Variations of the Lumbrical Muscles of the Hand S. S. BASU’ AND S. H A U R Y ’ Department of Anatomy, Yak University School of Medicine, New Haven, Connecticut The lumbrical muscles constitute an important part of the intrinsic musculature of the hand. A most distinctive feature is their origin from flexor tendons and insertions into extensor expansions. Although several deviations from normal or variations of the lumbricales have been described in standard textbooks of gross anatomy and other surgical or anatomical publications, a review of the basic anatomy of the lumbricales will be helpful. Usually they are 4 cylindrical muscles that arise from the profundus tendons and approach the radial aspects of the metacarpophalangeal joints ventral to the transverse metacarpal ligaments for their insertion to the extensor expansion. The first and second lumbricales are unipennate. The third and 4th lumbricales are bipennate in origin and arise from adjacent tendons of deep flexor muscles. During the present investigation previously undescribed variations of the lumbrical origins or insertions were noted. This paper describes the variations and presents data on the normal frequency as well as the frequency of the more common and previously described variations. MATERIALS AND METHODS The data for this report were obtained from dissections of 36 adult cadavers ( 5 female and 31 male). Because both right and left hands were observed, this study included a total of 72 hands and 287 lumbrical muscles. The dissections were done by students in the dissecting rooms and in most instances completed by the investigators who examined each of the specimens and recorded on sketches the details of the lumbrical musculature. OBSERVATIONS In 72 hands which were dissected the following observations were made. Only 6 cadavers had in both hands origins, insertions and distributions of the lumbricales that are described in most anatomical texts as being normal, that is, 4 lumbricales inserting in the radial side of the extensor expansion, the two lateral (radial) lumbricales being unipennate and the two medial bipennate (table 1 fig. 1), In addition to the 12 hands mentioned above, 9 other cadavers had a “normal” lumbrical musculature of the right hand and 9 had “normal” lumbricales in the left hand. A total of 30 of the 72 hands were thus “normar according to the usual textbook description of the lumbricales. The first lumbrical muscle consistently conformed to the usual pattern both in its origin and insertion. Sixteen of 72 (22.2% ) second lumbricales arose from the profundus tendons adjacent to the second and third digits (figs. 5, 7 and 8) and two (2.8% ) had bifid insertions, on adjacent sides of the second and third digits (fig. 7). All the third lumbricales showed the normal bipennate origin from the profundus tendons adjacent to the third and 4th digits. Fifteen of 72 (20.8% ) had bifid insertions to adjacent sides of the third and 4th digits (fig. 7) and 9 (12.5% ) were attached only to the ulnar side of the third digit (figs. 2, 4). The 4th lumbricales differed most extensively both in origin and insertion. Two of 71 (2.8%) presented unipennate origins from the radial side of the profundus tendon to the 5th digit (fig. 8 ) . In one right hand the lumbrical muscle was missing (fig. 6). Eight of 71 (11.2%) 4th lumbricales had bifid or split insertions that attached to the adjacent sides of the 4th and 5th digits (fig. 5), and 4 (5.6% ) were inserted only to the ulnar 1 International Co-operation Administration FelIow (1958-1959). Permanent address: S. C. B. Medical College, Cuttack, Orissa, India. 501 502 S . S . BASU AND S . HAZARY TABLE 1 Frequency of "normal" and of variations of lumbrical musculature as revealed by dissection of 72 hands Left hand Right hand Types' Normal 1 2 3 4 5 6 Bofh hands Number Per cent Number Per cent Number Per cent 15 20.8 9.7 1.4 13.9 4.2 2.8 1.4 5.5 2.8 15 9 1 5 6 0 0 4 2 20.8 12.5 30 16 2 15 9 2 1 8 4 41.7 7 1 10 3 2 1 4 2 7 8 1.4 6.9 8.3 - 5.5 2.8 22.2 2.8 20.8 12.5 2.8 1.4 11.2 5.6 - - 'Normal (see text). 1. Bipennate origin of the second lumbrical muscle. 2. Bifid insertion of the second lumbrical muscle. 3. B S d insertion of the third lumbrical muscle. 4. Insertion of the third lumbrical muscle on the ulnar side of the third digit. 5. Unipennate origin of the 4th lumbrical muscle. 6. Fourth lumbrical muscle missing. 7. Bifid insertion of the 4th lumbrical muscle. 8. Insertion of the 4th lumbrical muscle to the ulnar side of the fourth digit, TABLE 2 Combination of variations of lumbrical muscles as revealed by dissection of 72 hands Types1 1 and4 1 and 3 1,2and 3 3 and 7 4 and 5 1 and 5 1 and 7 4 and 7 1 and2 4 and 8 1 Right side Left side 1 2 1 2 I 1 0 0 0 0 0 2 0 0 0 0 1 1 1 1 Both 1 4 1 2 1 1 1 1 1 1 See table 1. side of the 4th digit (fig. 3 ) . Different combinations of variations in the lumbricales were aIso observed (table 2). DISCUSSION Standard textbooks of gross anatomy and other relevant literature reveal that the number of lumbrical mclscles vary from two to 5 or 6 (Gray, '59). Braithwaite et al. ('48) have stated that additional or accessory lumbricales occur more frequently than a reduction in number, the third being the one most frequently missing. Whereas Morris ('53) described absence or doubling of the third and 4th without stating the frequency. In the present series, except in one right hand in which the 4th lumbricale was missing, 4 lumbricales were found in all hands dissected. Lumbricales have been described with anomalous origins from any of the long flexor tendons in either the forearm or the hand, from the interosseous muscles, or from other lumbricales; the third lumbricalis most frequently had an anomalous origin (Russel and Sunderland, '38). Lane (1887) and du Bois-Reymond (1594) described unusual anomalous origins of extra slips that joined lumbrical muscles of otherwise normal origin. The first lumbricalis may arise from the opponens Follicis or the metacarpal of the thumb (Morris, '53). The present investigation revealed anomalous origins of only 16 of 72 second Iumbricales and two of 71 4th Iumbricales. The most frequent anomalous insertion involved splitting of the tendon and attachment to the adjacent digits or its attachment only on the ulnar side of a digit. The first, second and 4th lumbricales attach along the radial side of the second, third and 5th digits while the third lumbricalis runs to the radial side of the 4th digit or spIits to attach to the adjacent sides of the third and 4th digits (Spalteholz; Morris, '53). No abnormal insertion of the first and second lumbricales were observed in 32 hands by Eyler and Markee ('54), but 5 of 31 third lumbncales were attached to both the third and 4th digits VARIATIONS O F THE LUMBRICAL MUSCLES O F THE HAND 503 and two were attached to the ulnar side of known evolutionary or development prothe third digit; two of 29 4th lumbricales cesses. were attached to both the 4th and the 5th SUMMARY digits and two were attached on the ulnar 1. Lumbrical muscles of 36 adult caside of the 4th digit. davers (5 female and 31 male) or 72 The bifid attachment of the second hands were studied. In 6 cadavers lumbricales to the adjacent sides of the (16.7% ) the lumbrical muscles in both second and third digits (two in our series hands presented normal textbook pattern. of 72) had not been described prior to In 18 other cadavers (50.0% ) either the our study. Of 72 third lumbricales 15 right hand or the left had lumbricales that were bifid and attached to the adjacent showed no abnormality. Thus, a total of sides of the third and 4th digits and 9 were 30 hands (41.7%) were normal in the attached to the ulnar side of the third origins, insertions, and distributions of digit. Among the 71 4th lumbricales, 8 the lumbricales. were bifid and attached to the adjacent 2. Eight different types of variations in sides of the 4th and 5th digits, whereas 4 the lumbrical muscles were observed and were inserted into the ulnar side of the their frequency of combinations of differ4th digit. ent types of variations were recorded. In the present study, only 6 cadavers (16.7% ) had lumbrical muscles in both ACKNOWLEDGMENTS hands that presented the usual normal Our thanks are due to Dr. William U. pattern in their origins and insertions. Gardner, Chairman of the Department of When one hand, either the right or the left was considered, in 15 cadavers Anatomy, Yale University School of Medi(41.7% ) the lumbricales showed no abnor- cine, for his advice and help in writing mality. Two anomalies of the lumbricales this paper. were observed in the right hand of 7 LITERATURE CITED cadavers (19.4% ) and in the left hand of G.D. Channell, F. T. Moore and J. Braithwaite, F., 6 cadavers (16.7%). The right hand of Whillis 1948 The applied anatomy of the only one cadaver (2.8% ) had three varialumbrical and interosseous muscles of the hand. tions of the lumbricales. Guy’s Hosp. Rep., 97: 185-195. The present investigation shows that du Bois-Reymond, R. 1894 Beschreibung einer Anzahl Muskelvarietaten a n einem Individuum. either the 4th or the 5th digit may have no Anat. Anz., 9: 451. lumbrical muscle attached to it. It may be Eyler, D. L., and J. E. Markee 1954 The anaassumed, therefore, that some deficiency tomy and function of the intrinsic musculature of the fingers. J. Bone Joint Surg., 36:A 1-9. in the power of flexion of the metacarpoH. 1959 Anatomy of the Human Bodv, phalangeal joints of those digits may exist Gray, ed. C. M. Goss. Lea and F.ebiger, Philadelphia, during life. The 30 hands with normal p. 524. lumbrical musculature were present in 24 Lane, W. A. 187 Abnormal muscIe of the hand. J. Anat. Physiol., 21: 674. of the 36 cadavers. Two or more varia- Morris, H. 1953 Human Anatomy, ed. J. P. tions of the lumbrical muscles were noted Schaeffer. The Blakiston Co., Sect. V, p. 497. in either the right or left of 12 cadavers; Russel, K. F., and S. Sunderland 1938 Abnormalities of the lumbrical muscles of the hand. in one cadaver only and on the right side J. Anat., 72: 30&307. were multiple variations present (table 2). Spalteholz, W. Hand-Atlas of Human Anatomy, The patterns of the lumbrical muscula7th edition (in English). J. B. Lippincott Co., ture have permitted no association with Philadelphia, p. 337. PLATE 1 VARIATIONS OF THE LUMBRICAL MUSCLES OF THE HAND S. S. Basu and S. Hazary n A n n NORMAL Diagrammatic presentation of normal lumbrical musculature and 8 types of variations shown in different combinations actually obtained in cadavers. Figs. 2-8 1 Normal. 2 Type 4. 504 See table 1 for description and frequency of the several different variations. 3 4 Type 8. Types 4 and 7. 5 6 Types 1 and 7. Type 6. 7 Types 1, 2 and 3. 8 Types 1 and 5.