In a cadaveric study, Lindblom [8] firstly described far lateral disc prolapse as lumbar disc herniation outside the vertebral canal. As per Macnab 1971 [9], laminectomy failed in nerve root exploring in two cases with radicular symptoms attributable to lateral disc protrusion at L5–S1. Abdullah et al. [10] explicated the clinical entity of FLLDH on discography as infra-facetal extreme lateral herniation at the same level of lateral to intervertebral foramen. In opposition to postero-lateral disc protrusion, FLLDH encroaches on the nerve root at the same level ensuing intense radicular leg pain with L4–L5 being the most commonly involved [11].
FLLDH may adequately respond to conservative treatment composite of steroidal and non-steroidal anti-inflammatory drugs. However, failure of medical therapy, persistent pain, significant sensory deficit, or progressive motor weakness necessitates surgical intervention [12]. Many posterior surgical approaches such as medial facetectomy, inter-transverse technique, full facetectomy fusion, trans-pars technique, extra-foraminal technique have been advocated for treatment of FLLDH [13].
Medial facetectomy coupled with extended laminotomy or hemi-laminectomy could provide an access for dumbbell-shaped medial or foraminal sequestrated disc fragment with an extra-foraminal tail allowing its removal; however, it does not explore clearly the far lateral compartment making it a good choice for L5–S1 disc herniation where the pedicles are far apart [14]. In cases managed with total facetectomy, although the nerve root could be thoroughly visualized permitting adequate decompression, however, post-procedural low back pain and instability presupposing to fusion procedures have been reported. Nonetheless, Epstein [19] claimed low risk of instability with only 2% are in need for fusion [15,16,17,18,19]. Donaldson et al. [20] excised FLLDH with trans-pars extra-foraminal technique with 72% success rate, yet limited access to medial portion of the disc while accelerating risk of instability and recurrence rendered the technique ineffective by Epstein [21].
The inter-transverse technique permits direct visualization of the far lateral compartment while preserving stability in return for missing degenerative foraminal lesions increasing susceptibility for nerve root injury on blind attempts to remove residual disc fragments [22,23,24]. In 2 patients with FLLDH, Quaglietta et al. [25] emphasized the efficacy of a paramedian muscle-splitting inter-transverse approach awarding adequate nerve root and disc visualization with symptomatic sensorimotor betterment. Extreme lateral approach through a midline or paramedian muscle splitting technique was employed successfully in various reports [26,27,28] to remove far lateral fragments; however, it is flawed by postoperative recurrence since it has no access to the disk medially [6].
Towards minimally invasive 1-day surgeries with little post-procedural pain, different percutaneous, microscopic and endoscopic alternatives were introduced. Sasani et al. [29] reported advantages related to percutaneous endoscopic discectomy in 66 patients with foraminal and FLLDH yielding favorable results with reduced postoperative pain and minimized adhering and scarring. On the far side, the technique can not be employed in the setting of FLLDH at L5–S1 cause of impeding iliac wings as well as spinal degenerative process whether canal stenosis, degenerative spondylosis, or spondylolisthesis. Associated with preservation of the facet joint integrity and limited bone removal while providing direct access to the offending pathology, far lateral microdiscectomy was adopted heavily in the literature [5, 30,31,32]. Through microscopic-assisted technique, combining advantages of three-dimensional visual control with minimal surgical trauma reported with endoscopic procedures, Greiner-Perth et al. [32] managed 15 patients with FLLDH within 43 min as an average surgical time. A remarkable improvement of VAS leg pain from 7 to 3.6 as well as ODI reduction from 30.6 into 14.3 postoperatively was noticed. Patients were able to mobilize 4 h after the procedure with no reported complication exempting one case of recurrence that retreated in the same maneuver. In a similar retrospective study, Fuentes et al. [31] navigated tubular muscle retractor system combined with a microscope through a 12–15-mm paramedian incision to treat 26 patients with FLLDH ending in rapid rehabilitation and symptomatic improvement as denoted by VAS radicular pain reduction from 7.0 to 2.0 with no encountered complication.
A recent evolution is the reported microendoscopic discectomy technique coming up with several advantages: rapid rehabilitation, lower incidence of postoperative muscle pain and atrophy, and declined risk for iatrogenic instability since minimal bony resection is entailed [13, 33]. Beyond those advantages, the procedure is technically demanding with characteristic steep learning curve that was obvious through our results where the operating time was ranging from 166 min in the early operations; however, it was reduced lastly to 55 min. Yoshimoto et al. [11] declared that longer operative time in the early cases they operated were attributable to adopting the Foley et al [7] method where the exiting nerve is firstly identified then followed distally adding to difficulty approaching lesions at L5–S1; however, upon converting into a triangular working zone, the operative time reduced significantly to 60 min.
Many studies [7, 33, 34] emphasized the benefits following microendoscopic approaches to FLLDH encompassing less muscle, ligament damage; reduced operative time and blood loss; and rapid rehabilitation. Wu et al. [35] in a comparative retrospective study on 873 patients with lumbar disc herniation to assess long-term outcome between microendoscopic discectomy and open surgical groups found no statistically significant difference between the two groups concerning symptomatic improvement based on VAS scale; however, average length of hospital stay and time to return to normal activities were less in the microendoscopic cohort. In our study, the median intra-procedural EBL was 30 (range, 10–55) ml matching those who underwent minimally invasive discectomy in Wu et al [35]. where intra-procedural blood loss per level was approximately 44 ml.
We had satisfactory outcomes in all 33 patients who underwent minimally invasive described approach, including 28 (84.8%) excellent outcomes and 5 (15.2%) good outcomes with neither fair nor poor results. In Foley et al. [7], 10 cases reported excellent with only one good results out of 11 enrolled patients based on modified Macnab criteria while 9 out of 17 patients examined in Cervellini et al. [33] obtained excellent results. The remaining gave good results with neither fair nor poor outcome.
Our patients reported an overall symptomatic improvement denoted by resolution of sensory deficits in 80% (n = 16) out of 20 patients at 3 months follow-up as well as amelioration of median muscle power from free movement while eliminating gravity effect (grade 3.0) into normal motor power against full resistance (grade 5.0). In a similar study [7] after follow-up periods ranged from 12 to 27 months, the authors had not encountered any motor deficits in their series while four out of nine had residual motor deficits,
In line with Salame and Lidar [13] reporting significant progressive decrease of mean preoperative VAS score for radicular pain from 8.6 preoperatively to 3.8 on immediate post-procedural evaluation reaching from 1.3 after 6 months to finally 0.6 at the last follow-up visit, our patients proclaimed dramatic improvement of radicular leg symptoms at 6 months postoperatively from median score of 8.0 to 1.0 correlating closely to those rated as excellent on Macnab.
Potential complications met in minimally invasive approaches to FLLDH include nerve root damage, dural tear, CSF leakage, residual sequestered foraminal disc, and neuropathic pain resulting from manipulation of the dorsal root ganglion [36, 37]. In our study, we had only five minor complications in 15.2% of the cases with neither mortality nor a major morbid complication. One case experienced unintended dural tear yet with no subsequent CSF leakage or pseudo-meningocele formation. Salame and Lidar [13] described two incidents of dural tear management with tight fascial closure instead of primary suturing attributing it among drawbacks of their technique due to limited access; thence, dural violations may lead to CSF fistulas unless definitive management employed.
Excessive medial facetectomy was done unintentionally in three cases; however, no iatrogenic spinal instability was depicted in the current study. Postoperative neural complications in the form of transient dysesthesia were observed in one patient; however, dysesthesia was mild and resolved gradually over 2 weeks with no permanent complications. In Quaglietta et al. [25], three cases suffered from post-procedural same-level burning dysesthesia; however, it was transitory and disappeared 2–3 weeks sequent to medical treatment with indomethacin. Neuropathic pain was common in the series of Hodges et al. [6] which was theorized to be arising from intra-procedural dorsal root ganglion manipulation, yet it resolved 2–3 months following the surgery.
The incidence of recurrence in the case of FLLDH is 4% [38]. Within our cases, bearing in mind the limited follow-up period, we did not have any cases of recurrence at the final follow-up. Doi et al. [38], in their retrospective analysis of outcome following endoscopic decompression surgery intra -foraminal and extra-foraminal disc herniation, had 3 cases of late symptomatic recurrence on the ipsilateral side, and 2 patients on the contralateral side of the surgery which were speculated to be caused by the foraminal stenosis, thence the importance of precise interpretation of preoperative imaging [39].
