Introduction: Posterior long segment instrumentation (PLSI, instrumentation above and below 2 levels of fractured vertebrae) for acute unstable thoracolumbar fractures (TLFx) is known as a stable method and is widely used. In severe fractures, implant failure and related complications such as pain and kyphosis sometimes occur even in PLSI. There are very few studies on implant failure rates and related risk factors in PLSI. The aims of this study was to identify the incidence and risk factors for implant failure in TLFx treated with PLSI

Methods: This study reviewed 130 consecutive patients with TLFx treated with PLSI and followed up more than one year (All patients had 6 or more load sharing classification score). Implant failure rate, type, time of onset, presence of acute pain or progressive kyphosis, and subsequent revision surgery were analyzed. We evaluated the risk factor using multivariate regression analysis including age, gender, neurologic deficit, fracture level (thoracolumbar [T11-L2] vs. mid to low lumbar [L3-5]), AO fracture type, thoracolumbar injury classification and severity score, load sharing score, bi-segmental Cobb angle (CA), anterior compression ratio (ACR), and time to surgery.

Results: Even after PLSI for thoracolubmar and lumbar factures, there were 15 cases (11.5%) of implant failure. There were 5 rod fractures, 4 rod displacement, and 6 screw breakage. The mean time of onset was 21.7 ± 11.5 months after the operation. Among 15 cases, two patients had progressive kyphosis. One patient had temporary mild pain and there was no progression of kyphosis. The other underwent revisional surgery due to progressive kyphosis combind with severe pain. Multivariate logistic regression identified mid to low lumbar level facture (adjusted odds ratio=11.5, 95% confidence interval = 1.0-128.0) as independent predictors of a implant failure.

Discussion: In TLFx treated with PLSI, the implant failure rate was not lower than expected, but the incidence of acute pain or reoperation rate were very low. Mid to low lumbar fracture was the only risk factor for the implant failure in PLSI for thoracolumbar and lumbar fractures. In mid-to-lumbar fracuture, more attention should be paid to fusion during PLSI, or additional anterior fusion should be considered at an early stage.