A novel capacitive array sensor for real-time force measurements in total knee arthroplasty

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Lawley, Alistair and Brunt, Andrew and Zhang, Dayi and Jackson, William and Razii, Nima and Wallace, David and Vidakovic, Hrvoje and Riches, Philip and Hampson, Rory and Son, Jae and MacLeod, Charles and Dobie, Gordon (2026) A novel capacitive array sensor for real-time force measurements in total knee arthroplasty. IEEE Sensors Journal. ISSN 1530-437X (https://doi.org/10.1109/JSEN.2026.3671405)

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Abstract

Achieving accurate soft-tissue balance during total knee arthroplasty (TKA) is essential for patient satisfaction. Current intraoperative assessments rely on subjective judgment. This study introduces a thin capacitive array sensor integrated into a standard trial insert to provide real-time, compartment-specific force measurements without workflow disruption. The sensor was calibrated using a robotic platform and validated in four knees from two Thielembalmed cadaveric specimens undergoing mechanically aligned, measured resection TKA. During routine trialling, force data were recorded from 0° to 110° of flexion while tibiofemoral kinematics were tracked using the PhysioPilot navigation system. The sensor achieved positional accuracy within ±3% and total force error below 4 N. The femoral measurements were stable and repeatable across the arc of motion and captured alignment-dependent loading changes. The sensor matched known biomechanical kinematic force patterns, recording peak joint forces in full extension, with a rapid decline by 15°, and stable readings beyond 60°. The force profile is consistent with what is expected in the native knee and aligns with the kinematic philosophy of the Press-Fit Condylar (PFC) multi-radius implant design. Loading asymmetries correlated with preoperative alignment: valgus knees showed lateral compartment dominance in extension, shifting medially with flexion; varus knees exhibited the reverse. Integration into standard trial components required no modification to surgical technique. Capacitive array sensing enables accurate, mechanically compatible, real-time tibiofemoral force measurement during TKA using a low-profile insert. This system provides a practical pathway toward objective soft-tissue balancing and may improve intraoperative decision-making.

ORCID iDs

Lawley, Alistair ORCID logoORCID: https://orcid.org/0000-0002-0903-1116, Brunt, Andrew, Zhang, Dayi ORCID logoORCID: https://orcid.org/0000-0003-4611-4161, Jackson, William ORCID logoORCID: https://orcid.org/0000-0002-1360-4722, Razii, Nima, Wallace, David, Vidakovic, Hrvoje, Riches, Philip ORCID logoORCID: https://orcid.org/0000-0002-7708-4607, Hampson, Rory ORCID logoORCID: https://orcid.org/0000-0001-7903-7460, Son, Jae, MacLeod, Charles ORCID logoORCID: https://orcid.org/0000-0003-4364-9769 and Dobie, Gordon ORCID logoORCID: https://orcid.org/0000-0003-3972-5917;
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