bone growth. The discrepancy can lead to abnormal patellar positioning and dysfunctional knee biomechanics. Postural challenges of the lower extremity frequently play a role in the onset of chondromalacia. Genu valgum (commonly called knock-knee) is the most common postural challenge that may lead to chondromalacia. In this postural disorder, the varus angle of the femur is exaggerated more than usual and that means the patella is even more likely to be pulled in a lateral direction. The increased lateral pull drags the ridge of the patella against the lateral femoral condyle. Chondromalacia is difficult to assess with physical examination, so magnetic resonance imaging (MRI) is frequently used to validate the degree of cartilage degeneration on the underside of the patella. One of the challenges with this condition is that the degree of cartilage degeneration does not correlate well with the level of pain or severity of the problem. Cartilage is poorly innervated, so degeneration may be quite advanced before the condition is symptomatic with knee pain. Despite poor innervation of the cartilage, however, chondromalacia can be quite painful—particularly when the damage has reached the underlying bone. The layer of bone just below the cartilage is called sub-chondral bone and it is richly innervated. Irritation of subchondral bone is likely to be quite painful. Even in conditions where the cartilage is not seriously damaged, pain can still occur from low-level inflammatory responses to the tissue irritation. Chemical mediators from the inflammatory response can irritate nociceptors around the knee and cause pain. Inflammatory irritation of nociceptors may also help explain why some clients feel knee pain even though the damaged cartilage is poorly innervated. N e w ! A B M P P o c k e t P a t h o l o g y a t w w w. a b m p . c o m / a b m p - p o c k e t - p a t h o l o g y - a p p . 85 2 Patellofemoral Compression Test The patellofemoral compression test is one of the most common procedures used to assess the possibility of chondromalacia. In this procedure: • The client is seated on the edge of the treatment table with the knee in a flexed position. • The therapist places a hand directly over the top of the patella. • The therapist then has the client extend the knee while moderate pressure is maintained directly over the top of the patella. • There may be cartilage degeneration present if the client feels pain, grinding, or grating sensations during the flexion or extension. The practitioner may also feel the grinding or grating sensation during the patellofemoral compression test. Patellar ridge Bony ridge on underside of patella. Mediclip image copyright (1998) Williams & Wilkins. All rights reserved. Watch "Retinaculum Treatment"