[Stability of ventral, dorsal and combined spondylodesis in vertebral body prosthesis implantation]. / Stabilität ventraler, dorsaler und kombinierter Spondylodesen beim Wirbelkörperersatz.

The purpose of this study was to evaluate the biomechanical characteristics of short-segment anterior, posterior, and combined instrumentations in lumbar spine vertebral body replacement surgery. Eight fresh frozen human cadaveric thoracolumbar spine specimens (T12-L4) were prepared for biomechanical testing. Pure moments (2.5, 5, and 7.5 Nm) of flexion-extension, left-right axial torsion, and left-right lateral bending were applied to the top vertebra in a flexibility machine and the motions of L1 vertebra with respect to L3 were recorded with an optoelectronic motion measurement system after preconditioning. One anterior, two posterior pedicle screw systems, and two combined instrumentations were tested. Load-displacement curves were recorded and neutral zone (NZ) and range of motion (ROM) were determined. The anterior instrumentation, after vertebral body replacement, showed greater motion than the intact spine, especially in axial torsion. Posterior instrumentation provided greater rigidity than the anterior instrumentation, especially in flexion-extension. The combined instrumentation provided superior rigidity in all directions compared to all other instrumentations.

Capsular ligament stretches during in vitro whiplash simulations.

Clinical symptoms of whiplash are presently not well understood. Injuries to capsular and other spinal ligaments of the cervical spine during trauma are a possible pathomechanism that could explain some aspects of the whiplash symptom complex. This study quantified the elongations of capsular ligaments (CLs) at all cervical spinal levels during whiplash simulation using an in vitro model. Seven fresh human cadaveric specimens (occiput-C7 or T1) were carefully dissected, preserving the osteoligamentous structures. Spinal ligament transducers were attached across the CLs from C2-C3 to C6-C7 in each specimen, alternating the two sides. Physiological elongations of the CLs were measured with a standard flexibility test using 1 Nm of pure moments. Next, the specimen was fitted with a surrogate head representing 50th percentile human head. The specimen was mounted on a sled designed to simulate whiplash and subjected to 2.5, 4.5, 6.5, 8.5, and 10.5 g (1 g = 9.81 m/s2) horizontal accelerations sequentially. The dynamic elongations of the CLs were continuously recorded during the entire trauma and were later converted to strains. There were modest increases in capsular ligament strains during the trauma over the maximum physiological values. The two largest peak strains of 29.5 and 35.4% were seen at C6-C7 during the 6.5- and 10.5-g accelerations. We did not find strong correlation between the strain during the trauma and the trauma sled acceleration.

Stability potential of spinal instrumentations in tumor vertebral body replacement surgery.

STUDY DESIGN: The multidirectional stability potential of anterior, posterior, and combined instrumentations applied at L1-L3 was studied after L2 corpectomy and replacement with a carbon-fiber implant. OBJECTIVES: To evaluate the biomechanical characteristics of short-segment anterior, posterior, and combined instrumentations in lumbar spine tumor vertebral body replacement surgery. SUMMARY OF BACKGROUND DATA: The biomechanical properties of many different spinal instrumentations have been studied in various spinal injury models. Only a few studies, however, investigate the stabilization methods in spinal tumor vertebral body replacement surgery. METHODS: Eight fresh frozen human cadaveric thoracolumbar spine specimens (T12-L4) were prepared for biomechanical testing. Pure moments (2.5 Nm, 5 Nm, and 7.5 Nm) of flexion-extension, left-right axial torsion, and left-right lateral bending were applied to the top vertebra in a flexibility machine, and the motions of the L1 vertebra with respect to L3 were recorded with an optoelectronic motion measurement system after reconditioning. The L2 vertebral body was resected and replaced by a carbon-fiber cage. Different fixation methods were applied to the L1 and L3 vertebrae. One anterior, two posterior, and two combined instrumentations were tested. Load-displacement curves were recorded and neutral zone and range of motion parameters were determined. RESULTS: The anterior instrumentation provided less potential stability than the posterior and combined instrumentations in all motion directions. The anterior instrumentation, after vertebral body replacement, showed greater motion than the intact spine, especially in axial torsion (range of motion, 10.3 degrees vs 5.5 degrees; neutral zone, 2.9 degrees vs. 0.7 degrees; P < 0.05). Posterior instrumentation provided greater rigidity than the anterior instrumentation, especially in flexion-extension (range of motion, 2.1 degrees vs. 12.6 degrees; neutral zone, 0.6 degrees vs. 6.1 degrees; P < 0.05). The combined instrumentation provided superior rigidity in all directions compared with all other instrumentations. CONCLUSIONS: Posterior and combined instrumentations provided greater rigidity than anterior instrumentation. Anterior instrumentation should not be used alone in vertebral body replacement.

[Robot-assisted knee endoprosthesis]. / Roboterunterstützung in der Knieendoprothetik.

With the development of powerful computer systems, computer-assisted medical diagnosis and therapy have become common over the last 10 years. Even in the surgical field, computer- and robotic-assisted techniques are becoming practical but are not yet used on a daily basis. In the orthopaedic field, computer and robotic assistance is used in planning and performing demanding three-dimensional osteotomies, setting pedicle screws in the spine and milling the femoral medullary canal in total hip replacement. This article introduces a computer- and robotic-assisted system for performing arthroplasty in total knee replacement procedures.