The patella is the largest sesamoid bone in the human body. Its upper pole is connected to the quadriceps tendon, while its lower pole is anchored to the tibial tuberosity by the patellar ligament. By increasing the leverage of the quadriceps, the patella enhances the efficiency of knee extension. Its articular surface interacts with the medial and lateral condyles of the femur to form the patellofemoral joint. During knee flexion and extension, the patella slides in an S-shaped trajectory from proximal to distal between the femoral condyles, a motion referred to as the patellar tracking. Proper force distribution on the patella ensures its correct movement within the trochlear groove. Chondromalacia patellae refers to chronic damage to the patellar cartilage, characterized by swelling, erosion, fissuring, fragmentation, and detachment of the cartilage. Over time, similar pathological changes occur in the cartilage of the opposing femoral condyles, leading to the development of patellofemoral osteoarthritis.
Etiology
Congenital or Acquired Factors
Developmental abnormalities of the patella, malpositioning, or irregularities in femoral condyle size, as well as acquired conditions such as knee valgus or varus deformities and tibial external rotation deformities, contribute to patellar instability. During patellar movement, these factors concentrate pressure onto specific points in the patellofemoral joint, providing a basis for chronic injury.
Frequent and Repetitive Knee Movement
Prolonged forceful or rapid knee flexion and extension during activities such as cycling or ice skating increases wear and tear on the patellofemoral joint.
Cartilage Nutrition Impairment
The patellar cartilage primarily derives its nutrients from synovial fluid. Abnormalities in synovial fluid composition caused by various factors result in cartilage malnutrition, leaving the cartilage more susceptible to degenerative changes from minor trauma.
Clinical Manifestations
Prevalence in Young Athletes
The early stages are characterized by pain beneath the patella or anterior knee pain. With disease progression, pain episodes last longer than the intervals of relief, leading to difficulty squatting, climbing stairs, or descending steps and symptoms such as sudden knee weakness or instability.
Tenderness of the Patellar Margin
Tenderness is observed along the patellar edges. Compression or grinding of the patella in the extended knee position can produce a grinding sensation accompanied by pain. Isolated patellar cartilage damage does not cause joint effusion, but secondary synovitis related to advanced patellofemoral osteoarthritis can lead to increased joint effusion, resulting in a positive patellar floating test. Prolonged disease duration is often associated with quadriceps atrophy, with the vastus medialis being most affected.
Imaging Examinations
X-ray Imaging
The early stages typically show no abnormalities. Over time, bone spurs may form on the patellar edges, the patellofemoral joint surface may lose smoothness, or the joint space may narrow. X-rays can also identify abnormalities such as bipartite patella, high-riding patella, or flattened lateral femoral condyles.
MRI
T1-weighted images may show thickening of the patellar cartilage, while T2-weighted images may indicate edema in the thickened cartilage.
Radionuclide Bone Scintigraphy
Localized areas of increased radiotracer uptake in the patella can be observed, which is valuable for early diagnosis.
Treatment
Treatment primarily focuses on non-surgical approaches.
Following the onset of symptoms, limiting intense knee activity for 1–2 weeks may help. Resistance exercises for the quadriceps can enhance muscle strength, which helps maintain proper patellar tracking and increase knee joint stability.
In cases of sudden exacerbation of swelling and pain, cold compresses may alleviate symptoms during the initial 48 hours, followed by warm compresses and physical therapy.
Intra-articular injections of sodium hyaluronate (hyaluronic acid) can improve synovial fluid viscosity, enhance lubrication, protect cartilage, and promote healing and regeneration of the joint cartilage. Pain may also be relieved and joint mobility improved. Typically, 2 mL are injected weekly for a course of 4–5 sessions. Intra-articular injections of prednisolone acetate can reduce symptoms, although its inhibition of glycoprotein and collagen synthesis may hinder cartilage repair. Improper sterile technique during such injections may lead to bacterial joint infections with severe consequences, so caution is essential.
Surgical intervention may be considered for patients unresponsive to rigorous non-surgical treatment or those with congenital deformities. The goals of surgery include:
- Enhancing patellar stability during its sliding motion along the femoral condyles, such as through lateral retinacular release or lateral elevation of the femoral condyle.
- Removing small erosive lesions from the patellar cartilage to promote repair.
- For cases involving complete destruction of the patellar cartilage, patellectomy has been proposed by some as a way to delay progression to patellofemoral osteoarthritis, although postoperative knee weakness can be significant.
- Patellofemoral joint replacement is another surgical option in advanced cases.