The clinical presentation is most consistent with the quadrigia effect which is caused by overtensioning of the FDP tendon during surgical repair. The FDP tendons share a common muscle belly and have many interconnections. Overtensioning one tendon has a reciprocal effect on the length-tension curve of the remaining three muscle-tendon units, weakening grip strength in these digits.
Malerich et al performed a cadaveric study looking at FDP advancement on hand function. They determined advancement >1cm can lead to an imbalance of muscle function in the profundus system.
In another cadaver study, Kaufmann et al studied maximal grip strength and point of contact in the extrinsic system. They determined that FDP grip strength was optimized when the FDP point of contact was at the DIP. Thus moving the FDP insertion point distal or advancing a lacerated FDP tendon leads to a decrease in grip strength.
Malerich MM, Baird RA, McMaster W, et al. Permissible limits of FDP tendon advancement: An anatomic study. JHS Am1987; 12:30-33.
PMID:3805640 (Link to Abstract)
Kaufmann RA, Kozin SH, Mirarchi A, Holland B, Porter S. Biomechanical analysis of flexor digitorum profundus and superficialis in grip-strength generation. Am J Orthop (Belle Mead NJ). 2007 Sep;36(9):E128-32.
PMID:17948164 (Link to Abstract)