At the Authors best knowledge, This is the first study specifically analyzing the rate of recurrences at the same level or at a junctional level in patients with FLHD treated by the microsurgical trans pars approach
Despite the extensive debate in Literature as to what is the best approach in the surgical treatment of these conditions and despite its detractors claiming that the trans isthmus technique is burdened by a higher number of recurrences due to the narrow surgical corridor that would not allow optimal control toward the medial side of the herniation, our results show that out of 135 cases analyzed, 6 recurrences occurred at the same level (4,4%) and only 5 of them were retreated with surgery.
Moreover, the rate of junctional herniation after surgery was also low; only 3 cases out of 135 were detected (2,2%) and none of these cases required surgery.
In order to compare our results, we performed a brief literature review in which it emerges, as said before, that nowadays there are no available published studies specifically analyzing recurrence and/or junctional disc herniation rate after this kind of surgery.
The only pertinent results were obtained combining on Pubmed search the terms "foraminal disc herniation AND recurrence” and “foraminal disc herniation OR recurrence”, including studies which analyzed the rate of hernial recurrence after surgery also with far lateral techniques and excluding items of instrumented surgery, papers in which endoscopic techniques were used and articles in other languages than English (see table 4).
Porchet8 et al. published in 1999 results about 202 patients operated with far lateral technique (187 trans muscular, 15 para muscular). Only 9 out of 202 developed recurrence at the same level (4 re operated with far lateral technique, 5 with standard interlaminar technique given paramedian recurrence) with a calculated recurrence rate of 4.45%.
Kotil et al in 200713 published a paper analyzing 14 patients with foraminal/extra foraminal L5/S1 disc herniations treated with trans-muscular technique in which they reported no postoperative recurrence .
In 2018, resuming a technique already proposed in 2003 by Greiner-Perth14, Abdelgawaad and colleagues15 performed 76 surgeries with microscopic assisted percutaneous nucleotomy technique for foraminal and extraforaminal lumbar disc herniations obtaining recurrences in only two treated cases (2.63% of recurrence rate).
A more recent modification of the technique proposed by Abdelgaawad was developed in 2021 by Alhashash. According to this modification, 50 patients with herniated foraminal discs were treated obtaining only 2 recurrences (4%)16.
A Japanese 2021 study proposed an alternative technique for the treatment of lumbar foraminal pathologies involving hemilaminectomy with laminoplasty however this technique was only used in 4 patients with extraforaminal disc herniations and in 44 patients with lumbar herniations not specifying how many of these were foraminal and how many were paramedian. The recurrence rate was settled at 6.25% (3 recurrent disc hernias out of 48 treated) and in all cases that required re operation a TLIF (transforaminal lumbar inter body fusion) was performed16.
Except for Porchet's work in which 2 junctional recurrences are reported and Tanaka's work in which 1 junctional LDH is reported, no junctional recurrences are detected in the other cited works.
Few years ago De Bonis et. al. proposed a different, more conservative approach for the minimally invasive treatment of FLDH that would allow access to the foramen of conjugation only with minimal bony removal at the level of the isthmus: the trans pars interarticularis microscopic approach17.
Although this approach is not entirely new, it has long been criticized both because of its learning curve and because, in the eyes of its detractors, for the possible difficulty to manage any hernias that extend even medially, potentially thereby promoting the rate of recurrence in the absence, however, of specific literature on the subject.
Results of the present study is intended as a natural complement to the previous published in 2017 adding an analysis of 135 consecutive cases operated with this technique in terms of recurrence rate and the onset of junctional herniations.
Our results show the trans pars approach is comparable to other approaches reported in the current Literature (reported by Porchet, Abdelgawaad and Alhashash, sightly minor comparing it with the Tanaka’s work) in terms of recurrence rate (4.4%) and junctional herniation rate (2.2%) .
The trans pars technique is less invasive in terms of muscular damage than, for example, the far lateral trans muscular techniques, using a smaller skin incision, that is comparable to that used for the medial herniectomies (3 cm on average). Moreover, it totally preserves the segmental stability of the spine given the very small portion of bone removed at the pars interarticularis, without touching the articular complex in any way.
All of the above considerations also greatly affects the extremely short surgical times (the average duration of the surgery is about 70 minutes) as well as a shorter postoperative hospitalization and an earlier return to activities of daily living.
Lastly, the results obtained from statistical analyses show no significant correlations between the rate of LDH recurrence (whether junctional or at the same level) neither with the patient's age nor, more importantly, with BMI.
The latter finding about the non-correlation between BMI and recurrence rate is interesting and in contrast not only with the common thinking, that would like to see a higher probability of recurrences with higher values, but also with some studies published recently in literature although different surgical techniques were used.
As example, Siccoli et. al in 2022 18 found this correlation statistically significant (p = 0.017), the same has done by Wang et.al. in 2022 19 that found a significant correlation both with BMI and patient age (BMI p = 0.001, age p < 0.001) while Li et. al.20 showed that only a BMI above 25 is somehow related to an increased risk of recurrence considering a wide population sample but operated with percutaneous endoscopic technique.
The population sample analyzed in our study is undoubtedly smaller compared to that reported in previously cited papers but, to date, it appears to be the largest treated with the trans pars microscopic technique so this data, while not reaching statistical significance, are nonetheless important and worthy of future investigation perhaps by enlarging the sample.
Correlations between age and outcome, sex and outcome, age/sex/ BMI/treated level were also not significant in these analyses (table 2).