Vibration assessment of transfemoral implant stability: a longitudinal case series

The success of osseointegrated implants (OI) for individuals with transfemoral amputation (TFA) depends on the quality of the bone-implant interface (BII), which is difficult to track clinically. Vibration methods assess the biomechanical properties of the BII non-invasively and quantitatively. This study implements a vibration-based approach that quantifies BII stiffness ([Formula: see text]) for press-fit transfemoral osseointegrated implants . The primary objective is to assess the initial validity of using k to determine BII condition as individuals progress through rehabilitation and and after transition to unaided prosthesis use.

Implant stability measurements of four participants with TFA were longitudinally collected prospectively over a 2-year follow-up period. The measurements covered post-operative rehabilitation from static loading up to and including unaided prosthesis walking. Vibration signals were analyzed using a custom-developed application that estimates [Formula: see text] by comparing the clinically acquired vibration signal to a one-dimensional finite element model of the bone-implant system. The longitudinal changes in k were tracked, and the Mann Whitney U-test was used within each participant to compare the Early (after completion of static loading), Intermediate and Late (post-year 1) osseointegration phases. Complications and X-rays were tracked as per clinical standard.

Longitudinal [Formula: see text] measurements demonstrated high repeatability and sensitivity. Within participants, maximum to minimum [Formula: see text] ratio ranged from 2.8 to 88 times, indicating high sensitivity to potential BII changes (such as mechanical properties and/or bone-implant contact ratio) during rehabilitation. Observed patterns, such as reduced [Formula: see text] during loading followed by higher readings and plateaus later in rehabilitation, align with expectations of BII healing. At the individual level, Early and Late healing showed a significant difference [Formula: see text], with higher [Formula: see text] in the Late phase, indicating greater implant stability and sensitivity towards clinically meaningful healing.

The proposed measurement method shows promising potential for non-invasively tracking implant stability for individuals with TFA. The changes in [Formula: see text] were aligned with: expected bone-implant healing timelines, previously reported vibration assessments for other OI systems, implant survival and rehabilitation stages. The small sample size limits population level inference and generalizability of findings. Larger clinical cohorts are needed to enable population level comparisons and establish clinically relevant predictive [Formula: see text] stability/instability thresholds.