A Study of Extensor Pollicis longus and brevis and Abductor pollicis longus from the perspective of Evolution

Abstract

Background:The Extensor pollicis longus and brevis and abductor pollicis longus muscles have evolved progressively in different primates according to the function expected from the pollux finger. Analysis of individual muscles in different primates can help our understanding of evolution. Aims and objective: The present study was undertaken to study these three muscles and to note the variations therein and to attempt to explain the existence of these variations on the probable basis of their evolutionary history. Methodology: The extensor pollicis longus, brevis and abductor pollicis longus muscles were dissected meticulously in 100 upper limbs of adult cadavers. Results: In case of extensor pollicis longus and extensor pollicis brevis, 2% incidence of duplication of muscle and 1% of duplication of tendon and 1% incidence of duplication of muscle and 2% of duplication of tendon was observed respectively. In case of abductor pollicis longus 23% incidence of variation was observed. The muscle was observed to split into multiple tendons of muscles to have widespread attachment beyond the 1st metacarpal bone. Conclusion: The extensor pollicis longus with minimum variation seems to have settled in its evolutionary trajectory. In 8% of abductor pollicis longus studied, superficial and deep heads were observed. Oudenaarde states that the superficial head is used for range of movement and the deep set of fibers are used for strength of contraction. Elliot observes that the wide attachment of the abductor pollicis longus on the muscles abductor pollicis brevis and the opponens pollicis, the 1st carpometacarpal joint capsule and trapezium bone could be for better anchorage for radial deviation at the wrist joint. The extensor pollicis brevis muscle is seen as a separate muscle only in humans, hylobatids and gorillas whereas in all other primates. The chimpanzee hand seems to have evolved one step further with two extensor pollicis brveis muscles.

Anatomical variations in the first dorsal compartment of the wrist: meta-analysis

“…In contrast of APL, EPB dominates with its single-tendon variety, both in cadavers and in patients with de Quervain's disease. Our results differ from previous major studies regarding prevalence of all EPB variations [3,8,25,37,42,50,68]. Comparing other varieties of EPB in both groups, it can also be accompted, that there are no statistically significant differences between cadavers and patients with de Quervain's disease, when it comes to anatomical variations of EPB in the first dorsal compartment (p > 0.05).…”

“…Our results differ from previous major studies regarding prevalence of all APL variations [3,8,25,37,42,68]. Our results shows that mostly occurs the double-tendon APL variety with its 43.45% prevalence overall, 46.04% prevalence in cadavers and 45.33% prevalence in patients with de Quervain's disease.…”

“…However, many studies have showed multiple anatomical variations in the first dorsal compartment. Most frequently reported anomalies are multiple APL tendons, multiple EPB tendons and the presence of the intercompartmental fibro-osseus septum [3,8,25,42,50]. Unfortunately, studies describing those variations are not consistent.…”

Anatomical variations of the abductor pollicis longus: a pilot study

“…Different types of accessory band insertions have been described in the literature [2][3][4][5][6][7][8][9][10]13], and such great morphological variability is believed to have an embryological basis.…”

“…The APL demonstrates a high degree of variability with regard to the number of its accessory bands and their insertion [2][3][4][5][6][7][8][9][10]. The presence of multiple tendons originating from the APL is clinically relevant, as it can lead to the development of de Quervain's syndrome, which is caused by stenosing tenosynovitis.…”