The surgical management of thoracolumbar kyphosis in patients with ankylosing spondylitis (AS) requires precise planning to restore horizontal gaze. Traditionally, surgeons rely on the chin-brow vertical angle (CBVA) as a primary metric for determining the necessary correction. However, a recent retrospective study highlights that cervical range of motion (CROM) significantly influences the reliability of this parameter.

Impact of Cervical Mobility on Chin-Brow Vertical Angle

Researchers analyzed patients undergoing pedicle subtraction osteotomy (PSO) to understand the correlation between CBVA and the osteotomized vertebra angle (OVA). They categorized patients into three groups based on their CROM: rigid (≤ 10°), moderate (10°–30°), and flexible (≥ 30°). The findings suggest that while CBVA is highly reliable in rigid cervical spines, its accuracy diminishes as mobility increases.

In patients with high cervical flexibility, the neck can compensate for spinal malalignment. Consequently, the preoperative CBVA may not reflect the true deformity of the thoracolumbar segment. Therefore, surgeons must account for this compensatory capacity to avoid overcorrection. Specifically, the study indicates that OVA calculations based strictly on CBVA are most consistent in patients with a fused cervical spine. Furthermore, individuals with a mobile neck often exhibit a \"pseudo-improvement\" in gaze, which can mislead surgical planning.

Moreover, the study emphasizes that a single-level PSO is often sufficient for most cases. However, the degree of resection must be tailored to the individual’s CROM. For instance, patients in the high-mobility group required more nuanced adjustments to achieve optimal postoperative outcomes. These insights are crucial for orthopedic surgeons in India who frequently manage advanced AS cases with varied degrees of spinal fusion.

Refining Surgical Strategies

Clinicians should integrate CROM assessments into their preoperative workflow. If a patient possesses a flexible cervical spine, the chin-brow vertical angle should not be the sole determinant of the osteotomy angle. Instead, combining CBVA with other sagittal parameters ensures a more balanced correction. Ultimately, this approach reduces the risk of postoperative complications and improves long-term patient satisfaction.

Frequently Asked Questions

What is the ideal chin-brow vertical angle after surgery?

Most experts suggest a postoperative CBVA between 10° and 20° is ideal. This range balances horizontal gaze with the ability to perform downward-facing tasks like eating or walking down stairs.

Why does cervical range of motion affect surgical planning?

A flexible cervical spine allows the patient to tilt their head to compensate for kyphosis. This mobility masks the true severity of the thoracolumbar curve, making the CBVA a less reliable predictor of the needed bone resection.

Disclaimer: This content is for informational and educational purposes only. It does not constitute medical advice or establish a doctor-patient relationship. Always seek the advice of a qualified healthcare provider regarding a medical condition. Refer to the latest local and national guidelines for clinical practice.

References

Chang MH et al. Is the chin-brow vertical angle always a reliable parameter for surgical planning in the correction of thoracolumbar kyphosis secondary to ankylosing spondylitis? J Neurosurg Spine. 2026 Mar 27. doi: 10.3171/2025.10.SPINE25193. PMID: 41894803.

Song K et al. Optimal chin-brow vertical angle for sagittal visual fields in ankylosing spondylitis kyphosis. Eur Spine J. 2016 Aug;25(8):2596-604.

Suk KS et al. Significance of chin-brow vertical angle in correction of kyphotic deformity of ankylosing spondylitis patients. Spine (Phila Pa 1976). 2003 Sep 1;28(17):2001-5.