The idea of patellofemoral tracking syndrome is that the kneecap may not slide evenly as your knee flexes and extends, because of muscular control and/or a variety of other vague and unconfirmed structural problems, especially the idea that the connective tissues on the side of the knee are “tight.”
This uneven sliding, especially where the kneecap may be pulled too hard laterally, is considered to be stressful to the knee. Therefore PFTS is the usual suspect in cases of patellofemoral syndrome (PFPS) — the beating heart of the conventional wisdom. In fact, they are so closely associated that they are sometimes (erroneously) treated as being virtually synonymous — as if to have one is to have the other.
But like almost every biomechanical bogeyman, it’s not as simple as we’d like it to be.
Although a truly mind-boggling amount of scientific research has been done to try to understand the mechanics of the knee joint, the evidence is complex and contradictory. We are about to go “down the rabbit hole,” into one the worst scientific snarls in all of musculoskeletal health care. It’s not exactly “controversial,” because no one holds any position firmly enough for there to be controversy, but it’s definitely confusing. I will do my best to make it all clear.
Understanding patellar tracking matters. It matters because, if you don’t know better, your therapy dollars will get spent — and quite possibly wasted — on fixing tracking problems. PFTS is the reason and the target for most treatment recommendations for patellofemoral pain.
Alleged tracking problems are why physiotherapists will prescribe a variety of specific exercises, iliotibial band stretches,1 and knee taping. It is why doctors prescribe knee braces and straps. It is also why surgeons will cut up the side of the knee or move the attachment of your quadriceps, where it pulls on the shin. It is why massage therapists will work hard on the side of your thigh, and why chiropractors inevitably “adjust” your pelvis. And yet all of this therapeutic enthusiasm is a little dubious, because the only clear thing about tracking problems is that their relationship to PFPS is not clear, the list of problems with diagnosing tracking problems is long, starting with the fact that some studies simply haven’t found a tracking problem in PFPS patients.2
On the one hand, patellar tracking issues probably are some kind of factor in PFPS. This conventional wisdom has considerable weight, and it assumes that a tracking problem “must” be a problem.3 The idea certainly does seem reasonable, and any well-educated health care professional can easily cite scientific studies that seem to give the conventional wisdom the appearance of being firmly based on evidence. On the other hand …
The kneecap almost “floats” over the knee. The patella does not actually make solid contact with the femur until about 20˚ of flexion, at which point it slips into a deep groove and begins sliding downwards. But while your leg is straight or mostly straight, you can easily move the kneecap around. It can move up or down, left or right. It can tilt to face more out, or more in, or more up, or more down. And it can rotate, as though on an axle right through the center. And as the knee flexes and extends and the kneecap engages and disengages with the femur, it does a little dance as it slides, rotating and tilting and deviating. And every one of these movements has been studied by every imaginable high-tech method.4
In spite of all this research, “normal patellofemoral tracking is not well defined” (Tennant), and some of these studies have led the researchers to believe that abnormality is normal, that normal healthy kneecaps are quite clearly capable of doing downright odd things.
So, if you watch your knee, and you see that your kneecap looks a little wonky, maybe a bit off to the outside, that doesn’t necessarily mean anything: healthy knees do that, too. (In spite of all this, later on I will give instructions on how to self-evaluate your own patellar tracking. Just in case.)
In 2006, a research group at Queen’s University in Canada, tackled this uncertainty head on.9 “While it is widely believed that abnormal patellar tracking plays a role in the development of patellofemoral pain syndrome, this link has not been established,” they wrote. “And we aim to check it out thoroughly.” They looked at three groups of people:
They used super-duper amazing technology to accurately assess the alignment and tracking of all of those knees, and found that the results were all over the map: “features of patellar spin and tilt patterns varied greatly between subjects across all three groups, and no significant group differences were detected.” They did find a correlation between kneecaps that were slightly displaced laterally with PFPS, but it was only a “marginally significant” displacement at an incredibly subtle 2.25mm.
So they concluded that even with superhuman assessment accuracy (i.e. with their high-tech toys), it is “clear” that you can’t tell the difference between a hurtin’ knee and a non-hurtin’ knee by examining kneecap position and movement alone. Period. Can’t be done.
Not convinced? How about one more example like this? Perhaps a nice dissection study?
The nice thing about actually cutting people up and looking inside them is that the results are pretty hard to argue with.10 In 2007, the journal Clinical Anatomy — a respectable publication — weighed in on PFPS with a specific article about the way the muscle fibres of the inner thigh attach to the kneecap.11 The vastus medialis obliquus (VM or VMO, as it is usually abbreviated by therapists and anatomy wonks) is yet another presumed bad guy in PFPS cases. The almost universal assumption among us therapist types is that anatomical variation in how the VM attaches to the patella, and/or weakness (more on this soon), can result in generally crappy joint mechanics, and this is why you need to “fix”/strengthen the vastus medialis when you have PFPS — to compensate, in effect, for having been dealt a slightly bad anatomical hand.
Personally, I like to give nature more credit than that. I’d like to think that minor variations in anatomy do not generally cause severe chronic pain. If they did, I think we’d really be in trouble. And I’m pleased to say that Clinical Anatomy agrees with me. The emphasis is mine:
There was no significant correlation between any of VM insertion length, VM fiber angle, limb alignment, and patellofemoral joint dysfunction location and severity …
Peeler et al, “Structural parameters of the vastus medialis muscle and its relationship to patellofemoral joint deterioration,” Clinical Anatomy, 2007.
Swelling probably isn’t a problem either (although it may be a symptom).
It’s been proposed that swelling under the knee increases the pressure under the kneecap, aggravating PFPS, perhaps in a vicious cycle — the more irritated it gets, the more swollen it gets, which irritates it more, and so on. But this too falls apart. Not only is swelling fairly rare in PFPS, but in 2006 German researchers showed that this kind of swelling actually acts like a cushion and reduces pressure under the kneecap! And so yet another previously “safe” assumption falls apart.1213
Unfortunately, doctors and physical therapists often do jump to conclusions based on minor (and often imagined) signs of kneecap wonkiness.14
The most common of all such tests is the assessment of kneecap alignment. I was trained to look for odd kneecap behaviour (mostly basic alignment) as though finding it would be some kind of diagnostic slam dunk. So it’s a reflex (ha ha, pun intended) for most manual therapists to check patellar alignment — a staple of knee pain diagnosis, as inevitable as a doctor asking you to say “ah.”Doctors and physical therapists often do jump to conclusions based even on minor (and often imagined) signs of kneecap wonkiness.
And yet it’s been proven beyond a reasonable doubt that the current generation of manual therapists just cannot agree on the location of people’s kneecaps! If you get several of us to assess the same kneecap, they will come up with “variable” diagnoses.15 Great! So when a physiotherapist tells you that you have wonky kneecap movement, you know that you can pretty much count on the fact that the next physiotherapist will have a different opinion. Under these conditions, how can anyone have the slightest confidence in a diagnosis of patellar tracking syndrome?
If you’re doing a bunch of therapy based on the idea of patellar misalignment — and I mean both patients and professional — please reconsider it.
As you learn more about patellofemoral pain, it will only get more and more clear that an odd kneecap position alone does not necessarily mean you have a problem. You can quite easily have a tracking issue or alignment problem without knee pain, and knee pain without a reliably diagnosable tracking or alignment issue.
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.
This article is a free chapter from PainScience.com’s huge patellofemoral pain syndrome (PFPS) tutorial, one of 96 chapters in all. There are also several other articles on PainScience.com about patellofemoral pain and related topics:
— science update: added citation showing a lack of correlation between Q-angle and patellofemoral pain syndrome.
This study reports that people with patellofemoral (kneecap) pain tend to have higher kneecaps, and in turn those with high kneecaps are less likely to slide evenly on the knee. This contradicts my bias and I’m a bit skeptical. The researchers were probably biased in the other direction, and expected to find abnormalities correlating with pain. They title and abstract seem crafted to show that the study proves that tracking is a factor in patellofemoral pain, and yet I think the data shows exactly the opposite.
Strangely, they didn’t measure all that many knees, just 52, and it’s easy to find what you expect in small batches of data. They don’t report just how much higher kneecaps were in the abstract, which would be natural to do if it were an impressive number, so I suspect it’s not an impressive number. Similarly, the prevalence of maltracking was allegedly a little higher in patients with pain (32% in vs. 27%), but the statistical significance of the difference was not reported — so it probably wasn’t significant. Furthermore, the presence of maltracking or patella alta in people with pain did not increase pain level.
Even if the correlation is real, it doesn’t tell us anything about cause (maybe misbehaving kneecaps cause pain, or maybe knee pain causes kneecaps to misbehave). Almost half their subject had no abnormalities at all, which is consistent with other studies (Herrington et al) showing that you can find a roughly even mix of abnormalities in everyone, whether they have pain or not.BACK TO TEXT
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BACKGROUND: Patellofemoral pain syndrome is a prevalent condition in young people. While it is widely believed that abnormal patellar tracking plays a role in the development of patellofemoral pain syndrome, this link has not been established. The purpose of this cross-sectional case-control study was to test the hypothesis that patterns of patellar spin, tilt, and lateral translation make it possible to distinguish individuals with patellofemoral pain syndrome and clinical evidence of patellar malalignment from those with patellofemoral pain syndrome and no clinical evidence of malalignment and from individuals with no knee problems.
METHODS: Three-dimensional patellofemoral joint kinematics in one knee of each of sixty volunteers (twenty in each group described above) were assessed with use of a new, validated magnetic resonance imaging-based method. Static low-resolution scans of the loaded knee were acquired at five different angles of knee flexion (ranging between -4 degrees and 60 degrees). High-resolution geometric models of the patella, femur, and tibia and associated coordinate axes were registered to the bone positions on the low-resolution scans to determine the patellar motion as a function of knee flexion angle. Hierarchical modeling was used to identify group differences in patterns of patellar spin, tilt, and lateral translation.
RESULTS: No differences in the overall pattern of patellar motion were observed among groups (p>0.08 for all global maximum likelihood ratio tests). Features of patellar spin and tilt patterns varied greatly between subjects across all three groups, and no significant group differences were detected. At 19 degrees of knee flexion, the patellae in the group with patellofemoral pain and clinical evidence of malalignment were positioned an average of 2.25 mm more laterally than the patellae in the control group, and this difference was marginally significant (p=0.049). Other features of the pattern of lateral translation did not differ, and large overlaps in values were observed across all groups.
CONCLUSIONS: It cannot be determined from our cross-sectional study whether the more lateral position of the patella in the group with clinical evidence of malalignment preceded or followed the onset of symptoms. It is clear from the data that an individual with patellofemoral pain syndrome cannot be distinguished from a control subject by examining patterns of spin, tilt, or lateral translation of the patella, even when clinical evidence of mechanical abnormality was observed.
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Vastus medialis (VM) muscle dysfunction and abnormal limb alignment are commonly observed in patients who experience changes in patellofemoral joint (PFJ) function, leading many clinicians to assume that there is a direct relationship between VM structural parameters, leg alignment, and PFJ dysfunction. This study tested the hypothesis that there is a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of patellofemoral joint deterioration (PFJD). The dissection study used 32 limbs from 24 intact cadavers. Data were collected on limb alignment, angle of VM muscle fibers below the superior aspect of the patella, length of VM inserting on the medial aspect of the patella, and severity and location of PFJD. Parametric and nonparametric statistical analyses illustrated that PFJD was most commonly located on the middle third of the medial half of the patellar articular surface. The severity of PFJD did not vary with location. There was no significant correlation between any of VM insertion length, VM fiber angle, limb alignment, and PFJD location and severity lpar;r(2) < 0.34). The results of this study did not support the hypothesis of a relationship between structural parameters of the VM muscle, limb alignment, and the location and severity of PFJD in this subject group. Future research should examine the relationship between functional parameters of the entire quadriceps muscle group and PFJ dysfunction.
From the abstract: “ ...a simulated fat pad edema resulted in a significant (P < 0.05) decrease of the patellofemoral force between 120 degrees of knee flexion and full extension. The contact area was reduced significantly near extension (0 degrees -30 degrees ) by an average of 10% while the contact pressure was reduced at the entire range of motion up to 20%. Conclusion: An edema of the infrapatellar fat pad does not cause an increase of the patellofemoral pressure or a significant alteration of the patellofemoral glide mechanism ....”BACK TO TEXT
This paper reviewed nine reliability studies of 306 knees. (They noted that this is not much evidence, and more is needed. No kidding! We’re talking about one of the most common of all testing procedures for knee pain, and we’ve only properly studied its accuracy on 306 knees, ever? Think about how many bazillions of dollars of therapy money is spent on knee alignment issues!)
What evidence there is showed that assessment of patellar position was “variable” from one therapist to the next — if you get a bunch of clinicians to all assess the same kneecap, they will come up with a variety of diagnoses.
Of course it’s possible that there is a way — some unknown method, or even just unusual care in the use of current methods — to accurately assess patellar alignment, and maybe someday we’ll know that and all manual therapists will be properly trained in it. Maybe. But that doesn’t matter to patients now. These scientific tests of existing methods with competent practitioners should have produced clear agreement and strong reliability — not “variable” results. That’s pretty discouraging for patients.BACK TO TEXT