Minimally invasive lateral approach for adult degenerative scoliosis: lessons learned
Authors: Deukmedjian Armen R. , Ahmadian Amir , Bach Konrad , Zouzias Alexandros , Uribe Juan S. 
Published: August 2013

Object
Lateral minimally invasive thoracolumbar instrumentation techniques are playing an increasing role in the treatment of adult degenerative scoliosis. However, there is a paucity of data in determining the ideal candidate for a lateral versus a traditional approach, and versus a hybrid construct. The objective of this study is to present a method for utilizing the lateral minimally invasive surgery (MIS) approach for adult spinal deformity, provide clinical outcomes to validate our experience, and determine the limitations of lateral MIS for adult degenerative scoliosis correction.

Methods
Radiographic and clinical data were collected for patients who underwent surgical correction of adult degenerative scoliosis between 2007 and 2012. Patients were retrospectively classified by degree of deformity based on coronal Cobb angle, central sacral vertical line (CSVL), pelvic incidence, lumbar lordosis (LL), sagittal vertical axis (SVA), pelvic tilt (PT), presence of comorbidities, bone quality, and curve flexibility. Patients were placed into 1 of 3 groups according to the severity of deformity: “green” (mild), “yellow” (moderate), and “red” (severe). Clinical outcomes were determined by a visual analog scale (VAS) and the Oswestry Disability Index (ODI).

Results
Of 256 patients with adult degenerative scoliosis, 174 underwent a variant of the lateral approach. Of these 174 patients, 27 fit the strict inclusion/exclusion criteria (n = 9 in each of the 3 groups). Surgery in 17 patients was dictated by their category, and 10 were treated with surgery outside of their classification. The average age was 61 years old and the mean follow-up duration was 17 months. The green and yellow groups experienced a reduction in coronal Cobb angle (12° and 11°, respectively), and slight changes in CSVL, SVA, and PT, and LL. In the green group, the VAS and ODI improved by 35 and 17 points, respectively, while in the yellow group they improved by 36 and 33 points, respectively. The red subgroup showed a 22° decrease in coronal Cobb angle, 15° increase in LL, and slight changes in PT and SVA. Three patients placed in the yellow subgroup had “green” surgery, and experienced a coronal Cobb angle and LL decrease by 17° and 10°, respectively, and an SVA and PT increase by 1.3 cm and 5°, respectively. Seven patients placed in the red group who underwent “yellow” or “green” surgery had a reduction in coronal Cobb angle of 16°, CSVL of 0.1 cm, SVA of 2.8 cm, PT of 4°, VAS of 28 points, and ODI of 12 points; lumbar lordosis increased by 15°. Perioperative complications included 1 wound infection, transient postoperative thigh numbness in 2 cases, and transient groin pain in 1 patient.

Conclusions
Careful patient selection is important for the application of lateral minimally invasive techniques for adult degenerative scoliosis. Isolated lateral interbody fusion with or without instrumentation is suitable for patients with preserved spinopelvic harmony. Moderate sagittal deformity (compensated with pelvic retroversion) may be addressed with advanced derivatives of the lateral approach, such as releasing the anterior longitudinal ligament. For patients with severe deformity, the lateral approach may be used for anterior column support and to augment arthrodesis.