A sprained ankle, ICD-9 – 845.00, is a common presentation to the emergency department and in a one year span almost 35,000 cases were reported for coding and billing to web2pro Business Performance Services. A sprained ankle is an injury that occurs when you twist, roll or turn the ankle in an awkward way. This kind of movement, not standard with normal walking or movement, can stretch or tear the ligaments that hold the ankle bones together. “The ankle is supported laterally by the anterior talofibular ligament (ATL), the fibula-calcaneal ligament (FCL), and the posterior talofibular ligament (PTL). In ankle sprain, the ATL usually is ruptured first: only then can the FCL divide. If the ATL is ruptured, examination for concomitant rupture of the lateral FCL must be performed: 64% of persons injure the ATL alone, whereas 17% also injure the lateral FCL. The PTL rarely ruptures.”1

Treatment for a sprained ankle depends on the severity of the injury. Although self-care measures and over-the-counter medications may be all you need, a medical evaluation might be necessary to reveal how badly the ankle is sprained and to what is required for recovery. “Prophylactic control of rear foot motion using orthotics is indicated in these patients. Ankle sprain is treated according to its classification – see table below. Surgery is rarely indicated because the extreme fragmentation of ligaments makes repair difficult. Some surgeons use plaster casts for solitary ATL ruptures but recommend surgical repair if the FCL is torn.2

 ATC EM October 1

Coding for an ankle sprain requires a look-up in the alphabetical index of the ICD-9CM code book. Look for sprain, ankle, which shows the code 845.00 (and indented for sprain ankle and foot – 845.00). The final code choice is taken from the tabular index which shows sprained ankle final code choice of 845.00, additional codes are listed for the ligaments and tendon involvement – see table below. The codes in this section of the book can be used as final choice of code, based on the documentation.

Coding under ICD-10CM requires additional codes to support the laterality and encounter of incident in the individual characters of the code. The same process is in place for the final code choice. Start with the alphabetical index by looking for “sprain, ankle”. This shows a code of S93.40. This code requires two additional digits:

  1. Laterality, right side or left side or unspecified side, and
  2. Encounter of incident (A – initial encounter, D – subsequent encounter, and S – sequela).

Most encounters in the emergency department are initial encounters and would require the A as the final character – see table below for a complete breakdown of the codes.

There is a one to one crosswalk (ICD-9 to ICD-10) for sprained ankle, NOS – see table below, but both ICD-9 and ICD-10 contain other types of sprains of ankle region including, but not limited to, what is shown on the table below.

 ATC EM October 2

It is imperative that the provider document exactly what the examination and the diagnostic studies’ findings are, if any, to determine the exact course of action for the condition presented or defined after study. This will also allow the coding staff to select the most appropriate ICD-10 diagnosis code for reporting on the claim for reimbursement.

1 The Merck Manual Seventh Edition, Centennial Edition, Section 5, Page 483, Editor – Keryn A. G. Lane, Publisher – Gary Zelko, June 1999.
2 Ibid at 484.


  • ICD-10-CM, 2014 Complete Draft Code Set, Chapter 19, Page 917, Injury, Poisoning, and Certain Other Consequences of External Causes (S00-T88), AAPC, Optuminsight 2013
  • ICD-9-CM, 2014, Sixth Edition, 9th Revision, Clinical Modification, Chapter 17, Page 312, Injury and Poisoning, Editor – Anita C. Hart, Optuminsight August 2013
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About the author

Robert Bunting, CPC, CPC-H, CHC, CEDC, CEMC, CAC is Compliance Director – Emergency Medicine, web2pro Business Performance Services.