The lexicon for periprosthetic bone loss versus osteolysis after cervical disc arthroplasty: a systematic review.

BACKGROUND: Periprosthetic bone loss is a common observation following arthroplasty. Recognizing and understanding the nature of bone loss is vital as it determines the subsequent performance of the device and the overall outcome. Despite its significance, the term "bone loss" is often misused to describe inflammatory osteolysis, a complication with vastly different clinical outcomes and treatment plans. Therefore, the goal of this review was to report major findings related to vertebral radiographic bone changes around cervical disc replacements, mitigate discrepancies in clinical reports by introducing uniform terminology to the field, and establish a precedence that can be used to identify the important nuances between these distinct complications. METHODS: A systematic review of the literature was conducted following PRISMA guidelines, using the keywords "cervical," "disc replacement," "osteolysis," "bone loss," "radiograph," and "complications." A total of 23 articles met the inclusion criteria with the majority being retrospective or case reports. RESULTS: Fourteen studies reported periprosthetic osteolysis in a total of 46 patients with onset ranging from 15-96 months after the index procedure. Reported causes included: metal hypersensitivity, infection, mechanical failure, and wear debris. Osteolysis was generally progressive and led to reoperation. Nine articles reported non-inflammatory bone loss in 527 patients (52.5%), typically within 3-6 months following implantation. The reported causes included: micromotion, stress shielding, and interrupted blood supply. With one exception, bone loss was reported to be non-progressive and had no effect on clinical outcome measures. CONCLUSIONS: Non-progressive, early onset bone loss is a common finding after CDA and typically does not affect the reported short-term pain scores or lead to early revision. By contrast, osteolysis was less common, presenting more than a year post-operative and often accompanied by additional complications, leading to revision surgery. A greater understanding of the clinical significance is limited by the lack of long-term studies, inconsistent terminology, and infrequent use of histology and explant analyses. Uniform reporting and adoption of consistent terminology can mitigate some of these limitations. Executing these actionable items is critical to assess device performance and the risk of revision. LEVEL OF EVIDENCE IV: Diagnostic: individual cross-sectional studies with consistently applied reference standard and blinding.

Quantification of Ankle Dorsiflexion in Ponseti-managed Unilateral Clubfoot Patients During Early Childhood.

BACKGROUND: Following the initial correction of a clubfoot using the Ponseti method, diminished passive ankle dorsiflexion may be observed over time, which could represent a possible relapsed deformity. Alternatively, the change may be attributable to patient age or other variables. Our purpose was to quantify passive ankle dorsiflexion in the involved and contralateral unaffected limbs of Ponseti-managed unilateral clubfoot patients, and to determine what patient-related variables influence this finding. METHODS: In total, 132 unilateral clubfoot patients were studied. Passive ankle dorsiflexion was measured in both limbs at each visit. Data were excluded from visits in which patients showed clear evidence of a relapse. Mean ankle dorsiflexion for clubfeet and contralateral unaffected limbs were reported for annual age intervals and compared using paired t tests. A general linear model was established to assess the effects of age, severity, sex, and side on ankle dorsiflexion. RESULTS: Mean ankle dorsiflexion for unaffected limbs declined with age, measuring 53±6 degrees between 0 and 1 year of age and decreasing to 39±7 degrees by 4 to 5 years of age. Similarly, mean ankle dorsiflexion in treated clubfeet declined with age, measuring 44±7 degrees between 0 and 1 year and 29±7 degrees between 4 and 5 years. Overall, the difference between limbs in these patients averaged ~10 degrees for every age interval through 9 years (P<0.001). Ankle dorsiflexion of clubfeet in 95% of patients aged 0 to 2 years was at least 20 degrees, and in 95% of patients aged 3 to 5 years this was at least 15 degrees. Patient age (P<0.001) and severity of deformity (P<0.001) were found to be the only significant factors affecting ankle dorsiflexion in the affected limbs. CONCLUSIONS: Ankle dorsiflexion in the Ponseti-treated clubfeet was influenced by age of the patient and the initial severity of the affected limb. Furthermore, our data suggest that, in patients who showed no relapse, a minimum of 20 degrees of ankle dorsiflexion in the corrected clubfoot is maintained through age 3 years and a minimum of 15 degrees is maintained through age 5 years. LEVEL OF EVIDENCE: Level IV-this is a retrospective case series.

Preclinical biomechanical testing models for the tibiotalar joint and its replacements: A systematic review.

In recent years, total ankle replacements have gained increasing popularity as an alternative to fusion. Preclinical testing of TARs requires reliable in vitro models which, in turn, need thorough knowledge of the kinematics of the tibiotalar joint. Surprisingly few studies have been published to simulate the in vivo kinematics of the tibiotalar joint. Among these studies, there is a wide range of methods and magnitudes of applied loads. The purpose of the present review was to summarize the applied loads, positions that were tested during static simulations, and ranges of motion simulated that have been used in human cadaveric models of the tibiotalar joint. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, PubMed and Google Scholar were searched for studies pertaining to cadaveric tibiotalar joint kinematics. Our search yielded 12 appropriate articles that were included in the systematic review. While it is well known that loads at the tibiotalar joint are frequently as high as 5 times bodyweight [1], these studies reported applied loads varying from 200N-750N, below average bodyweight. Three studies used dynamic loading of custom apparatuses to drive cadaver limbs along predetermined paths to simulate gait. Conversely, the other nine studies applied static loads (∼300N), performed at discreet points during the stance phase, considerably lower than physiological conditions. The present systematic review calls for an urgent need to establish a consensus for preclinical evaluation of TARs for biomechanical function.

Biomechanical comparison of fixation stability using a Lisfranc plate versus transarticular screws.

BACKGROUND: To obtain adequate fixation in treating Lisfranc soft tissue injuries, the joint is commonly stabilized using multiple transarticular screws; however iatrogenic injury is a concern. Alternatively, two parallel, longitudinally placed plates, can be used to stabilize the 1st and 2nd tarsometatarsal joints; however this may not provide adequate stability along the Lisfranc ligament. Several biomechanical studies have compared earlier methods of fixation using plates to the standard transarticular screw fixation method, highlighting the potential issue of transverse stability using plates. A novel dorsal plate is introduced, intended to provide transverse and longitudinal stability, without injury to the articular cartilage. METHODS: A biomechanical cadaver model was developed to compare the fixation stability of a novel Lisfranc plate to that of traditional fixation, using transarticular screws. Thirteen pairs of cadaveric specimens were tested intact, after a simulated Lisfranc injury, and then following implant fixation, using one method of fixation randomly assigned, on either side of each pair. Optical motion tracking was used to measure the motion between each of the following four bones: 1st metatarsal, 2nd metatarsal, 1st cuneiform, and 2nd cuneiform. Testing included both cyclic abduction loading and cyclic axial loading. RESULTS: Both the Lisfranc plate and screw fixation method provided stability such that the average 3D motions across the Lisfranc joint (between 2nd metatarsal and 1st cuneiform), were between 0.2 and 0.4mm under cyclic abduction loading, and between 0.4 and 0.5mm under cyclic axial loading. Comparing the stability of fixation between the Lisfranc plate and the screws, the differences in motion were all 0.3mm or lower, with no clinically significant differences (p>0.16). CONCLUSIONS: Diastasis at the Lisfranc joint following fixation with a novel plate or transarticular screw fixation were comparable. Therefore, the Lisfranc plate may provide adequate support without risk of iatrogenic injury to the articular cartilage.

How Many Patients Who Have a Clubfoot Treated Using the Ponseti Method are Likely to Undergo a Tendon Transfer?

BACKGROUND: The Ponseti method has become the standard of care for the treatment of idiopathic clubfoot. A commonly reported problem encountered with this technique is a relapsed deformity that is sometimes treated in patients older than 2.5 years by an anterior tibial tendon transfer (ATTT) to the third cuneiform. Presently, there is insufficient information to properly counsel families whose infants are beginning Ponseti treatment on the probability of needing later tendon transfer surgery. METHODS: All idiopathic clubfoot patients seen at the authors' institution during the study period who met the inclusion criteria and who were followed for >2.5 years were included (N=137 patients). Kaplan-Meier Survival analysis was used to determine the probability of survival without the need for ATTT surgery. In addition, the influence of patient characteristics, socioeconomic variables, and treatment variables on need for surgery was calculated. RESULTS: On the basis of the survivorship analysis, the probability of undergoing an ATTT remained below 5% for all patients at 3 years of age, but exceeded 15% by 4 years of age, increasing steadily afterwards such that by 6 years of age, the probability of undergoing an ATTT reached 29% of all patients. Overall, controlling for all other variables in the analysis, parent-reported adherence with bracing reduced the odds of undergoing surgery by 6.88 times, compared with parent-reported nonadherence (P<0.01). CONCLUSIONS: This is the first study to report the probability of undergoing ATTT surgery as a function of age using survivorship analysis following Ponseti clubfoot treatment. Although the overall probability reached 29% at 6 years, this was significantly reduced by compliance with bracing. This information may be useful to the clinician when counseling families at the start of treatment. LEVEL OF EVIDENCE: Level III-theraputic.

Flexibility of thoracic spines under simultaneous multi-planar loading.

PURPOSE: The corrective potential of two posterior-only destabilization procedures for scoliosis deformity was quantified under single and multi-planar loading using cadaveric spines. METHODS: Ten full-length human cadaveric thoracic spines were mounted in an 8-df servohydraulic load frame. Cyclic, pure moments were applied in: (1) flexion-extension, (2) lateral bending, (3) axial rotation, (4) flexion-extension with axial rotation, and (5) lateral bending with axial rotation at 0.5°/s, to ±4 Nm. Each specimen was tested intact, and again after nine en bloc bilateral total facetectomies, and one, two, three, and four levels of Ponte osteotomies. Motion was measured throughout loading using optical motion tracking. RESULTS: Under single-plane loading, facetectomies and Ponte osteotomies increased thoracic spine flexibility in all three planes. Compared to total facetectomies, higher per-level increases were seen following Ponte osteotomies, with increases in total range of motion (total ROM) of up to 2.7° in flexion-extension, 1.4° in lateral bending, and 3.1° in axial rotation following each osteotomy. Compared to the facetectomies, four supplemental osteotomies increased total ROM by 23 % in flexion (p < 0.01) and 8 % in axial rotation (p < 0.01). Increases in lateral bending were smaller. Under multi-planar loading, each Ponte osteotomy provided simultaneous increases of up to 1.4°, 1.6°, and 2.2° in flexion-extension, lateral bending, and axial rotation. CONCLUSIONS: Ponte osteotomies provided higher per-level increases in ROM under single-plane loading than total facetectomies alone. Further, Ponte osteotomies provided simultaneous increase in all three planes under multi-planar loading. These results indicated that, to predict the correction potential of a surgical release, multi-planar testing may be necessary.

The Influence of Sex and Laterality on Clubfoot Severity.

BACKGROUND: Idiopathic clubfoot is bilateral in approximately 50% of cases and has been widely reported to affect males more frequently than females. Despite these observations, the correlation between sex and severity of the deformity has not been established. As well, the difference in severity between unilateral and bilateral clubfeet has not been extensively investigated. Therefore, the goals of the present study were to: (1) examine the relationship between sex and severity of deformity and (2) determine the relationship between laterality and severity of deformity. METHODS: The families of infants with idiopathic clubfoot deformity treated at our institution were prospectively invited to participate in this institutional review board-approved study. Severity of the deformity was assessed by a single surgeon for each patient using the Dimeglio criteria at the first clinic visit. After evaluating the distributions, the correlations were quantified by nonparametric analyses. RESULTS: Over 8 years, 240 infants met the inclusion criteria. There was no significant difference in the severity of deformity due to sex (P=0.61): the median Dimeglio score for males was 13 (variance 4.8) and for females, the median was 13.0 (variance of 5.1). In contrast, severity was distributed differently among unilateral versus bilateral patients. Although both unilateral and bilateral patients had a median Dimeglio score of 13, the ratio of bilateral patients was higher among those with moderate or very severe deformities compared with those with severe deformities (P<0.01). CONCLUSIONS: Although idiopathic clubfoot is commonly considered to affect male patients disproportionately, this is the first study to document no difference in severity due to sex. Further, this study demonstrated that on average, bilateral patients did not have increased severity, but presented with a larger range of severity than those patients with unilateral deformity. LEVEL OF EVIDENCE: Level III-prognostic.

Does Clubfoot Treatment Need to Begin As Soon As Possible?

INTRODUCTION: Parents of an infant with an idiopathic clubfoot deformity are often urged by their primary care physician to seek treatment as soon as possible. This advice frequently appears in many general pediatric and pediatric orthopaedic textbooks and monographs on the subject. This recommendation has not changed since the wide acceptance of the minimally invasive Ponseti method to treat clubfoot. We determined the correlations among patient-related variables, early treatment variables, and the age at which the patient was first seen to begin treatment. METHODS: Infants with moderate to very severe idiopathic clubfoot deformity were invited to participate. Age at which the patient presented to begin treatment was correlated against early treatment-related variables, including number of casts required, cast slippage, cast-related skin problems, brace-related skin problems, early noncompliance with brace wearing, and relapse before 1 year. Patient-related variables were also correlated against age at first visit. RESULTS: Over 7 years, 176 infants met the inclusion criteria. There were no significant differences in the aspects of the early management as a function of age at first visit, with the exception of cast slippage (P=0.05). CONCLUSIONS: The age at first visit influenced the incidence of cast slippage, but otherwise did not affect the early treatment of clubfoot. CLINICAL RELEVANCE: The treatment of idiopathic clubfoot deformity should not be considered an orthopaedic emergency, and parents whose infants are born with this deformity should be counseled accordingly.

Distal fibula fracture fixation: Biomechanical evaluation of three different fixation implants.

BACKGROUND: The goal of this study was to evaluate the biomechanical performance of three distal fibula fracture fixation implants in a matched pair cadaveric fibula model: (1) a 5-hole compression plate with lag screw, (2) a 5-hole locking plate with lag screw, and (3) the 6-hole tabbed-plate with locking screws. METHODS: Three-dimensional motions between the proximal and distal fibular segments were measured under cyclic valgus bending, cyclic compressive axial loading, and cyclic torsional external-rotation loading. During loading, strains were measured on the surfaces of each fibula near the simulated fracture site, and on the plate, to assess load transfer. Bone quality was quantified globally for each donor using bone mineral density (BMD) measured using Dual X-ray absorptiometry (DEXA) and locally at the fracture site using bone mineral content (BMC) measured using peripheral quantitative computed tomography (pQCT). RESULTS: Mean failure loads were below 0.2Nm of valgus bending and below 4Nm of external-rotational torque. Mean failure angulation was below 1degree for valgus bending, and failure rotation was below 7degrees for external-rotation. In the compression plate group, significant correlations were observed between bone quality (global BMD and local BMC) and strain in every one of the five locations (Pearson correlation coefficients >0.95, p<0.05). In contrast, in the locking and tabbed-plate groups, BMD and BMC correlated with far fewer strain locations. CONCLUSIONS: Overall, the tabbed-plate had similar construct stability and strength to the compression and locking plates. However, the distribution of load with the locking and tabbed-plates was not as heavily dependent on bone quality.

Can wear explain the histological variation around metal-on-metal total hips?

BACKGROUND: There is a general perception that adverse local tissue reactions in metal-on-metal hip arthroplasties are caused by wear, but the degree to which this is the case remains controversial. QUESTIONS/PURPOSES: To what extent is the magnitude of wear associated with (1) the histological changes; (2) presence of metallosis; and (3) likelihood of pseudotumor formation in the periprosthetic tissues? METHODS: One hundred nineteen metal-on-metal total hip arthroplasties and hip resurfacings were selected from a retrieval collection of over 500 implants (collected between 2004 and 2012) based on the availability of periprosthetic tissues collected during revision, clinical data including presence or absence of pseudotumor or metallosis observed intraoperatively, and wear depth measured using a coordinate measurement machine. Histological features of tissues were scored for aseptic lymphocytic vasculitis-associated lesions (ALVAL). Correlation analysis was performed on the three endpoints of interest. RESULTS: With the sample size available, no association was found between wear magnitude and ALVAL score (ρ=-0.092, p=0.423). Median wear depth (ball and cup) was greater in hips with metallosis (137 µm; range, 8-873 µm) than in those without (18 µm; range, 8-174 µm; p<0.0001). With the numbers available, no statistically significant association between wear depth and pseudotumor formation could be identified; median wear depth was 74 µm in hips with pseudotumors and 26 µm in those without (p=0.741). CONCLUSIONS: Wear alone did not explain the histopathological changes in the periprosthetic tissues. A larger sample size and more sensitive outcome variable assessments may have revealed a correlation. However, wear depth has been inconsistently associated with pseudotumor formation, perhaps because some patients with hypersensitivity may develop pseudotumors despite low wear. CLINICAL RELEVANCE: Metal wear alone may not explain the histological reactions and pseudotumors around metal-on-metal hip implants.

Application of the restoring force method for identification of lumbar spine flexion-extension motion under flexion-extension moment.

The restoring force method (RFM), a nonparametric identification technique established in applied mechanics, was used to maximize the information obtained from moment-rotation hysteresis curves under pure moment flexion-extension testing of human lumbar spines. Data from a previous study in which functional spine units were tested intact, following simulated disk injury, and following implantation with an interspinous process spacer device were used. The RFM was used to estimate a surface map to characterize the dependence of the flexion-extension rotation on applied moment and the resulting axial displacement. This described each spine response as a compact, reduced-order model of the complex underlying nonlinear biomechanical characteristics of the tested specimens. The RFM was applied to two datasets, and successfully estimated the flexion-extension rotation, with error ranging from 3 to 23%. First, one specimen, tested in the intact, injured, and implanted conditions, was analyzed to assess the differences between the three specimen conditions. Second, intact specimens (N = 12) were analyzed to determine the specimen variability under equivalent testing conditions. Due to the complexity and nonlinearity of the hysteretic responses, the mathematical fit of each surface was defined in terms of 16 coefficients, or a bicubic fit, to minimize the identified (estimated) surface fit error. The results of the first analysis indicated large differences in the coefficients for each of the three testing conditions. For example, the coefficient corresponding to the linear stiffness (a01) had varied magnitude among the three conditions. In the second analysis of the 12 intact specimens, there was a large variability in the 12 unique sets of coefficients. Four coefficients, including two interaction terms comprised of both axial displacement and moment, were different from zero (p < 0.05), and provided necessary quantitative information to describe the hysteresis in three dimensions. The results suggest that further work in this area has the potential to supplement typical biomechanical parameters, such as range of motion, stiffness, and neutral zone, and provide a useful tool in diagnostic applications for the reliable detection and quantification of abnormal conditions of the spine.

Systematic analysis of bisphosphonate intervention on periprosthetic BMD as a function of stem design.

The purpose of this study was to determine the effects of bisphosphonates periprosthetic BMD in THA patients as a function of stem design. Specifically, the goals were to determine if bisphosphonates as a group could significantly inhibit periprosthetic bone loss, time needed to see an effect, if one drug was more effective than the others, and if there was a difference due to stem design or cement. Thirteen articles met the inclusion criteria. Overall, groups treated with bisphosphonate therapy preserved significantly more BMD than the control groups as early as six months postoperatively, and orally delivered bisphosphonates were most effective. Furthermore, the biggest differences were in patients with non-cemented stems, and of those, the largest differences were seen in patients with fully coated CoCr stems.

An additively manufactured model for preclinical testing of cervical devices.

Purpose: Composite models have become commonplace for the assessment of fixation and stability of total joint replacements; however, there are no comparable models for the cervical spine to evaluate fixation. The goal of this study was to create the framework for a tunable non-homogeneous model of cervical vertebral body by identifying the relationships between strength, in-fill density, and lattice structure and creating a final architectural framework for specific strengths to be applied to the model. Methods: The range of material properties for cervical spine were identified from literature. Using additive manufacturing software, rectangular prints with three lattice structures, gyroid, triangle, zig-zag, and a range of in-fill densities were 3D-printed. The compressive and shear strengths for all combinations were calculated in the axial and coronal planes. Eleven unique vertebral regions were selected to represent the distribution of density. Each bone density was converted to strength and subsequently correlated to the lattice structure and in-fill density with the desired material properties. Finally, a complete cervical vertebra model was 3D-printed to ensure sufficient print quality. Results: Materials testing identified a relationship between in-fill densities and strength for all lattice structures. The axial compressive strength of the gyroid specimens ranged from 1.5 MPa at 10% infill to 31.3 MPa at 100% infill and the triangle structure ranged from 2.7 MPa at 10% infill to 58.4 MPa at 100% infill. Based on these results, a cervical vertebra model was created utilizing cervical cancellous strength values and the corresponding in-fill density and lattice structure combination. This model was then printed with 11 different in-fill densities ranging from 33% gyroid to 84% triangle to ensure successful integration of the non-homogeneous in-fill densities and lattice structures. Conclusions: The findings from this study introduced a framework for using additive manufacturing to create a tunable, customizable biomimetic model of a cervical vertebra.

Fixation of non-cemented total hip arthroplasty femoral components in a simulated proximal bone defect model.

An accelerated sequential proximal femoral bone loss model was used to measure the initial stability of three noncemented femoral stem designs: fully porous-coated, proximally porous-coated, and dual-tapered, diaphyseal press-fit (N=18). Only dual-tapered, diaphyseal press-fit stems remained stable with as much as 105 mm of bone loss, with average cyclic micromotion remaining below 25 µm in ML and below 10 µm in AP planes. In contrast, with proximally coated and fully coated stem designs with circular or oval cross-sections, 60mm of bone loss, resulting in lower than 10 cm of diaphyseal bone contact length, led to gross instability, increasing average cyclic micromotions to greater than 100 µm prior to failure. Therefore, the results provide support for using a dual-tapered stem in revision cases with proximal bone loss.

Observations of bony ongrowth and clinical fixation in two retrieved disc replacements.

Total disc replacements utilize textured coatings to maximize bony ongrowth. However, the contribution of direct bony attachment to overall fixation for total disc replacements has not been reported. The goal of the present study was to document the extent of bony attachment to the surfaces of two clinically functional total disc replacements that were securely fixed at the time of revision. Two metal-and-polymeric disc replacements, one cervical and one lumbar, were evaluated following surgical retrieval. The cervical device was retrieved at 8 months and the lumbar device at 28 months post-operative. Both devices were reported well-fixed at the time of removal, with large bone masses attached to one endplate of each device. Visual inspections, non-destructive gravimetric measurements, and surface metrology were performed to assess fixation. These inspections suggested that both devices had been fixed at the time of removal with little in vivo mechanical damage, as surgical extraction damage was noted on both devices and provided imaging showed a lack of device migration. Devices were then embedded and sectioned to evaluate the bone-implant interface. High resolution photographs and contact microradiographs were taken to assess bony attachment. In contrast to initial analysis, these images revealed radiolucent gaps between the endplates and bone masses. Little direct contact between the bone and endplate surface was identified and the original surgical cuts were still visible. Both devices were clinically fixed at the time of removal and neither had complications associated with loosening. However, osseointegration was minimal in one of the devices and altogether absent from the other. The findings of the present study suggest that other factors may influence overall clinical fixation such as the surgical preparation of the vertebral bone or the surface roughness of the treated endplates. Despite the limitations of the present study, this information is unique to the current total disc replacement literature and the ongrowth and fixation of devices should be considered as a topic for future investigation.

Can severity of trunnion damage be estimated by visual inspection alone?

Taper corrosion has been widely reported to be problematic for modular total hip arthroplasty implants. A simple and systematic method to evaluate taper damage with sufficient resolution is needed. We introduce a semiquantitative grading system for modular femoral tapers to characterize taper corrosion damage. After examining a unique collection of retrieved cobalt-chromium (CoCr) taper sleeves (n = 465) using the widely-used Goldberg system, we developed an expanded six-point visual grading system intended to characterize the severity, visible material loss, and absence of direct component contact due to corrosion. Female taper sleeve damage was evaluated by three blinded observers using the Goldberg scoring system and the expanded system. A subset (n = 85) was then re-evaluated following destructive cleaning, using both scoring systems. Material loss for this subset was quantified using metrology and correlated with both scoring systems. There was substantial agreement in grading among all three observers with uncleaned (n = 465) and with the subset of cleaned (n = 85) implants. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. Cleaning changed the average scores marginally using the Goldberg criteria (p = 0.290); however, using the VGS, approximately 40% of the scores for all observers changed, increasing the average score from 4.24 to 4.35 (p = 0.002). There was a strong correlation between measured material loss and new grading scores. The expanded scoring criteria provided a wider distribution of scores which ultimately correlated well with corrosion material loss. This system provides potential advantages for assessing taper damage without requiring specialized imaging devices.

Evaluation of Topology Optimization Using 3D Printing for Bioresorbable Fusion Cages: A Biomechanical Study in a Porcine Model.

STUDY DESIGN: Preclinical biomechanical study of topology optimization versus standard ring design for bioresorbable poly-ε-caprolactone (PCL) cervical spine fusion cages delivering bone morphogenetic protein-2 (BMP-2) using a porcine model. OBJECTIVE: The aim was to evaluate range of motion (ROM) and bone fusion, as a function of topology optimization and BMP-2 delivery method. SUMMARY OF BACKGROUND DATA: 3D printing technology enables fabrication of topology-optimized cages using bioresorbable materials, offering several advantages including customization, and lower stiffness. Delivery of BMP-2 using topology optimization may enhance the quality of fusion. METHODS: Twenty-two 6-month-old pigs underwent anterior cervical discectomy fusion at one level using 3D printed PCL cages. Experimental groups (N=6 each) included: Group 1: ring design with surface adsorbed BMP-2, Group 2: topology-optimized rectangular design with surface adsorbed BMP-2, and Group 3: ring design with BMP-2 delivery via collagen sponge. Additional specimens, two of each design, were implanted without BMP-2, as controls. Complete cervical segments were harvested six months postoperatively. Nanocomputed tomography was performed to assess complete bony bridging. Pure moment biomechanical testing was conducted in all three planes, separately. Continuous 3D motions were recorded and analyzed. RESULTS: Three subjects suffered early surgical complications and were not evaluated. Overall, ROM for experimental specimens, regardless of design or BMP-2 delivery method, was comparable, with no clinically significant differences among groups. Among experimental specimens at the level of the fusion, ROM was <1.0° in flexion and extension, indicative of fusion, based on clinically applied criteria for fusion of <2 to 4°. Despite the measured biomechanical stability, using computed tomography evaluation, complete bony bridging was observed in 40% of the specimens in Group 1, 50% of Group 2, 100% of Group 3, and none of the control specimens. CONCLUSION: A topology-optimized PCL cage with BMP-2 is capable of resulting in an intervertebral fusion, similar to a conventional ring-based design of the same bioresorbable material.

Site-specific quantification of bone quality using highly nonlinear solitary waves.

Osteoporosis is a well recognized problem affecting millions of individuals worldwide. The ability to diagnose problems in an effective, efficient, and affordable manner and identify individuals at risk is essential. Site-specific assessment of bone mechanical properties is necessary, not only in the process of fracture risk assessment, but may also be desirable for other applications, such as making intraoperative decisions during spine and joint replacement surgeries. The present study evaluates the use of a one-dimensional granular crystal sensor to measure the elastic properties of bone at selected locations via direct mechanical contact. The granular crystal is composed of a tightly packed chain of particles that interact according to the Hertzian contact law. Such chains represent one of the simplest systems to generate and propagate highly nonlinear acoustic signals in the form of compact solitary waves. First, we investigated the sensitivity of the sensor to known variations in bone density using a synthetic cancellous bone substitute, representing clinical bone quality ranging from healthy to osteoporotic. Once the relationship between the signal response and known bone properties was established, the sensor was used to assess the bone quality of ten human cadaveric specimens. The efficacy and accuracy of the sensor was then investigated by comparing the sensor measurements with the bone mineral density (BMD) obtained using dual-energy x-ray absorptiometry (DEXA). The results indicate that the proposed technique is capable of detecting differences in bone quality. The ability to measure site-specific properties without exposure to radiation has the potential to be further developed for clinical applications.

The current management of idiopathic clubfoot revisited: results of a survey of the POSNA membership.

BACKGROUND: In 2001, the members of the Pediatric Orthopaedic Society of North America (POSNA) were surveyed regarding their approach to treating idiopathic clubfoot deformity. Since that time, several studies have advocated a change in the approach to treating this deformity, moving away from surgical release and toward less invasive methods. The purpose of this study was to assess the recent approach to treating clubfoot among the POSNA membership. METHODS: A survey was emailed to all POSNA members to define their current treatment of idiopathic clubfoot deformity. RESULTS: We received 323 responses. Ninety-three percent of participants were fellowship trained and were in practice for an average of 17.2 years. On an average, physicians reported each treating 23.5 new clubfoot patients during the year of survey. Nearly all (96.7%) of those surveyed stated that they use the Ponseti treatment method. The average time to initial correction was estimated at 7.1 weeks. Eighty-one percent of patients were estimated to require a tenotomy; 52.7% were performed under general anesthesia or conscious sedation, whereas 39.4% were done under local. Those surveyed estimated that 22% of clubfeet relapsed and 7% required a comprehensive release. Seventy-five percent of the respondents stated that their current treatment approach differed from how they were trained, and 82.7% were trained in the Ponseti method in the last few years. CONCLUSIONS: Our study provides convincing evidence that a large majority of pediatric orthopaedic surgeons now prefer the Ponseti method to treat idiopathic clubfoot and indicates that the move away from extensive release surgery occurred during the past decade. LEVEL OF EVIDENCE: Not applicable.