Iliotibial Band Syndrome
The most likely diagnosis is iliotibial band (ITB) syndrome, given the characteristic presentation of lateral knee pain in a runner with localized tenderness at the lateral femoral epicondyle and pain reproduction at approximately 30 degrees of knee flexion during passive movement.
Clinical Presentation
This patient demonstrates the classic features of ITB syndrome:
- Lateral knee pain that initially occurs near the end of runs but progresses to pain at rest, which is the typical evolution of this overuse injury 1, 2
- Localized tenderness at the lateral femoral epicondyle just above the joint line, which is the pathognomonic finding for ITB syndrome 1, 2, 3
- Pain reproduction at 30 degrees of knee flexion with pressure over the affected area, corresponding to the maximal zone of impingement where the ITB repetitively rubs against the lateral femoral epicondyle 1, 3
Pathophysiology
ITB syndrome is the most common cause of lateral knee pain in runners, resulting from repetitive friction of the iliotibial band over the lateral femoral epicondyle 1, 2. Biomechanical studies demonstrate that maximal impingement occurs at approximately 30 degrees of knee flexion, which explains why this specific angle reproduces the patient's pain 1. The condition represents an overuse injury related to repetitive flexion and extension of the knee during running 2.
Diagnostic Approach
The diagnosis is primarily clinical, based on:
- History of new or increased running activity, which this patient clearly demonstrates 2, 4
- Progressive lateral knee pain that worsens with continued activity 1, 2
- Point tenderness at the lateral femoral epicondyle 1, 2, 3
- Positive provocative testing with pain at 30 degrees of flexion 1
Imaging is typically reserved for recalcitrant cases to rule out other pathology 3. Ultrasound can demonstrate soft-tissue edema or fluid collection between the ITB and lateral femoral epicondyle, though this is not necessary for diagnosis 5, 6.
Important Clinical Pearls
Common pitfall: Do not confuse this with lateral meniscal pathology, which would typically present with joint line tenderness directly at the joint line rather than above it at the epicondyle, and would likely have mechanical symptoms like catching or locking 1, 2.
Risk factors to assess: Weakness or inhibition of the lateral gluteal muscles (particularly gluteus medius) is a causative factor, as these muscles stabilize the pelvis during running 1, 4. Training errors including excessive mileage, downhill running, or running in the same direction on a track contribute to development 1.