PATELLOFEMORAL (ANTERIOR) KNEE PAIN
CAUSES OF ANTERIOR KNEE PAIN
Disorders of the patellofemoral joint can present perplexing situations in orthopedics and sports medicine. Despite several years of research and attention to this joint, vague use of the diagnose “patellofemoral pain syndrome” (PFPS) continues to be prevalently used to categorize patients. This is more evident when analyzing the myriad of surgical and rehabilitative interventions that are currently being utilized to alleviate symptoms and restore function in patients whose signs present as patellofemoral (PF) disorder.
A telling article from Dye et al (AJSM 1998) examined the conscious neurosensory mapping of the lead author’s knee during arthroscopy without intraarticular anesthesia (the physician literally had his partner scope his own knee without anesthesia!) The author rated the level of conscious pain on a scale from no sensation to severe pain.
Palpation to the anterior synovial tissues, retinaculum, fat pad and capsule produced moderate to severe pain that was accurately localized. Insertion sites onto the tibia and femur of the cruciate ligaments produced poor localized moderate 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 chondromalica was noted on the patella.
The implications of this study are worth noting. It appears that neither degenerative changes to the PF joint nor chondromalacia, was a source of pain. The author/subject in this research article was not even aware he had degenerative changes.
Patients with PF disorders often report diffuse anterior knee pain while undergoing a physical examination. The results of this study may provide an explanation for the vague description of pain that is often reported by patients; the majority of structures palpated in this study produced poor localized pain. It appears that majority of the pain coming from PF joint is the surrounding soft tissue (synovial tissue, retinaculum, fat pad, and capsule) and not from the osseous or degenerated articular cartilage.
Several authors have performed biopsies of the lateral retinaculum of asymptomatic vs patients undergoing a lateral release of the patella, Fulkerson et al (Clin Orthop 1985), Sanches-Alfonso (AJSM 2000). These authors reported nerve fibers in the lateral retinaculum were enlarged (neuromas) and reported a direct relationship between severity of pain and the severity of neural damage in the retinaculum.
Thus it appears that PF pain is multifactorial, with surrounding soft tissue showing localized pain and neural adaptations that appear to contribute to the source of PF pain.
TREATMENT OF PF DISORDERS
One of the most influential rehabilitation publications of the last 2 decades was presented on the treatment of the PF joint by Wilk, Davie, Mangine, Malone PF Disorders, JOSPT 1998. This manuscript was the first to offer treatment strategies based on specific diagnosis for PF pain. Today, this manuscript still holds insightful value in the rehabilitative orthopedic world.
The most critical component of treating the PF joint is an accurate diagnosis. WPT therapists are dedicated to find the cause of symptoms and the avoidance of “PF Pain” as the diagnosis. Through resources like the one referenced above and several years of experience, it has been proven that using a classification system to group types of diagnoses is most effective in creating better outcomes for patients.
Specific plans of care are developed based on functional movement patterns, impairments and activities that the patient desires to return to. Providing the exhaustive protocols that guide the rehab process is not practical for this review. However, the 10 keys principles of PF treatment can be found below and is a helpful guideline in the development of a personalized plan of care.
1. REDUCE SWELLING
2. REDUCE PAIN
3. RESTORE VOLITIONAL MUSCLE CONTROL
4. EMPHASIZE THE QUAD
5. CONTROL THE KNEE THROUGH THE HIP
6. ENHANCE SOFT TISSUE FLEXIBILITY
7. IMPROVE SOFT TISSUE MOBILITY
8. ENHANCE PROPRIOCEPTION AND NEUROMUSCULAR CONTROL
9. NORMALIZE GAIT
10. GRADUALLY PROGRESS BACK TO ACTIVITIES
CLASSIFICATION OF PF PAIN
“PF” pain is a vague diagnosis, therefore, PF pain is now considered an umbrella term. In other words, there are more specific diagnoses that classify more precisely under the general term PF pain disorder. It would be useful to briefly review the specific diagnoses that fall within “PF pain syndrome”.
Patellar compression describes pathologies involving excessive compression between the patella and their trochlea due to tight surrounding soft tissue. These can result in significant changes to the articular surfaces of the patella and trochlea over time. This can be broken down into two distinct type of compression syndromes:
1) EXCESSIVE LATERAL PRESSURE SYNDROME (ELPS)
ELPS defines when the patella is constrained by soft tissue tightness in the lateral retinaculum. There is often more medial discomfort as the medial retinaculum tissue is stretched due to laterally displaced patella. Malalignment in the lower extremities can also lead to this issue and can cause ELPS-like symptoms.
2) GLOBAL PATELLAR PRESSURE SYNDROME (GPPS)
GPPS occurs when there is general diffuse medial, lateral, superior, inferior soft tissue tightness that results in the patella being excessively compressed within the trochlea. This is commonly seen after direct trauma and immobilization.
On the other side of the PF disorder spectrum is patellar instability, which can range from an acute dislocation to recurrent instability. On examination, the patient will have excessive patellar mobility laterally. This is often associated with a shallow trochlea. Acute episodes may result in rupture of the medial PF ligament (MPFL) and subsequent medial knee pain. Diagnostically, a clinician can perform a lateral patellar glide at 0 degrees of flexion and then again at 30 deg of knee flexion. If the patella glides excessively at 30 degrees, it is an indicator that the patient is likely to have a shallow trochlea and poor static stability of the patella.
Biomechanical dysfunction is one of the most significant contributors in the clinic regarding “PF pain”. The knee absorbs significant amounts of stress when biomechanical faults are present both proximally and distally within the lower kinetic chain. Alterations in foot and ankle mechanics, hip strength, leg length discrepancy, flexibility deficiencies, and any combination of these factors can have negative impact on the forces absorbed at the PF joint.
Not only can biomechanical break down lead to increased stress, it can also lead to chronic adaptations in the joint an surrounding soft tissue. For example, someone with weak hip external rotators could be unable to dynamically control the hip adduction and internal rotation moment at the knee causing the femur to rotate into internal rotation during activities. This will cause the patella to shift laterally and can cause articular cartilage changes that will mimic a typical ELPS patient. In this case, stretching the tight lateral tissue will not yield great results for the patient. It is crucial to treat the root of the problem (in this case hip weakness). Otherwise, symptoms and dysfunction will continue to perpetuate and may lead to further disorders.
Since this type of knee pain is more common in females, the researchers tested 33 females with PF pain syndrome. During the first 4 weeks of physical therapy, about half of the patients did exercises that focused on the thigh or quadriceps muscles and soft tissue, while the other half did exercises that focused on the hip muscles. All of these patients then did the same exercises for 4 weeks to improve the strength of the entire leg. The patients’ responses on pain questionnaires and strength tests were used to determine which approach was better. By 4 weeks, the patients in the hip strengthening group had 43% less pain, while the knee strengthening group only had 3% less pain. JOSPT, Volume 41, 8, 2011.
There are multiple pathologies that can occur to the PF joint. The aforementioned considerations are not intended to be all-encompassing. The previously mentioned classifications are designed to create categories of diagnosis that have specific types of treatment guidelines. These guidelines promote optimal outcomes and to get to the root of the knee disorder.
Classifying anterior knee disorders as “PF pain syndrome” is broad and will likely not address specific treatment that would otherwise result in optimal outcomes. Obtaining a clear and accurate differential diagnosis is by far the most important aspect of treating the PF joint. Recently we gathered with all of our doctors of physical therapy to better integrate these clinical gems for better treatment outcomes. We collectively look forward to answering questions and collaborating at high levels in helping your patients return to what they love. Please email firstname.lastname@example.org with any questions or call us at any of our 6 Magic Valley locations.