Patellofemoral Pain Syndrome

Definition/Description[edit | edit source]

Patellofemoral Pain Syndrome (PFPS) is an umbrella term used for pain arising from the patellofemoral joint itself, or adjacent soft tissues. It is a chronic condition that tends to worsen with activities such as squatting, sitting, climbing stairs, and running.[1] [2]Historically it has been referred to as anterior knee pain but this is misleading as the pain can be felt in all aspects of the knee (including the popliteal fossa). Symptoms can develop slowly over time or brought on acutely.[3]PFP tends to reoccur after 2 years in 40% of cases. [4]

The differential diagnosis of PFPS include chondromalacia patellae and patellar tendinopathy. Both are not considered to be under the umbrella term of PFPS though patients will complain of similar symptoms.[5][6][7] The pathophysiology is thought to be different and therefore there is alternative treatment.[5][7]

Clinically Relevant Anatomy[edit | edit source]

Sagittal section of the knee joint Primal.png

The knee (art. Genus) consists of two major joints, the tibiofemoral joint and the patellofemoral joint. In this case, the problem will be localized in the patellofemoral joint:

The patella sits within the femoral groove; the fascies articularis patellae (posterior side) is covered with cartilage that glides over the cartilage of the anterior part of the femoral condyles (femoral groove). In this synovial joint movement and gliding creates minimal resistance due to the synovial fluid which is present around the knee and produced by the membrane synovialis, the internal part of the joint capsule during movement. Several bursae also produce synovial fluid within the capsule. The knee capsule is attached all around the patella, so only the fascies articularis patellae and femoralis are in contact with the synovial fluid. The collateral ligaments are merged with the capsule and they contributed in joint stability. On the anterior side of the patella between the patellar tendon (which is attached to the patella) and the skin, there is an extra bursa (prepatellaris) which is normally not in contact with the knee capsule and ensures a better gliding of the patellar tendon. There is a similar bursa (infrapatellaris) at the level of the tuberositas tibiae. When the knee is inflamed, these bursae can become hyperproductive (swollen). This is possible related to increase of anterior knee pain.

Although each ligament has its own responsibility in supporting and protecting the knee, ligaments also provide assistive support to other ligaments. But the two ligaments that are most associated with PFPS are the two collateral ligaments (lateral and medial), because they are merged with knee capsule. Epicondylopatellar and meniscopatellar ligaments form the medial and lateral retinaculum patellar part of a ligamentous complex which provides for a medial and lateral attachment of the patellar tendon at the level of the patella.

Epidemiology /Etiology[edit | edit source]

PFPS can be due to a patellar trauma, but it is more often a combination of several factors (multifactorial causes): overuse and overload of the patellofemoral joint, anatomical or biomechanical abnormalities, muscular weakness, imbalance or dysfunction. It’s more likely that PFPS is worsened and resistive to treatment because of several of these factors.

** Excessive overload and abnormal tracking of the patella are the main reasons behind PFP symptoms[8]

One of the main causes of PFPS is the patellar orientation and alignment. (fig.1) When the patella has a different orientation, it may glide more to one side of the facies patellaris (femur) and thus can cause overuse/overload (overpressure) on that part of the femur which can result in pain, discomfort or irritation. There are different causes that can provoke such deviations.

The patellar orientation varies from one patient to another; it can also be different from the left to right knee in the same individual and can be a result of anatomical malalignments. A little deviation of the patella can cause muscular imbalances, biomechanical abnormalities … which can possibly result in PFPS. Conversely, muscular imbalances or biomechanical abnormality can cause a patellar deviation and also provoke PFPS. For example: When the Vastus Medialis Obliquus isn’t strong enough, the Vastus Lateralis can exert a higher force and can cause a lateral glide, lateral tilt or lateral rotation of the patella which can cause an overuse of the lateral side of the facies patellaris and result in pain or discomfort. The opposite is possible but a medial glide, tilt or rotation is rare. Another structure that can cause a patellar deviation is the lateral retinaculum.

PFPS can also be due to knee hyperextension, lateral tibial torsion, genu valgum or varus, increased Q-angle, tightness in the iliotibial band, hamstrings or gastrocnemius. (see table 1)

Sometimes the pain and discomfort is localized in the knee, but the source of the problem is somewhere else. Pes planus (pronation) or Pes Cavus (supination) can provoke PFPS. Foot pronation (which is more common with PFPS) causes a compensatory internal rotation of the tibia or femur that upsets the patellofemoral mechanism. Foot supination provides less cushioning for the leg when it strikes the ground so more stress is placed on the patellofemoral mechanism. The hip kinematics can also influence the knee and provoke PFPS. A study has shown that patients with PFPS displayed weaker hip abductor muscles that were associated with an increase in hip adduction during running.

Table 1

Muscular etiologies of PFPS
Etiology Pathophysiology
Weakness in the quadriceps

It may adversely affect the PF mechanism.

Strengthening is often recommended.

Weakness in the medial quadriceps

It allows the patella to track too far laterally.

Strengthening of the VMO is often recommended.

Tight iliotibial band

It places excessive lateral force on the patella and can also externally rotate the tibia, upsetting the balance of the PF mechanism.

This can lead to excessive lateral tracking of the patella.

Tight hamstrings muscles

It places more posterior force on the knee, causing pressure between the patella and the femur to increase.

Weakness of tightness in the hip muscles

Dysfunction of the hip external rotators results in compensatory foot pronation.

Tight calf muscles

It can lead to compensatory foot pronation and can increase the posterior force on the knee.

Characteristics/Clinical Presentation[edit | edit source]

Patient's usually present with the complaint of anterior knee pain that is aggravated by activities that increase patellofemoral compressive forces such as: ascending/descending stairs, sitting with knees bent, kneeling, and squatting.

Differential Diagnosis[edit | edit source]

Different disease can provoke anterior knee pain, without being PFPS:

Diagnostic Procedures[edit | edit source]

The diagnostic procedure of PFPS should first involve exclusion of other pathologies. [9] [10]The clinical practice guideline for PFPS published by The American Physical Therapy Association made the following diagnostic criteria[10]:

  1. Presence of retropatellar or peripatellar pain
  2. Reproduction of retropatellar or peripatellar pain during squatting, or other functional activities loading the PFJ in a flexed position
  3. All other conditions that could cause anterior knee pain, such as tibiofemoral pathologies, should be excluded

Outcome Measures[edit | edit source]

Lower Extremity Functional Scale

Anterior Knee Pain Scale (AKPS)

Patellofemoral Pain and Osteoarthritis Subscale of the Knee Injury and Osteoarthritis Outcome Score (KOOS-PF)

Visual Analog Scale (VAS)

England and Pierrynowski Questionnaire (EPQ)

Examination[edit | edit source]

Subjective Examination[edit | edit source]

The subjective examination is crucial in determining the root cause as well as contributing factors of PFPS.

A thorough subjective examination will allow you to streamline your physical examination and develop an appropriate management plan.

Asking specific questions around the behaviour of symptoms and history of the condition will help you to clinically reason the cause of symptoms and contributing factors.

Identification of various intrinsic and extrinsic factors that lead to PFPS will guide your treatment plan. The more factors identified in an individual has been shown to be correlated with higher levels of pain and functional impairment [11].

History[edit | edit source]

A detailed history will give you a multitude of clues into the cause and contributing factors of PFPS.[9][12][13]

Subjective Finding Possible Clinical Reasoning
Insidious Onset Typical of PFPS
Overload event eg excessive stair climbing, longer distance Typical of PFPS
Traumatic incident Unlikely to be PFPS

Pain Behaviour[edit | edit source]

Anterior knee pain going up and down stairs, pain when sitting with knees flexed and pain with squatting, kneeling or returning from squat all implicate PFPS.[9]

The table below gives an overview of structures to examine depending on which subjective finding is identified[11][12][13]

Subjective Findings Possible Clinical Reasoning
Pain when sitting with flexed knee (cinema sign) Tight quadriceps (sitting they compresses PFJ)
Pain while sitting with legs crossed Tight ITB (Glut max and TFL tightness)
Pain walking downhill Loads PFJ
Pain walking uphill Tight Calf muscles

Impaired gluteal control

Pain when wearing high heels Increases load on PFJ

Increases distal instability

Pain when going downstairs PF Joint surface problems

Muscle length issues

Eccentric quads function

Pain when going upstairs Impaired gluteal control
Squat and kneel-

Going down into squat

In crouch position

Coming up from squat

Eccentric quads

Muscle length of quads

Gluteal control

Pain with tight clothing as you flex your knee

(eg skinny jeans)

Compressive forces- PFPS
Pain with tight clothing touching/ rubbing skin Possibly more of a Chronic Pain picture

with Sensitisation (Allodynia)

Patterns of Pain[12][13][edit | edit source]

Subjective Finding Possible Clinical Reasoning
Pain only during activity Think biomechanics
Pain only after activity especially much later or next day Think inflammatory
Pain that improves with exercise Think tendon/ muscle length

Clinical Signs[edit | edit source]

Cook et al suggest a positive diagnosis of patellofemoral pain syndrome when[14]:

  • Both pain on muscle contraction and pain on squatting are present
  • 2 out of 3 of the following are present - pain on muscle contraction and/or pain on squatting and/or pain on palpation
  • 3 out of 3 are present - pain on muscle contraction, pain on squatting and pain on kneeling

Objective Examination.[edit | edit source]

Due to the multifactorial etiology of PFPS, there are many things to consider, but key areas to look at include:

  • Observation-patella position, (eg tilt or lateralised), femoral position, relative muscle bulk, especially gluteals, vasti and calves. Presence of effusion and or Hoffa's fat pad oedema, foot position.
  • Level of hypermobility of tibiofemoral and patellofemoral joints.
  • ROM, especially loss of extension.
  • Single stance-pelvic, femoral, foot control. Excessive use of VL.
  • VMO-ability to fire, speed of firing, endurance capability at zero, ten, twenty and thirty degrees of knee F.
  • Gluteals-firing and endurance as abductor and external rotator in different degrees of hip flexion.
  • Muscle length-Modified Thomas test to assess hip flexors, quads and add in adduction for TFL. Hamstrings, gastrocnemius, soleus, gluteus maximus insertion into ITB, (adduction in hip flexion).
  • Stair assessment- consider eccentric control, is there excess use of pelvis or ankle to avoid knee flexion? Can pain be altered by correction of patella/femoral/foot position?
  • Gait and or running: Observing for the presence of early heel rise, level of pelvic and femoral control, scissoring, stride length,trunk flexion.

Medical Management[edit | edit source]

Onward referral to orthopaedic consultant should occur in the presence of:

  • History of patella dislocation.
  • Direct blow to the knee and suspicion of patellar fracture or osteochondrosis dissecans (OCD), (pain and or swelling not settling).
  • Repeated subluxing patella not responding to physiotherapy. (May suggest dysplastic PFJ).

Onward referral to pain specialist should be considered in the presence of:

  • Central sensitisation not responding to pacing/cv exercise.

Physical Therapy Management[edit | edit source]

Common interventions for the treatment of PFPS are listed below:

  • Manual Therapy
  • open vs. closed chain exercises
  • Quadriceps strengthening
  • Patellar Taping
  • Orthotics
  • Proximal Muscle strengthening
  • Modalities
  • Education[15]

There is largest body of evidence supports the use of exercise therapy in improving pain and function in the short, medium and long-term. International consensus recommends the combination of hip and knee exercise to be used in preference to knee exercise alone. [16][17][18][19][20][21]

International experts suggest the use of foot orthoses, patellar taping or manual therapy as adjuncts to exercise therapy. [21]

Gait or running retraining may be considered for PFPS although current evidence is mixed. [21]

Joint mobilisation and electrophysical agents are not recommended for treatment in PFPS. [21]

There is emerging appreciation of psychosocial pain processing features in PFPS. [22][23][24] Clinicians may consider strategies that address psychosocial impairments when treating PFPS.

No significant difference was noted in open vs. closed chain exercises with respect to functional outcomes. [25]

Exercise Therapy[edit | edit source]

Strengthening of the Quadriceps is a key in the rehabilitation program[26]

Pain-free exercises are very important when treating PFPS. Isometric exercises while the knee is fully extended (patella has no contact with condyles) can be used at the beginning of the therapy, because it minimizes stress on the patellofemoral-joint while reinforcing the Quadriceps. For example (exercise): 1. Straight-leg exercise Patient lies on his back, one knee bent at +/- 90° (! pain-free if that knee is affected by PFPS) and foot flat on the ground. The other knee is fully extended. Patient elevates extended leg and holds it for 10secs, before relaxing (concentric contraction and/or eccentric contraction is also possible, which makes it dynamic). Control that Patient keeps a normal lumbar lordosis and does not compensate with his basin. 2. Pillow squeeze exercise Patient sits comfortable with his trunk supported. Both knees extended. Place a pillow (or towel) under one knee (that knee might be slightly flexed). Patient tries to push the pillow/towel in the table by extending his or her knee. (Quadriceps contraction).

Closed kinetic chain exercises (CKC) VS Open kinetic chain (OKC) exercises[27][28]

CKC are more functional than OKC and they provoke lower patellofemoral joint stress, particularly in the terminal ranges of full extension (0° to max 40° knee flexion). Therefore exercises should be practiced within this range and pain-free. Example of exercise:

• Squats; be sure that the patient’s knee doesn’t come farther than his toes. Once his knee passes his toes, the stress on his patellofemoral-joint become too high and might provoke pain.

If patient is unable to tolerate CKC exercises, then OKC exercises might be a viable option because the load that will be used can be better controlled than in CKC, as long as the exercises are pain-free! When using OKC exercises, Patient should stay in within a pain-free range of motion (ROM) between 40° to 90° knee flexion.

Vastus medialis obliquus (VMO)[29]

Training of the VMO muscle is appropriate in some PFPS patients but not all. Assessment of the vmo should assess firing, cross-sectional muscle mass, endurance capabilities, and ability to fire at different knee angles, and used functionally. Too much focus on selective activation of the VMO muscle should be avoided as there is no evidence to suggest it can be isolated. However, it is extremely important in guiding the patella into the trochlea, and hence although it is active through range, its primary role is between zero and thirty degrees flexion. The need for better VMO function is enhanced with trochlea dysplasia, patella alta, medial patellofemoral ligament rupture or when a large TTTG is present.

The VMO is particularly adversely affected by swelling and or pain. 10ml of fluid will inhibit the VMO but 40ml to inhibit the VL. Similarly pain causes vmo delay, and the more pain, the greater the delay. This helps to explain why patients post trauma and/or surgery who will often have a joint effusion, are then left with PFPS. It also explains why resolution of an effusion is a primary goal, and avoidance, and reduction of pain are also paramount. Painful exercises are a waste of time.

VMO training although not isolating to the VMO should be aimed at 0-30 degrees, incorporate endurance holds, and be prescribed with a tonic bias to represent the postural function of the muscle.

Recent research demonstrates that VMOtype exercises will cause an alteration in the VMO fibre angle, (relative to the femoral axis). Fibre angle can change from a vertical 40 to a much more medialising 70 degrees.[30]

Hip muscles training[31]

Rehabilitation program for PFPS should also incorporate strengthening exercises of the hip abductors and lateral rotators. It has been proven that the pain during daily activities was lower and functionality was greater when knee exercises are combined with hip exercises. (Table 1 and 2 + figure 2 show which exercises were used in the research and proved to be efficient. Exercises were performed during 4 weeks)

Another research study found that PFPS patients had decreased eccentric hip abduction compared with healthy people. Thus, it is recommended to use eccentric hip abduction strengthening exercises.[27]

Proprioceptive training[32][33]

It has been proven that the proprioceptive quality in the knee of patients with PFPS is decreased. Even with unilateral PFPS, the proprioception is decreased in both knees (pathological and nonpathological knee)! Therefore proprioceptive training (pain-free exercises!) of the knee should be part of the rehabilitation program.

Electrotherapy[edit | edit source]

Some patients might suffer from PFPS because of a (neuromuscular) disbalance between the VMO and VL. The main cause is muscle atrophy of the VMO and excessive/abnormal lateral tracking of the patella, due to the remaining force of the VL. In case of neuromuscular disbalance between the VMO and VL, electrical stimulation of the VMO should be considered to complement the conservative (exercises) therapy, because it is selective and does not stress the patellofemoral joint.

An example of how you can accomplish the stimulation[34];

The patient sits with the trunk supported extended legs with slight knee flexion and lower limb muscles completely relaxed. Following parameters were used in research (isometric contraction of the VMO):

  • Electrode placing = 1 on the motor point and the other one next to it.
  • Asymmetric bipolar current
  • Pulse width = 0.5 milliseconds
  • Pulse frequency = 50Hz
  • Intensity = max. the patient can endure without pain- Time = 7 minutes => 6 repetitions, on for 6 seconds and off for twelve, and progressed to 30 minutes, 11 repetitions, on for 10 seconds and off for 12sec.

Evaluation[edit | edit source]

You can use EMG feedback to capture EMG activity of the VMO and VL before and after the therapy. While your patient is performing the functional test of stair stepping using the limb affected by PFPS; patient faces the stairs in standing position. He begins the movement by flexing the limb with PFPS, placing it on the first step, and then extends it in unilateral stance. In a continuous movement, he places the non-affected limb on the second step and finishing the stair stepping with full knee extension.[31] Be aware that stepping upon a stair can be very painful for PFPS patients. Only use this evaluation technique once the Patient can perform this test pain-free. Start with a very low stair, so the compression between the patella and the femur is minimal.

The main differences you should find are increased energy consumed by the VMO muscle in order to perform the test. → Change in force-generating capacity of the muscle. And faster (more accurate) activation of the VMO muscle after therapy.

Foot Orthoses[edit | edit source]

There are a few clinical predictors that can help decide if a patient is more likely to benefit from foot orthoses or not;[35][36][37]

  • Individuals with PFPS who wear less supportive footwear,
  • those who report lower levels of pain,
  • exhibit less ankle dorsiflexion range of motion,
  • Patient who reports an immediate reduction in pain with foot orthoses when performing a single-leg squat.

What kind of orthoses? In research prefabricated orthoses were used; made of ethylene-vinyl acetate of medium density (Shore A 55), containing built-in arch supports and 4-varus rearfoot wedging. Prefabricated foot orthoses significantly enhanced functional performance in individuals with PFPS after 12 weeks, and these improvements were greater than those observed immediately after the foot orthoses were used. These improvements may be important to long term prognosis and prevention of osteoarthritis development for some individuals with PFPS (further research is needed).

Resources[edit | edit source]

Knee Pain and Patello-femoral Pain Injury Rehabilitation Seminar | Feat. Tim Keeley | FILEX

References[edit | edit source]

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  2. Shi W, Li Y, Xiong B, Du M. Diagnosis of Patellofemoral Pain Syndrome Based on a Multi-Input Convolutional Neural Network With Data Augmentation. Frontiers in Public Health. 2021 Feb 11;9:643191.
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  19. Esculier JF, Bouyer LJ, Dubois B, Fremont P, Moore L, McFadyen B, Roy JS. Is combining gait retraining or an exercise programme with education better than education alone in treating runners with patellofemoral pain? A randomised clinical trial. British journal of sports medicine. 2018 May 1;52(10):659-66.
  20. Şahin M, Ayhan FF, Borman P, Atasoy H. The effect of hip and knee exercises on pain, function, and strength in patientswith patellofemoral pain syndrome: a randomized controlled trial. Turkish journal of medical sciences. 2016 Feb 17;46(2):265-77.
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  25. Witvrouw E, Danneels L, Van Tiggelen D, Willems TM, Cambier D. Open versus closed kinetic chain exercises in patellofemoral pain: a 5-year prospective randomized study. The American journal of sports medicine. 2004 Jul;32(5):1122-30.
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  28. Irish, SE; Millward, AJ; Wride, J; Haas, BM; Shum, GLK. The effect of closed-kinetic chain exercises and open-kinetic chain exercises on the muscle activity of the vastus medialis oblique and vastus lateralis.
  29. Simon F.T. Tang, Chih-Kuang Chen, Robert Hsu, MD, Shih-Wei Chou,Wei-Hsien Hong, MS, Henry L. Lew. Vastus Medialis Obliquus and Vastus Lateralis Activity in Open and Closed Kinetic Chain Exercises in Patients With Patellofemoral Pain Syndrome: An Electromyographic Study. Archives of Physical Medicine and RehabilitationfckLRVolume 82, Issue 10 , Pages 1441-1445, October 2001.
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  32. Akseki D, Akkaya G, Erduran M, Pinar H.Proprioception of the knee joint in patellofemoral pain syndrome. Acta Orthop Traumatol Turc. 2008 Nov-Dec;42(5):316-21.
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  34. Garcia FR, Azevedo FM, Alves N, Carvalho AC, Padovani CR, Negrão Filho RF. Effects of electrical stimulation of vastus medialis obliquus muscle in patients with patellofemoral pain syndrome: an electromyographic analysis. Rev Bras Fisioter, 2010 Nov-Dec;14(6):477-82.
  35. Barton CJ, Menz HB, Crossley KM. Clinical predictors of foot orthoses efficacy in individuals with patellofemoral pain. Med Sci Sports Exerc. 2011 Sep;43(9):1603-10. doi: 10.1249/MSS.0b013e318211c45d.
  36. Barton CJ, Menz HB, Crossley KM. The immediate effects of foot orthoses on functional performance in individuals with patellofemoral pain syndrome. Br J Sports Med. 2011 Mar;45(3):193-7. doi: 10.1136/bjsm.2009.069203. Epub 2010 Jul 20.
  37. Barton CJ, Menz HB, Crossley KM. Effects of prefabricated foot orthoses on pain and function in individuals with patellofemoral pain syndrome: a cohort study. Phys Ther Sport. 2011 May;12(2):70-5. doi: 10.1016/j.ptsp.2010.09.002. Epub 2010 Oct 14.