Hydroxyapatite deposition disease (HADD) at an unspecified anatomical site — calcium hydroxyapatite crystals deposited in or around a joint without documentation of which joint is affected.

Documentation tips

What should appear in the chart to support M11.00.

Source · Editorial brief grounded in 4 cited references ↓

• Document the specific joint by name (e.g., right shoulder, left hip) at every encounter — this unlocks a site-specific M11.0x code and avoids the unspecified fallback.
• Record imaging findings that confirm hydroxyapatite deposits: X-ray, ultrasound, or MRI findings noting calcific tendinitis or periarticular calcification, including size and location of deposits.
• Note whether the presentation is acute (inflammatory flare with warmth, swelling, severe pain) or chronic/recurrent, as this affects medical necessity narratives for procedures.
• If multiple joints are involved, document each joint separately so individual site-specific codes can be assigned rather than defaulting to M11.00.
• Distinguish HADD from chondrocalcinosis (M11.2x, CPPD) and gout (M10.x) in the clinical impression — crystal type drives code selection, not just the term 'crystal arthropathy.'

Related CPT procedures

Procedure codes commonly billed with M11.00. 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 M11.00 and adjacent codes.

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

• Using M11.00 when the affected joint is documented but the coder defaults to unspecified — always check the note for joint name and laterality before selecting this code.
• Confusing HADD (M11.0x) with chondrocalcinosis/CPPD (M11.2x) or gout (M10.x); these are distinct crystal types and distinct code families — do not interchange them based on a generic 'crystal arthropathy' label.
• Assigning M11.00 on a claim for a site-specific procedure (e.g., 23415 shoulder release) — the unspecified-site code creates a laterality mismatch that triggers medical necessity denials.
• Billing M11.00 for calcific tendinitis of the shoulder without querying whether the provider's intended diagnosis is HADD — calcific tendinitis of the shoulder has its own codes (M75.3x) and the distinction matters for accurate coding.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Sibling codes

Other billable codes under M11.0 (laterality / anatomic variants).