Surgical treatment of fragility sacrum fractures with percutaneous sacroiliac (SI) screw fixation is associated with high failure rates in terms of screw loosening, cut-through and turn-out. The latter is a common cause for complications, being detected in up to 20% of the patients. The aim of this study was to develop a new screw-in-screw concept and prototype implant for fragility sacrum fracture fixation and test it biomechanically versus transsacral and SI screw fixations. Twenty-seven artificial pelves with discontinued symphysis and a vertical osteotomy in zone 1 after Denis were assigned to three groups (n = 9) for implantation of their right sites with either an SI screw, the new screw-in-screw implant, or a transsacral screw. All specimens were biomechanically tested to failure in upright position with the right ilium constrained. Validated setup and test protocol were used for complex axial and torsional loading, applied through the S1 vertebral body. Interfragmentary movements were captured via optical motion tracking. Screw motions in the bone were evaluated by means of triggered anteroposterior X-rays. Interfragmentary movements and implant motions in terms of pull-out, cut-through, tilt, and turn-out were significantly higher for SI screw fixation compared to both transsacral screw and screw-in-screw fixations. In addition, transsacral screw and screw-in-screw fixations revealed similar construct stability. Moreover, screw-in-screw fixation successfully prevented turn-out of the implant, that remained at 0° rotation around the nominal screw axis unexceptionally during testing. From biomechanical perspective, fragility sacrum fracture fixation with the new screw-in-screw implant prototype provides higher stability than with the use of one SI screw, being able to successfully prevent turn-out. Moreover, it combines the higher stability of transsacral screw fixation with the less risky operational procedure of SI screw fixation and can be considered as their alternative treatment option

It is common belief that consolidated intramedullary nailed trochanteric femur fractures can result in secondary midshaft or supracondylar fractures, involving the distal screws, when short or long nails are used, respectively. In addition, limited data exists in the literature to indicate when short or long nails should be selected for treatment. The aim of this biomechanical cadaveric study was to investigate short versus long Trochanteric Femoral Nail Advanced (TFNA) fixation in terms of construct stability and generation of secondary fracture pattern following trochanteric fracture consolidation.

Eight intact human cadaveric femur pairs were assigned to 2 groups of 8 specimens each for nailing using either short or long TFNA with blade as head element. Each specimen was first biomechanically preloaded at 1 Hz over 2000 cycles in superimposed synchronous axial compression to 1800 N and internal rotation to 11.5 Nm. Following, internal rotation to failure was applied over an arc of 90° within 1 second under 700 N axial load. Torsional stiffness, torque at failure, angle at failure and energy at failure were evaluated. Fracture patterns were analyzed.

Outcomes in the groups with short and long nails were 9.7±2.4 Nm/° and 10.2±2.9 Nm/° for torsional stiffness, 119.8±37.2 Nm and 128.5±46.7 Nm for torque at failure, 13.5±3.5° and 13.4±2.6° for angle at failure, and 887.5±416.9 Nm° and 928.3±461.0 Nm° for energy at failure, respectively, with no significant differences between them, P≥0.167. Fractures through the distal locking screw occurred in 5 and 6 femora instrumented with short and long nails, respectively. Fractures through the lateral entry site of the head element were detected in 3 specimens within each group. For short nails, fractures through the distal shaft region, not interfacing with the implant, were detected in 3 specimens.

From biomechanical perspective, the risk of secondary peri-implant fracture after intramedullary nailed trochanteric fracture consolidation is similar when using short or long TFNA. Moreover, for both nail versions the fracture pattern does not unexceptionally involve the distal locking screw.

Purpose: The purpose of this study is to evaluate the biomechanical properties and the stability between locking clavicle plate, dynamic compression plate and external fixation systems on an unstable displaced fracture model under torsional and 3 point bending loading.

Materials and Methods: Forty eight human adult formalin fixed clavicles were paired according to their BMD (DEXA) homogeneously into three groups; Group 1: Locking clavicle plate, Group 2: Dynamic compression plate and Group 3: External fixator. Each specimen was then osteotomized in the midshaft; and a 5mm bone segment was removed in order to stimulate a displaced fracture model. Biomechanical tests were applied in a cyclic loading model in MTS, Bionix 2. Torsional and three point bending forces were performed for 1000 cycles in all subgroups, stiffness was recorded at 10 cycles (initial) and periodic every 100 cyclic intervals. Failure load and moment were obtained after 1000 cycles. Initial stiffness, failure loads and the percentage of initial stiffness for each subgroup were compared across each group. One-way ANOVA and Bonferoni post- hoc tests were utilized to determine which were significantly different from one another with the significance level set as p< 0.05.

Results: The mean initial stiffness(Nmm/deg) - mean failure moments(Nmm) for torsional tests were 703.2 – 7671.7 (locking plate), 448.1 – 4370.3 (compression plate), 365.2 – 2999.7 (ex-fix) and the mean initial stiffness(Nmm) – mean failure loads(N) for bending tests were 32.6 – 213.2 (locking plate), 23.4 – 131.1 (compression plate), 20.6 – 102.7 (ex-fix) respectively. ANOVA test confirmed an overall significant difference between the three constructs in terms of both failure loads and a significant difference only between locking plate and others in terms of initial stiffness. At all cyclic intervals after 100 cycles there was significant difference of percentage of initial stiffness between locking plate and others in bending and torsion. There was a significant difference between compression plate and ex-fix after 700 cycles in torsional group and no difference found in bending group between (any of) them at any cyclic interval.

Conclusions: Locking anatomic clavicle plate is significantly more stable than unlocked dynamic compression plate and external fixator under torsional and bending cyclic loading in an unstable displaced fracture or non-union clavicle model.

In severe cases of total knee & hip arthroplasty, where off-the-shelf implants are not suitable (i.e., in cases with extended bone defects or periprosthetic fractures), 3D-printed custom-made knee & hip revision implants out of titanium or cobalt-chromium alloy represent one of the few remaining clinical treatment options. Design verification and validation of such custom-made implants is very challenging. Therefore, a methodology was developed to support surgeons and engineers in their decision on whether a developed design is suitable for the specific case. A novel method for the pre-clinical testing of 3D-printed custom-made knee implants has been established, which relies on the biomechanical test and finite element analysis (FEA) of a comparable clinically established reference implant. The method comprises different steps, such as identification of the main potential failure mechanism, reproduction of the biomechanical test of the reference implant via FEA, identification of the maximum value of the corresponding FEA quantity of interest at the required load level, definition of this value as the acceptance criterion for the FEA of the custom-made implant, reproduction of the biomechanical test with the custom-made implant via FEA, decision making for realization or re-design based on the acceptance criterion is fulfilled or not. Exemplary cases of custom-made knee & hip implants were evaluated with this new methodology. The FEA acceptance criterion derived from the reference implants was fulfilled in both custom-made implants and subsequent biomechanical tests verified the FEA results. The suggested method allows a quantitative evaluation of the biomechanical properties of custom-made knee & hip implant without performing physical bench testing. This represents an important contribution to achieve a sustainable patient treatment in complex revision total knee & hip arthroplasty with custom-made 3D printed implants in a safe and timely manner

In severe cases of total knee arthroplasty which cannot be treated with off-the-shelf implants anymore custom-made knee implants may serve as one of the few remaining options to restore joint function or to prevent limb amputation. Custom-made implants are specifically designed and manufactured for one individual patient in a single-unit production, in which the surgeon is responsible for the implant design characteristics in consultation with the corresponding engineer. The mechanical performance of these custom-made implants is challenging to evaluate due to the unique design characteristics and the limited time until which the implant is needed. Nevertheless, the custom-made implant must comply with clinical and regulatory requirements. The design of custom-made implants is often based on a underlying reference implant with available biomechanical test results and well-known clinical performance. To support surgeons and engineers in their decision whether a specific implant design is suitable, a method is proposed to evaluate its mechanical performance. The method uses finite element analysis (FEA) and comprises six steps: (1) Identification of the main potential failure mechanism and its corresponding FEA quantity of interest. (2) Reproduction of the biomechanical test of the reference implant via FEA. (3) Identification of the maximum value of the corresponding FEA quantity of interest at the required load level. (4) Definition of this value as the acceptance criteria for the FEA of the custom-made implant. (5) Reproduction of the biomechanical test with the custom-made implant via FEA. (6) Conclusion whether the acceptance criteria is fulfilled or not. The method was applied to two exemplary cases of custom-made knee implants. The FEA acceptance criteria derived from the reference implants were fulfilled in both custom-made implants. Subsequent biomechanical tests verified the FEA results. This study suggests and applies a non-destructive and efficient method for pre-clinical testing of a single-unit custom-made knee implant to evaluate whether the design is mechanically suitable

Introduction. The Achilles tendon is the thickest and strongest tendon in the human body. Even though the tendon is so strong, it is one of the most frequently injured tendons. Treatment of patients after rupture is planned conservatively and surgically. Conservative treatment is generally applied to elderly patients with sedentary lives. If the treatment is surgical, it can be planned as open surgery or percutaneous surgery. In our study with rabbits, we wrapped a membrane made of plga (polylactic-co-glycolic acid) nanotubes impregnated with type 1 collagen around the tendon in rabbits that underwent open Achilles tendon repair surgery. After surgery, biomechanical and histological tests were performed on the tendons. Method. In the study consisting of 24 rabbits, 2 groups were created by random distribution. In the study group, after the Achilles tendon rupture was created, a type 1 collagen-impregnated plga-based membrane was placed around the tendon after the repair of 1 modified Kesslerr suture. In the control group, after the Achilles tendon rupture was created, 1 modified Kessler suture and Tendon repair was performed with the application of 3 primary sutures. At the end of the 6th week of the study, the rabbits in 2 groups were randomly distributed and histological examination was performed. Additionally, biomechanical testing was performed. Bonar and Movın scoring were used in histological examinations. Result. As a result of biomechanical tests, it was seen that the resistance of the tendon against rupture was higher in the study group than in the control group. In addition, it was observed that the tendon rupture time was longer in the study group than in the control group. Histological examinations gave supportive results from biomechanical tests. Conclusion. We think that the use of collagen-impregnated plga-based nanotubes in the surgical treatment of Achilles tendon ruptures has a positive healing effect. Although we think that the return to normal life after surgery may be faster, we believe that more clinical studies are needed

A novel EP4 selective agonist (KMN-159) was developed [1] and has been proven that it can act as an osteopromotive factor to repair critical-size femoral bone defects in rats at a dose-dependent manner [2]. Based on its osteopromotive properties, we hypothesized that KMN-159 could also aid in bone formation for spinal fusion. Therefore, the aim of this study was to investigate its spinal fusion effect in a dorsolateral spinal fusion model in rats. This study was performed on 192, 10-week-old male Wistar rats. The rats were randomized into 8 groups (n = 12 per group): 1) SHAM (negative control), 2) MCM (scaffold only), 3) MCM + 20 µg BMP-2 (positive control), 4-8) MCM + 0.2, 2, 20, 200 or 2000 µg KMN-159. A posterolateral intertransverse process spinal fusion at L4 to L5 was performed bilaterally by implanting group dependent scaffolds (see above) or left empty in the SHAM group (protocol no. 25-5131/474/38). Animals were euthanized after 3 weeks and 6 weeks for µCT and biomechanical testing analysis. The results showed that KMN-159 promoted new bone formation in a dose-dependent manner at 3 weeks and 6 weeks as verified by µCT. The biomechanical testing showed that the dose of 20, 200 and 2000 µg KMN-159 groups obtained comparable strength with BMP-2 group, which higher than SHAM, MCM and lower doses of 0.2 and 2 µg KMN-159 groups. In conclusion, KMN-159 could be a potential replacement of BMP-2 as a novel osteopromotive factor for spinal fusion. Acknowledgements: We are grateful to Ulrike Heide, Anna-Maria Placht (assistance with surgeries) as well as Suzanne Manthey & Annett Wenke (histology)

Abstract. Introduction. Persistent medial laxity increases the risk of failure for ACL reconstruction. To address this, multiple reconstruction techniques have been created. To date, no single strand reconstruction constructs have been able to restore both valgus and rotational stability. In response to this, a novel single strand Short Isometric Construct (SIC) MCL reconstruction was developed. Methods. Eight fresh-frozen cadaveric specimens were tested in three states: 1) intact 2) after sMCL and dMCL transection, and 3) after SIC MCL reconstruction. In each state, four loading conditions were applied at varying flexion angles: 90N anterior drawer, 5Nm tibial external rotation torque, 8Nm valgus torque, and combined 90N anterior drawer plus 5Nm tibial external rotation torque. Results. Transection of the sMCL and dMCL resulted in increased laxity with external rotation torque, valgus torque, and combined anterior drawer plus external rotation. SIC MCL reconstruction restored external rotation and valgus stability to intact levels throughout all degrees of flexion. In the combined test SIC MCL reconstruction also restored stability to intact levels for both anterior distraction and external rotation throughout the range of motion. No significant differences were noted between intact and SIC reconstruction. Conclusion. The single-limb short isometric construct (SIC) MCL reconstruction restored native valgus and rotatory stability to a sMCL- and dMCL-deficient knee in biomechanical testing

Introduction. A long nail is often recommended for treatment of complex trochanteric fractures but requires longer surgical and fluoroscopy times. A possible solution could be a nail with an appropriate length which can be locked in a minimally invasive manner by the main aiming device. We aimed to determine if such a nail model* offers similar structural stability on biomechanical testing on artificial bone as a standard long nail when used to treat complex trochanteric fractures. Method. An artificial osteoporotic bone model was chosen. As osteosynthesis material two cephalomedullary nails (CMN) were chosen: a superior locking nail (SL-Nail) which can be implanted with a singular targeting device, and a long nail (long-nail) with distal locking using free-hand technique. AO31-A2.2 fractures were simulated in a standardized manner. The insertion of the nail was strictly in accordance with the IFU and surgical manual of the manufacturer. The nail was locked dynamically proximally and statically distally. Axial height of the construct, varus collapse, and rotational deformity directly after nail insertion were simulated. A Universal Testing Machine was used. Measurements were made with a stereo-optic tracking system. Reactive movements were recorded and evaluated in all six degrees of freedom. A comparative analysis provided information about the stability and deformation of the assemblies to be compared. Result. There was a detectable difference in the axial fracture movement resulting in narrowing of the fracture gap. The load displacement was 1.7mm higher for the SL-Nail. There was no difference in varus collapse or rotational deformity between the nail variants. Conclusion. We conclude that there are small differences which are clinically insignificant and that a superior locking nail can safely be used to manage complex trochanteric fractures. *DCN SL nail, SWEMAC, Linköping, Sweden. Funding: no funding

Little information exists when using cell viability assays to evaluate cells within whole tissue, particularly specific types such as the intervertebral disc (IVD). When comparing the reported methodologies and the protocols issued by manufacturers, the processing, working times, and dye concentrations vary significantly, making the assay's reproducibility a costly and time-consuming trial and error process. This study aims to develop a detailed step-by-step cell viability assay protocol for evaluating IVD tissue. IVDs were harvested from bovine tails (n=8) and processed at day 0 and after 7 days of culture. Nucleus pulposus (NP) and the annulus fibrosus (AF) 3 mm cuts were incubated at room temperature (26˚C) with a Viability/Cytotoxicity Kit containing Calcein AM and Ethidium Ethidium homodimer-1 for 2 hr, followed by flash freezing in liquid nitrogen. Thirty µm sections were placed in glass slides and sealed with nail varnish or Antifade Mounting Medium. The IVD tissue was imaged within the next 4h after freezing using an inverted confocal laser-scanning microscope equipped with 488 and 543 nm laser lines. Cell viability at day 0 (NP: 92±9.6 % and AF:80±14.0%) and day 7 (NP: 91±7.9% and AF:76±20%) was successfully maintained and evaluated. The incubation time required is dependent on the working temperatures and tissue thickness. The calcein-AM dye will not be retained in the cells for more than four hours. The specimen preparation and culturing protocol have demonstrated good cell viability at day 0 and after seven days of culture. Processing times and sample preparation play an essential role as the cell viability components in most kits hydrolyse or photobleach quickly. A step-by-step replicable protocol for evaluating the cell viability in IVD will facilitate the evaluation of cell and toxicity-related outcomes of biomechanical testing protocols and IVD regenerative therapies

Polyetheretherketone (PEEK) interbody fusion cages combined with autologous bone graft is the current clinical gold standard treatment for spinal fusion, however, bone graft harvest increases surgical time, risk of infection and chronic pain. We describe novel low-stiffness 3D Printed titanium interbody cages without autologous bone graft and assessed their biological performance in a pre-clinical in vivo interbody fusion model in comparison to the gold standard, PEEK with graft. Titanium interbody spacers were 3D Printed with a microporous (Ti1: <1000μm) and macroporous (Ti2: >1000μm) design. Both Ti1 and Ti2 had an identical elastic modulus (stiffness), and were similar to the elastic modulus of PEEK. Interbody fusion was performed on L2-L3 and L4-L5 vertebral levels in 24 skeletally mature sheep using Ti1 or Ti2 spacers, or a PEEK spacer filled with iliac crest autograft, and assessed at 8 and 16 weeks. We quantitatively assessed bone fusion, bone area, mineral apposition rate and bone formation rate. Functional spinal units were biomechanically tested to analyse range of motion, neutral zone, and stiffness. Results: Bone formation in macroporous Ti2 was significantly greater than microporous Ti1 treatments (p=.006). Fusion scores for Ti2 and PEEK demonstrated greater rates of bone formation from 8 to 16 weeks, with bridging rates of 100% for Ti2 at 16 weeks compared to just 88% for PEEK and 50% for Ti1. Biomechanical outcomes significantly improved at 16 versus 8 weeks, with no significant differences between Ti and PEEK with graft. This study demonstrated that macroporous 3D Printed Ti spacers are able to achieve fixation and arthrodesis with complete bone fusion by 16 weeks without the need for bone graft. These significant data indicate that low-modulus 3D Printed titanium interbody cages have similar performance to autograft-filled PEEK, and could be reliably used in spinal fusion avoiding the complications of bone graft harvesting

Despite past advances of implant technologies, complication rates of fixations remain high at challenging sites such as the proximal humerus [1]. These may not only be owed to the implant itself but also to dissatisfactory surgical execution of fracture reduction and implant positioning. Therefore, the aim of this study was to quantify the instrumentation accuracy of a highly standardised and guided procedure and its influence on the biomechanical outcome and predicted failure risk. Preoperative planning of osteotomies creating an unstable 3-part fracture and fixation with a locking plate was performed based on CT scans of eight pairs of low-density proximal humerus samples from elderly female donors (85.2±5.4 years). 3D-printed subject-specific guides were used to osteotomise and instrument the samples according to the pre-OP plan. Instrumentation accuracies in terms of screw lengths and orientations were evaluated by comparing post-OP CT scans with the pre-OP plan. The fixation constructs were biomechanically tested until cyclic cut-out failure [2]. Failure risks of the planned and the post-OP configurations were predicted using a validated sample-specific finite element (FE) simulation approach [2] and correlated with the experimental outcomes. Small deviations were found for the instrumented screw trajectories compared to the planned configuration in the proximal-distal (0.3±1.3º) and anterior-posterior directions (-1.7±1.8º), and for screw tip to joint distances (-0.3±1.1 mm). Significantly higher failure risk was predicted for the post-OP compared to the planned configurations (p<0.01) via FE. When incorporating the instrumentation inaccuracies, the biomechanical results could be predicted well with FE (R. 2. =0.70). Despite the high instrumentation accuracy achieved using sophisticated subject-specific 3D-printed guides, even minor deviations from the pre-OP plan significantly increased the FE-predicted risk of failure. This underlines the importance of intraoperative guiding technology [3] in tandem with careful pre-OP planning to assist surgeons to achieve optimal outcomes. Acknowledgements. This study was performed with the assistance of the AO Foundation via the AOTRAUMA Network

Introduction. The main postoperative complications in fixation of ulna shaft fractures are non-union and implant irritation using currently recommended 3.5-mm locking compression plates. An alternative approach using a combination of two smaller plates in orthogonal configuration has been proposed. The aim of this study was to compare the biomechanical properties of a single 3.5-mm locking compression plate versus double plating using one 2.5-mm and one 2.0-mm mandible plate in a human ulna shaft fracture model. Method. Eight pairs human ulnar specimens with a standardized 10-mm fracture gap were pairwise assigned for instrumentation with either a single 3.5-mm plate placed posteriorly, or for double plating using a 2.5-mm and a 2.0-mm mandible plate placed posteriorly under the flexor muscles and laterally under the extensor muscles. All constructs were initially non-destructively biomechanically tested in axial compression, torsion, and bending, which was followed by cyclic torsional loading to failure. Interfragmentary movements were monitored by means of optical motion tracking. Result. There were no significant differences between the two plating techniques for axial stiffness (p=0.335), torsional stiffness in supination (p=0.462), torsional stiffness in pronation (p=0.307), medio-lateral bending stiffness (p=0.522), and antero-posterior bending stiffness (p=0.143). During cyclic torsional loading over the first 3000 cycles, there were no significant differences between the two plating techniques for shear displacement across the fracture gap, p=0.324. The numbers of cycles until clinically relevant failure of 5° angular deformation were 1366±685 for double plating and 2024±958 for single plating, which was statistically non-significantly different, p>0.05. The constructs treated with both plating techniques failed due to bone breakage at the most distal screw. Conclusion. From a biomechanical perspective double plating of ulna shaft fractures using a 2.5-mm and a 2.0-mm locking mandible plate demonstrated equivalent fixation strength as conventional plating using a single 3.5-mm locking compression plate

Reorientating pelvic osteotomies are performed to improve femoral head coverage and secondary degenerative arthritis. A rectangular triple pelvic innominate osteotomy (3PIO) is performed in symptomatic cases. However, deciding optimal screw fixation type to avoid complications is questionable. Therefore, this study aimed to investigate the biomechanical behavior of two different acetabular screw configurations used for rectangular 3PIO osteosynthesis. It was hypothesized that bi-directional screw fixation would be biomechanically superior to mono-axial screw fixation technique. A rectangular 3PIO was performed in twelve right-side artificial Hemi-pelvises. Group 1 (G1) had two axial and one transversal screw in a bi-directional orientation. Group 2 (G2) had three screws in the axial direction through the iliac crest. Acetabular fragment was reoriented to 10.5° inclination in coronal plane, and 10.0° increased anteversion along axial plane. Specimens were biomechanically tested until failure under progressively increasing cyclic loading at 2Hz, starting at 50N peak compression, increasing 0.05N/cycle. Stiffness was calculated from machine data. Acetabular anteversion, inclination and medialization were evaluated from motion tracking data from 250-2500 at 250 cycle increments. Failure cycles and load were evaluated for 5° change in anteversion. Stiffness was higher in G1 (56.46±19.45N/mm) versus G2 (39.02±10.93N/mm) but not significantly, p=0.31. Acetabular fragment anteversion, inclination and medialization increased significantly each group (p≤0.02) and remained non-significantly different between the groups (p≥0.69). Cycles to failure and failure load were not significantly different between G1 (4406±882, 270.30±44.10N) and G2 (5059±682, 302.95±34.10N), p=0.78. From a biomechanical perspective, the present study demonstrates that a bi-directional screw orientation does not necessarily advantageous versus mono-axial alignment when the latter has all three screws evenly distributed over the osteotomy geometry. Moreover, the 3PIO fixation is susceptible to changes in anteversion, inclination and medialization of the acetabular fragment until the bone is healed. Therefore, cautious rehabilitation with partial weight-bearing is recommended

Introduction. Pedicle screw loosening in posterior instrumentation of thoracolumbar spine occurs up to 60% in osteoporotic patients. These complications may be alleviated using more flexible implant materials and novel designs that could be optimized with reliable computational modeling. This study aimed to develop and validate non-linear homogenized finite element (hFE) simulations to predict pedicle screw toggling. Method. Ten cadaveric vertebral bodies (L1-L5) from two female and three male elderly donors were scanned with high-resolution peripheral quantitative computed tomography (HR-pQCT, Scanco Medical) and instrumented with pedicle screws made of carbon fiber-reinforced polyether-etherketone (CF/PEEK). Sample-specific 3D-printed guides ensured standardized instrumentation, embedding, and loading procedures. The samples were biomechanically tested to failure in a toggling setup using an electrodynamic testing machine (Acumen, MTS) applying a quasi-static cyclic testing protocol of three ramps with exponentially increasing peak (1, 2 and 4 mm) and constant valley displacements. Implant-bone kinematics were assessed with a stereographic 3D motion tracking camera system (Aramis SRX, GOM). hFE models with non-linear, homogenized bone material properties including a strain-based damage criterion were developed based on intact HR-pQCT and instrumented 3D C-arm scans. The experimental loading conditions were imposed, the maximum load per cycle was calculated and compared to the experimental results. HR-pQCT-based bone volume fraction (BV/TV) around the screws was correlated with the experimental peak forces at each displacement level. Result. The nonlinear hFE models accurately (slope = 1.07, intercept = 0.2 N) and precisely (R. 2. = 0.84) predicted the experimental peak forces at each displacement level. BV/TV alone was a weak predictor (R. 2. <0.31). Conclusion. The hFE models enable fast design iterations aiming to reduce the risk of screw loosening in low-density vertebrae. Improved flexible implant designs are expected to contribute to reduced complication rates in osteoporotic patients

The quest for optimal treatment of acute distal tibiofibular syndesmotic disruptions is still in progress. Using suture-button repair devices is one of the dynamic stabilization options, however, they may not be always appropriate for stabilization of length-unstable syndesmotic injuries. Recently, a novel screw-suture repair system was developed to address such issues. The aim of this study was to investigate the performance of the novel screw-suture repair system in comparison to a suture-button stabilization of unstable syndesmotic injuries. Eight pairs of human cadaveric lower legs were CT scanned under 700 N single-leg axial loading in five foot positions – neutral, 15° external/internal rotation and 20° dorsi-/plantarflexion – in 3 different states: (1) pre-injured (intact); (2) injured, characterized by complete syndesmosis and deltoid ligaments cuts simulating pronation-eversion injury types III and IV as well as supination-eversion injury type IV according to Lauge-Hansen; (3) reconstructed, using a screw-suture (FIBULINK, Group 1) or a suture-button (TightRope, Group 2) implants for syndesmotic stabilization, placed 20 mm proximal to the tibia plafond. Following, all specimens were: (1) biomechanically tested over 5000 cycles under combined 1400 N axial and ±15° torsional loading; (2) rescanned. Clear space (diastasis), anterior tibiofibular distance, talar dome angle and fibular shortening were measured radiologically from CT scans. Anteroposterior (AP), axial, mediolateral and torsional movements at the distal tibiofibular joint level were evaluated biomechanically via motion tracking. In each group clear space increased significantly after injury (p ≤ 0.004) and became significantly smaller in reconstructed compared with both pre-injured and injured states (p ≤ 0.041). In addition, after reconstruction it was significantly smaller in Group 1 compared to Group 2 (p < 0.001). AP and axial movements were significantly smaller in Group 1 compared with Group 2 (p < 0.001). No further significant differences were identified/detected between the groups (p ≥ 0.113). Although both implant systems demonstrate ability for stabilization of unstable syndesmotic injuries, the screw-suture reconstruction provides better anteroposterior translation and axial stability of the tibiofibular joint and maintains it over time under dynamic loading. Therefore, it could be considered as a valid option for treatment of syndesmotic disruptions

The quest for optimal treatment of acute distal tibiofibular syndesmotic disruptions is still in full progress. Using suture-button repair devices is one of the dynamic stabilization options, however, they may not be always appropriate for stabilization of length-unstable syndesmotic injuries. Recently, a novel screw-suture repair system was developed to address such issues. The aim of this study was to investigate the performance of the novel screw-suture repair system in comparison to a suture-button stabilization of unstable syndesmotic injuries. Eight pairs of human cadaveric lower legs were CT scanned under 700 N single-leg axial loading in five foot positions – neutral, 15° external/internal rotation and 20° dorsi-/plantarflexion – in 3 different states: (1) pre-injured (intact); (2) injured, characterized by complete syndesmosis and deltoid ligaments cuts simulating pronation-eversion injury types III and IV, and supination-eversion injury type IV according to Lauge-Hansen; (3) reconstructed, using a screw-suture (FIBULINK, Group 1) or a suture-button (TightRope, Group 2) implants for syndesmotic stabilization, placed 20 mm proximal to the tibia plafond/joint surface. Following, all specimens were: (1) biomechanically tested over 5000 cycles under combined 1400 N axial and ±15° torsional loading; (2) rescanned. Clear space (diastasis), anterior tibiofibular distance, talar dome angle and fibular shortening were measured radiologically from CT scans. Anteroposterior, axial, mediolateral and torsional movements at the distal tibiofibular joint level were evaluated biomechanically via motion tracking. In each group clear space increased significantly after injury (p ≤ 0.004) and became significantly smaller in reconstructed compared with both pre-injured and injured states (p ≤ 0.041). In addition, after reconstruction it was significantly smaller in Group 1 compared to Group 2 (p < 0.001). Anteroposterior and axial movements were significantly smaller in Group 1 compared with Group 2 (p < 0.001). No further significant differences were detected between the groups (p ≥ 0.113). Conclusions. Although both implant systems demonstrate ability for stabilization of unstable syndesmotic injuries, the screw-suture reconstruction provides better anteroposterior translation and axial stability of the tibiofibular joint and maintains it over time under dynamic loading. Therefore, it could be considered as a valid option for treatment of syndesmotic disruptions

Massive irreparable rotator cuff tears often lead to superior migration of the humeral head, which can markedly impair glenohumeral kinematics and function. Although treatments currently exist for treating such pathology, no clear choice exists for the middle-aged patient demographic. Therefore, a metallic subacromial implant was developed for the purpose of restoring normal glenohumeral kinematics and function. The objective of this study was to determine this implant's ability in restoring normal humeral head position. It was hypothesized that (1) the implant would restore near normal humeral head position and (2) the implant shape could be optimized to improve restoration of the normal humeral head position. A titanium implant was designed and 3D printed. It consisted of four design variables that varied in both implant thickness (5mm and 8mm) and curvature of the humeral articulating surface (high constraint and low constraint. To assess these different designs, these implants were sequentially assessed in a cadaver-based biomechanical testing protocol. Eight cadaver specimens (64 ± 13 years old) were loaded at 0, 30, and 60 degrees of glenohumeral abduction using a previously developed shoulder simulator. An 80N load was equally distributed across all three deltoid heads while a 10N load was applied to each rotator cuff muscle. Testing states included a fully intact rotator cuff state, a posterosuperior massive rotator cuff tear state (cuff deficient state), and the four implant designs. An optical tracking system (Northern Digital, Ontario, Canada) was used to record the translation of the humeral head relative to the glenoid in both superior-inferior and anterior-posterior directions. Superior-Inferior Translation. The creation of a posterosuperior massive rotator cuff tear resulted in significant superior translation of the humeral head relative to the intact cuff state (P=0.016). No significant differences were observed between each implant design and the intact cuff state as all implants decreased the superior migration of the humeral head that was observed in the cuff deficient state. On average, the 5mm low and high constraint implant models were most effective at restoring normal humeral head position to that of the intact cuff state (-1.3 ± 2.0mm, P=0.223; and −1.5 ± 2.3mm, P=0.928 respectively). Anterior-Posterior Translation. No significant differences were observed across all test states for anterior-posterior translation of the humeral head. The cuff deficient on average resulted in posterior translation of the humeral head, however, this was not statistically significant (P=0.128). Both low and high constraint implant designs were found to be most effective at restoring humeral head position to that of the intact cuff state, on average resulting in a small anterior offset (5mm high constraint: 2.0 ± 4.7mm, P=1.000; 8mm high constraint: 1.6 ± 4.9mm, P=1.000). The 5mm high constraint implant was most effective in restoring normal humeral head position in both the superior-inferior and anterior-posterior directions. The results from this study suggest the implant may be an effective treatment for restoring normal glenohumeral kinematics and function in patients with massive irreparable rotator cuff tears. Future studies are needed to address the mechanical efficiency related to arm abduction which is a significant issue related to patient outcomes

Distal radius fractures have an incidence rate of 17.5% among all fractures. Their treatment in case of comminution, commonly managed by volar locking plates, is still challenging. Variable-angle screw technology could counteract these challenges. Additionally, combined volar and dorsal plate fixation is valuable for treatment of complex fractures at the distal radius. Currently, biomechanical investigation of the competency of supplemental dorsal plating is scant. The aim of this study was to investigate the biomechanical competency of double-plated distal radius fractures in comparison to volar locking plate fixation. Complex intra-articular distal radius fractures AO/OTA 23-C 2.1 and C 3.1 were created by means of osteotomies, simulating dorsal defect with comminution of the lunate facet in 30 artificial radii, assigned to 3 study groups with 10 specimens in each. The styloid process of each radius was separated from the shaft and the other articular fragments. In group 1, the lunate facet was divided to 3 equally-sized fragments. In contrast, the lunate in group 2 was split in a smaller dorsal and a larger volar fragment, whereas in group 3 was divided in 2 equal fragments. Following fracture reduction, each specimen was first instrumented with a volar locking plate and non-destructive quasi-static biomechanical testing under axial loading was performed in specimen's inclination of 40° flexion, 40° extension and 0° neutral position. Mediolateral radiographs were taken under 100 N loads in flexion and extension, as well as under 150 N loads in neutral position. Subsequently, all biomechanical tests were repeated after supplemental dorsal locking plate fixation of all specimens. Based on machine and radiographic data, stiffness and angular displacement between the shaft and lunate facet were determined. Stiffness in neutral position (N/mm) without/with dorsal plating was on average 164.3/166, 158.5/222.5 and 181.5/207.6 in groups 1–3. It increased significantly after supplementary dorsal plating in groups 2 and 3. Predominantly, from biomechanical perspective supplemental dorsal locked plating increases fixation stability of unstable distal radius fractures after volar locked plating. However, its effect depends on the fracture pattern at the distal radius

Previous biomechanical studies of lateral collateral ligament (LCL) injuries and their surgical repair, reconstruction and rehabilitation have primarily relied on gravity effects with the arm in the varus position. The application of torsional moments to the forearm manually in the laboratory is not reproducible, hence studies to date likely do not represent forces encountered clinically. The aim of this investigation was to develop a new biomechanical testing model to quantify posterolateral stability of the elbow using an in vitro elbow motion simulator. Six cadaveric upper extremities were mounted in an elbow motion simulator in the varus position. A threaded screw was then inserted on the dorsal aspect of the proximal ulna and a weight hanger was used to suspend 400g, 600g, and 800g of weight from the screw head to allow torsional moments to be applied to the ulna. An LCL injured (LCLI) model was created by sectioning of the common extensor origin, and the LCL. Ulnohumeral rotation was recorded using an electromagnetic tracking system during simulated active and passive elbow flexion with the forearm pronated and supinated. A repeated measures analysis of variance was performed to compare elbow states (intact, LCLI, and LCLI with 400g, 600g, and 800g of weight). During active motion, there was a significant difference between different elbow states (P=.001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of weights did not significantly increase the external rotation (ER) of the ulnohumeral articulation (10°±7°, P=.268 400g, 10.5°±7.1°, P=.156 600g, 11°±7.2°, P=.111 800g) compared to the LCLI state (8.4°±6.4°) with the forearm pronated. However, with the forearm supinated, the addition of 800g of weight significantly increased the ER (9.2°±5.9°, P=.038) compared to the LCLI state (5.9°±5.5°) and the addition of 400g and 600g of weights approached significance (8.2°±5.7°, P=.083 400g, 8.7°±5.9°, P=.054 600g). During passive motion, there was a significant difference between different elbow states (P=.0001 pronation, P=.0001 supination). Post hoc analysis showed that the addition of 600g and 800g but not 400g resulted in a significant increase in ER of the ulnohumeral articulation (9.3°±7.8°, P=.103 400g, 11.2°±6.2°, P=.004 600g, 12.7°±6.8°, P=.006 800g) compared to the LCLI state (3.7°±5.4°) with the forearm pronated. With the forearm supinated, the addition of 400g, 600g, and 800g significantly increased the ER (11.7°±6.7°, P=.031 400g, 13.5°±6.8°, P=.019 600g, 14.9°±6.9°, P=.024 800g) compared to the LCLI state (4.3°±6.6°). This investigation confirms a novel biomechanical testing model for studying PLRI. Moreover, it demonstrates that the application of even small amounts of torsional moment on the forearm with the arm in the varus position exacerbates the rotational instability seen with the LCL deficient elbow. The effect of torsional loading was significantly worse with the forearm supinated and during passive elbow motion. This new model allows for a more provocative testing of elbow stability after LCL repair or reconstruction. Furthermore, this model will allow for smaller sample sizes to be used while still demonstrating clinically significant differences. Future biomechanical studies evaluating LCL injuries and their repair and rehabilitation should consider using this testing protocol