James D. Schwender, Kevin T. Foley, and Langston T. Holly

Description

Minimally invasive techniques have revolutionized the management of pathologic conditions in various surgical disciplines. The objective is to reduce the approach-related morbidity and at the same time allow the surgery to be performed in an effective and safe manner. The systems currently available consist of a series of concentric dilators and thin-walled tubular retractors of variable length. The tube circumferentially defines a surgical corridor through the erector spinae muscles.

Expectations

This technique is appropriate for the surgical treatment of lumbar disk herniation, spinal stenosis, or in cases that require stabilization. The current retractor systems are designed to allow exposure of one and two lumbar levels. In the case of stenosis, ipsilateral and contralateral decompression of central, subarticular, and foraminal stenosis is possible through a single paramedian incision.

Published outcomes for decompression surgery compare favorably to the traditional midline open technique. Same-day surgery has become the rule. Concerning one- and two-level fusions, in experienced hands, the blood loss and hospitalization are typically reduced by 50%. Outcomes again compare favorably to traditional techniques. Operative times and complication rates for both decompression and fusions are similar compared with open techniques.

Indications

The indications are the same as the surgeon would use for tradition open procedures at one or two levels in the lumbar spine for either decompression or fusion.

Contraindications

Relative contraindications currently include the following:

• More than two-level pathology
  
• Requirement to correct kyphosis. It is possible to correct 3 to 5 degrees of kyphosis with the transforaminal lumbar interbody fusion (TLIF) procedure; if more is required, an anterior approach continues to provide better lordosis.
  
• Obesity (body mass index >40). Working within a tubular retractor greater than 8 cm significantly reduces the degrees of freedom of the instruments, particularly if performing interbody fusions.
  
• Previous surgery. This approach appears to be easier because less scar tissue is encountered. Skin-related complications are rare, even if a previous midline incision scar exists.

Special Considerations

Knowledge of three-dimensional spinal anatomy is fundamental in the mastery of less invasive techniques. Not infrequently, the surgeon relies on live or virtual fluoroscopic images displayed on a monitor or threedimensional images from an image guidance system for anatomic orientation. This can be challenging for surgeons who have not had significant experience using two-dimensional images to determine their three-dimensional surgical position.

Tips, Pearls, and Lessons Learned

Patient positioning and good intraoperative imaging are essential. It is also important to choose the correct size retractor for the given procedure. For decompression, a smaller diameter retractor is required to allow placement medial to the facet joint. This minimizes the amount of soft tissue creep into the wound. The same holds true for fusions. In this case, a larger diameter retractor is docked over the facet joint to be fused again to prevent muscle creep. This allows for identification of the anatomy for decompression and fusion. Once the retractor is in the correct position, resist the temptation of moving the retractor often, which leads to creep of the muscle into the wound.

The treatment of an incidental durotomy should proceed in a similar fashion as if this complication was encountered in an open procedure. A primary suture repair is preferable if it is possible. If a watertight repair cannot be achieved, TisseelTM (Baxter, Deerfield, IL), DuraGenTM (Integra Life Sciences Corp., Plainsboro, NJ), or other dural repair products are useful. In our experience, the minimal dead-space created by the less invasive procedures seems to limit the formation of a symptomatic pseudomeningocele.

Key Procedural Steps

1. Patient selection
   
2. Intraoperative positioning of the patient in the prone position
   
3. Identification on orthogonal imaging of correct level of surgery
   
4. Placement of skin incision(s)
   
5. Correct diameter and depth of tubular retractor
   
6. Minimize movement of the retractor once in position to prevent tissue creep
   
7. Address pathology to avoid failure of execution