Patellofemoral Pain Syndrome

Original Editor - Farrie Bakalli, Elise Jespers, Margaux Jacobs

Definition

Patellofemoral Pain Syndrome (PFPS) is a common cause of anterior knee pain. There is an abnormal tracking of the patella through the femoral groove, this is often cited as the culprit. The result of the maltracking is pain and retropatellar cartilage loss. PFPS is a condition of both malalignment and muscular Dysfunction.
Patellofemoral pain is multifactorial and is therefore difficult to examine and treat.

Be aware that PFPS is sometimes confused with chondromalacia patellae (which is a cartilage problem) and patellar tendonitis. Patients will normally complain about similar symptoms, but those conditions have a different cause and treatment. 

Clinically Relevant Anatomy

File:Anatomy of the knee.jpg

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

The patella is the largest sesamoid bonein the human body and can be found in the trochlear groove of the distal femur. Its primary function is to improve flexion efficiency and leverage for knee extension and to protect the tibiofemoral joint. A common misconception is that the patella only moves up- and downwards. Actually, it also tilts and rotates, so there are numerous points of contact between the undersurface of the patella and the femur. Repetitive contact at any of these areas, sometimes combined with maltracking of the patella is the likely mechanism of the patellofemoral pain syndrome.
The combination of the quadriceps tendon, lateral retinaculum, medial retinaculum, and the patella tendon help stabilize the patella.
The patella has 5 facets: medial, lateral, superior, inferior, and odd. The odd facet is usually the first area which is affected in patellofemoral pain. The odd facet articulates with the femoral condyles at 135 degrees of flexion.
The facies articularis patellae, which is located on the posterior side, is covered with cartilage. This cartilage glides over the anterior part of the femoral condyles, also known as the femoral groove.

In this synovial joint movement and gliding creates minimal resistance is created due to the synovial fluid. This fluid is located around the knee and produced by the membrana synovialis, the internal part of the joint capsule during movement. Synovial fluid is also produced by several bursae within thejoint capsule. The facies articularis patellae and the facies articularis femoralis are in contact with the synovial fluid. Other pieces of the knee joint are surrounded by the joint capsule and are therefore not in contact with this 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 and the skin,an extra bursa can be found. This bursa normally does not adjoin to the knee capsule, but does ensure a better gliding of the patellar tendon. There is a similar bursa (infrapatellaris) at the level of the tuberositas tibiae,, the bursa infrapatellaris.

When the knee is inflamed, these bursae can become hyperproductive and start to swell. This is possibly related to the increase of anterior knee pain.
Each ligament has its own responsibility in supporting and protecting the knee, but some ligaments also provide assistive support to other ligaments. The two main ligaments most associated with PFPS are the medial and lateral collateral ligaments because they are merged with knee capsule.
Epicondylopatellar and ligaments form the medial and lateral retinaculum patellare part of a ligamentous complex. This provides for a medial and lateral attachment of the patellar tendon at the level of the patella.

Epidemiology /Etiology

PFPS can be due to a patellar trauma, but it is more often a combination of several factor:. The multifactorial causes are 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.
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. This can result in pain, discomfort or irritation. There are different causes that can provoke such deviations:

• Overuse injuries of the extensor apparatus, patella instability, chondral and osteochondral damage;
• Weakness in functional testing; gastrocnemius, hamstring, quadriceps or iliotibial band tightness;
• Generalized ligamentous laxity;
• Deficient hamstring or quadriceps strength;
• Hip musculature weakness;
• Excessive quadriceps (Q) angle.
  

The patellar orientation varies from one patient to another.There can also be a difference from the left to right knee within the same individual, which 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 abnormalities 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 muscle and ligament that can cause a patellar deviation is the iliotibial band or the lateral retinaculum, in case of an imbalance or weakness in one of these structures. (see table1)

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.

Sometimes the pain and discomfort is localized in the knee, but the source of the problem lies somewhere else. A pes planus (pronation) or a 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 adversly 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

Patients usually have a complaint of anterior knee pain , which is aggravated by activities that increase patellofemoral compressive forces. Such activities are: ascending/descending stairs, prolonged sitting, kneeling, running, and squatting.
The pain is frequently observed under and around the patella and described as “achy” and “sharp”. The instability is caused by a weakened contraction of the quadriceps. There must be made a distinction between instability caused by patella dislocation or subluxation, between a ligament injury or weakened contraction of the quadriceps.

Differential Diagnosis

There are different disaeses that can provoke anterior knee pain, without being PFPS

• Chondromalacia Patellae:  a disease by which the articular cartilage of the posterior surface of the patella is going through softening and degenerative changes. It is also known as “Runner’s knee”.
• Hoffa's fad syndrome: a condition in which the infrapatellar fat pad either suffers a contusion or an injury, resulting in damage and swelling. This can lead to the Hoffa's pad becoming trapped between the femur and the patella every time the leg is extended.
• Iiotibial band friction syndrome: an overuse injury, which is often concomitant with underlying weakness of hip abductor muscles. Pain appears in the region of the lateral femur epicondyle or a little more inferior.
• Sinding-Larson-Johansson syndrome: SLJ is an osteochondroses and traction epiphysitis affecting the extensor mechanism of the knee.
• Patellar tendinitis: also known as Jumper's knee, can be a source of considerable pain in athletes. The changes that occur with shearing of the tendinous fibers from repeated microtrauma can progress to significant degeneration and increase the risk of tendon rupture.
• Knee Osteoarthritis:inflammation of the bones and knee joint.
• Chondral lesions: damage to the articular cartilage, a common type of knee injury.
• medial meniscus tears: an injury characterized by tearing of cartilage tissue located at the inner aspect of the knee and typically causes pain in this region.
• Medial overload syndrome
• Popliteal Cyst (Baker's Cyst): A Baker's cyst is a swelling filled with fluid that is located in the popliteal region. It can be found incidentally during examination of the knee.
• ACL (anterior cruciate ligament) tear
• PCL injury/rupture
• Referred pain from the hip joint (e.g. slipped epiphysis in adolescents, FAI in young adult, OA)
• Referred pain from lumbar spine

Diagnostic Procedures

The clinical diagnosis has no pathognomonis sign or symptom. It is recommended that the diagnostic procedure to identify PFPS should involve first ruling out other pathologies that may cause anterior knee symptoms. The pain caused by PFPS worsens with squatting, running, prolonged sitting, or when ascending/descending steps.
The six following anatomic areas, which are involved in the increasing pain, are: the subchondral bone, synovium, retinaculum, skin, nerve and muscles. We also need to take account of the fact that other pathologies of anterior knee pain may have the same structures implicating in pain.
To exclude other pathologies, you can use the International Knee Documentation Committee (IKDC). This contains 18 items designed to measure symptoms associated with pain, stiffness, swelling, joint locking, and joint instability, whereas other items designed to measure knee function assess the ability to perform activities of daily living.

Outcome Measures

Lower Extremity Functional Scale

Examination

Subjective Examination:

• Useful questions to ask (positive answers increase the likelihood of a diagnosis of PFPS):
• Presence of pain on the stairs (up or down)
• Pain when sat with the knee flexed (cinema sign)
• Pain when squat or kneeling, or return from these positions
  

Objective Examination:

• Due to the multifactorial etiology of PFPS, there are many things to consider, but top of the pecking order would be.
• Observation-patella position, (e.g. 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 joint.
• 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 adbuctor 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-Eccentric break, 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.
• Patellar Grind Test: used to detect the presence of a patellofemoral joint disorder
• Patellar mobility test
• Patellar till test
• Mediolateral glide
• Patellar apprehension test
• Patellar compression
• Patellar tracking test

Medical Management

Onward referral to an orthopedic consultant should occur in the presence of:

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

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

• Central sensitisation not responding to pacing/cv exercise.

Physical Therapy Management 

Several studies have shown that physical therapy is effective for treating PFPS. However, there is not one program that will be effective for all patients.

The rehabilitation program should focus on correcting maltracking of the patella by addressing the findings identified on the physical examination.
Some patients may require significant strengthening of the quadriceps.
Others may have an excellent quadriceps strength but excessively tight lateral structures or poor quadriceps flexibility.
Soft tissue techniques and flexibility exercises can be helpful for these patients. Patients who require further assessment or ongoing instruction can be referred to a physical therapist.
Common interventions for the treatment of PFPS are listed below:

• Manual Therapy
• open vs. closed chain exercises www.physio-pedia.com/index.php
• Quadriceps strengthening
• Patellar Taping: McConnell was the first to describe patellar taping as a treatment for PFPS.
  Many therapists are trained in the McConnell method and will use taping during early treatment sessions when patients cannot perform certain exercises due to pain. If taping is effective with the patient, the technique can easily be taught to the patient.
  The usual taping method is to move the patella into proper alignment, typically to produce a medial stress on the patella. Thus correcting medial or lateral displacement.
  Taping is easy and convenient to use, but studies on its effectiveness have been mixed. A study using dynamic MRI showed that taping helped to correct medial or lateral patellar displacement. This study also showed that McConnell taping caused an inferior patellar shift.
  
• Orthotics
• Proximal Muscle strengthening
• Modalities

What treatments LACK support by current evidence?

• No significant difference was noted in open vs. closed chain exercises with respect to exercise type.
• Further evidence is needed to investigate the long term effects of patella taping, the mechanism of action and direction of force (medial, neutral, lateral).  Clinical evidence for the success of this intervention is still unclear due to an insufficient amount of high level evidence, inconsistency of tape application techniques, in ability to identify the precise mechanism of aciton, and variance in measurements of specific outcome variables.
• No date is available regarding massage, thermotherapy, TENS, electrical stimulation, and biofeedback for treatment of PFPS.

What treatments are SUPPORTED by the best available evidence?

• Tyler et al noted the role of hip muscle function in the treatment of PFPS.  A 93% success rate occurred with hip flexor strengh improvements and normalization of Ober (IT band/tensor fascia latae) and Thomas (hip flexor) tests.
• A case report by Mascal et al documented weakness of hip abductors, extensors and external rotators in testing of 2 patients with PFPS.  Treatment consisted of recruitment and endurance training of the hip, pelvis, and trunk musculature which resulted in a significant reduction in pain, improved LS kinematics during dynamic testing and ability to return to original level of function.
• Whittingham et al investigated the effectiveness of daily patella taping and exercise on pain and function in individuals with PFPS.  Results suggest that patella taping may be useful in conjunction with strengthening exercise to enhance speed of recovery.
• 2 articles were reviewed in regards to the effect of foot orthoses on PFPS.  Both studies suggest that the use of orthotics in patients who present with excessive pronation resulted in improved pain/stiffness (note: multiple interventions were used in these studies, including orthosis).  Patients with patellofemoral pain may benefit from the use of foot orthosis if the patient demonstrates the following: excessive foot pronation and/or a LE alignment profile that includes excessive lower extremity internal rotation during weight bearing and increased Q-angle.  Additional studies are needed to assess the treatment efficacy of foot orthosis for patients with PFPS.
• In a prospective, independent, group comparison by Chiu et al, 15 participants with and without PFPS were given an MRI evaluation for knee strength, patellofemoral joint contact area, and patellar tilt angle. All the participants performed lower-limb weight training 3 times a week for 8 weeks.
  The outcomes were evaluated both before and after training. The study concluded that the weight-training exercises increased knee muscle strength and the patellofemoral joint contact area. This may reduce mechanical stress in the joint, which would lessen pain and improve function for those with PFPS. A systematic literature review by Peters and Tyson indicated that proximal exercises are more effective than knee exercises in the treatment of PFPS. In an analysis of eight studies, the investigators found that proximal exercise programs consistently reduced pain and improved function, with patients demonstrating short- and long-term improvement, while the results from knee exercise programs were more variable.
  

Exercise Therapy

The objectives of the treatments are to decrease pain, to ameliorate patellofemoral tracking and alignment, and to reach the highest level of function as possible. The first week of treatment is pain control, the main goal (acute phase). The subsequent phase focuses on modification of risk factors and biomechanical deficits.

I. Acute phase

Most experts believe that overload plays a major role in the development of PFPS. It is important for patients to avoid activities that may cause pain during rehabilitation. Patients only need to stop extreme training (such as hill running and stadium step running) if they experience less severe symptoms.
No clinical and experimental researches are drawing conclusions that support the use of ultrasound, ionphoresis, phonophoresis, or electrical stimulation in the treatment of PFPS (both short and long-term).

II. Recovery phase

The treatment has to be all-inclusive. It has to treat potential problems of structures involved in the mobility of the lower extremity.
These structures include:

• o Hip abductors
• o Iliotibial band
• o Knee extensors (quadriceps)
• o Knee flexors (hamstrings)
• o Feet – excessive or insufficient pronation
• o Core muscles

To improve the rehabilitation, it is preferable for patients to start physical therapy under the supervision of a physical therapist or comparable professional. It is important to avoid pain during exercises. These exercises should not cause pain. If there is any experience of pain (more than mild soreness), the intensity of the exercises should be reduced. If the pain persist and get more severe because of the rehabilitation exercises, the clinician should reevaluated the treatment.
 Stretching
It has appeared that, by increasing the quadriceps, hamstring, and iliotibial band flexibility, the patellofemoral joint can decrease in stress. Some observational studies presume a connection between decreased quadriceps flexibility and PFPS.
In a prospective case control study, a program with exclusively quadriceps stretching decreased pain and improved function among patients with PFPS. Whoever, the improvement of functions did not correspond with the gains in quadriceps flexibility.

Strengthening of the Quadriceps is a key in the rehabilitation program

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. The patient elevates his extended leg and holds it for 10secs, before relaxing (concentric contraction and/or eccentric contraction is also possible, which makes it dynamic). Control that the patient keeps a normal lumbar lordosis and does not compensate with his basin.
2. Pillow squeeze exercise
The patient sits comfortable with his trunk supported. Both knees extended. Place a pillow (or towel) under one knee (that knee might be slightly flexed). The patient tries to push the pillow/towel in the table by extending his or her knee. (Q-ceps contraction).

Closed kinetic chain exercises (CKC) VS Open kinetic chain (OKC) exercises

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

Vastus medialis obliquus (VMO)

Training of the VMO muscle is appropriate for 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 explains why patients with post trauma and/or surgery 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 VMO type exercises will cause an alteration in the VMO fiber angle, (relative to the femoral axis). Fiber angle can change from a vertical 40 to a much more medialising 70 degrees, (Benjafield et al., 2014).  

Hip muscles training

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.
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.

Proprioceptive training

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 (pathologic and non-pathologic knee)! Therefore proprioceptive training (pain-free exercises!) of the knee should be part of the rehabilitation program.

Electrotherapy

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 patellofermoral joint. 

An example of how you can accomplish the stimulation;

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 pai- Time = 7 minutes => 6 repetitions, on for 6seconds and off for twelve, and progressed to 30 minutes, 11 repetitions, on for 10sec and off for 12sec.

III. Adjunctive therapy

  Foot orthoses
There are a few clinical predictors that can help decide if a patient is more likely to benefit from foot orthoses or not;
● 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 rear foot 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).

Bracing and patellar taping We can perform taping or using a brace if the patient cannot participate in the rehabilitation or make any progress because of the pain.
Tailored taping is effective for immediate pain relief and control the lateral tilt, glide, and rotation of the patella. Although, taping may be useless for people with a higher BMI.
It is not clear if bracing has a positive effect on the treatment of PFPS. It may be a support for the therapy. 

Barefoot running and minimalist shoes By using minimalist shoes or running barefoot, there is less risk to have an injury, including patellofemoral pain.

Corticosteroids and glycosaminoglycans For the use of intra-articular injection of corticosteroid or glycosaminoglycan polysulfate, there is little evidence available.

IV. Follow-up care:

Treatments show varying degrees of success. Some patients have successful short term outcomes and poor long term outcomes after finally returning to their pre-injury level. If the patient reports persistence knee pain or recurrence, the therapist has to readjust the treatment.
If the patient progress, the therapist should continue the therapy with the patient until he can perform all exercises without pain, and then slowly reintroduce activities which previously caused pain (e.g., running). The activity levels should be increased gradually until the patient achieves the deserve level. The therapist has to reexamine the patient and confirm the original diagnosis if the symptoms are unchanged and the patient appears to be compliant with both therapy and activity modification. If the complaints have not been reduced in three to six month, the therapist can ask for an MRI or orthopedic consultation (if not done before).

Evaluation

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. 
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. If you start with a low stair the compression between the patella and the femur will be minimal.
The main differences you should find, are increased energy consumed by the VMO muscle in order to perform the test. This leads to a change in force-generating capacity of the muscle and faster (more accurate) activation of the VMO muscle after therapy. ..

Recent Related Research (from Pubmed)

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