Tendon Variations of the Flexor Digitorum Superficialis of the Little Finger in Cadaveric and Physical Examination Evaluations

Abstract

IntroductionFlexor digitorum superficialis (FDS) is located in the intermediate layer of the forearm muscles. Typically, it consists of four tendons that enable the movement of the index, middle, ring and little finger. The tendon to the fifth digit is known to be greatly varied in both cadaveric and physical examination assessments. It has been reported to be absent or interconnected with the FDS tendon to the fourth digit, what might have an impact upon the hand‐grip strength. Some of the researchers state that absence of the FDS to the 5th digit does not impinge the finger's movement, whilst others maintain that absence of both the palmaris longus (PL) and the FDS to the little finger results in weaker response of the latter muscle. The FDS tendon can be used during the correction of the paralysis of the intrinsic muscles of the hand, e.g. in the claw finger deformity or radial/median nerve palsies.AimThis study aimed to present the up‐to‐date pooled prevalence estimate (PPE) of the presence or absence of the FDS tendon to the little finger, as well as its laterality, functional assessment during the physical examination, coexistence of its absence with the absence of the PL and probing for sources of heterogeneity.Materials and methodsA thorough search of the major medical online databases was conducted by the authors, who further enhanced it by checking the references of the primarily identified studies. The studies that met the inclusion criteria had their data extracted and analysed in this Meta‐analysis. The AQUA tool applied whilst evaluating the quality of the included studies.ResultsA total of 31 studies (13 538 hands) were assessed in this study. The overall PPE of the presence of the FDS tendon to the fifth digit was 92.7% (95% CI: 88.5–96.0), found slightly more often in cadaveric studies (97.7%, 95% CI:95.1–99.4) than in the physical examination (90.4% 95% CI: 84.9–94.8). It was the most commonly present in reports from Europe (94.6%, 95% CI: 82.9–100.0) and slightly more common amongst the male patients (90.8%, 95% CI: 79.5–98.2). In the functional assessment, the FDS to the little finger was predominantly independent (62.5%, 95% CI: 47.0–73.6), but the common function was also frequent (29.9%, 95% CI: 17.4–42.2). Both FDS and the PL were present in 81.0% (95% CI: 62.3–89.5), but the presence of of the FDS with the absence of the PL was also quite common (11.7%, 95% CI: 2.7–23.6).ConclusionsThis study showed that the FDS to the little finger is predominantly present. Notwithstanding, the common function was also very frequent (29.9%), what facilitates the need to be vigilant whilst evaluating clinically its function and not necessarily assuming the tendon's absence when a patient has troubles with flexing the proximal interphalangeal joint without the help from the flexor digitorum profundus.Support or Funding InformationThis study was supported by “The Best of the Best! 3.0 (Najlepszy z Najlepszych! 3.0)” Grant of the Polish Ministry of Science and Higher Education.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.