Effect of acetabular orientation on stress distribution of highly cross-linked polyethylene liners

Wear of a Highly Cross-Linked Polyethylene Liner of the Acetabular Component Placed With Excessive Acetabular Inclination

Few studies have investigated the influence of excessive acetabular inclination during total hip arthroplasty (THA) on the wear of highly cross-linked polyethylene (HXLPE). The goal of this study was to determine whether excessive acetabular inclination during THA causes prominent wear of the HXLPE liner. We retrospectively evaluated 62 hips of 54 women and 8 men who underwent primary THA with an HXLPE liner between January 2006 and September 2011. Postoperative anteroposterior pelvic radiographs were used to measure acetabular inclination and analyze polyethylene wear. Patients were divided into the following groups: the excessive acetabular inclination group (acetabular inclination angle ≥50°; n=20) and the control group (acetabular inclination angle <50°; n=42). Clinical information and imaging findings were compared and examined between the 2 groups. Further, we evaluated the correlation between the acetabular inclination angle and the polyethylene wear rate. In all cases, mean follow-up duration was 6.3 years. The annual liner wear was 0.00446 and 0.0254 mm/y in the control and excessive acetabular inclination groups, respectively. The excessive acetabular inclination group had significantly higher polyethylene liner wear compared with the control group (P=.00991). A weak correlation was seen between acetabular inclination angle and polyethylene wear rate in all cases (Spearman's rank correlation, r=0.283, P=.0258). Excessive acetabular inclination may increase HXLPE liner wear in the long term. [Orthopedics. 2022;45(2):e96-e100.].

Femoral-Acetabular Mating: The Effect of Femoral and Combined Anteversion on Cross-Linked Polyethylene Wear

BACKGROUND

Cross-linked polyethylene (XLPE) has generally low rates of wear and osteolysis at 10 years, but component position may become important with longer follow-up. At 5-13 years, neither acetabular component lateral opening angle nor version were significantly correlated to wear. In the present study, we analyzed the effects of femoral anteversion and combined anteversion on XLPE wear.

METHODS

Forty-two well-functioning primary total hip arthroplasties in 36 patients, performed by a single surgeon via a posterior approach, were followed for a minimum of 5 years (mean, 7.1 years; range, 5.0-10.3). All hips had a modular, XLPE liner with a ≥36-mm bearing. Femoral anteversion was measured on the modified Budin view. Wear was measured on radiographs using a validated, computer-assisted, edge-detection-based algorithm. The mean lateral opening angle was 40.4° (range, 22.6°-50.3°). The mean acetabular version was 19.1° (range, 11.3°-27.5°). Neither of these variables was significantly correlated to wear. Effects of femoral anteversion and combined anteversion on XLPE wear were assessed using linear and polynomial regression analysis.

RESULTS

Femoral anteversion (mean, 18.4°; range, 6.8°-30.7°) was significantly correlated to linear wear (mean, 0.06 mm/y; range, 0-0.16), showing an inverse parabolic relationship with the least wear occurring at 18.2° (P = .02). Combined anteversion (mean, 37.2°; range, 21.8°-54.3°) showed a similar significant relationship with the least wear at 38.1° (P < .001). Based on regression, combined anteversion between 24.6° and 50.4° resulted in linear wear rates less than 0.1 mm/y.

CONCLUSION

To the authors' knowledge, this is the first study to identify femoral anteversion as an independent factor influencing XLPE wear, with least wear occurring around 18°. At 5-10 years, average linear wear of XLPE is below 0.1 mm/y over a 25°-50° range of combined anteversion, with the least wear around 38°. Femoral-acetabular mating is a product of both components. Femoral component version and combined anteversion had a greater effect on wear than acetabular component lateral opening angle. Additional studies are warranted, but these results indicate that the sensitivity of wear studies is increased with version assessments.

Finite element modelling for assessing effect of acetabular component orientation on the basic stress path above acetabular dome

OBJECTIVE

To investigate the effect of acetabular component orientation on the basic stress path above the acetabular dome in the recommended safe zone.

METHODS

A subject-specific normal hip finite element model was generated and a convergence study carried out to determine the number of material properties for trabecular bone using a normal hip model. Four abduction angles (35°, 40°, 45° and 50°) and four anteversion angles (10°, 15°, 20° and 25°) from the recommended safe zone of acetabular cup orientation were chosen to simulate acetabular reconstruction. The distribution and level of periacetabular stress was assessed using a normal hip model as a control and 16 reconstructed acetabula in simulated single-legged stances.

RESULTS

The error of the average stress between plans four and five (50 and 100 materials for trabecular bone respectively) was 4.8%, which is less than the previously defined 5% error. The effect of acetabular component orientation on stress distribution in trabecular bone was not pronounced. When the acetabular component was at 15° anteversion and the abduction angle was 40° or 45°, the stress level on posterolateral cortical bone above the acetabular dome was as stable as that in the normal hip model.

CONCLUSIONS

Acetabular component orientation affects the basic stress path above the acetabular dome. Thus, orientation should be considered when attempting to restore normal biomechanics in the main load-bearing area.