Flexor pollicis longus tendon repair in patients with Linburg-Comstock anomaly

Dear Sir,

This letter discusses Linburg-Comstock anomaly in relation to repair of the flexor pollicis longus (FPL) tendon. Linburg-Comstock anomaly is usually a result of an anomalous intertendinous connection between the FPL and index finger flexor digitorum profundus (FDP) tendon at the level of the carpal tunnel or distal forearm. Less commonly, it results from a shared muscle belly between the FPL and FDP tendons. Epidemiological studies demonstrate that it is a relatively common, yet frequently unrecognized, anomaly that occurs in around a third of the population, more commonly in women than men and bilaterally rather than unilaterally (Hamitouche et al., 2000; Linburg and Comstock, 1979).

A 42-year-old lady re-presented with a rupture of her left thumb zone 2 four-strand modified Kessler repair of her FPL tendon on the sixth day following surgery. She had lifted an object with her fingers, whilst her thumb was still restrained in the splint. She was aware of her thumb flexing against the restraining velcro strap and then felt a pop. Afterwards, she was not able to flex at her interphalangeal joint (IPJ).

Re-exploration revealed that the ruptured proximal FPL tendon stump advanced or retracted when the index distal IPJ (DIPJ) was passively extended or flexed, demonstrating the presence of Linburg-Comstock anomaly. The FPL tendon was re-repaired using the same technique, but this time a dorsal hood including the fingers was fashioned, and no subsequent rupture occurred. Linburg-Comstock anomaly was confirmed post-operatively when the patient actively flexed her left index finger DIPJ, and the IPJ of the re-repaired thumb also flexed.

The increased rupture rate of FPL tendons, compared with other flexor tendons, is attributed to the comparative difficulty of repairing an FPL tendon, the relative avascularity of the FPL tendon in Zone 2, and the increased mobility of the thumb compared with the fingers (Sirotakova and Elliot, 2004). A literature search did not reveal any previous case of Linburg-Comstock anomaly being identified as a possible cause of rupture of an FPL tendon repair.

The author has devised a means of splintage that takes advantage of the Linburg-Comstock anomaly and should reduce the risk of FPL rupture; it has been used successfully on three subsequent patients. The thumb is splinted as per usual, but additionally, the index finger is splinted in full extension (Figure 1). This takes tension off the FPL repair site by holding the proximally divided portion of the lacerated FPL tendon out to length through its connection to the extended index FDP tendon. The exercise regimen should be modified such that both the index finger and thumb are mobilized, and immobilized, simultaneously.

OPEN IN VIEWER

Figure 1.

Splint designed for patient with Linburg-Comstock syndrome, with the dorsal thumb hood combined with a dorsal hood holding index finger in extension.

In conclusion, this letter hopes to bring to attention this relatively common anomaly of the flexor tendons that should be looked for in the pre-operative, intra-operative, and post-operative settings for all patients with FPL tendon injuries. When Linburg-Comstock anomaly is identified, splinting regimens should include both the index finger and thumb, and the exercise regimen modified to reduce the risk of tendon rupture.