Patellofemoral Pain Syndrome (PFPS) occurs due to imbalances of the pulling forces imposed upon the patella during extension and flexion knee motions. PFPS is a term known by the layman as “runner’s knee”, or more specific to the location, as “anterior knee pain”. As the layman’s name implies, this injury is typically associated with overuse types of trauma related to running or jumping sports. However, overuse trauma associated with PFPS is not limited to just running or jumping, but more generally may include any other compressive and repetitive activities that include walking, running, cycling, or any types of activities that may perpetuate stress on misaligned structures within the knee complex. The misalignment may occur because of a tight lateral quadriceps muscle or attached retinaculum, which can lead to an abnormal pulling of the patella, and therefore result in shearing forces which lead to cartilage breakdown within the patellofemoral joint.1 While the term “chondromalacia patella” is not synonymous with PFPS, the halmark feature of chondromalacia is the characteristic degeneration of the cartilaginous matrix within the retropatellar region, thereby causing pain associated with PFPS.16 Chondromalacia patella may be visualized (see Figure 1) as a grinding away of cartilage that one may experience as the problem gets progressively worse over time.
Figure 1: Image borrowed from: [http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001488/]
Figure 2: Image borrowed from: [http://www.aafp.org/afp/2007/0115/p194.html]
The bones of the patellofemoral joint consist of the femur and the patella, a long bone and sesamoid bone, respectively. The patella is of an approximated triangular shape; it tracks through the trochlear groove of the femur during extension and flexion movements of the knee. An important biomechanical function of the patella is that it acts as a lever, which confers a mechanical advantage to the quadriceps muscle in the sense that the patella positions the quad muscle more anteriorly in order to gain more force during extension of the leg.2
With respect to arterial knee anatomy, there are various anastomoses that comprise the blood supply to the knee (formed by five main arteries – see Figure 3). A lateral retinaculum release surgery is done to alleviate PFPS symptoms, but ironically may lead to a disruption of blood supply, due to lesion of these anastomoses. However, the ischemic effects are not permanent, since revascularization may occur to meet the blood supply demands of the structures of the PF joint.3
In regard to sensory receptors, studies have shown that a high level of substance-P, a neurotransmitter involved in pain transmission, exists within the fat pad, retinaculum and even periosteum of the PF joint bones, which may suggest the pain transmission role these soft tissue anatomical structures play, as it applies to PFPS.3
Figure 3: Image borrowed from: [http://medchrome.com/basic-science/anatomy/the-knee-joint/]
Several common risk factors are presented in the literature as being the common indicators of PFPS. Weakness in functional testing, muscle tightness and ligament laxity or lack of muscle strength were cited as being several of the many indicators for further examination for suspected PFPS.3 In particular, lower knee extension strength is associated with categorization of an individual as being high risk for PFPS; this underscores the great importance of maintaining adequate quad strength in the effort to prevent PFPS.4 Not to be outdone, the psychological perception of pain in the form of fear-avoidance beliefs has been shown to be a significant indication for how well one may progress in terms of restoration of function and decreasing pain levels after rehabilitation of PFPS. According to the literature, the degree a person rehabilitating from PFPS can decrease fear-avoidance beliefs associated with physical activities may be indicative of better outcomes during treatment of PFPS.5
The incidence for PFPS is such that females are 2.23 times more likely than males to develop the syndrome.6 PFPS accounts for nearly 1 out of every 3 knee disorders found in women and 1 in 5 for men. As was mentioned, PFPS affects those who are typically athletic, owing to the compressive forces involved in such activities that lead to symptoms of PFPS. This syndrome is seen less often in sedentary folks, or those who do not frequently overload the PF joint.7 Interestingly, research shows that nearly 1 in 5 runners presenting to sports medicine physical therapy clinics have PFPS.8
A patient with PFPS will present with complaints of pain originating at the anterior aspect of the knee, however, pain will not typically present internally, nor on either the medial or lateral aspects. In addition, as noted before in the Incidence section, many of these patients will be young (20s to 30s), athletic and many of them will be runners. Among these patients will be notable signs of lower extremity misalignment (leg length discrepancy), differences in dorsiflexion, genu varum and varus at the forefoot.1 In addition, there may be retropatellar effusion and pain upon examination. More specifically, upon objective examination of the patella itself, the examiner may find a notable maltracking movement, called a “J” sign (see Figures 4 and 5). In Figure 4 is a table that documents common objective findings that may help the clinician to gain a clearer picture of how the patient with PFPS will present in the clinic.
Figure 4: Image borrowed from 
Figure 5: Image borrowed from 
Many of the potential etiologies associated with PFPS were already mentioned within the context of how these patients will present clinically. However, research has shown a combination of potential causes of PFPS as actually being at the root of this syndrome. Vastus lateralis and IT band tightness, muscle weakness (VMO), too much exercise and abnormal lower body biomechanics (lower limbs) collectively have been found to be causes of PFPS.10 Together, these causes may lead to the increased patellar maltracking, breakdown of cartilage and increased shearing forces associated with occurrence of PFPS. The research also highlights a lack of hip strength, in particular, poor hip external rotator and hip abductor strength, as being a possible cause of PFPS.9 So because etiological causes of PFPS may not be limited to areas directly adjacent to the knee itself, careful consideration of the kinematic chain and examination of areas distal from the knee are of great importance when formulating a plan of care.
The following is a list11 of factors similar to those found in Figure 4 that may serve as possible etiologies of PFPS:
-Patellar dysplasia (e.g., patella alta or baja)
-Tight patellar retinaculum (especially lateral)
-Abnormal patellar tracking
-Abnormal patellar tilt or rotation
-Abnormal patellar alignment relative to the femur (e.g., Q-angle outside the normal 13° to 18°)
-Excessive genu valgum/varum
-Muscle weakness (e.g., vastus medialis obliquus, hip abductor and lateral rotators, ankle dorsiflexors)
-Muscle imbalance (e.g., quadriceps/hamstrings ratio)
-Excessive tibial torsion (especially medial)
-Foot malalignment (e.g., rearfoot varus or valgus, excessive pronation/supination of the foot)
-Muscle hypomobility (e.g., quadriceps, hamstrings, gastrocnemius, iliotibial band, hip adductors)
-Trauma to patella (e.g., dislocation, direct blow)
-Abnormal repetitive stress to patella (e.g., running on the same side of road or sidewalk continually [camber of road or sidewalk affects foot-knee mechanics])
-Training shoes worn (e.g., control shoe versus cushioning shoe, shoes "broken down")
-Excessive pelvic tilt (anterior/posterior/medial/lateral)
Imaging studies are not routinely used for patients who are suspected of having patellofemoral pain syndrome. In fact, radiography is selectively indicated as a diagnostic test for patients with a history of trauma or effusion. In addition, radiography is used to test patients who have had prior knee surgeries or who are older than 50, in order to rule out OA.1 Indeed, radiography may be used to test for PFPS in skeletally immature patients, in order to rule out other possible causes for the purpose of a thorough differential diagnosis.1
While other tests, such as the computed tomography (CAT scan) and Magnetic Resonance Imaging (MRI) tend not to be used as diagnostic tests for PFPS, MRI tends to hold some use in detecting cartilage damage and if patellofemoral ligament damage is noted on an MRI then this could potentially indicate patellar subluxation.1 Again, these represent more diagnostic clinical tests that are not typically used for differential diagnosis of the patient with PFPS. There are other such tests which typically have adequate reliability and validity to be used to test for PFPS; these are mentioned in the next section.
Evaluation/Special Orthopedic Tests:
The orthopedic tests and the associated positive signs (and accompanying validity and reliability assessments) are as follows:
1.) Patellar glide test: This test tests the mobility of the patella. If the patella can be moved less than a single quadrant this may be indicative of tight lateral soft tissue structures. If the patella can be moved by greater than three quadrants then this finding may suggest excessive patellar movement possibly due to weak medial restraints.1 According to research13, two positive likelihood ratios from two studies, of 1.8 and 1.9, were interpreted as giving a person with PFPS an average chance of getting a positive test result. Therefore, the validity of this test is questionable. Despite this fact, the test is still used in differential diagnosis of knee musculoskeletal pathologies.
Patellar Glide Test
2.) Patellar Tilt Test: This is a test that ascertains the tightness of lateral soft tissue structures. A positive test is discovered when the lateral part of the patella is fixed and cannot be raised to at least a horizontal position.1 According to research13, the patellar tilt test has a high positive likelihood ratio of 5.3. This represents evidence that the odds of a patient having PFPS when the patellar tilt test is done is quite high.
Patellar Tilt Test
3.) Patellar grind test (a.k.a. Clarke's Sign): The patellar grind test assesses the presence of abnormal patellar movement and accompanying degree of painful crepitation upon contraction of the quadriceps muscles. A positive test result includes painful crepitation at the patellofemoral joint.1According to research13, the patellar grind test was found to have a positive likelihood ratio of 7.4, and therefore has excellent diagnostic ability of PFPS. This means that the odds of having patellofemoral pain syndrome when the test is positive are excellent as well.
Patellar Grind Special Test (Clarke's Sign)
4.) Patellar apprehension test: This test assesses the degree of pain with lateral movement of the patella. A positive finding is indicated if pain occurs with lateral translation of the patella.1 According to the research, the Patellar apprehension test demonstrates a positive likelihood ratio of 2.26, and negative likelihood ratio of 0.79.11, 12 This means that the odds of having patellofemoral pain syndrome when the test is positive are average, and non significant. Therefore, the test has questionable validity value as a diagnostic tool.
Patellar Apprehension Test
5.) Other tests: According to Cook et al.13, the Active Instability Test and Stair Climbing Test each had very high positive likelihood ratios, of 249 and 11.6, respectively. The active instability test had the highest stand alone positive likelihood ratio, and it's sensitivity value was 100%.
According to one systematic review, the current gold standard used to treat PFPS is quadriceps strength training exercise.14 Specifically, this same review stated that specific VMO training exercises are often currently used to restore balance within the quadriceps muscle complex. The VMO training is of particular importance because one of the objectives of treatment of PFPS is to achieve the restoration of proper quadriceps muscle balance. More to the point, the goal of VMO strength training is to restore the timing of the VMO firing with the firing of the vastus lateralis muscle and other associated lateral muscles of the thigh and hip, in order to achieve proper patellar alignment during tracking. Other recent evidence advocates the clinical usefulness of hip muscle retraining in order to address weakness in hip abductors and external rotators that seems to be prevalent in patients with PFPS.15 With respect to the use of weight-bearing versus non-weight-bearing exercises, the research indicates that neither method confers a greater benefit than the other in terms of reducing pain or increasing functional use of the knee with PFPS.15
With regard to other modalities, one review states that ice, e-stim and ultra sound are used in the conservative management of PFPS, as is the case with many musculoskeletal injuries.15 Patellar bracing and knee bracing have both been found to confer limited benefit as additional conservative options to treat the lateral patellar tracking in patients with PFPS.14 Foot orthoses are used as well to treat PFPS in those patients who present with a high degree of pronation with tibial and femoral rotation.15
Surgery & post-op treatment:
According to recent research, the Fulkerson Osteotomy (anteriomedial tibial tubercle transfer) may be used as a surgical intervention for only those patients with PFPS who do not respond favorably to conservative treatment.17 However, despite this corrective surgery, the chondromalacia can return in the affected knee. Another surgical intervention used for PFPS is arthroscopic surgery with lateral retinaculum release.3 Again, this surgical intervention presents as another option that is used only if conservative treatment does not work. In addition, the release method is only effective for patients who keep weight down post-op to minimize loading forces on the patellofemoral joint. The patient planning on having this surgery undergoes an extensive weight loss program prior to surgery, in order to maximize benefits of rehabilitation.
Postoperative management of the patient who has a Fulkerson osteotomy will employ the use of preoperative proximal core and a kinetic chain muscle strengthening program. The focus of this program will be on the pelvis, leg, hip, lower back and thigh. Postoperatively the patient will wear compression dressing, be treated with cryotherapy, and have protective bracing. In addition, the patient will be monitored for any complications that may arise during this period of time.18
0-6 weeks: The patient is limited to simply touch weight bearing by using crutches. Additionally, the patient will transition to FWB status after the radiographs are considered acceptable at 6 weeks. At the 2 week mark, the patient's hinged knee brace that has been locked into extension becomes unlocked and discontinued per enough lower extremity control. This may occur at 8 weeks.18
6 weeks to 12 months (and beyond): Open chain kinetic knee exercises, quad stretching and core strengthening must be maintained, in order to maximize benefits of the post op procedures.
*On a side note, consistent and early core strengthening and quadriceps strengthening, as well as range of motion exercises for the knee are important in order to maximize recovery.18
Additional Web Based Resources:
1. Dixit S, Burton M, Mines B. Management of Patellofemoral Pain Syndrome. Am Fam Physician. 2007 Jan 15;75(2):194-202.
2. Zaffagnini S, Dejour D, Arendt E. Patellofemoral Pain, Instability, and Arthritis – Clinical Presentation, Imaging, and Treatment. New York: Springer; 2010.
3. Waryasz GR, McDermott AY. Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors. Dynamic Medicine. 2008, 7:9. doi:10.1186/1476-5918-7-9.
4. Lankhorst NE, Bierma-Zeinstra SMA, Middelkoop MV. Risk Factors for Patellofemoral Pain Syndrome: A Systematic Review. J Orthop Sports Phys Ther. Epub 25 October 2011. Doi: 10.2519/jospt 2012.3803.
5. Piva SR, Fitzgerald GK, Wisniewski S, Delitto A. Predictors of pain and function outcome after rehabilitation in patients with patellofemoral pain syndrome. J Rehabil Med. 2009; 41(8): 604–612. doi: 10.2340/16501977-0372.
6. Boling M, Padua D, Marshall S, Guskiewicz K, Pyne S, Beutler A. Gender differences in the incidence and prevalence of patellofemoral pain syndrome. Scand J Med Sci Sports. 2010 October; 20(5): 725-730. doi: 10.1111/j.1600-0838.2009.00996.x.
7. Neumann DA. KINESIOLOGY of the MUSCULOSKELETAL SYSTEM Foundations for Rehabilitation Second Edition. St. Louis, Miss.: Mosby Elsevier; 2010.
8. Taunton JE, Ryan MB, Clement DB, McKenzie DC, Lloyd-Smith DR, Zumbo BD. A retrospective case-control analysis of 2002 running injuries Br J Sports Med. 2002;36:95-101 doi:10.1136/bjsm.36.2.95.
9. Bolgla LA, Malone TR, Umberger BR, Uhl TL. Hip Strength and Hip and Knee Kinematics During Stair Descent in Females With and Without Patellofemoral Pain Syndrome. J Orthop Sports Phys Ther. 2008;38(1):12-18. doi:10.2519/jospt.2008.2462.
10. Fredericson M, Yoon K. Physical examination and patellofemoral pain syndrome. Am J Phys Med Rehabil. 2006 Mar;85(3):234-43.
11. Magee DJ. Orthopedic physical assessment. St. Louis, Miss.: Saunders Elsevier; 2008.
12. Nijs J, Van Geel C, Van der auwera C, Van de Velde B. Diagnostic value of five clinical tests in patellofemoral pain syndrome. Man Ther. 2006 Feb;11(1):69-77. Epub 2005 Jun 13.
13. Cook C, Mabry L, Reiman M, Hegedus E. Best tests/clinical findings for screening and diagnosis of patellofemoral pain syndrome: a systematic review Physiother. 2011, doi:10.1016/j.physio.2011.09.001.
14. Bogla LA, Boling MC. AN UPDATE FOR THE CONSERVATIVE MANAGEMENT OF PATELLOFEMORAL PAIN SYNDROME: A SYSTEMATIC REVIEW OF THE LITERATURE FROM 2000 TO 2010 Int J Sports Phys Ther. 2011 June; 6(2): 112–125.
15. Barton CJ, Webster KE, Menz HB. Evaluation of the Scope and Quality of Systematic Reviews on Nonpharmacological Conservative Treatment for Patellofemoral Pain Syndrome. J Orthop Sports Phys Ther. 2008;38(9):529-541. doi:10.2519/jospt.2008.2861.
16. KANNUS P, NATRI A, PAAKKALA T, JÄRVINEN M, FINLAND T. An Outcome Study of Chronic Patellofemoral Pain Syndrome. Seven-Year Follow-up of Patients in a Randomized, Controlled Trial. J Bone & Joint Surg. 1999; 81:355-63.
17. Karamehmetoğlu M, Oztürkmen Y, Azboy I, Caniklioğlu M. Fulkerson osteotomy for the treatment of chronic patellofemoral malalignment. Acta Orthop Traumatol Turc. 2007;41(1):21-30.
18. Sanchis-Alfonso V. Anterior Knee Pain and Patellar Instability Second Edition. London, UK.: Springer; 2011.