Positioning and the bony landmarks are similar to those in a retroperitoneal approach. It is recommended to utilize a bowel preparation to flatten the bowel and decrease contamination if a perforation is encountered. Longitudinal, transverse, or low-transverse (Pfannenstiel) incisions can be utilized. Appropriate preoperative planning is critical as there are limitations to expanding the transverse incisions to adjacent levels. The superficial dissection is similar to the retroperitoneal approach. The peritoneum is elevated with clamps or forceps to elevate off of underlying bowel to prevent unintentional perforation. For more proximal levels in the lumbar spine, the small bowel can be mobilized to the right and the sigmoid colon to the left. Alternatively, the peritoneum can be incised at the lateral reflection (white line of Toldt) and both small bowel and colon mobilized to the right. Bony palpation of the sacral promontory will approximate the appropriate level before incising the retroperitoneum. Radiographic confirmation is then recommended.

The primary goals of interbody fusion are to treat the patients’ pain and to stabilize the target spinal levels. An ideal interbody graft for an ALIF needs to provide good surface area for fusion and restore segmental alignment while providing structural stability. Biomechanically, increasing disc space height indirectly decompresses the neural foramen and the degenerative disc space is stabilized. Both of these target pain generators and, in theory, help relieve the patient of their symptoms.

The first interbody fusion for the treatment of spondylolisthesis [3] utilized an autogenous tibial dowel. Autogenous graft remained the mainstay for the interbody choice for several decades and even today is considered the “gold standard,” although it is not the most common interbody structural support used. Donor site morbidity and unacceptable pseudarthrosis rates, when used as a stand-alone construct, pushed for development of newer interbody options [20]. After approval of the BAK cage in 1997, a surge in interbody options was observed. Even with evolving technology, there is no current agreed upon graft design or material.

Allografts in the form of femoral rings, fibular struts, or iliac crest are seeing a resurgence. Traditionally, allograft was the answer to donor site morbidity. Graft subsidence was common but instrumentation with either anterior plates or posterior fixation has improved this technique. Graft dissolution, especially with the use of recombinant human bone morphogenetic protein-2 (rhBMP-2), is a concern with allograft. Although very low, the potential for disease transmission must be considered when choosing to use allograft. Improvements in screening protocols have greatly reduced this potential. Additionally, different preparation methods are now available including fresh-frozen or freeze-dried allografts. A prospective, randomized, single-site study examined the difference between frozen and freeze-dried allograft when used as part of a circumferential ALIF [21]. They compared 100 patients with a minimum 24 month follow-up and found that although the fresh-frozen graft took longer to incorporate, freeze-dried graft had a higher pseudarthrosis rate. Biomechanical studies have shown that fresh-frozen allograft fails at an average load 50 % less than freeze-dried, but this appears to not be clinically significant [22].

The first metal cage was developed to treat race horses with cervical stenosis. The BAK titanium cage (Zimmer Spine, Warsaw, IN) was a threaded cylinder that was screwed into the disk space. The Ray Fusion Cage (Stryker Spine, Allendale, NJ), a second generation titanium cage, was a lower profile threaded cylinder that allowed more bone graft to be inserted. As a third generation design, the LT-CAGE (Medtronic Sofamer Danek, Memphis, TN) quickly became the most utilized interbody cage in North America. The cage offered a trapezoidal lordotic design that increased surface area for improved fusion rates. Composite designs such as polyetheretherketone (PEEK) were developed to help reduce artifact and to mimic biomechanical properties of cortical bone. The ability to machine PEEK into any shape or size makes it desirable.

rhBMP-2 stimulates bone growth and was first found in the extracellular matrix surrounding bone. rhBMP-2 delivered on an absorbable collagen sponge (ACS) was first approved by the FDA for ALIF procedures in 2002 following the results of a prospective, randomized, multi-center clinical trial [23]. In this study, 279 patients who underwent ALIF for lumbar degenerative disc disease were divided into the experimental rhBMP-2/ACS group and the control autogenous iliac crest bone graft group. At 24 months postoperatively, the rate of fusion as determined by plain radiographs and computed tomography (CT) was higher for the experimental group (94.5 %) than for the control (88.7 %). One study found that rhBMP-2, when used in allograft femoral rings, significantly improved the fusion rates at 6, 12, and 24 month follow-up compared to allograft femoral rings alone [24]. In addition to the higher rate of fusion, the acceptance of rhBMP-2 use for ALIF was an important development because it gave surgeons an alternative that does not have the complications associated with harvesting autogenous or allograft bone [25]. In the years following FDA approval, rates of rhBMP-2 use rose dramatically from 0.69 % of all spinal fusions in 2002 to 24.9 % in 2006 [26]. The potential side-effects of rhBMP-2 use in ALIF are heavily debated [23–28] and further discussed later in the chapter.

Historically, failure or success of an ALIF was defined by the treating surgeon’s interpretation of whether spinal fusion was achieved. Studies have typically reported acceptable fusion rates between 47 % [29] and 96 % [10]. These fluctuations may be reflective of differing patient populations, individual surgeon technique, and fusion assessment technique. It is generally agreed that ALIF results in excellent restoration of disc height and lumbar lordosis [30]. The majority of published outcomes focus on spondylolisthesis at the L4-L5 and L5-S1 levels, as these are the most common levels affected. It has been noted that patients undergoing ALIF at more cephalad spinal levels tend to do worse [31], although this may be related to worse pathology rather than just characteristics intrinsic to the level or the approach to it. Here, a multivariate regression analysis of 242 patients undergoing ALIF demonstrated that level was an independent risk factor.

While more recent studies continue to report fusion rates and radiographic results, there has been a trend in the literature to focus on patient-perceived outcomes, especially within the last decade. Health related quality of life (HRQOL) questionnaires are used to assess pain reduction, patient function, and improvements in quality of life. This type of information more accurately measures how much patients benefit from the procedure than radiographic results alone. However, among all the various tools [e.g., Oswestry Disability Index (ODI), Visual Analog Scale, Short Form-36] that have been utilized, no one is used universally across all studies.

The Spinal Patient Outcomes Research Trial (SPORT) found that patients undergoing surgery experienced significantly greater improvements in pain, function, satisfaction, and progress measured by SF-36 over a 4-year time period than those who received non-operative treatment [32]. Furthermore, the treatment effect of surgery for spondylolisthesis was greater than for lumbar spinal stenosis and lumbar disc herniation [33, 34]. Although there were limitations to the study and not all surgical candidates underwent ALIF for the treatment of spondylolisthesis specifically, these results further highlight the important role of surgery in management of spondylolisthesis.

There have been several studies with long-term follow-up that demonstrate good outcomes for ALIF for both degenerative and isthmic spondylolisthesis. Takahashi et al. [35] followed 39 degenerative spondylolisthesis patients who underwent ALIF for a maximum of 30 years postoperatively, with a mean follow-up of 12.5 years. The authors stated that 76 % of patients had satisfactory results for 10 years postoperatively, 60 % for 20 years, and 52 % for 30 years. A “satisfactory result” was defined as at least 25 out of 29 points on the Japanese Orthopaedic Association index, a patient self-report which measures low back pain, leg pain, gait disturbance, and activities of daily living. This study concluded that at ultra-long-term follow-up, ALIF is a viable treatment option for spondylolisthesis. More recently, Riouallon et al. [36] described their study of 65 patients undergoing ALIF for low-grade isthmic spondylolisthesis with an average follow-up of 6.6 years. Their fusion rate was 91 %. Lumbar pain and radicular pain either completely disappeared or regressed in 69 and 85 % of patients, respectively, according to the Visual Analog Scale. Together, these two studies further reinforce the strength of ALIF for treatment of spondylolisthesis.

Comparison between ALIF and other lumbar fusion procedures can be dichotomized between interbody comparison (ALIF, PLIF, or TLIF) and stand-alone ALIF versus posterolateral fusion only. One study of 46 Japanese patients with degenerative spondylolisthesis at L4 compared non-instrumented (stand-alone) ALIF to posterolateral fusion and found that ALIF reduced back pain significantly more than posterolateral fusion, but that ALIF also required longer hospital stay and bed rest [37]. Interbody delivery options consist of anterior (ALIF), posterior (PLIF), and transforaminal (TLIF) approaches. Currently, there is debate to which delivery method is preferred, as several studies demonstrate they have similar radiographic and clinical outcomes [38]. Kim et al. [39] reported a comparison of ALIF and TLIF in 128 patients with low-grade isthmic spondylolisthesis. They found that functional scores for the ODI improved more in patients undergoing TLIF, but restoration of sagittal balance based on radiographs was more common in patients who underwent ALIF. They recommended TLIF at the L4-5 level and ALIF at the L5-S1 level.

The increased consistency in the use of patient-reported HRQOL outcomes has been instrumental in developing a platform for cost analysis. Although no study has directly looked at cost-comparison or cost-effectiveness of ALIF, several studies include patients undergoing ALIF in the analysis. Polly et al. [40] examined pooled SF-36 data on 1,826 lumbar spinal fusion cases, of which 935 were ALIF. They found a cost–benefit ratio comparable to other well-accepted medical interventions such as total hip replacement. Cost-effectiveness of the SPORT data also reported that surgery was good value for treating degenerative spondylolisthesis over a 4-year time period [41]. In the SPORT study, 46 of 372 patients underwent interbody fusion. Overall, these types of analysis are essential in an increasingly cost-conscious era.

Although ALIF is considered to be a safe procedure, complications can be devastating. Vascular complications are the most frequently encountered. The great vessels, bifurcation of the abdominal aorta into the iliac vessels, and numerous veins reside in the L4-S1 region. A recent review by Inamasu et al. [42] reported that the incidence of vascular injury is between 0 and 18.1 %. Vessel injuries occur more often in surgeries involving the L4-L5 level rather than those at L5-S1, due to the anatomic location of the major vessels. Venous injury is much more common than arterial injury. This occurs most commonly during vein retraction, but can also occur as a result of discectomy or graft placement [42]. The critical veins in this region are the left common iliac vein, the inferior vena cava, and the iliolumbar vein. If perforation of a vein occurs, manual compression followed by primary repair is effective in most scenarios.

The aorta and iliac arteries tend to be more elastic and can be retracted more readily than their corresponding veins, so injuries are less common. However, there is a potential for left iliac artery thrombosis after prolonged periods of retraction. Emergency thrombectomy or bypass surgery is needed immediately if this occurs [43]. The patient may have unclear symptoms, which include pain and motor/sensory deficits in the lower left extremity, and these are often mistaken for nerve root irritation. It has been suggested to periodically release the left iliac artery during surgery or to use a pulse oximeter on the left great toe in order to prevent or detect this complication [44].

A particular point that has been in discussion is the role of a vascular or general surgeon for anterior access. One argument says that the “access” surgeon has had more training and is more experienced in the abdominal cavity than a spine surgeon, particularly those who were trained in neurosurgery. This would seem practical in order to better avoid and address, if they occur, any complications. The current medicolegal climate likely plays a role in the decision to utilize an access surgeon as well. However, it has been reported [45] that there is no significant difference between ALIF surgeries undertaken by spine surgeons alone or with the help of an “access” surgeon. Other studies have indicated that procedures performed by only a spinal surgeon actually involve fewer complications [46]. This may be due to greater familiarity of the spinal surgeons specifically with respect to the approach required for ALIF. However, it should be noted that some surgeons, while undertaking ALIFs alone and effectively resolving vascular complications in the vast majority of cases, still retain the option to call on their vascular colleagues. In one instance, surgeons who performed 304 anterior lumbar spine surgeries “without the assistance of a vascular access surgeon in all cases” nonetheless required vascular surgeon aid in 9 (3 %) cases for complication management [47].