An investigation of range of motion preservation in fusionless anterior double screw and cord constructs for scoliosis correction.

PURPOSE: To evaluate the motion-preserving properties of vertebral body tethering with varying cord/screw constructs and cord thicknesses in cadaveric thoracolumbar spines. METHODS: In vitro flexibility tests were performed on six fresh-frozen human cadaveric spines (T1-L5) (2 M, 4F) with a median age of 63 (59-to-80). An ± 8 Nm load was applied to determine range of motion (ROM) in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) in the thoracic and lumbar spine. Specimens were tested with screws (T5-L4) and without cords. Single (4.0 mm and 5.0 mm) and double (4.0 mm) cord constructs were sequentially tensioned to 100 N and tested: (1) Single 4.0 mm and (2) 5.0 mm cords (T5-T12); (3) Double 4.0 mm cords (T5-12); (4) Single 4.0 mm and (5) 5.0 mm cord (T12-L4); (6) Double 4.0 mm cords (T12-L4). RESULTS: In the thoracic spine (T5-T12), 4.0-5.0 mm single-cord constructs showed slight reductions in FE and 27-33% reductions in LB compared to intact, while double-cord constructs showed reductions of 24% and 40%, respectively. In the lumbar spine (T12-L4), double-cord constructs had greater reductions in FE (24%), LB (74%), and AR (25%) compared to intact, while single-cord constructs exhibited reductions of 2-4%, 68-69%, and 19-20%, respectively. CONCLUSIONS: The present biomechanical study found similar motion for 4.0-5.0 mm single-cord constructs and the least motion for double-cord constructs in the thoracic and lumbar spine suggesting that larger diameter 5.0 mm cords may be a more promising motion-preserving option, due to their increased durability compared to smaller cords. Future clinical studies are necessary to determine the impact of these findings on patient outcomes.

Susceptibility to walking balance perturbations in young adults is largely unaffected by anticipation.

Despite progress in understanding the mechanisms governing walking balance control, the number of falls in our older adult population is projected to increase. Falls prevention systems and strategies may benefit from understanding how anticipation of a balance perturbation affects the planning and execution of biomechanical responses to mitigate instability. However, the extent to which anticipation affects the proactive and reactive adjustments to perturbations has yet to be fully investigated, even in young adults. Our purpose was to investigate the effects of anticipation on susceptibility to two different mechanical balance perturbations - namely, treadmill-induced perturbations and impulsive waist-pull perturbations. Twenty young adults (mean ± standard deviation age: 22.8 ± 3.3 years) walked on a treadmill without perturbations and while responding to treadmill belt (200 ms, 6 m/s2) and waist-pull (100 ms, 6% body weight) perturbations delivered in the anterior and posterior directions. We used 3D motion capture to calculate susceptibility to perturbations during the perturbed and preceding strides via whole-body angular momentum (WBAM) and anterior-posterior margin of stability (MoSAP). Contrary to our hypotheses, anticipation did not affect young adults' susceptibility to walking balance challenges. Conversely, perturbation direction significantly affected walking instability. We also found that susceptibility to different perturbation contexts is dependent on the outcome measure chosen. We suggest that the absence of an effect of anticipation on susceptibility to walking balance perturbations in healthy young adults is a consequence of their having high confidence in their reactive balance integrity. These data provide a pivotal benchmark for the future identification of how anticipation of a balance challenge affects proactive and reactive balance control in populations at risk of falls.

A Critical Analysis of Lateral Versus Central Endpoint in Distal Tibia Nailing: Does It Affect Alignment?

OBJECTIVES: To evaluate the effect of a traditional "center-center" end point for distal tibia nailing in comparison with a lateral-of-center end point on fracture malalignment in a cadaver model. METHODS: Nine matched pairs of human cadaveric lower-extremity specimens were used to model the effect of nail end point on fracture alignment in extra-articular distal tibia fractures. After simulation of the fracture through a standardized osteotomy, 1 member of each pair was fixed with an intramedullary nail using a "center-center" end point, whereas a lateral-of-center end point was used for the other member of the pair. Specimens were stripped of soft tissue, and digital calipers were used to measure fracture translation and gap medially, laterally, anteriorly, and posteriorly. Coronal plane angulation at each fracture was measured on the final mortise image. RESULTS: The average coronal angulation was 7.0 degrees of valgus (with a SD of 4.1) in central-end point specimens versus 0.2 degrees of valgus (SD = 1.5) in lateral-end point specimens ( P < 0.001). Lateral-end point specimens also demonstrated significantly less fracture gap medially (mean 0.2 vs. 3.1 mm for central-end point specimens, P < 0.001), anteriorly (mean 0.1 vs. 1.3 mm, P = 0.003), and posteriorly (mean 0.3 vs. 2.2 mm, P = 0.003). Lateral-end point specimens also showed less lateral translation (mean 0.6 vs. 1.6 mm, P = 0.006). CONCLUSIONS: Lateral-of-center nail end points may help surgeons restore native alignment in extra-articular distal tibia fractures and avoid valgus malalignment.