Patellar stress fracture
Distance runner with anterior knee pain.
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Linear hypointensity through the patella in the coronal plane reaches the inferomedial, non-articular cortex, and is surrounded by reactive marrow edema signal in keeping with stress fracture in evolution.
Intrasubstance intermediate signal in the proximal patellar tendon reflects chronic, low grade tendinosis due to repetitive overload/microtrauma. Note that there is no subcortical marrow hyperintensity immediately subjacent to the tendon origin, therefore this does not represent patellar tendinitis (Jumper's knee).
Swelling and edema signal in the quadriceps fat pad suggests overload/impingement. No quadriceps tendinopathy or enthesopathy/enthesitis.
Patellar stress fracture is a rare condition. It has been described in young athletes, patients with cerebral palsy, and following patellar resurfacing surgery.
In the athletic group, onset of pain is gradual and due to chronic overload. This is important to diagnose and treat (primarily through load management), as these will heal with appropriate rest, but could progress to frank fracture if unrecognised.
The radiographic appearance of stress fracture is marked by sclerotic margins, which reflect attempted reparation and osteoblastic activity. Conversely, acute traumatic patellar fractures are marked by lucent fracture margins. It is important to distinguish these entities from bipartite patella.
This case is unusual in that the fracture line is in the coronal plane. Patellar stress fractures are usually transverse, and occasionally longitudinal.
- 1 1. Transverse Stress Fracture of the Proximal Patella: A Case Report. (2016) Medicine. 95 (6): e2649. doi:10.1097/MD.0000000000002649 - Pubmed
- 2. Drabicki RR, Greer WJ, DeMeo PJ. Stress fractures around the knee. (2006) Clinics in sports medicine. 25 (1): 105-15, ix. doi:10.1016/j.csm.2005.08.002 - Pubmed