Impact of endplate-implant area mismatch on rates and grades of subsidence following stand-alone lateral lumbar interbody fusion: an analysis of 623 levels

OBJECTIVEStand-alone lateral lumbar interbody fusion (LLIF) is a useful minimally invasive approach for select spinal disorders, but implant subsidence may occur in up to 30% of patients. Previous studies have suggested that wider implants reduce the subsidence rate. This study aimed to evaluate whether a mismatch of the endplate and implant area can predict the rate and grade of implant subsidence.METHODSThe authors conducted a retrospective review of prospectively collected data on consecutive patients who underwent stand-alone LLIF between July 2008 and June 2015; 297 patients (623 surgical levels) met inclusion criteria. Imaging studies were examined to grade graft subsidence according to Marchi criteria. Thirty patients had radiographic evidence of implant subsidence. The endplates above and below the implant were measured.RESULTSA total of 30 patients with implant subsidence were identified. Of these patients, 6 had Marchi grade 0, 4 had grade I, 12 had grade II, and 8 had grade III implant subsidence. There was no statistically significant correlation between the endplate-implant area mismatch and subsidence grade or incidence. There was also no correlation between endplate-implant width and length mismatch and subsidence grade or incidence. However, there was a strong correlation between the usage of the 18-mm-wide implants and the development of higher-grade subsidence (p = 0.002) necessitating surgery. There was no significant association between the degree of mismatch or Marchi subsidence grade and the presence of postoperative radiculopathy. Of the 8 patients with 18-mm implants demonstrating radiographic subsidence, 5 (62.5%) required reoperation. Of the 22 patients with 22-mm implants demonstrating radiographic subsidence, 13 (59.1%) required reoperation.CONCLUSIONSThere was no correlation between endplate-implant area, width, or length mismatch and Marchi subsidence grade for stand-alone LLIF. There was also no correlation between either endplate-implant mismatch or Marchi subsidence grade and postoperative radiculopathy. The data do suggest that the use of 18-mm-wide implants in stand-alone LLIF may increase the risk of developing high-grade subsidence necessitating reoperation compared to the use of 22-mm-wide implants.

Lateral lumbar interbody fusion in the elderly: a 10-year experience

OBJECTIVEElderly patients, often presenting with multiple medical comorbidities, are touted to be at an increased risk of peri- and postoperative complications following spine surgery. Various minimally invasive surgical techniques have been developed and employed to treat an array of spinal conditions while minimizing complications. Lateral lumbar interbody fusion (LLIF) is one such approach. The authors describe clinical outcomes in patients over the age of 70 years following stand-alone LLIF.METHODSA retrospective query of a prospectively maintained database was performed for patients over the age of 70 years who underwent stand-alone LLIF. Patients with posterior segmental fixation and/or fusion were excluded. The preoperative and postoperative values for the Oswestry Disability Index (ODI) were analyzed to compare outcomes after intervention. Femoral neck t-scores were acquired from bone density scans and correlated with the incidence of graft subsidence.RESULTSAmong the study cohort of 55 patients, the median age at the time of surgery was 74 years (range 70–87 years). Seventeen patients had at least 3 medical comorbidities at surgery. Twenty-three patients underwent a 1-level, 14 a 2-level, and 18 patients a 3-level or greater stand-alone lateral fusion. The median estimated blood loss was 25 ml (range 5–280 ml). No statistically significant relationship was detected between volume of blood loss and the number of operative levels. The median length of hospital stay was 2 days (range 1–4 days). No statistically significant relationship was observed between the length of hospital stay and age at the time of surgery. There was one intraoperative death secondary to cardiac arrest, with a mortality rate of 1.8%. One patient developed a transient femoral nerve injury. Five patients with symptomatic graft subsidence subsequently underwent posterior instrumentation. A lower femoral neck t-score < −1.0 correlated with a higher incidence of graft subsidence (p = 0.006). The mean ODI score 1 year postoperatively of 31.1 was significantly (p = 0.003) less than the mean preoperative ODI score of 46.2.CONCLUSIONSStand-alone LLIF can be safely and effectively performed in the elderly population. Careful evaluation of preoperative bone density parameters should be employed to minimize risk of subsidence and need for additional surgery. Despite an association with increased comorbidities, age alone should not be a deterrent when considering stand-alone LLIF in the elderly population.

Graft subsidence as a predictor of revision surgery following stand-alone lateral lumbar interbody fusion

OBJECTIVELateral lumbar interbody fusion (LLIF) is a less invasive surgical option commonly used for a variety of spinal conditions, including in high-risk patient populations. LLIF is often performed as a stand-alone procedure, and may be complicated by graft subsidence, the clinical ramifications of which remain unclear. The aim of this study was to characterize further the sequelae of graft subsidence following stand-alone LLIF.METHODSA retrospective review of prospectively collected data was conducted on consecutive patients who underwent stand-alone LLIF between July 2008 and June 2015; 297 patients (623 levels) met inclusion criteria. Imaging studies were examined to grade graft subsidence according to Marchi criteria, and compared between those who required revision surgery and those who did not. Additional variables recorded included levels fused, DEXA (dual-energy x-ray absorptiometry) T-score, body mass index, and routine demographic information. The data were analyzed using the Student t-test, chi-square analysis, and logistic regression analysis to identify potential confounding factors.RESULTSOf 297 patients, 34 (11.4%) had radiographic evidence of subsidence and 18 (6.1%) required revision surgery. The median subsidence grade for patients requiring revision surgery was 2.5, compared with 1 for those who did not. Chi-square analysis revealed a significantly higher incidence of revision surgery in patients with high-grade subsidence compared with those with low-grade subsidence. Seven of 18 patients (38.9%) requiring revision surgery suffered a vertebral body fracture. High-grade subsidence was a significant predictor of the need for revision surgery (p < 0.05; OR 12, 95% CI 1.29–13.6), whereas age, body mass index, T-score, and number of levels fused were not. This relationship remained significant despite adjustment for the other variables (OR 14.4; 95% CI 1.30–15.9).CONCLUSIONSIn this series, more than half of the patients who developed graft subsidence following stand-alone LLIF required revision surgery. When evaluating patients for LLIF, supplemental instrumentation should be considered during the index surgery in patients with a significant risk of graft subsidence.

Sagittal Alignment of a Strut Graft Affects Graft Subsidence and Clinical Outcomes of Anterior Cervical Corpectomy and Fusion

<sec><title>Study Design</title><p>Retrospective study.</p></sec><sec><title>Purpose</title><p>The purpose of this study was to investigate the influence of sagittal alignment of the strut graft on graft subsidence and clinical outcomes after anterior cervical corpectomy and fusion (ACCF).</p></sec><sec><title>Overview of Literature</title><p>ACCF is a common technique for the treatment of various cervical pathologies. Although graft subsidence sometimes occurs after ACCF, it is one cause for poor clinical results. Malalignment of the strut graft is probably one of the factors associated with graft subsidence. However, to the best of our knowledge, no prior reports have demonstrated correlations between the alignment of the strut graft and clinical outcomes.</p></sec><sec><title>Methods</title><p>We evaluated 56 patients (33 men and 23 women; mean age, 59 years; range, 33–84 years; 45 with cervical spondylotic myelopathy and 11 with ossification of the posterior longitudinal ligament) who underwent one- or two-level ACCF with an autogenous fibular strut graft and anterior plating. The Japanese Orthopaedic Association (JOA) score recovery ratio for cervical spondylotic myelopathy was used to evaluate clinical outcomes. The JOA score and lateral radiograms were evaluated 1 week and 1 year postoperatively. Patients were divided into two groups (a straight group [group I] and an oblique group [group Z]) based on radiographic assessment of the sagittal alignment of the strut graft.</p></sec><sec><title>Results</title><p>Group I showed a significantly greater JOA score recovery ratio (<italic>p</italic>&lt;0.05) and a significantly lower graft subsidence than group Z (<italic>p</italic>&lt;0.01).</p></sec><sec><title>Conclusions</title><p>Our findings suggest that a straight alignment of the strut graft provides better clinical outcomes and lower incidence of graft subsidence after ACCF. In contrast, an oblique strut graft can lead to significantly increased strut graft subsidence and poor clinical results.</p></sec>

Vascularized Fibular Strut Autografts in Spinal Reconstruction after Resection of Vertebral Chordoma or Chondrosarcoma: A Retrospective Series

BACKGROUND: Margin-free en bloc resection is the best medical practice for primary vertebral chordoma and chondrosarcoma. Spinal reconstruction following total spondylectomy requires reconstructive interbody graft (allograft, devascularized autograft, vascularized autograft, or cage constructs) and instrumentation. An important consideration when choosing grafts and instrumentation is the durability and the long-term success of the fusion without subsidence. OBJECTIVE: To evaluate the potential use of vascularized fibular autograft as a reconstructive strategy after en bloc resection. METHODS: We present a series of 16 patients who underwent spondylectomy for primary vertebral chordoma or chondrosarcoma with reconstruction using a vascularized fibular autograft and anterior/posterior instrumentation between January 2011 and April 2014. We report postoperative neurological outcome, 6-mo rates of fusion and graft subsidence, and other complications. RESULTS: Two patients passed away prior to 6-mo follow-up, and 1 patient was lost to follow-up. The mean follow-up time for the remaining 13 patients was 32 mo. Of these patients, 9 (69%) had evidence of fusion on the 6-mo follow-up computed tomography (CT) scan. Of the 4 patients who did not fuse, 2 had undergone surgery for new tumor diagnoses, 1 for hardware failure, and 1 for graft nonunion. Two patients (15%) had eventual graft subsidence along with hardware failure. CONCLUSIONS: Vascularized fibular strut grafts are a viable method for reconstruction following spondylectomy. We present the largest series of patients to date utilizing this technique. Further comparative studies examining vascularized grafts vs nonvascularized grafts or metallic cage constructs will be important in choosing the best reconstructive strategy.

Comprehensive drilling of the C1–2 facets to achieve direct posterior reduction in irreducible atlantoaxial dislocation

OBJECT The cause of irreducibility in irreducible atlantoaxial dislocation (AAD) appears to be the orientation of the C1–2 facets. The current management strategies for irreducible AAD are directed at removing the cause of irreducibility followed by fusion, rather than transoral decompression and posterior fusion. The technique described in this paper addresses C1–2 facet mobilization by facetectomies to aid intraoperative manipulation. METHODS Using this technique, reduction was achieved in 19 patients with congenital irreducible AAD treated between January 2011 and December 2013. The C1–2 joints were studied preoperatively, and particular attention was paid to the facet orientation. Intraoperatively, oblique C1–2 joints were opened widely, and extensive drilling of the facets was performed to make them close to flat and parallel to each other, converting an irreducible AAD to a reducible one. Anomalous vertebral arteries (VAs) were addressed appropriately. Further reduction was then achieved after vertical distraction and joint manipulation. RESULTS Adequate facet drilling was achieved in all but 2 patients, due to VA injury in 1 patient and an acute sagittal angle operated on 2 years previously in the other patient. Complete reduction could be achieved in 17 patients and partial in the remaining 2. All patients showed clinical improvement. Two patients showed partial redislocation due to graft subsidence. The fusion rates were excellent. CONCLUSIONS Comprehensive drilling of the C1–2 facets appears to be a logical and effective technique for achieving direct posterior reduction in irreducible AAD. The extensive drilling makes large surfaces raw, increasing fusion rates.