Impaction grafting of lumbar pedicle defects: a biomechanical study of a novel technique for pedicle screw revision.

OBJECTIVE: The two most common revision options available for the management of loose pedicle screws are larger-diameter screws and cement augmentation into the vertebral body for secondary fixation. An alternative revision method is impaction grafting (pedicoplasty) of the failed pedicle screw track. This technique uses the impaction of corticocancellous bone into the pedicle and vertebral body through a series of custom funnels to reconstitute a new pedicle wall and a neomedullary canal. The goal of this study was to compare the biomechanics of screws inserted after pedicoplasty (impaction grafting) of a pedicle defect to those of an upsized screw and a cement-augmented screw. METHODS: For this biomechanical cadaveric study the investigators used 10 vertebral bodies (L1-5) that were free of metastatic disease or primary bone disease. Following initial screw insertion, each screw was subjected to a pullout force that was applied axially along the screw trajectory at 5 mm per minute until failure. Each specimen was instrumented with a pedicoplasty revision using the original screw diameter, and on the contralateral side either a fenestrated screw with cement augmentation or a screw upsized by 1 mm was inserted in a randomized fashion. These revisions were then pulled out using the previously mentioned methods. RESULTS: Initial screw pullout values for the paired upsized screw and pedicoplasty were 717 ± 511 N and 774 ± 414 N, respectively (p = 0.747) (n = 14). Revised pullout values for the paired upsized screw and pedicoplasty were 775 ± 461 N and 762 ± 320 N, respectively (p = 0.932). Initial pullout values for the paired cement augmentation and pedicoplasty were 792 ± 434 N and 880 ± 558 N, respectively (p = 0.649). Revised pullout values for the paired cement augmentation and pedicoplasty were 1159 ± 300 N and 687 ± 213 N, respectively (p < 0.001). CONCLUSIONS: Pedicle defects are difficult to manage. Reconstitution of the pedicle and creation of a neomedullary canal appears to be possible through the use of pedicoplasty. Biomechanically, screws that have been used in pedicoplasty have equivalent pullout strength to an upsized screw, and have greater insertional torques than those with the same diameter that have not been used in pedicoplasty, yet they are not superior to cement augmentation. This study suggests that although cement augmentation appears to have superior pullout force, the novel pedicoplasty technique offers promise as a viable biological revision option for the management of failed pedicle screws compared with the option of standard upsized screws in a cadaveric model. These findings will ultimately need to be further assessed in a clinical setting.

Comparison of 3D-printed titanium-alloy, standard titanium-alloy, and PEEK interbody spacers in an ovine model.

BACKGROUND CONTEXT: Osseointegration is a pivotal process in achieving a rigid fusion and ultimately a successful clinical outcome following interbody fusion surgery. Advancements in 3D printing technology permit commonly used titanium interbody spacers to be designed with unique architectures, such as a highly interconnected and specific porous structure that mimics the architecture of trabecular bone. Interbody implants with a microscale surface roughness and biomimetic porosity may improve bony ongrowth and ingrowth compared to traditional materials. PURPOSE: The purpose of this study was to compare the osseointegration of lumbar interbody fusion devices composed of surgical-grade polyetheretherketone (PEEK), titanium-alloy (TAV), and 3D-printed porous, biomimetic TAV (3DP) using an in vivo ovine model. STUDY DESIGN: In Vivo Preclinical Animal Study METHODS: Eighteen sheep underwent two-level lateral lumbar interbody fusion randomized with either 3DP, PEEK, or TAV interbody spacers (n=6 levels for each spacer per time point). Postoperative time points were 6 and 12 weeks. Microcomputed tomography and histomorphometry were used to quantify bone volume (BV) within the spacers (ingrowth) and the surface bone apposition ratio (BAR) (ongrowth), respectively. RESULTS: The 3DP-treatment group demonstrated significantly higher BV than the PEEK and TAV groups at 6 weeks (77.3±44.1 mm3, 116.9±43.0 mm3, and 108.7±15.2 mm3, respectively) (p<.05). At 12 weeks, there were no BV differences between groups (p>.05). BV increased in all groups from the 6- to 12-week time points (p<.05). At both time points, the 3DP-treated group (6w: 23.6±10.9%; 12w: 36.5±10.9%) had significantly greater BAR than the PEEK (6w: 8.6±2.1%; 12w: 14.0±5.0%) and TAV (6w: 6.0±5.7%; 12w: 4.1±3.3%) groups (p<.05). CONCLUSIONS: 3DP interbody spacers facilitated greater total bony ingrowth at 6 weeks, and greater bony ongrowth postoperatively at both 6 and 12 weeks, in comparison to solid PEEK and TAV implants. CLINICAL SIGNIFICANCE: Based on these findings, the 3DP spacers may be a reasonable alternative to traditional PEEK and TAV spacers in various clinical applications of interbody fusion.

Comprehensive Evaluation of Accessory Rod Position, Rod Material and Diameter, Use of Cross-connectors, and Anterior Column Support in a Pedicle Subtraction Osteotomy Model: Part I: Effects on Apical Rod Strain: An In Vitro and In Silico Biomechanical Study.

STUDY DESIGN: In silico finite element study. OBJECTIVE: The aim of this study was to evaluate the effect of six construct factors on apical rod strain in an in silico pedicle subtraction osteotomy (PSO) model: traditional inline and alternative Ames-Deviren-Gupta (ADG) multi-rod techniques, number of accessory rods (three- vs. four-rod), rod material (cobalt-chrome [CoCr] or stainless steel [SS] vs. titanium [Ti]), rod diameter (5.5 vs. 6.35 mm), and use of cross-connectors (CC), or anterior column support (ACS). SUMMARY OF BACKGROUND DATA: Rod fracture following lumbar PSO is frequently reported. Clinicians may modulate reconstructs with multiple rods, rod position, rod material and diameter, and with CC or ACS to reduce mechanical demand or rod contouring. A comprehensive evaluation of these features on rod strain is lacking. METHODS: A finite element model (T12-S1) with intervertebral discs and ligaments was created and validated with cadaveric motion data. Apical rod strain of primary and accessory rods was collected for 96 constructs across all six construct factors, and normalized to the Ti two-rod control. RESULTS: Regardless of construct features, CoCr and SS material reduced strain across all rods by 49.1% and 38.1%, respectively; increasing rod diameter from 5.5 mm to 6.35 mm rods reduced strain by 32.0%. Use of CC or lumbosacral ACS minimally affected apical rod strain (<2% difference from constructs without CC or ACS). Compared to the ADG technique, traditional inline reconstruction reduced primary rod strain by 32.2%; however, ADG primary rod required 14.2° less rod contouring. The inline technique produced asymmetrical loading between left and right rods, only when three rods were used. CONCLUSION: The number of rods and position of accessory rods affected strain distribution on posterior fixation. Increasing rod diameter and using CoCr rods was most effective in reducing rod strain. Neither CC nor lumbosacral ACS affected apical rod strain. LEVEL OF EVIDENCE: N/A.

Comprehensive In Silico Evaluation of Accessory Rod Position, Rod Material and Diameter, Use of Cross-connectors, and Anterior Column Support in a Pedicle Subtraction Osteotomy Model: Part II: Effects on Lumbosacral Rod and Screw Strain.

STUDY DESIGN: In silico finite element study. OBJECTIVE: The aim of this study was to evaluate effects of six construct factors on rod and screw strain at the lumbosacral junction in an in silico pedicle subtraction osteotomy (PSO) model: traditional inline and alternative Ames-Deviren-Gupta (ADG) multi-rod techniques, number of accessory rods (three-rod vs. four-rod), rod material (cobalt-chrome [CoCr] or stainless steel [SS] vs. titanium [Ti]), rod diameter (5.5 vs. 6.35 mm), and use of cross-connectors (CC), or anterior column support (ACS). SUMMARY OF BACKGROUND DATA: Implant failure and pseudoarthrosis at the lumbosacral junction following PSO are frequently reported. Clinicians may modulate reconstructs with multiple rods, rod position, rod material, and diameter, and with CC or ACS to reduce mechanical demand. An evaluation of these features' effects on rod and screw strains is lacking. METHODS: A finite element model (T12-S1) with intervertebral discs and ligaments was created and validated with cadaveric motion data. Lumbosacral rod and screw strain data were collected for 96 constructs across all six construct factors and normalized to the Ti 2-Rod control. RESULTS: The inline technique resulted in 12.5% to 51.3% more rod strain and decreased screw strain (88.3% to 95%) compared to ADG at the lumbosacral junction. An asymmetrical strain distribution was observed in the three-rod inline technique in comparison to four-rod, which was more evenly distributed. Regardless of construct features, rod strain was significantly decreased by rod material (CoCr > SS > Ti), and increasing rod diameter from 5.5 mm to 6.35 mm reduced strain by 9.9% to 22.1%. ACS resulted in significant reduction of rod (37.8%-59.8%) and screw strains (23.2%-65.8%). CONCLUSION: Increasing rod diameter, using CoCr rods, and ACS were the most effective methods in reducing rod strain at the lumbosacral junction. The inline technique decreased screw strain and increased rod strain compared to ADG. LEVEL OF EVIDENCE: N/A.

Reducing Core Stability Influences Lower Extremity Biomechanics in Novice Runners.

PURPOSE: The role of core stability in running and its influence on injury risk in runners is not well understood. The purpose of this study was to investigate the effect of core stability (and core fatigue) on running mechanics. We hypothesized that decreasing core stability in novice runners would result in altered running mechanics previously associated with increased risk for common lower extremity running injuries. METHODS: Three-dimensional running kinematics and kinetics and seated postural sway on an unstable surface were collected on 25 healthy, novice runners before and after they performed a core stability knockdown protocol (CSKP), designed to temporarily reduce participants' core stability in a single testing session. RESULTS: Linear mixed models demonstrated that the CSKP resulted in an increased peak knee flexion moment (0.51%BW·ht increase, effect size = 0.49, P = 0.021) and a decreased vertical average loading rate (4.5 BW·s decrease, effect size = 0.44, P = 0.037) during running, but no significant changes in peak knee adduction moment, knee adduction impulse, hip adduction moment, hip adduction impulse, or peak vertical ground reaction force (all P > 0.05). Of 25 runners, 20 demonstrated a measurable decrement in their core stability as defined by their seated postural sway center of pressure excursion changing more than the standard error of measurement of 76 mm. CONCLUSIONS: An experimentally induced decrement in core stability in novice runners caused an increased peak knee flexion moment during stance, which has previously been associated with increased patellofemoral contact pressure during running. Therefore, these results demonstrate that insufficient core stability in novice runners may be a risk factor for developing patellofemoral pain. Other results did not support a role of core stability in other common overuse running injuries in this population.

An investigational study of a dual-layer, chorion-free amnion patch as a protective barrier following lumbar laminectomy in a sheep model.

The inherent properties of the human amniotic membrane (HAM) suggest its potential for use as a physical barrier during surgery to protect neural elements and vessels from the surrounding environment. The objective of this study was to evaluate the effect of a dual-layer, chorion-free amnion patch (DLAM; ViaShield®, Globus Medical Inc., Audubon, PA, USA) processed from HAM as a protective barrier following lumbar laminectomy in a sheep model. A multiplex immunoassay was performed to quantify the inherent cytokines present in the amnion after processing. Twelve skeletally mature female crossbred Suffolk sheep were randomly divided into two equal post-operative periods (4 and 10 weeks). Each sheep underwent a laminectomy at L3 and L5, and one of the surgical sites randomly received the DLAM treatment. At each postsurgical time point, the extent of epidural fibrosis and neurohistopathological responses at the laminectomy sites was assessed based on epidural fibrosis-dura tenacity scores and decalcified histology, respectively. Immunoassay results showed that inflammatory mediators and immunomodulatory cytokines were present in the amnion after processing, but no proangiogenic cytokines were detected. At 10 weeks, tissue tenacity was significantly less in the DLAM treatment group when compared with the operative control (1.2 ± 0.4 vs. 2.8 ± 0.4, p < 0.05), demonstrating the ability of DLAM to act as a barrier and cover the dura. Gross observations showed fewer fibroblasts in the DLAM group in comparison with the control at both post-operative time points. Fibroblast infiltration analysis indicated that at both 4 and 10 weeks, there were significantly more infiltrated fibroblasts in the operative control sites than in the DLAM-treated sites, expressed as a percentage of the total number of fibroblasts present (4 weeks: 72.3 ± 10.2% vs. 10.8 ± 10.1%, p < .05; 10 weeks: 84.9 ± 15.8% vs. 43.1 ± 11.6%, p < .05). Additionally, fibroblasts travelled further into the dura in the operative control group compared with the DLAM-treated group at both time points. In conclusion, this study found that DLAM reduced fibroblast infiltration and tissue tenacity following lumbar laminectomy in a sheep animal model. These findings support the potential use of DLAM in clinical practice as a protective barrier for neural elements and anterior vessels.