What is Patellofemoral Pain Syndrome?
Patellofemoral pain syndrome (PFPS) refers to a pain in the front of the knee between the patella and femur (thigh bone). The pain is normally worse going up or down stairs or after prolonged sitting. Pain & cracking in the joint typically occurs during sitting or squatting movements.
Cause of Patellofemoral Pain
The exact cause of patellofemoral pain syndrome is uncertain; however, it is believed to be caused by an abnormal tracking of the patella along the groove of the femur into which it sits.
Muscle asymmetry around the hip & knee can cause abnormal tracking of the patella and over time may predispose to patellofemoral pain. Repetitive loading & jumping with abnormal kneecap tracking can cause an overload of the area & give rise to pain. This tends to get worse as loading intensity increases. This may give rise to injury & erosion of the cartilage underneath the patella. Research by Giles et al. (2015) reported that there was no wasting of the quadriceps in individuals with patellofemoral pain compared to those without the condition.
There has been much talk about wasting of the medial quadriceps (VMO) muscle compared with the lateral quadriceps muscle in athletes with knee pain. The authors of this study reported no selective wasting of the VMO relative to the vastus laterals. They state that wasting of all portions of the quadriceps muscles is present on the side of knee pain in individuals with patellofemoral pain. Research by Syme et al. (2009) corroborates these findings. They conclude that ‘clinicians should not overly focus on selective activation’ of the VMO or other structures of the knee.
Research by Witvrouw et al. (2000) found four potential predictors for patellofemoral pain:
- Delayed quadriceps response time
- A decrease in explosive strength
- A shortened quadriceps
- A hypermobile patella
Other risk factors identified in the research include:
5. Gender: females are at greater risk
6. Training load: increased training load is associated with increased risk of PFP
7. Navicular drop. The navicular is a large bone on the inside of the foot. A drop may indicate poor foot biomechanics
8. Tightness of the gastrocnemius (calf) muscle
What is the Source of Patellofemoral Pain
Although most experts discuss the erosion of the cartilage behind the kneecap as the source of injury in patellofemoral pain, in scientific experiments the cartilage itself was shown to be pain-free. The outer surface of the bone (subchondral bone) is highly innervated and has been shown to be a source of pain along with the fluid lining the knee joint (called synovial fluid). There is also a fat pad below the kneecap known as the infrapatellar or Hoffer’s fat pad which is thought to be a strong source of knee pain.
Best Treatment for patellofemoral pain
As there are a number of factors that may give rise to patellofemoral pain. A thorough physical examination is vital to identify all of the potential factors involved in each case. Rehabilitation will generally focus on developing control around the hip and trunk and building up strength around the knee where indicated.
A systematic review by Bolgla et al. (2011) suggests that research supports the use of quadriceps strengthening to address patellofemoral pain. The goal is to alter the loading mechanics in the knee during movement thus minimising pressure on the patellofemoral joint while running or jumping. By improving muscle balance around the knee this may help to address the abnormal tracking which is giving rise to pain. There is also evidence that strengthening some of the muscles around the hip can help alleviate symptoms & may be an important driver of knee symptoms.
Research by Ramazzina et al. (2016) demonstrated that selective muscle strengthening gave rise to a decrease in knee pain and improved function. The intervention consisted of muscle strengthening performed between 30-90° of knee flexion and 3 sets of 8 repetitions at 80% of maximum load for 4 weeks. This was followed by 4 weeks of 3 sets of 10 repetitions at 70% of maximum load. At one year follow-up the improvements were maintained. At 2 years, no athletes presented relapses.
A systematic review by Alba-Martin et al. (2015) reported that the optimal rehabilitation protocol for treating patellofemoral pain included proprioceptive neuromuscular, stretching and strengthening of the hip external rotator and abductor muscles and knee extensor muscles. In addition, the authors report that stretching of the knee and hip muscles might help improve pain, function and range of motion in patellofemoral pain syndrome.
Dolan et al. reported earlier pain relief when participants performed 4 weeks of exercises for the hip external rotators and abductor muscles compared with exercises for the quadriceps muscle.
Is Glucosamine & Chondroitin Good for Knee Pain?
The research has demonstrated mixed results in relation to the use of chondroitin & glucosamine for the treatment of knee pain & arthritis. The initial hype has died down somewhat & in most cases neither of these supplements will have a significant impact on patient symptoms. The trend seems to be that Glucosamine & Chondroitin may need to be taken for longer periods to provide benefit (Heinties et al. 2004; Rodriguez-Merchan 2014).
Are Orthotics good for Patellofemoral Pain?
The largest randomised controlled trial examining the use of orthoses reported reported improvements superior to flat inserts in the short-term, but no additional benefit when added to a multi-modal physiotherapy approach compared to physiotherapy alone (Collins et al. 2009)
Is Medication Effective for Patellofemoral Pain
A systematic review found that Naproxen reduces symptoms of knee pain in the short term. This may provide a window of opportunity in which patients can engage in physiotherapist guided rehabilitation prior to the symptoms returning. A two week trial to assess the benefit of such an approach is generally recommended (Heinties et al. 2004; Rodriguez-Merchan 2014)
Can I improve my running style to help my knee pain?
Research shows that running style determines the amount of load that the knee is exposed to. By modifying some of the running technique variables, it is possible to decrease knee pain and sustain a running routine while managing pain. One such technique is increasing step rate. Running tends to place a certain amount of strain on the patellofemoral joint.
Movement Modification for Patellofemoral Pain
This area of rehabilitation is garnering increasing attention. Increased hip adduction is suggested as being a risk factor for patellofemoral pain (Noehren et al. 2013). Cueing to avoid such movement patterns may be beneficial in reducing symptoms during running & stair climbing.
Increasing step rate by 10% has been shown to improve running form and encourage a vertical shin position at foot strike which helps to alleviate knee pain. A metronome app on your phone can be useful in monitoring step rate if assisted by self-monitoring using a GPS watch.
Is Taping Effective for Patellofemoral Pain
Taping of the kneecap or McConnell taping has been shown to be effective to address patella movement (Barton et al. 2014). Taping may induce its effects through altering muscle activation around and provides an opportunity to decrease pain while undergoing rehabilitation.
Witvrouw et al. (2000). Intrinsic risk factors for the development of anterior knee pain in an athletic population. American Journal of Sports Medicine; 28(4):480-489.
Barton, C.J. et al. (2015). The ‘best practice guide to conservative management of patellofemoral pain’: incorporating level 1 evidence with expert clinical reasoning. British Journal of Sports Medicine; 49(14): 923.
Bolglia, L., Boling, M. (2011). “An update for the conservative management of patellofemoral pain syndrome: A systematic review of the literature from 2000 to 2010”. International Journal of Sports Physical Therapy 6(2): 112-125
Ramazzina et al. (2016). Long term effect of selective muscle strengthening in athletes with patellofemoral pain syndrome. Acts Biomed; 15; 87, Suppl 1: 60-68.
Alba-Martin et al. (2015). Effectiveness of therapeutic physical exercise in the treatment of patellofemoral pain syndrome: a systematic review. J Phys There Sci; 27(7): 2387-90.
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