M24.60 identifies ankylosis — abnormal fusion or immobility of a joint — when the specific joint affected is not documented or cannot be determined from the record.

Documentation tips

What should appear in the chart to support M24.60.

Source · Editorial brief grounded in 4 cited references ↓

• Name the specific joint affected (e.g., right knee, left hip, right elbow) — this drives laterality-specific coding and avoids M24.60 entirely.
• Distinguish true bony ankylosis from fibrous ankylosis in the note; both fall under M24.6- but the distinction supports medical necessity for surgical intervention.
• Document whether ankylosis is post-traumatic, post-infectious, or idiopathic in origin — an underlying cause may require an additional diagnosis code.
• Record functional limitation and range-of-motion measurements to support medical necessity for physical therapy, manipulation under anesthesia, or joint arthroplasty.
• If imaging was performed, reference the modality and findings (e.g., plain film showing obliteration of joint space, CT confirming bony bridging) to corroborate the ankylosis diagnosis.
• Confirm the joint is a peripheral joint — spinal ankylosis requires M43.2- and must not be coded under M24.60.

Related CPT procedures

Procedure codes commonly billed with M24.60. 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 M24.60 and adjacent codes.

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

• Using M24.60 when the joint is named in the record — always code to the highest specificity available (e.g., M24.661 for right ankle); M24.60 is only valid when the joint is truly undocumented.
• Confusing joint stiffness (M25.6-) with ankylosis (M24.6-) — these are Excludes1 to each other and cannot be assigned together for the same joint.
• Applying M24.60 to spinal ankylosis — the spine is excluded from M24.6-; use M43.2- instead.
• Omitting the underlying etiology code when ankylosis is secondary to a specific condition such as rheumatoid arthritis or prior infection — payers may expect dual coding.
• Coding M24.60 for temporomandibular joint ankylosis — TMJ disorders are excluded from M24.6- and must be coded from M26.6-.

Clinical context

Source · Editorial summary grounded in 4 cited references ↓

Sibling codes

Other billable codes under M24.6 (laterality / anatomic variants).