The mechanism of spinal cord injury varies across the human population and this may be important for the development of effective therapies. Therefore, detailed understanding of how variables such as impact velocity and depth affect cord tissue damage is important. Studies have shown an independent effect of impact velocity and depth on injury severity, thereby suggesting importance of the interaction between the two for spinal cord injury. This work examines both the individual and interactive effects of impact velocity and impact depth on demyelination, tissue sparing, and behavioural outcomes in the rat cervical spinal cord. It also aims to understand the contribution of the energy applied during impact, not only the impact factors. Decoupling the effects of these two impact parameters will help to describe the injury mechanism. Maximum principal strain has also been shown to be useful as a predictor for neural tissue damage in vivo and in finite element (FE) models. A better understanding of this relationship with experimental results may help to elucidate the mechanics of spinal cord injury.Summary Statement
Introduction
Spinal flexibility in bending and axial torque has been shown to exhibit very modest changes with advancing disc degeneration. This study is the first to address the possible relationship in pure anterior shear and no clear relationship was observed. Disc degeneration (DD) is a risk factor for low back pain. Stable or unstable spine segments may be treated with an isolated decompression or instrumented stabilization, respectively. The effect of DD on spinal flexibility has been addressed by several groups in bending but not in shear; a highly relevant load direction in the lumbar spine is anterior shear. The objective of our study was to determine the effect of DD on anterior translation and specimen stiffness under shear loading in an Summary Statement
Introduction
This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting. Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured. Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum. The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.
