ALIF is a valuable technique with numerous advantages for spinal surgery. ALIF allows the expansion of disc space and foraminal height, as well as restoration of lumbar lordosis and spinal alignment without compromising posterior tension bands.
ALIF is the best method to restore foraminal height, segmental lordosis, and disc space height and has potentially improved sagittal balance and leads to better long-term outcomes compared to transforaminal lumbar interbody fusion8)
. In certain situations the canal and neural foramen may be indirectly decompressed and thus avoiding possible injury to the nervous system.
By accessing the lumbar spine through an anterior approach, we were able to achieve excellent anterior column exposure, with less muscular retraction, blood loss, and a shortened operative time. The complete removal of intervertebral discs allows for greater retraction of disc spaces, allowing for the insertion of large interbody devices for deformity correction.
Despite these advantages, some disadvantages to the procedure do exist. According to McDonnell et al.11)
, 11% of patients who underwent ALIF experienced major complications while 24% experienced minor complications. These unique complications are not seen in conventional surgery and include injuries to abdominal wall structures, great vessels, ureters, and numerous nerve plexuses.
The most harmful complication is vascular injury with reported frequencies ranging from 1% to 24%7)
. Specifically, the most common type of vascular injury is venous laceration the iliac vein, inferior vena cava and iliolumbar vein from vessel retraction. Arterial injuries occur less frequently than venous injuries due to their greater elasticity and mobility. Injuries to the left iliac artery and aorta injury are rare, occurring in less than 1% of cases10)
. There is also a risk of retrograde ejaculation from superior hypogastric plexus injury with a reported incidence occurring in 5.9-8% of cases7,11)
. Finally, lymphocoele formation is an additional serious but exceedingly rare complication19)
While complications of AILF may be more numerous when compared with the posterior spine surgical procedures recent efforts by many surgeons have been aimed at avoiding complications and have yielded many articles regarding safer techniques and have revealed intra-abdominal improved surgical approach8,9,24)
. Consequently, ALIF is a less demanding and dangerous procedure.
Many authors have reported on the disadvantages of disc space height reduction after ALIF and suggest subsidence will adversely affect foramen size and mechanical deformity correction3,6,18)
. Decreased disc space height after ALIF may lead to mechanical stresses such as increased intradisc pressure, intersegmental rotation, and contact force of facet joints.
Maintaining disc space height and segmental lordosis is important for preventing subsidence and adjacent segment degeneration23)
. In the present study, we have been applying a cage higher than 16 mm for all patients. Considering that we were able to maintain disc space height we possibly prevented subsidence. Moreover, obtaining a negative sagittal vertical axis and bending the spine posteriorly reduced anterior column stress force and provided a biomechanical load sharing effect. In this study, subsidence rate was 22.7% and the final follow-up lumbar lordosis was relatively maintained to approximately PI. Clinical studies have reported a wide range of subsidence occurrence, some studies of ALIF using a stand alone cage revealed subsidence rates of more than 40%4,21)
while other studies have reported posterior and transforaminal lumbar fusion subsidence rates of 26.5%5)
. Compared to previous reports, our procedure has the potential to reduce the rate of subsidence.
CT scan is more favorable tool to reduce inter-examiner bias for measuring the disc space height than plain radiograph. Because the CT scan was not checked routinely for all the patients, we only measured the subsidence by using the plain radiograph. Inter-observer reliability analysis for measurement of disc height by using plain radiograph demonstrated ICCs of 0.78 (good reliability). Further comparative study of subsidence rate by using CT scan in our center may suggest more reliable result and need to be done.
Our operation procedure had two stages in all patients. The first stage was a posterior facet release and pedicle screw fixation; the second stage was an anterior approach for interbody fusion and a posterior approach for achieving sagittal and coronal balance by rod insertion. One week after the first stage operation, all patients underwent a second stage operation. We named this method a posterior-anteroposterior (P-AP) approach. Single stage operations of the same procedure require a longer operating time and may have more blood loss at one time. Mean operation time of the first stage and second stage was approximately 2.5 hours and 4 hours, respectively. In our center, mean operation time of a single stage operation was approximately 7 hours. Although the total time required for a two stage operation was similar to a single operation, each time interval was shorter. Prolonged surgical times may increase risks of surgical site infection16)
. Therefore we suppose that two stage operation (P-AP approach) may reduce the risk of surgical site infection compared to single stage operations. In our procedure, the mean estimated blood loss for the first stage of the operation was approximately 800 mL and 500 mL for the second operation. Recently reported blood loss over 1 L is now considered to be a significant independent risk factor for perioperative infection16)
. In our cases, the intraoperative blood losses were less than 1 L and with no surgical site infections. However, this observation was not part of our study and we do not have statistics to confirm our observations. Additional analyses are needed to define the advances of the P-AP approach.
There is another advantage of a P-AP procedure. We performed a first stage operation to remove posterior spinal structures such as facets, the ligament flavum and ligaments surrounding the facet followed by a rest period of one week. This period provided more release of posterior structures and spontaneously corrected the kyphoscoliosis. Moreover, the release of the posterior structures gave us an opportunity to raise the cage height in the anterior disc space.
In some cases involving L5 and S1, we used an anchoring, cancellous screw in the anterior vertebral body because L5-S1 is the junction of the lumbar and sacral spine segments and has a larger slipping force compared to other spinal segments ().
During this study we found that using a higher cage and inserting the cage at lower levels allowed for the achievement of optimal sagittal balance which can be explained and visualized by simple spine modes ().
Fig. 4 Lower level and higher cage ALIF allows for a negative value of the SVA. Solid circle refers to the more posterior sagittal axis. A : Shows models inserted at the same angle and cage height at the upper and lower levels. B : Shows that a cage inserted (more ...)