MINIMAL ACCESS SPINE SURGERY

Transcription

1 MINIMAL ACCESS SPINE SURGERY Spinal ailments are amongst the most common ailments that afflict mankind. Back pain, for example, has achieved epidemic proportions worldwide in the last two decades and is the second most common ailment after common cold in US. Eight out of ten people will suffer from a significant episode of back pain at some point of their lifetime. It is responsible for the highest number of man hours lost in the industry. Most back ailments can be managed conservatively and only a small percentage of patients require a surgery. However since the prevalence of back ailments is so large, even this small percentage of patients requiring a surgery translate into a very large and significant number of spine surgeries. For example, an estimated 1.2 million spinal surgeries are performed in the US each year. Conventional spine surgery requires a long incision which is a cosmetic insult and generally not well accepted by the patients, especially the fairer sex. However more importantly, conventional spine surgery requires substantial separation of musculature from the bony elements and the resultant problems. The dissection of paraspinal muscles results in healing by scarring. This results in the various layers of the individual muscle to scar to one another and lose their independent function. The direct compression of the muscle tissue by the retractors and other instrumentation further adds to the insult. This damage could be compared with that caused by a tourniquet applied to the muscle of an extremity. The decreased blood flow to the muscles results in microvascular and metabolic changes in the muscle tissue. It also results in denervation of paraspinal muscles and devascularization of feeder vessels. The muscles thus undergo wasting and weakness which may be symptomatic as a fatigue type of back pain and/or limitation of normal physical function. The exposure also denervates the facet joints and has the potential of causing direct injury to these joints. The resultant compromise in outcome due to the involvement of the muscles and the facet joints is known as fusion disease. Thus the surgical approach (i.e., dissecting the muscles) contributes to the majority of the postoperative pain and delays return to full activity. It also necessitates the use of significant pain medication with their inherent side effects. Research and innovation to improve the outcome through addressing the above aspects led to the establishment of minimal access spine surgery. It involves the performance of surgery through smaller incision with or without the aid of endoscope/ laproscope/ thoracoscope. An endoscope is an instrument used for the examination of a hollow viscus such as the bladder or a cavity such as the chest. The endoscope is basically a camera mounted on a long thin lens with a cable and a light source. The light source is mounted onto the lens and provides light to illuminate the field to be visualized. The cable mounted on the camera connects to a TV screen, which displays the camera s field of focus. The endoscope allows the surgeon to have an illuminated and magnified view of the operating field without having to make a large incision. Endoscopy is the visual inspection of any cavity or hollow viscus by means of an endoscope. Thoracoscopy is the 1

2 visualization of the thoracic cavity or the chest. Laparoscopy is the visualization of the abdominal cavity. Traditional Surgical Approaches to Spine - Disadvantages Dissection of muscles produces the majority of the postoperative pain and delays return to normal and full activity Prolonged recovery time Minimal Access Spine Surgery - Advantages Minimal trauma to muscles reduces postoperative pain Shorter recovery time Reduced surgical complications Reduced surgical blood loss Reduced use of post-op narcotic pain medicines Reduced length of hospital stay Minimal Access Spine Surgery have been used for various surgeries like a. Discectomy b. Pedicle screw fixation c. Interbody fusion Transforaminal Lumbar Interbody fusion (TLIF) Anterior Lumbar Interbody fusion (ALIF) d. Thoracoscopic Spine Surgery e. Discectomies f.biopsy g. Scoliosis release h. Bone grafting i. Instrumentation for scoliosis correction, trauma, pott s spine j.decompression for trauma and pott s spine Discectomy k. Decompresion Surgeries for Lumbar canal stenosis l. Vertebroplasty / kyphoplasty Prolapse inter-vertebral disc with radicular pain or sciatica is a common clinical problem. A disc herniation happens when the nucleus inside the center of the disc pushes through the annulus, the ligaments surrounding the nucleus. The herniated disc material may push backward, causing pain. Numbness or weakness in the leg occurs when the nucleus pushes on the spinal nerve root. Most patients respond to conservative treatment. In a small percentage discectomy is required to relieve pressure on the ligaments, nerves, or spinal cord. Traditional discectomy involves a larger incision with elevation of paraspinal muscles. Microscopic Discectomy The use of microscope allowed better illumination and magnification as well as a relatively smaller incision. However it still involved elevation of the paraspinal muscles. 2

3 Microendoscopic Discectomy This technique combines the advantages of microscopic discectomy, that is better illumination and magnification with that of endoscopy, that is minimal damage to muscle tissue. The muscles are not cut or elevated from the attachments but are dilated, thus causing minimal damage. A spinal needle is placed into para-spinous musculature 1.5cm off the midline at the appropriate level confirmed using lateral fluoroscopy. The spinal needle is removed and a vertical incision, 8 to 10 mm in size, is made at the puncture site. The guide wire is placed through the incision. A series of dilators are then sequentially inserted in order to create the space for a tubular retractor which is placed over the sequential dilators, docking on the lamina. Fluoroscopy is used to confirm appropriate positioning. A Flexible Arm is attached to the Tubular Retractor and the ipsilateral bed rail in order to hold the tubular retractor in place. An endoscope can be placed anywhere within the 360 periphery of the retractor. The endoscope is focused and image orientation is done. Soft tissue over the lamina and interlaminar space is removed in order to maximize the working space within the Tubular Retractor. Discectomy procedure can now be performed as in the other techniques. If the pathology is beyond the confines of the Tubular Retractor, the retractor can be move or angled over the pathology by a process known as wanding. Wanding allows the surgeon to place the objects of interest in the center of the operative corridor. As for other endoscopic procedures, a learning curve is involved especially to orient to the two dimensional image as seen on the screen. Transforaminal Endoscopic Lumbar Discectomy In this technique access to the pathology is attained through the intervertebral foramen rather than the interlaminar space. The procedure is done under local anaesthesia administered at the skin level and in the musculature of the approach trajectory, taking care not to advance to the point of anesthetizing the neural structures at the foramen. In addition a light IV sedation is given only to the extent that patientphysician dialogue can be maintained relative to procedural sensations. The surgical approach is approximately 9 to 13 cm from the midline. A needle is advanced to the pars interarticularis and then directed medially and positioned at the foramen. A cannula is passed over the needle, the needle is removed, and the rod-lens working channel endoscope is then passed through the cannula with delivery to the foramen, from which intradiscal or epidural access can proceed. The optics and lighting provide for clarity of visualization to identify, inpect, and avoid critical structural anatomy and pursue the pathlogy. Approach structures may dictate the size and sturdiness of the endoscope with a working channel diameter that can accommodate surgical tools appropriate to the targeted pathology. 3

4 Within the safe neural working zone of the epidural space, manipulation of the endoscope allows delivery of instruments designed to address the pathology at distances from and angles to the scope. Since it involves using an approach different from the traditional interlaminar approach, a steeper learning curve is involved. Pedicle screw fixation systems The use of pedicle screws for spinal stabilization has become increasingly popular worldwide. Pedicle screws engage all three columns of the spine and can resist motion in all planes. Several studies suggest that pedicle screw fixation is a safe and effective treatment for many spinal disorders. Standard techniques for pedicle screw placement, however, require extensive tissue dissection to expose entry points and to provide for lateral-to-medial orientation for optimal screw trajectory. Minimally Invasive Pedicle Screw Fixation With the minimally invasive technique, posterior pedicle screw fixation is implanted without posterior exposure with percutaneous pedicle screw systems like, the Sextant Rod Insertion System for the lumbar spine and Longitude System for the thoracolumbar and thoracic spine. The pedicle entry sites are determined using fluoroscopic control. A small skin incision (25 mm) is made and a needle is secured to the pedicle entry site under fluoroscopy. The needle is replaced with a wire and sequential dilation is then performed using the dilator system. Once the retractor tube is secured, the dilators are removed. The pedicle is entered with a gearshift awl. A guide wire is placed into the pedicle and a cannulated tap threads the pedicle. This process is repeated for the second screw. Next, the cannulated pedicle screws with their extensions are advanced into the pedicles over the guide wires. The extensions are then connected to the alignment guide. A small proximal stab wound is made in the skin to allow the rod to bluntly pass through the paraspinal muscles into the top loading mechanism of the screws. The top loading nuts are then secured through the pedicle screw extension tubes. Fusion Procedures Fusion procedures have also been increasingly used worldwide as a safe and effective treatment for many spinal disorders. It initially started as non-instrumented posterior fusions but the incidence of pseudarthrosis with these procedures was significant. Therefore, internal-fixation systems were developed to increase the fusion rate to make clinical outcomes more predictable. Rigid internal-fixation systems were successful in 4

5 improving fusion rates. However, the increase in soft-tissue damage secondary to surgical exposure and operating time had a negative impact on outcome. A newer method called the 360 fusion emerged, in which bone was placed in the interbody space through either an anterior (Anterior Lumbar Interbody Fusion i.e. ALIF) or posterior approach (Posterior Lumbar Interbody Fusion i.e PLIF or Transforaminal Lumbar Interbody Fusion i.e. TLIF). Posterior pedicle screws and rods then supplemented the interbody construct. Fusion rates increase substantially and the incidence of subsidence and flat back deformities was low. However, there was a significant complication rate and fusion disease remained. Minimally invasive fusion procedures TLIF can be done through minimal access surgery by using the tubular retractor system (the same as the one used for discectomy) or expandable retractor systems (Quadrant, X-tube) on one side and percutaneous pedicle screw systems like, the Sextant Rod Insertion System on the other. In this case the tubular or expandable retractor system are used to not only insert the pedicle screws but also to do the decompression and the interbody fusion. TLIF can also be done through minimal access surgery by using the tubular or expandable retractor systems on both the sides. Minimal access has also revolutionized ALIF surgery. The anterior exposure is performed with a mini retroperitoneal approach to implant the threaded fusion cages in the standard manner or through laproscopic surgery. The patient is then repositioned prone and posterior fixation is implanted with percutaneous pedicle screw system like, the Sextant Rod Insertion System. In a new technique, ALIF for L5-S1 and L4-5 can be done by approaching the intervertebral disc through an approach anterior to the coccyx and the sacrum. Thoracoscopic Spine Surgery The Thoracoscope is a long, hollow tube that contains a camera, fiber optic lens and a light source. The surgeon sees the operative site through one small incision (1/2") and operates via two or more other smaller incisions through hollow tubes called portals. Just as arthroscopic surgery has revolutionized knee treatment, Video-Assisted Thoracic Spine Surgery (VATS) has accomplished similar goals in the treatment of spinal disorders. The indications for Thoracoscopic Spinal Surgery include deformity (e.g. an anterior release for scoliosis or Scheuermann's kyphosis), discectomies, biopsy, instability (in cases of vertebral fractures in addition to decompression, anterior column reconstruction using bone grafts and/or internal fixation devices can also be applied), neural compression and pathologic lesions (biopsy for infection or tumor, debridement/drainage of an abscess, resection of a tumor, or corpectomy). 5

6 Advantages of thoracoscopy over the conventional transthoracic open procedures include enhanced visualization while using standard instruments through minimal incisions, more extensive visualization of thoracic anatomy, decreased incisional pain, decreased need for chest tube drainage, decreased respiratory complications, decreased blood loss and decreased potential for infection besides the other routine advantages of minimal access surgery. Decompression Surgery for Lumbar Canal Stenosis Lumbar canal stenosis refers to the narrowing of the spinal canal or the intervertebral foramen due to ageing resulting in compression of the spinal cord or the nerve roots. This typically results in pain in the back radiating down the legs. Classically the pain increases gradually as the patient walks and forces him/her to stop after a particular distance. This distance gradually decreases with time as the canal narrows further. The pain may be associated with numbness and/or weakness in the legs. Although medication and physical therapy may temporarily help alleviate pain, surgery is often required, especially in those individuals in whom the symptoms interfere in the normal lifestyle. Standard open laminectomy, the traditional surgical treatment for stenosis, may result in pain or disability leading to a prolonged convalescence. The Micro-endoscopic system can be used for bilateral laminectomy from a unilateral approach to relieve lumbar stenosis pain, resulting in less postoperative pain, disability and complications than traditional open surgery. The tubular retractor is placed over the lamina and the camera as well as light source attached as per the technique already described. Soft tissue can be easily removed with cautery and ronguers exposing the lamina. Laminotomy is done using a Kerrison rongeur or power drill. It is important to expose and remove all the hypertrophied ligamentum flavum with a curette and rongeurs both ipsilaterally and contralaterally to fully decompress the lateral recess and foramina. Vertebroplasty and Kyphoplasty Posterior percutaneous procedures like vertebroplasty and kyphoplasty have led to revolutionization of management of vertebral compression fractures. Vertebroplasty This is a minimally invasive, non-surgical procedure that is designed to relieve the pain of compression fractures. In addition it also strengthens the weak vertebral body. A needle is passed under fluoroscopic control through the pedicle into the vertebral body. The position of the needle is confirmed by pushing a small amount of radiographic dye. A small amount of orthopedic cement, known as poly-methylmethacrylate (PMMA), is pushed through the needle into the vertebral body. When the cement is injected it is like a thick paste, but hardens rapidly. Usually each vertebral body is injected on both the 6

7 right and left sides, just off the midline of the back. Within a few hours, patients are up and moving around. Most go home the same day. Kyphoplasty This is a newer technique in which restoration of height and reduction of deformity are the main goals in addition to those of vertebroplasty. Kyphoplasty is performed under local or general anesthesia. Using image guidance x-rays, two small incisions are made and a probe is placed into the vertebral space where the fracture is located. Similar to vertebroplasty, a needle is placed into the vertebral body through the pedicle. A balloon, called a bone tamp, is inserted on each side. These balloons are then inflated with contrast medium (to be seen under fluoroscope) until they expand to the desired height and removed. The spaces created by the balloons are then filled with PMMA, the same orthopedic cement used in vertebroplasty, binding the fracture. The cement hardens quickly, providing strength and stability to the vertebra, restoring height and relieving pain. Thus to conclude, minimal access spine surgery has revolutionised spinal surgery and the management of spinal ailments. However, these techniques are highly technical and require a significant learning curve. It is imperative that the surgeons undergo proper training. ************ 7