Response to Letter to the Editor Regarding Rod Contour Angle and Postoperative Thoracic Kyphosis: Key Predictors of Proximal Junctional Kyphosis in Pediatric Neuromuscular Scoliosis After Spinopelvic Fusion

Response to Letter to the Editor

Dear Editor, We appreciate your thoughtful letter regarding our article on proximal junctional kyphosis (PJK) in nonambulatory pediatric neuromuscular scoliosis (NMS) patients following spinopelvic fusion. The authors raise important questions that warrant further discussion. We address each of these concerns below.

Clinical Applicability of Rod Contour Angle (RCA) Findings

We appreciate the questions about the clinical applicability of our RCA findings. While achieving precise RCA adjustments presents significant challenges in NMS patients with severe deformities, several strategies could potentially optimize this parameter.

First, patient-specific preoperative planning using advanced imaging analysis and simulation software may offer more precise reference values for rod contouring tailored to each patient’s unique anatomy and pathology. Second, we observed that the conventional distal-to-proximal rod application sequence can lead to challenges when the rod doesn’t align perfectly with proximal screws. In such cases, surgeons may perform in situ bending at the proximal end, potentially increasing RCA values. Third, when indicated, posterior osteotomy techniques could help achieve optimal thoracic kyphosis values. These approaches can be particularly valuable in complex cases with severe deformities.

Importantly, our findings reveal an interrelationship between RCA and postoperative thoracic kyphosis (T2-T12 kyphosis). Our ROC curve analysis found that target values of RCA <13.5° and postoperative T2-T12 kyphosis <42.5° could serve as helpful reference parameters for surgical planning.

Preoperative Proximal Junctional Angle (PJA) as a Predictor

Regarding preoperative PJA, our findings identified values <4.5° as a significant risk factor for PJK development. However, the modifiability of this parameter through preoperative interventions remains uncertain in nonambulatory NMS patients. The neuromuscular factors in this population—poor head and neck control, spasticity, and positioning difficulties—make assessing and modifying cervical alignment particularly challenging.

It is important to note that small preoperative PJA measurements can be very misleading in nonambulatory NMS patients and may represent artificial findings resulting solely from inadequate head and neck control. Many of these patients’ inability to maintain proper cervical positioning can lead to hyperextension during imaging, which may artificially decrease the measured PJA. When encountering low PJA values, it may be prudent to correlate these findings with the patient’s clinical presentation and assess cervical muscle control capabilities to ensure the radiographic measurements accurately reflect the patient’s functional alignment.

Rather than attempting direct preoperative modification of PJA, we suggest incorporating this parameter into surgical decision-making, potentially influencing upper instrumented vertebra selection, rod contouring strategy, and postoperative monitoring protocols. This approach acknowledges PJA as a risk marker that should inform surgical planning rather than as a directly modifiable target. Prospective studies examining whether surgical adaptations based on preoperative PJA values can reduce PJK incidence would be valuable additions to the literature.

PJK Definition and Clinical Impact

The letter raises an important point about the limitations of standardized radiographic criteria for PJK in the NMS population. We agree that radiographic parameters alone may not fully capture the functional implications of PJK in these patients.

The clinical assessment of PJK impact in nonambulatory NMS patients faces unique challenges not encountered in other populations. Communication limitations, baseline functional deficits, and complex comorbidities make traditional pain and function assessments inadequate. For example, many patients cannot verbalize discomfort, and changes in sitting posture might be attributed to multiple factors beyond PJK.

Future assessment frameworks should incorporate caregiver observations of comfort and positioning, objective measures of sitting tolerance and pressure distribution, respiratory function, swallowing capacity, and head/neck control relative to trunk position. These parameters could better capture the functional significance of PJK in this population. Such tools would significantly advance our understanding of when PJK becomes clinically significant in this population and help establish more meaningful intervention thresholds beyond purely radiographic criteria.

Management and Follow-Up of PJK

The letter appropriately questions whether the absence of revision surgeries in our cohort reflects a true lack of clinical impact or potentially an underestimation of the PJK burden. This is a thoughtful observation deserving of clarification.

The decision-making process regarding surgical intervention for PJK differs substantially in the NMS population compared to ambulatory patients with idiopathic or degenerative deformities. Our approach prioritizes functional outcomes and quality of life while carefully weighing surgical risks, which are often magnified in this medically complex population. The absence of revision surgeries reflects this risk-benefit calculus rather than suggesting PJK is clinically insignificant.

Our non-surgical management included wheelchair modifications, trunk support adaptations, and physical therapy. For early detection, more frequent monitoring of high-risk patients may be valuable. However, image assessment of the cervicothoracic junction can be challenging as most surgeons primarily focus on thoracolumbar and pelvic alignment. Future research should explore integrating radiographic findings with functional assessments to establish appropriate intervention thresholds.

Conclusion

We appreciate the authors’ thoughtful insights and questions regarding our work on PJK in nonambulatory NMS patients. Currently, no standardized methods exist to evaluate head-neck control or PJK criteria specific to this population, highlighting significant gaps in assessment approaches. Future research should develop validated functional assessment tools and establish intervention thresholds based on functional impact rather than radiographic criteria alone. A multidisciplinary approach remains essential for these vulnerable patients.

Thank you for the opportunity to address these important clinical considerations.