Surgical treatment of sacroiliac joint infection

Background Sacroiliac joint infection is rare and frequently missed; purpose of this study is to describe the clinical presentations, comorbidities, laboratory and imaging findings, surgical options and outcomes of this rare condition. Materials and methods We reviewed all cases of surgical treatment of sacroiliac joint infection operated at our institution between January 1994 and December 2011. Twenty-two patients were included: 14 females and 8 males, with mean age of 50 years. The mean follow-up period was 34 months. Twenty-four operations were performed. Coinciding infection was found in 11 cases (50 %). Twelve patients (54.5 %) presented acutely, while ten patients (45.5 %) had chronic infection. Results Tuberculous infection was diagnosed in 5 cases and nonspecific infection in 13 cases. In four cases, no organism was isolated. Eleven cases were subjected to debridement only, while debridement and arthrodesis was needed in 11 cases. Eight patients had excellent clinical results, five good, three fair and four poor; one patient was lost to follow-up, and one patient died after 2 weeks. The operative technique depended on the course of the infection, bone destruction and general condition of the patient. There was a significant change in C-reactive protein and erythrocyte sedimentation rate preoperatively and 6 weeks postoperatively, while the difference in white blood cell count was nonsignificant. Conclusions In acute cases, the primary aim should be to save joint integrity by early debridement, depending on joint destruction and general patient condition. When it is chronic, it is not secure only to debride the joint, which should be fused.


Introduction
Isolated sacroiliac joint (SIJ) infection is rare. Between 1878 and 1990, only 166 cases were documented in the English-language literature [1], although pyogenic sacroiliitis is estimated to account for 1-2 % of cases of septic arthritis or bone infection [2]. Skeletal tuberculosis accounts for 3-5 % of all tuberculosis, of which approximately 10 % occurs at the SIJ [3]. Predisposing factors include intravenous drug abuse, immune suppression, pregnancy, trauma and infection elsewhere in the body [4]. However, in over 40 % of patients, the primary site of infection may never be identified [1,5]. Clinical findings may be obscured, but usually include buttock pain and limping. In severe cases, the patient may be unable to find a comfortable position in bed and demonstrates a positive flexion, abduction and external rotation (FABER) test of the hip joint that dramatically aggravates the pain. Fever is not a constant finding [6]. Accurate diagnosis is frequently delayed due to lack of awareness of the condition by clinicians, non-specific clinical presentation and poorly localising signs of infection; mimicking features of septic arthritis of the hip, osteitis of the ilium and lumbar disc herniation [7][8][9]. Magnetic resonance imaging (MRI) has been proved to be the best tool for early diagnosis of SIJ infection. MRI findings in the acute phase are intra- articular fluid, subchondral bone marrow oedema, articular and periarticular post-gadolinium enhancement and soft tissue oedema, and in the chronic phase: periarticular bone marrow reconversion, replacement of articular cartilage by pannus, bone erosion, subchondral sclerosis, joint space widening or narrowing and ankylosis [10]. The purpose of this study is to describe the authors' experience regarding the clinical presentations, comorbidities, laboratory and radiological findings as well as operative options and postoperative outcome of sacroiliac joint infections.

Materials and methods
This is a retrospective clinical study in a single facility. Between January 1994 and December 2011, 22 patients were operated in our institution for treatment of sacroiliac joint infection. Cases of non-infectious sacroiliitis and conservatively treated infections were excluded from this study.
The criteria for diagnosis were: clinical; local pain and tenderness in the SIJ, limping, clinical manifestations and laboratory findings suggesting infection [chemical: elevated white blood cell (WBC) count, C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR); and microbiological: positive blood and/or intraoperative culture], in association with early MRI and late radiographic changes in the SIJ (periarticular bone destruction and cavitation, joint space widening, sclerosing); all confirming the diagnosis. Cases of non-specific infection were considered acute when presenting within 1 month of onset of clinical symptoms and chronic when presented later. All tuberculous cases were chronic. The mean follow-up (FU) period was 34 months (6-90 months). One patient was lost to FU, and one patient died 2 weeks after surgery due to multiple organ failure.
Clinical examination, laboratory investigations and plain radiographs were done routinely: preoperatively, 1 day and 2 weeks postoperatively and at the FU visits (6 weeks, 3 months, 1 year postoperatively and then every 2 years). Patients were followed up by their family physicians for clinical or laboratory changes. MRI was done preoperatively, after 3 months and 1 year (and when recurrence was suspected). Computed tomography (CT) was needed preoperatively only in nine cases for assessment of bone destruction and postoperatively for assessment of bony fusion, only when symptomatic.
Surgery was indicated (from senior author's experience, H.B.) in cases of failure of conservative measures, abscess formation from the beginning, bone destruction, septicaemia or neurological deficits.
All patients underwent operative treatment in the form of debridement with or without joint arthrodesis. The surgical approach was either posterior, anterior or combined anterior and posterior. The localisation of the infection (abscess and soft tissue infiltration) as demonstrated by MRI dictated the operative approach.
Postoperative treatment included culture-based antimicrobial therapy or broad-spectrum antibiotic therapy when no organism was isolated, for 6 weeks in non-specific infections and 6-12 months in tuberculous infections.
We concluded the final functional outcome by questionnaires including Odom's criteria [11] that categorised patients' satisfaction into four grades of excellent, good, fair and poor as follows: • Excellent: all preoperative symptoms relieved, abnormal findings unchanged or improved; • Good: minimum residual of preoperative symptoms not requiring medication or limiting activity, and abnormal findings unchanged or improved; • Fair: definite relief of some preoperative symptoms with others remaining unchanged or only slightly improved; • Poor: symptoms and signs unchanged from preoperative status or worse.
The infection was considered to be healed by the disappearance of clinical symptoms (pain, fever, fistula etc.) and laboratory parameters of infection (WBC, CRP and ESR) as well as radiographic and MRI confirmation of subsidence of infection (disappearance of bone oedema, abscess resolution etc.).
The joint was considered to be fused by the following radiographic criteria (when fusion is doubtful, follow-up CT after 1 year is advisable): 1. Absence of radiolucency crossing the entire joint space 2. Side-wall fusion and inter-run fusion 3. Absence of loosening or metal compromise in plain radiographs 4. Clinically: absence of local symptoms of the joint (pain and tenderness) Descriptive statistics were determined by calculation of the mean, standard deviation and range. Statistical analysis was needed to compare the preoperative laboratory

Results
Twelve patients (54.5 %) presented acutely, while ten patients (45.5 %) had chronic infection (Table 1). Marked weight loss was reported by two patients (9.1 %). At time of admission, coinciding infection was found in 11 cases (50 %), of which 6 cases were spondylodiscitis and 1 case was epidural abscess. Eight patients had received antimicrobial therapy.
Radiographs were done preoperatively in all patients. In the acute stage of non-specific infections it appeared to be normal, while in chronic cases it showed blurring of the outlines of the sacroiliac joint, widening of the joint space, periarticular osteopaenia, sclerosis and erosion of the joint margins. MRI was done preoperatively for all patients. It demonstrated abscess formation in the piriformis, iliacus, gluteus or iliopsoas muscle as well as inflammatory signal changes in the surrounding soft tissues. Anterior capsule may be stretched or damaged. Other findings included: bone oedema, soft tissue infiltration and myositis. CT was done preoperatively in nine cases with chronic infection and showed joint space widening, sclerosis of the margins of the joint, cavitations and sequestrum formation (Tables 2, 3).

Operative treatment
Eleven cases (50 %) were subjected to debridement only, while debridement and arthrodesis was needed in the other 11 cases. Two patients required revision because of recurrent infection (after complete healing); one was posteriorly debrided for the second time, and one had attempted fusion through anterior approach and was reoperated with a stand-alone cage; i.e. this study included 24 surgeries in the 22 reviewed patients ( Table 4). The mean operative time for debridement without fusion was 35 min for posterior approach, 62.5 min for anterior approach and 83.33 min for combined anterior and posterior approaches, while in debridement and fusion it was 85, 131 and 160 min, respectively (Fig. 1).
The postoperative immobilisation period depended on the general condition of the patient and the operative technique. Postoperative treatment included culture-based antimicrobial therapy or broad-spectrum antibiotic therapy when no organism was isolated (Table 4).
Sound fusion was achieved in ten cases (50 %) within the first year after surgery; in the other ten cases, no signs of fusion were found in final radiographs. Complications included recurrence of infection in two cases, delayed wound healing in three cases and chronic pain in three cases.

Discussion
SIJ infection is a rare condition [1] which is usually associated with multiple predisposing factors and infection elsewhere in the body [4]. Clinically, it may be obscured by hip pain and poorly localising signs of infection with or without fever [6][7][8][9].
Despite the limitations of this retrospective study, including a relatively heterogeneous group of patients with a wide variation of preoperative conditions and surgical methods and the lack of similar studies to compare with, it represents the largest series of surgical treatment of this rare condition. It identifies the clinical, laboratory and radiological findings as well as surgical options and outcomes of this joint infection.
Bacterial infection of the SIJ is thought to occur most commonly by haematogenous spread [5,12]. Vyskocil et al. [1] reviewed 166 reported cases of septic sacroiliitis and demonstrated that no associated factors were noted in 41 % of patients. In this series, there was an associated infection in 11 patients (50 %). Comorbidities were present in eight patients (36.36 %). The diagnosis of SIJ infection should be suspected in the presence of certain clinical, Fig. 2 a Case 9: MRI performed after admission showed high signal intensity in the right SIJ and adjacent muscles with abscess formation and bone oedema. b CT revealed widening of the joint space, cavitations and sequestrum formation. c Postoperative radiograph revealed good position of the cage and screws. The patient was allowed to bear weight with assistance after 6 weeks and to fully bear weight after 4 months, after confirmation of bony fusion of the joint. After 1 year, the patient had no complaints and was satisfied. d FU radiographs showed complete bony fusion of the joint. At the last FU visit (49 months postoperatively), she had excellent functional outcome, no pain and no limitations of daily activity. She returned to work and practised sport regularly laboratory and radiological findings. The clinical symptoms are local sacroiliac pain, low back pain with or without sciatic pain, associated with inability to bear weight in most cases. On the other hand, fever was not a constant presenting symptom [6]. In our study, only four patients (18.2 %) had fever. Other presenting symptoms included fistula and abscess formation. On local examination, there was always tenderness on direct pressure over the joint with positive Gaenslen's and FABER tests in all patients, which is consistent with the findings of Delbarre et al. [6] and Ramlakan and Govender [13].
Murphy et al. [14] showed that MRI in comparison with CT is both more sensitive for early diagnosis and superior in evaluation of cartilage integrity and early detection of osseous erosions in patients with inflammatory and infectious sacroiliitis. In our series, MRI was done in all patients preoperatively, while CT was done in only nine cases (40.1 %), in chronic cases for assessment of the extent of bony destruction and operative planning. Isotope bone scanning is a helpful tool for diagnosis; however, it has three main disadvantages: the inability to differentiate infectious from non-infectious sacroiliitis [2,8,12,15], the inability to differentiate sacroiliitis from psoas or gluteal abscess and the inability to identify spread of the infection from the joint into the surrounding tissues [16].
Our clinical results were excellent or good in 13 patients (65 %), these results being comparable to those of Schubert et al. [17], who performed debridement and primary arthrodesis in nine patients with pyogenic SIJ infections (Figs. 2, 3, 4).
There is debate over whether to perform arthrodesis of the joint or to limit surgery to drainage of the abscess and debridement of the joint. The operative management of SIJ infections, from our experience, consists of debridement in cases of acute soft tissue infection or cases of mild bone destruction. Joint arthrodesis is recommended in generally ill patients even with mild joint destruction for early  Preoperative MRI showed localised area of high signal inflammatory intensity in the right SIJ. The SIJ was debrided posteriorly. The patient was allowed to fully bear weight after 2 weeks. b CT confirmed solid joint fusion after 1 year. The last clinical FU after 86 months showed excellent outcome, no pain and normal daily activities assisted mobilisation as well as in patients with chronic joint affection (Fig. 5).
In acute cases, the primary aim should be to save joint integrity by early debridement, depending on joint destruction and general patient condition. When it is chronic, it is not secure only to debride the joint, which should be fused.