Orthopedic Coding Alert

Warning:  ICD-9 doesn't include a diagnosis code for this condition

If you can recognize an os trigonum procedure from the start, you can narrow your coding options pretty quickly. The key is to look for the foot surgeon's documentation of a posterior tibial impingement.

How it works: -Os trigonum- is a condition that results when the patient's lateral tuberosity does not fuse with the talus. Some experts believe that up to 15 percent of the population has an os trigonum, although many of these people never realize that they have the condition.

Generally, an os trigonum creates no problems, but if the os trigonum gets lodged in the wrong place, it  can cause impingement that creates pain and affects range of motion. Foot surgeons might refer to this condition as os trigonum syndrome, posterior ankle impingement (PAI) syndrome, or posterior tibiotalar impingement syndrome (PTTIS).

Typically, people who frequently assume plantarflexion (foot pointed downward) positions experience posterior impingement from this accessory bone. Ballet dancers, soccer players, runners and volleyball players are likely candidates.

Pinpoint the Right Diagnosis Code

Once you know you-re dealing with an os trigonum procedure, the challenging part is choosing the right ICD9 Code, because ICD-9 does not include a specific code for os trigonum syndrome, says Richard Odom, DPM, CPC, assistant professor in the department of surgery at Scott and White Hospital in Temple, Texas.

Your typical options are 726.70 (Enthesopathy of ankle and tarsus, unspecified) or 726.71 (Achilles bursitis or tendonitis). Other more non-specific diagnoses could be 719.57 (Stiffness of joint, not elsewhere classified; ankle and foot), 729.5 (Pain in limb), 755.67 (Anomalies of foot, not elsewhere classified) or 959.7 (Injury; knee, leg, ankle and foot).

Other common diagnoses are 726.72 (Tibialis tendonitis), 727.68 (Nontraumatic rupture of other tendons of foot and ankle), 727.81 (Contracture of tendon [sheath]) and 727.89 (Other disorders of synovium, tendon and bursa; other), says Annette Grady, CPC, CPC-H, CPC-P, healthcare consultant and certified PMCC instructor in Bismarck, N.D.
 
You may also find the 754.5x series (Varus deformities of feet) assigned to this condition. Just be sure to take a careful look at the doctor's charts so you can match the most appropriate ICD-9.

Cozy Up to the Op Note

After the foot surgeon verifies the os trigonum as the cause of the posterior tibial impingement and more conservative treatment methods have not helped the condition, he may opt to excise this small bone.
 
In most cases, the surgeon will make an incision behind the ankle, and once he identifies the os trigonum, he dissects it free of its surrounding soft-tissue attachment, Odom says. For this procedure, most coders report 28120 (Partial excision [craterization, saucerization, sequestrectomy, or diaphysectomy] bone [e.g., osteomyelitis or bossing]; talus or calcaneus), he adds. In addition, the American Orthopaedic Foot and Ankle Society recommends reporting 28120 for os trigonum excisions.

But because CPT does not include a code for removing an accessory bone, your payer might scrutinize 28120 if the surgeon isn't dealing with osteomyelitis or other diseased bone conditions. If this is the case, report 28899 (Unlisted procedure, foot or toes) with good documentation explaining that the surgeon performed an excision of an accessory foot bone.