COSC common mistakes
COSC · Understand the traps and how to avoid them.
Assigning CPT codes from the procedure title or surgeon's summary line at the top of the operative report instead of reading the body of the note.
Titles are shorthand and routinely omit approach, laterality, staged components, graft type, and whether a planned procedure was abandoned or converted.
What to do instead
Read the entire narrative and map each documented surgical action to a code. Use the title only as an index, then verify approach, implant, graft, and closure details in the body.
Coding a percutaneous pinning or closed reduction with fixation as open treatment because the report uses the words reduction and fixation.
Open refers to surgical exposure of the fracture site, not to the presence of fixation. Percutaneous pins and external fixators are closed treatment with fixation.
What to do instead
Look for documentation of incision and direct visualization of the fracture. If fixation is percutaneous or external, use the closed or percutaneous fixation code for that anatomic site.
Choosing a fracture code by bone name alone and ignoring the code's anatomic sub-site, such as proximal versus shaft versus distal, or intra-articular versus extra-articular.
Musculoskeletal fracture codes are highly site-specific and treatment-specific; a generic bone code may not exist or may describe a different injury.
What to do instead
Before selecting, identify the exact anatomic location, intra-articular involvement, and treatment from the report; read the full code descriptor and parenthetical notes.
Reporting an arthroscopic chondroplasty or limited debridement as a separate procedure in the same knee compartment as a meniscectomy.
NCCI and arthroscopy parentheticals bundle chondroplasty and debridement into definitive procedures such as meniscectomy when performed in the same compartment.
What to do instead
Check NCCI PTP edits and arthroscopy code parentheticals. Report chondroplasty separately only when it is in a distinct compartment, documentation supports it, and an appropriate modifier is allowed.
Using the primary total hip or knee arthroplasty code for a revision because the report simply says revision without specifying which components were exchanged.
Revision arthroplasty codes are component-specific; primary codes describe initial implantation and are wrong for removal or exchange of components.
What to do instead
Identify which components were removed and replaced, such as acetabular shell, liner, femoral head, stem, tibial tray, polyethylene, or patellar button, and select the revision code matching the component or components revised.
Assigning an ICD-10-CM injury code without the required seventh character, or defaulting to A for every encounter.
Injury codes require a seventh character for encounter type; A means active treatment, not necessarily the first visit, and subsequent or sequela encounters need different characters.
What to do instead
Determine the encounter type from the note and apply the correct seventh character, along with laterality and site specificity. Query the surgeon if the encounter stage is unclear.
Coding a pathologic fracture as a traumatic fracture and omitting the underlying condition code.
The operative report may document only fracture while imaging or history notes a lesion; traumatic site codes do not capture the pathologic nature or the underlying disease.
What to do instead
Look for terms such as pathologic, neoplasm, metastasis, osteoporosis, or prior radiation. Assign the pathologic fracture code with site and seventh character plus the underlying condition, sequencing per the reason for the encounter.
Appending modifier 25 to every E/M service billed on the same day as an orthopaedic procedure.
Coders fear denial and assume any separately documented E/M qualifies, but the surgical package already includes routine pre-, intra-, and post-operative care.
What to do instead
Use modifier 25 only when the note documents a significant, separately identifiable E/M problem above the usual procedure care, such as a new unrelated complaint or exacerbation. Do not use it for routine pre-op clearance or discussing the procedure.
Using modifier 59 to bypass an NCCI edit when a specific anatomic modifier such as RT, LT, FA, or T1-T9 would correctly describe the service.
Modifier 59 is familiar and broadly recognized, but NCCI and payers prefer the most specific modifier; inappropriate 59 use is a common audit target.
What to do instead
Apply laterality, digit, or site-specific modifiers first. Use 59 or an X modifier only when no more specific modifier exists, the services are truly distinct, and documentation supports it.
Treating every NCCI column-one and column-two edit pair as permanently bundled or, conversely, assuming any pair can be unbundled with a modifier.
Coders memorize code pairs instead of checking the PTP edit indicator, which determines whether a modifier is permitted.
What to do instead
Check the NCCI PTP indicator: 0 means no modifier allowed, 1 means a modifier is allowed with documentation, and 9 means the edit is not applicable. Unbundle only indicator 1 pairs with a supported modifier.