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This is a cross-sectional, clinical observational study. Finger range of motion (ROM) and functional performance are critical in many daily activities. Hand osteoarthritis (H-OA) is a prevalent disease that impairs both variables. Little quantitative research has been performed on finger kinematics during activities of daily living (ADLs) across health status and method of performance (with or without joint protection programs). The purpose of this research is to examine the effects of H-OA and method of performance on ROM in the thumb, index, and middle digits (flexion/extension and abduction/adduction) during ADLs. This study was conducted using 10 healthy participants (mean age: 28 years) and nine participants with H-OA (mean age: 72 years). All participants performed baseline ROM movements followed by 9 activities of daily living. These activities involved prehension type grasps and were performed with and without the recommended joint protection procedures specific to each task. Thumb IP and MCP, index distal interphalengeal (DIP) and proximal interphalengeal (PIP), and middle DIP and PIP joints were continuously recorded using an electromagnetic tracking system for ROM analysis. Participants with H-OA had a statistically significant decrease in ROM when comparing values measured in the healthy cohort during active ROM (25° decrease) and ADL ROM (25° decrease) in the flex/ext direction. Similarly, following joint protection instruction, a statistically significant decrease in ROM was found during tasks in the flex/ext direction (healthy participant decrease in ROM: 17°, H-OA decrease in ROM:10°) This study demonstrated that people with hand arthritis move through a smaller arc of motion when performing some functional tasks as compared with the controls, and that with instruction on joint protection techniques, participants made significant changes in the amount of movement used to perform tasks, which supports a proof of principle of joint protection. •This study used a novel joint kinematic analysis technique to quantify differences in the finger range of motion in individuals with and without hand arthritis during activities of daily living.•This study was able to quantify the decrease in the finger range of motion that is associated with hand arthritis while individuals are performing activities of daily living.•Joint protection strategies aimed at reducing joint deformity do not always reduce joint finger motion as previously thought.

Researchers have modified PLA materials to enhance their mechanical properties and meet the clinical requirements. However, the strength and stiffness of PLA are still significantly lower than those of metals. Building on the established chevron clinical procedure and considering the mechanical characteristics of PLA screws, we devised a modified chevron osteotomy (MCO) based on a load-reducing structure with the aim of reducing the load on the screws. Subsequently, in vitro quasi-static in situ compression and dynamic fatigue tests were conducted for both procedures. DIC, micro-CT, and SEM were used to elucidate the unloading effects and structural damage of different bone cutting and implant locations on the PLA bone screws, providing biomechanical data for clinical applications. In-vitro simulation studies indicated that the unloading structure of the MCO procedure reduced the load borne by the PLA screws. Within the load range of the first metatarsal during walking, the MCO procedure exhibited a compressive strength 2.5 times that of the traditional chevron osteotomy groups and even exceeded the titanium alloy screw groups by 25%, ensuring PLA screw fixation strength and stability that are not inferior to metallic materials. A stable load-reducing structure in osteotomy procedures is the key to PLA materials becoming viable alternatives to metal orthopedic fixation devices.

Background Proximal humerus fractures are the third most common in the human body but their management remains controversial. Open reduction and internal fixation with plates is one of the leading modes of operative treatment for these fractures. The development of technologies and techniques for these plates, during the recent decades, promise a bright future for their clinical use. A comprehensive review of in vitro biomechanical studies is needed for the comparison of plates’ mechanical performance and the testing methodologies. This will not only guide clinicians with plate selection but also with the design of future in vitro biomechanical studies. This review was aimed to systematically categorise and review the in vitro biomechanical studies of these plates based on their protocols and discuss their results. The technologies and techniques investigated in these studies were categorised and compared to reach a census where possible. Methods and results Web of Science and Scopus database search yielded 62 studies. Out of these, 51 performed axial loading, torsion, bending and/or combined bending and axial loading while 11 simulated complex glenohumeral movements by using tendons. Loading conditions and set-up, failure criteria and performance parameters, as well as results for each study, were reviewed. Only two studies tested four-part fracture model while the rest investigated two- and three-part fractures. In ten studies, synthetic humeri were tested instead of cadaveric ones. In addition to load–displacement data, three-dimensional motion analysis systems, digital image correlation and acoustic emission testing have been used for measurement. Conclusions Overall, PHILOS was the most tested plate and locking plates demonstrated better mechanical performance than non-locking ones. Conflicting results have been published for their comparison with non-locking blade plates and polyaxial locking screws. Augmentation with cement [calcium phosphate or poly(methyl methacrylate)] or allografts (fibular and femoral head) was found to improve bone-plate constructs’ mechanical performance. Controversy still lies over the use of rigid and semi-rigid implants and the insertion of inferomedial screws for calcar region support. This review will guide the design of in vitro and in silico biomechanical tests and also supplement the study of clinical literature.

BackgroundLumbar spinal stenosis is a common disease in the aging population. Decompression surgery represents the treatment standard, however, a risk of segmental destabilization depending on the approach and extent of decompression is discussed. So far, biomechanical studies on techniques were mainly conducted on non-degenerated specimens. This biomechanical in vitro study aimed to investigate the increase in segmental range of motion (ROM) depending on the extent of decompression in degenerated segments.MethodsTen fresh frozen lumbar specimens were embedded in polymethyl methacrylate (PMMA) and loaded in a spine tester with pure moments of ± 7.5 Nm. The specimens were tested in their intact state for lateral bending (LB), flexion/extension (FE) and axial rotation (AR). Subsequently, four different decompression techniques were performed: unilateral interlaminar decompression (DC1), unilateral with \"over the top\" decompression (DC2), bilateral interlaminar decompression (DC3) and laminectomy (DC4). The ROM of the index segment was reported as percent (%) of the native state.ResultsSpecimens were measured in their intact state prior to decompression. The mean ROM was defined as 100% (FE:6.3 ± 2.3°; LB:5.4 ± 2.8°; AR:3.0 ± 1.6°). Interventions showed a continuous ROM increase: FE (DC1: + 4% ± 4.3; DC2: + 4% ± 4.5; DC3: + 8% ± 8.3;DC4: + 20% ± 15.9), LB(DC1: + 4% ± 6.0; DC2: + 5% ± 7.3; DC3: + 8% ± 8.3; DC4: + 11% ± 9.9), AR (DC1: + 7% ± 6.0; DC2: + 9% ± 7.9; DC3: + 15% ± 11.5; DC4: + 19% ± 10.5). Significant increases in ROM for all motion directions (p < 0.05) were only obtained after complete laminectomy (DC4).ConclusionUnilateral and/or bilateral decompressive surgery resulted in a statistically insignificant ROM increase, whereas complete laminectomy showed statistically significant ROM increase. If this ROM increase also has an impact on the clinical outcome and how to identify segments at risk for secondary lumbar instability should be evaluated in further studies.

Introduction Current literature lacks recommendations regarding proper fixation of comminuted coronal plane fractures of the posterior femoral condyles (Hoffa fractures). Therefore, the aim of this study was to compare the biomechanical characteristics of different plate-augmented constructs to isolated posteroanterior screw fixation in comminuted lateral Hoffa fractures. Materials and methods Comminuted Letenneur type IIb lateral Hoffa fractures were simulated in 24 human cadaveric distal femora. The fractures were fixed with either isolated crossed posteroanterior screws or additionally with either a posterior plate, a lateral locking plate, or combined posterior and lateral locking plates. All specimens were biomechanically tested under progressively increasing cyclic loading until failure, while capturing the interfragmentary movements of the Hoffa and intercalary fragments via motion tracking. Results Plate-augmented posteroanterior screw fixation of the Hoffa fragment exhibited higher cycles to failure, higher failure loads ( p  < 0.05) and less axial displacements ( p  < 0.05) compared to isolated posteroanterior screw fixation. Both additional lateral locking and double plate fixations of the intercalary fragment provided higher cycles to failure, higher failure loads ( p  < 0.05) and less axial displacement ( p  < 0.05) than isolated posteroanterior screw fixation, whereas additional posterior plate fixation did not significantly increase cycles to failure, failure loads and axial displacement (n.s.). Fracture gap twisting and opening did not differ significantly between the four constructs for the Hoffa fragment, while plate-augmented constructs provided less fracture opening of the intercalary fragment compared to isolated posteroanterior screw fixation ( p  < 0.01). Conclusions Plate-augmented posteroanterior screw fixation of comminuted Letenneur type IIb Hoffa fractures provided greater biomechanical stability than isolated posteroanterior screw fixation. While additional lateral or double plate fixation improves the stability of both the intercalary and Hoffa fragment, posterior plating stabilized only the Hoffa fragment.

Introduction Traditionally, plate osteosynthesis of the anterior column combined with an antegrade posterior column screw is used for fixation of anterior column plus posterior hemitransverse (ACPHT) acetabulum fractures. Replacing the posterior column screw with an infraacetabular screw could improve the straightforwardness of acetabulum surgery, as it can be inserted using less invasive approaches, such as the AIP/Stoppa approach, which is a well-established standard approach. However, the biomechanical stability of a plate osteosynthesis combined with an infraacetabular screw instead of an antegrade posterior column screw is unknown. Material and methods Two osteosynthesis constructs were compared in a synthetic hemipelvis model with an ACPHT fracture: Suprapectineal plate + antegrade posterior column screw (APCS group) vs. suprapectineal plate + infraacetabular screw (IAS group). A single-leg stance test protocol with an additional passive muscle force and a cyclic loading of 32,000 cycles with a maximum effective load of 2400 N was applied. Interfragmentary motion and rotation of the three main fracture lines were measured. Results At the posterior hemitransverse fracture line, interfragmentary motion perpendicular to the fracture line ( p  < 0.001) and shear motion ( p  < 0.001) and at the high anterior column fracture line, interfragmentary motion longitudinal to the fracture line ( p  = 0.017) were significantly higher in the IAS group than in the APCS group. On the other hand, interfragmentary motion perpendicular ( p  = 0.004), longitudinal ( p  < 0.001) and horizontal to the fracture line ( p  = 0.004) and shear motion ( p  < 0.001) were significantly increased at the low anterior column fracture line in the APCS group compared to the IAS group. Conclusions Replacing the antegrade posterior column screw with an infraacetabular screw is not recommendable as it results in an increased interfragmentary motion, especially at the posterior hemitransverse component of an ACPHT fracture.

Purpose To compare biomechanical behaviour of the anterior root of the lateral meniscus (ARLM) after a transtibial repair (TTR) and after an in situ repair (ISR), discussing the reasons for the efficacy of the more advantageous technique. Methods Eight cadaveric human knees were tested at flexion angles from 0° to 90° in four conditions of their ARLM: intact, detached, reinserted using TTR, and reinserted using ISR. Specimens were subjected to 1000 N of compression, and the contact area (CA), mean pressure (MP), and peak pressure (PP) on the tibial cartilage were computed. For the TTR, traction force on the sutures was registered. Results ARLM detachment significantly altered contact biomechanics, mainly at shallow flexion. After ISR, differences compared to the healthy group persisted (extension, CA 22% smaller ( p  = 0.012); at 30°, CA 30% smaller ( p  = 0.012), MP 21%, and PP 32% higher (both p  = 0.017); at 60°, CA 28% smaller ( p  = 0.012), MP 32%, and PP 49% higher (both p  = 0.025). With TTR, alterations significantly decreased compared to the injured group, with no statistical differences from the intact ones observed, except for CA at extension (15% decrease, p  = 0.012) and at 30° (12% decrease, p  = 0.017). The suture tension after TTR, given as mean(SD), was 36.46(11.75)N, 44.32(11.71)N, 40.38(14.93)N, and 43.18(14.89)N for the four tested flexion angles. Conclusions Alterations caused by ARLM detachment were partially restored with both ISR and TTR, with TTR showing better results on recovering CA, MP, and PP in the immediate postoperative period. The tensile force was far below the value reported to cause meniscal cut-out in porcine models.

Preclinical testing of total knee replacements (TKR) is crucial for evaluating new implant designs. Dynamic experimental testing focus mostly on level walking and squats, failing to represent a full range of daily activities. Moreover, the contribution of the ligament apparatus is often simplified. Therefore, this study transferred five daily activity load cases—level walking, downhill walking, stair descent, squat, and sit-to-stand—onto a six-degree-of-freedom (6-DOF) joint simulator with a cruciate-retaining bicondylar TKR and a virtual ligament apparatus. Forces and kinematics were based on telemetric data from an ultra-congruent TKR. The resulting kinematics, kinetics, and tibiofemoral contact surfaces were evaluated. Additionally, variations of the virtual ligament apparatus on the joint simulator, e.g. resection of the posterior cruciate ligament (PCL), have been used to assess its influence on the resulting joint dynamics. Results showed that tibiofemoral contact area was more influenced by dynamics than kinematics. Virtual PCL resection shifted the tibia posteriorly (up to 3 mm) and increased abduction (up to 0.5°). Different results were seen across all load cases. The exceptions are the squat and sit-to-stand load cases with similar patterns. Thus, cruciate-retaining TKR can be tested using telemetric data from ultra-congruent TKR, aiding in comprehensive evaluations.

PurposeThe cortical bone trajectory (CBT) is an alternative to the traditional pedicle screw trajectory (TT) in posterior spinal instrumentation, enhancing screw contact with cortical bone and therefore increasing fixation strength. Additional to the trajectory, insertion depth (pericortical vs. bicortical placement) could be a relevant factor affecting the fixation strength. However, the potential biomechanical benefit of a bicortical placement of CBT screws is unknown. Therefore, the aim of this study was to quantify the fixation strength of pericortical- versus bicortical-CBT (pCBT versus bCBT) screws in a randomized cadaveric study.MethodsPedicle screws were either placed pericortical or bicortical with a CBT in 20 lumbar vertebrae (2 × 20 instrumented pedicles) from four human spine cadavers by using patient-specific templates. Instrumented specimens underwent physiological cyclic loading testing (1′800′000 cycles, 10 Hz), including shear and tension loads as well as bending moments. Translational and angular displacements of the screws were quantified and compared between the two techniques.ResultsThere was a slight decrease in translational (0.2 mm ± 0.09 vs. 0.24 mm ± 0.11) and angular displacements (0.06° ± 0.05 vs. 0.13° ± 0.11) of bCBT screws when compared with pCBT screws after 1′800′000 cycles. However, the results were non-significant (p > 0.05).ConclusionThe authors do not recommend placing CBT screws bicortically, as no relevant biomechanical advantage is gained while the potential risk for iatrogenic injury to structures anterior to the spine is increased.

Rigorous statistical analysis of biomechanical data is required to understand tissue properties. In biomechanics, samples are often obtained from multiple biopsies in the same individual, multiple samples tested per biopsy, and multiple tests performed per sample. The easiest way to analyze this hierarchical design is to simply calculate the grand mean of all samples tested. However, this may lead to incorrect inferences. In this report, three different analytical approaches are described with respect to the analysis of hierarchical data obtained from muscle biopsies. Each method was used to analyze an actual experimental data set obtained from muscle biopsies of three different muscles in the human forearm. The results illustrate the conditions under which mixed-models or simple models are acceptable for analysis of these types of data.