Towards markerless computer assisted surgery: Application to total knee arthroplasty.

PURPOSE: A new approach is proposed to localise surgical instruments for Computer Assisted Orthopaedic Surgery (CAOS) that aims at overpassing the limitations of conventional CAOS solutions. This approach relies on both a depth sensor and a 6D pose estimation algorithm. METHODS: The Point-Pair Features (PPF) algorithm was used to estimate the pose of a Patient-Specific Instrument (PSI) for Total Knee Arthroplasty (TKA). Four depth sensors have been compared. Three scores have been computed to assess the performances: The Depth Fitting Error (DFE), the Pose Errors, and the Success Rate. RESULTS: The obtained results demonstrate higher performances for the Microsoft Kinect Azure in terms of DFE. The Occipital Structure core shows better behavior in terms of Pose Errors and Success Rate. CONCLUSION: This comparative study presents the first depth-sensor based solution allowing the intraoperative markerless localization of surgical instruments in orthopedics.

Learning ultrasound gesture database: building and application to musculoskeletal ultrasound exams.

Our aim is to develop a frame work for virtually learning the ultrasound exams. In this paper we address the method used to build the image database required for this frame work. The used materiel and the proposed methodology are presented and explained. The realized prototype has been used to build the database of ultrasound images.

Finite element lifetime prediction of a miniature adjustable orthopedic device.

In Total Knee Arthroplasty (TKA), accurate balancing of the medial and lateral collateral ligaments is considered by orthopedic surgeons as one of the most challenging and complicated tasks to achieve. Therefore, an efficient solution is needed to assist the surgeons in achieving this crucial task without resulting in tibiofemoral misalignment. The required solution consists in developing either a completely automated smart ligament balancer for intraoperative use or adjustable tibial implant for postoperative use. The smart ligament balancer allows the surgeon to accurately balance the collateral ligaments at the time of surgery while the adjustable tibial implant can be controlled in the postoperative period in order to correct the residual ligament imbalance. In this paper, we propose a miniature device that can be used as a smart ligament balancer during TKA or as an adjustable tibial implant in the period following the surgery. Three designs of the smart ligament balancer have been developed using 3-Dimensional (3D) Computer Assisted Design (CAD) software. The proposed balancer can also be used as an adjustable tibial implant after slightly modifying its design. Finite element study of each design has been conducted in order to predict the lifetime of this implant in both cases of intraoperative or postoperative uses.

A self-powered telemetry system to estimate the postoperative instability of a knee implant.

Estimating in vivo the life span of a total knee replacement prosthesis is currently done by estimating the polyethylene (PE) wear rate from measurement of the femorotibial distance using X-ray photographies. This efficient method requires, however, waiting for few years to obtain a readout. This letter proposes using another metric that can be obtained within a couple of months of surgery, namely the center of pressure (COP). This metric represents the point, where the axial force applies the most onto the tibial tray. The displacement of the COP with respect to its ideal position can be used to estimate the wear and the life span of the PE. This requires the implant to be fitted with a telemetry system described briefly. The proposed method is supported by measures and simulations.

Design and evaluation of instrumented smart knee implant.

The goal of ligament balancing in total knee arthroplasty (TKA) is to distribute the tibiofemoral compressive forces symmetrically between the medial and lateral compartments of a well-aligned prosthetic knee, as well as to reestablish a rectangular and identical tibiofemoral gap in both flexion and extension. Nowadays, the proper alignment of knee mechanical axis and the perfect equalization of flexion and extension gaps are ensured by computer-assisted TKA (CATKA). Nevertheless, any residual imbalance of collateral ligaments at the time of surgery can lead to an excessive imbalance in the postoperative period during the weight-bearing activities, which subject the knee collateral ligaments to increased loading. This in turn leads to an accelerated polyethylene wear, and consequently, to early failure of TKA. The instrumented tibial implant proposed in this study can postoperatively assess and monitor the progression of residual postoperative ligament imbalance of a prosthetic knee, which is perfectly aligned during the surgery thanks to CATKA, via a center-of-pressure (COP)-based approach. This approach depends on the measurement of relative displacement of COP position during the postoperative period with respect to a reference position recorded at the beginning of this period. This measurement is performed for six predetermined flexion angles representative of an entire gait cycle. The tibial implant can also generate the electrical power in addition to their role in monitoring the COP position thanks to the piezoceramics embedded within the tibial tray to achieve this twofold task. Experimental and finite-element analysis (FEA) studies have been conducted to validate the methodology used for the postoperative assessment of residual knee laxity. The issues concerning electrical energy generation and data transmission will be thoroughly discussed in another paper.

Ligament imbalance metrics and an autonomous measurement system for post TKA.

This paper describes two useful metrics to estimate the ligament imbalance for post Total Knee Arthroplasty (TKA) scenario: the center of pressure and the net moments (varus-valgus and anterior posterior). Both metrics have been evaluated using high level models and experimental measurement. Self-powered analog and digital architectures for the center of pressure are elaborated here and complies with the Medical Implant Communication Service (MICS) standard. It is shown that the analog architecture is advantageous in terms of surface area and overall power consumption.

Self-powered instrumented knee implant for early detection of postoperative complications.

In-vivo measurement of tibiofemoral forces transmitted through Total Knee Replacement (TKR) during normal walking allows the early detection of postoperative complications such as the tibiofemoral misalignment and soft-tissue imbalance. In addition, the in-vivo data can help to improve the design of TKR in order to reduce polyethylene wear and consequently to increase the lifespan of knee implant. A self-powered custom-designed tibial implant instrumented with four piezoceramics has been developed in order to detect the aforementioned complications by measuring the relative change in pressure center (COP) position for different levels of eccentric compressive loading. Moreover, the energy harvested by the piezoceramics can be used to power a transmission system located at the stem of knee implant to wirelessly transmit the in-vivo data outside the implant for further processing and display.

Toward a dynamic approach of THA planning based on ultrasound.

The risk of dislocation after THA reportedly is minimized if the acetabular implant is oriented at 45 degrees inclination and 15 degrees anteversion with respect to the anterior pelvic plane. This reference plane now is used in computer-assisted protocols. However, this static approach may lead to postoperative instability because the dynamic variations of the pelvis influence effective cup orientation and are not taken into account in this approach. We propose an ultrasound tool to register the preoperative dynamics of the pelvis for THA planning during computer-assisted surgery. To assess this pelvic behavior and its consequences on implant orientation, we tested a new 2.5-dimensional ultrasound-based approach. The pelvic flexion was registered in sitting, standing, and supine positions in 20 subjects. The mean values were -25.2 degrees +/- 5.8 degrees (standard deviation), 2.4 degrees +/- 5.1 degrees , and 6.8 degrees +/- 3.5 degrees , respectively. The mean functional anteversion varied by 26 degrees and the mean functional inclination by 12 degrees depending on the pelvic flexion. We therefore recommend including dynamic pelvic behavior to minimize dislocation risk. The notion of a safe zone should be revisited and extended to include changes with activity.