How should physical therapy be approached for patients with bone metastases (bone mets) using the SINS (Spinal Instability Neoplastic Score) assessment?

SINS-Guided Physical Therapy for Bone Metastases

Physical therapy for patients with bone metastases must be preceded by SINS assessment, with stable lesions (SINS ≤6) cleared for progressive exercise programs, potentially unstable lesions (SINS 7-12) requiring modified activity with close monitoring, and unstable lesions (SINS ≥13) representing absolute contraindications to physical therapy until surgical stabilization is achieved. 1, 2

Risk Stratification Using SINS

The SINS classification system divides spinal metastases into three categories that directly determine physical therapy eligibility 3, 2:

• SINS 0-6 (Stable): Patients can proceed with physical therapy interventions without surgical consultation 1, 2
• SINS 7-12 (Potentially Unstable): Requires careful clinical judgment, modified activity restrictions, and consideration for neurosurgical referral 3, 1
• SINS ≥13 (Unstable): Absolute contraindication to physical therapy; mandatory neurosurgical evaluation for stabilization before any rehabilitation 1, 2

The introduction of SINS into routine practice has led to earlier detection of instability and more appropriate referrals, with studies showing decreased SINS scores in both surgical and radiotherapy cohorts after implementation, suggesting improved patient selection. 4

SINS Components Critical for Physical Therapy Planning

The score incorporates six radiographic and clinical parameters that physical therapists must understand 2:

• Location: Junctional regions (occiput-C2, C7-T2, T11-L1, L5-S1) and mobile spine segments carry higher instability risk 2
• Pain character: Mechanical or postural pain (worsening with movement or weight-bearing) indicates higher scores and greater instability 3, 2
• Bone quality: Assessed on MRI T1-weighted and STIR sequences; lytic lesions score higher than blastic or mixed lesions 2
• Spinal alignment: Subluxation/translation scores highest, followed by de novo deformity (kyphosis/scoliosis) 2
• Vertebral body collapse: Greater than 50% collapse increases instability risk 2
• Posterolateral involvement: Bilateral involvement of posterior elements carries the highest risk and predicts persistent instability even after radiotherapy 2, 5

Posterolateral involvement of spinal elements is the single most important predictor of continuous potentially unstable or unstable spine status at 1 month after radiotherapy, making it a critical red flag for physical therapy planning. 5

Physical Therapy Interventions by SINS Category

For SINS ≤6 (Stable Lesions)

Progressive exercise programs can be safely implemented 1:

• Aerobic exercise: Walking, stationary cycling, swimming progressing toward 150 minutes/week of moderate intensity 1
• Resistance training: Starting with isometric exercises, advancing to isotonic exercises, 2-3 sessions per week targeting unaffected areas 1
• Functional training: Gait training, transfer training, and balance exercises to maintain independence and prevent falls 1

For SINS 7-12 (Potentially Unstable Lesions)

This intermediate category requires individualized assessment with specific attention to pain character 3, 1:

• Patients with mechanical pain should be treated more conservatively, potentially requiring bracing or corset support before physical therapy 3
• Non-mechanical pain with SINS 7-9 may tolerate modified exercise programs with avoidance of axial loading and rotational movements 1
• SINS 10-12 carries significantly higher odds for requiring surgical management and warrants neurosurgical consultation before initiating therapy 2

For SINS ≥13 (Unstable Lesions)

Absolute contraindication to physical therapy until surgical stabilization is achieved 1. Additional absolute contraindications include:

• Acute spinal cord compression requiring emergency intervention 1
• Severe hypercalcemia requiring medical stabilization 1
• Mirels' score ≥9 for long bone lesions without surgical fixation 1

Integration with Radiotherapy and Surgical Planning

Physical therapy timing must account for treatment effects 5:

• Post-radiotherapy: SINS scores typically improve over 6 months as recalcification occurs, with median scores decreasing from 8 at baseline to 4 at 6 months 5
• Pain resolution occurs progressively, with 67% pain-free at 1 month and 100% by 6 months post-radiotherapy 5
• Vertebral body collapse and malalignment can still occur in some irradiated vertebrae despite overall improvement, requiring ongoing SINS reassessment 5

Post-operative physical therapy after surgical stabilization should include fractionated radiotherapy to prevent prosthesis failure and reduce need for subsequent surgery. 3

Critical Pitfalls to Avoid

• Never initiate physical therapy based solely on pain improvement: Pain relief does not equal mechanical stability; SINS must be reassessed with imaging 5
• Do not rely on SINS alone for SINS 7-12 range: This gray zone requires clinical correlation with pain character, patient performance status, and multidisciplinary input 3, 6
• Avoid delayed referral: Early SINS assessment and appropriate surgical referral when indicated prevents neurological deterioration and loss of ambulation 4, 7
• Recognize that conventional radiotherapy takes time: Spinal stability improves gradually over months, not immediately after treatment 5

Multidisciplinary Coordination

Physical therapy must be coordinated within a tumor board including medical oncology, radiation oncology, orthopedic surgery, and rehabilitation specialists 1. The LMNOP framework provides systematic integration: Location, Mechanical instability (SINS), Neurology, Oncology (radiosensitivity), and Patient factors 8.

Rehabilitation of patients with bone metastases demonstrates satisfactory outcomes in pain control, physical function, and quality of life with low risk of pathological fractures when appropriate SINS-based patient selection is employed. 1