Patellar tendinitis of the right knee — an enthesopathy involving inflammation of the patellar tendon at or near its attachment to the inferior pole of the patella, classified under lower limb enthesopathies (M76).

Documentation tips

What should appear in the chart to support M76.51.

Source · Editorial brief grounded in 6 cited references ↓

• Explicitly name the affected side — 'right knee' — in the diagnosis line; do not rely on laterality buried in the physical exam narrative alone.
• Document pain location as inferior patellar pole and note load-dependent or activity-related symptom pattern (jumping, stair descent, squatting) to support the enthesopathy diagnosis over nonspecific knee pain.
• Record imaging findings when obtained — ultrasound or MRI evidence of tendon thickening, hypoechogenicity, or neovascularization strengthens medical necessity and audit defensibility.
• Note prior conservative treatment (physical therapy, NSAIDs, activity modification) in the history if pursuing injection billing, as CMS Article A57079 requires medical necessity support.
• If an activity or occupational exposure caused or accelerated the tendinitis, append an appropriate external cause code to complete the clinical picture per ICD-10-CM guidelines.

Related CPT procedures

Procedure codes commonly billed with M76.51. 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 M76.51 and adjacent codes.

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

• Defaulting to M76.50 (unspecified knee) when the provider documented 'right knee' — specificity is available and required when laterality is in the record.
• Using a nonspecific knee pain code (M25.561) as the primary diagnosis when patellar tendinitis has been confirmed — M25.561 is appropriate only as an ancillary code if pain persists post-treatment, not as a stand-alone primary code for a confirmed diagnosis.
• Confusing patellar tendinitis (M76.51, enthesopathy) with prepatellar or infrapatellar bursitis (M70.4x/M70.5x) — these are distinct conditions with different codes; documentation of the exact structure involved is critical.
• Failing to append an external cause code when the tendinitis is clearly activity-related (e.g., sports overuse), which can leave medical necessity documentation incomplete for payers requiring cause context.
• Billing bilateral encounters under M76.51 alone — if both knees are treated, M76.51 and M76.52 must both be coded; there is no bilateral patellar tendinitis code in ICD-10-CM despite 'bilateral' appearing as an approximate synonym in some references.

Clinical context

Source · Editorial summary grounded in 6 cited references ↓

Sibling codes

Other billable codes under M76.5 (laterality / anatomic variants).