ABSTRACT
Waterjet cutting technology is considered a promising technology to be used for minimally invasive removal of interface tissue surrounding aseptically loose hip prostheses. The goal of this study was to investigate the feasibility of waterjet cutting of interface tissue membrane. Waterjets with 0.2 mm and 0.6 mm diameter, a stand-off distance of 5 mm, and a traverse speed of 0.5 mm/s were used to cut interface tissue samples in half. The water flow through the nozzle was controlled by means of a valve. By changing the flow, the resulting waterjet pressure was regulated. Tissue sample thickness and the required waterjet pressures were measured. Mean thickness of the samples tested within the 0.2 mm nozzle group was 2.3 mm (SD 0.7 mm) and within the 0.6 mm nozzle group 2.6 mm (SD 0.9 mm). The required waterjet pressure to cut samples was between 10 and 12 MPa for the 0.2 mm nozzle and between 5 and 10 MPa for the 0.6 mm nozzle. Cutting bone or bone cement requires about 3 times higher waterjet pressure (30-50 MPa, depending on used nozzle diameter) and therefore we consider waterjet cutting as a safe technique to be used for minimally invasive interface tissue removal.
Subject(s)
Hip Prosthesis , Minimally Invasive Surgical Procedures/methods , Prosthesis Failure , Water , Feasibility Studies , Humans , Membranes/cytology , Membranes/surgery , Minimally Invasive Surgical Procedures/instrumentation , PressureABSTRACT
The main cause of failure in total hip replacement is aseptic loosening which is associated with the formation of a periprosthetic fibrous (interface) tissue. Despite important applications for finite element modeling of loose implants, the mechanical properties of the bone-implant interface tissue have never been measured in humans. In this study, we performed unconfined compression tests to characterize the mechanical properties of the interface tissue and to determine the parameters of various hyperelastic material models which were fitted to the measurements. Human interface tissues were retrieved during 21 elective revision surgeries from aseptically loosened cemented (N=10) and uncemented hip implants (N=11). Specimens were tested at a fixed deformation rate of 0.1mm/min up to a maximum force of 10N. Elastic moduli for low and high strain regions of the stress-strain curves were determined. Interface tissue from aseptically loose cemented prostheses shows higher elastic moduli (mean=1.85MPa, 95% C.I.=1.76-1.95MPa) in the high strain region as compared to that of the interface tissue from the cementless group (mean=1.65MPa, 95% C.I.=1.43-1.88MPa). The 5-terms Mooney-Rivlin model ( [Formula: see text] ) described the stress-strain behavior the best. Large variations in the mechanical behavior were observed both between specimens from the same patient as between those of different patients. The material model parameters were therefore estimated for the mean data as well as for the curves with the highest and lowest strain at the maximum load. The model parameters found for the mean data were C1=-0.0074MPa, C2=0.0019MPa, C3=0MPa, C4=-0.0032MPa and C5=0MPa in the cemented group and C1=-0.0137MPa, C2=0.0069MPa, C3=0.0026MPa, C4=-0.0094MPa and C5=0MPa in the cementless group. The results of this study can be used in finite element computer.
Subject(s)
Arthroplasty, Replacement, Hip , Hip Joint/cytology , Hip Prosthesis , Materials Testing , Mechanical Phenomena , Prosthesis Failure , Aged , Aged, 80 and over , Compressive Strength , Elastic Modulus , Female , Humans , Male , Middle Aged , Models, BiologicalABSTRACT
Aseptic loosening is the major failure mode for hip prostheses. Currently, loosened prostheses are revised during open surgery. Because of a high complication rate, this demanding procedure cannot be performed in patients with a poor general health. We are developing an alternative minimally invasive refixation procedure that leaves the prostheses in place, but relies on removing the interface membrane and replacing it with bone cement. The aim of this study was to evaluate two interface tissue removal techniques - Ho:YAG laser and coblation - based on two criteria: thermal damage and the ablation rate. In vitro a loosened hip prosthesis was simulated by implanting a prosthesis in each of 10 cadaver femora. Artificially created peri-prosthetic lesions were filled with chicken liver as an interface tissue substitute. We measured temperatures in vitro at different radial distances from the site of removal. Temperatures during removal were recorded both inside the interface tissue and in the surrounding bone. This study demonstrated that temperatures generated in the bone do not result in thermal damage (increasing less than 10°C relative to body temperature). Temperatures inside the interface tissue are sufficiently high to destroy the interface tissue (T>50°C, duration>1 min). Using laser instead of coblation for the removal of interface tissue resulted in higher temperatures - thus a faster removal of interface tissue. This is in accordance with the ablation rate test. Ho:YAG laser is advantageous compared to coblation. We consider Ho:YAG laser a promising tool for interface tissue removal.
Subject(s)
Arthroplasty, Replacement, Hip/methods , Hip Prosthesis/adverse effects , Laser Therapy/methods , Lasers, Solid-State/therapeutic use , Prosthesis Failure , Aged , Aged, 80 and over , Biomedical Engineering , Bone Cements/therapeutic use , Cadaver , Female , Hot Temperature , Humans , In Vitro Techniques , Laser Therapy/adverse effects , Laser Therapy/instrumentation , Lasers, Solid-State/adverse effects , Male , Minimally Invasive Surgical Procedures/methods , Models, Biological , Reoperation/methodsABSTRACT
OBJECTIVE: Computed tomography is the modality of choice for measuring osteolysis but suffers from metal-induced artefacts obscuring periprosthetic tissues. Previous papers on metal artefact reduction (MAR) show qualitative improvements, but their algorithms have not found acceptance for clinical applications. We investigated to what extent metal artefacts interfere with the segmentation of lesions adjacent to a metal femoral implant and whether metal artefact reduction improves the manual segmentation of such lesions. MATERIALS AND METHODS: We manually created 27 periprosthetic lesions in 10 human cadaver femora. We filled the lesions with a fibrotic interface tissue substitute. Each femur was fitted with a polished tapered cobalt-chrome prosthesis and imaged twice--once with the metal, and once with a substitute resin prosthesis inserted. Metal-affected CTs were processed using standard back-projection as well as projection interpolation (PI) MAR. Two experienced users segmented all lesions and compared segmentation accuracy. RESULTS: We achieved accurate delineation of periprosthetic lesions in the metal-free images. The presence of a metal implant led us to underestimate lesion volume and introduced geometrical errors in segmentation boundaries. Although PI MAR reduced streak artefacts, it led to greater underestimation of lesion volume and greater geometrical errors than without its application. CONCLUSION: CT metal artefacts impair image segmentation. PI MAR can improve subjective image appearance but causes loss of detail and lower image contrast adjacent to prostheses. Our experiments showed that PI MAR is counterproductive for manual segmentation of periprosthetic lesions and should be used with care.
