Radiation Exposure in Minimally Invasive Transforaminal Lumbar Interbody Fusion: The Effect of the Learning Curve

Evolving Paradigms in Spinal Surgery: A Systematic Review of the Learning Curves in Minimally Invasive Spine Techniques

Our research examines the learning curves of various minimally invasive lumbar surgeries to determine the benefits and challenges they pose to both surgeons and patients. The advent of microsurgical techniques since the 1960s, including advances in fluoroscopic navigation and intraoperative computed tomography, has significantly shifted spinal surgery from open to minimally invasive methods. This study critically evaluates surgical duration, intraoperative conversions to open surgery, and complications as primary parameters to gauge these learning curves. Through a comprehensive literature search up to March 2024, involving databases PubMed, Cochrane Library, and Web of Science, this paper identifies a steep learning curve associated with these surgeries. Despite their proven advantages in reducing recovery time and surgical trauma, these procedures require surgeons to master advanced technology and equipment, which can directly impact patient outcomes. The study underscores the need for well-defined learning curves to facilitate efficient training and enhance surgical proficiency, especially for novice surgeons. Moreover, it addresses the implications of technology on surgical accuracy and the subsequent effects on complication rates, providing insights into the complex dynamics of adopting new surgical innovations in spinal health care.

Learning curve analyses in spine surgery: a systematic simulation-based critique of methodologies

BACKGROUND CONTEXT

Various statistical approaches exist to delineate learning curves in spine surgery. Techniques range from dividing cases into intervals for metric comparison, to employing regression and cumulative summation (CUSUM) analyses. However, their inherent inconsistencies and methodological flaws limit their comparability and reliability.

PURPOSE

To critically evaluate the methodologies used in existing literature for studying learning curves in spine surgery and to provide recommendations for future research.

STUDY DESIGN

Systematic literature review.

METHODS

A comprehensive literature search was conducted using PubMed, Embase, and Scopus databases, covering articles from January 2010 to September 2023. For inclusion, articles had to evaluate the change in a metric of performance during human spine surgery across time/a case series. Results had to be reported in sufficient detail to allow for evaluation of individual performance rather than group/institutional performance. Articles were excluded if they included cadaveric/nonhuman subjects, aggregated performance data or no way to infer change across a number of cases. Risk of bias was assessed using the Risk of Bias in Nonrandomized Studies of Interventions (ROBINS-I) tool. Surgical data were simulated using Python 3 and then examined via multiple commonly used analytic approaches including division into consecutive intervals, regression and CUSUM techniques. Results were qualitatively assessed to determine the effectiveness and limitations of each approach in depicting a learning curve.

RESULTS

About 113 studies met inclusion criteria. The majority of the studies were retrospective and evaluated a single-surgeon's experience. Methods varied considerably, with 66 studies using a single proficiency metric and 47 using more than 1. Operating time was the most commonly used metric. Interval division was the simplest and most commonly used method yet inherent limitations prevent collective synthesis. Regression may accurately describe the learning curve but in practice is hampered by sample size and model choice. CUSUM analyses are of widely varying quality with some being fundamentally flawed and widely misinterpreted however, others provide a reliable view of the learning process.

CONCLUSION

There is considerable variation in the quality of existing studies on learning curves in spine surgery. CUSUM analyses, when correctly applied, offer the most reliable estimates. To improve the validity and comparability of future studies, adherence to methodological guidelines is crucial. Multiple or composite performance metrics are necessary for a holistic understanding of the learning process.

Challenges in Contemporary Spine Surgery: A Comprehensive Review of Surgical, Technological, and Patient-Specific Issues

Spine surgery has significantly progressed due to innovations in surgical techniques, technology, and a deeper understanding of spinal pathology. However, numerous challenges persist, complicating successful outcomes. Anatomical intricacies at transitional junctions demand precise surgical expertise to avoid complications. Technical challenges, such as underestimation of the density of fixed vertebrae, individual vertebral characteristics, and the angle of pedicle inclination, pose additional risks during surgery. Patient anatomical variability and prior surgeries add layers of difficulty, often necessitating thorough pre- and intraoperative planning. Technological challenges involve the integration of artificial intelligence (AI) and advanced visualization systems. AI offers predictive capabilities but is limited by the need for large, high-quality datasets and the "black box" nature of machine learning models, which complicates clinical decision making. Visualization technologies like augmented reality and robotic surgery enhance precision but come with operational and cost-related hurdles. Patient-specific challenges include managing postoperative complications such as adjacent segment disease, hardware failure, and neurological deficits. Effective patient outcome measurement is critical, yet existing metrics often fail to capture the full scope of patient experiences. Proper patient selection for procedures is essential to minimize risks and improve outcomes, but criteria can be inconsistent and complex. There is the need for continued technological innovation, improved patient-specific outcome measures, and enhanced surgical education through simulation-based training. Integrating AI in preoperative planning and developing comprehensive databases for spinal pathologies can aid in creating more accurate, generalizable models. A holistic approach that combines technological advancements with personalized patient care and ongoing education is essential for addressing these challenges and improving spine surgery outcomes.

Feasibility of Saphenous Nerve Somatosensory-Evoked Potential Intraoperative Monitoring During Lumbar Spine Surgery: Early Results

STUDY DESIGN

Retrospective review.

OBJECTIVE

Assess the feasibility of saphenous nerve somatosensory evoked potentials (SN-SSEP) monitoring in lumbar spine surgeries.

BACKGROUND CONTEXT

SN-SSEPs have been proposed for detecting lumbar plexus and femoral nerve injury during lateral lumbar surgery where tibial nerve (TN) SSEPs alone are insufficient. SN-SSEPs may also be useful in other types of lumbar surgery, as stimulation of SN below the knee derives solely from the L4 root and provides a means of L4 monitoring, whereas TN-SSEPs often do not detect single nerve root injury. The feasibility of routine SN-SSEP monitoring has not been established.

METHODS

A total of 563 consecutive cases using both TN-SSEP and SN-SSEP monitoring were included. Anesthesia was at the discretion of the anesthesiologist, using an inhalant in 97.7% of procedures. SN stimulation was performed using 13 mm needle electrodes placed below the knee using 200-400 μsec pulses at 15 to 100 mA. Adjustments to stimulation parameters were made by the neurophysiology technician while obtaining baselines. Data were graded retrospectively for monitorability and cortical response amplitudes were measured by two independent reviewers.

RESULTS

Ninety-eight percent of TN-SSEPs and 92.5% of SN-SSEPs were monitorable at baseline, with a mean response amplitude of 1.35 μV for TN-SSEPs and 0.71 μV for SN-SSEPs. A significant difference between the stimulation parameters used to obtain reproducible TN and SN-SSEPs at baseline was observed, with SN-SSEPs requiring greater stimulation intensities. Body mass index is not associated with baseline monitorability. Out of 20 signal changes observed, 11 involved SN, while TN-SSEPs were unaffected.

CONCLUSION

With adjustments to stimulation parameters, SN-SSEP monitoring is feasible within a large clinical cohort without modifications to the anesthetic plan. Incorporating SN into standard intraoperative neurophysiological monitoring protocols for lumbar spine procedures may expand the role of SSEP monitoring to include detecting injury to the lumbar plexus.

LEVEL OF EVIDENCE

3.

Erector Spinae Plane Block Reduces Immediate Postoperative Pain and Opioid Demand After Minimally Invasive Transforaminal Lumbar Interbody Fusion

STUDY DESIGN

Matched cohort comparison.

OBJECTIVE

To determine perioperative outcomes of erector spinae plane (ESP) block for minimally invasive transforaminal lumbar interbody fusion (MI-TLIF).

SUMMARY OF BACKGROUND DATA

There is a paucity of data on the impact of lumbar ESP block on perioperative outcomes and its safety in MI-TLIF.

MATERIALS AND METHODS

Patients who underwent 1-level MI-TLIF and received the ESP block (group E ) were included. An age and sex-matched control group was selected from a historical cohort that received the standard-of-care (group NE). The primary outcome of this study was 24-hour opioid consumption in morphine milligram equivalents. Secondary outcomes were pain severity measured by a numeric rating scale, opioid-related side effects, and hospital length of stay. Outcomes were compared between the two groups.

RESULTS

Ninety-eight and 55 patients were included in the E and NE groups, respectively. There were no significant differences between the two cohorts in patient demographics. Group E had lower 24-hour postoperative opioid consumption ( P = 0.117, not significant), reduced opioid consumption on a postoperative day (POD) 0 ( P = 0.016), and lower first pain scores postsurgery ( P < 0.001). Group E had lower intraoperative opioid requirements ( P < 0.001), and significantly lower average numeric rating scale pain scores on POD 0 ( P = 0.034). Group E reported fewer opioid-related side effects as compared with group NE, although this was not statistically significant. The average highest postoperative pain score within 3 hours postprocedurally was 6.9 and 7.7 in the E and NE cohorts, respectively ( P = 0.029). The median length of stay was comparable between groups with the majority of patients in both groups being discharged on POD 1.

CONCLUSIONS

In our retrospective matched cohort, ESP blocks resulted in reduced opioid consumption and decreased pain scores on POD 0 in patients undergoing MI-TLIF.

LEVEL OF EVIDENCE

Level 3.

Does indirect decompression by oblique lateral interbody fusion produce similar clinical and radiological outcomes to direct decompression by open transforaminal lumbar interbody fusion

Objectives

Open transforaminal lumbar interbody fusion (O-TLIF) remains the most popular and widely practiced lumbar fusion method even today, providing direct decompression. Oblique lateral interbody fusion (OLIF) is a novel retroperitoneal approach that allows placement of a large interbody cage which provides an indirect neural decompression, and screws can be placed minimal invasively or through the Wiltse OLIF (W-OLIF) approach. We aim to find out the short-term efficacy of W-OLIF to O-TLIF in terms of radiological and clinical outcomes in patients of lumbar degenerative diseases.

Materials and Methods

Fifty-two patients were divided equally into two groups (group O-TLIF and group W-OLIF). Several parameters were measured, such as the spinal cord cross-sectional area (SC-CSA), foraminal cross-sectional area (F-CSA), disc height (DH), foraminal height (FH), Schizas grade for stenosis, and Meyerding's grading for olisthesis. Functional scores were measured using the visual analog scale (VAS) for low back pain (LBP) and lower limbs, Oswestry Disability Index. All parameters were repeat measured at 3 months follow-up. Statistical analysis was done using SPSS software.

Results

Both groups were similar in composition preoperatively. There was significant improvement in all clinical and radiological parameters post-surgery in either group. However, at 3 months, The DH, FH, FSA, and VAS (LBP) were better in the W-OLIF group than in O-TLIF. Procedure-related complications were seen in both groups (15% in the O-TLIF group and 19% in the W-TLIF group), but only one patient in O-TLIF required revision due to cage migration.

Conclusion

Similar improvement occurs in most of the clinical and radiological parameters in the W-OLIF group compared to the O-TLIF group. Few radiological parameters such as the DH, FH, and F-CSA and the VAS (LBP) correction are superior in the W-OLIF group in the short-term follow-up. We conclude that indirect decompression by W-OLIF provides equivalent, if not better, results than the traditional O-TLIF lumbar fusion.

Predictors of Subsidence and its Clinical Impact After Expandable Cage Insertion in Minimally Invasive Transforaminal Interbody Fusion

STUDY DESIGN

Retrospective review of prospectively collected multisurgeon data.

OBJECTIVE

Examine the rate, clinical impact, and predictors of subsidence after expandable minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) cage.

SUMMARY OF BACKGROUND DATA

Expandable cage technology has been adopted in MI-TLIF to reduce the risks and optimize outcomes. Although subsidence is of particular concern when using expandable technology as the force required to expand the cage can weaken the endplates, its rates, predictors, and outcomes lack evidence.

MATERIALS AND METHODS

Patients who underwent 1 or 2-level MI-TLIF using expandable cages for degenerative lumbar conditions and had a follow-up of >1 year were included. Preoperative and immediate, early, and late postoperative radiographs were reviewed. Subsidence was determined if the average anterior/posterior disc height decreased by >25% compared with the immediate postoperative value. Patient-reported outcomes were collected and analyzed for differences at the early (<6 mo) and late (>6 mo) time points. Fusion was assessed by 1-year postoperative computed tomography.

RESULTS

One hundred forty-eight patients were included (mean age, 61 yr, 86% 1-level, 14% 2-level). Twenty-two (14.9%) demonstrated subsidence. Although statistically not significant, patients with subsidence were older, had lower bone mineral density, and had higher body mass index and comorbidity burden. Operative time was significantly higher ( P = 0.02) and implant width was lower ( P < 0.01) for subsided patients. Visual analog scale-leg was significantly lower for subsided patients compared with nonsubsided patients at a >6 months time point. Long-term (>6 mo) patient-acceptable symptom state achievement rate was lower for subsided patients (53% vs . 77%), although statistically not significant ( P = 0.065). No differences existed in complication, reoperation, or fusion rates.

CONCLUSIONS

Of the patients, 14.9% experienced subsidence predicted by narrower implants. Although subsidence did not have a significant impact on most patient-reported outcome measures and complication, reoperation, or fusion rates, patients had lower visual analog scale-leg and patient-acceptable symptom state achievement rates at the >6-month time point.

LEVEL OF EVIDENCE

Level 4.

Learning curve in relation to radiation exposure, procedure duration and complications rate for Minimally Invasive Chevron Akin (MICA) osteotomy

BACKGROUND

Minimally invasive chevron Akin osteotomy (MICA) has become increasingly common and is compatible with the traditional open approaches for hallux valgus correction. However, it is impeded by concerns regarding the steep learning curve, increased radiation exposure and some specific complications. No standardized method for identifying a learning curve exists. We used a reproducible mathematical model to accurately define the learning curve of MICA with a focus on fluoroscopy time, procedure duration and complications rate.

METHODS

We conducted a retrospective study of MICA procedure performed by a single surgeon during his initial experience with this procedure. The chronologic case number was plotted against variables of interest and learning was identified as the point at which instantaneous rate of change of a curve fit to the data set equalled the average rate of change of the data set.

RESULTS

One hundred cases have been analysed. Learning plateau in operation time was achieved after 29 cases, with the first 29 cases requiring a median of 60 min compared to 40 min for the latter 71 cases. Proficiency in fluoroscopy application occurred in case 30. The median fluoroscopy time for the first 30 cases was 86 seconds compared to 70 seconds in another 70 cases. The complication rate plateau was reached after 42 cases, with 15 of 22 complications occurring in the group operated first.

CONCLUSION

Results demonstrate surgeon's comfort with MICA to minimize operative time and radiation exposure after 30 cases. The plateau is achieved later for complications. Findings impose lag between surgeon feeling comfortable with procedure and a decrease in complications. Further research is reasonable to analyse several surgeons learning curve and to generate a potential reference learning curve that could serve as a normative.

TRIAL REGISTRATION

UKC-MB-KME-33/19, retrospectively registered.

Preoperative cross-sectional area of psoas muscle correlates with short-term functional outcomes after posterior lumbar surgery

PURPOSE

To determine the optimal level for the measurement of psoas cross-sectional area and examine the correlation with short-term functional outcomes of posterior lumbar surgery.

METHODS

Patients who underwent minimally invasive posterior lumbar surgery were included in this study. The cross-sectional area of psoas muscle was measured at each intervertebral level on T2-weighted axial images of preoperative MRI. Normalized total psoas area (NTPA) (mm2/m2) was calculated as total psoas area normalized to patient height. Intraclass Correlation Coefficient (ICC) was calculated for the analysis of inter-rater reliability. Patient reported outcome measures including Oswestry disability index (ODI), visual analog scale (VAS), short form health survey (SF-12) and patient-reported outcomes measurement information system were collected. A multivariate analysis was performed to elucidate independent predictors associated with failure to reach minimal clinically important difference (MCID) in each functional outcome at 6 months.

RESULTS

The total of 212 patients were included in this study. ICC was highest at L3/4 [0.992 (95% CI: 0.987-0.994)] compared to the other levels [L1/2 0.983 (0.973-0.989), L2/3 0.991 (0.986-0.994), L4/5 0.928 (0.893-0.952)]. Postoperative PROMs were significantly worse in patients with low NTPA. Low NTPA was an independent predictor of failure to reach MCID in ODI (OR = 2.68; 95% CI: 1.26-5.67; p = 0.010) and VAS leg (OR = 2.43; 95% CI: 1.13-5.20; p = 0.022).

CONCLUSION

Decreased psoas cross-sectional area on preoperative MRI correlated with functional outcomes after posterior lumbar surgery. NTPA was highly reliable, especially at L3/4.

Patient-Reported Allergies Do Not Affect Long-Term Patient-Reported Outcome Measures After Spine Surgery

BACKGROUND

A gap in the literature exists regarding the association between number of allergies and patient-reported outcomes measures (PROMs) for patients undergoing spine surgery.

METHODS

Consecutive cervical or lumbar spine surgery patients were identified from a prospective registry from April 2017 to July 2020. Patients were grouped into those with 0, 1, 2, or ≥3 allergies. Demographics were compared between the groups. PROMs included Neck Disability Index, Oswestry Disability Index, visual analog scale (VAS) neck pain, VAS arm pain, VAS back pain, VAS leg pain, short form 12 (SF-12) physical component score, SF-12 mental component score, and patient-reported outcomes measurement information system physical function (PROMIS-PF), and outcomes were compared between the groups through multivariable analysis at up to 1-year follow-up. Associations between number of allergies and achieving a minimal clinically important difference (MCID) in the 9 aforementioned PROMs at 1-year follow-up were assessed.

RESULTS

This study included 148 cervical and 517 lumbar patients. After controlling for demographic differences, a higher number of allergies was associated with less improvement in VAS neck pain, SF-12 physical component score, and PROMIS-PF at 12 weeks following cervical surgery and less improvement in PROMIS-PF at 2 weeks following lumbar surgery (P < 0.05). However, these associations failed to persist after 6 months and 12 weeks following surgery in cervical and lumbar patients, respectively (P > 0.05). No association was identified between number of allergies and achievement of MCID in any of the 9 studied PROMs at 1-year follow-up.

CONCLUSIONS

The higher number of allergies was associated with less improvement in PROMs in the early postoperative period but not at longer-term follow-up.

CLINICAL RELEVANCE

These findings provide data that can be utilized while counseling patients and setting postoperative expectations.

LEVEL OF EVIDENCE: 3

Determining the learning curve for percutaneous endoscopic lumbar interbody fusion for lumbar degenerative diseases

PURPOSE

Percutaneous endoscopic lumbar interbody fusion (PELIF) is one of the least invasive procedures for lumbar degenerative disorders (LDD). There is limited knowledge of the learning curve for PELIF.

METHODS

A total of 93 consecutive patients who underwent PELIF performed by a single spine surgeon for LDD failed with conservative treatment were retrospectively reviewed. The case series was split into three groups based on timing: A (earliest third of patients); B (middle third of patients); and C (latest third of patients). The following were also recorded: operating time, X-ray exposure time, complications, radiologic fusion rates, pre- and postoperative patient-reported outcome measures (PROMs) scores (visual analogue scale (VAS) for back pain, VAS for leg pain, Japanese Orthopaedic Association, Oswestry Disability Index and MacNab criteria), length of hospital stay, and need for revision surgeries. A learning curve was then developed by a logarithmic curve-fit regression analysis.

RESULTS

The operative time gradually decreased over time, and an asymptote was reached after about 25 cases. Compared with group B or C, group A had significantly longer operative time, significantly longer length of hospital stay, needed significantly more x-ray exposure time. Though not significantly different, there are fewer complications and revision surgeries over time. There is no significant difference over time in PROMs scores except for the VAS back scores.

CONCLUSIONS

PELIF is an alternative for minimal invasive surgery for LDD, PELIF presents a learning curve to the practicing spine surgeon with regard to operative time, x-ray exposure time, length of hospital stay, clinical PROMs and radiographic outcomes and complications. The presented PELIF learning curve provided valuable insight to surgeons interested in performing this surgery.

Computed Tomography Evaluation of Percutaneous Pedicle Screws Inserted during Minimally Invasive Transforaminal Lumbar Interbody Fusion: Long-term Follow-up Results of Screw Violation

Background

To evaluate the accuracy of percutaneous pedicle screw (PPS) insertion in degenerative lumbar disease treated with minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) and to analyze risk factors and long-term clinical outcomes of screw violation.

Methods

Sixty-two consecutive patients (262 screws) were included. Based on postoperative computed tomography (CT) axial images, a PPS that perforated out of the pedicle was classified into a violation group, while screws surrounded by pedicular cortical bone were classified into a correct group. A logistic regression model was used for risk factor analysis of violation. We also observed the long-term clinical outcomes using the Oswestry disability index and visual analog scale.

Results

Of the 262 screws, 14 (5.3%) were considered to be violated (10 medial violations and 4 lateral violations). All violations of S1 and L5 were in the medial direction. In contrast, entire violations of L4 were always lateral and of the 2 violations of L3, one was lateral and the other was medial. There were no cases of superior or inferior violation. The mean pedicle convergence angle (CA) was significantly higher in the violation group (mean ± standard deviation, 27.0° ± 6.2°) than in the correct group (21.7° ± 5.4°). There were no significant differences according to vertebral rotational angle, body mass index, bone mineral density, and surgical timing (learning curve) between the two groups. Logistic regression analyses demonstrated that a high CA was a significant risk factor for pedicle wall violation (p = 0.002). There were no significant differences in clinical or radiographic results between the two groups in 60 patients who were followed up for more than 1 year and in 40 patients who were followed up for more than 5 years. There were 2 patients who required reoperation to replace a screw due to leg pain.

Conclusions

With PPS insertion during MI-TLIF, the rate of pedicle violation was 5.3% (14/262). An understanding of the anatomical characteristics of each vertebra and the unique structures of the patient is essential to prevent pedicle violations. Even in the violation group, PPS fixation was found to be a safe and useful procedure with successful long-term radiographic and clinical outcomes.

Recovery ratios and minimum clinically important difference for clinical outcomes in workers' compensation recipients undergoing MIS-TLIF versus ALIF

BACKGROUND

There is a scarcity of literature that examines clinical outcomes through patient-reported outcomes (PROs), minimum clinically important difference (MCID), and recovery ratios (RR) for workers' compensation (WC) recipients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) versus anterior lumbar interbody fusion (ALIF).

METHODS

WC claimants undergoing MIS-TLIF versus ALIF were propensity score matched to account for demographic differences. Demographics, perioperative characteristics, and PROs were collected. PROs of Patient-Reported Outcomes Measurement Information System Physical Function (PROMIS-PF), 12-Item Short Form Physical Composite Score (SF-12 PCS), Visual Analog Scale (VAS) back, VAS leg, and Oswestry Disability Index (ODI) were collected at preoperative and postoperative time points. MCID achievement was determined through comparison to values in literature. RR was calculated as the difference between postoperative and preoperative PROs over potential improvement. Comparison between surgical techniques was through non-parametric inferential statistics.

RESULTS

Eighty-four WC claimants, with 50 patients undergoing MIS-TLIF, were identified after propensity score matching. ALIF patients had higher estimated blood loss. MIS-TLIF patients had higher postoperative day (POD) 0 VAS pain and POD 0 + 1 narcotic consumption. Patients undergoing either MIS-TLIF or ALIF reported significant improvement in pain and disability. ALIF patients reported significant improvement in physical function. ALIF patients reported superior 1-year PROMIS-PF, 6-week SF-12 PCS, 6-month VAS back, and 12-week VAS leg. No significant differences in MCID achievement rates were noted between cohorts. ALIF patients had higher RR in 6-week and 1-year PROMIS-PF and 6-week SF-12 PCS.

CONCLUSION

Workers' compensation claimants undergoing either MIS-TLIF or ALIF reported significant improvement in pain and disability. ALIF patients reported superior postoperative physical function and pain. ALIF patients had higher recovery ratios in physical function. Workers' compensation claimants undergoing ALIF may experience greater physical function recovery and superior clinical outcomes in physical function and pain.

ODI <25 Denotes Patient Acceptable Symptom State After Minimally Invasive Lumbar Spine Surgery

STUDY DESIGN

Retrospective review of prospectively collected data.

OBJECTIVE

To determine the Oswestry Disability Index (ODI) cutoff for achieving Patient Acceptable Symptom State (PASS) at one year following minimally invasive lumbar spine surgery.

SUMMARY OF BACKGROUND DATA

An absolute score denoting PASS, rather than a change score denoting minimal clinically important difference (MCID), might be a better metric to assess clinical outcomes.

MATERIALS AND METHODS

Patients who underwent primary minimally invasive transforaminal lumbar interbody fusion or decompression were included. The outcome measure was ODI. The anchor question was the Global Rating Change: "Compared with preoperative, you feel (1) much better, (2) slightly better, (3) same, (4) slightly worse, or (5) much worse." For analysis, it was collapsed to a dichotomous outcome variable (acceptable=response of 1 or 2, unacceptable=response of 3, 4, or 5). Proportion of patients achieving PASS and the ODI cutoff using receiver operating characteristic curve analyses were assessed for the overall cohort as well as subgroups based on age, sex, type of surgery, and preoperative ODI. Differences between the PASS and MCID metrics were analyzed.

RESULTS

A total of 137 patients were included. In all, 87% of patients achieved PASS. Patients less than or equal to 65 years and those undergoing fusion were more likely to achieve PASS. The receiver operating characteristic curve analysis revealed an ODI cutoff of 25.2 to achieve PASS (area under the curve: 0.872, sensitivity: 82%, specificity: 83%). The subgroup analyses based on age, sex, and preoperative ODI revealed area under the curve >0.8 and ODI threshold values consistent between 25.2 and 25.5 (except 28.4 in patients with preoperative ODI >40). PASS was found to have significantly higher sensitivity compared with MCID (82% vs. 69%, P =0.01).

CONCLUSIONS

Patients with ODI <25 are expected to achieve PASS, irrespective of age, sex, and preoperative disability. PASS was found to have significantly higher sensitivity than MCID.

LEVEL OF EVIDENCE

3.

Improvement following minimally invasive transforaminal lumbar interbody fusion in patients aged 70 years or older compared with younger age groups

OBJECTIVE

The goal of this study was to assess the outcomes of minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) in patients ≥ 70 years old and compare them to younger age groups.

METHODS

This was a retrospective study of data that were collected prospectively. Patients who underwent primary single-level MI-TLIF were included and divided into 3 groups: age < 60, 60-69, and ≥ 70 years. The outcome measures were as follows: 1) patient-reported outcome measures (PROMs) (i.e., visual analog scale [VAS] for back and leg pain, Oswestry Disability Index [ODI], 12-Item Short-Form Health Survey Physical Component Summary [SF-12 PCS]); 2) minimum clinically important difference (MCID) achievement; 3) return to activities; 4) opioid discontinuation; 5) fusion rates; and 6) complications/reoperations.

RESULTS

A total of 147 patients (age < 60 years, 62; 60-69 years, 47; ≥ 70 years, 38) were included. All the groups showed significant improvements in all PROMs at the early (< 6 months) and late (≥ 6 months) time points and there was no significant difference between the groups. Although MCID achievement rates for VAS leg and ODI were similar, they were lower in the ≥ 70-year-old patient group for VAS back and SF-12 PCS. Although the time to MCID achievement for ODI and SF-12 PCS was similar, it was greater in the ≥ 70-year-old patient group for VAS back and leg. There was no significant difference between the groups in terms of return to activities, opioid discontinuation, fusion rates, and complication/reoperation rates.

CONCLUSIONS

Although patients > 70 years of age may be less likely and/or take longer to achieve MCID compared to their younger counterparts, they show an overall significant improvement in PROMs, a similar likelihood of returning to activities and discontinuing opioids, and comparable fusion and complication/reoperation rates following MI-TLIF.

Practical answers to frequently asked questions in minimally invasive lumbar spine surgery

BACKGROUND CONTEXT

Surgical counseling enables shared decision-making (SDM) by improving patients' understanding.

PURPOSE

To provide answers to frequently asked questions (FAQs) in minimally invasive lumbar spine surgery.

STUDY DESIGN

Retrospective review of prospectively collected data.

PATIENT SAMPLE

Patients who underwent primary tubular minimally invasive lumbar spine surgery in form of transforaminal lumbar interbody fusion (MI-TLIF), decompression alone, or microdiscectomy and had a minimum of 1-year follow-up.

OUTCOME MEASURES

(1) Surgical (radiation exposure and intraoperative complications) (2)Immediate postoperative (length of stay [LOS] and complications) (3) Clinical outcomes (Visual Analog Scale- back and leg, VAS; Oswestry Disability Index, ODI; 12-Item Short Form Survey Physical Component Score, SF-12 PCS; Patient-Reported Outcomes Measurement Information System Physical Function, PROMIS PF; Global Rating Change, GRC; return to activities; complications/reoperations) METHODS: The outcome measures were analyzed to provide answers to ten FAQs that were compiled based on the authors' experience and a review of literature. Changes in VAS back, VAS leg, ODI, and SF-12 PCS from preoperative values to the early (<6 months) and late (>6 months) postoperative time points were analyzed with Wilcoxon Signed Rank Tests. % of patients achieving minimal clinically important difference (MCID) for these patient-reported outcome measures (PROMs) at the two time points was evaluated. Changes in PROs from preoperative values too early (<6 months) and late (≥6 months) postoperative time points were analyzed within each of the three groups. Percentage of patients achieving MCID was also evaluated.

RESULTS

Three hundred sixty-six patients (104 TLIF, 147 decompression, 115 microdiscectomy) were included. The following FAQs were answered: (1) Will my back pain improve? Most patients report improvement by >50%. About 60% of TLIF, decompression, and microdiscectomy patients achieved MCID at ≥6 months. (2) Will my leg pain improve? Most patients report improvement by >50%. 56% of TLIF, 67% of decompression, and 70% of microdiscectomy patients achieved MCID at ≥6 months. (3) Will my activity level improve? Most patients report significant improvement. Sixty-six percent of TLIF, 55% of decompression, and 75% of microdiscectomy patients achieved MCID for SF-12 PCS. (4) Is there a chance I will get worse? Six percent after TLIF, 14% after decompression, and 5% after microdiscectomy. (5) Will I receive a significant amount of radiation? The radiation exposure is likely to be acceptable and nearly insignificant in terms of radiation-related risks. (6) What is the likelihood that I will have a complication? 17.3% (15.4% minor, 1.9% major) for TLIF, 10% (9.3% minor and 0.7% major) for decompression, and 1.7% (all minor) for microdiscectomy (7) Will I need another surgery? Six percent after TLIF, 16.3% after decompression, 13% after microdiscectomy. (8) How long will I stay in the hospital? Most patients get discharged on postoperative day one after TLIF and on the same day after decompression and microdiscectomy. (9) When will I be able to return to work? >80% of patients return to work (average: 25 days after TLIF, 14 days after decompression, 11 days after microdiscectomy). (10) Will I be able to drive again? >90% of patients return to driving (average: 22 days after TLIF, 11 days after decompression, 14 days after microdiscectomy).

CONCLUSIONS

These concise answers to the FAQs in minimally invasive lumbar spine surgery can be used by physicians as a reference to enable patient education.

Learning curve for minimally invasive transforaminal lumbar interbody fusion: a systematic review

PURPOSE

Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is commonly used to treat degenerative lumbar spinal disorders. It facilitates a full-scale spinal decompression and interbody fusion with minimal neural retraction using the tubular retractor system. Despite the benefits of surgical efficiency and minimalism, this technique requires a long learning curve. There is currently no consensus on the learning curve characteristics and proper training methods for MI-TLIF. Thus, this systematic review aimed to discuss the cutoff point at which technical proficiency is achieved and ways to enhance the learning process.

METHODS

Major databases, including PubMed, Embase, and Cochrane Library, were searched for learning curve studies that have evaluated the clinical outcome and learning progress of MI-TLIF using quantitative data. The qualities of the selected studies were assessed using the Newcastle‒Ottawa scale. The plateau points in the "learning curve" were analyzed according to various outcome measures.

RESULTS

Nine full-text articles, representing 753 cases, were included from 9743 screened studies. The most commonly used outcome measures were the operative time, followed by the complication rate. The mean cutoff point for the operative time was 31.33 ± 11.98 (range 13‒45) cases.

CONCLUSION

The plateau point in the learning curve for MI-TLIF may differ according to the outcome measures used. Most studies have demonstrated the learning progress based on simple task efficiency, rather than patient outcomes. Moreover, the learning rate may be affected by the patients' and technical conditions. Therefore, great care is required in interpreting the learning curve and cutoff point for MI-TLIF proficiency.

MIS-TLIF Procedure is Improving With Experience: Systematic Review of the Learning Curve Over the Last Decade

STUDY DESIGN

This was a systematic review.

OBJECTIVE

This review evaluates the minimally invasive transforaminal lumbar interbody fusions (MIS-TLIF) learning curve in the literature and compares outcomes during and after completing the curve.

SUMMARY OF BACKGROUND DATA

MIS-TLIF are performed for various spine conditions. Proponents cite improved clinical outcomes while critics highlight the steep learning curve to attain proficiency.

METHODS

Literature searches on Medline and Embase utilized relevant subject headings and keywords. Manuscripts reporting learning curve statistics were included. Monotonic trends of operative duration were assessed with Mann-Kendall nonparametric testing.

RESULTS

Nine studies met inclusion criteria. Number of patients ranged from 26 to 150 (average 83.2, median of 86). Commonly reported metrics included number of procedures to complete the curve, operative duration, blood loss, ambulation time, length of stay, complication rate, follow-up visual analogue scale (VAS) for back and leg pain, and fusion rate. Various methods were employed to determine number of cases to complete the curve, all involving operative duration. Number of cases ranged from 14 to 44. A significant negative trend for operative duration of cases during the learning curve (τ=-0.733, P =0.039) was found over the years that studies were published. Initial complication rates varied from 6.8% to 23.8%. Initial VAS-back and VAS-leg ranged from 0.8 to 2.9 and 0.5 to 2.3, respectively. While definitions of "good" fusion varied, fusion rates meeting Bridwell grade I or II during the learning curve ranged from 84.0% to 95.2%.

CONCLUSIONS

Surgeons in their learning curve have become faster at the MIS-TLIF procedure. Clinical outcomes including postoperative pain and fusion rates showed satisfactory results, but surgeons learning the procedure should take measures to minimize complications in early cases, such as utilizing novel navigation technology or supervision from more experienced surgeons. Learning curve research methodology could benefit from standardization.

Recovery Kinetics After Commonly Performed Minimally Invasive Spine Surgery Procedures

STUDY DESIGN

Single-center, multisurgeon, retrospective review.

OBJECTIVE

To evaluate the timing of return to commonly performed activities following minimally invasive spine surgery. Identify preoperative factors associated with these outcomes.

SUMMARY OF BACKGROUND DATA

Studies have reported return to activities with open techniques, but the precise timing of when patients return to these activities after minimally invasive surgery remains uncertain.

MATERIALS AND METHODS

Patients who underwent either minimally invasive lumbar laminectomy (MI-L) or minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) were included. Patient-reported outcome measures, return to drive, return to work, and discontinuation of opioids data were reviewed. Regression was conducted to identify factors associated with return to driving by 15 days, return to work by 30 days, and for discontinuing opioids by 15 days. A composite group analysis was also performed for patients who returned to all three activities by 30 days.

RESULTS

In total, 123 MI-L patients and 107 MI-TLIF patients were included. Overall, 88.8% of MI-L patients and 96.4% of MI-TLIF patients returned to driving in 11 and 18.5 days, respectively. In all, 91.9% of MI-L patients and 85.7% of MI-TLIF patients returned to work in 14 and 25 days. In all, 88.7% of MI-L patients and 92.6% of MI-TLIF patients discontinued opioids in a median of seven and 11 days. Overall, 96.2% of MI-L patients and 100% of MI-TLIF patients returned to all three activities, with a median of 27 and 31 days, respectively. Male sex [odds ratio (OR)=3.57] and preoperative 12-Item Short Form Physical Component Score (OR=1.08) are associated with return to driving by 15 days. Male sex (OR=3.23) and preoperative 12-Item Short Form Physical Component Score (OR=1.07) are associated with return to work by 30 days. Preoperative Visual Analog Scale back was associated with decreased odds of discontinuing opioids by 15 days (OR=0.84).

CONCLUSION

Most patients return to activity following MI-L and MI-TLIF. These findings serve as an important compass for preoperative counseling.

Minimally Invasive Lumbar Decompression Versus Minimally Invasive Transforaminal Lumbar Interbody Fusion for Treatment of Low-Grade Lumbar Degenerative Spondylolisthesis

STUDY DESIGN

A retrospective cohort comparison study.

OBJECTIVE

To compare perioperative outcomes, radiographic parameters, and patient-reported outcome measures (PROMs) between minimally invasive unilateral laminotomy with bilateral decompression (MIS-ULBD) versus MIS transforaminal lumbar interbody fusion (MIS-TLIF) for treatment of low-grade lumbar degenerative spondylolisthesis.

SUMMARY OF BACKGROUND DATA

While lumbar degenerative spondylolisthesis is a common condition, optimal surgical treatment remains controversial. Newer MIS techniques, which preserve bone, paraspinal musculature, and posterior midline stabilizers, are thought to reduce the risk of iatrogenic instability and may obviate the need for fusion. However, few comparative studies of MIS techniques for low-grade lumbar degenerative spondylolisthesis currently exist.

MATERIALS AND METHODS

Consecutive patients with low-grade (Meyerding grade I or II) lumbar degenerative spondylolisthesis treated with single-level MIS-ULBD or MIS-TLIF were identified retrospectively from a prospectively collected spine surgery registry from April 2017 to November 2021. Perioperative outcomes, radiographic data, and PROMs were assessed.

RESULTS

A total of 188 patients underwent either MIS-ULBD or MIS-TLIF (79 MIS-ULBD and 109 MIS-TLIF). Patients who underwent MIS-ULBD tended to be older, had higher Charlson Comorbidity Index, lower mean percentage back pain, higher percentage of L4/L5 pathology, shorter operative time, lower estimated blood loss, and lower postoperative pain ( P <0.05). In both groups, there were statistically significant improvements at one year for five of the six PROMs studied: Oswestry Disability Index (ODI), visual analog scale (VAS)-back pain, VAS-leg pain, Short Form 12 Physical Component Score (SF12-PCS), and Patient-Reported Outcomes Measurement Information System (PROMIS) ( P <0.05). On multivariate analysis controlling for confounders, there were no associations between procedure type and achieving minimal clinically important difference at one year in any of the PROMs studied.

CONCLUSIONS

The current study suggests that both MIS-ULBD and MIS-TLIF result in significant improvements in pain and physical function for patients with low-grade lumbar degenerative spondylolisthesis.

LEVEL OF EVIDENCES

3.

Robotics Reduces Radiation Exposure in Minimally Invasive Lumbar Fusion Compared With Navigation

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

To compare robotics and navigation for minimally invasive elective lumbar fusion in terms of radiation exposure and time demand.

SUMMARY OF BACKGROUND DATA

Although various studies have been conducted to demonstrate the benefits of both navigation and robotics over fluoroscopy in terms of radiation exposure, literature is lacking in studies comparing robotics versus navigation.

MATERIALS AND METHODS

Patients who underwent elective one-level or two-level minimally invasive transforaminal lumbar interbody fusion (TLIF) by a single surgeon using navigation (Stryker SpineMask) or robotics (ExcelsiusGPS) were included (navigation 2017-2019, robotics 2019-2021, resulting in prospective cohorts of consecutive patients for each modality). All surgeries had the intraoperative computed tomography workflow. The two cohorts were compared for radiation exposure [fluoroscopy time and radiation dose: image capture, surgical procedure, and overall) and time demand (time for setup and image capture, operative time, and total operating room (OR) time].

RESULTS

A total of 244 patients (robotics 111, navigation 133) were included. The two cohorts were similar in terms of baseline demographics, primary/revision surgeries, and fusion levels. For one-level TLIF, total fluoroscopy time, total radiation dose, and % of radiation for surgical procedure were significantly less with robotics compared with navigation (20 vs. 25 s, P <0.001; 38 vs. 42 mGy, P =0.05; 58% vs. 65%, P =0.021). Although time for setup and image capture was significantly less with robotics (22 vs. 25 min, P <0.001) and operative time was significantly greater with robotics (103 vs. 93 min, P <0.001), there was no significant difference in the total OR time (145 vs. 141 min, P =0.25). Similar findings were seen for two-level TLIF as well.

CONCLUSION

Robotics for minimally invasive TLIF, compared with navigation, leads to a significant reduction in radiation exposure both to the surgeon and patient, with no significant difference in the total OR time.

History and Evolution of the Minimally Invasive Transforaminal Lumbar Interbody Fusion

The minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is a popular surgical technique for lumbar arthrodesis, widely considered to hold great efficacy while conferring an impressive safety profile through the minimization of soft tissue damage. This elegant approach to lumbar stabilization is the byproduct of several innovations throughout the past century. In 1934, Mixter and Barr's paper in the New England Journal of Medicine elucidated the role of disc herniation in spinal instability and radiculopathy, prompting surgeons to explore new approaches and instruments to access the disc space. In 1944, Briggs and Milligan published their novel technique, the posterior lumbar interbody fusion (PLIF), involving continuous removal of vertebral bone chips and replacement of the disc with a round bone peg. The following decades witnessed several PLIF modifications, including the addition of long pedicle screws. In 1982, Harms and Rolinger sought to redefine the posterior corridor by approaching the disc space through the intervertebral foramen, establishing the transforaminal lumbar interbody fusion (TLIF). In the 1990s, lumbar spine surgery experienced a paradigm shift, with surgeons placing increased emphasis on tissuesparing minimally invasive techniques. Spurred by this revolution, Foley and Lefkowitz published the novel MIS-TLIF technique in 2002. The MIS-TLIF has demonstrated comparable surgical outcomes to the TLIF, with an improved safety profile. Here, we present a view into the history of the posterior-approach treatment of the discogenic radiculopathy, culminating in the MIS-TLIF. Additionally, we evaluate the hallmark characteristics, technical variability, and reported outcomes of the modern MIS-TLIF and take a brief look at technologies that may define the future MIS-TLIF.

Do preoperative clinical and radiographic characteristics impact patient outcomes following one-level minimally invasive transforaminal lumbar interbody fusion based upon presenting symptoms?

BACKGROUND CONTEXT

Patients undergoing minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) frequently present with lower extremity neurologic symptoms with or without associated lower back pain. While symptomatic improvement of leg and back pain has been reported, the resolution of back pain when it is a predominant presenting symptom remains underreported following MI-TLIF.

PURPOSE

The purpose of this study was to compare clinical outcomes at 1 year of patients undergoing MI-TLIF with lower extremity neurologic symptoms with and without a significant component of back pain.

STUDY DESIGN

A retrospective review of prospectively collected data from a single surgeon surgical database from 2017 to 2019 was performed.

PATIENT SAMPLE

Fifty one patients undergoing MI-TLIF.

OUTCOME MEASURES

Self-reported measures included the Oswestry Disability Index (ODI), Visual analog scale back pain (VAS-back), and VAS leg pain (VAS-leg).

METHODS

Patients were divided into two groups: Leg Pain Predominant (patients reported greater than 50% leg pain upon presentation) and Back Pain Predominant (patients reported 50% or greater back pain). Multivariate analysis was performed to determine differences between groups based upon any significantly baseline characteristics.

RESULTS

Preoperative demographic and radiographic outcomes were similar between the two groups. Both groups demonstrated significant improvement in ODI, VAS-Back and VAS-leg at 1-year postoperatively. On multivariate analysis, there were differences in ODI at 1-year, 1-year back pain, and 1-year leg pain between groups with those who initially presented with leg pain having a lower ODI, VAS Back, and VAS leg. Patients who presented with predominantly leg pain were more likely to meet minimal clinically important difference (MCID) criteria for ODI and VAS-back compared to those with predominantly back pain.

CONCLUSION

Following MI-TLIF, patients with lower extremity neurologic symptoms with and without a significant component of back pain have improvements in back pain, leg pain, and ODI regardless of their primary presenting pain complaint; however, patients who presented with predominantly leg pain were more likely to meet MCID criteria for improvement in their back pain and ODI score.

The Learning Curve of Murine Subretinal Injection Among Clinically Trained Ophthalmic Surgeons

Purpose

Subretinal injection (SRI) in mice is widely used in retinal research, yet the learning curve (LC) of this surgically challenging technique is unknown.

Methods

To evaluate the LC for SRI in a murine model, we analyzed training data from three clinically trained ophthalmic surgeons from 2018 to 2020. Successful SRI was defined as either the absence of retinal pigment epithelium (RPE) degeneration after phosphate buffered saline injection or the presence of RPE degeneration after Alu RNA injection. Multivariable survival-time regression models were used to evaluate the association between surgeon experience and success rate, with adjustment for injection agents, and to calculate an approximate case number to achieve a 95% success rate. Cumulative sum (CUSUM) analyses were performed and plotted individually to monitor each surgeon's simultaneous performance.

Results

Despite prior microsurgery experience, the combined average success rate of the first 50 cases in mice was only 27%. The predicted SRI success rate did not reach a plateau above 95% until approximately 364 prior cases. Using the 364 training cases as a cutoff point, the predicted probability of success for cases 1 to 364 was 65.38%, and for cases 365 to 455 it was 99.32% (P < 0.0001). CUSUM analysis showed an initial upward slope and then remained within the decision intervals with an acceptable success rate set at 95% in the late stage.

Conclusions

This study demonstrates the complexity and substantial LC for successful SRI in mice with high confidence. A systematic training system could improve the reliability and reproducibility of SRI-related experiments and improve the interpretation of experimental results using this technique.

Translational Relevance

Our prediction model and monitor system allow objective quantification of technical proficiency in the field of subretinal drug delivery and gene therapy for the first time, to the best of our knowledge.

Time-demand, Radiation Exposure and Outcomes of Minimally Invasive Spine Surgery With the Use of Skin-Anchored Intraoperative Navigation: The Effect of the Learning Curve

STUDY DESIGN

Retrospective review.

OBJECTIVE

The aim was to evaluate the learning curve of skin-anchored intraoperative navigation (ION) for minimally invasive lumbar surgery.

SUMMARY OF BACKGROUND DATA

ION is increasingly being utilized to provide better visualization, improve accuracy, and enable less invasive procedures. The use of noninvasive skin-anchored trackers for navigation is a novel technique, with the few reports on this technique demonstrating safety, feasibility, and significant reductions in radiation exposure compared with conventional fluoroscopy. However, a commonly cited deterrent to wider adoption is the learning curve.

METHODS

Retrospective review of patients undergoing 1-level minimally invasive lumbar surgery was performed. Outcomes were: (1) time for ION set-up and image-acquisition; (2) operative time; (3) fluoroscopy time; (4) radiation dose; (5) operative complications; (6) need for repeat spin; (7) incorrect localization.Chronologic case number was plotted against each outcome. Derivative of the nonlinear curve fit to the dataset for each outcome was solved to find plateau in learning.

RESULTS

A total of 270 patients [114 microdiscectomy; 79 laminectomy; 77 minimally invasive transforaminal lumbar interbody fusion (MI-TLIF)] were included. (1) ION set-up and image-acquisition: no learning curve for microdiscectomy. Proficiency at 23 and 31 cases for laminectomy and MI-TLIF, respectively. (2) Operative time: no learning curve for microdiscectomy. Proficiency at 36 and 31 cases for laminectomy and MI-TLIF, respectively. (3) Fluoroscopy time: no learning curve. (4) Radiation dose: proficiency at 42 and 33 cases for microdiscectomy and laminectomy, respectively. No learning curve for MI-TLIF. (5) Operative complications: unable to evaluate for microdiscectomy and MI-TLIF. Proficiency at 29 cases for laminectomy. (6) Repeat spin: unable to evaluate for microdiscectomy and laminectomy. For MI-TLIF, chronology was not associated with repeat spins. (7) Incorrect localization: none.

CONCLUSIONS

Skin-anchored ION did not result in any wrong level surgeries. Learning curve for other parameters varied by surgery type, but was achieved at 25-35 cases for a majority of outcomes.

LEVEL OF EVIDENCE

Level III.

Perioperative Modifications to the Open TLIF Provide Comparable Short-term Outcomes to the MIS-TLIF

STUDY DESIGN

This study is a retrospective review of patients' charts and data from longitudinally collected clinical outcomes and opioid use.

OBJECTIVE

In the current study, we aim to compare short-term outcomes data for 139 Open transforaminal interbody fusion (TLIF) patients to recently published data for tubular and endoscopic MIS-TLIF.

BACKGROUND CONTEXT

In response to the downsides associated with Open TLIF, such as large incision, blood loss, delayed ambulation, prolonged hospitalization, and opioid-reliance, spine surgeons developed tubular retractor based "minimally-invasive" TLIF. However, the traditional Open TLIF retains its significance in terms of providing successful fusion and improved patient-reported outcomes (PROs).

METHODS

We adapted several techniques with an aim to improve short-term outcomes for our Open TLIF patients that combined extensive perioperative counselling, an emphasis on early mobilization, avoidance of overuse of opioid analgesics, early discharge with home care arrangements, use of a posthospitalization drainage tube with intraoperative surgical modifications using small incisions (4-5 cm), a narrow 20 mm retractor, minimal muscle injury, and use of a cell saver to minimize net blood loss. The demographics and perioperative results were compared with data from recent MIS-TLIF studies using Student t test for continuous and χ2/exact test for categorical variables.

RESULTS

Among the total 139 patients, 115 underwent a single-level procedure, 90% of whom were discharged on the first postoperative day (length of stay=1.13±0.47 d) with an average net estimated blood loss of 176.17±87.88 mL. There were 24 two-level procedures with an average length of stay of 1.57±0.84 days, average net estimated blood loss was 216.96±85.70 mL. The patients had statistically significant improvements in PROs at 3 and 12 months.

CONCLUSIONS

The results of this study identify that patients who underwent modified Open TLIF demonstrated favorable short-term outcomes, as compared with the tubular MIS-TLIF, by virtue of avoidance of blood transfusions, shorter hospital stays, and significantly less opioid usage while experiencing satisfactory PROs.

Does loss of spondylolisthesis reduction impact clinical and radiographic outcomes after minimally invasive transforaminal lumbar interbody fusion?

BACKGROUND CONTEXT

Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is a common operative approach to address degenerative lumbar stenosis and spondylolisthesis which has failed nonoperative care. Compared to open TLIF, MI-TLIF relies to a greater extent on indirect decompression resulting in a heightened awareness of spondylolisthesis reduction among MI surgeons. To what extent intraoperative reduction is achieved as well as the rate and clinical impact of loss or reduction and slip recurrence remain unknown.

PURPOSE

To determine the rate and clinical impact of slip recurrence after MI-TLIF with expandable cage technology STUDY DESIGN/SETTING: Retrospective Cohort Study PATIENT SAMPLE: Patients undergoing MI-TLIF for degenerative spondylolisthesis using an articulating, expandable cage OUTCOME MEASURES: Patient-reported outcome measures (PROMs), including the Oswestry Disability Index (ODI), visual analog scale (VAS) for back/leg pain, Short Form-12 (SF-12), and PROMIS Physical Function (PF) METHODS: Patients undergoing MI-TLIF for degenerative spondylolisthesis using articulating, expandable cages from 2017 to 2019 were retrospectively studied. Lateral radiographs were reviewed and evaluated for the presence or absence of spondylolisthesis preoperatively, intraoperatively, and at follow-up times including 2 weeks, 6 weeks, 12 weeks, 6 months, and 1 year postoperatively. Spondylolisthesis was measured from the posterior inferior corner of the cephalad vertebra to the posterior superior corner of the caudal vertebra, with any measurement >1 mm classified as spondylolisthesis, and Meyerding grade was noted. Intraoperative reduction was measured, and loss of reduction was defined as >1 mm increase in spondylolisthesis comparing follow-up imaging to intraoperative films. PROMs were recorded at the preoperative and follow-up time points. Fusion was assessed at 1 year postoperatively via CT.

RESULTS

A total of 63 patients and 70 levels were included, with mean age 59.8 years (SD,13.8). 19 levels (27.1%) had complete reduction intraoperatively, 40 (57.1%) had partial reduction, and 11 (15.7%) had no reduction. Of the 30 levels with loss of reduction (50.8%), 20 (66.7%) occurred by 2 weeks postoperatively and 28 (93.3%) occurred by 12 weeks postoperatively. At 6 months, there were significant differences between those who had loss of reduction and those who did not in VAS back pain (3.0 vs. 0.9, p = .017) and SF-12 PCS (41.5 vs. 50.0, p = .035), but no differences were found between the groups for any instruments at any other time points. The overall fusion rate was 82.1% (32/39) at 1 year postoperatively. There was no significant difference in fusion rate between the loss of reduction (16/20) and no loss of reduction (20/23) groups. Patients with loss of reduction had no difference in reoperation rate (1/28) compared to those without loss of reduction (2/24).

CONCLUSIONS

While a majority of patients demonstrated reduction intraoperatively, 51% had loss of reduction, most commonly in the acute postoperative period. There were few differences in PROMs between patients who had loss of reduction and those who did not, suggesting that radiographic loss of reduction after MI-TLIF in the setting of degenerative spondylolisthesis may not be clinically meaningful.

Comparison of Radiation Exposure Between Anterior, Lateral, and Posterior Interbody Fusion Techniques and the Influence of Patient and Procedural Factors

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

The aim of this study was to elucidate the relative influence of multiple factors on radiation usage for anterior, lateral, and posterior based lumbar interbody fusion techniques.

SUMMARY OF BACKGROUND DATA

There has been substantial global growth in the performance of lumbar interbody fusions, due to evolution of techniques and approaches and increased attention to sagittal alignment. Utilization of intraoperative imaging guidance has similarly expanded, with a predominance of fluoroscopy and consequent increased radiation exposure. There have been no larger-scale studies examining the role of patient and procedural factors in driving radiation exposure across different interbody techniques.

METHODS

We used a clinical registry to review all single-level lumbar interbody fusions performed between January 2016 and October 2020. Operative records were reviewed for the amount of radiation exposure during the procedure. Patient age, biologic sex, body mass index (BMI), operative surgeon, surgical level, surgical time, and fusion technique were recorded. Multivariable adjusted analyses using negative binomial regression were used to account for confounding.

RESULTS

We included 134 interbody fusions; 80 performed with a posterior approach (TLIF/PLIF), 43 via an anterior approach (ALIF) with posterior pedicle fixation, and 9 performed with a lateral approach (LLIF/XLIF). Average radiation per case was 136.4 mGy (SE 17.3) for ALIF, 108.6 mGy (16.9) for LLIF/XLIF, and 60.5 mGy (7.4) for TLIF/PLIF. We identified lateral approaches, increased BMI, minimally invasive techniques, and more caudal operative levels as significantly associated with increased radiation exposure.

CONCLUSION

We identified several novel drivers of radiation exposure during interbody fusion procedures, including the relative importance of technique and the level at which the fusion is performed. More caudal levels of intervention and lateral based techniques had significantly greater radiation exposure.Level of Evidence: 4.

Development and Initial Internal Validation of a Novel Classification System for Perioperative Expectations Following Minimally Invasive Degenerative Lumbar Spine Surgery

STUDY DESIGN

This was a prospective consecutive clinical cohort study.

OBJECTIVE

The purpose of our study was to develop and provide an initial internal validation of a novel classification system that can help surgeons and patients better understand their postoperative course following the particular minimally invasive surgery (MIS) and approach that is utilized.

SUMMARY OF BACKGROUND DATA

Surgeons and patients are often attracted to the option of minimally invasive spine surgery because of the perceived improvement in recovery time and postsurgical pain. A classification system based on the impact of the surgery and surgical approach(es) on postoperative recovery can be particularly helpful.

METHODS

Six hundred thirty-one patients who underwent MIS lumbar/thoracolumbar surgery for degenerative conditions of the spine were included. Perioperative outcomes-operative time, estimated blood loss, postsurgical length of stay (LOS), 90-day complications, postoperative day zero narcotic requirement [in Morphine Milligram Equivalent (MME)], and need for intravenous patient-controlled analgesia (IV PCA).

RESULTS

Postoperative LOS and postoperative narcotic use were deemed most clinically relevant, thus selected as primary outcomes. Type of surgery was significantly associated with all outcomes (P<0.0001), except intraoperative complications. Number of levels for fusion was significantly associated with operative time, in-hospital complications, 24 hours oral MME, and the need for IV PCA and LOS (P<0.0001). Number of surgical approaches for lumbar fusion was significantly associated with operative time, 24 hours oral MME, need for IV PCA and LOS (P<0.001). Based on these parameters, the following classification system ("Qureshi-Louie classification" for MIS degenerative lumbar surgery) was devised: (1) Decompression-only; (2) Fusion-1 and 2 levels, 1 approach; (3) Fusion-1 level, 2 approaches; (4) Fusion-2 levels, 2 approaches; (5) Fusion-3+ levels, 2 approaches.

CONCLUSIONS

We present a novel classification system and initial internal validation to describe the perioperative expectations following various MIS surgeries in the degenerative lumbar spine. This initial description serves as the basis for ongoing external validation.

Combining Expandable Interbody Cage Technology With a Minimally Invasive Technique to Harvest Iliac Crest Autograft Bone to Optimize Fusion Outcomes in Minimally Invasive Transforaminal Lumbar Interbody Fusion Surgery

STUDY DESIGN

This was a retrospective cohort review.

OBJECTIVE

The objective of this study was to determine the rate of fusion associated with an expandable cage and iliac crest bone graft in minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) surgery.

SUMMARY OF BACKGROUND DATA

MI-TLIF is a commonly performed procedure, but challenges inherent in MI-TLIF technique can make achieving an interbody fusion difficult.

METHODS

A retrospective review was performed on consecutive patients treated with an MI-TLIF for degenerative lumbar pathology. Patients that completed patient-reported outcome measures and 1-year computed tomography (CT)-scans for fusion analysis were included. Fusion morphology was analyzed by evaluating CT scans for location of bridging trabecular bone in relation to the cage. Patients with bridging bone were considered fused. Preoperative and postoperative health-related quality of life scores were compared. A Kolmogrov-Smirnoff test was used to determine normality of health-related outcome scores. A Friedman 2-way analysis of variance by ranks with pairwise comparisons to determine statistical significance of differences between the date of a follow-up examination and preoperative examination was done.

RESULTS

Of 75 patients evaluated 23 patients were excluded due to loss to follow-up, adjacent segment degeneration, inability to obtain a CT scan, or reoperation for nonfusion related symptoms. Of 61 disk spaces that were included, 55 had bridging bone through the intervertebral cage, resulting in an overall fusion rate of 90.2%. There was a higher rate of fusion at L5-S1 as compared to L4-L5. There was mean improvement in patient-reported outcome measures for Oswestry Disability Index, Short Form-12 Physical Component Score, Visual Analog Scale Back/Leg pain, and Patient-Reported Outcome Measurement Information System Physical Function. There were no complications associated with iliac crest bone graft harvesting.

CONCLUSION

Combining an expandable cage with iliac crest autograft bone harvested through a minimally invasive technique can allow for improved fusion rates without graft-site complications in MI-TLIF surgery.

Minimally Invasive Transforaminal Lumbar Interbody Fusion Using Augmented Reality Surgical Navigation for Percutaneous Pedicle Screw Placement

STUDY DESIGN

This was a retrospective observational study.

OBJECTIVE

The aim of this study was to evaluate the accuracy of percutaneous pedicle screw placement using augmented reality surgical navigation during minimally invasive transforaminal lumbar interbody fusion (TLIF).

SUMMARY OF BACKGROUND DATA

Augmented reality-based navigation is a new type of computer-assisted navigation where video cameras are used instead of infrared cameras to track the operated patients and surgical instruments. This technology has not so far been clinically evaluated for percutaneous pedicle screw placement.

MATERIALS AND METHODS

The study assessed percutaneous pedicle screw placement in 20 consecutive patients who underwent single-level minimally invasive TLIF using augmented reality surgical navigation. Facet joint violation and depression by the inserted pedicle screws were evaluated. Secondary outcome such as radiation dose exposure, fluoroscopy time, and operative time were collected for 3 phases of surgery: preparation phase, pedicle screw placement, and decompression with cage placement.

RESULTS

A clinical accuracy for screw placement within the pedicle (Gertzbein 0 or 1) of 94% was achieved. One screw violated the facet joint with a transarticular pathway. The screw head did not depress the facet in 54%. The use of fluoroscopy during navigation correlated with patient body-mass index (r=0.68, P<0.0001). The pedicle screw placement time corresponded to 36±5% of the total operative time of 117±11 minutes. A statistically significant decrease of 10 minutes in operative time was observed between the first and last 10 procedures which corresponded to the pedicle screw placement time decrease (48±9 vs. 38±7 min, P=0.0142). The learning curve model suggests an ultimate operative time decrease to 97 minutes.

CONCLUSION

Augmented reality surgical navigation can be clinically used to place percutaneous screws during minimally invasive TLIF. However, the lack of tracking of the location of the device requires intraoperative fluoroscopy to monitor screw insertion depth especially in obese patients.

LEVEL OF EVIDENCE

Level III.

Perioperative Comparison of Robotic-Assisted Versus Fluoroscopically Guided Minimally Invasive Transforaminal Lumbar Interbody Fusion

OBJECTIVE

Robotic surgical systems have been developed to improve spine surgery accuracy. Studies have found significant reductions in screw revision rates and radiation exposure with robotic assistance compared with open surgery. The aim of the present study was to compare the perioperative outcomes between robot-assisted (RA) and fluoroscopically guided (FG) minimally invasive (MI) transforaminal lumbar interbody fusion (TLIF) performed by a single surgeon.

METHODS

The present retrospective cohort study analyzed all patients with lumbar degenerative disease who had undergone MI-TLIF by a single surgeon from July 2017 to March 2020. One group had undergone FG MI-TLIF and one group had undergone RA MI-TLIF.

RESULTS

Of the 101 patients included in the present study, 52 had undergone RA MI-TLIF and 49, FG MI-TLIF. We found no statistically significant differences in the operative time (RA, 241 ± 69.3 minutes; FG, 246.2 ± 56.3 minutes; P = 0.681). The mean radiation time for the RA group was 32.8 ± 28.8 seconds, and the mean fluoroscopy dose was 31.5 ± 30 mGy. The RA radiation exposure data were compared with similar data for the FG MI-TLIF group in a previous study (59.5 ± 60.4 mGy), with our patients' radiation exposure significantly lower (P = 0.035). The postoperative complications and rates of surgical revision were comparable.

CONCLUSIONS

Our results have demonstrated that RA MI-TLIF provides perioperative outcomes comparable to those with FG MI-TLIF. A reduced radiation dose to the patient was observed with RA compared with FG MI-TLIF. No differences were noted between the RA and FG cohorts in operative times, complication rates, revision rates, or length of stay.

Characterizing the Surgeon Learning Curve in Instrumented Minimally Invasive Spinal Surgery: Does the Evidence Account for Training and Experience? A Systematic Literature Review

STUDY DESIGN

This was a systematic literature review.

OBJECTIVE

The purpose of this systematic literature review was to aggregate all evidence characterizing the learning curve of instrumented minimally invasive surgery (MIS) techniques in spinal surgery and summarize what, if any, consideration has been given to surgeon training and experience.

SUMMARY OF BACKGROUND DATA

MIS techniques have become prevalent in spine surgery given the ability to diminish the intraoperative footprint, translating to quicker patient recovery, and improved long-term outcomes. However, technical demand on the surgeon can be significant, particularly during the procedural adoption (learning curve) phase. Many studies have sought to quantify the duration and severity of these learning curve phases, with the intent to characterize MIS procedural appropriateness and safety. However, while these studies are robust regarding outcome metrics, it is not well understood whether they adequately characterize surgeon training and experience.

METHODS

A systematic literature review was performed in the PubMed and MEDLINE databases in accordance with the PRISMA guidelines. All inclusion articles were screened for statements regarding surgeon experience/training. Statements were further classified by the types of metrics/variables utilized to establish a contextual history of experience/training. Descriptive statistics were reported.

RESULTS

Initial search criteria yielded 458 articles, 12 met final inclusion. Seven articles (58.3%) attempted a summary statement of experience which acknowledged at least one of the following metrics: total years in practice (41.7%), years/number of cases performed using the traditional/gold-standard technique (16.7%), specification of residency/fellowship training (16.7%), use/nonuse of cadaveric or course/lab training (16.7%), and/or design of operating team (8.3%). No articles considered experience as a quantitative variable in their study analyses.

CONCLUSIONS

Spine MIS learning curve studies for instrumented fusion procedures provide inadequate context/characterization of surgeon experience and training. Future efforts leveraging learning curve methodology utilized in other surgical specialties would be beneficial.

Intraoperative risks of radiation exposure for the surgeon and patient

Intraoperative radiological imaging serves an essential role in many spine surgery procedures. It is critical that patients, staff and physicians have an adequate understanding of the risks and benefits associated with radiation exposure for all involved. In this review, we briefly introduce the current trends associated with intraoperative radiological imaging. With the increased utilization of minimally invasive spine surgery (MIS) techniques, the benefits of intraoperative imaging have become even more important. Less surgical exposure, however, often equates to an increased requirement for intraoperative imaging. Understanding the conventions for radiation measurement, radiological fundamental concepts, along with deterministic or stochastic effects gives a framework for conceptualizing how radiation exposure relates to the risk of various sequela. Additionally, we describe the various options surgeons have for intraoperative imaging modalities including those based on conventional fluoroscopy, computer tomography, and magnetic resonance imaging. We also describe different ways to prevent unnecessary radiation exposure including dose reduction, better education, and use of personal protective equipment (PPE). Finally, we conclude with a reflection on the progress that has been made to limit intraoperative radiation exposure and the promise of future technology and policy.

Does interbody cage lordosis impact actual segmental lordosis achieved in minimally invasive lumbar spine fusion?

OBJECTIVE

In an effort to prevent loss of segmental lordosis (SL) with minimally invasive interbody fusions, manufacturers have increased the amount of lordosis that is built into interbody cages. However, the relationship between cage lordotic angle and actual SL achieved intraoperatively remains unclear. The purpose of this study was to determine if the lordotic angle manufactured into an interbody cage impacts the change in SL during minimally invasive surgery (MIS) for lumbar interbody fusion (LIF) done for degenerative pathology.

METHODS

The authors performed a retrospective review of a single-surgeon database of adult patients who underwent primary LIF between April 2017 and December 2018. Procedures were performed for 1-2-level lumbar degenerative disease using contemporary MIS techniques, including transforaminal LIF (TLIF), lateral LIF (LLIF), and anterior LIF (ALIF). Surgical levels were classified on lateral radiographs based on the cage lordotic angle (6°-8°, 10°-12°, and 15°-20°) and the position of the cage in the disc space (anterior vs posterior). Change in SL was the primary outcome of interest. Subgroup analyses of the cage lordotic angle within each surgical approach were also conducted.

RESULTS

A total of 116 surgical levels in 98 patients were included. Surgical approaches included TLIF (56.1%), LLIF (32.7%), and ALIF (11.2%). There were no differences in SL gained by cage lordotic angle (2.7° SL gain with 6°-8° cages, 1.6° with 10°-12° cages, and 3.4° with 15°-20° cages, p = 0.581). Subgroup analysis of LLIF showed increased SL with 15° cages only (p = 0.002). The change in SL was highest after ALIF (average increase 9.8° in SL vs 1.8° in TLIF vs 1.8° in LLIF, p < 0.001). Anterior position of the cage in the disc space was also associated with a significantly greater gain in SL (4.2° vs -0.3°, p = 0.001), and was the only factor independently correlated with SL gain (p = 0.016).

CONCLUSIONS

Compared with cage lordotic angle, cage position and approach play larger roles in the generation of SL in 1-2-level MIS for lumbar degenerative disease.

A Review of Techniques, Time Demand, Radiation Exposure, and Outcomes of Skin-anchored Intraoperative 3D Navigation in Minimally Invasive Lumbar Spinal Surgery

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

To describe our technique for and evaluate the time demand, radiation exposure and outcomes of skin-anchored intraoperative three-dimensional navigation (ION) in minimally invasive (MIS) lumbar surgery, and to compare these parameters to 2D fluoroscopy for MI-TLIF.

SUMMARY OF BACKGROUND DATA

Limited visualization of anatomic landmarks and narrow access corridor in MIS procedures result in greater reliance on image guidance. Although two-dimensional fluoroscopy has historically been used, ION is gaining traction.

METHODS

Patients who underwent MIS lumbar microdiscectomy, laminectomy, or MI-TLIF using skin-anchored ION and MI-TLIF by the same surgeon using 2D fluoroscopy were selected. Operative variables, radiation exposure, and short-term outcomes of all procedures were summarized. Time-demand and radiation exposure of fluoroscopy and ION for MI-TLIF were compared.

RESULTS

Of the 326 patients included, 232 were in the ION cohort (92 microdiscectomies, 65 laminectomies, and 75 MI-TLIFs) and 94 in the MI-TLIF using 2D fluoroscopy cohort. Time for ION setup and image acquisition was a median of 22 to 24 minutes. Total fluoroscopy time was a median of 10 seconds for microdiscectomy, 9 for laminectomy, and 26 for MI-TLIF. Radiation dose was a median of 15.2 mGy for microdiscectomy, 16.6 for laminectomy, and 44.6 for MI-TLIF, of this, 93%, 95%, and 37% for microdiscectomy, laminectomy, and MI-TLIF, respectively were for ION image acquisition, with the rest attributable to the procedure. There were no wrong-level surgeries. Compared with fluoroscopy, ION for MI-TLIF resulted in lower operative times (92 vs. 108 min, P < 0.0001), fluoroscopy time (26 vs. 144 s, P < 0.0001), and radiation dose (44.6 vs. 63.1 mGy, P = 0.002), with equivalent time-demand and length of stay. ION lowered the radiation dose by 29% for patients and 55% for operating room personnel.

CONCLUSION

Skin-anchored ION does not increase time-demand compared with fluoroscopy, is feasible, safe and accurate, and results in low radiation exposure.

LEVEL OF EVIDENCE

3.