Current Beliefs of Causes for PFPS
The consensus from most professionals on patellofemoral pain syndrome is that it’s multifactorial, although certain groups within the health care provider realm maintain that certain things are more prevalent than others. Let’s have a little look-see at what every body is talking about.
The American Association of Family Physicians (AAFP) says that retropatellar or peripatellar pain (diagnostic of PFPS) results from physical and/or biochemical changes in the patellofemoral joint. The repetitive contact of the patella and femur during patellar maltracking (misalignment) is the most likely cause of PFPS and this is multifactorial with respect to biomechanics, overuse, and overload of the joint. In short, the AAFP is using a catch-all approach to causes of patellar maltracking but it maintains that this is the most likely cause of PFPS.
Johns Hopkins orthopedic program says that malalignment of the kneecap, complete or partial dislocation of the patella, injury, tightness or imbalance, weakness of the thigh muscles, flat feet (pes planus), or referred pain can “result in a dull, aching pain under or around the patella that is NOT chondromalacia, and whose diagnosis requires SURGICAL confirmation.” They go on to implicate tightness of the quadriceps, hamstrings, IT band, and a relative weakness of the quadriceps’ muscles as being the most likely culprits in PFPS. Additionally, they say that excessive rotation of the hips (femoral anteversion), tibial torsion (rotation of the tibia relative to the femur), valgus knees, or a congenital or acquired hyperextended position of the knees might be implicated in PFPS. In summary, it’s multifactorial and we can’t nail down what is the sole cause, or if there is one.
A comprehensive review of all the available literature on PFPS was done by Waryasz et al from Tufts University School of Medicine and was published in a 2008 journal of Dynamic Medicine. The full article is freely available in pdf form online here (www.biomedcentral.com/content/pdf/1476-5918-7-9.pdf).
Risk factors include- weakness in functional testing, tightness in gastroc, hamstring, quadriceps, or IT band, lax ligaments, excessive q angle, deficient hamstring or quad strength, hip mm weakness, abnormal vmo/vl reflex timing. Instead of quoting every single section of the review I’ll summarize the main points.
- There may be a muscle-timing abnormality in those with PFPS where the vastus lateralis fires before the VMO. In normal populations (without PFPS) the reverse was observed. These results, however, were not statistically significant.
- Persons with PFPS have lower “strength” as tested by a vertical leap test, single leg press, and balance and reach tests. While non of these are actual strength measures, it does lend some credence to the fact that those with PFPS are generally less strong/powerful/conditioned physically than those without PFPS.
- Patients with PFPS tended to have between a 73% and 81% deficiency in strength of their hamstrings as determined by a very convoluted strength test based on fixed joint speeds.
- A greater Q angle (the angle of the femur and quadriceps relative to a vertical line dropping straight down to the ground from the edge of the hip bones) was not statistically correlated to PFPS. Women, on average, have a greater Q angle than men- normal range is 17-22- and this was theorized to be a driving factor for the increased prevalence in PFPS in women. Doesn’t hold much water, in my opinion.
- A weak/tight iliopsoas (hip flexor) and adductors tend to de-stabilize the pelvis thereby forcing the individual into an anterior pelvic tilt and internally rotated femur position. This can lead to increased patellofemoral joint stress.
- Substance P (a chemical in the soft tissue surrounding the patella) is involved in pain input to the spinal cord. It is expressed in higher levels in those with PFPS and functions as to be a vasodilator and produce inflammation.
- VMO weakness (compared to the VL) as a cause of PFPS was reviewed in 6 studies. VMO muscle isolation has been impossible to prove without direct electrode stimulation. Two studies found that a VMO and/or quadriceps’ strength deficiency was not statistically significant and three studies found that a weakness of the quadriceps was statistically significant. None of the papers found that the VMO specifically was weak, however.
Finally, the British Journal of Sports Medicine did a literature review of all studies involving PFPS and the following treatment modalities: hip strengthening, physical therapy with the goal of balancing VMO/VL activity, McConnell taping and EMG studies, open chain vs. closed chain movements. Their results are as follows:
- Hip strengthening has no significant benefit
- Physical therapy seems to restore quadriceps imbalances
- Taping needs to be further investigated
- Open and closed chain movements are both appropriate
- *Study was done by Vagan et al and published in 2008
Treatments for PFPS
The treatments for PFPS and general knee pain run the gamut from simple exercises done with a physical therapist all the way to a lateral release where some of the soft tissue around the lateral aspect of the patella is cut surgically after the joint and its structures are evaluated arthroscopically. Basically, the surgeon heads into the knee joint and sees if the diagnoses of a laterally shifted or tilted patella are correct. If it is, then he or she will release this excessive tension by making a few small incisions in the soft tissue around the joint.
Between both extreme modes of treatments lie various others that may or may not have efficacy. These include stretching of certain upstream and downstream (of the knee joint) muscles, taping of the knee joint, electric stimulation of certain muscles to induce localized activity in that muscle, etc. Discussing the worthiness of one or all of these treatment modalities, however, is beyond the scope of this article. What you might have already intuitively figured out is that PFPS probably isn’t from any one specific deficiency, but rather a more global deficiency that results in a perfect storm- and knee pain/PFPS ensues.
From my experience, both in research and actually training people with and without knee pain, the single biggest risk factor for developing PFPS is being weak and detrained, period. When I say weak I don’t mean relative to your peers (age, sex, and weight matched), but rather for your own genetic potential. At any given point in time a person occupies a specific place on his or her own strength continuum. Allow me to explain.
Let’s say an untrained (read: previously sedentary) has a genetic potential of a 400lb squat at their optimal bodyweight. Currently, however, they can only manage 95lbs x 5 reps x 3 sets. They are very weak given their potential, irrespective of their current bodyweight. They begin on a strength-training program that’s based upon linear progression and after 6 months of consistent training and recovery they can squat 275lbs x 5 reps x 3 sets. This is not unusual or remarkable at all for a male who will actually train diligently. At this point they are now further along in the strength continuum or in other words, closer to their strength potential. No longer could we possibly consider their quadriceps, hamstrings, adductors and abductors (or any other muscle group) weak. Similarly, the morphological changes within the soft tissue and support structures in the patellofemoral, hip, and ankle joints induced via actually training have resulted in a much more support, proper articulation patterns, and better motor control for the trainee. Additionally, the mobility of the trainee has improved greatly due to consistently being involved in a training modality that requires the bones, soft tissue, and joint capsules to be moved and stressed through large range of motions. I submit to you that this will adequately prepare someone to start to refine his or her selection of sport or activity without fear of pain or joint dysfunction as a result.
This is nothing new in the exercise science world, although you wouldn’t know it if you talked to virtually any clinician. The soviets and eastern-bloc countries have long held the belief that before a person starts to specialize in a specific sport or activity that they need to become establish a base level of conditioning and general physical preparedness, or GPP for short. There are certain levels of cardiorespiratory endurance, coordination, mobility, strength endurance, and overall strength that are required to have sufficient GPP to qualify someone for a more focused training program for sport/activity. The most arduous and difficult of these to attain is strength, which requires a dedicated plan of attack over a period of time. Additionally, strength training tends to produce increases in strength endurance by decreasing the relative difficulty of submaximal tasks- i.e. when a person’s bench press increases (of which a pushup is a certain percentage of their bench press) then their capacity to do pushups increases. Think of it like this, if a push up requires the force of 60% of someone’s body weight to complete and while training the bench press over a period of time someone’s bench press increases from 100lbs to 225lbs while gaining five pounds in bodyweight- this person’s pushup capacity will increase because the pushup is now an ever smaller percentage of their absolute strength. Strength training also improves motor coordination, mobility, and elicits compensatory adaptations in the cardiorespiratory system. Seems like strength training might be a good place to start for a deconditioned person. At some point in the strength program the simple linear progression will stop working- i.e. the trainee will not be able to get stronger every single workout and will need to switch to a slightly more complex program. In this latter stage, weight might be added to a lift every week (instead of every session) to allow for both more recovery and an accumulation of stress (over the whole week instead of a single training session) in order to allow the adaptation to occur. Also, at this point the trainee has developed enough of a strength base (likely) to start safely implementing other training modalities that require this strength base to be present- like running- a high impact conditioning tool that demands enough strength, coordination, and joint stability to be safely implemented. The point of this long-winded explanation of strength training is to make the case for dedicated strength work for detrained or under-trained individuals before they take part in other training modalities that cannot be scaled appropriately in terms of impact and forces on the skeletal structure and joints.
To sum all of this up, it is my belief that in order to prevent PFPS a person needs to build a base of strength first- before any activity that might require the joints to deal with taxing stressors- like running. Moreover, to ameliorate PFPS a person should likely discontinue any activity that exposes the patellofemoral joint to large stresses and compromised positions- like running, jumping/bounding, or sports like tennis, soccer, football, etc that expose the knee joint to large forces AND INSTEAD focus on strengthening their body in a systemic, progressive manner-like with an intelligent strength program. If we can prepare people’s knees (and other joints) for sport and activity through strength acquisition- which, if done appropriately DOES NOT overload the joints in such a way to impair healing and DOES allow for the proper morphological and biochemical adaptations to occur- then we can effectively reduce the prevalence of PFPS.
The conclusion is simple after all this: get strong, do conditioning work that does not compromise the joint’s integrity and current ability to retain proper mechanics, and once you’ve become somewhat proficient in this regard you can begin to implement other training modalities in a progressive fashion. Be smart out there, people, and get STRONG before you injure yourself.