L5/S1 anterior lumbar interbody fusion: anatomical and technical considerations

Introduction

The lumbosacral junction is a common site of anterior lumbar surgery given its propensity to degenerative change, biomechanical importance and unique surgical anatomy. Anterior lumbar surgery offers the benefits of a large fusion surface, powerful interbody correction, avoidance of neural structures and preservation of posterior neuromuscular elements.

The lumbosacral junction

The L5/S1 segment connects the mobile spine to the pelvis. The L5 vertebra is joined to the sacrum, held within the pelvis, by the lumbosacral disc. The sacral slope, measuring the sacral endplate inclination against the horizontal, is measured in normal populations between 25 and 55 degrees (1). The L5/S1 segment contributes significantly to the lumbar lordosis. Approximately 2/3 of the lumbar lordosis occurs between L4 and S1, with the lumbosacral junction constituting a major portion. This segmental lordosis is contributed to by the wedge shape of the L5 vertebral body and the lumbosacral disc—both being several mm higher anteriorly than posteriorly (2,3). Given this inclination, the lumbosacral disc is subject to significant shear stress (4). Stability is reinforced by the iliolumbar ligaments. The iliolumbar ligaments attach the transverse processes of the L5 vertebra to the anteromedial aspect of the ilium. They primarily resist the forward displacement of the L5 vertebra on the sacrum. Other important stabilizing ligaments include the anterior and posterior longitudinal ligaments (PLLs), the ligamentum flavum, the facet joint capsules and inter-spinous ligaments.

Vascular anatomy

The great vessels in the retroperitoneum pose the greatest obstruction to safe and adequate anterior exposure of the lumbar spine (Figure 1) (5). The aortic bifurcation normally lies over the body of L5, so that access to the lumbosacral disc can occur between the iliac vessels, without the need for significant mobilization of the great vessels. The aorta and its bifurcation lie to the left of the midline adjacent to the inferior vena cava. The right common iliac artery crosses the midline, over the left common iliac vein and then lies medial to the right common iliac vein. The left common iliac artery then continues downwards, lying adjacent to the left common iliac vein. The median sacral vessels arise from the aortic bifurcation/iliac vein confluence and run over the surface of the lumbosacral junction. The superior hypogastric plexus is part of the sympathetic nervous system which lies over the distal abdominal aorta and iliac arteries. Injury to the plexus can cause ejaculatory problems in males with implication for fertility. A detailed discussion about the plexus can be found later (see section “Superior hypogastric plexus”).

Figure 1 Regional anatomy of the lumbosacral disc space (5). (A) Medical illustration of the anterior lumbosacral anatomy showing the predominant left sided superior hypogastric sympathetic plexus. (B) Cadaveric anatomical dissection photograph showing the same anterior lumbosacral anatomy. 1, superior hypogastric plexus usually running left paramedian; 2, right hypogastric nerve; 3, left hypogastric nerve; 4, right common iliac artery; 5, left common iliac artery; 6, sacral promontory; 7, L5/S1 disc space; 8, left common iliac vein; 9, right common iliac vein; 10, median sacral vein. Reproduced with permission under the terms of the Creative Commons Attribution License (5).

Pathology and indications for surgery

The L5/S1 level is the level second most commonly affected by degenerative disc changes, after the L4/5 level (6). Discogenic back pain is a common indication for L5/S1 anterior lumbar interbody fusion (ALIF). However, fusion surgery for axial back pain is a somewhat controversial area and the importance of optimal patient selection for good outcomes is paramount. Potential surgical subjects must have undergone an appropriate period of conservative management. In addition to standard imaging, radionuclide bone scanning and provocative discography can assist in case selection.

Disc degeneration with disc space collapse may lead to foraminal narrowing and consequent nerve root compression. Restoration of disc space height can achieve indirect foraminal decompression of the nerve.

Ninety percent of pars defects occur at the L5 level and predispose the lumbosacral segment to the development of isthmic spondylolisthesis (7). Standalone ALIF at the lumbosacral junction for isthmic spondylolisthesis may have a high rate of failure because of the high shear stresses. In the absence of competent posterior elements secondary to the pars defects, supplementary posterior fixation may be required.

Cancellous bone of the sacrum limits the strength of sacral pedicle screw fixation and the significant shear stresses experienced at the lumbosacral junction result in a relatively high risk of pseudoarthrosis in L5/S1 fusions, particularly in long constructs (8). Interbody fusion can be an important adjunct to long fusion constructs, resisting the shear stresses, increasing segmental stability and promoting fusion. Combined with the ability to restore segmental lordosis, adjunctive ALIF at the L5/S1 level can be a powerful tool in long constructs in spinal deformity surgery.

The indications for ALIF at the lumbosacral junction therefore include symptomatic degenerative disc disease, foraminal stenosis, spondylolisthesis, revision of failed lumbar fusion, anterior column support in long fusion constructs or those constructs at high risk of non-union (Table 1).

Surgery

Preparation

Proper patient selection and appropriate indications for surgery are two of the most important factors in the pre-operative phase. If the surgeon is confident with performing the approach, it can be safely done as a single surgeon procedure. Otherwise, the availability of a general or vascular access surgeon should be confirmed pre-operatively. Pre-operative imaging studies should be reviewed. Attention should be paid to the vascular anatomy such as a transitional lumbosacral junction or a low-lying aortic bifurcation or venous confluence. In patients with a steep sacral slope a lateral X-ray showing the position of the pubic symphysis will determine the extent of disc space exposure. A history of lower abdominal surgery especially retroperitoneal surgery increases the difficulty of the approach. Measurements should be taken to obtain an estimate of the intended implant’s size and angle. Such calculations should take into account the sagittal alignment parameters—including the pelvic incidence and intended lumbar lordosis.

Anaesthesia and positioning

ALIF is performed under general anaesthesia with appropriate vascular access and indwelling urinary catheter. There is the option of lower limb pulse oximetry monitoring for continuous lower limb perfusion assessment. Vascular retraction can lead to ischaemia or thrombosis. The incidence of arterial thrombosis is reported as between 0.4–1% (9). The incidence of temporary ischaemia is higher at approximately 3% for single level L5/S1 exposure but up to 65% for multiple level arthroplasty; with vessel retraction time a risk factor (10). Intra operative neurological monitoring with motor evoked and somatosensory evoked potentials can be used for ALIF. The incidence of monitoring alert reported is low at approximately 1% (11).

L5/S1 ALIF is performed most commonly in the supine position. To promote lordosis, a table break or posterior lumbar support can be utilized. Trendelenburg positioning may help displace the abdomen superiorly to facilitate access. The operating table should be radiolucent to allow good anteroposterior (AP) radiography. Abduction of the arms enables improved surgical access and X-ray imaging. The ‘da Vinci’ or ‘French’ position, with the surgeon standing between abducted legs, allows more access to the surgical field for surgical personnel and a truer appreciation of the midline for accurate placement of hardware (Figure 2).

Figure 2 Patient positioning for L5/S1 ALIF surgery. This figure demonstrates the possible patient positions with the surgeon position indicated by ‘S’. (A) Supine; (B) French/supine legs spread/da Vinci; (C) right lateral decubitus single position. ALIF, anterior lumbar interbody fusion.

The direct lateral position is increasingly used to facilitate single position anterior and posterior fixation. The patient is positioned in the right lateral decubitus position, a bolster underneath the flank and the arm pit, with the chest and subtrochanteric thigh taped to secure the position. The legs are slightly bent with a pillow between, and taped to secure their position. The surgery is then performed via an oblique (Gridiron or Rutherford-Morrison’s) incision in the patient’s left iliac fossa in a muscle splitting technique to gain access to the retroperitoneum to then allow a medial visceral rotation. It is of great assistance in patients with significant abdominal obesity, as the lateral positioning allows the natural drop of the pannus inferiorly to ease medial visceral rotation. Care must be taken in the trajectory of cage insertion as the oblique approach may necessitate angled instruments for central placement of the hardware.

Approach

Several factors can influence the choice of incision. Access to the upper lumbar levels is easier from a left sided retroperitoneal approach. When L5/S1 ALIF is performed in conjunction with surgery at other levels, a left sided approach is appropriate. For isolated L5/S1 ALIF surgeries, it can be argued that a right sided approach will leave the left sided corridor unadulterated, in the case that surgery at the upper levels is needed at a later date.

Transverse (Pfannenstiel), oblique and vertical incisions have been described (Figure 3). Following incision, dissection through the superficial soft tissues leads to the anterior rectus sheath which, being below the arcuate line at the L5/S1 level, is formed by the aponeuroses of the transverse abdominal and the external and internal oblique muscles, which fuse in the midline to form the linea alba. With a transverse incision, the superior and inferior wound edges have to be elevated to allow sufficient cranio-caudal exposure of the rectus muscle.

Figure 3 ALIF surgical incisions. Transverse or Pfannenstiel, vertical and oblique incisions for lumbar ALIF surgery. ALIF, anterior lumbar interbody fusion.

Dissection

A trans-peritoneal or retroperitoneal approach can be used. The majority of surgeons use a retroperitoneal approach as there is a significantly reduced burden of abdominal morbidity and a reduced recovery period (12).

Both a para-rectus and midline rectus approach have been described. Through a midline approach, dissection continues through the central linea alba, before heading laterally in an extra-peritoneal plane, under the rectus.

With a para-rectal approach, the rectus is circumferentially mobilized. The inferior epigastric vessels lie on the deep aspect of the rectus muscle and should be inspected and protected as the rectus is retracted. The retroperitoneal dissection is then performed on the lateral aspect of the rectus, with the muscle retracted medially, to allow a more direct extra-peritoneal approach (13). Once adequate retroperitoneal exposure is achieved, the muscle is retracted laterally and fixed retraction is placed on the medial side of the mobilized rectus, for a straighter midline view of the disc space. There is a concern about rectus denervation with this extensive mobilization of the muscle on its lateral aspect.

With a midline rectus approach below the level of the arcuate line, the transversalis fascia separates the rectus muscle from the peritoneum. To enter the pre-peritoneal space, the transversalis fascia is divided. The peritoneum is then swept away medially, first from the underside of the rectus and then from the lateral body wall, to develop the extra-peritoneal corridor (Figure 4). The psoas muscle is the next major landmark. Running on the surface of the large fleshy psoas muscle, the genitofemoral nerve can often be identified. At this point, inspection of the reflected peritoneum will often reveal the ureter on its surface and should be protected. Any peritoneal tears should be recognised and repaired, to prevent the development of a post-operative hernia. When the psoas is encountered, further medial retraction of the peritoneum will expose the iliac vessels (Figure 5).

Figure 4 Development of extraperitoneal plane. Following incision through the linea alba, extraperitoneal place is developed starting on the underside of the rectus and extending laterally around the body wall. (A left sided approach though a vertical incision is illustrated).

Figure 5 Identification of the psoas muscle and iliac artery. Following further dissection, the iliac artery is encountered medial to the left psoas muscle. (A left sided approach though a vertical incision is illustrated).

Exposure of the disc space

The L5/S1 disc space normally lies within the bifurcation of the common iliac vessels. Identification of these vessels is important to prevent incidental vascular injury. From a right sided retroperitoneal approach, the right common iliac artery and vein are visualised and mobilized gently towards the psoas muscle. The peritoneum and its contents together with the ureter, are gently swept further medially using blunt dissection. Identification of the L5/S1 disc space is generally possible at this stage with palpation of the sacral promontory. The level can be checked with X-ray at this stage and AP X-ray allows radiographic confirmation of the midline. Fixed retraction may now be placed on the right lateral aspect of the L5/S1 disc space with further retraction of the vessels. The median sacral vessels are identified and should be ligated with ties and/or clips. Preservation of sympathetic nerves should be performed if identified in the surgical field (see section “Superior hypogastric plexus”). Further blunt dissection is performed over the anterior surface of the disc space with a peanut on a stick and gentle lateral left retraction. Care should be taken to identify where the left common iliac vessels as well as the aortic bifurcation and iliac vein confluence lie superiorly, although they do not need to be dissected out. With retraction of the left sided vessels, adequate exposure of the L5/S1 disc space will be achieved and further fixed retraction may be placed over the left lateral and inferior aspects of the disc space. If the level has not been confirmed with X-ray, this should be performed prior to discectomy.

Vascular injury is in the majority venous; incidence 1–24% compared to 0.4–1.5% incidence for arterial injuries (14). It is more common at the L4/5 level compared to L5/S1. Intra operative management consists of tamponade and primary venorrhaphy. The use of topical clot forming agents and patches can also be used. Arterial injuries require primary repair with additional endovascular stenting an option. In the event of vascular injury there is a significantly higher rate of thrombosis peri-operatively (15).

Superior hypogastric plexus

The risk of injury to the superior hypogastric plexus at the lumbosacral junction deserves special mention. The hypogastric plexus is a continuation of the abdominal aortic sympathetic plexus (16). It is described as a fenestrated network of fibers varying in shape, size, and degree of condensation. The major part of the plexus sits in front of the distal abdominal aorta and its bifurcation, slightly to the left, further resting on the left common iliac artery. At approximately the level of the sacral promontory the plexus divides into two hypogastric nerves that run bilaterally into the pelvis, parallel to the course of the ureters. The plexus lies in a sub-peritoneal layer in a tissue compartment that can be separately mobilized with minimal trauma to the nerves.

The superior hypogastric plexus supplies sympathetic innervation to the internal urethral sphincter. During ejaculation, the internal sphincter closes to prevent entry of the semen into the bladder. With damage to the superior hypogastric plexus and resultant failure of closure of the internal sphincter, retrograde flow of the seminal bolus into the bladder can occur. This can lead to decreased sperm volume and count and infertility. Male patients must be warned of this complication and should be offered the option of pre-operative sperm donation and banking (17). The risk of retrograde ejaculation is greatest at the L5/S1 level, where the plexus is most exposed to the surgical approach.

The risk of retrograde ejaculation is increased if a trans-peritoneal approach is used (18). In this approach, it is recommended that the peritoneal fascia be incised on the right side and swept towards the left to avoid injury to the plexus (19). It is unclear whether the direction of approach is critical for prevention when a retroperitoneal approach is used. Given that the plexus is situated in a subperitoneal layer, it is important to get to the ventral surface of the spine, at the lateral disc space, deep to the fascial coverings, and sweep those fascial layers off the disc space with the peritoneum before incising the disc space. The use of monopolar electrocautery in this area should be avoided, to prevent thermal injury to the plexus. While, one prominent study (20) suggested a link between the use of rh-bone morphogenetic protein 2 as a bone fusion adjunct and the development of retrograde ejaculation, further studies have failed to reproduce this finding (21,22).

Retraction

Once the retroperitoneal exposure of the lumbosacral disc space has been achieved, a retraction system is used to maintain the exposure and protect the great vessels (Figure 6). While there is a wide range of available systems, they are usually one of several types. The simplest system is to use several bone pins with a threaded tip which are screwed into the vertebral bodies to maintain retraction of the iliac vessels. While these are effective for retraction, they do not provide protection for the vessels that remain exposed between the pins. Bone secured retractors consist of blades with a channel for a threaded bone pin, so they can protect the vessels while maintain retraction. Table mounted retractors utilize retractor blades, often of varying shape, that are attached to a ring or bars secured to the operating table. They can provide very strong retraction forces and can be helpful during difficult exposures, freeing up ’surgical hands’ by providing retraction during a progressively deepening exposure.

Figure 6 Exposure of disc space and discectomy. Bone secured retractors are placed in L5 and the sacrum to protect the exposure. A distractor is positioned in the right side of the disc space to maintain distraction. (A left sided approach though a vertical incision is illustrated).

For adequate exposure of the lumbosacral disc, either 3 or 4 blades are usually employed. Varying retractor blade depths and configurations are available. Standard blades are usually straight with an angled lip at the distal end. Special configurations include the reverse angle lip (Brau retractor) which is intended to anchor to the edge of the vertebral body. A reverse angle lip with a protruding spike can be malleted into the sacrum. Corner blades can be useful to maintain a squared exposure.

Discectomy

Following radiographic confirmation of the correct level, a wide annulotomy is performed with a blade on a long handle. It is safer to make disc cuts with the knife facing towards the midline, away from the great vessels. Using a long Cobb elevator, the disc is separated from the vertebral endplates. Care should be taken to avoid violation of the endplates with the Cobb elevator. Gentle rotation of the instrument handle will help release some of the soft tissue constraints. A large ‘pituitary’ type rongeur is used to remove the disc. The disc may remain attached at the lateral extents of the annulotomy and the blade may need to be used again to cut remaining attachments.

Depending on the degree of disc collapse, varying methods may be needed to obtain and maintain appropriate disc distraction, including insert and rotate disc space paddles and hinged ratcheted distractors. Leaving a distractor on one side of disc will facilitate disc removal from the contralateral side (Figure 6). The distractor can then be moved to the other side, so that complete discectomy can be completed. Care must be taken to avoid endplate violation during distraction and discectomy.

Discectomy is continued using a combination of curettes and rongeurs. A cup curette can be useful in removing the nucleus of the disc. Angled cup curettes can facilitate clearance of the lateral disc. An open ‘uterine’-type curette and rasps can be used to clear the vertebral endplate of any remaining cartilage material.

With sufficient distraction, the PLL can be ruptured, often accompanied by an audible ‘crack’. Alternately, the PLL may be formally resected with rongeurs to allow more formal ventral decompression or removal of disc fragments. Care should be taken to avoid unintended durotomy, as dural repair is difficult through a ventral intervertebral approach. The continuity of the PLL also has important implications for reconstruction and must be considered. Often an intact PLL stretches with the intervertebral implant increasing the posterior disc space height and giving indirect foraminal decompression. However, an intact PLL may tether the posterior vertebral bodies together, so that an intervertebral implant will distract the space anteriorly but lead to foraminal narrowing posteriorly, with neural compression. With division of the PLL, the centre of segmental rotation will shift posteriorly, and an intervertebral implant should open both the disc space and foraminal height.

Reconstruction

The ultimate goal of anterior fusion at the lumbosacral junction is to obtain stable bony union through the interbody space. After discectomy and endplate preparation, this is achieved by the placement of an appropriate interbody graft and promotion of segmental stability.

Bone graft

Bone graft options include autograft, allograft, calcium ceramics and biologics including demineralized bone matrices and bone morphogenetic proteins. Iliac crest autograft can be harvested through a separate incision to provide a structural graft or in conjunction with an interbody cage. Structural femoral ring allograft or machined allograft are alternatives that provide both structural support and a scaffold for bone graft. Bone graft substitutes will also have to be contained within an intervertebral cage. The ‘ideal’ bone graft substitute would offer both osteoblastic cells (osteogenesis), scaffold (osteoconduction) and signals (osteoinduction). No currently available bone graft substitute will offer all 3 components and the choice will depend on cost, availability (including regulatory restrictions) and the perceived difficulty of the ‘fusion environment’.

Interbody support

Segmental stability will be achieved by a structural interbody strut, which maintains the disc distraction and interbody lordosis as well as a friction fit to minimize intervertebral rotation. This fixation can be complemented with supplementary fixation.

Options for the interbody strut include a structural graft, such as the allograft options mentioned above or an intervertebral cage. Modern cages have a more ‘anatomic’ design, are impacted into the disc space and rest on the intact vertebral endplates. They often have a central void that can be filled with graft that will eventually fuse between the adjacent levels.

A wide variety of materials has been used for manufacture of cages. Either surface treatments or coatings can be used to promote initial stability and bony ingrowth. Some solid cages have a porous structure that also encourages both initial friction stability and bony ingrowth. Increasingly, three-dimensional (3D) printing technologies have allowed the manufacture of cages with a lattice structure. These are now produced in polyether ether ketone (PEEK) and titanium alloy. There is increasing evidence that 3D printed titanium lattice cages have increased fusion rates and reduced subsidence rates (23).

Many commercially available cages are supplied in a range of sizes, heights and lordotic angulations. The recognition that the lumbo-sacral segment is an important contributor to overall lumbar lordosis has led to increasing number of ‘hyper-lordotic’ cages becoming available and there are also the option of expandable cages to increase lordosis. However, there is some evidence that cages with lordosis greater than 15 degrees can increase cage subsidence rates with minimal further improvement in sagittal balance (24).

Supplementary fixation

Supplementary fixation will enhance the initial stability of an interbody implant. An anterior tension band plate secured with screws in the vertebra provides very good fixation. Cages with integrated fixation mechanisms, whereby screws or staples pass through the cage and directly fix the interbody implant to the adjacent vertebrae are commonly used. The course of the descending nerves with the shape of the L5 vertebral body and sacrum mean the L5 and S1 nerve roots may be at risk during placement of anterior vertebral body screws (Figure 7A). At these levels, particular attention should be paid to maintaining midline hardware placement to avoid inadvertent nerve root injury.

Figure 7 Surgical challenges. (A) The yellow dashed line represents the back of the L5 vertebral body, as would be seen on a lateral X-ray. The yellow ovals demonstrate the course of the L5 nerves through the foramen, anterior to this plane. If screw placement is not midline, the screws may breach the foramen and impinge on the nerve. (B) The dashed line represents the projection of the sacral slope in a patient with a steep lumbosacral junction. It lies below the symphysis pubis, illustrated with an arrow. An anterior approach in this patient would be challenging and an alternate approach may be more appropriate.

In cases where there are concerns around efficacy of stand-alone anterior fusion, a separate posterior stabilization procedure with pedicle screw or facet joint fixation can be performed.

Implantation

Pre-operative measurements and planning should give some guide to the appropriate size and shape of the intended implant. Selected implants should undergo trial implantation and radiographs be obtained to check the implant positioning including the amount of distraction, reduction and lordotic angulation achieved. The implant should cover the endplate with no obvious point loading and no intrusion into the spinal canal. If satisfactory definitive implant can proceed. Final radiographs of the completed construct should be obtained.

Steep lumbosacral slope

The lumbosacral junction is oriented inferior to the horizontal. The sacral slope is measured in normal populations between 25 and 55 degrees to the horizontal (1). Patients with a developmental spondylolisthesis have greater sacral slope (25). With steeper angled segments access to the disc space can become challenging (Figure 7B). The projection of the sacral slope line defines the optimal approach to the disc space. If this line intersects or lies below the upper margin of the symphysis pubis, access will not be optimal. Pre-operative recognition and planning will allow the incision to be placed as low as possible. Intraoperatively, the use of a curved Cobb elevator in the disc space can lever against the L5 vertebral body to open the disc access anteriorly and partially reduce spondylolisthesis, if present. The use of angled and curved instruments may help access in the disc space. However, given the poor visualization, there is a greater risk of endplate violation or incomplete dorsal decompression. Judicious use of radiographic guidance can help determine the extent of discectomy. The placement of the interbody cage or screw in the L5 vertebra can be difficult due to the pubis symphysis restricting instruments. Articulated and angled inserters and drivers can overcome this. A technique for radiographically guided cage insertion in steep lumbosacral segments using freehand impactors has been described (26).

Difficult access to the disc space may be further exacerbated in spondylolisthesis where the ventral slip of the L5 vertebra and focal lumbosacral kyphosis may mean the inferior corner of the L5 vertebra obstructs disc exposure. This anterior-inferior corner of the vertebra can be resected to improve visualization as needed.

Closure

The retractors should be removed one-by-one and the great vessels inspected. Gradual removal of the retractors allows for careful inspection of the local structures and maintenance of exposure if bleeding from vessel injury becomes apparent. The iliac arterial pulses can be palpated after retractor removal and the veins palpated for thrombus. The ureter can be inspected on the peritoneum. The peritoneum is inspected and any further tears repaired. The inferior epigastric arteries are inspected and their pulse checked. The linea alba is closed with a strong monofilament slowly-absorbable suture (such as 0-polydiaxanone). The skin is normally closed with an absorbable subcuticular suture. Additional analgesia can be provided with local anesthetic infiltration or a transversus abdominis plane (TAP) block (27).

Post-operative care

Patients are encouraged to progressively mobilize with supervision from the first morning after surgery. If a patient-controlled analgesia (PCA) infusion has been necessary, it is converted to an appropriate dose of regular and breakthrough medication. In cases of chronic pain or high pre-operative analgesia requirements, additional analgesic agents may be needed and the involvement of the pain service is often sought.

Immediately after surgery, patients may have ice and sips of water for oral comfort care. The following day, if there is no significant nausea or vomiting and the abdomen is soft, early institution of a normal diet may commence. Patients are assessed on a daily basis and may require oral aperients or enema on day 3–4 if bowels have not opened. Due to mobilisation of the peritoneum and its contents, a postoperative ileus can occur. This may be exaggerated in patients with prior chronic opioid use. Standard deep venous prophylaxis is commenced with subcutaneous unfractionated or low molecular weight heparins, thromboembolic stockings (TEDS) and utilisation of sequential calf compressors. Bilateral lower limb venous duplexes may be performed for assessment of deep venous thrombosis in the immediate post-operative period.

Post-operative complications

Ileus occurs in 5% (28) of cases despite a cautious reintroduction of oral fluids and solids post operatively. Symptoms of bloating, abdominal pain, failure to pass flatus with nausea and vomiting should be investigated with abdominal X-ray or computed tomography (CT). Management consists of supportive measures with nil oral intake, nasogastric decompression of the gastric contents and intravenous fluids or parenteral nutrition if the ileus continues for more than 5–7 days. To try and reduce the incidence patients should have minimal opioid analgesia, early mobilization and regular cephalic vagal reflux stimulation with chewing gum can be used.

Retrograde ejaculation occurs in approximately 2% of ALIF cases after disruption of the superior hypogastric plexus (28). Diagnosis is only made in a delayed fashion with dry orgasms or cloudy urine after orgasm. The condition is often tolerated if the patient’s fertility is not a concern. There are medical treatments which attempt to restore antegrade ejaculation through bladder neck tone [sympathomimetics, tricyclic antidepressants and antihistamines (29)] and a urological opinion can be sought. Superior hypogastric plexus injury can also cause bladder and bowel dysfunction; loss of bladder tone can result in impaired voiding and incontinence. Autonomic bowel dysfunction can include constipation and overflow incontinence. A spinal injuries rehabilitation specialist opinion should be sought if this is suspected.

Abdominal visceral or ureteric injury are rare complications [under 1% (28)] and may present with symptoms ranging from abdominal pain to post operative sepsis. This diagnosis should be considered, and appropriate urgent CT imaging should be obtained if there is concern; with referral to general or urological surgery.

In a delayed setting there is approximately a 1–2% incidence of abdominal wall hernia. This often presents with a painful swelling at the operative site. Diagnosis is made initially with ultrasound imaging and management depends on patient symptoms and imaging findings but it may require operative repair.

Conclusions

L5/S1 ALIF is a highly effective procedure when performed with careful anatomical understanding and meticulous surgical technique. Recognition of patient-specific factors is essential to surgical success. Optimizing approach and execution can minimize complications and maximize the biomechanical and clinical benefits of anterior interbody fusion.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the Guest Editors (Prashanth J. Rao and Andrew Lennox) for the series “Anterior Lumbar Interbody Fusion - A Definitive Guide for Surgeons” published in Journal of Spine Surgery. The article has undergone external peer review.

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-167/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-167/coif). The series “Anterior Lumbar Interbody Fusion - A Definitive Guide for Surgeons” was commissioned by the editorial office without any funding or sponsorship. J.R.B. serves as an unpaid editorial board member of Journal of Spine Surgery from November 2024 to December 2026. M.J.G. reports accommodation and registration for DDU Deformity down under conference 2025 supplied by LifeHealthcare Australia. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All clinical procedures described in this study were performed in accordance with the ethical standards of the institutional and/or national research committees and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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