Causes / typical injury mechanism: Traumatic knee arthrotomy is a deep laceration that violates the knee joint capsule and thereby provides a direct line of communication between the external environment and the knee joint.

Classic history and presentation: This injury most commonly presents following motor vehicle accidents (42%) and gunshot wounds (32%). Traumatic knee arthrotomy can also occur due to falls (12%) or stab wounds (7%). In a military setting, blast injury is the most common cause of traumatic arthrotomy.

Prevalence:

• Age – Average age at time of injury is 25 years.
• Sex / gender – Men are more prone to this injury.

Pathophysiology: Wounds that penetrate the knee capsule can result in the potential risk for deep infection and septic arthritis.

Grade / classification system: Typically, traumatic soft tissue wounds of the knee are described based on size, location, and degree of contamination.

Collins and Temple open joint injury classification (1989)

I. Single capsular perforation or laceration without extensive soft tissue injury.
 A. With minimal (< 2 mm step-off or gap; area of comminution < 1 cm²) or no injury to any articular surface.
 B. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to a single articular surface.
 C. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to biarticular surfaces or meniscoligamentous disruption.

II. Single or multiple capsular perforations or lacerations with extensive soft tissue injury.
 A. With minimal (< 2 mm step-off or gap; area of comminution < 1 cm²) or no injury to any articular surface.
 B. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to a single articular surface.
 C. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to biarticular surfaces or meniscoligamentous disruption.

III. Open periarticular fracture with extension through the adjacent intraarticular surface.
 A. With minimal (< 2 mm step-off or gap; area of comminution < 1 cm²) or no injury to any articular surface.
 B. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to a single articular surface.
 C. With significant (> 2 mm step-off or gap; area of comminution > 1 cm²) injury to biarticular surfaces or meniscoligamentous disruption.

IV. Open dislocation or associated nerve or vascular injury requiring repair.