PATELLO-FEMORAL PAIN SYNDROME (PFPS)
PATELLO-FEMORAL PAIN SYNDROME (PFPS)
by Alex Blacke (Chiropractor)
What is it?
Patello-femoral pain syndrome (PFPS) is a common knee condition and basically a fancy name for pain at the front of the knee which is not due to injury of specific structures inside the knee. It has a multi-factorial cause and tends to arise when there are biomechanical deficits in the lower extremity such as the hip and ankle/foot.
What are the symptoms?
- Insidious onset of knee pain, usually described as behind the knee cap
- Pain is usually exacerbated by using stairs, sitting for prolonged periods, squatting and running
- Sometimes described as sharp or achy, with possible sensation of the knee giving way
- Sometimes there is mild swelling
- Can sometimes experience clicking
Who tends to get it?
- Runners most commonly get it, with PFPS encompassing 25% of knee injuries
- More common in women
- Anecdotally, at KC we see it often in weightlifters, yogis, runners and Crossfitter's to name a few
Anatomy and Biomechanics Involved in the Development of PFPS
- The patella (knee cap) is a triangular shaped bone that is positioned within the quadriceps tendon. It has little grooves (facets) at the back which help it to articulate with the condyles of the femur. It is held in place and stabilised by the quadriceps tendon and patella ligament and the medial and lateral retinaculum. The shape of the femoral condyles and the patella itself also provide a stabilising role.
- It protects the quadriceps tendon from excessive friction from the femur during knee flexion and also acts to increase the moment arm of the quadriceps.
ITB and Quadriceps
- The quadriceps group play an important role in dynamic stabilisation of the patella. The vastus medialis is the main active stabiliser of the patella medially and the vastus lateralis laterally.
- The patella also has strong lateral reinforcement from the Iliotibial band (ITB) and the lateral retinaculum, and it is often thought that these three structures often overpower the vastus medialis and medial retinaculum. This may therefore lead to excessive lateral pressure and tracking in the patella. Some studies support the idea that a weak vastus medialis obliquus is correlated to anterior knee pain in PFPS whereas some studies have found this to be an insignificant finding.
- In the research, there are studies for and against ITB tightness being a factor in PFPS. As for the quadriceps, some studies have found that patients with PFPS have quadriceps tightness, whereas some authors say that the tightness may have been present before PFPS developed and not a result of the condition itself.
Hamstrings and Gastrocnemius
- Hamstring tightness has been thought to cause mild knee flexion during activities or to overcome higher quadriceps forces.
- A study by Besier et al. (Peterson paper) found that patients with PFPS have greater co-contraction of the quads and hamstrings. Females with PFPS also tend to have increased hamstring and gastrocnemius muscle forces while walking and running compared to males. This may lead to increased patella-femoral joint contact force and joint stress in comparison with healthy patients.
- The knee is most vulnerable to patella dislocation during the early stages of knee flexion, therefore if the hamstring are already holding the knee in flexion due to tightness, this can impact on the stability of the patella-femoral joint.
- The gluteus medius and minimus muscles are important to keep the pelvis level for weight bearing activities such as walking, running, squatting, using stairs and so on.
- In a single leg stance (which temporarily occurs with activities such as walking and running) the hip abductor group on the stance side are responsible for keeping the pelvis horizontal.
- If they are weak the pelvis will tend to drop on the unsupported side and the person will shift their weight to the supported leg. When walking down stairs, if there is abductor weakness in the stance leg (the back leg) this will cause the stance knee to buckle inwards causing a dynamic valgus of the knee, and the foot to roll in more. This change in load to the knee can cause the patella to deviate and track abnormally.
- Many studies have found that there is a significant correlation between weakness in the hip abductors and external rotators in patients with PFPS.
- Two simple tests that can be easily done to give patients an indication to the strength of their hip abductors is the one-legged squat and single leg stance.
- One-legged squat: look to see if your stance knee collapses inwards – this indicates a positive test for weak hip abductors.
- Single leg stance: see if the pelvis is able to remain horizontal and see if it can remain horizontal for 1 minute, if not this also is a positive finding.
- When walking, we need 10° of dorsiflexion at the ankle and when running we need 15-25°. As said earlier, PFPS patients tend to have tight gastrocs and hamstrings. Tightness in these muscles can cause a decrease in ankle dorsiflexion and if this range is not available, compensatory increased pronation will occur.
- During walking, it is normal during the weight acceptance phase to pronate the foot to help absorb shock and accommodate the ground which leads to a relative internal rotation of the tibia.
- In patients with PFPS however, they have been found to have increased rear foot eversion and pronation at heel strike. This prevents the tibia from fully externally rotating during midstance and therefore prevents the knee from fully locking. To get around this, the femur internally rotates to compensate, which causes increased contact pressure between the patella and lateral condyle causing bone stress and PFPS symptoms.
- Treatment for PFPS involves symptomatic relief via non-steroidal anti-inflammatory drugs, patella taping/bracing and activity modification.
- Once symptoms have decreased, a rehabilitation program targeting the previously mentioned biomechanical faults is implemented.
- If the treatment regime is followed well, the prognosis for PFPS is very favourable.
By Alex Blacke
B.Chiro. Sci., M. Chiropractic.
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