What is the Source of Patellofemoral Pain? It Might Not be Chondromalacia…

Patellofemoral pain is one of the most commonly diagnosed knee pathologies.  Despite the prevalence of the diagnosis, the exact mechanism and source of pain continue to be unclear.  This lack of clarity is likely the reason why we continue to use such vague, non-descriptive terminology such as “patellofemoral pain.”  As rehabilitation specialists, it is often our job to disregard a diagnosis like this and instead rely on our clinical examination to find functional deficits, such as loss of strength or joint mobility, to lead our treatment plans.

The source of patellofemoral pain has long been debated.  One of the most common theories involves the deterioration of the articular cartilage on the undersurface of the patella, or chondromalacia. 

If you haven’t read or at least heard about it, there is an amazing article that was published in the American Journal of Sports Medicine 10 years by Scott Dye, MD (Dye, Vaupel, Dye: AJSM ’08).  In the study, the researches sought to establish the source of patellofemoral pain by physically palpating various structure within the knee during arthroscopy.  What is truly amazing about the study is that Dr. Dye himself actually had his knee scoped without anesthesia so that he could consciously quantify the level of discomfort he felt!  Dr. Dye can never be accused of not sacrificing himself for the sake of the advancement of sports medicine!

Cartilage defects did not cause discomfort

The first finding that was surprising was that palpation of the undersurface of his patella cause no discomfort, even with the prescene of grade III-IV articular cartilage defects.  This immediately questions the cartilage being a source of patellofemoral pain. 

Moderate to severe pain was caused by the retinaculum and fat pad

Conversely, the two areas of the knee that caused moderate to severe discomfort were the retinacular tissue and infrapatellar fat pad.  Even more interesting was that even though these areas produced discomfort, it was difficult for the subject to localize the source of pain.
This may also at least partially explain why patellofemoral pain is so vague in our patients.  This information coincides with that of Fulkerson (Clinical Orthopedics ’85) and Sanchis-Alfonso (AJSM ’98).  Fulkerson reported that patellofemoral pain may be caused by enlargement and small injuries of the nerve fibers in the retinaulum.  Sanchis-Alfonso report that patients with patellofemoral pain tend to have a higher amount nerve fibers and histological changes of the neural tissue.Interesting findings that seem to make sense.  

The cartilage tissue is avascular and fairly aneural where the fat pad and retinaculum is highly highly vascularized and full of neural tissue.  Patients with patella instability and chronic elongation of the medial retinaculum and tightening of the lateral retinaculum may have symptoms due to the chronic changes of the tissue and the corresponding stress on the neural fibers.

Clinical Implications

So what does this mean and how does this change the way we treat patients?  For one, I am not overly cautious with exercises and their effect on patellofemoral compression, unless this reproduces the patient’s symptoms.  Strengthening of the quadriceps is always going to be a large part of the treatment plan for these patients.  In order to do this most effectively you knee to perform open kinetic chain knee extension and work into deeper ranges of motion with closed kinetic chain exercises.  My rule of thumb is that if the exercise does not cause pain or excessive crepitation, I don’t mind doing it as tolerated.  But I must stress as tolerated.

It is also likley that we should treat the iritation of the retinacular tissue even if the pain is difficult to localize.  This can include your choice of treatment techniques and anti-inflammatory modaliities.

I write this post in an attempt to motivate thought next time you evaluate a patient with patellofemoral pain.  There is still a lot of uncertainty on this topic but with time I am sure we will continue to learn more.  Have you had success directly treating the retinacular tissue?  If so please share your experience.


5 replies
  1. John Vacovec, PT
    John Vacovec, PT says:

    Mike, great note.. I passed it along to my therapists, thank you.… sounds like using laser to the retinacular tissue should be beneficial to the nerve fibers and inflammation??!!!!

    John Vacovec, PT

    Reply
  2. Anonymous
    Anonymous says:

    Mike, I get many referrals from orthopedic doctors in south Florida who strictly contraindicate open chain Quad strengthening for their patellofemoral patients. I strongly agree with your article that pain should be the guideline for strengthening purposes. Many patellofemoral patients I get in the clinic cannot tolerate closed chain exercises early into the rehabilitation. It’s a touchy situation when they go to their f/u with their MD and they tell them they are performing open chain exercises. Please comment.

    Reply
  3. Mike Reinold
    Mike Reinold says:

    Ah, yes, sad but true experience! I think it is safe to say that rehabilitation specialists likely have a better understanding of rehabilitation than the doc, right? Tough situation, you basically need to follow orders or risk losing the referral…not a good idea I assume (though, sounds like it wouldn’t be too bad…). I assume they are trying to avoid the PF compressive force.

    To strengthen the quad, OKC knee extensions are very effective, but there are other ways around this. Leg press and single leg step-ups come to mind.

    To reduce PF force during exercises (if this is your rehab goal), you should perform OKC knee extension from about 100-40 deg, forces increase near TKE. For CKC it should be shallow, initially 0-30 deg and gradually progressing deeper. The deeper you go the more force is on the PF joint. Show your docs the MSSE study from 1998 by Escamilla. (Search pubmed, sorry I can’t get the HTML link to paste here well).

    Of course, pain and symptoms need to guide your treatments. Those recommendations above are just based on forces and do not take into consideration the patient’s source of pain, potential cartilage lesion

    Reply
  4. Anonymous
    Anonymous says:

    Very interesting study done by Dye, but isn’t simply palpating a cartilage defect vastly different from the high joint reaction forces that occur during squatting for example.
    My comment may be too late to get and discussion on this issue since it was posted in September.

    Reply

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