Distal cement mantle thickness with a triangular distal centralizer inserted into the stem tip in cemented total hip arthroplasty

Importance of a distal centralizer in experimental malpositioning of cemented stems. A biomechanical study on human femora

INTRODUCTION

Femoral centralizers in total hip arthroplasty (THA) are designed to improve the neutral implant position and ensure a homogeneous cement mantle without implant-bone impingement. To date there are no data about the cement mantle configuration and implant position after malinsertion, as seen in mini-open approaches or adipose patients with a limited view. The present biomechanical study was performed to investigate whether a distal centralizer may correct and optimize the position of a malinserted femoral stem.

MATERIAL AND METHODS

Thirteen MS 30 stems with and without a distal centralizer each were implanted in paired fresh human femora. Malinsertion was performed using a 3D guiding device with 10° deviation to the femoral axis in the sagittal plane. The thickness of the cement mantle was measured on the anterior, posterior, medial and lateral side of the implanted stem at a distance of 1 cm each. For each side data were taken at 13 points.

RESULTS

Digital evaluation of the cement mantle thickness revealed compareable values in frontal plane when a centralizer was used (p > 0.4). In contrast the cement mantle thicknesses without a centralizing device varied in the distal region between 3.38 mm and 5.09 mm (p ≤ 0.001) and in the central region between 3.52 mm and 4.19 mm (p ≤ 0.009).

CONCLUSIONS

A distal centralizer allows a more uniform cement mantle and neutral alignment even with a malinsertion of the femoral stem. This could reduce the failure rate and early loosening in complex THA.

Three-dimensional shape optimization of a cemented hip stem and experimental validations

This study proposes novel optimized stem geometry with low stress values in the cement using a finite element (FE) analysis combined with an optimization procedure and experimental measurements of cement stress in vitro. We first optimized an existing stem geometry using a three-dimensional FE analysis combined with a shape optimization technique. One of the most important factors in the cemented stem design is to reduce stress in the cement. Hence, in the optimization study, we minimized the largest tensile principal stress in the cement mantle under a physiological loading condition by changing the stem geometry. As the next step, the optimized stem and the existing stem were manufactured to validate the usefulness of the numerical models and the results of the optimization in vitro. In the experimental study, strain gauges were embedded in the cement mantle to measure the strain in the cement mantle adjacent to the stems. The overall trend of the experimental study was in good agreement with the results of the numerical study, and we were able to reduce the largest stress by more than 50% in both shape optimization and strain gauge measurements. Thus, we could validate the usefulness of the numerical models and the results of the optimization using the experimental models. The optimization employed in this study is a useful approach for developing new stem designs.

Fifteen-year results of precoated femoral stem in primary hybrid total hip arthroplasty

Background

There has been controversy whether methylmethacrylate precoating of the cemented femoral stem is a solution for aseptic loosening or rather contributes to increased failure rates in cemented total hip arthroplasties.

Methods

On a retrospective basis, we analyzed 76 primary hybrid total hip arthroplasties from 63 patients with precoated, cemented femoral stems between October 1990 and December 1995. The mean age of the patients was 46.8 years (range, 22 to 77 years) with a minimum follow-up of 14 years (mean, 15.5 years; range, 14 to 19.5 years). Third generation cementing techniques were employed in all cases.

Results

Twenty-four out of 76 cases (31.6%) showed aseptic loosening of the femoral stems, of which 23 stems were revised at an average revision time of 8 years (range, 3 to 14.8 years). The main mode of loosening was cement-stem interface failure in 22 hips (91.7%). Twenty-one out of 24 failed hips (87.5%) demonstrated C2 cementing grades (p < 0.001). Kaplan-Meier survivorship analysis using radiographic aseptic loosening of the femoral stem as the endpoint for failure showed survival rates of 76.5% at 10 years (95% confidence interval [CI], 71.4 to 81.6) and 63.2% at 19 years (95% CI, 57.3 to 69.1).

Conclusions

An early failure of the precoated femoral stem in this study was mainly due to an insufficient cementing technique. Achievement of good cement mantle may improve the survival rates.

The cement mantle of femoral hip implants is more influenced by stem-broach sizing than by shape: an in vitro CT analysis of straight Charnley-Kerboul and anatomic Lubinus SPII stems

INTRODUCTION

Both, the stem shape and the implantation technique could influence the quality of the cement mantle surrounding femoral hip implants. We investigated which of these two factors is most important for the stem-cement-bone construct.

METHODS

We compared morphological data of 22 straight Charnley-Kerboul and 18 anatomic Lubinus SPII plastic replicas implanted line-to-line with the broach or one size undersized in paired cadaver femora. Specimens were CT scanned and assessed with validated segmentation software.

RESULTS

According to a general linear model, the canal-filling capacity of the stem, the cement thickness, the amount of thin and deficient cement and cortical support to areas of weak cement, were exclusively related to the implantation technique. The anatomic shape of Lubinus stems did not improve centralization or alignment.

CONCLUSION

Stem shape was the most obvious difference between Lubinus SPII and Chanrley-Kerboul implants. However, comparing both, stem-broach sizing was the most important determining factor for the cemented stem construct.

Comparison of distal and proximal centralising devices in hip arthroplasty

Centralising devices were introduced to ensure that the prosthesis is implanted in a neutral position and that a cement mantle of optimal thickness is achieved proximally and distally. A distal centralising device (DCD) is compared with a proximal midshaft centralising device (PCD) to test which one provides a more neutral prosthetic alignment. Thirty consecutive patients undergoing hemiarthroplasties for femoral neck fractures were studied prospectively. Patients were blindly randomised to receive either a femoral component with proximal midshaft centraliser or distal centraliser. Both components were implanted following the manufacturer's protocol. Postoperative true anteroposterior and lateral radiographs were made to assess the stem position. There was no statistically significant difference between the two groups in zones 1, 2, 3, 4, 5, 6 and 7 in both anteroposterior and lateral radiographic measurements. DCP and PCD both have similar centralisation and cement mantle. Future studies should be done to evaluate their long-term effect.

Optimizing the femoral component cement mantle in total hip arthroplasty

Aseptic loosening is a common cause of long-term failure of cemented femoral components in hip arthroplasty. Initiation of aseptic loosening has been associated with suboptimal cement mantle thickness and uniformity with the resultant progressive development of detrimental cement mantle defects. Long-term success is highly dependent on maintaining and protecting the integrity of the cement mantle and its interfaces primarily by decreasing cement mantle stresses. High cement stresses that initiate debonding and cement fracture can be controlled and minimized through the use of various surgical techniques that assist in creating an optimally thick, symmetric, and homogeneous cement mantle.

New technology in cemented total hip arthroplasty

The long-term results of total hip arthroplasty (THA) are predicated by excellent surgical techniques. New technology offers the hope of improving outcomes by providing to surgeons tools that make surgical procedures predictable. Techniques that improve the bone-cement-prosthesis composite should enhance long-term fixation. Less invasive surgical techniques that allow rapid recovery from THA have been recently described. Image-guided surgery may enable surgeons to accurately reconstruct the arthritic hip and improve outcomes.