External validation of a prediction model for pain and functional outcome after elective lumbar spinal fusion.

OBJECTIVE: Patient-reported outcome measures following elective lumbar fusion surgery demonstrate major heterogeneity. Individualized prediction tools can provide valuable insights for shared decision-making. We externally validated the spine surgical care and outcomes assessment programme/comparative effectiveness translational network (SCOAP-CERTAIN) model for prediction of 12-month minimum clinically important difference in Oswestry Disability Index (ODI) and in numeric rating scales for back (NRS-BP) and leg pain (NRS-LP) after elective lumbar fusion. METHODS: Data from a prospective registry were obtained. We calculated the area under the curve (AUC), calibration slope and intercept, and Hosmer-Lemeshow values to estimate discrimination and calibration of the models. RESULTS: We included 100 patients, with average age of 50.4 ± 11.4 years. For 12-month ODI, AUC was 0.71 while the calibration intercept and slope were 1.08 and 0.95, respectively. For NRS-BP, AUC was 0.72, with a calibration intercept of 1.02, and slope of 0.74. For NRS-LP, AUC was 0.83, with a calibration intercept of 1.08, and slope of 0.95. Sensitivity ranged from 0.64 to 1.00, while specificity ranged from 0.38 to 0.65. A lack of fit was found for all three models based on Hosmer-Lemeshow testing. CONCLUSIONS: The SCOAP-CERTAIN tool can accurately predict which patients will achieve favourable outcomes. However, the predicted probabilities-which are the most valuable in clinical practice-reported by the tool do not correspond well to the true probability of a favourable outcome. We suggest that any prediction tool should first be externally validated before it is applied in routine clinical practice. These slides can be retrieved under Electronic Supplementary Material.

Improving recovery after elective degenerative spine surgery: 5-year experience with an enhanced recovery after surgery (ERAS) protocol.

OBJECTIVEEnhanced recovery after surgery (ERAS) has led to a paradigm shift in various surgical specialties. Its application can result in substantial benefits in perioperative healthcare utilization through preoperative physical and mental patient optimization and modulation of the recovery process. Still, ERAS remains relatively new to spine surgery. The authors report their 5-year experience, focusing on ERAS application to a broad population of patients with degenerative spine conditions undergoing elective surgical procedures, including anterior lumbar interbody fusion (ALIF).METHODSA multimodal ERAS protocol was applied between November 2013 and October 2018. The authors analyze hospital stay, perioperative outcomes, readmissions, and adverse events obtained from a prospective institutional registry. Elective tubular microdiscectomy and mini-open decompression as well as minimally invasive (MI) anterior or posterior fusion cases were included. Their institutional ERAS protocol contains 22 pre-, intra-, and postoperative elements, including preoperative patient counseling, MI techniques, early mobilization and oral intake, minimal postoperative restrictions, and regular audits.RESULTSA total of 2592 consecutive patients were included, with 199 (8%) undergoing fusion. The mean hospital stay was 1.1 ± 1.2 days, with 20 (0.8%) 30-day and 36 (1.4%) 60-day readmissions. Ninety-four percent of patients were discharged after a maximum 1-night hospital stay. Over the 5-year period, a clear trend toward a higher proportion of patients discharged home after a 1-night stay was observed (p < 0.001), with a concomitant decrease in adverse events in the overall cohort (p = 0.025) and without increase in readmissions. For fusion procedures, the rate of 1-night hospital stays increased from 26% to 85% (p < 0.001). Similarly, the average length of hospital stay decreased steadily from 2.4 ± 1.2 days to 1.5 ± 0.3 days (p < 0.001), with a notable concomitant decrease in variance, resulting in an estimated reduction in nursing costs of 46.8%.CONCLUSIONSApplication of an ERAS protocol over 5 years to a diverse population of patients undergoing surgical procedures, including ALIF, for treatment of degenerative spine conditions was safe and effective, without increase in readmissions. The data from this large case series stress the importance of the multidisciplinary, iterative improvement process to overcome the learning curve associated with ERAS implementation, and the importance of a dedicated perioperative care team. Prospective trials are needed to evaluate spinal ERAS on a higher level of evidence.

Machine learning-based preoperative predictive analytics for lumbar spinal stenosis.

OBJECTIVEPatient-reported outcome measures (PROMs) following decompression surgery for lumbar spinal stenosis (LSS) demonstrate considerable heterogeneity. Individualized prediction tools can provide valuable insights for shared decision-making. The authors aim to evaluate the feasibility of predicting short- and long-term PROMs, reoperations, and perioperative parameters by machine learning (ML) methods.METHODSData were derived from a prospective registry. All patients had undergone single- or multilevel mini-open facet-sparing decompression for LSS. The prediction models were trained using various ML-based algorithms to predict the endpoints of interest. Models were selected by area under the receiver operating characteristic curve (AUC). The endpoints were dichotomized by minimum clinically important difference (MCID) and included 6-week and 12-month numeric rating scales for back pain (NRS-BP) and leg pain (NRS-LP) severity and the Oswestry Disability Index (ODI), as well as prolonged surgery (> 45 minutes), extended length of hospital stay (> 28 hours), and reoperations.RESULTSA total of 635 patients were included. The average age was 62 ± 10 years, and 333 patients (52%) were male. At 6 weeks, MCID was seen in 63%, 76%, and 61% of patients for ODI, NRS-LP, and NRS-BP, respectively. At internal validation, the models predicted MCID in these variables with accuracies of 69%, 76%, and 85%, and with AUCs of 0.75, 0.79, and 0.92. At 12 months, 66%, 63%, and 51% of patients reported MCID; the observed accuracies were 62%, 74%, and 66%, with AUCs of 0.68, 0.72, and 0.79. Reoperations occurred in 60 patients (9.5%), of which 27 (4.3%) occurred at the index level. Overall and index-level reoperations were predicted with 69% and 63% accuracy, respectively, and with AUCs of 0.66 and 0.61. In 15%, a length of surgery greater than 45 minutes was observed and predicted with 78% accuracy and AUC of 0.54. Only 15% of patients were admitted to the hospital for longer than 28 hours. The developed ML-based model enabled prediction of extended hospital stay with an accuracy of 77% and AUC of 0.58.CONCLUSIONSPreoperative prediction of a range of clinically relevant endpoints in decompression surgery for LSS using ML is feasible, and may enable enhanced informed patient consent and personalized shared decision-making. Access to individualized preoperative predictive analytics for outcome and treatment risks may represent a further step in the evolution of surgical care for patients with LSS.

Gender differences in degenerative spine surgery: Do female patients really fare worse?

PURPOSE: Prior data has set the precedent that female patients fare somewhat worse than men after spine surgery. We aimed to evaluate the effect of gender on patient-reported outcomes after lumbar spine surgery for degenerative pathologies. METHODS: We identified a consecutive cohort of patients from a prospective registry. Absolute values, as well as change scores for back and leg pain severity (numeric rating scale [NRS]), functional disability (Oswestry disability index [ODI]), and health-related quality of life (HRQOL) as assessed by EQ-5D were compared among male and female patients. RESULTS: Of the 3279 included patients, 1543 (47%) were female. At baseline, women reported higher NRS for back and leg pain, higher ODI, but equal HRQOL (all p < 0.05). Otherwise, both groups had comparable baseline data. The absolute differences in patient-reported outcomes persisted at the 6-week, 12- and 24-months follow-up, with women now additionally reporting worse HRQOL as assessed by EQ-5D (all p < 0.05). For all outcome measures, change scores were equal among male and female patients, as were the incidences of complications and reoperations (all p > 0.05). Clinical success was achieved in 82% of men and 79% of women (p = 0.34). CONCLUSIONS: Female patients are generally scheduled for surgery with a more advanced disease state. While women seem to report more severe symptoms at long-term follow-up, the degree of improvement is equal among men and women. Female patients may thus fare worse in terms of absolute scores, but enjoy the same benefit from surgery in relative terms. These slides can be retrieved under Electronic Supplementary Material.

Are patient-reported outcome measures biased by method of follow-up? Evaluating paper-based and digital follow-up after lumbar fusion surgery.

BACKGROUND CONTEXT: Long-term follow-up of patient-reported outcome measures (PROM) is essential in both modern spinal care and research. Lack of time and staff are commonly reported barriers to implementing long-term follow-up of PROM. Automated and digital follow-up systems for PROM collection are seeing widespread use, yet their validity and comparative effectiveness have never been evaluated. PURPOSE: The present study aimed to assess the validity of digital follow-up systems in comparison with the conventional paper-based follow-up (PB-FU). STUDY DESIGN: This is a retrospective analysis of prospectively collected double follow-up data. PATIENT SAMPLE: Patients who underwent lumbar spinal fusion for spondylolisthesis or degenerative disc disease between 2013 and 2016 were included in the study. OUTCOME MEASURES: The study determined the Oswestry Disability Index (ODI) and Numeric Rating Scale (NRS) for back and leg pain severity at baseline, 6 weeks, 12 months, and 24 months. MATERIALS AND METHODS: After lumbar spinal fusion surgery, a double follow-up of PROM was carried out by conventional PB-FU during clinical visits, while simultaneously completing an automatically dispatched digital follow-up questionnaire. As the primary end point, we assessed the intraindividual discrepancy in PROM between PB-FU and automated digital follow-up (AD-FU). RESULTS: Forty patients completed all parts of the dual follow-up trajectory and were analyzed. We detected no discrepancy in ODI or NRS for back and leg pain severity at any of the baseline, 6-week, 12-month, or 24 month follow-ups (all p>.05). This was confirmed in a sensitivity analysis. CONCLUSIONS: In an analysis of dual paper-based and digital follow-up after lumbar fusion surgery, patients report highly similar values using either method of follow-up. It appears that AD-FU without incentives produces lower response rates. To reassess the validity of these systems for data collection in spinal patient care, a prospective validation with higher statistical power is warranted.

Predictors of loss of follow-up in a prospective registry: which patients drop out 12 months after lumbar spine surgery?

BACKGROUND CONTEXT: Long-term patient-reported outcomes (PROMs) are essential in clinical practice and research. Prospective trials and registries often struggle with high rates of loss of follow-up (LOFU), which may bias their findings. Little is known on risk factors for PROM nonresponse, especially for digitally mailed questionnaires. PURPOSE: To elucidate which patients are at high risk for LOFU by identifying associated predictors. STUDY DESIGN: Analysis of a prospective registry. PATIENT SAMPLE: Patients that underwent surgery for degenerative lumbar disease were included. OUTCOME MEASURES: Rate of PROM follow-up response at 12 months postoperatively. METHODS: Preoperatively and at 12 months postoperatively, patients were asked to complete a range of PROM questionnaires using a web-based tool. All patients who successfully completed their baseline questionnaire were included. Patients were not actively reminded upon nonresponse. Univariate and independent predictors of LOFU at 12 months were identified. RESULTS: We included 1,456 patients, of which 861 (59%) were lost to follow-up at 12 months. Univariately, lower age, American Society of Anesthesiologists (ASA) class 1, smoking, lack of prior surgery, higher pain scores and functional disability, and lower quality-of-life were associated with LOFU (all p<.05). Only lower age (OR: 0.98, p=.001), smoking (OR: 1.46, p=.019), lack of prior surgery (OR: 0.59, p=.019), and spondylolisthesis (OR: 0.47, p=.024) independently predicted LOFU. CONCLUSIONS: In a prospective registry of lumbar spine surgery patients based on web-based outcome capturing, younger age, active smoking status, lack of prior surgery, and nonspondylolisthesis surgery were independent predictors of loss of follow-up. In the future, it may become possible to preoperatively identify patients at high-risk for study dropout. As the implementation of prospective registries and the use of automated follow-up methods are on the rise, it is crucial to ensure efficiency and reduce bias of the methods on which all clinical research is based on.

Association of time to surgery with leg pain after lumbar discectomy: is delayed surgery detrimental?

OBJECTIVE: While it has been established that lumbar discectomy should only be performed after a certain waiting period unless neurological deficits are present, little is known about the association of late surgery with outcome. Using data from a prospective registry, the authors aimed to quantify the association of time to surgery (TTS) with leg pain outcome after lumbar discectomy and to identify a maximum TTS cutoff anchored to the minimum clinically important difference (MCID). METHODS: TTS was defined as the time from the onset of leg pain caused by radiculopathy to the time of surgery in weeks. MCID was defined as a minimum 30% reduction in the numeric rating scale score for leg pain from baseline to 12 months. A Cox proportional hazards model was utilized to quantify the association of TTS with MCID. Maximum TTS cutoffs were derived both quantitatively, anchored to the area under the curve (AUC), and qualitatively, based on cutoff-specific MCID rates. RESULTS: From a prospective registry, 372 patients who had undergone first-time tubular microdiscectomy were identified; 308 of these patients (83%) obtained an MCID. Attaining an MCID was associated with a shorter TTS (HR 0.718, 95% CI 0.546-0.945, p = 0.018). Effect size was preserved after adjustment for potential confounders. The optimal maximum TTS was estimated at 23.5 weeks based on the AUC, while the cutoff-specific method suggested 24 weeks. Discectomy after this cutoff starts to yield MCID rates under 80%. The 24-week cutoff also coincided with the time point after which the specificity for MCID first drops below 50% and after which the negative predictive value for nonattainment of MCID first surpasses ≥ 20%. CONCLUSIONS: The study findings suggest that late lumbar discectomy is linked with poorer patient-reported outcomes and that-in accordance with the literature-a maximum TTS of 6 months should be aimed for.

Is elective degenerative lumbar spine surgery in older adults safe in a short-stay clinic? Data from an institutional registry.

PURPOSE: Physicians are increasingly confronted with degenerative spinal pathologies and the possibility of elective surgical treatment in older adults. Little is known on safety and effectiveness of short-stay, elective lumbar spine surgery in this population. We aim to describe patient profiles of older adults undergoing surgery at a specialized short-stay clinic, and describe associated risk profiles and outcomes. METHODS: From a prospective registry, patients older than 65 were compared to younger controls. All patients underwent a strict anesthesiologic screening preoperatively, leading to a carefully selected cohort of relatively robust older adults suited for safe treatment at a short-stay clinic. A range of perioperative data and reoperations were available from all patients, and a subgroup of patients completed outcome assessments for disability, pain, and health-related quality of life (HRQOL). RESULTS: Of the 3279 included patients, 382 (12%) were older than 65. Older patients presented more often with spinal stenosis, and index levels were placed higher (p < 0.001). While there was no difference in complications, reoperations, and blood loss (p > 0.05), older people had longer surgical times and length of stay, although not by a clinically relevant margin (p < 0.001). Long-term patient-reported outcomes were equal (p > 0.05). However, older adults had worse 6-week outcomes for leg pain, functional disability, and HRQOL (all p < 0.05). CONCLUSIONS: Higher age should not be considered a contraindication for elective lumbar spine surgery at short-stay clinics. If the anesthesiologic risk can be controlled, conservative treatments have failed, and muscle-sparing techniques are applied, favorable outcomes can be achieved with an acceptable risk profile in a safe manner.

Patient-reported outcomes unbiased by length of follow-up after lumbar degenerative spine surgery: Do we need 2 years of follow-up?

BACKGROUND: In modern clinical research, the accepted minimum follow-up for patient-reported outcome measures (PROMs) after lumbar spine surgery is 24 months, particularly after fusion. Recently, this minimum requirement has been called into question. PURPOSE: We aim to quantify the concordance of 1- and 2-year PROMs to evaluate the importance of long-term follow-up after elective lumbar spine surgery. STUDY DESIGN: Retrospective analysis of data from a prospective registry. PATIENT SAMPLE: We identified all patients in our prospective institutional registry who underwent degenerative lumbar spine surgery with complete baseline, 12-month, and 24-month follow-up for ODI and numeric rating scales for back and leg pain (NRS-BP and NRS-LP). OUTCOME MEASURES: Oswestry Disability Index (ODI) and NRS-BP and NRS-LP at 1 year and at 2 years. METHODS: We evaluated concordance of 1- and 2-year change scores by means of Pearson's product-moment correlation and performed logistic regression to assess if achieving the minimum clinically important difference (MCID) at 12 months predicted 24-month MCID. Odds ratios (OR) and their 95% confidence intervals (CI), as well as model areas-under-the-curve were obtained. RESULTS: A total of 210 patients were included. We observed excellent correlation among 12- and 24-month ODI (r = 0.88), NRS-LP (r = 0.76) and NRS-BP (r = 0.72, all p <.001). Equal results were obtained when stratifying for discectomy, decompression, or fusion. Patients achieving 12-month MCID were likely to achieve 24-month MCID for ODI (OR: 3.3, 95% CI: 2.4-4.1), NRS-LP (OR: 2.99, 95% CI: 2.2-4.2) and NRS-BP (OR: 3.4, 95% CI: 2.7-4.2, all p <.001) with excellent areas-under-the-curve values of 0.81, 0.77, and 0.84, respectively. Concordance rates between MCID at both follow-ups were 87.2%, 83.8%, and 84.2%. A post-hoc power analysis demonstrated sufficient statistical power. CONCLUSIONS: Irrespective of the surgical procedure, 12-month PROMs for functional disability and pain severity accurately reflect those at 24 months. In support of previous literature, our results suggest that 12 months of follow-up may be sufficient for evaluating spinal patient care in clinical practice as well as in research.

Deep learning-based preoperative predictive analytics for patient-reported outcomes following lumbar discectomy: feasibility of center-specific modeling.

BACKGROUND CONTEXT: There is considerable variability in patient-reported outcome measures following surgery for lumbar disc herniation. Individualized prediction tools that are derived from center- or even surgeon-specific data could provide valuable insights for shared decision-making. PURPOSE: To evaluate the feasibility of deriving robust deep learning-based predictive analytics from single-center, single-surgeon data. STUDY DESIGN: Derivation of predictive models from a prospective registry. PATIENT SAMPLE: Patients who underwent single-level tubular microdiscectomy for lumbar disc herniation. OUTCOME MEASURES: Numeric rating scales for leg and back pain severity and Oswestry Disability Index scores at 12 months postoperatively. METHODS: Data were derived from a prospective registry. We trained deep neural network-based and logistic regression-based prediction models for patient-reported outcome measures. The primary endpoint was achievement of the minimum clinically important difference (MCID) in numeric rating scales and Oswestry Disability Index, defined as a 30% or greater improvement from baseline. Univariate predictors of MCID were also identified using conventional statistics. RESULTS: A total of 422 patients were included (mean [SD] age: 48.5 [11.5] years; 207 [49%] female). After 1 year, 337 (80%), 219 (52%), and 337 (80%) patients reported a clinically relevant improvement in leg pain, back pain, and functional disability, respectively. The deep learning models predicted MCID with high area-under-the-curve of 0.87, 0.90, and 0.84, as well as accuracy of 85%, 87%, and 75%. The regression models provided inferior performance measures for each of the outcomes. CONCLUSIONS: Our study demonstrates that generating personalized and robust deep learning-based analytics for outcome prediction is feasible even with limited amounts of center-specific data. With prospective validation, the ability to preoperatively and reliably inform patients about the likelihood of symptom improvement could prove useful in patient counselling and shared decision-making.

Safety and Efficacy of Anterior Lumbar Interbody Fusion for Discogenic Chronic Low Back Pain in a Short-stay Setting: Data From a Prospective Registry.

Introduction As a possible treatment option for chronic lower back pain (CLBP) due to single-level degenerative disc disorder (DDD), the efficacy of anterior lumbar interbody fusion (ALIF) has been reviewed various times in the existing literature. Nevertheless, a scarcity of data exists pertaining to ALIF procedures carried out in a short-stay setting using an Enhanced Recovery after Surgery (ERAS) protocol, particularly concerning the safety. Methods Prospectively collected data are analyzed to study the efficacy and safety of short-stay ERAS ALIF in treatment of single-level DDD. Visual Analog Scale (VAS) in both back and leg pain along with the Oswestry Disability Index (ODI) were used to collect measure outcomes. The primary endpoint was a minimum clinically important difference (MCID) of ≥30% for the ODI at 12 months. Results Forty-four patients underwent surgery after failed long-term conservative treatment. MCID was achieved in 78%. Age was the only significant factor in association with MCID (p = 0.03), while gender, Modic changes, results of prognostic tests, prior surgery and smoking status had no significant influence on either MCID or change scores for any outcome measure. One complication in the form of transient new radiculopathy occurred in one patient (2.3%). Conclusion With overall positive outcomes in terms of both efficacy and safety, an ALIF procedure with subsequent implementation of an ERAS protocol in a short-stay setting can be an option for strictly selected patients with CLBP. Further study, however, possibly with a larger sample size, would be necessary to substantiate these findings.

Tandem Disc Herniation of the Lumbar and Cervical Spine: Case Series and Review of the Epidemiological, Pathophysiological and Genetic Literature.

Introduction Lumbar disc herniation (LDH) and cervical disc herniation (CDH) represent a relevant public health problem. Patients with symptomatic tandem herniations of the cervical and lumbar spine are rare and not described in the literature. In these patients, certain variables may predispose the development of disc herniation which could increase the understanding of the development of disc herniations. Our aim is to present the first case series of tandem disc herniation, and to elucidate whether tandem herniation is attributable to a certain propensity for disc herniation or not. Methods  From a prospective registry, patients with symptomatic tandem disc herniations were included, and the literature was reviewed on the comparative pathophysiology, genetics, and epidemiology of disc herniation and disc degeneration. Results Out of 3,156 patients with disc herniations in our registry, 16 presented with symptomatic tandem LDH and CDH that required discectomy. Therefore, we estimate the incidence of tandem disc herniation at 0.51% (95% confidence interval (CI): 0.26% - 0.75%) in the surgical population. The mean number of degenerated lumbar discs was 2.1 ± 1.1. Compared to the 1,241 patients with isolated LDH, no investigated factors were significantly associated with tandem herniations. Conclusion From a genetic, pathophysiological, and epidemiological position, disc herniation is not commonly a consequence of disc degeneration. Rather, degeneration and herniation seem to exist as two separate and distinctly different processes. Based on the literature, it is tenable that tandem disc herniation does not deviate from the normal pathophysiology, but rather occurs in the rare case that two individual herniated discs coincide.

Recurrent Laryngeal Nerve Palsy Is More Frequent After Secondary than After Primary Anterior Cervical Discectomy and Fusion: Insights from a Registry of 525 Patients.

BACKGROUND: Recurrent laryngeal nerve (RLN) palsy is a common complication after anterior cervical discectomy and fusion (ACDF) and usually manifests with dysphagia, hoarseness, and respiratory difficulties. Next to proven risk factors, such as age and multilevel procedures, RLN palsy has been speculated to occur more frequently after secondary ACDF procedures. METHODS: We analyzed a prospective registry of all consecutive patients undergoing zero-profile ACDF for disc herniation, myelopathy, or stenosis. RLN palsy was defined as persistent patient self-reported dysphagia, hoarseness, or respiratory problems without other identifiable causes. RLN palsy was assessed at scheduled 6-week telephone interviews. RESULTS: Among 525 included patients, 511 primary and 40 secondary ACDF procedures were performed. Hoarseness was present in 12 (2.2%) cases, whereas dysphagia and respiratory difficulties both occurred in 3 (0.5%) cases. Overall incidence of RLN palsy was 2% after primary procedures and 8% after secondary procedures (P = 0.017). These rates are in line with the peer-reviewed literature, and the difference remained significant after controlling for confounders in a multivariate model (P = 0.033). Other reported risk factors, such as age, sex, surgical time, and multilevel procedures, had no relevant effect (P > 0.05). CONCLUSIONS: Based on our data and other published series in the literature, RLN palsy may occur more frequently after secondary ACDF procedures with a clinically relevant effect size. There is a striking lack of uniformity in methods and reporting in research on RLN injury.

Recurrent Lumbar Disc Herniation After Tubular Microdiscectomy: Analysis of Learning Curve Progression.

OBJECTIVE: Tubular microdiscectomy has become a staple technique among spine surgeons. Yet the associated learning curve, especially its later stages, has not been extensively studied. With studies reporting a higher rate of recurrent herniation using tubular microdiscectomy, surgeons' level of experience becomes of primary importance for the interpretation of such findings. We aimed to analyze possible improvements in the later stages of the learning curve and to identify factors independently associated with recurrent herniation. METHODS: A retrospective study was conducted using prospectively collected data from a consecutive cohort of all 1241 patients operated for single-level lumbar disc herniation with tubular microdiscectomy by a single surgeon who already had extensive experience with this technique. We collected demographic and perioperative data and consequently tracked all complications, recurrent herniations, and other reoperations. In addition, 495 patients (40%) provided complete outcome scores on a numeric rating scale for back and leg pain and the Oswestry Disability Index at baseline, 6 weeks, and 12 months postoperatively. RESULTS: A decrease in surgical time (P < 0.001) and recurrent herniations was observed (P = 0.012) over time. Increased leg pain at 6 weeks was independently associated with recurrent herniation (P = 0.01). Fifty-six patients (4.5%) experienced ipsilateral recurrent herniation. CONCLUSIONS: Relevant improvements in clinical results were seen even after the surgeon had already accumulated extensive experience. Any future studies should unambiguously report the level of experience of the participating surgeons, possibly including the number of cases previously treated using a particular technique.