April, 2011 | BACK TO FULL ISSUE

The Musculoskeletal System and ICD-10-CM

By Cortnie R. Simmons, MHA, RHIA, CCS

This is the second in a series of articles focusing on body systems, the systems' common medical terminology, and some differences in the systems' ICD-10-CM/PCS code assignments.

In the last article we explored the Endocrine System and the organization of ICD-10-CM. This month we will be exploring the musculoskeletal system anatomically and the important areas that surround this system from an ICD-10-CM perspective.

The Musculoskeletal System is comprised of two body systems, the muscular system and the skeletal system. The skeletal system provides the structural framework needed to support the body and protect internal organs. This system performs a number of important functions that include support, storage, protection, leverage, and blood cell production. The muscular system provides the body with the ability to move and protects underlying body structures. Motion is an essential function in the muscular system allowing muscles to work together with bones to provide movement.

In ICD-10-CM diseases, disorders, and injuries from the musculoskeletal system are coded within chapter 13: Disease of the Musculoskeletal and Connective Tissue (M00-M99), and chapter 19: Injury, Poisoning, and Certain Consequences of External Causes (S00-T88). To give you a clearer picture from an anatomical perspective we will be discussing both chapters as they refer to both the muscles and bones (including diseases, fractures and injuries) within this body system.

We see several changes in ICD-10-CM related to the musculoskeletal system. In ICD-9 CM chapters 13 and 17 are currently used to report diseases, diagnoses, and injuries that are of the anatomical musculoskeletal system, however chapter 17 in ICD-9-CM has moved to chapter 19 in ICD-10-CM. Additionally, there are a number of guideline and documentation modifications that are seen within both chapters that coders must be aware of. They include (but are not limited to):

  • Documentation of site and laterality
  • More specific information for fractures and injuries
  • Identification of episode of care
  • Additional coding instructions surrounding osteoporosis
  • Reorganization of codes

Let’s take a look at some of these different areas.

Specificity of Site and Laterality

The majority of codes in chapter 13 of ICD-10-CM have been expanded in some way. This is primarily due to the additional documentation that is required in regards to specificity of site and laterality. You will find in ICD-10-CM most of the codes within chapter 13 have site and laterality designations. The site represents either the bone, muscle, or joint involved. There is an option for multiple sites when a diagnosis concerns more than one bone, muscle or joint. When more than one bone, joint, or muscle is involved and there is not a multiple site option or code, multiple codes must be used to indicate the sites involved.

All codes that have laterality requirements require you to identify if the disease, injury, or diagnoses is located on the right or left region. For example, if a patient has a diagnosis of a trigger finger of the index finger, which is the result of narrowing of the tendon sheath in an affected thumb or finger, the code would be assigned to M65.321 Trigger finger, right index finger or M65.322 Trigger finger, left index finger. This is a big difference from what we see currently in ICD-9-CM. ICD-9-CM lacks site and laterality specificity identification.

Moved Codes

Several codes were moved from various chapters in ICD-9 to chapter 13 in ICD-10-CM due to the organization of ICD-10-CM. One such disease is gout, which is a form of arthritis caused by the disposition of urate crystals around one or more joints that causes severe inflammation and pain. Gout was moved from chapter 3: Endocrine, Nutritional, and Metabolic Diseases and Immunity Disorders in ICD-9-CM to chapter 13 in ICD-10-CM. Since gout primarily involves joints that are a part of the musculoskeletal system, it was logical to reorganize this disease in ICD-10-CM to chapter 13. Additionally, osteomalacia (268.2) was moved from chapter 3 and malocclusion (524.4) from chapter 9: Disease of the Digestive System, in ICD-9-CM.

Greater Detail

Some categories and subcategories in chapter 13 require the use of seventh character extensions in ICD-10-CM. For example, let’s look at a pathological fracture of the right humerus. This diagnosis is assigned to M84.421-. The seventh character (shown in the example as -) requires identification to the encounter of care. The seventh character extensions are as follows:

  • A             Initial encounter for fracture
  • D             Subsequent encounter for fracture with routine healing
  • G             Subsequent encounter for fracture with delayed healing
  • K             Subsequent encounter for fracture with nonunion
  • P             Subsequent encounter for fracture with malunion
  • S              Sequela

All pathological and stress fractures must have a seventh character that identifies one of the above. It is important that the medical record provides this documentation and the coder assigns the correct seventh character extension.

More Specific Information for Musculoskeletal Injuries and Fractures

From an anatomical perspective, the musculoskeletal body system has several diagnoses within chapter 19 that are involved in this body system. Some of these injuries and diagnoses are fractures, dislocations and sprains, muscle, fascia, tendon injuries, traumatic amputations, crush injuries, and other injuries to muscle, tendon, ligaments, bone, or other tissues of the musculoskeletal system.


ICD-10-CM has some significant changes related to the anatomical musculoskeletal body system coding compared to ICD-9-CM; more specific documentation is the trend seen here. The reason for this is to allow the capture of the most specific injury code. Codes are organized by the general site of the injury and then by type. General sites of injury as they relate to the musculoskeletal system are organized as follows:

  • Head
  • Neck
  • Thorax
  • Abdomen
  • Shoulder and upper arm
  • Elbow and forearm
  • Wrist and hand
  • Hip and thigh
  • Knee and lower leg
  • Ankle and foot

With each of the general sites, injures are then organized by type beginning with more superficial injuries and ending with injures involved deeper body structures.


Fractures in ICD-10-CM have seen a significant amount of changes, and will now require:

  • Documentation of the type of fracture as displaced or nondisplaced
  • Specific information to the fracture type
  • Specific site of the fracture
  • Documentation supporting laterality
  • Identification of episode of care
  • Identification of open or closed
  • Gustilo classification system for further classification of open fractures

Let’s look at an example: If a patient was diagnosed with a nonunion distal right humerus fracture it would be coded to 733.82 in ICD-9-CM, however in ICD-10 CM it is coded to S42.401K. The ICD-9-CM code only identifies that a patient had nonunion fracture, but the ICD-10-CM code shows that the patient had a nonunion fracture of the lower end of right humerus. As you can see much greater detail is provided with the ICD-10-CM code including the site and laterality. Another example is seen in the diagnosis of a closed traumatic fracture of the medial malleolus of the right ankle. The ICD-9 code is assigned to 824.0 and the ICD-10-CM code is S82.51xA, Displaced fracture of the medial malleolus of right tibia initial encounter for closed fracture. Look at the detail that was provided within that one code!

Another area that is new to us in fracture coding for ICD-10-CM is the Gustilo Open Fracture classification system. The Gustilo system classifies open fractures into three main categories: Type I, Type II, and Type III, with Type III injures being further divided into Type IIIA, Type IIIB, and Type IIIC subcategories. The categories are defined by three characteristics which include:

  • Mechanism of injury
  • Degree if bone injury or involvement
  • Extent of soft tissue damage


Osteoporosis is the thinning of bone tissue and loss of bone density over time. It is the most common type of bone disease. It is a systemic condition, meaning that all bones of the musculoskeletal system are affected. The identification of site is not a component in osteoporosis without a current pathological fracture (M81) but is a component when current pathological fractures are involved (M80). Category M81 is used for patients who do not currently have a pathological fracture due to the osteoporosis even if they have had a fracture in the past. Codes from category M80 should be used for any patient with known osteoporosis who suffers a fracture even if the patient had a minor fall or trauma at the time of the encounter. The site codes in this category identify the site of the fracture and not the osteoporosis.

We have seen the aspect of how ICD-10-CM code methodology compares to our current ICD-9-CM system as it applies to the anatomical musculoskeletal system. As you can see the anatomical musculoskeletal body system has several changes that are seen in ICD-10-CM, which allows us to provide greater specificity and detail than ICD-9-CM provides. The changes that have been made provide coders with the ability to assign codes that paint a clear picture of the patient’s condition. We will continue to see the benefits of using ICD-10-CM versus ICD-9-CM; it reinforces the need for appropriate clinical documentation to apply correct coding and understand our anatomical body systems. The next installment will focus on the integumentary body system.


Centers for Medicare and Medicaid Services. ICD-10. 2011. http://www.cms.gov/ICD10/.
Contexo Media. Advanced Anatomy and Physiology for ICD-10 2010. Salt Lake City: Contexo Media, 2010.
Tortora, Gerard, and Bryan Derrickson. Principles of Anatomy and Physiology 12th Edition. Wiley, 2008.


Cortnie Simmons is a national compliance manager at Kforce Healthcare and an AHIMA-approved ICD-10-CM/PCS trainer.

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