What radiographic sign contraindicates orthotic intervention for spondylolisthesis and suggests surgical candidacy?

When considering the management of spondylolisthesis through orthotic intervention, identifying the degree of vertebral slippage is crucial. In this context, slippage of the superior vertebra over the inferior vertebra greater than 50% is a significant indicator of instability. This degree of slippage suggests that the condition may be severe enough to warrant surgical intervention rather than conservative treatment with orthotics.

When there is more than 50% slippage, it generally reflects a more advanced stage of spondylolisthesis that likely affects spinal mechanics, stability, and may lead to nerve root compression or spinal canal stenosis. Thus, reliance on orthotic devices, which primarily aim to provide stability and support, might not be sufficient to manage symptoms effectively or to prevent further progression of the deformity.

In contrast, other options present signs that do not reach the level of severity indicating surgical intervention. For instance, anterior translation of the inferior vertebra, while indicative of spondylolisthesis, does not alone dictate when surgery might be necessary without accompanying evidence of excessive slippage. Verdin's angle exceeding 30 degrees can indicate instability, but it does not specifically dictate the level of vertebral translation necessary for surgical evaluation. Normal alignment