Long Adult Deformity Correction to L5: Risk Factors for Loss of Fixation

Summary: Adult deformity long fusion constructs ending at L4 or L5 are at high risk for fixation failure. The following risk factors were identified: osteoporosis, sagittal imbalance, and inadequate restoration of lumbar lordosis. In these patients, strong consideration for extension of the fusion to the sacrum, with possible additional pelvic fixation, should be considered. Restoration of the sagittal plumb line and a lumbar lordosis of greater than 35 degrees was found to be optimal.

Study Design: Retrospective clinical and radiographic analysis of long adult deformity fusions ending at L4 or L5.

Objective: To identify variables associated with an increased likelihood of loss of distal fixation among patients with long fusions to L4 or L5.

Methods: All patients over the age of 40 undergoing deformity correction of 8 levels or more ending at L4 or L5 at a single institution were included. From 1993 to 2002, 64 patients were reviewed. 31 patients had complete radiographic and clinical follow-up for a minimum of 2 years. Preoperative, early postoperative and last follow-up radiographs and chart review was performed. Variables included preoperative sagittal balance, coronal balance, thoracic kyphosis, and lumbar lordosis. The likelihood of loss of fixation as a function of baseline variables was estimated using logistic regression analysis. Receiver-operator-characteristics (ROC) curves were used to determine whether an association between coronal or sagittal balance, lordosis or kyphosis, and whether subsequent loss of fixation required revision surgery.

Results: 5 of 31 patients with fusions ending at L4 or L5 had frank distal implant failure requiring revision surgery. An additional 8 of 31 patients had radiographic evidence of loosening, yet did not require further revision surgery. Older age, osteoporosis, and smoking history all were associated with increased risk for loss of distal fixation. Preoperative sagittal balance > 70 mm was significant for increased risk of loosening, yet not predictive of frank failure. Preoperative lordosis less 26 degrees was associated with radiographic loosening. Preoperative C7 sagittal plumb line of > 60 mm was associated with loss of fixation and asymptomatic loosening. Lumbar lordosis of less 34 degrees was associated with increased risk for loss of distal fixation and for frank failure. Preoperative thoracic kyphosis was not associated with loss of fixation.