Clinical Biomechanics of Patellofemoral Pain Syndrome

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Introduction[edit | edit source]

Patellofemoral pain syndrome (PFPS) is a general term used to describe pain in the patellofemoral joint[1]. The cause of PFPS is commonly due to a combination of factors, such as overload/overuse of the joint or biomechanical abnormalities[1]. Patients often complain of gradual pain, which is associated with activities such as squatting or climbing stairs[2]. When the patellofemoral joint becomes unloaded, the patient rarely complains of the same pain[2]. Below are descriptions of the different biomechanical mechanisms examined in the research.


While patellar alignment is considered a potential mechanism for PFPS, it is important to look at the contradictory evidence.

Evidence for alignment

The first side argues that patellar alignment and tilt have an important role in the mechanism behind PFPS, as one study found that malalignment of the patella is often linked with hamstring tightness, iliotibial tract tightness, as well as imbalance of quadriceps[3]. The condition has been associated with varying biomechanical variables, such as a greater patellar tilt angle[4]. It was found in another study that patients diagnosed with PFPS had both a significant lateral tilt and superior shift of their patella whilst the knee was in full extension[5]. The patella also demonstrated a superior shift when the patellofemoral joint was in flexion in patients with PFPS, but who presented without signs of patellar instability in comparison to the controls[5]. Furthermore, once the PFPS-diagnosed patient was weight-bearing in knee extension, the patellar tilt was increased[5]. More research concerning muscular activation and strength is needed[5]. In patients diagnosed with PFPS, the results include a significant increase in the lateral shift, lateral spin, and a propensity for an increased lateral tilt of the patella[6].

Evidence against alignment

There is also evidence from a review done on patellar alignment and tracking in vivo, which found that when malalignment was detected on imaging, it did not necessarily mean that a successful outcome was correlational with conservative treatment[7]. Through a radiographic examination of asymptomatic controls and those living with PFPS, it has been also found that there was no significant variation in the patellar tilt or displacement when the knee was in flexion at 35 degrees[8]. This finding was presenting in both unloaded and loaded conditions[8]. Changes in alignment that accompany the contraction of the quadriceps femoris muscle did not vary between symptomatic and asymptomatic knees, as determined in an axial computed tomography study[9].


Many clinicians have the belief that PFPS comes from excessive compression of the patella onto the other bones in the joint[10], thus an examination into it is warranted. Knee flexion at 60 and 90 degrees generate the largest compression in the joint[11]. An increase in patellofemoral joint compression was found to lead to the development of patellofemoral pain[11]. The action of the forces on the patella led to abnormal patellar tracking (linking back to the first school of thought on patellar alignment), which increased the compression of the patella on the condyles of the femur[12]. This abnormal patellar tracking then led to instability, then increasing the compression forces across the facets of the patellar bone[12]. Compression across the patellar bone leads to degeneration of the articular cartilage of the joint[13]. The degeneration of articular cartilage means that the cartilage inappropriately distributes the patellofemoral contact forces[13]. Farrohki and colleagues, of whom includes Christopher Powers, have found through a finite element analysis that cartilage stress is significantly greater in patients diagnosed with PFPS[14]; this led the researchers to form the proposed association between joint stress and PFPS[14]. There has also been findings that the posterior patellofemoral joint reaction force contains the largest contribution to patellar compression against the trochlear surface[15]. Farrokhi and colleagues have found that there is apparently a need to consider the quadriceps, since the quadriceps (specifically vastus medialis and lateralis) have a posterior angle in relation to the femur[14]. Therefore, a decrease in the quadriceps force leads to a decreased posterior patellofemoral joint reaction force, which then sums to decreased compression on the patella[14]. Increased compression in the patellofemoral joint can lead to high subchondral bone stress[11].


While important to look at the biomechanics, it is also important to look at the mechanisms behind the treatment of such conditions. In terms of exercise prescription for the treatment of PFPS, there has been contrasting evidence between rest and exercise in order to increase function and reduce pain[16]. However, exercise has stronger support with a greater magnitude of improvement and is considered the favourable treatment for PFPS[16]. It has been found that retraining the motor skills of someone diagnosed with PFPS can address abnormal kinematics[17]. As a further specification of this, hip adduction was decreased by retraining the patient’s running technique[18], which is crucial as increased hip adduction was established as a risk factor for the development of patellofemoral pain[19]. There has been equal effectiveness found in both knee and hip strengthening programs[17]. There are quite encouraging results for complementing a knee programme with hip exercise[17]. There has also been evidence that the range of exercises currently prescribed are possibly too simple in order to tackle PFPS’s mechanisms[20]. Bracing has been found as an effective method to decrease pain and increase patellofemoral joint contact[21]; the authors caution, however, against attributing the pain reduction to the increase in contact area leading to a decrease stress[21]. It suggests that this warning should be strongly considered when prescribing bracing as a treatment as the increase in contact area could potentially be contradicted by an increase of the compressive forces within the joint[21]. While the authors recognize that it was not possible to determine how bracing works in the parameters of the above study, it was suggested that the braces worked in reducing pain by deviating the contact away from any sensitive areas and redistributing it to an area with less irritation[21]. Mulligan knee taping, when applied on patients diagnosed with PFPS who then performed a single leg squat, helped to reduce hip internal rotation and pain[22]. In an examination comparing Kinesio taping and McConnell taping, it was found that they both have benefits on quality of life augmented by those of pain relief[23]. McConnell taping has an effect on patellar alignment but has no benefit on motor function or proprioception, while Kinesio taping can relieve pain by applying it to the muscles[23]. More examination is needed into how the pain relief mechanism functions[23]. Whatever the choice of the therapist, PFPS is obviously a condition with multiple contributory factors that needs to be treated with an individualized rehabilitation program[24].


There are still questions to be answered in regard to the clinical biomechanics behind patellofemoral pain syndrome. One of the questions that needs to be answered is whether or not the compression from an increased joint reaction force could negatively balance the benefits of an increase in patella contact area[21]. Along with this, it needs to be determined whether or not compression of patella into the joint could change the contact area and not have an effect on the alignment of the patella[21]. As previously mentioned, current exercise prescriptions may not be appropriate for PFPS and the inclusion of exercises targeting power, strength, and neuromotor control has been suggested[20]; it is important to extensively examine any new exercise intervention for efficacy[20].

In conclusion, patellar alignment has contradicting evidence in terms of its role in the biomechanics of patellofemoral pain syndrome. The compression of the patella within the joint has been emerging as the new mechanism for patellofemoral pain syndrome. There have been numerous studies examining different interventions for the treatment of the condition and as with any topic, there are new avenues of research yet to be discovered.

References[edit | edit source]

  1. 1.0 1.1 Physiopedia [Internet]. UK: Physiopedia; 2021. Patellofemoral Pain Syndrome; [cited 2021 Apr 16]. Available from:
  2. 2.0 2.1 Crossley, K.M., Callaghan, M.J., van Linschoten, R. Patellofemoral pain. British Journal of Sports Medicine 2016; 50: 247-250. DOI: 10.1136/bjsports-2015-h3939rep.
  3. Petersen, W., Ellermann, A., Gösele-Koppenburg, A., Best, R., Rembitzki, I.V., Brüggemann, G-P., Liebau, C. Patellofemoral pain syndrome. Knee Surgery, Sports Traumatology, Arthroscopy 2014; 22(10): 2264-2274. DOI: 10.1007/s00167-013-2759-6.
  4. Lankhorst, N.E., Bierma-Zeinstra, S.M.A., van Middelkoop, M. Factors associated with patellofemoral pain syndrome: a systematic review. British Journal of Sports Medicine 2012; 47: 193-206. DOI: 10.1136/bjsports-2011-090369.
  5. 5.0 5.1 5.2 5.3 Esfandiarpour, F. Lebrun, C.M., Dhillon, S., Boulanger, P. In-Vivo Patellar Tracking in Individuals With Patellofemoral Pain and Healthy Individuals. Journal of Orthopaedic Research 2018; 36(8): 2193-2201. DOI: 10.1002/jor.23887.
  6. Wilson, N.A., Press, J.M., Koh, J.L., Hendrix, R.W., Zhang, L.Q. In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain. The Journal of Bone and Joint Surgery 2009; 91: 558-566. DOI: 10.2106/JBJS.G.00572.
  7. Song, C-Y., Lin, J-J., Jan, M-H., Lin, Y-F. The role of patellar alignment and tracking in vivo: The potential mechanism of patellofemoral pain syndrome. Physical Therapy in Sport 2011; 12: 140-147. DOI: 10.1016/j.ptsp.2011.02.008.
  8. 8.0 8.1 Laprade, J., Lee, R. Radiographic measures in subjects who are asymptomatic and subjects with patellofemoral pain syndrome. Clinical Orthopaedics and Related Research 2003; 414: 172-182. DOI: 10.1097/01.blo.0000079269.91782.f5.
  9. Jan, M.H., Lin, D.H., Lin, C.H., Lin, Y.F., Cheng, C.K. The effect of quadriceps contraction on different patellofemoral alignment subtypes: an axial computed tomography study. Journal of Orthopaedic and Sports Physical Therapy 2009; 39: 264-269. DOI: 10.2519/jospt.2009.2873.
  10. Bolgla, L.A., Boling, M.C. An update for the conservative management of patellofemoral pain syndrome: a systematic review of the literature from 2000 to 2010. The International Journal of Sports Physical Therapy 2011; 6(2): 112-125.
  11. 11.0 11.1 11.2 Mullaney, M.J., Fukunaga, T. Current concepts and treatment of patellofemoral compressive issues. The International Journal of Sports Physical Therapy 2016; 11(6): 891-902.
  12. 12.0 12.1 Rixe, J.A., Glick, J.E., Brady, J., Olympia, R.P. A Review of the Management of Patellofemoral Pain Syndrome. The Physician and Sportsmedicine, 2013; 41(3): 19-28. DOI: 10.3810/psm.2013.09.2023.
  13. 13.0 13.1 Besier, T.F., Draper, C.E., Gold, G.E., Beaupre, G.S., Delp, S.L. Patellofemoral joint contact area increases with knee flexion and weight-bearing. Journal of Orthopaedic Research 2005; 23(2): 345-350. DOI: 10.1016/j.orthres.2004.08.003.
  14. 14.0 14.1 14.2 14.3 Farrokhi, S., Keyak, J.H., Powers, C.M. Individuals with patellofemoral pain exhibit greater patellofemoral joint stress: a finite element analysis study. Osteoarthritis and Cartilage 2010; 19: 7-294. DOI: 10.1016/j.joca.2010.12.001.
  15. Chen, Y-J., Powers, C.M. Comparison of Three-Dimensional Patellofemoral Joint Reaction Forces in Persons With and Without Patellofemoral Pain. Journal of Applied Biomechanics 2014; 30: 493-500. DOI: 10.1123/jab.2011-0250.
  16. 16.0 16.1 Frye, J.L., Ramey, L.N., Hart, J.M. The Effects of Exercise on Decreasing Pain and Increasing Function in Patients With Patellofemoral Syndrome: A Systematic Review. Sports Health 2012; 4(3): 205-210. DOI: 10.1177/194138112441915.
  17. 17.0 17.1 17.2 Thomson, C., Krouwel, O., Kuisma, R., Hebron, C. The outcome of hip exercise in patellofemoral pain: a systematic review. Manual Therapy 2016; 26: 1-30. DOI: 10.1016/j.math.2016.06.003.
  18. Neal, B.S., Barton, C.J., Gallie, R., O’Halloran, P., Morrissey, D. Runners with patellofemoral pain have altered biomechanics which targeted interventions can modify: a systematic review and meta-analysis. Gait & Posture 2016; 45: 69-82. DOI: 10.1016/j.gaitpost.2015.11.018.
  19. Neohren, B., Hamill, J., Davis, I. Prospective evidence for a hip etiology in patellofemoral pain. Medicine & Science in Sports & Exercise,2013; 45(6): 1120-1124. DOI: 10.1249/MSS.0b013e31828249d2.
  20. 20.0 20.1 20.2 Dischiavi, S.L., Wright, A.A., Tarara, D.T., Bleakley, C.M. Do exercises for patellofemoral pain reflect common injury mechanisms? A systematic review. Journal of Science and Medicine in Sport 2021; 24: 229-240. DOI: 10.1016/j.jsams.2020.09.001.
  21. 21.0 21.1 21.2 21.3 21.4 21.5 Powers, C.M., Ward, S.R., Chan, L-D., Chen, Y-J., Terk, M.R. The Effect of Bracing on Patella Alignment and Patellofemoral Joint Contact Area. Medicine and Science in Sports and Exercise 2003; 36(7): 1226-1232. DOI: 10.1249/01.mss.0000132376.50984.27.
  22. Hickey, A., Hopper, D., Wild, C.Y. The Effect of Mulligan Knee Taping Technique Technique on Patellofemoral Pain and Lower Limb Biomechanics. The American Journal of Sports Medicine 2016; 44(5): 1179-1185. DOI: 10.1177/0363546516629418.
  23. 23.0 23.1 23.2 Chang, W-D., Chen, F-C., Lee, C-L., Lin, H-Y., Lai, P-T. Effects of Kinesio Taping versus McConnell Taping for Patellofemoral Pain Syndrome: A Systematic Review and Meta-Analysis. Evidence-Based Complementary and Alternative Medicine, 2015; 471208. DOI: 10.1155/2015471208.
  24. Dutton, R.A., Khadavi, M.J., Fredericson, M. Update on Rehabilitation of Patellofemoral Pain. Training, Prevention, and Rehabilitation, 2014; 13(3), 172-178.