The past decade has witnessed a virtual renaissance in spinal surgery. Both orthopaedic and neurological surgeons specialising in this field have seen a proliferation of new techniques and technologies for improving patient care and outcomes when a surgical correction is indicated
Perhaps nowhere has this been more obvious than in the field of minimally invasive surgery (MIS). While previous attempts at achieving minimally invasive decompression or fusion were feasible, they were never widely adopted. Thus, thoracoscopic techniques, muscles splitting approaches (such as the Wiltse technique), and endoscopic methods were only adopted by a minority of surgeons willing to undergo a significant learning curve.
The introduction of tubular dilator retractors was an integral catalyst in this latest wave of MIS techniques. However, the coincident availability of alternate surgical approaches, neuromonitoring, image guidance, and fixation implants, coupled with an increasing amount of surgeon education in MIS, has resulted in the use of MIS surgery for over 10% of spinal fusions.
Putative benefits of minimally invasive surgery
Because MIS surgery focuses on smaller incisions, more targeted localisation to the area of interest, and reduced muscle trauma, MIS advocates believe that this approach offers certain advantages. The minimally invasive approach for spinal surgery has the potential to reduce some of the peri-operative morbidity associated with traditional open spinal surgeries, including: 1) reduced postoperative pain and narcotic consumption, 2) decreased intra-operative blood loss, 3) more rapid mobilisation, 4) shorter hospital stay, 5) reduced cost, 6) lower infection rates, and ultimately 7) improved outcomes. While, these benefits have clearly been realised in other surgical arenas, such as endovascular surgery, arthroscopic joint surgery, and bariatric surgery, the verdict has been less clear in the spine. Several controlled studies have already demonstrated that for small surgeries, such as microdiscectomy, an MIS approach may not be worthwhile. However, this is in the setting where the “open” or traditional surgery is already minimally traumatic. For more complex procedures such as spinal fusions, the myriad of surgical procedures, complexities in patient selection, and lack of controlled studies has led to significant debate over the benefits of MIS in the spine.
MIS in the “compromised spine patient”
Degenerative thoracolumbar spinal deformities can result in crippling pain in the elderly population. Frequently, these patients will be disabled by the loss of normal mobility due to axial back pain or radicular symptoms. In addition, abnormal postures result in easy fatigability and in severe cases can predispose the patient to falls and accidents from alterations in altitudinal vision and weight distribution. The resultant reduced mobility and pain not only affects the patient’s lifestyle, but can ultimately compromise his or her cardiopulmonary status and overall medical health due to deconditioning from reduced mobility. However, these elderly patients frequently find that, despite a straightforward biomechanical aetiology for their affliction, surgical treatment will not be offered due to advanced age, anticipated life expectancy, co-morbid medical conditions, and osteoporosis.
The surgical enterprise of coronal and/or sagittal plane correction in adults is a significant undertaking for both the physician and patient. While the final results are frequently quite rewarding, complications arising from the surgical procedure can be daunting. Unlike the paediatric deformity population, these patients are frequently severely deconditioned, with rigid spines and poor bone density. The combination of the length of the anaesthetic treatment, number of levels to be fused, surgical blood loss, and prolonged recovery result in a high peri-operative morbidity rate. Indeed, the overall mortality from spinal surgery doubles between the ages of 65–69 and over 80 years of age.
Indeed, the major morbidity from surgical treatment of degenerative scoliosis has been reported to be as high as 28% to 86% in experienced hands, with increasing age being associated with longer hospitalisations and complications. Solutions to the problems encountered with prolonged surgery, anaesthesia, and blood loss include procedural staging, autologously donated blood, and the employment of multiple surgical teams to minimise surgeon fatigue. Measures to prevent the untoward post-operative sequelae include rapid mobilisation, selective use of anticoagulation, maintenance of near-normal haemodynamic parameters, and antibiotic washouts during surgery to prevent infection.
Nevertheless, the morbidity of open spinal surgery to correct their deformities prevents many of these patients from undergoing a corrective operation. This has been related largely to the soft tissue exposure necessary for traditional open long-segment spinal surgery. Sub-periosteal stripping of multiple spinal segments creates ongoing blood loss, is time consuming, and devitalises tissues. This introduces the risk of haemodynamic instability, the need for large volume intravenous infusions, and blood transfusions, all of which increase the likelihood of intraoperative cardiac events, pulmonary sequelae, and renal malfunction. Following surgery, the soft tissue destruction needed for spinal exposure results in prolonged immobility due to pain, increasing the risk of pneumonia, abdominal ileus, and deep venous thrombosis. In addition, the large operative surfaces which are frequently devitalised from retraction and electrocautery predispose the patient to a deep wound infection, which can result in sepsis, returns to the operating room, and prolonged immobility.
Minimally invasive lumbar surgery in the elderly
Minimally invasive non-fusion lumbar spinal surgeries have been studied by Rosen et al. In their clinical series 50 patients over the age of 75 years underwent microendoscopic surgery for bilateral spinal canal decompression. While the study had no control arm, the authors were able to demonstrate that the procedure could be performed efficiently and safely. Their mean length of hospitalisation was 29 hours, and 22 minor complications occurred in the 50 patients (44%), including five cases of delirium, one pneumonia, and one case of atrial fibrillation, highlighting the substantial degree of medical co-morbidities and the challenges encountered in treating this fragile patient population.
While minimally invasive multi-segmental fixation techniques for degenerative scoliosis have only recently been described in the peer-reviewed literature, short-segment (one- and two-level) percutaneous transpedicular screw-rod fixation systems have been commercially available for over five years, with numerous reports attesting to their safety and efficacy.
The development of instruments and implants for longer-segment fixation, fusion and segmental manipulation are thus a natural extension of the tools and techniques currently available to the modern spinal surgeon. While these fixation techniques are still quite limited in their ability to correct spinal deformities, they can be combined with anterolateral or posterior osteotomy procedures, which can also be performed in a minimally invasive fashion, but require supplemental posterior fixation.
Michael Y Wang is associate professor, Departments of Neurological Surgery and Rehabilitation Medicine, University of Miami Miller School of Medicine,