Are the Clinical Outcomes of Lumbar Stenosis in Achondroplasia Associated With the Severity of Stenosis and Sagittal Balance?

Abstract

BACKGROUND Lumbar spinal stenosis (LSS) is common in adults with achondroplasia and predisposes individuals to neurogenic claudication. It remains unverified whether the severity of stenosis in patients with achondroplasia is associated with clinical outcomes. Similarly, the role of sagittal balance parameters in clinical outcomes has not been determined. QUESTIONS/PURPOSES (1) Is the severity of LSS associated with the clinical outcomes of patients with achondroplasia who have LSS? (2) Are sagittal balance parameters associated with the clinical outcomes of LSS in patients with achondroplasia? (3) Is the combination of severe LSS and pathologic thoracolumbar kyphosis associated with worse clinical outcomes? METHODS Over the past decade, 102 patients with achondroplasia visited the neurosurgical outpatient clinic because of neurogenic claudication. After excluding seven patients because of the absence of lumbar MRI scans, 95 patients were deemed eligible for the study. Of these patients evaluated, 45 completed the survey and were included. Among them, 32 underwent surgical decompression because of the combination of the severity of their clinical presentation and the relevant stenosis on MRI. The median (range) follow-up time was 4.8 years (0.7 to 12.4). This study sought to examine the relationship between clinical outcomes and radiologic findings, so the follow-up duration is measured from the date of radiologic screening to the date of the follow-up response. To more accurately reflect the association, a shorter follow-up period is desirable, minimizing the impact of time delays and allowing for a more immediate evaluation of the relationship. The median (range) ages of the nonsurgical and surgical groups were 55 years (22 to 66) and 55 years (23 to 88), respectively. In the nonsurgical group, 54% (7 of 13) were men, and in the surgical group, 28% (9 of 32) were men. Surveys were distributed to 95 patients whose lumbar MRIs were available, and the follow-up questionnaires included the Oswestry Disability Index, VAS, EQ-5D, modified Japanese Orthopaedic Association (mJOA) scale, and the Hospital Anxiety and Depression Scale. MRI findings (Schizas grades [a visual classification based on the relationship between the dural sac and nerve roots, ranging from grade A (normal or mild stenosis) to grade D (severe stenosis)] and dural sac cross-sectional area [DSCA]) and sagittal balance parameters (thoracolumbar kyphosis, lumbar lordosis, and sagittal vertical axis) were evaluated using standing lateral radiographs. Associations between clinical and radiologic parameters were investigated by linear regression. RESULTS With the numbers of patients available, we observed no association between the severity of LSS and clinical outcome as assessed by the tools we used. We also observed that thoracolumbar kyphosis was the sole radiologic finding associated with the clinical outcomes measured by the EQ-5D index scores (B = -0.01 [95% confidence interval (CI) -0.01 to -0.002]; p = 0.003); while the coefficient of -0.01 per degree might appear small, a 20° thoracolumbar kyphosis was widely observed in patients with achondroplasia and was associated with a 0.2 decrease in the EQ-5D index score-a substantial reduction, given that the EQ-5D index ranges between 0 and 1. When we considered thoracolumbar kyphosis and degree of stenosis, we found that patients with achondroplasia and severe stenosis (DSCA < 62 mm2) and pathologic thoracolumbar kyphosis (> 20°) demonstrated worse functionality as quantified by mJOA scores (median [range] 11 [9 to 17] versus 16 [6 to 18]; p = 0.046). After controlling for confounding factors, pathologic thoracolumbar kyphosis and smaller DSCA were also associated with worse clinical outcomes as quantified by mJOA scores (B = -2.56 [95% CI -4.52 to -0.60]; p = 0.01), which can be interpreted as a 3-point lower (worse) score on an 18-point scale in those individuals. CONCLUSION In adult patients with achondroplasia experiencing from neurogenic claudication, thoracolumbar kyphosis is associated with worse functional outcomes as quantified by EQ-5D, and when in combination with severe stenosis, it is associated with less favorable mJOA scores. Controlling thoracolumbar kyphosis at an early age in a nonsurgical way may benefit patients. Larger cohorts of patients with prospectively collected data and long-term follow-up are needed to confirm whether early nonsurgical treatment to prevent the progression of thoracolumbar kyphosis can improve long-term clinical outcomes. Despite the limitations of an observational study, the current data stress the importance of maintaining thoracolumbar kyphosis within appropriate limits. LEVEL OF EVIDENCE Level III, therapeutic study.