A very few authors have taken the measurement of AHFPL, (2,3,7,18) but in our knowledge none of these authors have taken the tendon width at its insertion (Table 1).
(15) Anterior interosseous nerve syndrome (AINS) would be of complete type when the entire of AIN passes posterior underneath the AHFPL belly causing weakness of all the three muscles supplied by it and incomplete type of AINS is likely to occur when only the medial branches of AIN to the FDP which passes beneath the muscle belly is compressed.
CONCLUSION: Although the incidence of AHFPL is variable among the different races, (10) it can be one of the cause for AIN syndrome, pronator teres syndrome, carpel tunnel syndrome, or abnormal sensation in the lower part of the forearm.
Regarding the relationship between the AHFPL and AIN, we found the nerve running posterior to the belly.
It would seem plausible that AINS would be more likely to occur when the nerve passes posterior to the belly of the AHFPL. A complete AINS would be from Type III relationship where the whole nerve passes posteriorly underneath the belly causing weakness in the FPL, FDP of the index and middle fingers, and the pronator quadratus muscles.
The occurrence of the belly of AHFPL is possibly from the development of the common flexor mass in the embryo, which differentiates into superficial and deep layers.