Comparison of Different Locking Mechanisms in Total Hip Arthroplasty: Relative Motion between Cup and Inlay

Wear and performance of a tripolar total hip replacement

Background

An unconstrained tripolar hip replacement matches a large capacity two-piece metal/polyethylene acetabular component with a bipolar prosthesis. This combination of accepted technology is different than the relatively new dual mobility prosthesis. The goal is to protect against dislocation and allow close to a normal range of motion (ROM). So far there has not been enough information about wear and performance of tripolar hip replacement to support its wide use.

Methods

Twenty-four tripolar prostheses were retrieved from 23 patients after a mean of 14 years (range, 5-21 years). All implants had been placed in high-demand patients who participated in adventure sports, had occupations where a dislocation would be dangerous, or in patients undergoing revision. The tripolar prosthesis has three important design features: (I) the acetabular component uses highly cross-linked polyethylene with an internal diameter of 41-54 mm, (II) the bipolar is titanium nitride-coated, and (III) the bipolar prosthesis has positive eccentricity. The retrievals were evaluated for wear, performance, and mechanical function.

Results

The total volumetric wear was 24 mm3/yr. compared to 54 mm3/yr. For a dual mobility prosthesis and 38 mm3/yr. for a 40 mm conventional hip replacement. The jump distance was 16 mm compared to 12 mm for a 36 mm hip replacement. There was no osteolysis. The combined flexion/extension was 145 compared to 119 for a conventional prosthesis. The mean UCLA score was 7.9. Radiographs showed continued shared movement between the inner and outer articulations. The prosthetic bipolar separation force was 2,180 N. High-demand activities generate approximately 340 N.

Conclusions

The wear of this tripolar hip prosthesis is low below the osteolytic threshold. The increased ROM and increased jump distance provide the most stable unconstrained hip replacement available. The wear and mechanical performance seen in this study suggest a lifetime of use is possible in even the highest demand patients. The absence of intraprosthetic dislocation, metal wear reaction, and limited acetabular stress shielding make this a safer technology compared to a dual mobility prosthesis.

Dissociation of liner from cup in THA: does liner damage affect the risk of dissociation?

INTRODUCTION

A rare catastrophic failure of modular component Total Hip Arthroplasty is dissociation between liner and cup, which has been associated with component malposition and/or impingement and seems to be more frequently associated with the Pinnacle system. The goal of this study was to evaluate the resistance of a polyethylene liner to lever-out-forces of the Pinnacle locking mechanism and the locking mechanisms of two other current cup/liner systems using a standardized testing method (ASTM).

MATERIALS AND METHODS

Five of each of the following cups were evaluated with their corresponding polyethylene liners: Pinnacle Multihole cup with and without intact anti-rotation tabs (ART's); Allofit-S-Alloclassic and Plasmafit Plus7 cups. The ASTM test set-up was used to evaluate the lever-out force resulting in liner dissociation for each construct.

RESULTS

The Pinnacle construct with intact ARTs required the greatest force (F) to achieve dissociation (263.2 ± 79.2 N) followed by the Plasmafit Plus7 (185.8 ± 36.9 N) and the Allofit-S (101.4 ± 35.3 N) constructs, respectively. However, after removal of the ARTs, the Pinnacle system required the least force to achieve dissociation (75.1 ± 22.2 N) (p < 0.001).

CONCLUSIONS

The intact Pinnacle system appeared the most stable in lever-out tests when compared to the other systems. However, after removal of the ARTs, the Pinnacle system required the least force for dissociation, consistent with locking mechanism failure, and suggesting that the ARTs are a critical component of the locking mechanism. Our findings are consistent with the clinical experience of dissociated Pinnacle constructs displaying damaged or missing ARTs, and that damage to these may increase risk of liner dissociation.

Polyethylene Liner Dissociation in the Early Post-Operative Period Following Total Hip Arthroplasty: A Case Report and Literature Review

Polyethylene liner dissociation (PLD) is a rare but catastrophic complication following total hip arthroplasty (THA). When it occurs in the early postoperative period, it can be easy to miss the diagnosis. Liner dissociation has been reported previously with the Pinnacle^® (DePuy), Harris-Galante^® (Zimmer), and Trident^® (Stryker) acetabular components. To the best of our knowledge, this is the first case reporting PLD in the G7^® cup (Zimmer-Biomet). This case report, along with a review of the literature, highlights the clinical presentation, radiological imaging, treatment options, and technical tips to avoid PLD in the early postoperative period.

Parametric analysis of the effect of impaction load on the stability of head-neck junction in total hip arthroplasty

BACKGROUND

Tribocorrosion at head-neck interface is one of the main causes leading to the failure of hip implants in total hip arthroplasty. Impaction load has been acknowledged as one of the key factors influencing the stability of the taper junction. It is understood that the magnitude of impaction force differs from the surgeon to surgeon in primary total hip arthroplasty or revision. Clinically, it is sufficient enough to keep the male and female tapers inseparable utilizing a low impaction, which seems to contradict previous researches. The objective of this study was to investigate the effect of impaction loads on the stability of taper junction during assembly and gaits.

METHODS

A finite element model with 12/14 taper and the taper mismatch of 4' was developed for investigation. The impaction force profiles were collected from surgeon as the inputs, and then the contact mechanics over one or multiple gaits was further analyzed and validated utilizing hip simulator test.

FINDINGS

Impaction force ranging from 200 to 2000 N could provide the same taper connection effect after the first gait due to the secondary seating. As for impaction loads of 3000 N and above, an increased impaction force would lead to the tighter taper connection.

INTERPRETATION

The effect of impaction load on the stability of head-neck junction is a piecewise function, indicating that the stability of taper junction is not affected by different impaction loads and tends to be consistent while its magnitude is below the threshold. Instead, the stability of taper junction is positively correlated with impaction force.

Liner dissociation in a large-diameter ceramic-bearing acetabular component: a report of five cases

Background

Ceramic-on-ceramic (CoC) bearings for total hip arthroplasty (THA) have been offering very favorable results and survivorship since their introduction. In order to increase range of movement (ROM) and decrease dislocation rates, some manufacturers have introduced larger diameter head (LDH) CoC bearings. This has been achieved with the use of preassembled cup designs, in which the ceramic liner is already fitted into the metal backing and implanted as a monoblock component by the surgeon. In this report we present data from a series of 5 patients with ceramic liner dissociation from a monoblock cup.

Case presentation

All cases were overweight men with acetabular components of 56 or 58 mm. After a mean of 5.5 (range, 3.5-6.7) years, all patients reported sudden pain and audible noise when performing activities of daily living. Liner displacement was suspected on plain radiographs and confirmed by Ct-scan. Pneumarthrosis was present in all cases. Taper modular junction wear and corrosion signs were observed in the four revised patients.

Conclusion

Although one of our case is still treated conservatively, implant revision is probably inevitable. Further LDH CoC implant design should take in consideration this potential complication by avoiding bearing diameters over 40mm and/or improving locking mechanism or by providing a real monoblock acetabular implant.

How to Prevent Aseptic Loosening in Cementless Arthroplasty: A Review

Aseptic loosening is the main late postoperative complication of cementless total hip arthroplasties (THAs), leading to pain and functional impairment. This article aims to update the orthopedic surgeon on the various methods by which the aseptic loosening rate can be reduced. We performed a systematic review by searching the PubMed database for hip aseptic loosening. We included meta-analysis, randomized controlled trials, reviews, and systematic reviews in the last 10 years, which provided information on techniques that can prevent aseptic loosening in total hip arthroplasty. From a total of 3205 articles identified, 69 articles (2%) met the inclusion criteria, leading to a total of 36 recommendations. A lot of research has been conducted in terms of septic loosening in the last decade. Currently, we have various techniques by which we can reduce the rate of aseptic loosening. Nevertheless, further randomized clinical trials are needed to expand the recommendations for aseptic loosening prevention.