Abstract

Background: Learning curves (LC) are typically defined by the number of different spinal procedures surgeons must perform before becoming “proficient,” as demonstrated by reductions in operative times, estimated blood loss (EBL), length of hospital stay (LOS), adverse events (AE), fewer conversions to open procedures, along with improved outcomes. Reviewing 12 studies revealed LC varied widely from 10-44 cases for open vs. minimally invasive (MI) lumbar diskectomy, laminectomy, transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion (ALIF), and oblique/extreme lateral interbody fusions (OLIF/XLIF). We asked whether the risks of harm occurring during these LC could be limited if surgeons routinely utilized in-person/intraoperative mentoring (i.e., via industry, academia, or well-trained colleagues).

Methods: We evaluated LC for multiple lumbar operations in 12 studies.

Results: These studies revealed no LC for open vs. MI lumbar diskectomy. LC required 29 cases for MI laminectomy, 10-44 cases for MI TLIF, 24-30 cases for MI OLIF, and 30 cases for XLIF. Additionally, the LC for MI ALIF was 30 cases; one study showed that 32% of major vascular injuries occurred in the first 25 vs. 0% for the next 25 cases. Shouldn’t the risks of harm to patients occurring during these LC be limited if surgeons routinely utilized in-person/intraoperative mentoring?

Conclusions: Twelve studies showed that the LC for at different MI lumbar spine operations varied markedly (i.e., 10-44 cases). Wouldn’t and shouldn’t spine surgeons avail themselves of routine in-person/intraoperative mentoring to limit patients’ risks of injury during their respective LC for these varied spine procedures ?

Keywords: Learning Curve, Risks, Adverse Events, Neurological Deficits, Pros, Cons, Morbidity, Minimally Invasive (MI), Transforaminal Lumbar Interbody Fusions (TLIF), Anterior Lumbar Interbody Fusion (ALIF), Oblique/Extreme Lateral Interbody Fusions (OLIF/XLIF), Other Operations, Outcomes, Definition Learning Curve, Need for Mentoring

INTRODUCTION

For spinal surgeons, learning curves (LC) are defined by the number of spine procedures surgeons must perform before becoming “proficient” as demonstrated by reductions in operative times, estimated blood loss (EBL), length of hospital stays (LOS), adverse events (AE), fewer conversions to open procedures, and with improved outcomes. During neurosurgery or orthopedic residency training programs, the risks to patients during residents’ learning curves (LC) are limited by the attending surgeons’ “direct supervision”. However, how are these risks mitigated during the varied LC documented for new/different spine procedures introduced after residency (i.e., minimally invasive (MI) diskectomy, laminectomy, transforaminal lumbar interbody fusion (TLIF), anterior lumbar interbody fusion (ALIF), and oblique/extreme lateral interbody fusion (OLIF/XLIF), cervical fusions) [ Table 1 ]?[ 1 - 12 ] Specifically, we asked whether the risk of harm occurring during the varied LC (i.e., 10-44 cases) could be limited if spinal surgeons availed themselves of in-person/intraoperative mentoring opportunities provided by industry, academia, and/or well-trained colleagues.

Table 1:

Initial Learning Curves (LC) for Different Types of Spine Surgery.

Defining Learning Curves for Minimally Invasive (MI) Spine Operations

Minimally invasive (MI) spine operations were largely devised to reduce operative time, tissue trauma, and perioperative morbidity [ Table 1 ].[ 1 - 12 ] Learning curves (LC) for performing the different MI procedures are typically defined by marked reductions in operative times, estimated blood loss (EBL), length of stay (LOS), frequency of adverse events (AE), and fewer conversions to open procedures, with improved outcomes (i.e., better Visual Analog Outcomes Scores (VAS)) [ Table 1 ].[ 1 - 12 ] Specifically, Ferry (2021) added that spine surgeons’ education/expertise should allow them to meet the LC criteria by demonstrating a reduction of operative time, postoperative recovery times, and better results [ Table 1 ].[ 3 ] They further observed that just 59.3% of 12 studies summarized surgeon experience, 41.7% discussed total years of surgeon practice, and just 16.7% of surgeons had performed traditional open procedures, were fellowship trained, and had cadaver course/lab training prior to performing MI operations.

No Learning Curve for Microdiskectomy

Several studies documented no LC cases were required for conversion from open to performing MI microdiscectomy [ Table 1 ].[ 2 , 12 ] Epstein’s (2017) review of the literature showed there was no learning curve required to achieve “proficiency” for performing MI diskectomies.[ 2 ] Vaishnav et al. (2022) also confirmed the absence of a LC for completing 114 microdiskectomies.[ 12 ]

Learning Curve for MI Transforaminal Lumbar Interbody Fusion (TLIF)

Six studies focused on the wide variation in LC reported for MI TLIF [ Table 1 ].[ 1 , 2 , 5 , 9 , 10 , 12 ] Reviewing 14 articles involving 966 operations, Sclafani and Kim (2014) defined the overall LC as; “... the change in frequency of complications and length of surgical time as case number increased” for 5 spine operations.[ 10 ] These 5 procedures included; MI lumbar decompression, MI TLIF, MI percutaneous pedicle screw insertion, laparoscopic anterior lumbar interbody fusion (ALIF), and MI cervical surgery; the learning curves for these procedures ranged from 20-30 cases [ Table 1 ].[ 10 ] Lee et al. (2014) discussed the first 44 MI TLIF as LC cases (vs. the latter 46 cases) as required before one surgeon (2004-2009) demonstrated “proficiency” (i.e., defined by reduced average operative times, duration of fluoroscopy, and better outcome) [ Table 1 ].[ 5 ] Interestingly, both of Lee’s patient groups sustained comparable AE; the first 44 patients had 1 dural tear and 2 asymptomatic cage migrations vs. the latter 46 patients who experienced 1 asymptomatic cage migration. Additionally, fusion rates were similar for both groups, and no patient from either group required conversion to an open procedure. For 65 consecutive patients undergoing 1-level MI TLIF followed for at least 1 postoperative year (2008-2011), Nandyala et al. (2014) observed that the first 33 cases (Group A) were required to satisfy the LC (i.e., vs. the latter 32 cases (Group B)). [ Table 1 ].[ 9 ] Group A patients required; longer average operating room times, more EBL, more intravenous fluids, longer anesthesia times, 1 had a CT-documented medial pedicle wall breach, 2 pseudarthroses occurred, 1 demonstrated graft migration, while 2 patients required revision procedures. Group B patients had fewer AE; 2 exhibited pseudarthrosis, one had an infection, while 3 patients required additional surgery. Notably, patients from each group sustained 2 dural tears, 2 instances of “neuroforaminal bone growth,” and comparable LOS. In 2017, Epstein defined the LC for MI TLIF as ranging from 10-44 cases, while LC for other procedures warranted 20-30 cases (i.e., including MI diskectomy, MI cervical procedures, MI ALIF, and thoracolumbar pedicle screw techniques).[ 2 ] Ahn et al. (2022) further determined in 9 articles, including 753 patients, that the LC for MI TLIF required 31.33 +/- 11.98 cases (range 13-45 cases) [ Table 1 ].[ 1 ] Vaishnav et al. (2022) found the LC for MI TLIF required 31 cases [ Table 1 ].[ 12 ]

LC for MI Oblique Lumbar Interbody Fusion (OLIF) and Extreme Lateral Interbody Fusion (XLIF)

Two studies showed the LC for OLIF was achieved after 24-30 cases vs. 30 cases required to satisfy the LC for XLIF [ Table 1 ].[ 6 , 7 ] In 2019, Liu et al. determined the LC for MI OLIF occurred after the first 24 (Group A) vs. the latter 25 cases (Group B); Group A patients still required more operating room time, longer X-ray exposure times, and demonstrated a much higher 37.5% rate of AE rate (i.e., thigh numbness, motor deficits, neural injuries, and ileus) vs. 20% for group B patients [ Table 1 ].[ 7 ] Nevertheless, both groups exhibited similar clinical and radiological outcomes. The LC in Li et al. (2019) patients undergoing OLIF or XLIF occurred after the first 30 cases. [ Table 1 ].[ 6 ] Interestingly, a 10% rate of AE was seen for XLIF vs. a much higher 33.3% AE rate for OLIF, with the latter demonstrating more neurological and vascular injuries during the LC. Nevertheless, patients’ average ages were similar for both groups (i.e., 58.4 for XLIF vs. 56.1 for OLIF.), and they showed comparable clinical findings, operative times, EBL, number of operated levels, and follow-up durations.

LC for MI Anterior Lumbar Interbody Fusions (ALIF)

Mirza et al. (2022) found the LC included the first 25 - 30 cases out of 120 MI ALIF performed with posterior percutaneous instrumentation at the L45 and L5S1 levels (2010-2018) [ Table 1 ].[ 8 ] The 1^st 25 patients demonstrated more adverse events, including a higher 32% incidence of major vascular injuries requiring primary repair/packing vs. a 0% incidence in the 2^nd group of 25 patients. Additionally, although the 1st 30 patients had higher average estimated intraoperative EBL, the average operative times were comparable for the 1st 30 and the latter 90 patients.

Satisfied with In-Person/Intraoperative Mentoring Provided by Manufacturers, Academia, or Well-Trained Colleagues Could Limit the LC for MI Spine Surgery

Although some companies/manufacturers of spinal instrumentation provide “mentors” to directly scrub/supervise spine surgeons performing new operations, how many spine surgeons request and/or receive this “help”? Most likely, inexperienced spine surgeons return home and begin performing these procedures. Typically, they don’t consult experts or well-trained colleagues at surrounding academic/non-academic institutions, particularly if they are in competing groups or specialties (i.e., neurosurgery vs. orthopedics) or at surrounding institutions.

Risks and Remediation of Spinal Surgeons’ Learning Curves for MI Spine Operations

Several authors focused on the risks to patients during spine surgeons’ LC for different MI spine procedures, and potential remediation maneuvers [ Table 1 ].[ 2 , 4 , 10 , 11 ] Recommendations for remediation have included; practicing on cadavers/models, using virtual/augmented/surgical simulators, and, most critically, in-person/intraoperative surgeon-mentors [ Table 1 ].[ 2 , 4 , 10 , 11 ] In 14 studies involving 966 patients, Sclafani et al. (2014) found the overall LC for performing 5 types of MI fusions required 20-30 cases/procedures (i.e., “... MIS lumbar decompression procedures, TLIF, percutaneous pedicle screw insertion, laparoscopic ALIF, and MIS cervical procedures); their 11% complication rate (i.e., 109/966) was largely attributed to dural tears, implant malposition, nerve injuries, and non-unions [ Table 1 ].[ 10 ] In 2017, Epstein pointed out that the LC rates varied markedly for TLIF (i.e., between 10-44 cases), while other procedures’ LC warranted 20-30 cases (i.e., MI laminectomy, MI cervical, MI ALIF, Thoracic/Lumbar Pedicle Screw Techniques) [ Table 1 ].[ 2 ] Epstein concluded that; “...better oversight measures and or mentoring programs could limit the morbidity/AE occurring during these “LC” in the future.” Sharif et al. (2018) observed a 30-case LC frequency for different MI spine operations that involved less “familiar anatomy”, reduced “tactile feedback”, and often new instrumentation (i.e., endoscopes) [ Table 1 ].[ 11 ] Their recommendation included the use of; “Structured training with cadavers and lots of practice, preferably while working under the guidance of experienced surgeons.”. Kimchi et al. (2020) concluded after performing 230 open vs. MI thoracic/lumbar spine operations that; “The main challenge facing the MIS community is constructing an education program for MIS surgeons in order to reduce the learning curve-induced complications” [ Table 1 ].[ 4 ] They further concluded; “Advancement of educational aids for MIS skill improvement including spine models, virtual and augmented reality aids, and surgical simulators may reduce the learning curve of spine surgeons”.

CONCLUSION

Twelve studies showed that the LC for different MI lumbar spine operations varied markedly (i.e., 10-44 cases) [ Table 1 ].[ 1 - 12 ] Shouldn’t spine surgeons avail themselves of more routine in-person/intraoperative mentoring or other “educational simulation modalities” to limit the risks to patients during the LC for these varied spine procedures?

Ethical approval

Institutional Review Board approval is not required.

Declaration of patient consent

Patient’s consent not required as there are no patients in this study.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Use of artificial intelligence (AI)-assisted technology for manuscript preparation

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Disclaimer

The views and opinions expressed in this article are those of the authors and do not necessarily reflect the official policy or position of the Journal or its management. The information contained in this article should not be considered to be medical advice; patients should consult their own physicians for advice as to their specific medical needs.

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