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the variability and non-comparability of certain femoral stem designs and stem-neck couplings, with some even being withdrawn from the market, this review offers an in-depth analysis of predominant implant performances.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.
Keywords: Adverse tissue reactions; corrosion; exchangeable neck; implant-related complication; interchangeable neck; modular femoral component; modular neck stems; titanium.
Total hip arthroplasty (THA) is a surgical procedure where the hip joint is replaced with an artificial one. This research paper dives deep into the use of dual-modular stems in THA. These stems were designed to provide surgeons with more control over certain aspects of the surgery, like leg length and hip stability. However, there’s been some debate about their effectiveness and safety compared to single-modular stems. Going back in history, single-modular stems were the standard in THA procedures. These types of stems are simple in design, with the neck and stem made of one piece of metal. After inserting the stem in the femoral canal, a separate head or ball is attached intraoperatively thus completing the femoral part of the THA. In 1987, dual-modular stems, also called bimodular stems, were introduced. These had two parts and offered theoretical benefits such as better hip biomechanics, which could potentially lead to longer-lasting implants. But studies have shown mixed results, with some suggesting that dual-modular stems didn’t offer clear benefits over the simpler, single-modular stems. This research review looks at both the history of dual-modular stems and the complications associated with them. Some of these stems even had to be recalled from the market. Diagnostic tools to evaluate these stems, the models available in the market, and alternative treatments are also discussed. The authors noted that while dual-modular systems were believed to offer benefits, the evidence isn’t clear-cut. Moreover, these systems come with their own set of potential complications. One of the challenges faced with dual-modular stems is their potential for mechanical complications, which could complicate recovery after surgery. The use of cobalt-chromium necks in these titanium alloy stems introduced another challenge: enhanced corrosion at the point where the neck meets the stem. Despite these challenges, dual-modular stems may still be useful in specific cases, like when patients have severe hip dysplasia or deformities. But it’s crucial to consider patient factors like weight, activity level, and hip offset when deciding to use these stems. The primary goal of using modular designs in THA is to better restore hip biomechanics, adjust leg length, and improve stability. Single-modular designs have shown consistent success, but dual-modular stems have faced challenges. For example, titanium alloy necks in these stems faced issues like fatigue breakage from mechanically assisted corrosion (tribocorrosion), which led to the introduction of cobalt-chromium necks. But even this solution had its problems, introducing a different type of corrosion when coupled with the original stem. As a result, these dual-modular stems should be used cautiously and in specific cases. In those instances, the newest designs, combined with titanium alloy necks, are recommended. However, surgeons are advised against using long necks in overweight patients, and certain design combinations should be avoided. There are alternatives to these stems, such as single-modular THA stems with different proximal shape and personalized implants. These alternatives are still being studied, and we need more data on their long-term performance. In conclusion, while THA has seen many advancements, it remains a field with potential for improvement. Modular designs, particularly dual-modular stems, have both benefits and challenges. The future of THA might focus more on personalized treatments, utilizing advances in imaging, materials, and manufacturing. We might soon see implants custom-made for individual patients, tailored to their anatomy and lifestyle. But before we get there, the current designs need improvement, and we need a better understanding of their failure modes. The goal is to continue innovating to provide the best outcomes for patients, keeping their safety and well-being at the forefront of all developments.