A biomechanical study shows the direction of compression influences the amount of lordosis gained in lumbar fusion.

STUDY DESIGN: Biomechanical model study. BACKGROUND: Lumbar lordosis is usually lost in the degenerative process, and when lumbar fusion is required, its restoration is one of the modern metrics of a successful operation. We sought to investigate the hypothesis that changing direction of compression during surgical fusion, would gain more lordosis. METHODS: Using a biomechanical Sawbones™ model we inserted polyaxial pedicle screws from S1 to L4. A rod was placed in the screws without requiring reduction. Markers were attached to the spinous processes to allow photographic analysis of lordosis. Two methods were compared. Method A - caudal screws were locked first and compression proceeded in a cranial direction prior to locking. Method B - cranial screws were locked first and compression proceeded caudally. Increasing levels of surgical invasiveness were tested; intact, interbody cage, inferior facet resection, and Ponte resection and using different rods including: lordotic, hyperlordotic and straight. FINDINGS: Method B demonstrated to be consistently superior to Method A, regardless of the type of rod used and for every level of surgical invasiveness performed. (P < 0.001). INTERPRETATION: locking the top screws first was a consistently superior method of compression, gaining more lordosis. To explain this finding we suggest the following: During posterior compression of pedicle screws along a fixed rod, screw motion is limited by the conflict between the fixed lordotic rod position, and the need for the moving screw to move in a kyphotic arc which is determined by the cage which acts as a pivot point.

Consent for spine surgery: an observational study.

BACKGROUND: The tension between the ideal of informed consent and the reality of the process is under-investigated in spine surgery. Guidelines around consent imply a logical, plain-speaking process with a clear endpoint, agreement and signature yet surgeons' surveys and patient interviews suggest that surgeons' explanation is anecdotally variable and patient understanding remains poor. To obtain a more authentic reflection of practice, spine surgeons obtaining 'informed consent' for non-instrumented spine surgery were studied via video recording and risk/benefit discussions were analysed. METHODS: A prospective observational study was conducted at a single neurosurgical institution. Twelve video recordings involving six surgeons obtaining an informed consent for non-instrumented spine surgery were transcribed verbatim and blindly analysed using descriptive quantification and linguistic ethnography. RESULTS: Ten (83%) consultations discussed surgical benefit but less than half (41%) quantified the likelihood of benefit from surgery. The most discussed risks were nerve damage or paralysis (92%), bleeding (92%), infection (92%), cerebrospinal fluid leak (83%) and bowel and bladder dysfunction (75%). Surgeons commonly used a quantitative statement of risk (58%) but only half of the risks were explained in words patients were likely to understand. CONCLUSIONS: This study highlights inconsistencies in the way spine surgeons explain risks and obtain informed consent for 'simple' spine procedures in a real-world setting. There are wide disparities in the provision of informed consent, which may be encountered in other surgical fields. Direct observation and qualitative analysis can provide insights into the limitations of current informed consent practice and help guide future practice.

Morphometric anatomy of the lumbar sympathetic trunk with respect to the anterolateral approach to lumbar interbody fusion: a cadaver study.

BACKGROUND: An approach to lateral lumbar interbody fusion (LLIF) utilizing an oblique corridor anterior to the psoas muscle was first described by Mayer in 1997 and subsequently by other authors. The only consistent structure of note in this corridor is the lumbar sympathetic trunk (LST), which at times must be mobilized in order to perform a discectomy and interbody fusion, thereby placing the LST at risk. This study was designed to describe the morphometric anatomy of the LST in relation to surgically relevant landmarks for the anterolateral approach to the lumbar spine at L3/L4 to L5/S1. METHODS: Twenty-four embalmed cadavers (13 males, 11 females, age range, 50-89) were dissected to expose the LST. Bilateral measurements were recorded using a calliper under direct visualization, using the midsagittal plane of the lumbar spine as the reference landmark. The points were then marked with radio-opaque needles, and 14 cadavers were scanned with CT to validate the measurements. RESULTS: Of 48 LSTs, there was minimal difference in the direction of its course between sides; 14/24 specimens had concordant directions. The majority (n=28) had a medial to lateral cephalocaudal course. If osteophytes were present at the L4/L5 level, the majority of LSTs (n=7, of 8) were displaced lateral to the osteophyte. At the L5/S1 level, half of the cases with osteophytes (n=3, of 6) stretched the LST over the top of the osteophyte. The LST was adherent to the L4/L5 disc space bilaterally in 93% of cases. CONCLUSIONS: With the development of lumbar fusion techniques which utilize an oblique corridor and the retraction of psoas muscle, LST has become an important neural structure to define, protect and mobilize. In our morphometric analysis of 24 specimens, the position has been identified and quantified, and this paper notes variations, particularly distortions caused by degenerative processes. In this study, the LST ran in a medial to lateral direction from L3 to S1, and osteophytes typically displace and adhere to the LST.

Maintenance of Segmental Lordosis and Disk Height in Stand-alone and Instrumented Extreme Lateral Interbody Fusion (XLIF).

STUDY DESIGN: A prospective single-surgeon nonrandomized clinical study. OBJECTIVE: To evaluate the radiographic and clinical outcomes, by fixation type, in extreme lateral interbody fusion (XLIF) patients and provide an algorithm for determining patients suitable for stand-alone XLIF. SUMMARY OF BACKGROUND DATA: XLIF may be supplemented with pedicle screw fixation, however, since stabilizing structures remain intact, it is suggested that stand-alone XLIF can be used for certain indications. This eliminates the associated morbidity, though subsidence rates may be elevated, potentially minimizing the clinical benefits. MATERIALS AND METHODS: A fixation algorithm was developed after evaluation of patient outcomes from the surgeon's first 30 cases. This algorithm was used prospectively for 40 subsequent patients to determine the requirement for supplemental fixation. Preoperative, postoperative, and 12-month follow-up computed tomography scans were measured for segmental and global lumbar lordosis and posterior disk height. Clinical outcome measures included back and leg pain (visual analogue scale), Oswestry Disability Index (ODI), and SF-36 physical and mental component scores (PCS and MCS). RESULTS: Preoperatively to 12-month follow-up there were increases in segmental lordosis (7.9-9.4 degrees, P=0.0497), lumbar lordosis (48.8-55.2 degrees, P=0.0328), and disk height (3.7-5.5 mm, P=0.0018); there were also improvements in back (58.6%) and leg pain (60.0%), ODI (44.4%), PCS (56.7%), and MCS (16.1%) for stand-alone XLIF. For instrumented XLIF, segmental lordosis (7.6-10.5 degrees, P=0.0120) and disk height (3.5-5.6 mm, P<0.001) increased, while lumbar lordosis decreased (51.1-45.8 degrees, P=0.2560). Back (49.8%) and leg pain (30.8%), ODI (32.3%), PCS (37.4%), and MCS (2.0%) were all improved. Subsidence occurred in 3 (7.5%) stand-alone patients. CONCLUSIONS: The XLIF treatment fixation algorithm provided a clinical pathway to select suitable patients for stand-alone XLIF. These patients achieved positive clinical outcomes, satisfactory fusion rates, with sustained correction of lordosis and restoration of disk height.

Choice of Approach Does Not Affect Clinical and Radiologic Outcomes: A Comparative Cohort of Patients Having Anterior Lumbar Interbody Fusion and Patients Having Lateral Lumbar Interbody Fusion at 24 Months.

STUDY DESIGN: Retrospective analysis of prospectively collected registry data. OBJECTIVE: This study aimed to compare the clinical and radiologic outcomes between comparative cohorts of patients having anterior lumbar interbody fusion (ALIF) and patients having lateral lumbar interbody fusion (LLIF). METHODS: Ninety consecutive patients were treated by a single surgeon with either ALIF (n = 50) or LLIF (n = 40). Inclusion criteria were patients age 45 to 70 years with degenerative disk disease or grade 1 to 2 spondylolisthesis and single-level pathology from L1 to S1. Patient-reported outcome measures included pain (visual analog scale), disability (Oswestry Disability Index [ODI]), and quality of life (Short Form 36 physical component score [PCS] and mental component scores [MCS]). Assessment of fusion and measurement of lordosis and posterior disk height were performed on computed tomography scans. RESULTS: At 24 months, patients having ALIF had significant improvements in back (64%) and leg (65%) pain and ODI (60%), PCS (44%), and MCS (26%; p < 0.05) scores. Patients having LLIF had significant improvements in back (56%) and leg (57%) pain and ODI (52%), PCS (48%), and MCS (12%; p < 0.05) scores. Fourteen complications occurred in the ALIF group, and in the LLIF group, there were 17 complications (p > 0.05). The fusion rate was 100% for ALIF and 95% for LLIF (p = 0.1948). ALIF added ∼6 degrees of lordosis and 3 mm of height, primarily measured at L5-S1, and LLIF added ∼3 degrees of lordosis and 2 mm of height between L1 to L5. Mean follow-up was 34.1 months. CONCLUSIONS: In comparative cohorts of patients having ALIF and patients having LLIF at 24 months postoperatively, there were no significant differences in clinical outcomes, complication rates, or fusion rates.

Complex Spine Pathology Simulator: An Innovative Tool for Advanced Spine Surgery Training.

Background Technical advancements in spine surgery have made possible the treatment of increasingly complex pathologies with less morbidity. Time constraints in surgeons' training have made it necessary to develop new training models for spine pathology. Objective To describe the application of a novel compound, Stratathane resin ST-504 derived polymer (SRSDP), that can be injected at different spinal target locations to mimic spinal epidural, subdural extra-axial, and intra-axial pathologies for the use in advanced surgical training. Material and Methods Fresh-frozen thoracolumbar and cervical spine segments of human and sheep cadavers were used to study the model. SRSDP is initially liquid after mixing, allowing it to be injected into target areas where it expands and solidifies, mimicking the entire spectrum of spinal pathologies. Results Different polymer concentrations have been codified to vary adhesiveness, texture, spread capability, deformability, and radiologic visibility. Polymer injection was performed under fluoroscopic guidance through pathology-specific injection sites that avoided compromising the surgical approach for subsequent excision of the artificial lesion. Inflation of a balloon catheter of the desired size was used to displace stiff cadaveric neurovascular structures to mimic pathology-related mass effect. Conclusion The traditional cadaveric training models principally only allow surgeons to practice the surgical approach. The complex spine pathology simulator is a novel educational tool that in a user-friendly, low-cost fashion allows trainees to practice advanced technical skills in the removal of complex spine pathology, potentially shortening some of the aspects of the learning curve of operative skills that may otherwise take many years to acquire.

Anterior to psoas (ATP) fusion of the lumbar spine: evolution of a technique facilitated by changes in equipment.

BACKGROUND: Lateral interbody cages have been proven useful in spinal fusions. Spanning both lateral cortical rims while sparing the Anterior Longitudinal Ligament, the lateral interbody cages restore and maintain disc height while adding stability prior to supplemental fixation. The standard approach for their insertion is by a 90-degree lateral transpsoas method. This is relatively bloodless compared to other techniques although has its limitations, requiring neuro-monitoring and being, at times, very difficult at L4/5 due to iliac crest obstruction or an anterior plexus position. An oblique approach, with the patient in lateral decubitus, passes anterior to the iliac crest, retroperitoneal, and being anterior to psoas, eliminates the need for neuro-monitoring. METHODS: Twenty-one consecutive patients underwent surgery for a total of 32 levels instrumented with the ATP technique. Mean age at the time of surgery was 62.4±7.4 years. There was a 6 months minimum clinical follow up, with imaging to assess fusion, at 6 and 12 months. Indications included symptomatic degenerative lumbar spondylosis +/- spondylolisthesis, leg and back pain. All patients were assessed with the Oswestry Disability Index (ODI), Visual Analog Scale 100 mm for back pain (VASb) and for leg pain (VASl) preoperatively, at 3, 6 and 12 months. Last follow-up was at 12 months for 9 patients and the rest had 6 months follow up. RESULTS: Statistical analysis showed significance for the results in ODI, VASb and VASl with improvement in all components except for one patient with worsening VASl. Eight patients had complications related to surgery which were still present at last follow-up including moderate weakness of hip flexion and EHL weakness. Lateral cutaneous nerve (LCN) palsy on the side of the approach was also seen as well as sympathectomy effect related to the mobilization of the sympathetic trunk. One patient, who also suffered from multiple sclerosis, experienced psoas abscess 3 months post op that required drainage. CONCLUSIONS: The left sided anterior to psoas approach offers the most natural corridor to the disc space. The novel instruments and method described here allows insertion of large lateral cages between L2 to L5, without the problems associated with the transpsoas approach, particularly at L4/5.

Assessment and classification of subsidence after lateral interbody fusion using serial computed tomography.

OBJECT Intervertebral cage settling during bone remodeling after lumbar lateral interbody fusion (LIF) is a common occurrence during the normal healing process. Progression of this settling with endplate collapse is defined as subsidence. The purposes of this study were to 1) assess the rate of subsidence after minimally invasive (MIS) LIF by CT, 2) distinguish between early cage subsidence (ECS) and delayed cage subsidence (DCS), 3) propose a descriptive method for classifying the types of subsidence, and 4) discuss techniques for mitigating the risk of subsidence after MIS LIF. METHODS A total of 128 consecutive patients (with 178 treated levels in total) underwent MIS LIF performed by a single surgeon. The subsidence was deemed to be ECS if it was evident on postoperative Day 2 CT images and was therefore the result of an intraoperative vertebral endplate injury and deemed DCS if it was detected on subsequent CT scans (≥ 6 months postoperatively). Endplate breaches were categorized as caudal (superior endplate) and/or cranial (inferior endplate), and as ipsilateral, contralateral, or bilateral with respect to the side of cage insertion. Subsidence seen in CT images (radiographic subsidence) was measured from the vertebral endplate to the caudal or cranial margin of the cage (in millimeters). Patient-reported outcome measures included visual analog scale, Oswestry Disability Index, and 36-Item Short Form Health Survey physical and mental component summary scores. RESULTS Four patients had ECS in a total of 4 levels. The radiographic subsidence (DCS) rates were 10% (13 of 128 patients) and 8% (14 of 178 levels), with 3% of patients (4 of 128) exhibiting clinical subsidence. In the DCS levels, 3 types of subsidence were evident on coronal and sagittal CT scans: Type 1, caudal contralateral, in 14% (2 of 14), Type 2, caudal bilateral with anterior cage tilt, in 64% (9 of 14), and Type 3, both endplates bilaterally, in 21% (3 of 14). The mean subsidence in the DCS levels was 3.2 mm. There was no significant difference between the numbers of patients in the subsidence (DCS) and no-subsidence groups who received clinical benefit from the surgical procedure, based on the minimum clinically important difference (p > 0.05). There was a significant difference between the fusion rates at 6 months (p = 0.0195); however, by 12 months, the difference was not significant (p = 0.2049). CONCLUSIONS The authors distinguished between ECS and DCS. Radiographic subsidence (DCS) was categorized using descriptors for the location and severity of the subsidence. Neither interbody fusion rates nor clinical outcomes were affected by radiographic subsidence. To protect patients from subsidence after MIS LIF, the surgeon needs to take care with the caudal endplate during cage insertion. If a caudal bilateral (Type 2) endplate breach is detected, supplemental posterior fixation to arrest progression and facilitate fusion is recommended.

Lumbar interbody fusion: techniques, indications and comparison of interbody fusion options including PLIF, TLIF, MI-TLIF, OLIF/ATP, LLIF and ALIF.

Degenerative disc and facet joint disease of the lumbar spine is common in the ageing population, and is one of the most frequent causes of disability. Lumbar spondylosis may result in mechanical back pain, radicular and claudicant symptoms, reduced mobility and poor quality of life. Surgical interbody fusion of degenerative levels is an effective treatment option to stabilize the painful motion segment, and may provide indirect decompression of the neural elements, restore lordosis and correct deformity. The surgical options for interbody fusion of the lumbar spine include: posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), minimally invasive transforaminal lumbar interbody fusion (MI-TLIF), oblique lumbar interbody fusion/anterior to psoas (OLIF/ATP), lateral lumbar interbody fusion (LLIF) and anterior lumbar interbody fusion (ALIF). The indications may include: discogenic/facetogenic low back pain, neurogenic claudication, radiculopathy due to foraminal stenosis, lumbar degenerative spinal deformity including symptomatic spondylolisthesis and degenerative scoliosis. In general, traditional posterior approaches are frequently used with acceptable fusion rates and low complication rates, however they are limited by thecal sac and nerve root retraction, along with iatrogenic injury to the paraspinal musculature and disruption of the posterior tension band. Minimally invasive (MIS) posterior approaches have evolved in an attempt to reduce approach related complications. Anterior approaches avoid the spinal canal, cauda equina and nerve roots, however have issues with approach related abdominal and vascular complications. In addition, lateral and OLIF techniques have potential risks to the lumbar plexus and psoas muscle. The present study aims firstly to comprehensively review the available literature and evidence for different lumbar interbody fusion (LIF) techniques. Secondly, we propose a set of recommendations and guidelines for the indications for interbody fusion options. Thirdly, this article provides a description of each approach, and illustrates the potential benefits and disadvantages of each technique with reference to indication and spine level performed.