Patellofemoral pain syndrome (PFPS) is a very common cause of anterior knee pain in the pediatric and adult population. PFPS is also known as runner's knee; however, most people who develop PFPS are not, in fact, runners. The exact etiology of the pain is unknown, but PFPS is thought to be due to abnormal tracking of the patella during knee range of motion. PFPS is typically treated initially with a trial of physical therapy.
Symptoms
Symptoms of patellofemoral pain syndrome include pain around or under the patella (knee cap). Typically, the pain is worse when going up or down stairs, kneeling, squatting or sitting with a bent knee for an extended duration of time.
Risk Factors
According to Waryasz's 2008 review article on PFPS, the potential risk factors include weakness in functional testing of the lower extremity musculature, tightness of the calves, hamstrings, quadriceps or iliotibial band, generalized ligamentous laxity, deficient strength of the hips, quadriceps or hamstrings, a Q-angle in excess of 20 degrees, contraction dysynchrony between the quadriceps muscles and a patellar tilt. These risk factors have been studied in limited studies, however. More research is needed to clearly define what exactly predisposes an individual to PFPS.
Physical Exam Findings in PFPS
The physical examination of the knee is a very important diagnostic test for PFPS. PFPS can occur in conjunction with other knee pathologies which can make the diagnosis difficult or often overlooked. Common findings on physical exam include tenderness with palpation of the lateral patella and pain with range of motion of flexion and extension of the knee. The patella will deviate during flexion/extension to give a "J sign" when there is tightness of the lateral soft tissues. Patients with isolated PFPS will not have pain over the patellar tendon or over the joint line. Ligaments should be intact on examination.
Imaging and PFPS
Physicians will order plain x-rays of the knee. A sunrise view of the knee can be obtained. This view allows the physician to see how well the patella is aligned in the trochlear groove. The trochlear groove refers to the surface of the femur where the patella tracks during movement. The patella often will be deviated laterally in PFPS, suggesting that the lateral soft tissue structures are tight.
Some clinicians will order sequential CT scan images to visualize exactly what the relationship of the patella is to the femur in different anatomic positions. The role of MRI can be to help delineate if there are changes suggestive of patellofemoral arthritis due to chronic misalignment.
Treatment
Treatment with physical therapy for isolated PFPS is successful when continued in approximately two-thirds of patients. The exercises are typically aimed at strengthening the quadriceps. Tyler reported in 2006 that there are significant hip strength deficiencies in patellofemoral pain syndrome. More revised physical therapy programs have incorporated more hip stretches and strengthening exercises to create a more balanced lower body.
Surgical treatment may be indicated when physical therapy fails. A lateral release procedure involves decreasing the lateral pull on the patella by the lateral retinaculum (lateral soft tissues) by making in incision through some of the layers of the retinaculum.
The tibial tubercle transfer procedures involve realigning the patella by transferring the tibial tubercle with the intact patellar tendon. The goal of these procedures are to reduce the abnormal contact forces on the patella by attempting to correct the anatomic alignment.
References
- "Am J Sports Med"; The Role of Hip Muscle Function in the Treatment of Patellofemoral Pain Syndrome; TF Tyler et al; 2006
- "Am J Phys Med and Rehab" Physical Examination and Patellofemoral Pain Syndrome; M Fredericson and K Yoon; 2006
- Dynamic Medicine: Patellofemoral Pain Syndrome (PFPS)
