Is There Safety Outside the "Safe Zone" in Total Hip Replacement? A Retrospective Observational Study

Background and Objectives: The safe zone in total hip replacement was introduced many years ago. Its aim was to provide guidelines for orthopedic surgeons in order to avoid complications such as instability. With the growing interest in spinopelvic alignment, some new insights suggest that the safe zone is an obsolete concept. This study aims to show that, even outside the safe zone, the effect of total hip replacement can be satisfactory. This could be used as preliminary study for an analysis of a larger group. Materials and Methods: Fifty-nine consecutive patients with end-stage osteoarthritis treated by total hip replacement were enrolled into the study and divided into two groups: inside the safe zone and outside the safe zone. A physical examination during postoperative visits was performed; the range of movement was measured using a goniometer; and the HHS and VAS were taken to measure functional outcomes and pain, respectively. An analysis of the radiological outcomes was performed. Results: There was no significant difference in regard to changes in total offset, pain, HHS and other complications. There were no signs of instability among patients during the follow-up. Conclusions: The results of this study show that the "safe zone" is a more complicated term that was previously thought. A proper soft tissue balance and spinopelvic alignment could be factors that change the "safe zone" for each patient and make it more individual.