• Hip and knee surgery
• Traumatology

Although total hip arthroplasty (THA) is one of the most successful procedures in orthopaedics, there are potential disabling complications. To address instability issues, the dual-mobility (DM) THA concept was developed in France in the 1970s and has gained popularity, especially in the treatment of femoral neck fractures (FNF) and revision surgery, but it is also increasingly used in elective surgery for coxarthrosis (CA). Few studies have investigated potential wear issues associated with the DM concept or functional outcomes of DM THA, and no studies have addressed migration profiles in elderly patients.
The main aim of this thesis was to investigate the performance of primary DM THA in different clinically relevant settings in elderly patients with displaced FNF and CA. All patients included in studies I–III came from the same study cohort of FNF patients operated on between 2005 and 2016. In studies I–III, we evaluated wear of the plastic polyethylene (PE) liners and the dislocation and revision rate, as well as the postoperative functioning, health status, and satisfaction, of FNF patients. Additionally, in study IV, we wanted to evaluate radiostereometric analysis (RSA) assessed early migration patterns in cemented and cementless fixated DM THA in elderly patients who received surgery for CA.

In Study I a computer-assisted program assessed PE wear in cemented and cementless cups in 132 FNF patients, and radiographic evaluation was performed. We found that both cemented and cementless cups showed high in vivo PE wear, and cementless fixated cups had statistically significant higher PE wear compared to cemented cups. Both cup fixation methods had PE wear rates above the established osteolysis limit, but we found very few osteolytic lesions during short-term follow-up period.

Study II was a comparative cohort study in which we investigated 124 FNF patients’ functioning, health status, and satisfaction and compared the findings to a matched cohort of CA patients and the general population. At the mean follow-up period of 2.8 years, we found that 89% were satisfied with the operation’s outcome; the EQ-5D in DM THA in FNF patients was similar to the matched general population’s index, and their Oxford hip scores (OHSs) were similar to those of the matched CA THA group.

In Study III, we evaluated dislocation and revision risk in a large historic cohort of 966 consecutive patients who received DM THA for FNF. We observed 45 (4.7%) large articulation dislocations and 8 (0.8%) cup revisions. There was a non-significant trend of increased
dislocation risk in cognitively impaired patients. We observed eight intraprosthetic dislocations (IPDs), which is a complication only seen in DM THA, and six of the IPDs occurred in relation to a reduction of large articulation dislocation.

Study IV was a randomized, controlled RSA study of 30 cemented and 30 cementless DM cups in elderly patients with CA. We observed generally low migration below the migration threshold limits, which is indicative of later cup loosening. However, at the 2-year follow-up, the cementless cups showed more absolute and continuous rotational migration compared to cemented cups, as well as poorer fixation in patients with preoperartive low bone quality.
There is still much to learn about the performance of DM implants in FNF patients, as well as in patients with DM THA for CA. The findings of this thesis provide novel insights concerning the PE wear profile and functional outcomes. It is currently the single largest evaluation of complications in FNF patients, and we conducted the first RSA cup migration profile of DM THA in elderly patients.
The findings of this thesis provide novel insights concerning about PE wear, functional results, complications as well as prosthetic migration in DM implants. The dissertation highlights important perspectives of treatment and outcome that may help initiate forward progression towards improved patient care.

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