Palmaris Longus Muscle Anatomy

Overview
Origin Medial epicondyle of humerus (via common flexor tendon)
Insertion Palmar aponeurosis and flexor retinaculum of hand
Action Flexion at the wrist joint
Stabilizes palmar aponeurosis
Nerve Median nerve (C7-C8)
Artery Median artery
Anterior branch of ulnar recurrent artery

Location & Overview

The palmaris longus muscle is located in the superficial anterior compartment of the forearm and is a narrow muscle which is wider in the middle and narrower at its ends (fusiform shaped). It is located between the flexor carpi radialis muscle and the flexor carpi ulnaris muscle. It is also superficial to the flexor digitorum superficialis and part of the palmaris longus muscle overlaps the median nerve [1].

The palmaris longus can have variations which differ between individuals. Examples of this are: fusion with another muscle, an additional muscle belly, multiple tendinous insertions, or being entirely absent from one of both arms. Exact amounts of the population missing this muscle vary between studies, but have it has been suggested to be somewhere within the range of 2.5% to 26%. The proportion of people missing this muscle also varies depending on the demographic of population studied (e.g ethnicity or gender) [2] [3] [4] [5].

palmaris longus muscle

Here we can see the palmaris longus muscle in isolation.

palmaris longus muscle from a superficial view

Here we can see the palmaris longus muscle from a superficial view amongst the other muscles of the arm.

Origin & Insertion

The palmaris longus muscle originates on the medial epicondyle of humerus via the common flexor tendon. The common flexor tendon also serves as an attachment point for the flexor carpi ulnaris, palmaris longus, flexor carpi radialis, pronator teres, and flexor digitorum superficialis. The palmaris longus then inserts at the palmar aponeurosis and flexor retinaculum of the hand. The flexor retinaculum contributes to forming the carpal tunnel [6] [7].

origin of the palmaris longus on the medial epicondyle

Here we can see the origin of the palmaris longus on the medial epicondyle of the humerus (highlighted in red).

insertion of the palmaris longus on the flexor retinaculum

Here we can see the first insertion of the palmaris longus which is the flexor retinaculum of the hand (highlighted in blue).

insertion of the palmaris longus on the palmar aponeurosis

Here we can see the second insertion of the palmaris longus which is the palmar aponeurosis (highlighted in blue).

Actions

The actions of the palmaris longus are to flex the hand at the radiocarpal (wrist) joint and to stabilize the palmar aponeurosis (which can improve the stability of the overlying palmar skin). The contribution of this muscle to flexion is minimal and it is considered just an accessory muscle during wrist flexion [8].

Innervation

The palmaris longus is innervated by the median nerve (C7-C8) [9] [10] [11].

Blood Supply

Blood is supplied to the palmaris longus via the median artery and the anterior branch of ulnar recurrent artery [12].

Want some flashcards to help you remember this information? Then click the link below:
Palmaris Longus Flashcards

References

References
1, 2, 7, 11 Olewnik Ł, Wysiadecki G, Polguj M, Podgórski M, Jezierski H, Topol M. Anatomical variations of the palmaris longus muscle including its relation to the median nerve – a proposal for a new classification. BMC Musculoskelet Disord. 2017;18(1):539. Published 2017 Dec 19. doi:10.1186/s12891-017-1901-x
3 Georgiev GP, Iliev AA, Dimitrova IN, Kotov GN, Malinova LG, Landzhov BV. Palmaris Longus Muscle Variations: Clinical Significance and Proposal of New Classifications. Folia Med (Plovdiv). 2017 Sep 1;59(3):289-297. doi: 10.1515/folmed-2017-0035. PMID: 28976893.
4, 6, 8, 10, 12 Cooper DW, Burns B. Anatomy, Shoulder and Upper Limb, Hand Palmaris Tendon. 2021 Sep 3. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30137801.
5 Ioannis D, Anastasios K, Konstantinos N, Lazaros K, Georgios N. Palmaris Longus Muscle’s Prevalence in Different Nations and Interesting Anatomical Variations: Review of the Literature [published correction appears in J Clin Med Res. 2016 Jan;8(1):62]. J Clin Med Res. 2015;7(11):825-830. doi:10.14740/jocmr2243w
9 Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.