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Journal of Craniovertebral Junction and Spine
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Year : 2015  |  Volume : 6  |  Issue : 4  |  Page : 162-165  

"NIMS technique" for minimally invasive spinal fixation using non-fenestrated pedicle screws: A technical note

Department of Neurosurgery, Nizam's Institute of Medical Sciences, Hyderabad, Telangana, India

Date of Web Publication21-Oct-2015

Correspondence Address:
Dr. Alugolu Rajesh
Department of Neurosurgery, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad - 500 082, Telangana
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0974-8237.167858

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Study Design: Case series. Objective: To reduce the cost of minimally invasive spinal fixation. Background: Minimally invasive spine (MIS) surgery is an upcoming modality of managing a multitude of spinal pathologies. However, in a resource-limited situations, using fenestrated screws (FSs) may prove very costly for patients with poor affordability. We here in describe the Nizam's Institute of Medical Sciences (NIMS) experience of using routine non-FSs (NFSs) for transpedicular fixation by the minimally invasive way to bridge the economic gap. Materials and Methods: A total of 7 patients underwent NFS-minimally invasive spine (MIS) surgery. Male to female distribution was 6:1. The average blood loss was 50 ml and the mean operating time was 2 and 1/2 h. All patients were mobilized the very next day after confirming the position of implants on X-ray/computed tomography. Results: All 7 patients are doing well in follow-up with no complaints of a backache or fresh neurological deficits. There was no case with pedicle breach or screw pullout. The average cost of a single level fixation by FS and NFS was `1, 30,000/patient and `32,000/patient respectively ($2166 and $530, respectively). At the end of 1-year follow-up, we had two cases of screw cap loosening and with a displacement of the rod cranio-caudally in one case which was revised through the same incisions. Conclusions: Transpedicular fixation by using NFS for thoracolumbar spinal pathologies is a cost-effective extension of MIS surgery. This may extend the benefits to a lower socioeconomic group who cannot afford the cost of fenestrated screw (FS).

Keywords: Cost-effective, fenestrated screws, minimally invasive, non-fenestrated screws, pedicle fixation

How to cite this article:
Rajesh A, Pelluru PK, Kumar A. "NIMS technique" for minimally invasive spinal fixation using non-fenestrated pedicle screws: A technical note. J Craniovert Jun Spine 2015;6:162-5

How to cite this URL:
Rajesh A, Pelluru PK, Kumar A. "NIMS technique" for minimally invasive spinal fixation using non-fenestrated pedicle screws: A technical note. J Craniovert Jun Spine [serial online] 2015 [cited 2023 Jun 4];6:162-5. Available from: https://www.jcvjs.com/text.asp?2015/6/4/162/167858

   Introduction Top

Traditionally, traumatic thoracolumbar fractures are treated with open technique of spinal fixation. The open techniques of treating these pathologies have given way (in certain indications) to minimally invasive spine (MIS) surgery in recent times. Open techniques usually results in extensive muscle dissection from the midline until the pedicular entry points which induce pain by activating peripheral receptors that transmit the information through spinal cord to the brain where it is modulated. [1] Periosteal pain is believed to be the most severe as the periosteum has the lowest pain threshold nerve fibers of the deep somatic structures. [2],[3] There has been a paradigm shift in treating these fractures through MIS surgery with less tissue damage due to direct trajectory and minimal tissue dissection and hence, minimal surgical inflammatory response (inflammatory mediators such as interleukins, cytokines, and prostaglandins) compared to conventional surgery. [4] However, the cost of such instrumentation is still high and hence, MIS surgery may not be a viable option at many places in the world where cost does matter.

The background of this work is the observations made by the senior author (AR) during a minimally invasive fixation with fenestrated screws (FSs). Accidental removal of the guide wire was the basis for this serendipitous discovery/invention of new technique. We herein describe the indigenous method of spinal fixation in a minimally invasive fashion with routine pedicle screws thus, cutting down the cost of treatment enormously.

   Materials and Methods Top

All 7 patients underwent percutaneous pedicle screw fixation with non-FSs (NFS) for traumatic fractures involving thoracolumbar junction between 2011 and 2014 at our institute were included in the study. Neurological status was assessed using the classification system set forth by the American Spinal Injury Association's (ASIA) standard neurologic classification of spinal cord injury, ranking neurologic status from A (complete neurologic injury) to E (completely neurologically intact).

Surgical technique

The patients were operated in prone position, rested over bolsters with padding over the pressure points and lax abdomen. The levels of surgery were marked using fluoroscopy [Figure 1]. The pedicle entry points were identified on true anteroposterior (AP) view. The skin was incised with a stab and pedicles were tapped with pedicle access kit from the lateral pedicular margin until it reached the medial margin of pedicle in AP view. The position of the tip was then confirmed on lateral view to have crossed the pedicle-body junction [Figure 2]. After confirming the same, the needle was advanced further and was threaded with a guide wire. The pedicle needle was removed keeping the guide wire in situ. The soft tissue track was dilated with serial dilators [Figure 3]. With the last dilator and guidewire in situ, the pedicle and body were tapped with FS driver of diameter 5 mm less than that of the intended screw thickness. This was done as a precautionary measure to have a tight but still negotiable track. The screwdriver and the dilator were removed and the trajectory and the angle were observed. Until this point the procedure is the same as any standard minimally invasive pedicle screw fixation. The guide wire is the removed and an NFS is threaded into the pedicle hole along the trajectory [Figure 4]. The guiding forces for correct placement of the screw without the guidewire were the fluoroscopy in lateral view and the bony tactile sensation while threading the screw (Note: The very interesting finding we noticed serendipitously was that with the narrow path created directly over the pedicle entry point, there is no place for a screw to go except for the path created. It is something akin to single key slot in the door which can only take in the key). We used fixed angle screws which were coded externally for the direction of the hub for rod placement. Percutaneous tunneling was done and the connecting rod en routed through the subcutaneous tunnel, using free hand technique [Figure 5]. Screw caps were placed under direct visualization. For reduction, manual pressure was applied over the affected spinous process by the assistant and the screw caps were tightened simultaneously on one side, each acting as counter-torq for the other. Postoperative X-ray/computed tomography was used to confirm the position of the hardware [Figure 6] and [Figure 7]. The radiation exposure was approximately 90 shots (2 min, 15 s) which have to be taken into account and can be reduced.
Figure 1: Marking the entry points for pedicles on anteroposterior view on fluoroscopy

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Figure 2: Tapping the pedicle by pedicle access kit

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Figure 3: Serial dilatations of the track for proposed screw trajectory

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Figure 4: Tapping of the proposed screw trajectory over a guidewire

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Figure 5: Insertion of screws after removal of guidewire and the tap. Complete construct after rod insertion can be visualized. Also seen is the minimal length of incisions

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Figure 6: Postoperative X-ray of one of the patients confirming the satisfactory position of screws and also showing the healed scar

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Figure 7: Pre- and post-operative X-ray and computed tomography scan image of the patient showing the accuracy of screw placement

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   Results Top

All the patients included in the study had suffered trauma and presented with persisting back ache even after 1-2 months post injury. There was no gross subluxation/instability noted. The mean age of presentation was 29 years. The mean body mass index was 23.5 kg/m 2 . All patients were ASIA Grade E having wedge compression fractures of the dorsolumbar junction. They underwent bilateral non-fenestrated percutaneous pedicle screw placement (D12-3, L1-3, respectively). Patients having L1 wedge compression fracture underwent D12-L2 and D12 fracture underwent D11-L1 percutaneous transpedicular fixation, respectively. Preoperative visual analog scale (VAS) score in 60% of patients was 6, compared to postoperative VAS score of 2. All patients were mobilized the following day and mean length of hospital stay was about 4 days. No patient experienced a worsening radiculopathy or new neurological deficit that could be attributed to screw malposition. The average cost of a single level fixation by FS and NFS was `1, 30,000/patient and `32,000/patient, respectively ($2166 and $530, respectively). The postoperative hospital stay was same for both categories, and there were no major complications including wound healing. At 1-year follow-up, we had 1 patient who had loosening of the screw head and subsequent displacement of rod on one side. The wound was re-explored from the previous incisions, rods readjusted, and screw caps replaced under general anesthesia [Figure 8].
Figure 8: Anteroposterior and lateral views showing the migrated screw cap and displaced rod

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   Discussion Top

The most common site of injury to the spine is the thoracolumbar junction which is the mechanical transition junction between the rigid thoracic and the more flexible lumbar spine. The use of pedicle screw fixation is has been the conventional treatment for spinal stabilization. Standard midline posterior spinal approaches have been shown to cause significant muscle morbidity resulting from iatrogenic muscle denervation (particularly with exposure lateral to the facet), increased intramuscular pressure, ischemia, and revascularization injury. [1],[2],[3] All of these effects can lead to paraspinal muscular atrophy, scarring, and decreased extensor strength and endurance. [4],[5],[6],[7] Kim et al. compared trunk muscle strength among patients treated with open posterior instrumentation versus percutaneous instrumentation. Patients undergoing percutaneous instrumentation displayed more than 50% improvement in extension strength. [8] Minimally invasive fixation of the lumbar spine was first described by Magerel [9] and later Lowery and Kulkarni. [10] described a percutaneous lumbar pedicle screw fixation device using rods as longitudinal connectors. Pedicle screws engage all the three columns of spine thus providing better stability. Minimal manipulation is required to place the rods in a standard submuscular position and the need for direct visual feedback is avoided. The medial angulation is easily achieved, because extensive soft tissue and muscle retraction is avoided. Since the first documented case by Foley and Gupta. [11] in 2002, several clinical case series using this system in traumatic fractures have been described in the literature. There has been no study until date comparing fenestrated, and NFSs and this study though limited by numbers reflects upon the path-breaking use of NFSs in MIS surgeries. The procedure is completed within minutes and the operative time, blood loss, and hospital stay are also significantly shortened. A traditional open surgery may be an overtreatment in all these cases, considering blood loss, possible complications, hospital stay, and delayed functional recovery. The surgeon relies more on his tactile sensation than imaging and the facet and transverse process junction can be easily felt intraoperatively. Once initial access through the pedicle is made, normal screws can easily follow the same trajectory. This is confirmed on fluoroscopy. The accuracy of screw placement is similar to that reported for other techniques and the disadvantages associated with standard open approaches are also reduced. [12] Some of the advantages of this minimally invasive surgery include small skin incisions, minimal paraspinal muscle dissection, sparing the posterior elements, that is, lamina, spinous process, supraspinous and interspinous ligaments, and paravertebral muscles, less intra-operative bleeding, superior postoperative muscle strength, less exposure to anesthetic drugs, quick recovery, early mobilization, and shorter hospitalization stay.


Our initial experience is limited to a small number of thin patients who had undisplaced fractures who were stabilized across a vertebral body, without the requirement of bony decompression/fusion. The radiation exposure is bit high which can be brought down by consciously reducing them or by using neuronavigation (if affordable).

   Conclusions Top

It may be a poorman's alternative for open approaches or minimally invasive surgeries using regular non-fenestrated screws. The accuracy of screw placement is similar to that reported for other techniques.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Kawaguchi Y, Matsui H, Tsuji H. Back muscle injury after posterior lumbar spine surgery. Part 1: Histologic and histochemical analyses in rats. Spine (Phila Pa 1976) 1994;19:2590-7.  Back to cited text no. 1
Kawaguchi Y, Matsui H, Tsuji H. Back muscle injury after posterior lumbar spine surgery. Part 2: Histologic and histochemical analyses in humans. Spine (Phila Pa 1976) 1994;19:2598-602.  Back to cited text no. 2
Kawaguchi Y, Yabuki S, Styf J, Olmarker K, Rydevik B, Matsui H, et al. Back muscle injury after posterior lumbar spine surgery. Topographic evaluation of intramuscular pressure and blood flow in the porcine back muscle during surgery. Spine (Phila Pa 1976) 1996;21:2683-8.  Back to cited text no. 3
Jackson RK. The long-term effects of wide laminectomy for lumbar disc excision. A review of 130 patients. J Bone Joint Surg Br 1971;53:609-16.  Back to cited text no. 4
Macnab I, Cuthbert H, Godfrey CM. The incidence of denervation of the Sacrospinalis muscles following spinal surgery. Spine 1977;2:294-8.  Back to cited text no. 5
Mayer TG, Vanharanta H, Gatchel RJ, Mooney V, Barnes D, Judge L, et al. Comparison of CT scan muscle measurements and isokinetic trunk strength in postoperative patients. Spine 1989;14:33-6.  Back to cited text no. 6
Reichling DB, Levine JD. Critical role of nociceptor plasticity in chronic pain. Trends Neurosci 2009;32:611-8.  Back to cited text no. 7
Kim DY, Lee SH, Chung SK, Lee HY. Comparison of multifidus muscle atrophy and trunk extension muscle strength: Percutaneous versus open pedicle screw fixation. Spine (Phila Pa 1976) 2005;30:123-9.  Back to cited text no. 8
Magerel F. External skeletal fixation of the lower thoracic and lumbar spine iUH. In: Stahl E, editor. Current Concepts of External Fixation of Fractures. Berlin: Springer-Verlag; 1982. p. 353-6.  Back to cited text no. 9
Lowery GL, Kulkarni SS. Posterior percutaneous spine instrumentation. Eur Spine J 2000;9 (Suppl 1):S126-30.  Back to cited text no. 10
Foley KT, Gupta SK. Percutaneous pedicle screw fixation of the lumbar spine: Preliminary clinical results. J Neurosurg 2002;97(1 Suppl):7-12.  Back to cited text no. 11
Ringel F, Stoffel M, Stüer C, Meyer B. Minimally invasive transmuscular pedicle screw fixation of the thoracic and lumbar spine. Neurosurgery 2006;59 4 Suppl 2:ONS361-6.  Back to cited text no. 12


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]


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