What is the significance of the Spinal Instability Neoplastic Score (SINS) in assessing spinal stability in patients with neoplastic conditions?

Spinal Instability Neoplastic Score (SINS): A Critical Tool for Assessing Spinal Stability in Neoplastic Conditions

The Spinal Instability Neoplastic Score (SINS) is an essential clinical tool that accurately categorizes spinal stability in patients with neoplastic disease, enabling appropriate surgical referrals and improving patient outcomes through early intervention for unstable or potentially unstable spinal lesions. 1

What is SINS?

SINS is a composite scoring system developed by the Spine Oncology Study Group (SOSG) that evaluates spinal stability in patients with metastatic spinal disease. The score ranges from 0 to 18 points and classifies spinal lesions into three categories:

• Stable: 0-6 points
• Potentially unstable: 7-12 points
• Unstable: 13-18 points 1

Components of SINS

The SINS assessment includes six parameters:

1. Location: Junctional spine (occiput-C2, C7-T2, T11-L1, L5-S1) = 3 points; Mobile spine (C3-C6, L2-L4) = 2 points; Semi-rigid spine (T3-T10) = 1 point; Rigid spine (S2-S5) = 0 points
2. Pain: Mechanical/postural pain = 3 points; Occasional pain but not mechanical = 1 point; Pain-free = 0 points
3. Bone quality: Lytic lesion = 2 points; Mixed lytic/blastic = 1 point; Blastic = 0 points
4. Radiographic alignment: Subluxation/translation = 4 points; De novo deformity (kyphosis/scoliosis) = 2 points; Normal alignment = 0 points
5. Vertebral body collapse: >50% collapse = 3 points; <50% collapse = 2 points; No collapse with >50% body involved = 1 point; None of the above = 0 points
6. Posterolateral involvement: Bilateral = 3 points; Unilateral = 1 point; None = 0 points 1

Clinical Significance and Validation

Reliability and Validity

• SINS demonstrates excellent validity (κ = 0.85) when compared to spine surgeon consensus standards 2
• Radiologists using SINS show substantial interobserver agreement (κ = 0.76) and excellent intraobserver reproducibility (κ = 0.82) 3
• Radiation oncologists demonstrate substantial interobserver (κ = 0.76) and excellent intraobserver (κ = 0.80) reliability when using SINS 2

Impact on Clinical Decision-Making

• SINS effectively guides surgical consultation decisions by distinguishing between stable and potentially unstable/unstable lesions 1, 3
• When using the binary scale (stable vs. current/possible instability), SINS shows excellent reliability across different specialties 3, 2
• Introduction of SINS in clinical practice has led to earlier referrals for surgical intervention, with decreased average SINS scores in both surgical and radiotherapy cohorts 4

Patient-Reported Outcomes

SINS correlates significantly with patient-reported symptoms:

• Higher SINS scores are associated with greater severity of preoperative pain (p=.03) 5
• Increasing SINS correlates with severity of preoperative disability in walking (p=.04) and activity (p=.006) 5
• Surgical stabilization significantly improves patient-reported outcomes for those with indeterminate and unstable SINS 5

Clinical Application

When to Use SINS

• For all patients with known or suspected spinal metastases
• When evaluating new back pain in patients with cancer
• When assessing vertebral compression fractures in patients with malignancy 1

Recommended Actions Based on SINS

1. SINS 0-6 (Stable):

   • No surgical consultation required for stability concerns
   • Proceed with appropriate oncologic treatment (radiation, systemic therapy) 1

2. SINS 7-12 (Potentially Unstable):

   • Surgical consultation recommended
   • May benefit from stabilization procedures before or after radiation therapy 1, 5

3. SINS 13-18 (Unstable):

   • Urgent surgical consultation required
   • High likelihood of requiring surgical stabilization 1

Limitations and Considerations

• Despite excellent reliability, the Dutch National Guideline notes that prospective validation of SINS's predictive power for progressive debilitating instability is still lacking 1
• Some studies report contradictory findings on inter- and intra-rater reliability 1
• The guideline advises against using SINS as the sole predictor for progressive spinal instability but acknowledges its value for communication between physicians and facilitating surgical consultation decisions 1
• Higher SINS was not associated with shorter survival or worse outcomes following radiotherapy in some studies 6

Integration with Other Assessment Tools

For comprehensive evaluation of patients with spinal metastases, SINS should be used alongside:

• Prognostic survival models (Van der Linden, Bartels, or Bollen models) 1
• Bilsky classification for extent of spinal cord infiltration in cases of metastatic epidural spinal cord compression 1
• Mirels' score (equivalent to SINS) for long bone metastases 1

Conclusion

SINS provides a standardized approach to evaluating spinal stability in neoplastic conditions, facilitating appropriate and timely referrals to spine surgeons. Its implementation in clinical practice has improved communication between specialists and led to earlier interventions for unstable spinal lesions, potentially improving patient outcomes and quality of life.