Prosthetic liner wear in total hip replacement: a longitudinal 13-year study with computed tomography

Effect of head size, head material, and radiation dose on the repeatability of CT-RSA measurements of femoral head penetration

BACKGROUND

The risk of early revision of total hip arthroplasty (THA) for polyethylene wear is now low, but there remains a need to perform wear measurements in patients for clinical surveillance. The gold standard of wear measurements has been radiostereometric analysis (RSA), which has limited availability. The use of computed tomography (CT) to perform THA wear measurement was described a decade ago and found to have acceptable accuracy and precision, but high radiation dose was a concern. Additionally, the use of larger femoral head sizes and ceramic femoral heads has risen in the past decade. The objectives of the study were to determine the effect of femoral head size, femoral head material, and lowered radiation dose on femoral head penetration measurement repeatability.

METHODS

A cadaveric hip was implanted with a cementless THA implant system. CT scans were acquired at a conventional radiation dose and at a reduced dose and repeated for a 32 mm and 36 mm cobalt-chromium femoral heads and a 32 mm ceramic femoral head. Apparent translation of the femoral head versus the acetabular cup was measured between the repeated scans using a CT-RSA software, where deviations from zero indicated measurement precision.

RESULTS

The mean and standard deviation of translations in all planes was <0.200 mm. There was no effect for 3D translation of increasing cobalt-chromium head size (p = 0.2252). Cobalt-chromium heads had superior repeatability compared to ceramic heads at reduced dose (p = 0.022), but not at conventional dose (p = 0.1265). Further, superior repeatability was achieved with the reduced dose scan for the cobalt-chromium head (p = 0.0058), however there was no difference between doses for the ceramic head (p = 0.8148).

DISCUSSION

CT-based wear measurement repeatability is excellent and consistent with prior literature even when implementing a larger femoral head, a ceramic femoral head, or reducing radiation dose to 25% of a conventional clinical scan.

Development and Validation of a Finite Element Model of Wear in UHMWPE Liner Using Experimental Data From Hip Simulator Studies

The wear of acetabular liner is one of the key factors determining osseointegration and long-term performance of total hip joint replacement implants. The experimental measurements of wear in total hip replacement components are time and cost-intensive. While addressing this aspect, a finite element model of a hip joint bearing consisting of zirconia-toughened alumina femoral head and ultrahigh molecular weight polyethylene liner was developed to predict the dynamic wear response of the liner. The Archard-Lancaster equation, consisting of surface contact pressure, wear rate, and sliding distance, was employed to predict the wear of the acetabular liner. The contact pressure and wear at the articulating surface were found to decrease over time. A new computational method involving three-dimensional point clouds from the finite element analyzed results were used to construct wear maps. The model was able to predict the linear wear, over 2 × 106 cycles with relative errors ranging from 9% to 36% when compared to the published results. The increasing error percentage occurring primarily from the use of a constant wear rate was reduced to a maximum of 17% by introducing a correction factor. The volumetric rate was predicted with a maximum relative error of 7% with the implementation of the correction factor. When the model was implemented to study acetabular liners of diameters ranging from 28 to 36 mm, the linear wear was seen to decrease with an increase in femoral head diameter, which is in agreement with the clinical data. This study emphasizes the need to develop more such FEA-based computational studies to reliably predict and correlate with experimentally measured temporal evolution of wear of load-bearing articulating joints.

Volume fusion of CT images to measure femoral symmetricity

Purpose

Pre-operative planning is widely used in orthopaedic surgery. In case of trauma with fracture or previous injury with malunion, the contralateral extremity is used as a surrogate for planning with an assumption of symmetry between sides. The aim of this study was to investigate femoral symmetricity in human adults.

Methods

Ten randomly selected lower extremity computerized tomography (CT) images were analyzed for femur symmetry using 3D Trauma and CT motion analysis (CTMA). Mirrored images of the left femur were created using the right as a template. The 3D images from each side were merged, and translational and rotational differences reported.

Results

There were no statistically significant differences between mirrored images of the left and right femurs. Differences in rotation and translation of bony segmentation showed a greater variation in internal and external rotation of the distal femur (CI − 0.7° to 4.9°) compared to varus/valgus (CI − 1.3° to 0.8°) or flexion/extension (CI − 0.5° to 0.6°), though none of these differences were significant.

Conclusion

The left and right femurs of healthy adults are symmetrical. Pre-operative templating relying on the contralateral healthy femur is encouraged.

Comparison of ceramic-on-ceramic bearing vs ceramic-on-highly cross-linked polyethylene-bearing surfaces in total hip arthroplasty for avascular necrosis of femoral head: a prospective cohort study with a mid-term follow-up

Background

The ideal bearing surface for patients of avascular necrosis (AVN) undergoing total hip arthroplasty (THA) remains controversial. The purpose of this study is to evaluate the clinical outcomes, health-related quality of life (HRQL), and wear of the bearing surface between ceramic-on-ceramic (CoC) and ceramic-on-highly cross-linked polyethylene (CoXPE) THA for patients of AVN after midterm follow-up.

Methods

We performed a retrospective case-control analysis of 93 CoC and 77 CoXPE consecutive THAs for patients of AVN. The cases were followed at a minimum 5 years follow-up (average 7 years). Harris hip score (HHS) score and bearing-related complications were assessed. The health-related quality of life (HRQL) was assessed with the Short Form 36 (SF-36). Plain radiographs and computed tomography (CT) were used for radiographic evaluation.

Results

Both the CoC group and CoXPE group showed statistically significant improvements in HHS scores with no difference between the two bearing surfaces. There was no significant difference as for SF-36 at the latest follow-up between two groups, except for significant higher scores in the dimensions of general health in the CoC group (75.7 vs 64.7, P = 0.032). No radiographic evidence of osteolysis and loosening was present at the final follow-up. The mean wear rate of the CoC was 0.0096 mm/year and the CoXPE was 0.047 mm/year after evaluation with reconstructed CT.

Conclusions

CoC THAs acts as well as CoXPE THAs for patients with femoral head avascular necrosis after midterm follow-up. CoC bearing can significantly decrease the wearing rate than CoXPE bearing.