Summary*: The efficacy and safety of the load applied on transfemoral osseointegrated implants by bone-anchored prostheses fitted with Power Knee (ÖSSUR) were investigated. This work contributes to systematic recording, analysis and reporting of ecological prosthetic loading profiles applied by bionics bone-anchored prostheses. Introduction/Basics*: Microprocessor-controlled knees are recommended for transfemoral bone-anchored prostheses (BAP) because they can increase efficacy and safety of implant/bone coupling (e.g., auto adaptive stance and swing control, stumble recovery, push off functions).[1, 2] To date, biomechanical advantages of BAP have been investigated for basic and state-of-the-art knees.[3-5] There is a need to broaden the evaluation of knees prescribed such as the Power Knee (ÖSSUR). This study: • Presented the loading profile applied by transfemoral BAP fitted with the Power Knee (ÖSSUR) during daily activities, • Compared the loading boundaries applied with other knees prescribed (i.e., Total Knee, Rheo Knee (ÖSSUR)), • Investigated (B) the efficacy of the load profile applied by Power Knee (i.e., walking cadence, weight acceptance, propelling load), • Investigate the safety of the loading profile considering the margin of safety between loading boundaries and the maximum loads extracted from a literature. Material/methods*: Twenty participants fitted with a transfemoral osseointegrated implant participated in this cross-sectional study (59±14 yrs, 1.74±0.10 m, 89.04±17.20 kg). An iPecsLab (RTC Electronics) measured the load applied by the Power Knee on the anatomical axes of the implant.[3, 5] The loading boundaries (maximum forces and moments) were extracted during walking, ascending and descending ramp and stairs at self-selected speed. Efficacy was assessed considering walking cadence (i.e., no more than 20% slower that benchmark data), weight acceptance (i.e., between 80%BW and 120%Bw in the first part of support phase), and propelling load (i.e., anterior force more than 10%BW and mediolateral moment more than 3 %BWm in last part of support phase). The margin of safety (MoS) calculated using loading boundary and data extracted from a study reporting internal constraints applied on femur of able-bodied during running. A MoS≥3 was deemed unlikely to compromise the integrity of bone/implant coupling.[6] Results: A total of 2,155 steps were analysed with a cadence ranging between 33±8 and 48±11 strides/min. The resultants and the components of the average absolute maximum of forces and moments applied on and around the long, anteroposterior and mediolateral axes of the implant across all activities were 99±10%BW, 98±10%BW, 18±6%BW, and 9±3%BW as well as 5.5±1.4%BWm, 0.9±0.3%BWm, 3.1±1.1%BWm, and 4.6±1.7%BWm, respectively. The resultant loading boundaries for the forces and moments applied by Power Knee were comparable to those applied by Total Knee and Rheo Knee during daily activities and noticeably smaller to those applied during a fall (Figure 1). The walking cadence was approximately 15% slower than benchmark data. The weight acceptance was between 84%BW and 102%BW. The propelling load included anterior force more than 16%BW and mediolateral moment 3.3 %BWm. These outcomes suggested that the Power Keen can restore ambulation effectively whilst applying relevant loads at the interface with the osseointegrated implant. The margin of safety across all forces and moments ranged between 3.78 and 17.62 suggesting that regular daily usage of the Power Knee could hardly be held responsible for mechanical damages, let alone catastrophic failures, of healthy bone/implant coupling. However, more work is needed to assess the MoF considering the load required to create periprosthetic fractures and breakage of implant’s parts.
Discussion/Conclusion for clinical practice*: These outcomes confirmed the efficacy and safety of the loading profile applied by the Power Knee on transfemoral osseointegrated implants. This study is an important milestone toward an evidence-based prescription of the Power Knee for transfemoral bionics BAP. More work is needed to investigate the relationships between loading profile applied by state-of-the-art bionics knees and the load-related adverse events affecting implant/bone interface (e.g., infection, loosening, periprosthetic fractures, breakage of parts). In all cases, this study provided new benchmark loading data applied by a transfemoral BAP fitted with Power Knee. It contributed to systematic recording, analysis, and reporting of ecological prosthetic loading profiles applied by lower limb BAP, that we will, hopefully, improve safety and efficacy of bionic solutions becoming available to the growing number of individuals with limb loss worldwide.
Literature references:

1. Niswander, W., W. Wang, and A.P. Baumann, Characterizing loads at transfemoral osseointegrated implants. Med Eng Phys, 2020. 84: p. 103-114.
2. Thesleff, A., et al., Loads at the Implant-Prosthesis Interface During Free and Aided Ambulation in Osseointegrated Transfemoral Prostheses. IEEE Transactions on Medical Robotics and Bionics, 2020. 2(3): p. 497-505.
3. Frossard, L., et al., Load applied on osseointegrated implant by transfemoral bone-anchored prostheses fitted with state-of-the-art prosthetic components. Clin Biomech (Bristol, Avon), 2021. 89: p. 105457.
4. Frossard, L., Loading characteristics data applied on osseointegrated implant by transfemoral bone-anchored prostheses fitted with basic components during daily activities. Data in Brief, 2019. 26: p. 104492.
5. Frossard, L., et al., Loading characteristics data applied on osseointegrated implant by transfemoral bone-anchored prostheses fitted with state-of-the-art components during daily activities. Data in Brief, 2022. 41: p. 107936.
6. Edwards, W.B., et al., Internal femoral forces and moments during running: implications for stress fracture development. Clin Biomech (Bristol, Avon), 2008. 23(10): p. 1269-78.