M23.51 Chronic instability of knee, right knee

Billable ICD-10-CM code, FY2026.

Applies from M23 Internal derangement of knee

Excludes1 (never code together)

• ankylosis (M24.66)
• deformity of knee (M21.-)
• osteochondritis dissecans (M93.2)

Excludes2 (not included here)

• current injury - see injury of knee and lower leg (S80-S89)
• recurrent dislocation or subluxation of joints (M24.4)
• recurrent dislocation or subluxation of patella (M22.0-M22.1)

MS-DRG index

Defines the logic of DRG(s) 564-566 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 717.85 Old disruption of other ligaments of knee (approximate)
• 718.86 Other joint derangement, not elsewhere classified, lower leg (approximate)

Code annotations containing back-references to M23.51

Back-references to M23.5

• Type 2 Excludes: M24.2 Disorder of ligament ("internal derangement of knee (M23.5-M23.8X9)")

Back-references to M23

• Type 2 Excludes: M24.1 Other articular cartilage disorders ("internal derangement of knee (M23.-)")
• Type 2 Excludes: S83 Dislocation and sprain of joints and ligaments of knee ("internal derangement of knee (M23.-)")

Nearby codes

• M23.40 Loose body in knee, unspecified knee
• M23.41 Loose body in knee, right knee
• M23.42 Loose body in knee, left knee
• M23.5 Chronic instability of knee
• M23.50 Chronic instability of knee, unspecified knee
• M23.51 Chronic instability of knee, right knee (this code)
• M23.52 Chronic instability of knee, left knee
• M23.6 Other spontaneous disruption of ligament(s) of knee
• M23.60 Other spontaneous disruption of unspecified ligament of knee
• M23.601 Other spontaneous disruption of unspecified ligament of right knee
• M23.602 Other spontaneous disruption of unspecified ligament of left knee