High-grade spondylolisthesis (HGSL) with a Meyerding grade of >II is a surgical predicament. Reduced contact surface for fusion, segmental kyphosis, and abnormal spinopelvic parameters are surgical concerns [1–3]. A controlled slip reduction and kyphosis correction that restores spinopelvic anatomy is the standard surgical approach [4,5]. An open reduction and inter-body fusion remain the preferred treatment [6,7]. Advent percutaneous screws (PS) and micro-surgical approaches have helped minimize soft tissue injury, but their role in HGSL remains sparsely described in the literature [8,9]. The Authors describe a hybrid technique that combines PS insertion with the midline microscopic transforaminal decompression (MTFD) approach for controlled adult lytic HGSL reduction. This study aims to investigate the effectiveness of this technique in reducing listhesis and its clinic-radiological outcomes. Authors have used “MTFD” as a hybrid technique for convenience of description.

The average follow-ups were 5.76±0.57 years and 5.77±0.51 years and the average age was 45.84±12.70 years (nine males and 16 females) and 49.26±13.33 years (eight males and 15 females) in the MTFD and open groups, respectively. Further, 22 and three patients in the MTFD group and 19 and four patients in the open group had grades III and IV listhesis, respectively. Unilateral leg pain (ULP) and bilateral leg pain (BLP) were observed in 18 (17 with grade III and one with grade IV) and seven (five with grade III and two with grade IV) patients in the MTFD group and 14 (13 with grade III and one with grade IV) and nine (six with grade III and three with grade IV) patients in the open group, respectively. Moreover, 18 patients in the MTFD group required UTFD, of which 15 (14 with grade III and one with grade IV) had ULP and three (with grade III) had BLP. The remaining seven patients underwent BTFD, of which three (with grade III) had ULP and four (two with grade III and two with grade IV) had BLP. A demographic detail is listed in Table 1.

High-grade slips (grades III/IV) pose a different set of clinical and radiological challenges as compared to low-grade slips. Open reduction is preferred for reduction. The technical challenges of cannulation of dysmorphic lytic pedicles, optimum disk preparation, and controlled reduction have been highlighted [12,13]. The screw trajectory is of paramount importance for maximum purchase which allows a mono-segmental reduction. Far lateral and proximal dissection would require negotiating kyphosis and medial angulation of lytic pedicles in the conventional approach. The advent of PS allows the selection of precise trajectory while avoiding excessive soft tissue dissection. Deep-seated lytic pedicles and segmental kyphosis make the delineation of pedicles difficult. Positioning the C-arm requires experience, and radiation was a concern. The use of neuro-navigation reduced radiation exposure in the present series (n=5), as shown by Tian et al. [14]. The mobility of the rattler helps to maneuver instruments during disk preparation. Overhang of the caudal vertebra and segmental kyphosis needs to be negotiated to introduce disk shavers in the index disk space. End-plate perforation is of concern, which reduces effective distraction and results in cage migration. This was not observed in our series. Optimal disk release across the midline improves segment mobility. This reduces the stress on screws. The disk release could be performed across the midline by “looking into the canal” in MTFD. Out of 22 grade III slip, 17 improved to grade II after disk preparation, while one with grade IV slip was reduced to grade II. A restoration of foraminal height through a unilateral approach indirectly decompressed the contra-lateral exiting root [15–17]. We also preferred UTFD (n=18) in MTFD. Of the 18 patients, three had BLP. UTFD approach reduced listhesis, restored foraminal height, and alleviated bilateral symptoms. A listhesis was stiff even after unilateral disk release in seven patients, in which BTFD was done to achieve reduction and reduce the stress on implants.

HGSL reduction improves spinopelvic alignment and correlates with better clinical outcomes [4,5,18]. A correction of slip percentage in this series (preoperative slip–postoperative slip divided by preoperative slip×100) is 87% in MTFD group and 85% in open group with mono-segment fixation. This is comparable to the reported literature [6,15,19]. It proves the effectiveness of the hybrid technique in reducing a high-grade slip.

Harvesting bone graft in the present technique was identical to the open surgery although through a micro-fenestration. En-mass resection of a portion of the lamina and the inferior facet provided adequate bone graft. The average bone graft harvested in UTFD was 3.27±0.73 mL and in BTFD was 7.57±0.90 mL. We have not used bone substitutes. The fusion rate is comparable to open techniques reported in the literature [4,20,21]. Microscopic decompression is advantageous in minimizing BL, infection, and exposure-related morbidity. MTFD group had lesser BL, OT, and hospital stays compared to open group in this series. The VAS and ODI favorably improved in both groups. The MTFD technique equally proved as effective in relieving radicular symptoms as the conventional technique.

The reported complication rate in literature after the conventional surgery was 10%–29%, including deep wound infection, nerve root deficit, dural injury, pseudoarthrosis, and implant failure/malposition [3,4,22–24]. Our series revealed similar incidences of early perioperative complications in both groups. The most concerning complication is L5 neuropraxia as described by Petraco et al. [25]. A wide and far lateral decompression of the nerve root before reduction would require to prevent stretch to the exiting root [2,3,12,26]. We could achieve a far lateral decompression of the exiting root (similar to open reduction) on the ipsilateral through TFD. Our series revealed that two patients had L5 root neuropraxia, one in each group. It happened on the ipsilateral side of the surgical decompression in MTFD. We have not reported a contra-lateral neurological deficit. Moreover, the portion of the skin between the screws and midline retractor needs careful attention in MTFD. One patient had central wound maceration in early experience. It was further prevented by lateralizing the skin incisions for screws and relaxing a midline retractor intermittently during surgery.

This series revealed that the incidence rate of significant ASD is comparable in both groups (MTFD group: 4%, open group: 8.69%). The benefit of minimally invasive surgery to reduce ASD remains unclear in the literature [27,28]. The midline dissection remained at the edges of laminotomy, without violating the adjacent segment during decompression in the hybrid technique; henceforth, authors preferred the term “contained midline decompression.” At present, concluding the role of the current technique to reduce ASD was difficult for authors. A larger study would be required.

This study had a few limitations. All surgeries were performed by a single senior surgeon. This creates a bias about the learning curve. The learning curve may get shortened for the surgeons familiar with the midline approach. The authors have not experienced other minimally invasive techniques. Rajakumar et al. [15] and Quraishi et al. [29] have described the feasibility and effectiveness of the tubular system for HGSL reduction. All patients involved in this series had stiff lytic HGSL with a less severe lumbopelvic deformity, vertebral remodeling, and rigidity compared to dysplastic listhesis. However, the author has started using this technique in dysplastic listhesis which is not a part of this study.

A hybrid technique is effective to reduce HGSL, with outcomes similar to the conventional approach. It combines the benefits of limiting soft tissue dissection by microscopic decompression and optimal screw trajectory using PS. It has lesser OT, BL, and hospital stay than the conventional approach. Long-term clinical and radiological outcomes are favorable.