Minimally Invasive Lumbar Decompression: A Review of Indications, Techniques, Efficacy and Safety

Figures & data

Figure 1. Axial cross-section of spinal cord depicting ligamentum flavum hypertrophy.

(A) LF thickness (AP) measured perpendicular to the border of the lamina corresponding to the intervertebral disc. (B) MRI cross-sectional image demonstrating LSCS. Arrow demonstrates LFH measurement.

Figure 2. Pitch of lamina determines the working angle (A–C).

Figure 3. Preoperative epidurogram establishes a baseline for evaluating the epidural space and creating a safe visual field to direct the operative devices.

Figure 4. An AP image with the vertebral endplates squared with the fluoroscopic beam is recommended to evaluate the interlaminar space.

Figure 5. mild portal stabilizer that mitigates ventral migration of the operating devices while allowing for superior and inferior movement to sculpt the interlaminar space.

Figure 6. Images demonstrating a deployed bone rongeur (A) and tissue sculptor (B) between the lamina and within the epidural space.

Table 1. Evidence for efficacy.

Study (year)	Study design	Patients (n) & selection criteria	Control	Interventions	Follow-up period	Outcome measures	Results	Conclusion	Ref.
Deer et al. (2010)	Retrospective multicenter observational study	n = 90; Symptomatic LSS, failed conservative therapy	–	mild procedure	–	Incidence of dural puncture/tear, blood transfusion, nerve injury, epidural bleeding, hematoma	There were no major adverse events or complications related to the devices or procedure. No incidents of dural puncture or tear, blood transfusion, nerve injury, epidural bleeding or hematoma were observed	The mild procedure is a safe treatment option, and complication rates associated with this procedure may be lower than the complication rates reported for both open and minimally invasive LSS surgeries. However, additional studies with larger patient populations are needed for further evaluation	[26]
Chopko et al. (2010) (MiDAS I)	Prospective, multicenter study	n = 78; Symptomatic LSS, failed conservative therapy	–	mild procedure	6 weeks	VAS, ODI, ZCQ, SF-12v2^® Health Survey	At 6 weeks, results showed statistically and clinically significant reduction of pain, and improved mobility and physical functionality as measured by VAS, ODI, ZCQ and SF-12v2 Average baseline VAS was 7.3 (3–10); at 6-week follow-up, average VAS improved to 3.7 (0–10), demonstrating a mean improvement of 3.6 from baseline to 6-week follow-up (p < 0.0001). For mobility, average baseline ODI was 47.4 (16–84); at 6-week follow-up, average ODI improved to 29.5 (0–72), demonstrating a mean improvement of 17.9 from baseline to 6-week follow-up (p < 0.0001). ZCQ physical function and symptom severity (in both pain and neuro-ischemic sub-domains) were statistically significantly improved (p < 0.001, paired t-test) from baseline and patients were satisfied with their outcomes.For SF-12v2, health status was improved for the two summary surveys (PCS and MCS) and all eight survey scales at 6-week follow-up compared with baseline. This improvement was statistically significant (95% CI) for all but the GH survey scaleThere were no major device or procedure-related complications reported	The mild procedure has good therapeutic efficacy for lumbar spinal canal stenosis, but additional studies are needed for further evaluation	[27]
Lingreen et al. (2010)	Retrospective study	n = 42; Symptomatic LSS, failed conservative therapy	–	mild procedure	30 days	VAS	Baseline mean VAS of 9.6 (± 0.42) with standing and ambulation decreased to 5.8 (± 2.5) at 30 days post procedure (p < 0.05). All patients reported functional impairment prior to the procedure; 71% reported improvement in function following the mild procedure. There were no major adverse events reported	The mild procedure is a safe and effective treatment modality for neurogenic claudication attributed to central stenosis due to ligamentum flavum hypertrophy in patients who have failed conservative therapy. Further RCTs comparing safety and efficacy of the mild Procedure to other treatments for spinal stenosis are warranted	[28]
Chopko (2011)	Case series	n = 14; symptomatic LSS; failed conservative therapy	–	PRLL technique (mild procedure)	Average follow-up of 23.5 weeks	VAS, ODI	Mean preoperative VAS was 7.61 ± 2.0, whereas the average postoperative VAS score was 3.61 ± 2.9, which demonstrated statistically significant improvement of 52.6% (p = 0.05) ODI scores decreased from a preoperative average of 50% to a postoperative average of 43.9%, but the change was not statistically significant No obvious dural tears, CSF leaks or wound-healing complications were observed	The mild procedure is a safe procedure and showed therapeutic efficacy to treat LSS in high-risk patients	[29]
Schomer et al. (2011)	Meta-analysis	n = 107; symptomatic LSS, failed conservative therapy	–	mild procedure	3 months	VAS, ODI	Average baseline VAS of 7.4, decreased to 3.9 at 3-month follow-up, a statistically significant improvement of 3.5 points (p < 0.0001) Mean baseline ODI of 48.0 decreased to 30.9 at 3-month follow-up, a statistically significant improvement of 17.1 points (p < 0.0001)	When compared with open surgery, mild efficacy results compare favorably, and complication rates are much lower	[30]
Basu et al. (2012)	Case series	n = 27; symptomatic LSS, failed conservative therapy	–	mild procedure	6 months	VAS, ODI, ZCQ	Patients experienced a statistically significant improvement in the VAS pain score from a mean of 9.1 (95% CI ± 0.59) at baseline to 3.9 (95% CI ± 2.25) 6 months after the mild procedure, an improvement of 5.2 points (p < 0.0001) Baseline average ODI of 55.1 (95% CI ± 6.34) showed statistically significant improvement at 6-month follow-up with a mean ODI of 31.1 (95% CI ± 9.29), an improvement of 24.0 points (p < 0.0004) ZCQ change was statistically significant and demonstrated improvement in all domains (p < 0.001). The average ZCQ Patient Satisfaction score was 1.86 (95% CI ± 0.34) at 6-month follow-up, indicating that patients were ‘satisfied’ to ‘very satisfied’ with the treatment There were no significant mild device or procedure-related adverse events observed or reported	The mild procedure has been shown to be a safe, effective and cost-effective treatment for LSS patients with neurogenic claudication. However, further randomized, prospective clinical studies would be beneficial	[31]
Deer et al. (2012)	Prospective, single-center study	n = 46; symptomatic LSS, failed conservative treatment	–	mild procedure	12 weeks, 6 months, and 1 year	VAS, ODI, ZCQ	Mean baseline VAS of 6.9 (95% CI ± 0.6) improved to 4.0 (95% CI ± 1.0) at 1-year follow-up, a 2.9-point improvement (p < 0.0001) Mean baseline ODI of 49.4 (95% CI ± 2.5) improved to 32.0 (95% CI ± 5.8) at 1-year follow-up, a 17.4-point improvement (p < 0.0001) Statistically significant improvements were achieved in all ZCQ domains, including symptom severity, both symptom severity sub-domains (pain and neuro-Ischemic) and physical function (paired t-test; p < 0.0001)	The mild procedure demonstrated statistically and clinically significant improvement in physical function, as well as reduction of pain intensity	[32]
Levy et al. (2012)	Systematic safety review and meta-analysis	n = 373; symptomatic LSS, failed conservative treatment	–	mild procedure	1 year	VAS, ODI, Safety data	Mean baseline VAS of 7.4 decreased to 3.5, resulting in a mean pain improvement of 3.9 (95% CI ± 0.42) at 1-year follow-up. Mean baseline ODI of 46.6 improved to 30.6, a 16.0 point mean mobility improvement at 1-year follow-up There were no reports of major device- or procedure-related adverse events, and there were no mortalities in this study	The mild procedure provides statistically significant improvement in pain and mobility, as well as an excellent safety profile	[33]
Mekhail et al. (2012)	Prospective single-center study	n = 40; symptomatic LSS, failed conservative treatment	–	mild procedure	1 year	PDI, RMQ, Standing Time, Walking Distance, VAS	Mean baseline PDI of 41.4 decreased to an average of 18.8 at 1 year post procedure, a statistically significant improvement of 55% The mean RMQ baseline score of 14.3 decreased to an average score of 6.6 at 1 year post procedure, a statistically significant improvement of 54% standing time improved from a baseline of 8 to 56 min at 1-year follow-up walking distance improved from a baseline mean of 246 feet to 3956 feet at 1-year follow-up VAS improved from 7.1 at baseline to 3.6 at 1-year follow-up	The mild procedure provides therapeutic efficacy with regard to improved functionality and decreased disability in patients with neurogenic claudication	[25]
Mekhail et al. (2012)	Prospective, multicenter study	n = 58; symptomatic LSS; failed conservative treatment	–	mild procedure	1 year	VAS, ODI, ZCQ, SF-12v2	Baseline mean VAS of 7.4 (95% CI ± 0.5) improved to a mean of 4.5 (95% CI ± 0.8) at 1-year follow-up, a statistically significant improvement of 2.9 points (p < 0.0001) Baseline average ODI of 48.6 (95% CI ± 3.8) decreased to an average of 36.7 (95% CI ± 5.8) at 1-year follow-up, a statistically significant improvement of 11.9 points (p < 0.0001) Regarding ZCQ, patients in the mild treatment group reported statistically significant improvements in all domains at 1-year follow-up. Average patient satisfaction score was 2.20 (95% CI ± 0.26), and 74% of patients reported that they were satisfied with the outcome of the procedure There were no reports of major intra- or postoperative mild device or procedure-related adverse events	The mild procedure provides therapeutic efficacy and has an excellent safety profile	[34]
Wong (2012)	Case series	n = 17; symptomatic LSS; failed conservative therapy	–	mild procedure	1 year	VAS, ODI	Baseline mean VAS of 7.6 decreased to 2.3 at 1-year follow-up, an improvement of 5.4 (95% CI) Average baseline ODI of 48.4 decreased to 21.7 at 1 year, an improvement of 26.6 points (95% CI) There were no major device- or procedure-related complications	The mild procedure provides significant pain relief and increased mobility for patients with LSS who have failed injection therapy	[35]
Brown (2012)	Prospective, single-center, double-blind, randomized controlled trial	n = 38; symptomatic LSS; failed conservative therapy	ESI	mild procedure	6 and 12 weeks	VAS, ODI, ZCQ	In the mild treatment group, average VAS baseline of 6.3 (95% CI ± 0.7) improved to a mean of 3.8 (95% CI ± 1.3) at 6-week follow-up and to a mean of 3.4 at 12-week follow-up (the change from baseline to week 6 and baseline to week 12 was significant (p < 0.01), but the change from 6 weeks to 12 weeks was not significant). In the ESI treatment group, mean VAS was 6.4 (95% CI ± 1.0) at baseline compared with 6.3 (95% CI ± 1.4) at 6-week follow-up, an insignificant improvement of 0.1 points, which was not statistically significant (p > 0.05) In the mild treatment group, mean ODI at baseline was 38.8 (95% CI ± 4.2) compared with a mean of 27.4 (95% CI ± 7.0) at 6-week follow-up, an improvement of 11.4 points. At 12 weeks, ODI improved by a mean of 18.6 in the mild treatment group. The change from baseline to 6 weeks post mild and baseline to 12 weeks post mild was significant (p < 0.05 and p < 0.01, respectively), but the change from 6 weeks to 12 weeks was not significant (p > 0.05). In the ESI treatment group, the mean baseline ODI was 40.5 (95% CI ± 5.9) and improved to 34.8 (95% CI ± 8.2) at 6-week follow-up, an improvement of 5.7 points, which was not statistically significant (p > 0.05) At 6-week follow-up, the mean ZCQ Patient Satisfaction score for the mild treatment group was 2.2 (95% CI ± 0.5) and 2.8 (95% CI ± 0.5) for the ESI treatment group. At 12-week follow-up, the average ZCQ patient satisfaction score was 1.8 for mild indicating a high level of patient satisfaction. No major mild or ESI device or procedure-related complications were reported	The mild procedure provides statistically significantly better pain reduction and improved functional mobility compared with treatment with ESI	[36]
Durkin et al. (2013)	Retrospective observational study	n = 50; symptomatic LSS; failed conservative therapy	–	mild procedure	1, 3 and 6 months	NRS, ZCQ, ODI, NIH PROMIS, patients’ self-reported low back and lower extremity pain distribution	Mean baseline NRS of 7.52 (4–10) improved to an average of 5.18 (0–10) at 1 month, 5.31 (0–10) at 3 months and 5.60 (0–10) at 6-month follow-up (p < 0.0001) Mean baseline ODI of 40.58 (10–78) improved to an average of 32.52 (0–62.22) at 1 month (p = 0.0002), 32.22 (0–66) at 3 months (p = 0.0002) and 29.24 (0–73.33) at 6-month follow-up (p = 0.0004) Mean baseline NIH PROMIS score of 63.39 improved to an average of 58.53 at 1 month (p = 0.0006), 58.88 at 3 months (p = 0.008) and 58.30 at 6-month follow-up (p = 0.014) For patients’ self-reported pain patterns, 64.3% of mild patients at 3 months reported that their pain was less; 35.7% of patients also reported no pain at 3 months post procedure. However, 19% of mild patients at 3 months did not indicate reduction in leg pain when standing and walking; 16.7% of patients reported worsening of their pain compared with baseline For ZCQ, 31.7% of mild patients at 3 months and 22% of mild patients at 6 months experienced a ‘clinically meaningful’ ZCQ pain score reduction of at least 20% post mild	The mild procedure holds great promise to improve pain and functional outcomes for LSS patients. Further studies are warranted	[37]
Chopko (2013)	Prospective, multicenter study	n = 45; symptomatic LSS, failed conservative therapy	–	mild procedure	2 years	VAS, ODI, ZCQ	Mean baseline VAS of 7.2 (95% CI ± 0.6) decreased to 4.8 (95% CI ± 0.8) at 2-year follow-up, a statistically significant improvement of 2.4 points (p < 0.0001) Average baseline ODI of 48.4 (95% CI ± 4.4) decreased to 39.8 (95% CI ± 5.6) at 2-year follow-up, a statistically significant improvement of 8.6 points (p < 0.0001) All ZCQ domains showed statistically significant improvement at 2-year follow-up, including the physical function domain (p = 0.0006), and both the pain subdomain (p < 0.0001) and the neuroischemic subdomain (p = 0.0002). No major device or intraprocedural adverse events were reported.	The mild procedure provides therapeutic efficacy for patients with neurogenic claudication associated with LSS	[38]
Wang et al. (2013)	Health economics	n = 22; symptomatic LSS; failed conservative therapy	–	mild procedure	–	The amount of time spent in specialty care and the number of interventional procedures performed before and after mild	The mean chronic pain management resource usage was 9.33 between initial consultation and receiving mild and improved to 5.11 post mild. Prior to undergoing the mild procedure, these patients received an average of 0.395 interventional pain procedures per month	Not only is mild a reliable method to treat LSS, but mild also appears to reduce the consumption of limited healthcare resources	[39]
Udeh et al. (2015)	Cost- effectiveness analysis using decision analytic model	NA	ESI, laminectomy	mild procedure	2 years	QALY	The optimal choice in terms of costs and benefits was the mild strategy at $43,760 per QALY. The next best alternative was ESI at an additional $37,758 per QALY. Laminectomy surgery demonstrated to be both more costly and less effective than either mild or ESI according to the baseline analysis ($125,985 per QALY)	The mild procedure is a cost-effective alternative for appropriate patients rather than continuing with conservative treatment and repeated serial ESI or proceeding to laminectomy surgery	[40]
Benyamin et al. (2016)	Prospective, multicenter, randomized controlled trial	n = 302; symptomatic LSS; failed conservative therapy	ESI	mild procedure	6 months, 1 year	ODI, NPRS, ZCQ	At 1-year follow-up, ODI, NPRS and all ZCQ domains demonstrated statistically significant superiority of mild vs ESIs. For primary efficacy, the ODI responder rate in the mild group was statistically significantly higher than the responder rate in the ESI group (p < 0.001) Within-group change in the mild group from baseline to 1-year follow-up for all efficacy end points including ODI, NPRS, ZCQ physical function and ZCQ symptom severity was statistically significant (p < 0.001) The ZCQ Patient Satisfaction score for mild demonstrated a statistically significantly higher level of patient satisfaction with the mild procedure vs ESIs There were no significant differences in the safety profiles between groups	This RCT provides level I evidence of the superior effectiveness of mild vs ESIs in the treatment of LSS patients with neurogenic claudication associated with central stenosis due to ligamentum flavum hypertrophy	[22]
Staats et al. (2018)	Prospective, multicenter, randomized controlled trial	n = 143; symptomatic LSS, failed conservative therapy	–	mild procedure	6 months, 1 year, 2 years	ODI, NPRS, ZCQ	At 2 years, ODI improved by 22.7 points (95% CI, 18.5–26.9), NPRS improved by 3.6 points (95% CI, 3.1–4.2), and ZCQ symptom severity and physical function domains improved by 1.0 (95% CI, 0.8–1.2) and 0.8 points (95% CI, 0.6–0.9), respectively During 2-year follow-up, 8 of 143 (5.6%) patients underwent a subsequent surgical procedure at the index level, 22 of 143 received an ESI or nerve block at the level of surgery, and one of these patients also received a spinal cord stimulator as a treatment for the pain at the index level. One additional patient received a rhizotomy at the index level, and one patient received an intrathecal infusion pump There were no serious device/procedure-related adverse events, and 1.3% experienced a device-or procedure-related adverse event	The mild procedure provides therapeutic efficacy and is an excellent choice for first-line therapy for select patients with central spinal stenosis suffering from neurogenic claudication symptoms with hypertrophic ligamentum flavum	[24]
Jassal (2019)	Retrospective single-center study	n = 20, symptomatic LSS; failed conservative therapy	–	mild procedure	6 months	VAS, Opioid reduction	Of the 20 patients evaluated at 6-month follow-up post mild, there was a 64% reduction in opioid use and a 72% improvement in VAS scores	The mild procedure demonstrated significant pain relief, and reduction of opioids and improvement in VAS score	[41]

ESI: Epidural steroid injection; GH: General health; LSS: Lumbar spinal stenosis; MCS: Mental Component Summary; NA: Not applicable; NIH PROMIS: National Institutes of Health Patient-Reported Outcomes Measurement Information System; NPRS: Numeric Pain Rating Scale; NRS: Numerical Rating Scale; ODI: Oswestry Disability Index; PCS: Physical Component Summary; PDI: Pain Disability Index; PRLL: Percutaneous remodeling of ligamentum flavum and lamina; QALY: Quality-adjusted life years; RCT: Randomized controlled trial; SF-12v2^®: Short Form-12 Version 2 Health Survey; VAS: Visual Analog Scale; ZCQ: Zurich Claudication Questionnaire.

Table 2. Comparison of complications between various decompression procedures.

2-year outcomes	mild ^†	Interspinous process distraction		Surgical decompression^‡	Fusion^§
		Superion^¶	X-Stop^#
Reoperation	5.6%	20%	14.4–26%	6–7.8%	12.5–16.9%
Device- and procedure-related adverse events	1.3%	Device		Intraoperative: 9.9%	23.3%
		11.6%	7.5%
		Procedure related			18% early
		14.2%	15.9%
Device and procedure-related serious AEs	0%	8.4%	9.5%	Postoperative: 12.3%	6% late
Lumbar spine fractures	0%	16.3%	8.5%	–	4.2%
Removal of hardware	No implants	16.3%	12.4%	No implants	4.3%

mild (Vertos Medical, CA, USA), Superion (Vertiflex, CA, USA), X-Stop (Medtronic, CA, USA).

† Data taken from [24].

‡ Data taken from [44,45].

§ Data taken from [46–50].

¶ Data taken from [51].

# Data taken from [44,51].

Created using data from [24].

Table 3. Comparing advantages and disadvantages of the mild procedure.

Advantages

Disadvantages & limitations

• Broad patient selection: neurogenic claudication + ligamentum flavum hypertrophy (≥2.5 mm) – even in patients with comorbidities • As safe as an epidural steroid injection • Lowest complication rate vs other lumbar spinal stenosis treatments • Low reoperation rates • Clinically significant long-term improvement in mobility and reduction in pain • Minimally invasive procedure • Intact spinal anatomy and minimal tissue trauma • No implants • Steroid-free procedure, thereby limiting immunosuppression risk • No requirement for general anesthesia or hospital stay • Resumption of normal activity within 24 h with no restrictions • Maintenance of range of motion – both flexion and extension • No contraindication for patients with osteoporosis • No limitations regarding future interventions • Cost effective

• Treatment of stenosis secondary to ligamentum flavum hypertrophy • Contraindication for performing at site of previous surgery • Some radiation exposure

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