Disc (degenerate disc infection study with contaminant control) discussion on methods, interim analysis and comparison between pilot study and the disc trial: The pitfalls of not sending contaminant control

BACKGROUND CONTEXT: Studies that implicate disc infection in the majority of patients with axial back /neck pain or leg/arm pain is potentially scandalous and irresponsible. As the majority of these studies are underpowered and lack a contaminant arm, the current study is aimed to fulfill these basic criteria. PURPOSE: To evaluate if degenerative disc related back or neck pain and/ or radicular symptoms are caused by true infection with low virulent bacterial organisms. To obtain the true infection rate in the degenerative disc population as compared to the nondegenerateive population. To obtain the contamination rate in spine surgery patients and ascertain the true disc infection if in a subset. To compare disc culture positivity when a contaminant control sample is taken and not taken. STUDY DESIGN/SETTING: Multicentric trial involving 6 spine centers with 15 spine surgeons contributing. The study is a prospective casecontrol study: cases are patients undergoing discectomy for degenerative disc pathology and controls being patients undergoing discectomy for non-degenerative pathology like trauma, scoliosis or tumor cases. All patients undergoing discectomy (cervical/thoracic/lumbar) whether as microdiscectomy for radicular symptoms or a part of interbody fusion will be eligible to participate at the participating centers. Patients who consent for the study will undergo spine surgery as deemed appropriate by the respective spine surgeon. PATIENT SAMPLE: The study is planned as a prospective case- control study: cases are patients undergoing discectomy for degenerated disc pathology and controls being patients undergoing discectomy for nondegenerated pathology like trauma, scoliosis or tumor cases. All patients undergoing discectomy (cervical/thoracic/lumbar) whether as microdiscectomy for radicular symptoms or a part of interbody fusion will be eligible to participate at the participating centers. Patients who consent for the study will undergo spine surgery as deemed appropriate by the respective spine surgeon. OUTCOME MEASURES: 1. Disc culture positivity. 2. True disc positive culture. 3. Contamination rate. METHODS: Institutional ethics approval was obtained (HREC 13/218). The study is a multi-centric trial involving 6 spine centers with 15 spine surgeons contributing. The study is planned as a prospective case-control study. This includes patients undergoing discectomy for degenerative disc pathology and controls being patients undergoing discectomy for nondegenerative pathology such as trauma, scoliosis or tumor. In each case, disc material and paraspinal tissue were obtained, and prolonged aerobic and anaerobic cultures performed. True disc positivity was inferred if the culture of disc was positive and the paraspinal tissue sample was negative. RESULTS: To date, a total of 303 patients have been enrolled, with male: female = 52: 48. Group A (pilot study) includes 99 cases with disc only cultures; Group B includes 138 cases with disc and paraspinal tissue cultures; and Group C with 4 control cases. Surgical caseload includes: 29% anterior cervical fusion, 28% anterior lumbar fusion, 45% lumbar discectomy and 8% posterior lumbar fusions. Twelve patients presented with neck pain, 49 with arm pain, 113 with leg pain and 129 with leg/back pain. Seven patients had diabetes and 29 patients were smokers. Twenty percent of the patients received transforaminal or epidural or facet joint injections prior to surgery. Group A patients included those as a part of the initial pilot study. In Group A, 18% were culture positive with p. acnes predominant (52%). In Group B, 8.7% were true positive (disc +ve / paraspinal -ve) with paraspinal positive samples in 38.4% on its own or with disc being positive, too (34 cases). In cervical cases, the disc-only cultures were positive in 35.7 % whereas true disc culture positive was found in only one patient (1/31 = 3%). Similarly in lumbar discectomy patients with disc-only cultures there were 16.7% culture positive (p. acnes = 80%) while in both disc and the contaminant arm (group B), there were 2/37 cases positive (5%). CONCLUSIONS: 1. The true rate of disc culture positivity in the degenerative disc population is significantly lower than previous literature reports. 2. At the interim analysis stage, the DISC study heavily favours performing disc cultures strictly with a contaminant control.