Instrumented knee joint implants: innovations and promising concepts

Abstract

This article focuses on in vivo implementations of instrumented knee implants and recent prototypes with highly innovative potential. An in-depth analysis of the evolution of these systems was conducted, including three architectures developed by two research teams for in vivo operation that were implanted in 13 patients. The specifications of their various subsystems: sensor/transducers, power management, communication and processing/control units are presented, and their features are compared. These systems were designed to measure biomechanical quantities to further assist in rehabilitation and physical therapy, to access proper implant placement and joint function and to help predicting aseptic loosening. Five prototype systems that aim to improve their operation, as well as include new abilities, are also featured. They include technology to assist proper ligament tensioning and ensure self-powering. One can conclude that the concept of instrumented active knee implant seems the most promising trend for improving the outcomes of knee replacements.

Keywords:

• energy harvesting
• instrumented orthopedic implant
• knee arthroplasty
• knee joint replacement
• load measurement
• medical device
• orthopedics
• telemetry
• therapeutic actuator

Financial & competing interests disclosure

The authors were supported by Portuguese Foundation for Science and Technology – project EXPL/EMS-SIS/2128/2013. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Key issues

• Even though considerable research has been conducted to improve implant design, revision rates of TKR are about 6% after 5 years and 12% after 10 years. The number of primary TKR procedures is increasing, especially in a younger demographic.

• Instrumented knee implants are proposed as research tools to measure biomechanical quantities in vivo. Their purpose is to collect data (forces and moments) to validate models defining the implants’ biomechanical behavior; optimize the mechanical design of standard implants; carry out preclinical testing; and track patient healing and rehabilitation after arthroplasty.

• Three architectures of instrumented TKR, comprising RF telemetry systems and resistive load measuring sensors, powered by an inductive power link, were implanted into 13 human patients.

• Up to 7 years of successful operation and in vivo data acquisition have been achieved. No revision procedures or side effects have been reported.

• None of the architectures validated in vivo were designed with therapeutic actuation systems. Only one research team proposed a prototype comprising an actuation system to control the lateral ligament tensioning, such that failures in the ligament tensioning can be overcome postoperatively.

• Currently, data acquisition events are limited to laboratorial settings due to the need of external power supply technology and supplementary kinematic measurement systems.

• New developments to acquire other biomechanical quantities, such as those related with kinematics, as well as to include sensors for monitoring critical areas where component wear (polyethylene insert) and loosening (femoral and tibial fixations) may occur.

• Improvement and optimization of electric power supply systems, especially self-powering methods, is mandatory such that the autonomy of instrumented implants can be maximized.

• Further research on patient-specific implants and ligament tensioning assistance tools may help in reducing revision risks and postoperative pain in TKR patients.

• Development of embedded noninvasive stimulation systems (electrical and/or mechanical) for instrumented implants may effectively induce and control bone growth in regions where aseptic loosening occurs.

• The design of instrumented active implants with therapeutic actuation systems seems to be the most promising trend to detect/prevent failure states (aseptic loosening, infection or component wear) in real time.