After institutional review board approval, we retrospectively enrolled 968 consecutive patients undergoing hemiarthroplasty from a trauma database at a single academic institution from January 2008 to December 2015. The inclusion criteria were patients with displaced femoral neck fractures who were older than 60 years. Patients with a non-displaced fracture, those aged under 60 years, and those with multiple trauma, valgus impacted fracture, or open fracture were excluded. After application of the exclusion criteria, 844 patients with displaced femoral neck fracture undergoing cemented or cementless hemiarthroplasty were included in this study.
All patients underwent a preoperative medical examination that included a resting electrocardiogram, chest radiography and blood exam. Following this screening, they were seen by an anesthesiologist before surgery. Subsequently, a cardiology consultation was obtained if concerns were raised by the anesthesiologist. The cardiologist or physician evaluated the patients undergoing non-cardiac surgery based on the 2007 ACC/AHA guidelines on perioperative cardiovascular evaluation [5]. As per the guidelines, routine screening with non-invasive stress testing was not performed in patients undergoing low-risk non-cardiac surgery. However, if the test result may have affected our decision-making, including canceling the operation or changing the perioperative care, it was arranged for patients with an elevated cardiac risk and a poor metabolic equivalent of task (MET < 4). If the patient had an elevated cardiac risk but a moderate functional capacity (MET > 4), no further testing was required.
Patients were divided into two categories based on receipt of a dipyridamole-based thallium scan. The control group included patients who underwent surgery without a thallium scan after consultation with an anesthesiologist or cardiologist, while the study group included patients who received a dipyridamole-thallium scan. Patients with abnormal thallium scan results were further evaluated by a cardiologist with regards to coronary angiography intervention. Indications for coronary angiography were based on clinical findings, such as new or medically unstable angina, previous or recent myocardial infarction, or persistent angina. Stent implantation or balloon angioplasty during angiography was performed if coronary arterial stenosis was greater than 50%, multiple-vessel disease was present, or if left main coronary artery occlusion was observed.
Variables of interest were extracted by electronic query of medical records and were reviewed manually. The following information was obtained: basic demographic data, age, gender, body mass index (BMI), ASA grade, and preoperative comorbidities, including ischemic heart disease, congestive heart failure, valvular heart disease, cerebrovascular accident (CVA), diabetes, chronic obstructive pulmonary disease (COPD), rheumatoid arthritis, liver disease, renal disease, and a history of cancer. In addition, the duration from hospital presentation to surgery, anesthesia type (regional or general), use of a cemented or cementless stem, operation duration, and need for transfusion were also obtained.
All displaced femoral neck fractures were treated with hemiarthroplasty using a posterolateral approach in a lateral decubitus position. All patients were treated using a cemented or cementless fixation technique by well-trained orthopedic surgeons. The cemented or press-fit implants were chosen based on preoperative imaging evaluation for osteoporosis and intraoperative trial implantation at the discretion of the treating surgeons. Intra-operative joint capsules were approximated by sutures, and a closed drainage tube was inserted, which was removed within 24–48 hours. A partial weight-bearing rehabilitation program was initiated by a physical therapist from postoperative day 1. If a patient was unable to ambulate using crutches, wheelchair ambulation was recommended.
Outcome measurement
The outcomes of this study included cardiac complications and mortality within 90 days after the index hemiarthroplasty. Cardiac complications were defined as coronary disease, heart failure, arrhythmia, or acute myocardial infarction, while mortality was defined as any death after the surgery. We traced all medical records after discharge and made phone calls if patients were lost to follow-up through outpatient clinics for post-op 90 days.
Statistical analysis
All variables were tested for normality using the Kolmogorov-Smirnov test. Student’s t-test was utilized for normally-distributed data, and the Mann-Whitney U test was used for nonparametric data. Fisher’s exact test or the chi-squared test was used for categorical variables. We used the propensity score-matching (at a 1:3 ratio) technique with a logistic regression model to adjust the covariates, including basic demographic data (age, gender, BMI and ASA grade), preoperative comorbidities (all cardiac comorbidities, CVA, diabetes, COPD, rheumatoid disease, liver disease, renal disease and cancer history), surgical variables (anesthesia type, use of a cemented or cementless stem, operation duration, and transfusion) and duration to surgery, in order to decrease the differences in baseline conditions between groups and to minimize the selection bias of thallium scan application. Univariate and multivariate logistic regression analysis was also applied to determine whether or not dipyridamole-thallium scanning was an independent factor affecting the 90-day cardiac complications and mortality after adjusting for the cofounding factors listed above. Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated, and a p-value of less than 0.05 was used to evaluate statistical significance. All statistical analyses were performed using the Statistical Package for Social Science (SPSS) version 22 software (SPSS Inc., IBM, Armonk, New York, USA) and the NCSS Statistical Analysis and Graphics software program (NCSS, LLC, Kaysville, Utah, USA).