What Causes Patellofemoral Pain?

Patellofemoral disorders are often considered the most common knee pathology encountered by orthopedic and sports medicine clinicians.  Some sources say that in the general population, 1 out of 4 will likely experience patellofemoral symptoms at some time in their life.  Although patellofemoral disorders represent a common pathology, there is no consensus on the optimal management of this condition. This may be explained, in part, due to the various sources of pain that may be contributing to the disorder. Unfortunately, terms such as “anterior knee pain” and “patellofemoral pain” have become accepted diagnoses with treatment often implemented without clear definitions of the underlying pathophysiology. The common use of such ambiguous and non-specific terms only adds to the confusion regarding optimal care for these patients.

This is part 2 of a series on solving the patellofemoral mystery:

Source of Patellofemoral Pain

Rehabilitation programs designed for the patellofemoral patient must match the specific disorder and dysfunction.  Part 4 of this series will discuss the differential diagnosis of patellofemoral pain, however it is important to understand the source of patellofemoral pain in addition to any possible diagnosis.  In recent years, several authors have attempted to provide an explanation for the potential source of patellofemoral pain.

image Dye et al (AJSM 1998) examined the conscious neurosensory mapping of the lead author’s knee during arthroscopy without intraarticular anesthesia.  (This in itself is an amazing study, he literally had his partner scope his own knee without anesthesia!)  The authors rated the level of conscious awareness from no sensation to severe pain. These findings were further subdivided based on the ability to accurately localize the sensation. Palpation to the anterior synovial tissues, retinaculum, fat pad and capsule produced moderate to severe pain that was accurately localized. The insertion sites onto the tibia and femur of the cruciate ligaments produced poorly localized moderate to severe pain. Slight to moderate poorly localized sensation was produced at the capsular margins. No sensation was detected on the patellar articular cartilage even though asymptomatic grade II and III chondromalacia was noted on the central ridge the patella.

Within the clinical setting, patients often complain of diffuse patellofemoral pain while undergoing physical examination. The results of this study may provide an explanation for the vague description of pain that is often reported by patellofemoral patients; the majority of structures palpated produced poorly localized sensation.

pf cartilage The implications of this are interesting.  It appears that degenerative changes to the patellofemoral joint, or chondromalacia, was not a source of pain.  The author/subject didn’t even know his patella had degenerative changes.  Numerous authors (Chrisman OD: Clin North AM 1986, Dye SF: Orthop Clin North AM 1986, Fulkerson: Disorders of the Patellofemoral Joint 2004 – as an aside, this may be a glitch but this is a great book by Fulkerson and listed at $2.76 on Amazon right, now, follow the link to purchase…) have also documented that patellofemoral chondromalacia does not necessarily produce patellofemoral pain. Based on the results of these studies, it appears that the majority of patellofemoral symptoms may be originating from the anterior synovial tissues, retinaculum, fat pad and capsule, rather than from degeneration of the patellofemoral articular surfaces.

It appears that the majority of patients complaining of patellofemoral pain originates from the surrounding soft tissues and not from the osseous or articular cartilage structures.

Furthermore, several authors have also postulated that patellofemoral pain may originate in the lateral retinacular soft tissues. Fulkerson et al (Clin Orthop 1985) performed a histological analysis on lateral retinacular and underlying synovial tissue of patellofemoral patients biopsied during lateral retinacular releases. These biopsies were compared to cadaveric specimens and biopsies taken from asymptomatic, non-patellofemoral patients undergoing surgery to address anterolateral rotary instability. Nerve fibers originating in the lateral retinaculum appeared enlarged with moderate lose of myelinated fibers in the patellofemoral patient. The authors state that nerves within the retinaculum may degenerate from the chronic stretching associate with muscular imbalances around the patellofemoral joint and present as a potential source of patellofemoral pain.

image Sanchis-Alfonso et al (AJSM 1998) biopsied the lateral retinaculum of patients undergoing a lateral retinacular release to address patellofemoral complaints. The authors found neuromas within the biopsied tissues similar to the results of Faulkerson et al (Clin Orthop 1985). The authors reported a direct relationship between the severity of pain and the severity of neural damage within the lateral retinaculum; patients presenting with moderate to severe complaints of pain were found to have the highest number of nerves and neural area. These findings were further supported in a follow-up study by Sanchis-Alfonso and Rosello-Sastre (AJSM 2000). The authors repeated the prior experiment, noting similar results with the additional finding of increased levels of substance P within the lateral retinaculum of patellofemoral patients.

Thus it appears that the source of pain in patellofemoral patients is multifactoral, with the surrounding soft tissues showing evidence of localized pain perception and neural adaptations that appear to contribute to the source of patellofemoral pain.

Have you found that the majority of your patients have vague and diffuse pain?  I’ve had patients with pretty severe changes to their patella and trochlea, what do you think about degenerative changes NOT being associated with patellofemoral pain?  Is this always true?

Continue on to Part 3: Classification and differential diagnosis of patellofemoral pain.

Dye SF, Vaupel GL, Dye CC. (1998). Conscious neurosensory mapping of the internal structures of the human knee without intraarticular anesthesia. Am J Sports Med DOI: 9850777

11 replies
  1. Jordan
    Jordan says:

    Also, from what I have researched it is probably a combination of running on uneven surfaces, weak ankles, weak leg muscles, and definitely overuse of knees on that day being the main cause. Also the pain, when I do have it is usually on the front or above the knee cap for both knees and inside of knee for only the left knee. Also my knees feel numb throughout most of the day.

  2. Jordan
    Jordan says:

    Mike, back in September/October of 2013 I went and ran 3 miles and biked around 15 miles on the same day. (I had been running about 2/3 miles once or twice a week for 4 or 5 weeks before this.) Immediately after I got off my bike I could barely walk. My knee or kneecaps felt really really weird and for the next couple weeks I could hardly walk. My knees have felt weird ever since. My knees would give out sometimes and would like would catch/click when I bent them or twisted my body. They were getting a little better but still felt weird. I stopped all physical activity other than walking. On Christmas I ran around a little bit with my dogs just back and forth in the yard and for the whole next couple weeks they felt weird especially when I bent or twisted my body. They feel weird and hurt some too especially if my knees bend all the way or when straightening them out like for a hurdler stretch. My left one still catches/clicks when I bend it. I feel pressure when my knee are bent. My kneecaps hurt if I press into them. Also it feels really weird and almost hurts when I try to run or jump at all. I’m 24, at healthy weight and have always played sports. Only other medical history is that I have rolled both of my ankles in the past couple years, not at the same time. I have never had an injury before in my life other than the ankle sprains a couple years ago. What do u think I have? What home treatment would you advise? I just want to get back to playing sports and being active in order to help people learn about God through physical activity and wellness. Thank you, in advance.

  3. Anonymous
    Anonymous says:

    I have had patellar femoral syndrome and I was told it was because I had a tight lateral retinaculum and a weak VMO. The doctor said that my knee cap wasn't in the groove and my pattelar was causing lateral tracking. If this is so then why was I having medial knee pain? If my patellar is laterally tracking then shouldn't I have had lateral knee pain?

  4. Anonymous
    Anonymous says:

    hi, im 10wks post lateral release, realignment, tracking etc on knee , still sore when bending, squatting, walking and getting up from chair, was told recovery was 12wks also ive got bursa on hip same side and alot of pain with sacroiiliac muscle on otherside , this been going on for a year but apparently its cos im compensating for my prob knee before i got it done , what do you think

  5. Lenny M. MSPT, SCS, CSCS
    Lenny M. MSPT, SCS, CSCS says:

    remember why surgeons do the microfracture procedure in the first place. It’s not the cartilage that is causing the pain response, it’s the exposed subchondral bone that no longer has its force dissipators (articular cartilage, sufficient quad strength, possible biomechanical malalignment). Placing a layer of fibrocartilage (although inferior in strength to hyaline cartilage) may help alleviate the symptoms short term.

  6. Larry
    Larry says:

    As you go through your series of posts, it will be interesting to hear how (if any) your thoughts change as you read through Stecco’s book/articles.

  7. Mike Reinold
    Mike Reinold says:

    To answer Amy’s question, microfracture can be appropriate if used on the correct patient. Compare these two scenarios:

    1. Patient 1 has vague anterior knee pain with no specific increase in symptoms during functional activities. Symptoms have not resolved with PT for taping, VMO training, and stretching (shocker…). Ends up having arthroscopy that shows a grade III lesion to the patella. Undergoes microfracture.

    2. Patient 2 has been having knee pain when squatting past 60 degrees while at work. Symptoms gradually worsened over the last 2-3 years and is becoming difficult to work. PT helps but when they go back to work symptoms slowly come back, even though they are doing their home exercise program emphasizing VMO (sorry I had to throw that in again…). Physician performs arthroscopy and finds a small but focal 1cm x 2cm grade IV defect on trochlea in a spot that articulates with the patella at 60 degrees of knee flexion. Undergoes microfracture.

    See the difference? Treating the PF joint is often difficult because it is hard to accurately diagnose the true source of symptoms. This is why i believe that our treatments are often unsuccessful and patellofemoral pain is so challenging to improve, sometimes we are not treating the cause!

    Obviously, much more to come on this in future posts but I am liking the discussion on this series already!

  8. Mike Reinold
    Mike Reinold says:

    That is right Nolan and exactly why I posed that question at the end of the post! There are patients that will have a grade IV articular cartilage defect that will have PF pain, no doubt.

    The differential diagnosis invovles identifying a specific mechanical symptom during a specific activitiy, such as squatting to a certain depth as you mentioned.

    This is the first critical component to understand when treating the PF joint. Not all patients have “chondromalacia.” Many will have vague anterior knee pain from the surrounding soft tissue. These are probably the patients that don’t always respond to certain treatments and exercise. Differentiating between those with vague discomfort with someone that has pain precisely with any squatting past 70 degree of knee flexion is the first step in diagnosing and treating.

    Great thought Nolan! Thanks for commenting.

  9. Nolan Williams
    Nolan Williams says:

    Correct me if I’m wrong, but aren’t the high joint reaction forces that occur within the patellofemoral joint during activities such as squatting much different than the forces delivered when just palpating the joint with a probe????

  10. amy castillo
    amy castillo says:

    If the patellar surface is not a significant pain contributor…. Is patellar/trochlear micofracutre appropriate?

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