Chapter XIII
Diseases of the musculoskeletal system and connective tissue
(M00-M99)

Arthropathies
(M00-M25)

Disorders affecting predominantly peripheral (limb) joints

Other joint disorders
(M20-M25)

Excludes: joints of the spine ( M40-M54 )

M20 Acquired deformities of fingers and toes
Excludes: acquired absence of fingers and toes ( Z89.- )
congenital:
· absence of fingers and toes ( Q71.3 , Q72.3 )
· deformities and malformations of fingers and toes ( Q66.- , Q68-Q70 , Q74.- )
M20.0 Deformity of finger(s)
Boutonnière and swan-neck deformities
Excludes: clubbing of fingers ( R68.3 )
palmar fascial fibromatosis [Dupuytren] ( M72.0 )
trigger finger ( M65.3 )
M20.1 Hallux valgus (acquired)
Bunion
M20.2 Hallux rigidus
M20.3 Other deformity of hallux (acquired)
Hallux varus
M20.4 Other hammer toe(s) (acquired)
M20.5 Other deformities of toe(s) (acquired)
M20.6 Acquired deformity of toe(s), unspecified

M21 Other acquired deformities of limbs
[See site code at the beginning of this chapter ]
Excludes: acquired absence of limb ( Z89.- )
acquired deformities of fingers or toes ( M20.- )
congenital:
· absence of limbs ( Q71-Q73 )
· deformities and malformations of limbs ( Q65-Q66 , Q68-Q74 )
coxa plana ( M91.2 )
M21.0 Valgus deformity, not elsewhere classified
Excludes: metatarsus valgus ( Q66.6 )
talipes calcaneovalgus ( Q66.4 )
M21.1 Varus deformity, not elsewhere classified
Excludes: metatarsus varus ( Q66.2 )
tibia vara ( M92.5 )
M21.2 Flexion deformity
M21.3 Wrist or foot drop (acquired)
M21.4 Flat foot [pes planus] (acquired)
Excludes: congenital pes planus ( Q66.5 )
M21.5 Acquired clawhand, clubhand, clawfoot and clubfoot
Excludes: clubfoot, not specified as acquired ( Q66.8 )
M21.6 Other acquired deformities of ankle and foot
Excludes: deformities of toe (acquired) ( M20.1-M20.6 )
M21.7 Unequal limb length (acquired)
M21.8 Other specified acquired deformities of limbs
M21.9 Acquired deformity of limb, unspecified

M22 Disorders of patella
Excludes: dislocation of patella ( S83.0 )
M22.0 Recurrent dislocation of patella
M22.1 Recurrent subluxation of patella
M22.2 Patellofemoral disorders
M22.3 Other derangements of patella
M22.4 Chondromalacia patellae
M22.8 Other disorders of patella
M22.9 Disorder of patella, unspecified

M23 Internal derangement of knee
The following supplementary subclassification to indicate the site of involvement is provided for optional use with appropriate subcategories in M23.-; see also note at the beginning of this chapter.
0 Multiple sites
1 Anterior cruciate ligament or Anterior horn of medial meniscus
2 Posterior cruciate ligament or Posterior horn of medial meniscus
3 Medial collateral ligament or Other and unspecified medial meniscus
4 Lateral collateral ligament or Anterior horn of lateral meniscus
5 Posterior horn of lateral meniscus
6 Other and unspecified lateral meniscus
7 Capsular ligament
9 Unspecified ligament or Unspecified meniscus
Excludes: ankylosis ( M24.6 )
current injury - see injury to the knee and lower leg ( S80-S89 )
deformity of knee ( M21.- )
disorders of patella ( M22.- )
osteochondritis dissecans ( M93.2 )
recurrent dislocation or subluxation ( M24.4 )
· patella ( M22.0-M22.1 )
M23.0 Cystic meniscus
M23.1 Discoid meniscus (congenital)
M23.2 Derangement of meniscus due to old tear or injury
Old bucket-handle tear
M23.3 Other meniscus derangements
Degenerate
Detached
Retained
}
}
}
meniscus
M23.4 Loose body in knee
M23.5 Chronic instability of knee
M23.6 Other spontaneous disruption of ligament(s) of knee
M23.8 Other internal derangements of knee
Laxity of ligament of knee
Snapping knee
M23.9 Internal derangement of knee, unspecified

M24 Other specific joint derangements
[See site code at the beginning of this chapter ]
Excludes: current injury - see injury of joint by body region
ganglion ( M67.4 )
snapping knee ( M23.8 )
temporomandibular joint disorders ( K07.6 )
M24.0 Loose body in joint
Excludes: loose body in knee ( M23.4 )
M24.1 Other articular cartilage disorders
Excludes: chondrocalcinosis ( M11.1-M11.2 )
internal derangement of knee ( M23.- )
metastatic calcification ( E83.5 )
ochronosis ( E70.2 )
M24.2 Disorder of ligament
Instability secondary to old ligament injury
Ligamentous laxity NOS
Excludes: familial ligamentous laxity ( M35.7 )
knee ( M23.5-M23.8 )
M24.3 Pathological dislocation and subluxation of joint, not elsewhere classified
Excludes: dislocation or displacement of joint:
· congenital - see congenital malformations and deformations of the musculoskeletal system ( Q65-Q79 )
· current injury - see injury of joints and ligaments by body region
· recurrent ( M24.4 )
M24.4 Recurrent dislocation and subluxation of joint
Excludes: patella ( M22.0-M22.1 )
vertebral subluxation ( M43.3-M43.5 )
M24.5 Contracture of joint
Excludes: acquired deformities of limbs ( M20-M21 )
contracture of tendon (sheath) without contracture of joint ( M67.1 )
Dupuytren's contracture ( M72.0 )
M24.6 Ankylosis of joint
Excludes: spine ( M43.2 )
stiffness of joint without ankylosis ( M25.6 )
M24.7 Protrusio acetabuli
M24.8 Other specific joint derangements, not elsewhere classified
Irritable hip
Excludes: that involving iliotibial band syndrome ( M76.3 )
M24.9 Joint derangement, unspecified

M25 Other joint disorders, not elsewhere classified
[See site code at the beginning of this chapter ]
Excludes: abnormality of gait and mobility ( R26.- )
calcification of:
· bursa ( M71.4 )
· shoulder (joint) ( M75.3 )
· tendon ( M65.2 )
deformities classified to M20-M21
difficulty in walking ( R26.2 )
M25.0 Haemarthrosis
Excludes: current injury - see injury of joint by body region
M25.1 Fistula of joint
M25.2 Flail joint
M25.3 Other instability of joint
Excludes: instability of joint secondary to:
· old ligament injury ( M24.2 )
· removal of joint prosthesis ( M96.8 )
M25.4 Effusion of joint
Excludes: hydrarthrosis of yaws ( A66.6 )
M25.5 Pain in joint
M25.6 Stiffness of joint, not elsewhere classified
M25.7 Osteophyte
M25.8 Other specified joint disorders
M25.9 Joint disorder, unspecified