Proceedings of the Institution of Mechanical Engineers,Part H: Journal of Engineering in Medicine

Radiolucent lines (RLLs) observed adjacent to a cementless stem following Total Hip Arthroplasty (THA) have been linked to stem loosening. Their manual assessment is susceptible to observer error. In this study a semi-automated (Auto) method was developed to characterise RLLs from Anterior-Posterior (AP) and Lateral (Lat) radiographs, evaluate their time progression and effects on clinical outcomes. The study comprised of 237 subjects with postoperative, 1 and 10 Y radiographs. Of these 131 also had 4–7 Y radiographs. All subjects also had accompanying implant, demographic and clinical outcomes data. An algorithm was written to evaluate the incidence of RLLs and post-processing was performed to characterise RLLs as ‘not present’ or ‘benign’, or significant (‘SigRLL’). The criteria for SigRLL were tuned to minimise the number of false negatives compared to a manual characterisation. The incidence of SigRLL using AP/Lat or AP only was compared and the latter was used to monitor their development over time. The relationship with clinical outcomes was evaluated. Incidence of SigRLLs using the Auto and Manual AP/Lat methods agreed in 199/237 (84.0%) of subjects. The discrepancies included seven false negatives. The Auto AP/Lat and AP methods agreed in 221/237 (93.2%) of subjects. Twenty-eight subjects with a 4–7 Y review had SigRLLs at 10 Y. Of these, 23 had SigRLLs at 4–7 Y. Greater pain was reported in the SigRLLs group (p = 0.003). Four out of five stems subsequently revised for loosening exhibited 10 Y SigRLLs.

Most commercially available knee implant components are confined to standardised size ranges, hindering precise anatomical alignment and proper gap filling. This study focuses on producing silicone moulds for patient-specific knee implants using an indirect rapid tooling process. Total knee replacement (TKR) components were generated from CT scan data via image segmentation, CAD modelling, STL correction and resection planning. The profile for the tibial insert was extracted from the CAD models of femoral and tibial components of TKR. Further, the profile as obtained was employed to fabricate a pattern of the tibial insert by Fused Filament Fabrication (FFF) using PLA filaments. Two post-processing techniques, chemical immersion and chemical vapour smoothing, were used and compared to improve the surface finish. The more effective chemical vapour smoothing method was applied to the pattern. The effects on surface quality were assessed using an optical tilt microscope. The 3D surface plots confirmed that the post-processing improved the surface finish of the patterns by about 80%. Evaluation of geometric deviation confirmed that chemical vapour smoothing uniformly modifies the entire surface while maintaining global geometric conformity. The result encouraged us to fabricate the silicone moulds, which can further be used to produce patient-specific tibial inserts by casting viable epoxy-based composite biomaterials. FFF-fabricated tibial insert moulds showed Ra 26.87 µm, Rq 33.58 µm, Rsk −1.19, and Rku 3.12. Rapid tooling with an unsmoothed pattern increased roughness (Ra 54.60 µm, Rq 57.31 µm) and altered height distribution (Rsk 0.31, Rku 2.40). Vapour smoothing prior to moulding significantly reduced Rq and stabilised Rsk and Rku, indicating improved surface morphology and uniform asperity distribution.

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Although fully cortical-threaded screws are introduced as a design adaptation tailored to the cortical-dominant load path of modified cortical bone trajectory (MCBT) fixation, the biomechanical consequences of this design across the screw–bone interface and fusion construct remain insufficiently defined. Therefore, this study compared fully cortical-threaded MCBT screws with clinically used dual-threaded screws through an integrated experimental and finite element (FE) framework, spanning in vitro ovine vertebral biomechanical test and specimen-specific L4 vertebra and L1–S1 fusion models. At the screw level, compared with the control group, fully cortical-threaded MCBT screws increased maximum pull-out strength by 111.2% and multidirectional stiffness by 75%–89% in L4 vertebral FE analysis, with biomechanical testing showing corresponding increases of 39.1% in insertion torque and 41.9% in maximum pull-out strength. At the fusion-construct level, fully cortical-threaded MCBT fixation limited fused-segment motion and decreased stress across the cage, instrumentation, and vertebral bone, indicating a more coordinated load-transfer pattern rather than a simple increase in interface-level strength. These effects were consistent across fusion strategies, but procedure-specific mechanics remained evident, with PLIF producing more symmetric load sharing and TLIF retaining intrinsic asymmetry owing to unilateral facet joint resection. Overall, the fully cortical-threaded screw design for MCBT promoted continuous and stable bone–screw load transfer, translating interface-level gains into coordinated load distribution, greater fusion-construct stability, and lower deformation-driven stress concentration. These findings indicate that aligning screw architecture with the cortical-dominant load path is a mechanically rational design strategy within MCBT fixation, particularly in biomechanically demanding settings.

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Femoral neck fractures necessitate effective fracture fixation techniques to ensure optimal outcomes. The study evaluates the bone remodelling around Dynamic Hip Screw with anti-rotational screw (DHS + AR) and Femoral Neck System (FNS) used for treating femoral neck fractures of Pauwels types I, II and III. Femur models were developed using CT imaging data. Fractures were modelled assuming smooth fracture surfaces. Isotropic heterogeneous CT-grey value-based bone material properties were employed in the bone model, and Ti-alloy was incorporated as implant material. Bone remodelling algorithm based on strain energy density was employed to predict the implants’ effects under two loading conditions: normal walking and stair climbing. The density change (Δρ) was iteratively updated until convergence occurred (Δρ < 0.005 g/cm³ between two consecutive iterations). The investigation compared post-operative (PO) conditions with equilibrium (AE) states. Results revealed that strain shielding was approximately 27% lower in FNS-implanted models than DHS + AR models, indicating better biomechanical performance under adopted modelling assumptions. From PO to AE, axial deformation and rotational stability of the femoral head were reduced more in FNS models, with reductions of up to 13.57% and 83%, respectively. Micromotion was (below 100 μm) in all models except for FNS in Pauwels III fractures under PO conditions. However, it was reduced below 100 μm at AE. Lower bone loss was observed in FNS-implanted models while DHS + AR implanted models exhibited higher resorption. These findings suggest that FNS implants are predicted to provide better stability and favourable bone remodelling outcomes compared to DHS + AR screws.

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Prolonged stooping induces sustained high spinal loading and low back pain (LBP). While passive exoskeletons provide a potential solution, they are limited by poor kinematic compatibility and insufficient degrees of freedom (DOF). This study proposes a novel kinematic-compatible passive spinal exoskeleton (KC-PSE) using parallelepiped units. It offers multiple degrees of freedom to adapt to spinal motions in sagittal and coronal planes. Based on potential energy conservation, complete gravity compensation conditions are rigorously derived. Numerical simulations on a 4-unit design validate full gravity compensation, and distributed force models characterize output torque. Prototype tests confirm the exoskeleton effectively compensates gravity while tracking spinal motions, enhancing kinematic compatibility. This mechanism and framework provide a promising engineering-medical strategy for reducing spinal loads.

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Falls by subjects riding a ski lift while in transit are rare but can cause significant injury. Falls can occur at variable heights and can occur to small children through to adults of both genders. The current study was designed to investigate the mechanics associated with falls to elucidate this phenomenon. Five crash dummies served as surrogates for children (3-, 6-, and 10-year-old) and adults (5th percentile female and 50th percentile male). The subjects were seated in a simulated ski lift chair with a detailed seating procedure. The shorter length of the 3- and 6-year-old surrogates’ thighs was associated with slouched posture while the remaining surrogates sat in an upright fashion. All subjects were fit with winter clothing, skis, boots, helmet, and goggles. The ski lift chair was slowly tilted forward to represent wind gusts, ski lift cable catenary, or activation of the lift emergency stop. As a worst-case scenario, a restraint bar was not used since field data suggests poor usage rates. The seat was covered with three different frictional interfaces to represent different seat designs and environmental conditions. The results showed that the 10-year-old and fifth percentile female surrogates required the greatest tilt angles to initiate a fall with increasing friction requiring greater tilt angles. The remaining surrogates exhibited significantly lower tilt angles with no significant effect observed for the different frictional interfaces. These data suggest that subject size and frictional interface create variable effects. As such, uniform use of restraint bars and footrests, where available, is recommended.

Individuals with transfemoral amputation (TFA) often experience gait adaptations when walking under environmental and cognitive challenges. This study examined the influence of passive prosthetic knee mechanisms on self-reported mobility and gait biomechanics during single-task and dual-task walking over an uneven compliant surface. Participants were grouped as able-bodied individuals (AB; n = 15), individuals with TFA using polycentric knees (TFA_P; n = 6), and individuals with TFA using fluid-controlled knees (TFA_FC; pneumatic/hydraulic; n = 5). The dual-task condition involved walking while performing an auditory Stroop task. Outcome measures included self-report questionnaires, joint kinematics, joint kinetics, and ground reaction forces. Biomechanical variables were analysed using linear mixed-effects models to examine group, task, and group × task interaction effects. Self-reported outcomes indicated reduced functional mobility in individuals with TFA compared with AB. Biomechanical findings showed altered gait patterns in both TFA groups compared with AB, particularly reduced knee flexion and ankle plantarflexion. For kinetic outcomes, significant group effects were observed for selected joint moment and power variables, although Bonferroni-adjusted pairwise differences were identified only for maximum stance hip extension moment (HM1), with lower values in TFA_FC compared with AB. A significant task effect was observed for maximum stance ankle dorsiflexion (AA2) during dual-task walking across all groups. A significant group × task interaction was found for maximum hip eccentric power during late stance (HP2), with increased hip power during dual-task walking in TFA_P. Overall, passive prosthetic knee mechanisms showed limited differences, although task-specific adaptations were evident under combined uneven surface and cognitive demands.

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Articulated endoscopic instruments can enhance dexterity within constrained workspaces; however, their complexity and cost limit accessibility for training, prototyping, and early-stage evaluation. Additive manufacturing offers a practical approach for developing mechanically functional, low-cost articulated devices for engineering exploration and simulation-oriented applications. This study describes the mechanical design, bench-top characterization, and preliminary proof-of-concept assessment of two additively manufactured, cable-driven endoscopic prototypes: a flexible endoscope with an integrated working channel and bidirectional distal articulation, and a 4-mm steerable surgical forceps with independent jaw actuation. Both devices were fabricated using fused deposition modeling. Bench-top experiments quantified distal deflection, motion repeatability, force-related behavior, simulated task execution, and user perception. The flexible endoscope achieved effective distal deflections of 178° ± 2° vertically and 171° ± 3° horizontally while maintaining compatibility with standard 2.8-mm endoscopic instruments. During cyclic testing, it demonstrated sub-centimeter positional consistency after 1000 articulation cycles, with 95th percentile errors below 8 mm in both directions. The steerable forceps exhibited a geometric articulation range of 180°, an effective distal deflection of 85° ± 2°, and repeatable tip motion over 500 cycles, with a mean positional error of 0.26 mm. Simulated tasks were completed with high user perception scores for both prototypes. Fabrication costs were USD 166.49 for the endoscope and USD 27.75 for the forceps. These findings suggest that cable-driven architectures combined with additive manufacturing can reproduce key kinematic principles of articulated endoscopic instruments using low-cost fabrication methods. The prototypes should be interpreted as early-stage engineering demonstrators rather than clinically deployable devices.