Frailty, Disability, and Multimorbidity in Spine Deformity Patients: Why Getting the Labels Right Matters
A multicenter study of 861 patients finds that true medical frailty is rare in adult spinal deformity patients — and that conflating it with disability or multimorbidity carries real risks for patient care and research accuracy.
OPENING SUMMARY
In adult spinal deformity care, the word "frail" carries significant weight. It shapes surgical decisions, influences risk conversations with patients and families, and drives research priorities. But what if that label is frequently misapplied — used to describe patients who are not truly frail, but rather disabled by their spine condition, burdened by multiple chronic diseases, or simply older? This study examines the degree to which frailty, disability, and multimorbidity overlap in ASD patients, using validated measures of each condition in a large multicenter cohort. Its central finding is both clarifying and consequential: true medical frailty was rare in this population, the three conditions do not form neat, separable categories, and the field may need to move away from categorical labels altogether in favor of more nuanced, continuous measures of vulnerability.
STUDY SNAPSHOT
Study type – Retrospective cohort study using a multicenter registry
Number of patients – 861
Female – 68%
Median age – 66 years (IQR 55.1–71.6)
Primary surgery – Majority undergoing primary ASD surgery
Frailty measure – Edmonton Frail Scale
Disability measure – Oswestry Disability Index (ODI)
Multimorbidity measure – Charlson Comorbidity Index (CCI)
Biological age measure – PhenoAge
Classified as frail – 6% of cohort
Statistical approach – Exploratory factor analysis (EFA); correlation analyses
Published in – Spine, Volume 51, Issue 5, March 1, 2026, pages 343–353
DOI – 10.1097/BRS.0000000000005508
WHY THIS MATTERS
Frailty has become one of the most frequently cited risk factors in spine surgery research. Studies consistently report that frail patients have worse postoperative outcomes — more complications, longer hospital stays, higher readmission rates, greater mortality risk. As a result, frailty assessment has been increasingly recommended as part of preoperative evaluation for ASD surgery, and frailty status often influences surgical decision-making.
But frailty is a specific clinical syndrome — not a synonym for being old, sick, or disabled. It describes a state of reduced physiological reserve and increased vulnerability to stressors, distinct from the disability caused by a painful, deforming spine condition and distinct from the burden of carrying multiple chronic diseases. When these conditions are conflated — when a patient disabled by their spinal deformity is labeled frail, or when comorbidity burden is treated as equivalent to frailty — the result is imprecise risk stratification, potentially inappropriate surgical decision-making, and research findings that may not mean what they appear to mean.
This study takes a rigorous, measurement-based approach to asking how much these conditions actually overlap in ASD patients — and what the implications of that overlap are for clinical practice and research.
UNDERSTANDING THE THREE CONDITIONS
Frailty is a clinical syndrome characterized by diminished physiological reserve across multiple organ systems, resulting in increased vulnerability to stressors. It is distinct from both aging and disease, though it is more common with both. In this study, frailty was measured using the Edmonton Frail Scale — a validated, multidimensional tool that assesses cognition, health status, functional independence, social support, medication use, nutrition, mood, continence, and functional performance.
Disability refers to functional limitation — difficulty performing activities of daily life due to pain, physical impairment, or both. In ASD patients, disability is frequently caused directly by the spinal deformity itself: pain, postural imbalance, and neurological symptoms can profoundly limit function even in a patient who is not medically frail. In this study, disability was measured using the Oswestry Disability Index, a widely validated patient-reported outcome measure specific to spinal conditions.
Multimorbidity refers to the presence of two or more chronic medical conditions in the same patient. It is distinct from frailty — a patient can carry many chronic conditions without being frail — though the two often coexist. In this study, multimorbidity was captured using the Charlson Comorbidity Index, a validated composite score that weights conditions by their association with mortality risk.
Biological age (PhenoAge) was also examined as a variable. PhenoAge is an estimate of biological age derived from clinical laboratory values, which can diverge meaningfully from chronological age and may more accurately reflect physiological aging status.
KEY FINDINGS
1. True medical frailty was rare — present in just 6% of the cohort. Despite the frequency with which frailty is discussed in ASD surgery literature, only 6% of the 861 patients in this cohort were classified as frail using the Edmonton Frail Scale. This is a striking finding in a population whose median age was 66 years, and it challenges the assumption that frailty is a common feature of the ASD surgical population. The vast majority of patients who might colloquially be described as "frail" were not, by validated clinical criteria, actually frail.
2. Disability and frailty overlap — but they are not the same. Exploratory factor analysis found overlap between subjective and objective measures of disability, function, and frailty. This overlap is what creates the conflation risk: because the conditions share some measurement territory, using a frailty scale in a highly disabled patient may produce an elevated score that reflects spine-related disability rather than true systemic frailty. The study confirms that this conflation is a real and measurable risk — not a theoretical concern.
3. Disability and frailty exist along a continuum, not in discrete categories. The analysis found no evidence of distinct clusters separating frail from non-frail, or severely disabled from mildly disabled patients. Instead, the data showed a continuity of condition severity — patients distributed across a spectrum rather than falling into clearly separable groups. This is a fundamental challenge to categorical approaches to frailty and disability classification, and it has direct implications for how these concepts are used in both clinical assessment and research design.
4. Biological age was a stronger correlate of frailty and disability than chronological age. Both chronological age and PhenoAge showed weak to moderate associations with disability and frailty — but PhenoAge performed better. This suggests that how quickly a patient is aging biologically, rather than simply how many years they have lived, may be a more informative indicator of vulnerability in this population. As biological age measurement tools become more accessible, their integration into preoperative ASD assessment warrants further investigation.
5. The field may need to move beyond categorical labels. The study's conclusions explicitly call for abandoning categorical frailty and disability labels in favor of continuous measures for both clinical assessment and research. This is a meaningful methodological recommendation — one that would change how studies are designed, how risk scores are calculated, and how preoperative conversations are framed. Rather than asking "is this patient frail?", the more informative question may be "where on the vulnerability continuum does this patient sit, and what does that mean for their surgical risk and recovery?"
PRACTICAL IMPLICATIONS
Surgeons should be cautious about applying frailty labels to ASD patients based on disability alone. A patient who is severely disabled by their spinal deformity — unable to walk far, dependent on pain medication, limited in daily activities — may score as frail on some assessment tools not because they have reduced physiological reserve, but because the tool is capturing spine-related disability. Conflating these conditions risks mischaracterizing the patient's medical status and potentially withholding surgery from someone who is not truly frail and could benefit significantly from correction.
Frailty assessment in ASD patients should use validated, multidimensional tools rather than proxy measures. The Edmonton Frail Scale, which assesses multiple domains beyond physical function, is better positioned to distinguish true frailty from spine-related disability than simpler tools that rely heavily on functional performance measures. When the goal is to assess medical frailty specifically — rather than overall vulnerability or disability — the choice of measurement tool matters significantly.
Risk stratification in ASD surgery should incorporate continuous measures rather than categorical cutoffs. The finding that disability and frailty exist along a continuum rather than in discrete categories suggests that binary classifications — frail vs. not frail, severely disabled vs. not — may oversimplify what is actually a graded phenomenon. Continuous risk scores that capture where a patient sits on the vulnerability spectrum may provide more accurate and clinically useful information than categorical labels.
Research into frailty and ASD outcomes should account for the overlap between frailty and disability. Studies that report frailty as a risk factor for poor outcomes in ASD patients may be partially capturing the effect of spine-related disability rather than true systemic frailty. Future research designs should use instruments that more cleanly separate these constructs — or should explicitly model their overlap — to ensure that findings attributed to frailty are not artifacts of measurement conflation.
Biological age may be a more informative vulnerability marker than chronological age in this population. The stronger performance of PhenoAge over chronological age in correlating with frailty and disability suggests an opportunity to incorporate biological aging metrics into preoperative assessment. While PhenoAge is not yet standard in clinical practice, its availability from routine laboratory values makes it a practically accessible tool worth further validation in ASD surgical populations.
CONCLUSION
This study delivers a clear and evidence-grounded message to both clinicians and researchers working in adult spinal deformity: frailty is not the same as disability, and treating it as such carries real consequences. In this multicenter cohort of 861 patients, true medical frailty was present in only 6% — a fraction of those who might be described as vulnerable based on disability or comorbidity burden alone. The conditions overlap in their measurement but do not reduce to one another, and they exist along a continuum rather than in discrete categories. For the field to make progress in risk stratification, perioperative optimization, and outcome prediction, it needs measurement tools and research frameworks that respect these distinctions — and this study makes a compelling case for what that shift should look like.
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