Subfracture insult to the human cadaver patellofemoral joint produces occult injury

Abstract

The current criterion used by the automotive industry for injury to the lower extremity is based on visible bone fracture. Studies suggest, however, that chronic joint degeneration may occur after subfracture impact loads on the knee. We hypothesized that subfracture loading of the patellofemoral joint could result in previously undocumented microtrauma in areas of high contact pressure. In the current study, seven patellofemoral joints from human cadavers were subjected to impact with successively greater energy until visible fracture was noted. Transverse and comminuted fractures of the patella were noted at 6.7 kN of load. Approximately 45% of the impact energy then was delivered to the contralateral joint. Subfracture loads of 5.2 kN resulted in no gross bone fracture in five of seven specimens. Histological examination of the patellae horizontal split fracture in the subchondral bone, at the tidemark, or at the interface of calcified cartilage and subchondral bone. The trauma appeared predominantly on the lateral facet, adjacent to or directly beneath preexisting fibrillation of the articular surface. Surface fibrillation was noted in histological sections of control patellae (not subjected to impact loading), but occult damages were not observed. Although the mechanism of this occult trauma is unknown, similar damage has been shown to occur from direct shear loading. As these microcracks can potentiate a disease process in the joint, this study may suggest that the current criterion for injury, based on bone fracture alone, is not sufficiently conservative.

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

“…and tissues were procured from donors with no prior history of joint trauma or evidence of advanced joint pathology (areas of denuded bone, advanced chondromalacia, etc.). The baseline health of the articular cartilage was verified by brushing the articular surface with India ink [2]. Specific details of the joint preparation and the test protocol follow earlier studies [2,12].…”

“…The baseline health of the articular cartilage was verified by brushing the articular surface with India ink [2]. Specific details of the joint preparation and the test protocol follow earlier studies [2,12]. Briefly, all specimens included the distal femur and proximal tibia and measured approximately 20 cm long.…”

“…To record the contact area and contact pressure associated with the impact event, a packet of pressure-sensitive film (Prescale, Itochu Int.. Quebec, Canada) was inserted into the joint prior to each impact event through medial and lateral incisions [2]. The filni was encased in two sheets of polyethylene film approximately 0.05 mm thick to prevent exposure to body fluids and help reduce shear loading artifacts [2].…”

“…The filni was encased in two sheets of polyethylene film approximately 0.05 mm thick to prevent exposure to body fluids and help reduce shear loading artifacts [2]. The strips of film were sufficiently long enough to pass through the patellofemoral joint and cover the anterior surface of the patella.…”

“…There have also been a limited number of subfracture studies using human joints impacted at 90" of flexion [2,3]. Unlike the canine studies, the patellae were transversely sectioned for histological analysis, and occult, horizontal microfractures on the medial and lateral facets were documented.…”