Single and bi-compartment poro-elastic model of perfused biological soft tissues: FEniCSx implementation and tutorial

Soft biological tissues demonstrate strong time-dependent and strain-rate mechanical behavior, arising from their intrinsic visco-elasticity and fluid-solid interactions. The time-dependent mechanical properties of soft tissues influence their physiological functions and are related to several pathological processes. Poro-elastic modeling represents a promising approach because it allows the integration of multiscale/multiphysics data to probe biologically relevant phenomena at a smaller scale and embeds the relevant mechanisms at the larger scale. The implementation of multiphase flow poro-elastic models however is a complex undertaking, requiring extensive knowledge. The open-source software FEniCSx Project provides a novel tool for the automated solution of partial differential equations by the finite element method. This paper aims to provide the required tools to model the mixed formulation of poro-elasticity, from the theory to the implementation, within FEniCSx. Several benchmark cases are studied. A column under confined compression conditions is compared to the Terzaghi analytical solution, using the L2-norm. An implementation of poro-hyper-elasticity is proposed. A bi-compartment column is compared to previously published results (Cast3m implementation). For all cases, accurate results are obtained in terms of a normalized Root Mean Square Error (RMSE). Furthermore, the FEniCSx computation is found three times faster than the legacy FEniCS one. The benefits of parallel computation are also highlighted.

Customised bi-compartmental knee arthroplasty shows encouraging 3-year results: findings of a prospective, multicenter study

PURPOSE

The purpose of this study was to assess the clinical and patient-reported outcomes of a customised, individually made (CIM) bi-compartmental knee arthroplasty (BKA).

METHODS

A prospectively recruited cohort of 79 patients was implanted with a CIM-BKA (patello-femoral plus either medial or lateral tibio-femoral, iDuo G2 system, Conformis, Billerica MA) at eight centres in the US and Germany. Patients were assessed for the 2011 KSS, KOOS, and ROM pre-operatively and at 2 weeks, 6 weeks, 12 weeks, 1 year, and 2 years post-operatively.

RESULTS

The objective KSS score significantly improved from 69 at the pre-operative visit, to 94 at the 2-year post-operative time-point. Similar improvements were observed for the KSS function and satisfaction domains. Significant improvements from pre-operative levels were observed across all five domains of the KOOS. Two patients have undergone surgery to revise their CIM-BKA implant to total knees, resulting in a survivorship rate of 97.5% at an average follow-up of 2.6 years.

CONCLUSIONS

CIM-BKA compares favourably to published scores as well as revision rates for previously available monolithic OTS-BKA implants. CIM-BKA implants provide surgeons with a viable and patient-specific monolithic implant solution as an option for patients presenting with bi-compartmental disease, who might, otherwise, be treated by performing uni-condylar + patello-femoral joint or bicruciate sparing TKA surgeries. Longer follow-up and higher numbers have to be awaited for further validation of these encouraging early results.

LEVEL OF EVIDENCE

3b (individual case-controlled study).