Injuries produced by blunt trauma to the human patellofemoral joint vary with flexion angle of the knee

Abstract

Patellofemoral joint impact trauma during car accidents, sporting activities, and falls can produce acute gross fracture of bone, microfracture of bone, and soft tissue injury. Field studies of car accidents, however, show that most patellofemoral traumas are classified as 'subfracture' level injuries. While experimental studies have shown that the influence of flexion angle at impact is not well understood, flexion anglc may influence injury location and severity. In the current study, 18 pairs of isolated human cadaver knees were subjected to blunt impact at flexion angles of 60°, 90°, or 120". One knee from each cadaver was sequentially impacted until gross fracture of bone was produced. The contralateral knee was subjected to a single, subfracture impact at 45% of the impact energy producing fracture in the first knee. The fracture experiments produced gross fracture of the patella and femoral condyles with the fracture plane positioned largely within the region of patellofemoral contact. The fracture location and character changed with flexion angle; at higher flexion angles the proximal pole of the patella and the femoral condyles were more susceptible to injury. For the 90" flexion angle, the patella was fractured centrally, while a t 60" the distal pole fractured transversely at the insertion of the patellar tendon. In addition, the load magnitude required to produce fracture increased with flexion angle. i n the 'subfracture' knees, injuries were documented for all flexion angles: occult microfractures of the subchondral and trabecular bone and fissures of the articular surface. Similar to the fracture-level experiments, the injuries coincided with the patellofemoral contact region. These data show that knee flexion angle plays an important role in impact related knee trauma. Such data may be useful in the clinical setting, as well as in the design of injury prevention strategies.

Inhomogeneous Cartilage Properties Enhance Superficial Interstitial Fluid Support and Frictional Properties, But Do Not Provide a Homogeneous State of Stress

“…Donzelli et al also found that changing the curvature of the articular layers influences the patterns of stress distribution, a phenomenon that was not investigated in the current study. In a clinical context it is of importance to note that experimental studies of the impact response of articular cartilage [60,61] have demonstrated that fissures may appear both at the articular surface and at the cartilage-bone interface. This suggests that fissures at the articular surface may occur due to excessive tensile stresses, shear stresses, or strain-energy density, while failure at the cartilage-bone interface may occur due to excessive normal or shear strains [17,62].…”

Two-dimensional strain fields on the cross-section of the human patellofemoral joint under physiological loading

“…The strain distribution across the articular layers under such physiological load magnitudes has not been well described; thus it is unclear whether cartilage strains are on the order of ∼10% or ∼50%, or some other representative value, for normal activities of daily living. Furthermore, it is uncertain whether the greatest strain magnitudes occur near the articular surface or near the cartilage-bone interface; under impact loading, failure of cartilage has been reported at both locations (Atkinson and Haut, 1995; Atkinson and Haut, 2001b; Haut et al, 1995; Thompson et al, 1993). …”

The shock attenuation properties of straight standing knee joints using different shock absorbers and energy inputs

“…Research on the effect of impact loading on the knee joint includes only a few major categories; e.g., local injury mechanics (Radin et al, 1973;Repo and Finlay, 1977;Torzilli et al, 1999;Zhang et al, 1999) and biomechanics of components, such as articular cartilage or subchondral bone, the biological response of lower extremity due to blunt impact loading (Atkinson et al, 2001;Atkinson and Haut, 1995;Atkinson and Haut, 2001a;Atkinson and Haut, 2001b;Donohue et al, 1983;Hurwitz, 1984;Thompson et al, 1991), and global biomechanics such as kinematics and kinetics of total knee joint during impact loading (Chu et al, 1986;Hoshino and Wallace, 1987). Although there are many knee injury studies, how external devices or strategies can help to minimize knee injury from external impact loading has still not been addressed.…”