Chapter 13

M00–M99: Diseases of the Musculoskeletal System and Connective Tissue

Diseases of the Musculoskeletal System and Connective Tissue diagnostic classification updated for 2026.

Chapter Instructions

Excludes2(Not included here. Code separately if applicable.)
  • arthropathic psoriasis (L40.5-)
  • certain conditions originating in the perinatal period (P04-P96)
  • certain infectious and parasitic diseases (A00-B99)
  • compartment syndrome (traumatic) (T79.A-)
  • complications of pregnancy, childbirth and the puerperium (O00-O9A)
  • congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)
  • endocrine, nutritional and metabolic diseases (E00-E88)
  • injury, poisoning and certain other consequences of external causes (S00-T88)
  • neoplasms (C00-D49)
  • symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)
Internal Codes
  • M21.15

    Varus deformity, not elsewhere classified, hip

  • M21.151

    Varus deformity, not elsewhere classified, right hip

  • M21.152

    Varus deformity, not elsewhere classified, left hip

  • M21.159

    Varus deformity, not elsewhere classified, unspecified hip

  • M21.16

    Varus deformity, not elsewhere classified, knee

  • M21.161

    Varus deformity, not elsewhere classified, right knee

  • M21.162

    Varus deformity, not elsewhere classified, left knee

  • M21.169

    Varus deformity, not elsewhere classified, unspecified knee

  • M21.17

    Varus deformity, not elsewhere classified, ankle

  • M21.171

    Varus deformity, not elsewhere classified, right ankle

  • M21.172

    Varus deformity, not elsewhere classified, left ankle

  • M21.179

    Varus deformity, not elsewhere classified, unspecified ankle

  • M21.2

    Flexion deformity

  • M21.20

    Flexion deformity, unspecified site

  • M21.21

    Flexion deformity, shoulder

  • M21.211

    Flexion deformity, right shoulder

  • M21.212

    Flexion deformity, left shoulder

  • M21.219

    Flexion deformity, unspecified shoulder

  • M21.22

    Flexion deformity, elbow

  • M21.221

    Flexion deformity, right elbow

  • M21.222

    Flexion deformity, left elbow

  • M21.229

    Flexion deformity, unspecified elbow

  • M21.23

    Flexion deformity, wrist

  • M21.231

    Flexion deformity, right wrist

  • M21.232

    Flexion deformity, left wrist

  • M21.239

    Flexion deformity, unspecified wrist

  • M21.24

    Flexion deformity, finger joints

  • M21.241

    Flexion deformity, right finger joints

  • M21.242

    Flexion deformity, left finger joints

  • M21.249

    Flexion deformity, unspecified finger joints

  • M21.25

    Flexion deformity, hip

  • M21.251

    Flexion deformity, right hip

  • M21.252

    Flexion deformity, left hip

  • M21.259

    Flexion deformity, unspecified hip

  • M21.26

    Flexion deformity, knee

  • M21.261

    Flexion deformity, right knee

  • M21.262

    Flexion deformity, left knee

  • M21.269

    Flexion deformity, unspecified knee

  • M21.27

    Flexion deformity, ankle and toes

  • M21.271

    Flexion deformity, right ankle and toes

  • M21.272

    Flexion deformity, left ankle and toes

  • M21.279

    Flexion deformity, unspecified ankle and toes

  • M21.3

    Wrist or foot drop (acquired)

  • M21.33

    Wrist drop (acquired)

  • M21.331

    Wrist drop, right wrist

  • M21.332

    Wrist drop, left wrist

  • M21.339

    Wrist drop, unspecified wrist

  • M21.37

    Foot drop (acquired)

  • M21.371

    Foot drop, right foot

  • M21.372

    Foot drop, left foot

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