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Spondylolisthesis describes the displacement of a vertebrae or the vertebral column in relation to the vertebrae below. The term “spondylolisthesis” was coined in 1854, from the Greek language “spondylo” for vertebrae and “olisthesis” for slip. These "slips" occur most commonly in the lumbar spine.
A ~~hangman's fracture[[ is a specific type of spondylolisthesis where the C1 vertebra is displaced anteriorly relative to the C2 vertebra due to fractures of the C2 vertebra's pedicles.
In the late 1890s, several cadaver studies demonstrated the characteristic pars defect of isthmic spondylolisthesis, leading to many different theories concerning the etiology of the defect. The first theory proposed a failure of ossification during embryonic development, leading to a pars defect at birth, which then progressed to an isthmic slip after the infant began ambulating. Following the development of the Roentgenogram in 1895, population X-ray studies showed that isthmic spondylolisthesis is, in fact, quite common. A population study by Fredrickson, et al demonstrated that the pars defect began to appear around age six and became progressively more common till age 16. After age 16, the incidence fell and rarely developed after adolescence. This study confirmed that the pars defect was developmental and not a congenital defect. It is currently thought that the defect develops from small stress fractures that fail to heal and form a chronic nonunion. There have been reports that the defect is more common among athletes who participate in sports with repeated hyperextension, such as gymnastics, ballet, and American football.
Spondylolysis also runs in families and is more prevalent in some populations, suggesting a hereditary component, such as a tendency toward thin vertebral bone.
Spondylolysis is the most common cause of spondylolisthesis. The hereditary factor mentioned above is quite notable, since the frequency of spondylolisthesis in Eskimos is 30–50%.
Spondylolisthesis is officially categorized into five different typed by the]]Wiltse classification system[[: Dysplastic, Isthmic, Degenerative, Traumatic, and Pathologic.
Dysplastic spondylolisthesis is a true congenital spondylolisthesis that occurs because of malformation of the lumbosacral junction with small, incompetent facet joints. Dysplastic spondylolisthesis is very rare, but tends to progress rapidly, and is often associated with more severe neurological deficits. It is difficult to treat, because the posterior elements and transverse processes tend to be poorly developed, leaving little surface area for a posterolateral fusion.
Isthmic spondylolisthesis is the most common form of spondylolisthesis. Isthmic spondylolisthesis (also called spondylolytic spondylolisthesis) is a common condition with a reported prevalence of 5%-7% in the U.S. population. Fredrickson, et al demonstrated that the spondylolytic defect is usually acquired between the ages of 6 and 16 years, and that the slip often occurs shortly there after. Once the slip has occurred, it rarely continues to progress, although one study did find an association between disc desiccation and slip progression during middle-age. It is though that the vast majority of isthmic slips do not become symptomatic, but the incidence of symptoms is unknown. One very long-term prospective study by Fredrickson, et al that followed a cohort of 22 patients from the development of their slip into middle-age, reported that many of the patients experienced occasional back pain, but so does the vast majority of people without isthmic spondylolisthesis. One patient did undergo]]spinal fusion[[at the slipped level, but the study could not verify if the isthmic slip was the indication for surgery. Roughly 90% of isthmic slips are low-grade(less than 50% slip) and 10% are high-grade (greater than 50% slip).
The most common grading system for spondylolisthesis is the Meyerding grading system for severity of slip. The system categorizes severity based upon measurements on lateral X-ray of the distance from the posterior edge of the superior vertebral body to the posterior edge of the adjacent inferior vertebral body. This distance is then reported as a percentage of the total superior vertebral body length:
- Grade 1 is 0–25%
- Grade 2 is 25–50%
- Grade 3 is 50–75%
- Grade 4 is 75–100%
- Over 100% is Spondyloptosis, when the vertabra completely falls off the supporting vertabra.
Degenerative spondylolisthesis is a disease of the older adult that develops as a result facet arthritis and facet remodeling. As the facets remodel, they take on a more sagittal orientation, allowing a mild slip to occur. These slips are very common, a study of osteoporosis found a 30% incidence among Caucasian women older than 65 years and a 60% incidence among African-American women older than 65 years. Most slips are asymptomatic, but can worsen the symptoms of neurogenic claudication when associated with lumbar]]spinal stenosis[[. Degenerative spondylolisthesis with spinal stenosis is one of the most common indications for spine surgery among older adults and current evidence suggests that patients have much better success rates and more clinical benefit with decompression and fusion than decompression alone.
Traumatic spondylolisthesis is very rare and may be associated with acute fracture of the inferior facets or pars interarticularis. It is treated in the same manner as other spinal fractures and there are only a handful of case reports on this type.
Pathologic spondylolisthesis is the last type and is also very rare. This type can occur following damage to the posterior elements from metastases or metabolic bone disease. These slips have been reported in cases of]]Paget’s disease~~ of bone, tuberculosis, giant-cell tumors, and tumor metastases.
Low-Grade Isthmic Spondylolisthesis
Patients with symptomatic low-grade (<50% slippage) isthmic spondylolisthesis typically present with activity related back pain and often with radicular symptoms as well, but despite the large number of individuals with radiographic evidence of isthmic spondylolisthesis, few of them become symptomatic or require treatment.
Additionally, the cause of pain in patients with isthmic spondylolisthesis remains unclear. The first theory of pain production was segmental instability with excessive forward translation during flexion. This notion was logical from the mechanical standpoint as the pars defect eliminated the vertebral body’s primary restraint to forward translation, the inferior facet joint. This theory has now been evaluated by multiple radiographic studies, none of which were able to demonstrate excessive forward translation as a common feature of isthmic spondylolisthesis. A more contemporary theory of pain generation is excessive tension on the annulus of the inferior disc and foraminal stenosis at the level of the slip. Excessive annular tension is also mechanically logical as without the restraint of the inferior facet joints; the disc has to both resist shear forces from the slip and compressive forces from the body’s mass. However, this theory does not explain why some patients have symptoms while so many others do not, since the inferior discs all patients with isthmic spondylolisthesis are subjected to similar forces. Foraminal stenosis is also thought to play a role, but long-term studies on surgical outcome have shown that many patients have poor results following decompression alone. Since the mid-1950s, surgeons have been advocating the combination of decompression and fusion. A recent biomechanical study of flexion-extension X-rays in patients with isthmic spondylolisthesis and normal controls found paradoxical motion at the level of the slip in 46% of patients and 0% of controls without back pain. Paradoxical motion has not been previously reported in cases of spondylolisthesis, but its role in the symptomatic and asymptomatic patient is unclear.
High-Grade Isthmic Spondylolisthesis
High-grade isthmic spondylolisthesis and dysplastic spondylolisthesis are regarded as separate clinical entities from low-grade isthmic slips. High-grade slips are defined as those with greater than 50% forward displacement. These slips are also accompanied by a significant amount of lumbosacral kyphosis, which is forward bending of the L5 vertebral body over the sacral promontory. Rounding of the sacral body and trapezoidal deformation of L5 are also common features. High-grade slips are much rarer than low-grade slips, representing less than 10% of all isthmic slips, and the vast majority present during adolescence, most during the early teenage years.
Unlike low-grade slips, many patients present without pain. Instead symptoms like bodily deformity, neurologic abnormalities, tight hamstrings, and abnormal gait are often the reason for consultation. The natural history of high-grade spondylolisthesis is also quite different from those with low-grade slips. The majority of low-grade slips are asymptomatic and do not progress past a patient’s initial presentation. Prospective studies on children with low-grade slips have demonstrated that once a slip occurs, it rarely worsens, even after 40+ years of follow-up1. However, high-grade slips do continue to progress in many cases and are much more likely to cause pain. One natural history study by a Swedish researcher, Saraste, found that roughly 60% of patients with slips greater than 15 mm (which is roughly a meyerding grade 2 or greater) had persistent daily symptoms, including both back pain and radiculopathy. The low-grade slips in Saraste's study were only symptomatic in 10% of patients.
Some cases do eventually progress to complete spondyloptosis and prevention of progression is the primary focus of surgery for high-grade slips. Why low-grade slips tend not to progress and why certain slips ultimately become severe is not known. There have been few long-term follow-up studies on patients with high-grade spondylolisthesis who did not undergo surgery. Harris and Weinstein reported on eleven patients after a mean follow-up of 18 years, all of which had greater than 50% slip and did not have surgery. Thirty-six percent of patients were asymptomatic, 55% of patients had relatively mild symptoms, and only one (9%) was disabled. The patients with mild symptoms were all able to work and participate in recreational activities, although they did need to make modifications to their lifestyle. No patient developed fulminant cauda equina syndrome, severe neurologic symptoms, or incontinence. Forty-five percent of patients had some neurologic abnormalities on exam, including weakness, paresthesias, and diminished deep tendon reflexes. Patient symptoms were primarily related to mild to moderate neurologic symptoms, muscle weakness, especially abdominal muscles, inactivity/deconditioning, obesity, lack of spinal mobility, and the late development of degenerative scoliosis with lateral listhesis (a deformity associated with advanced osteoarthritis of the lumbar spine). The patients in this study were a group of 21 patients who had undergone classic posterior interlaminar fusion from L4 to S1 for their severe slip with. The surgically treated patients were less symptomatic with 57% reporting no symptoms and no limitations, 36% reporting mild symptoms, and 5% reporting severe symptoms12. It should also be noted that the outcomes of posterior interlaminar fusions were poorer than newer posterolateral and circumferential techniques now utilized. Patients with posterior-only fusions tend to have more progression of their spondylolisthesis following surgery and more pain as well.
Unlike isthmic spondylolisthesis, degenerative spondylolisthesis is not associated with a neural arch defect, meaning that the forward translation of the vertebral body also causes narrowing of the central spinal canal at the level of the slip. In contrast, patient's with isthmic spondyolisthesis almost universally have widening of the central spinal canal at the level of the slip. This narrowing of the canal in degenerative spondylolisthesis has been termed the "napkin ring effect", an illustrative description as one imagines the spinal canal as a series of napkin rings with one of the rings slid forward in comparison to the others. The classic symptomolgy of patients with symptomatic degenerative spondylolisthesis are similar to those with symptomatic lumbar spinal stenosis; which can be either neuorgenic claudication or radiculopathy (either unilateral or bilateral radiculopathy) with or without low back pain.
Neurogenic claudication is thought to result from central canal narrowing that is exacerbated by the listhesis (forward slip). The classic symptoms of neurogenic claudication are bilateral (both legs) posterior leg pain that worsens with activity, but is relieved by sitting or forward bending.
The appropriate treatment of patients with isthmic spondylolisthesis is just as controversial as the cause of symptoms. Patients with isthmic spondylolisthesis are usually divided into two general classes for both treatment and for study: low grade isthmic spondylolisthesis (<50% slip) and high grade isthmic spondylolisthesis (>50% slip). Patients with low grade spondylolisthesis are usually young adults (90% adults and 10% adolescents) who present with low back pain and often with radiculopathy. High grade spondylolisthesis may also present with back pain, but may also present with cosmetic deformity, hamstring tightness, radiculopathy, abnormal gait, or it may be asymptomatic.
The first-line treatment for patients with isthmic spondylolisthesis is a non-operative course of NSAIDs, bracing with a lumbar corset, brief activity limitation (but not more than 2 days of bedrest), and possibly a course of physical therapy with lumbar stabilization exercises. Roughly 60–70% of patients respond favorably to this treatment regimen6.
Surgical treatment for Low-Grade Isthmic Spondylolisthesis
Surgical treatment is only considered after at least 6 weeks and often 6–12 months of non-operative therapy has failed to relieve symptoms. Several authors have noted that patients with only low-back pain are more likely to respond to non-operative therapy than patients with radiculopathy, but this has not been formally documented and likely reflects the weakness of our current diagnostic system. Currently, there are no means of effectively differentiating a patient with low-back pain and an incidental finding of spondylolisthesis from a patient whose symptoms are the result of their spondylolisthesis. However, in cases of a bilateral radiculopathy in a dermatomal distribution that matches the patient’s segment with spondylolisthesis, the differential diagnosis is narrower and the diagnostic accuracy higher
Posterolateral fusion in adult lumbar isthmic spondylolisthesis results in a significant improvement in 2 year outcomes, but the difference between surgical and nonsurgical treatment narrows with time.1 There has been one randomized controlled trial for low-grade isthmic spondylolisthesis that compared non-operative therapy to surgery. 2,3,4 The study evaluated the severity of pain and limitations of daily function in patients with 'lumbar isthmic spondylolisthesis of any grade, at least 1 year of low back pain or sciatica, and a severely restricted functional ability in individuals 18 to 55 years of age'. At two years follow-up, patients who underwent surgery had significantly better scores for both pain and daily function. 2,3 The benefits were reduced after nine years. 4 While the patients undergoing non-operative care did show some improvement in pain, their daily activities and physical function did not change during the follow-up period. The follow-up was relatively short, but the study clearly favored surgery and was the first prospective randomized trial for spondylolisthesis . This was also the first prospective trial demonstrating that surgery could be effective for the treatment of some types of low-back pain. Several other retrospective studies have found significant and reliable benefit for patients with isthmic spondylolisthesis, but none compared the results of surgery to natural history of the disorder. Nevertheless, posterolateral fusion for isthmic spondylolisthesis has been one of the least controversial surgeries for spinal pathology and has consistently demonstrated good outcomes.
Uncontrolled studies have focused on the role of fusion in patient with both back pain and radicular pain. The success of stand-alone posterolateral fusion for treating adolescent isthmic spondylolisthesis has led some authors to speculate about the effectiveness of posterolateral fusion without a decompression for patients with both back and leg pain. In 1989, Drs. Peek and Wiltse, et al reported on eight cases of adults with high-grade spondylolisthesis who presented with back pain and severe radicular pain. 5 These patients were all treated with an in situ uninstrumented posterolateral fusion and followed for an average of 5.5 years. At final follow-up, all eight patients reported complete relief of their back pain and leg pain, no patients were taking analgesics for back pain, and all patients were unrestricted with respect to work and recreational activities. The mean time to complete resolution of symptoms was 2.8 months and all patients achieved a solid fusion. No patients underwent subsequent surgery for either back pain or leg pain throughout the follow-up period. This was the first report of excellent relief of leg pain in cases of isthmic spondylolisthesis from posterolateral fusion without decompression. Another study by de Loubresse, et al6 reported on 48 adults with low grade isthmic spondylolisthesis and radiculopathy, half treated by posterolateral fusion or posterolateral fusion and a Gill laminectomy . With respect to radicular pain during activity, 92% of patients treated by posterolateral fusion reported complete relief, while only 65% of those treated with fusion and decompression reported relief. Several natural history studies have also reported that foraminal stenosis is common among asymptomatic isthmic patients and does not correlate well with radiculopathy.
Fusion with decompression
The addition of decompression does not appear to improve clinical outcome in addition to fusion for the treatment of low-grade isthmic spondylolisthesis in patients without serious neurological deficit. 7 A randomized controlled trial compared fusion with a decompression to fusion without a decompression in adult cases of isthmic spondylolisthesis . The study enrolled 42 patients, all of which had both leg pain and back pain, but no evidence of cauda equina syndrome or motor strength less than 5-. The mean post-operative follow-up was 4.5 years. Clinical success was evaluated by a series of visual analog scales (VAS) for leg pain, back pain, analgesic use, and overall function. Scores are numbered from 0–10 with lower scores meaning less pain. Success was defined as leg and back pain of three or less on the VAS scale with an analgesic score above six (meaning only sporadic use of NSAIDs or Tylenol) and functional score above six (meaning infrequent limitations of activity that does not effect employment or important recreational activities). All smokers received pedicle screw fixation to decrease the risk of pseudoarthrosis while non-smokers were not instrumented. The results showed no benefit to performing a decompression for isthmic spondylolisthesis; in fact, patients undergoing decompression had worse clinical outcomes and a higher rate of pseudoarthrosis. Of the patients managed without a decompression 96% of the reached clinical success (as defined above), patients who received a decompression had a clinical success rate of only 66%. Interestingly, the rate of persistent leg pain was much higher in the group managed with a decompression (average VAS for leg pain was 3.8 for patients after decompression versus 1.4 for those without). Although the number of enrolled patients was small the difference was statistically significant (p=0.01). The pseudoarthrosis rate among those who received a decompression was 22% compared to 0% for those without a decompression, pseudoarthrosis was strongly associated with persistent symptoms (p=0.0001). The results seem to strongly support the argument for fusion alone in the management of adults with isthmic spondylolisthesis. The majority of adults treated for isthmic spondylolisthesis are managed with an instrumented posterolateral fusion and a decompression, perhaps this represents improper management of the disorder. The results of Dr. Carragee’s study should be verified with a large multi-center study with many more patients that hopefully can definitively answer the question of which approach is most effective.
Surgical treatment for High-Grade Isthmic Spondylolisthesis
There are several forms of surgery that have been advocated for the treatment of high-grade isthmic spondylolisthesis, including posterior interlaminar fusion, in situ posterolateral fusion, in situ anterior fusion (ALIF), in situ circumferential fusion, instrumented posterolateral fusion, and surgical reduction with instrumented posterolateral interbody fusion (PLIF). Advocates of these different techniques all cite specific advantages of each approach, but they all have established risks and some are much more complication-prone than others.
The role of surgical reduction in the treatment of high-grade isthmic is a controversial topic. Advocates of surgical reduction state that fusion in situ leaves too much residual deformity and impairs the natural mechanics of the lumbar spine. Patients with high-grade isthmic tend to have hyper-lordosis of the lumbar spine that compensates for the lumbosacral kyphosis associated with the severe slip and many feel that this hyper-lordosis will lead to early arthritis and low back pain. Seitsalo, et al reported on the largest, long-term cohort of adolescents operated on for high-grade isthmic spondylolisthesis with 87 patients and mean follow-up of 14 years . Of the patients, 54 had posterior interlaminar fusions, 30 had posterolateral fusion, and 3 had an anterior interbody fusion (ALIF). The authors did note an association between hyper-lordosis and back pain after fusion in situ, particularly when contact and/or sclerosis is noted between adjacent spinous processes, called “kissing spinous processes”. This pain tends to be worsened by hyperextension, but is does not usually cause much pain at rest or during normal activities. Overall, 63% of patients in the study were asymptomatic, 24% reported frequent back pain, but only 7% had taken analgesics for back or leg pain in the last month. The authors did note a significant progression of lumbosacral kyphosis in many of their patients. They also noted that patients undergoing single-level fusions had much worse outcomes (p<0.0001) and they recommend fusing patients to L4 in virtually all cases. The authors also concluded that the clinical outcome, while much better than prior to surgery, still left several patients with significant symptoms and progression of deformity. The authors felt that reduction may offer patients a better chance of excellent long-term outcomes.
Reduction became feasible with the development of pedicle screws, allowing the reduction to be maintained. Several authors have published the results of reduction with pedicle screws and posterior interbody fusion with posterolateral fusion . While the improvement in percent slipped and lumbosacral kyphosis is significant, many have noted a 10–20% rate of nerve root injury and a few cases reports of complete cauda equina, especially with complete reduction of the deformity. While many of these injuries improve, several patients are left with permanent deficits. The clinical outcomes after reduction and instrumentation do not appear to be significantly superior to fusion in situ using modern techniques, despite the higher complication rate. It should also be noted that recurrence of deformity is common after reduction and many patients will either bend their hardware or bend at the sacrum, which is often fully segmented during adolescence. These facts have tarnished the notion of reduction and instrumentation for high-grade slips, but the technique is still utilized with theoretical benefits and some authors, particularly Dr Harry Shufflebarger, has reported both low complication rates and good clinical outcomes . Dr. Shufflebarger currently performs reductions for all high-grade slips that are referred to him and is a leading advocate of the technique. It should also be noted that the use of pedicle screw fixation is much more extensive in the U.S. than other countries and that these surgeons are somewhat more inclined to reduce patients, at least partially, while instrumenting. The routine use of pedicle screws for one or two level pediatric fusions (not long fusions for correcting scoliosis) is without proven benefit in clinical outcome or fusion rate, but is associated with more blood loss, increased rate of nerve root injury, and more cases of reoperation.
Until very recently, there was no data comparing the long-term outcome of reduction with instrumented fusion to an uninstrumented in situ fusion. Poussa, et al recently published the first long-term follow-up report comparing reduction with instrumented posterolateral fusion to uninstrumented circumferential fusion in situ with a mean follow-up of 14.8 years . There were two groups of eleven patients and the patients were not randomized. The patient selection process reflected the differing opinions of surgeons at the author’s institution. However the patients’ preoperative symptoms were the same and patient demographics were identical. There was a tendency for patients with a greater percentage of vertebral slip to receive reduction, but the degree of lumbosacral kyphosis was similar between the two groups. At final follow-up, patients also underwent physical exam and were asked to fill out an Oswestry Disability Index (ODI) and Scoliosis Research Society Questionnaire-22 (SRS-22) .
Although the number of patients in the study was small, patient outcomes clearly favored the fusion in situ group. The average ODI score was 7.6 (range 0–20) in the reduction group and 1.6 (range 0–4) for the fusion in situ group (p<0.01). The SRS-22 similarly favored the fusion in situ with a total score of 103.9 (range 93–120) compared to an average of 90 (range 39–107) for the reduction group (p<0.05). The domains of pain and function differed most significantly between the two groups. Additionally, the radiographic measures did not differ as greatly between the two groups as the authors had expected. Many of the reduction patients experienced a recurrence of their deformity especially the lumbosacral kyphosis. At final follow-up, the average kyphosis measured 20 degrees in the reduction group and 23 degrees in the circumferential group. Finally, MRI studies demonstrated a higher incidence of disc degeneration and psoas muscle atrophy. The authors concluded that reduction and instrumented fusion resulted in poorer long-term outcome than fusion in situ and that the deformity tended to recur following reduction. The increased risks and more extensive surgery associated with reduction did not translate into better outcomes or permanent correction of deformity.
In addition to the ongoing debate of reduction versus fusion in situ, there is also new evidence emerging as to what form of fusion is most effect for eliminating symptoms and controlling deformity. This discussion of surgical technique has been much enhanced recently by the publication of a long-term follow-up study comparing three different techniques of fusion in situ for treating high-grade spondylolisthesis. The study by Helenius, et al compared the outcomes for posterolateral fusion, anterior interbody fusion (ALIF), and circumferential fusion that is a combination of posterolateral and anterior fusion . Anterior fusion is a relatively new technique to spine surgery, emerging during the last two decades. It involves either a retroperitoneal or transperitoneal (through the abdomen) approach to the lumbosacral junction with mobilization of the iliac arteries and veins. The surgeon then performs a total discectomy and places a bone graft into the intervertebral space; the graft is usually either a tricortical iliac crest or a femoral ring allograft. For circumferential fusion, after completing the anterior fusion, the patient is turned and a one or two level posterolateral fusion without instrumentation is performed. Circumferential fusion can either be performed under one run of general anesthesia with patient repositioning or the procedure can be staged. Helenius, et al followed 70 patients for a mean period of 17 years who had been treated by one of the above procedures. Patient selection for each procedure was not randomized, but represented an evolving technique at the Hospital for Invalid Children, in Helsinki, Finland. At last follow-up each patient underwent physical exam, lumbar spine X-rays, and completed several questionnaires including an Oswestry disability index (ODI), Scoliosis Research Society Questionnaire (SRS-22), and two 100 mm visual analog scales for leg and back pain. There were 21 patients treated with posterolateral fusion (PLF), 23 patients treated with anterior fusion (ALIF), and 26 treated with circumferential fusion (CIRC). No patient was intentionally reduced, although some reduction did take place during positioning and during placement of anterior grafts. There was no use of instrumentation. The patients in the circumferential group had the worst preoperative slip and lumbosacral kyphosis by an average of 9% and 10 degrees (p<0.05 and p<0.005). Otherwise, all patients had the same pre-operative symptoms and had very similar demographics.
At final follow-up, the patients in the circumferential group had the best scores for function and pain by a statistically significant margin. Mean VAS back pain score was 22.6 mm for PLF, 24.1 for ALIF, and 5.5 for CIRC. Mean VAS leg pain was 7.6, 16.1, and 2.0 for PLF, ALIF, and CIRC respectively. Total functional scores were also significantly better for the ODI (lower is better) and SRS-22 (higher is better), mean ODIs were 9.7, 8.9, and 3.0 for PLF, ALIF, and CIRC with SRS means of 89.7, 93.2, and 100. The standard deviations were also different with the range of scores much narrower for CIRC compared to PLF or ALIF. No CIRC patient reported back pain at rest or was taking analgesics for back or leg pain. Three patients in both the PLF and ALIF group reported back pain often at rest. The CIRC patients showed the least progression of deformity with both percent slip and kyphosis improving over the follow-up period, mostly the result of vertebral remodeling. Both the PLF and ALIF showed modest increases in kyphosis over the follow-up period. Finally, the complication rate for CIRC was not significantly higher than the other two techniques with a trend towards fewer complications in the CIRC group, which is surprising since the circumferential fusion represents the combination of the other two procedures. Nevertheless, the infection rate and blood loss were not significantly higher and both stages of the operation could be completed together for the majority of cases. Overall, the authors concluded that circumferential fusion provided the best long-term outcomes among the three techniques with excellent long-term outcomes and a low complication rate.
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