In vitro and in vivo mechanical properties of human ulnar and median nerves.

Peripheral nerves are often subjected to mechanical stretching, which in excess results in various degrees of impairment of their function. An understanding of the biomechanical behavior of peripheral nerves is important to the prevention of nerve injury during surgical manipulation. Here, in vitro mechanical properties and viscoelastic behavior of human ulnar/median nerves were measured with a tensile tester.

Cumulative multiple freeze-thaw cycles and testing does not affect subsequent within-day variation in intervertebral flexibility of human cadaveric lumbosacral spine.

Study Design: An in vitro biomechanical study on 3-dimensional flexibility of human lumbosacral motion segments after multiple freeze-thaw cycles and cumulative testing.

Objective: To determine the significance of multiple freeze-thaw cycles and extended testing duration on between-day and within-day variations in motion segment flexibility.

Summary Of Background Data: Previous studies have found no significant effect of single freeze-thaw cycle on creep behavior of human spinal motion segments.

Local autograft retrieval from a cervical vertebral body: biomechanical consequences.

Object: To avoid the cost of bone graft substitutes and the morbidity of iliac crest bone graft retrieval, locally harvested vertebral body bone has been used to fill interbody cages. When marginal hypertrophic osteophytes are used, there is little impact on the adjacent vertebrae, but when cancellous bone is removed from the central part of the vertebral body, it is not clear how significantly this procedure weakens the vertebra. The objective of this study was to investigate the immediate mechanical response of the cervical spine after removing bone from the central vertebral body.

The effect of tibial tuberosity realignment procedures on the patellofemoral pressure distribution.

Purpose: The study was performed to characterize the influence of tibial tuberosity realignment on the pressure applied to cartilage on the patella in the intact condition and with lesions on the lateral and medial facets.

Methods: Ten knees were loaded in vitro through the quadriceps (586 N) and hamstrings (200 N) at 40°, 60°, and 80° of flexion while measuring patellofemoral contact pressures with a pressure sensor. The tibial tuberosity was positioned 5 mm lateral of the normal position to represent lateral malalignment, 5 mm medial of the normal position to represent tuberosity medialization, and 10 mm anterior of the medial position to represent tuberosity anteromedialization.

Oblique lumbar interbody fixation: a biomechanical study in human spines.

Study Design: In vitro spine biomechanics.

Objective: To determine the biomechanical properties of oblique lumbar interbody fixation (OLIF) in human cadaveric spines.

Summary Of Background Data: OLIF has been used for stabilization of degenerative spondylolisthesis at the lumbosacral junction.

The difference in spine specimen dual-energy X-ray absorptiometry bone mineral density between in situ and in vitro scans.

Background Context: Human cadaveric specimens are commonly used to evaluate bone-implant interface strength in osteoporotic spine fixation. Dual-energy X-ray absorptiometry (DXA) scans are usually carried out on explanted spine specimens to measure bone mineral density (BMD) before in vitro biomechanical studies are carried out.

Purpose: The purposes of this study were to verify and quantify the difference in DXA BMD between unexplanted (in situ) and explanted (in vitro) scans and to develop and validate a correction factor (CF) between in vitro and in situ DXA BMD.

The effect of cement augmentation and extension of posterior instrumentation on stabilization and adjacent level effects in the elderly spine.

Study Design: An in vitro cadaveric study comparing different implant fixation techniques using a repeated measures design.

Objective: To compare the effects of cement augmentation of pedicle screws and extension of posterior fixation on (i) 3-dimensional stabilization, and (ii) adjacent level effects in the aging spine.

Summary Of Background Data: Device loosening and adjacent level effects are concerns in implant fixation in the elderly spine.

Cement augmentation of vertebral screws enhances the interface strength between interbody device and vertebral body.

Study Design: An in vitro cadaveric study comparing cage-vertebra interface strengths for 3 different screw-cement configurations.

Objectives: To determine the effects of cement augmentation of pedicle screws on cage-vertebra interface failure properties for 2 interbody device shapes (elliptical or cloverleaf); and to compare between pedicle and anterior vertebral body screws with cement augmentation.

Summary Of Background Data: Pedicle or anterior screw fixation is commonly used with interbody device fixation.

The effect of interbody cage positioning on lumbosacral vertebral endplate failure in compression.

Study Design: A biomechanical investigation using a human cadaver, multisegmental lumbosacral spine model.

Objectives: To determine if 2 small, posterolaterally positioned titanium mesh interbody cages would provide superior construct strength and stiffness in compression compared to central cage placement. In addition, determine construct stiffness with interbody cages as opposed to an intact spine and assess the effect of bone mineral density (BMD).

Wrist impact velocities are smaller in forward falls than backward falls from standing.

The wrist is a common fracture site for both young and older adults. The purpose of this study was to compare wrist kinematics in backward and forward falls with different fall protective responses. We carried out within-subject comparison of impact velocities and maximum velocities during descent of the distal radius among three different fall configurations: (a) backward falls with knees flexed, (b) backward falls with knees extended and (c) forward falls with knees flexed.

Interbody device shape and size are important to strengthen the vertebra-implant interface.

Study Design: An in vitro cadaveric study to compare compressive failure load, strength, and stiffness of the implant-vertebra interface.

Objectives: To determine the effect of cage shape (kidney, cloverleaf, or oval) and cage surface area on endplate failure strength and secondly to determine the extent and pattern of trabecular failure adjacent to an interbody device.

Summary Of Background Data: Recent studies indicate that the posterolateral and peripheral regions of the endplate are stronger than the central.

Pedicle screw motion in the osteoporotic spine after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement: a comparative analysis.

Study Design: A biomechanical study addressing the motion of pedicle screws in a human cadaveric, osteoporotic spine model.

Objectives: To compare the fixation of pedicle screws in an osteoporotic spine model after augmentation with laminar hooks, sublaminar wires, or calcium phosphate cement and to determine the kinematic patterns of these screws.

Summary Of Background Data: Numerous techniques exist for improving the quality of fixation within the osteoporotic spine, including supplementing the construct with laminar hooks, sublaminar wires, or calcium phosphate cement.