Background context:

Rod fractures (RF) and pseudarthrosis are a frequent occurrence after adult spinal deformity (ASD) surgery and may be problematic. However, not all rod fractures signal nonunion and cause clinical concern. An improved understanding of the sequelae after rod fracture occurrence is valuable for further management.

Purpose:

To characterize the radiographic findings, clinical outcomes, and revision rates between patients who developed unilateral rod fracture (URF) and bilateral rod fracture (BRF) following thoracolumbar posterior spinal fusions to the sacrum for ASD and identify patient characteristics associated with clinically significant rod fracture that lead to subsequent revision surgeries and detection of nonunion.

Study design/setting:

A retrospective single-center cohort study was performed.

Patient sample:

Patients undergoing long-construct posterior spinal fusions to the sacrum performed at a single institution from 2004 to 2014 and developed a rod fracture postoperatively were included.

Outcome measures:

Patient demographics, radiographic parameters, surgical data, Oswestry Disability Index (ODI), Scoliosis Research Society-22 (SRS-22), and revision rates.

Methods:

Inclusion criteria were ASD patients age >18 who had ≥5 vertebrae instrumented and fused posteriorly to the sacrum and development of RF. Data were compared among patients: who developed unilateral-nondisplaced RF (UNRF), unilateral-displaced RF (UDRF), bilateral-nondisplaced RF (BNRF) and bilateral-displaced RF (BDRF) at baseline and follow-up. Oswestry Disability Index (ODI) and Scoliosis Research Society-22 (SRS-22) scores were assessed at baseline, 1 year postoperatively, the time of RF occurrence, and latest follow-up.

Results:

Of 526 patients who met inclusion criteria, 96 (18.3%) developed rod fracture [URF n=70 (73%); BRF n=26 (27%)]. Preoperative demographics and surgical parameters were similar between the groups. BRF patients had substantial loss of sagittal correction from 1-year postoperatively to the time of rod fracture, including loss of sagittal vertical axis (4.8 cm v. 2.2 cm; p<0.001), loss of lumbar lordosis (14.8° v. 4.9°; p=0.010) and loss of PI-LL mismatch (5.0° v. 14.6°; p=0.020) compared to those of URF patients. The BDRF group had more loss of ODI scores (13.4 v. 4.2; p=0.013), Scoliosis Research Society (SRS) pain score (0.8 v. 0.2; p=0.024), SRS function score (0.3 v. 0; p=0.020) and SRS Subscore (0.4 v. 0.1; p=0.148) from 1-year postoperatively to the time of rod fracture and underwent revision surgery more often than the UNRF group (87.5% v. 4.8%; p<0.0001). At final follow-up (median 2.8 years, range 1-10.3 years after rod fracture detection), URF patients who did not undergo revision surgeries still maintained equivalent sagittal alignment correction (SVA, LL and PI-LL; all p>0.05) and had similar, not worse, mean ODI scores, SRS Subscore and SRS pain compared to the time at rod fracture and 1-year follow-up.

Conclusions:

Rod fractures are not uncommon after ASD operations. Asymptomatic, UNRF in our study did not jeopardize clinical outcomes or radiographic alignment parameters and, in most cases, did not represent a nonunion, as opposed to BRF. BRF patients exhibited loss of sagittal correction, loss of clinical outcome improvements, as measured by ODI, SRS pain and SRS Subscore at the time of rod fracture, and were revised more often than URF patients.