Chapter 13: Diseases of the Musculoskeletal System and Connective Tissue (M00-M99)

a. Site and laterality

Most of the codes within Chapter 13 have site and laterality designations. The site represents the bone, joint or the muscle involved. For some conditions where more than one bone, joint or muscle is usually involved, such as osteoarthritis, there is a "multiple sites" code available. For categories where no multiple site code is provided and more than one bone, joint or muscle is involved, multiple codes should be used to indicate the different sites involved.

1) Bone versus joint

For certain conditions, the bone may be affected at the upper or lower end, (e.g., avascular necrosis of bone, M87, Osteoporosis, M80, M81). Though the portion of the bone affected may be at the joint, the site designation will be the bone, not the joint.

b. Acute traumatic versus chronic or recurrent musculoskeletal conditions

Many musculoskeletal conditions are a result of previous injury or trauma to a site, or are recurrent conditions. Bone, joint or muscle conditions that are the result of a healed injury are usually found in chapter 13. Recurrent bone, joint or muscle conditions are also usually found in chapter 13. Any current, acute injury should be coded to the appropriate injury code from chapter 19. Chronic or recurrent conditions should generally be coded with a code from chapter 13. If it is difficult to determine from the documentation in the record which code is best to describe a condition, query the provider.

c. Coding of Pathologic Fractures

7th character A is for use as long as the patient is receiving active treatment for the fracture. While the patient may be seen by a new or different provider over the course of treatment for a pathological fracture, assignment of the 7th character is based on whether the patient is undergoing active treatment and not whether the provider is seeing the patient for the first time. 7th character D is to be used for encounters after the patient has completed active treatment. The other 7th characters, listed under each subcategory in the Tabular List, are to be used for subsequent encounters for routine care of fractures during the healing and recovery phase as well as treatment of problems associated with the healing, such as malunions, nonunions, and sequelae. Care for complications of surgical treatment for fracture repairs during the healing or recovery phase should be coded with the appropriate complication codes. See Section I.C.19. Coding of traumatic fractures.

d. Osteoporosis

Osteoporosis is a systemic condition, meaning that all bones of the musculoskeletal system are affected. Therefore, site is not a component of the codes under category M81, Osteoporosis without current pathological fracture. The site codes under category M80, Osteoporosis with current pathological fracture, identify the site of the fracture, not the osteoporosis.

1) Osteoporosis without pathological fracture

Category M81, Osteoporosis without current pathological fracture, is for use for patients with osteoporosis who do not currently have a pathologic fracture due to the osteoporosis, even if they have had a fracture in the past. For patients with a history of osteoporosis fractures, status code Z87.310, Personal history of (healed) osteoporosis fracture, should follow the code from M81.

2) Osteoporosis with current pathological fracture

Category M80, Osteoporosis with current pathological fracture, is for patients who have a current pathologic fracture at the time of an encounter. The codes under M80 identify the site of the fracture. A code from category M80, not a traumatic fracture code, should be used for any patient with known osteoporosis who suffers a fracture, even if the patient had a minor fall or trauma, if that fall or trauma would not usually break a normal, healthy bone.