Migration analysis after total joint arthroplasty are performed using EBRA analysis (Krismer et al., 1997) or - more accurate but also much more cost-intensive and time-consuming – via radiostereometric analysis (RSA). For the latter, additional radiographs from two inclined perspectives are needed in regular intervals in order to define the position of the implant relative to tantalum bone markers which have been implanted during surgery of the artificial joint (Fig. 1). Modern analysis software promises a migration precision along the stem axis of a hip implant of less than 100 μm (Witvoet-Brahm et al., 2007). However, as the analysis is performed semi-automatically, the results are still dependent on the subjective evaluation of the X-rays by the observer. Thus, the present phantom study aims at evaluating the inter- and intra-observer reliability, the repeatability as well as the precision and gives insight into the potential and limits of the RSA method. Considering published models, an RSA phantom model has been developed which allows a continuous and exact positioning of the prostheses in all six degrees of freedom (Fig. 2). The position sensitivities of the translative and rotative positioning components are 1 μm and 5 to 24, respectively. The roentgen setup and Model-Based RSA software (3.3, Medis specials bv, Leiden, Netherlands) was evaluated using the SL-PLUS® standard hip stem (size 7, Smith & Nephew, Baar, Switzerland). The inter-observer (10 repetitions) and intra-observer (3 observers) reliability have been considered. Additionally, the influences of the model repositioning and inclination as well as the precision after migration and rotation along the stem axis are investigated.Background
Materials and Methods
Although osteochondral grafting techniques have nearly been perfected, donor site morbidity still causes concern. A synthetic β-tricalcium phospate cement was used in the attempt to obtain a primary closure of such osteochondral defects, while supplying a scaffold for tissue ingrowth. Twenty merino sheep underwent an osteochondral grafting procedure. The paste-like β-TCP cement was used to fill the ensuing cylindrical, full-thickness defect. Animals were sacrificed after 3 or 6 months. The macroscopic observations revealed neither osteophytes nor synovial proliferation, while demonstrating coverage of the defect with cartilage-like tissue. After 6 months, all defects were covered with a ”neo-cartilage” and the congruity of the joint surface was restored in 6 of 10 animals. A surface depression was found in the remaining cases. A demarkation of the defect border at the interface with the original cartilage could only be seen in 2 instances. The x-rays of the retrieved distal femurs revealed only traces of the dense β-TCP particles. Microradiographs demonstrated the incorporation of the implant. Fluorescent staining showed continuous bone ingrowth. Histologically, masses of unabsorbed TCP were irregularly distributed through-out the defect. Newly formed bone had filled much of the defect. The histological evaluation confirmed that the surface of the cement was covered with a cartilage-like tissue. This study showed, that the newly developed in-situ self-hardening resorbable β-tricalcium phosphate cement is easy to handle, hardens in a clinical-type setting, is bioactive and resorbable. Its osteoconductive effect lead to a restoration of biomechanically stable bone and allows for a normal remodeling process. Biomaterials made of β-TCP promise to play a role as a biodegradable scaffold, allowing osteo-blast ingrowth and cartilagenous resurfacing, while being fully resorbed during the process. The cement may also be used to deliver bioactive agents and cells for defect repair in the near future.
