The initial hypothesis dealt with the question of whether the CCD angle of the prosthesis decreases in the postoperative course. The results showed that after an initial decrease within the first 6 months, the averaged CCD angle was constant. In summary, the first hypothesis was confirmed.
Kutzner et al. investigated the biomechanical influence of the CCD angle using the metaphyseal anchored Optimys
® short-stem prosthesis (Mathys Ltd., Bettlach, Switzerland) in a postoperative interval of 2 years. They found that valgus alignment leads to increased initial migration, but the clinical outcomes remain unaffected [
23,
24]. Moreover, no significant correlation was found between the CCD angle and the process of “stress shielding” or cortical hypertrophy. Accordingly, a varus-emphasized positioning would allow the tip of the prosthesis to be supported along the lateral cortex, as is desired for metaphyseal short-stem prostheses. In valgus alignment, as well as if the stem sizes were chosen too small, this contact would often be absent. Luger et al. found that varus stem alignment greater than 3° increased hip offset and led to the risk of undersizing the prosthesis [
25]. Another investigation showed that there was no difference in early fracture or failure rates between varus and neutrally aligned stems. Forced intraoperative correction of mild varus stem alignment may not be necessary and would unnecessarily increase fracture risk [
26]. Another study investigated a short- to medium-term migration analysis of the Metha
® prosthesis using EBRA-FCA [
27]. Notable varus and valgus tilt were observed within the first 3 months. Especially for the Metha® prosthesis, a valgus position should be avoided, which could lead to migration without proximal-lateral support [
28]. Neither the present work nor the previously mentioned studies did the CCD angle continue to increase during the course after the initial increase. Accordingly, the initial change could be interpreted as the “settling” of the prosthesis and would depend solely on the initial positioning. A change in position would therefore be considered a sign of loosening for the Metha® prosthesis if it occurs after the initial phase of the first 6 to 12 months of “settling” [
15].