Does spinopelvic alignment affect femoral head cartilage and the proximal femoral physis in slipped capital femoral epiphysis? A finite element analysis.

BACKGROUND: Slipped capital femoral epiphysis is a prevalent pediatric hip disorder. Recent studies suggest the spine's sagittal profile may influence the proximal femoral growth plate's slippage, an aspect not extensively explored. This study utilizes finite element analysis to investigate how various spinopelvic alignments affect shear stress and growth plate slip. METHODS: A finite element model was developed from CT scans of a healthy adult male lumbar spine, pelvis, and femurs. The model was subjected to various sagittal alignments through reorientation. Simulations of two-leg stance, one-leg stance, walking heel strike, ascending stairs heel strike, and descending stairs heel strike were conducted. Parameters measured included hip joint contact area, stress, and maximum growth plate Tresca (shear) stress. FINDINGS: Posterior pelvic tilt cases indicated larger shear stresses compared to the anterior pelvic tilt variants except in two leg stance. Two leg stance resulted in decreases in the posterior tilted pelvi variants hip contact and growth plate Tresca stress compared to anterior tilted pelvi, however a combination of posterior pelvic tilt and high pelvic incidence indicated larger shear stresses on the growth plate. One leg stance and heal strike resulted in higher shear stress on the growth plate in posterior pelvic tilt variants compared to anterior pelvic tilt, with a combination of posterior pelvic tilt and high pelvic incidence resulting in the largest shear. INTERPRETATION: Our findings suggest that posterior pelvic tilt and high pelvic incidence may lead to increased shear stress at the growth plate. Activities performed in patients with these alignments may predispose to biomechanical loading that shears the growth plate, potentially leading to slip.

Pelvic Ring Fractures: A Biomechanical Comparison of Sacral and Lumbopelvic Fixation Techniques.

BACKGROUND CONTEXT: Pelvic ring fractures are becoming more common in the aging population and can prove to be fatal, having mortality rates between 10% and 16%. Stabilization of these fractures is challenging and often require immediate internal fixation. Therefore, it is necessary to have a biomechanical understanding of the different fixation techniques for pelvic ring fractures. METHODS: A previously validated three-dimensional finite element model of the lumbar spine, pelvis, and femur was used for this study. A unilateral pelvic ring fracture was simulated by resecting the left side of the sacrum and pelvis. Five different fixation techniques were used to stabilize the fracture. A compressive follower load and pure moment was applied to compare different biomechanical parameters including range of motion (contralateral sacroiliac joint, L1-S1 segment, L5-S1 segment), and stresses (L5-S1 nucleus stresses, instrument stresses) between different fixation techniques. RESULTS: Trans-iliac-trans-sacral screw fixation at S1 and S2 showed the highest stabilization for horizontal and vertical displacement at the sacral fracture site and reduction of contralateral sacroiliac joint for bending and flexion range of motion by 165% and 121%, respectively. DTSF (Double transiliac rod and screw fixation) model showed highest stabilization in horizontal displacement at the pubic rami fracture site, while the L5_PF_W_CC (L5-Ilium posterior screw fixation with cross connectors) and L5_PF_WO_CC (L5-Ilium posterior screw fixation without cross connectors) showed higher rod stresses, reduced L1-S1 (approximately 28%), and L5-S1 (approximately 90%) range of motion. CONCLUSIONS: Longer sacral screw fixations were superior in stabilizing sacral and contralateral sacroiliac joint range of motion. Lumbopelvic fixations displayed a higher degree of stabilization in the horizontal displacement compared to vertical displacement of pubic rami fracture, while also indicating the highest rod stresses. When determining the surgical approach for pelvic ring fractures, patient-specific factors should be accounted for to weigh the advantages and disadvantages for each technique.

How Much Bullying and Discrimination Are Reported by Sexual and Gender Minorities in Orthopaedics?

BACKGROUND: Discriminatory practices against minority populations are prominent, especially in the workplace. In particular, lesbian, gay, bisexual, transgender, and queer or questioning (LGBTQ+) individuals experience several barriers and stressors more often than individuals who do not identify as LGBTQ+. Mistreatment is common among these individuals in their personal and professional lives. However, representation and perceptions of discrimination and bullying among attendings, residents, medical students, and other professionals who identify as LGBTQ+ and are "out" (openly acknowledging and expressing one's sexual orientation or gender identity) is seldom studied in orthopaedic surgery. QUESTIONS/PURPOSES: (1) How often are orthopaedic trainees and professionals who identify as LGBTQ+ out in their workplaces? (2) What proportion of these individuals report experiencing discrimination, bullying, or differential treatment? (3) Is there regional variation in these reported experiences of bullying and discriminatory behaviors by orthopaedic trainees and professionals in the LGBTQ+ community? METHODS: Individuals registering for Pride Ortho, a community of LGBTQ+ individuals and their allies established in 2021 to provide mentorship, networking, and a sense of community among its members, completed an internet-based survey developed by organization leadership. A total of 156 individuals registering for the Pride Ortho community were eligible to participate in the internet-based survey. In all, 92% (144 of 156) fully completed the survey, 6% (10 of 156) partially completed it, and 1% (2 of 156) did not complete any part of the survey. Most respondents (64% [100 of 156]) identified as being LGBTQ+, with 77 members at the attending level of their careers. More than half of LGBTQ+ members (56% [56 of 100]) identified as cisgender women (individuals who identify as women and who were born female). Demographic information was privately collected and deidentified, and included sex assigned at birth, gender expression or identity (the social constructed role that an individual chooses to inhabit, regardless of that individual's assigned sex at birth), sexual orientation, self-identified race, location, level of training, and orthopaedic subspecialty. RESULTS: Ninety-four percent (94 of 100) of LGBTQ+ respondents reported being out at their workplace, with nearly one-third of respondents indicating they were only partially out. Most (74% [74 of 100]) respondents reported either "yes" or "maybe" to perceived experiences of bullying, discrimination, or being treated differently. All individuals who partially completed the survey were straight or heterosexual and did not answer or answered "not applicable" to being out in their workplace. These individuals also all answered "no" to experiencing bullying, discrimination, or being treated differently. There was no geographic variation in reported experiences of bullying and discriminatory behaviors by orthopaedic trainees and professionals. CONCLUSION: Most LGBTQ+ orthopaedic trainees and professionals are out in their workplaces, although they report experiencing discrimination and bullying more than do non-LGBTQ+ individuals. Bullying and discrimination can deter individuals from beginning and completing their training in orthopaedic surgery. We recommend that orthopaedic institutions not only enforce existing antidiscrimination legal mandates but also increase the visibility of LGBTQ+ faculty and residents. This effort should include the implementation of diversity and sensitivity training programs, strengthened by a structured process of monitoring, reporting, and integrating feedback from all members in the workplace to continuously refine policy adherence and identify the root cause of the reported perceptions of bullying and discrimination. CLINICAL RELEVANCE: To deepen our understanding of the experiences faced by sexual and gender minorities in orthopaedic surgery settings, it is crucial to quantify reports of perceived bullying and discrimination. Addressing these issues is key to creating a more diverse and empathetic workforce within orthopaedic institutions, which in turn can lead to improved patient care and a better work environment. Recognizing and understanding the specific contexts of these experiences is an essential starting point for developing a truly inclusive environment for both trainees and attending physicians.

Fracture risk assessment of vascularized medial femoral condylar bone graft: A finite element analysis.

BACKGROUND: Vascularized medial femoral condyle (MFC) bone graft is useful for pseudarthrosis and osteonecrosis, but has the risk of fracture as a complication. This study aimed to create multiple three-dimensional (3D) finite element (FE) femur models to biomechanically evaluate the fracture risk in the donor site of a vascularized MFC bone graft. METHODS: Computer tomography scans of the femurs of nine patients (four males and five females) with no left femur disease were enrolled in the study. A 3D FE model of the left femur was generated based on the CT images taken from the patients. The descending genicular artery (DGA), the main nutrient vessel in vascularized MFC bone grafts, divides into the proximal transversal branch (TB) and the distal longitudinal branch (LB) before entering the periosteum. Thirty-six different bone defect models with different sizes and locations of the harvested bone were created. RESULTS: The highest stress was observed in the proximal medial and metaphyseal portions under axial and external rotation, respectively. In the bone defect model, the stress was most elevated in the extracted region's anterior or posterior superior part. Stress increased depending on proximal location and harvested bone size. CONCLUSION: Increasing the size of the bone graft proximally raises the stress at the site of bone extraction. For bone grafting to non-load-bearing areas, bone grafting distally using LB can reduce fracture risk. If TB necessitates a larger proximal bone extraction, it is advisable to avoid postoperative rotational loads.

Posterior Fixation for Different Thoracic-Sacrum Alignments Containing a Thoracolumbar Vertebral Fracture: A Finite Element Analysis.

OBJECTIVE: Thoracolumbar vertebral fractures are one of the most common fractures; however, there is a lack of mechanical analyses for what the posterior fixation is for different spine alignments. METHODS: This study used a three-dimensional finite element model of a T1-sacrum. Three alignment models were created: intact, degenerative lumbar scoliosis (DLS), and adolescent idiopathic scoliosis (AIS). The burst fracture was assumed to be at the L1 vertebral level. Posterior fixation models with pedicle screws (PS) were constructed for each model: 1 vertebra above to 1 below PS (4PS) and 1 vertebra above to 1 below PS with additional short PS at the L1 (6PS); intact-burst-4PS, intact-burst-6PS, DLS-burst-4PS, DLS-burst-6PS, AIS-burst-4PS, and AIS-burst-6PS models. T1 was loaded with a moment of 4 Nm assuming flexion and extension. RESULTS: The vertebrae stress varied with spinal alignment. The stress of L1 in intact burst (IB), DLS burst, and AIS burst increased by more than 190% compared with each nonfractured model. L1 stress in IB, DLS, and AIS-4PS increased to more than 47% compared with each nonfractured model. L1 stress in IB, DLS, and AIS-6PS increased to more than 25% compared with each nonfractured model. In flexion and extension, stress on the screws and rods of intact-burst-6PS, DLS-6PS, and AIS-6PS was lower than in the intact-burst-4PS, DLS-4PS, and AIS-4PS models. CONCLUSIONS: It may be more beneficial to use 6PS compared with 4PS to reduce stresses on the fractured vertebrae and instrumentation, regardless of the spinal alignment.

The Effect of Posterior Lumbar Interbody Fusion in Lumbar Spine Stenosis with Diffuse Idiopathic Skeletal Hyperostosis: A Finite Element Analysis.

OBJECTIVE: Lumbar spinal canal stenosis (LSS) with diffuse idiopathic skeletal hyperostosis (DISH) can require revision surgery because of the intervertebral instability after decompression. However, there is a lack of mechanical analyses for decompression procedures for LSS with DISH. METHODS: This study used a validated, three-dimensional finite element model of an L1-L5 lumbar spine, L1-L4 DISH, pelvis, and femurs to compare the biomechanical parameters (range of motion [ROM], intervertebral disc, hip joint, and instrumentation stresses) with an L5-sacrum (L5-S) and L4-S posterior lumbar interbody fusion (PLIF). A pure moment with a compressive follower load was applied to these models. RESULTS: ROM of L5-S and L4-S PLIF models decreased by more than 50% at L4-L5, respectively, and decreased by more than 15% at L1-S compared with the DISH model in all motions. The L4-L5 nucleus stress of the L5-S PLIF increased by more than 14% compared with the DISH model. In all motions, the hip stress of DISH, L5-S, and L4-S PLIF had very small differences. The sacroiliac joint stress of L5-S and L4-S PLIF models decreased by more than 15% compared with the DISH model. The stress values of the screws and rods in the L4-S PLIF model was higher than in the L5-S PLIF model. CONCLUSIONS: The concentration of stress because of DISH may influence adjacent segment disease on the nonunited segment of PLIF. A shorter-level lumbar interbody fixation is recommended to preserve ROM; however, it should be used with caution because it could provoke adjacent segment disease.

Effects of Sacral Slope Changes on the Intervertebral Disc and Hip Joint: A Finite Element Analysis.

OBJECTIVE: Spinopelvic parameters are vital components that must be considered when treating patients with spinal disease. Several finite element (FE) studies have explored spinopelvic parameters such as sacral slope (SS) and the impact on the lumbar spine, although no study has examined the effect on the hip and sacroiliac joint (SIJ) on varying SS angles. Therefore, it is necessary to have a biomechanical understanding of the impact on the spinopelvic complex. METHODS: An FE lumbar, pelvis, and femur model was created from computed tomography scans of a 55-year-old female patient with no abnormalities. Three models were created: a normal model (SS = 26°), a model with high SS (SS = 30°), and a model with low SS (SS = 20°). These models underwent loading for flexion, extension, lateral bending, and axial rotation. Range of motion (ROM), intradiscal pressures, hip joint, and SIJ contact stresses were analyzed. RESULTS: The high SS model (SS = 30°) indicated the highest ROM in the L5-S1 (slip angle) level and the highest intradiscal pressures. The highest average hip and SIJ contact stresses were present in this model, although the low SS model (SS = 20°) in extension had the largest stresses for the hip and SIJ. CONCLUSIONS: The results provide evidence that patients with higher SS may be more prone to increased ROM at the slip angle (L5-S1). In addition, patients with higher SS were shown to have higher contact stresses on the hip joint and SIJ, potentially leading to SIJ dysfunction. Clinically, correcting lumbar lordosis including SS is important; however, a high SS may have a negative impact on the intervertebral disc, SIJ, and hip joint.

The Effect of Anterior-Only, Posterior-Only, and Combined Anterior Posterior Fixation for Cervical Spine Injury with Soft Tissue Injury: A Finite Element Analysis.

OBJECTIVE: This finite element analysis aimed to investigate the effects of surgical procedures for cervical spine injury. METHODS: A three-dimensional finite element model of the cervical spine (C2-C7) was created from computed tomography. This model contained vertebrae, intervertebral discs, anterior longitudinal ligament, and posterior ligament complex. To create the cervical spine injury model, posterior ligament complex and anterior longitudinal ligament at C3-C4 were resected and the center of the intervertebral disc was resected. We created posterior-only fixation (PF), anterior-only fixation (AF), and combined anterior-posterior fixation (APF) models. A pure moment with a compressive follower load was applied, and range of motion, annular/nucleus stress, instrument stress, and facet forces were analyzed. RESULTS: In all motion except for flexion, range of motion of PF, AF, and APF models decreased by 80%-95%, 85%-93%, and 97%-99% compared with the intact model. C3-C4 annulus stress of PF, AF, and APF models decreased by 28%-72%, 96%-100%, and 99%-100% compared with the intact model. Facet contact forces of PF, AF, and APF models decreased by 77%-79%, 97%-99%, and 77%-86% at C3-C4 compared with the intact model. Screw stress in the PF model was higher than in the APF model, and plate stress in the AF model was lower than in the APF model, but bone graft stress in the AF model was higher than in the APF model. CONCLUSIONS: Cervical stabilization was preserved by the APF model. Regarding range of motion, the PF model had an advantage compared with the AF model except for flexion. An understanding of biomechanics provides useful information for the clinician.

Effect of posterior decompression with and without fixation on a kyphotic cervical spine with ossification of the posterior longitudinal ligament.

STUDY DESIGN: Biomechanical study. OBJECTIVE: Cervical ossification of the posterior longitudinal ligament (C-OPLL) causes myelopathy. Though posterior decompression for C-OPLL showed positive results, poor outcomes were seen in patients with a kyphotic alignment. Posterior decompression with fusion (PDF) tends to show better results compared to posterior decompression. The aim of this study is to evaluate the effects of the posterior procedures for C-OPLL. SETTING: Yamaguchi University. METHODS: Based on 3D finite element C2-C7 spine created from medical images and a spinal cord, the following compression models were created: the intact model, K-line 0 mm model, and K-line 2 mm model. These models were used to analyze the effects of posterior decompression with varied lengths of fixation. The stress of the spinal cord was calculated for intact, K-line 0 mm, and K-line 2 mm as preoperative models, and laminectomy (LN)-K-line 0 mm, PDF (C4-C5)-K-line 0 mm, PDF (C3-C6)-K-line 0 mm, LN-K-line 2 mm, PDF (C4-C5)-K-line 2 mm, and PDF (C3-C6)-K-line 2 mm model as operative models in a neutral, flexion, and extension. RESULTS: As the compression increased, stress on the spinal cord increased compared to the intact model. In the neutral, posterior decompression decreased the stress of the spinal cord. However, in flexion and extension, the stress on the spinal cord for LN-K-line 0 or 2 mm, PDF (C4-C5)-K-line 0 or 2 mm, and PDF (C3-C6)-K-line 0 or 2 mm models decreased by more than 40%, 43%, and 70% respectively compared to the K-line 0 or 2 mm model. CONCLUSIONS: In kyphotic C-OPLL, it is essential to control intervertebral mobility in the posterior approach.

Sagittal Imbalance May Lead to Higher Risks of Vertebral Compression Fractures and Disc Degeneration-A Finite Element Analysis.

BACKGROUND: Sagittal balance is an important clinical parameter of the spine for its normal function. Maintenance of the sagittal balance is crucial in the clinical management of spinal problems. METHODS: Three different finite element models with spinal alignments based on Schwab's classification were developed: (1) Balanced/Normal model (sagittal vertical axis [SVA] = 0 mm, lumbar lordosis [LL] = 50°, thoracic kyphosis [TK] = 25°, pelvic incidence [PI] = 45°, pelvic tilt [PT] = 10°, sacral slope [SS] = 35°); (2) Balanced with compensatory mechanisms/Flatback model (SVA = 50 mm, LL = 20°, TK = 20°, PI = 45°, PT = 30°, SS = 15°); and (3) Imbalanced/Hyperkyphotic model (SVA = 150 mm, LL = -5°, TK = 25°, PI = 45°, PT = 40°, SS = 5°). All 3 models were subjected to the follower loads simulating bodyweight/muscular contractions along with the moments to simulate flexion, extension, lateral bending, and axial rotation. The maximum cortical vertebral stress, annular stress, and intradiscal pressure (IDP) were calculated and compared. RESULTS: The results showed that the hyperkyphotic model had higher stresses in the vertebrae (25% higher), the annulus fibrosus (48% higher) and the IDP (8% higher) than the normal models in flexion. The segments near the thoracolumbar junction (T10-L1) showed the highest increase in the vertebral body stress, the annulus fibrosus stress, and the IDP. CONCLUSIONS: This study showed that the imbalance in sagittal alignment might be responsible for disc degeneration and atraumatic vertebral fractures at the thoracolumbar regions, supporting clinical findings.

Biomechanical analysis of laminectomy, laminoplasty, posterior decompression with instrumented fusion, and anterior decompression with fusion for the kyphotic cervical spine.

PURPOSE: Anterior and posterior decompressions for cervical myelopathy and radiculopathy may lead to clinical improvements. However, patients with kyphotic cervical alignment have sometimes shown poor clinical outcomes with posterior decompression. There is a lack on report of mechanical analysis of the decompression procedures for kyphotic cervical alignment. METHODS: This study employed a three-dimensional finite element (FE) model of the cervical spine (C2-C7) with the pre-operative kyphotic alignment (Pre-OK) model and compared the biomechanical parameters (range of motion (ROM), annular stresses, nucleus stresses, and facet contact forces) for four decompression procedures at two levels (C3-C5); laminectomy (LN), laminoplasty (LP), posterior decompression with fusion (PDF), and anterior decompression with fusion (ADF). Pure moment with compressive follower load was applied to these models. RESULTS: PDF and ADF models' global ROM were 40% at C2-C7 less than the Pre-OK, LN, and LP models. The annular and nucleus stresses decreased more than 10% at the surgery levels for ADF, and PDF, compared to the Pre-OK, LN, and LP models. However, the annular stresses at the adjacent cranial level (C2-C3) of ADF were 20% higher. The nucleus stresses of the caudal adjacent level (C5-C6) of PDF were 20% higher, compared to other models. The PDF and ADF models showed a less than 70% decrease in the facet forces at the surgery levels, compared to the Pre-OK, LN, and LP models. CONCLUSION: The study concluded that posterior decompression, such as LN or LP, increases ROM, disc stress, and facet force and thus can lead to instability. Although there is the risk of adjacent segment disease (ASD), PDF and ADF can stabilize the cervical spine even for kyphotic alignments.

Soft Tissue Injury in Cervical Spine Is a Risk Factor for Intersegmental Instability: A Finite Element Analysis.

OBJECTIVE: Soft tissue cervical spine injury (CSI) has the possibility of causing cervical segmental instability, which can lead to spinal cord injury. There is a lack of certainty in assessing whether soft tissue CSI is unstable or not. This biomechanical study aimed to investigate the risk factors of soft tissue CSI. METHODS: A 3-dimensional finite element model of the ligamentous cervical spine (C2-C7) was created from medical images. Three soft tissue injury models were simulated at C4-C5: 1) posterior ligament complex (PLC) injury, 2) intervertebral disk (ID) with anterior longitudinal ligament injury (IDI), and 3) anterior longitudinal ligament, PLC, and ID injury (API) model. Pure moment with compressive follower load was applied, and the range of motion, annular stress, nucleus stress, and facet forces were analyzed. RESULTS: For the IDI and API models, the range of motion increased at the injury level in extension (by 101%) and left/right axial rotations (>30%) compared with the intact model. The IDI and API models showed an increase of >50% in annular and nucleus stresses at the injury level in extension and left/right rotations compared with the intact model. The PLC injury showed similar stresses as the intact model except for flexion. The facet contact forces of IDI and API models increased more than 100% compared with other models in all motions. CONCLUSIONS: In CSI, all soft tissues have a key role in stabilizing cervical spine, but ID is the most important component of all.

Iatrogenic muscle damage in transforaminal lumbar interbody fusion and adjacent segment degeneration: a comparative finite element analysis of open and minimally invasive surgeries.

PURPOSE: Lumbar procedures for Transforaminal Lumbar Interbody Fusion (TLIF) range from open (OS) to minimally invasive surgeries (MIS) to preserve paraspinal musculature. We quantify the biomechanics of cross-sectional area (CSA) reduction of paraspinal muscles following TLIF on the adjacent segments. METHODS: ROM was acquired from a thoracolumbar ribcage finite element (FE) model across each FSU for flexion-extension. A L4-L5 TLIF model was created. The ROM in the TLIF model was used to predict muscle forces via OpenSim. Muscle fiber CSA at L4 and L5 were reduced from 4.8%, 20.7%, and 90% to simulate muscle damage. The predicted muscle forces and ROM were applied to the TLIF model for flexion-extension. Stresses were recorded for each model. RESULTS: Increased ROM was present at the cephalad (L3-L4) and L2-L3 level in the TLIF model compared to the intact model. Graded changes in paraspinal muscles were seen, the largest being in the quadratus lumborum and multifidus. Likewise, intradiscal pressures and annulus stresses at the cephalad level increased with increasing CSA reduction. CONCLUSIONS: CSA reduction during the TLIF procedure can lead to adjacent segment alterations in the spinal element stresses and potential for continued back pain, postoperatively. Therefore, minimally invasive techniques may benefit the patient.