Patellofemoral Pain Syndrome (Runner’s Knee)

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Patellofemoral Pain

The term Patellofemoral Pain (PFP) is used to cover a number of conditions that result in pain in the retropatellar and peripatellar regions. It is one of the most common diagnoses for knee conditions seen in clinical practice. It is often seen in athletes who participate in running and kicking sports. While the preferred term is Patellofemoral Pain, other names that are commonly used include Runner’s Knee, Patellofemoral Pain Syndrome, Lateral Facet Compression Syndrome, and Idiopathic Anterior Knee Pain.

The patella is a sesamoid bone that resides within the quadriceps tendon and whose primary function is to improve leverage for knee extension. Correct tracking of the patella within the trochlear groove requires a balance of the forces derived from the quadriceps and other structures including retinaculae, ligaments and bands. Several mechanisms have been proposed to explain the development of Patellofemoral Pain including overuse and overload, biomechanical dysfunction and muscular imbalance.

• Retropatellar or peripatellar pain
• Pain provoked or aggravated by flexion of the knee while weight-bearing such as with squatting, climbing stairs, running or cycling
• Patients may also report pain or stiffness after prolonged sitting with the knee in flexion (“theatre sign” or “movie-goer’s sign”)
• History of repetitive activities that involve knee flexion and extension (e.g., running and kicking sports or cycling)

• Pain on squatting
• Tenderness on palpation of the medial or lateral patellar facets.
• Resisted knee extension may reproduce or aggravate the patient’s pain
• The Patellar Tilt, Eccentric Step, McConnell’s or Waldron’s tests may be positive
• The Clarke’s Sign may be positive
• Performance of the Patellar Apprehension test may cause reproduction of knee pain

PFP is a clinical diagnosis but imaging may be required in the differential diagnosis of other causes of anterior knee pain. Plain radiography can help identify osteoarthritis, patellar fractures, and osteochondritis. Diagnostic Ultrasound is useful to help identify conditions such as Sinding-Larsen-Johansson Disease and Patellar Bursitis. MRI is useful for assessing the condition of the patellar cartilage and in identifying Chondromalacia Patellae.

The following are examples of “red flags” for patients presenting with knee pain:

• History of a significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain
• Unexplained weight loss
• Fever
• Deformity
• Large joint swelling
• Significant loss of range of motion
• Significant neurological impairment
• Severe tenderness on palpation or severe pain with any examination procedure

If any “red flags” are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Anterior Knee Pain Differential Diagnosis

In addition to Patellofemoral Pain, the differential diagnosis of anterior knee pain in adults should include other conditions such as:

• Myofascial pain syndrome involving the vastus medialis or rectus femoris muscles
• Prepatellar bursitis (pain and swelling anterior to the patella)
• Patellar tendinopathy or “Jumper’s Knee” (pain localized to the inferior pole of the patella at the patellar tendon attachment)
• Osgood Schlatter’s disease (pain and swelling over the tibial tuberosity at the insertion of the patellar tendon)
• Fracture of the patella (swelling and localized sharp pain)
• Torn patellofemoral ligament
• Quadriceps injury
• Supra and infrapatellar bursitis