Identifying the Most Significant Risk Factors for Adjacent Segment Disease Developing after Lumbar Fusion

Introduction Spinal segment arthrodesis has become a widely accepted treatment for numerous pathological conditions of the spine. For today rigid internal fixation with 360 degree fusion has been viewed as the gold standard for spine stabilizing surgery. However, spinal fusion alters the normal biomechanics of the spine and eliminates mobile segments causing overload of adjacent segments. Thus, spinal fusion, according to some authors can accelerate the degeneration of adjacent segments. Methods This retrospective study evaluated 120 patients underwent 360 degree fusion lumbar surgery from 2007 to 2012 for the treatment of degenerative conditions of the lumbar spine. We compare two groups: first group include 60 patients with long lumbar fusion (3 and more levels), second group include 60 patients with short lumbar fusion (1–2 levels). There were 64% females. Mean age of 56 years (range, 19–78). Mean follow-up of 3 years (range, 2–7 years). MRI evaluation of adjacent segment condition and long cassette standing anteroposterior and lateral radiographs were performed on the preoperative, postoperative, and follow-up visits. In all cases we studied preoperative, postoperative, and f/up sagittal plane alignment according to Schwab sagittal modifiers. Adjacent segment condition was evaluated by MRI and scored with modified Pfirrmann classification. Results In group I symptomatic ASD was found in 19 cases (28%) during 1 year follow-up. There were 14 cases (75%) with sagittal imbalance and 5 cases (25%) with incipient stage of disc degeneration according to preoperative MRI. After 3 years f/up in group I showed increasing ASD to the 31 cases (52%), however at this period preoperative adjacent disc degenerative changes prevailed over the sagittal imbalance cases as 3:1 (9 cases with Pfirrmann 2–5 grade and only 3 cases with sagittal imbalance). Summary after 3 years f/up in group I symptomatic ASD was diagnosed in 31 cases (52%), in which 17 patients (53%) had postoperative sagittal balance disturbance and 14 patients (47%) had preoperative incipient disc degenerative changes by MRI. Overall, 87% of them required revision surgery. In group II at 1 year f/up 12 patients (17%) had symptomatic ASD. Among these cases the preoperative disc degenerative changes were identified in 10 patients (Pfirrmann 2–5 grade). Sagittal imbalance was found only in two cases with ASD at 1 year f/up. At 3 years f/up the number of patients with symptomatic ASD was increased to 16 (23%). Among them 13 patients had the preoperative adjacent disc degenerative changes Pfirrmann 2–5 grade and only five patients had postoperative sagittal balance disturbance. Conclusion Patients with postoperative sagittal imbalance have statistically significant increasing risks of developing ASD because of overloading the adjacent segments and limitation compensatory capacities due to the large number of fixed mobile segments. On the other hand, in the short instrumentation we did not find so statistically significant dependency between ASD and postoperative sagittal imbalance. In the case of a short fixation preoperative degenerative changes are more important in the ASD development.