Can a Computational Model Predict the Effect of Lesion Location on Cam-type Hip Impingement?

BACKGROUND: The Warwick consensus defined femoroacetabular impingement syndrome as a motion-related clinical disorder of the hip with a triad of symptoms, clinical signs, and imaging findings representing symptomatic premature contact between the proximal femur and acetabulum. Several factors appear to cause labral and cartilage damage, including joint shape and orientation and patient activities. There is a lack of tools to predict impingement patterns in a patient across activities. Current computational modeling tools either measure pure ROM of the joint or include complexity that reduces reliability and increases time to achieve a solution. QUESTIONS/PURPOSES: The purpose of this study was to examine the efficacy of a low computational cost approach to combining cam-type hip shape and multiple hip motions for predicting impingement. Specifically, we sought to determine (1) the potential to distinguish impingement in individual hip shapes by analyzing the difference between a cam lesion at the anterior femoral neck and one located at the superior femoral neck; (2) sensitivity to three aspects of hip alignment, namely femoral neck-shaft angle, femoral version angle, and pelvic tilt; and (3) the difference in impingement measures between the individual activities in our hip motion dataset. METHODS: A model of the shape and alignment of a cam-type impinging hip was created and used to describe two locations of a cam lesion on the femoral head-neck junction (superior and anterior) based on joint shape information available in prior studies. Sensitivity to hip alignment was assessed by varying three aspects from a baseline (typical alignment described in prior studies), namely, femoral neck-shaft angle, femoral version, and pelvic tilt. Hip movements were selected from an existing database of 18 volunteers performing 13 activities (10 male, eight female; mean age 44 ± 19 years). A subset was selected to maximize variation in the range of joint angles and maintain a consistent number of people performing each activity, which resulted in nine people per activity, including at least three of each sex. Activities included pivoting during walking, squatting, and golf swing. All selected hip motion cases were applied to each hip shape model. For the first part of the study, the number of motion cases in which impingement was predicted was recorded. Quantitative analyses of the depth of penetration of the cam lesion into the acetabular socket and qualitative observations of impingement location were made for each lesion location (anterior and superior). In the second part of the study, in which we aimed to test the sensitivity of the findings to hip joint orientation, full analysis of both cam lesion locations was repeated for three modified joint orientations. Finally, the results from the first part of the analysis were divided by activity to understand how the composition of the activity dataset affected the results. RESULTS: The two locations of cam lesion generated impingement in a different percentage of motion cases (anterior cam: 56% of motion cases; superior cam: 13% of motion cases) and different areas of impingement in the acetabulum, but there were qualitatively similar penetration depths (anterior cam: 6.8° ± 5.4°; superior cam: 7.9° ± 5.8°). The most substantial effects of changing the joint orientation were a lower femoral version angle for the anterior cam, which increased the percentage of motion cases generating impingement to 67%, and lower neck-shaft angle for the superior cam, which increased the percentage of motion cases generating impingement to 37%. Flexion-dominated activities (for example, squatting) only generated impingement with the anterior cam. The superior cam generated impingement during activities with high internal-external rotation of the joint (for example, the golf swing). CONCLUSION: This work demonstrated the capability of a simple, rapid computational tool to assess impingement of a specific cam-type hip shape (under 5 minutes for more than 100 motion cases). To our knowledge, this study is the first to do so for a large set of motion cases representing a range of activities affecting the hip, and could be used in planning surgical bone removal. CLINICAL RELEVANCE: The results of this study imply that patients with femoroacetabular impingement syndrome with cam lesions on the superior femoral head-neck junction may experience impinging during motions that are not strongly represented by current physical diagnostic tests. The use of this tool for surgical planning will require streamlined patient-specific hip shape extraction from imaging, model sensitivity testing, evaluation of the hip activity database, and validation of impingement predictions at an individual patient level.

Characteristics of hip joint reaction forces during a range of activities.

The paper reports the characteristics of joint forces for 9 activities in 18 normal healthy subjects. Activities included Walk, Walk Turn, Stand to Sit, Sit to Stand, Squat, Stand Reach, Kneel Reach, Lunge, and Golf Swing. Within the cohort ∼30% variability occurred in the manner in which each activity was completed. Within the activities the average maximum load characteristics varied in magnitude (0.5-6.4 ρBWT) and also in duration (0.96-5.89 s.) when compared to walking (3.1 ρBWT,1.1 s.). The corresponding impulse ranged from 1.6 during the Walk to 6.7 ρ.BWT.s for the Golf Swing . As high loads with low sliding velocities have been shown in the literature to be damaging to the tribology of compliant contact surfaces the findings are postulated by the authors to be specifically important for the pre-clinical testing of cartilage substitutional materials. Note: Force was normalized to body weight (ρBWT) throughout the study.

Comparison of axial-rotational postoperative periprosthetic fracture of the femur in composite osteoporotic femur versus human cadaveric specimens: A validation study.

Postoperative periprosthetic femoral fracture following hip replacement has been the subject of many varied experimental approaches. Cadaveric samples offer realistic fit and fracture patterns but are subject to large between-sample variation. Composite femurs have not yet been validated for this purpose. We compared the results of composite femurs to cadaveric femurs using an established methodology. In vitro postoperative periprosthetic fracture results using axial-rotational loading were compared between 12 composite femurs and nine fresh frozen femurs, which were implanted with an otherwise identical collarless (6 composite vs 4 cadaveric) or collared (6 composite vs 5 cadaveric) cementless femoral stem using identical methodology. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. Fractures patterns were graded according to the Unified Classification System. Fracture torque, displacement, torsional stiffness and fracture patterns for cadaveric and composite femurs were similar between groups. There was a trend for a greater rotational displacement in the cadaveric groups, which lead to a decrease in torsional stiffness and a significantly greater rotational work prior to fracture for all cadaveric specimens (collarless stems: 10.51 [9.71 to 12.57] vs 5.21 [4.25 to 6.04], p = 0.01 and for collared stems: 15.38 [14.01 to 17.05] vs 5.76 [4.92 to 6.64], p = 0.01). Given comparable fracture torque and the similarity in fracture patterns for fracture trials using composite samples versus cadaveric femurs, the use of composite femur models may be a reasonable choice for postoperative periprosthetic femoral fracture studies within certain limitations.

Comparison of Mechanical Performance between Circular Frames and Biplanar Distraction Devices for Knee Joint Distraction.

AIM AND OBJECTIVE: This study was designed to test and compare the mechanical performance of the biplanar ArthroSave KneeReviver and a circular frame construct with the intended use of providing a mechanically favourable environment for cartilage regeneration across a knee joint. MATERIALS AND METHODS: Three similar constructs of the two devices were applied to biomechanical testing sawbones, with the knee distracted by 8 mm. The constructs were vertically loaded to 800 N in an Instron testing machine at 20 mm/minute. Tests were conducted in neutral hip flexion and at 12° of hip flexion and extension, to mimic leg position in gait. Displacement measurements were taken from the Instron machine, and three-dimensional joint motion was recorded using an Optotrak Certus motion capture system. RESULTS: Overall axial rigidity was similar between the two devices (circular frame, 81.6 N/mm ± 5.9; and KneeReviver, 79.5 N/mm ± 25.1 with hip neutral) and similar in different hip positions. At the point of joint contact, the overall rigidity of the circular frame increased significantly more than the KneeReviver (491 N/mm ± 27 and 93 N/mm ± 32, respectively, p <0.001). There was more variability between models in the KneeReviver. There was more off-axis motion in the KneeReviver, mainly due to increasing knee flexion on loading. This was exacerbated with the hip in flexion and extension but remained small, with the maximal off-axis displacement being 7 mm/3°. CONCLUSION: The circular frame provides a similar mechanical environment to the novel KneeReviver device, for which most clinical data are available. These findings suggest that both devices appear a viable option for knee joint distraction (KJD). Further clinical data will help inform mode of application. CLINICAL SIGNIFICANCE: KJD is a relatively novel technique for use in osteoarthritis (OA), and it remains unclear which distraction devices provide appropriate mechanics. Our testing gives evidence to support either option for further use. HOW TO CITE THIS ARTICLE: Chowdhury JMY, Lineham B, Pallett M, et al. Comparison of Mechanical Performance between Circular Frames and Biplanar Distraction Devices for Knee Joint Distraction. Strategies Trauma Limb Reconstr 2021;16(2):71-77.

Analysis of hip joint cross-shear under variable activities using a novel virtual joint model within Visual3D.

Cross-shear forces occur between bearing surfaces at the hip and have been identified as a key contributor to prosthesis wear. Understanding the variation in relative motion paths between both individuals and activities, is a possible explanation for increased revision rates for younger patients and could assist in improved pre-clinical testing regimes. Additionally, there is little information for the pre-clinical testing of cartilage substitution therapies for younger more active individuals. The calculation of motion paths has previously relied on computational modelling software which can be complex and time-consuming. The aim of this study was to determine whether the motion paths calculations could be integrated into gait analysis software to improve batch processing, reduce analysis time and ultimately improve the efficiency of the analysis of cross-shear variation for a broader range of activities. A novel Virtual Joint model was developed within Visual3D for calculating motion paths. This model was compared to previous computational methods and found to provide a competitive solution for cross shear analysis (accuracy <0.01 mm error between methods). The virtual hip model was subsequently applied to 13 common activities to investigate local aspect ratio's, velocities and accelerations. Surprisingly walking produced the harshest cross shear motion paths in subjects. Within walking, of additional interest was that the localised change in acceleration for subjects was six times greater compared to the same point on an equivalent smoothed simulator cycle. The Virtual hip developed in Visual 3D provides a time saving technique for visualising and processing large data sets directly from motion files. The authors postulate that rather than focussing on a generalised smoothed cross-shear model that pre-clinical testing of more delicate structures should consider localised changes in acceleration as these may be more important in the assessment of cartilage substitutes sensitive to shear.

Calcar-collar contact during simulated periprosthetic femoral fractures increases resistance to fracture and depends on the initial separation on implantation: A composite femur in vitro study.

BACKGROUND: A calcar collar may reduce risk of periprosthetic fracture of the femur, through collar contact. We estimated the effect of collar contact on periprosthetic fracture mechanics using a collared fully coated cementless femoral stem and then estimated the effect of initial calcar-collar separation on the likelihood of collar contact. METHODS: Three groups of six composite left femurs with increasing calcar-collar separation in each group, underwent periprosthetic fracture simulation in a materials testing machine. Fracture torque and rotational displacement were measured and torsional stiffness and rotational work prior to fracture were estimated. Calcar collar contact prior to fracture was identified using high speed camera footage. FINDINGS: Where calcar-collar contact occurred fracture torque was greater (47.33 [41.03 to 50.45] Nm versus 38.26 [33.70 to 43.60] Nm, p = 0.05), Rotational displacement was less (16.6 [15.5 to 22.3] degrees versus 21.2 [18.9 to 28.1] degrees, p = 0.07), torsional stiffness was greater (151.38 [123.04 to 160.42] rad.Nm-1 versus 96.86 [84.65 to 112.98] rad.Nm-1, p < 0.01) and rotational work was similar (5.88 [4.67, 6.90] J versus 5.31 [4.40, 6.56] J, p = 0.6). Odds ratio (OR) of not achieving collar contact (95% confidence interval) increased 3.8 fold (95% CI 1.6 to 30.2, p < 0.05) for each millimetre of separation in the regression model. 95% chance of collar contact was associated with a separation of 1 mm or less. INTERPRETATION: Surgeons should reduce calcar-collar separation at stem implantation to a maximum of 1 mm to increase the chance of calcar-collar contact during injury and reduce the risk of early post-operative femoral fracture.

Passive eDNA collection enhances aquatic biodiversity analysis.

Environmental DNA (eDNA) metabarcoding is a sensitive and widely used approach for species detection and biodiversity assessment. The most common eDNA collection method in aquatic systems is actively filtering water through a membrane, which is time consuming and requires specialized equipment. Ecological studies investigating species abundance or distribution often require more samples than can be practically collected with current filtration methods. Here we demonstrate how eDNA can be passively collected in both tropical and temperate marine systems by directly submerging filter membranes (positively charged nylon and non-charged cellulose ester) in the water column. Using a universal fish metabarcoding assay, we show that passive eDNA collection can detect fish as effectively as active eDNA filtration methods in temperate systems and can also provide similar estimates of total fish biodiversity. Furthermore, passive eDNA collection enables greater levels of biological sampling, which increases the range of ecological questions that eDNA metabarcoding can address.

Measurement of Wire Deflection on Loading may Indicate Union in Ilizarov Constructs: A Pilot Study.

INTRODUCTION: No entirely reliable method to assess union during Ilizarov treatment exists. Premature frame removal results in treatment failure, and alternative methods of assessment warrant investigation. Wire deflection might provide an indication of fracture site deformation on weight-bearing, indicating progress towards union. A previous in vitro study from our group demonstrated this approach may be clinically applicable. We investigated translation of this method into clinical practice in an observational pilot study. MATERIALS AND METHODS: Patients with tibial shaft fractures treated with Ilizarov frames were recruited. A prototype depth gauge was used to measure wire deflection on weight-bearing. Investigators undertaking the measurement were blinded to the clinical stage of treatment, and clinicians caring for the patient were blinded to deflection results. Patient records were reviewed at the end of treatment to determine likely fracture stability at each time point. Deflection per kg of weight applied, per mm from the ring was compared between stable and unstable situations. RESULTS: Thirty-one measurements were obtained in 14 patients. The situation was deemed stable at 13 and unstable at 18 measurements. The median deflection in the stable group was 0.030 microns/kg/mm (IQR 0.005-0.104) and 0.165 microns/kg/mm (IQR 0.072-0.328) in the unstable group. This difference was statistically significant (Wilcoxon Mann-Whitney test p = 0.0014). ROC curve analysis revealed that wire deflection was able to predict clinical stability (AUC 0.84, p <0.0001). Various technical problems were encountered when using the device which would potentially limit its clinical utility in its current form. CONCLUSION: In this set of observations, wire deflection was significantly associated with clinically and radiologically determined stability. Though various practical limitations were encountered in using the prototype measurement device, this proof-of-concept study supports further development of this approach. The research group plan to develop a smaller, more reliable device for further clinical testing in a larger group of patients. HOW TO CITE THIS ARTICLE: Lineham B, Stewart T, Ward J, et al. Measurement of Wire Deflection on Loading may Indicate Union in Ilizarov Constructs: A Pilot Study. Strategies Trauma Limb Reconstr 2021;16(3):132-137.

Foot trajectories and loading rates in a transfemoral amputee for six different commercial prosthetic knees: An indication of adaptability.

BACKGROUND: The relationship between the functional loading rate and heel velocities was assessed in an active unilateral transfemoral amputee (UTFA) for adaptation to six different commercial prosthetic knees. OBJECTIVE: To Investigate the short-term process of adaptability for UTFA for two types of prosthetic knees were evaluated, based on the correlation between heel vertical velocity and transient loading rate. METHODS: The loading rate was calculated from the slope of ground reaction forces (GRF) and the corresponding time. The heel velocities and GRF were obtained by a motion analysis system. RESULTS: Biomechanical adaptation was evident following a short period of prosthetic knee use based upon the mean transient impact (loading rate) and the heel vertical velocity in slow, normal and fast walking. Trend lines of transient impact versus vertical heel velocity for a set of actively controlled variable damping (microprocessor) and mechanically passive prosthetic knees were all negatively correlated, except for an amputated leg during normal pace and healthy leg during fast pace. For an amputee to adapt well to a prescribed prosthesis excellent coordination between the intact and amputated limbs is required to control placement of the amputated leg to achieve a gait comparable to healthy subjects. CONCLUSION: There are many factors such as the hip, knee flexion/extension and the ankle plantarflexion/dorsiflexion contributing to the control of the transient impact of an amputee during walking. Therefore, for enhanced control of a prosthetic knee, a multifaceted approach is required. This study showed that UTFA adaption to different prosthetic knees in the short term with slower than self-selected speed is completely achievable based on the negative correlation of ground reaction forces versus linear velocity. Reduced speed may provide the prosthetists with the vision of the amputees' progression of adaptation with a newly prescribed prosthetic knee.

Hip surgeons and leg length inequality after primary hip replacement.

BACKGROUND:: This study reports the results of 2 separate surveys of British Hip Society (BHS) members relating to leg length inequality (LLI) after primary total hip replacement (THR). SURVEY 1:: Investigates the members' opinions on the effect of LLI on the outcome of THR and explores the acceptable limits of LLI. SURVEY 2:: Reports on the intraoperative techniques currently used by BHS members to minimise LLI after THR. RESULTS - SURVEY 1:: 97% of all surgeons completing the survey believed that LLI can affect the outcome of THR. RESULTS - SURVEY 2:: All surgeons reported using at least 1 intraoperative technique for assessing leg length with a median of 5 techniques. Over 50% of surgeons use 2 or more tests. CONCLUSION - SURVEY 1:: 89% of surgeons agreed that 15 mm of LLI after primary uncomplicated THR was always acceptable. 90% of surgeons felt that LLI more than 22.74 mm was never acceptable. CONCLUSION - SURVEY 2:: Despite the multiple published papers on various methods of assessing leg length intraoperatively, the problem of LLI post THR persists. This study highlights the need for further research to develop a simple intraoperative technique with high accuracy and reproducibility.

Can the radiopaque marker in surgical swabs scratch orthopaedic implant surfaces?

AIMS: To determine whether the radiopaque marker strip, which is woven in surgical swabs, causes measureable wear on metal implants at pressures typically used to wipe off fluid from their surface. MATERIALS AND METHODS: Finger pressure used to wipe a surface was measured and used as a reference pressure for further testing. A tribological wear rig was then used to analyse the wear caused on polished titanium plates by a cobalt chromium pin (the control test), the pin covered by a surgical swab and the pin covered by a radiopaque marker strip. RESULTS: It was found that the cotton part or the radiopaque marker of surgical swabs on polished medical grade titanium plates caused no significant wear. In contrast severe scratching was observed from the cobalt chromium pin on its own. CONCLUSION: To our knowledge, this is the first study in the literature analysing the wear caused by the surgical swabs and radiopaque strip on metal implants. The results suggest that surgical swabs are safe to use on metallic implants at pressures typical of a wiping motion.

Biomechanical analysis of walking gait when simulating the use of an Ilizarov external fixator.

The Ilizarov frame is an external fixation device, primarily used for the treatment of complex fractures. The authors postulate that the size and weight of the frame may lead to biomechanical adaptations to gait, independent to any injury. Temporospatial characteristics, kinetics and kinematics were assessed when simulating the use of an Ilizarov frame. Fifteen healthy participants performed walking trials, with and without the simulated frame. Significant changes to temporospatial characteristics were identified, with a decreased mean walking speed (with: 1.24 m s-1; without: 1.29 m s-1) and increased mean step width (with: 0.14 m; without: 0.11 m). The push-off phase of gait differed significantly between test conditions with mean increases in ankle dorsiflexion angles (with: 90.4°; without: 89.0°) and extension moments (proportional to body weight or P BWT) at the knee and ankle (knee with: 0.8 P BWT·m; without: 0.7 P BWT·m; ankle with: 1.6 P BWT·m; without: 1.6 P BWT·m). Although changes were small and likely to be clinically insignificant, the size and weight of the frame led to adaptations which may be magnified for patient groups with associated injury and pain at the lower limb. Results provide an argument for the potential redesign of the frame.

Hip stem fatigue: : The implications of increasing patient mass.

General trends of increasing body mass index have been observed in many western countries along with an increasing demand for joint replacement. Standards have been developed for testing the fatigue properties of femoral stems; however, the loads that these apply are based on a historic patient weight and may not be valid in the current patient population. Several fatigue tests were conducted using distally fixed titanium alloy stems positioned according to the ISO standard but with a cyclic load based on a current 75th percentile patient sample. Smaller sized stems (currently not weight restricted) fractured in; 30,000 cycles, while larger sized stems were found to have excellent durability under loads simulating walking and stumbling. The results suggest that while the fatigue properties of medical grade titanium are very good, the ISO pre-clinical durability testing standard does not represent the influence of femoral offset or stem size sufficiently to reflect safe design practice.

Measurement of wire deflection on loading may indicate union in Ilizarov constructs, an in vitro model.

No entirely reliable method exists for assessing union during Ilizarov treatment. Premature removal results in potential treatment failure; hence, alternative methods warrant investigation. Wire deflection might provide an indication of fracture site deformation on weight bearing, indicating progress towards union. This study aimed to test a method for assessing wire deflection within an Ilizarov frame. (1) To assess the repeatability of our novel measurement method in measuring wire deflection within an Ilizarov frame in vitro. (2) To compare the amount of wire deflection in an unstable model with that in an intact bone model. (3) To assess accuracy of this method by comparing wire deflection measured with overall machine extension. Tests were performed on clinical grade-tensioned fine wire 4-ring Ilizarov constructs stabilising a simulated fracture, with and without an unstable defect. Models were sequentially loaded to 700 N using an Instron testing machine. A digital depth gauge attached to the superior ring measured relative wire displacement at the ring closest to the fracture. Tests were repeated 3 times. (1) Both unstable and stable bone models produced highly repeatable load deformation curves (R2 = 0.98 and 0.99). (2) In the unstable model, wires tensioned at 882 and 1274 N produced mean maximum deflections of 2.41 and 2.69 mm compared with 0.05 and 0.04 mm in the intact bone model (significant p < 0.0001). (3) Wire deflection and machine extension results were strongly correlated (r = 0.99). A measurable difference in wire deflection between stable and unstable situations exists using this method which appears accurate and repeatable, with clear correlation between displacement and load and displacement and machine extension. This approach might be clinically applicable, and further clinical testing is required.

What Are the Biomechanical Properties of the Taylor Spatial Frame™?

BACKGROUND: The Taylor Spatial Frame™ (TSF) is a versatile variant of the traditional Ilizarov circular fixator. Although in widespread use, little comparative data exist to quantify the biomechanical effect of substituting the tried-and-tested Ilizarov construct for the TSF hexapod system. QUESTIONS/PURPOSES: This study was designed to investigate the mechanical properties of the TSF system under physiologic loads, with and without the addition of a simulated bone model, with comparison to the standard Ilizarov frame. METHODS: The mechanical behaviors of three identical four-ring TSF and Ilizarov constructs were tested under levels of axial compression, bending, and rotational torque to simulate loading during normal gait. An acrylic-pipe fracture model subsequently was mounted, using fine wires and 5 mm half pins, and the testing was repeated. Load-deformation curves, and so rigidity, for each construct were calculated, with statistical comparisons performed using paired t-tests. RESULTS: Under axial loading, the TSF was found to be less rigid than the Ilizarov frame (645 ± 57 N/mm versus 1269 ± 256 N/mm; mean difference, 623 N/mm; 95% CI, 438.3-808.5 N/mm; p < 0.001), but more rigid under bending and torsional loads (bending: 42 ± 9 Nm/degree versus 78 ± 13 Nm/degree; mean difference, 37 Nm/degree; 95% CI, 25.0-47.9 Nm/degree; p < 0.001; torsion: 16 ± 2 Nm/degree versus 5 ± 0.35 Nm/degree; mean difference, 11 Nm/degree; 95% CI, 9.5-12.2 Nm/degree; p < 0.001). On mounting the bone models, these relationships broadly remained in the half-pin and fine-wire groups, however the half-pin constructs were universally more rigid than those using fine wires. This effect resulted in the TSF, using half pins, showing no difference in axial rigidity to the fine-wire Ilizarov (107 ± 3 N/mm versus 107 ± 4 N/mm; mean difference, 0.05 N/mm; 95% CI, -6.99 to 7.1 N/mm; p > 0.999), while retaining greater bending and torsional rigidity. Throughout testing, a small amount of laxity was observed in the TSF construct on either side of neutral loading, amounting to 0.72 mm (±0.37 mm) for a change in loading between -10 N and 10 N axial load, and which persisted with the addition of the synthetic fracture model. CONCLUSIONS: This study broadly shows the TSF construct to generate lower axial rigidity, but greater bending and torsional rigidity, when compared with the Ilizarov frame, under physiologic loads. The anecdotally described laxity in the TSF hexapod strut system was shown in vitro, but only at low levels of loading around neutral. It also was shown that the increased stiffness generated by use of half pins produced a TSF construct replicating the axial rigidity of a fine-wire Ilizarov frame, for which much evidence of good clinical and radiologic outcomes exist, while providing greater rigidity and so improved resistance to potentially detrimental bending and rotational shear loads. CLINICAL RELEVANCE: If replicated in the clinical setting, these findings suggest that when using the TSF, care should be taken to minimize the observed laxity around neutral with appropriate preloading of the construct, but that its use may produce constructs better able to resist bending and torsional loading, although with lower axial rigidity. Use of half pins in a TSF construct however may replicate the axial mechanical behavior of an Ilizarov construct, which is thought to be conducive to bone healing.

What Are the Biomechanical Effects of Half-pin and Fine-wire Configurations on Fracture Site Movement in Circular Frames?

BACKGROUND: Fine-wire circular frame (Ilizarov) fixators are hypothesized to generate favorable biomechanical conditions for fracture healing, allowing axial micromotion while limiting interfragmentary shear. Use of half-pins increases fixation options and may improve patient comfort by reducing muscle irritation, but they are thought to induce interfragmentary shear, converting beam-to-cantilever loading. Little evidence exists regarding the magnitude and type of strain in such constructs during weightbearing. QUESTIONS/PURPOSES: This biomechanical study was designed to investigate the levels of interfragmentary strain occurring during physiologic loading of an Ilizarov frame and the effect on this of substituting half-pins for fine-wires. METHODS: The "control" construct was comprised of a four-ring all fine-wire construct with plain wires at 90°-crossing angles in an entirely unstable acrylic pipe synthetic fracture model. Various configurations, substituting half-pins for wires, were tested under levels of axial compression, cantilever bending, and rotational torque simulating loading during gait. In total three frames were tested for each of five constructs, from all fine-wire to all half-pin. RESULTS: Substitution of half-pins for wires was associated with increased overall construct rigidity and reduced planar interfragmentary motion, most markedly between all-wire and all-pin frames (axial: 5.9 mm ± 0.7 vs 4.2 mm ± 0.1, mean difference, 1.7 mm, 95% CI, 0.8-2.6 mm, p < 0.001; torsional: 1.4% ± 0.1 vs 1.1% ± 0.0 rotational shear, mean difference, 0.3%, 95% CI, 0.1%-0.5%, p = 0.011; bending: 7.5° ± 0.1 vs 3.4° ± 0.1, mean difference, -4.1°, 95% CI, -4.4° to -3.8°, p < 0.001). Although greater transverse shear strain was observed during axial loading (0.4% ± 0.2 vs 1.9% ± 0.1, mean difference, 1.4%, 95% CI, 1.0%-1.9%, p < 0.001), this increase is unlikely to be of clinical relevance given the current body of evidence showing bone healing under shear strains of up to 25%. The greatest transverse shear was observed under bending loads in all fine-wire frames, approaching 30% (29% ± 1.9). This was reduced to 8% (±0.2) by incorporation of sagittal plane half-pins and 7% (±0.2) in all half-pin frames (mean difference, -13.2% and -14.0%, 95% CI, -16.6% to 9.7% and -17.5% to -10.6%, both p < 0.001). CONCLUSIONS: Appropriate use of half-pins may reduce levels of shear strain on physiologic loading of circular frames without otherwise altering the fracture site mechanical environment at levels likely to be clinically important. Given the limitations of a biomechanical study using a symmetric and uniform synthetic bone model, further clinical studies are needed to confirm these conclusions in vivo. CLINICAL RELEVANCE: The findings of this study add to the overall understanding of the mechanics of circular frame fixation and, if replicated in the clinical setting, may be applied to the preoperative planning of frame treatment, particularly in unstable fractures or bone transport where control of shear strain is a priority.

Validation of the modified Sgarbossa criteria for acute coronary occlusion in the setting of left bundle branch block: A retrospective case-control study.

BACKGROUND: The modified Sgarbossa criteria were proposed in a derivation study to be superior to the original criteria for diagnosing acute coronary occlusion (ACO) in left bundle branch block (LBBB). The new rule replaces the third criterion (5 mm of excessively discordant ST elevation [STE]) with a proportion (at least 1 mm STE and STE/S wave ≤-0.25). We sought to validate the modified criteria. METHODS: This retrospective case-control study was performed by chart review in 2 tertiary care center emergency departments (EDs) and 1 regional referral center. A billing database was used at 1 site to identify all ED patients with LBBB and ischemic symptoms between May 2009 and June 2012. In addition, all 3 sites identified LBBB ACO patients who underwent emergent catheterization. We measured QRS amplitude and J-point deviation in all leads, blinded to outcomes. Acute coronary occlusion was determined by angiographic findings and cardiac biomarker levels, which were collected blinded to electrocardiograms. Diagnostic statistics of each rule were calculated and compared using McNemar's test. RESULTS: Our consecutive cohort search identified 258 patients: 9 had ACO, and 249 were controls. Among the 3 sites, an additional 36 cases of ACO were identified, for a total of 45 ACO cases and 249 controls. The modified criteria were significantly more sensitive than the original weighted criteria (80% vs 49%, P < .001) and unweighted criteria (80% vs 56%, P < .001). Specificity of the modified criteria was not statistically different from the original weighted criteria (99% vs 100%, P = .5) but was significantly greater than the original unweighted criteria (99% vs 94%, P = .004). CONCLUSIONS: The modified Sgarbossa criteria were superior to the original criteria for identifying ACO in LBBB.

Dangers of Prehospital Cooling: A Case Report of Afterdrop in a Patient with Exertional Heat Stroke.

BACKGROUND: Exertional heat stroke is a potentially life-threatening disease with varying clinical presentations and severity. Given the severe morbidity that can accompany the disease, the immediate management often begins in the prehospital setting. It is important to have not only a comprehensive understanding of the prehospital cooling methods in addition to hospital management strategies, but an understanding of their potential complications as well. CASE REPORT: A 32-year-old male presented to a San Antonio hospital in March 2014 with progressive confusion, nausea, nonbloody emesis, and ataxia. Initial presentation was concerning for exertional heat stroke, as the patient was recorded in the field to have a temperature of 42.1°C (106.2°F). The patient, on arrival to the emergency department, was found to have a core body temperature of 38.1°C (100.6°F). All active cooling measures were terminated and active rewarming was initiated. Despite adequate resuscitation and rapid identification of the patient's overcorrection in core body temperature, the lowest recorded temperature was 36.0°C (96.8°F). Why Should an Emergency Physician Be Aware of This? This case represents the dangers associated with exertional heat stroke, overcorrection of core body temperature, and the potentially lethal complication of afterdrop. It also represents the need for immediate recognition of the condition and initiation of appropriate medical care. Although this patient's clinical outcome was good, the event could have caused serious morbidity or could have potentially been fatal.