Progressing Flexion Deformity of the Middle, Ring, and Small Fingers With a Rare Congenital Anatomic Difference of Flexor Digitorum Profundus

Background: A flexion deformity caused by a congenital anomaly of the flexor digitorum profundus (FDP) of the middle, ring, and small fingers is extremely rare, and it has previously been described only in isolated case reports. Hence, there has been no consensus with regard to the clinical presentation, etiology, and treatment. Methods: We retrospectively analyzed our 10 cases (5 male individuals and 5 female individuals) for congenital FDP abnormalities. We obtained radiography, computed tomography, and magnetic resonance imaging on our patients. Nerve studies were performed in 7 of 10 patients, except for 3 patients below 5 years of age who were unable to co-operate. We used the grading criteria (Wang classification) to evaluate the restricted extension of the affected fingers and the active flexion function. An abnormal fibrous cord was seen intraoperatively in the proximal part of the belly of the FDP that was destined for the affected fingers. It originated from a bony prominence on the proximal part of the ulna. On resection of the aberrant cord, extension of the affected fingers was immediately improved. Pathologic examination of the removed aberrant cord revealed dense fibrous connective tissue. Results: Nerve conduction studies and electromyography revealed that there was no substantial damage to the median and/or ulnar nerves. Plain radiography revealed no bone or joint anomalies. Computed tomography showed a slight bony prominence at the proximal part of the ulna. However, magnetic resonance imaging indicated a demonstrably abnormal fibrous cord in the FDP that originated from a bony prominence at the proximal part of the ulna and extended toward the middle, ring, and small fingers. On the basis of the Wang classification criteria for functional evaluation, 7 were moderate, and 3 were severe. Patients were followed-up for 2 to 36 months with a mean follow-up of 16 months. The postoperative outcomes were excellent in 8 cases and fair in 2 cases. The flexion and extension functions were regained, and there was no relapse of deformity. Conclusion: On the basis of its pathologic features, we recommend that this condition be treated by resection of the abnormal cord. Level of Evidence: Level IV.