Introduction:

Lumbar disc herniation (LDH) is the most frequent lumbar degenerative illness that causes patients to have redundant pain (Ravindra et al., 2018). Lower back pain (LBP) and sciatica symptoms, such as leg pain (LP) and leg numbness (LN), are common in patients with LDH (Deyo et al., 2016). In addition, LN is a major factor influencing clinical outcomes and patient satisfaction following decompression surgery (Ogura et al., 2021; Li et al., 2021). Lumbar decompression surgery, such as microdiscectomy, can enhance LPB and LP but not LN (Owens et al., 2018; Hareni et al., 2021; Stienen et al., 2016). Shi et al. (2023) have frequently observed that patients improve in LBP and LP following surgery but have residual leg numbness (RLN) or no alleviation. Many patients are still concerned about post-operative numbness or paresthesia (Katz et al., 1999; Brox et al., 2006). Postoperative RLN may be a significant contributing factor to postoperative discontent (Toyone et al., 2005).

Comment on “numbness sensation”

The term “numbness” is frequently used to describe a variety of symptoms, such as the sensation of walking on cobblestones or the sensation that the soles of the feet are encircled by socks, as well as paresthesia, numbness, or loss of sensation (Grovle et al. 2013).

Sensory nerves are made up of the A-beta, A-delta, and C fibres. Manzano et al. (2008) define A-beta fibers as thick myelinated fbers with the highest conduction velocities, A-delta fbers as thin myelinated fbers with intermediate conduction velocities, and C fbers as unmyelinated fbers with the lowest conduction velocities. Touch pressure sensation and rapid pain can be transmitted by large nerve fibres with myelin sheaths (such as A-beta fibres) (Manzano et al., 2008). C fibre provides pain and temperature information. Previous clinical studies reported that numbness and paresthesia are related to the injury of large myelinated nerve fibres and that the function of unmyelinated nerve fibres improved significantly within 6 weeks after surgery but not significantly within 12 months (Nygaard et al., 1998; Wolf et al., 2012). Small unmyelinated nerve fibres (such as C fibres) have been shown to heal faster and more completely than myelinated nerve fibres (such as A-delta fibres) involved in LN and pain symptoms (Nygaard et al., 1998; Iizuka et al., 2009). These findings are consistent with our findings that the improvement in the visual analogue score for leg numbness (VAS-LN) score was worse than the improvement in the VAS-LP score, and LN improved substantially slower than LP after lumbar decompression surgery (LDS). The numbness and compression symptoms continue longer, which may result in more irreparable nerve damage and a slower recovery from numbness. A longer period of preoperative LN is related to more nerve root compression, which may result in permanent nerve root and RLN damage (Wu et al., 2019).

Investigate the potential risk factors for postoperative RLN in patients with LDH following lumbar microdiscectomy

Shi et al. (2023) collected and analysed prospectively patients with LDH who underwent microdiscectomy and discovered that reoperative LN NRS score, duration of preoperative LN, RLN at discharge, revision surgery, and SROM were risk factors for RLN during long-term follow-up of patients with LDH after a microdiscectomy.

A] Preoperative LN NRS score

According to Taiji et al. (2017), a higher preoperative LBP visual analogue scale (VAS) score (70mm) was a risk factor for residual LBP (Taiji et al., 2021).

Ogura et al. (2020) discovered that 60% of patients with LSS had postoperative persistent numbness (average follow-up of 25 months) in a study of 116 individuals. Diabetes mellitus, intraoperative durotomy, and a higher preoperative NRS score for numbness were also identified as risk factors for RLN.

Zou et al. (2022) discovered that a preoperative high LN VAS score can independently predict the presence of residual LN at 12 months postoperatively in a study of 314 patients with lumbar degenerative illnesses.

Shi et al. (2023) discovered that patients with LDH who had higher preoperative LN numeric rating scale (NRS) values were more likely to develop RLN postoperatively, which was consistent with earlier research.

B] Duration of preoperative LN

Preoperative LN length is associated with postoperative RLN (Oba et al., 2017; Yan et al., 2020).

Oba et al. (2017) found that patients with greater preoperative symptom duration had poorer improvement in LN in a prospective trial of 139 patients with LLS.

Yi et al. (2022) discovered that LN following spinal endoscopic surgery was linked with prolonged symptom duration, pelvic incidence, preoperative LBP VAS score, and LDH combined with lumbar spine stenosis (LSS) in 73 patients with LDH.

A study on symptomatic postoperative lumbar epidural hematoma by Tsujimoto et al. (2023) discovered that, as compared to early removal of hematoma, delayed removal of hematoma can also alleviate LBP and LP but not LN.

In the current investigation, Shi et al. (2023) discovered that patients in the RLN group had a longer preoperative LN duration. A longer period of preoperative LN is related to prolonged compression of the nerve root, which may result in permanent nerve root and RLN damage.

C] RLN at discharge

Shi et al. (2023) discovered a link between the RLN’s early postoperative condition (at discharge) and its final postoperative follow-up state. Although some patients with RLN at discharge had complete alleviation of LN at the final follow-up, patients with RLN at discharge had a greater likelihood of RLN at the last follow-up (at least 2 years of follow-up). Patients who had complete LN alleviation upon discharge, on the other hand, had a decreased risk of acquiring RLN at the last follow-up. This suggests that the RLN’s status at discharge can anticipate the potential of a long-term RLN.

D] Revision surgery

When compared to the initial operation, revision lumbar discectomy reduces patient satisfaction and quality of life (Lubelski et al., 2015; Fritzell et al., 2015).

According to Lubelski et al. (2015), primary surgery can improve quality of life, pain, disability, and psychosocial effects.

Fritzell et al. (2015) discovered that pain relief following revision surgery was inferior to that after the first LDH surgery, with lower patient satisfaction.

Shi et al. (2023) examined the frequencies of revision surgery (re-microdiscectomy) for symptomatic and radiographically verified recurrent LDH and first surgery (primary microdiscectomy) for LDH in the RLN and non-RLN groups. Shi et al. (2023) discovered that the RLN group had greater revision surgery rates than the non-RLN group. This means that patients who had a re-microdiscectomy had a greater RLN rate than those who had the first microdiscectomy. This is to be expected because scar formation may occur in the primary surgical region, resulting in nerve root disruption and traction when the scar is removed or excised during revision surgery.

E] Sagittal range of motion [SROM]

Shi et al. (2023) discovered that the RLN group’s SROM was much greater than the non-RLN group’s. SROM is also one of the risk factors for RLN following a lumbar microdiscectomy. In addition, the RLN group had greater postoperative LBP, LP numeric rating scale (NRS) scores, and OSwestry disability index (ODI) scores than the non-RLN group. This suggests that postoperative LBP, LN, and LN are perhaps connected (Inada et al., 2018).

Higher SROM is thought to be associated with lumbar instability (Hicks et al., 2003), which can result in prolonged neurologic impairment after microdiscectomy (Leone et al., 2007; Kanemura et al., 2009).

Kanemura et al. (2009) discovered that patients with more than 3mm translation and more than 10° angulation (SROM > 10°) had more severe LBP and LP. As a result, patients with high SROM, particularly those with SROM >10 °, must be fully informed about the possibility of RLN after lumbar microdiscectomy prior to surgery.

Patients who have inadequate postoperative LN relief may also have inadequate postoperative LBP and LP relief. Early decompression surgery is indicated in individuals with severe or protracted preoperative LN to reduce the occurrence of postoperative RLN.

In summary

The term “numbness” is frequently used to describe a variety of symptoms. Patients with greater preoperative LN NRS ratings and SROM, preoperative LN and RLN duration at discharge, and revision surgery were more likely to have RLN during long-term follow-up after lumbar microdiscectomy. Early surgery is indicated for patients with higher preoperative LN NRS scores or longer preoperative LN duration to lower the risk of postoperative RLN. This information could be used to better manage expectations in LDH patients.

Abbreviations

• [LDH] Lumbar disc herniation
• [LSS] lumbar spine stenosis
• [LN] leg numbness
• [LP] leg pain
• [RLN] residual leg numbness
• [LDS] lumbar decompression surgery
• [VAS] visual analog scale
• [ODI] oswestry disability index
• [VAS-LP] visual analogue score for leg pain
• [VAS-LN] visual analogue score for leg numbness
• [NRS] numeric rating scale
• [SROM] Sagittal range of motion

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