Superficial and deep fascia was split longitudinally along with blunt splitting of sacrospinalis, identifying the clear cleavage plane between the natural gap of multifidus medially and longissimus laterally (figure1). Small amount of fat helped to delineate this plane. The muscles were then meticulously teased apart in avascular plane till the transverse process. Following this the transverse process and facet joints were palpated and after retraction with Meyerding’s retractors, the entry point for the pedicle screws was identified at mamillary process.

Slightly nibbling the base of superior articular facets, the desired size pedicle screws were inserted into the appropriate vertebra after, inspecting the walls of the channel with a ball-tipped probe. The direction and position of pedicle screw placement was confirmed with fluoroscopy. For applying another pedicle screw, the retractor was moved up or down, maintaining it between the inter-muscular planes.

The required numbers of pedicle screws were inserted and then assembly was completed by placing connecting rods. In case, of spinal trauma only pedicles screws were inserted whereas in cases of spondylolisthesis, the facet joint was removed and bone filled inter body cage, was additionally inserted after discectomy and preparation of vertebral body endplates by high speed burr.

Local bone grafts were harvested from posterior iliac crest with same incision in case of L5 vertebral burst fracture for posterolateral fusion whereas in cases of listhesis bone graft removed during decompression and facet removed was used for inter body fusion. After checking decompression, fixation and reduction under image intensifier the closure was done with both sides of fascia with running suture without any drain.

Postoperatively, patients were mobilized with help of lumbar corset from second postoperative day and discharged after three to five days. Suture removal was done at two weeks. Patients were followed monthly for three months and then three monthly up to one year. All patients were assessed for pain by VAS score, neurology, blood loss, duration of surgery and hospital stay. Fixation of the pedicle screws was assessed radiologically.

Results

12 patients of single level lumbar spine instability at L4-L5 or L5-S1 were included in the study. The mean age in the group was 34.6 years (range 16 to 45 years). 4 patients were male and 8 were female. Out of 12 patients, 2 patients were with L5 vertebral body burst fracture, 6 patients had L4-5 and 4 patients had L5-S1 isthmic spondylolisthesis.

Mean blood loss for the surgery was 150 ml (range 134 to 170 ml). The average C arm exposure was 12.5 (range 8 to 21). The average length of hospital stay was 3.5 days. None of the patients had any postoperative neurological complications or deterioration. The mean VAS score improved from 8.3 pre-operatively to 3.3 at 3^rd post-operative day and finally to 1.2 at one-year follow-up.

This paraspinal muscle damage have been described by numerous authors and also confirmed by increased muscular edema and levels of inflammatory mediators in patients undergoing conventional midline muscle-stripping approach versus those undergoing surgery by minimally invasive approach [8-13].

Wiltse’s, paraspinal sacrospinalis-splitting or trans-sacrospinalis approach to the lumbar spine, prevents these complications by reducing excessive retraction of paraspinal muscles because this approach involves access to the spine from lateral side through the muscular plane between multifidus and the longissimus parts of the sacrospinalis muscle [2-4]. The advantage of this approach is that it offers a more direct route to the pedicle screws entry point i.e. transverse processes and facets of the lumbar spine with almost minimal muscle stretching and less bleeding than through the midline approaches [14,15].

Olivier et al in their cadaveric study documented that two incisions 3 cm away from the midline, are in the middle of the two vascular networks which prevents the skin necrosis [16]. Further, moving the retractor between and maintaining the intermuscular planes, places minimal pressure on the muscles and that too only for very short time which avoids any undue pressure on the muscle, thereby decreasing muscle ischemia and related problem. Thus this approach maintains the integrity of the paraspinal musculature and soft tissues. Wiltse Paraspinal approach, being a muscle sparing approach, has many advantages as compared to the traditional midline approach like excellent exposure to transverse process, minimal intraoperative bleeding, low infection rate, low postoperative morbidity and improved outcomes [17].

We retrospectively reviewed the results of this modified Wiltse’s approach, used for fixation of 12 patients with mean age 36.4 years of single level lumbar instability in vertebral burst fracture or in spondylolisthesis at L4-L5 or at L5-S1 level and found the approach to be safe, minimally disruptive, less damage to the paraspinal musculature and improved outcome as seen in improved VAS score. The radiation exposure in our series was also quiet low by this approach, which is due to better direct visualization of the pedicle screw entry point which is a therapeutic benefit of this approach, in contrary to increased radiation exposure by percutaneous techniques which are associated with higher radiation exposure [18].

Recently this approach is widely used for non-fusion dynamic lumbar spine stabilization as it is quicker and safer [18,19]. The approach can be done via minimally invasive means also for easy access to extraforaminal and foramina part of disc space, which further decreases muscle damage and blood loss.

Wiltse approach is limited by lesser operating space and less obvious surrounding anatomic landmarks which can be overcome by better magnification with loop and clear intraoperative imaging. It allows for placement of screws from the facet in a more lateral to medial trajectory leading to higher chances of facet violation, and hence the surgeon must be very careful when placing screws [21].