Percutaneous Pedicle Screw and Rod Insertion for the Treatment of Thoracic and Lumbar Spine Fracture

Introduction: Standard techniques for lumbar pedicle screw and rod fi xation involve open exposure and extensive muscle dissection. Percutaneous pedicle screw system minimises the morbidity associated with traditional open approaches without compromising the quality of spinal fi xation. A preliminary experience with this device has been encouraging. The purpose of this study was to demontrate operative techniques and experiences with percutaneous lumbar pedicle screw and rod insertion for internal fi xation of the lumbar spine without use of Zig. Methods: It was hospital based retrospective interventional study done at the department of Orthopaedics, B.P.Koirala Institute of Health Sciences, Dharan,Nepal over a period of 2 and half years. The study enrolled 30 patients aged 18-55 years who had presented with traumatic fracture of thoracic and lumbar spine. All thirty patients underwent percutaneous pedicle screw and rod fi xation and successful percutaneous single/two level fusions. The follow up period ranged from 6 to 24 months. Results: The study comprised of 25 males and 5 females. Average patient’s age was 36.5 years (range 18-55 years). The common mode of injury was fall from height, road traffi c accident, physical assault followed by sports related injury. All patients were having unstable spine fracture without neurological defi cit. Operation time, loss of blood, post operative pain was less in percutaneous method. Post operative rehabilitation was easier. Spinal fusion was achieved in all patients in 6 months to 1 year time. There was no post-operative neurological defi cit, infection, implant failure. Conclusion: Our early experiance suggests that Minimally invasive approaches for performing lumbar fusion, is able to achieve the same clinical results as conventional open procedures.


INTRODUCTION
The uses of pedicle screws for spinal stabilisation have become increasingly popular worldwide.Pedicle screw system engages all three columns of the spine and can resist motion in all planes.Several studies suggest that pedicle screw fi xation is a safe and effective treatment for many spinal disorders 1,2 .Standard techniques for pedicle screw placement require extensive tissue dissection to expose entry points and to provide lateral-to-medial orientation for optimal screw trajectory.Open pedicle screw and rod fi xation have been associated with wide paraspinal muscle dissection, extensive blood loss, lengthy hospital stays, and high cost 3 .Mager l4 , who used an external fi xator, fi rst described percutaneous fi xation of the lumbar spine.Mathews and Long 5 fi rst described and performed percutaneous lumbar pedicle fi xation technique in which they used plates as the longitudinal connectors.Lowery and Kulkarni 6 subsequently described a similar technique in which rods were placed.Although the latter authors reported high success rate, Mathews and Long noted a signifi cant rate of non-union.In all cases, the longitudinal connectors were placed either externally 4 or superfi cially, just beneath the skin 5-7 .This has several potential disadvantages.First, the superfi cial hardware can be irritating and requires routine removal 6 .Second, longer screws are required, producing a less effective biomechanical stabilisation than that achieved using standard pedicle fi xation systems and leading to a higher potential for implant failure.The use of the percutaneous pedicle screw and rod fi xation system offers several distinct advantages over conventional pedicle screw fi xation.The system eliminates the need for a large midline incision and signifi cant paraspinous muscle dissection.Both the pedicle screws and the pre contoured rods are placed through stab incisions.The paraspinal muscles are bluntly split rather than divided, leading to shorter periods of hospitalisation and recovery 7,8,9 .Blood loss and tissue trauma are minimised.An ideal lateral-to-medical screw trajectory is much more easily accomplished, especially in larger patients, as signifi cant paraspinous tissue retraction is avoided 10 .The aim of the study was to demonstrate N OAJ J a n -J uly 2 01 3 | Vo l 3| Is s u e 1 operative techniques and preliminary experiences with percutaneous pedicle screw fi xation without use of any Zig in terms of: Pain, Operative time, Radiation time, Blood loss and Post-operative complications ( Infection, Post operative neurological defi cit).

METHODS
It was hospital based retrospective interventional study done at the department of Orthopaedics, B.P.Koirala Institute of Health Sciences, Dharan,Nepal over a period of 2 and half years.The study enrolled 30 patients aged 18-55 years who had presented with traumatic fracture thoracic and lumbar spine.All thirty patients underwent percutaneous pedicle screw and rod fi xation and successful percutaneous single/two level fusions.The followed up period ranged from 6 to 24 months.Operation time, radiation time, loss of blood, post operative pain, infection, post operative rehabilitation was evaluated to objectify possible advantages for the percutaneous operation technique.Patients were also evaluated for exposure related morbidity.patients with Stable spine injury, Degerative disc disease, Tuberculosis of spine, Spondylolisthesis and Pathological fractures were excluded from this study.

Patient positioning
The percutaneous posterior fi xation of the dorsolumbar spine is performed under general anaesthesia.The patients were positioned prone, on top of chest and pelvic rolls with the abdomen free, knee chest position was avoided.Fluoroscopic images of the pedicles were obtained in both an AP and lateral view before proceeding.position was adjusted and securely fi xed.

Initial Skin Incisions and Pedicle Identifi cation and fi xation.
After having a good orientation of pedicle in image intensifi er in anteroposterior view a stab incision [Fig: 1a,b,c] was given on the lateral border(margin) of pedicle.Soft tissues were dissected with the help of artery forceps.1.8/2mm K-wire [Fig: 1a] was used to verify the appropriate location of the pedicle.The K-wire was positioned on the skin incision directly over lateral border of the pedicle on an AP image.The needle was then pushed down till the medial border of pedicle was reached and it was confi rmed on lateral view in which K-wire should just touching the posterior border of vertebra, it should not voilet the medial border of pedicle in AP image.Both AP and lateral images should confi rmed that the appropriate starting place has been determined.K-wire was then removed and hole was made in the pedicle with the help of pedicle awl.Tapping was done with bone tap and pedicle screw of adequate diameter and length was put in the pedicle hole.The process was repeated for the second screw on the same side.After inserting both, the screw assemblies were made approximately of the same height and the entire process was repeated for the contra lateral side.Precontoured or contoured rods were placed on either side of screw slot by retracting skin, spine can be either compressed or distracted and fi nally tightening of inner screw (set screw) was done.All these procedure were performed without the help of Zig.
The fi nal construct can then be viewed with AP and lateral fl uoroscopy [Fig 3 a, b, c, d].Closure was accomplished with a few interrupted stitches in the fascia, subcuticular skin suture and dressing was done.

RESULTS
The study comprised of 25 males and 5 females.Average patient's age was 36.5 years (range: 18-55 years).The common mode of injury was fall from height, road traffi c accident, physical assault, sports related injury etc.All patients were having unstable spine fracture without neurological defi cit.Operation time, loss of blood, post operative pain was less in percutaneous operation.Post operative rehabilitation was easier.Intra operative exposure with radition was more in percutaneous technique in early phase of learning curve most probably due to lack of experience in part of surgeon about this new technique and unavailability of expert image technician.Spinal fusion was achieved in all patients in 6 months to 1 year time.There was no post-operative neurological defi cit, infection, implant failure.

DISCUSSION
Lumbar spinal fusion was fi rst performed by Albee 10 and Hibbs 11 in the early 1900's for the surgical management of spinal deformity related to Pott's disease.Due to its initial success, the indications for this technique were later expanded to include traumatic injuries and scoliosis.

N OAJ J a n -J uly 2 01 3 | Vo l 3| Is s u e 1
However, an undesired consequence of this technique is the iatrogenic paraspinal muscle injury that occurs during the exposure for screw placement.A number of authors\ have described the deleterious effects of the extensive muscle stripping and retraction that occur during lumbar fusion surgery 14-19 .
Gejo et al 14 analysed postoperative MRI and trunk muscle strength following lumbar surgery in 80 patients.They determined that damage to the low back muscles was directly related to the muscle retraction time during surgery.The incidence of low back pain was also signifi cantly higher in those who had long muscle retraction times.
These conclusions support the studies of Kawaguchi et al [15][16] who examined the effects of retractor pressure on the paraspinal muscles during lumbar surgery.They found that muscle injury, as demonstrated by elevated serum levels of creatine phosphokinase MM isoenzyme, is directly related to the retraction pressure and duration.
Similarly, Styf et al 17 reported that the retractor blades may in fact increase intramuscular pressure in the paraspinous muscles to ischemic levels.
Rantanen et al 18 concluded that patients with poor outcomes following lumbar surgery are more likely to have persistent pathological changes within the paravertebral muscles.Percutaneous lumbar fi xation was designed, in part, to minimize the paravertebral muscle injury that occurs with conventional open procedures.
Mager l4 fi rst reported the use of percutaneous pedicle screw combined with an external fi xator in 1982.The most obvious limitation of this technique was the risk of infection, not to mention the discomfort of an external appliance.Matthews et a l5 described the use of percutaneous pedicle screws with longitudinal connectors placed under direct vision in the suprafascial, subcutaneous space.This superfi cial instrumentation was uncomfortable to the patient and associated with a signifi cant non-union rate as well, perhaps secondary to the long lever arms of the hardware.The system allows for placement of percutaneous screws and rods through paramedian stab incisions.The conventional anatomic position of the construct avoids the instrumentationrelated discomfort that was associated with earlier versions of percutaneous fusion.
There are several distinct advantages of the system compared to standard open lumbar pedicle fi xation.The paraspinal muscles are bluntly separated rather than stripped from their attachments and are minimally retracted using a sequential dilation technique as described by Foley and smith 9 for micro endoscopic discectomy.This results in signifi cantly less intraoperative blood loss, less iatrogenic muscle injury, and less postoperative pain.
Patients are therefore able to ambulate and mobilize much more quickly, resulting in a decreased cost 20 .From a technical perspective, it is also easier to achieve the desired lateral to medial pedicle screw trajectory as there is not a wall of soft tissue that limits the angulation of the instruments (as can be encountered in the open surgery).This is particularly helpful in obese patients, as more extensive exposure and retraction can be avoided.
Operative time is also signifi cantly lessened; it takes only one hour for the surgeon to place four screws and two rods.

CONCLUSION
The clinical utility of system appears promising, as our early experience suggests that the system is able to achieve the same clinical results as conventional open procedures while signifi cantly reducing the exposure related morbidity.

Boucher 12
fi rst described the pedicle screw in 1959 and Roy-Camille et al 13 reported a dorsal construct consisting of a pedicle screw and plate several years later.Spinal pedicle screw fi xation has continued to undergo modifi cations since its inception.Its effectiveness in the management of a variety of spinal disorders has made it a mainstay in the armamentarium of most spine surgeons.