Height and volume restoration in osteoporotic vertebral compression fractures: a biomechanical comparison of standard balloon kyphoplasty versus Tektona® in a cadaveric fracture model.

BACKGROUND: Standard balloon kyphoplasty represents a well-established treatment option for osteoporotic vertebral compression fractures. Aim of the present study was to evaluate two different methods of percutaneous augmentation (standard balloon kyphoplasty (BKP) versus Tektona® (TEK)) with respect to height restoration. METHODS: Four-teen vertebral bodies of two female cadavers were examined. Fractures were created using a standardized protocol. CT-scans were taken before and after fracture, as well as after treatment. Afterwards two groups were randomly assigned in a matched pair design: 7 vertebral bodies (VB) were treated with BKP (Kyphon, Medtronic) and 7 vertebral bodies by TEK (Spineart, Switzerland) Anterior, central and posterior vertebral body heights were evaluated by CT-scans. Volumetry was performed using the CT-scans at three different timepoints. RESULTS: Values before fracture represent 100%. The anterior height after fracture was reduced to 75.99 (± 4.8) % for the BKP group and to 76.54 (± 9.17) % in the TEK Group. Statistically there was no difference for the groups (p = 1). After treatment the values increased to 93.06 (± 5) % for the BKP Group and 87.71 (± 6.2) % for the TEK Group. The difference before and after treatment was significant for both groups (BKP p = 0.0006; TEK p = 0.03). Within the groups, there was no difference (p = 0.13). The Volume of the vertebral body was reduced to 82.29 (± 8.4) % in the BKP Group and to 76.54 (± 8.6) % in the TEK Group. After treatment the volume was 89.26 (± 6.9) % for the BKP Group and 88.80 (± 8.7) % for the TEK Group. The difference before and after treatment was significant only for the TEK group (BKP p = 0.0728 n.s.; TEK p = 0.0175). Within the groups, there was no difference (p = 0.2). The average cement volume used was 6.1 (range 3.6-9 ml) for the BKP group and 5.3 (3-7.2 ml) for the TEK group respectively. CONCLUSIONS: Based on our results the new System Tektona® in osteoporotic compression fractures might represent a promising alternative for the clinical setting, especially preserving bone. Further biomechanical tests and clinical studies have to proof Tektona®`s capabilities.

A New 3D Reconstruction Method To Assess Anatomical Restoration In Vertebral Compression Fractures.

Deformation of the spine following vertebral compression fracture (VCF) can be associated with severe spinal dysfunction. Anatomical restoration is described as the complete reduction and stable fixation of the fracture with the goal to restore the pre-fracture local and global spine properties. The essential need to obtain endplate reduction, and consider the whole vertebral body in the management of vertebral fractures is pointed out. A new 3D imaging technique is described. A new assessment method based on CT scans 3D reconstructions was developed. This new method was used to assess the anatomical restoration of the fractured vertebrae. A procedure consisting in placing two expandable titanium implants for fracture reduction, together with stabilization with a high viscosity PMMA cement was used to demonstrate the method. The cases presented here are demonstrating that this 3D-mapping software is a tool which can address the lack of a valid, reproducible and user-friendly method to evaluate the anatomical restoration in VCF. The evaluation of the anatomical restoration of the fractured vertebrae raises some issues in terms of interpretation because of a lack of consensus in the existing reporting methods. A 3D-reconstruction method, using CT scans and a newly-developed software, is proposed to evaluate the anatomical restoration in a clear, valid, reproducible and user-friendly way.

Mono- versus polyaxial locking plates in distal femur fractures - a biomechanical comparison of the Non-Contact-Bridging- (NCB) and the PERILOC-plate.

BACKGROUND: The aim of this cadaveric study was to compare a polyaxial (NCB®, Zimmer) to a fixed-angle monoaxial locking plate (PERILOC®, Smith & Nephew) in comminuted fractures of the distal femur regarding stability of the construct. Up to date there is no published biomechanical data concerning polyaxial plating in cadaveric distal femurs. METHODS: Fourteen formalin fixed femora were scanned by dual-energy x-ray absorptiometry. As fracture model an unstable supracondylar comminuted fracture was simulated. Fractures were pairwise randomly fixed either with a mono- (group A) or a polyaxial (group B) distal femur plate. The samples were tested in a servohydraulic mechanical testing system starting with an axial loading of 200 N following an increase of 200 N in every step with 500 cycles in every sequence up to a maximum of 2 000 N. The end points were implant failure or relevant loss of reduction. Data records included for each specimen time, number of cycles, axial load and axial displacement. Statistical analysis was performed using the exact Wilcoxon signed rank test. RESULTS: The mean donor age at the time of death was 75 years. The bone mass density (BMD) of the femurs in both groups was comparable and showed no statistically significant differences. Five bones failed before reaching the maximum applied force of 2000 N. Distribution curves of all samples in both groups, showing the plastic deformation in relation to the axial force, showed no statistically significant differences. CONCLUSIONS: Operative stabilization of distal femur fractures can be successfully and equally well achieved using either a monoaxial or a polyaxial locking plate. Polyaxial screw fixation may have advantages if intramedullary implants are present.

Designing for passengers' information needs on fellow travelers: A comparison of day and night rides in shared automated vehicles.

Shared automated mobility-on-demand promises efficient, sustainable, and flexible transportation. Nevertheless, security concerns, resilience, and their mutual influence - especially at night - will likely be the most critical barriers to public adoption since passengers have to share rides with strangers without a human driver on board. Prior research points out that having information about fellow travelers could alleviate the concerns of passengers and we designed two user interface variants to investigate the role of this information in an exploratory within-subjects user study (N=24). Participants experienced four automated day and night rides with varying personal information about co-passengers in a simulated environment. The results of the mixed-method study indicate that having information about other passengers (e.g., photo, gender, and name) positively affects user experience at night. In contrast, it is less necessary during the day. Considering participants' simultaneously raised privacy concerns, balancing security and privacy demands poses a substantial challenge for resilient system design.

Implementation and Evaluation of a Gait Training Assistant for the Use of Crutches: Usability Study.

BACKGROUND: Surgical procedures on the lower extremities often require weight-bearing on crutches as part of the rehabilitation process. Orthopedic elective procedures enable patients to learn the correct use of crutches in a controlled preoperative setting. Digital assistance systems can safely circumvent a shortage of skilled staff and any contact restrictions that may be necessary. OBJECTIVE: The usability of a newly developed gait training assistant (GTA) for the use of crutches will be evaluated. An intervention group trained to use crutches by the digital trainer will be compared with a control group trained to use crutches conventionally by a physiotherapist. METHODS: As part of the development and implementation of a novel GTA, 14 patients learned to walk with crutches by completing specific exercises while receiving live feedback. Their movements were detected by a depth sensor and evaluated in real time. Specific parameters (step length, synchronous movement, crutch angle, and crutch distance to the feet) were compared with a control group (n=14) trained to use crutches by physiotherapists. The intervention group was also assessed by a physiotherapist. At the end of the study, the patients completed questionnaires to evaluate the usability of the system (Brooke's System Usability Scale score) and patient satisfaction. RESULTS: All patients trained by the novel GTA were able to use crutches correctly. The intervention group showed significantly better values for crutch angle (mean -6.3°, SD 3.5° vs mean -12.4°, SD 4.5°; P<.001) and crutch position (mean 3.3, SD 5.1 cm vs mean -8.5, SD 4.9 cm; P=.02). Both groups reported that they felt confident in the use of crutches, were able to follow the instructions, and enjoyed the training. Even though the majority (12/14, 86%) preferred physical therapy over a purely digital approach, most participants enjoyed using the system (13/14, 93%) and were interested in trying out other digital assistants (11/14, 79%). The usability of the GTA was rated above average by the majority (9/14, 64%) of the patients. CONCLUSIONS: The newly designed GTA is a safe method of teaching the use of crutches and is statistically superior to training by a physiotherapist. Even if patients prefer interaction with a physiotherapist over a purely digital approach, digital devices provide a safe and motivating opportunity to learn the essential locomotor skills for rehabilitation.

Percutaneous minimally invasive instrumentation for traumatic thoracic and lumbar fractures: a prospective analysis.

Open posterior instrumentation is still the standard procedure for unstable traumatic thoracic and lumbar fractures. There is a general tendency towards minimally invasive approaches in various surgical disciplines. The Sextant II Rod Insertion system is one of these. The authors prospectively studied this system in 51 patients with thoracic and lumbar fractures, between October 2007 and January 2011. Most fractures (31/51) were situated at the lumbar level. In 7 older patients the technique was combined with kyphoplasty and/or cement augmentation of the pedicle screws. The median operative time was 61 minutes (range: 26-130). The median fluoroscopy time was 132 seconds (range: 24-414). Most pedicle screws were correctly placed: 197 out of 204 screws. All fractures showed bony union after 6 weeks, but the multiaxial pedicle screws were not able to conserve the slight correction obtained peroperatively via positioning and longitudinal traction. Percutaneous minimally invasive stabilization of the spine needs further improvement.

Impact of 2 different posterior screw fixation techniques on primary stability in a cervical translational injury model: A biomechanical evaluation.

BACKGROUND: In case of injuries to the subaxial cervical spine, especially in osteoporotic bone, the question of the most stable operative technique arises. There are several techniques of screw fixation available regarding dorsal stabilization. This study investigates 2 techniques (lateral mass screws (LMS) vs cervical pedicle screws (CPS)) in the subaxial cervical spine regarding primary stability in a biomechanical testing using a translational injury model. METHODS: A total of 10 human formalin fixed and 10 human fresh-frozen specimens (C 4 - T 1) were investigated. Specimens were randomized in 2 groups. Fracture generation of a luxation injury between C 5 and C 6 was created by a transection of all ligamentous structures as well as the intervertebral disc and a resection of the facet joints.Dorsal stabilization of C 4/C 5 to C 6/C 7 was performed in group A by lateral mass screws, in group B by pedicle screws. In the biomechanical testing, the specimens were loaded at 2 N/s in translation direction until implant failure. RESULTS: Formalin fixed specimen: Mean load failure was 513.8 (±86.74) Newton (N) for group A (LMS) and 570.4 (±156.5) N for group B (CPS). There was no significant difference (P = .6905).Fresh frozen specimen: Mean load failure was 402.3 (±96.4) N for group A (LMS) and 500.7 (±190.3) N for group B (CPS). There was no significant difference (P = .4206). CONCLUSION: In our loading model respecting the translational injury pattern and a flexion movement we could not verify statistically significant differences between lateral mass screws and cervical pedicle screws. Mean loading failure was slightly higher in the CPS group though.

Monoaxial versus polyaxial locking systems: a biomechanical analysis of different locking systems for the fixation of proximal humeral fractures.

OBJECTIVE: The development of locking plate systems has led to polyaxial screws and new plate designs. This study compares monoaxial head locking screws (PHILOS© by Synthes) and a new generation of polyaxial locking screws (NCB-LE© by Zimmer) with respect to biomechanical stability. METHODS: On nine pairs of randomised formalin fixed humerus specimens, standardised osteotomies and osteosyntheses with nine monoaxial (group A) und nine polyaxial (group B) plate/screw systems were performed. A material testing machine by Instron (M-10 14961-DE) was used for cyclic stress tests and crash tests until defined breakup criteria as endpoints were reached. RESULTS: After axial cyclic stress 200 times at 90 N, plastic deformation was 1.02 mm in group A and 1.25 mm in group B. After the next cycle using 180 N the additional deformation averaged 0.23 mm in group A and 0.39 mm in group B. The deformation using 450 N was 0.72 mm in group A compared to 0.92 mm in group B. The final full power test resulted in a deformation average of 0.49 mm in group A and 0.63 mm in group B after 2,000 cycles using 450 N. When reaching the breakup criteria the plastic deformation of the NCB plate was 9.04 mm on average. The PHILOS plate was similarly deformed by 9.00 mm. As a result of the crash test, in group A the screws pulled out of the humeral head four times whereas the shaft broke one time and another time the implant was ripped out. The gap was closed four times. In group B, there were three cases of screw cut-through, four shaft fractures/screw avulsions from the shaft and two cases of gap closure. CONCLUSION: The two systems resist the cyclic duration tests and the increasing force tests in a similar manner. The considerable clinical benefits of the polyaxial system are enhanced by equal biomechanical performance.

Combining Dynamic Passive Haptics and Haptic Retargeting for Enhanced Haptic Feedback in Virtual Reality.

To provide immersive haptic experiences, proxy-based haptic feedback systems for virtual reality (VR) face two central challenges: (1) similarity, and (2) colocation. While to solve challenge (1), physical proxy objects need to be sufficiently similar to their virtual counterparts in terms of haptic properties, for challenge (2), proxies and virtual counterparts need to be sufficiently colocated to allow for seamless interactions. To solve these challenges, past research introduced, among others, two successful techniques: (a) Dynamic Passive Haptic Feedback (DPHF), a hardware-based technique that leverages actuated props adapting their physical state during the VR experience, and (b) Haptic Retargeting, a software-based technique leveraging hand redirection to bridge spatial offsets between real and virtual objects. Both concepts have, up to now, not ever been studied in combination. This paper proposes to combine both techniques and reports on the results of a perceptual and a psychophysical experiment situated in a proof-of-concept scenario focused on the perception of virtual weight distribution. We show that users in VR overestimate weight shifts and that, when DPHF and HR are combined, significantly greater shifts can be rendered, compared to using only a weight-shifting prop or unnoticeable hand redirection. Moreover, we find the combination of DPHF and HR to let significantly larger spatial dislocations of proxy and virtual counterpart go unnoticed by users. Our investigation is the first to show the value of combining DPHF and HR in practice, validating that their combination can better solve the challenges of similarity and colocation than the individual techniques can do alone.

Catering to the patient - development, validation and psychometric properties of an innovative assessment instrument.

Introduction: It has been shown that communication skills acquired during undergraduate medical education are of great importance. Hence, many countries require teaching communication as part of their medical curricula. To assess students' learning progress, "Catering to the Patient", as an aspect of showing empathy, should be evaluated. Since there was no description of a validated instrument fitting for this purpose, one had to be developed. To describe its process of development and its psychometric properties were the aims of this study. Methods: Based on the Calgary-Cambridge Observation Guide (CCOG), items describing catering to the patient were selected and modified. Cognitive pretest interviews were conducted to check understandability. Therefore, 7 raters assessed 1 video each (R=7, V=1). In a following pilot study (R=3, V=10) first psychometric properties were evaluated and necessary corrections in the preliminary evaluation form were carried out before the final evaluation form was used to assess students' ability to cater to the patient and psychometric properties were described in detail (R=2, V=35). Results: The final assessment instrument, "catering to the patient - Marburg evaluation form", contains 11 checklist items and two global ratings (items 12 and 13). In the final evaluation the inter-rater reliability (IRR) ranged from 0 to 0.562, the median was r=0.305. Concerning item 13 (a global rating), 88.6% of the videos were scored with the maximum difference of one point. The internal consistency was very high (Cronbach's α: α=0.937 and α=0.962), and the correlation between the checklist items and the global rating was high (Pearson's r: r=0.856 and r=0.898). Discussion: The assessment instrument "catering to the patient" is suitable for giving feedback and for using it in formative examinations. Its use for summative examinations can be considered. Further examinations should evaluate if a three-point Likert scale could reach higher values and if item 13 can be used as a stand-alone item.

Pull-out strength evaluation of cement augmented iliac screws in osteoporotic spino-pelvic fixation.

INTRODUCTION: Spino-pelvic fixation has been widely accepted for surgical treatment of sacral tumor, scoliosis surgery and pelvic fractures. Cement augmentation of screws is an option to improve implant stability in osteoporotic bone quality. Aim of the present study is to compare iliac screw fixation without cement fixation and two cement application options in a biomechanical testing. HYPOTHESIS: Cement augmentation of iliac screws leads to superior pull-out strength. MATERIAL AND METHODS: Thirty female and osteoporotic human iliac bones were used. Three operation treatment groups were generated: Screw fixation (cannulated screws) without cement augmentation [Operation treatment (OT) A], screw fixation with cement augmentation before screw placement (cannulated screws) (OT B) and screw fixation with perforated screws and cement augmentation after screw placement (OTC). Pull-out tests were performed with a rate of 6mm/min. A load versus displacement curve was generated. Maximum pull-out force (N) was measured in the load-displacement curve. RESULTS: Paired group 1 (OT A vs. OT B): Screw fixation without cement augmentation: 592.6N±335.07 and screw fixation with cement augmentation before screw placement: 996N±287.43 (p=0.0042). Paired group 2 (OT A vs. OT C): screw fixation without cement augmentation: 716.2N±385.86 and fenestrated screw fixation with cement augmentation after screw placement: 1324.88N±398.76 (p=0.0489). Paired group 3 (OT B vs. OT C): Screw fixation with cement augmentation before screw placement: 1077.2±486.66 and fenestrated screw fixation with cement augmentation after screw placement: 1298.2N±726.19 (p=0.3286). DISCUSSION: Regarding iliac screw fixation for spino-pelvic ostesynthesis in osteoporotic bone, cement augmentation is significantly superior to solid iliac screw fixation respecting pull-out-strength. Nevertheless, further biomechanical studies are needed to verify these findings. LEVEL OF EVIDENCE: Not applicable; biomechanical cadaver study.

Kyphoplasty for the treatment of incomplete osteoporotic burst fractures.

Kyphoplasty has become a standard procedure in the treatment of painful osteoporotic compression fractures. According to current guidelines, involvement of the posterior wall of the vertebral body is a relative contraindication. From February 2002 until January 2008, 97 patients with at least one AO classification A 3.1 fracture were treated by kyphoplasty. There was a structured follow-up for the medium-term evaluation of the patients' outcome. Ninety-seven patients (68 of whom were females and 29 of whom were males) with involvement of the vertebra's posterior margin averaging 76.1 +/- 12.36 (59-98) years were treated by kyphoplasty. The fractures of 75 patients were caused by falls from little height, 5 patients had suffered traffic accidents and in the case of 17 patients, no type of trauma was remembered. According to the AO classification, there were 109 A 3.1.1 and one A3.1.3 injuries. Prior to surgery, all patients were neurologically without pathological findings. Seventy-nine fractures were accompanied by a narrowing of the spinal canal [average of 15% (10-40)]. Overall, 134 vertebras were treated by Balloon kyphoplasty (81 x 1 segment, 22 x 2 segments, 3 x 3 segments). In 47.4% of the patients, cement leakage was observed after surgery. All patients with cement extravasation, however, were clinically unremarkable. Using the visual analog scale, patients stated that prior to surgery their pain averaged 8.1, whereas after surgery it significantly decreased and averaged 1.6 (p < 0.001). In geriatric patients with osteoporotic vertebral fractures with partial inclusion of the posterior wall of the vertebral body, kyphoplasty is an effective procedure with few complications.

Immersive Process Model Exploration in Virtual Reality.

In many professional domains, relevant processes are documented as abstract process models, such as event-driven process chains (EPCs). EPCs are traditionally visualized as 2D graphs and their size varies with the complexity of the process. While process modeling experts are used to interpreting complex 2D EPCs, in certain scenarios such as, for example, professional training or education, also novice users inexperienced in interpreting 2D EPC data are facing the challenge of learning and understanding complex process models. To communicate process knowledge in an effective yet motivating and interesting way, we propose a novel virtual reality (VR) interface for non-expert users. Our proposed system turns the exploration of arbitrarily complex EPCs into an interactive and multi-sensory VR experience. It automatically generates a virtual 3D environment from a process model and lets users explore processes through a combination of natural walking and teleportation. Our immersive interface leverages basic gamification in the form of a logical walkthrough mode to motivate users to interact with the virtual process. The generated user experience is entirely novel in the field of immersive data exploration and supported by a combination of visual, auditory, vibrotactile and passive haptic feedback. In a user study with N=27 novice users, we evaluate the effect of our proposed system on process model understandability and user experience, while comparing it to a traditional 2D interface on a tablet device. The results indicate a tradeoff between efficiency and user interest as assessed by the UEQ novelty subscale, while no significant decrease in model understanding performance was found using the proposed VR interface. Our investigation highlights the potential of multi-sensory VR for less time-critical professional application domains, such as employee training, communication, education, and related scenarios focusing on user interest.

Long-term results of elastic-stable intramedullary nailing (ESIN) of diaphyseal forearm fractures in children.

Since its introduction by Metaizeau and Prevot, elastic-stable intramedullary nailing (ESIN) has been used for almost all diaphyseal fractures in children. Here, we present a retrospective study analyzing the long-term results of ESIN of forearm fractures in children.A total of 122 patients with diaphyseal forearm fractures and single subtypes in childhood were treated from 2000 to 2007 at our University Hospital by ESIN. At follow-up, the current conditions of the patients were evaluated using the Disabilities of Arm, Shoulder, and Hand (DASH) Score, and the Mayo Wrist score. Moreover, an individual questionnaire with 16 items was used to collect further information about the patient's condition and limitations as adults.The evaluation was performed at 12.4 years (average) after surgery. In our study population (n = 90), the average DASH scores for sports, performing arts, and work were 0.4 (standard deviation: 1.45), 0.9 (standard deviation: 5.68), and 0.3 (standard deviation: 7.39), respectively. Furthermore, 77% of our patients achieved a DASH Score of 0 (optimum outcome). The average Mayo Wrist Score was 97.64 (standard deviation: 7.39), and 82% of the study population achieved a score of 100 (optimum outcome). A correlation between the DASH and Mayo Wrist Scores was found in few patients. Overall, the DASH Score, Mayo Wrist Score, and results of our individual questionnaire demonstrated convincing point values.This study demonstrated favorable long-term results achieved by ESIN of forearm fractures in children. It seems that good outcomes, reported by various studies with short- to mid-term follow-up beforehand, do not deteriorate over time.Level of Evidence: Level III; retrospective study; therapeutic study.

Psychological principles of successful aging technologies: a mini-review.

Based on resource-oriented conceptions of successful lifespan development, we propose three principles for evaluating assistive technology: (a) net resource release; (b) person specificity, and (c) proximal versus distal frames of evaluation. We discuss how these general principles can aid the design and evaluation of assistive technology in adulthood and old age, and propose two technological strategies, one targeting sensorimotor and the other cognitive functioning. The sensorimotor strategy aims at releasing cognitive resources such as attention and working memory by reducing the cognitive demands of sensory or sensorimotor aspects of performance. The cognitive strategy attempts to provide adaptive and individualized cuing structures orienting the individual in time and space by providing prompts that connect properties of the environment to the individual's action goals. We argue that intelligent assistive technology continuously adjusts the balance between 'environmental support' and 'self-initiated processing' in person-specific and aging-sensitive ways, leading to enhanced allocation of cognitive resources. Furthermore, intelligent assistive technology may foster the generation of formerly latent cognitive resources by activating developmental reserves (plasticity). We conclude that 'lifespan technology', if co-constructed by behavioral scientists, engineers, and aging individuals, offers great promise for improving both the transition from middle adulthood to old age and the degree of autonomy in old age in present and future generations.

Osteoporotic Pelvic Fractures.

BACKGROUND: The estimated incidence of osteoporotic pelvic fractures among persons over age 60 in Germany is 224 per 100 000 persons per year, and rising. A number of surgical treatment options are available, but clinical long-term data are lacking. METHODS: This review is based on pertinent publications and guidelines retrieved by a selective literature search, and on the authors' clinical experience. RESULTS: Patients often report one or more relatively trivial traumatic incidents leading up to the fracture. They complain of pain in the hip, groin, or lower lumbar region, or of low back pain and sciatica. A new classification scheme entitled Fragility Fractures of the Pelvis (FFP) takes the morphology of the fracture into account and can be used as an aid to therapeutic decision-making (evidence level IV). The goal of treatment is early mobilization with adequate pain relief. Isolated anterior pelvic ring fractures (FFP I) and nondisplaced posterior pelvic ring fractures (FFP II) are usually stable and can be treated conservatively. Type III and IV injuries are unstable and should generally be treated surgically. CONCLUSION: Retrospective analyses have shown that osteoporotic pelvic fractures are associated with decreased mobility and independence and with a one-year mortality ranging from 9.5% to 27%. Prospective therapeutic trials are urgently needed.

Anterior cement augmentation of adjacent levels after vertebral body replacement leads to superior stability of the corpectomy cage under cyclic loading-a biomechanical investigation.

BACKGROUND: In the operative treatment of osteoporotic vertebral body fractures, a dorsal stabilization in combination with a corpectomy of the fractured vertebral body might be necessary with respect to the fracture morphology, whereby the osteoporotic bone quality may possibly increase the risk of implant failure. To achieve better stability, it is recommended to use cement-augmented screws for dorsal instrumentation. Besides careful end plate preparation, cement augmentation of the adjacent end plates has also been reported to lead to less reduction loss. PURPOSE: The aim of the study was to evaluate biomechanically under cyclic loading whether an additional cement augmentation of the adjacent end plates leads to improved stability of the inserted cage. STUDY DESIGN/SETTING: Methodical cadaver study. MATERIALS AND METHODS: Fourteen fresh frozen human thoracic spines with proven osteoporosis were used (T2-T7). After removal of the soft tissues, the spine was embedded in Technovit (Kulzer, Germany). Subsequently, a corpectomy of T5 was performed, leaving the dorsal ligamentary structures intact. After randomization with respect to bone quality, two groups were generated: Dorsal instrumentation (cemented pedicle screws, Medtronic, Minneapolis, MN, USA)+cage implantation (CAPRI Corpectomy Cage, K2M, Leesburg, VA, USA) without additional cementation of the adjacent endplates (Group A) and dorsal instrumentation+cage implantation with additional cement augmentation of the adjacent end plates (Group B). The subsequent axial and cyclic loading was performed at a frequency of 1 Hz, starting at 400 N and increasing the load within 200 N after every 500 cycles up to a maximum of 2,200 N. Load failure was determined when the cages sintered macroscopically into the end plates (implant failure) or when the maximum load was reached. RESULTS: One specimen in Group B could not be clamped appropriately into the test bench for axial loading because of a pronounced scoliotic misalignment and had to be excluded. The mean strength for implant failure was 1,000 N±258.2 N in Group A (no cement augmentation of the adjacent end plates, n=7); on average, 1,622.1±637.6 cycles were achieved. In Group B (cement augmentation of the adjacent end plates, n=6), the mean force at the end of loading was 1,766.7 N±320.4 N; an average of 3,572±920.6 cycles was achieved. Three specimens reached a load of 2,000 N. The differences between the two groups were significant (p=.006 and p=.0047) regarding load failure and number of cycles. CONCLUSIONS: Additional cement augmentation of the adjacent end plates during implantation of a vertebral body replacement in osteoporotic bone resulted in a significant increased stability of the cage in the axial cyclic loading test.

Shifty: A Weight-Shifting Dynamic Passive Haptic Proxy to Enhance Object Perception in Virtual Reality.

We define the concept of Dynamic Passive Haptic Feedback (DPHF) for virtual reality by introducing the weight-shifting physical DPHF proxy object Shifty. This concept combines actuators known from active haptics and physical proxies known from passive haptics to construct proxies that automatically adapt their passive haptic feedback. We describe the concept behind our ungrounded weight-shifting DPHF proxy Shifty and the implementation of our prototype. We then investigate how Shifty can, by automatically changing its internal weight distribution, enhance the user's perception of virtual objects interacted with in two experiments. In a first experiment, we show that Shifty can enhance the perception of virtual objects changing in shape, especially in length and thickness. Here, Shifty was shown to increase the user's fun and perceived realism significantly, compared to an equivalent passive haptic proxy. In a second experiment, Shifty is used to pick up virtual objects of different virtual weights. The results show that Shifty enhances the perception of weight and thus the perceived realism by adapting its kinesthetic feedback to the picked-up virtual object. In the same experiment, we additionally show that specific combinations of haptic, visual and auditory feedback during the pick-up interaction help to compensate for visual-haptic mismatch perceived during the shifting process.

Risk-benefit analysis of navigation techniques for vertebral transpedicular instrumentation: a prospective study.

BACKGROUND CONTEXT: Pedicle screws in spinal surgery have allowed greater biomechanical stability and higher fusion rates. However, malposition is very common and may cause neurologic, vascular, and visceral injuries and compromise mechanical stability. PURPOSE: The purpose of this study was to compare the malposition rate between intraoperative computed tomography (CT) scan assisted-navigation and free-hand fluoroscopy-guided techniques for placement of pedicle screw instrumentation. STUDY DESIGN/SETTING: This is a prospective, randomized, observational study. PATIENT SAMPLE: A total of 114 patients were included: 58 in the assisted surgery group and 56 in the free-hand fluoroscopy-guided surgery group. OUTCOME MEASURES: Analysis of screw position was assessed using the Heary classification. Breach severity was defined according to the Gertzbein classification. Radiation doses were evaluated using thermoluminescent dosimeters, and estimates of effective and organ doses were made based on scan technical parameters. METHODS: Consecutive patients with degenerative disease, who underwent surgical procedures using the free-hand, or intraoperative navigation technique for placement of transpedicular instrumentation, were included in the study. RESULTS: Forty-four out of 625 implanted screws were malpositioned: 11 (3.6%) in the navigated surgery group and 33 (10.3%) in the free-hand group (p<.001). Screw position according to the Heary scale was Grade II (4 navigated surgery, 6 fluoroscopy guided), Grade III (3 navigated surgery, 11 fluoroscopy guided), Grade IV (4 navigated surgery, 16 fluoroscopy guided), and Grade V (1 fluoroscopy guided). There was only one symptomatic case in the conventional surgery group. Breach severity was seven Grade A and four Grade B in the navigated surgery group, and eight Grade A, 24 Grade B, and one Grade C in free-hand fluoroscopy-guided surgery group. Radiation received per patient was 5.8 mSv (4.8-7.3). The median dose received in the free-hand fluoroscopy group was 1 mGy (0.8-1.1). There was no detectable radiation level in the navigation-assisted surgery group, whereas the effective dose was 10 µGy in the free-hand fluoroscopy-guided surgery group. CONCLUSIONS: Malposition rate, both symptomatic and asymptomatic, in spinal surgery is reduced when using CT-guided placement of transpedicular instrumentation compared with placement under fluoroscopic guidance, with radiation values within the safety limits for health. Larger studies are needed to determine risk-benefit in these patients.

Creating reproducible thoracolumbar burst fractures in human specimens: an in vitro experiment.

OBJECT: The treatment of traumatic burst fractures unaccompanied by neurological impairment remains controversial and ranges from conservative management to 360° fusion. Because of the heterogeneity of fracture types, classification systems, and treatment options, comparative biomechanical studies might help to improve our knowledge. The aim of the current study was to create a standardized fracture model to investigate burst fractures in a multisegmental setting. METHODS: A total of 28 thoracolumbar fresh-frozen human cadaveric spines were used. The spines were dissected into segments (T11-L3). The T-11 and L-3 vertebral bodies were embedded in Technovit 3040 (cold-curing resin for surface testing and impressions). To simulate high energy, a metallic drop tower was designed. Stress risers were used to ensure comparable fractures. CT scans were acquired before and after fracture. All fractures were classified using the AO/OTA classification. RESULTS: The preparation and embedding of the spine segments worked well. No repositioning or second embedding of the specimen, even after fracture, was required. It was possible to create single burst fractures at the L-1 level in all 28 spine segments. Among the 28 fractures there were 16 incomplete burst fractures (Type A3.1), 8 burst-split fractures (Type A3.2), and 4 complete burst fractures (Type A3.3). The differences before and after fracture for stiffness and for anterior, posterior, and central heights were all significant (p < 0.05). CONCLUSIONS: The ability to create reproducible burst fractures of a single vertebral body in a thoracolumbar spine segment may serve as a basis for future biomechanical studies that will provide better understanding of mechanical properties or fixation techniques.