Patellofemoral Syndrome usually involves abnormal alignment of the knee or patella and excessive pull or imbalance of certain muscles around the knee. Therefore, it is important to evaluate certain biomechanical elements of the lower extremity. In addition to testing for range of motion and strength, the examiner must also consider a series of special tests that will give the clinician a clearer idea of what needs to be corrected during the patient's rehabilitation.
Patellofemoral (PF) Syndrome is a general term used to describe pain and dysfunction in or around the patellofemoral joint. The cause of pain and dysfunction often results from either abnormal forces (e.g. increased pull of the lateral quadricep retinaculum with acute or chronic lateral PF subluxation/dislocation) or prolonged repetitive compressive or shearing forces (running or jumping) on the PF joint. The result is thinning of the articular cartilage under the patella and/or on the medial or lateral femoral condyles, synovial irritation and inflammation and subchondral bony changes in the distal femur or patella known as "bone bruises". Secondary causes of PF Syndrome are fractures, internal knee derangement, OA of the knee and bony tumors in or around the knee.1
Specific populations at high risk of primary Patellofemoral Syndrome include runners, basketball players, young athletes and females especially those who have an increased angle of genu valgus. Typically patients will complain of localized anterior knee pain which is exacerbated by sports, walking or stair climbing. Descending stairs may be worse than ascending. Unless there is an underlying pathology in the knee, swelling is usually mild to nil. Palpation as well is usually unremarkable.
Because the pathophysiology of primary PF Syndrome usually involves abnormal alignment of the knee or patella and excessive pull (or imbalance) of certain muscles around the knee, it is important to evaluate certain biomechanical elements of the lower extremity. The following special tests along with a standard knee exam of palpation, manual muscle testing (MMT), gait assessment and range of motion (ROM) measurement should give the clinician a clear idea of what needs to be corrected in rehabilitation.
Check muscle lengths. The PF Syndrome examination should include evaluation of hamstring, quadricep, Iliotibial (IT) band or Tensor Fascia Latae (TFL) and rectus femoris muscle lengths.
For rectus femoris length2 use the Thomas Test. The patient lies supine with both lower legs (below the knee) off the table's edge. The patient brings either knee (for our example, let us say the left knee) toward the chest and holds it there with both hands (they should remember to breath). Normal rectus femoris length will allow about 80 degrees of right knee flexion. If the posterior aspect of the right thigh does not touch the table (neutral hip extension) with the knee flexed to 80 degrees then the iliopsoas muscle (hip flexor) is probably tight.
The hamstring can best be assessed supine with a passive straight leg raise. The low back must be flat on the table with the opposite hip and knee extended. Normal hamstring length is at least 70 degrees of hip flexion. Short hip flexor muscles on the opposite side may give a false measurement of short hamstrings. To adjust for short hip flexors, place a pillow under the opposite knee so that the pelvis and lumbar spine will flex and therefore flatten the low back against the table.2
For the IT band and TFL (Ober test)2, the patient assumes a sidelying position near the table's edge with the under side lower limb slightly flexed at the hip and knee. The lateral trunk on the under side should remain flat on the table. Keeping the top limb's knee extended, extend the limb posteriorly and while stabilizing the pelvis. Lower the limb toward or in some cases off the edge of the bed. Once you feel the pelvis pulling or dropping downward or the under side lateral trunk arch, stop lowering the limb (the IT band is pulling the pelvis down at this point). Measure the distance between the foot and the bed. If the foot does not reach the bed, the IT band or TFL is tight.
Check the knee: Hungerford and Barry in 1979 described two main problems in PF pain patients namely increased Q angle and increased genu valgus which places more lateral force upon the patella leading to PF pain or more specifically lateral subluxation or dislocation.3 More recently however there has been a question about the role these two factors play. For example, a recent article by Sheehan reported that increased Q angle may actually cause a shift of the patella medially not laterally.4 Nevertheless, it is important to assess the tracking of the patella and any structural factors which may influence gliding of the PF joint. So in addition to performing screening tests for meniscus damage and ligament laxity which may be associated with PF pain1, consider the following:
Q angle is measured by determining the angle between two lines: the first line is made from the anterior superior iliac spine (ASIS) and the center of the patella and the second line is made from the tibial tubercle and the center of the patella. A high Q angle is greater than 16 degrees and low is less than 9 degrees.5
Excessive genu valgum (“knock knees”): In adults, the normal angle between the long shaft of the femur and tibia approaches 15 degrees of genu valgum.6 Measurements should be done in supine and standing.
Patella gliding: Palpation of the patella during active knee flexion in supine, squatting or stepping up or down on a stool will give information on presence of crepitus, PF stability, pain levels and how the patella is gliding in the trochlear groove. Additionally, observation during these maneuvers will help assess the quality of motion in the PF joint and the willingness of the patient to perform these basic motions.
Check the feet. The feet should not be neglected when considering knee problems including PF Syndrome. Pes planus (flat feet) and over pronation of the midfoot is often coupled with a toe out gait and a subsequent internal rotation of the tibia. The extent of the pes planus can be determined by tracing the feet in standing. During walking or running, as the heel hits the ground and the foot flattens, overpronation will excessively internally rotate the tibia and cause an increased genu valgus stress.7 As a result the patella may be pulled laterally causing pain and dysfunction.
Conflict of interest statementNo conflict of interest to report.
CITE THIS ARTICLE:
Tom Plamondon PA-C. Special tests in the clinical examination of patellofemoral syndrome. Doctors Lounge. Available at: https://www.doctorslounge.com/index.php/articles/page/287. Accessed January 22 2022.
- Waryasz GR, McDermott AY. Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors. Dyn Med. 2008;7:9.
- Kendall F, McCreary E. Muscles Testing and Function, 3rd Edition, Willliams and Wilkins, 1983: 148-168.
- Hungerford DS, Barry M. Biomechanics of the patellofemoral joint. Clin Orthop Relat Res. Oct 1979(144):9-15.
- Sheehan FT, Derasari A, Fine KM, Brindle TJ, Alter KE. Q-angle and J-sign: Indicative of Maltracking Subgroups in Patellofemoral Pain. Clin Orthop Relat Res. May 9 2009.
- Pantano KJ, White SC, Gilchrist LA, Leddy J. Differences in peak knee valgus angles between individuals with high and low Q-angles during a single limb squat. Clin Biomech (Bristol, Avon). Nov 2005;20(9):966-972.
- Genu Valgum: Wheeless Orthopaedics website, available at http://www.wheelessonline.com. accessed Sept 16 2009
- When the feet hit the ground everything changes. Biomechanics Seminar, Ft. Lauderdale Fl, 1994.