Flexible growing rods: polymer rods provide stability to -skeletally immature spines

Introduction: Surgical treatments for early onset scoliosis typically require multiple operations and many complications. A more flexible growing rod construct might result in a more flexible spine with fewer complications. Polymer rods (polyetheretherketone, PEEK) are relatively flexible in bending, and therefore might allow for greater range of motion (ROM) during treatment. The purpose of this study was to determine changes in spine ROM after implantation of simulated growing rod constructs with a range of clinically relevant structural properties. Methods: Biomechanical tests were conducted on six skeletally immature porcine thoracic spines (domestic pigs, age 2–4 months, 35–40 kg, T1–T13). Paired pedicle screws were inserted into T3 and T4 proximally, and T10 and T11 distally. Specimens were tested under the following conditions: (i) control, then dual rods of (ii) PEEK (6.25 mm, n = 6), (3) titanium (4 mm, n = 6), and (4) CoCr alloy (5 mm, n = 4). Lateral bending (LB) and flexion--extension (FE) moments of ±5 Nm were applied. Vertebral rotations were measured using video analysis. ROM for the treated region was determined by averaging all maximum side-to-side rotations at each instrumented level. Differences were determined by t-tests and Bonferroni posthoc. Results: In LB, ROM of specimens with PEEK rods was lower than control at each instrumented level. ROM was greater for PEEK rods than both Ti and CoCr at every instrumented level. Mean ROM at proximal and distal uninstrumented levels was lower for PEEK than for Ti and CoCr. In FE, mean ROM at proximal and distal uninstrumented levels was lower for PEEK than for Ti and CoCr. Combining treated levels, in LB ROM for PEEK rods was 35% of control (p \u3c 0.0001) and 270% of CoCr rods (p \u3c 0.05). In FE, ROM for PEEK rods was 27% of control (p \u3c 0.005) and 180% of CoCr rods (p \u3c 0.05). Conclusions: PEEK rods provided increased flexibility versus metal rods, but also significantly greater stiffness than controls. Smaller increases in ROM at proximal and distal adjacent motion segments occurred with PEEK compared with the metal rods, which may decrease probability of junctional kyphosis. This biomechanical feasibility study of flexible polymer rod constructs showed that PEEK rods provided increased flexibility compared with CoCr and Ti rods, but also significantly greater stiffness than uninstrumented controls. Acknowledgments: Surgical technical assistanceby Max F. DeCarvalo MD; student support by Charlotte Schmidlapp Women’s Scholar Program and UC/CCHMC SURF Program

Flexible growing rods: a pilot study to determine if polymer rod constructs may provide stability to skeletally immature spines

Abstract Background Surgical treatments for early onset scoliosis (EOS), including growing rod constructs, involve many complications. Some are due to biomechanical factors. A construct that is more flexible than current instrumentation systems may reduce complications. The purpose of this preliminary study was to determine spine range of motion (ROM) after implantation of simulated growing rod constructs with a range of clinically relevant structural properties. The hypothesis was that ROM of spines instrumented with polyetheretherketone (PEEK) rods would be greater than metal rods and lower than noninstrumented controls. Further, adjacent segment motion was expected to be lower with polymer rods compared to conventional systems. Methods Biomechanical tests were conducted on 6 skeletally immature porcine thoracic spines (domestic swine, 35-40 kg). Spines were harvested after death from swine that had been utilized for other studies (IACUC approved) which had not involved the spine. Paired pedicle screws were used as anchors at proximal and distal levels. Specimens were tested under the following conditions: control, then dual rods of PEEK (6.25 mm), titanium (4 mm), and CoCr (5 mm) alloy. Lateral bending (LB) and flexion-extension (FE) moments of ±5 Nm were applied. Vertebral rotations were measured using video. Differences were determined by two-tailed t-tests and Bonferroni correction with four primary comparisons: PEEK vs control and PEEK vs CoCr, in LB and FE (α=0.05/4). Results In LB, ROM of specimens with PEEK rods was lower than control at each instrumented level. ROM was greater for PEEK rods than both Ti and CoCr at every instrumented level. Mean ROM at proximal and distal noninstrumented levels was lower for PEEK than for Ti and CoCr. In FE, mean ROM at proximal and distal noninstrumented levels was lower for PEEK than for metal. Combining treated levels, in LB, ROM for PEEK rods was 35% of control (p<0.0001) and 270% of CoCr rods (p<0.01). In FE, ROM with PEEK was 27% of control (p<0.001) and 180% of CoCr (p<0.01). Conclusions PEEK rods decreased flexibility versus noninstumented controls, and increased flexibility versus metal rods. Smaller increases in ROM at proximal and distal adjacent motion segments occurred with PEEK compared to metal rods, which may help decrease junctional kyphosis. Flexible growing rods may eventually help improve treatment options for young patients with severe deformity.http://deepblue.lib.umich.edu/bitstream/2027.42/134537/1/13013_2015_Article_967.pd

Flexible growing rods: a biomechanical pilot study of polymer rod constructs in the stability of skeletally immature spines

Abstract Background Surgical treatments for early onset scoliosis (EOS) correct curvatures and improve respiratory function but involve many complications. A distractible, or ‘growing rod,’ implant construct that is more flexible than current metal rod systems may sufficiently correct curves in small children and reduce complications due to biomechanical factors. The purpose of this pilot study was to determine ranges of motion (ROM) after implantation of simulated growing rod constructs with a range of clinically relevant structural properties. The hypothesis was that ROM of spines instrumented with polymer rods would be greater than conventional metal rods and lower than non-instrumented controls. Methods Biomechanical tests were conducted on six thoracic spines from skeletally immature domestic swines (35–40 kg). Paired pedicle screws were used as anchors at proximal and distal levels. Specimens were tested under the following conditions: control, then dual rods of polyetheretherketone (PEEK) (diameter 6.25 mm), titanium (4 mm), and cobalt-chrome alloy (CoCr) (5 mm). Lateral bending (LB) and flexion-extension (FE) moments were applied, and vertebral rotations were measured. Differences were determined by two-tailed t-tests and Bonferroni for four primary comparisons: PEEK vs control and PEEK vs CoCr, in LB and FE (α = 0.05/4). Results In LB, ROM of spine segments after instrumenting with PEEK rods was lower than the non-instrumented control condition at each instrumented level. ROM was greater with PEEK rods than with Ti and CoCr rods at every instrumented level. Combining treated levels, in LB, ROM for PEEK rods was 35 % of control (p < 0.0001) and 270 % of CoCr rods (p < 0.01). In FE, ROM with PEEK was 27 % of control (p < 0.001) and 180 % of CoCr (p < 0.01). At proximal and distal adjacent non-instrumented levels in FE, mean ROM was lower for PEEK than for either metal. Conclusions PEEK rods increased flexibility versus metal rods, and decreased flexibility versus non-instrumented controls, both over the entire instrumented segment and at each individual level. Smaller mean increases in ROM at proximal and distal adjacent motion segments occurred with PEEK compared to metal rods, which may help decrease complications, such as junctional kyphosis. Flexible growing rods may eventually help improve treatment options for young patients with severe deformity.http://deepblue.lib.umich.edu/bitstream/2027.42/134642/1/13013_2016_Article_87.pd

Displacements of the menisci under joint load: An in vitro study in human knees

The purpose of this study was to test whether the menisci displace under joint compression combined with internal-external torques and anterior-posterior forces at fixed flexion angles. We further determined differences in displacements between the medial and lateral menisci. Loads were applied to the joint, and joint load and displacements were measured. Meniscal displacements were measured radiographically. With a joint compressive load of 1 kN, internal and external joint rotations caused the lateral meniscus to displace, on average, 0.37 mm deg-1 in the anterior-posterior direction, while the medial meniscus displaced 0.19 mm deg-1. Anterior and posterior joint translation, performed under 1 kN joint compression, caused the lateral meniscus to displace, on average, 0.66 mm mm-1 in the anterior-posterior direction, while the medial meniscus displaced 0.43 mm mm-1. Greater meniscal displacements were found at 15 and 30[deg] flexion than at 0[deg] for the lateral meniscus in internal rotation. Lateral meniscal displacements were larger than those of the medial with posterior tibial translation at full extension and with internal rotation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/31682/1/0000618.pd

13Th International Conference On Conservative Management Of Spinal Deformities And First Joint Meeting Of The International Research Society On Spinal Deformities And The Society On Scoliosis Orthopaedic And Rehabilitation Treatment – Sosort-Irssd 2016 Meeting

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