Clinical Results Of A Lamina With Spinous Process And An Iliac Graft As Bone Grafts In The Surgical Treatment Of Single-Segment Lumbar Pyogenic Discitis: A Retrospective Cohort Study

Background: A retrospective study investigated and compared the results of a lamina withspinous process (LSP) and an iliac graft (IG) as bone grafts in single-segment lumbar pyogenic discitis (LPD) through one-stage-posterior-only approach with radical debridement and internal instrumentation. Methods: Data from 37 patients were reviewed. A LSP was placed in 17 patients (group A), and an IG was implemented in 20 patients (group B). The surgery time, surgery hemorrhage, hospital stay, drainage, and follow-up (FU) were reviewed. The visual analogue scale (VAS), Oswestry Disability Index (ODI), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, segmental angle, intervertebral height and bony fusion time were compared preoperatively and at the nal FU. Results: All patients were followed-up for a mean of 27.94±2.35 months in group A and 30.29±1.89 months in group B, without a difference. The mean age was younger in group A than in group B (P<0.05). The surgery time, surgery hemorrhage, and hospitalization cost were lower in group A than in group B (P<0.05), except for the hospital stay and drainage time. Fever occurred in 10 patients in group A and 12 patients in group B. The ESR, CRP level, and VAS and ODI scores were signicantly decreased, and there were no signicant differences between the groups at the nal FU. The distribution of bacterial agents in blood culture was 1 case of Aerobacter cloacae, 2 of Staphylococcus aureus, 2 of Escherichia coli, and 1 of Streptococcus viridis in group A and 1 of S. aureus (cid:0) 1 of Staphylococcus warneri and 2 of Klebsiella pneumoniae in group B. Pyogenic infection was observed in the pathological ndings of all patients. No signicant difference was found in the mean segmental angle or mean intervertebral height preoperation and at the nal FU

Results: All patients were followed-up for a mean of 27.94±2.35 months in group A and 30.29±1.89 months in group B, without a difference. The mean age was younger in group A than in group B (P<0.05). The surgery time, surgery hemorrhage, and hospitalization cost were lower in group A than in group B (P<0.05), except for the hospital stay and drainage time. Fever occurred in 10 patients in group A and 12 patients in group B. The ESR, CRP level, and VAS and ODI scores were signi cantly decreased, and there were no signi cant differences between the groups at the nal FU. The distribution of bacterial agents in blood culture was 1 case of Aerobacter cloacae, 2 of Staphylococcus aureus, 2 of Escherichia coli, and 1 of Streptococcus viridis in group A and 1 of S. aureus 1 of Staphylococcus warneri and 2 of Klebsiella pneumoniae in group B. Pyogenic infection was observed in the pathological ndings of all patients. No signi cant difference was found in the mean segmental angle or mean intervertebral height preoperation and at the nal FU between the groups.
Conclusion: The use of LSP as a new bone graft is reliable, safe, and effective for surgical management for the LPD while surgery is proposed as a good management strategy for LPD in carefully selected patients.

Background
Lumbar pyogenic discitis (LPD) is di cult to diagnose because of its insidious start and indolent course, and it is a rare infection with an increase in the growing number of human immunode ciency virus (HIV) coinfections, bacterial resistance and population migration [1][2][3]. The diagnosis of LPD is usually delayed a few months and may initially be misdiagnosed and mishandled as a degenerative disease [3][4]. LPD is often monomicrobial and most commonly due to Staphylococcus aureus. The management should be depend on the results of culture and in vitro susceptibility test [5][6].
Most patients are cured after 6 weeks or more of antimicrobial therapy, but a few patients may require surgical debridement and/or spinal reconstruction during or after antimicrobial therapy [5][6]. LPD can result in destructive lesions or neurological impairment, which is indicated for surgery. Although the surgical approaches for LPD are controversial, surgical treatment can provide better pain relief and quality of life. After meticulous and radical debridement, bone grafts play a key role in surgery by curing LPD, as they can rebuild spinal stability and maintain alignment when patients suffering from neurological de cits are indicated for surgery [7][8][9][10]. In our study, we compared a lamina with spinous process (LSP) and an iliac graft (IG) as bone grafts in treating single-segment LPD through a posterioronly approach with debridement and internal instrumentation.

Patient selection
From January 2014 to December 2016, 37 patients with single-level LPD were reviewed retrospectively and were divided into two groups. When we communicated with patients before surgical management, the advantages and disadvantages of the therapy plans with the two types of bone grafts were fully introduced so that the patients could choose the right therapy. The surgeries were performed by the same senior spine team. The inclusion criteria were as follows: adult single-level LPD, a one-stage-posterior-only approach, internal xation and fusion, and patients indicated for surgery due to failure to respond to antimicrobial treatment or source control, neurological de cits, or bone destruction affecting stability. The exclusion criteria were as follows: spinal tuberculosis, fractures, spine metastasis and cancer.

Surgical procedure
After the successful general anaesthesia and the patients placed in the prone position, through a midline incision, the posterior spinal elements including the lamina and facet joints were fully exposed. The pedicle screws were xed exactly according to imaging and C-arm X-ray ndings. Decompression and complete debridement were performed. The LSP or IG was cut off for complete resection, and they were trimmed for a suitable bone graft ( Figure 1). According to the area remaining after complete debridement, one graft was implanted and appropriately locked with strong instrumentation. Vancomycin (1.0 g) mixed with gelatine was used locally around the graft. The drainage and lavage with saline were applied postoperatively. The specimens were sent for bacterial culture and pathological testing. The patients wore a brace for 6-8 weeks after surgery.

Postoperative care
Rehabilitation therapist-guided ambulation exercises were started 1 week after the operation.All the patients were recommended to undergo antimicrobial therapy for 8-12 weeks after surgery. All patients underwent clinical and imaging examinations 1 week, 12-week, 6-month, 1-year and annually after surgery.

Follow-up index
The following data were recorded perioperatively and during FU. (1) The surgery time, surgery hemorrhage, hospital stay, drainage, the FU time and bony fusion time were recorded. (2) Pathological ndings: tissue edema or in ammatory cell in ltration. 3 The segmental angle was recorded. According to the Cobb method, the segmental angle was de ned as the angle formed between the superior endplate of the upper vertebral body and the inferior endplate of the lower vertebral body. (4) The intervertebral height was de ned as the vertical height between the upper and lower vertebral bodies of the fused segment on lateral X-ray. (5) The VAS and ODI were recorded. (6) The ESR and CRP were recorded. Bony fusion was evaluated by X-ray and CT when necessary, by Bridwell criteria [11]. All radiographic data and measurements were reviewed by one senior spine surgeon and one senior radiologist.

Statistical analysis
The statistical analysis was performed using the Statistical Analysis System (SAS Institute Inc., Cary, NC, USA). The results are expressed as the mean ± SD. Differences with P values < 0.05 were considered statistically signi cant.

Clinical assessments
All patients were followed up on average of 27.94±2.35 months in group A and 30.29±1.89 months in group B,with no difference (P>0.05).The mean age was younger in group A than in group B (P<0.05).The surgery time, blood loss, and hospitalization cost were lower in group A than in group B (P<0.05), except for the hospital stay and drainage time (Table 1). Fever occurred in 10 patients in group A and 12 patients in group B, without a difference (P>0.05). The mean time of antibiotic therapy before surgery was 17.62±3.76 days in group A and 13.86±4.71 days in group B, without a difference (P>0.05). The ESR, CRP level, and VAS and ODI scores were signi cantly decreased, and there were no signi cant differences between the groups at the nal FU ( Table 2). The distribution of bacterial agents in blood culture was 1 case of Aerobacter cloacae, 2 cases of Staphylococcus aureus, 2 cases of Escherichia coli, and 1 case of Streptococcus viridis in group A and 1 case of S.aureus, 1 case of Staphylococcus warneri and 2 cases of Klebsiella pneumoniae in group B (Table 3). In stool, urine or surgical material culture, no bacterium was isolated. Pyogenic infection was observed in the pathological ndings of all the patients (Figure 2).

Radiological assessments
LPD was fully cured, and the bone fusion at a mean time of 11.30±4.751 months in group A was longer than that in group B (6.80±1.50) (Figures 3, 4). No signi cant differences were found in the mean segmental angle or mean interventricular height preoperation and at the nal FU between the groups (P>0.05).

Complications
Some postoperative complications occurred, such as super cial infection (4 cases in group A and 5 in group B), which healed with dressing changes.   Discussion LPD diagnosis can be very di cult, especially in a resource-poor environment. This challenge stems from the relative rarity of the disease, a much higher incidence of non-speci c back pain in the whole population, changes in protein expression, non-pathogenic imaging and positive rates from culture [11][12]. The main means of diagnosis are spinal imaging and spinal biopsy materials for microbiological examination and ideal histopathology. In any infectious disease, the therapy should be based on the results of culture and in vitro susceptibility testing. According to Infectious Diseases Society of America(IDSA) clinical practice guideline for the diagnosis and treatment of native vertebral osteomyelitis in adults, LPD is frequently monomicrobial and most often due to Staphylococcus aureus [5][6][13][14]. The local administration of VCM was usually performed for better control of infection. However, in our study, although blood culture isolated the bacterium, the positive culture rate was 35.2% in group A and 20% in group B, but there were no ndings in the stool, urine or surgical material culture [15][16]. There were only 3 cases of Staphylococcus aureus in the two groups. Perhaps because the regimens of antibiotic therapy and the methods of administration were empirical, in the study, the mean times of antibiotic therapy before surgery, which were 17.62 ± 3.76 days in group A and 13.86 ± 4.71 days in group B, could explain why we had more di culty with the diagnosis as well as the morbidity and mortality of effective treatment, and the culture positive rate was low.
Most patients are cured with a course of 6 weeks or more of antimicrobial therapy, but a few patients may need surgical debridement and/or spinal reconstruction during or after antimicrobial therapy. After complete lesion debridement, numerous interbody bone grafts are applied to recover and reconstruct spinal stability [17][18][19]. Titanium mesh cages(TMCs) lled with autologous bone grafts have been widely applied and could achieve high bony fusion rates. However, the surgical planning and results could be affected by the subsidence, stress shielding, and radio-opacity [20]. Thus, our research aimed to nd a new bone graft that could provide biomechanical support and achieve bony fusion to reduce the incidence of complications. The use of a LSP as the bone graft has several advantages. Firstly, compared with the IG, the LSP were more minimally invasive, shorten the surgery time, and reduce postoperative complication rates. Secondly, in the study, the mean time of bone fusion was 11.30 ± 4.751 months in group A, which was longer than that in group B (6.80 ± 1.50). Although the LSP gained a longer time of bone healing, with the correction of segmental kyphosis, there was no signi cance among the groups. Hence, the LSP could provide excellent biomechanical support, strength, and bone fusion properties.
Furthermore, the LSP, as an autologous bone graft, has a cortical bony structure supporting the bone defect space and can ensure and maintain segmental stability and alignment. After the surgery, the VAS and ODI scores were improved signi cantly, which improved the life quality of the patients.
Although the diagnosis of LPD is very di cult, some clues can be identi ed: severe low back pain, fever, increasing infection indexes, magnetic resonance imaging (MRI), C-arm-guided biopsy, and clear pathogenic bacteria from cultures [17][18][21][22][23]. However, there is a50% misdiagnosis rate,and pathological ndings are still the gold standard despite the culture of blood, urine, stool, or surgical tissue being negative. MRI is considered the modalityof choice for radiographic diagnosis, especially in severe lower back pain. Previous studies have reported an MRI sensitivity of 96%, a speci city of 93% and an accuracy of 94% in LPD, and MRI plays the key role in the continuous observation of LPD [24][25][26][27].
However, we declare that the study had a few limitations. First, the retrospective natureof the smallsample study may be associated with bias, more patients need to be included in the study. Second, the single LSP as a bone graft had a long bony fusion time and may be a risk factor for the delay of bony fusion.Third, the study did not consider intra-or inter-observer differences, which was associated with bias. In the future, prospective, randomized studies with long-term follow-up periods are needed.

Conclusion
Our study results showed that the use of a LSP could be a new bone graft in treatingsingle-segment LPD in carefully selected patients, resulting in good bone fusion and spinal stability restoration,as it could be a reliable, safe, and effective bone grafting method. The Institutional Review Board of the First A liated Hospital of Chongqing Medical University approved this study and conducted in accordance with the Declaration of Helsinki. All participants provided written informed consent before their data were stored in our hospital database.

Figure 1
Photographs of one LSP that was implanted (A, B), and the LSP was veri ed for stability(C).

Figure 2
The pathological ndings demonstrated oedema and in ammatory cell in ltration in the tissue