The main indication for surgery for lumbar disc herniation is leg pain or sciatica. Spine surgeons have traditionally considered patients where the chief complaint is sciatica to be good candidates for surgery. This study confirms this long-held belief.
Our study shows leg pain without back pain to be a relatively common finding in patients scheduled for LDH surgery as almost one in ten reports no back pain whatsoever. The findings of our study suggest that the surgical outcome is more favorable in LDH patients if back pain is absent preoperatively. A substantially larger proportion of the NBP patients are pain free or much better with regards to leg pain after surgery compared with the LPB patients (87 vs 76%).
Type of surgery may affect outcome at the one-year follow-up. In Swespine, surgery for LDH can be classified as discectomy with or without the use of microscope. We have no information about if tubular or other minimally invasive approaches were conducted, i.e., endoscopic surgery. The same applies for information about the amount of disc material removed, which is not registered in Swespine. Aggressive discectomy may result in more back pain, but in current practice, most surgeons perform sequestrectomy.
However, also patients with concomitant preoperative back pain improve significantly following surgery in all PROMs in the present study. Patients in the NBP and LBP group achieve similar improvements, but the LBP group is left with more pronounced postoperative disability. These findings fit well into our current frame of reference as patients with LDH and high burden of back pain may be a more heterogeneous group of patients both in terms of symptoms and morphological disease. Although there are statistically significant differences between the NBP and the LBP groups at the one-year follow-up milestone, it should be noted that the differences are relatively small and may not consistently be clinically relevant.
To our knowledge, the cohort of LDH patients that report no preoperative back pain has not previously been selectively studied. The outcome following surgery in this cohort is reported with less preoperative disability reflected in better self-estimated walking distance, lower consumption of analgesics, better quality of life and less disability as compared to patients with preoperative LBP. The NBP group report increased back pain postoperatively as compared to preoperatively (13% NBP vs 39% LBP with back pain difference > MCID). One possible explanation is that the disc herniation may represent the beginning of a symptomatic segmental disease of the spine. The degree of back pain present at one-year follow-up in patients without preoperative back pain is however probably of lesser importance since this is lower than the MCID for back pain in 87% of the patients after LDH surgery  and does not reflect in poor postoperative quality of life (SF-36, EQ-5D) or disability (ODI).
We found some baseline differences in patients that were preoperatively without back pain but subsequently developed significant back pain at the one-year follow-up and those who remained pain free. Female sex and smoking were associated with increased risk for having clinically significant back pain at the one-year follow-up. Furthermore, patients that developed clinically significant back pain at the one-year follow-up had preoperatively more disability in terms of the ODI and lower quality of life in terms of the EQ-5D. However, the baseline differences in ODI and EQ-5D in these patient groups were small and not clinically significant.
Patients with LDH without back pain are good candidates for surgery. The increased knowledge regarding this patient population can be used by surgeons preoperatively when discussing surgery with patients with LDH. It allows for more nuanced preoperative information and patients may thus attain well founded expectations with regards to the outcome of surgery. Outcome of surgery in well-informed patients is associated with a better surgical result and a higher degree of patient satisfaction [11, 12].
Shortcomings of the present study those associated with register studies such as the obvious inclusion bias and the retrospective analysis of prospectively collected data. However, the study includes a very large number of patients in the setting of a nationwide span with a heterogenous study population as regarding patient selection and comorbidities. In the Swespine, only the reason for surgery is registered, but the individual patients may have other spinal conditions and or psychosomatic conditions that may impact the outcome of surgery. These potential comorbidities remain unaccounted for. Another shortcoming of the present study is the absence of information regarding preoperative non-surgical treatment which may influence the outcome of surgery. Regular practice in Sweden is to offer non-operative treatment (analgesics and physiotherapy) of symptomatic LDH for at least 8-week period before surgery is considered.
The transition question for evaluation of leg pain outcome may be affected by recall bias and there are previous reports that show that perceived change is influenced by the current health state. Strengths of this study include a large patient material and the use of validated PROMs. 29% of the patients did not have complete data and were excluded; however, a loss of 30% have been reported to not influence the outcome in spine register studies , but conflicting opinions has also been reported .
To conclude, patients with no preoperative back pain seem to have a better outcome following LDH as compared to patients with concomitant back pain and with a higher degree of patient satisfaction. 13% of the patients where back pain is absent preoperatively develop clinically significant back pain at the one-year follow-up.