A new technique for measuring wear in total hip arthroplasty using computed tomography

Effect of head size, head material, and radiation dose on the repeatability of CT-RSA measurements of femoral head penetration

BACKGROUND

The risk of early revision of total hip arthroplasty (THA) for polyethylene wear is now low, but there remains a need to perform wear measurements in patients for clinical surveillance. The gold standard of wear measurements has been radiostereometric analysis (RSA), which has limited availability. The use of computed tomography (CT) to perform THA wear measurement was described a decade ago and found to have acceptable accuracy and precision, but high radiation dose was a concern. Additionally, the use of larger femoral head sizes and ceramic femoral heads has risen in the past decade. The objectives of the study were to determine the effect of femoral head size, femoral head material, and lowered radiation dose on femoral head penetration measurement repeatability.

METHODS

A cadaveric hip was implanted with a cementless THA implant system. CT scans were acquired at a conventional radiation dose and at a reduced dose and repeated for a 32 mm and 36 mm cobalt-chromium femoral heads and a 32 mm ceramic femoral head. Apparent translation of the femoral head versus the acetabular cup was measured between the repeated scans using a CT-RSA software, where deviations from zero indicated measurement precision.

RESULTS

The mean and standard deviation of translations in all planes was <0.200 mm. There was no effect for 3D translation of increasing cobalt-chromium head size (p = 0.2252). Cobalt-chromium heads had superior repeatability compared to ceramic heads at reduced dose (p = 0.022), but not at conventional dose (p = 0.1265). Further, superior repeatability was achieved with the reduced dose scan for the cobalt-chromium head (p = 0.0058), however there was no difference between doses for the ceramic head (p = 0.8148).

DISCUSSION

CT-based wear measurement repeatability is excellent and consistent with prior literature even when implementing a larger femoral head, a ceramic femoral head, or reducing radiation dose to 25% of a conventional clinical scan.

Implant migration and bone mineral density measured simultaneously by low-dose CT scans: a 2-year study on 17 acetabular revisions with impaction bone grafting

Background and purpose - Early postoperative implant migration predicts failure of joint replacements. Bone mineral density reflects bone quality and bone-graft incorporation. Implant migration and bone densitometry analysis usually require special equipment. We investigated cup migration and bone mineral density changes simultaneously with low-dose CT scans after acetabular revision hip arthroplasty using impaction bone grafting.Patients and methods - We performed a low-dose CT postoperatively, after 6 weeks, and after 2 years in 17 patients, all revised using impaction bone grafting and a graft-compressing titanium shell in the acetabulum. 6 patients had combined segmental and cavitary acetabular defects. Cup migration was analyzed using CT-based micromotion analysis (CTMA). Bone mineral density was determined in the graft and in surrounding native bone using volumetric quantitative computed tomography (QCT). The bone graft volume was calculated from 3D reconstructions.Results - At 2 years, the translations were 1.5 (95% CI 0.4-2.6) mm in proximal direction, -0.6 (CI -1.6 to 0.4) in the medial direction and 0.3 (CI 0.0-0.6) in the anterior direction. The mean volume of impacted bone graft was 40 cm³ (CI 28-52). In the graft bone mineral density increased 14% after 6 weeks and 23% after 2 years. There was 1 mechanical failure.Interpretation - Proximal migration of the acetabular component was low and comparable to previous reports. There was a rapid increase of bone mineral density in the bone graft. Low-dose CT scans make migration analysis and bone densitometry measurements possible in the same setting, offering great diagnostic potential for hip arthroplasty patients.

Prosthetic liner wear in total hip replacement: a longitudinal 13-year study with computed tomography

This case report follows a woman who had a total hip replacement in 1992 when she was 45 years old. Six serial computed tomography (CT) examinations over a period of 13 years provided information that allowed her revision surgery to be limited to liner replacement as opposed to replacement of the entire prosthesis. Additionally, they provided data that ruled out the presence of osteolysis and indeed none was found at surgery. In 2004, when the first CT was performed, the 3D distance the femoral head had penetrated into the cup was determined to be 2.6 mm. By 2017, femoral head penetration had progressed to 5.0 mm. The extracted liner showed wear at the thinnest part to be 5.5 mm, as measured with a micrometer. The use of modern CT techniques can identify problems, while still correctable without major surgery. Furthermore, the ability of CT to assess the direction of wear revealed that the liner wear changed from the cranial to dorsal direction.

Avaliação radiográfica e tomográfica de cães submetidos à artroplastia coxofemoral total híbrida

RESUMO A artroplastia total da articulação coxofemoral é a técnica cirúrgica mais efetiva para o tratamento da displasia coxofemoral canina grave. Na atualidade, o exame radiográfico é o método mais utilizado para se avaliar esse procedimento em cães, porém possui algumas limitações. Já o exame tomográfico por meio de tomografia computadorizada possibilita a aquisição de imagens sem sobreposições e, dessa forma, a determinação do posicionamento dos componentes protéticos com maior precisão. A presente pesquisa teve como objetivo avaliar, por meio de exames radiográficos e tomográficos, a utilização de uma prótese total modular híbrida da articulação coxofemoral desenvolvida e confeccionada no Brasil, aplicada experimentalmente em cães sadios. Foram utilizados seis cães esqueleticamente maduros, previamente submetidos ao procedimento cirúrgico da articulação coxofemoral esquerda. Os cães foram submetidos ao exame tomográfico aos 360 dias e três anos após a cirurgia. Todos os animais apresentaram bom posicionamento dos componentes protéticos e redução articular adequada. Ao exame tomográfico, entretanto, foram detectadas áreas de preenchimento irregular em alguns animais. Adicionalmente, o exame tomográfico permitiu a detecção e monitoração de áreas de reabsorção óssea ao redor do componente acetabular. Assim, o exame tomográfico mostrou-se útil na avaliação das articulações protéticas, com a vantagem de apresentar ótima definição das imagens e permitir quantificar alterações periprotéticas e mensurar relações articulares, fundamentais para o acompanhamento pós-cirúrgico tardio.

Accuracy and Precision of Three-Dimensional Low Dose CT Compared to Standard RSA in Acetabular Cups: An Experimental Study

Background and Purpose. The gold standard for detection of implant wear and migration is currently radiostereometry (RSA). The purpose of this study is to compare a three-dimensional computed tomography technique (3D CT) to standard RSA as an alternative technique for measuring migration of acetabular cups in total hip arthroplasty. Materials and Methods. With tantalum beads, we marked one cemented and one uncemented cup and mounted these on a similarly marked pelvic model. A comparison was made between 3D CT and standard RSA for measuring migration. Twelve repeated stereoradiographs and CT scans with double examinations in each position and gradual migration of the implants were made. Precision and accuracy of the 3D CT were calculated. Results. The accuracy of the 3D CT ranged between 0.07 and 0.32 mm for translations and 0.21 and 0.82° for rotation. The precision ranged between 0.01 and 0.09 mm for translations and 0.06 and 0.29° for rotations, respectively. For standard RSA, the precision ranged between 0.04 and 0.09 mm for translations and 0.08 and 0.32° for rotations, respectively. There was no significant difference in precision between 3D CT and standard RSA. The effective radiation dose of the 3D CT method, comparable to RSA, was estimated to be 0.33 mSv. Interpretation. Low dose 3D CT is a comparable method to standard RSA in an experimental setting.

A novel method to measure femoral component migration by computed tomography: a cadaver study

INTRODUCTION

Radiostereometric analysis (RSA) is the most accurate technique to measure implant migration. However, it requires special equipment, technical expertise and analysis software and has not gained wide acceptance. The current paper analyzes a novel method to measure implant migration utilizing widely available computer tomography (CT).

METHODS

Three uncemented total hip replacements were performed in three human cadavers and six tantalum beads were inserted into the femoral bone similar to RSA. Six different 28 mm heads (-3, 0, 2.5, 5.0, 7.5 and 10 mm) were added to simulate five reproducible translations (maximum total point migration) of the center of the head. Implant migration was measured in a 3-D analysis software (Geomagic Studio 7). Repeat manual reconstructions of the center of the head were performed by two investigators to determine repeatability and accuracy.

RESULTS

The accuracy of measurements between the centers of two head sizes was 0.11 mm with a CI 95 % of 0.22 mm. The intra-observer repeatability was 0.13 mm (CI 95 % 0.25 mm). The interrater-reliability was 0.943.

CONCLUSION

CT based measurement of head displacement in a cadaver model were highly accurate and reproducible.

In vivo and ex vivo measurement of polyethylene wear in total hip arthroplasty: comparison of measurements using a CT algorithm, a coordinate-measuring machine, and a micrometer

BACKGROUND

Determination of the amount of wear in a polyethylene liner following total hip arthroplasty (THA) is important for both the clinical care of individual patients and the development of new types of liners.

PATIENTS AND METHODS

We measured in vivo wear of the polyethylene liner using computed tomography (CT) (obtained in the course of regular clinical care) and compared it to coordinate-measuring machine (CMM) readings. Also, changes in liner thickness of the same retrieved polyethylene liner were measured using a micrometer, and were compared to CT and CMM measurements. The distance between the centers of the acetabular cup and femoral head component was measured in 3D CT, using a semi-automatic analysis method. CMM readings were performed on each acetabular liner and data were analyzed using 3D computer-aided design software. Micrometer readings compared the thickest and thinnest regions of the liner. We analyzed 10 THA CTs and retrievals that met minimal requirements for CT slice thickness and explanted cup condition. RESULTS - For the 10 cups, the mean difference between the CT readings and the CMM readings was -0.09 (-0.38 to 0.20) mm. This difference was not statistically significant (p = 0.6). Between CT and micrometer, the mean difference was 0.11 (-0.33 to 0.55) mm. This difference was not statistically significant (p = 0.6). INTERPRETATION - Our results show that CT imaging is ready to be used as a tool in clinical wear measurement of polyethylene liners used in THA.

A new automated way to measure polyethylene wear in THA using a high resolution CT scanner: method and analysis

As the most advantageous total hip arthroplasty (THA) operation is the first, timely replacement of only the liner is socially and economically important because the utilization of THA is increasing as younger and more active patients are receiving implants and they are living longer. Automatic algorithms were developed to infer liner wear by estimating the separation between the acetabular cup and femoral component head given a computed tomography (CT) volume. Two series of CT volumes of a hip phantom were acquired with the femoral component head placed at 14 different positions relative to the acetabular cup. The mean and standard deviation (SD) of the diameter of the acetabular cup and femoral component head, in addition to the range of error in the expected wear values and the repeatability of all the measurements, were calculated. The algorithms resulted in a mean (± SD) for the diameter of the acetabular cup of 54.21 (± 0.011) mm and for the femoral component head of 22.09 (± 0.02) mm. The wear error was ± 0.1 mm and the repeatability was 0.077 mm. This approach is applicable clinically as it utilizes readily available computed tomography imaging systems and requires only five minutes of human interaction.