2.1. Treatment protocol

The following clinical signs, symptoms, and laboratory tests were considered suggestive of post‐spinal surgery SSI: postoperative fever, gradual aggravation of lumbar nerve root irritation, deep local tenderness and percussion pain, low back and leg pain that was exacerbated by turning over and other movements, redness and swelling of the wound, fluctuation around the incision, C‐reactive protein, ESR and procalcitonin levels were abnormally elevated compared to the first day after surgery. Once spinal infection was suspected, further magnetic resonance imaging or ultrasound examination was performed for confirmation and empirically‐chosen broad‐spectrum antibiotics were administered. CSI or percutaneous micro‐drainage tube irrigation was implemented immediately after diagnosis of spinal infection on the basis of clinical signs and symptoms and laboratory test and imaging findings. CSI was the standard procedure before we developed percutaneous micro‐drainage tube irrigation, so all patients underwent CSI. Once we had developed percutaneous micro‐drainage tube irrigation, a subset of patients with post‐operative spinal infections underwent the new procedure. For patients whom ultrasound examination showed a large amount of effusion at the surgical site, we chose micro‐drainage tube irrigation for treatment, while other patients chose CSI for treatment.

For patients in the microtube drainage group, bedside US examination was performed to determine the optimal site of puncture for insertion of one or more catheters. The surgical field was then routinely disinfected and covered with a sterile surgical cloth. After induction of local anaesthesia at the puncture site, an epidural needle was inserted into the infected cavity and exudate aspirated for bacterial culture and drug sensitivity testing. An epidural puncture catheter (microtube) was placed along the inner core of the needle. After removing the needle core, the microtube was secured to the skin with strong tape to prevent its detachment (Figure 1D–F). The number of microtube inserted varied on the basis of the size of the cavity. One end of each microtube was connected to a high negative pressure drainage device, after which the device was opened. When local injection of antibiotics was required, the negative pressure drainage device was clamped and the drug(s) injected via the microtube for several hours, after which negative pressure was again applied. Antibiotics were adjusted on the basis of the results of bacterial culture and drug sensitivity testing, the required agents being injected along the microtube into the infection site as needed. Changes in white cell count, C‐reactive protein, ESR and procalcitonin were monitored. The drain was removed after 3 consecutive days of almost no drainage and normal laboratory findings.

Two cases of surgical site infection after spinal surgery were treated by two methods. (A) Appearance of surgical site exudation on day 12 after spinal fixation surgery. (B) Thorough debridement was performed to remove pus that had emerged around the internal fixation device. (C) CSI system was used after debridement. (D) Surgical site exudation occurred 4 days after spinal fixation surgery. (E) Procedure of PMDTI combined with high NPTD operation. (F) Micro‐drainage tube irrigation and high negative pressure tube drainage was treated.

In the patients who underwent meticulous debridement followed by CSI, the debridement was performed by opening the original surgical incision. During this procedure, further specimens were collected for bacterial culture and drug sensitivity testing and the implants were checked for looseness or instability. All pus, inflammatory necrotic tissue, contaminated bone graft, and granulation tissue attached to the surfaces of the internal fixation were completely removed. The incision was washed repeatedly with a diluted iodine complex and large volumes of normal saline. One or two flushing tubes were placed at the proximal end of the incision and one or two drainage tubes at its distal end. The flushing and drainage tubes were placed across each other, and the muscles, lumbar dorsal fascia, and skin were intermittently sutured (Figure 1A–C). Antibiotic therapy was adjusted on the basis of the results of bacterial culture and drug sensitivity testing. The wound was washed daily with 8000 mL gentamicin or antibiotics to which the cultured organisms were sensitive, at a rate of 150 drops per minute. The washout time was generally about 12 h. The flushing tubes were removed once indicators of infection had resolved, including drainage fluid culture being negative on two consecutive occasions.

The timing of discharge was determined by the surgeon—generally 2–3 days after removal of the drainage or negative pressure suction tubes, provided laboratory indicators were acceptable. After discharge, all patients continued to take oral antibiotics as directed by their doctors and were followed up regularly. SF‐36 physical function scores were estimated at 3 and 6 months of follow‐up.