Minimally Invasive Spine Osteosynthesis (MISO) Technique for Fractures Spine: A Case Series 14 Cases

Background: The choice of treatment of dorso-lumbar spinal fractures in the absence of neurological deficit depends on the classification and severity of injury. In the conventional open approach with posterior pedicle screw fixation, detachment of the Para spinal muscles may be required. In addition, this open approach may be disadvantaged by prolonged operative time, increased intraoperative bleeding and delayed functional rehabilitation. All these problems appear to encourage orthopedic surgeons to limit secondary iatrogenic insult in these patients by mini open surgery. The goal of this study is to evaluate the effectiveness of minimally invasive treatment of dorsolumbar fractures by mini open surgical pedicle screw fixation and to discuss the potential benefits and drawbacks of this procedure. Patients and methods: This is a prospective study involves 14 Patients (10 males) treated and followed between Feb. 2010 to Feb 2014. All had acute traumatic single level dorso-lumbar spine fractures, age range 17-47 years (mean 30.1 ± 7.9 yrs). Patients with pathological fractures, neurological injury, anatomical variations of the cord or vertebrae, mental illness, significant surgical contraindications, osteoporosis, refusing to sign informed consent and those with (TLICS) score ≤4 or load sharing score ≥7 were excluded from the study. All the cases had been treated by minimal invasive posterior approach. Total of 56 screws and 28 rods were applied utilizing the conventional posterior instrumentation. Results: Mean post-operative hospital stay 3.8 days. No major complications as spinal cord, nerve root or blood vessel injuries occurred. No screws were broken and just two screws were malpositioned. All patients improved clinically, and the outcome (according to modified MacNab criteria) was considered excellent in six patients, good in seven, and poor in one patient. Conclusion: Mini open surgery for posterior pedicle screws fixation has attracting increasing attention as it brings a multitude of advantages including: less bleeding, lower incidence of postoperative intractable low back pain and reduced hospitalization stay. However; some shortcomings as limited indications, unsuitability for long segment fusion and high load-sharing score patients restricts its worldwide prevalence.


Introduction
Spine fractures are serious injuries and thoracolumbar spine is one of the most common areas for spinal fractures [1]. Regardless of selected protocol of treatment, the target continues to be restoration of spinal stability, decompression of spinal canal and earlier mobilization of the patient [2]. Short-segment pedicle fixation (SS) had been developed for operative stabilization of thoracolumbar and lumbar fractures. It has become increasingly popular worldwide as they engage all three columns of the spine and can resist motion in all planes [3,4].

Pedicular screws can be inserted either by Standard open techniques
which involve open exposures and extensive muscle dissection or through percutaneous approach which needs specialized equipments and long learning curve before implementation [5,6].
The purpose of this study is describing and evaluating minimal invasive posterior fixation technique of thoracolumbar spine using ordinary pedicular screws and instrumentations.

Patients and Methods
This prospective case series study involved 14 patients (10 males and 4 females) with acute traumatic single level dorsal or lumbar spine fractures without neurological insult. They underwent minimally invasive spine fixation between 2010 and 2014. Causative injuries were fall from height (9 patients), road traffic accidents (4 patients) and in one case drop of heavy box over the back while working. Age range 17 to 47 years (mean 30.1 ± 7.9 yrs). Six patients (L1) fracture 2 patients (L2) fractures, 2 patients (L3) fractures and 4 patients (D 12) fractures.
Inclusion criteria involved: single segment vertebral fractures without neurological deficits, patient not in need for decompression of the neural elements, mechanically unstable burst fractures and displaced bony fragments which could be reduced by ligamentotaxis within 48 to 72 hours after injury. Exclusion criteria involved: pathological fractures, neurological injury, anatomical variations of the cord or vertebrae, mental illness, significant surgical contraindications, osteoporosis, patients refusing to sign informed consent and those with (TLICS)score ˂4 or load sharing score ≥7.
In all our cases (TLICS) score was ≥4 and load sharing score was 6 or less who were suitable for short-segment posterior spinal instrumentation and not in need for decompression or supplementary anterior stabilization. All procedures had been approved by the board of ethical committee of the hospital and a written consent had been obtained from all patients [7,8].

Surgical technique
Patient positioning and anesthesia performed as similar as the conventional posterior open approach ( Figure 1A and 1B). The target segment determined by C-arm. One level above and below the fractured vertebra incised and the length of the incision was about 2 cm ( Figure 2). Thoracolumbar fascia incised lateral to the supraspinous ligament, and the paraspinal muscles were stripped subperiostially along the sides of the spinous processes and vertebral laminae till the outer edge of facet joints with a Cobb elevator and a gauze swab in both sides from the same incision. Dissection continued down the lateral side of the facet and onto the transverse process with proper homeostasis of the area. Care should be taken not to injure the facet joint capsule if no fusion technique was planned.
The entry point was determined through anatomical landmarks used in the conventional open technique, rechecked by C-arm imaging. Pedicle screw entry site and screw side trajectory were properly identified under direct vision and the screw was inserted using the free hand technique with C-arm control ( Figure 3). After application of 4 screws, a contoured rod passed in sub-muscular plan with minimal manipulation, essentially no muscle dissection and without the need for directs visual feedback.
The reduction and screws position were checked by the image intensifier ( Figure 4). Application of distraction by distractor until correction of vertebral height (if possible) was achieved and the correction was maintained by tightening screw head nuts ( Figure 5). The wounds were closed in layers and in most of cases no need for drain required.

Postoperative care
Patient was neurologically tested before leaving the operating room and kept flat for a period of 24 hours after surgery with close observation to vital signs. Post-operative antibiotics were continued for 5 days. All our patients were mobile 48 hours after surgery and were discharged on postoperative day 2 (7 cases), day 3 (5 cases) and 2 patients were discharged on postoperative day 5 and 7 days due to associated injuries.  The mean hospital stay was 3.8 days. Routine clinical and radiological checks up were done monthly for first three months ( Figure 6), then every three months afterwards. Multi slice CT scans were performed and repeated every 6 months till assurance of bone healing.

Results
The follow-up period ranged 8 to 14 months (mean 6.8 months). We used the following parameters which had been utilized by many authors [9,10]. They included: operative time, blood loss, radiation exposure time, kyphotic angle correction, vertebral height index, diameter of medullary canal in immediate and post-operative CT scans, accuracy rate of screws position, hospital stays and visual analog    The angle improved by mean of 25.3° (21.4° to 29.3°). Vertebral height index (VHI) value was determined by the following formula: The mean height of fractured vertebral body/the mean height of upper and lower vertebral bodies × 100%. Tables 2 and  3 respectively. Accuracy of pedicle screws positions were assessed by examining postoperative CT scans. Total number of 56 screws and 28 rods were applied of which 2 screws in two patients were malpositioned (3.1%). Intraoperative correction was done in one case and open conversion surgery was done in the second case due to difficulty in rod positioning. The accuracy rate of screw placement was 96.9%.

Excellent
Complete resolution of all symptoms and free of pain; no restriction of mobility; able to return to normal work and activities

Good
Marked reduction of pain with the patient generally satisfied, returning to work or usual daytime activities, and taking analgesics seldom or not at all

Worse
Clinical symptoms considered worse than before receiving procedure  Pain was evaluated via visual analogue scale (VAS) preoperatively, three days and one week postoperatively. Preoperative pain was high in all patients with mean (VAS) 7.9/10 (range 6-10) decreased to 4.2 at time of discharge (range 0-7) and to 0.7 at last follow-up (range 0-2) ( Table 2 and 3).
All patients improved clinically, and the outcome (according to modified MacNab criteria) was considered excellent in six patients, good in seven, and poor in one patient (Figure 7).

Discussion
It is known that traditional open approaches to spine surgery lead to increased paraspinal muscle injury secondary to prolonged retraction. In addition, there is an electrical-burn damage from electric knife [12]. Minimally invasive spine surgery has its roots in mid-twentieth century, but it has now developed into a large field of progressive spinal surgery [13]. As the technique became more mainstream over the past ten years, we try through this study to utilize the technique in spinal osteosynthesis of selected cases of thoraco-lumber and lumber fractures without neurological insults.
Interpretations of results of our study show that the technique is not in need for specialized instrumentations or screws and the pedicles are addressed via usual steps. Commonly partial spontaneous reduction is achieved when the patient turned to the prone position that restored the normal dorsal kyphotic and lumbar lordotic curves. Further indirect reduction and decompression are achieved by correction of Kyphosis and recreation of normal lordosis through application of contoured rod.
Less number of incisions, scars (2 small scars of approximately 2 centimeters) and minimal soft tissue damage are encountered. Radiation exposure for patient and surgeon had always been the focus of attention. It is about 11.3 ± 2.2 seconds in our study which does not differ markedly from open conventional and less than percutaneous approach [14,15]. The need of blood transfusion decreased and none of our patients required it as the mean blood loss not exceeding 40 ml. In addition; we achieved restoration of vertebral body height, improvement of Cobb's angle and high accuracy rate of screw placement with results near to the open approach [16]. Also we have some loss of vertebral height in long-term follow-up similar to the open approach [17]. The operative time ranged between 50 to 105 minutes (mean 73.8 minutes) with the longer operative times occurring in early cases. A steep learning curve could be gained easily to build the necessary skills and experience as most of spinal surgeons are familiar with pedicle targeting. The approach had rapid recovery and patient activity was permitted two weeks after surgery and all patients were satisfied from cosmetic appearance of the scare.
Our approach is more advantageous than percutaneous technique which requires specialized equipment's and long learning curve before implementation. In addition, there is high incidence of screw malposition and large doses of radiation exposure [18].
The great protests directed to our approach is the narrow scale for indication as it is unsuitable for long segment posterior laminectomy and posterolateral fusion, limitations to cases with single segment thoracolumbar or lumbar vertebral fractures and cases with loadsharing score 6 or maximally 7 points because these figures ascertain efficacy of only posterior stabilization [19].

Conclusion
Minimally invasive screw osteosynthesis (MISO) technique is a safe and worthwhile method of managing spine fractures in cases not in need for decompression. Although this study is limited by its small sample size but the results demonstrate that it is advantageous regarding, minimal soft tissue dissection and lack of need for special instrumentations consequently it is cost effective with short hospital stay and faster return to work and daily activities. Mastering the technique not only require practice but also familiarity with pedicular screw insertion. By experience; the technique enables surgeons to achieve the same surgical objectives as with a traditional open procedure.