Laboratory Studies
See the list below:
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Laboratory studies generally are not indicated for the diagnosis of patellofemoral syndrome.
Imaging Studies
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Imaging studies usually are not necessary in order for a physician to diagnose or recommend treatment for patellofemoral syndrome (PFS). Imaging studies should be considered for unusual presentations and for persons in whom the syndrome is refractory to conservative management.
Sunrise views should be included with anterior-posterior (AP) and lateral radiographic imaging of the knee. Limited positions of flexion are available for such viewing. These radiographs provide more of an indirect observation of what is happening within the articulation.
Lateral patellar tilt and a high-riding patella (patella alta) may be observed.
Osteophytes or joint space narrowing may be identified, suggesting arthritic changes in the articular cartilage. [7]
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Nuclear scans are less likely to be of value in defining PFS and are more useful in helping to identify other, less common conditions that may mimic PFS, as outlined in the differential diagnoses. When changes have occurred in the retropatellar cartilage, mild increases in uptake of radionucleotide may be observed. Increased uptake of radionucleotide is not limited to the patella; it may be seen in the proximal tibia, distal femur, or patella. [8]
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Computed tomography (CT) scanning and magnetic resonance imaging (MRI)
CT scanning and MRI allow for imaging at various angles of flexion.
CT scanning with the knee in full extension has been demonstrated to more accurately detect patellar subluxation.
Cross-sectional viewing allows more direct visualization of the articulation between the patella and femur.
Schutzer et al identified 3 patterns of malalignment using CT scanning [9] :
Type 1 includes patellar subluxation without tilt.
Type 2 is described as patellar subluxation with tilt.
Type 3 is patellar tilt without subluxation.
Other Tests
Serology, joint aspiration, and related tests are indicated only when alternative diagnoses are suspected. Such investigations are not likely to provide useful information in this syndrome, as it is not a disease entity but rather a group of symptoms occurring sometimes in association with multiple factors (intrinsic and extrinsic). [10]
A study by Ferrari et al indicated that surface electromyography (sEMG) can be used in patients with referred anterior knee pain to diagnose PFS. In the study, which involved 22 persons with PFS and 29 persons without pain, the investigators found that by using the medium frequency ̶ band parameter, it was possible to differentiate between the two groups. They concluded that EMG signals from the vastus lateralis and vastus medialis muscles with referred anterior knee pain can be used in the diagnosis of PFS. [11]
Procedures
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Arthroscopy
Arthroscopy helps to confirm the diagnosis of patellofemoral syndrome (PFS) by allowing direct visualization of the cartilage surface. Arthroscopic evaluation also provides assessment of joint structures that may cause symptoms that mimic PFS when they are impaired.
Arthroscopy also has the ability to facilitate surgical alteration of patellar tracking (eg, lateral release). Visualization of the patella may allow for some revision of the cartilage surface. However, most authors agree that surgical treatment is rarely indicated.
Histologic Findings
Histologic findings are dependent on the extent to which the cartilage surfaces have been compromised. Shearing stresses may result in changes in subchondral bone and dysplasia of the cartilage surface. More severe cartilage changes have been identified in persons with patellofemoral syndrome that has been refractory to conservative measures.
