Personalised high tibial osteotomy has mechanical safety equivalent to generic device in a case-control in silico clinical trial

Effect of different constraining boundary conditions on simulated femoral stresses and strains during gait

Finite element analysis (FEA) is commonly used in orthopaedic research to estimate localised tissue stresses and strains. A variety of boundary conditions have been proposed for isolated femur analysis, but it remains unclear how these assumed constraints influence FEA predictions of bone biomechanics. This study compared the femoral head deflection (FHD), stresses, and strains elicited under four commonly used boundary conditions (fixed knee, mid-shaft constraint, springs, and isostatic methods) and benchmarked these mechanics against the gold standard inertia relief method for normal and pathological femurs (extreme anteversion and retroversion, coxa vara, and coxa valga). Simulations were performed for the stance phase of walking with the applied femoral loading determined from patient-specific neuromusculoskeletal models. Due to unrealistic biomechanics observed for the commonly used boundary conditions, we propose a novel biomechanical constraint method to generate physiological femur biomechanics. The biomechanical method yielded FHD (< 1 mm), strains (approaching 1000 µε), and stresses (< 60 MPa), which were consistent with physiological observations and similar to predictions from the inertia relief method (average coefficient of determination = 0.97, average normalized root mean square error = 0.17). Our results highlight the superior performance of the biomechanical method compared to current methods of constraint for  both healthy and pathological femurs.

Developing and Validating a Model of Humeral Stem Primary Stability, Intended for In Silico Clinical Trials

In silico clinical trials (ISCT) can contribute to demonstrating a device's performance via credible computational models applied on virtual cohorts. Our purpose was to establish the credibility of a model for assessing the risk of humeral stem loosening in total shoulder arthroplasty, based on a twofold validation scheme involving both benchtop and clinical validation activities, for ISCT applications. A finite element model computing bone-implant micromotion (benchtop model) was quantitatively compared to a bone foam micromotion test (benchtop comparator) to ensure that the physics of the system was captured correctly. The model was expanded to a population-based approach (clinical model) and qualitatively evaluated based on its ability to replicate findings from a published clinical study (clinical comparator), namely that grit-blasted stems are at a significantly higher risk of loosening than porous-coated stems, to ensure that clinical performance of the stem can be predicted appropriately. Model form sensitivities pertaining to surgical variation and implant design were evaluated. The model replicated benchtop micromotion measurements (52.1 ± 4.3 µm), without a significant impact of the press-fit ("Press-fit": 54.0 ± 8.5 µm, "No press-fit": 56.0 ± 12.0 µm). Applied to a virtual population, the grit-blasted stems (227 ± 78µm) experienced significantly larger micromotions than porous-coated stems (162 ± 69µm), in accordance with the findings of the clinical comparator. This work provides a concrete example for evaluating the credibility of an ISCT study. By validating the modeling approach against both benchtop and clinical data, model credibility is established for an ISCT application aiming to enrich clinical data in a regulatory submission.

A simple formula to control posterior tibial slope during proximal tibial osteotomies

BACKGROUND

High tibial osteotomy surgery is a widely successful joint-preserving procedure which alters the hip-knee-ankle axis which can delay the progression of osteoarthritis; however, conventional osteotomy surgical procedures do not adequately control the posterior tibial slope. This study aimed to determine the key variables influencing posterior tibial slope during high tibial osteotomy and provide a simple means of implementing the findings during pre-operative planning.

METHODS

A virtual cohort of twenty-eight proximal tibia geometries of knee osteoarthritis patients was used in the study. Firstly, absolute posterior tibial slope values were contrasted using anatomical and posterior mechanical axis measurement approaches. Secondly, the influence of variables affecting posterior tibial slope change during osteotomy surgery was investigated using 3D preoperative planning surgical simulation and analytical modelling.

FINDINGS

There was a poor correlation (R2 = 0.38) between the different clinical measurements of posterior tibial slope; with an average of 7.0 ± 1.3° and 14.8 ± 2.2° respectively. An analytical solution for the change in posterior tibial slope was derived based on the hinge axis angle and the osteotomy opening angle. For three different opening angles (6°, 9° and 12°) and seven different hinge axis orientations (-30° to +30°), the results obtained were identical for the analytical model and the 3D preoperative planning.

INTERPRETATION

This study determined that the key variables affecting posterior tibial slope during high tibial osteotomy are the osteotomy opening angle and the hinge axis orientation. The derived formula provides a simple means of determining the change in posterior tibial slope resulting from a particular surgical approach.

Personalised opening wedge high tibial osteotomy with patient-specific plates and instrumentation accurately controls coronal correction and posterior slope: Results from a prospective first case series

BACKGROUND

Patient specific devices represent a promising tool to improve accuracy and simplify high tibial osteotomy (HTO) procedures. The current study aims to assess accuracy of the correction of alignment and posterior tibial slope (PTS), and provide patient reported outcomes (PROMs) of a new personalised cutting guide and fixation plate (TOKA) system for HTO in patients with medial osteoarthritis (OA) and varus knee.

METHODS

25 patients (mean age 54.4 years) with medial OA and varus knee malalignment who underwent HTO with the TOKA system were prospectively evaluated pre-operatively, 1, 3, 6 and 12-months follow-up. Standing long-leg and lateral radiographs of the knee were used to assess the hip-knee-ankle (HKA) angle and the PTS, respectively. Accuracy was defined as the difference in planned minus achieved correction. The patient reported outcomes collected were the KOOS score, EQ5D, KSS score, and VAS pain scores. All statistical analyses were performed using IBM SPSS Statistics for Windows.

RESULTS

The mean preoperative HKA was 170.7° (SD ± 3.2°); the mean postoperative HKA was 177.4° (SD ± 2.9°). The overall mean difference between planned and achieved correction in terms of HKA was 2.1° (SD ± 2.0°). The mean difference between planned and achieved PTS was 0.2° (SD ± 0.4°). All the assessed PROMs had a significant (p < 0.001) increase from the pre-operative value to postoperative evaluation and showed a significant (p < 0.001) improvement with follow-up time.

CONCLUSIONS

TOKA personalised HTO system showed accurate correction in terms of both coronal and sagittal alignment, and excellent patient reported outcomes.

LEVEL OF EVIDENCE

4, prospective case series. Registration in public trial registry: registered at ClinicalTrial.gov [NCT04574570].