Quadriceps tendon with a patellar bone block may be a viable alternative to Achilles tendon for anterior cruciate ligament reconstruction (ACL-R) if it is, at a minimum, a biomechanically equivalent graft. The objective of this study was to directly compare the biomechanical properties of quadriceps tendon and Achilles tendon allografts. Quadriceps and Achilles tendon pairs from nine research-consented donors were tested. All specimens were processed to reduce bioburden and terminally sterilized by gamma irradiation. Specimens were subjected to a three phase uniaxial tension test performed in a custom environmental chamber to maintain the specimens at a physiologic temperature (37 ± 2 °C) and misted with a 0.9 % NaCl solution. There were no statistical differences in seven of eight structural and mechanical between the two tendon types. Quadriceps tendons exhibited a significantly higher displacement at maximum load and significantly lower stiffness than Achilles tendons. The results of this study indicated a biomechanical equivalence of aseptically processed, terminally sterilized quadriceps tendon grafts with bone block to Achilles tendon grafts with bone block. The significantly higher displacement at maximum load, and lower stiffness observed for quadriceps tendons may be related to the failure mode. Achilles tendons had a higher bone avulsion rate than quadriceps tendons (86 % compared to 12 %, respectively). This was likely due to observed differences in bone block density between the two tendon types. This research supports the use of quadriceps tendon allografts in lieu of Achilles tendon allografts for ACL-R.

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Subsidence is a type of failure associated with implanted cervical cages or artificial intervertebral discs. It is defined as a loss of postoperative disc height. Actuarial rates show a risk of subsidence at 16 weeks at 70.7 percent. This study examines the changes in the vertebral endplate morphology and the resulting effect on the stresses developed in the endplate and in the vertebral core. A three-dimensional linear elastic model was created from computed tomographic (CT) scans and material properties were assigned according to various studies. Particular care was taken in the superior endplate that was modeled according to experimental measurements. Von Mises stress values were examined in the vertebral endplates and the cancellous core. The stresses were the result of a static load analysis. The stresses analyzed comparing a model with an idealized half-millimeter endplate to anthropometrically based models see if the half-millimeter thick endplate is an adequate approximation. The stresses in the cancellous core were measured at various levels to see how stress propagated through the core with the adjustment of the endplate. The core stresses were investigated to identify regions of potential failure. Ideally this information would be used to improve intervertebral device design.

The cervical region of the spine is the superiorly located vertebrae that make-up the neck. Like the thoracic and lumbar vertebrae, it is prone to diseases. The geometry of the vertebral bodies is both intricate and delicate as it includes bony and soft tissue musculature. The cervical vertebrae protect the spinal cord while maintaining flexibility and allowing movement in all directions. Institutional Review Board approval was obtained to access patient charts, computed tomography (CT), and limited magnetic resonance imaging (MRI) data. 15 finite element (FE) models were developed from various CT/MRI images. The FE models were homogenous, continuum, linear elastic models that were separated into two hierarchical structures. A comparison was made between a degenerated disc model and a model that considers a disc replacement with various materials used in artificial disc replacement devices. The models were loaded with 2% global strain and analyzed for maximum and minimum principal strains. Strain was analyzed because its uniformity is independent of anatomical position. Yield strain was used as an indicator of failure initiation in the vertebral bodies with benchmark values of 400 and −450 × 10 −6 for max and min principal strains, respectively. The results of this FE study show that failure based on yield criteria initiates in the trabecular core, which had higher strain levels than that of the cortical shell. It also indicates that the introduction of the much stiffer disc replacement material increases the strain values of the vertebral bodies by approximately ten times. This information will be important in the development of devices in identifying regions of failure initiation and how endplate materials affect the failure and subsidence of the vertebral bodies.