Spine Surgery - Minimally Invasive Posterior Lumbar Spine Surgery
– What you and your patient should know
Minimally Invasive techniques are employed in many areas of surgery and is increasingly being used in spine surgery. At Singapore General Hospital, we have been performing minimally invasive posterior lumbar spine surgery since 2004. Conditions for which minimally invasive spine surgery (MISS) can be used include prolapsed intervertebral disc, spinal stenosis and spondylolisthesis.
The goal of minimally invasive spine surgery is to achieve clinical outcomes comparable to those of conventional open surgery, while minimising the iatrogenic soft-tissue damage inherent with traditional spinal exposures. In conventional posterior lumbar surgery, paraspinal muscle retraction and extensive soft tissue dissection is required to adequately expose the spine. Multiple authors have documented the harmful effects of this extensive muscle dissection and retraction. It has been found that during retraction, the intramuscular pressure and intramuscular perfusion pressure are increased to the extent that the muscles are ischaemic. This significant iatrogenic muscle and soft tissue injury is associated with increased postoperative pain, lengthened recovery time, and impaired spinal function. The significant degree of the perioperative pain necessitates the use of more pain medication with their inherent side effects and also delays return to normal daily activities. Moreover, the dissection of the paraspinal muscles from their normal anatomic points of attachment results in healing by scarring of these muscles. The various layers of the individual muscles scar to one another losing their independent function. In addition, the extensive dissection results in the loss of innervation of the muscles with subsequent wasting away. It has been shown that the strength and density of the lumbar muscles are reduced after open lumbar surgery resulting in a permanent weakness of the back muscles. This weakness itself may be symptomatic (as a back fatigue-type pain) and/or limit the patient’s function - particularly in those who perform physical work. Therefore the most obvious benefit of a minimally invasive approach to the spine is that it greatly reduces the damage to the paraspinal musculature and surrounding ligaments and this translates to less postoperative pain, shorter hospital stay, less blood loss, and faster recovery from the surgical procedure. The smaller incisions used for minimally invasive procedures heal with minimal scarring and therefore are appealing to many patients.
With a small skin incision, the exposure of the spine is limited, hence the skin incision must be placed directly over the pathologic segment. Therefore pre-operative imaging is very important as they help the surgeon plan the approach. Fluoroscopy and/or other image guidance technology are used to assist in localising the segment to be operated and in positioning of the instruments. During the surgery, the surgeon
uses high-powered illumination and magnification to adequately visualise the spinal anatomy.
Minimally invasive techniques are employed in many areas of surgery and is increasingly being used in spine surgery. At Singapore General Hospital, we have been performing minimally invasive posterior lumbar spine surgery since 2004. Conditions for which minimally invasive spine surgery (minimally invasive spine surgery) can be used include prolapsed intervertebral disc, spinal stenosis and spondylolisthesis.
With the minimally invasive technique, access to the spine can be achieved through a working channel of only 14-26mm in diameter. The traditional retractor used in open surgery is replaced by a tubular retractor (Fig 1). This employs a muscle dilation technique by using a series of dilators to sequentially dilate the muscle to open a space between muscle fascicles to expose the spine. Using the tubular retractor, procedures such as
lumbar decompression,
discectomy (Fig. 2) and
interbody graft placement (Fig. 3) can be performed. In patients whose surgery requires pedicle screws and rods for fusion, the screws are inserted percutaneously (Fig. 4). Under fluoroscopic guidance, a needle is inserted into the pedicle percutaneously. A K-wire is then passed through the needle to serve as a guide for the screw placement. Using cannulated instruments, the pedicle screw is passed over the K-wire into the pedicle.
The indications for minimally invasive spine surgery include spinal stenosis, prolapsed herniated disc and spondylolisthesis. Relative contraindications include revision surgery due to extensive scarring and morbid obesity as this increases the working distance from the skin to the spine which makes the surgery technically more difficult.
There has been several studies conducted in the West which showed good clinical outcomes with minimally invasive spine surgery. Post-operative MRIs showed muscle trauma was less and resolved faster in patients with minimally invasive spine surgery when compared to those with open surgery. Studies also have shown that patients with minimally invasive spine surgery have less systemic inflammatory response as evidenced by a lower value of post-operative inflammatory markers. In SGH, so far we have performed 108
spinal fusions and 249 decompression/
discectomies using the minimally invasive technique.
We have compared our patients who had minimally invasive spine surgery with those with open lumbar surgery and found that the minimally invasive spine surgery group had a faster recovery in terms of earlier ambulation, shorter hospital stay and earlier return to work and full function. They also had less blood loss, less post-operative pain and less analgesic use.
The minimally invasive spine surgery group also had significant improvement in back pain and leg symptoms, as well as, “Quality of Life” scores after surgery.
Costs incurred by the patient undergoing minimally invasive spine surgery may be decreased by several factors. A shorter hospital stay results in a smaller hospital bill and less risk of catching a nosocomial infection. With a faster recovery, there is less need of inpatient rehabilitation. Less postoperative pain also translates into reduced cost of post-operative analgesia.
The complications of minimally invasive spine surgery are similar to those of open surgery. These are bleeding, infection, nerve root injury, cerebrospinal fluid leak, deep vein thrombosis, pseudoarthrosis (in fusion cases) and implant failure (if inserted). All patients are carefully counselled about these potential risks.
In conclusion, minimally invasive spine surgery is a safe and efficacious technique. It is associated with smaller wounds, less tissue trauma and faster recovery. SGH has performed various minimally invasive spine procedures with good clinical outcomes and patients have shown improvement in their symptoms and quality of life.
Appointments with the SGH spine surgeons can be made by calling 6321 4377.