Chondromalacia patellae (CMP) is a disorder that primarily affects athletes and younger individuals leading to patella cartilage degeneration and softening.
CMP patients present with knee pain that may vary from mild to severe with the occasional burning sensation . The location of pain is highly variable and may be total knee pain or specific locations around the knee. Retropatellar crepitation may or may not be painful. Patients may describe a painful giving way or catching of the knee. Determine whether change in exercise intensity has occurred as this is often related to pain. Activities that are commonly shown to produce symptoms of CMP include hiking, uphill running, stair climbing, knee bends, squatting and prolonged sitting with knees flexed . Patients may note pain after completing these activities. In some cases trauma is the cause of pain, such as a fall on the anterior knee or knee impact following a motor vehicle accident, however an inciting event is commonly unknown. Knee pain may be observed in other family members. Children undergoing growth spurts may experience knee pain that is often caused by abnormal forces placed on the patella leading to maltracking.
A detailed physical exam focusing on the knee, including observing movement and applying pressure, should be performed to dismiss other disorders that produce similar signs and symptoms. Imaging tests, including X-rays, computerized tomography (CT) scan and magnetic resonance imaging (MRI), may be used to view the bone and soft tissue conditions and locations to verify diagnosis .
Resting the knee is the most common recommendation to treat CMP. Patients may also apply ice or a cold pack wrapped in a towel to their knee four times a day for 15-20 minutes (applying ice directly to knee is not recommended) . Nonsteroidal anti-inflammatory drugs (NSAIDs), including ibuprofen, naproxen and aspirin, may be given to manage pain. To treat soft tissue pain topical pain medication (creams or patches) may be used on the affected area of the knee. Analgesics, like acetaminophen for moderate pain and tramadol hydrochloride for severe pain, may be used but these medications do not exhibit anti-inflammatory properties. In certain patient groups dietary changes may provide some benefit. Although no scientific proof exists demonstrating the beneficial effects of hyaluronic acid, chondroitin and glucosamine on cartilage regeneration, some patients report decreased pain and swelling and improved mobility with these supplements.
Surgical intervention is not recommended for the acute phase of CMP and should be performed only if conservative measures have been unsuccessful for 6 months . Furthermore other causes should be excluded before surgery is considered. Patients with patellar tilt and/or subluxation that see no improvement after 12 months of nonsurgical treatment may benefit from lateral retinacular release (optional medial capsular reefing). If lateral release fails to alleviate symptoms and malpositioning of the patella is observed then a patellar realignment (tibial tubercle transfer) may be performed. The 3 procedures that shift the tibial tubercle are 1) the Elmslie-Trillat procedure which repositions the tibial tubercle medially, 2) the Macquet procedure which moves the tibial tubercle lateral and 3) the Fulkerson procedure which repositions the tibial tubercle medial and anterior.
Successful treatment is typically achieved through conservative means. Currently, the standard of care for CMP includes 1) physiotherapy for biomechanical issues including quadriceps-based strengthening, 2) stretching of the quadriceps, hamstring and iliotibial band, 3) proximally focused hip stabilization programs and 4) bracing, taping and orthotics . Individualized exercise programs to address each patient's needs should be given since no exercise modality has been demonstrated to be superior for the treatment of CMP . Symptoms generally resolve within four to six weeks and successful long-term outcomes have been reported in 67-85% of cases with comprehensive home exercise programs .
The cause of CMP is not well understood, although it is believed that injury, postural distortion (malposition or dislocation) and patellofemoral contact, chondrocyte damage (leading to enzymatic digestion of the matrix), repetitive micro-trauma, inflammatory conditions and patellar instability or maltracking, contribute to disease onset and progression  . The general description of CMP is malalignment of the femur and patella due to overload injury, including overuse or misuse. In some cases muscle imbalance of the VL and VM, especially weakening of the VM, cause lateral pull of the patella, leading to grinding of the patella on the condylus lateralis and subsequent degenerative disease.
One in four knee injuries reported at sports medicine clinics are CMP . One study performed in the United States (US) on athletes, demonstrated that 18.1% of male knee injuries (7.4% of total) and 33.2% of female knee injuries (19.6% of total) were diagnosed as CMP . A similar study performed in Canada on patients with running injuries found that the primary complaint was CMP (16.5%) . Of the individuals in this study complaining of CMP most were women (62% female and 38% men) . CMP occurs most frequently between the ages of 20 and 40.
The exact pathophysiology of CMP is unclear. Numerous forces are constantly acting on the patella which must be balanced for proper patellar tracking. An imbalance in the forces from any direction may alter normal patella movement leading to joint stress. Excess stress may result in microdamage, inflammation and pain. Specifically, imbalances in the VM and VL, for example delayed VM activity compared to VL activity will cause patellar maltracking. A significant correlation between patellar maltracking and delayed VM activity has been indentified in patients with CMP .
Abnormal shear stress may be transmitted to the subchondral bone through the cartilage that is exposed to excessive stress in an irregular direction. Elevated metabolism of the bone at the patellofemoral joint is observed in patients with CMP. Pain is likely transmitted through nerve receptors associated with the subchondral bone blood supply which are exposed to increased strain between the femur and patella. Repeated patella dislocation observed in CMP may cause destabilization and nerve damage that may appear histopathologically as Morton neuroma .
Patients can prevent CMP by correcting biomechanical imbalances which may include arch support, orthotics, working on flexibility, strength training and proprioceptive programs focusing mainly on the VMO   . Sports equipment may be modified such as seat height for cycling and proper shoes for running. Cyclist who have tibial torsion or femoral anteversion should use cycles with pedals that have shims or floating clips to help prevent CMP. All activities should be performed in moderation and intensity should not be dramatically changed in a short period of time to avoid CMP. New unfamiliar activities should be performed using a slow, progressive approach. A good rule of thumb for runners is to follow the 10% rule which states that time and distance should only be increased by 10% per week.
Chondromalacia patellae (CMP) is characterized by degeneration of the posterior cartilage in the knee leading to anterior knee pain . Signs of CMP include changes to the hyaline cartilage associated with the patella such as erosion and swelling along with sclerosis of the bone.
The structures involved in CMP may include the four major bones that intersect at the knee, which are the femur, tibia, fibula and patella. The trochlear groove of the femur is where the patella articulates this bone and the articular hyaline cartilage provides a smooth interface between these bones. This cartilage is critical for motion of the knee, however, lateral pressure while turning may have negative nutritional effects on the medial and central areas of the articular cartilage, where degenerative changes are likely to occur.
The quadriceps femoris, which is a group of four muscles, inserts on the patella. These muscles include the rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM) and the vastus intermedius (VI). The quadripceps, especially the VL (lateral side) and the vastus medialis obliques (VMO) on the medial side, actively stabilize the knee during extension. The function of the VMO is not to extend the knee but it is the only muscle that actively stabilizes the medial facet and keeps the patella in place on the trochlea, therefore, even the smallest changes dramatically effect the patella positioning. Along with the quadriceps there are a number of passive structures that provide lateral support to the patella, including the iliotibial band (ITB). A tight ITB may cause excessive lateral tracing and lateral patellar tilt.
Other anatomical features or conditions that may impact the stability of the patella are femoral anteversion and the Q-angle (quadriceps angle which is the spatial relationship between the pelvis, tibia, patella and femur). Femoral anteversion is characterized by medial femur torsion which changes patella alignment and may cause overuse injuries.
CMP is a disorder characterized by degeneration of the cartilage below the kneecap, which is observed more commonly in younger individuals, athletes and females . The cause for CMP is thought to be overuse, injury or placing excessive force on the knee. In older individuals CMP may be a sign of kneecap arthritis. Individuals with previous knee injury, fracture or dislocation are more likely to develop CMP. Symptoms of CMP include a gating or grinding sensation upon extension of the knee, front knee pain that gets worse after long periods of sitting, knee pain that gets worse when using stairs or rising from a chair and tenderness of the knee.
To test for CMP physicians will perform a physical exam to identify tenderness, swelling and to determine if the kneecap is properly aligned. X-rays are used to rule out other causes of knee pain and to verify CMP. If CMP is diagnosed treatments will include rest, nonsteroidal anti-inflammatory drugs (NSAIDs, eg. ibuprofen) for pain and physical therapy to stretch the hamstring and strengthen the quadriceps. Until pain subsides patients should limit their participation in sports or other strenuous activities and avoid any activities that lead to increased knee pain, including deep knee bends. If conservative measures are not able to correct the alignment of the kneecap surgery may be considered. Physicians may recommend less invasive (arthroscopic) or more invasive (open) surgery depending on the degree and type of knee misalignment.