Many reports have described controversies about treatment for thoracolumbar and lumbar fractures, due to the high frequency of these injuries and the differences in the severity of instability [1,2,21
]. Three approaches are available for the surgical treatment of thoracic and lumbar burst fracture, using anterior, posterior, or combined methods. No ideal procedure exists, due to the wide variety of clinical and radiological features present in indivisual cases [1,2,21,22
In cases of severely unstable lumbar burst fractures, anterior column reconstruction and decompression are necessary. To reconstruct the anterior column in lumbar spine, resection of the affected vertebra and strut bone graft or replacement with a cage can be managed from an anterior approach. However, anterior instrumentation for L5 or S1 are restricted by anatomical factors such as the presence of major vessels, the iliopsoas muscles, and iliac crests, so combined posterior instrumentation is definitely needed in cases of L4, 5 fractures [7,8,13
Recently, single-stage posterior corpectomy and replacement with various types of cage followed by pedicle screw instrumentation for thoracolumbar burst fractures have been reported [18-20
]. Sasani and Ozer [20
] showed excellent outcomes for corpectomy and replacement with an expandable cage using a posterior approach for the treatment of T8 to L4 burst fracture in non-elderly patients (average age, 40.3 years). They proposed that a single-stage posterior approach may be preferable to the combined anterior-posterior approach and that this procedure is associated with fewer complications than the traditional combined approach. Haiyun et al. [19
] reported a similar three-column reconstruction of thoracolumbar fracture above L2 through a single posterior approach with mesh cages and pedicle screws. They noted that use of an adequate shorter nonexpandable cage can provide sufficient biomechanical stability and has benefits in the treatment of thoracolumbar burst fractures. Using an expandable cage allows easier restoration of body height than use of a nonexpandable cage or strut bone. However, shortening reconstruction for unstable burst fracture with a shorter cage appears to offer several advantages: 1) acute spinal column shortening within the safe range increases spinal cord blood flow, which is important for recovery of spinal cord function [23
], 2) biomechanical comparisons among different cages have shown no significant differences [24
], and 3) resected local bone (affected vertebra, lamina, articular and spinal processes) can maintain bone-grafting inside and around the cage with no complications at the donor site.
We applied this surgical technique for not only the thoracolumbar junction, but also the mid to low lumbar level. The biggest advantage of shortening reconstruction with a titanium mesh cage from a solely posterior approach is that circumferential decompression and fixation containing anterior column reconstruction for mid to low lumbar segments can be introduced as conveniently as for thoracolumbar lesion without anatomical restrictions on instrumentation. Inserting a 22-mm-diameter cage between the upper and lower nerve roots without sacrificing a root may appear technically difficult, but no complications involving cage insertion, such as neural injury or dural tear, were observed in our study. We found that if the surgeon's thumb (with double gloves) can be inserted into the resected vertebral cavity through the inter-nerve space, the cage can be easily introduced without dural or nerve root injuries.
Another difficulty in reconstruction of the mid to low lumbar region is the maintenance of lordosis. The general alignment of the straight thoracolumbar junction spreads the axial load uniformly on the cage, but an unbalanced axial load and shearing force may appear in the lumbar region. In our cases involving mid to low lumbar lesions, patients were elderly at the time of surgery and BMD was relatively low. Although clinical results in those patients with mid to lower lumbar lesions were comparable with those with thoracolumbar lesions, the radiologic results of the former were poorer than the latter because three of four patients in the former group experienced subsidence of the cage and correction loss of more than 10°. These findings suggest that especially in mid to low lumbar burst fractures with low BMD, further modification is essential when using this surgical procedure. Because a single 22 mm cage may not be enough to work as an anterior support without postoperative sinking into the adjacent vertebral bodies in the mid or lower lumbar levels, but inserting cages larger than 22 mm through the nerve roots plexus without injuring the nerve roots seems to be difficult, use of multiple cages may be a solution. Positioning of the cage on the peripheral rim of the vertebral endplate may be another solution. Other types of cages may be required to achieve a wider contact area with the endplates to obtain better stability [25
]. Furthermore, multiple sublaminar anchoring with polyethylene tapes may help to stabilize the spinal column.
The posterior surgery techniques in this paper offer considerable advantages, such as a familiar approach for spine surgeons, fewer anatomical limitations due to the presence of major vessels, and circumferential decompression followed by pedicle screwing reconstruction with a reduced risk of complication compared to anterior or combined approaches. This procedure can be applied to all types of lumbar burst fractures, however, the indication should be limited to massive destructed fractures with more than 7-points of LSS. For burst fractures with fewer than 6-points of LSS, less invasive procedures, such as conventional posterolateral fusion, vertebroplasty, or shortening osteotomy with posterior decompression and instrumentation should be selected.