Introduction
Osteoporosis generally increases bone fragility and leads to an increased risk of fractures, with older women the most severely affected. Vertebral fractures are the most common clinical manifestation of the disease; however, most osteoporotic vertebral fractures respond well to non-surgical management [
1]. However, vertebral fractures may fail to heal in some cases, resulting in progressive collapse and/or pseudoarthrosis. This pathology has been defined as osteoporotic vertebral collapse (OVC) [
23]. Symptomatic OVC often requires surgery due to intolerable pain, progressive spinal kyphosis, and/or neurologic symptoms including paraparesis. With increased aging of society, the demand for instrumentation surgery for a symptomatic osteoporotic spine has been increasing [
14].
In elderly patients undergoing surgical treatment for OVC with decompression and/or fusion with instrumentation, the presence of multiple comorbid conditions is not uncommon, particularly among patients with secondary osteoporosis. Although proper planning and patient preparation can optimize the medical condition of patients and help decrease the perioperative risk [
5], primary diseases or conditions associated with secondary osteoporosis, including diabetes mellitus, chronic kidney disease, and glucocorticoid use, may increase the perioperative risk.
However, to the best of our knowledge, no studies have aimed to compare the rate or severity of perioperative complications after spinal instrumentation surgery between patients with primary osteoporosis and those with secondary osteoporosis. Therefore, the present retrospective study aimed to investigate whether perioperative complications after posterior approach spinal instrumentation surgery for OVC are more frequent in patients with secondary osteoporosis than in those with primary osteoporosis.
Discussion
Progressive and symptomatic OVC should be surgically treated where possible to maintain the quality of life of patients. Indications for spinal instrumentation surgery in the elderly and patients with secondary osteoporosis should be carefully considered as these populations have a greater prevalence of comorbidities than patients with primary osteoporosis. However, to the best of our knowledge, no studies comparing patients with primary osteoporosis and those with secondary osteoporosis with regard to perioperative medical complications after spinal instrumentation surgery have been reported.
The present study was the first to directly compare perioperative medical complications after posterior approach spinal instrumentation surgery for OVC between patients with primary osteoporosis and those with secondary osteoporosis. The present study found no significant differences between the groups in terms of age, gender, BMD, osteoporosis treatment, OVC distribution, surgical procedure, or parameters for operative invasiveness. Postoperative SSI resulted from multiple patient- and procedure-related factors. Surgeons typically tend to select less invasive surgical procedures for patients with comorbidities, and this may reduce the incidence of complications. However, the results of the present study indicated that the incidences of perioperative medical complications are comparable between the primary and secondary osteoporosis groups under the same conditions of patient background and operative invasiveness.
In the present study, the incidence of perioperative medical complications did not significantly differ between the primary and secondary osteoporosis groups (16.1% vs. 22.9%); however, SSI was 6.3 times more common in the secondary osteoporosis group (11.4%) than in the primary osteoporosis group (1.8%; p<0.05). Furthermore, 2 patients in the secondary osteoporosis group, but none in the primary osteoporosis group, developed deep SSI requiring surgical intervention. In particular, 1 patient in the secondary osteoporosis group experienced severe deep SSI involving MRSA. These results suggest that the overall incidence of perioperative medical complications is similar between the primary and secondary osteoporosis groups under the same conditions of patient background and operative invasiveness; however, careful observations for the development of severe SSI should be performed in patients with secondary osteoporosis.
SSI should be avoided after spinal instrumentation surgery. In general, the presence of instruments increases the risk of SSI following spine surgery. The reported incidence of SSI following spinal instrumentation surgery (3.2%–7.2%) [
10111213] was higher than that following non-instrumented surgery (0.9%–2.6%) [
1415]. Established patient-related risk factors for SSI include advanced age, obesity, diabetes mellitus, malnutrition, smoking, glucocorticoid use, and previous spinal surgery [
1617]. Osteoporosis is also considered to be a patient-related risk factor for spinal instrumented arthrodesis [
17]. Schimmel et al. [
8] reviewed 1,568 patients (1,615 procedures) who underwent lumbar or thoracolumbar spine fusion and compared 36 patients with deep SSI (2.2%) after surgery with 135 randomly selected uninfected patients to identify risk factors for SSI. Diabetes mellitus was the most important patient-related risk factor, with the risk of SSI almost six times higher than that in non-diabetic patients (odds ratio [OR], 5.92; 95% confidence interval [CI], 1.23–28.5;
p=0.026), followed by smoking habits (OR, 2.33; 95% CI, 1.02–5.32;
p=0.045) [
8]. Diabetes and smoking are associated with tissue ischemia and small vessel damage, predisposing to an increased risk of SSI [
16]. In the present study, diabetes mellitus was the most frequent cause of secondary osteoporosis.
Among comorbidities, kidney disease is considered the greatest risk factor for complications, including SSI. Puvanesarajah et al. [
18] recently reported data from the Medicare database in the United States and found that among patients who underwent lumbar spinal fusion, the kidney disease cohort had increased rates of all medical complications compared to the control cohort comprising all other patients (21.3% vs. 14.2%; OR 1.64, 95% CI 1.44–1.85,
p<0.001), with increased rates of infection also observed in the kidney disease cohort (4.4% vs. 1.8%; OR, 2.43; 95% CI, 1.87–3.16;
p<0.001). Both 90-day (1.1% vs. 0.2%; OR, 5.05; 95% CI, 2.90–8.77;
p<0.001) and 1-year (1.9% vs. 0.7%; OR, 2.77; 95% CI, 1.87–4.11;
p<0.001) mortalities were significantly higher in the kidney disease cohort than in the control cohort [
18]. According to Puvanesarajah et al. and our experience in the present study of 1 patient with chronic renal failure who developed the most severe complication in our series of deep SSI with MRSA that required instrument removal, careful observation and strict anti-infection control are required to prevent SSI in patients with kidney disease.
Although the present study is, to our knowledge, the first to address the question of whether secondary osteoporosis is associated with more perioperative medical complications than primary osteoporosis after posterior approach spinal instrumentation surgery for OVC, several study limitations should be addressed. First, the present study was a retrospective study of a single cohort. Future prospective studies are required to determine the precise incidence of perioperative complications. Second, the present study focused only on medical complications; however, implant-related complications are also an important issue in patients with osteoporosis. The simultaneous assessment of medical and surgery-related complications for patients with primary osteoporosis and those with secondary osteoporosis should therefore be addressed in future studies. Third, the relatively small number of subjects compared to that previously reported epidemiological studies meant that we were unable to conduct multivariate analyses to evaluate the most significant factors affecting perioperative medical conditions in patients with primary osteoporosis and those with secondary osteoporosis. Further studies with larger populations are needed to verify our findings.