Bone marrow stromal cells generate an osteoinductive microenvironment when cultured on titanium-aluminum-vanadium substrates with biomimetic multiscale surface roughness.

Osseointegration of titanium-based implants possessing complex macroscale/microscale/mesoscale/nanoscale (multiscale) topographies support a direct and functional connection with native bone tissue by promoting recruitment, attachment and osteoblastic differentiation of bone marrow stromal cells (MSCs). Recent studies show that the MSCs on these surfaces produce factors, including bone morphogenetic protein 2 (BMP2) that can cause MSCs not on the surface to undergo osteoblast differentiation, suggesting they may produce an osteogenic environmentin vivo. This study examined if soluble factors produced by MSCs in contact with titanium-aluminum-vanadium (Ti6Al4V) implants possessing a complex multiscale biomimetic topography are able to induce osteogenesis ectopically. Ti6Al4V disks were grit-blasted and acid-etched to create surfaces possessing macroscale and microscale roughness (MM), micro/meso/nanoscale topography (MN), and macro/micro/meso/nanoscale topography (MMNTM). Polyether-ether-ketone (PEEK) disks were also fabricated by machining to medical-grade specifications. Surface properties were assessed by scanning electron microscopy, contact angle, optical profilometry, and x-ray photoelectron spectroscopy. MSCs were cultured in growth media (GM). Proteins and local factors in their conditioned media (CM) were measured on days 4, 8, 10 and 14: osteocalcin, osteopontin, osteoprotegerin, BMP2, BMP4, and cytokines interleukins 6, 4 and 10 (IL6, IL4, and IL10). CM was collected from D14 MSCs on MMNTMand tissue culture polystyrene (TCPS) and lyophilized. Gel capsules containing active demineralized bone matrix (DBM), heat-inactivated DBM (iDBM), and iDBM + MMN-GM were implanted bilaterally in the gastrocnemius of athymic nude mice (N= 8 capsules/group). Controls included iDBM + GM; iDBM + TCPS-CM from D5 to D10 MSCs; iDBM + MMN-CM from D5 to D10; and iDBM + rhBMP2 (R&D Systems) at a concentration similar to D5-D10 production of MSCs on MMNTMsurfaces. Legs were harvested at 35D. Bone formation was assessed by micro computed tomography and histomorphometry (hematoxylin and eosin staining) with the histology scored according to ASTM 2529-13. DNA was greatest on PEEK at all time points; DNA was lowest on MN at early time points, but increased with time. Cells on PEEK exhibited small changes in differentiation with reduced production of BMP2. Osteoblast differentiation was greatest on the MN and MMNTM, reflecting increased production of BMP2 and BMP4. Pro-regenerative cytokines IL4 and IL10 were increased on Ti-based surfaces; IL6 was reduced compared to PEEK. None of the media from TCPS cultures was osteoinductive. However, MMN-CM exhibited increased bone formation compared to iDBM and iDBM + rhBMP2. Furthermore, exogenous rhBMP2 alone, at the concentration found in MMN-CM collected from D5 to D10 cultures, failed to induce new bone, indicating that other factors in the CM play a critical role in that osteoinductive microenvironment. MSCs cultured on MMNTMTi6Al4V surfaces differentiate and produce an increase in local factors, including BMP2, and the CM from these cultures can induce ectopic bone formation compared to control groups, indicating that the increased bone formation arises from the local response by MSCs to a biomimetic, multiscale surface topography.

Proximal junctional failure after surgical instrumentation in adult spinal deformity: biomechanical assessment of proximal instrumentation stiffness.

STUDY DESIGN: Assessment of different proximal instrumentation stiffness features to minimize the mechanical proximal junctional failure-related risks through computer-based biomechanical models. OBJECTIVE: To biomechanically assess variations of proximal instrumentation and loads acting on the spine and construct to minimize proximal junctional failure (PJF) risks. The use of less-stiff fixation such as hooks or tensioned bands, compared to pedicle screws, at the proximal instrumentation level are considered to allow for a gradual transition in stiffness with the adjacent levels, but the impact of such flexible fixation on the loads balance and complications such as PJF remain uncertain. METHODS: Six patients with adult spine deformity who underwent posterior spinal instrumentation were used to numerically model and simulate the surgical steps, erected posture, and flexion functional loading in patient-specific multibody analyses. Three types of upper-level fixation (pedicle screws (PS), supralaminar hooks (SH), and sublaminar bands (SB) with tensions of 50, 250, and 350 N) and rod stiffness (CoCr/6 mm, CoCr/5.5 mm, Ti/5.5 mm) were simulated. The loads acting on the spine and implants of the 90 simulated configurations were analyzed using Kruskal-Wallis statistical tests. RESULTS: Simulated high-tensioned bands decreased the sagittal moment at the adjacent level proximal to the instrumentation (1.3 Nm at 250 N; 2.5 Nm at 350 N) compared to screws alone (PS) (15.6 Nm). At one level above, the high-tensioned SB increased the sagittal moment (17.7 Nm-SB vs. 15.5 Nm-PS) and bending moment on the rods (5.4 Nm and 5.7 Nm vs. 0.6 Nm) (p < 0.05). SB with 50 N tension yielded smaller changes in load transition compared to higher tension, with moments of 8.1 Nm and 16.8 Nm one and two levels above the instrumentation. The sagittal moment at the upper implant-vertebra connection decreased with the rod stiffness (1.0 Nm for CoCr/6 mm vs. 0.7 Nm for Ti/5.5 mm; p < 0.05). CONCLUSION: Simulated sublaminar bands with lower tension produced smaller changes in the load transition across proximal junctional levels. Decreasing the rod stiffness further modified these changes, with a decrease in loads associated with bone failure, however, lower stiffness did increase the rod breakage risk. LEVEL OF EVIDENCE: N/A.

Influence of spinal lordosis correction location on proximal junctional failure: a biomechanical study.

STUDY DESIGN: Assessment of sagittal lordosis distribution on mechanical proximal junctional failure-related risks through computer-based biomechanical models. OBJECTIVE: To biomechanically assess how lordosis distribution influences radiographical and biomechanical indices related to Proximal Junctional Failure (PJF). The "optimal" patient-specific targets to restore the sagittal balance in posterior spinal fusion are still not known. Among these, the effect of the lumbar lordosis correction strategy on complications such as PJF remain uncertain. METHODS: In this computational biomechanical study, five adult spinal deformity patients who underwent posterior spinal fixation were retrospectively reviewed. Their surgery, first erect posture and flexion movement were simulated with a patient-specific multibody model. Three pedicle subtraction osteotomy (PSO) levels (L3, L4, and L5) were simulated, with consistent global lordosis for a given patient and pelvic tilt adjusted accordingly to the actual surgery. Computed loads on the anterior spine and instrumentation were analyzed and compared using Kruskal-Wallis statistical tests and Spearman correlations. RESULTS: In these models, no significant correlations were found between the lordosis distribution index (LDI), PSO level and biomechanical PJF-related indices. However, increasing the sagittal vertical axis (SVA) and thoracolumbar junction angle (TLJ) and decreasing the sacral slope (SS) increased the bending moment sustained by the rods at the proximal instrumented level (r = 0.52, 0.57, - 0.56, respectively, p < 0.05). There was a negative correlation between SS and the bending moment held by the adjacent proximal segment (r = - 0.71, p < 0.05). CONCLUSION: Based on these biomechanical simulations, there was no correlation between the lordosis distribution and PJF-associated biomechanical factors. However, increasing SS and flattening the TLJ, as postural adjustment strategies required by a more distal PSO, did decrease such PJF-related factors. Sagittal restoration and PJF risks remain multifactorial, and the use of patient-specific biomechanical models may help to better understand the complex interrelated mechanisms.

How do additional rods reduce loads on the primary rods in adult spinal instrumentation with pedicle subtraction osteotomy?

BACKGROUND: Additional auxiliary rods have been used in spinal instrumentation across pedicle subtraction osteotomy to reduce stresses in the primary rods. The auxiliary rods can be connected through dual-rod-screws, fixed-angle multi-rod connectors or variable-angle multi-rod connectors. The objective was to assess rod bending in conventional bilateral-rod construct vs. constructs with auxiliary rods. METHODS: Computer models of two adult patients were developed to evaluate bending loads across a pedicle subtraction site in a control construct with bilateral rods vs. constructs with auxiliary rods bilaterally or unilaterally connected to the primary rods through either dual-rod-screws, fixed-angle multi-rod connectors, or variable-angle multi-rod connectors. Postoperative rod bending loads were computed and compared. FINDINGS: Normalizing loads on the primary rods in the multi-rod constructs to the control construct, primary rod loads in multi-rod constructs were 17% to 48% lower than the control construct. Constructs with bilateral auxiliary rods through dual-rod-screws, fixed-angle multi-rod connectors, or variable-angle multi-rod connectors could result in similar primary rod bending loads. Bending loads on the auxiliary rods were higher or lower than those on the primary rods depending on how their curvatures matched the primary rods, and how they were locked onto the primary rods. INTERPRETATION: Auxiliary rods noticeably reduced the bending loads on the primary rods compared with a standard bilateral-rod construct. Loads in the auxiliary rods were higher or lower than those in the primary rods depending on how their curvatures matched the primary rods, and how they were locked onto the primary rods.

Instrumentation of the sacroiliac joint with cylindrical threaded implants: A detailed finite element study of patient characteristics affecting fixation performance.

The sacroiliac joint (SIJ) is a known pain generator that, in severe cases, may require surgical fixation to reduce intra-articular displacements and allow for arthrodesis. The objective of this computational study was to analyze how the number of implants affected SIJ stabilization with patient-specific characteristics such as the pelvic geometry and bone quality. Detailed finite element models were developed to account for three pelvises of differing anatomy. Each model was tested with a normal and low bone density (LD) under two types of loading: compression only and compression with flexion and extension moments. These models were instrumented with one to three cylindrical, threaded and fenestrated implants through a posterior oblique trajectory, requiring less muscle dissection than the more common lateral trajectory used with triangular implants. Compared with the noninstrumented pelvis, the change in range of motion (ROM) and stress distribution were used to characterize joint stabilization. Noninstrumented mobility ranged from 0.86 to 2.55 mm and from 1.37° to 6.11°. Across patient-specific characteristics, the ROM reduction with one implant varied from 3% to 21% for vertical and 15% to 47% for angular displacements. With two implants, the ROM reduction ranged from 12% to 41% for vertical and from 28% to 61% for angular displacements. Three implants, however, did not further improve the joint stability (14% to 42% for vertical and 32% to 63% for angular displacements). With respect to patient characteristics, an LD led to a decreased stabilization and a higher volume of stressed bone (>75% of yield stress). A better understanding of how patient characteristics affect the implant performance could help improve surgical planning of sacroiliac arthrodesis.

In silico patient-specific optimization of correction strategies for thoracic adolescent idiopathic scoliosis.

BACKGROUND: With modelling and simulation (or in silico) techniques, patient-specific optimization algorithms represent promising tools to support the surgical decision-making process, particularly in 3D correction of adolescent idiopathic scoliosis, where the best intraoperative instrumentation strategy and the correction goals are debated. METHODS: 1080 biomechanical intraoperative simulations of a representative pediatric thoracic curve were run according to a full-factorial design approach. Widely accepted instrumentation configurations (5 screw patterns, 4 upper and 3 lower instrumented vertebrae, 6 rod curvatures and 3 rod stiffnesses) were analyzed, assuming concave rod rotation and en bloc derotation as main correction maneuvers. Results in terms of 3D correction and mobility were rated using an objective function for thoracic scoliosis also including surgeon-dependent correction objectives. An extensive sensitivity analysis on correction objectives was performed. FINDINGS: Multiple optimal strategies were identified, depending on the selected correction objective. They provided significantly better coronal (67% vs. 55%) correction, using comparable instrumented levels (9.9 ± 1.6 vs. 10.7 ± 2.1), screw patterns and significantly higher implant density (1.6 ± 0.3 vs. 1.4 ± 0.2 screws/vertebra) compared to worst ones. Optimal strategies typically included the neutral and the last touching vertebrae in the construct and high stiffness (CoCr, 6 mm) differentially/highly contoured rods. INTERPRETATION: The computerized algorithm determined the best instrumentation parameters to achieve optimal correction for the considered thoracic case. Multiple clinically equivalent strategies may be used, as supported by the variety of considered correction objectives. The current approach could be translated to any scoliotic curves, including surgeon preferences in terms of instrumentation parameters, intraoperative correction maneuvers and correction objectives.

Clinically relevant finite element technique based protocol to evaluate growing rods for early onset scoliosis correction.

OBJECTIVE: The emergence of distraction-based growing rods has provided the means to reduce the progression of spinal deformity in early onset scoliosis (EOS). The current protocols for evaluating spinal implants (ie, ASTM-F1717 and ISO-12189) were developed for fusion/dynamic devices. These protocols do not feature long unsupported rod lengths subjected to distraction. Due to the unsuitability of the existing guidelines for the evaluation of growing rods, a new distraction-based finite element protocol is presented herein for the first time. METHOD: A vertebrectomy (VO) model from current protocols was modified to accommodate multi-spinal segments (ie, MS model) in which springs with appropriate stiffness were simulated in between the plastic blocks. To assess the efficacy of the protocol, two different computational studies were conducted: (a) compression-bending (MS-CB) with no distraction, and (b) distraction followed by compression-bending (MS-D + CB). In each study, the model with no axial connector (rods-only) was modified to include a) 80-mm long tandem (LT) connectors, and b) side-by-side (SBS) connectors. Stiffness and yield loads were calculated as per ASTM-F1717 guidelines and compared with the corresponding VO models with no distraction. In the MS-D + CB models, distraction was applied at the top block, stretching the spring-block construct in a simulation of scoliosis surgery prior to locking the construct at the connector-rods' interface. RESULTS: MS-CB models predicted higher stiffness and yield loads, compared to the VO models. The locking mechanism produced pre-existing stresses on the rod-connector interface, which caused a shift in the location of high-stress regions to the distraction site. Distraction led to a decrease in the construct's stiffness and yield load. DISCUSSION: The proposed protocol enables the simulation of clinical parameters that are not feasible in the F1717 models and predicted stress patterns in the hardware consistent with observed clinical failures.

Lordosis Recreation in Transforaminal and Posterior Lumbar Interbody Fusion: A Cadaveric Study of the Influence of Surgical Bone Resection and Cage Angle.

STUDY DESIGN: Controlled cadaveric study of surgical technique in transforaminal and posterior lumbar interbody fusion (TLIF and PLIF) OBJECTIVE.: To evaluate the contribution of surgical techniques and cage variables in lordosis recreation in posterior interbody fusion (TLIF/PLIF). SUMMARY OF BACKGROUND DATA: The major contributors to lumbar lordosis are the lordotic lower lumbar discs. The pathologies requiring treatment with segmental fusion are frequently hypolordotic or kyphotic. Current posterior based interbody techniques have a poor track record for recreating lordosis, although recreation of lordosis with optimum anatomical alignment is associated with better outcomes and reduced adjacent segment change needing revision. It is unclear whether surgical techniques or cage parameters contribute significantly to lordosis recreation. METHODS: Eight instrumented cadaveric motion segments were evaluated with pre and post experimental radiological assessment of lordosis. Each motion segment was instrumented with pedicle screw fixation to allow segmental stabilization. The surgical procedures were unilateral TLIF with an 18° lordotic and 27 mm length cage, unilateral TLIF (18°, 27 mm) with bilateral facetectomy, unilateral TLIF (18°, 27 mm) with posterior column osteotomy (PCO), PLIF with bilateral cages (18°, 22 mm), and PLIF with bilateral cages (24°, 22 mm). Cage insertion used and "insert and rotate" technique. RESULTS: Pooled results demonstrated a mean increase in lordosis of 2.2° with each procedural step (lordosis increase was serially 1.8°, 3.5°, 1.6°, 2.5°, and 1.6° through the procedures). TLIF and PLIF with PCO increased lordosis significantly compared with unilateral TLIF and TLIF with bilateral facetectomy. The major contributors to lordosis recreation were PCO, and PLIF with paired shorter cages rather than TLIF. CONCLUSION: This study demonstrates that the surgical approach to posterior interbody surgery influences lordosis gain and PCO optimizes lordosis gain in TLIF. The bilateral cages used in PLIF are shorter and associated with further gain in lordosis. This information has the potential to aid surgical planning when attempting to recreate lordosis to optimize outcomes. LEVEL OF EVIDENCE: N/A.

Stainless steel wear debris of a scoliotic growth guidance system has little local and systemic effect in an animal model.

Options to treat early-onset scoliosis include guided-growth systems with sliding action between rods and pedicle screws. The wear was previously measured in an in vitro test, and in this in vivo rabbit model, we evaluated the local and systemic biological response to the stainless steel debris. Compared to the previous study, a relatively higher volume of representative wear particles with a median particle size of 0.84 µm were generated. Bolus dosages were injected into the epidural space at L4-L5 for a minimum of 36 rabbits across three treatment groups (negative control, 1.5 mg, and 4.0 mg) and two timepoints (12 and 24 weeks). Gross pathology evaluated distant organs and the injection site with a dorsal laminectomy to examine the epidural space and dosing site. Peri-implanted particle tissues were stained for immunohistochemical and quantitatively analyzed for IL-6 and TNF-α cytokines. Based on ISO 10993-6:2007 scoring, particles in the high-dose group were primarily non-irritant (12 weeks) with one slightly irritant. At 24 weeks, inflammatory cell infiltration was non-existent to minimal with all groups considered non-irritant at the injection site. Material characterization confirmed that particles detected in distant organs were stainless steel or contaminants. At 12 weeks, stainless steel groups demonstrated statistically increased amounts of cytokine levels compared to control but there was a statistical decrease for both at 24 weeks. These findings indicate that stainless steel wear debris, comparable to the expected usage from a simulated growth guidance system, had no discernible untoward biological effects locally and systemically in an animal model. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1980-1990, 2018.

Biomechanical simulations of costo-vertebral and anterior vertebral body tethers for the fusionless treatment of pediatric scoliosis.

Compression-based fusionless tethers are an alternative to conventional surgical treatments of pediatric scoliosis. Anterior approaches place an anterior (ANT) tether on the anterolateral convexity of the deformed spine to modify growth. Posterior, or costo-vertebral (CV), approaches have not been assessed for biomechanical and corrective effectiveness. The objective was to biomechanically assess CV and ANT tethers using six patient-specific, finite element models of adolescent scoliotic patients (11.9 ± 0.7 years, Cobb 34° ± 10°). A validated algorithm simulated the growth and Hueter-Volkmann growth modulation over a period of 2 years with the CV and ANT tethers at two initial tensions (100, 200 N). The models without tethering also simulated deformity progression with Cobb angle increasing from 34° to 56°, axial rotation 11° to 13°, and kyphosis 28° to 32° (mean values). With the CV tether, the Cobb angle was reduced to 27° and 20° for tensions of 100 and 200 N, respectively, kyphosis to 21° and 19°, and no change in axial rotation. With the ANT tether, Cobb was reduced to 32° and 9° for 100 and 200 N, respectively, kyphosis unchanged, and axial rotation to 3° and 0°. While the CV tether mildly corrected the coronal curve over a 2-year growth period, it had sagittal lordosing effect, particularly with increasing initial axial rotation (>15°). The ANT tether achieved coronal correction, maintained kyphosis, and reduced the axial rotation, but over-correction was simulated at higher initial tensions. This biomechanical study captured the differences between a CV and ANT tether and indicated the variability arising from the patient-specific characteristics. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:254-264, 2018.

Correction Capability in the 3 Anatomic Planes of Different Pedicle Screw Designs in Scoliosis Instrumentation.

STUDY DESIGN: Computer simulations to compare the correction capabilities of different pedicle screws in adolescent idiopathic scoliosis (AIS) instrumentations. OBJECTIVE: To compare the correction and resulting bone-screw forces associated with different pedicle screws in scoliosis instrumentations. SUMMARY OF BACKGROUND DATA: Pedicle screw fixation is widely used in surgical instrumentation for spinal deformity treatment. Screw design, correction philosophies, and surgical techniques are constantly evolving to achieve better control of the vertebrae and correction of the spinal deformity. Yet, there remains a lack of biomechanical studies that quantify the effects and advantages of different screw designs in terms of correction kinematics. METHODS: The correction capabilities of fixed-angle, multiaxial, uniaxial, and saddle axial screws were kinematically analyzed, simulated, and compared. These simulations were based on the screw patterns and correction techniques proposed by 2 experienced surgeons for 2 AIS cases. Additional instrumentations were assessed to compare the correction and resulting bone-screw forces associated with each type of screw. RESULTS: The fixed-angle, uniaxial and saddle axial screws had similar kinematic behavior and performed better than multiaxial screws in the coronal and transverse planes (8% and 30% greater simulated corrections, respectively). Uniaxial and multiaxial screws were less effective than fixed-angle and saddle axial screws in transmitting compression/distraction to the anterior spine because of their sagittal plane mobility between the screw head and shank. Only the saddle axial screws allow vertebra angle in the sagittal plane to be independently adjusted. CONCLUSIONS: Pedicle screws of different designs performed differently for deformity corrections or for compensating screw placement variations in different anatomic planes. For a given AIS case, screw types should be determined based on the particular instrumentation objectives, the deformity's stiffness and characteristics so as to make the best of the screw designs.

Biomechanical analysis of lateral interbody fusion strategies for adjacent segment degeneration in the lumbar spine.

BACKGROUND CONTEXT: Surgical treatment of symptomatic adjacent segment disease (ASD) typically involves extension of previous instrumentation to include the newly affected level(s). Disruption of the incision site can present challenges and increases the risk of complication. Lateral-based interbody fusion techniques may provide a viable surgical alternative that avoids these risks. This study is the first to analyze the biomechanical effect of adding a lateral-based construct to an existing fusion. PURPOSE: The study aimed to determine whether a minimally invasive lateral interbody device, with and without supplemental instrumentation, can effectively stabilize the rostral segment adjacent to a two-level fusion when compared with a traditional posterior revision approach. STUDY DESIGN/SETTING: This is a cadaveric biomechanical study of lateral-based interbody strategies as add-on techniques to an existing fusion for the treatment of ASD. METHODS: Twelve lumbosacral specimens were non-destructively loaded in flexion, extension, lateral bending, and torsion. Sequentially, the tested conditions were intact, two-level transforaminal lumbar interbody fusion (TLIF) (L3-L5), followed by lateral lumbar interbody fusion procedures at L2-L3 including interbody alone, a supplemental lateral plate, a supplemental spinous process plate, and then either cortical screw or pedicle screw fixation. A three-level TLIF was the final instrumented condition. In all conditions, three-dimensional kinematics were tracked and range of motion (ROM) was calculated for comparisons. Institutional funds (<$50,000) in support of this work were provided by Medtronic Spine. RESULTS: The addition of a lateral interbody device superadjacent to a two-level fusion significantly reduced motion in flexion, extension, and lateral bending (p<.05). Supplementing with a lateral plate further reduced ROM during lateral bending and torsion, whereas a spinous process plate further reduced ROM during flexion and extension. The addition of posterior cortical screws provided the most stable lateral lumbar interbody fusion construct, demonstrating ROM comparable with a traditional three-level TLIF. CONCLUSIONS: The data presented suggest that a lateral-based interbody fusion supplemented with additional minimally invasive instrumentation may provide comparable stability with a traditional posterior revision approach without removal of the existing two-level rod in an ASD revision scenario.

Computed tomography-guided tissue engineering of upper airway cartilage.

Normal laryngeal function has a large impact on quality of life, and dysfunction can be life threatening. In general, airway obstructions arise from a reduction in neuromuscular function or a decrease in mechanical stiffness of the structures of the upper airway. These reductions decrease the ability of the airway to resist inspiratory or expiratory pressures, causing laryngeal collapse. We propose to restore airway patency through methods that replace damaged tissue and improve the stiffness of airway structures. A number of recent studies have utilized image-guided approaches to create cell-seeded constructs that reproduce the shape and size of the tissue of interest with high geometric fidelity. The objective of the present study was to establish a tissue engineering approach to the creation of viable constructs that approximate the shape and size of equine airway structures, in particular the epiglottis. Computed tomography images were used to create three-dimensional computer models of the cartilaginous structures of the larynx. Anatomically shaped injection molds were created from the three-dimensional models and were seeded with bovine auricular chondrocytes that were suspended within alginate before static culture. Constructs were then cultured for approximately 4 weeks post-seeding and evaluated for biochemical content, biomechanical properties, and histologic architecture. Results showed that the three-dimensional molded constructs had the approximate size and shape of the equine epiglottis and that it is possible to seed such constructs while maintaining 75%+ cell viability. Extracellular matrix content was observed to increase with time in culture and was accompanied by an increase in the mechanical stiffness of the construct. If successful, such an approach may represent a significant improvement on the currently available treatments for damaged airway cartilage and may provide clinical options for replacement of damaged tissue during treatment of obstructive airway disease.

Growth guidance system for early-onset scoliosis: comparison of experimental and retrieval wear.

STUDY DESIGN: Laboratory study conducted using an in vitro wear simulator with a growth guidance system. Analysis of variance performed to compare in vitro specimens (n = 6) with in vivo retrieval components (n = 5). OBJECTIVE: To characterize the stainless steel, wear debris potential of a spinal growth guidance system by developing an in vitro model and validating tested implants with retrospectively obtained retrievals. SUMMARY OF BACKGROUND DATA: Growth enabling, surgical treatments have been developed to provide fusionless options for patients with early-onset scoliosis. There exist few data regarding the wear debris associated with such spinal systems. METHODS: In this study, we determined in vitro wear from the stainless steel components of the SHILLA™ Growth Guidance System. An analogue lumbar spine model was adapted from ISO 12189:2008 to assess the growth guidance system. In a multistation wear simulator, 6 assembled constructs were tested under displacement control for 5 million cycles (Mc) with diluted bovine serum, and the wear was measured gravimetrically at end of the test. The components were compared quantitatively for wear scar depth with retrieved growth guidance implants (n = 5), and qualitatively for wear, corrosion, and other surface damage. RESULTS: The average total wear rate over 5 Mc was 0.39 ± 0.13 mm/Mc (3.12 ± 1.01 mg/Mc) with an average particle size of 1.3 µm in equivalent circular diameter. Prominent wear scars were noticed on both the tested and retrieved specimens with no statistical difference in the wear scar depths of the tested and retrieved components when set and multiaxial screws when compared collectively. CONCLUSION: An in vitro wear analysis for a spinal growth guidance system was conducted using a novel protocol and validated against retrieved implants. This is the first study establishing a baseline value for the wear of "growth enabling" devices for the treatment of early-onset scoliosis.

Long-term functional outcome of tibial plateau leveling osteotomy versus extracapsular repair in a heterogeneous population of dogs.

OBJECTIVE: To compare the long-term outcome of tibial plateau leveling osteotomy (TPLO) and extracapsular repair (ECR) for treatment of a ruptured cranial cruciate ligament (RCCL). STUDY DESIGN: Prospective clinical trial. ANIMALS: Normal adult dogs (control, n = 79); dogs with unilateral CCL disease (n = 38). METHODS: Dogs had TPLO (n = 15) or ECR (n = 23) for treatment of RCCL. Force plate gait analysis was performed for the control group at one time point and for treatment groups at serial points: preoperatively, 2 weeks, 8 weeks, 6 and 12 months postoperatively. Symmetry indices (SIs) were calculated between operated and unoperated pelvic limb for ground reaction forces (GRFs), including peak vertical force (PVF), contact time (CT), and vertical impulse (VI). GRFs of the treatment groups and control group were compared using a general linear model and Kaplan-Meier survival analysis. RESULTS: At 8 weeks, for PVF and VI, the TPLO group had more symmetric limb loading than the ECR group at the walk and trot. SIs of the TPLO group were not different from the control group by 6 months to 1 year postoperatively. SIs for the ECR group were less symmetrical than the control group at all time periods. Using survival analysis, median time to normal function was no different at the walk between groups, but was shorter for the TPLO group for VI and PVF. CONCLUSIONS: Dogs achieved normal limb loading faster after TPLO than ECR. TPLO resulted in operated limb function that was indistinguishable from the control population by 1 year postoperatively.

A transducer for measuring force on surgical sutures.

The objective of this study was to validate, both in vitro and in an ex vivo model, a technique for the measurement of forces exerted on surgical sutures. For this purpose, a stainless steel E-type buckle force transducer was designed and constructed. A strain gauge was mounted on the central beam of the transducer to measure transducer deformation. The transducer was tested and calibrated on a single strand of surgical suture during cyclic loading. Further validation was performed using a previously published cadaveric model of laryngoplasty in the horse. Linear regression of transducer output with actual force during calibration tests resulted in mean R² values of 1.00, 0.99, and 0.99 for rising slope, falling slope, and overall slope, respectively. The R² was not less than 0.96 across an average of 75 cycles per test. The difference between rising slope and falling slope was 4%. Over 45 846 samples, the predicted force from transducer output showed a mean error of 4%. In vitro validation produced an adjusted R² of 0.99 when the force on the suture was regressed against translaryngeal pressure in a mixed-effects model. E-type buckle force transducers showed a highly linear output over a physiological force range when applied to surgical suture in vitro and in an ex vivo model of laryngoplasty. With appropriate calibration and short-term in vivo implantation, these transducers may advance our knowledge of the mechanisms of success and failure of techniques, such as laryngoplasty, that use structural suture implants.

Cementless total hip replacement in an alpaca.

OBJECTIVE: To report management of a chronic slipped capital femoral epiphysis (SCFE) in an alpaca using cementless total hip replacement (THR). STUDY DESIGN: Case report. ANIMAL: An 18-month-old, 47 kg alpaca male. METHODS: Cementless THR was performed in an alpaca with a chronic, right SCFE, and secondary osteoarthritis. Force plate gait analysis was performed before and 8 weeks after surgery. Outcome was determined through clinical evaluation, radiography, and force plate gait analysis. RESULTS: Cementless THR resulted in marked improvement in the alpaca's comfort level, degree of lameness, and range of motion. On preoperative force plate gait analysis there was decreased contact time (P=.01) and vertical impulse (P<.01) of the affected limb, whereas at 8 weeks postoperatively significant differences in gait analysis between pelvic limbs were not apparent. CONCLUSION: THR using a BioMedtrix canine cementless modular prosthesis restored hip function in an alpaca with coxofemoral osteoarthritis from chronic SCFE. CLINICAL RELEVANCE: THR may be an appropriate treatment for selected traumatic and degenerative conditions of the coxofemoral joint in alpacas.

Simultaneous Determination of Tuning and Calibration Parameters for Computer Experiments.

Tuning and calibration are processes for improving the representativeness of a computer simulation code to a physical phenomenon. This article introduces a statistical methodology for simultaneously determining tuning and calibration parameters in settings where data are available from a computer code and the associated physical experiment. Tuning parameters are set by minimizing a discrepancy measure while the distribution of the calibration parameters are determined based on a hierarchical Bayesian model. The proposed Bayesian model views the output as a realization of a Gaussian stochastic process with hyperpriors. Draws from the resulting posterior distribution are obtained by the Markov chain Monte Carlo simulation. Our methodology is compared with an alternative approach in examples and is illustrated in a biomechanical engineering application. Supplemental materials, including the software and a user manual, are available online and can be requested from the first author.

Stemmed implants improve stability in augmented constrained condylar knees.

We previously combined experimental and computational measures to ascertain whether tibial stem augmentation reduces bone strains beneath constrained condylar implants. Using these same integrated approaches, we examined the benefit of a stem when a wedge is used. Implants were removed from the eight paired cadaver specimens from our previous experiment, and oblique defects created that were restored with 15 degrees metallic wedges cemented in place. We applied a varus moment and an axial load and monitored relative motion between implant and bone. Specimen-specific 3-D finite element models were constructed from CT scans and radiographs to examine bone stress in the proximal tibia. Implants with a wedge but no stem had greater motion than the previous control with no stem or wedge. Use of a modular stem with a wedge maintained the same level of motion as the primary case, suggesting that a stem is preferable when a wedge is utilized. The computational models confirmed this conclusion with a 30% reduction in bone stress compared to 17% in the primary case without a wedge. The wedge carried more axial load compared to the primary implant due to its support on stiff metaphyseal bone.

Image-guided tissue engineering of anatomically shaped implants via MRI and micro-CT using injection molding.

This study demonstrates for the first time the development of engineered tissues based on anatomic geometries derived from widely used medical imaging modalities such as computed tomography (CT) and magnetic resonance imaging (MRI). Computer-aided design and tissue injection molding techniques have demonstrated the ability to generate living implants of complex geometry. Due to its complex geometry, the meniscus of the knee was used as an example of this technique's capabilities. MRI and microcomputed tomography (microCT) were used to design custom-printed molds that enabled the generation of anatomically shaped constructs that retained shape throughout 8 weeks of culture. Engineered constructs showed progressive tissue formation indicated by increases in extracellular matrix content and mechanical properties. The paradigm of interfacing tissue injection molding technology can be applied to other medical imaging techniques that render 3D models of anatomy, demonstrating the potential to apply the current technique to engineering of many tissues and organs.