A. Classification of patellofemoral joint etiology
Many people have experienced patellofemoral joint (prepatellar) pain, adolescents, middle-aged and elderly patients are often told that you have chondromalacia patellae, and some patients do not get better after treatment, and patients are often confused and annoyed by this.
Chondromalacia patella refers to clinical symptoms such as popping sensation and pain in patellofemoral activity with chondromalacia patellae, which is secondary to stress overload of the patellofemoral joint, alignment abnormalities, trauma and idiopathic. With the development of modern medicine, the understanding of chondromalacia patellae has been further deepened, and the current concept includes a group of different manifestations of patellofemoral joint dysplasia, implying different degrees of enlarged Q-angle in the lower extremity, high patellae, shallow femoral glide, outward displacement of patellar glide trajectory, hypoplasia of the medial femoral oblique head, anterior femoral tilt, and compensatory tibial external rotation. It is difficult for the orthopedic surgeon to distinguish between so many etiologies, which is conceivable for the patient.
Patellofemoral arthropathy is divided into five types.
1, post-traumatic patellofemoral arthropathy;
2, patellofemoral dysplasia;
3, atopic chondromalacia of the patella;
4, exfoliative osteochondritis;
5 synovial crepitus.
Second, the causes of patellofemoral joint pain
At present, it is believed that chondromalacia patellae is a secondary lesion of patellofemoral dysplasia. The possible causes of prepatellar pain are.
(1) Excessive loading of the lateral patellar bone surface;
(2) Excessive tension on the lateral patellar ligament, causing degenerative or neuroma changes in the nerves within the lateral support band;
(3) Poor patellofemoral joint alignment resulting in pain associated with the unique anatomic morphology of the patella (Figure 1). The abnormal shear stresses caused by abnormal patellar trajectory and force lines are transmitted to the subchondral bone, and the continuous and repeated deforming action of the central crest of the patella can cause softening and fissures in the cartilage.
Third, the diagnosis of patellofemoral dysplasia
Patellofemoral dysplasia, which is characterized by varying degrees of bone structure abnormalities, is mainly seen in adolescents and middle-aged people. Patients often complain of patellofemoral joint pain, instability or both. Patellofemoral dysplasia includes.
1, lateral patellar compression syndrome.
2, chronic patellar subluxation;
3, recurrent patellar dislocation;
4, chronic patellar dislocation. All of these disorders eventually lead to patellar tenderness and patellofemoral arthritis.
(A) lateral patellar compression syndrome: there is no true patellar dislocation during knee extension and flexion, the patella is stable within the femoral talus, but tension in the lateral patellar support band of the knee joint increases the stress on the patella outward. increased Q angle, poor lower extremity alignment and alignment are the main causes of lateral patellar compression syndrome.
1, clinical manifestations: prepatellar pain is characterized by relatively vague and difficult to localize pain, often aggravated by increased knee flexion load symptoms when going up stairs and squatting.
2, physical examination: patella externally displaced (strabismus sign), Q angle greater than 20° is abnormal. The assessment of the tension of the lateral patellar support band is important for the diagnosis of lateral patellar compression syndrome.
①Patellar movement test (Figure 2): under normal conditions the patella can be pushed medially up to 1/4 of the width of the patella, and if the medial shift is less than 1/4, the lateral patellar support band is considered tight;
②Passive patellar tilt test (Figure 3): in the extension position, the patella can be tilted normally up to 15°, and if the transverse axis of the patella cannot be elevated above the horizontal plane, the lateral patellar support band is considered to be tight;
③ Patellar squeeze test and half squat test: can induce pain due to patellofemoral articular surface lesions.
3.Radiological examination
X-ray and CT examination: some minor abnormalities of patellar slip trajectory may be found.
(1) Patellofemoral index (Figure 4): greater than 1.6 suggests abnormal patellofemoral trajectory.
(2) Lateral patellofemoral angle (Figure 5): a lateral patellofemoral angle <8° is abnormal, suggesting tension in the lateral patellar support band.
(2) Chronic patellar subluxation: anterior patellar pain and lateral subluxation of the patella on axial patellar images or CT images.
It is important to note that patellar subluxation can be asymptomatic for a long time. Patients diagnosed with patellar subluxation often ask their physicians, “My knee is not traumatized and it did not hurt in the past! How did I become subluxated? How did I get it? The anatomical abnormality of patellofemoral dysplasia can be both congenital and acquired, and is manifested as an outward displacement of the patellar glide path. The causes of pain are described above.
1, clinical presentation: symptoms are similar to those of lateral patellar extrusion syndrome.
2, physical examination: in addition to the test to assess the tension of the lateral patellar support band, an experienced specialist can basically determine the diagnosis by physical examination, palpation reveals that the outer edge of the patella projects lateral to the lateral femoral condyle, and the “J” sign is positive for signs of patellar track externality.
3, radiological examination.
X-ray film and CT examination: CT can more effectively show the abnormal patellar trajectory and force lines. In addition to the lateral patellar compression syndrome measurements described above, the glide angle, anastomosis angle (Figure 6), lateral patellar displacement (Figure 7), and TT-TG values should be measured. The Insall-Salvati index >1.2 was measured on the lateral radiograph as a high patella.
What the patient was able to read was the lateral displacement of the patella (Figure 7), and the distance between the normal medial edge of the patella and the vertical line of the apex of the medial femoral condyle was not more than 1 mm to the lateral side.
There are three possible types of malalignment in patellar position on CT scan of patellar subluxation as follows.
A: subluxation with patella displaced externally and a positive anastomosis angle of more than 10°;
B: tilted, with the lateral patellofemoral angle less than 8°;
C: both subluxation and tilt deformities are present (Figures 8, 9, 10).
In some patients with patellofemoral dysplasia, the first symptom is patellar dislocation rather than pain, and the unstable patella can be re-dislocated due to minor injury. In addition, patellar dislocation is defined as “habitual patellar dislocation” if it occurs more than twice a year.
Factors associated with the development of patellar dislocation include both internal and external factors. Internal factors include
(1) deformity of the patellofemoral joint bone;
② soft tissue abnormalities;
(iii) extensive ligamentous laxity. External injury factors.
Bone structure abnormalities are best detected by CT examination, such as high patella, lateral dominant patella, flat femoral glide, lateral subluxation, patellar tilt, lateral displacement of the tibial tuberosity, and excessive anteversion of the femur, while soft tissue problems need to be clarified by physical examination. The most common sign of patellar dislocation is lateral patellar subluxation in extension, with the patella repositioning in the center of the talus when the knee is flexed at 90°.
(C) Recurrent patellar dislocation
Patients with recurrent patellar dislocation often have a history of recurrent episodes of knee instability. The difference with patellar dislocation is only with the time the patella stays in the lateral aspect of the knee joint, so anyone with patellar subluxation should be considered as recurrent patellar instability. Some of these are academic issues and patients do not need to look deeper.
(iv) Chronic patellar dislocation
Chronic patellar dislocation refers to the persistent prolapse of the patella beyond the femoral talus. In this case, the patella is dislocated regardless of whether the knee joint is straightened or flexed. It often occurs in children up to 10 years of age. This knee disorder can be classified as congenital or acquired. Acquired etiologies, such as repeated injections in the infant thigh or, less commonly, such as trauma, chronic dislocation of the patella is associated with quadriceps contracture.