There is much missing information here. In particular which tendons "ruptured" (strained) many years ago and more recently? Were they flexors or extensors of the foot/toes? Were they the tendons of muscles originating in the lower leg (i.e. long toe flexors or extensors), or muscles within the foot (intrinsic muscle of the foot)? Were these tendon "ruptures" Traumatic or Atraumatic/Spontaneous, or possible one of each?
If they were Traumatic, you should look at S96.01, S96.11, and S96.21, depending on which tendons they were. You could use the 7th Character of S, with "Chronic Foot Pain" being the Sequela. M79.67 _ would apply to Foot Pain. Adding G89.21 for "Chronic pain due to trauma" is "iffy." M79 does not Exclude G89, but G89 Excludes(2) M79, so it could still be added to help clarify the situation.
If they were "Spontaneous/Atraumatic" Ruptures, then that is different. Atraumatic/Spontaneous tendon ruptures occur in diseased tendons that are "weakened" by the disease process so that they rupture during normal levels of activity. The most common in the foot and ankle region is the Posterior Tibialis as a result of Chronic Posterior Tibialis Tendonitis. Other long toe flexors could also do this if also diseased. In the foot, the flexors are the most likely to do this, rarely the extensors. As such, the coding for these would be M66.37 _. If the underlying disease is identifiable, then it should also be coded. You could still use the M79.67 _ code as above, but the G89.21 code couldn't, but G89.28 for "Other chronic post-procedural pain" might since there has been a previous surgical tendon repair.
Hopefully, your situation is not a matter of one being a "Traumatic" tendon rupture/strain and the other a "Spontaneous/Atraumatic" rupture/strain. That would really make coding this this fun.
For further discussion of Tendon Ruptures, I would refer you to my Blog on this subject at icd10orthocoder.com/blog.
Hopefully this helps some.
Respectfully submitted, Alan Pechacek, M.D.
icd10orthocoder.com