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M18.1 ICD-10-CA code: Other primary arthrosis of first carpometacarpal joint

M18.1 is the ICD-10-CA code for “Other primary arthrosis of first carpometacarpal joint” in CIHI’s FY 2026–2027 release, in effect from Apr 1, 2026.

Official description

M18.1

Other primary arthrosis of first carpometacarpal joint

Short description: Oth prim arthrs 1st carpometacarpal jt

ICD-10-CA · Canada · Also written M181

Index terms

Entries in CIHI’s alphabetical index that lead to M18.1. Searching the index by the condition the note names is how coders reach this code.

  • Arthrosis (deformans) (degenerative), first carpometacarpal joint, primary (unilateral)
  • Osteoarthritis, joint(s), first carpometacarpal NOS, unilateral or unspecified (laterality), primary

Notes for M18.1

As CIHI prints them, with any note M18.1 takes from the headings above it.

Includes

  • Primary arthrosis of first carpometacarpal joint:• NOS• unilateral
  • Disorders affecting predominantly peripheral (limb) jointsFrom M00-M25 Arthropathies

Excludes

Conditions classified elsewhere.

  • Osteoarthritis of:• spine (M47.-)• temporomandibular joint (TMJ) (K07.68)From M15-M19 Arthrosis
  • Certain:• conditions originating in the perinatal period (P00-P96)• disorders of the temporomandibular joint (K07.6)• infectious and parasitic diseases (A00-B99)compartment syndrome (T79.6)complications of pregnancy, childbirth and the puerperium (O00-O99)congenital malformations, deformations and chromosomal abnormalities (Q00-Q99)endocrine, nutritional and metabolic diseases (E00-E90)injury, poisoning and certain other consequences of external causes (S00-T98)neoplasms (C00-D48)symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R99)From Chapter 13: Diseases of the musculoskeletal system and connective tissue (M00-M99)

Note

  • In this block the term osteoarthritis is used as a synonym for arthrosis or osteoarthrosis. The term primary has been used with its customary clinical meaning of no underlying or determining condition identified.From M15-M19 Arthrosis
  • The following fifth characters represent the following sites of involvement:0 Multiple sites1 Shoulder region: clavical , scapula — joint acromioclavicular, glenohumeral, sternoclavicular2 Upper arm: humerus — elbow joint,3 Forearm: radius , ulna — wrist joint,4 Hand: carpus, fingers, metacarpus — joints between these bones,5 Pelvic region and thigh: buttock , femur , pelvis — joint hip , sacroiliac6 Lower leg: fibula , tibia — knee joint7 Ankle and foot: metatarsus, tarsus, toes — other joints in foot8 Other:head neck ribs skull trunk vertebral column9 Site unspecifiedFrom Chapter 13: Diseases of the musculoskeletal system and connective tissue (M00-M99)

Where M18.1 sits

  1. 1ChapterChapter 13: Diseases of the musculoskeletal system and connective tissue (M00-M99)
  2. 2Block M00-M25Arthropathies
  3. 3Block M15-M19Arthrosis
  4. 4Category M18Arthrosis of first carpometacarpal joint
  5. 5Valid code M18.1Other primary arthrosis of first carpometacarpal joint

Source and release

Data release
ICD-10-CA · FY 2026–2027
Effective date
Apr 1, 2026
Publisher
CIHI

This page is built from the ICD-10-CA catalog that Vero Codes reads when it suggests codes: Canadian Institute for Health Information’s FY 2026–2027 release, imported from the publisher’s file and checked against it. The description, notes and structured data come from the same record.

See M18.1 in the CIHI source

Frequently asked questions

What does ICD-10-CA code M18.1 mean?

M18.1 is the ICD-10-CA code for “Other primary arthrosis of first carpometacarpal joint” in CIHI’s ICD-10-CA FY 2026–2027 release.

Where is M18.1 in ICD-10-CA?

M18.1 sits under M18 Arthrosis of first carpometacarpal joint, within M15-M19 Arthrosis, within M00-M25 Arthropathies, within Chapter 13: Diseases of the musculoskeletal system and connective tissue (M00-M99).

What coding notes apply to M18.1?

ICD-10-CA lists Includes, Note, Excludes notes for M18.1, including those from the headings it sits under. They are listed on this page with where each one comes from.

Which ICD-10-CA release does this page use?

It uses CIHI’s FY 2026–2027 release, in effect from Apr 1, 2026 to Mar 31, 2027. It is a reference: confirm the code against the current list and the payer’s rules before you submit it.

Codes beside M18.1

M18.0Primary arthrosis of first carpometacarpal joints, bilateralM18.2Post-traumatic arthrosis of first carpometacarpal joints, bilateralM18.3Other post-traumatic arthrosis of first carpometacarpal jointM18.4Other secondary arthrosis of first carpometacarpal joints, bilateralM18.5Other secondary arthrosis of first carpometacarpal jointM18.9Arthrosis of first carpometacarpal joint, unspecified