Introduction: To restore the lumbar lordosis when deformity correction for degenerative sagittal imbalance, a cage is inserted through lateral interbody fusion, but the loss of the lordosis during follow-up period may occur due to end-plate injury and cage subsidence. However, there are few studies on how much lordosis loss occurs, what effect cage subsidence has on it, and which risk factors are involved in it. Therefore, this study aimed to determine how the lumbar lordosis changes of fusion construct during follow-up period and to find out which factors related to cage subsidence affect the loss of lumbar lordosis after deformity correction for degenerative sagittal imbalance
Materials and Methods: We reviewed 62 patients who underwent deformity correction including T12-iliac fixation and were followed up more than 2 years after surgery. Patients were classified as maintenance of lordosis group (group M, n=43), and loss of lordosis group (group L, n=19) based on loss of lordosis 5° during follow-up period. Demographic, radiologic, and operative factors affecting cage subsidence were analyzed, and the process of lordosis loss during follow-up period was determined.
Results: The value of lordosis loss during the follow-up period was 3.8°±6.9° in group L and 11.6°±5.6° in group M (p<0.001). During the follow-up period, most of the loss of lordosis occurred at 3months after surgery (62.0°±8.9° -> 52.2°±8.6°, p<0.001) in group L. As for demographic factors, there was no difference in the rate of osteoporosis between two groups (p=0.356). As for operative factors, the posterior column osteotomy was performed more frequently in group L than group M (57.9% vs 25.6%, p=0.036).
Conclusions: Settling-down of fusion construct after deformity correction occurs in about 27.9% (19/62) of patients, and it is more likely occur when posterior column osteotomy is performed. Additionally, most of the lordosis loss occurred within 3 months after surgery.