Softening or breakdown of the cartilage on the underside of the kneecap, coded without specification of which knee is affected.

Documentation tips

What should appear in the chart to support M22.40.

Source · Editorial brief grounded in 5 cited references ↓

• Record the affected side by name (right or left) at every encounter — if laterality is known, M22.40 is the wrong code; use M22.41 or M22.42.
• Document the Outerbridge grade or arthroscopic grading of cartilage damage if obtained; this supports medical necessity for surgical intervention and differentiates the diagnosis from nonspecific anterior knee pain.
• Include MRI findings (cartilage signal change, fissuring, patellar tilt, trochlear morphology) or arthroscopic observation to substantiate the chondromalacia diagnosis rather than relying on symptom description alone.
• Note the patient's conservative care history (physical therapy, NSAIDs, activity modification) before any surgical or procedural claim — payers commonly require documented failed conservative management.
• If the reason laterality is unspecified is that the patient is being evaluated for bilateral symptoms before imaging, state that explicitly in the assessment to preempt an audit query.

Related CPT procedures

Procedure codes commonly billed with M22.40. Linking the right diagnosis to the right procedure is what establishes medical necessity.

Source · CMS LCDs · AAOS specialty guidance · claims-pattern analysis

Common coding pitfalls

The recurring mistakes coders make with M22.40 and adjacent codes.

Source · Editorial brief grounded in CDC ICD-10-CM tabular guidance, AAOS coding references, and cited references ↓

• Defaulting to M22.40 when laterality is documented in the note — always assign M22.41 (right) or M22.42 (left) when the side is known; unspecified codes can trigger payer edits and downcoding.
• Confusing chondromalacia patellae (M22.4x) with patellofemoral disorder (M22.2Xx) — patellofemoral syndrome is a broader pain syndrome not synonymous with documented cartilage softening; use the code that matches the documented diagnosis.
• Coding M22.40 alongside M22.90 (unspecified disorder of patella, unspecified knee) — these are redundant; pick the more specific chondromalacia code and drop the nonspecific one.
• Failing to add a secondary diagnosis code for an underlying cause (e.g., patellar malalignment M22.2X9) when the provider documents one — chondromalacia is often secondary to tracking abnormalities that should also be coded.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M22.4 (laterality / anatomic variants).