Biomechanical Characteristics of Kissing Spine During Extension Using a Human Cadaveric Lumbar Spinal Model.

Introduction: Although kissing spine syndrome in the lumbar spinal region is a relatively common condition in older adults, no study examining its biomechanical characteristics has been reported. We hypothesized that kissing of the spinous processes during extension causes an increase in the flexural rigidity of the spine and significantly limits the deformation behavior of extension, which in turn might cause lower back pain. Methods: Three test models (human cadavers A, B, and C) were prepared by removing supraspinal/interspinous ligaments between L4 and L5. The dental resin was attached to the cephalocaudal spinous process so that the spinous processes between L4 and L5 were almost in contact with each other to simulate the condition of a kissing spine. The flexion-extension direction's torque-range-of-motion (torque-ROM) curve was generated with a six-axis material tester for biomechanical measurements. Results: In all three models, the maximum ROMs at the time of extension were smaller than those at the time of flexion, and no sudden increase in torque was observed during extension. Conclusion: The results indicated no apparent biomechanical effects of kissing between the spinous processes, suggesting that the contact between the spinous processes has little involvement in the onset of lower back pain.

Effect of plate design on maintenance of anterior and posterior gaps and posterior tibial slope after cyclic loading in medial open-wedge high tibial osteotomy: A biomechanical study using porcine's tibia.

Purpose: We aimed to investigate whether a plate adapted to the anatomy of the proximal medial porcine's tibia would provide maintenance of the anterior gap (AG), posterior gap (PG) and posterior tibial slope (PTS). Methods: Twenty-seven porcine tibias were biomechanically evaluated by performing MOWHTO and placing TOMOFIX (n = 9), AC plate (n = 9) and TriS (n = 9) anteromedially. Cyclic testing (800 N, 2000 cycles, 0.5 Hz) was performed to investigate the PTS over time for MOWHTO. The particular displacement calculated from the maximum to the minimum point with the load-displacement curve along the mechanical axis during cyclic testing, the final AG and PG changes at the osteotomy site, the increased PTS calculated by subtracting AG from PG after 2000 cycles were compared among the three groups. The displacement was evaluated by repeated-measures analysis of variance (ANOVA), and changes in AG and PG and increased PTS were evaluated by one-way ANOVA. The sample size for α and ß errors were <0.05 and <0.20, and the effect size was 0.64 for one-way ANOVA and 0.49 for repeated-measures ANOVA. Results: There were no significant differences in displacement among the groups. A significant difference was observed in the AG (p = 0.044) and PG (p = 0.0085) changes. There were no significant differences in increased PTS among the groups. Conclusion: When anteromedially placed, the AC plate and TriS resulted in significant maintenance of AG and PG compared with that of TOMOFIX in MOWHTO after cyclic loading. Level of Evidence: Level Ⅳ.

Endplate weakening during cage bed preparation significantly reduces endplate load capacity.

PURPOSE: To analyze the effect of endplate weakness prior to PLIF or TLIF cage implantation and compare it to the opposite intact endplate of the same vertebral body. In addition, the influence of bone quality on endplate resistance was investigated. METHODS: Twenty-two human lumbar vertebrae were tested in a ramp-to-failure test. One endplate of each vertebral body was tested intact and the other after weakening with a rasp (over an area of 200 mm2). Either a TLIF or PLIF cage was then placed and the compression load was applied across the cage until failure of the endplate. Failure was defined as the first local maximum of the force measurement. Bone quality was assessed by determining the Hounsfield units (HU) on CT images. RESULTS: With an intact endplate and a TLIF cage, the median force to failure was 1276.3N (693.1-1980.6N). Endplate weakening reduced axial endplate resistance to failure by 15% (0-23%). With an intact endplate and a PLIF cage, the median force to failure was 1057.2N (701.2-1735.5N). Endplate weakening reduced axial endplate resistance to failure by 36.6% (7-47.9%). Bone quality correlated linearly with the force at which endplate failure occurred. Intact and weakened endplates showed a strong positive correlation: intact-TLIF: r = 0.964, slope of the regression line (slope) = 11.8, p < 0.001; intact-PLIF: r = 0.909, slope = 11.2, p = 5.5E-05; weakened-TLIF: r = 0.973, slope = 12.5, p < 0.001; weakened-PLIF: r = 0.836, slope = 6, p = 0.003. CONCLUSION: Weakening of the endplate during cage bed preparation significantly reduces the resistance of the endplate to subsidence to failure: endplate load capacity is reduced by 15% with TLIF and 37% with PLIF. Bone quality correlates with the force at which endplate failure occurs.

Biomechanical characteristics of the meniscocapsular junction of the posterior segment of the medial meniscus.

PURPOSE: Despite extensive literature available on the mechanical properties of knee ligaments and menisci, research on the mechanical properties of the meniscus-capsular junction (MCJ) is lacking. This study aims to investigate the biomechanical behavior of the MCJ of the medial meniscus using a tensile failure test. MATERIALS AND METHODS: Seven dissected cadaveric knees were used for biomechanical analysis. Tensile failure tests were performed using an INSTRON ElectroPuls E1000 stress system to measure stress/strain curves, maximum load at failure, elastic limit load, elongation at break, elongation at the elastic limit, and linear stiffness, were collected and analyzed. RESULTS: All ruptures occurred at the MCJ. The MCJ displayed similar mechanical properties to knee ligaments. Average values were: maximum load at failure (63.9 ± 3.2 N), yield load (52.9 N ± 2.6 N), elongation at break (2.5 mm ± 0.3 mm), elongation at the elastic limit (1.25 mm ± 0.15 mm), strain at break (47.0% ± 3.5%), strain at yield (23.2% ± 2.3%), and stiffness (56.6 ± 9. N/mm-1). CONCLUSION: The meniscus-capsular junction's mechanical properties are similar to other knee ligaments and may play a role in knee stability. The findings provide insights into the the behavior of the meniscus-capsular junction could have clinical implications for diagnosing and surgical treatment of meniscocapsular lesions.

The effect of Ding's screws and tension band wiring for treatment of olecranon fractures: a biomechanical study.

Although tension band wiring (TBW) is popular and recommended by the AO group, the high rate of complications such as skin irritation and migration of the K-wires cannot be ignored. Ding's screw tension band wiring (DSTBW) is a new TBW technique that has shown positive results in the treatment of other fracture types. The objective of this study was to evaluate the stability of DSTBW in the treatment of olecranon fractures by biomechanical testing. We conducted a Synbone biomechanical model by using three fixation methods: DSTBW, intramedullary screw and tension band wiring (IM-TBW), and K-wire TBW, were simulated to fix the olecranon fractures. We compared the mechanical stability of DSTBW, IM-TBW, and TBW in the Mayo Type IIA olecranon fracture Synbone model using a single cycle loading to failure protocol or pullout force. During biomechanical testing, the average fracture gap measurements were recorded at varying flexion angles in three different groups: TBW, IM-TBW, and DSTBW. The TBW group exhibited measurements of 0.982 mm, 0.380 mm, 0.613 mm, and 1.285 mm at flexion angles of 0°, 30°, 60°, and 90° respectively. The IM-TBW group displayed average fracture gap measurements of 0.953 mm, 0.366 mm, 0.588 mm, and 1.240 mm at each of the corresponding flexion angles. The DSTBW group showed average fracture gap measurements of 0.933 mm, 0.358 mm, 0.543 mm, and 1.106 mm at the same flexion angles. No specimen failed in each group during the cyclic loading phase. Compared with the IM-TBW and TBW groups, the DSTBW group showed significant differences in 60° and 90° flexion angles. The mean maximum failure load was 1229.1 ± 110.0 N in the DSTBW group, 990.3 ± 40.7 N in the IM-TBW group, and 833.1 ± 68.7 N in the TBW group. There was significant difference between each groups (p < 0.001).The average maximum pullout strength for TBW was measured at 57.6 ± 5.1 N, 480.3 ± 39.5 N for IM-TBW, and 1324.0 ± 43.8 N for DSTBW. The difference between maximum pullout strength of both methods was significant to p < 0.0001. DSTBW fixation provides more stability than IM-TBW and TBW fixation models for olecranon fractures.

Finite Element Analysis of Six Internal Fixations in the Treatment of Pauwels Type III Femoral Neck Fracture.

OBJECTIVE: The current investigation sought to utilize finite element analysis to replicate the biomechanical effects of different fixation methods, with the objective of establishing a theoretical framework for the optimal choice of modalities in managing Pauwels type III femoral neck fractures. METHODS: The Pauwels type III fracture configuration, characterized by angles of 70°, was simulated in conjunction with six distinct internal fixation methods, including cannulated compression screw (CCS), dynamic hip screw (DHS), DHS with de-rotational screw (DS), CCS with medial buttress plate (MBP), proximal femoral nail anti-rotation (PFNA), and femoral neck system (FNS). These models were developed and refined using Geomagic and SolidWorks software. Subsequently, finite element analysis was conducted utilizing Ansys software, incorporating axial loading, torsional loading, yield loading and cyclic loading. RESULTS: Under axial loading conditions, the peak stress values for internal fixation and the femur were found to be highest for CCS (454.4; 215.4 MPa) and CCS + MBP (797.2; 284.2 MPa), respectively. The corresponding maximum and minimum displacements for internal fixation were recorded as 6.65 mm for CCS and 6.44 mm for CCS + MBP. When subjected to torsional loading, the peak stress values for internal fixation were highest for CCS + MBP (153.6 MPa) and DHS + DS (72.8 MPa), while for the femur, the maximum and minimum peak stress values were observed for CCS + MBP (119.3 MPa) and FNS (17.6 MPa), respectively. Furthermore, the maximum and minimum displacements for internal fixation were measured as 0.249 mm for CCS + MBP and 0.205 mm for PFNA. Additionally, all six internal fixation models showed excellent performance in terms of yield load and fatigue life. CONCLUSION: CCS + MBP had the best initial mechanical stability in treatment for Pauwels type III fracture. However, the MBP was found to be more susceptible to shear stress, potentially increasing the risk of plate breakage. Furthermore, the DHS + DS exhibited superior biomechanical stability compared to CCS, DHS, and PFNA, thereby offering a more conducive environment for fracture healing. Additionally, it appeared that FNS represented a promising treatment strategy, warranting further validation in future studies.

Biomechanical Comparison of Short-, Mid-, and Long-Length Proximal Femoral Nails for Femoral Intertrochanteric Fracture (AO/OTA 31A3.3) Fixation.

Introduction: In surgeries for unstable AO/OTA 31A3.3 fractures, surgeons use various lengths of intramedullary nails (IMNs). However, there is insufficient evidence regarding the appropriate nail length for these fractures. This study compared the biomechanical properties of IMNs of different lengths for AO/OTA 31A3.3 fractures. Methods: 30 synthetic femora of AO/OTA 31A3.3 fracture model were randomly assigned to the following three groups: short- (170 mm), mid- (235 mm), and long-length (300 mm) nail groups, and were performed fixation surgery. The translation patterns of the constructs were examined by cyclic testing and compared among three groups. Additionally, changes in the neck-shaft and shaft-nail angles after cyclic testing were evaluated using radiological images. Results: The translation patterns during cyclic loading did not differ among the groups. Conversely, one-way analysis of variance (ANOVA) revealed a significant difference in the neck-shaft angle change (5.8° ± 1.8°, 2.8° ± 1.3°, and 1.9° ± .9° in the short-, mid-, and long-length groups, respectively; P < .001), and post-hoc analysis revealed that the change was greater in the short-length group than in the mid- and long-length groups (P < .001 and P < .001, respectively). Furthermore, one-way ANOVA revealed a significant difference in the shaft-nail angle change (3.1° ± 2.1°, 1.4° ± 1.4°, and .1° ± .6° in the short-, mid-, and long-length groups, respectively; P < .001), and post-hoc analysis revealed that the change was greater in the short-length group than in the mid- and long-length groups (P = .044 and P < .001, respectively). Conclusions: Short-length nails were associated with relevant changes in the neck-shaft and shaft-nail angles in our AO/OTA 31A3.3 fracture model. Thus, the selection of mid- or long-length nails instead of short-length nails might be better in IMN surgery for these fractures to prevent postoperative varus deformity.

Higher contact pressure of the lateral tibiofemoral joint in lateral extra-articular tenodesis with tensioned graft in external rotation than in neutral rotation: A biomechanical study.

OBJECTIVE: To determine the mean contact pressure, peak contact pressure, and mean contact area of the lateral tibiofemoral joint in lateral extra-articular tenodesis (LET) with tension on the graft in tibial neutral and external rotation. METHODS: A total of eight Thiel-embalmed cadaveric knees were prepared and divided into two groups (4 knees in each group): the LET-NR group (lateral extra-articular tenodesis tension in neutral rotation) and (2) the LET-ER group (lateral extra-articular tenodesis tension in external rotation). Each knee was prepared according to the corresponding technique. A hydraulic testing system (E10000, Instron) simulates an axial load of 735 â€‹N for 10 â€‹s in each group. RESULTS: The LET-ER group exhibited a statistically significant higher peak contact pressure compared to the LET-NR group. The peak contact pressure values in the LET-NR and LET-ER groups were 702.3 â€‹± â€‹233.9 â€‹kPa and 1235.5 â€‹± â€‹171.4 â€‹kPa, respectively (p â€‹= â€‹0.010, 95% CI, -888.0 to -178.5). The mean contact pressure values in the LET-NR and LET-ER groups were 344.9 â€‹± â€‹69.0 â€‹kPa and 355.3 â€‹± â€‹34.9 â€‹kPa, respectively (p â€‹= â€‹0.796, 95% CI, -105.1-84.2). The mean contact area values in the LET-NR and LET-ER groups were 36.8 â€‹± â€‹3.1 mm2 and 33.3 â€‹± â€‹6.4 mm2, respectively (p â€‹= â€‹0.360, 95% CI, -5.2-12.2). CONCLUSIONS: The peak contact pressure of the lateral tibiofemoral joint is greater in LET when the graft is tensioned in external rotation than in neutral rotation. However, no statistically significant difference in the mean contact pressure or the mean contact area was observed between the two groups. LEVEL OF EVIDENCE: III.

Biomechanical comparisons of plate placement for medial tibial plateau fractures (Schatzker type IV): A biomechanical study using porcine tibias.

INTRODUCTION: Biomechanical studies on medial tibial plateau fractures (MTPFs) (Schatzker classification type IV) are currently few, while studies using locking plates (LPs) placed on medial proximal tibias are unavailable. Hence, we compared the biomechanical properties of plate osteosynthesis at the medial and anteromedial placements using large- and small-fragment LPs in porcine bones. MATERIALS AND METHODS: MTPFs were internally fixed using LPs on 40 porcine tibias. Specimens were equally divided into four groups: medial placement using a large-fragment LP (LPs for the medial (LM) group), anteromedial placement using a large-fragment LP (LAM group), medial placement using a small-fragment LP (SM group), and anteromedial placement using a small-fragment LP (SAM group). The translation patterns of the constructs in each group were examined by cycling loading test (displacement and translation along the mechanical axis at 10-100, 100-500, 500-1000, 1000-1500, and 1500-2000 cycles). Then, articular gaps and step-off changes after 2000 cycles were compared among the four groups. RESULTS: One-way analysis of variance (ANOVA) revealed no significant differences in displacement and translation during cyclic loading. One-way ANOVA followed by post hoc analysis revealed that the anterior gap was lower in LPs for the medial (LM) than in SM (P = 0.029) and SAM (P = 0.0026). The central gap was also lower in LM than in SM (P = 0.042) and SAM (P < 0.001), and it was lower in LAM than in SAM (P = 0.047). Likewise, the posterior gap was lower in LM than in LAM (P = 0.025) and SAM (P < 0.001). Furthermore, the central step-off of SAM was higher than that of LM, LAM, and SM (P < 0.001, P = 0.0014, and P = 0.0077, respectively). The posterior step-off was lower in LM than in SAM and LAM (P = 0.037 and P < 0.001), and it was also lower in SM than in SAM (P = 0.0082). CONCLUSION: Medial LP placement for MTPFs in porcine bones resulted in significantly lower posterior step-offs after cyclic loading than anteromedial placement, and large-fragment LPs for MTPFs caused significantly lower fracture gaps in the central articular after cyclic loading than small-fragment LPs.

Evaluation of the Stability of Internal Fixation Constructs in a Low Distal Tibia Extra-articular Cadaveric Fracture Model: A Comparative Biomechanical Study.

Introduction Despite the recent advances in implant design, the choice of an internal fixation modality for extra-articular distal tibia fractures remains controversial, and there is sparse literature comparing the stability of intramedullary nails and locked plates for such fractures. Hence, we conducted a biomechanical study on an AO type 43A3 tibia fracture cadaveric model stabilized by four different constructs, viz., intramedullary (IM) interlocking nail, anteromedial plate, anterolateral plate, and posterior plate. An AO type 43A3 fracture is defined as an extra-articular fracture of the distal tibia with metaphyseal comminution. Methods A biomechanical comparative study on formalin-preserved human cadaveric tibiae was undertaken; a total of four groups were tested, with eight bones in each group. Out of the 32 cadaveric tibiae, 19 bones belonged to male cadavers, and 13 bones belonged to female cadavers. All bones were dissected from age-appropriate cadavers and fixed with an implant, followed by the creation of a 1 cm osteotomy to simulate an AO type 43A3 fracture. All fixation constructs were subjected to three-point bending tests in the anteroposterior (AP) and mediolateral (ML) planes. Three parameters, viz., bending stiffness, peak fracture gap angle, and neutral zone, were evaluated on the load-displacement curves. A fixation construct was deemed biomechanically stable if it had a high bending stiffness, a low neutral zone (inherent toggle in the construct by its weight), and a low peak fracture gap angle. Results Out of the four implants tested, locked IM nails exhibited the maximum biomechanical stability in terms of higher bending stiffness, smaller peak fracture gap angle, and smaller neutral zones. The IM nail exhibited the highest bending stiffness in the AP plane, and the anterolateral plate had the lowest bending stiffness, and the difference was statistically significant (p= 0.032). In the AP plane, the anterolateral plate exhibited a bending stiffness of 1.51 ± 0.69 Nm/degree, whereas the intramedullary nail exhibited a bending stiffness of 2.34 ± 0.81 Nm/degree, and the posterior locked plate had a bending stiffness of 1.57 ± 0.44 Nm/degree. In the ML plane, the anterolateral plate exhibited the highest neutral zone as compared to the intramedullary nail, which had the lowest neutral zone, and the difference was statistically significant (p = 0.019). The intramedullary nail exhibited the lowest neutral zone of 0.46 ± 0.31 degrees, whereas the posterior locked plate exhibited a neutral zone of 0.78 ± 0.43 degrees in the ML plane. The anterolateral plate exhibited a neutral zone of 1.43 ± 1.00 (expressed as mean ± SD) degrees in the mediolateral plane. Conclusion Our biomechanical study supports the recommendations of using a locked intramedullary nail for AO type 43A3 fractures. We concluded that the anterolateral plate construct exhibited the least biomechanical stability, in terms of lower AP bending stiffness and higher neutral zone. If the surgeon must choose a locked plating technique for any reason, the anterolateral locking plate should be avoided. If plating is at all required, we can recommend both anteromedial and posterior locked plating as biomechanically sound options.

Efficacy of poller screw in addition to lag screw in the treatment of intertrochanteric fractures with proximal femoral nail: a biomechanical evaluation.

PURPOSE: The most common type of failure in treating intertrochanteric fractures with proximal femoral nails is cut-out due to varus collapse. We aim to evaluate the effect of the poller screw applied to the proximal fragment and the lag screw on varus collapse and stability in intertrochanteric fractures. METHODS: An unstable intertrochanteric fracture model without medial support was simulated in 20 synthetic femur models. In the poller screw group, in addition to the lag screw, pole screws were applied to the proximal fragment superior and inferior to the lag screw. In the progressive cyclic loading test, starting from 100 N, the loading was increased by 50 N in each cycle, and the test was continued until the maximum load at which failure occurred as a result of conditioning cycles and progressive cyclic loading tests, stiffness, type of failure, force at failure, lag screw displacement, and varus collapse were recorded. RESULT: The average stiffness was found to be 124.705 N/mm in the poller screw group and 102.77 N/mm in the control group (P < 0.001). The maximum load to failure was 1897.10 N in the poller screw group and 1475.20 N in the control group (P < 0.001). The average displacement of the lag screw within the femoral head was 0.85 mm in the poller screw group and 3.60 mm in the control group (P < 0.001). CONCLUSION: As a result, it has been shown that poller screws applied around the lag screw increase fixation stiffness and reduce varus collapse.

Comparative biomechanical analysis of reconstruction and cephalomedullary nails in the treatment of osteoporotic subtrochanteric fractures.

INTRODUCTION: This study aimed to compare the biomechanical properties of two types of intramedullary nails - reconstruction nails (RCN) and cephalomedullary nails (CMN) - each with different proximal fixations, in a model of an osteoporotic subtrochanteric femoral fracture. This study focused on assessing stiffness and load to failure of RCN and CMN nails to provide insight into their clinical applications in osteoporotic fracture treatments. MATERIALS AND METHODS: Ten synthetic osteoporotic femoral models were used to generate a comminuted subtrochanteric fracture model. Five femurs were fixed using an RCN, and the remaining five were fixed using a CMN. The constructs were subjected to axial compression to measure their structural stiffness, load to failure, and failure modes. RESULTS: The CMN group demonstrated a slightly higher load to failure (mean, 2250 N) than the RCN group (mean, 2100 N), which was statistically significant (p = 0.008). However, the stiffness in both groups was statistically similar (RCN, 250 N/mm; CMN, 255 N/mm; p = 0.69). Both groups showed a load to failure exceeding 1500 N, a typically exerted load on the femoral head by a 75 kg individual. The failure patterns differed, with CMN failures starting at the nail insertion area and RCN failures starting at the reconstruction screw area. CONCLUSION: The RCN offers stiffness comparable to that of the CMN; although its load to failure is slightly lower than that of the CMN, it still exceeds the physiological tolerance limit. These findings suggest that the RCN is a viable alternative for treating osteoporotic subtrochanteric fractures.

[Research progress on distal interlocking screws of cephalomedullary nails in intertrochanteric fractures].

Objective: To summarize the new research progress in distal interlocking screws of cephalomedullary nails for the treatment of intertrochanteric fractures. Methods: Relevant domestic and foreign literature was extensively reviewed to summarize the static/dynamic types of distal interlocking screw holes, biomechanical studies, clinical studies and application principles, effects on toggling in the cavity, and related complications of distal interlocking screws. Results: The mode of the distal interlocking screw holes can be divided into static and dynamic. Distal interlocking screws play the role of anti-rotation, maintaining femur length, resisting compression stress, increasing torque stiffness, resisting varus stress, etc. The number of the screws directly affects the toggling of the main nail in the cavity. At present, regardless of whether long or short nails are used, distal interlocking screws are routinely inserted in clinical practice. However, using distal interlocking screws can significantly increase the duration of anesthesia and operation, increase fluoroscopy exposure time, surgical blood loss, and incision length. There is a trend of trying not to use distal interlocking screws in recent years. No significant difference is found in some studies between the effectiveness of dynamic and static interlocking for AO/Orthopaedic Trauma Association (AO/OTA) 31-A1/2 fractures. At present, the selection of the number and mode of distal interlocking screws is still controversial. When inserting distal interlocking screws, orthopedists should endeavor to minimize the occurrence of complications concerning miss shot, vascular injuries, local stress stimulation, and peri-implant fractures. Conclusion: Distal interlocking screws are mainly used to prevent rotation. For stable fractures with intact lateral walls, long cephalomedullary nails can be used without distal interlocking screws. For any type of intertrochanteric fractures, distal interlocking screws are required when using short cephalomedullary nails for fixation. Different interlocking modes, the number of interlocking screws, and the application prospects of absorbable interlocking screws may be future research directions.

Biomechanical evaluation of the ST-knot: A new suture for flexor tendon repair.

PURPOSE: Although tendon lacerations are common, there is currently no consensus on choice of suture. Easy and fast sutures that impart enough strength to allow mobilization are needed. This study compared the ex vivo biomechanical strength (force required to create a 2 mm tendon gap) of a novel suture (ST-knot) with that of a conventional suture (double Kessler). MATERIALS AND METHODS: Forty fresh deep flexor tendons from porcine forelimbs were used. Both repaired tendon ends were mounted on standard traction jaws of an axial traction machine at an initial distance of 40 mm for all tendons. A high-definition camera was used to determine the force forming a 2 mm gap. Ten tendons in group 1 (ST-knot) and 10 in group 2 (double Kessler) were prepared with PDS 4.0 (single thread for Kessler, double thread for ST-knot). Tendons in groups 3 (ST-knot) and 4 (double Kessler) were repaired with PDS 1.0 using the same principle. RESULTS: There was no significant difference in the force required to form a 2 mm tendon gap between groups 1 and 2, and this trend was identical when using a stronger thread in groups 3 and 4. The maximum force before rupture, mode of repair failure, stress and stiffness were also comparable, with no significant differences between groups 1 and 2, or between groups 3 and 4. CONCLUSIONS: The ST-knot showed comparable results to the double-Kessler knot, whichever the thread used. Because it involves fewer steps than conventional techniques and is easy to perform, the ST-knot may offer a therapeutic solution, particularly in complex trauma with multiple tendon injury.

The Impact of Complex Loadings on the Structure of the L2-L3 Intervertebral Disc in a Sheep Spine Cadaver Model: A Biomechanical and Histological Evaluation.

Background The human vertebral column generates movements under versatile, dynamic loads. Understanding how the spine reacts to these movements and loads is crucial for developing new spine implants and surgical treatments for intervertebral disc injuries. Mechanically uni-axial compression models have been extensively studied. However, the spine's daily loading is not limited to compression, so it is crucial to measure its behavior in all movements (flexion-extension, rotation, and axial compression). Methods This study utilized L1-L5 segments from 19 healthy adult sheep spines. The L2-L3 disc of the first spine underwent only histological evaluation without biomechanical testing to define basic histological parameters. The remaining 18 were divided into three groups of six and subjected to biomechanical tests. Different mechanisms for three groups of spinal segments were prepared, and tests were performed on Shimadzu AG-IS 10 KN (Universal Drawing Press, Kyoto, Japan). An axial load (800 N) was applied to the first group, an axial load with 15 degrees of flexion to the second group, and an axial load with 10 degrees of rotation plus 15 degrees of flexion to the third group. A biomechanical evaluation of the maximum elongation amounts (MEAs) was performed and compared between the groups. Then, the L2-L3 discs were removed from the sheep spines, and a histological examination of the discs was conducted using Hematoxylin-Eosin (HE), Alcian Blue (AB), and Masson's Trichrome (MT) staining. Results The mean MEA ± Standard Deviation (Range) was 1.39 ± 0.38 (0.91-1.94) for Group 1, 2.02 ± 0.75 (0.91-3.01) for Group 2, and 2.47 ± 1.09 (0.64-3.9) for Group 3. Biomechanically, although MEAs increased from Group 1 to Group 3 (meaning that the mean MEAs increased as the number of types of applied force increased), there was no statistically significant difference between the groups regarding the MEAs (P = 0.092). Histologically, no significant differences were observed between all groups after HE staining. In all groups, hypercellularity, edema in the connective tissue, separation between tissue layers, delamination, and signs of swelling and necrosis in the cells were observed similarly. For the AB staining, there was a decrease in the glycosaminoglycan (GAG) structure in the tissue samples compared to the control tissue, but no significant differences were observed between the groups. However, it was observed that the stratification in Group 3 was slightly more deteriorated than in the other groups. For the MT staining, collagen structure deterioration was observed in all groups. It was observed that the amount of collagen was significantly reduced compared to the control tissue. Conclusion As a result, when the axial load is applied biomechanically, there is more displacement of the vertebral discs in Group 3 with multidimensional movements. Furthermore, histological studies revealed deterioration between tissue layers when exposed to complex movements, and the degradation of stratification in group 3 compared to other loading combinations in groups 2 and 3 may indicate the role of complex loads in the formation of disc herniation.

Biomechanical Effects of Thoracic Flexibility and Stiffness on Lumbar Spine Loading: A Finite Element Analysis Study.

OBJECTIVE: To determine the effects of thoracic stiffness on mechanical stress in the lumbar spine during motion. METHODS: To evaluate the effect of preoperative thoracic flexibility, stiff and flexible spine models were created by changing the material properties of ligaments and discs in the thoracic spine. Total laminectomy was performed at L4/5 in stiff and flexible models. A biomechanical investigation and finite element analysis were performed preoperatively and postoperatively. A hybrid loading condition was applied, and the range of motion (ROM) at each segment and maximum stress in the discs and pars interarticularis were computed. RESULTS: In the preoperative model with the stiff thoracic spine, lumbar disc stress, lumbar ROM, and pars interarticularis stress at L5 increased. In contrast, as the thoracic spine became more flexible, lumbar disc stress, lumbar ROM, and pars interarticularis stress at L5 decreased. All L4/5 laminectomy models had increased instability and ROM at L4/5. To evaluate the effect of thoracic flexibility on the lumbar spine, differences between the stiff and flexible thoracic spine were examined: Differences in ROM and intervertebral disc stress at L4/5 in flexion between the stiff and flexible thoracic spine were respectively 0.7° and 0.0179 MPa preoperatively and 1.5° and 0.0367 MPa in the L4/5 laminectomy model. CONCLUSIONS: Biomechanically, disc stress and pars interarticularis stress decrease in the flexible thoracic spine. Flexibility of the thoracic spine reduces lumbar spine loading and could help to prevent stress-related disorders.

Is just one screw really enough? Single- versus double-screw in the medial malleolus in supination-external rotation ankle fractures: A comparative biomechanical study using partially threaded cancellous screws.

OBJECTIVE: The aim of this study is to investigate stiffness and the maximum load to failure values of single- and double-screw fixation of oblique medial malleolus fractures using partially threaded cancellous screws. Our hypothesis is that single-screw fixation of medial malleolus fractures after SER injuries provides similar stiffness when compared with double-screw fixation. DESIGN: Biomechanical study. METHODS: Twelve composite polyurethane synthetic right distal tibiae were used in the experiment. Oblique fractures of the medial malleolus were created with a band saw using a custom-made osteotomy guide to standardize the cuts in all models. Bone models were randomly separated into two groups and fixed with one (n = 6) or two (n = 6) 4.0 mm partially threaded cancellous screws placed perpendicular to the fracture line. These were tested by applying an offset axial tension at 10 mm/minute up to maximum load displacement, defined as subsidence of the medial malleolus fragment. Maximum load to failure was determined for the groups at the point where the curve ceased to be linear and suffered an inflection. Force versus displacement curves were obtained and recorded. The student's t-test for independent samples was used to compare stiffness (N / mm) and maximum load (N) between experimental groups, with a p value of < 0.05. RESULTS: There were no significant differences in stiffness (p = 0.290) and maximum load (p = 0.191) among the two fixation constructs. Mean stiffness was 62.26 (±SD 21.11) N/mm for double-screw fixation group and 48.24 (±SD 22.40) N/mm for single-screw fixation group. Mean maximum load was 387.83 (±SD 115.78) N for double-screw fixation group and 306.64 (±SD 81.97) N for single-screw fixation group. CONCLUSION: Fixation with one 4.0 mm partially threaded cancellous screw was not shown to be biomechanically inferior to fixation with two 4.0 mm partially threaded cancellous screws in an oblique fracture of the medial malleolus, supporting previous clinical studies that have shown that one screw is sufficient for fractures of the medial malleolus.

Influence of Placement of Lumbar Interbody Cage on Subsidence Risk: Biomechanical Study.

OBJECTIVE: Lumbar spinal fusion is a common surgical procedure that can be done with a variety of different instrumentation and techniques. Despite numerous research studies investigating subsidence risk factors, the impact of cage placement on subsidence is not fully elucidated. This study aims to determine whether placement of an expandable transforaminal lumbar interbody fusion cage at the center end plate or at the anterior apophyseal ring affects cage subsidence. METHODS: A transforaminal lumbar interbody fusion cage was placed centrally or peripherally between 2 synthetic vertebral models of L3 and L4. A compression plate attached to a 10 KN load cell was used to uniaxially compress the assembly. The ultimate force required for the assembly to fail and subsidence stiffness were analyzed. Computed tomography scans of each L3 and L4 were obtained, and maximum end plate subsidence was measured in the frontal plane. RESULTS: Anterior apophyseal cage placement resulted in higher stiffness of the vertebrae-cage assembly (Ks, 962.89 N/mm) and a higher subsidence stiffness (Kb,987.21 N/mm) compared with central placement (P < 0.05). Ultimate compressive load of the vertebrae-cage assembly did not increase. Moreover, the maximum subsidence depth did not significantly vary between placements. CONCLUSIONS: The subsidence stiffness increased with anterior apophyseal cage placement. Periphery end plate cortical bone architecture may play a role in resisting the impact of cage subsidence. To fully understand the effect of cage placement on cage subsidence, future studies should investigate its implications on native and diseased spine.

In silico analysis of rib force distribution in postscapulothoracic arthrodesis model.

Scapulothoracic arthrodesis (STA) is carried out by fixing the scapula to thoracic ribs which in turn allows the patient suffering from Facioscapulohumeral Muscular Dystrophy to carry out shoulder-joint dependent activities of daily living. A biomechanical analysis of this procedure has not been conducted in the literature and, for the first time, this study investigates the finite element calculated glenohumeral-applied load distributions on ribs by creating a post-STA model. Three loading directions on the glenohumeral joint are designated: anterior-posterior, superior-inferior, and lateral-medial. Reaction forces on the ribs are calculated based on the glenoid force percent. Simulations are repeated by removing a singular rib contact to observe the change in force distributions in the case of missing levels or failed bonding as well as the impact of clavicle osteotomy. Total load distribution is observed highest at T2 followed by T3 and T6. In the T2 missing scenario, total loads on T3 and T4 increase. In the T4 missing case, the most affected level is T3. In the T6 missing scenario, total loads on T5 and T7 increase. In the clavicular osteotomy scenario, all levels' loads increase; the highest is recorded in T7 by 460%, followed by T5, T4, T2, T6, and T3. While all levels contribute to fixation strength, T2 is subjected to the highest loads, and, in the missing level scenarios, the loads are tolerated sufficiently by the remaining levels. Missing T4 scenario has the least effect on the system, which is interpreted as potentially the only skippable level of fixation. Clavicular osteotomy has the highest effect on the arthrodesis site.

Biomechanical Efficacy of Three Methods for the Fixation of Posterior Malleolar Fractures: A Three-Dimensional Finite Element Study.

Introduction: We investigated the biomechanical behaviour of different fixations of the tibial posterior malleolus (TPM), simulating distinct situations of involvement of the tibiotalar articular surface (TTAS) through a finite element model (FEM). Material and methods: A 3D computer-aided design model of the left ankle was obtained. The materials used were divided according to their characteristics into ductile and non-ductile, and all materials were assumed to be linear elastic, isotropic, and homogenous. Three different fracture lines of the TPM were defined, with sagittal angles of 10°, 25°, and 45°. For biomechanical comparison, different constructions using a trans-syndesmotic screw (TSS) only (Group T), a one-third tubular plate only with (Group PT) and without (Group PS) a TSS, and a locked compression plate with (Group LCPT) and without (Group LCPS) a TSS were tested. FEM was used to simulate the boundary conditions of vertical loading. Load application regions were selected in the direction of the 700 N Z-axis, 90% on the tibia and 10% on the fibula. Data on the displacement and stress in the FEM were collected, including the total principal maximum (MaxT) and total principal minimum (MinT) for non-ductile materials, total displacement (desT), localized displacement at the fragment (desL), localized displacement at syndesmosis (desS), and Von Mises equivalent stress for ductile materials. The data were analysed using ANOVA and multiple comparison LSD tests were used. Results: For TPM fractures with sagittal angles 10° and 25°, desL in the PT and LCP groups was significantly lower, as well as Von Mises stress in Group LCPT in 10°, and PT and LCPT groups in 25°. For TPM fractures with a sagittal angle of 45°, desL in the LCP group and Von Mises stress in Group LCPS and LCPT were significantly lower. We found that any TPM fracture may indicate instability of the distal tibiofibular syndesmosis, even when the fragment is small. Conclusion: Our study showed that in fragments involving 10% of the TTAS, the use of a TSS is sufficient, but when the involvement is greater than 25% of the TTAS, either a non-locked or locked plate must be used to buttress the TPM. In posterior fragments affecting 45% or more of the TTAS, the use of a locking plate is recommended.