Ideally, minimally invasive surgery (MIS) allows less extensive manipulation of surrounding tissues than a conventional open procedure while accomplishing the same goals and objectives at the target structure. Long-term follow-up combined with appropriate outcome measures are necessary to prove the safety and effectiveness of MIS. For MIS procedures to be widely adopted, they must have an acceptable learning curve. Special skills are needed and are beyond those of traditional open surgery, By definition, as compared with conventional open surgeries, minimally invasive procedures typically involve smaller incisions and less extensive surgical manipulation of the tissues that surround the target structure. Ideally, once the target structure has been reached, the minimally invasive procedure should accomplish the same goals and objectives as its open surgical counterpart. Thus, although minimally invasive surgeries are aimed at reducing the morbidity associated with open surgical approaches, they should not hinder the surgeon’s ability to perform a successful operation. In other words, minimal invasion should not equate to minimally effective.
One of the difficulties in defining success for MIS is the lack of universally accepted outcome measures. This may be particularly difficult with minimally invasive procedures, where advantages may be seen early in the patient’s postoperative course, before many outcome measures for spinal surgery are traditionally recorded. In order to validate MIS techniques, proponents must prove the safety and effectiveness of these approaches. These procedures should not be performed merely because they represent advances in technology. Further study, coupled with long-term follow-up may validate these techniques, as has been seen with laparoscopic cholecystectomy. The opposite may also occur, as illustrated by the fact that laparoscopic approaches to lumbar fusion have not proven to offer advantages over more conventional mini-open approaches.
Certainly, the purported advantages of minimally invasive spinal surgery over traditional approaches have not been proven. In the absence of this data, these techniques should not be driven by patient demand and marketing. Early postoperative outcomes that should be quantified are blood loss, operative time, postoperative pain, length of hospital stay, and costs. The intermediate outcome data should include factors such as return to work and activity (activities of daily living, recreation, etc.), pain, and function. Long-term measures should include such factors as pain, function, and quality of life.
With any new procedure, there is a learning curve. For MIS to gain wide acceptance, this learning curve must be reasonable. The ability to master a new technique depends not only on its technical difficulty, but also on the frequency with which it is performed. MIS procedures require special skills beyond those required in traditional open surgery, and it is uncertain how difficult they will be to teach and master.
While the techniques discussed in this review are intriguing, none yet fully meet the criteria outlined above. We look forward to long-term studies with rigorous outcome data to validate these innovative approaches to spinal surgery.