Paper of the Week: Occult infection in pseudarthrosis revision after spinal fusion

Marco D. Burkhard, MD; Ruben Loretz, MD; Ilker Uçkay, MD; David E. Bauer, MD; Michael Betz, MD; Mazda Farshad, MD, MPH

The Spine Journal 2021; (3):370-376
DOI: 10.1016/j.spinee.2020.10.015

Summary by Gregory R. Toci, BS

Revision surgery following spinal fusion is not uncommon, and pseudarthrosis has been reported as the indication in over 40% of revision procedures.¹ Pseudarthrosis results from inadequate bony fusion following a spinal fusion procedure and there are many suspected causes, including instability of the implanted construct, poor bone quality, and infection.^2,3 However, the specific cause is rarely determined and many surgeons do not perform a microbiologic workup unless they suspect infection.

To determine the rate of underlying infection in revision spine surgery for pseudarthrosis, Buckhard et al. retrospectively reviewed 128 patients with detailed microbiological workup for presumed aseptic pseudarthrosis of the thoracolumbar spine. Pseudarthrosis was determined by postoperative imaging, and asymptomatic patients were excluded. During each procedure, at least three tissue samples were collected and the removed hardware was sonicated. The primary outcome of the study was infection, which was diagnosed if at least two intraoperative samples showed growth of the same species or if at least 50 colonies of a bacterial species grew in the sonication fluid.

Of the 128 patients, 13 (10.2%) were diagnosed with infection. The predominant pathogen was Cutibacterium acnes (46.2%), followed by coagulase-negative staphylococci (38.5%). Infection was associated with elevated CRP on admission (9.4 mg/L vs. 5.7 mg/L, p=0.031), increased BMI (30.9 kg/m² vs. 28.2 kg/m², p=0.049), and fusion involving the thoracolumbar junction at the index procedure (46.2% vs. 18.3%, p=0.019). Infection was more common in patients with CRP >5.0 mg/L (63.6% vs. 33.0%, p=0.049).

The authors concluded that occult infection is present in approximately 10% of revisions for aseptic pseudarthrosis, and it is more common in patients with elevated CRP, increased BMI, and fusion of the thoracolumbar junction. However, there are limitations to these findings which warrant discussion. First, it is unknown if the microbiologic findings were related to pre-revision symptoms, as the most common pathogen was C. acnes, which is frequently found in indolent shoulder infections.⁴ Further, the infection rate of 10% may be related to contamination, and the authors were unable to distinguish colonization from low-grade infection. Lastly, whether antibiotic treatment would improve outcomes or limit further complications in these patients remains unclear, and future research should be performed to determine if these occult infections are of clinical significance.

References:

1. Pichelmann MA, Lenke LG, Bridwell KH, et al. Revision Rates Following Primary Adult Spinal Deformity Surgery. Spine 2010;35:219–26.
2. WITTENBERG RH, SHEA M, SWARTZ DE, et al. Importance of Bone Mineral Density in Instrumented Spine Fusions. Spine 1991;16:647–52.
3. Hollern DA, WOODS BI, SHAH NV, et al. Risk Factors for Pseudarthrosis After Surgical Site Infection of the Spine. Int J Spine Surg 2019;13:507–14.
4. Saper D, Capiro N, Ma R, et al. Management of Propionibacterium acnes infection after shoulder surgery. Curr Rev Musculoskelet Medicine 2015;8:67–74.