Aims: Periprosthetic osteolysis, generally ascribed to cup polyethylene debris is the most common reason for revision THR. We carried out a radiological – retrieval study in 63 patients undergoing revision THR in order to explore potential correlation between osteolysis and wear in the cup. Material and Methods: 43 intact polyethylene liners were retrieved following revision THR because aseptic loosening. Radiological osteolysis was assessed from the De Lee and Gruen zones. The linear wear depth in the cups was measured using the shadowgraph technique and the volumetric wear was assessed using the Hashimoto formula. Statistical analysis was performed using the SPSS® software package. Results: There was a statistically significant inverse correlation between Volumetric Wear Rate (VWR)-Total Femoral Osteolysis (TFO) (p=0.024), VWR -Total Osteolysis TO (p=0.003), Volumetric Wear (VW) – TFO (p=0.015), and a trend between VW – TO (p=0.087). This shows that increased levels of osteolysis appear to be associated with lower VWR. Conclusions: Overall these results demonstrate an overall inverse relationship between long term wear of the polyethylene and periprosthetic osteolysis in pre-revision patients. Restriction in the mobility-activity could be a reason for that.

Aims: The reliability of accurately determining wear in polyethylene cups using plain x-rays has been questioned by many authors. In order to explore the accuracy of wear assessment radiologically, we carried out a radiological-retrieval study in 63 patients undergoing revision THR.

Methods:We retrieved 45 intact polyethylene liners from patients after revision THR. The Linear Wear Depth (LWD) in the cups was assessed radiologically measuring the femoral head eccentricity on the plain non-weight bearing x-ray films. The LWD was assessed in the laboratory using the shadowgraph technique. Statistical analysis was performed using the SPSS® software package.

Results: Themean radiological eccentricity of the femoral head was 2.09±2.17 mm (ranging from 0 to 9.50) and the mean LWD 3.52±1.85 mm (ranging from 0.50 to 9.29). The results of Wilcoxon sign ranks test indicated that this 1.43mm-difference is statistically significant (p< 0.001). The measured wear on the plain x-rays was 40,6% less than the true linear wear measured on the retrieved cup.

Conclusions: It is obvious that the radiological eccentricity of the femoral head underestimates the Linear Wear Depth (“true wear”) quite substantially. That difference could be less if the x-rays had been taken weight bearing.

Aims: It is well established that implant characteristics influence the Volumetric Wear Rate (VWR) of the polyethylene cup at the Total Hip Replacement (THR). In order to explore these, a retrieval study in 63 patients having revision THR was carried out. Methods: 45 intact THR components were retrieved from patients after revision THR. The polyethylene VWR was assessed in the laboratory using the shadowgraph technique. Implant features such as femoral head size, stem/cup modularity and liner thickness were recorded. Statistical analysis to identify potential correlations with the VWR was performed. Results: 22 mm diameter femoral heads produced significantly lower VWR values than 28 mm (p=0.006) and 32 mm (p< 0.001), however, there was no significant difference between the 28mm and 32mm (p=0.375) heads. There was no statistically significant difference between the mean VWR in the metal-backed and the all-polyethylene cups with the first 25% higher than the second. However, the femoral stems with a modular head generated a VWR about 3.5 times higher than the solid monoblock femoral components (p< 0.001). Polyethylene thickness didn’t influence statistically significantly the VWR (p=0.135). Conclusions: Modular implants with large femoral head size significantly influence the polyethylene wear rate. However, in this study, the liner thickness did not influence the wear rate, although it is recognised that there is probably a critical thickness below which wear is accelerated.

Aims: Although there have been theoretical expectations of increased polyethylene wear rate with the time a THR is in situ, wear rate is reported to slow down. We performed this study aiming to identify the relationship between wear rate and time of service for the prosthesis. Material and Methods: 45 intact polyethylene liners were retrieved from patients undergoing revision THR. The LWD was measured in the laboratory using the shadowgraph technique. Dividing LWD with time the prosthesis was in place allowed assessment of the Linear Wear Rate (LWR). A correlation between LWR and time of service was explored. Statistical analysis was performed using the SPSS® software package. Results: Linear Wear Rate (LWR) was not stable with time. There was a significant inverse correlation (p< 0.001) between the time that the prosthesis was in place and LWR. This relationship was stronger for the first 6 years of the THR service (p=0.005), while LWR does not change significantly after the 6th year of prosthesis implantation (p=0.060). Conclusions: The LWR is higher in the beginning either as result of the initial higher creep or because of initial lower conformity of the femoral head within the acetabular cup. As conformity increases, the LWR reduces to a more stable value.