Spontaneous rupture of the flexor digitorum superficialis tendon of the little finger with aplasia of the flexor digitorum profundus tendon

Abstract

Dear Sir,

A 54-year-old woman was referred with inability to flex her dominant right little finger (Fig 1). Four weeks earlier, she had felt a snap in the hand when she squeezed a towel and suddenly became unable to flex the proximal interphalangeal joint of the finger. She had been unable to flex the distal interphalangeal joint in the same finger since birth. She also had 20° flexion contractures of the proximal interphalangeal joints of both little fingers. She had no history of previous hand injury, tenosynovitis or inflammatory arthritis. X-ray and computed tomography showed no bony abnormalities. MRI showed that the flexor digitorum profundus (FDP) tendon was completely absent and the flexor digitorum superficialis (FDS) tendon was not in continuity in the distal palm (Fig 2). The cross-section of the FDS tendon at the base of proximal phalanx was less than 50% of that in the contralateral little finger on the MRI. Spontaneous rupture of the FDS tendon and aplasia of the FDP tendon were diagnosed.

Fig 1.

Absence of active flexion of both the distal and proximal interphalangeal joints of the little finger.

Fig 2.

MRI indicates the absence of the FDP tendon in the left little finger. The arrowhead on the left shows the distal stump of the ruptured FDS tendon that was confirmed at operation. The cross-section of the FDS tendon (arrow, right) at the base of the proximal phalanx is less than 50% of that of the contralateral tendon.

Surgical exploration 6 weeks after the incident confirmed absence of the FDP tendon and an intratendinous rupture of the FDS tendon in the proximal part of zone II. There was no bony prominence or exposed joint on the floor of the sheath. The tissue obtained when refreshing the ruptured ends of the FDS tendon was sent for histological examination, which revealed a nonspecific mild fibrosis of the tendon stump. The ruptured tendon was repaired with a four-strand cruciate suture and a running circumferential epitendinous suture. The patient has regained nearly full motion of the proximal interphalangeal joint and returned to her original job as a dental hygienist.

Most closed ruptures of the flexor tendons have predisposing pathological conditions that include bone abnormalities, rheumatoid arthritis, tenosynovitis and infection. Spontaneous rupture of a flexor tendon, defined as a rupture that occurs within the tendon substance in the absence of underlying pathology, is infrequent but occurs most frequently in the little finger (62%) (Bois et al., 2007). The majority of the reported cases of spontaneous tendon ruptures are those of the FDP; concomitant ruptures of the FDS tendon have been reported in a small proportion (4 of 46) of cases (Bois et al., 2007). Isolated spontaneous rupture of the FDS has not been reported, possibly because there is little functional limitation. However, the rupture of the FDS in our patient became symptomatic because of congenital absence of the FDP tendon. Anomalies of the FDP tendons are rare. Furrer et al. (2007) reported a case of a 9-year-old boy with aplasia of the FDP of the little finger. They also noted that the little finger was slightly hypoplastic, although the FDS was functional and the patient had no functional limitations.

A classic experiment with Achilles’ tendons in rats showed that normal tendons do not rupture in their substance unless approximately 50% of the fibres are severed (McMaster, 1933). The cross-sectional size of the FDS tendon in our patient was less than 50% of that in the contralateral little finger. Focal avascularity has also been implicated as a possible cause of spontaneous tendon ruptures. Lundborg et al. (1977) investigated the vascular supply to the flexor tendons within the digital sheath and showed that the FDS is nourished by two separate vascular systems and that a short segment is devoid of intrinsic vascular supply at the base of the proximal phalanx. This avascular area becomes larger with increasing age. The location of the rupture of our patient occurred in the avascular zone of the FDS tendon. Hypoplasia of the tendon and hypovascularity within the tendon might have been factors in the spontaneous rupture of the FDS tendon.

Toshiki Miura, MD, PhD, Naoto Tokuyama, MD and Junichi Ohya, MD Department of Orthopaedic Surgery, Faculty of Medicine, The University of Tokyo, Tokyo, Japan E-mail: MIURA-ORT@h.u-tokyo.ac.jp

Footnotes

Conflict of interests

None declared.

References

Bois

Johnston

Classen

. Spontaneous flexor tendon ruptures of the hand: case series and review of the literature. J Hand Surg Am. 2007, 32: 1061–71.

Furrer

Schweizer

Meuli-Simmen

. Aplasia of the flexor digitorum profundus tendon of the small finger. J Hand Surg Eur. 2007, 32: 111–12.

Lundborg

Myrhage

Rydevik

. The vascularization of human flexor tendons within the digital synovial sheath region – structural and functional aspects. J Hand Surg. 1977, 2: 417–27.

McMaster

. Tendon rupture and muscle ruptures. Clinical and experimental studies on the causes and location of subcutaneous ruptures. J Bone Joint Surg. 1933, 15: 705–22.