Table 6 Reason for Algorithm Misclassification

Lumbar Herniated Disc (n = 29)

False Positive (n = 13)

Spinal Stenosis Case (n = 8)

Severe Incontinence Diagnosis (n = 1)

Cervical or Thoracic Spine Case (n = 1)

Flatback Syndrome Case (n = 1)

Spondylolisthesis Case (n = 1)

Revision Discectomy Case (n = 1)

False Negative (n = 16)

Incorrectly Classified as Spinal Stenosis (n = 9)

Procedure Billing Codes not included in Data (n = 4)

Incorrectly Marked as Non-Primary Indication because of urinary incontinence diagnosis (n = 2)

Incorrectly Marked as Non-Primary Indication because of cauda equina diagnosis (n = 1)

Lumbar Spinal Stenosis (n = 46)

False Positive (n = 16)

Herniated Disc Case (n = 9)

Cervical or Thoracic Spine Case (n = 4)

Infection Present (n = 1)

Flatback Syndrome Case (n = 1)

Epidural Abscess Case (n = 1)

False Negative (n = 30)

Procedure Billing Codes not included in Data (n = 11)

Incorrectly Classified as Herniated Disc (n = 8)

CPT code (63046, 63267) not included in algorithm (n = 6)

Incorrectly Marked as Non-Primary Indication because of collapsed vertebra diagnosis (n = 2)

Incorrectly Marked as Non-Primary Indication because of fecal incontinence diagnosis (n = 1)

Incorrectly Marked as Non-Primary Indication because of fracture diagnosis (n = 1)

Incorrectly marked as Non-Primary Indication because of bladder dysfunction diagnosis (n = 1)

Knee Osteoarthritis (n = 11)

False Positive (n = 2)

Procedure was actually to revise previous knee replacement (n = 1)

Rheumatoid Arthritis Case (n = 1)

False Negative (n = 9)

Procedure Billing Codes not included in Data (n = 6)

CPT code (27486, 27487) not included in algorithm (n = 2)

Incorrectly Marked as Non-Primary Indication because of osteonecrosis diagnosis (n = 1)

Hip Osteoarthritis (n = 23)

False Positive (n = 2)

Osteonecrosis Diagnosis (n = 1)

Developmental Hip Dysplasia Case (n = 1)

False Negative (n = 21)

Incorrectly Marked as Non-Primary Indication because of osteonecrosis diagnosis (n = 12)

Procedure Billing Codes not included in Data (n = 6)

CPT code (27134) not included in algorithm (n = 1)

Incorrectly Marked as Non-Primary Indication because of fracture diagnosis (n = 1)

Incorrectly Marked as Non-Primary Indication because of neoplasm diagnosis (n = 1)