What Is The Correct Code For PTTD?

Over the years, many colleagues have asked me what diagnosis code they should use for patients with PTTD. When ICD-10 was being introduced several years ago, I assumed that the long-ignored condition of posterior tibial tendon dysfunction (PTTD) would finally have its own diagnosis code. Although disappointing, but not surprising, the coding experts who gave input into the new ICD-10 terminology did not think that PTTD was worthy of an individual code despite its frequency in the general population. Researchers have estimated that 3 out of 100 people in the general population suffer from PTTD.¹

Confounding this issue is the terminology clinicians use in the academic literature to describe a patient who has a progressive symptomatic flatfoot deformity Originally, researchers attributed this condition solely to rupture of the posterior tibial tendon.^2,3Subsequently, studies of cadaver flatfoot models and magnetic resonance imaging (MRI) verified that the multiplanar deformity in patients with PTTD was the result of rupture of key ligaments in the ankle, the hindfoot and midfoot.^4,5

Accordingly, multiple authors proposed the term adult-acquired flatfoot deformity (AAFD) due to the recognition that PTTD was inappropriately attributing the condition to a tendon injury alone and neglecting to recognize the more critical pathology of ligamentous disruption.^6-8While most cases of AAFD start with rupture of the posterior tibial tendon, AAFD can result from conditions other than injury to the posterior tibial tendon. These conditions include trauma, degenerative arthritis and neuromuscular disorders.⁹

In a recent systematic review, Ross and co-workers explored the use of the terms PTTD and AAFD in research studies published in the medical literature, and found that these terms are used interchangeably to describe the same clinical condition.¹⁰However, these authors point out that the two disorders are not identical. For a progressive flatfoot condition characterized with medial ankle pain and evidence of tendon injury, they recommend the term PTTD. Ross and colleagues note that AAFD describes a deformity which may or may not be the result of rupture of the posterior tibial tendon. Adult-acquired flatfoot deformity can be caused by multiple factors including rupture of key ligaments in the ankle, hindfoot and midfoot.¹⁰

However, what do insurance companies recognize in terms of a diagnosis code for an adult patient with a painful, progressive flatfoot deformity? Sadly, there is no code for PTTD. There is not even a code for rupture of this specific tendon. There is a diagnosis code for posterior tibial tendinitis: M76.82.¹¹However, this would only be applicable to stage 1 PTTD, which precedes attenuation and rupture of the posterior tibial tendon which occurs in stage 2 PTTD.²

When billing Medicare for an AFO device, I always recommend using two diagnosis codes, one which describes the disease or injury and another code to describe weakness or deformity. Therefore, stage 2 and 3 PTTD involves an injury, which is a rupture of the posterior tibial tendon that one can describe and code as: Rupture of Flexor Tendon; Ankle and Foot M66.37.¹¹For the deformityitself, it is best to describe and code it as: Pes Planus (acquired) M21.4, and/or Valgus Deformity, ankle M21.07.¹¹

References

1. Kohls-Gatzoulis J, Woods B, Angel JC, Singh D. The prevalence of symptomatic posterior tibialis tendon dysfunction in women over the age of 40 in England. Foot Ankle Surg. 2009;15(2):75-81.
2. Funk DA, Cass JR, Johnson KA. Acquired adult flat foot secondary to posterior tibial-tendon pathology. J Bone Joint SurgAm. 1986; 68(1):95–102.
3. Johnson KA. Tibialis posterior tendon rupture. Clin Orthop Relat Res. 1983;(177):140–7.
4. Deland JT, de Asla RJ, Sung IH, Ernberg LA, Potter HG. Posterior tibial tendon insufficiency: which ligaments are involved? Foot Ankle Int.2005; 26(6):427–35.
5. Perry MB, Premkumar A, Vernzon DJ, Shawker TH, Gerber LH. Ultrasound, magnetic resonance imaging, and posterior tibialis dysfunction. Clin Orthop Relat Res.2003; 1(408):225–31.
6. Deland JT. Adult-acquired flatfoot deformity. J Am Acad Orthop Surg. 2008; 16(7):399-403.
7. Pinney SJ, Lin SS. Current concept review: acquired adult flatfoot deformity. Foot Ankle Int.2006; 27(1):66–75.
8. Henceroth WD, 2nd, Deyerle WM. The acquired unilateral flatfoot in the adult: some causative factors. Foot Ankle.1982; 2(5):304–8.
9. Lee MS, Vanore JV, Thomas JL, Catanzariti AR, Kogler G, Kravitz SR, et al. Diagnosis and treatment of adult flatfoot. J Foot Ankle Surg. 2005; 44(2):78–113. 

10. Ross MH, Smith MD, Vicenzino B (2017) Reported selection criteria for adult acquired flatfoot deformity and posterior tibial tendon dysfunction: Are they one and the same? A systematic review. PLoS ONE. 12(12): e0187201.
11. International Classification of Diseases, Tenth Revision. (ICD-10). Centers for Disease Control and Prevention. https://www.cdc.gov/nchs/icd/icd10.htm