Without seeing the Op Report, this is hard to help you with. But, I can think of a couple of scenarios where these two codes could be considered together. The first is for the repair of a Flexor Digitorum Profundus tendon to a finger of relatively recent up to chronic origin, most likely traumatic such as from a laceration for which it was decided to do a "Delayed repair." Since 26370 is for Repair/advancement of a Profundus Tendon with intact Sublimis/superficialis tendon, this repair is is going to be in the distal finger near the DIP joint to the distal phalanx or the distal "stump" of the Profundus. In this situation, any exploration, dissection, identification, isolation, mobilization, and debridement of scar tissue or synovium (Synovectomy) for the proximal portion of the tendon, this code is going to include all of this as part of 26370, and the 26145 (Synovectomy, tendon sheath, radical tenosynovectomy, flexor tendon, palm &/or finger, each tendon) would not be allowed as a separate procedure. The longer the time frame from the original injury to the delayed repair, the more dissection, etc. will be required to accomplish the mobilization and repair. Although the proximal tendon rarely retracts all the way back into the palm, the post-traumatic inflammatory and scarring reaction may extend back to the palm level so the surgery may have to go back that far to mobilize the tendon. Even then, the 26370 would include all that was necessary to accomplish the ultimate repair.
The other scenario that comes to mind is in the case of a chronic proliferative, destructive tenosynovitis of the flexor tendons, such as Rheumatoid Arthritis, where the chronic inflammation progressively damages and weakens the flexor tendon to the point that a tendon ruptures. This usually is going to be at the wrist and palm level of the hand. To repair a "ruptured" Profundus Tendon in this situation might require dissection, debridement/synovectomy, and mobilization of the distal tendon out into the finger far enough to accomplish the repair (26145). However it is unlikely that this inflammatory synovitis situation is only going to apply to one flexor, because the inflammation/tenosynovitis usually affects all the flexors such that 25115: Radical Flexor Tenosynovectomy of the Wrist and Hand would be a more likely procedure than just 26145. In this scenario, the Synovectomy would be the primary procedure, and the tendon repair (26370) would be secondary with the appropriate modifier (probably 51).
My best "guess" is that you are dealing with the first scenario. As such, if you are going to appeal the 26145 portion of your claim, then the Operative Report is going to have to clearly document that there was a sufficient amount of time and energy/work done during the procedure to "justify" this additional code. The Op Report will have to be included with your appeal.
I hope this helps some.
Respectfully submitted, Alan Pechacek, M.D.