CLINICAL UTILITY OF T-SMART TOMOSYNTHESIS FOR THE EVALUATION OF BONE INGROWTH AND PROXIMAL LOAD TRANSFER IN MICRO MAX STEM TOTAL HIP ARTHROPLASTY

Background Cementless short stems have the advantages of easy insertion, reduced thigh pain and being suitable for minimally-invasive surgery, therefore cementless short stem implants have been becoming more widely used. The revelation microMAX stem is a cementless short stem with a lateral flare design that allows for proximal physiological load transmission and more stable initial fixation. Images acquired with T-smart tomosynthesis using a new image reconstruction algorithm offer reduced artifacts near metal objects and clearer visualization of peri-implant trabeculae. Therefore, these images are useful for confirming implant fixation status after total hip arthroplasty (THA). We believe that T-smart tomosynthesis is useful for estimating the condition of microMAX stem fixation and will hereby report on observation of the postoperative course of microMAX stem. Materials and Methods Subjects comprised 19 patients (20 hips) who underwent THA using micro MAXstem between July 2012 and November 2014 (males: 7, females: 12, mean age: 67 years, ranging from 38 to 83 years). Four patients had femoral head necrosis and 15 patients had osteoarthritis of the hip. All patients continuously underwent anterior-posterior and lateral view X-ray examination and an anterior-posterior T-smart tomosynthesis scan after the operations. Results No stem loosening was noted in any subjects. X-ray images taken over time indicated spot welds in 12 hips (60%), while T-smart tomosynthesis showed spot welds in 19 hips (95%). Furthermore, reactive radiodense lines (tensile area) were noted on X-ray images of eight hips (40%), whereas they were detected by T-smart tomosynthesis in 10 hips (50%). A prominent reactive line around the tip of the stem was noted on X-ray images in three hips (15%), and this was detected by T-smart tomosynthesis in four hips (20%). Discussion Compared to X-ray examination, T-smart tomosynthesis made it possible to perform detailed confirmation of trabecular structure. In this series, spot welds were confirmed in the proximal load area according to the micro MAXstem design concept. Tomosynthesis images of trabeculae and trabecular structure can be confirmed in more detail than X-ray or computed tomography images. This information is beneficial for understanding the state of load transmission and implant fixation. Conclusions The addition of tomosynthesis to micro MAXstem postoperative evaluation made it possible to accurately grasp the state of fixation between implant and bone.