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Dural Scarring and Repair Issues
Background
A vast majority (up to 80%) of the US population are estimated to experience an episode of low back pain (LBP) during their lifetime. A subset of these individuals will go on to develop chronic LBP, which can limit their ability to perform activities of daily living (ADLs) and frequently, may hinder the ability to maintain gainful employment. This imposes a significant economic burden on the healthcare system via the increased utilization of healthcare resources. The extent to which chronic LBP affects the US population cannot be overstated. A cross-sectional survey of over 5000 American households, published in 2009, found the prevalence of chronic LBP to be 10.2% in 2006, a substantial increase from a similar analysis performed by the same authors in 1992 (3.9%). Of patients with debilitating back pain, an estimated 3% will require surgical intervention.
Although the index operation may portend excellent clinical outcomes for some, a subset of patients will develop either recurrence of their symptoms or new onset symptomatology (including either ipsilateral or contralateral back and/or leg pain) in the months to years following their initial operation. The rationale for why this occurs is grounded in multiple factors including the initial condition that was treated, whether a decompression was performed alone or in combination with a single-level or multi-level fusion, and the development of distinct pathological processes that can occur secondary to the index operation. These processes include adjacent segment degeneration/disease (ASD), lumbar pseudarthrosis, recurrent disc herniation, residual or recurrent spinal stenosis, instrumentation failure, wound-related complications, iatrogenic flatback syndrome, and cerebrospinal fluid (CSF) leak/pseudomeningocele development. Other factors that can influence the success of the index surgery include the duration of symptoms before surgery, the patient’s psychosocial health, and patient-specific factors such as other medical comorbidities, body mass index (BMI), smoking status, bone quality, and chronological age.
Revision Lumbar Spine Surgery
In patients with recurrent radicular pain and/or symptomatic spondylosis following surgery who present with radiographic evidence of pathological changes within the lumbar spine, revision lumbar spine surgery may be necessary. The incidence with which these patients are reoperated varies considerably in the neurosurgical literature, depending on the presenting pathology. The rates of recurrent lumbar disc herniation after discectomy, for example, can vary from 5% to 15%, with a subset of patients requiring repeat surgery to address persistent symptoms after failing conservative measures. Other pathologies, such as ASD following a lumbar fusion, can occur more frequently, necessitating that a greater fraction of patients are reoperated. Ghiselli et al., for example, documented a 27.4% reoperation rate (decompression with and without arthrodesis) in their series on 215 patients who had originally undergone posterior lumbar fusions because of symptomatic degeneration at adjacent segments. This rate, the authors observed, was higher in patients in whom the fusion was limited to the lumbar spine, and which did not extend to either the thoracic or sacral spines.
Regardless of the rationale for repeat lumbar surgery, the operating surgeon must be cognizant that a revision procedure is typically more technically challenging to perform and is associated with more inconsistent outcome results than the index surgery. The possibility for a compromised vascular supply during the revision surgery leading to wound healing-related complications, the potential for increased intraoperative blood loss, the presence of a distorted anatomy making it difficult to locate bony landmarks, and epidural scarring or fibrosis increasing the risk for durotomy are all aspects of a revision lumbar spine surgery that the surgeon must be aware of. The management of this last aspect, the possibility for epidural scarring/fibrosis which can predispose to durotomy, will be discussed in greater detail in this chapter.
History Taking and Physical Examination
Careful selection of patients in whom revision lumbar surgery is indicated is essential. Obtaining a thorough history and performing a meticulous neurological examination are the first steps in the work-up of patients presenting with either recurrent or new symptoms of back and/or leg pain who have previously undergone lumbar spine surgery. Key elements to gather from the history include any changes in motor function, any sensory abnormalities (i.e., numbness or tingling), any autonomic difficulties (bowel, bladder, or sexual dysfunction), and any reports of pain. Important components of the history include whether a CSF leak occurred during the index surgical procedure. This is best determined by asking the patient directly as well as by carefully reviewing the operative report from the initial surgery. Patients should also be asked whether a lumbar subarachnoid drain was used in the perioperative period. In addition, the patient should be queried as to whether they had persistent wound drainage or whether revision surgery was necessary to repair a CSF leak.
The physical examination should include a detailed general evaluation and a comprehensive neurological examination that include a full evaluation of motor and sensory function, assessment of deep tendon reflexes, and gait assessments. Additionally, the range of motion of the hip and knee joints should be evaluated to rule these out as occult causes of pain. A full assessment of the patient’s mental status and psychological health should be performed during this initial meeting. This is particularly important, as addressing any issues with regards to this before revision surgery has been shown to improve outcomes.
Using the combination of the clinical history and the physical examination is important in attempting to identify the pain generator/pathology at this stage, often before obtaining the necessary imaging studies. The presence of constitutional symptoms such as a fever, chills, weight loss, and/or night sweats in combination with back pain may point the practitioner toward infectious or neoplastic etiologies rather than toward a degenerative or mechanical one. The presence of radicular pain and signs of neurological compression in a patient who had previously undergone a lumbar discectomy and had been asymptomatic for several (6 or more) months may be indicative of a recurrent disc herniation. A pseudarthrosis, meanwhile, can present with recurrent mechanical back pain and neurological symptoms in a patient with a prior fusion attempt months to years after the index surgery. Importantly, in patients with prior posterior lumbar surgery, myofascial pain secondary to dissection of the paravertebral musculature can be present and is important to distinguish from true neuropathic pain.
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