ABSTRACT
Objective:
To identify the factors related to the non-occurrence of cage subsidence in standalone lateral lumbar interbody fusion procedures.
Methods:
Case-control study of single level standalone lateral lumbar interbody fusion (LLIF) including 86 cases. Patients without cage subsidence composed the control group (C), while those in the subsidence group (S) developed cage subsidence. Preoperative data were examined to create a risk score based on correlation factors with S group. The proven risk factors were part of an evaluation score.
Results:
Of the 86 cases included, 72 were in group C and 14 in group S. The following risk factors were more prevalent in group S compared to C group: spondylolisthesis (93% vs 18%; p<0.001); scoliosis (31% vs 12%; p=0.033); women (79% vs 38%; p=0.007); older patients (average 57.0 vs 68.4 years; p=0.001). These risk factors were used in a score (0-4) to evaluate the risk in each case. The patients with higher risk scores had greater subsidence (p<0.001). Scores ≥2 were predictive of subsidence with 92% sensitivity and 72% specificity.
Conclusions:
It was possible to correlate the degree of subsidence in standalone LLIF procedures using demographic (age and gender) and pathological (spondylolisthesis and scoliosis) data. With a score based on risk factors and considering any score <2, the probability of non-occurrence of subsidence following standalone LLIF (negative predictive value) was 98%.
Keywords:
Spine; Lumbar vertebrae; Spinal fusion; Complications; Risk factors; Patient selection
RESUMO
Objetivo:
Identificar os fatores relacionados a não ocorrência de subsidência de cage em procedimentos de fusão lombar intersomática por via lateral em um só nível.
Métodos:
Estudo de caso controle em fusão intersomática lombar por via lateral (LLIF) em um só nível, incluindo 86 casos. Os pacientes sem subsidência do cage formaram o grupo controle (C), enquanto os do grupo subsidência (S) desenvolveram subsidência do cage. Os dados pré-operatórios foram examinados para criar um escore de risco com base em fatores de correlação com o grupo S. Os fatores de risco comprovados fizeram parte de um escore de avaliação.
Resultados:
Dos 86 casos incluídos, 72 estavam no grupo C e 14 no grupo S. Os seguintes fatores de risco foram mais prevalentes no grupo S com relação ao grupo C: espondilolistese (93% vs. 18%; p < 0,001); escoliose (31% vs. 12%; p = 0,033); mulheres (79% vs. 38%; p = 0,007); pacientes idosos (média de 57,0 vs. 68,4 anos; p = 0,001). Esses fatores de risco foram utilizados em um escore (0-4) para avaliar o risco em cada caso. Os pacientes com escores mais altos de risco tiveram maior subsidência (p < 0,001). Os escores ≥ 2 foram preditivos de subsidência com sensibilidade de 92% e especificidade de 72%.
Conclusões:
Foi possível correlacionar o grau de subsidência em procedimentos LLIF em um só nível com a utilização de dados demográficos (idade e sexo) e patológicos (espondilolistese e escoliose). Com um escore baseado em fatores de risco e considerando qualquer pontuação <2, a probabilidade de não ocorrência de subsidência depois de LLIF em um só nível (valor preditivo negativo) foi de 98%.
Descritores:
Coluna vertebral; Vértebras lombares; Fusão vertebral; Complicações; Fatores de risco; Seleção de pacientes
RESUMEN
Objetivo:
Identificar los factores relacionados con la ausencia de subsidencia de cage en los procedimientos de fusión intersomática lumbar por vía lateral en un solo nivel.
Métodos:
Estudio de caso-control en la fusión intersomática lumbar por vía lateral (LLIF) en un solo nivel, incluyendo 86 casos. Los pacientes sin subsidencia del cage formaron el grupo control (C), mientras que el grupo de subsidencia (S) desarrolló subsidencia del cage. Los datos preoperatorios fueron examinados para crear una puntuación de riesgo basada en factores de correlación con el grupo S. Los factores de riesgo comprobados formaron parte de una puntuación de evaluación.
Resultados:
De los 86 casos incluidos, 72 formaron el grupo C y 14 el grupo S. Los siguientes factores de riesgo son más prevalentes en el grupo S con respecto al grupo C: espondilolistesis (93% vs. 18%, p <0,001); escoliosis (31% vs. 12%, p = 0,033); mujeres (79% vs. 38%, p = 0,007); ancianos (media de 57,0 a 68,4 años; p = 0,001). Estos factores de riesgo se utilizaron en una puntuación (0-4) para evaluar el riesgo en cada caso. Los pacientes con puntuaciones más altas de riesgo tuvieron mayor subsidencia (p < 0,001). Las puntuaciones ≥ 2 fueron predictivas de la subsidencia con una sensibilidad del 92% y una especificidad del 72%.
Conclusiones:
Se ha podido relacionar el grado de subsidencia en los procedimientos LLIF en un solo nivel con el uso de los datos demográficos (edad y sexo) y patológicos (espondilolistesis y escoliosis). Con una puntuación basada en factores de riesgo y considerado un puntaje < 2, la probabilidad de no ocurrencia de subsidencia después de LLIF en un solo nivel (valor predictivo negativo) fue del 98%.
Descriptores:
Columna vertebral; Vértebras lumbares; Fusión vertebral; Complicaciones; Factores de riesgo; Selección de paciente
INTRODUCTION
Lateral lumbar interbody fusion (LLIF) has evolved into an effective and less invasive treatment option adopted for different toracolumbar conditions.11. Lehmen JA, Gerber EJ. MIS lateral spine surgery: a systematic literature review of complications, outcomes, and economics. Eur Spine J. 2015;24(Suppl 3):287-313.
2. Amaral R, Marchi L, Oliveira L, Coutinho T, Castro C, Coutinho E, et al. Minimally invasive lateral option for thoracic -lumbar intersomatic arthrodesis. Coluna/Columna. 2011;10(3):239-43.-33. Oliveira D de A, Fernandez JS, Falcon RS, Menezes CM. Fusion via transpsoas lateral approach: considerations and initial results. Coluna/Columna. 2014;13(3):214-218. Biomechanical features of LLIF constructions provide better rigidity than other constructions.44. Pimenta L, Turner AWL, Dooley ZA, Parikh RD, Peterson MD. Biomechanics of lateral interbody spacers: going wider for going stiffer. ScientificWorldJournal. 2012;2012:1-6.,55. Cappuccino A, Cornwall GB, Turner AW, Fogel GR, Duong HT, Kim KD, et al. Biomechanical analysis and review of lateral lumbar fusion constructs. Spine (Phila Pa 1976). 2010;35(26 Suppl):S361-7. It uses large diameter, hollow spacers that can engage the peripheral margins of the endplate, the design and positioning of which seems to be superior to others.66. Lowe TG, Hashim S, Wilson LA, O'Brien MF, Smith DA, Diekmann MJ, et al. A biomechanical study of regional endplate strength and cage morphology as it relates to structural interbody support. Spine (Phila Pa 1976). 2004;29(21):2389-94. In conventional lumbar fusion techniques, the interbody cage is always supplemented by internal fixation. In LLIF, the anterior and posterior longitudinal ligaments (ALL and PLL, respectively) are preserved. For this reason, a stand-alone construction can provide good stabilization, comparable to a TLIF supplemented with pedicle screws.44. Pimenta L, Turner AWL, Dooley ZA, Parikh RD, Peterson MD. Biomechanics of lateral interbody spacers: going wider for going stiffer. ScientificWorldJournal. 2012;2012:1-6. Good results and complications from non-supplemented LLIF have been reported;77. Malham GM, Ellis NJ, Parker RM, Blecher CM, White R, Goss B, et al. Maintenance of Segmental Lordosis and Disc Height in Standalone and Instrumented Extreme Lateral Interbody Fusion (XLIF). Clin Spine Surg. 2016 May 26. [Epub ahead of print] PubMed PMID: 24662286.
8. Nemani VM, Aichmair A, Taher F, Lebl DR, Hughes AP, Sama AA, et al. Rate of revision surgery after stand-alone lateral lumbar interbody fusion for lumbar spinal stenosis. Spine (Phila Pa 1976). 2014;39(5):E326-31.
9. Ahmadian A, Bach K, Bolinger B, Malham GM, Okonkwo DO, Kanter AS, et al. Stand-alone minimally invasive lateral lumbar interbody fusion: multicenter clinical outcomes. J Clin Neurosci. 2015;22(4):740-6.
10. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Stand-alone lateral interbody fusion for the treatment of low-grade degenerative spondylolisthesis. ScientificWorldJournal. 2012;2012:456346.-1111. Castro C, Oliveira L, Amaral R, Marchi L, Pimenta L. Is the lateral transpsoas approach feasible for the treatment of adult degenerative scoliosis? Clin Orthop Relat Res. 2014;472(6):1776-83. however, the ideal indication is not clear.
Cage settling and vertebral body fracture are potential and significant complications. When using LLIF standalone constructions, this risk may be even higher. The severity of cage subsidence is correlated with its extension.1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8. The consequences may range from a lack of clinical symptoms, to loss of disc height, loss of segmental angulation, acute low back pain, restenosis, or even a fracture of the adjacent vertebral bodies.1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.
13. Oliveira L, Marchi L, Coutinho E, Pimenta L. A radiographic assessment of the ability of the extreme lateral interbody fusion procedure to indirectly decompress the neural elements. Spine (Phila Pa 1976). 2010;35(26 Suppl):S331-7.
14. Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73.
15. Tempel ZJ, Gandhoke GS, Bolinger BD, Okonkwo DO, Kanter AS. Vertebral body fracture following stand-alone lateral lumbar interbody fusion (LLIF): report of two events out of 712 levels. Eur Spine J. 2015;24(Suppl 3):409-13.-1616. Dua K, Kepler CK, Huang RC, Marchenko A. Vertebral body fracture after anterolateral instrumentation and interbody fusion in two osteoporotic patients. Spine J. 2010;10(9):e11-5. Prevention of cage subsidence is, therefore, an issue of great research interest.
Some study groups have recently discovered that the use of wider LLIF cages results in more stable biomechanical constructions44. Pimenta L, Turner AWL, Dooley ZA, Parikh RD, Peterson MD. Biomechanics of lateral interbody spacers: going wider for going stiffer. ScientificWorldJournal. 2012;2012:1-6. and decreased subsidence rates.1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.,1414. Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73.,1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91. Based on this data, the use of 22mm or even wider cages is now recommended. Even more recent evidence has revealed that impaired bone quality1818. Tempel ZJ, Gandhoke GS, Okonkwo DO, Kanter AS. Impaired bone mineral density as a predictor of graft subsidence following minimally invasive transpsoas lateral lumbar interbody fusion. Eur Spine J. 2015;24(Suppl 3):414-9. and inadvertent intraoperative endplate damage1919. Santoni BG, Alexander GE 3rd, Nayak A, Cabezas A, Marulanda GA, Murtagh R, et al. Effects on inadvertent endplate fracture following lateral cage placement on range of motion and indirect spine decompression in lumbar spine fusion constructs: A cadaveric study. Int J Spine Surg. 2013;7:e101-8.,2020. Agarwal V, Bagley J, Knott K, Owens T, Brown C, Isaacs R. Correlation between Intraoperative Endplate Violation and Subsidence of Polyetheretherketone Intervertebral Cages in Extreme Lateral Interbody Fusion. In: The International Society for the Advancement of Spine Surgery, april 30 - may 2, 2014. (Paper #436). can contribute to a poorer outcome. Despite the lack of research on cage settling issues, the case selection for standalone LLIFs that do not evolve to subsidence needs elucidation; the objective of this work was to identify the factors correlated with lack of cage subsidence in standalone LLIF procedures.
METHODS
A single center retrospective case-control study with a database spanning the years 2008 to 2015. This observational study was reviewed by the research ethics review board of our institution. The informed consent was waived because it was a retrospective research involving medical records. Inclusion criteria: single-level stand-alone lumbar LLIF. Exclusion criteria: cages with 18mm anteroposterior dimension (due to their demonstrated inferiority;1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.,1414. Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73.,1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91. any previous lumbar arthrodesis/arthroplasty surgery; any kind of supplementation (posterior/lateral/anterior). The interbody cages were packed with synthetic bone substitute.
The patients were grouped into Control group (C) and Subsidence group (S), according to the degree of interbody cage settling. Subsidence grading was evaluated in 3-month lateral orthostatic radiographs and classified on a 4-point scale (0-III) described previously1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8. (Grade 0, 0%-24%; Grade I, 25%-49%; Grade II, 50%-74%; and Grade III, 75%-100% collapse of the level). The choice of the 3-month time point was based on a previous 12-month follow-up study in which patients who presented subsidence at the 12-month time point already presented a detectable subsidence in the 3-month evaluation. The C group comprised grade 0 and I cases (low-grade), while the S group had the grades II and III cases (high-grade), this division was based on the clinical impairment (pain outcome) that had already been demonstrated1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8. in the S group, in comparison with the C group.
The preoperative diagnosis and images were reviewed, to identify the presence of spondylolisthesis and scoliosis. The intraoperative fluoroscopy images and surgical reports were reviewed aiming to identify the occurrence of unintentional anterior longitudinal ligament (ALL) rupture or cortical bone breaks during the preparation of the intervertebral space. These cases were excluded from the analysis. The anteroposterior dimension and height of the cage were measured. The influence of each factor in each subsidence grade subgroup was analyzed. A risk score was established based on preoperative factors with significant correlation with cage subsidence.
Statistical analyses were performed using SPSS software (SPSS, Version 10, SPSS, Chicago, Ill., USA). The Mann-Whitney U test was used for unpaired data, analysis of variance (ANOVA), Fischer's exact test, and the Chi-square test with Pearson's correlation were used with an alpha of 0.05.
RESULTS
Of 719 cases treated with LLIF, 100 stand-alone LLIF cases were identified; 14 were excluded due lack of images, and 86 cases were eligible for analysis (86 levels). Average age of 58.8 years(25-84, range), mean body mass index (BMI) of 27.9 (19-49, range), 38 were females (44%). The surgeries involved L4L5 in 83% (71/86) of the total cases (L1L2, 1 case; L2L3, 5 cases; L3L4, 8 cases; L5VT, 1 case). Twenty-six cases (30%) had spondylolisthesis (grade I), 13 cases (15%) had degenerative scoliosis, and the remainder had either degenerative disc disease (DDD), instability and/or stenosis.
Subsidence analysis in the 3-month follow-up images revealed the following results: grade 0= 62 cases (72%); grade I= 10 cases (12%); grade II= 10 cases (12%); grade III= 4 cases (5%). The C group had 72 cases (84%) and the S group had 14 cases (16%). Surgical revision was necessary in seven cases from the S group (50%) and only 1 case from the C group (1%).
The following preoperative factors were more prevalent in the S group than in the C group: (Table 1) spondylolisthesis (93% vs 18%; p<0.001); scoliosis (31% vs 12%; p=0.033); female sex (79% vs 38%; p=0.007); older patients (average 57 vs 68 years; p=0.001). BMI and surgery at L4L5 did not show statistical difference.
Surgical factors were also compared between groups. Non-intentional ALL rupture occurrence was too low in this sample, and no significance was seen (1 vs 1 case; p=0.301). Another factor that did not show a statistical trend for either the S or C group was cage AP dimension (p=0.351; 22 vs 24 vs 26mm; Table 2). The cage height was observed to be higher in the S group than in the C subset (9.8 vs 10.9mm; p=0.035), while in the S group 50%, of the cases had 12mm cages and only 22% had 12mm cages in the C group.
To investigate whether there was a cumulative effect of the individual risk factors found above, the cases were scored by adding one unit for each risk factor found. The SCORE was comprised of the following criteria: female gender; spondylolisthesis; scoliosis; age > 61 years (confidence interval upper bound value from C group = 60.5 years). Minimum SCORE = 0 and maximum SCORE = 4. Accordingly, it was demonstrated that higher SCORES were correlated with higher severity of subsidence. (Table 3; p<0.001)
Table 4 shows the association between exposure (SCORE ≥ 2) and outcome (subsidence). The specificity and sensitivity of a SCORE < 2 for predicting which case would not develop high-grade cage subsidence are 75% and 93%, respectively. So, for any particular positive SCORE result (≥2) in our sample, the probability that it is true positive was 42% (positive predictive value; PPV). For any particular negative SCORE result (<2), the probability that it is true negative was 98% (negative predictive value; NPV).
DISCUSSION
Standalone LLIF procedures are feasible, but carry the risk of cage subsidence. Cage selection to prevent subsidence is only now beginning to be understood. The present report shows subsidence risk factors in a retrospective case-control study in a LLIF cohort with only single-level standalone cases. Preoperative risk factors were identified: elderly and female patients, and also diagnoses of scoliosis and spondylolisthesis at the index level. A score based on those factors was applied, to determine in which case a standalone indication would evolve without subsidence. The test showed great sensitivity, with extremely low false negative test results (2%).
Lumbar interbody fusion performed with lateral implants has been shown to be biomechanically superior to other constructions,44. Pimenta L, Turner AWL, Dooley ZA, Parikh RD, Peterson MD. Biomechanics of lateral interbody spacers: going wider for going stiffer. ScientificWorldJournal. 2012;2012:1-6.,55. Cappuccino A, Cornwall GB, Turner AW, Fogel GR, Duong HT, Kim KD, et al. Biomechanical analysis and review of lateral lumbar fusion constructs. Spine (Phila Pa 1976). 2010;35(26 Suppl):S361-7. as the larger diameter hollow spacers appear to be favorable for engaging the peripheral margins of the end plate.66. Lowe TG, Hashim S, Wilson LA, O'Brien MF, Smith DA, Diekmann MJ, et al. A biomechanical study of regional endplate strength and cage morphology as it relates to structural interbody support. Spine (Phila Pa 1976). 2004;29(21):2389-94. The good stiffness achieved with lateral wide implants enables standalone constructions to be performed in some cases. However, it remains an off label indication to date. The selection of the appropriate instrumentation option is still a topic of debate. Recently, Tohmeh2121. Tohmeh AG. The choice of supplemental fixation in lateral interbody fusion: video lecture. Eur Spine J. 2015;24(Suppl 3):447-8. published a video lecture with a preliminary scoring system to guide the choice of internal spinal fixation modality. Based on a literature review and author's opinion, this algorithm attributes scores according to the severity of the spondylolisthesis, degenerative disc, facet disease and adjacent segment disease.
The occurrence of cage settling generates radiological and clinical consequences. In the radiological field, Tohmeh et al.1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91. and Marchi et al.1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8. demonstrated loss of both disc and foramen height, decreased lordosis gain, but no negative effects on bone fusion. Inadvertent endplate fracture following lateral cage placement is a fracture that can impair the biomechanical stability.1919. Santoni BG, Alexander GE 3rd, Nayak A, Cabezas A, Marulanda GA, Murtagh R, et al. Effects on inadvertent endplate fracture following lateral cage placement on range of motion and indirect spine decompression in lumbar spine fusion constructs: A cadaveric study. Int J Spine Surg. 2013;7:e101-8. Although there is no congruent data regarding the clinical impact of subsidence,77. Malham GM, Ellis NJ, Parker RM, Blecher CM, White R, Goss B, et al. Maintenance of Segmental Lordosis and Disc Height in Standalone and Instrumented Extreme Lateral Interbody Fusion (XLIF). Clin Spine Surg. 2016 May 26. [Epub ahead of print] PubMed PMID: 24662286.,99. Ahmadian A, Bach K, Bolinger B, Malham GM, Okonkwo DO, Kanter AS, et al. Stand-alone minimally invasive lateral lumbar interbody fusion: multicenter clinical outcomes. J Clin Neurosci. 2015;22(4):740-6.,1616. Dua K, Kepler CK, Huang RC, Marchenko A. Vertebral body fracture after anterolateral instrumentation and interbody fusion in two osteoporotic patients. Spine J. 2010;10(9):e11-5. some groups have found poorer clinical outcomes in short,1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.,1515. Tempel ZJ, Gandhoke GS, Bolinger BD, Okonkwo DO, Kanter AS. Vertebral body fracture following stand-alone lateral lumbar interbody fusion (LLIF): report of two events out of 712 levels. Eur Spine J. 2015;24(Suppl 3):409-13. medium88. Nemani VM, Aichmair A, Taher F, Lebl DR, Hughes AP, Sama AA, et al. Rate of revision surgery after stand-alone lateral lumbar interbody fusion for lumbar spinal stenosis. Spine (Phila Pa 1976). 2014;39(5):E326-31. and long-term1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91. follow-up for subsidence in LLIF. The short-term results were attributed to transient painful micromotion, in addition to pain from the fracture itself. Moreover, along with the loss of correction, restenosis may occur in high-grade subsidence, and there is the need of further direct decompression. Including the results from the current work, the rate of re-intervention due to subsidence varies from 0% to 50%, depending on the supplementation option chosen. Vertebral fracture is rare, but possible.1515. Tempel ZJ, Gandhoke GS, Bolinger BD, Okonkwo DO, Kanter AS. Vertebral body fracture following stand-alone lateral lumbar interbody fusion (LLIF): report of two events out of 712 levels. Eur Spine J. 2015;24(Suppl 3):409-13. Considering the possible consequences of cage settling, the topic must be better understood in order to avoid subsidence.
The first strong evidence of subsidence prevention in LLIF came from retrospective comparative studies1212. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.,1414. Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73. which demonstrated that cages with a larger anteroposterior diameter (22 x 18mm) could decrease the rate of cage settling. It is now known that other intraoperative features also influence the occurrence of subsidence: endplate damage during preparation and overdistraction of the disc space. Santoni et al.1919. Santoni BG, Alexander GE 3rd, Nayak A, Cabezas A, Marulanda GA, Murtagh R, et al. Effects on inadvertent endplate fracture following lateral cage placement on range of motion and indirect spine decompression in lumbar spine fusion constructs: A cadaveric study. Int J Spine Surg. 2013;7:e101-8. reported the harmful role of intraoperative endplate damage in a cadaveric model. Accordingly, a clinical study1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91. demonstrated that the magnitude of subsidence is lower if the cage does not sink into the endplates during surgery. Taller interbody grafts are correlated with higher distractive and compressive forces in vitro.2222. Truumees E, Demetropoulos CK, Yang KH, Herkowitz HN. Effects of disc height and distractive forces on graft compression in an anterior cervical discectomy model. Spine (Phila Pa 1976). 2002;27(22):2441-5. In clinical practice, we observed more cases with 12mm-height cages in subsidence versus the control group, as was also seen by other reports on LLIF.1717. Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91.,2020. Agarwal V, Bagley J, Knott K, Owens T, Brown C, Isaacs R. Correlation between Intraoperative Endplate Violation and Subsidence of Polyetheretherketone Intervertebral Cages in Extreme Lateral Interbody Fusion. In: The International Society for the Advancement of Spine Surgery, april 30 - may 2, 2014. (Paper #436). Other possible issues include insufficient contralateral annular release, and improper cage sizing in the lateral dimension, which may result in failure to cover the apophyseal ring.
A significant trend of increasing subsidence rates has been correlated with LLIF with longer constructions1414. Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73. and more instable pathologies.1010. Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Stand-alone lateral interbody fusion for the treatment of low-grade degenerative spondylolisthesis. ScientificWorldJournal. 2012;2012:456346.,1111. Castro C, Oliveira L, Amaral R, Marchi L, Pimenta L. Is the lateral transpsoas approach feasible for the treatment of adult degenerative scoliosis? Clin Orthop Relat Res. 2014;472(6):1776-83.,2323. Fogel GR, Turner AW, Dooley ZA, Cornwall GB. Biomechanical stability of lateral interbody implants and supplemental fixation in a cadaveric degenerative spondylolisthesis model. Spine (Phila Pa 1976). 2014;39(19):E1138-46. Another pathology-related criterion has been studied in LLIF subsidence: poor bone quality. Similarly to the present study, Tempel et al.1818. Tempel ZJ, Gandhoke GS, Okonkwo DO, Kanter AS. Impaired bone mineral density as a predictor of graft subsidence following minimally invasive transpsoas lateral lumbar interbody fusion. Eur Spine J. 2015;24(Suppl 3):414-9. conducted a case-control study to analyze bone mineral density (BMD) in cases that evolved with subsidence following LLIF. They found that a DEXA T score of less than -1.0 predicts subsidence, with sensitivity and specificity of 78.3 and 63.2%, respectively. Female sex and age may be potential confounders of the association between osteoporosis and cage subsidence, as the incidence of osteoporosis and osteoporotic fractures increases markedly with age and female sex.2424. European Prospective Osteoporosis Study (EPOS) Group, Felsenberg D, Silman AJ, Lunt M, Armbrecht G, Ismail AA,et al. Incidence of vertebral fracture in europe: results from the European Prospective Osteoporosis Study (EPOS). J Bone Miner Res. 2002;17(4):716-24. Along with poorer bone quality, spinal muscular atrophy could negatively affect cage stabilization and spinal bone mineral density in the elderly postmenopausal population.2525. Ito M, Hayashi K, Uetani M, Yamada M, Ohki M, Nakamura T. Association between anthropometric measures and spinal bone mineral density. Invest Radiol. 1994;29(9):812-6.
Some limitations of this study must be pointed out. (1) The major limitation is inherent to the study design: a retrospective study. However, it is feasible as a preliminary investigation of a suspected risk factor, and sometimes a case-control study is the only ethical way to investigate an association. (2) The study only analyzed single-level constructions. Readers must, therefore, be cautious when extrapolating the conclusions for multi-level fusion. (3) The DEXA scan results were not available for all patients, so they could not be included in the analysis. (4) The results are based in a single-center experience.
CONCLUSION
The present study correlated cage subsidence in stand-alone LLIF procedures with the following preoperative risk factors: age, gender, spondylolisthesis and scoliosis. With a score based on those risk factors, in our sample, the probability of a particular stand-alone LLIF procedure with a score of <2 evolving without subsidence was 98%. This could be the first step towards the understanding of case selection for LLIF with no internal fixation.
REFERENCES
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11Castro C, Oliveira L, Amaral R, Marchi L, Pimenta L. Is the lateral transpsoas approach feasible for the treatment of adult degenerative scoliosis? Clin Orthop Relat Res. 2014;472(6):1776-83.
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12Marchi L, Abdala N, Oliveira L, Amaral R, Coutinho E, Pimenta L. Radiographic and clinical evaluation of cage subsidence after stand-alone lateral interbody fusion. J Neurosurg Spine. 2013;19(1):110-8.
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13Oliveira L, Marchi L, Coutinho E, Pimenta L. A radiographic assessment of the ability of the extreme lateral interbody fusion procedure to indirectly decompress the neural elements. Spine (Phila Pa 1976). 2010;35(26 Suppl):S331-7.
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14Le TV, Baaj AA, Dakwar E, Burkett CJ, Murray G, Smith DA, Uribe JS. Subsidence of polyetheretherketone intervertebral cages in minimally invasive lateral retroperitoneal transpsoas lumbar interbody fusion. Spine (Phila Pa 1976). 2012;37(14):1268-73.
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15Tempel ZJ, Gandhoke GS, Bolinger BD, Okonkwo DO, Kanter AS. Vertebral body fracture following stand-alone lateral lumbar interbody fusion (LLIF): report of two events out of 712 levels. Eur Spine J. 2015;24(Suppl 3):409-13.
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17Tohmeh AG, Khorsand D, Watson B, Zielinski X. Radiographical and clinical evaluation of extreme lateral interbody fusion: effects of cage size and instrumentation type with a minimum of 1-year follow-up. Spine (Phila Pa 1976). 2014;39(26):E1582-91.
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18Tempel ZJ, Gandhoke GS, Okonkwo DO, Kanter AS. Impaired bone mineral density as a predictor of graft subsidence following minimally invasive transpsoas lateral lumbar interbody fusion. Eur Spine J. 2015;24(Suppl 3):414-9.
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19Santoni BG, Alexander GE 3rd, Nayak A, Cabezas A, Marulanda GA, Murtagh R, et al. Effects on inadvertent endplate fracture following lateral cage placement on range of motion and indirect spine decompression in lumbar spine fusion constructs: A cadaveric study. Int J Spine Surg. 2013;7:e101-8.
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20Agarwal V, Bagley J, Knott K, Owens T, Brown C, Isaacs R. Correlation between Intraoperative Endplate Violation and Subsidence of Polyetheretherketone Intervertebral Cages in Extreme Lateral Interbody Fusion. In: The International Society for the Advancement of Spine Surgery, april 30 - may 2, 2014. (Paper #436).
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21Tohmeh AG. The choice of supplemental fixation in lateral interbody fusion: video lecture. Eur Spine J. 2015;24(Suppl 3):447-8.
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22Truumees E, Demetropoulos CK, Yang KH, Herkowitz HN. Effects of disc height and distractive forces on graft compression in an anterior cervical discectomy model. Spine (Phila Pa 1976). 2002;27(22):2441-5.
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23Fogel GR, Turner AW, Dooley ZA, Cornwall GB. Biomechanical stability of lateral interbody implants and supplemental fixation in a cadaveric degenerative spondylolisthesis model. Spine (Phila Pa 1976). 2014;39(19):E1138-46.
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24European Prospective Osteoporosis Study (EPOS) Group, Felsenberg D, Silman AJ, Lunt M, Armbrecht G, Ismail AA,et al. Incidence of vertebral fracture in europe: results from the European Prospective Osteoporosis Study (EPOS). J Bone Miner Res. 2002;17(4):716-24.
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25Ito M, Hayashi K, Uetani M, Yamada M, Ohki M, Nakamura T. Association between anthropometric measures and spinal bone mineral density. Invest Radiol. 1994;29(9):812-6.
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Study conducted at the Universidade Federal de São Paulo (UNIFESP), Departamento de Diagnóstico por Imagem, São Paulo, SP, Brazil.
Publication Dates
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Publication in this collection
Jul-Sep 2016
History
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Received
27 Apr 2015 -
Accepted
29 Feb 2016