In the present study, decompression surgery for LSS significantly improved LBP: 55% of patients achieved an MCID, and 48% achieved an MSS. The prevalence of postoperative persistent LBP was 33%, with 10% of patients having severe LBP. The independent risk factors for residual LBP were sex and the presence of baseline severe LBP, while postoperative improvement was not different when female and male patients were propensity score matched by patient background. Interestingly, none of the radiographic parameters correlated with postoperative LBP. Several recent studies have described that DISH, the presence of spinal instability, and the progression of vertebral spondylolisthesis can be the cause of LBP in patients with LSS.
There are several possible reasons for this difference. First, decompression surgery for LSS was carefully chosen in these patients. Therefore, only 8 patients developed segmental spinal instability at 10° or more at 2 years after surgery. Similarly, only 4 patients had a significant progression of spondylolisthesis (greater than 25% of vertebral body). Second, in the present study, 59 patients had DISH, but the prevalence of persistent LBP after surgery in these patients was not different from those who did not have DISH (DISH vs. non-DISH; 33.9% vs. 32.9%, P = 0.88). This might be because while a higher prevalence of back pain in patients with DISH has been described, the most common symptom is mild pain and stiffness in the upper back.[32,33] Indeed, when looking at the severity of LBP in patients with DISH after surgery, a tendency for a higher VAS score was seen in this patient population, although the difference was not statistically significant (DISH vs. non-DISH; 3.53 ± 3.33 vs. 3.22 ± 2.91, P = 0.22).
In the present study, female sex was identified as an independent risk factor for persistent LBP after surgery. Moreover, female patients were 1.7-fold more likely to have baseline severe LBP, which was a significant risk factor for persistent LBP after surgery. However, when males and females were propensity score matched by confounders, there was no difference in the degree of improvement in LBP 2 years after surgery.
Several previous studies have described that female sex is a risk factor for LBP in degenerative spinal disorders. Kim et al. described that female patients showed increased LBP due to LSS compared to male patients, and this difference may be partly mediated by pain sensitivity.[34,35] Kobayashi et al. also described that female patients had greater sensitivity to and/or lower tolerance for pain than men, which led to lower HRQOL mental health scores preoperatively. However, Racine et al. stated in their systematic review that no consistent conclusion could be drawn for sex-related differences in pain perception.[37,38] They also advocated that to optimize the approach and gather useful information, it would be more relevant to pursue analyses of sex differences in patients with pain.[37,38] Taken together, these results indicate that when compared with male patients, female patients with LSS tend to have more LBP or do not have surgery until LBP becomes severe. Since it can also be considered that female patients are more likely to report pain as being severe, previous literature written by Hashizume et al. described that the VAS score for LBP in healthy subjects did not differ by sex in each age group. Therefore, it is likely that part of the LBP of LSS patients originates from neuropathic pain due to LSS and that part depends on other factors, such as psychological problems or mental status, as sequelae of preoperative long-lasting LBP. The risk analyses also indicated that baseline mental status was an independent risk factor for baseline LBP. In the present study, LSS patients who had mental problems were 3.8-fold more likely to have persistent LBP after surgery. Furthermore, among the 135 patients with baseline severe LBP, the patients who answered #1 for any of questions Q5–3, 4, or 6 in the JOABPEQ mental health section were 2.6-fold more likely to have postoperative persistent LBP.
This study has some limitations. First, there is a lack of data on the preoperative duration of symptoms in each individual. The preoperative duration of symptoms is a well-known prognostic factor for persistent LBP after spinal surgery in adult patients.[39–41]
Radcliff et al. retrospectively reviewed the cases of 405 patients who underwent lumbar decompression for LSS and described that patients with LSS with a symptom duration of less than 12 months experienced significantly better outcomes with surgical and nonsurgical treatment relative to those with a symptom duration greater than 12 months. Cushnie et al. also described that longer symptom duration was found to correlate with less improvement in pain and disability after LSS surgery. In contrast, it is difficult to strictly determine how long each patient had been experiencing LBP in a clinical setting because patients with LSS do not have periodic hospital visits in the early stages of the disease. Therefore, although we can obtain data on the duration of symptoms of most of the patients from their chart based on the patient interview, we decided not to take this information into account in the present study because it was not objectively reliable. Second, we did not use a specific questionnaire that focused on mental status in patients with illness, such as the Pain Catastrophizing Scale (PCS). The PCS is the most commonly used instrument to evaluate the mental status of patients who have persistent pain. The PCS consists of 13 items in 3 domains (Rumination, Magnification and Helplessness) that describe an individual's specific beliefs about their pain and evaluate catastrophic thinking about pain. Wada et al. described that an evaluation of both physical function and pain catastrophizing is needed when investigating LSS in elderly individuals. The JOABPEQ mental health section questions Q5–3, 4, and 6 are similar to those in the three domains of the PCS. Although the answers on JOABPEQ questions Q5-3, -4, and -6 are not directly convertible and comparable with those on the PCS, the findings of the present study strongly emphasize the importance of intervention for mental status in patients who have severe LBP before surgery to further improve their clinical outcomes of decompression surgery for LSS.
In the present study, it is possible to conclude that female patients and those with preoperative severe LBP were more likely to have persistent LBP after surgery than those without preoperative severe LBP. However, when patients were propensity score matched for patient background, the amount of improvement was comparable between female and male patients. Further analyses including different patient populations will be necessary to validate the importance of intervention for mental status in patients who have severe LBP before surgery.
Spine. 2022;47(7):557-564. © 2022 Lippincott Williams & Wilkins