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

Abstract

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.

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

“…The most severe corrosion damage is exhibited for alloys with carbides due to phase boundary corrosion, hard phase detachment, and consequent metal ion release [ 41 ]. A combination of an extra-long head and a long interchangeable Ti alloy neck in a dual modular stem prosthesis can, in certain biomechanical situations, such as stumbling, when forces greater than eight times the patient’s body weight may apply, create tensile stresses so high that they surpass the limits of the tensile strength of a Ti6Al4V alloy [ 42 , 43 , 44 , 45 ]. A recent retrospective study of 50 THAs with Profemur Z (Wright Medical Technology Inc., dual modular) and 52 THAs with Alloclassic–Zweymüller (Zimmer, monoblock) of otherwise similar design performed by a single surgeon demonstrated, on average, higher magnitudes of shear forces appearing with dual modular femoral implants compared to monoblock stems [ 46 ].…”

“…Even taking all known predisposing factors into account, it currently appears impossible to accurately pinpoint when a fracture is going to occur. A recent report for a patient with the same type of dual modular stem implanted on both hips described a modular neck fracture after 3 years on the left side and after 20 years on the right side post-implantation, respectively, with identical risk factors applying for both implants [ 43 ].…”

“…The most severe corrosion damage is exhibited for alloys with carbides due to phase boundary corrosion, hard phase detachment, and consequent metal ion release [41]. A combination of an extra-long head and a long interchangeable Ti alloy neck in a dual modular stem prosthesis can, in certain biomechanical situations, such as stumbling, when forces greater than eight times the patient's body weight may apply, create tensile stresses so high that they surpass the limits of the tensile strength of a Ti6Al4V alloy [42][43][44][45].…”

Fracture of femoral neck in modular total hip arthroplasty: a systematic review of the literature

“…79 articles remained eligible from which 32 were included in this article, reporting the fracture of a modular femoral neck after primary THA. There were 25 case reports 16–40 and 7 clinical studies. 5,7,41–45 Figure 1 demonstrates the study selection process based on PRISMA guidelines.…”