M67.51 classifies plica syndrome specifically affecting the right knee — an irritation or thickening of the synovial plica fold within the right knee joint, categorized under other disorders of synovium and tendon.

Documentation tips

What should appear in the chart to support M67.51.

Source · Editorial brief grounded in 5 cited references ↓

• Specify laterality explicitly — 'right knee' must appear in the provider's assessment or plan, not just the HPI, to justify M67.51 over M67.50.
• Document the clinical basis: medial or anterior knee pain pattern, palpable plica band, provocative test findings (plica test), and response or failure of conservative measures (NSAIDs, PT).
• If arthroscopy confirms plica pathology, record the arthroscopic findings (thickened, fibrotic, or inflamed plica) and the specific anatomical location (medial, suprapatellar, infrapatellar) in the operative report.
• Note the chronicity and any prior imaging (MRI findings of a thickened synovial band) to support medical necessity for surgical intervention.
• If bilateral symptoms exist but only the right knee is treated in this encounter, document that explicitly to justify single-side coding without raising symmetry questions.

Related CPT procedures

Procedure codes commonly billed with M67.51. 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 M67.51 and adjacent codes.

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

• Using M67.50 (unspecified knee) when the provider clearly documented 'right knee' — specificity is available and required; unspecified codes invite downcoding or denial.
• Coding plica syndrome alongside tendinitis NOS (M77.9-) in the same encounter — the Excludes1 note at M67 prohibits this combination; select the code that best reflects the primary diagnosis.
• Failing to add a second code (M67.52) when bilateral plica syndrome is diagnosed and treated in the same visit — there is no combined bilateral code, so both laterality codes must be reported.
• Confusing plica syndrome with meniscal pathology or patellofemoral syndrome and defaulting to a more familiar code — plica syndrome has its own discrete code family and should not be coded as 'knee pain' (M25.561) when the diagnosis is confirmed.
• Applying a 7th-character extension to M67.51 — M-codes in Chapter 13 do not use 7th-character encounter extensions; that convention applies to injury S-codes only.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

Other billable codes under M67.5 (laterality / anatomic variants).