Purpose: A long spinal fusion across the thoracolumbar region is sometimes applied in scoliosis. Adjacent level degeneration below these constructs has been documented. Treatment with an artificial disc replacement below the fusion has been proposed to prevent degeneration there. There is currently little data detailing the expected biomechanics of this situation. The objective of this study was to evaluate range of motion (ROM) and helical axis of motion (HAM) changes due to one- and two-level Maverick total disc replacement adjacent to a long spinal fusion.

Method: A multidirectional flexibility testing protocol with compressive follower preload was used to test seven human cadaveric spine specimens (T8-S1). A continuous pure moment ±5.0 Nm was applied in flexion-extension (FE), lateral bending (LB) and axial rotation (AR), with a compressive follower preload of 400 N. The motion of each vertebra was monitored with an optoelectronic camera system. The test was completed for the intact condition and after each surgical technique:

T8-L4 fusion and facet capsulotomy at L4–L5 and L5-S1;

Maverick total disc replacement and fusion with the CD Horizon system was performed. Repeated measures ANOVA was used to analyze changes in ROM and HAM of the L4–L5 and L5-S1 segments.

Results: Following L4-L5 Maverick replacement, L4-L5 ROMs tended to decrease slightly (on average from 6.2°±2.8° to 5.1°±3.8° in FE, 1.1°±1.1° to 0.9°±0.5° in LB and 1.3°±0.9° to 1.0°±0.6° in AR). With two-level Maverick implantation, L5-S1 ROMs tended to increase slightly in FE (from 6.6°±2.6° to 7.1°±3.9°), and to decrease slightly in LB (from 1.5°±0.9° to 1.0°±0.3°) and AR (from 1.5°±1.5° to 1.1°±0.6°), compared to the fused condition. As a trend, HAM location shifted posteriorly in FE and AR, and inferiorly in LB following Maverick replacement. However, neither ROM nor HAM at these two segments showed any significant change due to the implantation of one-or two-level Maverick total disc replacement in any of the three directions.

Conclusion: The present results suggested that lower lumbar segments with Maverick disc replacement exhibited intact-like kinematics in both extent and quality of motion.

Testing of cadaver ankle specimens was conducted to investigate the changes in kinematics with lateral ligament reconstructions. Testing included an intact condition, after injury at the ATFL and CFL sites, and separately a Brostrom repair and an anatomical gracil-lis graft reconstruction. Calcaneal range of motion was determined about the axis of applied moment in plantarflexion-dorsiflexion and in inversion-eversion directions. The injury and reconstructions were most sensitive during IE applied moment. Both reconstructions appeared to behave similar to intact motion. Failure of some Brostrom repairs however, suggest that the gracillis-graft reconstruction is initially a stronger repair.

Limited research has biomechanically investigated lateral ankle ligament reconstruction procedures. The objective of this study was to determine the changes in ankle kinematics with a dual ligament Brostrom repair and an anatomical gracillis graft reconstruction.

Seven cadaveric ankle specimens were tested independently in an intact condition, after an ATFL/CFL injury model, and two reconstructions. The anatomical graft reconstruction wove a gracillis tendon through the calcaneus and fibula to dually reconstruct the ATFL and CFL, and anchored to the talus. Moments were applied to the calcaneus for three cycles in plantarflexion-dorsiflexion (PD) and inversion-eversion (IE) while allowing unconstrained motion. Three dimensional motions of the calcaneus and tibia were optoelectronically tracked. Range of motion (ROM) was calculated about the axis of applied moment for the calcaneus with respect to the tibia.

The ROM increase from the intact condition with the injury model was only significant for IE (p=0.001). No significant differences were found between intact and any treatments in the PD configuration. In IE, both the graft reconstruction and the Brostrom repair were significantly different from the injury model (p=0.002 and p=0.015 respectively), where the gracillis reconstruction appears more similar to the intact condition. For two specimens the Brostrom repaired ATFL failed during applied inversion moment.

The injury and reconstructions were most sensitive during IE applied moment. Both reconstructions appeared to behave similar to the intact condition. Failure of some Brostrom repairs however, suggest that the gracillis-graft reconstruction is initially a stronger repair.

Funding: Workers Compensation Board of British Columbia