Hydroxyapatite deposition disease (HADD) involving two or more anatomically distinct joint sites simultaneously, classified under the crystal arthropathy family of diagnoses.

Documentation tips

What should appear in the chart to support M11.09.

Source · Editorial brief grounded in 5 cited references ↓

• List every affected joint by name and side — 'bilateral shoulders and right hip' is sufficient to support M11.09; 'multiple joints' alone is not.
• Specify the crystal type as hydroxyapatite (not simply 'calcific tendinitis' or 'crystal arthropathy') to justify M11.0x over M11.8x or M11.9.
• Record imaging findings — radiographic calcification, ultrasound echogenic foci, or MRI signal changes — at each affected site to substantiate multi-site involvement.
• Note symptom duration and acuity (acute flare vs. chronic) at each site; this supports medical necessity for procedures performed at multiple joints on the same date.
• If a systemic or metabolic condition is suspected or confirmed as the etiology of HADD, document and code it additionally.

Related CPT procedures

Procedure codes commonly billed with M11.09. 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 M11.09 and adjacent codes.

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

• Using M11.09 when only one joint is affected — 'multiple sites' requires documentation of two or more anatomically distinct regions; otherwise use the single-site code.
• Conflating HADD with CPPD: chondrocalcinosis codes (M11.1x, M11.2x) apply to calcium pyrophosphate crystals, not hydroxyapatite — the crystal type must be explicitly documented or inferable.
• Defaulting to M11.9 (Crystal arthropathy, unspecified) when the crystal type is documented as hydroxyapatite — M11.09 is more specific and should be used.
• Assigning M11.00 (unspecified site) when multiple sites are documented — M11.09 is the correct code for confirmed polyarticular involvement.
• Failing to add a secondary code for an underlying metabolic condition (e.g., hyperparathyroidism E21.x, renal osteodystrophy N25.0) when the provider links HADD to a systemic cause.

Clinical context

Source · Editorial summary grounded in 5 cited references ↓

Sibling codes

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