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

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