Morphometric measurements can improve prediction of progressive vertebral deformity following vertebral damage.

PURPOSE: A damaged vertebral body can exhibit accelerated 'creep' under constant load, leading to progressive vertebral deformity. However, the risk of this happening is not easy to predict in clinical practice. The present cadaveric study aimed to identify morphometric measurements in a damaged vertebral body that can predict a susceptibility to accelerated creep. METHODS: A total of 27 vertebral trabeculae samples cored from five cadaveric spines (3 male, 2 female, aged 36 to 73 (mean 57) years) were mechanically tested to establish the relationship between bone damage and residual strain. Compression testing of 28 human spinal motion segments (three vertebrae and intervening soft tissues) dissected from 14 cadaveric spines (10 male, 4 female, aged 67 to 92 (mean 80) years) showed how the rate of creep of a damaged vertebral body increases with increasing "damage intensity" in its trabecular bone. Damage intensity was calculated from vertebral body residual strain following initial compressive overload using the relationship established in the compression test of trabecular bone samples. RESULTS: Calculations from trabecular bone samples showed a strong nonlinear relationship between residual strain and trabecular bone damage intensity (R2 = 0.78, P < 0.001). In damaged vertebral bodies, damage intensity was then related to vertebral creep rate (R2 = 0.39, P = 0.001). This procedure enabled accelerated vertebral body creep to be predicted from morphological changes (residual strains) in the damaged vertebra. CONCLUSION: These findings suggest that morphometric measurements obtained from fractured vertebrae can be used to quantify vertebral damage and hence to predict progressive vertebral deformity.

The association between crawling as a first mode of mobilisation and the presentation of atraumatic shoulder instability: a retrospective cohort study.

BACKGROUND AND PURPOSE: To investigate if there is an association between whether an infant crawls as their first mode of mobilisation and the subsequent presentation of atraumatic shoulder instability. PATIENTS AND METHODS: A retrospective cohort of 50 consecutive patients who had presented to a national specialist centre for shoulder instability with a diagnosis of atraumatic instability was compared with a cohort of 50 participants who did not have shoulder instability. Primary outcomes were presence of atraumatic shoulder instability and whether or not the patient crawled as their first mode of mobility. A Pearson chi-squared test was used to evaluate associations. RESULTS: There was a significant association between crawling and shoulder instability (X 2(1) ≥ 11.93, p = 0.001) with a higher prevalence of non-crawlers in the group with shoulder instability compared to the control group. INTERPRETATION: There may be an association between developmental milestones and atraumatic shoulder instability. It cannot be concluded from this study whether association is causal and additional research is needed to further investigate this relationship. Asking patients presenting with shoulder instability about their developmental milestones as part of a full subjective history could guide a more targeted sensorimotor rehabilitation programme.

Physicians' and nurses' work time allocation and workflow interruptions in emergency departments: a comparative time-motion study across two countries.

BACKGROUND: Globally, emergency department (ED) work is fast-paced and subject to interruptions, placing high coordination and communication demands on staff. Our study aimed to compare ED staffs' work time allocation and interruption rates across professional roles and two national settings. METHODS: We conducted a time-motion study with standardised expert observations of ED physicians and nurses in Germany and the USA. Observers coded ED staffs' activities and workflow interruptions. General and generalised linear models were used to examine differences in activities and interruption rates between countries and ED professions. RESULTS: 28 observations were conducted in the USA and 30 in Germany. Overall, the largest portion of time spent by ED staff in both settings was in documentation (22.0%). Physicians spent more time in verbal interaction with patients (9.9% vs 5.2% in nurses; p=0.006), in documentation (29.4% vs 15.6%; p<0.001) and other professional activities (13.0% vs 4.8%; p=0.002). Nurses allocated significantly more time to therapeutic (22.3% vs 6.0% in physicians; p<0.001) and organisational activities (20.4% vs 9.5%; p<0.001). Overall mean interruption rate per hour was 10.16 (US ED: 8.15, German ED: 12.04; p<0.001). American physicians and German nurses were most often disrupted by colleagues of the same profession (country: B=-.27, p=0.027; profession: B=0.35, p=0.006). German ED staff were interrupted more often by patients (B=-.78, p=0.001) and other sources (B=-.76, p<0.001) than American ED staff. DISCUSSION: Our findings corroborate that professional roles largely determine time allocation to specific activities. However, interruption rates indicate differences between countries, suggesting the need for context-specific solutions to work stressors.

A predictive model for creep deformation following vertebral compression fractures.

Many vertebral compression fractures continue to collapse over time, resulting in spinal deformity and chronic back pain. Currently, there is no adequate screening strategy to identify patients at risk of progressive vertebral collapse. This study developed a mathematical model to describe the quantitative relationship between initial bone damage and progressive ("creep") deformation in human vertebrae. The model uses creep rate before damage, and the degree of vertebral bone damage, to predict creep rate of a fractured vertebra following bone damage. Mechanical testing data were obtained from 27 vertebral trabeculae samples, and 38 motion segments, from 26 human spines. These were analysed to evaluate bone damage intensity, and creep rates before and after damage, in order to estimate the model parameter, p, which represents how bone damage affects the change of creep rate after damage. Results of the model showed that p was 1.38 (R2 = 0.72, p < 0.001) for vertebral trabeculae, and 1.48 for motion segments (R2 = 0.22, p = 0.003). These values were not significantly different from each other (P > 0.05). Further analyses revealed that p was not significantly influenced by cortical bone damage, endplate damage, disc degeneration, vertebral size, or vertebral areal bone mineral density (aBMD) (P > 0.05). The key determinant of creep deformation following vertebral compression fracture was the degree of trabecular bone damage. The proposed model could be used to identify the measures of bone damage on routine MR images that are associated with creep deformation so that a screening tool can be developed to predict progressive vertebral collapse following compression fracture.

How are adjacent spinal levels affected by vertebral fracture and by vertebroplasty? A biomechanical study on cadaveric spines.

BACKGROUND CONTEXT: Spinal injuries and surgery may have important effects on neighboring spinal levels, but previous investigations of adjacent-level biomechanics have produced conflicting results. We use "stress profilometry" and noncontact strain measurements to investigate thoroughly this long-standing problem. PURPOSE: This study aimed to determine how vertebral fracture and vertebroplasty affect compressive load-sharing and vertebral deformations at adjacent spinal levels. STUDY DESIGN: We conducted mechanical experiments on cadaver spines. METHODS: Twenty-eight cadaveric spine specimens, comprising three thoracolumbar vertebrae and the intervening discs and ligaments, were dissected from fourteen cadavers aged 67-92 years. A needle-mounted pressure transducer was used to measure the distribution of compressive stress across the anteroposterior diameter of both intervertebral discs. "Stress profiles" were analyzed to quantify intradiscal pressure (IDP) and concentrations of compressive stress in the anterior and posterior annulus. Summation of stresses over discrete areas yielded the compressive force acting on the anterior and posterior halves of each vertebral body, and the compressive force resisted by the neural arch. Creep deformations of vertebral bodies under load were measured using an optical MacReflex system. All measurements were repeated following compressive injury to one of the three vertebrae, and again after the injury had been treated by vertebroplasty. The study was funded by a grant from Action Medical Research, UK ($143,230). Authors of this study have no conflicts of interest to disclose. RESULTS: Injury usually involved endplate fracture, often combined with deformation of the anterior cortex, so that the affected vertebral body developed slight anterior wedging. Injury reduced IDP at the affected level, to an average 47% of pre-fracture values (p<.001), and transferred compressive load-bearing from nucleus to annulus, and also from disc to neural arch. Similar but reduced effects were seen at adjacent (non-fractured) levels, where mean IDP was reduced to 73% of baseline values (p<.001). Vertebroplasty partially reversed these changes, increasing mean IDP to 76% and 81% of baseline values at fractured and adjacent levels, respectively. Injury also increased creep deformation of the vertebral body under load, especially in the anterior region where a 14-fold increase was observed at the fractured level and a threefold increase was observed at the adjacent level. Vertebroplasty also reversed these changes, reducing deformation of the anterior vertebral body (compared with post-fracture values) by 62% at the fractured level, and by 52% at the adjacent level. CONCLUSIONS: Vertebral fracture adversely affects compressive load-sharing and increases vertebral deformations at both fractured and adjacent levels. All effects can be partially reversed by vertebroplasty.

End-tidal carbon dioxide and occult injury in trauma patients: ETCO2 does not rule out severe injury.

OBJECTIVE: To determine if early measurement of end-tidal carbon dioxide (ETCO2) in nonintubated patients triaged to a level 1 trauma center has utility in ruling out severe injury. METHODS: We performed a prospective cohort study of adult patients triaged to our urban, academic, level 1 trauma center. Included patients had ETCO2 measured within 30 minutes of arrival. Chart review was performed on enrolled patients to identify severe injury defined by: admission to an intensive care unit, need for an invasive procedure, blood product transfusion, acute blood loss anemia, and acute clinically significant finding on computed tomographic scan. RESULTS: Of 170 patients enrolled, 115 met the outcome of no severe injury. Mean ETCO2 for patients without and with severe injury was 33.1 mm Hg (SD, 5.8) and 30.3 mm Hg (SD, 6.7), respectively. This difference reached statistical significance (P=.05), but did not demonstrate added clinical utility when combined with Glasgow Coma Scale, systolic blood pressure, and age in predicting the primary outcome (area under curve, 0.70 with ETCO2 vs area under curve, 0.68 without ETCO2, P=.5). Patients with ETCO2 ≤30 mm Hg were found to be older, more likely to require intensive care unit admission or emergency operative intervention, develop acute blood loss anemia, and have an acute finding on computed tomography than patients with a higher ETCO2. CONCLUSION: End-tidal carbon dioxide cannot be used to rule out severe injury in patients meeting criteria for trauma center care. The ETCO2 ≤30 mm Hg may be associated with increased risk of traumatic severe injury.

The relationship of intravenous fluid chloride content to kidney function in patients with severe sepsis or septic shock.

BACKGROUND: Previous studies suggest a relationship between chloride-rich intravenous fluids and acute kidney injury in critically ill patients. OBJECTIVES: The aim of this study was to evaluate the relationship of intravenous fluid chloride content to kidney function in patients with severe sepsis or septic shock. METHODS: A retrospective chart review was performed to determine (1) quantity and type of bolus intravenous fluids, (2) serum creatinine (Cr) at presentation and upon discharge, and (3) need for emergent hemodialysis (HD) or renal replacement therapy (RRT). Linear regression was used for continuous outcomes, and logistic regression was used for binary outcomes and results were controlled for initial Cr. The primary outcome was change in Cr from admission to discharge. Secondary outcomes were need for HD/RRT, length of stay (LOS), mortality, and organ dysfunction. RESULTS: There were 95 patients included in the final analysis; 48% (46) of patients presented with acute kidney injury, 8% (8) required first-time HD or RRT, 61% (58) were culture positive, 55% (52) were in shock, and overall mortality was 20% (19). There was no significant relationship between quantity of chloride administered in the first 24 hours with change in Cr (ß = -0.0001, t = -0.86, R(2) = 0.92, P = .39), need for HD or RRT (odds ratio [OR] = 0.999; 95% confidence interval [CI], 0.999-1.000; P = .77), LOS >14 days (OR = 1.000; 95% CI, 0.999-1.000; P = .68), mortality (OR = 0.999; 95% CI, 0.999-1.000; P = .88), or any type of organ dysfunction. CONCLUSION: Chloride administered in the first 24 hours did not influence kidney function in this cohort with severe sepsis or septic shock.

Is kyphoplasty better than vertebroplasty at restoring form and function after severe vertebral wedge fractures?

BACKGROUND CONTEXT: The vertebral augmentation procedures, vertebroplasty and kyphoplasty, can relieve pain and facilitate mobilization of patients with osteoporotic vertebral fractures. Kyphoplasty also aims to restore vertebral body height before cement injection and so may be advantageous for more severe fractures. PURPOSE: The purpose of this study was to compare the ability of vertebroplasty and kyphoplasty to restore vertebral height, shape, and mechanical function after severe vertebral wedge fractures. STUDY DESIGN/SETTING: This is a biomechanical and radiographic study using human cadaveric spines. METHODS: Seventeen pairs of thoracolumbar "motion segments" from cadavers aged 70-98 years were injured, in a two-stage process involving flexion and compression, to create severe anterior wedge fractures. One of each pair underwent vertebroplasty and the other kyphoplasty. Specimens were then compressed at 1 kN for 1 hour to allow consolidation. Radiographs were taken before and after injury, after treatment, and after consolidation. At these same time points, motion segment compressive stiffness was assessed, and intervertebral disc "stress profiles" were obtained to characterize the distribution of compressive stress on the vertebral body and neural arch. RESULTS: On average, injury reduced anterior vertebral body height by 34%, increased its anterior wedge angle from 5.0° to 11.4°, reduced intradiscal (nucleus) pressure and motion segment stiffness by 96% and 44%, respectively, and increased neural arch load bearing by 57%. Kyphoplasty caused 97% of the anterior height loss to be regained immediately, although this reduced to 79% after consolidation. Equivalent gains after vertebroplasty were significantly lower: 59% and 47%, respectively (p<.001). Kyphoplasty reduced vertebral wedging more than vertebroplasty (p<.02). Intradiscal pressure, neural arch load bearing, and motion segment compressive stiffness were restored significantly toward prefracture values after both augmentation procedures, even after consolidation, but these mechanical effects were similar for kyphoplasty and vertebroplasty. CONCLUSIONS: After severe vertebral wedge fractures, vertebroplasty and kyphoplasty were equally effective in restoring mechanical function. However, kyphoplasty was better able to restore vertebral height and reverse wedge deformity.

End-tidal carbon dioxide as a goal of early sepsis therapy.

OBJECTIVE: To determine the use of end-tidal carbon dioxide (etco2) as an end point of sepsis resuscitation. METHODS: This was a prospective, observational, single-center cohort study of emergency department patients receiving treatment for severe sepsis with a quantitative resuscitation protocol. Three etco2 readings were taken during a 1-minute time frame at 0, 3, and 6 hours of treatment. Linear regression was used to characterize the association between etco2 and central venous oxygen saturation (SCVo2) and lactate and also to determine the relationship between their change. Analysis of variance was used to determine the relationship between etco2 and disposition. RESULTS: Sixty-nine patients were included in our final analysis. For baseline values, linear regression failed to show a relationship between etco2 and SCVo2 (ß = -0.04, t(70) = -0.53, P = .60) but showed a nearly significant relationship (ß = -0.51, t(70) = -1.90, P = .06) with lactate. There was no significant relationship between etco2 and SCVo2 at 3 hours (ß = 0.12, t(70) = 1.43, P = .16) or 6 hours (ß = 0.05, t(64) = 0.82, P = .67). There was also no significant relationship between 6-hour change in etco2 and change in SCVo2 (ß = 0.04, t(64) = 0.43, P = .67) or lactate (ß = 0.04, t(59) = 0.52, P = .60) or disposition (F(4) = 0.78, P = .54). CONCLUSION: End-tidal carbon dioxide is unlikely to be a useful clinical end point for sepsis resuscitation, although it may be useful as a triage tool in suspected sepsis because baseline values may reflect initial lactate.

Proactive rounding by the rapid response team reduces inpatient cardiac arrests.

OBJECTIVE: Rapid response teams (RRTs) are frequently employed to respond to deteriorating inpatients. Proactive rounding (PR) consists of the RRT nurse rounding through the inpatient wards identifying high risk patients and intervening preemptively. At our institution, PR began in July of 2007. Our objective was to determine the effect of PR by the RRT at our institution on non-ICU cardiac arrests, code deaths, RRT interventions, and transfers to a higher level of care. Also, to report ICU transfer survival and survival to discharge rates after the start of PR. DESIGN: Retrospective review of a prospectively collected database. SETTING: A tertiary, academic, level 1 trauma center with 696 beds and a rapid response system. PATIENTS: 1253 Non-ICU cardiac arrests from 2005 through June of 2012. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: The total study period included 223,267 inpatient admissions (70,129 pre-PR and 153,138 post-PR) and 1,250,814 patient days (391,088 pre-PR and 859,726 post-PR). The quarterly code rate before PR was 66 and the code rate after the institution of PR was 30 (difference=36.8, 95% CI 25.6-48.0, p<.001). Quarterly code deaths decreased from 29 to 7 (difference=21.95, 95% CI 16.3-27.6, p<.001). This decrease in floor codes and code deaths was still present after adjusting for inpatient admission and inpatient days. Average quarterly RRT interventions increased from 141 in the pre-PR period to 690 in the post-PR period (difference=549, 95% CI 360-738, p<.001). Average quarterly transfers to HLC went up from 38 pre-PR to 164 post-PR (difference=126, 95% CI 79-172, p<.001). CONCLUSIONS: The institution of proactive rounding at a tertiary care, academic, level 1 trauma center results in reduced floor codes and code deaths as well as increased RRT interventions and transfers to a higher level of care.

Is kyphoplasty better than vertebroplasty in restoring normal mechanical function to an injured spine?

INTRODUCTION: Kyphoplasty is gaining in popularity as a treatment for painful osteoporotic vertebral body fracture. It has the potential to restore vertebral shape and reduce spinal deformity, but the actual clinical and mechanical benefits of kyphoplasty remain unclear. In a cadaveric study, we compare the ability of vertebroplasty and kyphoplasty to restore spine mechanical function, and vertebral body shape, following vertebral fracture. METHODS: Fifteen pairs of thoracolumbar "motion segments" (two vertebrae with the intervening disc and ligaments) were obtained from cadavers aged 42-96 years. All specimens were compressed to induce vertebral body fracture. Then one of each pair underwent vertebroplasty and the other kyphoplasty, using 7 ml of polymethylmethacrylate cement. Augmented specimens were compressed for 2 hours to allow consolidation. At each stage of the experiment, motion segment stiffness was measured in bending and compression, and the distribution of loading on the vertebrae was determined by pulling a miniature pressure transducer through the intervertebral disc. Disc pressure measurements were performed in flexed and extended postures with a compressive load of 1.0-1.5 kN. They revealed the intradiscal pressure (IDP) which acts on the central vertebral body, and they enabled compressive load-bearing by the neural arch (F(N)) to be calculated. Changes in vertebral height and wedge angle were assessed from radiographs. The volume of leaked cement was determined by water displacement. Volumetric bone mineral density (BMD) of each vertebral body was calculated using DXA and water displacement. RESULTS: Vertebral fracture reduced motion segment compressive stiffness by 55%, and bending stiffness by 39%. IDP fell by 61-88%, depending on posture. F(N) increased from 15% to 36% in flexion and from 30% to 58% in extension (P<0.001). Fracture reduced vertebral height by an average 0.94 mm and increased vertebral wedging by 0.95 degrees (P<0.001). Vertebroplasty and kyphoplasty were equally effective in partially restoring all aspects of mechanical function (including stiffness, IDP, and F(N)), but vertebral wedging was reduced only by kyphoplasty (P<0.05). Changes in mechanical function and vertebral wedging were largely maintained after consolidation, but height restoration was not. Cement leakage was similar for both treatments. CONCLUSIONS: Vertebroplasty and kyphoplasty were equally effective at restoring mechanical function to an injured spine. Only kyphoplasty was able to reverse minor vertebral wedging.

Vertebroplasty: only small cement volumes are required to normalize stress distributions on the vertebral bodies.

STUDY DESIGN.: Biomechanical study of vertebroplasty in cadaver motion segments. OBJECTIVES.: To determine how the volume of injected cement influences: (a) stress distributions on fractured and adjacent vertebral bodies, (b) load-sharing between the vertebral bodies and neural arch, and (c) cement leakage. SUMMARY OF BACKGROUND DATA.: Vertebroplasty is increasingly used to treat vertebral fractures, but there are problems concerning adjacent level fracture and cement leakage, both of which may depend on the volume of injected cement. METHODS.: Nineteen thoracolumbar motion segments from 13 cadavers (42-91 years) were loaded to induce fracture. Fractured vertebrae received 2 sequential injections (VP1 and VP2) of 3.5 cm of polymethylmethacrylate cement. Before and after each intervention, motion segment stiffness was measured in compression and in bending, and "stress profilometry" was used to quantify the distribution of compressive stress in the intervertebral disc (which presses equally on fractured and adjacent vertebrae). Stress profiles were obtained by pulling a pressure transducer through the disc while the motion segment was compressed in flexed and extended postures. Stress profiles yielded the intradiscal pressure (IDP), the magnitude of stress peaks in the anterior and posterior (SPP) anulus, and the percentage of the applied compressive force resisted by the neural arch (FN). Cement leakage and vertebral body volume were quantified using water-immersion, and the percentage cement fill was estimated. RESULTS.: Bending and compressive stiffness fell by 37% and 50% respectively following fracture, and were restored only after VP2. Depending on posture, IDP fell by 59-85% after fracture whereas SPP increased by 107- 362%. VP1 restored IDP and SPP to prefracture values, and VP2 produced no further changes. Fracture increased FN from 11% to 39% in flexion, and from 33% to 59% in extension. FN was restored towards prefracture values only after VP2. Cement leakage increased after VP2 and was negatively correlated to vertebral body volume. Following VP2, increases in IDP and compressive stiffness were proportional to percentage fill. CONCLUSION.: About 3.5 cm of PMMA largely restored normal stress distributions to fractured and adjacent vertebral bodies, but 7 cm were required to restore motion segment stiffness and load-sharing between the vertebral bodies and neural arch. Cement leakage, IDP and compressive stiffness all increased with percentage fill.

A randomized trial of vertebroplasty for osteoporotic spinal fractures.

BACKGROUND: Vertebroplasty is commonly used to treat painful, osteoporotic vertebral compression fractures. METHODS: In this multicenter trial, we randomly assigned 131 patients who had one to three painful osteoporotic vertebral compression fractures to undergo either vertebroplasty or a simulated procedure without cement (control group). The primary outcomes were scores on the modified Roland-Morris Disability Questionnaire (RDQ) (on a scale of 0 to 23, with higher scores indicating greater disability) and patients' ratings of average pain intensity during the preceding 24 hours at 1 month (on a scale of 0 to 10, with higher scores indicating more severe pain). Patients were allowed to cross over to the other study group after 1 month. RESULTS: All patients underwent the assigned intervention (68 vertebroplasties and 63 simulated procedures). The baseline characteristics were similar in the two groups. At 1 month, there was no significant difference between the vertebroplasty group and the control group in either the RDQ score (difference, 0.7; 95% confidence interval [CI], -1.3 to 2.8; P=0.49) or the pain rating (difference, 0.7; 95% CI, -0.3 to 1.7; P=0.19). Both groups had immediate improvement in disability and pain scores after the intervention. Although the two groups did not differ significantly on any secondary outcome measure at 1 month, there was a trend toward a higher rate of clinically meaningful improvement in pain (a 30% decrease from baseline) in the vertebroplasty group (64% vs. 48%, P=0.06). At 3 months, there was a higher crossover rate in the control group than in the vertebroplasty group (51% vs. 13%, P<0.001) [corrected]. There was one serious adverse event in each group. CONCLUSIONS: Improvements in pain and pain-related disability associated with osteoporotic compression fractures in patients treated with vertebroplasty were similar to the improvements in a control group. (ClinicalTrials.gov number, NCT00068822.)

Mechanical efficacy of vertebroplasty: influence of cement type, BMD, fracture severity, and disc degeneration.

INTRODUCTION: Osteoporotic vertebral fractures can be treated by injecting bone cement into the damaged vertebral body. "Vertebroplasty" is becoming popular but the procedure has yet to be optimised. This study compared the ability of two different types of cement to restore the spine's mechanical properties following fracture, and it examined how the mechanical efficacy of vertebroplasty depends on bone mineral density (BMD), fracture severity, and disc degeneration. METHODS: A pair of thoracolumbar "motion-segments" (two adjacent vertebrae with intervening soft tissue) was obtained from each of 15 cadavers, aged 51-91 years. Specimens were loaded to induce vertebral fracture; then one of each pair underwent vertebroplasty with polymethylmethacrylate (PMMA) cement, the other with another composite material (Cortoss). Specimens were creep loaded for 2 h to allow consolidation. At each stage of the experiment, motion segment stiffness in bending and compression was measured, and the distribution of compressive loading on the vertebrae was investigated by pulling a miniature pressure transducer through the intervertebral disc. Pressure measurements, repeated in flexed and extended postures, indicated the intradiscal pressure (IDP) and neural arch compressive load-bearing (F(N)). BMD was measured using DXA. Fracture severity was quantified from height loss. RESULTS: Vertebral fracture reduced motion segment stiffness in bending and compression, by 31% and 43% respectively (p<0.001). IDP fell by 43-62%, depending on posture (p<0.001), whereas F(N) increased from 14% to 37% of the applied load in flexion, and from 39% to 61% in extension (p<0.001). Vertebroplasty partially reversed all these effects, and the restoration of load-sharing was usually sustained after creep-consolidation. No differences were observed between PMMA and Cortoss. Pooled results from 30 specimens showed that low BMD was associated with increased fracture severity (in terms of height loss) and with greater changes in stiffness and load-sharing following fracture. Specimens with low BMD and more severe fractures also showed the greatest mechanical changes following vertebroplasty. CONCLUSIONS: Low vertebral BMD leads to greater changes in stiffness and spinal load-sharing following fracture. Restoration of mechanical function following vertebroplasty is little influenced by cement type but may be greater in people with low BMD who suffer more severe fractures.

Can vertebroplasty restore normal load-bearing to fractured vertebrae?

STUDY DESIGN: Cadaver motion segments were used to evaluate the effects of vertebroplasty on spinal loading following vertebral fracture. OBJECTIVES: To determine if vertebroplasty reverses fracture-induced changes in the distribution of compressive stress in cadaver motion segments. SUMMARY OF BACKGROUND DATA: Vertebroplasty involves reinforcement of vertebrae by injection of cement and is now being used increasingly to treat osteoporotic vertebral fractures. However, its effects on spinal load-bearing are largely unknown. We hypothesize that vertebroplasty, following vertebral fracture, helps to equalize stress acting on the intervertebral disc and adjacent vertebral bodies. METHODS: Nineteen cadaver thoracolumbar motion segments (age 64-90 years) were induced to fracture by compressive overload. Specimens were then subjected to vertebroplasty, and subsequently creep loaded for 1 hour at 1.5 kN. The compressive stress acting on the intervertebral disc was measured before and after fracture, after vertebroplasty, and after creep, by pulling a pressure transducer mounted in a 1.3-mm needle across the disc's midsagittal diameter. This information was then used to calculate neural arch load-bearing. At each time point, measurements were also made of compressive stiffness. RESULTS: Vertebral fracture reduced motion segment compressive stiffness, decompressed the adjacent nucleus, increased stress concentrations in the posterior anulus, and increased neural arch load-bearing, all by a significant amount. Vertebroplasty partially, but significantly, reversed all of these fracture-induced changes. CONCLUSIONS: Vertebroplasty reduces stress concentrations in the anulus and neural arch resulting in a more even distribution of compressive stress on the intervertebral disc and adjacent vertebral bodies.