In vitro serum levels of metal ions released from orthopaedic implants

Bimodular femoral stems in primary total hip arthroplasty

INTRODUCTION

This review critically examines the efficacy of dual-modular stems in primary total hip arthroplasty. Given the variability and non-comparability of certain femoral stem designs and stem-neck couplings, with some even being withdrawn from the market, this review offers an in-depth analysis of predominant implant performances.

AREAS COVERED

The paper explores a brief historical summary related to dual-modular stems, including the complications associated with their use, diagnostic tools for evaluation, analysis of both recalled and currently available models, as well as alternative therapeutic options. This information is pertinent for both clinical and research domains.

EXPERT OPINION

While dual-modular systems were initially touted to offer several advantages, the evidence substantiating these benefits has been ambiguous. Further, these systems introduce the risk of alternative complications. In specific cases involving patients with developmental hip dysplasia and certain proximal femoral deformities requiring complex reconstructions, dual-modular systems might be relevant. Nonetheless, the use of long interchangeable necks in patients with a body mass index above 30 kg/m2 is discouraged, and pairing a long varus-oriented neck with an extra-long femoral head should be avoided in all patients.

Dual Modular Titanium Alloy Femoral Stem Failure Mechanisms and Suggested Clinical Approaches

Titanium (Ti) alloys have been proven to be one of the most suitable materials for orthopaedic implants. Dual modular stems have been introduced to primary total hip arthroplasty (THA) to enable better control of the femoral offset, leg length, and hip stability. This systematic review highlights information acquired for dual modular Ti stem complications published in the last 12 years and offers a conclusive discussion of the gathered knowledge. Articles referring to dual modular stem usage, survivorship, and complications in English were searched from 2009 to the present day. A qualitative synthesis of literature was carried out, excluding articles referring solely to other types of junctions or problems with cobalt-chromium alloys in detail. In total, 515 records were identified through database searching and 78 journal articles or conference proceedings were found. The reasons for a modular neck fracture of a Ti alloy are multifactorial. Even though dual modular stems have not shown any clinical benefits for patients and have been associated with worse results regarding durability than monolithic stems, some designs are still marketed worldwide. Orthopaedic surgeons should use Ti6Al4V dual modular stem designs for primary THA in special cases only.

Bilateral neck fracture in bimodular femoral stem after primary total hip arthroplasty: a case report

Background

Bi-modular stems were introduced in primary total hip arthroplasty (THA) to enable better control of the femoral offset, leg length, and hip stability. Despite numerous reports on modular femoral neck fractures, some designs are still marketed worldwide. While the risk factors for the sudden failure are multifactorial and mostly known, the timing of this new THA complication is not predictable by any means.

Case presentation

In this report, the literature regarding one of the most popular bi-modular stems with specific neck-stem coupling (oval Morse taper) is reviewed and illustrated with a case of bilateral modular neck fracture in a patient with idiopathic aseptic necrosis of femoral heads treated with primary bi-modular THA. Because of bilateral modular femoral neck fracture, which occurred 3 years on the left side and 20 years after implantation on the right side, the patient required a total of 6 revisions and 208 days of hospitalized care.

Conclusion

To our knowledge, this is the first report of bilateral modular neck fracture in a single patient. Even though the same surgeon performed both operations and used the same neck length and orientation, fractures occurred with a 17-year time difference after implantation. This shows that we cannot predict with certainty when a fracture might occur. Orthopaedic surgeons should use bi-modular stem designs for primary THA very cautiously.

Modular femoral neck failure after revision of a total hip arthroplasty: a finite element analysis

The authors report on a case of modular femoral neck fracture which appeared 21 months after revision of acetabular component. The revision surgery was performed 8 years after the primary total hip arthroplasty due to aseptic loosening of the acetabular component. During acetabular revision, the primary implanted short (S, - 3.5 mm) femoral head was also exchanged with extra-long (XL, + 7.0 mm) femoral head fitting the modular femoral neck with a longer lever arm. Numerical analysis has shown that this has resulted in a 19.9% increase in tensile stress at the neck-stem coupling during normal walking cycle. This could result in microcrack initiation and propagation and finally lead to modular neck failure of the otherwise well-fixed stem. Surgeons should avoid excessive loading of the exchangeable neck (dual-modular) femoral stem designs as the stem-neck couplings are subject to corrosion and are not as reliable as monoblock stems.