Experimental constraint can affect injury patterns

in the human knee during tibial-femoral joint loading

The Stapp Car Crash Journal. 45:449-467, 2001.

Jayaraman, VM, Sevensma, ET, Kitagawa, M, Haut, RC.

ABSTRACT:

According to the National Accident Sampling System (NASS), 10% of all automobile accident injuries involve the knee. These injuries involve bone fracture and/or “soft tissue” injury. Previous investigators have determined the tibial-femoral (TF) joint fracture load for a constrained human knee at 90° flexion. However, during automotive accidents, the knee may not be flexed 90° or constrained. It was therefore the objectives of this study to document effects of flexion angle and joint constraint on the nature and severity of knee injuries during TF joint loading.

The effect of flexion angle was examined using 10 unconstrained human knees from 5 cadavers aged 73.2±9.4 years. The joints were loaded in compression using a servo-hydraulic testing machine until gross failure with 60°and 120° flexion. Pressure sensitive film measured the distribution of internal joint loads. All preparations failed by rupture of the anterior cruciate ligament (ACL) at 4.6±1.2 kN, and the internal joint loads were significantly higher (2.6±1.5 kN) on the medial versus the lateral (0.4±0.5 kN) aspect of the tibial plateau.

The effect of anterior-posterior (AP) constraint was investigated in a second series of tests, using the same TF joint loading protocol on 5 pairs of human joints flexed at 90°. The primary mode of failure for the AP constrained joints was fracture of bone via the femoral condyle or in combination with slight ACL tear at a maximum load of 9.7±2.5 kN. The mode of failure for unconstrained joints was primarily due to rupture of the ACL at a maximum load of 6.0±3.2 kN. Again, the pressure film indicated an unequal internal load distribution for the unconstrained knee (medial plateau 5.1±1.4 kN versus lateral plateau 0.8±0.9 kN). However, there was an equal distribution of internal loads between the medial (5.5±1.0 kN) and lateral (3.7±3.2 kN) tibial plateaus in the constrained joints.

This study showed that the mechanism of tibial-femoral knee joint injury and internal joint load distribution depends on the degree of AP constraint offered by the test apparatus. The findings from this study may be useful in understanding the complex interaction between an unconstrained knee and the instrumental panel during automobile crashes. Information from this study will be relevant in optimizing instrumental panel or knee bolster design.

Orthopaedic Biomechanics Laboratories,

College of Osteopathic Medicine,

Michigan State University,

East Lansing, Michigan 48824

Please address correspondence to:

Roger C. Haut, Ph.D.,

Orthopaedic Biomechanics Laboratory,

College of Osteopathic Medicine,

A414 East Fee Hall,

Michigan State University,

East Lansing, MI 48824,

Tel: (517)355-0320,

Fax: (517)353-0789,

E-mail: haut@msu.edu