Aim

Rifampicin as a biofilm-active antibiotic drug has a significant role in the treatment of periprosthetic joint infection (PJI). However, rifampicin resistance is an increasing threat to PJI treatment. This study aimed to evaluate the prevalence of rifampicin resistant staphylococci over time and its association with infection-free survival after PJI in a single centre in Sweden.

Introduction

Several short femoral stems have been introduced in primary total hip arthroplasty, supposedly in order to save proximal bone stock. We intended to analyse primary stability, changes in periprosthetic bone mineral density (BMD), and clinical outcome after insertion of the uncemented collum femoris preserving (CFP)-femoral device.

Background: Hydroxyapatite (HA) coating is widely used for total hip arthroplasty as it has been suggested to improve implant ingrowth and long-term stability. However, the evidence behind the use of HA in femoral stems is ambiguous.

Methods: We investigated a non-cemented, tapered titanium femoral stem that was available either with or without HA coating. This stem had been used in 3,116 total hip arthroplasties (THAs) in 2,608 patients registered in the Swedish Hip Arthroplasty Register (1992–2007). Kaplan-Meier survival analysis and a Cox regression model including type of coating, age, sex, primary diagnosis, and the type of cup fixation were used to calculate adjusted risk ratios (RR) of the risk for revision for various reasons.

Results: 63.7% of the stems were coated with HA, 36.3% were uncoated. It was found that the investigated HA-coated stem had an excellent 10-year survivorship of 97.7% (95% CI 96.5–98.9), and that the stem without HA coating had a 10-year survivorship of 97.6% (95% CI 96.2–99.0) when revision due to any reason was defined as the endpoint. There was no significant difference between these two groups (p> 0.05, log rank Mantel-Cox). A Cox regression model showed that the presence of HA coating did not significantly influence the risk of stem revision due to any reason (RR 1.3; 95% CI 0.7–2.4), or due to aseptic loosening (RR 1.0; 95% CI 0.3–3.4). The risk for revision due to infection, dislocation, or fracture was also not affected by the presence of HA coating.

Interpretation: Our results show HA coating of this non-cemented tapered stem with excellent 10-year survivorship does not affect the risk for revision. The assumed beneficial effect of HA coating of femoral stems in total hip arthroplasty is thus questionable.

Background: Hydroxyapatite (HA) is the main inorganic component of bone, and HA coating is widely used on acetabular cups in hip arthroplasty. It has been suggested that this surface finish improves cup survival, but there is little evidence to support this.

Patients and methods: All patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2007 with an uncemented acetabular implant that was available with or without HA coating were identified. A study population of 8,043 hips with the most common cup types manufactured either with or without HA coating (Harris-Galante, Romanus and Trilogy) was investigated. Kaplan-Meier survival analysis and a Cox regression model including type of coating, age, sex, primary diagnosis, cup type, and type of stem fixation were used to calculate adjusted risk ratios (RR) of the risk for revision.

Results: Kaplan-Meier analysis of all patients indicated a non-significant trend towards inferior performance of the HA-coated cups (p=0.78). When stratified for age, Kaplan-Meier analysis revealed inferior survival of HA-coated cups when compared to non-coated cups in the age group < 50 years (p=0.031). A Cox regression model showed that HA coating was a significant risk factor for cup revision due to aseptic loosening (adjusted RR 1.645; 95% CI 1.315–2.058). Age at primary arthroplasty < 50 years, a diagnosis of paediatric hip disease, a cemented stem, and the Romanus and Harris-Galante cup types were also associated with significantly increased risk for cup revision due to aseptic loosening. There was no difference in the hazard patterns when the risk for revision for any reason was chosen as the endpoint of the analysis. The risk for revision due to infection was not influenced by the type of coating.

Discussion: Our results derived from register data on 8,043 hips indicate that HA coating does not enhance survival of cups when using aseptic loosening as an endpoint. On the contrary, hydroxyapatite coating is a significant risk factor for cup revision due to aseptic loosening when adjusted for other covariates such as age, sex, cup design and primary diagnosis. HA coating cannot be generally recommended as a surface treatment of acetabular cups in younger patients. This conclusion is medically and economically relevant, as many young patients today receive HA-coated cups, and because HA-coated implants are more expensive.