Does Anterior Lumbar Interbody Fusion Reduce Mechanical Complication and Pseudarthrosis Rate at the Lumbosacral Junction in Adult Spinal Deformity Surgery in Comparison to Posterior Lumbar Interbody Fusion?

Discussion

Pseudarthrosis following spinal fusion procedures often results in mechanical complications, lumbar pain due to segmental instability, and, ultimately, the need for revision surgeries. The lumbosacral junction, in particular, is prone to biomechanical complications due to the load transfer from the spine to the pelvis.20,21 With the development of modern cage designs, there has been an increasing trend toward addressing complex spinal pathologies using dorsal single-step approaches. However, our study suggests that ventral counter-stabilization with a large ALIF cage is biomechanically and clinically superior to purely dorsal procedures in long-segment constructs for ASD correction surgery.

Patients operated through an ALIF approach at the lumbosacral junction showed significantly less lumbosacral pseudarthrosis and mechanical complication rates, mainly screw loosening and rod fracture. Consequently, the patient group treated with ALIF required significantly fewer revision surgeries due to mechanical complications in the caudal segments of the long-segment spinal deformity construct. Similarly, Adogwa et al found increased rod fracture rates in patients who underwent transforaminal lumbar interbody fusion compared with ALIF at the caudal levels of a long-segment spinal deformity construct.22 However, the study group did not analyze pseudarthrosis and overall mechanical complications in detail.22 Compared with the pure dorsal techniques, the ALIF approach to the spine allows for a centered view of the disc space at L5/S1 and can extend to expose the vertebral bodies’ lateral aspects. This permits efficient and rapid endplate preparation, thorough release of contracted tissue and osteophytes, and complete discectomy. Thus, a cage with a larger footprint and greater angulation can be implanted, facilitating aggressive correction of lordosis and foraminal height restoration and allowing for a greater volume of bone graft placement.23 Therefore, the ALIF cage offers greater biomechanical support, providing greater primary construct stability. PLIF cages, on the other hand, seem less sufficient to withstand these forces in long-segment constructs.24 This biomechanical benefit seems particularly relevant in primary multilevel fusions, where high compressive and shear forces occur, especially at the lumbosacral junction.25

Furthermore, dorsal interbody fusion procedures create direct communication between the dorsal surgical site and the intervertebral disc space, which may permit contamination of the disc space in cases of deep or low-grade infections. These infections, more common in elderly patients due to comorbidities and impaired wound healing, can compromise the fusion process and contribute to higher pseudarthrosis rates.20 In contrast, a key advantage of ALIF cages is the avoidance of this direct connection, as the anterior approach isolates the intervertebral disc space from the posterior wound. This separation may protect the disc space from infection-related healing disturbances. This aspect becomes particularly relevant in long-segment constructs, where dorsal wound infections play a more significant clinical role compared with short-segment fusions.26

Conversely, PLIF remains advantageous in scenarios requiring simultaneous neural decompression and fusion, such as in cases of severe neuroforaminal stenosis or spondylolisthesis. When wide dorsal decompression with foraminotomy and removal of retrospondylophytes is indicated in the lumbosacral junction, opening the disc space with cage implantation is no longer a significant technical or time challenge. This also applies when reducing high-grade spondylolisthesis. Furthermore, the single-stage dorsal approach avoids the challenges of retroperitoneal access, which requires a highly experienced spine surgeon or interdisciplinary collaboration with vascular or visceral surgeons. While major vessel or peritoneal injuries are rare with a primary anterior approach when performed correctly, ALIF can be associated with lumbosacral plexus injury. This risk is particularly relevant for younger patients, as plexus injury has been linked to vulvar dryness in women and erectile dysfunction in men, both of which can significantly impact the quality of life.20 In contrast to our initial assumption, PLIF was not associated with a reduction in operative time. In fact, ALIF demonstrated significantly lower blood loss and transfusion requirements, likely due to the minimally invasive retroperitoneal approach, which avoids extensive dorsal decompression and minimizes manipulation of vascularized posterior structures.13 This reduced blood loss and shorter ICU stays highlight ALIF’s utility in reducing perioperative risks, particularly in patients with higher surgical risk profiles associated with blood loss.

These findings have direct implications for surgical decision-making. The lower rates of pseudarthrosis, implant-related pain, and reoperation in the ALIF group suggest that it may offer superior long-term outcomes, particularly in patients at higher risk for mechanical failure. While ALIF demonstrated significant advantages in reducing blood loss and mechanical complications, it is not universally applicable. PLIF provides a more versatile approach by combining dorsal decompression and fusion in a single stage. Conversely, ALIF is most beneficial when the primary goal is anterior column support to restore biomechanical stability and lumbar lordosis rather than direct decompression of neural structures at the lumbosacral junction.

Our study has some limitations. Despite analyzing prospectively collected data, the retrospective evaluation inherently limits its ability to establish causality between surgical techniques and outcomes. Prospective randomized controlled trials provide stronger evidence for the observed differences. This is particularly relevant since the decision to perform ALIF vs PLIF was influenced by patient-specific factors including L5/S1 foraminal stenosis or former abdominal surgeries. This potentially introduces a selection bias that may confound the results such as the total operative time. In addition, bone quality—which was not assessed preoperatively—may have influenced the fusion rates. On the other hand, a strength of our study is that the demographic patient data did not differ in a clinically relevant manner, reducing the likelihood of baseline disparities influencing the outcomes. Nonetheless, 1 notable difference between the 2 groups is the choice of the fusion material. In the ALIF group, hydroxyapatite paste was used, whereas the PLIF group received autologous bone grafts and homologous bone from a bone bank. The hydroxyapatite paste used in ALIF is a purely osteoconductive material, whereas autologous bone—used in PLIF—also possesses osteoinductive properties. Therefore, with regard to fusion potential, the bone graft material used in PLIF may offer a biological advantage. However, ALIF showed significantly better fusion rates than PLIF. Thus, our findings suggest that, based on previous findings, it is unlikely that the choice of graft material significantly influenced the fusion rates in our cohort. According to Benzel et al, 4 key factors are critical in determining fusion success: the surface area of bone graft-to-endplate contact, the surface area of implant-to-endplate contact, the stability and integrity of the construct, and adequate endplate preparation. These biomechanical and technical aspects are likely to have had a greater impact on the fusion outcomes observed in our study than the graft material itself or even the additional use of bone marrow aspirate.27,28

Furthermore, the single-center nature of this study may limit the generalizability of the findings, as surgical techniques, perioperative protocols, and patient populations can vary significantly across institutions and countries. Strict inclusion and exclusion criteria limited our sample size to 56 patients. Therefore, the study may lack sufficient power to detect subtle differences between the ALIF and PLIF groups, particularly with regard to less common complications. However, given the complexity and duration of the surgeries, the study provides an acceptable patient cohort, and the significant differences observed emphasize the clinical relevance of the findings. Nevertheless, multicenter studies are needed to validate and generalize these results. Although the inclusion criteria encompassed a minimum 2-year follow-up period, which is sufficient to assess early outcomes, longer-term follow-up is necessary to evaluate the durability of fusion and the risk of late mechanical complications. We are able to present an acceptable and clinically relevant average follow-up duration of 5 years. By this time, solid fusion at the lumbosacral junction is typically achieved, resulting in a lower incidence and clinical relevance of mechanical complications in this region. Although the SD of 29 months limits statistical verification, data analysis indicated that the majority of mechanical complications occurred within the first 2 years postoperatively. Only isolated cases developed mechanical complications at the lumbosacral junction beyond the 2-year follow-up period. In contrast, beyond the 5-year mark, the focus of concern shifts toward proximal junctional degeneration or proximal junctional kyphosis. These aspects should be addressed in future long-term follow-up studies. Additionally, the inclusion of patient-reported outcomes after complete construct healing and bony fusion would be highly desirable, as these metrics are critical for evaluating the overall success of spinal deformity correction surgeries. The analysis of these data for long-term follow-up is planned.