In spine surgery, lumbar disc herniation (LDH) is one of the most common indications [1]. However, symptomatic LDH is often not primarily of surgical relevance [2], since the vast majority of pain due to LDH can be resolved spontaneously through conservative methods [3-8]. However, patients suffering from neurological deficits, such as motor deficits or bladder disturbance, or unbearable pain may profit from early lumbar discectomy [9-12]. Additionally, patients with prolonged symptom duration despite conservative treatment might be considered for surgical treatment. However, especially for the latter type of patients without emergent surgery indication, arriving at a surgical timing that is evidence-based remains difficult [13].

Several studies have been conducted for the ideal timing in lumbar discectomy, however without consensus in their results [6,13-16]. Generally, a minimum waiting time of 6 to 8 weeks has been established due to the high probability of spontaneous symptom resolution [7,8,13]. However, it is still unclear whether a longer time to surgery (TTS) also leads to worse outcomes, and - if so - whether there is an optimal maximum TTS for favorable patient outcomes. The studies generally indicated an association between longer symptom duration and poorer surgical outcomes [2,15,16]. However, the reports often evaluate pre hoc defined TTS cutoffs, or do not take into account long-term patientreported outcome, or are based on retrospective data [2,13,15-19].

A recent analysis indicated that delayed surgery is associated with a lower probability of improvement in leg pain at 1 year postoperatively and that a TTS cutoff of 24 weeks should be aimed for to maximize chances of symptomatic improvement [18]. However, this study focused solely on leg pain outcome. In fact, little is known on the influence of TTS on patient-reported functional impairment outcomes after elective discectomy [15]. Therefore, the aim of this study was to evaluate the impact of TTS on functional outcome after lumbar discectomy, as well as to evaluate different thresholds to determine the optimal maximum TTS, up to which the most favorable surgical results can be obtained.

In an analysis of 372 patients undergoing first-time lumbar discectomy from a prospective registry, lower TTS was associated with a higher probability for a favorable surgical outcome in terms of functional disability. The qualitative method based on MCID achievement percentages at different cutoffs showed a continuous drop of the MCID achievement with increasing TTS values, with values of > 80% MCID up to week 14. The quantitative AUC-anchored analysis both indicated an optimal maximum TTS of 22 weeks. Therefore, based on the calculation method, our data suggest that a maximum TTS of 14 to 22 weeks should be targeted for a favorable postoperative outcome in functional disability, while surgery after these thresholds leads to the lower likelihood for success.

TTS is an important topic of surgical planning. There are only a few absolute indications to immediate discectomy to avoid permanent functional deficits, such as cauda equina syndrome or progressive motor weakness [9-12]. Another more relative indication to near-term surgical intervention is unbearable pain, were an operation can lead to a better health-related quality of life [30,31]. In addition, it was shown that a prolonged noxious stimulus can lead to changes in the neural system, such as preservation of the pain even after removing the stimulus [32].

However, without these indications, conservative methods should be primarily considered before surgery, as over a third of LDH tend to regress without therapy at all [11]. Nonetheless, as symptom duration is prolonged, the probability of a conservative cure is reduced. In addition, longer symptom duration may also lead to worse outcome [13]. Our data as well suggests that patients achieving MCID were generally operated earlier on [18]. These findings reinforce the idea of starting with conservative therapy, but already taking surgery into consideration early on, especially if no improvement can be achieved after 6 to 8 weeks.

However, the optimal maximum TTS for a favorable surgical outcome in terms of functional impairment outcomes—as measured by ODI here—remains unclear [33,34]. Several studies investigating surgical timing provide different results. Some studies implied a maximum duration of conservative treatment only for 2–3 months or less [2,8,35], as for instance it was shown that earlier decompression was associated with more pronounced regenerative effects in rat spines [36]. On the other hand, some studies found conservative management and surgery to be equivalent in their 1-year outcomes [14,37].

In a recent analysis of our data, focusing on NRS leg pain outcomes in association with TTS, we established that a maximum waiting time of 24 weeks—or 6 months—should be considered if patients are to have the highest likelihood of improvement in terms of leg pain severity [18]. Interestingly, the current analysis of our data, focusing on functional impairment as measured by ODI, provided slightly differing results: While the detrimental effect of waiting too long for surgery remains obvious in all analyses, it appears that improvement of functional impairment generally requires earlier surgical intervention (at 14–22 weeks after symptom onset) than for improvement of leg pain severity. While it is certainly hard to explain this difference, it is possible that—in the presence of (subclinical) motor deficits—motoric nerve fibers may be less resilient than sensory nerve fibers. However, we are unable to corroborate this potential explanation with published data from the literature.

Sabnis and Diwan [13] conducted a meta-analysis in 2014, and found that long duration of preoperative sciatica was associated with poor outcome. They further were only able to derive a broad time range of 2–12 months, underlining the heterogeneity in the different studies. They stated, therefore, a minimum conservative treatment of 2 months, as earlier surgery without indications might be superfluous due to spontaneous regression, and a maximum TTS of 12 months, as longer waiting time decreases the likelihood of positive surgical outcome. In addition, they were able to outline a most common optimal maximum TTS of 6 months. One of our methods of analyzing the influence of TTS resulted in an optimum TTS of 22 weeks (=5.5 months), which may reinforce the results of Sabnis and Diwan [13] as well as Siccoli et al. [18].

In addition, our qualitative analysis showed a continuous decrease in MCID achievement with increasing TTS, and this finding is supported by most of the studies [13,16,18,19,35,38-41]. For example, Støttrup et al. [19] found that even surgery after 3 months leads to worsened outcomes at 1 year already. However, their analysis was focused solely on leg pain. In our study, we also see a drastic decrease in MCID achievement just before the 12-month mark in our analyses, which would imply a poor outcome after this cutoff and would underline the very maximum threshold defined by Sabnis and Diwan [13].

Our data also suggest that very early surgery within 14 weeks had better MCID achievement than longer TTS. Nevertheless, this finding must be taken with a grain of salt. As the general management of LDH is strictly conservative in the first weeks, these very early operation are mainly patients with surgical indication, such as neurological deficits, and were a MCID achievement may be easier due to a much worse baseline value. In addition, most patients with radiculopathy due to LDH are most hampered by their pain or by functional impairment secondary to pain, and in this context surgery at up to 24 weeks has been shown to lead to favorable outcomes [18].

Our study should not be taken as a call for early discectomy in the general symptomatic LDH population. It is still proper therapeutic management to propose conservative methods to the patients before surgery. However, it is also important to early discuss surgical treatment with the patients, especially when no improvement can be achieved conservatively after a few weeks. At the end, LDH treatment remains a shared decision-making between physicians and patients, and must also be adapted to the patients somatic and psychological characteristics. However, our data suggest that surgery should be carried out without delay and within 14–22 weeks from symptom onset.

Our study is primarily limited by its retrospective nature. Although all data were collected in a prospective registry and events captured systematically, and all patients with sufficient data and meeting the inclusion criteria were included, the presence of selection bias cannot be ruled out. In addition, all data stems from a single center and by one senior surgeon, possibly creating center bias. The analysis was not predefined, and we observed a high rate of loss of follow-up, as seen in other prospective registries before [26]. It remains unclear if this occurrence may be associated with further biases [42-44]. Further-on, our data and results cannot be claimed as generalized, as for the lack of external validation. Because this registry only included low-risk patients, thus those with a BMI< 33 kg/m², ASA physical status classification I or II, and age up to 80 years, our data and conclusions should not be expanded to high-risk patients such as octo- and nonagenarians, or such with systemic comorbidities. Moreover, our results may only be valid for patients undergoing tMD, and some patients received analgesic medication, nerve blocks, or manual- or physiotherapy preoperatively, on which we do not have robust data. We also do not have data on outcomes of patients who did not, in the end, undergo surgery. Therefore, our results can only indicate that, among patients who finally underwent surgery, earlier surgery was clearly associated with a better chance at MCID. However, another interesting point which cannot be inferred from our data is that the true utility of waiting longer is not postoperative outcomes, but rather the possibility that patients’ symptoms will improve to the point that they can avoid surgery altogether. The TTS values are based on the patients’ medical histories, and might, therefore, vary in their reliability and accuracy—recall bias may be present. We, therefore, only used integer values for weeks to better counteract such interpatient differences in TTS reporting during medical history taking. We rated subjective functional impairment based on the ODI. While the ODI is certainly a widely adopted and gold-standard outcome measure, other questionnaires like the Short Form 36 may have captured other dimensions of functional disability.

Our data suggest that patients undergoing lumbar discectomy earlier on are generally associated with a better improvement in terms of functional impairment after 1 year postoperatively. Different methods suggested an optimum TTS of 14–22 weeks, which is further validated by different other literature reports. Moreover, we find that improvement in functional impairment may potentially require earlier surgical intervention than improvement in leg pain severity does. Further studies have to be conducted for an improved understanding of surgical timing of lumbar discectomy, to improve personalized decision-making medicine for the optical therapeutic management of LDH.