Radiographic assessment of surgical treatment of post-traumatic syringomyelia

Abstract

Context: Symptomatic post-traumatic syringomyelia can affect the quality of life in patients whose neurologic function has already been impacted by a spinal cord injury.

Objective: To investigate the radiographic and clinical outcomes following surgery for syringomyelia, we present a literature review along with a case series from a single surgeon’s experience.

Methods: A retrospective review was conducted on patients with post-traumatic syringomyelia who were treated by a single surgeon. Thirty-four patients who underwent surgical treatment consisting of syrinx fenestration, lysis of adhesions, and duraplasty were identified. In addition, a narrative literature review was conducted with a primary focus on diagnosis and management of post-traumatic syringomyelia.

Results: Literature review suggests that regardless of age, sex, vertebral location, or severity of trauma, patients who experience a spinal cord injury should be closely monitored for post-traumatic syringomyelia. Retrospective review of our 34 patients revealed 24 patients for whom pre- and post- operative MRI was available. The predominant location of the injury was cervical (15). The average syrinx length, measured in spinal segments, was similar when comparing pre- and post-operative MRIs; average syrinx length was 5.5 and 5.4 spinal segments, respectively. In contrast, syrinx axial dimension was decreased in 16 of the patients post-operatively and stable or increased in the other eight. The change in syrinx size did not correlate with clinical outcomes.

Conclusion: Current surgical treatment of post-traumatic syringomyelia involves restoration of normal CSF flow dynamics; further prospective work is needed to correlate the clinical state, radiographic measures, and efficacy of surgical intervention.

Introduction

Post-traumatic syringomyelia (PTS) poses a therapeutic challenge to the treating neurosurgeon. Symptomatic PTS can affect neurologic function and the quality of life in patients whose neurologic function has already been impacted by a spinal cord injury. Some nonsurgical treatments such as analgesics and antidepressants address pain and its consequences, while others such as physical therapy and rehabilitation attempt to maintain functional ability and quality of life. The pathophysiology of PTS involves abnormality of cerebrospinal fluid (CSF) flow dynamics; surgical treatment involves bypassing the site of CSF blockage or restoration of normal CSF flow dynamics. The natural history of syringomyelia is not well understood and can be quite variable. Treatment recommendations are based upon careful consideration of both clinical and radiographic findings. Surgical treatment is directed at the pathological process resulting in CSF obstruction.¹ In this study, we review the current literature and understanding of PTS. In addition, we report on a single institution’s experience and radiographic results following the surgical treatment of PTS consisting of lysis of adhesions, cyst fenestration without shunt placement.

Methods

The literature search included a computerized database search of PubMed and Ovid MEDLINE and a reference search. Keywords utilized in the search were the following: (1) post-traumatic syringomyelia, (2) syrinx, (3) spinal cord injury, and (4) syringomyelia. Subsequently, the reference results were examined for additional studies. Multiple reviewers (YL, AG) screened the obtained titles and abstracts for relevance.

A retrospective review of all patients surgically treated for PTS from the years 2004–2015 was performed. All operations were performed by the senior author (AG). The study was approved by the Institutional Review Board of Northwestern University. A total of 34 patients were screened. Pre- and postoperative MRI was available for 24 patients; syrinx length and diameter was measured by a neuroradiologist. Syrinx axial dimension was calculated as the product of the maximum antero-posterior and transverse dimensions.

All 24 patients underwent surgical treatment consisting of a combination of the following: laminectomy, lysis of adhesions, cyst fenestration, and duraplasty. Pre-operative MRI and CT-myelogram were obtained in an attempt to diagnose and localize subarachnoid stenosis. Typically, following laminectomy and dural opening, a somewhat dormant subarachnoid space was encountered; free flow of CSF was not appreciated (Figs 1 and 2). A combination of both blunt and sharp dissection was undertaken to restore CSF flow (Fig. 3); lysis of adhesions, untethering of the spinal cord, excision of scar tissue, and fenestration of cysts were utilized to restore CSF flow (Figs 3 and 4). Duraplasty was performed with bovine pericardium (Fig. 5). Neurophysiologic monitoring was used in all cases.

Figure 1.

Intraoperative view after laminectomy. Dura is reflected laterally with the use of 4-0 Neurolon suture. Of note, no free flow of CSF is appreciated in the compartment.

Figure 2.

Schematic of intraoperative view following laminectomy. Dura is reflected laterally with the use of 4-0 Neurolon suture.

Figure 3.

Schematic of sharp dissection for scar excision. Arachnoid knife is used to sharply excise layers of scar tissue.

Figure 4.

Schematic demonstrating sequential lysis of arachnoid adhesions. A combination of sharp and blunt dissection and scar excision facilitates visualization of the spinal cord with surface vasculature.

Figure 5.

Schematic demonstrating expansile duraplasty using 4-0 Neurolon and bovine pericardium.

Results

Literature review

The first description of PTS was in the nineteenth century by Bastian and later Strumpell; both noted a cystic cavitation of the spinal cord in the setting of spinal column or cord injury.^2,3 It is well recognized that PTS can occur post-spinal column and/or cord injury; prior history of spinal surgery, location and severity of the injury have no influence upon the subsequent development of PTS. In the pre-MRI era, an incidence of 2–5% has been quoted; however, in the MRI era literature, a higher incidence of 20–30% is observed. Squier undertook a pathologic analysis of 20 spinal cords in patients who had suffered a spinal cord injury; four of these harbored a syrinx.⁴ In these cases, cyst formation was felt to be the consequence of necrosis of a myelomalacic core without evidence of hematoma or liquefaction thereof. Notably, their reported incidence of PTS of 20% is closer to the incidence of PTS noted in post-MRI series.

Of the 19 total articles reviewed, eight primarily focused on the diagnosis of PTS.^4–11 PTS symptomatology is varied and may manifest itself as any change in neurologic function, progression of pain, or autonomic dysfunction. Pain has been reported in anywhere from 60% to 80% of patients and can be radicular or central in nature.^5,12 The sensory disturbance associated with PTS may be a dissociated sensory loss: loss of spinothalamic function and preservation of posterior column function. Other sensory abnormalities may include alteration/loss of sensation or new onset of ascending sensory loss. Both upper and lower motor dysfunction may be seen; paresis or changes in spasticity have been reported in as many as 30%.⁵ Autonomic dysfunction may manifest itself as hyperhidrosis, change in bladder/bowel function, or a new Horner’s syndrome.^8,12–15

It is well recognized that the development of PTS displays variability in regards to timing; the development of PTS can occur months to decades after spinal cord injury. Similarly, a delay of months to years can precede diagnosis of PTS.^6,13,16–18 The best data in regards to the natural history of PTS is derived from the Schurch et al. prospective study of 449 patients from the years 1987–93; in this group, time from onset of spinal cord injury to symptomatology from syringomyelia ranged anywhere from 2 months to thirty years. Time to diagnosis ranged from 9 months to 30 years.⁵ However, it is to be noted that syringomyelia can also occur acutely after injury, although it is typically rare and uncommon. Bayramoglu et al. report on a single case of a 21-year-old female who presented to the emergency room after a fall complaining of weakness and loss of sensation in her legs. Although she had a normal CT, an MRI performed demonstrated a syringomyelic cavity extending from T6 to T8.¹¹

The pathophysiology of syringomyelia, regardless of etiology, involves some alteration of CSF flow dynamics. A combination of both internal and external factors, both at the time of and subsequent to initial injury, result in an environment in which inflammation and scar tissue impede CSF flow. It has been shown that meningeal inflammation can exacerbate parenchymal cord inflammation and scarring; this can lead to syrinx formation. Brodbelt and Stoodley have, in an animal model, demonstrated preferential flow of the CSF in this setting into a vulnerable spinal cord via Virchow Robin spaces.¹⁹ As has been demonstrated in most studies, syrinx formation typically occurs at the site of injury and subsequently extends in cephalad and caudal directions.^19,20 Spinal cord edema, ischemia, or hematoma can all increase the vulnerability of the spinal cord while hematoma, inflammation, and surgery all can lead to arachnoiditis that can secondarily cause spinal cord tethering and obstruction of the CSF flow in the subarachnoid space.

PTS has been observed in those with a spinal column injury, cord injury, or concomitant cord and column injuries. However, PTS has also been observed in those who do not demonstrate any evidence of injury and are neurologically intact.¹¹ The onset of early, defined as within 5 years of spinal cord injury, syringomyelia has not been shown to be associated with the level or severity of cord injury, surgical intervention or canal compromise.¹⁰

From our review of the current literature, nine studies focused on treatment strategies for PTS.^{12–14,17,18,21–24} Historically, the treatment of PTS involved bypass of the obstructed subarachnoid space; via a variety of options, including syringo-subarachnoid, pleural, and peritoneal shunts.^7,8,16 More recently, a syringo-subarachnoid-peritoneal shunt has been described.²⁵ A meta-analysis published in 2010 reviewed 22 articles on the surgical management of PTS; in the authors’ opinion, no one surgical technique was found to be superior to another. Complications of shunts include obstruction, disconnection, and infection. The panel gave a weak recommendation to untethering and duraplasty without shunting as the preferred first-line treatment of PTS.²⁶

The same analysis demonstrated that the surgical treatment of PTS is most effective in halting or improving motor dysfunction. However, surgical treatment is less effective at halting sensory dysfunction or improving pain syndromes. At present time, there is no indication that decompression at the time of initial injury or surgical treatment for a radiographic but asymptomatic syrinx is indicated as a prophylactic measure.²⁶

Most of the available literature consists of retrospective case series. Schaan et al. presented their experience of 30 patients treated over a 9-year period; 18 of these patients were treated with shunting.²¹ Five of these patients were treated by shunting and creation of a pseudomeningocele; an additional 7 were treated solely by creation of a pseudomeningocele. Statistical analysis showed better outcomes with pseudomeningocele formation. Shunt complication rate in this series was as high as 12%; hematoma formation, mechanical disconnection, and infection were all causes of shunt malfunction. The authors recommended pseudomeningocele as a primary preferred surgical treatment for PTS with shunting being reserved for refractory cases.

Karam presented a retrospective series of 27 patients with PTS who were treated over the years from 1963 to 2008.²³ Of these, 14 patients underwent one surgical procedure; the other 13 underwent more than one procedure. Of the 11 patients who initially went duraplasty, 3 required reoperation for persistent syrinx size and clinical symptomatology. For the 16 patients whose surgical treatment involved shunt placement, 10 required reoperation. The authors concluded that shunting procedures alone are associated with higher rates of reoperation and less desirable outcomes; duraplasty and arachnolysis are preferred treatments of PTS by restoring CSF flow. In this series, serial MRIs were available for 11 patients; a significant correlation was noted between reduction in syrinx length and clinical condition.

Despite surgical treatment, recurrence of syringomyelia is a noted occurrence: Leahy et al. in 2015 reviewed a series of six patients with spinal cord injury and PTS.²⁴ Time from the initial injury to development of syringomyelia ranged anywhere from 2 years to over 38 years. Of note, all patients presented with decline of motor function. All underwent surgical treatment: 3 underwent detethering and shunt placement, 2 underwent detethering, and 1 underwent shunt placement. All patients experienced deterioration of their neurologic function post-operatively; in addition, syringomyelia recurred in all 6 patients. Time to recurrence ranged from 6 weeks to 18 years with a median time to recurrence of 2 years.

Retrospective review of cases

Thirty-four patients with surgically treated PTS were identified; pre- and post-operative spinal MRIs were available for syrinx measurement in 24 patients. Of these 24, 19 patients were male and 5 were female. The mechanism of injury was motor vehicle accident (15), gunshot wound (3), fall (2), diving accident (2), boating accident (1), military injury (1), and football injury (1). One patient had a history of both a motor vehicle accident and a gunshot wound (Table 1). The syrinx location was cervical in 19 patients, thoracic in 14 patients, and lumbar in 1 patient. Several patients demonstrated a syrinx that spanned several spinal segments. Prior to our surgical intervention, the majority of the patients’ neurologic function, as defined by the American Spinal Cord Injury Association, was categorized as AIS A (N = 12, 50%). The rest of the patients were AIS C (N = 2, 8%), AIS D (N = 9, 37%), or AIS E (N = 1, 4%). None of the subjects were an AIS B. In terms of clinical symptoms, patients presented with weakness, spasticity, numbness, pain, and/or gait difficulties. The mean age at the time of surgery for PTS was 44 years (range 23–76 years). The average time interval from initial spinal injury to surgery for PTS was 14 years (range 1–50 years). A total of 18 patients had previously undergone surgery related to their spinal injury (Table 2).

Table 1. Demographics of 24 patients with post-traumatic syringomyelia.

Sex	Male	19	79%
	Female	5	21%
Age	20–29	3	12%
	30–39	5	21%
	40–49	10	42%
	50–59	4	17%
	60+	2	8%
AIS score	A	12	50%
	B	0	0%
	C	2	8%
	D	9	38%
	E	1	4%
Mechanism of injury	Motor vehicle accident	15	62%
	Gunshot wound	4	17%
	Fall	2	8%
	Diving	2	8%
	Boating	1	4%
	Sports	1	4%
Location of syrinx*	Cervical	19	79%
	Thoracic	14	58%
	Lumbar	1	4%

*Some syrinxes spanned more than one region.

Table 2. Surgical procedures carried out before study period.

Previous surgical procedures	Number of procedures
Fusion	10
Laminectomy	5
Lysis of adhesions	1
Shunt placement	4
Duraplasty	1
Stabilization	4
Circumferential spine surgery	1

*Some patients underwent more than one previous procedure.

All patients were treated at a single institution by the senior author (A.G.). In regard to the surgical treatment of PTS, 21 of the patients underwent laminectomies, 21 patients underwent intradural lysis of adhesions, 17 underwent cyst fenestration, and 19 underwent duraplasty. In four patients, pre-existing syrinx shunts were removed; in two others, syrinx shunts (syringo-pleural and -subarachnoid) were placed. Pre- and post-operative MRI were available for all 24 patients (Fig. 6). Independent measurement of syrinx length, measured in spinal segments, and syrinx axial dimension, defined as the product of maximum syrinx transverse and antero-posterior dimensions, was performed by a neuroradiologist on pre- and post- operative MRI. Average post-operative follow-up was 21.3 months. The average syrinx length, measured in spinal segments, was similar when comparing pre- and post-operative MRIs; average syrinx length was 5.5 and 5.4 spinal segments, respectively. In contrast, syrinx axial dimension was decreased in 16 of the patients post-operatively and stable or increased in the other eight (Table 3).

Figure 6.

Pre- and post-operative sagittal T2 MRI of a patient with cervical syringomyelia and bulbia who underwent intradural exploration, lysis of adhesions, fenestration of cyst.

Table 3. Clinical summary and surgical results in 24 patients with post-traumatic syringomyelia.

Patient No.	Age at surgery	Sex	Level of injurya	Interval	AIS score	Location of syrinxa	Treatmentb	Results
								Syrinx length	Syrinx diameter
1	26	F	T1–T4	6	D	C7–T5	Ly/Fn/Dr	Increase	Increase
2	60	F	L2	6	D	T9–L1	Lm/Ly/Fn/Dr	Decrease	Decrease
3	43	M	T3	3	A	C2–T12	Lm/Ly/Fn	Stable	Increase
4	48	M	C5–C7	20	A	C6–C7	Lm/Ly/Fn/Dr	Decrease	Decrease
5	42	M	C3–C6	14	D	C2–C4	Lm	Increase	Decrease
6	37	M	C4	19	D	C3–C5	Lm/Fn	Increase	Increase
7	38	F	T8	11	A	C1–T8	Lm/Ly/Fn/Dr	Stable	Decrease
8	25	F	T5–T6	8	D	C7–T5	Lm/Ly/Fn/Dr	Increase	Increase
9	38	M	C7	6	A	C3–T3	Lm/Ly/Fn	Stable	Decrease
10	51	M	C4	27	A	C2–C6	Lm/Fn/Dr	Stable	Decrease
11	35	M	T8	9	A	C3–T10	Lm/Ly/Fn	Decrease	Increase
12	30	M	T4	12	D	T4–T5	Lm/Ly/Dr	Stable	Stable
13	44	M	C7	4	A	C7–C7	Lm/Ly/Dr	Decrease	Decrease
14	47	M	T5	2	A	C2–T4	Lm/Ly/Dr	Decrease	Decrease
15	44	M	T10	17	A	T9–T11	Lm/Ly/Fn/Dr	Stable	Decrease
16	76	M	C5	50	D	C4–C6	Lm/Ly/Fn/Dr	Stable	Decrease
17	53	M	T7	2	D	T6–T7	Ly/Dr	Decrease	Decrease
18	59	M	T5	1.5	C	T3–T11	Lm/Fn/Dr	Stable	Decrease
19	45	M	C5	11	E	C1–C7	Lm/Ly/Dr	Decrease	Decrease
20	45	M	C6	28	A	C4–T1	Lm/Ly/Fn/Dr	Decrease	Decrease
21	55	M	C4	35	D	C3–C5	Lm/Ly/Dr	Stable	Decrease
22	23	M	T4	4	A	C1–T7	Lm/Ly/Fn/Dr	Decrease	Decrease
23	49	M	C6	26	C	C5–C7	Lm/Ly/Fn/Dr	Decrease	Decrease
24	41	F	C5	20	A	C4–C7	Lm/Ly/Fn/Dr	Stable	Increase

^aC-cervical, T-thoracic, L-lumbar.

^bLm-laminectomy, Ly-lysis of adhesions, Fn-fenestration of cyst, Dr-duraplasty

Motor, sensory, bladder/bowel, and overall functional status were assessed post-operatively in regard to symptom improvement, stabilization or deterioration. Of the 24 patients, 23 remained clinically stable in regards to motor, sensory, and bowel/bladder function. Only one subject experienced neurologic deterioration; in this patient, motor function decline was noted post-operatively. Of note, in this subject (Table 3, patient no. 2), surgical treatment involved syringo-subarachnoid shunt placement at the time of surgery; it was felt that the motor function decline was related to shunt placement.

Discussion

Syringo-myelia and -bulbia can be a result of congenital, traumatic, inflammatory, infectious, or tumor-related conditions; the common denominator for these various etiologies appears to be disturbance of normal CSF flow dynamics. In this manuscript, we report a review of the literature as well as a single institution experience with PTS.

Our literature review focused on 19 articles (Table 4), of which eight articles addressed issues around diagnosis and nine articles addressed issues around management and outcomes. In the majority of the studies focusing on diagnosis of PTS, MRI was the study of choice. Due to the wide range of time between the initial spinal cord injury and the development of PTS, our review suggests that regardless of age, sex, vertebral location, or severity of trauma, patients who experience a spinal cord injury should be closely monitored for post-traumatic syringomyelia. With regards to PTS management, surgical intervention has the greatest potential to halt the progression of the myelopathy. Surgical treatments such as detethering, arachnolysis, and duraplasty that attempt to restore normal cerebrospinal fluid dynamics are preferred and lead to more satisfactory outcomes. Although shunting was once regarded as the primary option for post-traumatic syringomyelia, a more long-term assessment of the procedure and its variations has demonstrated higher rates of complication or reoperation and only short-term improvement.

Table 4. Summary of literature review.

Study	Study type	n	Mean time from injury to PTS	Conclusions
Squier (1994)	Retrospective	20	NR	PTS development caused from cavitation of myelomalacic core Direct trauma to the spinal cord not necessary for the formation of myelomalacic core
Hida et al. (1994)	Retrospective	14	NR	PTS can extend in cephalad direction to medulla oblongata Syringosubarachnoid shunting should be the first surgical option for patients with PTS
Schurch et al. (1996)	Prospective	449	9.4 years	Need regular checkups due to delay between initial symptoms and deterioration Cord compression, tense syrinx, and kyphosis linked to cyst enlargement and further neurological deterioration
el Masry (1996)	Retrospective	815	8.6 years	PTS incidence twice as high in those with complete injuries versus those with incomplete injuries.
Sgouros (1996)	Retrospective	57	10.7 years	Decompressive laminectomy with subarachnoid space reconstruction is an effective surgical option for PTS; in complete paraplegia, spinal cord transection is an alternative
Asano et al. (1996)	Retrospective	9	6.1 years	Preoperative MRI could be used to predict the efficacy of shunting procedures A flow-void positive MRI was indicative of a “high-pressure syrinx” which responds well to shunting techniques
Kramer (1997)	Retrospective	21	2.2 years	Patients who underwent surgical decompression of the syrinx reported higher rates of satisfaction after long term follow-up
La Haye (1998)	Retrospective	8	7.4 years	No association between severity of injury and subsequent syrinx development PTS can be temporally and spatially remote from the initial site of spinal trauma
Schaller et al. (1999)	Retrospective	12	12.2 years	Initial fracture reduction after injury may help prevent development of PTS Shunt placement can increase arachnoid scarring leading to poor outcomes Lysis of arachnoid adhesions and dural grafting can be effective alternatives
Schaan et al. (2001)	Prospective	30	3.5 years	Shunting procedures used to treat PTS display only short-term neurologic improvement in patients and have high rates of complication Aim of operative treatment should be to restore original CSF dynamics
Lee et al. (2001)	Retrospective	53	6.5 years	Untethering alone can reduce cyst size and alleviate symptoms in majority of cases Untethering coupled with an expansile duraplasty may be a more physiologic way of treating a tethered cord
Brodbelt et al. (2003)	Review	N/A	N/A	Combination of arachnolysis and duraplasty appears to be a preferable treatment to shunting in most cases In select patients, syringopleural or syringosubarachnoid shunt insertion is an alternative
Carroll et al. (2005)	Retrospective	16	<5 years	Wide range of outcomes from surgery (31% improved, 31% stable, 38% worsened, one death)
Agrawal et al. (2007)	Case report	1	15 years	The onset of PTS following spinal cord injury can be extremely delayed Surgical intervention in these patients may halt the progression of the myelopathy
Bonfield et al. (2010)	Systematic Review	22 articles	N/A	All identified articles were of low or very low evidence levels Strong recommendation for surgery in the setting of motor deterioration secondary to PTS No strong evidence to support the superiority of one surgical technique over the others
Ko et al. (2012)	Retrospective	502	3.2 years	No association between injury severity and PTS development; Incidence of PTS development similar amongst patients who underwent surgical and non-surgical treatment
Bayramoglu et al. (2013)	Case report	1	<1 year	PTS should be considered in trauma patients with neurological deficits even in the absence of a vertebral fracture MRI is preferred exam for PTS diagnosis
Karam et al. (2014)	Retrospective	27	12 years	PTS development correlated with deformity and stenosis in patients Shunting alone is associated with higher rates of reoperation and poor outcomes Duraplasty and arachnolysis are preferred treatment for PTS
Leahy et al. (2015)	Retrospective	6	7.5 years	Incidence of PTS development similar in complete vs. incomplete SCI Detethering and duraplasty are preferred initial treatment for PTS

Abbreviations: NR = not reported, PTS = post-traumatic syringomyelia, SCI = spinal cord injury.

We also present a single surgeon’s 11-year experience and radiographic assessment of the surgical treatment of PTS. Independent comparison of pre- and post- operative syrinx length and diameter was undertaken by a neuroradiologist. Of note, while pre-and post-operative syrinx length was unchanged, the axial syrinx dimension, defined as the product of maximum syrinx transverse and antero-posterior dimensions was significantly decreased in 16 of the patients postoperatively. It may be that the axial syrinx dimension versus syrinx length is more reflective of actual syrinx volume; unfortunately, the decreased axial syrinx dimension in these 16 patients did not correlate with an improvement in clinical condition. Perhaps in this population, halting of neurologic decline is an admirable goal. From our review, we confirm the use of MRI for diagnosis and monitoring of PTS. In addition, surgical treatment, with the goal of restoring CSF flow through lysis of adhesions, fenestration of cyst, and/or duraplasty, can halt progression of the syrinx as well as reduce the cross-sectional size. In general, we utilize intraoperative ultrasound and intraoperative exploration to ascertain restoration of CSF flow. The former is helpful in demonstrating a cyst like space within the spinal cord that lends itself to drainage via fenestration. Whenever possible, cyst fenestration was carried out by dorsal midline myelotomy. Eccentric cysts, however, may not be amenable to this approach. In these cases, gross inspection may lead to identification of a myelomalacic corridor to allow for cyst decompression. Review of the literature reveals that shunt placement due to its high complication rate is not the preferred treatment for this condition; we use it selectively in patient who have undergone multiple procedures for the treatment of PTS with documented radiographic and clinical progression.

Conclusions

For the patient affected by a spinal cord injury, any further loss of neurologic function can significantly impact the quality of life. The subset of patients diagnosed with PTS are at risk for further loss of function; as a result of this condition, these patients may develop motor, sensory, or autonomic dysfunction. While nonsurgical treatments may be effective in symptomatic relief, for some patients, surgical treatment offers the potential to halt radiographic expansion and clinical deterioration. Further prospective work needs to be undertaken to correlate the clinical state, radiographic measures, and efficacy of surgical intervention.

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Contributors None.

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Conflicts of interest None.