Patellofemoral Pain Syndrome: a scientific review

The Patellofemoral Pain Syndrome (PFPS) is one of the most common musculoskeletal disorders that commonly affects young athletes (18-35 years), especially women [ 1 , 2 ] . It is described as anterior knee pain or non-specific peri-patellar pain [ 3 , 4 ] with an onset often related to activities such as climbing stairs, squatting, holding a prolonged sitting or kneeling position [ 5 , 6 ] . In the scientific literature there is agreement in defining it as an overuse pathology  ”Which increases pain and compressive strength of the patellofemoral joint, which are generally not the result of trauma or intra-articular damage to the knee [ 8 ] .

Anatomy of the patellofemoral joint

The patellofemoral joint is one of the three knee joints and it is located between the posterior articular surface of the patella (or posterior face ) and the anterior articular surface of the femoral trochlea (or patellar face of the femur ) [ 9 ] . It is a synovial joint , classified as flat (“ Synovial: plane ”) [ 10 ] .  

Analysing the patella -femoral joint, the role of the patella cannot be ignored . The latter is the largest sesamoid bone in our body, which fulfills three fundamental functions [ 11 ] :  

1. Anteriorization of the quadriceps tendon, assisting the extension of the knee by increasing the lever arm of the quadriceps muscle;
2. Increasing the contact area between the quadriceps tendon and the femur by distributing the compressive forces over a wider area;
3. Protection of the extension compartment.

For further information on the anatomy and biomechanics of the PF joint, which is not the topic of this article, consult the references [ 7 , 9 , 11 , 12 ] .    

Pathophysiology: myths and reality

In 1999, there was consensus in the literature on the difficulty of fully explaining the aetiology of PFPS or anterior knee pain[ 13 ] , attributing it to:

• Subchondral bone
• Capsule
• Retinacles
• Hoffa’s body

The genesis of patellofemoral syndrome is supposed to be attributable to an increase in joint stress at the level of the PF joint causing pain from the subchondral tissues of the patella or femur. This consideration sets aside an old myth that pain, in patellofemoral syndrome, comes from articular cartilage, which does not have blood vessels or nerve endings [ 14 ] , thus mainly attributing the problem to an abnormal distribution of loads probably on the subchondral bone. However, the peak of cartilage stress, which was hypothesized to follow a degeneration of the cartilage and compromise of the subchondral bone, is not present in all patients with patellofemoral joint pain. [ 15 ]

Therefore, research has seen an increasing interest in other factors that could provide a better explanation for the genesis of pain in patients with patellar knee pain.

Introduction to the quadriceps femoris muscle : the quadriceps femoris muscle, primary stabilizer of the patellofemoral joint, does not act on the patella by exerting only a cranial thrust , but also lateral and posterior thrust during extension of the femoral-tibial joint . Overall, the omnipresent quadriceps muscle line of force possesses a cranial and lateral direction , due in part to the greater cross-sectional area of ​​the vastus lateralis. The patella is anatomically located between the quadriceps tendon and the patellar tendon, therefore the cranio-lateral traction line of the quadriceps, associated with the direction of force present on the patellar tendon, exerts a continuous thrust force on the patella in the lateral direction (“Bowstringing force on patella “) [ 7 ] . For this reason, in research, we tried to provide an objective measure of this line of force by introducing the quadriceps angle, that is the angle formed with the intersection between the line that connect the anterior-superior iliac spine (ASIS) and the center of the patella and the line passing through the center of the patella and the patellar tuberosity [ 16 ] . However, the usefulness of one of this measure has been widely criticized in the literature due to its poor association with patellofemoral syndrome and especially its inability to provide dynamic alignment measures [ 17-19 ] .       

In order to understand the influence of the close regional interdependence of the joints of the lower limb on the continuous Bowstringing force on the patella , it is essential not to focus exclusively on the knee district but to observe the kinematics of the lower limb as a whole on the three planes of movement.

In this regard, the latest edition of Donald A. Neumann’s encyclopedic bible of kinesiology, “ Kinesiology of the musculoskeletal system” [ 7 ] , also divides the factors that influence patella tracking into three broad categories: 

• Local factors (acting directly on the patella);
• Proximal factors and distal factors (related to the alignment of the bones and joints of the lower limb).

Anterior Knee Pain: local factors involved

Some of the local factors that we have to consider when we talk about anterior knee pain are: Q angle, Vasto Mediale Oblique, Femur, Medial retinaculum, Ilio-tibial band.

Despite the criticisms leveled at the Q angle, it is believed that it can still be held as a simple and popular clinical index of the potential lateral thrust of the quadriceps to damage the patella. Biomechanically, an increase in the Q angle produces an increase in the Bowstringing force on the patella , tending to move the patella laterally in a region of minor joint contact and increase the mechanical stresses [ 7 ] .  

As will be explained later, this angle is affected by the position in the space of other districts.

Vasto Mediale Oblique: In 1968 it was stated that the key to successful treatment of patients with patellofemoral joint syndrome was the training of the vastus medial oblique, whose weakness was believed to be responsible for patellar maltracking (abnormal sliding of the patella in the intercondylar groove of the in flexion-extension movements of the tibio-femoral), thus attributing the function of alignment of the patella to the vastus medialis oblique [ 20 ] . In 1998, the functional imbalance between the vastus medialis oblique (VMO) and vastus laterally (VL) was widely accepted in the literature, so much so as to recommend exercises to improve the timing of activation of VMO-VL and the use of bandages and braces to support the exercises reinforcement of the vastus medialis oblique [ 21 ] .    

In 1997, literature faces a crossroads: does the vast medial oblique really exist or not? 

Well, a paper by Hubbard (1997) [ 22 ] concludes by reporting that there was no evidence of the presence of an intermuscular septum between VMO and vastus medialis longus (VML) (the two components of the vastus medialis, VM) and that there was only one innervation of the VM. In 2009, a review by Smith (699 healthy – 591 PFPS) found an orientation of the VMO and VML fibers respectively of 49.9 ° and 21.8 ° on average, but at the same time the lack of a real intermuscular septum. between VMO and VML and a common innervation in 59% of cases [ 23 ] . In light of these scientific discoveries, the researchers wondered if and to what extent it was possible to selectively recruit VMO, concluding with ” strong evidence ” that VMO could not be preferentially recruited and trained, recommending to clinicians not to direct their attention to reinforcement. of the VMO but, rather, on the general strengthening of the quadriceps [ 24 , 25 ] . This does not mean that, in anatomical terms, the orientation of the VMO fibers has no function, in fact in a study conducted on cadavers the cutting of the VMO fibers produced a loss of medial stability of the patella on average of 27% [ 26 ] . However, it must be recognized that this scenario is unlikely to occur in the clinic as selective VMO paralysis is extremely rare [ 7 ] .  

Femur. The lateral facet of the trochlear groove of the femur is usually steeper than the medial one and prevents excessive lateral displacement of the patella [ 7 ] . Its flattening implies a loss, on average, of 55% of the medial stability of the patella during the range of motion (ROM) of the femoro-tibial joint [ 27 ] . 

Medial retinaculum. The scientific literature often refers to these fibers as the medial patellofemoral ligament (MPFL), which includes a large, but fine, set of fibers that interconnect the medial surface of the patella, femur, tibia, meniscus medial and inferior surface of the VMO [ 28 ] . This ligament is well respected in the literature for its stabilizing function at the level of the patella [ 7 ] , in fact a cut of the MPFL involves, on average, a 27% loss of medial stability of the patella during the ROM of the femoro-tibial joint [ 27 ] .  

Ilio-tibial band. Excessive tension of the iliotibial band or lateral patellar retinaculum fibers may add to the natural lateral thrust of the patella [ 7 ] . 

Patellofemoral syndrome: global factors

As a general rule, factors that resist excessive knee valgus or extreme degrees of rotation of the femoro-tibial joint promote optimal tracking of the FR joint.

An excessive knee valgus , as a result of activities in the load, can increase the Q angle and therefore increase the BF applied to the patella, increasing the stress on the PF joint, especially laterally [ 29, 30 ] . This condition could be the result of a laxity of the medial collateral ligament (MCL), but also indirectly of an increased hip adduction in the loaded position [ 7 ] , possibly secondary to a muscle weakness of the hip abductor muscles or to a stiffness of the hip adductor muscles [ 30 , 31 ] . It is no coincidence, in fact, that people with a weakness of the hip abductor muscles manifest, in an activity such as the single leg squat , an ipsilateral trunk inclination to the symptomatic side so that the center of gravity moves laterally to the center of rotation of the coxo -femoral joint, reducing the external adductor moment , to which the hip abductors respond. However, this inclination of the trunk shifts the ground reaction force line (GRF) lateral to the knee, thus increasing the external valgizing moment [ 32 ] . Even an excessive pronation joint sub-talar can increase the load valgus at the knee level, the base of which there are a series of cascade reactions in ascending sense: the calcaneus induces a talar adduction, a ” navicular drop (fall) ”of the scaphoid with consequent reduction of the medial longitudinal arch, an internal rotation of the entire lower limb and an increase in valgus stress at the level of the knee [ 7 ] . Excessive external rotation of the knee could also induce an increase in the Q angle and increase the amount of BF applied to the patella [ 33 ] . This external rotation tends to be expressed as an internal rotation of the femur with respect to the fixed or relatively fixed leg [ 7 ] . The internal rotation of the femur can be consequent to a reduction of the strength of the hip abductor muscles, excessive femoral anteversion, excessive external tibial rotation or alteration of the motor control of the same muscles [ 7 , 31 , 33 , 34 ] .                   

This brief biomechanical review of the reciprocal influence between the joints of the lower limb, pelvis and trunk, especially on the PF joint, was drafted as an invitation to a conception of the pathology far beyond what can be a “local” vision ”Of the joint itself. Remembering the importance of regional interdependence between the joints, the role of motor control of the pelvis and lower limb muscles, the dynamic and functional aspect of the pathology, could represent the key to the success of the interventions, despite the current literature the lack of a complete understanding of the patellofemoral pathology could make it one of the most difficult treatments in physical and sports medicine [ 7 ] .   

References

1. Roush, J.R. and R. Curtis Bay, Prevalence of anterior knee pain in 18-35 year-old females. Int J Sports Phys Ther, 2012. 7(4): p. 396-401.
2. Bevilacqua-Grossi, D., L.R. Felicio, and L.P. Leocàdio, Analysis of the reflex response time of the patellar stabilizer muscles in individuals with patellofemoral pain syndrome. Brazilian Journal of Physical Therapy, 2008. 12(1): p. 26-30.
3. Biedert, R.M. and K. Warnke, Correlation between the Q angle and the patella position: a clinical and axial computed tomography evaluation. Arch Orthop Trauma Surg, 2001. 121(6): p. 346-9.
4. Wilk, K.E. and M.M. Reinold, Principles of Patellofemoral Rehabilitation. Sports Medicine and Arthroscopy Review. 9(4): p. 325-336.
5. Cowan, S.M., et al., Delayed onset of electromyographic activity of vastus medialis obliquus relative to vastus lateralis in subjects with patellofemoral pain syndrome. Arch Phys Med Rehabil, 2001. 82(2): p. 183-9.
6. Freddolini, M., et al., Quadriceps muscles activity during gait: comparison between PFPS subjects and healthy control. Musculoskelet Surg, 2017.
7. Neumann, D.A., Kinesiology of the Musculoskeletal System – Foundations for Rehabilitation. Third ed, ed. Elsevier. 2017.
8. Glaviano, N.R., et al., Demographic and Epidemiological trends in patellofemoral pain. Int J Sports Phys Ther, 2015. 10(3): p. 281-90.
9. Shunku, M., et al., Prometheus – Anatomia Generale e Apparato Locomotore. Seconda ed, ed. EdiSES. 2015.
10. Cleland, J.A., S. Koppenhaver, and J. Su, Netter’s Orthopaedic Clinical Examination – An Evidence-Based Approach. Third ed, ed. Elsevier. 2016.
11. Atkins, E., J. Kerr, and E. Goodlad, A practical Approach to MUSCULOSKELETAL MEDICINE – Assessment, Diagnosis, Treatment. Fourth ed, ed. Elsevier. 2016.
12. Waryasz, G.R. and A.Y. McDermott, Patellofemoral pain syndrome (PFPS): a systematic review of anatomy and potential risk factors. Dyn Med, 2008. 7: p. 9.
13. Thomee, R., J. Augustsson, and J. Karlsson, Patellofemoral pain syndrome: a review of current issues. Sports Med, 1999. 28(4): p. 245-62.
14. Sophia Fox, A.J., A. Bedi, and S.A. Rodeo, The Basic Science of Articular Cartilage: Structure, Composition, and Function. Sports Health, 2009. 1(6): p. 461-8.
15. Besier, T.F., et al., The Role of Cartilage Stress in Patellofemoral Pain. Med Sci Sports Exerc, 2015. 47(11): p. 2416-22.
16. Hahn, T. and A. Foldspang, The Q angle and sport. Scand J Med Sci Sports, 1997. 7(1): p. 43-8.
17. Herrington, L. and C. Nester, Q-angle undervalued? The relationship between Q-angle and medio-lateral position of the patella. Clin Biomech (Bristol, Avon), 2004. 19(10): p. 1070-3.
18. Lankhorst, N.E., S.M. Bierma-Zeinstra, and M. van Middelkoop, Risk factors for patellofemoral pain syndrome: a systematic review. J Orthop Sports Phys Ther, 2012. 42(2): p. 81-94.
19. Powers, C.M., The influence of altered lower-extremity kinematics on patellofemoral joint dysfunction: a theoretical perspective. J Orthop Sports Phys Ther, 2003. 33(11): p. 639-46.
20. Lieb, F.J. and J. Perry, Quadriceps function. An anatomical and mechanical study using amputated limbs. J Bone Joint Surg Am, 1968. 50(8): p. 1535-48.
21. Powers, C.M., Rehabilitation of patellofemoral joint disorders: a critical review. J Orthop Sports Phys Ther, 1998. 28(5): p. 345-54.
22. Hubbard, J.K., H.W. Sampson, and J.R. Elledge, Prevalence and morphology of the vastus medialis oblique muscle in human cadavers. Anat Rec, 1997. 249(1): p. 135-42.
23. Smith, T.O., et al., Do the vastus medialis obliquus and vastus medialis longus really exist? A systematic review. Clin Anat, 2009. 22(2): p. 183-99.
24. Cerny, K., Vastus medialis oblique/vastus lateralis muscle activity ratios for selected exercises in persons with and without patellofemoral pain syndrome. Phys Ther, 1995. 75(8): p. 672-83.
25. Smith, T.O., et al., Can vastus medialis oblique be preferentially activated? A systematic review of electromyographic studies. Physiother Theory Pract, 2009. 25(2): p. 69-98.
26. Amis, A.A., W. Senavongse, and A.M. Bull, Patellofemoral kinematics during knee flexion-extension: an in vitro study. J Orthop Res, 2006. 24(12): p. 2201-11.
27. Senavongse, W. and A.A. Amis, The effects of articular, retinacular, or muscular deficiencies on patellofemoral joint stability: a biomechanical study in vitro. J Bone Joint Surg Br, 2005. 87(4): p. 577-82.
28. Amis, A.A., et al., Anatomy and biomechanics of the medial patellofemoral ligament. Knee, 2003. 10(3): p. 215-20.
29. Mizuno, Y., et al., Q-angle influences tibiofemoral and patellofemoral kinematics. J Orthop Res, 2001. 19(5): p. 834-40.
30. Noehren, B., J. Hamill, and I. Davis, Prospective evidence for a hip etiology in patellofemoral pain. Med Sci Sports Exerc, 2013. 45(6): p. 1120-4.
31. Souza, R.B. and C.M. Powers, Differences in hip kinematics, muscle strength, and muscle activation between subjects with and without patellofemoral pain. J Orthop Sports Phys Ther, 2009. 39(1): p. 12-9.
32. Nakagawa, T.H., et al., Frontal plane biomechanics in males and females with and without patellofemoral pain. Med Sci Sports Exerc, 2012. 44(9): p. 1747-55.
33. Salsich, G.B. and W.H. Perman, Patellofemoral joint contact area is influenced by tibiofemoral rotation alignment in individuals who have patellofemoral pain. J Orthop Sports Phys Ther, 2007. 37(9): p. 521-8.
34. Mascal, C.L., R. Landel, and C. Powers, Management of patellofemoral pain targeting hip, pelvis, and trunk muscle function: 2 case reports. J Orthop Sports Phys Ther, 2003. 33(11): p. 647-60.
35. MacIntyre, N.J., et al., Patellofemoral joint kinematics in individuals with and without patellofemoral pain syndrome. J Bone Joint Surg Am, 2006. 88(12): p. 2596-605.