One large randomised trial (n = 283) with a low risk of bias compared early surgery to prolonged conservative treatment followed by surgery if needed in patients with severe sciatica for 6–12 weeks. At 1 year of follow-up, 95% of patients in both treatment groups had experienced satisfactory recovery, and no subsequent differences were found. This lack of a difference between groups was maintained for the following year .
One small trial (n = 56) compared microdiscectomy with conservative treatment in patients with sciatica for 6–12 weeks. Overall, no significant differences were found for leg pain or back pain, and subjective disability throughout the 2 years of follow-up .
A large trial (n = 501) with a low risk of bias in patients with sciatica for at least 6 weeks and confirmed disc herniation showed that both the surgery as well as the conservative treatment group improved substantially over 2 years for all primary and secondary outcome measures. The intention-to-treat analysis showed no statistically significant differences for any of the primary outcome measures. 
A systematic review conducted last year (2015) collating multiple trials concluded the following:
Most studies included in the review demonstrated no substantial difference between surgically treated versus conservatively treated groups for sciatica, as the following table indicates:
From the points raised above, it is clear that the treatment administered during the acute sciatica attack does not exert a decisive influence on the long-term prognosis .
In conclusion, there is no convincing evidence that lumbar discectomy is superior to conservative management for long term outcomes. The costs of surgery are higher than conservative treatment for patients or the health care system. Also, potential complications are more prevalent and more severe with surgery.
The results of these studies thus appear to confirm the view that acute sciatica episodes run a relatively brief course in most cases, regardless of the treatment administered. It is also generally acknowledged that the attacks are caused by lumbar disc degeneration. However, this disc degeneration is a common finding in the asymptomatic population: 
1. Peul WC, van Houwelingen HC, van den Hout WB, Brand R,Eekhof JA, Tans JT, Thomeer RT, Koes BW (2007) Surgery versus prolonged conservative treatment for sciatica. N Engl J Med 356:2245–2256
2. Osterman H, Seitsalo S, Karppinen J, Malmivaara A (2006) Effectiveness of microdiscectomy for lumbar disc herniation: a randomized controlled trial with 2 years of follow-up. Spine (Phila Pa 1976) 31:2409–2414
3. Weinstein JN, Tosteson TD, Lurie JD, Tosteson AN, Hanscom B, Skinner JS, Abdu WA, Hilibrand AS, Boden SD, Deyo RA (2006) Surgical vs nonoperative treatment for lumbar disk herniation: the Spine Patient Outcomes Research Trial (SPORT): a randomized trial. JAMA 296:2441–2450
4. Anders Hakelius (1970) Prognosis in Sciatica: A Clinical Follow-Up of Surgical and Non-Surgical Treatment, Acta Orthopaedica Scandinavica, 41:sup129, 1-76
5. Systematic Literature Review of Imaging Features of Spinal Degeneration in Asymptomatic Populations. Brinjikji W, Luetmher PH et al. AJNR, 2014 Nov 27 (Epub ahead of print)