According to a study from Washington University, Saint Louis, USA, multilevel posterior cervical fusions can be safely stopped at C7, rather than the upper thoracic spine, without increasing the risk of complications or subsequent fusion extension at short- to mid-term follow-up. Stopping such procedures at C7 did not prompt a loss of cervical lordosis, or cervical sagittal imbalance, calling into question the traditional assumption that long posterior cervical fusions should extend to the upper thoracic spine to prevent transitional degeneration at the cervico-thoracic junction.
The single-centre, retrospective cohort study was presented by David B Bumpass at the 30th Annual Meeting of the North American Spine Society (NASS; 14–17 October, Chicago, USA). Using a single-institution database for three cervical surgeons, the researchers selected 76 patients with degenerative or traumatic etiologies for further investigation. This population was made up of 22 “C7” patients, and 54 “upper thoracic” patients, denoting where their cervical fusion surgeries had been stopped. The participants’ data were compared for patient-reported outcomes (PROs), surgical outcomes and radiographic results.
Surgical outcomes were as expected, with the average estimated blood loss in the C7 group significantly less than in the upper thoracic group. When asked why this may be the case, Bumpass told Spinal News International that this was likely due to the more extensive surgical dissection required by the placement of instrumentation in the thoracic spine. The mean operating time was also lower in this group, but this difference was not found to be significant. There was also no significant difference found between the rate of complications or reoperations between the groups. By comparing the radiographic measurements of C1-2 lordosis, C2-7 lordosis, C2-7 sagittal vertical axis, T1 slope and thoracic inlet angle, the researchers found no significant differences in changes in sagittal alignment radiographic parameters between groups. Too, no differences were found between the progressions of adjacent level degeneration in either of the proximal or distil segments. No significant differences were noted between the groups PROs, which included Neck Disability Index (NDI), modified Japanese Orthopaedic Association myelopathy scores and Visual Analogue Scale (VAS) Neck and Arm.
The team concluded that, at a minimum one-year follow-up, long posterior fusions that stopped at C7 did not have a worse risk for complications, or for subsequent fusion extension, than those which stopped at T1-T4. The shorter stopping point, too, did not increase the likelihood of a patient’s development of cervical sagittal imbalance or cervical lordosis.
As well as by its retrospective design and short patient follow-up interval, the study may have been limited by a potential age bias, according to Bumpass, who told Spinal News International, “Older patients may have been preferentially selected for fusion to the upper thoracic spine because surgeons felt that the likelihood of poor bone quality and the desire to avoid future surgeries merited extension into the upper thoracic spine, a known safe stopping point for these fusions.” In his presentation Bumpass emphasised, too, the need to clarify whether outcomes may be influenced by concomitant anterior fusion, and whether the condition of the C7-T1 disk might play an important role in deciding where to stop fusions.
The researchers, seeking to address the limits of their study design, are initiating a multi-centre prospective study to bolster research into the question of where is best to stop multilevel posterior cervical fusions. Bumpass told Spinal News International, “I think that our results provide an important initial step in answering this question, and we did not see a superiority of stopping in the upper thoracic spine as we thought we might. However, and I want to emphasise this, we have not conclusively proven that stopping fusions at C7 is an equally viable or superior strategy to stopping in the upper thoracic spine. In order to perform a high-quality prospective study, we first needed to analyse our retrospective data to inform our power analysis.”