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Surgical management of ossification of the posterior longitudinal ligament in the cervical spine
Journal of Clinical Neuroscience xxx (xxxx) xxx
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Clinical study
Surgical management of ossification of the posterior longitudinal ligament in the cervical spine Christian D. Cerecedo-Lopez a,b, Ian Tafel a,b,⇑, Asad M. Lak a,b, John Chi b, Yi Lu b, Michael Groff a,b,1, Hasan A. Zaidi a,b,1 a b
Computational Neuroscience Outcomes Center, Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
a r t i c l e
i n f o
Article history: Received 3 September 2019 Accepted 1 December 2019 Available online xxxx Keywords: Cervical spine DISH Enthesopathy OPLL Myelopathy
a b s t r a c t OPLL is a progressive process that can result in spinal cord compression and myelopathy. Various surgical approaches for the management of OPLL in the cervical spine exist. Our goal is to present our institution’s experience in the management of OPLL over the last 20 years. Sixty-eight patients underwent surgery for cervical OPLL. Mean age at surgery was 56.9 years. No differences between demographic characteristics and surgical approach were identified. There were no significant differences between the approaches regarding the mean estimated blood loss, occurrence of durotomy, reoperation rate, positive K-line and preoperative cervical spine sagittal balance. Number of levels operated on was significantly different (anterior approach 2 ± 0.8 levels, posterior approach 4.3 ± 1.3 levels, combined approach 3.3 ± 0.9 levels, p-value <0.01), but postoperative sagittal balance was not (anterior approach Cobb angle 11.9 ± 5.8 degrees, posterior approach Cobb angle 7 ± 3.5 degrees, combined approach Cobb angle 16.7 ± 7.3 degrees, p-value = 0.09). Functional outcomes were good for 70% of patients and did not significantly differ across approaches (anterior approach 28%, posterior approach 33%, combined approach 9%, pvalue = 0.46). Good functional outcomes were more commonly observed in patients with a positive Kline (OR 0.2, 95% CI 0.04–0.9, p-value 0.05) while poor outcomes were most commonly observed in patients with an occupational ratio >0.6 (OR 6.9, 95% CI 1.35–42.7, p-value 0.02). OPLL is a rare disease for which prompt referral for surgical decompression may lead to good clinical outcomes. Ó 2019 Published by Elsevier Ltd.
1. Introduction Ossification of the posterior longitudinal ligament (OPLL) is part of a group of diseases known as enthesopathies, which are characterized by chronic inflammation of tendons and ligaments that leads to their degeneration and calcification [1]. OPLL is a subtype of diffuse idiopathic skeletal hyperostosis (DISH) and is characterized by hypertrophy and calcification of the posterior longitudinal ligament [2,3]. The prevalence of OPLL is 0.1–1.3% in the United States and even greater in Asia [3]. OPLL can involve any level of the vertebral column, but is most common in the cervical spine [3]. Asian ancestry, male gender and age >50 years are risk factors for OPLL [4]. Moreover, various genetic mutations have been associated with OPLL [5–7].
OPLL is a cause of myelopathy and, in almost half of all cases, radiculopathy [2,3,10]. Although the initial presentation may vary depending on the magnitude of medullary compression, all cases of OPLL eventually progress with cervical disk herniation being an important risk factor for more rapid progression [8]. The degree of compression caused by OPLL correlates with neuronal damage in the spinal cord [9]. Surgery is the mainstay of treatment for OPLL with progressive myelopathy and it is recommended at an early stage to prevent irreversible neuronal damage. We present a case series of OPLL patients managed at our center during the last 20 years with an analysis of some of the outcomes associated with the various surgical approaches used.
2. Methods ⇑ Corresponding author at: Department of Neurosurgery, Computational Neurosciences Outcomes Center, Brigham and Women’s Hospital, Harvard Medical School, 15 Francis Street, Boston, MA 02115, USA. E-mail address: [email protected] (I. Tafel). 1 Senior author.
2.1. Patient selection and data extraction After obtaining institutional review board approval with a waiver of consent, a retrospective case series was performed to
https://doi.org/10.1016/j.jocn.2019.12.015 0967-5868/Ó 2019 Published by Elsevier Ltd.
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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C.D. Cerecedo-Lopez et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
identify patients managed at two of our centers between January 1st, 1997 and December 31st, 2017 who had operative notes containing the terms ‘‘OPLL”, ‘‘ossification posterior longitudinal ligament” or ‘‘ossification of the posterior longitudinal ligament”. Programming language (Python 3.5) was used to exclude patients who did not have ICD-9 or ICD-10 coded procedures relevant to spinal surgery, resulting in 82 potential OPLL cases. We then reviewed the operative notes and identified 74 confirmed cases of OPLL managed surgically and subsequently used software with a programming language (Python 3.5) to obtain patient data. 2.2. Surgical note analysis We performed a review of the surgical notes of all patients managed at two of our centers, who were identified as previously mentioned, and included those patients whose surgical notes specifically stated OPLL as the diagnosis. We coded the surgical variables included in the results table from this operative note analysis. Coded variables were then processed with the rest of the data obtained from our institution’s electronic medical record software. 2.3. Radiographic measures The K-line was defined as the position of the most posterior component of the ossified PLL visible in a lateral cervical x-ray film relative to an imaginary line drawn from the midpoint between the posterior aspect of the vertebral body and the intersection between the laminae of the C2 and C7 vertebrae with a positive K-line being an ossified PLL localized in front of the line and a negative K-line being an ossified PLL in contact with or localized posterior to the line previously described. Sagittal balance was defined as the Cobb angle between lines parallel with the inferior endplate of the C2 and C7 vertebrae. The canal space occupation ratio was defined as the proportion of the spinal canal diameter occupied by the ossified PLL and was measured in either a sagittal CT or MR images. Radiographic types of OPLL were defined according to a previously reported classification [10]. 2.4. Clinical outcome To measure clinical outcome, we estimated the Nurick grade from progress notes at latest follow-up [11]. The Nurick grading system measures severity of cervical myelopathy by assessing components of ambulatory status and has a moderate to strong correlation with the Japanese orthopedic association scoring system [11,12]. Functional outcome was defined by dichotomizing Nurick grade into good and poor outcome using the ability to be employed full-time (grades 0–2) as cut-off point. 2.5. Statistical analysis Statistical analysis was performed using the open-sourced programming language ‘‘R” (R Core Team 2014). The relationship between dichotomous or categorical demographic variables and surgical approach was evaluated using a chi-square test of independence. The relationship between continuous demographic variables and surgical approach was evaluated using linear regression with a goodness of fit F-test. The relationship between surgical approach and dichotomous surgical outcomes was evaluated using a one-way ANOVA with a likelihood ratio test. The relationship between surgical approach and continuous surgical outcomes was evaluated using a linear regression with a goodness of fit Ftest. Similarly, relationships between radiographic dichotomous and continuous outcomes, and surgical approach, were evaluated using a one-way ANOVA with a likelihood ratio test and a linear
regression with a goodness of fit F-test, respectively. Associations between functional outcome and surgical approach, preoperative myelopathy, signal change, fusion, durotomy, use of intraoperative monitoring, surgeon’s experience, positive K-line, preoperatory Cobb angle, occupation ratio, and OPLL type were explored using univariate logistic regressions. 3. Results 3.1. Demographic characteristics Sixty-eight patients with cervical OPLL were included in this analysis; 24 women and 44 men. Patients’ mean age at surgery was 56.9 years. The most common ethnicity was White (67.65%), followed by Asian (17.65%), Black (8.82%) and other races (5.88%). Of patients for whom data was available, most presented with preoperatory myelopathy (92.19%) and T2 signal change within the spinal cord on MRI (89.47%). Six patients presented with acute spinal cord injury following a fall (8.82%). No significant differences were found between any of the demographic characteristics based on the surgical approach used. 3.2. Surgical characteristics The mean number of operated levels was 3.43. A significant difference in the mean number of levels between approaches was identified (Table 1). The decision to operate according to a particular approach was made by the treating surgeon. All patients treated with an anterior or combined approach received discectomies. Most patients who underwent anterior or combined approaches received a corpectomy (73.91% and 87.5% for anterior and combined approaches respectively). Laminectomies or laminoplasties were performed in all posterior approaches, with laminectomies being more common (78.95% vs. 21.05% for laminectomies and laminoplasties respectively). Laminectomies or laminoplasties were also performed in most of the combined approaches (75% vs. 12.5% for laminotomies and laminectomies respectively). Foraminotomies were performed in 27.94% of all cases, with no significant differences between surgical approaches. Allografts were applied in 52.94% of patients and occurred more commonly in anterior and combined approaches (78.26%, 32.43% and 87.5% for anterior, posterior and combined approaches respectively). Spinal fusion was performed in 67.65% of all cases, with a significant difference between surgical approaches (Table 1). The mean estimated blood loss was 357 mL, and there was no significant difference in mean blood loss between groups. Intraoperative microscopy was used in 45.59% of cases and a significant difference in the proportion of surgeries using microscopy between approaches was identified. Similarly, fluoroscopy was used in all anterior and mixed approaches, but in only a fraction of posterior approaches (63.16%). Durotomy occurred in 20.59% of all surgeries, however no significant differences existed between approaches. Intraoperative monitoring use was similar between groups; in total 45.59% of cases used monitoring. Twelve patients (17.65%) underwent reoperation, with the most common reason for reoperation being persistent myelopathy, followed by wound infection and CSF leak. Mean experience of the primary surgeon was 10.3 years. No major differences in surgical experience were identified between the three main approaches. 3.3. Radiographic characteristics Preoperative and postoperative X-rays were available for 14 patients. Ten patients had a positive K-line and no significant difference in the proportion of positive K-lines was identified
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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C.D. Cerecedo-Lopez et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx Table 1 Cervical OPLL Demographic, Surgical and Radiographic Characteristics. Approach
Demographic n (%) Age (years)* ± sd Female (%) Race (%) White Black Asian Other Veteran Preoperative myelopathy+ (%) Signal change+ (%) Acute spinal cord injury (%) Surgical n levels ± sd Discectomy (%) Corpectomy (%) Laminectomy (%) Laminoplasty (%) Foraminotomy (%) Allograft (%) Fusion (%) Estimated blood loss+ (mL) ± sd Microscope (%) Fluoroscopy (%) Durotomy (%) Intraoperative monitoring (%) Reoperation (%) Length of follow-up (months) ± sd Surgeon’s experience (years) ± sd Radiographic Positive K-line+ (%) Preoperative C2-C7 Cobb angle ± sd Postoperative C2-C7 Cobb angle ± sd Occupation ratio+ ± sd Occupation ratio > 0.5+ (%) Occupation ratio > 0.6+ (%) OPLL type+ Continuous Segmental Mixed Other Outcome Postoperative Nurick grade+ ± sd Functional outcome+ Good (%) Poor (%)
Total
p-value
Anterior
Posterior
Combined
23 (33.8) 55 ± 11.4 10 (43.5)
37 (54.4) 58.7 ± 13.9 13 (35.1)
8 (11.8) 54 ± 11.8 1 (12.5)
68 (100) 56.9 ± 12.9 24 (35.3)
0.26 0.29
15 (65.2) 4 (17.4) 3 (13) 1 (4.4) 2 (8.7) 20 (90.9) 12 (81.7) 2 (8.7)
26 (70.3) 1 (2.7) 7 (18.9) 3 (8.1) 6 (16.2) 31 (83.8) 18 (48.7) 4 (10.8)
5 1 2 0 3 8 4 0
46 (67.7) 6 (8.8) 12 (17.7) 4 (5.9) 11 (16.2) 59 (92.2) 34 (89.5) 6 (8.8)
0.53 0.53 0.53 0.53 0.16 0.68 0.71 0.62
2 ± 0.8 23 (100) 17 (73.9) 0 (0) 0 (0) 5 (21.7) 18 (78.3) 21 (91.3) 303.3 ± 202.9 18 (78.3) 23 (100) 7 (30.4) 11 (47.8) 6 (26.1) 16.4 ± 18.9 9.1 ± 7.7
4.3 ± 1.3 0 (0) 0 (0) 29 (78.4) 8 (21.6) 12 (32.4) 12 (32.4) 19 (51.4) 389.8 ± 380.1 7 (18.9) 24 (64.9) 5 (13.5) 15 (40.5) 5 (13.5) 33 ± 42.9 11.6 ± 10
3.3 ± 0.9 8(100) 7 (87.5) 6 (75) 1 (12.5) 2 (25) 7 (87.5) 7 (87.5) 337.5 ± 47.9 6 (75) 7 (87.5) 2 (25) 5 (62.5) 1 (12.5) 19.3 ± 25.3 7.9 ± 6.6
3.43 ± 1.5 30 (44.1) 24 (35.3) 35 (51.5) 9 (13.2) 19 (28) 36 (53) 46 (67.7) 357.1 ± 313.1 31 (45.6) 54 (79.4) 14 (20.6) 31 (45.6) 12 (17.7) 25.9 ± 35.3 10.3 ± 9
<0.01 <0.01 <0.01 <0.01 0.01 0.66 <0.01 <0.01 0.70 <0.01 <0.01 0.28 0.51 0.44 0.26 0.43
3 (75) 4.1 ± 2.2 11.9 ± 5.8 0.4 ± 0.1 4 (30.8) 0 (0)
6 (75) 9 ± 10.1 7 ± 3.5 0.5 ± 0.1 18 (69.2) 8 (30.8)
1 (50) 12.4 ± 9.7 16.7 ± 7.3 0.5 ± 0.1 2 (40) 1 (20)
10 (71.4) 8.1 ± 8.4 10.3 ± 5.8 0.5 ± 0.1 24 (54.5) 9 (18.8)
0.77 0.51 0.09 0.03 0.06 0.08
2 1 2 7
13 (30) 2 (5) 9 (21) 2 (5)
0 2 2 1
15 (35) 5 (12) 13 (30) 10 (23)
<0.01 <0.01 <0.01 <0.01
0.9 ± 1.5
1.9 ± 1.9
1.2 ± 1.9
1.5 ± 1.8
0.16
15 (28) 3 (6)
18 (33) 12 (22)
5 (9) 1 (2)
38 (70) 16 (30)
0.46 0.46
(5) (2.5) (5) (7.5)
(62.5) (12.5) (25) (0) (37.5) (100) (50) (0)
(0) (5) (5) (2.5)
*Age at moment of surgery (years). +Data not available for all subjects, percentages calculated based on available data. sd = standard deviation.
between surgical approach groups. Similarly, preoperative cervical sagittal balance was similar between groups, while postoperative cervical sagittal balance demonstrated a trend towards a statistically significant difference between groups (p = 0.87). The mean canal space occupation ratio was 0.5 and a significant difference between approaches was identified (p = 0.03). Differences in the proportion of cases with a canal space occupation ratio 0.5 or 0.6 showed a tendency towards significance (p = 0.06 and 0.08). The most common type of OPLL was continuous, followed by mixed, other and segmental (Fig. 1). A significant difference in the proportion of OPLL types between all three approaches was identified (p = 0.004). 3.4. Clinical outcome Nurick grade at latest follow-up was estimated for 54 patients. Mean Nurick grade was 1.5 (Table 1). After dichotomizing the Nurick grade into good (0–2) or poor (3–5) functional outcome, 38 patients (70%) had a good outcome (Table 1). Exploratory analyses
from univariate analyses revealed an association between poor neurological outcome and positive K-line (OR, 0.2 [0.04–0.9], pvalue 0.05) and occupation ratio >0.6 (OR, 6.9 [1.35–42.7], pvalue 0.02) (Table 2). No evidence of association was observed in other exploratory analyses (Table 2).
4. Discussion Extensive experience in the management of OPLL has been accumulated in geographical areas with a higher prevalence of OPLL, particularly Japan. OPLL was originally reported in the United Kingdom almost two centuries ago, yet experience with OPLL and its management outside Asia is limited as evidenced by a scarcity of publications on the topic outside of this geographic region [13–19]. In the US, the estimated the prevalence of OPLL is 0.7% [14]. Presented here is our experience on the surgical management of OPLL accumulated at our centers over the previous two decades. Our case series included 68 patients who underwent surgery for
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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C.D. Cerecedo-Lopez et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
Fig. 1. Examples of the four types of OPLL from this case series A. Mixed B. Localized C. Continuous D. Segmental.
Table 2 Association between Patient Characteristics and Poor Functional Outcome.
Approach Anterior Posterior Combined Preoperative myelopathy Signal change Fusion Durotomy Intraoperative neuromonitoring Surgeon experience Positive K-line Preoperative Cobb angle Occupation Ratio >0.5 >0.6 OPLL Type Continuous Segmental Mixed Other
OR
95% CI
p-value
1 3.3 1 1.3 0.4 0.6 2.4 1.1 1 0.2 1.1
0.86–16.7 0.04–10.1 0.2–27.8 0.5–4.2 0.2–2.2 0.6–9.7 0.3–3.6 0.9–1.1 0.04–0.9 0.9–1.2
0.1 1 0.82 0.46 0.41 0.21 0.86 0.76 0.05 0.29
2.3 6.9
0.6–10.7 1.35–42.7
0.25 0.02
1 0.7 3.4 0.3
0.03–6.7 0.6–21.6 0.02–2.9
0.76 0.17 0.38
cervical OPLL, with 56 reported as non-Asian. To the best of our knowledge this is the largest series of OPLL cases managed outside of Asia. Mean age at diagnosis was similar to previously reported values in both Asian and non-Asian series [15,16]. We also observed a
slight male predominance in our series, which closely resembled the 2:1 male-to-female ratio found in previous reports [15]. Most individuals in our case series presented with signs and symptoms of myelopathy and most of them had a T2 signal change on MRI (~90%). The proportion of T2-signal change in our patients was much higher than previously reported by a Japanese series (43%) and may be explained by the unfamiliarity of physicians in our area with the disease, leading to delayed referral [17]. While no association between signal change and poor functional outcome was observed in this series, this finding reinforces the importance of physicians being familiar with the manifestations of OPLL as preoperative T2-signal change has been associated with poor longterm outcomes in other case series [18]. By continuing to report on the management of OPLL we expect our paper contributes to increasing awareness of this condition in physicians of the Western world. The proportion of patients identifying as white or black ethnicity closely resembled that of the largest case series of OPLL in nonAsian patients previously reported in the US, while the proportion of Hispanic patients was considerably lower in our case series [16]. This may be explained by the higher proportion of patients with Hispanic ancestry living in the area of the previously reported case series (i.e. Miami) [16]. Another case series evaluating the radiographic prevalence of OPLL in an area with a relatively high proportion of people with Hispanic ancestry (i.e. San Francisco) reported racial proportions very similar to the ones reported in the Miami series [19]. Thus, although our case series revealed a low propor-
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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tion of OPLL case series in races other than White, Black or Asian individuals, physicians practicing in areas with a high proportion of individuals with Hispanic ancestry should be aware that this subset of the population presents OPLL with a relatively higher frequency. Three approaches were used by surgeons in our center: anterior, posterior or a combination of both (Figs. 2–4). Contrasting previous studies, the number of levels operated on in our center significantly differed between the groups [20]. No significant difference in estimated blood loss between surgical approaches was observed. This again contrasted with a previous metanalysis reporting higher intraoperative blood loss in the anterior approach groups [21]. Although almost 20% of patients in our series had a durotomy, only two patients underwent reoperation for CSF leak management. Surgeons should be aware that durotomies may present during the management of OPLL and plan accordingly to approach this potential complication. Other than reoperations, no major complications were reported for the patients in our series and the reoperation rate was similar to previously reported case series [21]. Radiographic parameters have been proposed as aids for deciding the appropriate approach to manage OPLL. Two of the most common radiographic parameters used in the decision making are the canal space occupation ratio and the K-line [22]. We did not observe a significant difference in the proportion of positive K-lines between surgical approaches. The mean canal space occupying ratio significantly differed between approaches and a greater
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proportion of lesions occupying 0.5 or 0.6 of the canal space were managed with a posterior approach. It is important to note that most of the patients in this series had undergone surgical management of OPLL before the literature demonstrated worse outcomes with OPLL lesions occupying 60% of the spinal canal managed with posterior decompression [23]. Continuous OPLL was the most common type observed in our series and most continuous OPLL cases were managed with a posterior approach. This is in accord with previous series of OPLL managed in the United States [16]. The anterior approach was more commonly used for OPLL classified as other type, again closely resemble the previously published American OPLL case series [16]. As previously mentioned, radiographic parameters other than the type of OPLL may perhaps be better suited to aid surgeons in deciding the optimal surgical approach [22,23]. Prospective randomized studies evaluating the optimal approach selection for OPLL may provide further insights into this matter, as current prospective studies on OPLL are scant [21]. The advantages of our case series on OPLL are that it includes many non-Asian patients and is the largest case series outside of Asia, which distinguishes it from all of the previously published case series. Our study highlights the differences in diagnosis and treatment of a condition that is much more commonly addressed in other parts of the world. The average follow-up for all patients in the series was 26 months. While this is a significant amount of time, our study would have been improved by longer followup time and data availability. Unfortunately, in our area of practice
Fig. 2. Anterior only approach in a 34-year-old female. A. Preoperative cervical X-ray demonstrating minimal OPLL (yellow shadow) with a positive K-line (green line). B. Preoperative sagittal CT scan demonstrating multiple osteophytes and minimal OPLL. C. Preoperative axial CT scan demonstrating OPLL at the C5–C6 region. D. Postoperative cervical X-ray status post C4–C7 anterior cervical discectomies and fusion. Estimated Nurick grade at three months for this patient was 0 (some residual symptoms of radiculopathy without any myelopathy).
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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Fig. 3. Posterior only approach in a 52-year-old male. A. Preoperative cervical X-ray demonstrating two regions of OPLL occupying a large proportion of the spinal canal (yellow shadow) with a negative K-line (green line). B. Preoperative sagittal CT scan demonstrating multiple osteophytes and two regions of OPLL at C3–C4 and C5–C6. C. Preoperative axial CT scan demonstrating OPLL at the C5–C6 region. D. Postoperative axial CT scan demonstrating complete decompression of the C5–C6 level and pedicle screw fixation. E. Postoperative cervical X-ray status post C3–C7 posterior cervical laminectomies and fusion. Estimated Nurick grade at twelve months for this patient was 2 (slight difficulty in walking that does not prevent full-time employment).
Fig. 4. Combined approach in a 53-year-old male. A. Preoperative cervical X-ray demonstrating three regions of OPLL occupying a large proportion of the spinal canal (yellow shadow) with a positive K-line (green line). B. Preoperative sagittal CT scan demonstrating widespread OPLL spanning C2–C5. C. Preoperative axial CT scan demonstrating OPLL at the C4 level. D. Preoperative axial MRI demonstrating severe compression at the C4 level with a slit-like appearance of the spinal cord (red arrow). E. Postoperative axial MRI demonstrating decompression of the spinal cord at the C4 level (red arrow). F. Postoperative cervical X-ray status post C3–C5 anterior cervical discectomies and fusion and C3–C6 posterior cervical laminectomies and fusion. Estimated Nurick grade at five months for this patient was 1 (signs or symptoms of myelopathy but no difficulty in walking).
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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our patient population commonly has treatment at one hospital and follow-up in another or even in a different part of the country. Our posterior only approach patients had a smaller Cobb angle that trended towards statistical significance (P < 0.1), and a larger patient population is needed to determine if this could become a significant finding. Despite having a high number of patients with myelopathy and/ or spinal cord signal change, functional outcomes were good for the majority of our patients. Our exploratory analysis revealed two interesting associations. First, the association between a positive K-line and improved functional outcomes. Fujiyoshi et al. compared outcomes after OPLL decompression stratified by K-line status reporting higher rates of functional recovery in patients having a positive K-line (66% vs. 14% for K-line + and K-line respectively) [22]. While the percentages of patients with good functional outcome in our series differ from those of Fujiyoshi et al. (85% vs. 57% for K-line + and K-line respectively), our findings reinforce those of previous series suggesting a positive K-line may be predictive of better functional outcomes. Our analysis also revealed a strong association between an occupation ratio >0.6 and poor functional outcomes. This goes in line with what was previously reported by Kato et al. [24], and reinforces the idea that increased awareness of the disease leading to prompt recognition and early surgical decompression may lead to improved functional outcomes. 5. Conclusion In this case series of 68 patients with OPLL managed outside of Asia the surgical management of OPLL was effective and lead to high rates of functional recovery. Increased awareness leading to prompt referral for surgical decompression is expected to improve clinical outcomes of OPLL patients. Conflicts of interest The authors report no conflict of interest. Disclosure of financial support This project did not receive any sort of financial support or funding from any organization, institution or person in the public, commercial, or not-for-profit sectors. The authors have no personal or institutional financial interest in drugs, materials or devices described in this submission. Acknowledgement The authors have no acknowledgement. References [1] Sudoł-Szopin´ska I, Kwiatkowska B, Prochorec-Sobieszek M, Mas´lin´ski W. Enthesopathies and enthesitis. Part 1. Etiopathogenesis. J Ultrason 2015;15:72–84. https://doi.org/10.15557/JoU.2015.0006. [2] Resnick D, Guerra J, Robinson C, Vint V. Association of diffuse idiopathic skeletal hyperostosis (DISH) and calcification and ossification of the posterior longitudinal ligament. Am J Roentgenol 1978;131:1049–53. https://doi.org/ 10.2214/ajr.131.6.1049. [3] Hirai T, Yoshii T, Iwanami A, Takeuchi K, Mori K, Yamada T, et al. Prevalence and distribution of ossified lesions in the whole spine of patients with cervical ossification of the posterior longitudinal ligament a multicenter study (JOSL CT study). PLoS ONE 2016;11:1–13. https://doi.org/10.1371/journal. pone.0160117.
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The pathogenesis of the spinal cord disorder associated with cervical spondylosis. Brain 1972;95:87–100. https://doi.org/10.1093/brain/95.1.87. [12] Revanappa KK, Rajshekhar V. Comparison of Nurick grading system and modified Japanese Orthopaedic Association scoring system in evaluation of patients with cervical spondylotic myelopathy. Eur Spine J 2011;20:1545–51. https://doi.org/10.1007/s00586-011-1773-y. [13] Key C. On paraplegia depending on disease of the ligaments of the spine. In: Barlow G, Babington J, editors. Guy’s Hosp. Reports (Series 1). London: Samuel Highley; 1838. p. 17–34. [14] Firooznia H, Benjamin VM, Pinto RS, Golimbu C, Rafii M, Leitman BS, et al. Calcification and ossification of posterior longitudinal ligament of spine: its role in secondary narrowing of spinal canal and cord compression. N Y State J Med 1982;82:1193–8. [15] Saetia K, Cho D, Lee S, Kim DH, Kim SD. Ossification of the posterior longitudinal ligament: a review. Neurosurg Focus 2011;30:E1. https://doi. org/10.3171/2010.11.FOCUS10276. [16] Wang MY, Thambuswamy M. Ossification of the posterior longitudinal ligament in non-Asians: demographic, clinical, and radiographic findings in 43 patients. Neurosurg Focus 2011;30:E4. https://doi.org/10.3171/2010.12. FOCUS10277. [17] Koyanagi I, Iwasaki Y, Hida K, Imamura H, Abe H. Magnetic resonance imaging findings in ossification of the posterior longitudinal ligament of the cervical spine. J Neurosurg 1998;88:247–54. https://doi.org/10.3171/ jns.1998.88.2.0247. [18] Yagi M, Ninomiya K, Kihara M, Horiuchi Y. Long-term surgical outcome and risk factors in patients with cervical myelopathy and a change in signal intensity of intramedullary spinal cord on magnetic resonance imaging. J Neurosurg Spine 2010;12:59–65. https://doi.org/10.3171/2009.5.SPINE08940. [19] Fujimori T, Le H, Hu SS, Chin C, Pekmezci M, Schairer W, et al. Ossification of the posterior longitudinal ligament of the cervical spine in 3161 Patients: a CTbased study. Spine (Phila Pa 1976) 2015(40):394–E403. https://doi.org/ 10.1097/BRS.0000000000000791. [20] Kommu R, Sahu BP, Purohit AK. Surgical outcome in patients with cervical ossified posterior longitudinal ligament: a single institutional experience. Asian J Neurosurg 2014;9:196–202. https://doi.org/10.4103/17935482.146602. [21] Feng F, Ruan W, Liu Z, Li Y, Cai L. Anterior versus posterior approach for the treatment of cervical compressive myelopathy due to ossification of the posterior longitudinal ligament: a systematic review and meta-analysis. Int J Surg 2016;27:26–33. https://doi.org/10.1016/j.ijsu.2016.01.038. [22] Fujiyoshi T, Yamazaki M, Kawabe J, Endo T, Furuya T, Koda M, et al. A new concept for making decisions regarding the surgical approach for cervical ossification of the posterior longitudinal ligament: the K-line. 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Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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Clinical study
Surgical management of ossification of the posterior longitudinal ligament in the cervical spine Christian D. Cerecedo-Lopez a,b, Ian Tafel a,b,⇑, Asad M. Lak a,b, John Chi b, Yi Lu b, Michael Groff a,b,1, Hasan A. Zaidi a,b,1 a b
Computational Neuroscience Outcomes Center, Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA, USA
a r t i c l e
i n f o
Article history: Received 3 September 2019 Accepted 1 December 2019 Available online xxxx Keywords: Cervical spine DISH Enthesopathy OPLL Myelopathy
a b s t r a c t OPLL is a progressive process that can result in spinal cord compression and myelopathy. Various surgical approaches for the management of OPLL in the cervical spine exist. Our goal is to present our institution’s experience in the management of OPLL over the last 20 years. Sixty-eight patients underwent surgery for cervical OPLL. Mean age at surgery was 56.9 years. No differences between demographic characteristics and surgical approach were identified. There were no significant differences between the approaches regarding the mean estimated blood loss, occurrence of durotomy, reoperation rate, positive K-line and preoperative cervical spine sagittal balance. Number of levels operated on was significantly different (anterior approach 2 ± 0.8 levels, posterior approach 4.3 ± 1.3 levels, combined approach 3.3 ± 0.9 levels, p-value <0.01), but postoperative sagittal balance was not (anterior approach Cobb angle 11.9 ± 5.8 degrees, posterior approach Cobb angle 7 ± 3.5 degrees, combined approach Cobb angle 16.7 ± 7.3 degrees, p-value = 0.09). Functional outcomes were good for 70% of patients and did not significantly differ across approaches (anterior approach 28%, posterior approach 33%, combined approach 9%, pvalue = 0.46). Good functional outcomes were more commonly observed in patients with a positive Kline (OR 0.2, 95% CI 0.04–0.9, p-value 0.05) while poor outcomes were most commonly observed in patients with an occupational ratio >0.6 (OR 6.9, 95% CI 1.35–42.7, p-value 0.02). OPLL is a rare disease for which prompt referral for surgical decompression may lead to good clinical outcomes. Ó 2019 Published by Elsevier Ltd.
1. Introduction Ossification of the posterior longitudinal ligament (OPLL) is part of a group of diseases known as enthesopathies, which are characterized by chronic inflammation of tendons and ligaments that leads to their degeneration and calcification [1]. OPLL is a subtype of diffuse idiopathic skeletal hyperostosis (DISH) and is characterized by hypertrophy and calcification of the posterior longitudinal ligament [2,3]. The prevalence of OPLL is 0.1–1.3% in the United States and even greater in Asia [3]. OPLL can involve any level of the vertebral column, but is most common in the cervical spine [3]. Asian ancestry, male gender and age >50 years are risk factors for OPLL [4]. Moreover, various genetic mutations have been associated with OPLL [5–7].
OPLL is a cause of myelopathy and, in almost half of all cases, radiculopathy [2,3,10]. Although the initial presentation may vary depending on the magnitude of medullary compression, all cases of OPLL eventually progress with cervical disk herniation being an important risk factor for more rapid progression [8]. The degree of compression caused by OPLL correlates with neuronal damage in the spinal cord [9]. Surgery is the mainstay of treatment for OPLL with progressive myelopathy and it is recommended at an early stage to prevent irreversible neuronal damage. We present a case series of OPLL patients managed at our center during the last 20 years with an analysis of some of the outcomes associated with the various surgical approaches used.
2. Methods ⇑ Corresponding author at: Department of Neurosurgery, Computational Neurosciences Outcomes Center, Brigham and Women’s Hospital, Harvard Medical School, 15 Francis Street, Boston, MA 02115, USA. E-mail address: [email protected] (I. Tafel). 1 Senior author.
2.1. Patient selection and data extraction After obtaining institutional review board approval with a waiver of consent, a retrospective case series was performed to
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Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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identify patients managed at two of our centers between January 1st, 1997 and December 31st, 2017 who had operative notes containing the terms ‘‘OPLL”, ‘‘ossification posterior longitudinal ligament” or ‘‘ossification of the posterior longitudinal ligament”. Programming language (Python 3.5) was used to exclude patients who did not have ICD-9 or ICD-10 coded procedures relevant to spinal surgery, resulting in 82 potential OPLL cases. We then reviewed the operative notes and identified 74 confirmed cases of OPLL managed surgically and subsequently used software with a programming language (Python 3.5) to obtain patient data. 2.2. Surgical note analysis We performed a review of the surgical notes of all patients managed at two of our centers, who were identified as previously mentioned, and included those patients whose surgical notes specifically stated OPLL as the diagnosis. We coded the surgical variables included in the results table from this operative note analysis. Coded variables were then processed with the rest of the data obtained from our institution’s electronic medical record software. 2.3. Radiographic measures The K-line was defined as the position of the most posterior component of the ossified PLL visible in a lateral cervical x-ray film relative to an imaginary line drawn from the midpoint between the posterior aspect of the vertebral body and the intersection between the laminae of the C2 and C7 vertebrae with a positive K-line being an ossified PLL localized in front of the line and a negative K-line being an ossified PLL in contact with or localized posterior to the line previously described. Sagittal balance was defined as the Cobb angle between lines parallel with the inferior endplate of the C2 and C7 vertebrae. The canal space occupation ratio was defined as the proportion of the spinal canal diameter occupied by the ossified PLL and was measured in either a sagittal CT or MR images. Radiographic types of OPLL were defined according to a previously reported classification [10]. 2.4. Clinical outcome To measure clinical outcome, we estimated the Nurick grade from progress notes at latest follow-up [11]. The Nurick grading system measures severity of cervical myelopathy by assessing components of ambulatory status and has a moderate to strong correlation with the Japanese orthopedic association scoring system [11,12]. Functional outcome was defined by dichotomizing Nurick grade into good and poor outcome using the ability to be employed full-time (grades 0–2) as cut-off point. 2.5. Statistical analysis Statistical analysis was performed using the open-sourced programming language ‘‘R” (R Core Team 2014). The relationship between dichotomous or categorical demographic variables and surgical approach was evaluated using a chi-square test of independence. The relationship between continuous demographic variables and surgical approach was evaluated using linear regression with a goodness of fit F-test. The relationship between surgical approach and dichotomous surgical outcomes was evaluated using a one-way ANOVA with a likelihood ratio test. The relationship between surgical approach and continuous surgical outcomes was evaluated using a linear regression with a goodness of fit Ftest. Similarly, relationships between radiographic dichotomous and continuous outcomes, and surgical approach, were evaluated using a one-way ANOVA with a likelihood ratio test and a linear
regression with a goodness of fit F-test, respectively. Associations between functional outcome and surgical approach, preoperative myelopathy, signal change, fusion, durotomy, use of intraoperative monitoring, surgeon’s experience, positive K-line, preoperatory Cobb angle, occupation ratio, and OPLL type were explored using univariate logistic regressions. 3. Results 3.1. Demographic characteristics Sixty-eight patients with cervical OPLL were included in this analysis; 24 women and 44 men. Patients’ mean age at surgery was 56.9 years. The most common ethnicity was White (67.65%), followed by Asian (17.65%), Black (8.82%) and other races (5.88%). Of patients for whom data was available, most presented with preoperatory myelopathy (92.19%) and T2 signal change within the spinal cord on MRI (89.47%). Six patients presented with acute spinal cord injury following a fall (8.82%). No significant differences were found between any of the demographic characteristics based on the surgical approach used. 3.2. Surgical characteristics The mean number of operated levels was 3.43. A significant difference in the mean number of levels between approaches was identified (Table 1). The decision to operate according to a particular approach was made by the treating surgeon. All patients treated with an anterior or combined approach received discectomies. Most patients who underwent anterior or combined approaches received a corpectomy (73.91% and 87.5% for anterior and combined approaches respectively). Laminectomies or laminoplasties were performed in all posterior approaches, with laminectomies being more common (78.95% vs. 21.05% for laminectomies and laminoplasties respectively). Laminectomies or laminoplasties were also performed in most of the combined approaches (75% vs. 12.5% for laminotomies and laminectomies respectively). Foraminotomies were performed in 27.94% of all cases, with no significant differences between surgical approaches. Allografts were applied in 52.94% of patients and occurred more commonly in anterior and combined approaches (78.26%, 32.43% and 87.5% for anterior, posterior and combined approaches respectively). Spinal fusion was performed in 67.65% of all cases, with a significant difference between surgical approaches (Table 1). The mean estimated blood loss was 357 mL, and there was no significant difference in mean blood loss between groups. Intraoperative microscopy was used in 45.59% of cases and a significant difference in the proportion of surgeries using microscopy between approaches was identified. Similarly, fluoroscopy was used in all anterior and mixed approaches, but in only a fraction of posterior approaches (63.16%). Durotomy occurred in 20.59% of all surgeries, however no significant differences existed between approaches. Intraoperative monitoring use was similar between groups; in total 45.59% of cases used monitoring. Twelve patients (17.65%) underwent reoperation, with the most common reason for reoperation being persistent myelopathy, followed by wound infection and CSF leak. Mean experience of the primary surgeon was 10.3 years. No major differences in surgical experience were identified between the three main approaches. 3.3. Radiographic characteristics Preoperative and postoperative X-rays were available for 14 patients. Ten patients had a positive K-line and no significant difference in the proportion of positive K-lines was identified
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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C.D. Cerecedo-Lopez et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx Table 1 Cervical OPLL Demographic, Surgical and Radiographic Characteristics. Approach
Demographic n (%) Age (years)* ± sd Female (%) Race (%) White Black Asian Other Veteran Preoperative myelopathy+ (%) Signal change+ (%) Acute spinal cord injury (%) Surgical n levels ± sd Discectomy (%) Corpectomy (%) Laminectomy (%) Laminoplasty (%) Foraminotomy (%) Allograft (%) Fusion (%) Estimated blood loss+ (mL) ± sd Microscope (%) Fluoroscopy (%) Durotomy (%) Intraoperative monitoring (%) Reoperation (%) Length of follow-up (months) ± sd Surgeon’s experience (years) ± sd Radiographic Positive K-line+ (%) Preoperative C2-C7 Cobb angle ± sd Postoperative C2-C7 Cobb angle ± sd Occupation ratio+ ± sd Occupation ratio > 0.5+ (%) Occupation ratio > 0.6+ (%) OPLL type+ Continuous Segmental Mixed Other Outcome Postoperative Nurick grade+ ± sd Functional outcome+ Good (%) Poor (%)
Total
p-value
Anterior
Posterior
Combined
23 (33.8) 55 ± 11.4 10 (43.5)
37 (54.4) 58.7 ± 13.9 13 (35.1)
8 (11.8) 54 ± 11.8 1 (12.5)
68 (100) 56.9 ± 12.9 24 (35.3)
0.26 0.29
15 (65.2) 4 (17.4) 3 (13) 1 (4.4) 2 (8.7) 20 (90.9) 12 (81.7) 2 (8.7)
26 (70.3) 1 (2.7) 7 (18.9) 3 (8.1) 6 (16.2) 31 (83.8) 18 (48.7) 4 (10.8)
5 1 2 0 3 8 4 0
46 (67.7) 6 (8.8) 12 (17.7) 4 (5.9) 11 (16.2) 59 (92.2) 34 (89.5) 6 (8.8)
0.53 0.53 0.53 0.53 0.16 0.68 0.71 0.62
2 ± 0.8 23 (100) 17 (73.9) 0 (0) 0 (0) 5 (21.7) 18 (78.3) 21 (91.3) 303.3 ± 202.9 18 (78.3) 23 (100) 7 (30.4) 11 (47.8) 6 (26.1) 16.4 ± 18.9 9.1 ± 7.7
4.3 ± 1.3 0 (0) 0 (0) 29 (78.4) 8 (21.6) 12 (32.4) 12 (32.4) 19 (51.4) 389.8 ± 380.1 7 (18.9) 24 (64.9) 5 (13.5) 15 (40.5) 5 (13.5) 33 ± 42.9 11.6 ± 10
3.3 ± 0.9 8(100) 7 (87.5) 6 (75) 1 (12.5) 2 (25) 7 (87.5) 7 (87.5) 337.5 ± 47.9 6 (75) 7 (87.5) 2 (25) 5 (62.5) 1 (12.5) 19.3 ± 25.3 7.9 ± 6.6
3.43 ± 1.5 30 (44.1) 24 (35.3) 35 (51.5) 9 (13.2) 19 (28) 36 (53) 46 (67.7) 357.1 ± 313.1 31 (45.6) 54 (79.4) 14 (20.6) 31 (45.6) 12 (17.7) 25.9 ± 35.3 10.3 ± 9
<0.01 <0.01 <0.01 <0.01 0.01 0.66 <0.01 <0.01 0.70 <0.01 <0.01 0.28 0.51 0.44 0.26 0.43
3 (75) 4.1 ± 2.2 11.9 ± 5.8 0.4 ± 0.1 4 (30.8) 0 (0)
6 (75) 9 ± 10.1 7 ± 3.5 0.5 ± 0.1 18 (69.2) 8 (30.8)
1 (50) 12.4 ± 9.7 16.7 ± 7.3 0.5 ± 0.1 2 (40) 1 (20)
10 (71.4) 8.1 ± 8.4 10.3 ± 5.8 0.5 ± 0.1 24 (54.5) 9 (18.8)
0.77 0.51 0.09 0.03 0.06 0.08
2 1 2 7
13 (30) 2 (5) 9 (21) 2 (5)
0 2 2 1
15 (35) 5 (12) 13 (30) 10 (23)
<0.01 <0.01 <0.01 <0.01
0.9 ± 1.5
1.9 ± 1.9
1.2 ± 1.9
1.5 ± 1.8
0.16
15 (28) 3 (6)
18 (33) 12 (22)
5 (9) 1 (2)
38 (70) 16 (30)
0.46 0.46
(5) (2.5) (5) (7.5)
(62.5) (12.5) (25) (0) (37.5) (100) (50) (0)
(0) (5) (5) (2.5)
*Age at moment of surgery (years). +Data not available for all subjects, percentages calculated based on available data. sd = standard deviation.
between surgical approach groups. Similarly, preoperative cervical sagittal balance was similar between groups, while postoperative cervical sagittal balance demonstrated a trend towards a statistically significant difference between groups (p = 0.87). The mean canal space occupation ratio was 0.5 and a significant difference between approaches was identified (p = 0.03). Differences in the proportion of cases with a canal space occupation ratio 0.5 or 0.6 showed a tendency towards significance (p = 0.06 and 0.08). The most common type of OPLL was continuous, followed by mixed, other and segmental (Fig. 1). A significant difference in the proportion of OPLL types between all three approaches was identified (p = 0.004). 3.4. Clinical outcome Nurick grade at latest follow-up was estimated for 54 patients. Mean Nurick grade was 1.5 (Table 1). After dichotomizing the Nurick grade into good (0–2) or poor (3–5) functional outcome, 38 patients (70%) had a good outcome (Table 1). Exploratory analyses
from univariate analyses revealed an association between poor neurological outcome and positive K-line (OR, 0.2 [0.04–0.9], pvalue 0.05) and occupation ratio >0.6 (OR, 6.9 [1.35–42.7], pvalue 0.02) (Table 2). No evidence of association was observed in other exploratory analyses (Table 2).
4. Discussion Extensive experience in the management of OPLL has been accumulated in geographical areas with a higher prevalence of OPLL, particularly Japan. OPLL was originally reported in the United Kingdom almost two centuries ago, yet experience with OPLL and its management outside Asia is limited as evidenced by a scarcity of publications on the topic outside of this geographic region [13–19]. In the US, the estimated the prevalence of OPLL is 0.7% [14]. Presented here is our experience on the surgical management of OPLL accumulated at our centers over the previous two decades. Our case series included 68 patients who underwent surgery for
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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Fig. 1. Examples of the four types of OPLL from this case series A. Mixed B. Localized C. Continuous D. Segmental.
Table 2 Association between Patient Characteristics and Poor Functional Outcome.
Approach Anterior Posterior Combined Preoperative myelopathy Signal change Fusion Durotomy Intraoperative neuromonitoring Surgeon experience Positive K-line Preoperative Cobb angle Occupation Ratio >0.5 >0.6 OPLL Type Continuous Segmental Mixed Other
OR
95% CI
p-value
1 3.3 1 1.3 0.4 0.6 2.4 1.1 1 0.2 1.1
0.86–16.7 0.04–10.1 0.2–27.8 0.5–4.2 0.2–2.2 0.6–9.7 0.3–3.6 0.9–1.1 0.04–0.9 0.9–1.2
0.1 1 0.82 0.46 0.41 0.21 0.86 0.76 0.05 0.29
2.3 6.9
0.6–10.7 1.35–42.7
0.25 0.02
1 0.7 3.4 0.3
0.03–6.7 0.6–21.6 0.02–2.9
0.76 0.17 0.38
cervical OPLL, with 56 reported as non-Asian. To the best of our knowledge this is the largest series of OPLL cases managed outside of Asia. Mean age at diagnosis was similar to previously reported values in both Asian and non-Asian series [15,16]. We also observed a
slight male predominance in our series, which closely resembled the 2:1 male-to-female ratio found in previous reports [15]. Most individuals in our case series presented with signs and symptoms of myelopathy and most of them had a T2 signal change on MRI (~90%). The proportion of T2-signal change in our patients was much higher than previously reported by a Japanese series (43%) and may be explained by the unfamiliarity of physicians in our area with the disease, leading to delayed referral [17]. While no association between signal change and poor functional outcome was observed in this series, this finding reinforces the importance of physicians being familiar with the manifestations of OPLL as preoperative T2-signal change has been associated with poor longterm outcomes in other case series [18]. By continuing to report on the management of OPLL we expect our paper contributes to increasing awareness of this condition in physicians of the Western world. The proportion of patients identifying as white or black ethnicity closely resembled that of the largest case series of OPLL in nonAsian patients previously reported in the US, while the proportion of Hispanic patients was considerably lower in our case series [16]. This may be explained by the higher proportion of patients with Hispanic ancestry living in the area of the previously reported case series (i.e. Miami) [16]. Another case series evaluating the radiographic prevalence of OPLL in an area with a relatively high proportion of people with Hispanic ancestry (i.e. San Francisco) reported racial proportions very similar to the ones reported in the Miami series [19]. Thus, although our case series revealed a low propor-
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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tion of OPLL case series in races other than White, Black or Asian individuals, physicians practicing in areas with a high proportion of individuals with Hispanic ancestry should be aware that this subset of the population presents OPLL with a relatively higher frequency. Three approaches were used by surgeons in our center: anterior, posterior or a combination of both (Figs. 2–4). Contrasting previous studies, the number of levels operated on in our center significantly differed between the groups [20]. No significant difference in estimated blood loss between surgical approaches was observed. This again contrasted with a previous metanalysis reporting higher intraoperative blood loss in the anterior approach groups [21]. Although almost 20% of patients in our series had a durotomy, only two patients underwent reoperation for CSF leak management. Surgeons should be aware that durotomies may present during the management of OPLL and plan accordingly to approach this potential complication. Other than reoperations, no major complications were reported for the patients in our series and the reoperation rate was similar to previously reported case series [21]. Radiographic parameters have been proposed as aids for deciding the appropriate approach to manage OPLL. Two of the most common radiographic parameters used in the decision making are the canal space occupation ratio and the K-line [22]. We did not observe a significant difference in the proportion of positive K-lines between surgical approaches. The mean canal space occupying ratio significantly differed between approaches and a greater
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proportion of lesions occupying 0.5 or 0.6 of the canal space were managed with a posterior approach. It is important to note that most of the patients in this series had undergone surgical management of OPLL before the literature demonstrated worse outcomes with OPLL lesions occupying 60% of the spinal canal managed with posterior decompression [23]. Continuous OPLL was the most common type observed in our series and most continuous OPLL cases were managed with a posterior approach. This is in accord with previous series of OPLL managed in the United States [16]. The anterior approach was more commonly used for OPLL classified as other type, again closely resemble the previously published American OPLL case series [16]. As previously mentioned, radiographic parameters other than the type of OPLL may perhaps be better suited to aid surgeons in deciding the optimal surgical approach [22,23]. Prospective randomized studies evaluating the optimal approach selection for OPLL may provide further insights into this matter, as current prospective studies on OPLL are scant [21]. The advantages of our case series on OPLL are that it includes many non-Asian patients and is the largest case series outside of Asia, which distinguishes it from all of the previously published case series. Our study highlights the differences in diagnosis and treatment of a condition that is much more commonly addressed in other parts of the world. The average follow-up for all patients in the series was 26 months. While this is a significant amount of time, our study would have been improved by longer followup time and data availability. Unfortunately, in our area of practice
Fig. 2. Anterior only approach in a 34-year-old female. A. Preoperative cervical X-ray demonstrating minimal OPLL (yellow shadow) with a positive K-line (green line). B. Preoperative sagittal CT scan demonstrating multiple osteophytes and minimal OPLL. C. Preoperative axial CT scan demonstrating OPLL at the C5–C6 region. D. Postoperative cervical X-ray status post C4–C7 anterior cervical discectomies and fusion. Estimated Nurick grade at three months for this patient was 0 (some residual symptoms of radiculopathy without any myelopathy).
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
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Fig. 3. Posterior only approach in a 52-year-old male. A. Preoperative cervical X-ray demonstrating two regions of OPLL occupying a large proportion of the spinal canal (yellow shadow) with a negative K-line (green line). B. Preoperative sagittal CT scan demonstrating multiple osteophytes and two regions of OPLL at C3–C4 and C5–C6. C. Preoperative axial CT scan demonstrating OPLL at the C5–C6 region. D. Postoperative axial CT scan demonstrating complete decompression of the C5–C6 level and pedicle screw fixation. E. Postoperative cervical X-ray status post C3–C7 posterior cervical laminectomies and fusion. Estimated Nurick grade at twelve months for this patient was 2 (slight difficulty in walking that does not prevent full-time employment).
Fig. 4. Combined approach in a 53-year-old male. A. Preoperative cervical X-ray demonstrating three regions of OPLL occupying a large proportion of the spinal canal (yellow shadow) with a positive K-line (green line). B. Preoperative sagittal CT scan demonstrating widespread OPLL spanning C2–C5. C. Preoperative axial CT scan demonstrating OPLL at the C4 level. D. Preoperative axial MRI demonstrating severe compression at the C4 level with a slit-like appearance of the spinal cord (red arrow). E. Postoperative axial MRI demonstrating decompression of the spinal cord at the C4 level (red arrow). F. Postoperative cervical X-ray status post C3–C5 anterior cervical discectomies and fusion and C3–C6 posterior cervical laminectomies and fusion. Estimated Nurick grade at five months for this patient was 1 (signs or symptoms of myelopathy but no difficulty in walking).
Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015
C.D. Cerecedo-Lopez et al. / Journal of Clinical Neuroscience xxx (xxxx) xxx
our patient population commonly has treatment at one hospital and follow-up in another or even in a different part of the country. Our posterior only approach patients had a smaller Cobb angle that trended towards statistical significance (P < 0.1), and a larger patient population is needed to determine if this could become a significant finding. Despite having a high number of patients with myelopathy and/ or spinal cord signal change, functional outcomes were good for the majority of our patients. Our exploratory analysis revealed two interesting associations. First, the association between a positive K-line and improved functional outcomes. Fujiyoshi et al. compared outcomes after OPLL decompression stratified by K-line status reporting higher rates of functional recovery in patients having a positive K-line (66% vs. 14% for K-line + and K-line respectively) [22]. While the percentages of patients with good functional outcome in our series differ from those of Fujiyoshi et al. (85% vs. 57% for K-line + and K-line respectively), our findings reinforce those of previous series suggesting a positive K-line may be predictive of better functional outcomes. Our analysis also revealed a strong association between an occupation ratio >0.6 and poor functional outcomes. This goes in line with what was previously reported by Kato et al. [24], and reinforces the idea that increased awareness of the disease leading to prompt recognition and early surgical decompression may lead to improved functional outcomes. 5. Conclusion In this case series of 68 patients with OPLL managed outside of Asia the surgical management of OPLL was effective and lead to high rates of functional recovery. Increased awareness leading to prompt referral for surgical decompression is expected to improve clinical outcomes of OPLL patients. Conflicts of interest The authors report no conflict of interest. Disclosure of financial support This project did not receive any sort of financial support or funding from any organization, institution or person in the public, commercial, or not-for-profit sectors. The authors have no personal or institutional financial interest in drugs, materials or devices described in this submission. Acknowledgement The authors have no acknowledgement. References [1] Sudoł-Szopin´ska I, Kwiatkowska B, Prochorec-Sobieszek M, Mas´lin´ski W. Enthesopathies and enthesitis. Part 1. Etiopathogenesis. J Ultrason 2015;15:72–84. https://doi.org/10.15557/JoU.2015.0006. [2] Resnick D, Guerra J, Robinson C, Vint V. Association of diffuse idiopathic skeletal hyperostosis (DISH) and calcification and ossification of the posterior longitudinal ligament. Am J Roentgenol 1978;131:1049–53. https://doi.org/ 10.2214/ajr.131.6.1049. [3] Hirai T, Yoshii T, Iwanami A, Takeuchi K, Mori K, Yamada T, et al. Prevalence and distribution of ossified lesions in the whole spine of patients with cervical ossification of the posterior longitudinal ligament a multicenter study (JOSL CT study). PLoS ONE 2016;11:1–13. https://doi.org/10.1371/journal. pone.0160117.
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Please cite this article as: C. D. Cerecedo-Lopez, I. Tafel, A. M. Lak et al., Surgical management of ossification of the posterior longitudinal ligament in the cervical spine, Journal of Clinical Neuroscience, https://doi.org/10.1016/j.jocn.2019.12.015