What Factors Are Associated With Neck Fracture in One Commonly Used Bimodular THA Design? A Multicenter, Nationwide Study in Slovenia

Abstract

Background Femoral stems with bimodular (head-neck as well as neck-body) junctions were designed to help surgeons address patients’ hip anatomy individually. However, arthroplasty registers have reported higher revision rates in stems with bimodular junctions than in stems with modularity limited to the head-neck trunnion. However, to our knowledge, no epidemiologic study has identified patient-specific risk factors for modular femoral neck fractures, and some stems using these designs still are produced and marketed. Questions/purposes The purposes of this study were (1) to establish the survival rate free from aseptic loosening of one widely used bimodular THA design; (2) to define the proportion of patients who experienced a fracture of the stem’s modular femoral neck; and (3) to determine factors associated with neck fracture. Methods In this retrospective, nationwide, multicenter study, we reviewed 2767 bimodular Profemur® Z stems from four hospitals in Slovenia with a mean followup of 8 years (range, 3 days to 15 years). Between 2002 and 2015, the four participating hospitals performed 26,132 primary THAs; this implant was used in 2767 of them (11%). The general indications for using this implant were primary osteoarthritis (OA) in 2198 (79%) hips and other indications in 569 (21%) hips. We followed patients from the date of the index operation to the date of death, date of revision, or the end of followup on March 1, 2018. We believe that all revisions would be captured in our sample, except for patients who may have emigrated outside the country, but the proportion of people immigrating to Slovenia is higher than the proportion of those emigrating from it; however, no formal accounting for loss to followup is possible in a study of this design. There were 1438 (52%) stems implanted in female and 1329 (48%) in male patients, respectively. A titanium alloy neck was used in 2489 hips (90%) and a cobalt-chromium neck in 278 (10%) hips. The mean body mass index (BMI) at the time of operation was 29 kg/m2 (SD ± 5 kg/m2). We used Kaplan-Meier analysis to establish survival rates, and we performed a chart review to determine the proportion of patients who experienced femoral neck fractures. A binary logistic regression model that controlled for the potential confounding variables of age, sex, BMI, time since implantation, type of bearing, diagnosis, hospital, neck length, and neck material was used to analyze neck fractures. Results There were 55 (2%) aseptic stem revisions. Survival rate free from aseptic loosening at 12 years was 97% (95% confidence interval [CI] ± 1%). Fracture of the modular neck occurred in 23 patients (0.83%) with a mean BMI of 29 kg/m2 (SD ± 4 kg/m2.) Twenty patients with neck fractures were males and 19 of 23 fractured necks were long. Time since implantation (odds ratio [OR], 0.55; 95% CI 0.46-0.66; p < 0.001), a long neck (OR, 6.77; 95% CI, 2.1-22.2; p = 0.002), a cobalt-chromium alloy neck (OR, 5.7; 95% CI, 1.6-21.1; p = 0.008), younger age (OR, 0.91; 95% CI, 0.86-0.96; p < 0.001), and male sex (OR, 3.98; 95% CI, 1.04-14.55; p = 0.043) were factors associated with neck fracture. Conclusions The loosening and neck fracture rates of the Profemur® Z stem were lower than in some of previously published series. However, the use of modular femoral necks in primary THA increases the risk for neck fracture, particularly in young male patients with cobalt-chromium long femoral necks. The bimodular stem we analyzed fractured unacceptably often, especially in younger male patients. For most patients, the risks of using this device outweigh the benefits, and several dozen patients had revisions and complications they would not have had if a different stem had been used. Level of Evidence Level III, therapeutic study.

How to Proceed with Asymptomatic Modular Dual Taper Hip Stems in the Case of Acetabular Revision

“…For Ti alloy hip stem designs with Ti alloy neck adapters, the main implant-related clinical failure mode is fatigue fracture of the neck taper in the highly stressed neck-stem junction due to fretting corrosion, local stress concentration and crack initiation by multi-directional bending and torsion [16,[23][24][25][26][27]. For CoCr neck adapters only few fatigue failures have been reported clinically for a Profemur Z titanium alloy stem (Profemur Hip System, Wright, Arlington, TN, USA) with long 8 • varus type CoCr alloy modular necks in overweight or obese patients with considerable physical activity [28][29][30]. For CoCr neck adapters, the main clinical failure mechanism is the generation of particulate Co and Cr wear debris and metal ion release from the neck adapter due to tribo-corrosion, that may cause adverse local tissue reactions (ALTR) [17,[31][32][33][34] like osteolysis, metallosis and pseudo-tumor formation in the surrounding tissue [19,35,36] as well as elevated serum ion levels [17,33,[37][38][39] and systemic toxicity [40,41].…”

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

“…Fit prosthesis with the same oval Morse taper neck-stem junction) bi-modular series stem implantation and found 6% neck fractures at 50 months mean follow up [ 19 ]. Finally, Kovač et al studied the long-term behaviour of the Profemur Z modular stem on a national basis (2767 hips followed) and found out that the mean time for bi-modular femoral neck fracture (0.83%) was 4.7 years (SD ± 2.2 years) [ 4 ]. Furthermore, long neck, Co-Cr modular neck, which was introduced by the producer (Wright Medical Technology, now MicroPort Orthopedics Inc.) in 2010 to reduce the failure rate of titanium alloy made necks, and male gender represent the independent risk factors for modular neck fracture [ 4 ].…”

“…Finally, Kovač et al studied the long-term behaviour of the Profemur Z modular stem on a national basis (2767 hips followed) and found out that the mean time for bi-modular femoral neck fracture (0.83%) was 4.7 years (SD ± 2.2 years) [ 4 ]. Furthermore, long neck, Co-Cr modular neck, which was introduced by the producer (Wright Medical Technology, now MicroPort Orthopedics Inc.) in 2010 to reduce the failure rate of titanium alloy made necks, and male gender represent the independent risk factors for modular neck fracture [ 4 ]. In contrast, Pelayo-de-Tomás et al found only 1 modular neck fracture in their cohort of 317 consecutive patients followed for 6.1 (range, 2–8) years after bi-modular stem (H-MAX M, Lima, San Danielle, Italy) THA [ 20 ].…”

“…Studies have linked implant failures to mechanically assisted crevice corrosion (MACC), which also includes the most common damage process fretting corrosion [ 3 ]. Corrosion products can cause adverse local tissue reactions that lead to THA failure [ 4 ].…”

“…Several orthopaedic studies on bi-modular THA’s have identified risk factors that can lead to modular neck fracture. These include time since implantation, a long neck, a cobalt-chromium alloy neck, younger age, male sex, and higher BMI [ 4 ].…”