Early biochemical muscle injury and one-year clinical and imaging outcomes following microsurgical versus endoscopic lumbar discectomy: A prospective comparative study

Methods

This was a prospective comparative study undertaken by the department of neurosurgery, Sri Venkateswara Institute of Medical Sciences (SVIMS), Tirupati, Andhra Pradesh, India. The study was conducted between January 2022 and October 2024. Ethical approval was obtained from the Institutional Ethics Committee, and written informed consent was taken from all participants in accordance with the Declaration of Helsinki (2013). The study includes consecutive patients with single-level L4–L5 or L5–S1 disc herniation who fulfilled the inclusion and exclusion criteria. All eligible patients during the study period were enrolled and underwent either MLD (n = 97) or PELD (n = 95) by the same senior neurosurgeon. The near-equal numbers in each group reflect the balanced use of both techniques in routine clinical practice at our centre. The study included 192 consecutive patients with MRI-confirmed single-level lumbar disc herniation at L4–L5 or L5–S1 who had persistent radicular pain for at least six weeks despite conservative management. Patients with multilevel disease, recurrent herniation, spinal instability, infection, trauma, neoplasm, or systemic inflammatory disorders were excluded.

Results

Baseline demographic and clinical characteristics were comparable between the two groups ( Table I). The majority of patients were in the fifth decade of life, with a male predominance in both groups. The L5–S1 level was the most frequently affected, followed by L4–L5. No significant differences were observed between groups regarding age, sex distribution, presenting symptoms, or preoperative VAS and ODI scores, indicating that both cohorts were well matched at baseline.

Both MLD and PELD groups demonstrated marked improvement in pain and functional outcomes at one year. As shown in Table I, back pain and leg pain VAS scores significantly reduced in both groups, and ODI scores showed comparable improvement at one year, with no statistically significant intergroup differences. BMI was similar between groups, and correlation analysis did not show any significant association between BMI and biochemical markers, MRI parameters, or clinical outcomes.

Postoperative biochemical changes are summarised in Table II. All markers (CPK, IL-6, and hs-CRP) showed postoperative elevations in both groups, following expected physiological trends. Postoperative values were consistently lower in the PELD group at both POD 1 and POD 3, with statistically significant differences across all major markers at both timepoints.

MRI-based paraspinal muscle and disc parameters are presented in Table III. At the one-year follow-up, the reduction in paraspinal muscle cross-sectional area was lower in the PELD group compared with MLD, and progression of Goutallier grade was less marked. Changes in disc height index were mild and comparable between groups. Representative axial MRI images for each surgical technique are displayed in Figure 1 (MLD) and Figure 2 (PELD), demonstrating postoperative decompression and visual differences in paraspinal muscle appearance at one year.

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Fig. 1.

Axial T2-weighted MRI of a patient with L4–L5 central disc herniation treated with Microsurgical Lumbar Discectomy (MLD). (A) Pre-operative scan showing marked central canal stenosis from a central disc. (B) One-year postoperative scan showing adequate decompression with increased canal diameter and reduced paraspinal muscle bulk with fatty change. MLD, microsurgical lumbar discectomy.

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Fig. 2.

Axial T2-weighted MRI of a patient with L4–L5 right paracentral disc herniation treated with Percutaneous Endoscopic Lumbar Discectomy (PELD). (A) Pre-operative scan showing right paracentral disc compressing the nerve root. (B) One-year postoperative scan showing good muscle preservation with minimal fatty infiltration after decompression. PELD: Percutaneous Endoscopic Lumbar Discectomy.

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Operative and postoperative details are summarised in Table IV. Compared with MLD, the PELD group had shorter operative duration, smaller incision size, and lower intraoperative blood loss. Length of hospital stay was also shorter in the PELD cohort. Postoperative complications were infrequent in both groups. MLD reported a small number of dural tears and superficial wound infections, while PELD reported a few cases of residual or recurrent disc requiring revision surgery. No major neurological deficits or postoperative instability occurred in either group.

Discussion

Both MLD and PELD resulted in substantial improvement in pain and disability at one year, confirming that both techniques are effective for lumbar disc herniation. However, PELD was associated with less early biochemical evidence of muscle injury and better preservation of paraspinal musculature on MRI, reflecting reduced surgical trauma.⁷

The comparable improvement in pain and ODI scores align with the established evidence that long-term outcomes largely depend on the adequacy of neural decompression rather than the size of exposure or approach used.⁸ BMI was recorded for all patients and included in our analysis. Although the mean BMI was comparable between the groups, it showed no significant association with biochemical injury markers, paraspinal muscle morphology on MRI, or one-year clinical outcomes.⁹ This suggests that BMI was not an influencing variable in our cohort. Postoperative elevations in serum CPK and IL-6 indicate skeletal muscle injury and acute inflammatory response, respectively.¹⁰ The lower CPK and IL-6 levels on postoperative days 1 and 3 in the PELD group reflect reduced iatrogenic muscle damage. This can be attributed to minimal retraction, limited fascial dissection, and continuous irrigation, which collectively prevent ischaemia and mechanical strain on paraspinal fibres.¹¹ Similarly, high-sensitivity C-reactive protein (hs-CRP), a downstream inflammatory marker induced by IL-6, peaked on postoperative day 3 and was significantly lower in PELD, suggesting a milder systemic inflammatory cascade.¹² These findings collectively demonstrate that PELD elicits a reduced biochemical stress response compared with MLD. Radiologically, postoperative MRI revealed better preservation of paraspinal muscle cross-sectional area and lower progression of fatty infiltration in the PELD group. Muscle atrophy and fatty replacement after lumbar surgery are multifactorial, driven by intraoperative retraction, denervation, and postoperative disuse.¹³ Lesser reduction in muscle cross-sectional area and minimal progression in Goutallier grades in PELD patients indicate that endoscopic access preserves muscle integrity and vascularity. Importantly, disc height index remained comparable between groups, confirming that the decompression adequacy and spinal mechanics were maintained across both approaches. In our cohort, the higher biochemical peaks and greater muscle CSA reduction observed in the MLD group did not translate into worse one-year VAS or ODI scores, suggesting that while these parameters objectively quantify tissue injury, their impact on long-term disability may be limited when adequate decompression is achieved.¹⁴ The shorter operative time, smaller incision, lesser blood loss, and reduced hospital stay reflect the efficiency of the minimally invasive approach.¹⁵ Despite the steeper learning curve associated with endoscopic techniques, once mastered, they enable efficient decompression with minimal collateral muscle injury. The overall complication rates were low and comparable between groups. This difference reflects the respective procedural risks: broader exposure in MLD increases wound-related issues, whereas limited visualisation in PELD carries a small risk of incomplete fragment removal.¹⁶ There were no instances of postoperative neurological deficit or segmental instability in either group, reaffirming the safety of both approaches.

A key strength of this study is the integration of biochemical and radiological analyses to quantify tissue preservation objectively. The observed correlation between lower early CPK and IL-6 peaks and better muscle morphology at one year suggests that biochemical markers may serve as early predictors of long-term muscle integrity.¹⁷ This combined analysis provides a more comprehensive evaluation of surgical invasiveness than clinical scores alone, bridging a gap in prior literature where studies focused on isolated parameters.¹⁸ As the allocation to MLD or PELD was based on predefined anatomical and clinical criteria rather than randomisation, a degree of selection bias cannot be excluded, and this has been acknowledged as a limitation of our study. Future multicentric studies with larger sample sizes could extend this work by directly comparing different endoscopic paradigms, including pure endoscopic approaches and endoscopic sheath-assisted techniques, to determine whether the biochemical and MRI-based advantages we observed with PELD are consistent across endoscopic variants.

In conclusion, although both MLD and PELD are effective, PELD offers a distinctly less invasive, tissue-preserving, and recovery-enhancing alternative for lumbar disc herniation surgery. These findings support wider adoption of PELD—where feasible—as a muscle-sparing, recovery-enhancing alternative to MLD, guiding both clinical practice and policy toward minimally invasive spine care.