Adult degenerative lumbar scoliosis is a 3-dimensional deformity defined as a coronal Cobb angle of greater than 10 °. The reported incidence of scoliosis in adulthood has varied from 1.5–29.4%[7–10]. At present, the pathogenesis of degenerative lumbar scoliosis is not clear. Decreased bone density was previously associated with the etiopathogenesis of degenerative scoliosis. The pathophysiology of degenerative scoliosis involves the asymmetric degeneration of the intervertebral disks and the facet joints at different levels, leading to unequal loading of the spinal column[12, 13]. At a biological level, osteophytes are formed at the facet joint and vertebral endplates, further narrowing the spinal canal, and instability of the spinal column ensues secondary to the destruction of the facet joints and intervertebral disks. The spinal curvature seen in degenerative scoliosis tends to progress at a rate of 1° to 6° per year, with an average increase of 3° per year. Clinical manifestations of DLS include low back pain, neurogenic claudication and radiological pain of lower limbs. Radioleptic pain and neurogenic claudication of the lower limbs may result from the nerve root tension on the convex side or nerve root compression on the concave side. At present, the surgical methods for the treatment of DLS include decompression alone; decompression and posterior spinal fusion with instrumentation; decompression, anterior spinal fusion, and posterior spinal fusion with instrumentation; fusion and instrumentation to the sacrum and pelvis. The methods of minimally invasive surgery include Mis-T/PLIF, X/DLIF, and OLIF. At present, there is a great controversy over whether to choose traditional open surgery or minimally invasive surgery. For different patients, especially elderly patients with internal medical diseases, the risk of surgery is high, which makes it difficult for clinicians to choose between the minimum trauma and the best clinical effect, so the operation method should vary with each individual. The selection of fixed segments is also controversial. However, the general principle of treatment is to achieve a balance of the sagittal and coronal positions of the spine, maintain the vertebral sequence, and reconstruct the lumbar lordosis.
In this study, OLIF technique and PILF technique were used to treat DLS. We find that the OLIF group had less intraoperative blood loss and shorter operative time, bed rest duration, and hospital stay than the PLIF group. The OLIF group had shorter incision length (6.84 ± 1.71 cm) than the PLIF group(14.05 ± 2.09 cm). The average bed rest duration in the OLIF group (2.89 ± 0.81 d) was shorter in PLIF group (5.10 ± 1.18 d). The VAS score for back pain and ODI in the OLIF group were significantly improved than that in the PLIF group at 7 days and 3 months after surgery. All this was reasonable because that in OLIF, the paravertebral muscles were not dissected, and the facet joints, interspinous and superior spinous ligments were not removed.
In terms of radiographic outcomes, the Lumbar scoliosis Cobb Angle, SVA, CVA, LL, PT, SS, and DH for both groups shows significant improvement from preoperative(P༜0.05). The OLIF group achieved the balance of bilateral paravertebral muscle strength and reconstructed the intervertebral stable system by implanting larger and wider fusion devices, while the PLIF group was improved by pedicle fixation system. The OLIF group showed higher DH and greater LL than the PLIF group postoperatively. This is reasonable because we inserted a relatively larger and wider cage into the target disc in OLIF. The larger and wider cage has a 4°-8° lumbar lordosis itself, which makes higher DH and greater LL than the PLIF group. The Cobb angle was more decreased than the PLIF group at any time points after surgy. This is reasonable because the large implanted fusion device can reach the cortical area of the contralateral annulus fibrosus, which makes the upper and lower margins of the adjacent vertebral segments of scoliosis restore to be parallel.
We found that one cage was transverse shifting to the left in 1 patient who underwent a 6-month postoperative examination. Another patient was found one cage subsidence, we considered that it was due to suffer from osteoporosis postoperatively or injury the endplate during the surgery. But there was no clinical symptoms in the two patients, we recommend wearing a waist support and regular follow-up. The cage was no further displacement/subsidence at last follow-up. All the surgical segments were merged at the last follow-up. To avoid the subsidence and displacement of the fusion cage after OLIF, it is recommended preoperatively to evaluate for osteoporosis, which may cause subsidence and displacement of the cage and supply postoperative calcium for patients with osteoporosis. It is also recommended to avoid to excessively deal with the endplate during the operation, and strictly wear a waist support for 3 months after the operation to prohibit lumbar rotation and strenuous exercise. At the last follow-up, the OLIF group had normal lumbar mobility, while the PLIF group had 8 cases of lumbar stiffness, which may be related to the formation of pseudarthrosis and fixation of the lower end to S1. In this study, the follow-up time was short, and no adjacent segment degenerative disease was found. Shinya Okuda studied 1000 cases with PLIF and found that the overall ASD rate was 9.0%, and the average ASD period was 4.7 years after primary surgery, as for ASD by fusion length, age, and preoperative pathologies, ASD incidence was increased by fusion length, while the time period to ASD was significantly shorter in elderly patients and those with degenerative lumbar scoliosis. Kyu-Jung Cho reported that the fusion level at L1 or L2 showed the highest incidence of the proximal adjacent segment, whereas fusion to T10 or above showed the least incidence of it. Suk et al.[21, 20] advocated that fusion to T10 or more cephalad might be beneficial for preventing adjacent segment disease. But fusion to T11 or T12 was found to be acceptable as upper vertebra for adult degenerative scoliosis since there was no significant difference in the rate of the proximal adjacent segment between fusion to T10 and fusion to T11 or T12. Bridwell KH reported that decompensation in the coronal and sagittal planes, in large curves, often requires a fusion to the sacrum. Islam found that a marked decrease in pseudoarthrosis rate on extensions of fusions to the sacrum when a combination of anterior fusion at L5–S1, S1 screws and iliac fixation was used. With an average follow-up of 41 months, the pseudoarthrosis rate with S1 screws only was reported to be 53%, whereas the rate for iliac fixation only and S1 screws plus iliac fixation were 42% and 21%, respectively.
Of course, there are several limitations in this study. Firstly, this is a retrospective, small-sized study. Secondly, the follow-up period of cases is slightly short. It needs to make further follow-up to compare and analyse the long-term efficacy of both surgical methods.