Virtual Structural Analysis of Bone Fracture Healing from Low-Dose Clinical CT Scans

Bone fractures often heal by forming a soft external bridge called a callus, which gradually hardens over time and restores the structural stiffness of the bone. In clinical studies focused on bone healing, healing progress is usually tracked using subjective assessments such as pain and mobility scores, qualitative observations of callus on X-rays, and incidence of complications such as implant fatigue failure. This data can be highly variable, leading to study designs that require very large multi-center trials with thousands of cases to detect differences between groups.Accordingly, the purpose of this thesis is to propose a new technique for assessing bone healing using virtual mechano-structural analysis of computer tomography (CT) scan data. In this work, CT scans from 19 fractured human tibiae (shinbones) at 12 weeks after surgery were segmented and prepared for finite element analysis (FEA). Boundary conditions were applied to the models to simulate a torsion test that is commonly used to access the structural integrity of long bones in animal models of fracture healing. The output of each model was the virtual torsional rigidity (VTR) of the healing zone, normalized to the torsional rigidity of that same patient’s virtually reconstructed tibia. This provided a structural measure to track the percentage of healing each patient had undergone. Callus morphometric measurements were also collected from the CT scans.Results from this study showed that morphometric data such as callus volume and density had weak non-significant correlations to a patient’s healing. However, VTR had a strong correlation of R2 = 0.699 (p \u3c 0.0001) with the reconstructed VTR. Furthermore, more than 75% of patients achieved a normalized VTR (torsional rigidity relative to uninjured bone) of 75% or above. This finding suggests that a new clinically relevant guideline – the “75/75” rule – may be useful for benchmarking expectations for normal healing. Under this rule, surgeons should expect 75% of tibial fracture patients to achieve at least 75% of their own intact rigidity at 12 weeks post-op.In summary, this study is the first-ever application of image-based structural analysis to clinical (human) CT scan data for assessment of bone healing. The methods proposed may provide the foundation for a new paradigm of robust and statistically powerful clinical research in orthopaedic trauma

Evaluation of Cannulated Compression Headless Screw (CCHS) as an alternative implant in comparison to standard S1-S2 screw fixation of the posterior pelvis ring: a biomechanical study

BACKGROUND/PURPOSE: Posterior pelvis ring injuries represent typical high-energy trauma injuries in young adults. Joint stabilization with two cannulated sacroiliac (SI) screws at the level of sacral vertebrae S1 and S2 is a well-established procedure. However, high failure- and implant removal (IR) rates have been reported. Especially, the washer recovery can pose the most difficult part of the IR surgery, which is often associated with complications. The aim of this biomechanical study was to evaluate the stability of S1-S2 fixation of the SI joint using three different screw designs. METHODS: Eighteen artificial hemi-pelvises were assigned to three groups (n = 6) for SI joint stabilization through S1 and S2 corridors using either two 7.5 mm cannulated compression headless screws (group CCH), two 7.3 mm partially threaded SI screws (group PT), or two 7.3 mm fully threaded SI screws (group FT). An SI joint dislocation injury type III APC according to the Young and Burgess classification was simulated before implantation. All specimens were biomechanically tested to failure in upright standing position under progressively increasing cyclic loading. Interfragmentary and bone-implant movements were captured via motion tracking and evaluated at four time points between 4000 and 7000 cycles. RESULTS: Combined interfragmentary angular displacement movements in coronal and transverse plane between ilium and sacrum, evaluated over the measured four time points, were significantly bigger in group FT versus both groups CCH and PT, p ≤ 0.047. In addition, angular displacement of the screw axis within the ilium under consideration of both these planes was significantly bigger in group FT versus group PT, p = 0.038. However, no significant differences were observed among the groups for screw tip cutout movements in the sacrum, p = 0.321. Cycles to failure were highest in group PT (9885 ± 1712), followed by group CCH (9820 ± 597), and group FT (7202 ± 1087), being significantly lower in group FT compared to both groups CCH and PT, p ≤ 0.027. CONCLUSION: From a biomechanical perspective, S1-S2 SI joint fixation using two cannulated compression headless screws or two partially threaded SI screws exhibited better interfragmentary stability compared to two fully threaded SI screws. The former can therefore be considered as a valid alternative to standard SI screw fixation in posterior pelvis ring injuries. In addition, partially threaded screw fixation was associated with less bone-implant movements versus fully threaded screw fixation. Further human cadaveric biomechanical studies with larger sample size should be initiated to understand better the potential of cannulated compression headless screw fixation for the therapy of the injured posterior pelvis ring in young trauma patients

Implementation of a novel nursing assessment tool in geriatric trauma patients with proximal femur fractures

BACKGROUND Geriatric trauma patients represent a special challenge in postoperative care and are prone to specific complications. The goal of this study was to analyse the predictive potential of a novel nursing assessment tool, the outcome-oriented nursing assessment for acute care (ePA-AC), in geriatric trauma patients with proximal femur fractures (PFF). METHODS A retrospective cohort study of geriatric trauma patients aged ≥ 70 years with PFF was conducted at a level 1 trauma centre. The ePA-AC is a routinely used tool that evaluates pneumonia; confusion, delirium and dementia (CDD); decubitus (Braden Score); the risk of falls; the Fried Frailty index (FFI); and nutrition. Assessment of the novel tool included analysis of its ability to predict complications including delirium, pneumonia and decubitus. RESULTS The novel ePA-AC tool was investigated in 71 geriatric trauma patients. In total, 49 patients (67.7%) developed at least one complication. The most common complication was delirium (n = 22, 44.9%). The group with complications (Group C) had a significantly higher FFI compared with the group without complications (Group NC) (1.7 ± 0.5 vs 1.2 ± 0.4, p = 0.002). Group C had a significantly higher risk score for malnutrition compared with Group NC (6.3 ± 3.4 vs 3.9 ± 2.8, p = 0.004). A higher FFI score increased the risk of developing complications (odds ratio [OR] 9.8, 95% confidence interval [CI] 2.0 to 47.7, p = 0.005). A higher CDD score increased the risk of developing delirium (OR 9.3, 95% CI 2.9 to 29.4, p < 0.001). CONCLUSION The FFI, CDD, and nutritional assessment tools are associated with the development of complications in geriatric trauma patients with PFF. These tools can support the identification of geriatric patients at risk and might guide individualised treatment strategies and preventive measures

Is a Washer a Mandatory Component in Young Trauma Patients with S1-S2 Iliosacral Screw Fixation of Posterior Pelvis Ring Injuries? A Biomechanical Study

Background and purpose: Cannulated screws are standard implants for percutaneous fixa-tion of posterior pelvis ring injuries. The choice of whether to use these screws in combination with a washer is still undecided. The aim of this study was to evaluate the biomechanical competence of S1-S2 sacroiliac (SI) screw fixation with and without using a washer across three different screw designs. Material and Methods: Twenty-four composite pelvises were used and an SI joint injury type APC III according to the Young and Burgess classification was simulated. Fixation of the posterior pelvis ring was performed using either partially threaded short screws, fully threaded short screws, or fully threaded long transsacral screws. Biomechanical testing was performed under progressively increasing cyclic loading until failure, with monitoring of the intersegmental and bone-implant movements via motion tracking. Results: The number of cycles to failure and the corresponding load at failure (N) were significantly higher for the fully threaded short screws with a washer (3972 ± 600/398.6 ± 30.0) versus its counterpart without a washer (2993 ± 527/349.7 ± 26.4), p = 0.026. In contrast, these two parameters did not reveal any significant differences when comparing fixations with and without a washer using either partially threaded short of fully threaded long transsacral screws, p ≥ 0.359. Conclusions: From a biomechanical perspective, a washer could be optional when using partially threaded short or fully threaded long transsacral S1-S2 screws for treatment of posterior pelvis ring injuries in young trauma patients. Yet, the omission of the washer in fully threaded short screws could lead to a significant diminished biomechanical stability

Evaluation of cannulated compression headless screws as an alternative implant for superior pubic ramus fracture fixation: a biomechanical study.

BACKGROUND/PURPOSE Pubic ramus fractures account for the most common types of pelvic fractures. The standard surgical approach for superior pubic ramus fractures (SPRF) is a minimally invasive percutaneous screw fixation. However, percutaneous closed reduction and internal fixation of anterior pelvic ring injuries have high failure rates of up to 15%. The aim of this biomechanical study was to evaluate the stability of SPRF following stabilization with retrograde placed cannulated compression headless screw (CCHS) versus conventional fully and partially threaded screws in an artificial pelvic bone model. METHODS SPRF type II as described by Nakatani et al. was created by means of osteotomies in eighteen anatomical composite hemi-pelvises. Specimens were stratified into three groups of six specimens each (n = 6) for fixation with either a 7.3 mm partially threaded cannulated screw (group RST), a 7.3 mm fully threaded cannulated screw (group RSV), or a 7.5 mm partially threaded cannulated CCHS (group CCS). Each hemi-pelvic specimen was tested in an inverted upright standing position under progressively increasing cyclic axial loading. The peak load, starting at 200 N, was monotonically increased at a rate of 0.1 N/cycle until 10 mm actuator displacement. RESULTS Total and torsional displacement were associated with higher values for RST versus CCS and RSV, with significant differences between RST and CCS for both these parameters (p ≤ 0.033). The differences between RST and RSV were significant for total displacement (p = 0.020), and a trend toward significance for torsional displacement (p = 0.061) was observed. For both failure criteria 2 mm total displacement and 5° torsional displacement, CCS was associated with significantly higher number of cycles compared to RST (p ≤ 0.040). CONCLUSION CCHS fixation presented predominantly superior stability to the standard surgical treatment and could therefore be a possible alternative implant for retrograde SPRF screw fixation, whereas partially threaded screws in group RST were associated with inferior biomechanical stability

The Araucaria Project. The Distance to the Local Group Galaxy NGC 6822 from Cepheid Variables discovered in a Wide-Field Imaging Survey

We have obtained mosaic images of NGC 6822 in V and I bands on 77 nights. From these data, we have conducted an extensive search for Cepheid variables over the entire field of the galaxy, and we have found 116 such variables with periods ranging from 1.7 to 124 days. We used the long-period ($>$ 5.6 days) Cepheids to establish the period-luminosity relations in V, I and in the reddening-independent Wesenheit index, which are all very tightly defined. Fitting the OGLE LMC slopes in the various bands to our data, we have derived distance values for NGC 6822 in V, I and ${\rm W}_{\rm I}$ which agree very well among themselves. Our adopted best distance value from the reddening-free Wesenheit index is 23.34 $\pm$ 0.04 (statistical) $\pm$ 0.05 (systematic) mag. This value agrees within the combined 1 sigma uncertainties with a previous distance value derived for NGC 6822 by McAlary et al. from near-IR photometry of 9 Cepheids, but our new value is significantly more accurate. We compare the slopes of the Cepheid PL relation in V and I as determined in the five best-observed nearby galaxies, which span a metallicity range from -1.0 to -0.3 dex, and find the data consistent with no metallicity dependence of the PL relation slope in this range. Comparing the magnitudes of 10-day Cepheids with the I-band magnitudes of the TRGB in the same set of galaxies, there is no evidence either for a significant variation of the period-luminosity zero points in V and I. The available data limit such a zero point variation to less than 0.03 mag, in the considered low-metallicity regime.Comment: Latex, Astronomical Journal accepte

Anterior column acetabulum fracture fixation with a screw-augmented acetabular cup-a biomechanical feasibility study

BACKROUND: The beneficial effects of unrestricted postoperative full weight bearing for elderly patients suffering hip fractures have been demonstrated. However, there is still existing disagreement regarding acetabular fractures.The aim of this biomechanical study was to evaluate the initial load bearing capabilities of different fixation constructs of anterior column fractures (ACFs) in osteoporotic bone. METHODS: Artificial pelvises with ACFs were assigned to three groups (n = 8) and fixed with either a 7.3 mm partially threaded antegrade cannulated screw (group AASS), an anteriorly placed 3.5 mm plate (group AAPF), or a press-fit acetabular cup with screw augmentation (group AACF). All specimens underwent ramped loading from 20 N preload to 200 N at a rate of 18 N/s, followed by progressively increasing cyclic testing at 2 Hz until failure performed at a rate of 0.05 N/cycle. Relative displacements of the bone fragments were monitored by motion tracking. FINDINGS: Initial stiffness (N/mm) was 118.5 ± 34.3 in group AASS, 100.4 ± 57.5 in group AAPF, and 92.9 ± 44.0 in group AACF, with no significant differences between the groups, p = 0.544. Cycles to failure were significantly higher in groups AACF (8364 ± 2243) and AAPF (7827 ± 2881) compared to group AASS (4440 ± 2063), p ≤ 0.041. INTERPRETATION: From a biomechanical perspective, the minimally invasive cup fixation with screw augmentation demonstrated comparable stability to plate osteosynthesis of ACFs in osteoporotic bone. The results of the present study do not allow to conclusively answer whether immediate full weight bearing following cup fixation shall be allowed. Given its similar performance to plate osteosynthesis, this remains rather an utopic wish and a more conservative approach deems more reasonable

Evaluation of cannulated compression headless screws as an alternative implant for superior pubic ramus fracture fixation: a biomechanical study

BACKGROUND/PURPOSE: Pubic ramus fractures account for the most common types of pelvic fractures. The standard surgical approach for superior pubic ramus fractures (SPRF) is a minimally invasive percutaneous screw fixation. However, percutaneous closed reduction and internal fixation of anterior pelvic ring injuries have high failure rates of up to 15%. The aim of this biomechanical study was to evaluate the stability of SPRF following stabilization with retrograde placed cannulated compression headless screw (CCHS) versus conventional fully and partially threaded screws in an artificial pelvic bone model. METHODS: SPRF type II as described by Nakatani et al. was created by means of osteotomies in eighteen anatomical composite hemi-pelvises. Specimens were stratified into three groups of six specimens each (n = 6) for fixation with either a 7.3 mm partially threaded cannulated screw (group RST), a 7.3 mm fully threaded cannulated screw (group RSV), or a 7.5 mm partially threaded cannulated CCHS (group CCS). Each hemi-pelvic specimen was tested in an inverted upright standing position under progressively increasing cyclic axial loading. The peak load, starting at 200 N, was monotonically increased at a rate of 0.1 N/cycle until 10 mm actuator displacement. RESULTS: Total and torsional displacement were associated with higher values for RST versus CCS and RSV, with significant differences between RST and CCS for both these parameters (p ≤ 0.033). The differences between RST and RSV were significant for total displacement (p = 0.020), and a trend toward significance for torsional displacement (p = 0.061) was observed. For both failure criteria 2 mm total displacement and 5° torsional displacement, CCS was associated with significantly higher number of cycles compared to RST (p ≤ 0.040). CONCLUSION: CCHS fixation presented predominantly superior stability to the standard surgical treatment and could therefore be a possible alternative implant for retrograde SPRF screw fixation, whereas partially threaded screws in group RST were associated with inferior biomechanical stability

Anterior column acetabulum fracture fixation with a screw-augmented acetabular cup-a biomechanical feasibility study.

BACKROUND The beneficial effects of unrestricted postoperative full weight bearing for elderly patients suffering hip fractures have been demonstrated. However, there is still existing disagreement regarding acetabular fractures.The aim of this biomechanical study was to evaluate the initial load bearing capabilities of different fixation constructs of anterior column fractures (ACFs) in osteoporotic bone. METHODS Artificial pelvises with ACFs were assigned to three groups (n = 8) and fixed with either a 7.3 mm partially threaded antegrade cannulated screw (group AASS), an anteriorly placed 3.5 mm plate (group AAPF), or a press-fit acetabular cup with screw augmentation (group AACF). All specimens underwent ramped loading from 20 N preload to 200 N at a rate of 18 N/s, followed by progressively increasing cyclic testing at 2 Hz until failure performed at a rate of 0.05 N/cycle. Relative displacements of the bone fragments were monitored by motion tracking. FINDINGS Initial stiffness (N/mm) was 118.5 ± 34.3 in group AASS, 100.4 ± 57.5 in group AAPF, and 92.9 ± 44.0 in group AACF, with no significant differences between the groups, p = 0.544. Cycles to failure were significantly higher in groups AACF (8364 ± 2243) and AAPF (7827 ± 2881) compared to group AASS (4440 ± 2063), p ≤ 0.041. INTERPRETATION From a biomechanical perspective, the minimally invasive cup fixation with screw augmentation demonstrated comparable stability to plate osteosynthesis of ACFs in osteoporotic bone. The results of the present study do not allow to conclusively answer whether immediate full weight bearing following cup fixation shall be allowed. Given its similar performance to plate osteosynthesis, this remains rather an utopic wish and a more conservative approach deems more reasonable