Julia M. Balboni, OMS-III³; Rajeev Rao, M.D.¹; Brian Perri, D.O.²; Albert Wong, M.D.^2 
1Cedars-Sinai Medical Center
²DOCS Spine + Orthopedics
³University of New England

Declaration of Conflict of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. This study was funded in its entirety by the DOCS Spine + Orthopedics.

ABSTRACT

Lumbar total disc replacement has become increasingly common in the treatment of chronic low back pain. Despite this recent rise in popularity, revision surgery is sometimes necessary due to long-term wear or errors in implant sizing and positioning. Although the left retroperitoneal plane is often the preferred course when exposing the lumbar spine anterolaterally, the benefits associated with a right-side approach warrant exploration. When reoperation follows the same trajectory as the primary surgery, prior surgical scarring can increase the risk of iatrogenic injury. Despite this, a repeat left-side approach is commonly performed. This study identified a right-side retroperitoneal approach as a clinically relevant and feasible strategy in primary lumbar total disc replacement surgery to preserve the left-side retroperitoneal plane should reoperation become necessary in the future.

Keywords: right-side, exposure, lumbar spine, primary surgery, revision, anterior, retroperitoneal

Background
While spinal fusion remains a viable option in the surgical management of discogenic pathologies, arthroplasty has become an increasingly popular alternative. With the advent of lumbar total disc replacement (LTDR), researchers around the globe have conducted countless trials comparing the efficacy of lumbar fusion to that of LTDR in the treatment of low back pain. The evidence amassed by these studies has demonstrated benefits and drawbacks associated with both techniques, suggesting that ultimately, a variety of factors, such as patient demographics, lifestyle, and spinal level dictate which procedure is likely to yield the best results. While spinal fusion for the treatment of axial low back pain is not always successful, neither is LTDR. With fusion, there is concern regarding accelerated degeneration of adjacent levels.^[1,2] With LTDR, however, there is controversy surrounding long-term durability and longevity. Nonetheless, both fusion and LTDR remain viable options for the treatment of intractable low back pain, a debilitating condition that effects 38% of the global population annually.^[3]

Statistically, L4-5 and L5-S1 are the two levels most commonly affected by degenerative disc disease.^[4] When clinically indicated, current evidence supports LTDR over fusion at the L4-5 level due to better total motion after surgery.^[5,6] In younger, more physically active patients where motion preservation is vital, LTDR can be used to protect against kinematic alterations at both the operative and adjacent intervertebral disc levels. By preserving mobility, LTDR mitigates the risk of subsequent degenerative changes that occur following spinal fusion due to overloading.^[7]

Despite the many advantages of LTDR, implant longevity remains uncertain, and reoperation is sometimes necessary.^[8] Several studies have investigated the rate of reoperation of LTDR at 5-year follow-up visits with two independent studies reporting rates of 15.8% ^[9] and 16% ^[10], respectively. Given this data, the approach to primary LTDR surgery should consider the possibility of reoperation.

When revision follows the same trajectory and approach as the primary surgery, index surgery scarring can severely hinder remobilization, increasing the risk of vascular or visceral complications.^{[11, 12]} Secondary exposure of the lumbar spine or explanation of the disc prosthesis is often complicated by adherence of the ureter, aorta, and iliac vessels at the operative site. In fact, much of the literature supports contralateral exposure of the lumbar spine during revision.^[13] Despite this, a repeat left-side approach is commonly used for both primary and revision LTDR surgery due to the notion that a right-side approach is more challenging and less safe.

Due to the anatomical location of the great vessels, a left-side approach is preferred. In comparison to the inferior vena cava, the abdominal aorta can be moved a greater distance during vessel mobilization and is more easily palpable, making it better suited as an initial anatomical landmark. However, Edgard-Rosa et al. described a midline anterior approach to the lumbar spine from the right side by mobilizing the vena cava from right to left between L2-L5. Using the results of 469 patients, the researchers evaluated the risk associated with this approach and found it to be a safe alternative compared with the traditional left-side approach.^[14]

When applied to LTDR, a right-side approach, albeit inherently more complicated, is best facilitated during the primary exposure when scaring and adhesions are absent. This study examines a small case series of LTDR index surgeries performed by exposing the disc space anterolaterally from the right side. Study objectives aim to evaluate the application of a right-side anterior retroperitoneal approach to primary LTDR surgery at the L4-5 level, thereby preserving a virgin left-side retroperitoneal plane should reoperation be necessary at the same level, or at an adjacent level, in the future.

Methods
The study included two patients who underwent primary lumbar total disc replacement surgery at the L4-5 level. The first of which was a 30-year-old male with clinical indications for lumbar total disc replacement who was identified as an appropriate candidate for anterior retroperitoneal surgery. Upon examination, the patient presented with severe low back pain and lower extremity radiculopathy, which was determined to be the result of degenerative disc disease at the L4-5 level. Despite attempts to alleviate symptoms with non-surgical interventions, the patient remained unresponsive to nonsteroidal anti-inflammatory drugs, muscle relaxants, corticosteroids, and physical therapy. Due to the patient’s age and active lifestyle, artificial disc replacement was selected over lumbar fusion to preserve vertebral motion and prevent adjacent segment degeneration. A right retroperitoneal approach was planned based on review of the preoperative MRI and anticipated implant longevity.

The second patient was a 59-year-old male with evidence of a small fracture and inflammatory changes on the right side of the L5 vertebrae. Due to the location of the vertebral injury in this patient, the surgeon elected to use a right-sided approach to safeguard against undue risk when gaining access to the lumbar spine and ensure safe instrumentation. This study proceeded under Institutional Review Board exemption and with informed consent from all patients. All appropriate measures were taken to uphold HIPPA Privacy Rule standards.

Surgical Technique
Prior to the start of the procedure, a skin mark was made over the L4-5 level using lateral and anteroposterior fluoroscopy images. A midline incision in the external oblique initiated vascular exposure, after which a plane was developed posterior to the right rectus abdominis. The retroperitoneal space was then entered below the arcuate line. The peritoneum and ureter were swept towards the patient’s left, exposing the right common iliac artery and right common iliac vein. The medial border of the right iliac artery and vein were visualized and dissection was carried down to the anterior surface of the L4-5 disc space.

Despite an initial attempt to perform the exposure below the iliac bifurcation, the confluence of the right and left iliac veins just above the level of L4-5 caused retraction of the iliac vessel laterally to be deemed unsafe by the surgeon. Instead, dissection was carried laterally along the distal vena cava and the right common iliac vein. The iliolumbar vein and L4 segmental vessels on the right side were ligated with vascular clips and then divided. This allowed blunt mobilization of the IVC and right iliac vein towards the patient’s left to expose the anterior surface of the L4-5 disc space. Finally, a needle was placed in the disc space and a lateral fluoroscopy image was obtained to verify exposure of the index level.

Results
When performed jointly by a vascular surgeon and spine surgeon team, a right-sided anterior retroperitoneal exposure can be safely executed during primary LTDR surgery without heightened risk of surgical complications. In both cases, the peritoneum, ureter, and iliac vessels were intact upon completion of the right retroperitoneal exposure. Blood loss averaged 100mL in each case and oxygen saturation remained uninterrupted. In the post-operative course, there were no reports of retroperitoneal hematoma, retrograde ejaculation, or deep vein thrombosis. Furthermore, neither patient experienced intraoperative vascular injury requiring primary repair with suturing and both were discharged the following day.

Discussion
This study identified a right-side retroperitoneal exposure of the anterior lumbar spine as a clinically relevant and feasible strategy in primary LTDR surgery to preserve the left-side retroperitoneal plane should reoperation become necessary in the future. Although the two cases described in this report were without complication, concerns regarding the right-sided approach stem from the fear of increased vascular complications and risk of retrograde ejaculation.^[15] While the incidence of vascular injury following an anterior approach to the lumbar spine remains low, there have been reports in the literature of fatal acidosis from rhabdomyolysis, thrombosis, and hemorrhage.^[16] The left-side approach is often preferred due to the ability to encounter the abdominal aorta as the first anatomic landmark rather than the inferior vena cava, thereby reducing the likelihood of a venous tear. However, the common iliac veins are the most likely vasculature structures to be injured during anterior lumbar spine surgery. Extensive mobilization is required regardless of whether the approach is from the right or the left as these vessels course obliquely past the L4-5 and L5-S1 disc spaces bilaterally.^[17] In contrast to that of a left-sided approach, the vascular retraction necessary to achieve a right-side exposure does not result in arterial occlusion; this significantly reduces surgical risk in those patients with atherosclerosis and peripheral arterial disease. The left lateralization of the superior hypogastric plexus represents another reason why the right-side approach may be more practical at the L5-S1 level. Edgard-Rosa et al. proposed that by approaching this plexus from the right and then transposing from right to left, the risk of retrograde ejaculation may be reduced.^[14]

 As has been cited by previous studies, the low rate of venous injury associated with a right-side retroperitoneal exposure is likely explained by the increased sidewall thickness of the vena cava compared to that of the left common iliac vein.^[14] Nonetheless, due to the potentially grave implications of a venous tear, the skill and confidence of the vascular surgeon to repair a venous tear should be considered prior to performing a right-side approach. Furthermore, patients at increased risk of vascular injury, such as those with morbid obesity, vascular calcifications, or congenital deformities, should be recognized as poor surgical candidates for this procedure.

It is important to note that the index surgery provides the greatest opportunity for an optimal outcome as safe mobilization of the left common iliac vein is best facilitated in the absence of prior manipulation. However, in some cases, a right-sided approach is preferable due to the nature of the pathology. For example, the 59-year-old patient described in this study presented with a vertebral fracture on the right side of L5, and a right-sided approach was critical in ensuring safe exposure of the lumbar spine. Surgeons familiar with both the left and right approach can elect to perform a right-side exposure for not only the primary procedure, but also for the revision surgery in patients who have previously undergone a left-side approach.

 While this approach is associated with an additional 30 minutes of operative time, when revision follows the same trajectory as the index surgery, exposure of the anterior lumbar spine can be complicated by prevertebral scarring and adhesions, often increasing total operative time by 30 minutes or more. In severe cases, such complications can even preclude anterior exposure altogether.^[18] As with all studies, this study is subject to limitations. Additional studies are needed to increase the size of the investigative sample, as well as to evaluate the long-term utility of this approach.

Conclusion
Lumbar total disc replacement has become increasingly common in the treatment of chronic low back pain. Despite this, revision is sometimes necessary due to long-term wear or errors in implant sizing and positioning. Preservation of a virgin left-side retroperitoneal plane during the index surgery can significantly reduce the increased risk associated with reoperation by eliminating the need for a redundant left-side exposure. When the left retroperitoneal space has not been previously violated, revision surgery can be performed without heightened risk of peritoneal or left urethral injury. Furthermore, in the absence of abdominal scarring and vascular adhesions, the disc space can be more easily navigated, facilitating removal and reimplantation of the new prosthesis.

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