Measuring the Position and Mobility of the Patella

Measuring the Position and Mobility of the Patella

Measuring the position and mobility of the patella is still a very important component of my clinical examination of the knee.  It gives me a great sense of soft tissue restrictions that may be present when patellar hypomobility is noted.  This is especially common after knee surgery.  But measuring patella mobility is also important to assess generalized laxity when patellar hypermobility is observed.

The first time you feel either of these during your clinical exam, you’ll know what I mean.

But if you read through the literature, you may find conflicting results regarding the validity and reliability of assessing patella position and mobility.

The Reliability of Measuring Patella Mobility

One study that I reference often is a systematic review by Smith, who looked at the reliability of assessing patella position, specifically in the medial-lateral position.  Like any examination technique that is commonly performed, it is necessary to establish that the test has adequate intra-rater and inter-rater reliability. The test needs to be easily replicated and produce accurate results both between two different clinicians but also when repeated during re-evaluation with the same clinician.

Otherwise, the test may have limited use and not be able to provide helpful information.

The authors conclude the intra-tester reliability is good to assess medial-lateral patellar position, but inter-tester reliability was variable.  The variability is interesting to me and makes me wonder if we just aren’t standardizing how we look at patella mobility.

Another study by Herrington demonstrated that a group of 20 experienced therapists could reliably measure patellar position.  This tells me that a group of similar trained or skilled clinicians will show greater inter-tester reliability than a randomized selection of clinicians.  When I see that a test has good intra-tester and worse inter-tester reliability, I think one of two things:
The test is difficult to perform and/or is more accurate with more experience.

Reliability can be enhanced if we all use the same examination techniques. There may be subtle differences in techniques that may produce poor inter-tester reliability. This is what came to my mind when the Herrington study showed good inter-tester reliability with a group of experienced clinicians.

The Validity of Measuring Patella Mobility

In regard to validity of the measurements, the authors conclude that the criterion validity of this test is at worse moderate, based on limited evidence.  However, a couple of interesting studies were referenced.  A study by McEwan demonstrated that a lateral tilt of the patella greater than 5 degrees can be detected.  This was confirmed with MRI measurements.  The previously reported study by Herrington also reported that medial-lateral patellar position could accurately be measured as confirmed by MRI measurements.

A Simple Way to Measure Patella Mobility

It appears that clinical measurements of patellar positions can be both reliable and valid.  While intra-tester reliability, or your own ability to accurately repeat a test, appears to be more accurate, inter-tester reliability may be enhanced with a standardized examination technique.

Taking all this into consideration, I honestly do not try to “measure” patellar position.

I will assess the position but I do not try to place a label, such as millimeters or degrees, on the exact position.  If I want or need this information, I would much rather obtain this from a MRI.  I focus more on assessing the amount of hypomobility or hypermobility.

And there is a really simple way that we can do this that I think will great enhance our reliability.

To simplify this measurement, I try to just use a percentage of the patella that I feel can displace.  Here is how I do it:

  1. I break the patella down into 4 equal segments representing 25% of the width of the patella each.
  2. I visually try to establish where I believe the midline of the trochlea is located when I am measuring position.  If I am measuring displacement, I will visualize the edge of the lateral trochlea.
  3. I then measure the percentage of the patella that is positioned beyond the midline of the trochlea and then displace the patella and attempt to determine if 25%, 50%, 75%, or 100% of the patella can displace beyond the lateral edge of the trochlea, as in the image below:

Measuring the Position and Mobility of the Patella

I’ve learned over the years that knee experts, such as Dr. Frank Noyes, consider 50% displacement to be “normal.”  I use that as a frame of reference, but comparing side-to-side is probably even more important.

I feel that this provides me with plenty of information to compare to the other extremity and simplifies the process, which I hope would enhance intra- and inter-tester reliability.  If we all do it this way, I think we’ll be far more accurate.

What do you think? Is this too simple? How do you measure patellar mobility?


19 replies
  1. Mike Reinold
    Mike Reinold says:

    Love the research ideas Trevor. I wonder if we could all collaborate on a project together as a group!

    Amy, thanks for joining in, both of those articles came to my mind as well. We have so much more we need to learn about how the body functions. Luckily we are making progress, just 10 years ago this discussion would have been regarding how our PF pain patients never seem to be getting better and we couldn’t figure out why!

  2. amy castillo
    amy castillo says:

    All great points and I think they all apply depending on the individual patient. Is it a proximal influence, will tape help, is basic quad strengthening/NMES indicated?

    And as Mike pointed out, maybe the key is classification. Isn’t patellofemoral pain / syndrome, etc. analogous to low back pain? There many causes for the same complaint.

    Two articles come to mind.
    JOSPT Lesher Nov 2006 in an attempt to classify who will respond to patellar taping. 53% responded and factors such as tibial angulation, ankle dorsiflexion ROM, patellar tilt and relaxed calcaneal stance appeared to be related to the success.

    And this month’s JOSPT Vaughn’s case study on regional interdependence bolsters Power’s work on proximal influences.

    As far as measuring patellar position, I use thirds instead of fourths. I also feel I am looking more for symmetry than an absolute measure.

  3. Trevor Winnegge DPT,MS,OCS,CSCS
    Trevor Winnegge DPT,MS,OCS,CSCS says:

    Great dialogue on this site!!!! In response to anonymous’ comments…….I agree with Mike in that every PF patient does not need or get NMES. It is another tool in our PT toolbox that can be very effective. Snyder-Mackler was able to demonstrate quite nicely the effects of NMES on quad strength in 2 different populations. While the studies were for those two specific knee surgeries, i feel we can extrapolate that data and use it for other diagnoses. Do I rely on NMES to cure my patients? no way. I do feel it builds quad strength a lot quicker, however. And this fits into your less is more philosophy. If we can build muscle strength quicker, it is safe to say the patient will likely need less visits. Thereby protecting your report card from third parties. One of the clinical indications for NMES is torebuild an atrophied muscle. I ask you to measure girth of the quads, just above patella, 6 inches above and 12 inches above. I think you will find many (not all) of your PF patients do in deed have a significant amount of quad atrophy. Mike-two good study ideas-looking at quadriceps girth in PF patients, correlating it to pain. Also the role of NMES on PF pain. In Summary, I do not feel using NMES is in any way leading to excessive use of PT modalities, or “using everything at our disposal”. I think the therapists out there who use heat, ultrasound, massage, and estim for every patient do in fact use everything. Billing for two units of exercise and one unit of neuro re-ed is not excessive in my mind. i find NMES to be a very effective adjunct to therex and the other inteventions (tape, orthotics, lumbar stuff etc)

  4. Mike Reinold
    Mike Reinold says:

    Anony- I’ve been thinking about this and wanted to add that it is very difficult to perform studies that document efficacy in PF pain patients due to one main reason: “PF Pain” is not a pathology but a junk term. Thus, taping, hip activation, modalities, NMES to quad, stretching, orthotics, lumbar mobs, and any other technique may work on some but not other PF pain patients depending on what the source of pain is actually coming from.

    This leads me to another idea for a future post…discussing a classification system for PF pain! Thanks Anony!

  5. Anonymous
    Anonymous says:

    Yes, pain and effusion have an inhibitory effect on quadricep activation. Clinically, for the general run of the mill patient with patellofemoral pain, how frequently is effusion observed, measured or noted to be an existing factor?

    I do believe that NMES is a nice option for someone who has difficulty in activating the quadriceps – in particular patients who have an extensor lag. (I also believe it will definitely be useful with patients that have had a total knee arthroplasty.) I haven’t seen any patient with a patellofemoral pain complaint have an extensor lag yet. Based on specificity of training, I’m not quite sure the value of the strength gains while using NMES performing a straight leg raise, unless of course the patient happened to be a British soldier. :)

    As I had mentioned previously (since I’m the same anonymous), if the patient is able to perform an activity that replicates pain in the clinic (such as ascending stairs, squat or descending stairs) and after the tape is applied the complaint is eliminated, then the tape will be useful. Not all patients demonstrate poor neuromuscular control, so not all patients would need activities to improve control and hip abductor strength.

    Wainner recently published the potential for a subgroup of patients with patellofemoral pain to respond to lumbopelvic manipulation. “Respond” was defined as a 50% or greater reduction in pain level performed during specific activities compared to prior to the manipulation. Work still needs to be done on this, but preliminary data was published.

    I’m a physical therapist that gets a “report card” from a third party payor. I have always considered the impact of the cost of the services I provide. This particular third party payor categorizes providers based on number of visits. Cost reports and treatment interventions are also shared. (Depending on the category the physical therapist is rated determines how much extra hurdles have to be jumped to get paid for services.) When I see reports from the payor on a quarterly basis, the less is more philosophy is in everyone’s best interest. (What the payor doesn’t have is outcome data. That is a very huge chunk of the equation that should also be considered.) I’m under the assumption that most physical therapists aren’t intentionally performing treatments just to increase charges… but I sometimes wonder if self-reflecting and thought goes into a treatment plan that also considers the financial impact. Do we sometimes get ourselves into a habit to such a degree that we don’t test if other options are potentially more efficient and more cost-effective? I know this last bit is off-track, but the comment of using everything at our disposal really had in impact on me and was very thought-provoking for me.

  6. Mike Reinold
    Mike Reinold says:

    NMES is very useful to me in my practice. Not for VMO strengthening, I agree with you that this is not helpful, but for quad strength and volitional control. To me, Lynn’s data can be used for more than just postop ACL and TKA patients. I don’t think that NMES was effective because of the surgery performed, I think that the papers show that NMES is effective to enhance quadriceps strength and volitional control in general. I also showed that NMES is effective in increasing volitional force following rotator cuff repair as well (it is AJSM epub right now waiting for print).

    Of course you would need to assess for weakness or inhibition to determine if NMES is appropriate. I don’t think anyone has said you have to do this for every PF patient. But I don’t think you would find many PF patients that couldn’t improve their quad function. Both pain and effusion have been shown to have an inhibitory effect on quadriceps strength (Young MSSE ’83, DeAndrade JBJS ’65, Spencer Arch Phys Med ’84). Bob Mangine performed a study that he presented many years back and found that only 30-40cc’s of fluid would reduce quad peak torque by almost 50%.

    To throw your own questions back at you, you mention taping and training the hip. Do you do this in all PF patients or do you determine if these treatment techniques are needed?

    Regarding your comments about reimbursement etc., I am a believer that I will use any treatment technique that I believe would help the patient. I agree that we should not be using modalities or other techniques without justification. I am a firm believer in NMES. I personally do not make clinical decisions based on insurance restrictions or the cost of a treatment, I base my decisions solely on what I believe is best for the patient and never perform treatments just to increase charges. Unfortunately, these people do exist…

  7. Anonymous
    Anonymous says:

    I’m slightly confused. The patient in front of you has patellofemoral pain. Why are responders mentioning NMES? Snyder-Mackler has done her work in that area and research is positive for NMES post total knee arthroplasty and if I recall correctly ACL reconstruction.

    Maybe I’ve missed something over the years, but I don’t recall any supporting evidence for NMES for patellofemoral pain. How do you translate Snyder-Mackler’s work into patellofemoral patients having inhibition of the quads? How do you measure quad/VMO inhibition to know there is inhibition? There may be a subpopulation of patients that have this issue, but shouldn’t it be measured then addressed versus assumed?

    For those of you in private practice in the United States 1) we obviously have major health care issues 2) do we contribute to those issues with the current fee for service system by “using everything at our disposal” to get people better and 3) with higher and higher co-pays… is it financially worth it for patients to pay 10,20,30% of the fee schedule for NMES? (Do you believe NMES is a valuable contribution to the care that you’d be willing to pay for that service? If third party payors didn’t reimburse for that CPT code, would you want the patient to pay for it in full OR eat the cost yourself?)

    Instead of using everything at our disposal to improve function and decrease pain, in my opinion, we really need to be thinking about cost-effectiveness and having the “less is more” attitude in approaching the treatment plans we design.

  8. Mike Reinold
    Mike Reinold says:

    Trevor – I like your suggestion of using the function squat test. That is a great idea.

    Mike – Thanks for the comments. I can't say that I believe that our treatments can change the amount of patella mobility (i.e. reduce amount of translation from 50% to 25%, for example), but this is still useful for me to compare to the contralateral limb as well as my own experience for what is normal (typically greater than 50% is a lot to me, > 75% is a red flag). If someone exhibits excessive mobility (especially compared to the opposite leg), this may be a problem that we can not address and may need surgical intervention.

  9. Mike Monahan, PT
    Mike Monahan, PT says:

    Mike M here(former Excel),Great blog, you’ve got some well informed readers. I’m glad to see clinicians looking at the whole leg: tight gastroc, inflexible gluts, planus, as sources of knee dysfunction, there are too many that don’t.
    (if anyone is tracking, count me in on starting with SLR series plus NMES and early strapping to alleviate sx [like Trevor], thereby minimizing inhibition to vmo)
    Back to your original point: I like the method you proposed to quantify the patella position and lateral displacement. It seems you could easily compare with the opposite knee (hopefully-asymptomatic) in a quantitative way to glean insight. Have you actually seen enough tangible change, to go from 25% to 50%, etc.? or is it more for your own assessment?

  10. Trevor Winnegge DPT,MS,OCS,CSCS
    Trevor Winnegge DPT,MS,OCS,CSCS says:

    I think everyone here has some really great points. I agree with Mike in that we have to use everything at our disposal to get people better. Neglecting SLR completely would be detrimental. That does not mean however, that you can stick a PF patient in the corner and have them do only SLR to get better. I too use and love NMES on most of my knee patients. I love the portable EMPI for home use in my post op knees. I also agree that the hip is a problem source for a lot of athletes, particularly female patients with knee problems. I also think taking every PF patient and working only on hip strength isn’t that effective. Gastroc tightness is also an area to look at. i use the functional squat test to rule in/out gastrocs as a cause of knee pain. tight gastrocs, restrict dorsiflexion with squatting, creating a pronated foot, and a valgus moment at the knee, which in turn leads to that lateral tracking/positioned patella and medial knee pain. Treating the entire kinetic chain is the best way to go with these patients. In regards to taping, i have gotten some good results but do not tape everyone. I particularly like a technique described by McConnell to unload the infrapatella fat pads and remove the inferior pole of the patella fromt hese structures. Works great to give symptom relief to those people who have two golf balls for fat pads. Use it only for symptom relief while peforming all aforementioned exercises.

  11. Mike Reinold
    Mike Reinold says:

    I agree as well, the question of “function” comes into play many times when we make decisions in our practice. Obviously, the position of the patella is one variable, and I agree 100% that it is a small variable. I do see benefit of knowing this information, again due to the potential effect on chronic adaptations of the soft tissue around the knee. How many times have you had a patient with vague medial knee pain that doesn’t seem meniscal in nature? Could it be from chronic elongation of the retinaculum? Sure, it could be, but not always.

    I like the comments on the hip. This is a gigantic part of PF treatment. Could it be from poor hip mechanics (both static and dynamic) that cause chronic adaptions that present with lateral tilt and position of the patella? I agree that this may be the “cause” of the PF pain but the “source” of the pain could be retinacular. I would treat the cause (hip) as you mention but also try to treat the source (retinaculum) to minimize pain and inhibition.

    I do disagree with the SLR comment, though. I perform quad sets, SLR, etc. with NMES applied to the quad in most of my knee patients. This is seldom my only treatment and typically used as an active warm-up prior to other therapeutic exercises. I am not trying to strengthen the VMO or anything along those lines, but any pain or effusion in the knee will have a reciprocal inhibition of the quad. I have had great success using NMES for these patients.

    I believe you need to be multifaceted when treating these PF pain patients because their symptoms and pathology are multifaceted. Treat the knee symptomatically, focus on hip strength and dynamic control (goes distal in the chain too, don’t forget the feet!), and work on quad re-education.

    Will definitely be posting on training the hip for PF pain patients soon based on this discussion!

  12. Eirik Hellerud
    Eirik Hellerud says:

    I absolutely agree with anonymous, see the big picture, and motor control. I never had any lasting effects with patellar taping, tried it a few times with handball players, its more annoying than usefull. Motor control hip (and VMO in my opinion..) does the trick more often than taping.

    Best regards,

  13. Eirik Hellerud
    Eirik Hellerud says:

    I absolutely agree with anonymous, see the big picture, and motor control. I never had any lasting effects with patellar taping, tried it a few times with handball players, its more annoying than usefull. Motor control hip (and VMO in my opinion..) does the trick more often than taping.

  14. Anonymous
    Anonymous says:

    Actually, I don’t measure patellar mobility any more. Stopped doing it probably 5 years ago because we really don’t make much of an impact on it… stopped doing all the straight leg raises at that time too. Again, VMO strengthening wasn’t giving results.

    Instead… Powers’ work made a lightbulb go off in my head… focus on the hip and neuromuscular control. If tape is helpful (meaning pain eliminated during a just previously performed activity that was painful), tape and work on neuromuscular control and hip abductor strengthening in a weight bearing position. What I’ve observed in my patient population is more of a higher frequency of poor motor programming.

    How do you think patellar positioning affects our treatments? If there is potentially a “no pain” zone on the posterior surface (although I would wonder about that because it seems as though the degree of chondromalacia would be a factor) and the pain may be a factor of the retinacular tissues, specifically it’d have to be nerves that are sending the message of “something” being interpreted as pain, is it really patellar position/mobility that is the factor? Mind you, you are assessing patellar position in a supine, inactive, relaxed position… how functional is that? Does patellar mobility and position in a supine, relaxed, inactive position correlate to function?

  15. Mike Reinold
    Mike Reinold says:

    I like thought provoking comments! I think patellar position does have an impact on our treatments. Specifically in regard to my past post discussing the Dye information, if PF pain is from the retinacular tissue, than a patella with a lateral position or tilt may indicate that the lateral retinacular tissue is tight, but more importantly that the medial tissue is being stretched. Over time, that elongated tissue can put pressure on the pain receptors and produce that vague PF pain that we all know and love!

    Agree with your comments on the tape, I have never had good results and do not commonly use it in my bag of tricks.

    Love the comments from any and all, even anonymous, but don’t be shy about posting your name! I hope that we can all comment and discuss with each other.

    Do you measure patella mobility and position? If not, why? Thanks for commenting.


    • Kathy
      Kathy says:

      I found your post from 2008. Still relevant today. I would add that I have learned I need to address up and down patellar lack of movement as week for most of our post surgical patients especially TKAs

  16. Anonymous
    Anonymous says:

    In light of what you posted about patellofemoral pain, specifically the article by Dye, what’s the rationale for measuring patellar position and mobility?

    In light of research suggesting that patellar taping doesn’t alter the patellar position AND no matter how the tape is applied symptoms can be reduced (even with just lying the tape on the skin without any forces to alter patellar position), again, does patellar position really matter?

Trackbacks & Pingbacks

Comments are closed.