Operating time and survival of primary total hip replacements: an analysis of 31,745 primary cemented and uncemented total hip replacements from local hospitals reported to the Norwegian Arthroplasty Register 1987-2001.

Background: Some studies have found a significant decrease in operating time as a result of standardizing programs for hip surgery. To study the influence of operating time (skin to skin) on survival of total hip replacements, we investigated the operating time in local hospitals in Norway. We have found no other large published series of THRs investigating operating time and revision.

Patients and methods: The study was based on 31,745 primary THRs reported to the Norwegian Arthroplasty Register from 47 local hospitals during 1987-2001. Operating time was divided into 7 categories, and for each category separate Kaplan-Meier curves and adjusted failure rate ratios were calculated.

Results: The mean operating time for all local hospitals in Norway was 96 (68-130) min. Increasing operating volume from less than 10 THRs/hospital/year to more than 200 THRs/hospital/year was associated with a 25-min decrease in mean operating time in cemented THRs and a 35-min decrease in the case of uncemented THRs. With the operating time category of 71-90 min as reference category, cemented THRs that lasted more than 150 min had a two-fold increased (95% CI: 1.6-2.6) revision rate. For uncemented implants, the revision rate was 1.3 times higher (95% CI: 0.8-2.2). Cemented implants with operating time under 51 min and over 90 min were associated with an increased risk of revision due to aseptic loosening. Cemented implants with operating time over 150 min were associated with an increased risk of revision due to infection.

Interpretation: Hospitals with long operating times should consider the potential benefit of reducing these times, as this may lead to lower revision rates and increased operating volumes. Shorter operation times could be achieved by standardization programs, but one should bear in mind that for cemented implants very short operating times also increased revision risk due to aseptic loosening.