Complications of Modular Neck-Stems

Abstract

Modularity in total hip arthroplasty (THA) allows surgeons to optimize implant reconstruction to patient anatomy intraoperatively. Dual-modular femoral neck-stem or “dual-taper” THA implants possess interchangeable necks, providing additional modularity at the neck-stem interface. Modular taper designs have the potential to allow precise reconstruction of center of rotation of the hip by facilitating adjustments in limb length, femoral neck version, and hip offset in order to optimize hip biomechanical parameters. Recently, there is increasing concern regarding this stem design as a result of the growing numbers of clinical failures due to fretting and corrosion at neck-stem taper junction, in a process that has been described as mechanically assisted crevice corrosion (MACC). Implant, surgical, and patient factors have been identified as likely contributing factors responsible for taper corrosion in dual-modular neck-stem THA. There should be a low threshold to conduct a systematic clinical evaluation of patients with dual-modular neck-stem THAs as early recognition and diagnosis will ensure prompt and appropriate treatment. As painful dual-modular neck-stem THAs have various intrinsic and extrinsic causes, patients should be evaluated utilizing systematic risk stratification algorithms. Although specialized test such as metal ion analysis and cross-sectional imaging modalities such as MARS MRI and ultrasound should be used to optimize clinical decision making, over-reliance on any single investigative tool in the clinical decision-making process should be avoided. Further research is required to gain understanding of implant, surgical, and patient risk factors associated with taper corrosion in dual-modular neck-stem THA.