Patellar tracking disorder refers to patella (kneecap) moving out of place when you bend or extend your knee. Many physical therapists and other clinicians believe that this “imbalance” is the cause of most types of knee pain, such as patellofemoral pain syndrome (PFPS). If you look up “knee tracking” on YouTube, you would likely find tons of videos about correcting or fixing knee tracking — taping, exercises, adjustments, etc.
But do you really need to fix your knee tracking? Is patellar tracking disorder actually a primary cause of knee pain? Should you even worry about it?
What is patellar tracking?
When you extend your knee, your thigh muscles (quadriceps) pull the patella toward the femur at the trochlea, which is a groove in the front of the femur. When you bend your knee, the hamstrings pull the tibia back and the patellar tendon pulls the patellar away from the trochlea. There is minimal side-to-side movement as the kneecap glides.
This is not the same as patellar subluxation, or dislocation, of the kneecap.
What causes patellar tracking disorder?
Some research finds that the source of the knee malalignment comes from the weak hip external rotators and abductor muscles, which causes the knee to internally rotate. They also find that women are more likely to have PFPS than men, associating patellar malalignment as a contributor to knee pain.
Other contributors could be delayed activation of the vastus medialis muscle of the quadriceps, an imbalance activation between the vastus medialis and vastus lateralis, excessive knee valgus, or the degree of the Q-angle, which is the angle relationship between the pelvis and the knee. But none of these ideas show a direct causal relationship between PFPS and knee misalignment.
While knee injuries, such as a blow to one side of the knee, may cause the patella to move out of place, current research finds that many people who have this condition do not have knee pain.
Symptoms of patellar tracking disorder
The symptoms of patellar tracking disorder are similar to typical PFPS. These include pain when you bend your knee (usually in the front part of the knee), knee instability or feeling “loose” like your knees will give out when you stand or walk, and a popping or cracking sound when you get up from a sitting position or climbing stairs.
However, research has shown that even if the patella is out of alignment, many people do not have knee pain, knee instability, or other symptoms.
A team of Swiss researchers, led by Dr. Henrik Behrend from Kantonssptital St. Gallen, published two systematic reviews that examined the variability of knee alignment and anatomical shapes among healthy knees and osteoarthritic knees.
In the osteoarthritic knee review, the team pooled data from eight qualified studies and measured various angles of the patella, tibial tuberosity, trochlea, and the trochlear groove. But not all studies were consistent with what was measured. What they found to be most important is the “high variability of all measured values” of the patellofemoral joint in the combined studies.
The sulcus angle of the trochlea, for example, has an average of 130 degrees with standard deviations from about 6.5 to 10 degrees from all eight studies. That means a person’s osteoarthritic knee could range from around 120 degrees to 140 degrees.
Some limitations in the review include the lack of reporting of the range of measurement differences in some of the studies and the usage of different imaging techniques and protocols. Even so, there is enough evidence to highlight the variability among osteoarthritic knees.
“[Patellofemoral] alignment is extremely variable in osteoarthritic knees,” Behrend and colleagues wrote. “A more precise knowledge of the complex relationship between the patella and the trochlea may help to better diagnose PF malalignment in patients considered for [total knee arthroplasty]” to reduce the risk of anterior knee pain after a knee surgery.
In the healthy knees review, the story is similar. After they sifted through more 1,400 papers and whittled it down to 15 qualified studies. Using the same knee alignment measurements as the healthy knee review, Behrend and his colleagues could not find any “normal” range of knee tracking.
While some of the measurements fall within a certain range, they wrote that a “normal” range of where the kneecap moves is unknown.
But the differences of what type of imaging is used, how the patellofemoral joint was measured, and imaging protocols can affect the measurement results and how the studies are interpreted. For example, a Canadian study that used a computed tomography (CT) scan to measure a group of healthy women’s patellar tilt angle with their knee fully extended had an average of 0.7 degrees with a standard deviation of 5.
A Japanese study that had measured knees with magnetic resonance imaging (MRI) with the same leg position from young, healthy volunteers found an average of 6.8 degrees with a standard deviation of 6.6. That is quite a difference between both countries’ sample populations.
Behrend and his colleagues wrote that race may be a factor in the differences of these measurements. Since there is some overlap in knee misalignment between healthy and osteoarthritic knees, clinicians who base their knee tracking literature like the Canadian study may mistake healthy, asymptomatic people likely to have knee pain.
Considerations about patellar tracking disorder
The two systematic reviews highlighted several problems of how the measurements were done. This issue was further questioned by a team of researchers led by Dr. Camila Grant from the National Institutes of Health in Bethesda, Maryland.
They wanted to find out if quadriceps activity increases the clinicians’ ability to find poor knee tracking; do patients with only PFPS move differently than those with PFPS plus knee dislocation; do other factors influence the measurements of the knee tracking?
Ultimately, their “overarching” question was “Is patellar maltracking associated with [PFPS]?”
After examining 40 qualified studies, Grant and her colleagues found that a lateral shift of the patella and “tilt maltracking” are strongly associated with PFPS only and PFPS with dislocation. Assessing knee tracking also requires the quadriceps muscles to activate to improve diagnoses. While their findings “do not prove cause and effect” that knee misalignment is a cause of pain, they support the idea that changes in muscle forces are part of the root of PFPS.
Even so, the studies have varying degrees and types of quadriceps contraction, which may affect the measurements and outcome interpretation. For example, static contraction of the muscles would likely produce different pain response and patellar tilt than contracting the muscles dynamically where the knee bends and extends repeatedly.
Although the systematic review suggests that quadriceps activation may play a role in PFPS, recent research has shown otherwise. A joint U.S. and Taiwanese study found “no difference in absolute and normalized individual muscle volumes between individuals with and those without [PFPS].” In other words, the lack of certain quadriceps muscles firing is not a primary cause of this type of knee pain.
Grant and her colleagues concluded that their study “exposed large methodological variability across the literature, which not only hinders the generalization of results, but ultimately mitigates our understanding of the underlying mechanism of [PFPS].”
The inconsistent methods across the studies make it almost impossible for researchers and clinicians to determine a clear feature that defines what exactly is patellar tracking disorder.
Their purpose is not to find out whether one method of experiment or outcome variable is better than another; they want to “explore the sources of variability across the literature in an attempt to provide clarity and unity for future studies.”
The lead authors of these research were emailed, but they have not responded.
Should you get knee misalignment treated?
With such variability of knee alignment among those with or without knee pain, it may not be a huge factor to contribute pain or instability. Whether you should get treated or not, it would depend on your specific case. Clinicians should not jump to the conclusion that everyone who has a knee out of place should get a treatment.
Like most types of joint pain, the biopsychosocial model of pain still applies to PFPS and other types of knee pain. Instead of just focusing on the knee or patellar tracking and jumping to their favorite treatment, clinicians should take other factors into considerations, such as the patients’ health history and narrative behind their pain, sleep habits, amount and type of physical activity, lifestyle, and various psychosocial factors.
Given the current evidence in the literature about patellar tracking disorder, knee tracking probably is not as big of a problem as many physical therapists and other clinicians make you think. There are too many variables that affect PFPS and other types of knee pain, especially when what constitutes “normal” or not overlap between healthy and painful knees.
“Alleged tracking problems are why physiotherapists will prescribe a variety of specific exercises, iliotibial band stretches, 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…” ~ Paul Ingraham, Patellofemoral Tracking Syndrome