The Effect of Forearm Shortening on Forearm Range of Motion.

PURPOSE: Osseous shortening of the forearm is performed during forearm replantation; however, no large clinical reviews have discussed its effects on patient outcomes. A recent cadaver study demonstrated the progressive loss of forearm pronation/supination ranges of motion with increased shortening lengths using external fixation. Our study aimed to quantify the effects of shortening on passive forearm motion using internal fixation after 2, 4, and 6 cm of mid-forearm shortening. METHODS: A volar Henry approach and direct approach to the ulna were used on 8 cadaveric specimens. The forearms were sequentially shortened by 2, 4, and 6 cm. Fixation was performed on the volar surfaces of the radius and ulna. Pronation and supination of the forearms were tested by applying 1 Nm of torque at baseline and after the fixation of both the radius and ulna using osteotomy. Radiographs and measurements were obtained at each phase to determine the maximum radial bow and radioulnar gap. Data were analyzed using a linear mixed-effects model. RESULTS: Greater shortening of the radius and ulna led to progressively greater reductions in both pronation and supination range of motion. Larger differences were seen in supination at 2-4 cm of shortening and in pronation at 4-6 cm of shortening. Changes in supination were found to be associated with the radial bow and radioulnar gap; changes in pronation were found to be associated with the radial bow and radial bow's location. CONCLUSIONS: This study demonstrates that quantifiable effects on passive forearm motion occur after osseous shortening of the forearm. CLINICAL RELEVANCE: This information may improve surgeons' and patients' understanding of the changes in forearm motion expected after shortening in the setting of replantation or tumor resection or in the setting of limb salvage of a mangled extremity.

The effect of proximal tibiofibular joint dislocation on knee mechanics: reduction and fixation matters.

PURPOSE: Proximal tibiofibular joint (PTFJ) dislocations are under-investigated injuries. There is scant basic science or clinical evidence to direct management. The purpose of this study was twofold; first to investigate the pathomechanics of PTFJ dislocation on knee mechanics. The second purpose was to evaluate knee mechanics following reduction and fixation. METHODS: Six cadaveric legs were tested on a mechanical platform. A 5 Nm external rotation force was applied to each knee and the external rotation and fibular translation was measured for several study conditions at 0°, 30°, and 90° of flexion. Conditions included: the native state, transection of the posterior PTFJ ligament, transection of the anterior and posterior ligaments, screw fixation, and suspensory fixation. Screw fixation was performed using a single quadricortical 3.5 mm screw. Suspensory fixation was performed using an Arthrex TightRope device RESULTS: Transection of the anterior and posterior ligaments increased external rotation by 4.3°, 5.9°, and 5.6°, at 0°, 30°, and 90° (p ≤ 0.001), respectively. Screw and suspensory fixation returned external rotation to a near native state with mild overconstraint. Complete transection of anterior and posterior ligaments resulted in pathologic anterior fibular translation of 1.51 mm (p = 0.001), 1 mm, (p = 0.02) and 0.44 mm (p = 0.69) for 0°, 30°, 90° of knee flexion. Screw and suspensory fixation restored native translation at all points with a small degree of overconstraint. CONCLUSION: Disruption of the PTFJ causes pathologic external rotation and anterior fibular translation. Fixation restores near native motion with minor overconstraint. Surgeons should consider reduction and fixation of PTFJ injuries to restore native knee mechanics.

Changes in scapular bone density vary by region and are associated with age and sex.

BACKGROUND: Decreases in bone density of the scapula due to age and disease can make orthopedic procedures such as arthroplasty and fracture fixation challenging. There is limited information in the literature regarding the effect of age and sex on the patterns of these density changes across the bone. Characterizing these changes could assist the surgeon in planning optimal instrumentation placement. METHODS: Ninety-seven 3-dimensional models of the scapula were segmented from routine clinical computed tomography scans, and an opportunistic quantitative computed tomography approach was used to obtain detailed calibrated bone density measurements for each bone model. The effects of age and sex on cortical and trabecular bone density were assessed for the entire scapula. Specific regions (eg, scapular spine) where these factors had a significant effect were identified. Three-dimensional models were generated to allow clear visualization of the changes in density patterns. RESULTS: Cortical bone loss averaged 1.0 mg/cm3 and 0.3 mg/cm3 per year for female and male subjects, respectively, and trabecular bone loss averaged 1.6 mg/cm3 and 1.2 mg/cm3, respectively. However, several regions had loss rates several times greater. Areas that were significantly affected by age included the acromion, scapular spine, base of the coracoid, inferior glenoid neck, and glenoid vault. Areas that were significantly affected by sex were the scapular spine and body. CONCLUSIONS: These findings provide evidence that the bone density distribution across the scapula changes non-uniformly because of factors including sex and age. Despite overall trends of bone loss, there remains significant variability between individuals, and subject-specific tools for planning surgical procedures in which scapular fixation is required may be beneficial.

Metatarsal Shape and Foot Type: A Geometric Morphometric Analysis.

Planus and cavus foot types have been associated with an increased risk of pain and disability. Improving our understanding of the geometric differences between bones in different foot types may provide insights into injury risk profiles and have implications for the design of musculoskeletal and finite-element models. In this study, we performed a geometric morphometric analysis on the geometry of metatarsal bones from 65 feet, segmented from computed tomography (CT) scans. These were categorized into four foot types: pes cavus, neutrally aligned, asymptomatic pes planus, and symptomatic pes planus. Generalized procrustes analysis (GPA) followed by permutation tests was used to determine significant shape differences associated with foot type and sex, and principal component analysis was used to find the modes of variation for each metatarsal. Significant shape differences were found between foot types for all the metatarsals (p < 0.01), most notably in the case of the second metatarsal which showed significant pairwise differences across all the foot types. Analysis of the principal components of variation showed pes cavus bones to have reduced cross-sectional areas in the sagittal and frontal planes. The first (p = 0.02) and fourth metatarsals (p = 0.003) were found to have significant sex-based differences, with first metatarsals from females shown to have reduced width, and fourth metatarsals from females shown to have reduced frontal and sagittal plane cross-sectional areas. Overall, these findings suggest that metatarsal bones have distinct morphological characteristics that are associated with foot type and sex, with implications for our understanding of anatomy and numerical modeling of the foot.

Metatarsal Loading During Gait-A Musculoskeletal Analysis.

Detailed knowledge of the loading conditions within the human body is essential for the development and optimization of treatments for disorders and injuries of the musculoskeletal system. While loads in the major joints of the lower limb have been the subject of extensive study, relatively little is known about the forces applied to the individual bones of the foot. The objective of this study was to use a detailed musculoskeletal model to compute the loads applied to the metatarsal bones during gait across several healthy subjects. Motion-captured gait trials and computed tomography (CT) foot scans from four healthy subjects were used as the inputs to inverse dynamic simulations that allowed the computation of loads at the metatarsal joints. Low loads in the metatarsophalangeal (MTP) joint were predicted before terminal stance, however, increased to an average peak of 1.9 times body weight (BW) before toe-off in the first metatarsal. At the first tarsometatarsal (TMT) joint, loads of up to 1.0 times BW were seen during the early part of stance, reflecting tension in the ligaments and muscles. These loads subsequently increased to an average peak of 3.0 times BW. Loads in the first ray were higher compared to rays 2-5. The joints were primarily loaded in the longitudinal direction of the bone.

Reproducibility of a peripheral quantitative computed tomography scan protocol to measure the material properties of the second metatarsal.

BACKGROUND: Peripheral quantitative computed tomography (pQCT) is an established technology that allows for the measurement of the material properties of bone. Alterations to bone architecture are associated with an increased risk of fracture. Further pQCT research is necessary to identify regions of interest that are prone to fracture risk in people with chronic diseases. The second metatarsal is a common site for the development of insufficiency fractures, and as such the aim of this study was to assess the reproducibility of a novel scanning protocol of the second metatarsal using pQCT. METHODS: Eleven embalmed cadaveric leg specimens were scanned six times; three times with and without repositioning. Each foot was positioned on a custom-designed acrylic foot plate to permit unimpeded scans of the region of interest. Sixty-six scans were obtained at 15% (distal) and 50% (mid shaft) of the second metatarsal. Voxel size and scan speed were reduced to 0.40 mm and 25 mm.sec(-1). The reference line was positioned at the most distal portion of the 2(nd) metatarsal. Repeated measurements of six key variables related to bone properties were subject to reproducibility testing. Data were log transformed and reproducibility of scans were assessed using intraclass correlation coefficients (ICC) and coefficients of variation (CV%). RESULTS: Reproducibility of the measurements without repositioning were estimated as: trabecular area (ICC 0.95; CV% 2.4), trabecular density (ICC 0.98; CV% 3.0), Strength Strain Index (SSI) - distal (ICC 0.99; CV% 5.6), cortical area (ICC 1.0; CV% 1.5), cortical density (ICC 0.99; CV% 0.1), SSI - mid shaft (ICC 1.0; CV% 2.4). Reproducibility of the measurements after repositioning were estimated as: trabecular area (ICC 0.96; CV% 2.4), trabecular density (ICC 0.98; CV% 2.8), SSI - distal (ICC 1.0; CV% 3.5), cortical area (ICC 0.99; CV%2.4), cortical density (ICC 0.98; CV% 0.8), SSI - mid shaft (ICC 0.99; CV% 3.2). CONCLUSIONS: The scanning protocol generated excellent reproducibility for key bone properties measured at the distal and mid-shaft regions of the 2(nd) metatarsal. This protocol extends the capabilities of pQCT to evaluate bone quality in people who may be at an increased risk of metatarsal insufficiency fractures.

Healthcare segregation in orthopedic surgery: A statewide analysis of American Indian and Alaska Native patients.

Significant health disparities have been described for American Indian and Alaska Native (AIAN) patients undergoing various surgical procedures, however, research into healthcare segregation within orthopedic surgery has been limited. In this study, our purpose was to assess if AIAN patients were more likely to be treated by lower-volume surgeons and at lower-volume hospitals. AIAN and White patients who underwent one of four common orthopedic procedures (knee or hip arthroplasty, femur or tibia repair) were identified from a Washington state inpatient database. Demographic, socioeconomic, geographic, and procedure data were surveyed, and volumetric thresholds were established for lower versus higher volume surgeons and hospitals. Adjusted odds ratios were calculated for AIAN patients receiving care from a lower volume surgeon or hospital, including covariates for patient demographics, geographic, and socioeconomic status. AIAN patients were more likely to receive care from a lower-volume surgeon for all procedures except tibial repair. Adjusted odds ratios of 1.53 (95% confidence interval [CI]: 1.22, 1.92) and 1.68 (95% CI: 1.26, 2.21) were found for AIAN patients receiving knee or hip arthroplasty from a lower volume surgeon, respectively. There was no strong evidence of AIAN patients being more likely to receive care at a lower-volume hospital. Finally, AIAN patients having knee arthroplasty at a higher volume hospital were more likely to have their surgery performed by a lower volume surgeon. These data suggest that there may be significant healthcare segregation among AIAN patients across common orthopedic surgical procedures.

Exploring the mechanical properties of 3D-printed multilayer lattice structures for use in accommodative insoles.

Full-contact insoles fabricated from multilayer foams are the standard of care (SoC) for offloading and redistributing high plantar pressures in individuals with diabetes at risk of plantar ulceration and subsequent lower limb amputation. These devices have regional variations in total thickness and layer thickness to create conformity with a patient's foot. Recent work has demonstrated that metamaterials can be tuned to match the mechanical properties of SoC insole foams. However, for devices fabricated using a multilayer lattice structure, having regional variations in total thickness and layer thickness may result in regional differences in mechanical properties that have yet to be investigated. Three lattices, two dual-layer and one uniform-layer lattice structure, designed to model the mechanical properties of SoC insoles, were 3D-printed at three structure/puck thicknesses representing typical regions seen in accommodative insoles. The pucks underwent cyclic compression testing, and the stiffness profiles were assessed. Three pucks at three structure/puck thicknesses fabricated from SoC foams were also tested. Initial evaluations suggested that for the latticed pucks, structure thickness and density inversely impacted puck stiffness. Behaving most like the SoC pucks, a dual-layer lattice that increased in density as structure thickness increased demonstrated consistent stiffness profiles across puck thicknesses. Identifying a lattice with constant mechanical properties at various structure thicknesses may be important to produce a conforming insole that emulates the standard of care from which patient-specific/regional lattice modulations can be made.

Improving Patient Understanding of Femoroacetabular Impingement Syndrome With Three-Dimensional Models.

INTRODUCTION: Three-dimensional (3D) printed models may help patients understand complex anatomic pathologies such as femoroacetabular impingement syndrome (FAIS). We aimed to assess patient understanding and satisfaction when using 3D printed models compared with standard imaging modalities for discussion of FAIS diagnosis and surgical plan. METHODS: A consecutive series of 76 new patients with FAIS (37 patients in the 3D model cohort and 39 in the control cohort) from a single surgeon's clinic were educated using imaging and representative 3D printed models of FAI or imaging without models (control). Patients received a voluntary post-visit questionnaire that evaluated their understanding of the diagnosis, surgical plan, and visit satisfaction. RESULTS: Patients in the 3D model cohort reported a significantly higher mean understanding of FAIS (90.0 ± 11.5 versus 79.8 ± 14.9 out of 100; P = 0.001) and surgery (89.5 ± 11.6 versus 81.0 ± 14.5; P = 0.01) compared with the control cohort. Both groups reported high levels of satisfaction with the visit. CONCLUSION: In this study, the use of 3D printed models in clinic visits with patients with FAIS improved patients' perceived understanding of diagnosis and surgical treatment.

A lateral extra-articular tenodesis without additional hardware: Surgical technique and biomechanical comparison with an anatomic anterolateral ligament reconstruction in the augmentation of anterior cruciate ligament reconstruction.

BACKGROUND: The aims of this study were to describe a lateral extra-articular tenodesis (LET) using no additional hardware and compare the tibiofemoral kinematics of anterior cruciate ligament (ACL) reconstruction augmented with either the LET or a standard anatomic anterolateral ligament (ALL) reconstruction using intra-tunnel fixation. METHODS: Ten cadaveric knees were mounted on a robotic testing system and underwent a kinematic assessment of anterior tibial translation and internal tibial rotation under a simulated pivot-shift in the following states: ACL-intact, ACL-sectioned, ACL-sectioned/anterolateral complex (ALC)-sectioned, ACL-reconstructed/ALC-sectioned, ACL-reconstructed/ALL-reconstructed, and ACL-reconstructed/LET. For the LET, an iliotibial autograft was passed under the fibular collateral ligament and secured to the femur with the pull sutures of the ACL reconstruction femoral cortical suspensory fixation device, positioned at the distal ridge of Kaplan's fibers. RESULTS: Anterior tibial translation was restored to normal by ACL reconstruction without meaningful benefit of augmentation with LET or ALL. ACL reconstruction restored internal tibial rotation close to normal between 0° and 30°, but increased internal tibial rotation persisted between 45° and 90°. Augmentation of ACL reconstruction with the LET reduced internal rotation close to normal between 45° and 90°, whereas increased internal rotation persisted after ALL reconstruction. CONCLUSION: ACL reconstruction and LET are complementary in controlling tibiofemoral kinematics of knees with a combined ACL and ALC injury: ACL reconstruction restored native tibiofemoral kinematics except for internal rotation at flexion greater than 30°. The increased internal rotation at flexion greater than 30° was restored to normal with an LET, but not with an ALL reconstruction.

pressuRe: an R package for analyzing and visualizing biomechanical pressure distribution data.

In many biomechanical analyses, the forces acting on a body during dynamic and static activities are often simplified as point loads. However, it is usually more accurate to characterize these forces as distributed loads, varying in magnitude and direction, over a given contact area. Evaluating these pressure distributions while they are applied to different parts of the body can provide effective insights for clinicians and researchers when studying health and disease conditions, for example when investigating the biomechanical factors that may lead to plantar ulceration in diabetic foot disease. At present, most processing and analysis for pressure data is performed using proprietary software, limiting reproducibility, transparency, and consistency across different studies. This paper describes an open-source software package, 'pressuRe', which is built in the freely available R statistical computing environment and is designed to process, analyze, and visualize pressure data collected on a range of different hardware systems in a standardized manner. We demonstrate the use of the package on pressure dataset from patients with diabetic foot disease, comparing pressure variables between those with longer and shorter durations of the disease. The results matched closely with those from commercially available software, and individuals with longer duration of diabetes were found to have higher forefoot pressures than those with shorter duration. By utilizing R's powerful and openly available tools for statistical analysis and user customization, this package may be a useful tool for researchers and clinicians studying plantar pressures and other pressure sensor array based biomechanical measurements. With regular updates intended, this package allows for continued improvement and we welcome feedback and future contributions to extend its scope. In this article, we detail the package's features and functionality.

Intra-Articular Antegrade Intramedullary Screw Fixation for Proximal Phalanx Fractures: Impact of Articular Surface Defects on Joint Contact Pressures.

BACKGROUND: Intramedullary headless screw fixation is increasingly used for fixation of proximal phalanx fractures. However, the impact of screw entry defects on joint contact pressures is not well defined and may have implications for arthrosis. The objective of this cadaveric biomechanical study was to assess joint contact pressures at the metacarpophalangeal (MCP) joint before and after passage of 2 sizes of antegrade intramedullary fixation. METHODS: Seven fresh frozen cadaver specimens without arthritis or deformity were included in this study. Antegrade intramedullary screw fixation of proximal phalanx fracture was simulated using an intra-articular technique. Flexible pressure sensors were inserted into the MCP joints and cyclic loading was performed. Peak contact pressures were determined and averaged across loading cycles for each finger in the native state, with 2.4- and 3.5-mm drill defects in line with the medullary canal. RESULTS: Peak pressure increased with the size of the drill hole defect. Contact pressure increases were greater in extension, with peak contact pressures increased by 24% for the 2.4-mm defect and 52% for the 3.5-mm defect. Increase in peak contact pressure was statistically significant with a 3.5-mm articular defect. Contact pressures were not consistently increased for the 2.4-mm defect. Testing in flexion of 45° resulted in reduced contact pressure for these defects. CONCLUSIONS: Our study demonstrates that antegrade intramedullary fixation of proximal phalanx fractures can increase MCP joint peak contact pressures, particularly in an extended joint position. Effect increases with defect size. This has implications for the management of proximal phalanx fractures using this technique.

Biomechanics of Proximal Hamate Autograft in Scaphoid Nonunion.

Purpose Treatment of proximal scaphoid fractures remains a challenge with a risk of nonunions and avascular necrosis due to its retrograde blood supply. The ipsilateral proximal hamate has been described as a viable autograft option for osteochondral reconstruction of the proximal scaphoid. Our study evaluated the changes in the contact area and pressure of the radioscaphoid joint after proximal hamate autograft reconstruction. Methods Thin sensors (Tekscan Inc., Boston, MA) were placed in the radiocarpal joints of six fresh-frozen cadaveric forearms. Each specimen's tendons were loaded to 150 N in neutral, 45-degree flexion/extension positions through five cycles. Through a dorsal wrist approach, the proximal 10 mm of the scaphoid and hamate was excised. The proximal hamate autograft was affixed to the scaphoid with K-wires. Peak contact pressures and areas at the scaphoid facet were determined and averaged across loading cycles. Results At the radioscaphoid facet, peak contact pressures were equivalent, although an increasing trend in the neutral and extended wrist position was seen. At the radiolunate facet, contact pressure had an increasing trend in the hamate reconstructed wrists in all wrist positions. Contact areas had a decreasing trend and were nonequivalent at the radioscaphoid facet in the hamate reconstructed wrist. Conclusion After hamate autograft, the contact areas were not equivalent between the native and reconstructed wrists but contact pressures were equivalent in the facets. The proximal hamate has a more pointed morphology compared with the proximal scaphoid, which would explain the change in contact area in the hamate autografted wrist. Our study suggests hamate autograft may present a viable reconstruction for the proximal pole of the scaphoid without significantly altering peak contact pressures at the radioscaphoid facet.

The effect of foot-stretcher position and stroke rate on ergometer rowing kinematics.

Rowing ergometers are popular tools for general fitness and competitive crew teams. The effect of the equipment set up on the rowing stroke has received limited attention. This study aimed to determine the effects of altering the foot-stretcher position on rowing kinematics across different stroke rates. Eleven college-level rowers took part in this study. A rowing ergometer was modified to allow the height and angle of the foot-stretcher to be adjusted. Seven foot-stretcher positions were tested, each at rates of 22, 26, and 32 strokes per minute. Sagittal plane kinematic waveforms were compared between conditions for all major joints using statistical parametric mapping, and temporal variables were assessed (p < 0.05). Stroke rate was found to affect kinematic patterns for all joints. The effect of the foot-stretcher position was limited to the ankle and hip. Similarly, the timing of events during the rowing stroke was affected by the stroke rate, but not foot position. These results indicate that while some limited changes to the stroke technique can be caused by altering the foot-stretcher position, the changes were largely compensated for by the rowers and are generally smaller than differences between stroke rates.

Ideal Length and Diameter for Intramedullary Screw Fixation of Metacarpal Fractures: A Biomechanical Study.

Purpose: This biomechanical study evaluated the effect of intramedullary screw diameter and length relative to 3-point bending force and torsional force when used to stabilize metacarpal shaft fractures. Methods: Transverse osteotomies were made in the proximal metacarpal shaft in 36 middle finger metacarpal fourth-generation composite Sawbones. To compare screw diameters, antegrade intramedullary screws of 30-mm length were placed in 6 metacarpals, which included 4.7-mm Acutrak 2, Standard Acutrak 2 (4.0 mm), and Mini-Acutrak 2 (3.5 mm) screws. To compare screw lengths, metacarpals were fixated with Standard Acutrak 2 screws of 26, 30, or 34 mm in length, with screw tips bypassing the osteotomy by 6, 10, or 14 mm, respectively. A 6 degrees of freedom robot was used for torsional and 3-point bending testing. Results: Increasing screw diameter demonstrated significant differences in both 3-point bending and torsional strengths. Maximum torsional loads were 69 Ncm (4.7-mm Acutrak 2), 45 Ncm (Standard Acutrak 2), and 27 Ncm (Mini-Acutrak 2) (P < .05). Loads to failure in the 3-point bending tests were 916 N (4.7-mm Acutrak 2), 713 N (Standard Acutrak 2), and 284 N (Mini-Acutrak 2) (P < .05). Differing screw lengths demonstrated significant differences with maximum torsional loads when comparing the 26-mm screws (22 Ncm) with 30- and 34-mm screws (45 and 55 Ncm, respectively) (P < .05). The 3-point dorsal bending strengths were significantly different between the 26-mm screws (320 N) and 30- and 34-mm screws (713 N and 702 N, respectively) (P < .05). Conclusions: The results demonstrated significantly higher torsional strength and resistance to 3-point bending with larger intramedullary screw diameters. Further, when selecting the intramedullary screw length, the screw tip should pass at least 10 mm beyond the fracture. Clinical Relevance: This study provided biomechanical evidence to guide surgeons in selecting intramedullary screw diameter and length for treating metacarpal fractures.

Assessment of regional sacral bone quality: A step towards patient-specific fracture fixation.

Characterizing changes in sacral bone density could help us to inform instrumentation choices for procedures involving the sacrum. The aim of this study is to provide detailed maps of changes in sacral bone density across a series of patients using opportunistic quantitative computed tomography (QCT). We hypothesized that there would be significant differences in local cortical and trabecular bone density associated with age and sex. Fifty-four three-dimensional sacral models were segmented from routine clinical computed tomography scans, and detailed bone density estimates were derived for each bone using a calibrated opportunistic QCT approach. The effects of age and sex on cortical and trabecular bone density were determined across the sample. Overall cortical bone loss averaged 2.1 and 0.9 mg/cc per year, and trabecular bone loss was 1.6 and 0.7 mg/cc for female and males, respectively. Several regions had loss rates several times greater. Areas that were significantly affected by age included the vertebral bodies, bilateral ala, apex, and areas adjacent to both the anterior and posterior sacral foramina. Areas that were significantly affected by sex were the anterior sacral promontory, aspects of the ala. Bone density distribution across the sacrum changes nonuniformly due to factors including sex and age. Despite these overall trends, there remains significant variability between individuals. Clinical significance: This study provides detailed bone density information for both cortical and trabecular bone that could assist orthopaedic surgeons in planning surgical approaches to sacral fracture fixation.

Quantification and visualization of anterior pelvis bone density to optimize screw fixation: A novel technique.

Plate fixation of anterior pelvic ring fractures is often a vital component when surgically treating unstable pelvis fractures. Certain plate and screw configurations can have premature implant loosening, potentially in part due to insufficient pullout strength in lower density bone. This study sought to define densities about the anterior pelvic ring using a novel computer-based technique. Thirty-three patients who received a computed tomography (CT) of the abdomen/pelvis for reasons other than pelvis fracture in a 1-month time period were included. Three statistically distinct density regions of the anterior pelvis were identified based on the three-dimensional (3D) density map. The densest regions included both the anterior and posterior aspects of the superior pubic ramus, along with the region of bone along the inferior cotyloid fossa. The intermediate density region included the caudal and medial pubic body. The least dense region included the anterior aspect of the inferior pubic ramus (IPR), the posterior pubic body, and the posterior/inferior IPR. This study presents specific quantification of anterior pelvis bone density based on a novel technique using opportunistic CT scans. Clinical Significance: Anterior surgical fixation of unstable pelvic ring injuries may benefit from targeting areas of higher density as described in this novel technique.

Computer-aided design of customized foot orthoses: reproducibility and effect of method used to obtain foot shape.

OBJECTIVE: To determine, for a number of techniques used to obtain foot shape based around plaster casting, foam box impressions, and 3-dimensional scanning, (1) the effect the technique has on the overall reproducibility of custom foot orthoses (FOs) in terms of inter- and intracaster reliability and (2) the reproducibility of FO design by using computer-aided design (CAD) software in terms of inter- and intra-CAD operator reliability for all these techniques. DESIGN: Cross-sectional study. SETTING: University laboratory. PARTICIPANTS: Convenience sample of individuals (N=22) with noncavus foot types. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Parameters of the FO design (length, width at forefoot, width at rearfoot, and peak medial arch height), the forefoot to rearfoot angle of the foot shape, and overall volume match between device designs. RESULTS: For intra- and intercaster reliability of the different methods of obtaining the foot shape, all methods fell below the reproducibility quality threshold for the medial arch height of the device, and volume matching was <80% for all methods. The more experienced CAD operator was able to achieve excellent reliability (intraclass correlation coefficients >0.75) for all variables with the exception of forefoot to rearfoot angle, with overall volume matches of >87% of the devices. CONCLUSIONS: None of the techniques for obtaining foot shape met all the criteria for excellent reproducibility, with the peak arch height being particularly variable. Additional variability is added at the CAD stage of the FO design process, although with adequate operator experience good to excellent reproducibility may be achieved at this stage. Taking only basic linear or angular measurement parameters from the device may fail to fully capture the variability in FO design.

Embracing additive manufacture: implications for foot and ankle orthosis design.

BACKGROUND: The design of foot and ankle orthoses is currently limited by the methods used to fabricate the devices, particularly in terms of geometric freedom and potential to include innovative new features. Additive manufacturing (AM) technologies, where objects are constructed via a series of sub-millimetre layers of a substrate material, may present the opportunity to overcome these limitations and allow novel devices to be produced that are highly personalised for the individual, both in terms of fit and functionality.Two novel devices, a foot orthosis (FO) designed to include adjustable elements to relieve pressure at the metatarsal heads, and an ankle foot orthosis (AFO) designed to have adjustable stiffness levels in the sagittal plane, were developed and fabricated using AM. The devices were then tested on a healthy participant to determine if the intended biomechanical modes of action were achieved. RESULTS: The adjustable, pressure relieving FO was found to be able to significantly reduce pressure under the targeted metatarsal heads. The AFO was shown to have distinct effects on ankle kinematics which could be varied by adjusting the stiffness level of the device. CONCLUSIONS: The results presented here demonstrate the potential design freedom made available by AM, and suggest that it may allow novel personalised orthotic devices to be produced which are beyond the current state of the art.

What happens at the L5/S1 facet joint when implants are placed across the sacroiliac joint?

BACKGROUND: Injuries to the posterior pelvic ring are often stabilized with fixation across the sacroiliac joint (SIJ). However, the compensatory changes at the neighboring L5/S1 facet joint are unknown. The objective of this study was to determine the compensatory change in pelvic kinematics and contact forces at the L5/S1 facet joint after fixation across the sacroiliac joint (SIJ) using a cadaveric model. METHODS: Five fresh-frozen cadaveric pelvis specimens were dissected to remove non-structural soft tissue. Retroreflective markers were fixed to the L5 body, S1 body and bilateral anterior superior iliac spines to represent the motion of L5, S1 and the ileum, respectively. Pressure sensors were inserted in both L5/S1 facet joints. Testing was performed using a robotic system that applied load to mimic ambulation. Testing was performed prior to SIJ fixation, after unilateral SIJ fixation and bilateral fixation. RESULTS: Contact force at the L5/S1 facet joint significantly increased by 55% from 48.4 N to 75.2 N following unilateral fixation (p = 0.0161) and increased by 100% to 96.9 N after bilateral fixation (p = 0.0038). Unilateral SIJ fixation increased flexion of the ilium relative to L5 from 1.2° to 2.0° (p = 0.01) and increased axial rotation of L5 relative to S1 from 0.7° to 1.6° (p = 0.001). Bilateral fixation increased flexion of the ilium relative to L5 to 2.0° from 1.2° prior to fixation (p = 0.001), increased axial rotation of L5 relative to S1 to 1.2° from 0.7° prior to fixation (p = 0.002) and increased flexion of L5 relative to S1 to 2.4° from 1.5° prior to fixation (p = 0.04). CONCLUSION: The L5/S1 facet joint experiences compensatory increased motion under increased contact force after unilateral and bilateral SIJ fixation, possibly predisposing it to adjacent segment arthritis. LEVEL OF EVIDENCE: V, cadaveric study.