Reduction of spondylolisthesis and restoration of lumbar lordosis after anterior lumbar interbody fusion (ALIF)

We present the results of 96 patients who underwent ALIF for degenerative spine pathologies where spondylolisthesis was present. In most cases, the procedure was combined with additional dorsal instrumentation using pedicle screws and rods.

Most patients (n = 94, 97.92%) were not rated as having high-grade spondylolisthesis (Meyerding III or IV). This finding is in accordance with the results of other studies, as all our patients were adults with degenerative diseases of the spine, which are typically associated with lower grades of spondylolisthesis. Viglione et al. (2017) state that adult low-grade spondylolisthesis and adolescent high-grade spondylolisthesis should be clearly distinguished, suggesting different pathological entities in these age groups [8]. High-grade spondylolisthesis typically develops in adolescents with isthmic spondylolisthesis when the posterior arch is not completely ossified and the intervertebral disc is very elastic. Low-grade spondylolisthesis is more common in older patients when the intervertebral disc is less elastic due to degenerative changes [8‐10].

In our sample, median spondylolisthesis was significantly reduced postoperatively, by 3.00 mm (IQR: 4.08), along with a reduction of the relative subluxation from 21.63% (IQR: 17.10) to 13.71% (IQR: 11.61). This is a 33.71% reduction from the preoperative value. Our findings are similar to the reductions reported in the literature. In 2020, Kalani et al. reported a mean reduction of spondylolisthesis by 58.7% in combined procedures with anterior fusion and dorsal instrumentation [11]. Rao et al. (2015) detected a reduction from 14.8% in preoperative spondylolisthesis, measured as the relative subluxation, to 9.4% at the latest follow-up [2]. Tu et al. (2021) and Riouallon et al. (2013) report a mean spondylolisthesis reduction of 30% [3, 4]. In a meta-analysis of 2019, Cho et al. [12] compared anterior and posterior approaches for spondylolisthesis treatment. Only three out of eight studies reported the degree of spondylolisthesis [13‐15] after anterior fusion procedures. In these studies, mean preoperative slippage was 19.8% (Meyerding grade I), and this was postoperatively reduced to a mean slippage of 7.8% (12% points difference). With a mean reduction of 8%, the achieved slippage reduction was similar in our sample. Comparing our sample with posterior-only techniques, Moreau et al. (2016) report a decrease of spondylolisthesis by 50% using a posterior-only fusion technique for L5/S1 spondylolisthesis cases and therefore a similar reduction rate of spondylolisthesis [16].

Most studies investigating the reduction of spondylolisthesis after ALIF have relatively low sample size numbers, with case numbers between 5 and 65 participants [3‐5, 11, 13, 14, 17] and most studies having fewer than 30 participants [4, 5, 11, 14, 17]. With 96 cases, we present, to our knowledge, one of the most extensive single-center studies investigating this topic.

Additional dorsal instrumentation did not significantly change the lordosis values’ postoperative outcome or the amount of spondylolisthesis reduction. As in most cases of spondylolisthesis, dorsal instrumentation is recommended for reasons of stability and good results concerning bony fusion. Studies comparing standalone procedures with dorsal instrumentation are scarce, and to our knowledge, we present one of the first studies to show that the anterior procedure is the main contributor to the improvement of spondylolisthesis and lordosis.

Knowledge and research on the sagittal alignment of the spine have multiplied over the last few years. Sagittal alignment and LL are of significant importance when treating patients with spondylolisthesis [12], as sagittal malalignment and loss of LL can lead to chronic lower back pain [18]. Cho et al. (2019) found in their meta-analysis that LL and SL were significantly higher after anterior approach with dorsal instrumentation procedures compared to posterior fusion techniques with dorsal instrumentation [12]. In our study, median lordosis increased significantly, with a median increase in LL of 4.20° (IQR: 10.25), in SL median of 9.05° (IQR: 5.48), and in L4/S1 lordosis median of 6.00° (IQR: 6.40). Again, these findings are similar to those reported in the literature. Moreau et al. (2016) found an LL increase of 7° [16] and Caprariu et al. (2021) an increase of 8° [16, 17]. Kalani et al. detected increases in mean SL, defined as L4–S1 lordosis, and overall (L1–S1) LL after ALIF with dorsal instrumentation of 23.6% and 16.6%, respectively [11].

The finding that L4/S1 and SL in the operating segment are postoperatively more increased than the total LL might indicate that the lumbar spine as a whole partly compensates for correction of the SL within the segment where fusion was performed. However, further research on this topic should be conducted, as specific physiological mechanisms are not described in the literature leading to these results.

A meta-analysis from 2016 comparing complication rates in ALIF and extreme lateral interbody fusion procedures found an overall complication rate of 26.47% for ALIF versus 16.61% for extreme lateral interbody fusion [19]. Most of the complications were neurological, like motor weakness, hypoesthesia, or thigh symptoms, although almost half (48.1%) of all neurological complications resolved within 42 days. Revision surgery was performed in 4.60% of all ALIF procedures, with the most frequent reason being pseudarthrosis, followed by hardware failure. The wound infection rate was 5.75% [19]. In our sample, the most frequent complication was an intraoperative injury to venous structures during the anterior approach. Rates of vascular injury vary between different studies. A recent review found a venous injury rate of 10.4%, similar to the rate we found in our study [20]. Another review reports a wide range of vascular injury rates, from 0% up to 18.1%, with arterial injuries being less frequent than venous lacerations [21]. Mean blood loss was 384.38ml in our sample (median 150ml). This is similar to blood loss values reported in the literature. Tu et al. (2021), for example, found a mean blood loss of 300ml, and Teng et al. (2017) report a mean blood loss of 200-300ml, which, however, can increase drastically in the case of vascular injury [4, 22]. Blood loss associated with venous vessel injury ranged from 250ml to 10,000ml in our sample. The four patients with venous injuries had estimated blood losses of 1,000ml or higher. The patient with an arterial injury had a blood loss of 1,400ml. When considering the potentially fatal consequences of vascular injury, one of the major limitations of ALIF is evident. Care should be taken especially to rule out a relatively low level of the bifurcation of the abdominal aorta and the confluence of the inferior vena cava. Inamasu et al. investigated the level of the aortic bifurcation and found a low bifurcation level in 18% with the bifurcation at the height of the vertebral body L5. Considering the level of the confluence of the inferior vena cava, they found a rate of 1% of all cases where the confluence is located at L5/S1 or below [23]. Surgical access can be complicated when encountering the vascular structures and especially any vascular bifurcation directly ventral of the L5/S1 intervertebral disc. Before indicating ALIF surgery, individual vascular anatomy should be examined on appropriate radiological examinations like magnetic resonance imaging (MRI) or computer-assisted tomography (CT) to minimize the risk of vascular injury.

Our study was limited by several factors. First, the results may be biased due to the retrospective study design. Also, the sample size of the patients who underwent standalone ALIF was relatively small. We recommend conducting prospective, multi-center studies with large sample sizes to investigate sagittal alignment and spondylolisthesis after ALIF surgery.