The weak cement-bone and prosthesis-cement interfaces can cause aseptic loosening of femoral component. Reliable evaluation of cementation quality as well as the research of methods to enhance these two interfaces influences the long-term fixation of the stem.
In this PhD project we investigated a new radiological evaluation method of cementing technique, the influence of proximal stem centralizer on adequacy of cement mantle and the effect of prosthesis’ preheating on migration rates of femoral component after the total hip arthroplasty.
I. Assessment of the cementing quality after hip arthroplasty: comparison of Barrack’s grading with a new simplified cementation score.
II. No benefit of a proximal stem centralizer in cementing of femoral prosthesis in human cadaveric femora. Measures of intramedullary pressure, cement penetration, cement mantle thickness, and positioning of the stem
III. Preheating of cemented femoral component in hip arthroplasty. Prospective randomized double-blinded study using radiostereometry, dual-energy X-ray absorptiometry and clinical scores.
IV. In-vivo temperature profile at cement-bone interface under cementation of preheated femoral component.
Short description of the studies:
Paper I: Postoperative radiographs after total hip arthroplasty and hemi-hip arthroplasty were evaluated by three observers independently on two occasions. To determine the reliability of the two grading systems, inter- and intraobserver agreement was calculated by using the weighted kappa statistic. Both systems showed a low rate of intra- and interobserver agreement; therefore, conclusions about cementation quality of the femoral stem based on their use are unreliable. In assessing cementation quality the use of conventional radiographs cannot be advised.
Paper II: Eight femoral prostheses with and eight femoral prostheses without proximal centralizer were cemented in eight pairs of embalmed cadaveric femora. Intamedullary pressures under stem insertion were recorded. Computer tomography scanning of specimens was performed to evaluate stem alignment, whereas cement penetration, the thickness of the cement mantle and stem centralization at the metaphyseal part of femur were measured using stereology.
No significant differences of any measured parameters were found between the groups. Proximal stem centralizer did not increase neither the intramedullary pressures nor cement penetration when using the high viscosity cement. It has also failed to improve the positioning of the femoral component at medullary canal. New prosthesis designs and improvements of cementation technique should be investigated thoroughly at true-to life trials before clinical use.
Paper III. This prospective double blind randomized clinical study was approved by local ethical committee. We have randomly allocated 80 patients undergoing the hybrid total hip arthroplasty to either the group 1, where femoral component was preheated to 40° of Celsius prior cementation or the group 2 where femoral component was of room temperature. The patients were followed both clinically and radiographically (radiostereometry and DEXA) at 3, 12 and 24 months postoperatively. Preheating improved the initial stability of stem, especially subsidence inside the cement mantle was inhibited. However the loss of stability after 1 year among small-sized stems in both groups strongly indicates that this particular stem had a great risk to debond and to develop aseptic loosening.
Paper IV. We performed in vivo temperature measurements at cement-bone interface during cementation of femoral components. This investigation was a part of the previous study (Paper III), where temperature profiles of preheated and non-preheated stems were compared. Mean peak temperature was increasing in preheated stem group (55.1° vs 51.9°), and a mean duration of temperature exceeding 50° was 16 sec longer than in control group (70 vs 54 sec). Registering of cement curing temperature at cement-bone interface in vivo is a difficult task. However, a better understanding of heat generation at cement-bone interface when cementing stems of different temperatures can be achieved.