Biomechanical changes in the proximal femur before and after removal of femoral neck system.

BACKGROUND: As an innovative internal fixation system, FNS (femoral neck system) is increasingly being utilized by surgeons for the treatment of femoral neck fractures. At present, there have been numerous finite element analysis experiments studying the immediate stability of FNS and CSS in treating femoral neck fractures. However, there is scarce mechanical analysis available regarding the effects post internal fixation removal. This study aimed to investigate the alterations in mechanical parameters of the proximal femur before and after the removal of FNS (femoral neck system), and to assess potential distinctions in indicators following the extraction of CSS (Cannulated Screws). METHODS: A proximal femur model was reconstructed using finite element numerical techniques. The models for CSS and FNS were formulated utilizing characteristics and parametric definitions. The internal fixation was combined with a normal proximal femur model to simulate the healing state after fracture surgery. Within the framework of static analysis, consistent stress burdens were applied across the entirety of the models. The total deformation and equivalent stress of the proximal femur were recorded before and after the removal of internal fixation. RESULTS: Under the standing condition, the total deformation of the model before and after removing CSS was 0.99 mm and 1.10 mm, respectively, indicating an increase of 12%. The total deformation of the model before and after removing FNS was 0.65 mm and 0.76 mm, respectively, indicating an increase of 17%. The equivalent stress for CSS and FNS were 55.21 MPa and 250.67 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of CSS was 7.76 MPa and 6.11 MPa, respectively. The average equivalent stress on the cross-section of the femoral neck before and after removal of FNS was 9.89 MPa and 8.79 MPa, respectively. CONCLUSIONS: The retention of internal fixation may contribute to improved stability of the proximal femur. However, there still existed risks of stress concentration in internal fixation and stress shielding in the proximal femur. Compared to CSS, the removal of FNS results in larger bone tunnels and insufficient model stability. Further clinical interventions are recommended to address this issue.

Impact of 3D collagen-based model and hydrostatic pressure on periodontal ligament fibroblast: A morpho-biochemical analysis.

This study developed a customized hydrostatic pressure-based loading environment to investigate the effect of static hydrostatic pressure on the periodontal ligament fibroblasts (PDLf) in a three-dimensional (3D) collagen-based model. The cylindrical tissue constructs were comprised of PDL fibroblast cells seeded in type I collagen matrices and divided into three experimental groups: Control (no load), low-load (∼0.07 kPa), and high-load (∼60 kPa), all subjected to 24 h of experimental duration. Cells in the 3D construct were stained with fluorophore-conjugated antibodies for cytoskeletal protein F-actin and matricellular protein periostin. Cell culture supernatant was assessed for receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG) expression. Transmission electron microscopy examined the contact between the cells and the collagen matrix. Ultrastructural changes in the 3D collagen matrix were also analyzed using scanning electron microscopy. Experiments were performed in triplicates, and data was analyzed using one-way ANOVA (p < 0.05). The 3D PDLf constructs from the low-load group demonstrated the highest levels of homogeneous cell distribution and higher expression of F-actin and periostin with enhanced interaction with the matrix. The collagen matrix in this group showed more closely packed fibers forming thicker bundles when compared to the control and the high-load 3D PDLf constructs. Nonuniform cell distribution with decreased expression of F-actin and periostin was observed in the control and high-load PDLf constructs. The high-load group showed the highest RANKL/OPG expression. This study demonstrated low-level hydrostatic pressure's role in regulating PDLf functions and extracellular matrix response, while excessive hydrostatic pressure may be detrimental to PDL fibroblast cell function.

Biomechanical analysis of single- and double-level cervical disc arthroplasty using finite element modeling.

Recently, many different types of artificial discs have been introduced to persevere the biomechanical behavior of the cervical spine. This study compares the biomechanical behavior of single- and double-level cervical disc arthroplasty, that is "Prestige LP and Mobi-C" on the index and adjacent segment. A three-dimension finite element model of C2-C7 was developed and validated. In single-level prostheses, the Prestige LP or Mobi-C was implanted in the segment C5-C6, while the double-level arthroplasty was integrated at both segments C4-C5 and C5-C6 in the FE model. The intact FE and prosthesis-modified models were constrained from the inferior endplate of the vertebra C7 and applied a compressive load of 73.6 N with a moment load of 1 Nm on the odontoid process of the vertebra C2 to produce flexion/extension, lateral bending, and axial rotation. The prosthesis-modified model's range of motion and intradiscal pressure were determined and compared to the intact model. Also examined the impact of the prostheses on the stress at the bone-implant interface. The range of motion of the implanted segments in both single- and double-levels arthroplasty was increased while that of the adjacent segment of implanted segments decreased. The intradiscal pressure in both levels of arthroplasty was greater than in the intact model. In conclusion, Mobi-C's cervical prostheses could better preserve the normal range of motion and maintain intradiscal pressure than the Prestige LP.

Should cannulated screws be removed after a femoral neck fracture has healed, and how? A finite element analysis of the femur before and after cannulated screw removal.

PURPOSE: The removal of three inverted triangular parallel cannulated screws after the femoral neck fracture healing is sometimes accompanied by osteonecrosis of the femoral head (ONFH) or its refracture. The purpose of this study was to determine the biomechanical changes of the femur before and after the screw removal using a finite element analysis. METHODS: The CT data of the femurs were obtained from a 69-year-old healthy female to establish the femur models. The established finite element models consisted of N, C, and R groups: N group, the normal femur; C group (to simulate the femoral neck fracture healing after the internal fixation), the normal femur with three inverted triangular parallel cannulated screws (C1) or with two upper parallel screws (C2). For the R1 or R2 groups, the screws in the model of the C1 or C2 individuals were gradually removed in seven or three types of different screw combinations, respectively. The stresses and displacements of the femur were determined. RESULTS: (1) Compared with the N group, a uniform stress distribution was stopped by the addition of three screws in the C1 group; in contrast, all screw removals resulted in the stress concentration on the screw holes and the disappearance of stress shielding. Moreover, the average stress of the femoral head in C1 group increased by 37.85%, while that of the femoral neck decreased by 23.03%. (2) Compared with the C1 group, while only the lowest femoral calcar screw was removed, there was a similar stress distribution in the proximal femur, and the average stress of the femoral head increased only by 0.35% although that of the femoral neck increased by 63.62%; however, removal by any other means resulted in a significant stress concentration in the proximal femur and a significant increase in the average stresses of the femoral head and neck (5.96-40.95% and 12.82-75.46%, respectively). (3) Compared with the N or C1 group, there was a significant stress concentration on the screws and its surrounding proximal femur in the C2 group. (4) Compared with the C2 group, the simultaneous removal of two upper screws not only did not cause a significant stress concentration on the proximal femur but also significantly reduced the average stresses of the femoral head and neck by 87.49% and 65.51% respectively. On the contrary, the gradual removal of two screws caused a significant stress concentration on the screw and its surrounding proximal femur although the average stresses of the femoral head and neck decreased by 88.79-89.06% and 67.00-67.22%, respectively. (5) Compared with the N group, the average displacements of the femoral head and neck in the C1 group increased only by 3.12% and 3.37%, respectively. Additionally, compared with the C1 group, while three, two, or one screw was simultaneously removed, the average displacements of the femoral head and neck only fluctuated - 5.51-1.65% and 1.78-9.03%, respectively. CONCLUSIONS: Residual internal fixation after femoral neck fracture healing may lead to stress concentration on screws and stress shielding around screws. The first removal of the lowest femoral calcar screw and then the second removal of two upper residual screws have a minimum effect on the stress concentration on the proximal femur and the average stress on the femoral head. The incorrect screw removal and resulting femoral load may well be closely related to occurrence in ONFH or its refracture.

The biomechanical effect of the relevant segments after facet-disectomy in different diameters under posterior lumbar percutaneous endoscopes: a three-dimensional finite element analysis.

OBJECTIVE: To evaluate the biomechanical influence after percutaneous endoscopic lumbar facetectomy in different diameters on segmental range of motion (ROM) and intradiscal pressure (IDP) of the relevant segments by establishing three dimensional finite element (FE) model. METHODS: An intact L3-5 model was successfully constructed from the CT of a healthy volunteer as Model A (MA). The Model B (MB), Model C (MC) and Model D (MD) were obtained through facetectomy on L4 inferior facet in diameters 7.5 mm, 10 mm and 15 mm on MA for simulation. The ROM and IDP of L3/4 and L4/5 of four models were all compared in forward flexion, backward extension, left and right bending, left and right rotation. RESULTS: Compared with MA, the ROM of L4/5 of MB, MC and MD all increased. MD changed more significantly than MB and MC in backward extension, right bending and right rotation. But that of MB and MC on L3/4 had no prominent change, while MD had a slight increase in backward extension. The IDP of MB and MC on L4/5 in six states was similar to MA, yet MD increased obviously in backward extension, right bending, left and right rotation. The IDP on L3/4 of MB and MC was resemble to MA in six conditions, nevertheless MD increased slightly only in backward extension. CONCLUSION: Compared with the facetectomy in diameters 7.5 mm and 10 mm, the mechanical effect brought by facetectomy in diameter 15 mm on the operating segment changed more significantly, and had a corresponding effect on the adjacent segments.

Biomechanical effect of different plate-to-disc distance on surgical and adjacent segment in anterior cervical discectomy and fusion - a finite element analysis.

BACKGROUND: The plate-to-disc distance (PDD) is an important factor affecting the degeneration of adjacent segments after anterior cervical discectomy and fusion (ACDF). However, the most suitable PDD is controversial. This study examined the adjacent intervertebral disc stress, bone graft stress, titanium plate stress and screw stress to evaluate the biomechanical effect of different PDD on surgical segment and adjacent segment following C5/C6 ACDF. METHODS: We constructed 10 preoperative finite element models of intact C4-C7 segments and validated them in the present study. We simulated ACDF surgery based on the 10 intact models in software. We designed three different distance of plate-to-disc titanium plates: long PDD (10 mm), medium PDD (5 mm) and short PDD (0 mm). The changes in C4/C5 and C6/C7 intervertebral disc stress, bone graft stress, titanium plate stress and screw stress were analyzed. RESULTS: The von Mises stress of C4/C5 and C6/C7 intervertebral discs had no significant differences (P > 0.05) in three different PDD groups. Titanium plate stress increased as the PDD decreased. The bone graft stress and screws stress decreased as the PDD decreased. The maximum stress of each part occurred was mostly in the conditions of rotation and lateral bending. CONCLUSIONS: The PDD has no effect on adjacent intervertebral disc stress, but it is an important factor that affecting the bone graft stress, titanium plate stress and screws stress after ACDF. Shorter PDD plate can provide better stability to reduce stress on screws and bone graft, which may be helpful to prevent cage subsidence, pseudarthrosis and instrument failure. This can serve as a reference for clinical choice of plate.

Finite element analysis of biomechanical effects of residual varus/valgus malunion after femoral fracture on knee joint.

OBJECTIVE: Post-operative femoral shaft fractures are often accompanied by a residual varus/valgus deformity, which can result in osteoarthritis in severe cases. The purpose of this study was to investigate the biomechanical effects of residual varus/valgus deformities after middle and lower femoral fracture on the stress distribution and contact area of knee joint. METHODS: Thin-slice CT scanning of lower extremities and MRI imaging of knee joints were obtained from a healthy adult male to establish normal lower limb model (neutral position). Then, the models of 3°, 5°, and 10° of varus/valgus were established respectively by modifying middle and lower femur of normal model. To validate the modifying, a patient-specific model, whose BMI was same to former and had 10° of varus deformity of tibia, was built and simulated under the same boundary conditions. RESULT: The contact area and maximum stress of modified models were similar to those of patient-specific model. The contact area and maximum stress of medial tibial cartilage in normal neutral position were 244.36 mm2 and 0.64 MPa, while those of lateral were 196.25 mm2 and 0.76 MPa. From 10° of valgus neutral position to 10° of varus, the contact area and maximum stress of medial tibial cartilage increased, and the lateral gradually decreased. The contact area and maximum stress of medial meniscus in normal neutral position were 110.91 mm2 and 3.24 MPa, while those of lateral were 135.83 mm2 and 3.45 MPa. The maximum stress of medial tibia subchondral bone in normal neutral position was 1.47 MPa, while that of lateral was 0.65 MPa. The variation trend of medial/lateral meniscus and subchondral bone was consistent with that of tibial plateau cartilage in the contact area and maximum stress. CONCLUSION: This study suggested that varus/valgus deformity of femur had an obvious effect on the contact area and stress distribution of knee joint, providing biomechanical evidence and deepening understanding when performing orthopedic trauma surgery or surgical correction of the already existing varus/valgus deformity.

Physiological and biomechanical effects on the human musculoskeletal system while carrying a suspended-load backpack.

Many people need to carry heavy loads in a backpack to perform occupational, military, or recreational tasks. Suspended-load backpacks have been shown to reduce dynamic peak forces acting on the body and lower an individual's metabolic cost during walking. However, little is known about the physiological and biomechanical effects of a suspended-load backpack on the human musculoskeletal system. The goal of this study was to determine the impact of different types of backpacks on metabolic cost, joint kinetics, gait kinematics, and muscle activity while individuals carried the same load of 15 kg at a walking speed of 5 km/h and running speed of 7 km/h on an instrumented treadmill. A group of six healthy participants participated in experiments in which two different backpacks were worn under three different conditions: suspended-load backpack working condition (SLB_ON), suspended-load backpack locking condition (SLB_OFF), and ordinary backpack condition (ORB). The results showed that carrying the backpack in the SLB_ON condition can reduce lower limb muscle activities and biological joint work while decreasing the metabolic cost by 15.25 ± 4.21% and 8.81 ± 2.46% during walking and 12.53 ± 2.39% and 6.99 ± 2.37% during running compared to carrying the backpack in the SLB_OFF and the ORB conditions, respectively. However, the SLB_ON condition may cause increased shoulder strain and dynamic stability and balance problems. These results suggest that the control of load movement in a suspended-load backpack should be considered when locomotion performance is optimized in future studies.

Biomechanical Effect of L4 -L5 Intervertebral Disc Degeneration on the Lower Lumbar Spine: A Finite Element Study.

OBJECTIVE: To ascertain the biomechanical effects of a degenerated L4 -L5 segment on the lower lumbar spine through a comprehensive simulation of disc degeneration. METHODS: A three-dimensional nonlinear finite element model of a normal L3 -S1 lumbar spine was constructed and validated. This normal model was then modified such that three degenerated models with different degrees of degeneration (mild, moderate, or severe) at the L4 -L5 level were constructed. While experiencing a follower compressive load (500 N), hybrid moment loads were applied to all models to determine range of motion (ROM), intradiscal pressure (IDP), maximum von Mises stress in the annulus, maximum shear stress in the annulus, and facet joint force. RESULTS: As the degree of disc degeneration increased, the ROM of the L4 -L5 degenerated segment declined dramatically in all postures (flexion: 5.79°-1.91°; extension: 5.53°-2.62°; right lateral bending: 4.47°-1.46°; left lateral bending: 4.86°-1.61°; right axial rotation: 2.69°-0.74°; left axial rotation: 2.69°-0.74°), while the ROM in adjacent segments increased (1.88°-8.19°). The largest percent decrease in motion of the L4 -L5 segment due to disc degeneration was in right axial rotation (75%), left axial rotation (69%), flexion (67%), right lateral bending (67%), left lateral bending right (67%), and extension (53%). The change in the trend of the IDP was the same as that of the ROM. Specifically, the IDP decreased (flexion: 0.592-0.09 MPa; extension: 0.678-0.334 MPa; right lateral bending: 0.498-0.205 MPa; left lateral bending: 0.523-0.272 MPa; right axial rotation: 0.535-0.246 MPa; left axial rotation: 0.53-0.266 MPa) in the L4 -L5 segment, while the IDP in adjacent segments increased (0.511-0.789 MPa). The maximum von Mises stress and maximum shear stress of the annulus in whole lumbar spine segments increased (L4 -L5 segment: 0.413-2.626 MPa and 0.412-2.783 MPa, respectively; adjacent segment of L4 -L5 : 0.356-1.493 MPa and 0.359-1.718 MPa, respectively) as degeneration of the disc progressively increased. There was no apparent regularity in facet joint force in the degenerated segment as the degree of disc degeneration increased. Nevertheless, facet joint forces in adjacent healthy segments increased as the degree of disc degeneration increased (extension: 49.7-295.3 N; lateral bending: 3.5-171.2 N; axial rotation: 140.2-258.8 N). CONCLUSION: Degenerated discs caused changes in the motion and loading pattern of the degenerated segments and adjacent normal segments. The abnormal load and motion in the degenerated models risked accelerating degeneration in the adjacent normal segments. In addition, accurate simulation of degenerated facet joints is essential for predicting changes in facet joint loads following disc degeneration.

Effects of Blast Wave-induced Biomechanical Changes on Lung Injury in Rats.

OBJECTIVE: To observe the dynamic impacts of shock waves on the severity of lung injury in rats with different injury distances. METHODS: Simulate open-field shock waves; detect the biomechanical effects of explosion sources at distances of 40, 44, and 48 cm from rats; and examine the changes in the gross anatomy of the lungs, lung wet/dry weight ratio, hemoglobin concentration, blood gas analysis, and pathology. RESULTS: Biomechanical parameters such as the overpressure peak and impulse were gradually attenuated with an increase in the injury distance. The lung tissue hemorrhage, edema, oxygenation index, and pathology changed more significantly for the 40 cm group than for the 44 and 48 cm groups. The overpressure peak and impulse were significantly higher for the 40 cm group than for the 44 and 48 cm groups ( P < 0.05 or P < 0.01). The animal mortality was significantly higher for the 40 cm group than for the other two groups (41.2% vs. 17.8% and 10.0%, P < 0.05). The healing time of injured lung tissues for the 40 cm group was longer than those for the 44 and 48 cm groups. CONCLUSIONS: The effects of simulated open-field shock waves on the severity of lung injuries in rats were correlated with the injury distances, the peak overpressure, and the overpressure impulse.

Effects of Blast Wave-induced Biomechanical Changes on Lung Injury in Rats / 生物医学与环境科学（英文）

Objective@#To observe the dynamic impacts of shock waves on the severity of lung injury in rats with different injury distances.@*Methods@#Simulate open-field shock waves; detect the biomechanical effects of explosion sources at distances of 40, 44, and 48 cm from rats; and examine the changes in the gross anatomy of the lungs, lung wet/dry weight ratio, hemoglobin concentration, blood gas analysis, and pathology.@*Results@#Biomechanical parameters such as the overpressure peak and impulse were gradually attenuated with an increase in the injury distance. The lung tissue hemorrhage, edema, oxygenation index, and pathology changed more significantly for the 40 cm group than for the 44 and 48 cm groups. The overpressure peak and impulse were significantly higher for the 40 cm group than for the 44 and 48 cm groups ( < 0.05 or < 0.01). The animal mortality was significantly higher for the 40 cm group than for the other two groups (41.2% . 17.8% and 10.0%, < 0.05). The healing time of injured lung tissues for the 40 cm group was longer than those for the 44 and 48 cm groups.@*Conclusions@#The effects of simulated open-field shock waves on the severity of lung injuries in rats were correlated with the injury distances, the peak overpressure, and the overpressure impulse.

The biomechanical effect of acupuncture for poststroke cavovarus foot: study protocol for a randomized controlled pilot trial.

BACKGROUND: Poststroke cavovarus foot greatly affects patients' activities of daily life and raises the risks of falls and consequent fractures. Acupuncture appears to be safe and effective in promoting motor functions and enhancing the activities of daily life among patients with poststroke cavovarus foot. The current study aims to study the biomechanical effect of acupuncture for poststroke cavovarus foot with objective outcome measurements. METHODS/DESIGN: This is an assessor and analyst-blinded, randomized, controlled pilot study. A total of 60 eligible patients with poststroke cavovarus foot will be allocated by a 1:1 ratio into an acupuncture treatment group and a control group. Patients in the control group will receive conventional rehabilitation therapies, whereas a combination of acupuncture and conventional rehabilitation therapies will be applied in the acupuncture group. The primary outcome measures are three objective biomechanical parameters from the RSSCAN gait system: varus angle, dynamic plantar pressure distribution, and static plantar contact area. Scores of the Berg Balance Scale, the Fugl-Meyer Assessment, and the Stroke-Specific Quality of Life Scale, as well as other biomechanical parameters such as the step length and width, step time phase, and weight shifting phase will be selected as secondary outcome measurements. All assessments will be conducted at baseline, 4 weeks after the treatment course, and after a follow-up period of 3 months. DISCUSSION: Results of the current study will provide detailed interpretations of the biomechanical effect of acupuncture for stroke rehabilitation and foundations for future larger clinical studies. TRIAL REGISTRATION: Chinese Clinical Trial Registry: ChiCTR-IPC-15006889 (8 August 2015).

Immediate Clinical and Biomechanical Effects of Low-dye Taping in Patients with Plantar Heel Pain / 대한스포츠의학회지

Plantar heel pain is common musculoskeletal disorder of the foot related to sports activity. Treatment of the plantar heel pain is usually conservative including low-dye (LD) taping. We evaluated the immediate clinical and biomechanical effect of LD taping. 19 patients who had plantar heel pain with fat pad tenderness or tenderness on plantar fascia insertion area participated in this study. We assessed plantar pressure change with foot pressure analysis system, fat pad depth changes with ultrasonography, pain improvement with visual analogue scale before and after LD taping. Patient treated with LD taping showed the decrease in maximum peak pressure and pressure time integral, and there was not a significant difference between pre and post maximal velocity, average velocity, distance of center of pressure. Fat pad depth increase (mean 1.67 mm, p<0.05) and pain improvement (mean 1.91 on visual analog scale, p<0.05). LD taping restrict midtarsal joint, correct hindfoot pronation, and provide fat pad depth increase and pain improvement, immediately.

Stress distribution analysis during an intermaxillary dysjunction: A 3-D FEM study of an adult human skull.

BACKGROUND: With the increased interest in adult orthodontics, maxillary width problems in the nongrowing patients have been encountered with greater frequency. In view of the negative outlook for successful nonsurgical palatal expansion in adult patients it seemed appropriate to evaluate the biomechanical effects of nonsurgical rapid maxillary expansion (RME) in adults using the finite element method (FEM). OBJECTIVES: To evaluate the biomechanical effects of RME on the craniofacial complex as applied to three-dimensional (3D) model of an adult human skull using the finite element method. SETTINGS AND DESIGN: The Department of Orthodontics and Dentofacial Orthopedics at Government Dental College and Hospital, Nagpur. The study was done on an analytical model developed from a dry human skull of an adult female with an approximate age of 20 years. MATERIALS AND METHODS: A 3D finite element analysis of the craniofacial complex was developed from sequential computed tomography scan images. Known transversal (X) displacement with magnitudes of 1, 3, and 5 mm were applied and the displacement and Von-Mises stresses in different planes were studied on different nodes located at various structures of the craniofacial complex. RESULTS: Transverse orthopedic forces not only produced an expansive force at the intermaxillary suture but also high forces on various structures of the craniofacial complex, particularly at the base of the sphenoid bone and frontal process of the zygomatic bone. Lateral bending of the free ends of the pterygoid plates were noted. CONCLUSION: RME must be used judiciously in adults because of its far-reaching effects involving heavy stresses being noted at the sphenoid bone, zygomatic bone, nasal bone, and their adjacent sutures.