Can a previous patellar fracture lead to degenerative arthritis in the knee?

Can a Previous Patellar Fracture Lead to Degenerative Arthritis in the Knee?

Yes, a previous patellar fracture significantly increases the risk of developing degenerative arthritis in the knee, with patients facing an 83% increased risk of knee arthroplasty compared to those without a prior patellar fracture. 1

Evidence for Post-Traumatic Osteoarthritis Risk

Patellar fractures are definitively associated with subsequent knee osteoarthritis development. The most compelling evidence comes from a large Danish national cohort study of 6,096 patients with patellar fractures followed for a mean of 14.3 years, which demonstrated:

• Patients with patellar fractures had a hazard ratio of 1.83 (95% CI 1.57-2.13) for developing knee arthroplasty compared to matched controls without fractures 1
• The risk was highest in the first five years post-fracture (HR 3.02,95% CI 2.26-4.03), but remained elevated lifelong 1
• Patients also faced nearly 4 times higher risk of requiring knee arthroscopy (HR 3.94,95% CI 3.49-4.46) 1

This aligns with broader evidence showing that fractures represent one of several single-structure knee injuries that increase the odds of symptomatic osteoarthritis with moderate-certainty evidence 2, 3.

Mechanisms of Arthritis Development

The pathway from patellar fracture to osteoarthritis involves multiple factors:

• Failure to restore anatomical articular surface contour results in posttraumatic arthritis 4
• Any step-off greater than 2-3 mm or displacement exceeding 1-4 mm disrupts normal joint mechanics and should be treated surgically to minimize arthritis risk 4
• Even with optimal surgical treatment, residual cartilage damage and altered biomechanics contribute to progressive degeneration 5

Clinical Implications for Patient Counseling

Patients must be informed that patellar fractures carry a lifelong increased risk of knee arthroplasty, not just a short-term complication 1. This is particularly important because:

• Post-traumatic OA accounts for approximately 12% of all OA cases globally (36 million people), with the knee being the most commonly affected joint 2, 3
• Painful and functional complications including knee stiffness, loss of extension, and patellofemoral osteoarthritis can be very disabling and compromise return to professional or recreational activities 4

Treatment Considerations to Minimize Arthritis Risk

Anatomical reconstruction of the articular surface is the only way to prevent development of posttraumatic osteoarthritis 4. Specific treatment principles include:

• Surgical treatment is recommended for fractures with >2-3 mm step-off or >1-4 mm displacement, or those disrupting the extensor mechanism 4
• Undisplaced fractures with intact extensor mechanism can be treated conservatively 4
• Pre-operative CT scanning should be strongly considered, as it frequently modifies both classification and treatment choice by revealing fracture complexity not apparent on plain radiographs 4

Prevention Strategies Post-Fracture

In the absence of high-certainty evidence for modifiable risk factors after traumatic knee injury, prevention efforts should focus on addressing modifiable risk factors for non-traumatic OA 2, 3:

• Minimize unhealthy adiposity through weight management programs 2
• Address quadriceps weakness through structured strengthening exercises 2
• Implement evidence-based injury prevention programs to avoid additional trauma 2

Common Pitfalls

The consequences of patellar fractures are more severe than historically considered 1. Clinicians should avoid:

• Underestimating the long-term arthritis risk when counseling patients about prognosis 1
• Accepting inadequate articular surface reduction, as even minor step-offs lead to accelerated degeneration 4
• Relying solely on plain radiographs for surgical planning without considering CT when fracture complexity is suspected 4