The patella, commonly known as the kneecap, is a sesamoid bone formed in the quadriceps tendon and is also the largest sesamoid bone in the body. It is flat and millet-shaped, located under the skin and easy to feel. The bone is wide at the top and pointed downward, with a rough front and a smooth back. It can move up and down, left and right, and protects the knee joint. The back of the patella is smooth and covered with cartilage, connecting to the patellar surface of the femur. The front is rough, and the quadriceps tendon passes through it.
Patellar chondromalacia is a common knee joint disease. In the past, this disease was common in middle-aged and elderly people. Now, with the popularization of sports and fitness, this disease also has a high incidence rate among young people.
I. What is the true meaning and cause of chondromalacia patella?
Chondromalacia patellae (CMP) is a patellofemoral joint osteoarthritis caused by chronic damage to the patellar cartilage surface, which causes cartilage swelling, cracking, breaking, erosion, and shedding. Finally, the opposite femoral condyle cartilage also undergoes the same pathological changes. The true meaning of CMP is: there is a pathological change of patellar cartilage softening, and at the same time, there are symptoms and signs such as patellar pain, patellar friction sound, and quadriceps atrophy.
Since articular cartilage has no nerve innervation, the mechanism of pain caused by chondromalacia is still unclear. CMP is the result of the combined effects of multiple factors. Various factors that cause changes in patellofemoral joint pressure are external causes, while autoimmune reactions, cartilage dystrophy, and changes in intraosseous pressure are internal causes of chondromalacia patellae.
II.The most significant feature of chondromalacia patellae is the specific pathological changes. So from the perspective of pathological changes, how is chondromalacia patellae graded?
Insall described four pathological stages of CMP: stage I is cartilage softening caused by edema, stage II is due to cracks in the softened area, stage III is the fragmentation of articular cartilage; stage IV refers to the erosive changes of osteoarthritis and exposure of subchondral bone on the articular surface.
The Outerbridge grading system is most useful for evaluating patellar articular cartilage lesions under direct visualization or arthroscopy. The Outerbridge grading system is as follows:
Grade I: Only the articular cartilage is softened (closed cartilage softening). This usually requires tactile feedback with a probe or other instrument to assess.
Grade II: Partial-thickness defects not exceeding 1.3 cm (0.5 in) in diameter or reaching the subchondral bone.
Grade III: The cartilage fissure is greater than 1.3 cm (1/2 inch) in diameter and extends to the subchondral bone.
Grade IV: Subchondral bone exposure.
III. Both pathology and grading reflect the essence of chondromalacia patella. So what are the most meaningful signs and examinations for diagnosing chondromalacia patella?
The diagnosis is mainly based on pain behind the patella, which is caused by the patellar grinding test and the single-leg squat test. The focus needs to be on distinguishing whether there is a combined meniscus injury and traumatic arthritis. However, there is no correlation between the severity of patellar chondromalacia and the clinical symptoms of anterior knee pain syndrome. MRI is a more accurate diagnostic method.
The most common symptom is dull pain behind the patella and inside the knee, which worsens after exertion or going up or down stairs.
Physical examination reveals obvious tenderness in the patella, peripatella, patellar margin and posterior patella, which may be accompanied by patellar sliding pain and patellar friction sound. There may be joint effusion and quadriceps atrophy. In severe cases, knee flexion and extension are limited and the patient cannot stand on one leg. During the patellar compression test, there is severe pain behind the patella, indicating patellar articular cartilage damage, which is of diagnostic significance. The apprehensive test is often positive, and the squat test is positive. When the knee is flexed 20° to 30°, if the range of internal and external movement of the patella exceeds 1/4 of the transverse diameter of the patella, it indicates patellar subluxation. Measuring the Q angle of 90° knee flexion can reflect abnormal patellar movement trajectory.
The most reliable auxiliary examination is MRI, which has gradually replaced arthroscopy and become a non-invasive and reliable means of CMP. Imaging examinations mainly focus on these parameters: patellar height (Caton index, PH), femoral trochlear groove angle (FTA), lateral surface ratio of femoral trochlear (SLFR), patellar fit angle (PCA), patellar tilt angle (PTA), among which PH, PCA, and PTA are reliable knee joint parameters for auxiliary diagnosis of early CMP.
X-ray and MRI were used to measure patellar height (Caton index, PH): a. Axial X-ray in weight-bearing standing position with knee flexed at 30°, b. MRI in position with knee flexed at 30°. L1 is the patellar inclination angle, which is the distance from the lowest point of the patellofemoral joint surface to the anterior superior angle of the tibial plateau contour, L2 is the length of the patellofemoral joint surface, and Caton index = L1/L2.
Femoral trochlear groove angle and patellar fit angle (PCA) were measured by X-ray and MRI: a. Axial X-ray with knee flexed at 30° in weight-bearing standing position; b. MRI with knee flexed at 30°. The femoral trochlear groove angle is composed of two lines, namely the lowest point A of the femoral trochlear groove, the highest point C of the medial trochlear articular surface, and the highest point B of the lateral trochlear articular surface. ∠BAC is the femoral trochlear groove angle. The femoral trochlear groove angle was drawn on the axial image of the patella, and then the bisector AD of ∠BAC was drawn. Then a straight line AE was drawn from the lowest point A of the femoral trochlear groove as the origin through the lowest point E of the patellar crest. The angle between the straight line AD and AE (∠DAE) is the patellar fit angle.
X-ray and MRI were used to measure the patellar tilt angle (PTA): a. Axial X-ray in weight-bearing standing position with knee flexed at 30°, b. MRI in position with knee flexed at 30°. The patellar tilt angle is the angle between the line connecting the highest points of the medial and lateral femoral condyles and the transverse axis of the patella, i.e. ∠ABC.
Radiographs are difficult to diagnose CMP in its early stages until the advanced stages, when extensive cartilage loss, loss of joint space, and associated subchondral bone sclerosis and cystic changes are evident. Arthroscopy can achieve a reliable diagnosis because it provides an excellent visualization of the patellofemoral joint; however, there is no clear correlation between the severity of patellar chondromalacia and the degree of symptoms. Therefore, these symptoms should not be an indication for arthroscopy. In addition, arthrography, as an invasive diagnostic method and a modality, is generally only used in the advanced stages of the disease. MRI is a noninvasive diagnostic method that promises the unique ability to detect cartilage lesions as well as internal derangements of the cartilage before morphological cartilage loss is visible to the naked eye.
IV. Chondromalacia patellae may be reversible or may progress to patellofemoral arthritis. Effective conservative treatment should be given promptly in the early stages of the disease. So, what does conservative treatment include?
It is generally believed that in the early stage (stage I to II), the patellar cartilage still has the ability to repair, and effective non-surgical treatment should be performed. This mainly includes activity restriction or rest, and the use of non-steroidal anti-inflammatory drugs when necessary. In addition, patients should be encouraged to exercise under the supervision of a physical therapist to strengthen the quadriceps muscle and enhance knee joint stability.
It is worth noting that during immobilization, knee braces or knee orthoses are generally worn, and plaster fixation is avoided as much as possible, as it can easily lead to disuse injury of the articular cartilage; although blockade therapy can relieve symptoms, hormones should not be used or used sparingly, as they inhibit the synthesis of glycoproteins and collagen and affect the repair of cartilage; when joint swelling and pain suddenly worsen, ice compresses can be applied, and physical therapy and warm compresses can be applied after 48 hours.
V. In late-stage patients, the repair ability of articular cartilage is poor, so conservative treatment is often ineffective and surgical treatment is required. What does surgical treatment include?
Indications for surgery include: after several months of strict conservative treatment, patellar pain still exists; if there is congenital or acquired deformity, surgical treatment can be considered. If Outerbridge III-IV cartilage damage occurs, the defect can never be filled with real articular cartilage. At this time, simply shaving the cartilage damage area with chronic overload cannot prevent the process of articular surface degeneration.
Surgical methods include:
(1)Arthroscopic surgery is one of the effective means of diagnosing and treating chondromalacia patella. It can directly observe the changes in the cartilage surface under the microscope. In mild cases, the smaller erosion lesions on the patellar articular cartilage can be scraped to promote repair.
(2) lateral femoral condyle elevation; (3) patellar cartilage surface resection. This surgery is performed for patients with small cartilage damage to promote cartilage repair; (4) patellar resection is performed for patients with severe damage to the patellar cartilage surface.
Post time: Nov-15-2024
