Frailty and sarcopenia do not predict adverse events in an elderly population undergoing non-complex primary elective surgery for degenerative conditions of the lumbar spine

Background context: Sarcopenia measured by normalized total psoas area (NTPA) has been shown to predict mortality and adverse events (AEs) in numerous surgical populations. The relationship between sarcopenia and postoperative outcomes after surgery for degenerative spine disease (DSD) has not been investigated.

Purpose: This study aimed to determine the relationships between sarcopenia, frailty, and postoperative AEs in the elderly DSD population. Secondary objectives were to describe the distribution and predictors of NTPA and to determine the relationship between sarcopenia, frailty, and length of stay, discharge to a facility, and in-hospital mortality.

Study design: This is an ambispective study from a quaternary care academic center.

Patient sample: A total of 102 patients over 65 years old who underwent elective thoracolumbar surgery for DSD between 2009 and 2013 were included in this study.

Outcome measures: The primary outcome was a composite of perioperative AEs; the secondary outcomes were length of stay, discharge disposition, and in-hospital mortality.

Methods: Total psoas area (TPA) at mid-L3 level on preoperative computed tomography scan adjusted for height (NTPA) defined sarcopenia. The modified frailty index (mFI) of 11 clinical variables defined frailty. The distribution and predictors of sarcopenia (NTPA) were determined. The association of NTPA with AEs, length of stay, discharge disposition to care facility, and mortality was analyzed, including adjusting for known and suspected confounders using multivariate regression.

Results: Median Spine Surgical Invasiveness Index was 8 (interquartile range 2-10), and mean NTPA was 674 mm²/m² (293.21-1636.25). Using the mFI, 20.6% were pre-frail and 19.6% were frail. Inter- and intraobserver reliability for determining NTPA were near perfect with kappa 0.95-0.97 and 0.94-1.00, respectively. The NTPA was independently associated with patient gender and body mass index (BMI) but not frailty (mFI). Age, BMI, mFI, and American Anesthesiologists' Society score were not associated with incidence of postoperative AEs. The NTPA did not predict the occurrence of AE (odds ratio [OR] 1.06 per 100 mm²/m², 95% confidence interval [CI] 0.91-1.23, p=.45). Similarly, NTPA was not predictive of length of stay (rho=-0.04, p=.67), discharge home (OR 0.95 (95% CI 0.76-1.20) per 100 mm²/m², p=.70), or death (OR 1.12 (95% CI 0.83-1.53) per 100 mm²/m², p=.47). In contrast, increasing mFI was associated with increased risk of mortality (OR 3.12 (95% CI 1.21-8.03) per 0.1 increase in frailty score, p=.006).

Conclusions: In contrast to other surgical groups, sarcopenia (NTPA) or frailty (mFI) did not predict acute care complications in a selected population of elderly patients undergoing simple lumbar spine surgery for DSD. Although NTPA can be reliably measured in this population, it may be an inappropriate surrogate for sarcopenia given its anatomical relationship to spinal function.