Patellofemoral Pain Syndrome (PFPS) is a common musculoskeletal condition in young athletic populations, accounting for 25% of knee injuries seen in clinical practise. Indeed, the incidence of PFPS is around 22/1,000 person-years, and is 2.23 times more common in females than in males. PFPS can be due to acute trauma to the patellar, but is more commonly due to a combination of biomechanical and neuromuscular changes. There are several proposed mechanisms responsible for PFPS and often these factors occur simultaneously in individuals. Tissues can become overloaded or overused, leading to dysfunction. It is for these factors that PFPS can be a challenging musculoskeletal disorder to conservatively manage, and often requires multimodal management.
Relevant anatomy in patellofemoral pain syndrome
The knee consists of two major joints: the tibiofemoral joint, and the patellofemoral joint. The patella (i.e., knee cap) sits within the femoral groove (i.e., shallow dip on the front end part of the thigh bone), which is covered by articular cartilage on the front part of the femoral condyles. This joint is filled with synovial fluid, which acts to reduce friction by lubricate the joint and providing nutrients to the joint. Several bursae also produce synovial fluid in the knee capsule. There are bursae inside the joint and also on the front part of the knee. When the knee is inflamed, these bursae can become swollen causing knee pain. Collateral ligaments come together and give stability to the joint.
Causes of patellofemoral pain syndrome
PFPS can either be due to trauma or biomechanical abnormalities, but is often due to a combination of several factors (i.e., multifactorial):
- Traumatic: acute (i.e., sudden) due to a fall or blunt strike causes local tissue damage and inflammation of the surrounding tissues of the patellofemeral joint; or chronic (i.e., longstanding) like overuse and overload of the patellofemoral joint.
- Biomechanical abnormalities: includes shallow femoral groove, previous knee injuries, muscular power imbalances or weaknesses and dysfunctional tracking of the patella over the femoral groove, which causes additional friction and articular damage and inflammation.
Patella orientation and dysfunctional tracking in patellofemoral pain syndrome
One of the main causes of PFPS is the orientation and alignment of the patella in the femoral groove. The image below shows the varying alignment issues that can arise with the patellofemoral joint (NB below: A-D show undersurface of knee with patella facing front; E and F show the front aspect of the knee with patella removed).
When the patella has a different orientation, it may track or glide more to one side of the femoral condyle and can cause overuse/overload (i.e., overpressure) on that part of the femur, resulting in pain, discomfort and inflammation. There are different causes that can provoke such deviations, as listed above. It is important to note that everyone has a slightly different patella alignment, which is normal to that individual and doesn’t cause any issues. However, even slight changes in patella tracking has shown to lead to symptoms of PFPS.
Underactive muscles in patellofemoral pain syndrome
The Vastus Medialis Obliquus (VMO) is a muscle part of the quadraceps group in the inner front part of the thigh. When the VMO isn’t strong enough, its opposing muscle, the Vastus Lateralis (VL) can exert a higher force and can cause a lateral glide, lateral tilt or lateral rotation of the patella. This leads to overuse of the lateral side of the femoral condyle, resulting 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 (ITB) that is located along the outer side of the thigh.
Other biomechanical causes in patellofemoral pain syndrome
- Knee: PFPS can also be due to knee hyperextension (i.e., excessive bending backwards), lateral tibial torsion (i.e., twisting of the femur on the tibial plateau), genu valgum or varus (i.e., knocked or bowed knees), increased Q-angle (i.e., the line of force of the quadriceps made up by connecting a point near the ASIS on the pelvis to the mid-point of the patella), and ITB, hamstrings or gastrocnemius muscle tightness.
- Ankle & foot: Pes planus (i.e., pronation) or pes cavus (i.e., supination) can provoke PFPS. Foot pronation is more common in PFPS and causes a compensatory internal rotation of the tibia or femur that leads to dysfunctional patellofemoral tracking. Foot supination provides less cushioning for the leg when it strikes the ground so more stress is placed on the patellofemoral mechanism.
- Hip: Hip kinematics (i.e., the movement of the joint) can also influence the knee and provoke PFPS. A study has shown that patients with PFPS showed weaker hip abductor muscles that were associated with an increase in hip adduction during running.
Signs and symptoms of patellofemoral pain syndrome
Patient’s usually present with anterior knee pain, aggravated by activities that increase patellofemoral compressive forces such as: ascending/descending stairs, sitting with knees bent, kneeling, and squatting.
Conservative management strategies for patellofemoral pain syndrome
Several physical therapy interventions can be prescribed to patients with PFPS, including:
- Manual therapy (e.g., soft tissue massage, mobilisations, manipulations, stretching)
- Open vs. closed chain exercises
- Muscle group strengthening (e.g., quadriceps and gluteal muscle strengthening)
- Patellar taping (e.g., kinesiotaping to improve patella tracking)
- Orthotics (i.e., to improve foot and ankle mechanics)
There are several physical therapy interventions for the treatment of PFPS supported by the current scientific evidence:
- Hip muscle strength: A 93% success rate with hip flexor (i.e., iliopsoas and rectus femoris muscles) strength improvements.
- Hip, pelvis and trunk training: Weakness of hip abductors and external rotators (i.e., gluteals, piriformis, tensor fascia latae and sartorious), and extensors (i.e., hamstrings, glueteals and adductor magnus) was evident in patients with PFPS. Thus, treatment consisted of recruitment and endurance of the hip, pelvis and trunk muscles. This resulted in a significant reduction in self-reported pain, improved biomechanics during dynamic testing and return to normal function.
- Taping: Daily kinesiotaping to improve patellofemoral biomechanics might be useful in improving speed to recovery if used in conjunction with strengthening exercises.
- Foot orthoses: May be useful in patients that have excessive pronation and/or lower extremity with PFPS. Studies showed improved pain/stiffness after orthoses use in patients with lower extremity biomechanical issues.
Strong evidence for the effectiveness of quadriceps muscle strengthening to manage PFPS exists in the scientific literature. A graded exercise program in which gradual load is introduced into the tendons of the quadriceps, hamstrings, gluteal and iliopsoas muscle groups is optimal:
- Isometric exercises. Refers to activation of the muscle without changing its length. It is often prescribed first to manage pain. These kind of exercises may include straight leg raises and pillow between knees squeeze. These exercises should be performed within pain-free ranges.
- Slow-heavy exercises. After isometrics, we can begin to gradually increase force into the muscles and tendons by changing the length of the muscle under gradual load. Slow-heavy progression exercises for PFPS may include squats and heavy squats (against resistance), leg presses, lunges and crab walks with theraband.
- Energy storage exercises. Exercise in this stage places faster loads on the tendon, causing the tendon to store more energy and begin to act like a spring. Examples of exercises for PFPS include skipping, hopping, jumping and fast stair climbing.
- Energy storage and release exercises. These exercises are a progression from stage 3, where the speed increases and the release of energy from the tendon occurs. Examples for PFPS include faster skipping, running drills with directional changes.
Closed kinetic chain exercises are often more function than open kinetic chain exercises, and often provoke lower patellofemoral joint stress, especially at the end of full extension (0° to max 40° knee flexion). So, exercises should done within this pain-free range. An example is the squat; although, it is important for patients to avoid having their knees pass their toes during the squat as forces through the patellofemoral joint becomes too high causing pain.
Please visit our S3C website articles and blog page for more information about knee and leg pain:
- Hamstring Injuries and the Askling L-Protocol
- Thermotherapy vs. Cryotherapy: Mechanisms & Evidence
- Tendinopathy: Evidence-Based Management Strategies
- How Can Chiropractic Help After a Sports Injury?
- Medial collateral ligament (MCL) Injury
- Medial meniscus tear
- Anterior cruciate ligament tear
- Iliotibial band syndrome
- Jumpers knee
- Osgood Schlatters disease
- Lateral collateral ligament (LCL) injury
- Shin splints
- Calf pain
- Calf strain
- Achilles tendonitis
- Peroneal tendonitis