Medium Term Outcome For A Constrained Acetabular Component At A Single Institution: What Is Important For Success?

The use of constrained Total Hip Replacements (THR) is controversial due to lack of definite indications and potentially high failure rates because of mechanical loosening or component failure. A review was performed to assess a departmental use of a single constrained acetabular component over a ten years period.

Patient demographics, operative indications, complications and patient follow-up were recorded. Post-operative Oxford Hip Scores (OHS) were obtained via a combination of New Zealand Joint Registry interrogation and telephonic questioning. Cup version and inclination angles were obtained from standardised anteroposterior radiographs using established techniques.

Forty-four constrained components (in 39 patients) were implanted between 2005 and 2014. The mean age was 78 years with mean ASA 2.7 and mean follow-up 37.2 months (range 13-116). The mean post-operative OHS was 36 (SD 9.25), and there were 4 failures (3 dislocations and 1 peri-prosthetic fracture). The 3 dislocations had either cup ante version (AV) or inclination angles (IA) outside the data set interquartile range (AV 13-24°, IA 40-50°). The cup inclination was significantly lower (p<0.01) in patients with pain on sitting. At post-operative follow-up, 14/39 patients had died from unrelated causes, with only 1 patient surviving beyond 6 years.

Constrained acetabular components offer a solution to hip instability in a difficult group of patients. This study has shown good medium-term outcomes of a single component type in a predominantly frail group of low demand patients. Despite constraint, correct cup placement (particularly inclination) remains important to prevent dislocation or poor reported outcome.