A Comparative Analysis of Radiographic Intervertebral Disc Height Following Full-Endoscopic Lumbar Discectomy: Interlaminar versus Transforaminal Approach

Abstract

Study Design

This is a retrospective cohort study.

Introduction

Full-endoscopic lumbar discectomy (FELD), a minimally invasive surgical procedure used to treat lumbar disc herniation (LDH), has been shown to be highly effective with fewer complications. This procedure can be performed using the interlaminar (IL) or transforaminal (TF) approach. The IL approach involves more anatomical structures than the TF approach. However, comprehensive data regarding preoperative and postoperative intervertebral disc height (IDH) changes for patients undergoing full-endoscopic discectomy through the IL versus the TF approach is yet to be documented.

Objective

To compare the preoperative and postoperative IDH on radiographs in patients who underwent the FELD using the IL or TF approach.

Materials and Methods

The medical records of patients diagnosed with LDH who underwent FELD between 2014 and 2022 were collected and analyzed. Pre- and postradiographic IDH and clinical scores, including visual analog scale-back pain (VAS-B), Oswestry disability index (ODI), and recurrent LDH, were assessed and compared over a follow-up period of at least 2 years.

Results

A total of 110 patients were included, 82 undergoing the IL procedure and 28 undergoing the TF procedure. The median IDH variance was consistent at 1.0 (interquartile range [IQR] 0.5, 2) for the IL and TF procedures, indicating no significant statistical variance. The IDH ratio was also comparable between the two groups, with the IL group at 84% and the TF group at 85%. However, a notable disparity was observed in postoperative IDH, with a median of 7.5 (IQR 6.5, 8.5) for the IL approach and 8.5 (IQR 7, 9.5) for the TF approach. Importantly, no statistical differences were found in clinical outcomes, including VAS-B, ODI, and recurrent LDH.

Conclusion

After a 2-year follow-up for FELD, there is no significant difference in radiographic outcomes, IDH difference, and IDH ratio between the IL and TF approaches. Additionally, there is no apparent correlation between reductions in IDH and IDH ratio and the decrease in back pain scores (VAS-B) or ODI after the procedures.

Keywords

intervertebral disc height - lumbar disc herniation - radiographic - full-endoscopic lumbar discectomy - interlaminar - transforaminal

Introduction

Lumbar disc herniation (LDH) represents the most prevalent diagnosis among degenerative abnormalities of the lumbar spine. This condition arises from the displacement of the intervertebral disc's content (nucleus pulposus) through its outer layer membrane (annulus fibrosus).[1] The primary symptom of LDH is low back pain,[2] which significantly impacts daily activities. Lumbar discectomy stands as the standard treatment performed in cases of failed conservative treatment.[3] It can be performed through various techniques, including open surgery, the gold standard microscopic approach, and full-endoscopic methods.[4] Full-endoscopic lumbar discectomy (FELD) has emerged as a dependable surgical option for patients with LDH. This procedure aligns with minimally invasive spine surgery principles and is believed to cause less damage to surrounding soft tissues.[1] The procedure can be conducted via interlaminar (IL) and transforaminal (TF).[5] It is recognized that the IL approach involves more anatomical structures than the TF approach.[6] Nevertheless, comparative data regarding changes in preoperative and postoperative intervertebral disc height (IDH) in patients undergoing full-endoscopic discectomy via the IL versus TF approach are yet to be reported.

Materials and Methods

The retrospective review of the medical records of patients diagnosed with symptomatic LDH at a single level who had undergone full-endoscopic discectomy between 2014 and 2022 was collected and analyzed. A total of 110 patients met the inclusion criteria, with a minimum 2-year postoperative follow-up period. Exclusion criteria comprised prior or subsequent surgery at any other spinal level, concomitant surgeries in addition to endoscopic discectomy, and evidence of infection, fracture, or tumors. Out of the total, 82 patients underwent the IL approach, while 28 patients underwent the TF approach. The study evaluated preoperative and postoperative radiographic IDH as well as clinical outcomes, including visual analog scale-back pain (VAS-B), Oswestry disability index (ODI), and recurrent LDH after a minimum 2-year follow-up, comparing the IL and TF approaches.

Surgical Technique

We employed a Richard Wolf endoscopy system featuring a 6.9-mm scope for both TF and IL discectomy procedures. A critical consideration in our surgical approach is the meticulous extent of disc removal associated with these techniques. During discectomy, our focus is solely on excising the protruding fragments of the disc, ensuring that the intervertebral retained disc material remains intact. This strategy is supported by literature indicating that such a selective resection can markedly diminish the likelihood of subsequent disc degeneration. In contrast, excessive removal of the retained intervertebral disc typically accelerates disc degeneration, instability, or recurrence of the disc herniation.[7] [8] [9]

Radiological Measurement

Radiographic measurements were obtained from standing lateral radiographs of the lumbosacral spine before surgery and during the postoperative follow-up, which lasted for a minimum of 2 years. The measurement included the assessment of IDH and intervertebral disc height ratio (IDH ratio) ([Fig. 1]). All measurements were conducted using the tools available in the Picture Archiving and Communication Systems (PACS). The measurements were performed by three researchers independently over a span of 3 consecutive weeks.

Fig. 1 An illustration delineating the technique for assessing intervertebral disc height (IDH, 1A) and IDH ratio (1B) from standing lateral radiographs of the lumbosacral spine.[10]

Statistical Analysis

The statistical analysis was performed using SPSS software to assess significance, where a p-value of less than 0.05 was considered significant. Age at operation, body mass index, and operative time were presented as mean ± standard deviation, while sex, smoking, level of LDH, type of LDH, and incidence of LDH were expressed as percentages. The IDH difference, IDH ratio, VAS, and ODI were also reported as median ± interquartile range (IQR). The relationship between radiographic outcomes (IDH difference and IDH ratio) and clinical outcomes (VAS-B, ODI, and recurrent LDH) was assessed using Spearman's rank correlation test.

Results

The study comprised 110 patients, 82 in the IL group and 28 in the TF group. The median IDH difference for the IL and TF approaches was 1.0 (IQR 0.5, 2), indicating no statistically significant difference ([Table 1]). Moreover, the IDH ratio was similar between the two groups (IL: 84% and TF: 85%). However, a notable contrast was evident in postoperative IDH, with the median values being 7.5 (IQR 6.5, 8.5) for the IL approach and 8.5 (IQR 7, 9.5) for the TF approach ([Table 2]). No statistically significant differences were observed in clinical outcomes, including VAS-B, ODI ([Table 3]), and recurrent LDH, as presented in [Tables 4] and [5].

Table 1 Demographic data

Patient's characteristics	Interlaminar approach	Transforaminal approach	p-Value
Sex (male)	35 (42.7%)	17 (60%)	0.09[a]
Age at operation (y), median (IQR)	39 (33, 51)	34 (30, 45)	0.20[b]
Smoking	18 (22%)	6 (21.4%)	0.95[b]
BMI (kg/m2)	24 (22, 26)	25 (22, 27)	0.82[b]
Level of LDH
L3/4	6 (7.3%)	4 (14.3%)
L4/5	31 (27.8%)	24 (85.7%)
L5/S1	45 (54.9%)	0
Type of LDH
Protrusion	26 (31.7%)	12 (42.9%)
Extrusion	51 (62.2%)	16 (57.1%)
Sequestration	5 (6.1%)	0
Operative time (min)	45 (35, 60)	40 (30, 50)	0.01[b]

Abbreviations: BMI, body mass index; IQR, interquartile range; LDH, lumbar disc herniation.

^a Chi-square test.

^b Mann–Whitney's U test.

Table 2 Radiographic outcome (primary outcomes)

Parameters	Interlaminar approach	Transforaminal approach	p-Value
Preoperative IDH	9.04 (2.08)	9.51 (2.58)	0.34[a]
Postoperative IDH, median (IQR)	7.5 (6.5, 8.5)	8.5 (7, 9.5)	0.03[b]
IDH difference, median (IQR)	1.0 (0.5, 2)	1.0 (0.5, 2)	0.85[b]
IDH ratio	84 (71, 91)	85 (73, 94)	0.48[b]

Abbreviations: IDH, intervertebral disc height; IQR, interquartile range.

^a Independent t-test.

^b Mann–Whitney's U test.

Table 3 Secondary outcomes (VAS-B and ODI)

Clinical outcomes	Interlaminar approach	Transforaminal approach	p-Value
VAS-B, median (IQR)	2 (0, 3)	2 (1, 3)	0.86[a]
ODI, median (IQR)	11 (6, 16)	9 (3, 15)	0.27[a]
Recurrent LDH	6 (7.2%)	2 (7.1%)	0.97[b]

Abbreviations: IQR, interquartile range; LDH, lumbar disc herniation; ODI, Oswestry disability index; VAS-B, visual analog scale-back pain.

^a Mann–Whitney's U test.

^b Chi-square test.

Table 4 The secondary outcomes (VAS-B and ODI): analysis of association with IDH difference (delta IDH)

			VAS-B 2 y	ODI 2 y	Delta IDH
Spearman's rho	VAS-B 2 y	Correlation coefficient	1.000	0.416[a]	0.185
		Sig. (two-tailed)		<0.001	0.053
		N	110	110	110
	ODI 2 y	Correlation coefficient	0.416[a]	1.000	0.115
		Sig. (two-tailed)	<0.001		0.232
		N	110	110	110
	Delta IDH	Correlation coefficient	0.185	0.115	1.000
		Sig. (two-tailed)	0.053	0.232
		N	110	110	110

Abbreviations: IDH, intervertebral disc height; ODI, Oswestry disability index; Sig., significance; VAS-B, visual analog scale-back pain.

^a Correlation is significant at the 0.01 level (two-tailed).

Table 5 The secondary outcomes (VAS-B and ODI): analysis of association with IDH ratio

Spearman's rho	IDH ratio 2 y	Correlation coefficient	1.000	−0.033	−0.036
		Sig. (two-tailed)		0.736	0.708
		N	110	110	110
	VAS-B 2 y	Correlation coefficient	−0.033	1.000	0.416[a]
		Sig. (two-tailed)	0.736		<0.001
		N	110	110	110
	ODI 2 y	Correlation coefficient	−0.36	0.416[a]	1.000
		Sig. (two-tailed)	0.708	<0.001
		N	110	110	110

Abbreviations: IDH, intervertebral disc height; ODI, Oswestry disability index; Sig., significance; VAS-B, visual analog scale-back pain.

^a Correlation is significant at the 0.01 level (two-tailed).

Discussion

The retrospective cohort study yielded insights into the radiographic outcomes of IDH following FELD utilizing both the IL and TF approaches. The primary objective was to evaluate whether these two approaches displayed significant differences in IDH changes. Contrary to the initial hypothesis, the study indicated no statistically significant variance in IDH difference or IDH ratio between the IL and TF approaches, implying that both techniques effectively maintain IDH postoperatively.

Intervertebral Disc Height and Clinical Outcomes

The anatomical variances between the IL and TF approaches, specifically regarding the degree of interaction with adjacent structures, do not appear to impact the preservation of the IDH postdiscectomy. This observation suggests that both techniques are equally effective in upholding spinal stability. Notably, the lack of correlation between IDH preservation and clinical outcomes, as evidenced by VAS-B scores and ODI, is significant. These findings are consistent with prior research, indicating that IDH reduction alone may not strongly correlate with clinical amelioration or patient-reported outcomes. It implies that factors beyond IDH, such as nerve decompression and inflammation resolution, may substantially influence patients' recovery and symptom alleviation.

Postoperative Disc Height

The study revealed a noteworthy variance in postoperative IDH, indicating that the TF approach exhibited a slightly higher median IDH than the IL approach. While this dissimilarity holds statistical significance, it is imperative to assess its clinical relevance. The absence of variance in clinical outcomes despite the IDH difference suggests that the higher postoperative IDH in the TF group may not directly correlate with improved functional outcomes.

Implications for Practice

The findings, as mentioned earlier, have important implications for surgical decisions and patient education. Spinal surgeons can assure patients that, based on radiographic evidence, either the IL or TF approach can be chosen without compromising the preservation of IDH, a typical patient concern. Furthermore, as the reduction of IDH has not shown a correlation with worsened clinical outcomes, the focus of surgical success should shift toward achieving adequate decompression rather than solely prioritizing the preservation of IDH.

Limitations

Our study has certain limitations. First, its retrospective design may intrinsically introduce selection bias. Second, the data may need to be more applicable to the broader population of patients with LDH, as it encompasses only those who underwent full-endoscopic interlaminar discectomy at our institution. Furthermore, the small sample size may elevate the risk of statistical error.

Conclusion

This study indicates that, with a minimum follow-up period of 2 years for FELD, there is no noteworthy variance in radiographic outcomes, IDH difference, and IDH ratio between the IL and TF approaches. Additionally, IDH and IDH ratio reductions do not appear to correlate with decreased back pain scores (VAS-B) or ODI following the procedures. Subsequent research is necessary to improve comprehension and provide backing for preoperative counseling.

Conflict of Interest

None declared.

Ethical Approval

The study was approved by the ethics committee of Lerdsin Hospital.

• References

• 1 Vialle LR, Vialle EN, Suárez Henao JE, Giraldo G. Lumbar disc herniation. Rev Bras Ortop 2015; 45 (01) 17-22
• 2 Pruttikul P, Chobchai W, Pluemvitayaporn T, Kunakornsawat S, Piyaskulkaew C, Kittithamvongs P. Comparison of post-operative wound pain between interlaminar and transforaminal endoscopic spine surgery: which is superior?. Our J Orthop Surg Traumatol 2021; 6: 24-26
• 3 Mixter WJ, Barr JS. Rupture of the intervertebral disc with involvement of the spinal canal. J Neurosurg 1964; 21 (01) 74-81
• 4 Williams RW. Microlumbar discectomy: a conservative surgical approach to the virgin herniated lumbar disc. Spine 1978; 3 (02) 175-182
• 5 Keorochana G. Full Endoscopic Lumbar Discectomy: Transforaminal Technique. In: The Textbook of Spine. Vol 49 Bangkok: Spine Society of Thailand; 2022: 349
• 6 Keorochana G. Pruttikul Full-Endoscopic Lumbar Discectomy: Surgical Technique. In: The Textbook of Spine. Vol 50 Bangkok: Spine Society of Thailand; 2022: 350-366
• 7 Mochida J, Nishimura K, Nomura T, Toh E, Chiba M. The importance of preserving disc structure in surgical approaches to lumbar disc herniation. Spine 1996; 21 (13) 1556-1563 , discussion 1563–1564
• 8 Heo JH, Kim CH, Chung CK. et al. Quantity of disc removal and radiological outcomes of percutaneous endoscopic lumbar discectomy. Pain Physician 2017; 20 (05) E737-E746
• 9 Lin RH, Chen HC, Pan HC. et al. Efficacy of percutaneous endoscopic lumbar discectomy for pediatric lumbar disc herniation and degeneration on magnetic resonance imaging: case series and literature review. J Int Med Res 2021; 49 (01) 300060520986685
• 10 Wilke HJ, Rohlmann F, Neidlinger-Wilke C, Werner K, Claes L, Kettler A. Validity and interobserver agreement of a new radiographic grading system for intervertebral disc degeneration: part I. Lumbar spine. Eur Spine J 2006; 15 (06) 720-730

Publication History

Article published online:
21 May 2025