Evaluation and Reasons for Failed Back Surgery
First defined by North in 1991, failed back surgery syndrome (FBSS) is a global term defining a non-satisfactory outcome of a spine surgery characterized by persistent axial pain with or without a neurological component.1 This pathology comprises a mismatch of situations including patient dissatisfaction and surgeon disappointment from their surgical expectations.2
In recent years, a thorough comprehension of spine mechanics and pain pathophysiology has contributed to a better evaluation and reasonable understanding of FBSS, thus facilitating comprehensive treatment options.
With time, the number of spine surgeries, particularly spinal fusion, is exponentially increasing3 and hence the FBSS. In the literature, its reported incidence is variable depending on the surgical procedure performed. Lumbar diskectomy has the lowest incidence of FBSS ranging from 8.4%4 to 19%.5 After decompressive lumbar surgery, FBSS occurs in 25% to 30% of patients.6,7 Chan and Peng reported a 10% to 40% failure rate after lumbar decompression with or without fusion.2
Recently, more and more aggressive surgeries have been performed to treat difficult cases in adults and old patients. With all the problems inherent in their pathology such as spine deformities and osteoporosis, the rate of FBSS has increased.
REASONS OF FBSS
The etiology of FBSS is multifactorial. It could be divided into preoperative, perioperative and postoperative factors.2
Preoperative factors are especially related to the patient’s characteristics, to the spinal problem itself, and to the surgical procedure per se.
Patient psychological factors such as anxiety, depression, and hypochondriasis increase the rate of FBSS. Additionally, the social framework of the patient including workers’ compensation injuries, litigation, and poor socioeconomic status have a negative impact on surgical outcomes.2 Carragee et al.8 demonstrated that psychological factors are more important in some cases than structural abnormalities in prediction of low back pain. Many studies have described genetic predisposing factors to chronic pain, particularly the A118 gene.9
Clearly, all these factors do not exclude the presence of an organic problem, but require special attention and optimization before surgery.10 Thus, patients presenting with lumbar disk disease symptoms with poor psychometric scores may benefit from an earlier surgical intervention as prolonged distress and pain may reduce further the already compromised benefits from surgical intervention.11
This category incorporates several factors, all due to insufficient understanding of the patient’s pathology and poor surgical technique. They can be divided into two main subcategories: those related to decompression and those related to fusion with or without instrumentation.
Problems of Decompression
The incidence of incorrect level of operation is between 2.1% and 2.7%, particularly in minimally invasive techniques.2 Inability to achieve an adequate release of a nerve root particularly in the lateral recess and the neural foramen is a frequent reason of FBSS.12 In many cases, even with good surgical technique, the manipulation of the nervous structures can lead to ongoing problems and recurrence of pain.2
Extensive decompression may lead to instability if more than 50% of the facets are removed bilaterally or 100% unilaterally.12 On the other hand, the incidence of spinal instability also increases with the number of surgeries performed: 12% after the first surgery and up to 50% after the fourth surgery.13
Problems of Instrumentation and Fusion
Any technical insufficiency, such as implant malpositioning, can produce a new symptom of pain following surgery.
A comprehensive understanding of the spine biomechanics and balance is mandatory when spinal instrumentation and fusion is performed. Glassman et al.14 have demonstrated the importance of coronal balance restoration with a C7 vertical axis lying less than 4 cm from the central sacral vertical line. This issue has been found to be a very good predictor of postoperative clinical outcomes. On the other hand, restoring sagittal balance corresponding to patient’s age is of greatest importance because sagittal malalignment has been proved to correlate with disability.15 Hence, restoration of a sagittal vertical axis (SVA) less than 5 cm,16 a lumbar lordosis that fits the patient’s pelvic incidence,17 a pelvic tilt and thoracic kyphosis that fit the patient’s age,18 and pelvic incidence19 have been found to have a direct correlation with patient’s postoperative quality of life. Even more, Schwab et al.15 described an age-adjusted alignment threshold to reach, taking into account pelvic tilt, lumbar lordosis, and SVA.
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