The leap from ICD-9 to ICD-10 is a big one, so it’s easy to feel a bit overwhelmed. However, you can better digest the codes if you understand their structure. Let’s break it down.

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The Usual Cast of Characters

Codes in the ICD-10-CM code set can have three, four, five, six, or seven characters. Many three-character codes are used as headings for categories of codes; these three-character codes can further expand to four, five, or six characters to add more specific details regarding the diagnosis.

ICD10 Achilles Strain

The first three characters of an ICD-10 code designate the category of the diagnosis. In this instance, the letter “S” designates that the diagnosis relates to “Injuries, poisoning and certain other consequences of external causes related to single body regions.” “S,” used in conjunction with the numerals “8” and “6,” indicates that the diagnosis falls into the category of “Injury of muscle, fascia and tendon at lower leg.” A three-character category that has no further subdivision (i.e., no greater specificity) can stand alone as a code. In this case, however, greater specificity is possible, and you should fill in as many “blanks” as you can.

The next three characters (characters three through six) correspond to the related etiology (i.e., the cause, set of causes, or manner of causation of a disease or condition), anatomic site, severity, or other vital clinical details. So, in this case, the numbers “0,” “1,” and “1” indicate a diagnosis of “Strain of the right Achilles tendon.”

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The Tricky Seventh Character

Finally, there’s the seventh character. As this article explains, the seventh character represents one of the most significant differences between ICD-9 and ICD-10 because ICD-9 does not provide a mechanism to capture the details that the seventh character provides. You must assign a seventh character to codes in certain ICD-10-CM categories as noted within the Tabular List of codes—primarily Chapter 19 (Injury, poisoning and certain other consequences of external causes) and Chapter 15 (Pregnancy, childbirth and the puerperium). This character must always be in the seventh position; if a code has fewer than six characters and requires a seventh character extension, you must fill in all of the empty character spaces with a placeholder “X.”

Rehab therapists generally do not deal with pregnancy and childbirth, but they very well may deal with conditions related to injuries. For injuries, poisonings, and other external causes, the seventh character provides information about the episode of care, and there are seventh character extensions for most of these conditions (with the exception of fractures, which have their own seventh character system).

Seventh character extensions for injuries include:

A - Initial encounter. This describes the entire period in which a patient is receiving active treatment for the injury, poisoning, or other consequences of an external cause. So, you can use “A” as the seventh character on more than just the first claim. In fact, you can use it on multiple claims.

D - Subsequent encounter. This describes any encounter after the active phase of treatment, when the patient is receiving routine care for the injury during the period of healing or recovery. (This generally includes rehabilitation therapy.) In the example above, let’s assume a physician referred the patient to a physical therapist for rehabilitation of the patient’s strained Achilles tendon. Rehab therapy would be considered part of the healing and recovery phase, so you would code for “subsequent encounter,” thus assigning the seventh character “D.”

S - Sequela. The seventh character extension “S” indicates a complication or condition that arises as a direct result of an injury. An example of a sequela is a scar resulting from a burn.

Multiple Codes. Single Condition.

In some instances, you may need to record multiple codes for a single condition. Notes in the Tabular List indicate whether you’re required to report more than one code. These notes use verbiage such as “Use additional code” or “Code first.” (“Code first” indicates you should code the underlying condition first.) You should also be aware that ICD-10 includes several combination codes, which are single codes used to classify two or more conditions that often occur together.

With injury codes, you often will submit external cause codes that further describe the scenario that resulted in the injury. You will find these codes in Chapter 20: External cause codes. These are secondary codes, which means they further describe the cause of an injury or health condition by capturing how it happened (cause), the intent (intentional or accidental), the place the event occurred, the activity the patient was engaged in at the time of the event, and the person’s status (e.g., civilian or military). You can assign as many external cause codes as necessary to explain the patient’s condition to the fullest extent possible.

In this case, let’s say the patient strained his or her Achilles tendon while running on a treadmill at a gym. To code for this particular set of circumstances, you will need an activity code, a place of occurrence code, and an external cause status code.

ICD10 Treadmill

ICD 10 External cause

As shown above, the appropriate activity code for running on a treadmill is Y93.A1; the place of occurrence code for a gym is Y92.39; and the external cause status code in this case would be Y99.8, recreating or sport not for income or while a student.

So, in this example, you would submit a grand total of four ICD-10 codes to accurately describe that the patient presented with an Achilles tendon sprain in his or her right foot—an injury the patient suffered while recreationally running on a treadmill at a gym.

Other Notes for Rehab Therapists

  • In addition to codes found in Chapter 19: Injury, poisoning and certain other consequences of external causes, many of the codes applicable to rehab therapists appear in Chapter 13: Diseases of the musculoskeletal system and connective tissue. Most of these codes have site and laterality designations to describe the bone, joint, or muscle related to the patient’s condition.
  • For conditions involving multiple sites, such as osteoarthritis, there often is a “multiple sites” code available. If no “multiple sites” code is available, you should report multiple codes to indicate all of the different sites involved.
  • Bone vs. Joint: In some cases, the bone is affected at the lower end (e.g., Osteoporosis, M80, M81). Even though the affected area may be located at the joint, the site of the condition is still considered the bone, not the joint.
  • Acute traumatic vs. Chronic or Recurrent: Many musculoskeletal conditions are the result of previous injury or trauma, or they are recurrent conditions. Most bone, joint, or muscle conditions resulting from healed injuries appear in Chapter 13 (the “M” chapter). This chapter also includes most recurrent bone, joint, or muscle conditions. So, while you generally should code chronic or recurrent injuries using Chapter 13 codes, you should code current, acute injuries using the appropriate injury code from Chapter 19.


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