Okajimas Folia Anat. Jpn.. 69(2-3): 77-84, August, 1992 Insertions of the Lumbrical and Interosseous Muscles in the Human Foot By Hideki OUKOUCHI, Takuro MURAKAMI and Akio KIKUTA Section of Human Morphology, Department of Anatomy, Okayama University Medical School, 2-5-1 Shikata-cho. Okayama 700, Japan -Received for Publications, February 5, 1992- Key Words: Human foot, Lumbrical muscle, Plantar interosseous muscle, Dorsal interosseous muscle, Dorsal aponeurosis, neurosis, Dorsal digital expansion Summary: The lumbrical and interosseous muscles in twenty-five feet of Japanese adult cadavers were dissected. The lumbrical muscles mainly continued into the dorsal aponeuroses or the terminal tendons of the extensor digitorum longus muscle, though they occassionally issued some accessory and slender tendons inserting into the bases of the proximal phalanges. Rarely, the lumbrical muscle showed an atavistic anomaly. In this anomaly, the lumbrical muscle was divided into two tails which continued into the bases of the proximal phalanges of the contiguous toes. The plantar and dorsal interosseous muscles were mainly attached to the bases of the proximal phalanges. Frequently, the plantar and dorsal interosseous muscles issued some accessory and small tendons continuing into the dorsal aponeuroses. This fact suggests that the plantar and dorsal interosseous muscles in the foot, like the palmar and dorsal interosseous muscles in the hand, are composite muscles derived from the flexor brevis, contrahens and other muscles. The lumbrical muscles of the human foot are human foot (Fig. 1, 2, 3). These muscles were num- generally regarded as being inserted into the pro- bered from the medial side of the foot (Figs. 1, 2, 3). ximal phalanges (Henle, 1871; Frohse and Frãnkel, No morphological difference of the lumbrical, dorsal 1913; Paturet, 1951; Mortenson and Pettersen, 1966; interosseous and plantar interosseous muscles was Gardner, Gray and O'Rahilly, 1971; Tillman and observed between the male and female cadavers and TOndury, 1987). However, our recent dissection also between the right and left feet. of Japanese feet has revealed that the lumbrical The dorsal aponeurosis of the toe consisted of the muscles mainly end in the dorsal aponeuroses. These tendons of the extensor digitorum longus and brevis are reported in the present paper. The insertions of muscles and the outer and inner tendinous mem- the interosseous muscles are also described and dis- branes arising, together with the deep plantar meta- cussed in relation to their phylogenetic compositions. tarsal ligaments, from the plantar aspect of the neck of the metatarsal bone (Figs. 4, 5, 6). The inner tendinous membranes ran around the neck of the Materials and Methods metatarsal bone, and enclosed the tendons of the extensor digitorum longus and brevis muscles at a Twenty-five feet of Japanese adult cadavers of level between the neck of the metatarsal bone and both sexes, which had been fixed with 10% formalin the head of the proximal phalanx (Fig. 5). Thus, the by vascular perfusion and dehydrated with 60-70% inner tendons extended bilaterally along the proxi- ethanol, were dissected with sharpened forceps under mal phalanx (wing tendons) (Figs. 4, 6). The outer a dissection light microscope. tendinous membrane was thick and band-like, and firmly surrounded the plantar and dorsal interosseous muscles and the enclosed tendons of the extensor Results muscles (see above) (Figs. 5, 6). This band-like outer membrane (annular ligament) only extended at a There were four lumbrical, four dorsal interos- level of the neck of the metatarsal bone (Figs. 4. 6). seous and three plantar interosseous muscles in the The lumbrical muscles arose from the tendons of Address for correspondence: Takuro Murakami, Human Morphology Section, Department of Anatomy, Okayama University Medical School, 2-5-1 Shikata-cho, Okayama 700, Japan. 77 78 H. Oukouchi et al . Fig. 2. Arrangements, origins and insertions of the dorsal inter- osseous muscles in the human foot (right foot Fig. 1. Schematicdiagram showing the arrangements, origins , plantar aspect). D1—D4 first to fourth dorsal interosseous muscles . and insertionsof the lumbricalmuscles in the human foot MB metatarsal bones, PP proximal phalanges. (rightfoot, plantar aspect). L1—L4 first to fourthlumbrical muscles.DP distal phalanges,FH tendonof the flexor at a level of the metatarso-phalangeal joints, some hallucislongus muscle, FL tendonsof the flexordigitorum accessory and slender tendons which were inserted longusmuscle, MB metatarsalbones, MP middle phal- into the bases or basal portions of the proximal anges,PP proximalphalanges, WT wingtendons of the phanges (Fig. 4) (Table 1). dorsalaponeuroses. In one of the twenty-five feet, the third and fourth lumbrical muscles were divided into two (medial the flexor digitorum longus muscle, as far back as and lateral) tails, which reached the contiguous their angles of separation, and, with the exception sides of the adjacent fingers (Fig. 7). More strictly, of the first one which arose only from the medial the medial and lateral tails of the fourth lumbrical border of the first tendon of the flexor digitorum muscle and the lateral tail of the third lumbrical longus muscle, each sprang from two adjacent ten- muscle were further divided into the two tendons dons (Fig. 1). which were inserted into the wing tendons of the The lumbrical muscles ran plantar to the deep dorsal aponeuroses and the bases of the proximal plantar metatarsal ligaments, and ended, at a level phalanges; the medial tail of the third lumbrical of metatarsophalangeal joints, in tendons which, muscle was solely inserted into the base of the pro- passed distally on the medial sides of the four lesser ximal phalanx (Fig. 7). toes and formed the distal ridges of the medial wing The dorsal interosseous muscles were bipennate tendons (see above) of these toes (Figs. 1, 4, 6). muscles, each arising by two heads from the adjacent Occasionally, the tendons of the lumbrical muscles sides of two metatarsal bones; the first one reached were attached to or mixed with the medial terminal the medial side of the second toe, the other three tendons of the extensor digitorum longus muscle, ones passing to the lateral sides of the second, third and inserted into the dorso-proximal parts of middle and fourth toes (Fig. 2). The plantar interosseous and distal phalanges (Fig. 4). In addition to these muscles arose from the bases and medial sides of the insertions, the lumbrical muscles occasionally issued, third, fourth and fifth metatarsal bones, and reached Lumbrical and Interosseous Muscles in the Human Foot 79 Fig. 3. Arrangements, origins and insertions of the plantar interosseous muscles in the human foot (right foot, plantar aspect). P1—P3 plantar interosseous muscles. MB Meta- tarsal bones, PP proximal phalanges. Fig. 4. Dorsal aponeurosis of the third toe (right foot, dorsal aspect). Note that the dorsal aponeurosis (DA) was formed by the tendons of the extensor digitorum longus (EL) and brevis (EB) muscles and the outer (OL) and inner (IL) membranous ligaments arising from the plantar aspect of the metatarsal bone (MB). The distal and bilateral segments of the inner ligment are referred to as the wing tendons (WT). Also note that the second lumbrical muscle (L2) ends in the tendon (thick arrowhead), which forms the distal ridge of the medial wing tendon and continues into the medial terminal tendon of the extensor digitorum longus muscle, and that this lumbrical muscle issues an accessory and slender tendon (thin arrowhead) which is inserted into the base of the proximal phalanx. Further- more, it should be noted that the third dorsal (D3) and first plantar (P1) interosseous muscles are attached to the bases of the proximal phalanx (thick arrow), and that the first plantar interosseous muscle issues a small slip (thin arrow) continuous with the wing tendon. DP distal phalanx, LT lateral terminal tendon of the flextor digitorum longus muscle, MT medial teminal tendon of the flexor digitorum longus muscle, MP middle phalanx, PP proximal phalanx, TL deep transverse metatarsal ligament. 80 H. Oukouchi et al. Table 1. Combinations and occurrence of main and accessory tendons of the first to forth lumbrical muscles (L1—L4) in 25 human feet. The main tendon (M) is inserted into the wing tendon of the dorsal aponeurosis or mixed into the medial terminal tendon of the extensor digitorum longus muscle, while the accessory one (A) is attached to the base of the proximal phalanx (see text). Aberrant cases are shown in Figure 7 (see text) Lumbrical Muscles the medial sides of the same toes (Fig. 3). The dorsal and plantar interosseous muscles ended, just proximal to the metatarsophalangeal Fig. 5. Dorsal aponeurosis (transeversely cut form, at a level of joints, in their terminal tendons which were attached the neck of the third metatarsal bone, right foot, proximal to the bases of the proximal phalanges (Figs. 2, 3, 4) aspect). Note that the dorsal aponeurosis (DA) is formed (Table 2). In addition to these main insertions, the by the outer (OL) and inner (IL) membranous ligaments dorsal and planter interosseous muscles frequently continuous with the deep plantar metatarsal ligament (TL). gave off, near the metatarsophalangeal joints, some EL and EB tendons of the extensor digitorum longus and accessory and small tendons or slips which were brevis muscles, D3 and P1 third dorsal and first plantar inserted into the wing tendons of the dorsal apo- interosseous muscles, L2 second lumbrical muscle, MB neuroses (Fig. 4) (Table 2). third metatarsal bone. sules of the metatarsophalangeal joints. These find- Discussion ings are consistent with the descriptions of the pre- vious authors, including Henle (1871). However, few The present study reveals that the lumbrical authors have described the additional insertions of muscles of the human foot have constant and thick the interosseous muscles into the dorsal aponeuroses insertions into the dorsal aponeuroses of the toes, of the toes or into the capsules of the metatarso- though they occasionally have some accessory and phalangeal joints.