Imaging indicators and fusion analysis of percutaneous endoscopic posterior lumbar interbody fusion and modified posterior lumbar interbody fusion for the treatment of lumbar degenerative diseases

Introduction

Degenerative diseases of the lumbar spine are prevalent among the elderly and are characterized by functional decompensation, with primary symptoms including low back pain, radiating pain in the lower limbs, and intermittent claudication (1). Lumbar degenerative disease (LDD) is a prevalent spinal disorder that encompasses conditions such as lumbar spondylolisthesis and lumbar spinal stenosis. As the population ages, the prevalence of LDD continues to rise, prompting a shift in surgical treatment techniques toward minimally invasive approaches (2). Currently, for patients with LDD who do not respond to standardized conservative treatment (3), lumbar interbody fusion (LIF) is a common intervention when symptoms persist or worsen (4). LIF has a broad range of clinical applications, including pain relief, alleviation of nerve root compression, correction of spinal lordosis, and rectification of spinal deformities, and is typically employed in patients who do not respond adequately to conservative treatment (5). LIF is a widely utilized surgical technique for the treatment of LDD.

Posterior LIF (PLIF) is an effective technique for the treatment of LDD. However, conventional PLIF requires extensive resection of the lamina, spinous process, supraspinous ligament, interspinous ligament, ligamentum flavum, and facet joints (4). This extensive removal can damage the posterior ligamentous complex of the spine, impair spinal stability, and increase the risk of adjacent segmental degeneration (ASD) (5).

Modified PLIF (MPLIF) minimizes damage to the normal structure of the spine, preserves the spinous process and the posterior spinal ligament complex, and demonstrates good clinical efficacy (6). Therefore, compared to traditional PLIF, MPLIF employs more minimally invasive and refined surgical techniques, offering advantages such as reduced surgical trauma, improved fusion rate, and fewer complications (7).

With the advancement of minimally invasive techniques, an increasing number of surgeons are utilizing percutaneous endoscopic PLIF (PE-PLIF) to treat patients with LDD (8). Numerous studies have confirmed that PE-PLIF is a safe and effective minimally invasive approach for managing LDD, demonstrating satisfactory short-term outcomes (9), a low complication rate, and the benefit of adequate decompression of the central canal and neural structures (10). However, most of the approaches described in the early literature were transforaminal techniques. Although these methods have demonstrated satisfactory clinical efficacy, they have notable drawbacks, including a limited scope of decompression and an increased risk of injury to the outlet root due to the restricted space within the Kambin triangle. PE-PLIF is a uniaxial endoscopic technique that establishes a working channel by excising the medial aspect of the articular synchondrosis and a portion of the ipsilateral lamina. Our preliminary studies indicate that this approach is both safe and effective (11).

Our team previously conducted a detailed analysis of various clinical efficacy measures [e.g., Japanese Orthopedic Association (JOA), Visual Analogue Scale (VAS), Oswestry Disability Index (ODI)] (12). The current study aimed to further compare the efficacy of PE-PLIF with that of MPLIF in the treatment of LDD, utilizing comprehensive imaging data including the intervertebral space height (mm), segmental Cobb angle (°), bone graft area (mm²), and bone graft range. We present this article in accordance with the STROCSS reporting checklist (available at https://qims.amegroups.com/article/view/10.21037/qims-24-2268/rc).

Methods

Study design and sample

From January 2018 to October 2023, a total of 181 patients with LDD were screened. A total of 88 patients were excluded according to the inclusion and exclusion criteria. Eventually, 93 patients met the criteria for inclusion (PE-PLIF, n=43; MPLIF, n=50). During the final follow-up period, there were 7 lost cases in the PE-PLIF group (19.4%) and 11 in the MPLIF group (28.2%), with no significant difference in attrition rates between groups (P=0.38) (Figure 1). Lost cases were defined as patients unable to complete the clinical and radiographic assessment despite three contact attempts via phone, email, and registered mail. Finally, 36 cases were included in the PE-PLIF group and 39 cases in the MPLIF group (Figure 1).

Figure 1 Patient enrollment diagram. MPLIF, modified posterior lumbar interbody fusion; PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion.

All patients provided informed consent. All procedures were performed by the same senior spine surgeon, who has extensive experience in both endoscopic and open surgery. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study has been approved by the Ethics Committee of Wuhan Hospital of Integrated Traditional Chinese and Western Medicine Orthopedics (Affiliated Hospital of Wuhan Institute of Physical Education) (No. 672HRBC20241022-L48).

Inclusion and exclusion criteria

Surgical indications followed North American Spine Society (NASS) guidelines (13). Referring to these guidelines, we listed the inclusion and exclusion criteria for this study and strictly adhered to this surgical indication.

Inclusion criteria

• Patients diagnosed with single-segment LDD had signs and symptoms consistent with findings from lumbar spine X-rays, computed tomography (CT) scans, and magnetic resonance imaging (MRI). Screen the exact clinical symptoms of the patients (including at least two of the following items):
  • Persistent low back pain (VAS ≥4 points, duration >3 months);
  • Radiculopathy symptoms (meeting any of the following conditions): abnormal sensations in the distribution of specific dermatomes (decreased needle-like sensation/tactile sensation), muscle strength decline (muscle strength grade ≤4), abnormal reflexes (weakened or absent knee/ankle reflexes);
  • Neurogenic intermittent claudication (symptoms induced by walking distance <500 m).
• Patients exhibiting persistent neurological symptoms or characteristic intermittent claudication symptoms.
  • Sensory dysfunction: decreased needle-like sensation or mild tactile impairment;
  • Motor dysfunction: decreased muscle strength;
  • Reflex abnormalities (corresponding to the involved segments): weakened or absent knee reflex (L3–L4) (compared with the healthy side), weakened or absent ankle reflex (S1), and the presence of pathological reflexes (if the Babinski sign is positive, upper motor neuron lesions need to be excluded);
  • Positive neurological traction sign: a straight leg elevation test of less than 60° induced root pain, and positive femoral nerve traction test;
  • Neuroelectrophysiological confirmation: electromyography (EMG) shows damage to the corresponding segmental nerve roots.
• Patients whose symptoms did not resolve or worsened for at least 3 months after nonsurgical treatment.
• Patients undergoing PE-PLIF or MPLIF surgery.

Exclusion criteria

• Patients with significant scoliosis or kyphosis;
• Incomplete pre-operative and post-operative imaging;
• Patients with a history of lumbar spine surgery;
• Patients with severe osteoporosis;
• Patients with lumbar spine tumors, tuberculosis, or infections;
• The patients and their families did not provide consent for the study;
• Patients with psychological or psychiatric disorders.

Surgical methods

PE-PLIF

After administering routine general anesthesia in the prone position, the operating table was adjusted, the lumbar spine was moderately immobilized, and the intervertebral space was appropriately enlarged. C-arm fluoroscopy was utilized to identify the pedicle of the affected segment, which was marked on the body surface, disinfected, and covered with tape. A pedicle guidewire was percutaneously inserted at the marked location, with the skin incision made adjacent to the targeted space, approximately 3 cm from the spinous process. The incision was gradually enlarged using a sleeve to facilitate the insertion of the working trocar.

Using a large-channel spinal endoscopy system (Unintech system, Joimax, Karlsruhe, Germany), the anatomical structures, including the upper and lower vertebral plates at the level of the affected interspace, the articular synovial joints, and the ligamentum flavum, were visualized endoscopically with both straight and curved forceps in conjunction with a plasma radiofrequency cutter head (APS-A-01-N-7030, Aceso Technology, Suzhou, China). After achieving clear microscopic exposure, decompression of the bony structures in the surgical area was performed sequentially along the superior vertebral body’s vertebral plate, the inferior articular process (IAP), the lateral saphenous fossa, and part of the inferior vertebral body’s vertebral plate. This was accomplished using a visual ring saw to delineate the beginning and end points of the ligamentum flavum, while preserving only the lateral wall of the superior articular process to protect the exiting nerve root. Following the resection of the ligamentum flavum, the nerve roots, dural sac, and intervertebral discs were exposed. The working trocar was rotated so that its bevel faced outward, preventing the nerve root from entering the workspace. The intervertebral disc was resected using a gun vice, and the cartilaginous endplates were trimmed with a reamer and spatula (Figures 2,3).

Figure 2 Intraoperative fluoroscopy and instrumentation in PE-PLIF procedure. (A,B) C-arm anteroposterior and lateral fluoroscopy confirms that the puncture needle enters the pedicle. (C) Screw placement under C-arm fluoroscopy. (D) Insert cage under C-arm fluoroscopy. (E) Surgical instruments with screws inserted. From left to right: puncture needle, stepwise sleeve. (F) Establish a working channel. PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion.

Figure 3 Endplate preparation technique in PE-PLIF and MPLIF procedures. (A) PE-PLIF surgery: after routine treatment of the endplate, prepare for the condition of the endplate before bone grafting. No obvious fibrocartilage plate residue, visible punctate bleeding in the bony endplate. (B) MPLIF surgery: routine treatment of the endplate, placement of an endoscope to monitor the endplate treatment before preparing for bone grafting. MPLIF, modified posterior lumbar interbody fusion; PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion.

After the final plate was prepared, autogenous bone, allograft bone (Shanxi Ori, OSTEORAD Biomaterial Co., Ltd., Taiyuan, China), bone repair material [recombinant human bone morphogenetic protein-2 (rhBMP-2)] (Hangzhou Jiuyuan Gene Engineer Co., Ltd., Hangzhou, China), and a height-adjustable fusion device (Shanghai Ruizhi Medical Devices Co., Ltd., Shanghai, China) were implanted.

After satisfactory fluoroscopy, the positions of the decompression and cage were confirmed microscopically. Following this confirmation, the endoscope and working trocar were removed. A percutaneous pedicle screw was then placed along the guidewire, which was subsequently removed. The connecting rod was secured, and the tail of the pedicle screw was broken. The skin incision was sutured, and a drain was typically not placed. However, if the patient experienced significant intraoperative blood loss (IBL; evidenced by visible oozing of blood endoscopically after saline irrigation is turned off), one drain could be inserted at the discretion of the surgical team. Depending on the volume of drainage, the drain could be removed 1–2 days post-surgery. The incision was then wrapped, and the procedure was completed.

MPLIF

After administering routine general anesthesia in the prone position, the operating table was adjusted, and the lumbar spine was moderately immobilized. The surgical area was sterilized, and a sterile towel was draped. A longitudinal incision was made along the midline of the spinous process, ensuring that the spinous process was preserved and the posterior ligamentous complex was intact. Subperiosteal dissection of the paraspinal muscles was performed on both sides to expose the lateral margin of the articular process. Pedicle screws were then placed in the lateral superior margin of the apex of the vertebrae under fluoroscopy, and a decompression was made of the affected side (unilateral or bilateral), removing about 1/3 of the IAP and the superior articular process. After satisfactory fluoroscopy of the implanted pedicle screws, the affected side (unilateral or bilateral) was decompressed, the upper and lower portions of the vertebral plate, about 1/3 of the IAP, and the superior articular process were removed, the ligamentum flavum was occluded, the nerve roots of the dural sacs were protected, the vertebral space was processed until the cartilage endplate bled punctiformly and the intervertebral implant was placed into the appropriate cage, and the bone repair material (rhBMP-2) was added. Bilateral connecting rods were installed for proper pressure fixation, and then the incision was closed with hemostasis and drainage (Figures 2,3).

Postoperative treatment

Patients in both groups were routinely confined to bed for 1–2 days after surgery and received the same rehydration regimen, which included low-dose hormones and analgesics (13). Appropriate thromboprophylaxis regimens were selected based on the Caprini score. After the operation, both groups of patients received mechanical preventive measures (pneumatic therapy for both lower extremities, once in the morning and once in the afternoon); elastic stockings were required to be worn for more than 8 hours per day. Rehabilitation exercise plans were formulated based on the individual conditions of the patients, and guidance was provided to the patients and their families. After the operation, the responsible nurse guided the family members to perform lower limb massage on the patients, starting from the distal end and gradually moving towards the proximal end. Each massage lasted for 15 minutes, repeated three times a day. Lower limb functional exercises included ankle pump exercises and straight leg elevation exercises. Patients without drains underwent lumbar spine X-rays and CT scans on the first postoperative day, whereas those with drains were examined on the day of drain removal. Once all findings were normal and the trauma had stabilized, patients were instructed to get out of bed with the assistance of a support device (14).

Observation indicators

Imaging indicators

• Frontal and lateral views of the lumbar spine were obtained during the initial preoperative assessment, the first postoperative follow-up, and the final follow-up visit. Additionally, lumbar CT scans were conducted at the first postoperative follow-up. Measurements of the intervertebral space height, bone graft area, and bone graft extent were performed using the software from The Affiliated Hospital of Wuhan Sports University film-reading system (WebViewer, version: v1.0.0.1, revised version: 20140617; 3dhistech, Budapest, Hungary). Segmental Cobb angles were measured before and after surgery using Surgimap software (version: 2.3.2.1, Nemaris, New York, NY, USA) (15).
  All imaging indices were measured by a single specialist. In the event of a disagreement, the final result was determined through intra-group discussion.
  • Height of the intervertebral space of the operated segment (mm): height of the intervertebral space at the operated segment = (anterior margin of the intervertebral space + posterior margin of the intervertebral space)/2 (Figure 4A,4B);
    

    Figure 4 Intervertebral space assessment. (A) Preoperative anterior (a) and posterior (b) margins of the intervertebral space; (B) preoperative anterior (a') and posterior (b') margins of the intervertebral space.
  • Preoperative segmental Cobb angle (α) and postoperative segmental Cobb angle (α’): the angle between the superior vertebral endplate and the inferior vertebral endplate in the region of the operated segment (Figure 5A,5B);
    

    Figure 5 Cobb angle assessment. (A) Preoperative segmental Cobb angle (α). (B) Postoperative segmental Cobb angle (α').
  • The implant area (mm²) of the surgery (Figure 6) refers to the middle level of the intervertebral space on the CT cross-section, and is calculated as follows (16): bone graft area for surgery = (area of graft block + area of cage) − area of cage in cross section.
    

    Figure 6 The bone graft area ratio was calculated by measuring three key components: (A) the bone graft area, which included both the borders of the morselized bone graft and the mid-disc level; (B) the superior endplate area, measured at the adjacent superior vertebral endplate corresponding to the graft level; and (C) the inferior endplate area, measured at the adjacent inferior vertebral endplate. The bone graft area ratio (%) was then determined using the formula: [bone graft area/average endplate area] × 100% = [a/(b + c)/2] × 100%.
  • The specific calculation of the bone graft extent of the procedure (Figure 6) is as follows (16): bone grafting extent of surgery = bone grafting area of surgery/[(upper endplate area + lower endplate area)/2].
• Lumbar CT was conducted at 3 and 6 months postoperatively to compare the fusion rate between the two groups. Fusion rates were evaluated using the Bridwell criteria (17) for final fusion grade based on CT images. Fusion rates = number of fusion cases/total number of cases.

Surgery-related indicators

Surgery-related outcomes were recorded for both groups, primarily including operation time, IBL, time to ambulation postoperatively, duration of hospitalization, and complications. The modified MacNab criterion was applied at the last follow-up to evaluate the therapeutic effect of the patients. The improved MacNab criteria (18) are divided into four grades, as follows: excellent: all symptoms completely disappear, and one can resume their original work and life; good: symptoms are mild, activities are slightly restricted, and there is no impact on work and life; general: symptoms ease, activity is restricted, and normal life and work are affected; poor: no difference from before the operation, or symptoms are even worse.

Clinical efficacy indicators

All the patients were evaluated by lumbar/leg VAS score, JOA score, and ODI score before the operation, 3 days after the operation, 1 month after the operation, and at the last follow-up (18,19).

Statistical analysis

Statistical analysis was performed using SPSS 27.0.1 software (IBM Corp., Armonk, NY, USA). The normality of the data was assessed using the Shapiro-Wilk test. Normally distributed data were expressed as mean ± standard deviation, whereas non-normally distributed data were expressed as median and interquartile range (IQR). The Mann-Whitney U test was used to compare differences between two groups, and the Friedman test was used to compare differences between groups at different time points and for multiple comparisons. Categorical variables were expressed as frequencies and percentages and compared with the Chi-squared test or Fisher’s exact test. Pearson and Spearman correlation analyses and multiple linear regression analyses were used to establish associations between several independent factors. A P value <0.05 was considered statistically significant and P<0.001 was considered highly statistically significant.

Results

Baseline data

We collected clinical data on patients with LDD who underwent PLIF with PE-PLIF and MPLIF at our institution. The PE-PLIF group comprised 36 cases with an average age of 59.00±15.00 years, whereas the MPLIF group included 39 cases with an average age of 58.50±17.50 years.

There were no significant differences between the two groups regarding gender, age, type of disease, surgical segment, and follow-up time (P>0.05) (Table 1). The preoperative baseline data of the PE-PLIF group and MPLIF group were comparable.

Imaging indicators

Height of the intervertebral space

There was no statistical difference in the comparison of preoperative intervertebral space heights between the two groups of patients (P>0.05) (Figure 7).

Figure 7 Comparison of imaging parameters between the PE-PLIF group and the MPLIF group. The green bars represent the PE-PLIF group, and the orange bars represent the MPLIF group. MPLIF, modified posterior lumbar interbody fusion; PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion.

The intervertebral space heights of the first postoperative review and the final follow-up in both groups were higher than those of the preoperative period (P<0.05), and the intervertebral space heights at the final follow-up were not statistically significant compared with those at the first postoperative review (P>0.05) (Figure 7).

The intervertebral space height was significantly higher in the PE-PLIF group than in the MPLIF group at both the first postoperative review and the final follow-up (P<0.001) (Figure 7).

Cobb angle

There was no statistically significant difference in the preoperative Cobb angle between the two groups of patients (P>0.05) (Figure 7).

The Cobb angle at the first postoperative review and the final follow-up was higher than that of the preoperative period in both groups (P<0.05), and there was no statistically significant difference in the Cobb angle at the final follow-up compared with the first postoperative review (P>0.05) (Figure 7).

The Cobb angle was significantly higher in the PE-PLIF group than in the MPLIF group at both the first postoperative review and the final follow-up (P<0.001) (Figure 7).

Bone graft area and extent of bone graft

The bone graft area (bone graft volume) and bone graft range in the PE-PLIF group were smaller than those in the MPLIF group (P<0.05) (Table 2).

Fusion rate

At 3 months postoperatively, the fusion rate was 88.89% in the PE-PLIF group and 69.23% in the MPLIF group, which were statistically different (P<0.05) when compared with each other (Table 3).

At 6 months postoperatively, intervertebral fusion was present in both groups.

Surgery-related indicators

The mean operative time was significantly longer in the PE-PLIF group than in the MPLIF group (P<0.001). IBL was significantly less in the PE-PLIF group than it was in the MPLIF group (P<0.001). The postoperative bed rest time in the PE-PLIF group was significantly shorter than that in the MPLIF group (P<0.001) (Figure 8).

Figure 8 Comparison of surgery-related outcomes between groups. ***, denotes statistically significant differences between groups, i.e., P<0.001. MPLIF, modified posterior lumbar interbody fusion; PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion.

Both groups of patients successfully completed the surgery without perioperative serious complication situations, including cauda equina injury, sinking or displacement of the fusion device, fracture or displacement of the internal fixation, nerve root injury, hematoma, and incision infection (Table 4).

At the last follow-up, according to the modified MacNab criteria, the excellent rate was 94.4% in the PE-PLIF group (P>0.05) and 89.7% in the MPLIF group, with no significant difference (Table 4).

Clinical efficacy indicators

There was no statistically significant difference in the VAS scores of leg pain and low back pain, JOA score, and ODI score before the operation between the PE-PLIF and MPLIF groups (P>0.05) (Figure 9).

Figure 9 Clinical outcomes comparison between PE-PLIF and MPLIF groups. JOA, Japanese Orthopedic Association; MPLIF, modified posterior lumbar interbody fusion; ODI, Oswestry Disability Index; PE-PLIF, percutaneous endoscopic posterior lumbar interbody fusion; VAS, Visual Analogue Scale.

The VAS scores of the two groups of patients at any follow-up point after the operation were significantly lower than those before the operation (P<0.001), the ODI scores of the two groups of patients at any follow-up point after the operation were significantly lower than those before the operation (P<0.001), and the JOA scores of the two groups of patients 3 days after the operation were significantly increased (P<0.001) (Figure 9).

Comparing the two groups, the VAS and ODI of the PE-PLIF group at any follow-up point after the operation were significantly better than those of the MPLIF group, and there was no statistical difference at the other time points. The JOA score of the PE-PLIF group at 3 days after the operation was also significantly better than that of the MPLIF group (P<0.001), and there was no statistical difference at other time points (Figure 9).

Discussion

This study demonstrates that PE-PLIF achieves superior radiographic outcomes (improved intervertebral height restoration and Cobb angle stability, P<0.05) compared with MPLIF, despite utilizing significantly less bone graft volume. The technique’s endoscopic precision enables faster early fusion (3-month follow-up) through optimal endplate preparation under direct visualization—a critical advantage over MPLIF’s blind endplate handling. Our work challenges two prevailing paradigms in endoscopic fusion: first, PE-PLIF achieved high fusion rates with ≤5 mL graft volume, suggesting that endplate preservation outweighs quantity; second, the stability-invasiveness trade-off, as PE-PLIF’s stepwise dilation minimized structural damage while yielding better early VAS/ODI scores (P<0.05) and shorter hospitalization duration. As the first study to quantify the biomechanical advantages of PE-PLIF through imaging indicators, these research results have addressed a key knowledge gap in the literature of endoscopic fusion (20). Although the technique’s learning curve affects operative time and long-term subsidence risks require further follow-up, our results establish PE-PLIF can reconcile the minimally invasive benefits and biomechanical stability, and is worthy of vigorous promotion.

LDD represents a major global health challenge, affecting 10% of adults worldwide with prevalence escalating from 15% (40–49 years) to 40% (≥60 years), of whom 5% require surgical intervention [Global Burden of Disease Study 2019 (GBD 2019)] (21). The condition disproportionately impacts women (spondylolisthesis 2:1; stenosis 3:1) except for disc herniation (male predominance 1.2:1), and causes severe functional impairment—50% of patients report ADL limitations, 35% develop chronic pain-related depression, and 15% progress to permanent disability (ODI worsening 30–40%). With LDD ranking among the top 5 causes of musculoskeletal years lost due to disease (YLDs; 18.7 million annually) and costing over $10 billion/year in the US alone (22).

Results and analysis of imaging and fusion rates in the PE-PLIF and MPLIF groups

The results of this study indicated that the height of the intervertebral space was greater than that observed during the preoperative period, and the Cobb angle was also larger than that recorded preoperatively, both at the first postoperative review and at the final follow-up visit in both groups (P>0.05). This finding suggests that the surgery effectively improved the height of the intervertebral space and stabilized the intervertebral structures in both groups. Notably, the intervertebral space height at the first postoperative review and the last follow-up in the PE-PLIF group was significantly higher than that in the MPLIF group, and the Cobb angle was also greater in the PE-PLIF group (P<0.05). This implies that PE-PLIF has a superior effect on enhancing intervertebral stability compared to MPLIF. It is possible that the fusion using the mirror fusion technique is performed with a supportive cage, offering the advantage of small size implantation and large size support, which meets biomechanical requirements while accommodating the principles of minimally invasive surgery. The small volume and contraction of the metal-supportable interbody fusion device during implantation, combined with the increased volume of support after implantation in the intervertebral space, effectively restores the height of the intervertebral space and reestablishes immediate stability (23), and the enhancement of segmental physiological curvature resulting from this surgery also contributes to greater stability of the intervertebral space. Additionally, because PE-PLIF technology is performed using percutaneous endoscopy, the procedure is conducted in a manner that minimizes paravertebral soft tissue disruption by gradually expanding the trocar (24), causing less damage to the normal structures of the lumbar spine (25), and preserving the spinal stability to the fullest extent possible while adequately decompressing the spine (26). The refinement of the PE-PLIF procedure has also resulted in an increase in lumbar intervertebral space height and physiologic curvature (27), both of which have resulted in a more stable lumbar spine, and have had a very positive impact on the biomechanics of the lumbar spine and the improvement of the outcome of the lumbar spine after undergoing surgery (28). Meanwhile, the difference in the height of the intervertebral space and the Cobb angle between the last postoperative follow-up and the first postoperative review in the two surgical groups was not statistically significant. This indicates that the surgically implanted fusion did not collapse, and there was no loss of intervertebral space height in either group, thereby reducing the risk of postoperative complications. However, the research findings indicated that both the intervertebral disc space height and Cobb angle in the MPLIF group exhibited a reduction compared to the last follow-up. However, considering that all patients had achieved successful fusion at the final follow-up, further collapse is theoretically unlikely to occur. When compared with the decrease observed during the first postoperative follow-up, this result may potentially be attributed to the elastic modulus of the cage. Studies have confirmed that as the patient’s weight-bearing capacity and age increase, there exists a possibility of subsidence of the fusion device (29). In light of this, we subsequently implemented corresponding adjustments. For detailed information, please refer to our forthcoming article publications; at this stage, it is not feasible to disclose these details.

Perfect fusion of the lumbar intervertebral space maintains the long-term stability of the lumbar spine and carries the loads of the spine, resulting in less stress on the pedicle screws (30). However, when the intervertebral fusion is prolonged or not fused, it can lead to later lumbar instability and increase the risk of complications such as fusion displacement and internal fixation breakage (31). Evaluating postoperative fusion rates in patients with lumbar spine surgery is therefore critical, and fusion outcomes in endoscopic lumbar fusion in the spine have been an important concern for spinal surgeons (32). Numerous studies have confirmed that the fusion rate of the lumbar intervertebral spine is related to the amount of bone graft (implant area), and that, in general, as the amount of bone graft increases, the shorter the time required for complete fusion of the grafts, the higher the early fusion rate, and the lower the loss of spinal space height (33). The reason for this analysis is that more bone tissue provides a more stable environment for intervertebral support and healing. A recent study has demonstrated that increasing the amount of bone graft can significantly improve the fusion rate of intervertebral vertebrae in the early postoperative period (34). At the same time, the research also indicates that there is a risk of non-fusion of bone grafting when the bone graft volume is less than 5 mL, and it is advocated that the bone graft volume should be 5 mL or more (35). Closkey et al. (36) found that intervertebral implants up to 30% or more of the endplate area provided effective intervertebral support fusion. Steffen et al. (37) reported that the fusion of the intervertebral space is closely related to the blood supply of the bony endplates, so when the intervertebral bone graft has a larger contact area with the endplates, namely, an larger amount of bone graft, it not only provides effective support for the anterior column, but also facilitates the crawling of the intervertebral autogenous bone with the endplates into the bone and reduces the time for the formation of the fibrous connection between the bone particles and the bone particles with the endplates. In this study, the amount of bone graft (bone graft area) and the extent of bone grafting in the PE-PLIF group were significantly smaller than they were in the MPLIF group.

However, there was no significant difference in the fusion rate between the PE-PLIF group and the MPLIF group when both the amount and the extent of bone grafting were insufficient, a situation that is consistent with what has been previously reported in the literature (24-26). All patients in both groups showed fusion at 6 months postoperatively, and even the fusion rate was higher in the PE-PLIF group than it was in the MPLIF group at 3 months postoperatively. Therefore, we believe that the biggest factor affecting the fusion rate may be the endplate handling situation. PE-PLIF allows endplates to be handled under direct endoscopic visualization and prevents endplate subchondral bone damage as much as possible; this is superior to MPLIF, which handles endplates by feel alone (see Figure 3 for specific comparison). This is an advantage of PE-PLIF that cannot be replaced by MPLIF. The present study found a higher fusion rate in the PE-PLIF group than in the MPLIF group at 3 months postoperatively, suggesting that the time required for fusion may be shorter for PE-PLIF, a result that is similar to that of previous studies (2). Some studies have shown that blindly increasing the amount of intervertebral bone graft and the contact area between the intervertebral bone graft and the endplate is not effective in increasing the intervertebral fusion rate if the endplate is not handled with sufficient extent. Therefore, the researchers recommend that the treatment of the endplate requires removal of at least 60% of the intervertebral space tissue (38), with a focus on the mid-anterior portion of the intervertebral space to ensure an effective intervertebral implant bed area.

We also observed the inadequate quantity and extent of bone grafting in the PE-PLIF procedure during the subsequent surgery. Consequently, we implanted a mixture of autogenous and allograft bone into the intervertebral space, as fewer vertebral plates and articular eminences were resected intraoperatively in the PE-PLIF group.

Surgery-related indicators and analysis of PE-PLIF group and MPLIF group

The PE-PLIF group in this study experienced a longer operative time compared to the MPLIF group. This discrepancy may be attributed to the use of a small channel during the preoperative phase of PE-PLIF, which presents challenges such as reduced work efficiency, a steep learning curve similar to that encountered in endoscopic surgery, and an extended preoperative duration. However, as the number of surgeries increases, the adoption of larger-channel instruments and advancements in surgical techniques has contributed to a gradual reduction in operative time.

Compared with the MPLIF group, IBL was significantly reduced in the PE-PLIF group. This reduction may be attributed to the fact that PE-PLIF is conducted under direct endoscopic visualization, which facilitates radiofrequency ablation and early hemostasis (39), which can reduce IBL but also ensures a clear surgical field. Additionally, the intraoperative use of a visual circular saw for resecting the articular eminence resection allows greater control of the extent of bone resection, leading to less bony bleeding and further contributing to the reduction of IBL (40). However, studies have demonstrated that total postoperative blood loss may significantly exceed the visible IBL due to the presence of occult blood loss (41). The amount of occult blood loss will also be analyzed in detail by our team in another study.

At the same time, due to the advantages of PE-PLIF surgery, including minimal surgical blood loss and smaller incisions, patients in this group experienced shorter postoperative bed rest and hospitalization times compared to those in the MPLIF group.

Clinical efficacy indicators and analysis of the PE-PLIF and MPLIF groups

Our research results showed that the VAS scores of the two groups of patients at any follow-up point after the operation were significantly lower than those before the operation, suggesting that the pain of the patients after the operation had improved significantly. The ODI scores of the two groups of patients at any follow-up point after the operation were significantly lower than those before the operation, suggesting that the functional recovery of the patients after the operation was good. The JOA scores of the two groups of patients were significantly increased 3 days after the operation, suggesting that the neurological recovery of the patients was good after the operation. The VAS and ODI of the PE-PLIF group at any follow-up point after the operation were significantly better than those of the MPLIF group. The JOA score of the PE-PLIF group 3 days after the operation was also significantly better than that of the MPLIF group. The analysis of the reason might be that the PE-PLIF technology reduces the damage to the normal structure through the stepwise expansion of the casing. The postoperative pain of patients in the PE-PLIF group was relieved quickly, and to a certain extent, the adverse effects caused by analgesic drugs were also alleviated. Meanwhile, the improvement of neurological function and the degree of limb impairment also promoted the postoperative recovery of patients and enhanced their quality of life in the early postoperative period.

Limitations

The limitations of this study include the following: (I) this is a retrospective, non-randomized controlled study, which may introduce partial bias (e.g., surgeon experience variations, patient compliance with rehab). Future prospective studies should implement stratified randomization by surgeon volume and use standardized rehab protocols to control these factors. (II) The sample size is small, and a larger sample is necessary to enhance the reliability of the findings. (III) The follow-up period was brief; an extended follow-up duration is required to assess long-term efficacy and complications. (IV) Given the subjective nature of the measurement process, there is a potential for measurement errors that could lead to bias. Artificial intelligence-assisted measurement can be adopted to achieve measurement with an error of less than 0.5°.

Conclusions

The findings in this study suggest that PE-PLIF may be more effective than MPLIF in restoring the height of the intervertebral space and enhancing intervertebral stability. Several advantages were documented, including reduced IBL, improved endplate management, a reliable interbody fusion rate, and a quicker recovery time. Due to these contributing factors, PE-PLIF may represent a safer and more effective minimally invasive surgical option for the treatment of LDD. However, further research is needed to validate these findings (42). Therefore, within the appropriate indications, PE-PLIF can serve as an alternative therapy for the treatment of single-segment LDD. With advancements in technique, instruments, and procedures, this approach can gradually be applied to patients with multisegmental LDD. It is essential to promote this method in clinical practice while ensuring patient safety.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROCSS reporting checklist. Available at https://qims.amegroups.com/article/view/10.21037/qims-24-2268/rc

Data Sharing Statement: Available at https://qims.amegroups.com/article/view/10.21037/qims-24-2268/dss

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-2268/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study has been approved by the Ethics Committee of Wuhan Hospital of Integrated Traditional Chinese and Western Medicine Orthopedics (Affiliated Hospital of Wuhan Institute of Physical Education) (No. 672HRBC20241022-L48), and informed consent was obtained from all individual participants.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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