Biomechanical effects of position and angle of insertion for all-suture anchors in arthroscopic Bankart repair

BackgroundThe biomechanical properties of all-suture anchor for labral repair depending on the insertion angle and location are lacking. The purpose of this study was to quantify the biomechanical fixation characteristics of the anchor position and insertion angle of all-suture anchors for arthroscopic Bankart repair.MethodsTwenty-four fresh frozen cadaveric glenoid were used. All-suture anchors with 1.5-mm diameter were randomly inserted at 2:30, 4:00, and 5:30 o'clock positions on the glenoid edge, with either 30°, 45° or 60° insertion angles to the mediolateral axis of the glenoid. Anchors were preloaded to 5 N and cyclically loaded from 5 N to 20 N for 10 cycles, followed by a load to failure test at 60 mm/min. Permanent, non-recoverable displacement was quantified at the end of the cyclic loading test to yield load.FindingsAll-suture anchors implanted at the 2:30 o'clock position of the glenoid provided greater stiffness, yield load, and ultimate load than those inserted at the 4:00 and 5:30 o'clock positions, regardless of the insertion angle. Displacement at yield and ultimate load were similar among the positions and insertion angles (yield load, vs. 4:00, p = 0.01; vs. 5:30, p = 0.045; ultimate load, vs. 4:00, p < 0.01; vs. 5:30, p < 0.01). The insertion angles of 30°, 45° and 60° did not influence mechanical stability between the 4:00 and 5:30 o'clock positions.InterpretationThe insertion angle of all-suture anchors does not significantly affect the stability at antero-inferior quadrant of the glenoid.     

3D correction over 2 years with anterior vertebral body growth modulation: A finite element analysis of screw positioning,cable tensioning and postoperative functional activities

BackgroundAnterior vertebral body growth modulation is a fusionless instrumentation to correct scoliosis using growth modulation. The objective was to biomechanically assess effects of cable tensioning, screw positioning and post-operative position on tridimensional correction.MethodsThe design of experiments included two variables: cable tensioning (150/200 N) and screw positioning (lateral/anterior/triangulated), computationally tested on 10 scoliotic cases using a personalized finite element model to simulate spinal instrumentation, and 2 years growth modulation with the device. Dependent variables were: computed Cobb angles, kyphosis, lordosis, axial rotation and stresses exerted on growth plates. Supine functional post-operative position was simulated in addition to the reference standing position to evaluate corresponding growth plate’s stresses.FindingsSimulated cable tensioning and screw positioning had a significant impact on immediate and after 2 years Cobb angle (between 5°–11°, p < 0.01). Anterior screw positioning significantly increased kyphosis after 2 years (6°–8°, p = 0.02). Triangulated screw positioning did not significantly impact axial rotation but significantly reduced kyphosis (8°–10°, p = 0.001). Growth plates' stresses were increased by 23% on the curve's convex side with cable tensioning, while screw positioning rather affected anterior/posterior distributions. Supine position significantly affected stress distributions on the apical vertebra compared to standing position (respectively 72% of compressive stresses on convex side vs 55%).InterpretationThis comparative numerical study showed the biomechanical possibility to adjust the fusionless instrumentation parameters to improve correction in frontal and sagittal planes, but not in the transverse plane. The convex side stresses increase in the supine position may suggest that growth modulation could be accentuated during nighttime.     

How does differential rod contouring contribute to 3-dimensional correction and affect the bone-screw forces in adolescent idiopathic scoliosis instrumentation?

BackgroundDifferential rod contouring is used to achieve 3-dimensional correction in adolescent idiopathic scoliosis instrumentations. How vertebral rotation correction is correlated with the amount of differential rod contouring is still unknown; too aggressive differential rod contouring may increase the risk of bone-screw connection failure. The objective was to assess the 3-dimensional correction and bone-screw forces using various configurations of differential rod contouring.MethodsComputerized patient-specific biomechanical models of 10 AIS cases were used to simulate AIS instrumentations using various configurations of differential rod contouring. The tested concave/convex rod configurations were 5.5/5.5 and 6.0/5.5 mm diameter Cobalt-chrome rods with contouring angles of 35°/15°, 55°/15°, 75°/15°, and 85°/15°, respectively. 3-dimensional corrections and bone-screw forces were computed and analyzed.FindingsIncreasing the difference between the concave and convex rod contouring angles from 25° to 60°, the apical vertebral rotation correction increased from 35% (SD 17%) to 68% (SD 24%), the coronal plane correction changed from 76% (SD 10%) to 72% (SD 12%), the thoracic kyphosis creation from 27% (SD 60%) to 144% (SD 132%), and screw pullout forces from 94 N (SD 68 N) to 252 N (SD 159 N). Increasing the concave rod diameter to 6 mm resulted in increased transverse and coronal plane corrections, higher thoracic kyphosis, and screw pullout forces.InterpretationsIncreasing the concave rod contouring angle and diameter with respect to the convex rod improved the transverse plane correction but with significant increase of screw pullout forces and thoracic kyphosis. Rod contouring should be planned by also taking into account the 3-dimensional nature and stiffness of the curves and combined with osteotomy procedures, which remains to be studied.     

Scapular bone grafting with allograft pin fixation for repair of bony Bankart lesions: A biomechanical study

BACKGROUNDSevere bony Bankart lesions are a difficult challenge in clinical treatment and research. The current treatment methods consist mostly of Latarjet-Bristow surgery and its modified procedures. While good results have been achieved, there are also complications such as coracoid fracture, bone graft displacement, and vascular and nerve injury.AIMTo analyze the techniques and biomechanical properties of transversely fixing a bone block from the scapular spine using bone allograft pins with suture threads to repair bony Bankart lesions.METHODSFresh human shoulder joint specimens and a cadaver specimen model for scapular bone grafting with allograft pin fixation for repair of bony Bankart lesions were used. When the humeral rotation angles were 0°, 30°, 60° and 90°, and the axial loads were 30 N, 40 N, and 50 N, the humerus displacement was studied by biomechanical experiments.RESULTSWhen the angle of external rotation of the humerus was 0°, 30°, 60°, and 90°, with axial loads of 30 N, 40 N, and 50 N, the data of the normal control group, allograft pin repair group, and titanium alloy hollow screw repair group were compared with each other by the q-test, which showed that there were no statistically differences among the three groups (P > 0.05).CONCLUSIONThe joints repaired with bone block from the scapular spine transversely fixed with allograft bony pins to repair bony Bankart lesions show good mechanical stability. The bone block has similar properties to normal glenohumeral joints in terms of biomechanical stability.     

Biomechanical comparison of cervical discectomy/fusion model using allograft spacers between anterior and posterior fixation methods (lateral mass and pedicle screw)

BackgroundThe purpose of this study is to investigate effects of different fixation methods on the physical stress on allospacers, endplate-vertebral body, and implants using finite element model analyses.MethodsStress distribution and subsidence risk according to the fixation methods under the condition of hybrid motion control were analyzed. The detailed finite element model of a previously validated, three-dimensional, intact cervical spinal segment model, with C5–C6 segmental fusion using allospacer, was used to evaluate the biomechanical characteristics of different fixation combinations, such as anterior plate/screws, lateral mass screw, and posterior pedicle screw.FindingsThe load sharing on allospacers increased in extension in order of posterior pedicle screws (21.4%), lateral mass screws (31.5%), and anterior plate/screws (56.6%). lateral mass screw demonstrated the highest load sharing (68.1%) on the allospacer in flexion. The Peak von Mises stress of the allospacer was the lowest in flexion and axial rotation but the highest in extension with anterior plate/screws. Allospacer subsidence risk was the lowest in extension, lateral bending, and axial rotation with posterior pedicle screws but the lowest in flexion with anterior plate/screws. The bone-screw loosening risk was the lowest in all modes with posterior pedicle screws but the highest with anterior plate/screws.InterpretationPosterior pedicle screws demonstrated the best mechanical stability of allospacer failure-subsidence and the lowest risk of screw loosening. Different motion restrictions depending on the fixation method should be considered for implant and allospacer safety.     

动态CT观察髌股关节排列异常

目的 分析动态CT评估髌股关节排列的方法 和价值.方法 分别在屈膝0°、10°、20°、30°时用CT检测30例60膝髌股关节,观察膝关节不同屈曲角度髌股关节的排列,测量各屈曲度髌股关节的股骨滑车角、相称角及外侧髌股角,分析不同角度对髌股排列异常的检出率.结果 本组分别在膝关节0°、10°、20°、30°选取髌骨棘与股骨滑车凹最深的层面测量,有15膝的相称角大于16°,为髌骨外侧半脱位,16膝为髌骨外倾,10膝髌骨外侧倾斜合并半脱位.统计学分析证实膝关节屈曲10°和20°对髌骨外倾、半脱位检出率高.结论 动态CT能评估髌股关节排列,膝关节屈曲10°和20°是诊断髌股关节排列异常的重要位置.     

Interaction of scapular dyskinesis with hand dominance on three-dimensional scapular kinematics

IntroductionThis study aimed to evaluate the effect of scapular dyskinesis and its interaction with hand dominance and humerothoracic angles on three-dimensional scapular kinematics in asymptomatic individuals in all planes of arm motion.MethodsForty-five asymptomatic participants, seventeen men and twenty-eight women, were separated into two groups: with (n = 22) and without scapular dyskinesis (n = 23) according to the Yes/No classification. Scapular kinematic data of dominant and non-dominant sides in both groups were measured with an electromagnetic tracking device during arm elevation and lowering phases in scapular, frontal and sagittal planes. A linear mixed model of covariance adjusted for age and BMI was used, which included hand dominance (dominant and non-dominant), group (with and without scapular dyskinesis), angles (30°, 60°, 90°, and 120°), and the interaction effect (group × hand dominance × humerothoracic angle).ResultsThere was a significant interaction effect on scapular anterior tilt and upward rotation in the sagittal plane, and for internal rotation and anterior tilt in the frontal and scapular planes. The effects of hand dominance on three-dimensional scapular kinematics, as increased anterior tilt, internal rotation and upward rotation, were greater in individuals without scapular dyskinesis.ConclusionThe effects of dominant side as increased upward rotation, internal rotation, and anterior tilt at higher humerothoracic angles for all planes of arm motion, were greater in individuals without scapular dyskinesis. Our findings may assist the scapular assessment which in individuals without scapular dyskinesis, bilaterally, possible between side differences in the scapular motions may be related to a dominance effect.     

下颈椎前路内固定联合后路经关节金属螺钉置入固定的生物力学稳定性

背景：对退变性颈椎管狭窄单纯采用前路椎体次全切除或椎间盘切除或单纯后路单开门椎管扩大成行均不能彻底完成脊髓减压和脊柱三柱稳定。目的：探讨下颈椎前路固定联合后路经关节螺钉固定的生物力学稳定性。方法：正常成人尸体颈椎标本,每具分别制作以下两种模型：①经后路C3～C7单开门和下颈椎前路C5椎体次全切除钛网支撑植骨、ORION内固定模型（对照组）。②经后路C3～C7单开门和经关节螺钉内固定及下颈椎前路C5椎体次全切除钛网内植骨、ORION内固定模型（实验组）。结果与结论：实验组在前屈、后伸、左、右侧屈及左、右旋转移位角度均小于对照组（P〈0.001）。提示：①在生物力学实验中,下颈椎前路固定联合后路经关突节螺钉固定的生物力学性能优良,对抗前屈、后伸、左、右旋转的作用力更强,颈椎可获得更可靠的稳定性。②下颈椎前路固定联合后路经关节螺钉固定在对抗颈椎前屈运动时力学稳定性更为强大。     

肱骨头关节面直径对多层螺旋CT容积再现技术测量肱骨头扭转角的影响

目的探讨肱骨头关节面直径对多层螺旋CT容积再现测量肱骨头扭转角的影响。方法收集24侧成人肩关节标本,行16层螺旋CT扫描,容积再现技术三维重建测量肱骨头扭转角。肱骨头关节面直径确定采用画圆拟合确定法及目测法,两种方法测得的肱骨头扭转角与二维CT测量法测得的肱骨头扭转角对照研究,行统计学处理。结果肱骨头扭转角最小值11°,最大值53°,三组肱骨头扭转角数据为(26.4±9.9)°,(27.1±9.7)°,(27.3±9.7)°。经统计学检验三种方法测值无显著性差异。结论肱骨头扭转角变异较大;多层螺旋CT容积再现目测法确定肱骨头关节面直径是获得肱骨头扭转角近端定义线更简单、更快捷的方法。     

Effectiveness of a 12-Week Physical Exercise Program on Lower-Limb Malalignment in School-age Rugby: A Randomized Clinical Trial

ObjectiveWe sought to assess the effectiveness of 12 weeks of a physical exercise program (PEP) in child rugby players with lower-limb overpronation during gait.MethodsThis was a randomized clinical trial. A total of 123 young athletes (mean ± standard deviation age, 10.35 ± 1.22 years) were evaluated, 20 of whom had lower-limb overpronation (n = 40 extremities). Participants were randomly assigned to 2 groups: the experimental group, who performed their normal training and a PEP for 12 weeks, and the control group, who continued with their normal training for the same time. The PEP was focused on stretching the hypertonic muscle and potentiating the weakened muscles of the lower body. All participants underwent biomechanical analysis including the Helbing angle, the femorotibial angle, and the Fick angle in both limbs.ResultsAll participants (n = 20) completed the study. Baseline measurements showed no significant differences between groups in any of the variables tested. After 12 weeks, there were significant differences between groups (P < .001 for all angles). No improvement was found in the control group; however, meaningful improvement was found in all variables in the experimental group: Helbing angle (175°, P < .001, effect size [ES] = 1.94), femorotibial angle (173°, P < .001, ES = 1.77), Fick angle (12°, P < .001, ES = 1.55). The number needed to treat was 2 for femorotibial angle and Helbing angle, and 3 for Fick angle.ConclusionA 12-week PEP produced significant improvements in these 3 biomechanical variables. We also conclude that young athletes with a pathological gait pattern reached a normal gait pattern.     

Combined effect of change in humeral neck-shaft angle and retroversion on shoulder range of motion in reverse total shoulder arthroplasty — A simulation study

BackgroundWe studied combined effect of change in humeral neck shaft angle and retroversion on shoulder ROM in reverse total shoulder arthroplasty using 3-dimensional simulations.MethodsUsing a 3D model construct based on the CT scans of 3 males and a 3-dimensional analysis program, a humeral component of reverse total shoulder arthroplasty was implanted in 0°, 10°, 20°, 30°,40° retroversion and 135°, 145°, and 155° neck shaft angle. Total horizontal range of motion (sum of horizontal adduction and abduction) at 30° and 60° scaption, adduction in the scapular plane and IR behind the back were measured for various combinations of neck shaft angle and retroversion.FindingsChange in retroversion didn't show any effect on total horizontal range of motion. Total horizontal range of motion at both 30° and 60° scaption, showed maximum values at 135° neck shaft angle and minimum values at 155° neck shaft angle. With any combination of retroversion angles, adduction deficit was maximum at 155° neck shaft angle and no adduction deficit at 135° neck shaft angle. Every 10° decrease in neck shaft angle resulted in an average 10.4° increase in adduction. For every 10° increase in retroversion, there was loss of internal rotation behind the back up to at least one vertebral level.Interpretation135° neck shaft angle resulted in maximum total horizontal range of motion both at 30° and 60° scaption regardless of retroversion angles. 135° neck shaft angle also reduced the chances of scapular impingement. Decrease in retroversion angle resulted in more amount of internal rotation behind the back.     

Biomechanical evaluation of anterior lumbar interbody fusion with various fixation options: Finite element analysis of static and vibration conditions

BackgroundAnterior lumbar interbody fusion combined with supplementary fixation has been widely used to treat lumbar diseases. However, few studies have investigated the influence of fixation options on facet joint force and cage subsidence. The aim of this study was to explore the biomechanical performance of anterior lumbar interbody fusion with various fixation options under both static and vertical vibration loading conditions.MethodsA previously validated finite element model of the intact L1–5 lumbar spine was employed to compare five conditions: (1) Intact; (2) Fusion alone; (3) Fusion combined with anterior lumbar plate; (4) Fusion combined with Coflex-F fixation; (5) Fusion combined with bilateral pedicle screw fixation. The models were analyzed under static and vertical vibration loading conditions respectively.FindingsBilateral pedicle screws provided highest stability at surgical level. Applying supplementary fixation diminished the dynamic responses of lumbar spine. Compared with anterior lumbar plate and Coflex-F device, bilateral pedicle screws decreased the stress responses of the endplates and cage under both static and vibration conditions, while increased the facet joint force at adjacent levels. As for comparison between Coflex-F device and anterior lumbar plate, results showed a similarity in biomechanical performance under static loading, and a slightly higher dynamic response of the latter under vertical vibration.InterpretationThe biomechanical performance of lumbar spine was significantly influenced by the variation of fixations under both static and vibration conditions. Bilateral pedicle screws showed advantages in stabilizing surgical segment and relieving cage subsidence, but may increase the facet joint force at adjacent levels.     

髌骨轴位摄影角度与屈膝角度的相关性

目的 探讨髌骨轴位摄影角度与屈膝角度的相关性.方法 选取30例患者的标准髌骨侧位膝关节屈膝过程的动态影像.在髌骨侧位动态影像中,以股骨前缘线与胫骨前缘线的夹角作为胫股角,以股骨前缘线与髌骨后缘线的夹角作为髌股角(X线入射角度),选择胫股角为50°～170°,每隔5°分别测量对应的髌股角.统计各胫股角相对应的髌股角的均值,对测量数据进行相关分析和回归分析.结果 胫股角在50°～110°范围时,胫股角和髌股角存在直线相关关系(r=0.92,P<0.01),回归方程为Y=60.71+0.60X.胫股角在115°～170°范围时,胫股角与髌股角的差值(髌胫角)基本恒定,其均值为15.04°±3.76°.结论 髌骨轴位摄影角度与胫股角具有直线相关性,在髌骨轴位摄影中可根据回归方程Y=60.71+0.60X或15°角选择相应的摄影角度.     

Biomechanical comparison of three different compression screws for treatment of odontoid fractures evaluation of a new screw design

BackgroundLag screw osteosynthesis in odontoid fractures shows a high rate of pseudarthrosis. Biomechanical properties may play a role with insufficient fragment compression or unnoticed screw stripping. A biomechanical comparison of different constructed lag-screws was carried out and the biomechanical properties determined.MethodsTwo identical compression screws with different pilot holes (1.25 and 2.5 mm), a double-threaded screw and one sleeve-nut-screw were tested on artificial bone (Sawbone, densities 10-30pcf). Fragment compression and torque were continuously measured using thin-film force sensors (Flexiforce A201, Tekscan) and torque sensors (PCE-TM 80, PCE GmbH).FindingsThe lowest compression reached the double-threaded screw. Compression and sleeve-nut-screw achieved 214–298% and 325–546%, respectively, of the compression force of double-threaded-screw, depending on the test material. The pilot hole optimization led to a significant improvement in compression only in the densest test material. Screw stripping took place significantly later with increasing density of the test material on all screws. In compression screws this was done at a screw rotation of 180–270°, in sleeve nut screw at 270–720° and in double-threaded screws at 300–600° after reaching the maximum compression.InterpretationDouble-threaded screw is robust against screw stripping, but achieves only low fragment compression. The classic compression screws achieve better compression, but are sensitive to screw stripping. Sleeve-nut screw is superior in compression and as robust as double-threaded screw against screw stripping. Whether the better biomechanical properties lead to a reduction in pseudarthrosis must be proven in clinical trials.     

Effect of insonation angle on peak systolic velocity variation

ObjectivesAs point of care ultrasound (POCUS) has become more integrated into emergency and critical care medicine, there has been increased interest in utilizing ultrasound to assess volume status. However, recent studies of carotid POCUS on volume status and fluid responsiveness fail to recognize the effect insonation angle has on their results. To address this, we studied the effect of insonation angle on peak systolic velocity (PSV) change associated with respiratory variation (RV) and passive leg raise (PLR).MethodsDoppler measurements were obtained from 51 subjects presenting to the ED. Minimal and maximal PSV were obtained using insonation angles of 46°, 60°, and 90°. ∆PSV was calculated using PLR and RV as trial methods. Results were categorized into two groups, those with a ∆PSV > 10% and those with a ∆PSV ≤ 10%. ∆PSV mean and standard error, as well as measures of agreement were calculated.ResultsMean ∆PSV associated with PLR test was 9% in the 46° and 60° groups, and 18% in the 90° group, with standard errors of 6, 7, and 14%, respectively. Using 46° as our relative gold standard, Kappa was 0.23 at 60° and 0.11 at 90° with RV as the trial method, and 0.23 at 60° and 0.01 at 90° with a PLR as the trial method.ConclusionsVariation in PSV is heavily dependent on insonation angle. There was only slight to fair agreement in ∆PSV among the various insonation angles. Further investigation of the optimal insonation angle to assess ∆PSV should be undertaken.     

Biomechanical evaluation of femoral anteversion in developmental dysplasia of the hip and potential implications for closed reduction

BackgroundEarlier clinical reports have identified femoral anteversion as a factor associated with developmental dysplasia of the hip. This study investigates the biomechanical influence of femoral anteversion on severe dislocations and its effect on hip reduction using the Pavlik harness.MethodsA computational model of an infant lower-extremity, representing a ten-week old female was used to analyze the biomechanics of anteversion angles ranging from 30° to 70° when severe dislocation was being treated with the Pavlik harness. Specifically, the effects and relationships between muscle passive response and femoral anteversion angle were investigated over a range of hip abduction and external rotation.FindingsResults of this study suggest that increased femoral anteversion may decrease the success rate for treatment of high-grade developmental dysplasia of the hip when using the Pavlik harness. However, hip external rotation and decreased abduction in the harness may facilitate initial reduction in these cases.InterpretationThis biomechanical study may help explain why dissections of newborn specimen with developmental dysplasia of the hip have shown normal distribution of femoral anteversion in contrast to studies of patients requiring surgery where greater frequency of increased femoral anteversion has been reported. This study also suggests that adjusting the Pavlik harness to increase external hip rotation and decrease hip abduction may facilitate initial reduction for severe dislocations with increased femoral anteversion.     

A new choice of stent for transjugular intrahepatic portosystemic shunt creation: Viabahn ePTFE covered stent/bare metal stent combination

ObjectivesTo compare the clinical outcomes in terms of structure and function between the insertion of a transjugular intrahepatic portosystemic shunt (TIPS) created with the Viabahn ePTFE covered stent/bare metal stent (BMS) combination and the Fluency ePTFE covered stent/BMS combination.MethodsA total of 101 consecutive patients who received a TIPS from February 2016 to August 2018 in our center were retrospectively analyzed. Sixty-four subjects were enrolled in the Viabahn group and 37 were enrolled in the Fluency group. The geometry characteristics of the TIPS were calculated, and the associated occurrence of shunt dysfunction, survival, overt hepatic encephalopathy, and variceal rebleeding were evaluated.ResultsThe technical success rate was 100%. After the insertion of the TIPS, the rate of shunt dysfunction during the first 3 months was significantly different between the Viabahn and Fluency groups (1.6% and 13.5%, respectively; p ​= ​0.024). Multivariate analysis indicated that the angle of portal venous inflow (α) was the only independent risk factor for shunt dysfunction (hazard ratio ​= ​1.060, 95% confidence interval ​= ​1.009–1.112, p ​= ​0.020). In addition, 3 months after the TIPS insertion, the α angle distinctly increased from 20.9° ​± ​14.3°–26.9° ​± ​20.1° (p ​= ​0.005) in the Fluency group but did not change significantly in the Viabahn group (from 21.9° ​± ​15.1°–22.9° ​± ​17.6°, p ​= ​0.798).ConclusionsShunt dysfunction was related to the α angle owing to the slight effect on the α angle after the implantation of the TIPS. The Viabahn ePTFE covered stent/BMS combination was more stable in structure and promised higher short-term stent patency compared with the Fluency ePTFE covered stent/BMS combination.     

Biomechanical analysis of sagittal correction parameters for surgical instrumentation with pedicle subtraction osteotomy in adult spinal deformity

BackgroundHigh complication rate has been documented in spinal instrumentation with pedicle subtraction osteotomy. The objective was to analyze the biomechanics of spinal instrumentation with pedicle subtraction osteotomy as functions of three instrumentation parameters.MethodsPatient-specific biomechanical computer models of 3 adult patients who were instrumented with pedicle subtraction osteotomy were used to simulate the actual instrumentations and alternative instrumentations derived by varying instrumentation parameters: pedicle subtraction osteotomy wedge angle and rod contouring angle, location of the osteotomy, and number of rods (2 vs. 4).FindingsA change of the sagittal correction by +7.5° (−7.5°) resulted in a change in the screw axial forces and rods bending loads around the osteotomy by +38% (−19%) and +28% (−11%), respectively. The bending moments in the rods were 31% lower at the osteotomy site when it was located at one level above, and 20% higher when it was located at a level below. Additional rods allowed the rod bending and screw axial loads to be reduced by 24% and 22%, respectively.InterpretationThe amount of sagittal correction was positively correlated with loads sustained by the screws and rods. Rods were subjected to higher bending loads at the pedicle subtraction osteotomy site when it was done at a lower level. A 4-rod construct is an effective way to reduce the risk of rod breakage by reducing the loads sustained by the rods.     

Intraoperative experiments combined with gait analyses indicate that active state rather than passive dominates the spastic gracilis muscle's joint movement limiting effect in cerebral palsy

BackgroundIn cerebral palsy, spastic muscle's passive forces are considered to be high but have not been assessed directly. Although activated spastic muscle's force-joint angle relations were studied, this was independent of gait relevant joint positions. The aim was to test the following hypotheses intraoperatively: (i) spastic gracilis passive forces are high even in flexed knee positions, (ii) its active state forces attain high amplitudes within the gait relevant knee angle range, and (iii) increase with added activations of other muscles.MethodsIsometric forces (seven children with cerebral palsy, gross motor function classification score = II) were measured during surgery from knee flexion to full extension, at hip angles of 45° and 20° and in four conditions: (I) passive state, after gracilis was stimulated (II) alone, (III) simultaneously with its synergists, and (IV) also with an antagonist.FindingsDirectly measured peak passive force of spastic gracilis was only a certain fraction of the peak active state forces (maximally 26%) measured in condition II. Conditions III and IV caused gracilis forces to increase (for hip angle = 45°, by 32.8% and 71.9%, and for hip angle = 20°, by 24.5% and 45.1%, respectively). Gait analyses indicated that intraoperative data for knee angles 61–17° and 33–0° (for hip angles 45° and 20°, respectively) are particularly relevant, where active state force approximates its peak values.InterpretationActive state muscular mechanics, rather than passive, of spastic gracilis present a capacity to limit joint movement. The findings can be highly relevant for diagnosis and orthopaedic surgery in individuals with cerebral palsy.