Background and research question Surgical implantation of osseointegration fixations enabling fitting of bone-anchored prostheses (BAP) could be cost-effective and improve quality of life in individuals with a transfemoral limb loss [1]. However, the safety of rehabilitation procedure must be improved before BAPs are collegially accepted as a standard of care by healthcare decision makers. Efforts are required to prevent load-related adverse events due to mechanical stresses surrounding sites of bone integration. Rehabilitation exercises following transfemoral implantation intend to apply an increasing load onto the long axis of the implant until the full bodyweight can be tolerated.

Figure 1. Monitoring osseointegration during static load bearing exercises using the current approach incorporating household bodyweight scales (A) [2] and medical imaging (B) [3]; as well as the innovative approach offered by monitoring device like Thomax 2.0 (C), that combines a portable kinetic system (D) [4], non-invasive quantitative ultrasonography (E) with 3D medical imaging (G) to inform the design of a digital twin of the residuum (F) [3] and strength of osseointegration using a handheld device (H).

Current approaches monitor the effectiveness of these exercises using mechanical personal scales (Fig 1A), which may lack measurement precision, and are moderated by pain [2]. Quantitative measures of bone structure around the medullar part of the implant, an important factor for positive clinical outcome, can be assessed using medical imaging and computational models (Fig 1B) [3]. Unfortunately, there are limited practical ways to establish the cause-and-effect relationship between the loading regime prescribed and the cortical bone thickening throughout the rehabilitation program and beyond. The study aims were (A) to review the literature on biomechanical aspects of load bearing exercises applied during rehabilitation prior to the fitting of a transfemoral BAP and (B) to identify knowledge gaps and research opportunities.

Methods The literature review focused on the monitoring of mechanical load applied during load bearing exercises following the four-phase PRISMA methods. We used MeSH keywords associated with BAP and load bearing exercises to search for references published between 2000 and 2023 in PubMed and Web of Science. Data extraction included the quantitative and qualitative characterization of publications.

Results We screened 44 references and selected 3 cohort studies focusing on the design of apparatus, loading reliability and compliance [4-6]. There are knowledge gaps regarding loading variability, stability, quantity and requirement due to the absence of instruments capable of recording the loads applied during the static and dynamic exercises and the true compliance of end-users with a prescribed load regime. This review indicated that there are research opportunities to develop load bearing monitoring devices. In 2010, a reference presented a basic apparatus relying on a tri-axial transducer [4]. Further efforts should focus a portable monitoring device (e.g., Thomax 2.0) featuring an adjustable loading frame, loading sensors (Fig 1D), and quantitative ultrasonography (Fig 1E) estimating the bone density surrounding an implant [7].

Conclusion Innovative monitoring device can productively disrupt rehabilitation pathways and health service delivery of BAP, provided that all relevant technological parts can be integrated and deemed acceptable by clinicians.