THE ANATOMY OF THE SUPERFICIALIS RELEVANT

FLEXOR DIGITORUM TO TENDON TRANSFERS

J. AGEE, H. RELTON McCARROLL From the Harbor

U.C.L.A. Medical

and ANNE HOLLISTER

Center, Torrance, California,

U.S.A.

The flexor digitorum superficialis is a digastric muscle with a proximal muscle belly from which the tendons to the index, ring and little fingers arise. These tendons are not independent and are not good motors for non-synergistic transfers, such as for finger extension. The muscle and tendon to the middle finger arise separately and are therefore more suitable for non-synergistic transfers. Journal

of Hand

Surgery

(British

Volume,

1991)

The flexor digitorum superhcialis has been used as a motor for a wide variety of tendon transfer operations in the hand. Most of these transfers are on the volar side of the hand and are used to restore synergistic actions (such as opposition of the thumb) or as intrinsic replacements. Boyes (1960) recommended the use of the superficialis tendon to the middle finger to provide non-synergistic extension of the M.P. joint. Other surgeons have used other superficialis tendons for the same purpose, but we have noticed that the superficialis tendon of the ring finger does not work as reliably in this transfer as it does with synergistic procedures. This can be explained in part by the digastric nature of the anatomy of the superhcialis. Theile (1843) described the muscle belly of the superficialis muscle as having a superficial and deep head, and noted that the deep head is a digastric muscle. The tendon of origin of its proximal belly arises from the medial epicondyle and this belly gives rise to an intermediate tendon. Theile observed that the tendons to the index and little finger come from muscle bellies which arise from this tendon. Brand (1985) found that the distal third of the superficialis to the ring finger also arises from this

16B:

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intermediate tendon. He provides a clear description of the flexor digitorum superficialis. There is a fusiform muscle belly proximally, which gives rise to a central tendon. From this tendon arise the distal bellies of the F.D.S. to the index and little fingers and a substantial part of that to the ring finger (Fig. 1). The only portion of the muscle which does not have an origin from the central tendon is that going to the middle finger. Since the superficialis tendons to the index, ring and little fingers have a common proximal muscle belly and act as a conjoined unit, they do not have completely independent action. If the tendon of the ring finger is used for a synergistic transfer (such as an opponensplasty) where the transfer and the finger flexors are used together, the proximal and distal bellies will contract synchronously and the full strength and excursion of the muscle connected to the ring finger tendon will be available for the transfer. For transfers on the palmar side, both the transferred and untransferred tendons cross the wrist on the flexor side, and will have nearly the same excursion for wrist motion. The independent excursion in the distal muscle belly is sufficient to allow independent action of the transferred tendon.

Long

of origin Fig.

68

1

The flexor digitorum superficialis has a proximal muscle belly arising from the medial epicondyle tendon. The muscle bellies to the index, little and most of the ring finger arise from this intermediate long) finger arises separately. (Modified, with permission, from Brand, 1985).

which tendon.

THE

gives rise to an intermediate The muscle for the middle (or

JOURNAL

OF HAND

SURGERY

ANATOMY

OF THE

FLEXOR

DIGITORUM

SUPERFICIALIS

In a non-synergistic transfer, only the portion of the superficialis to the ring finger, which has an independent origin, or two-thirds of the cross-sectional area of the muscle (Brand 1985) would be available for independent function. In transfers of the ring finger tendon for finger extension, the transferred tendon must work when the other finger flexors are relaxed. Tension in the proximal belly would limit the passive excursion of the tendons to the index and little fingers to the excursion of the distal belly (about 4$ cm) when the transferred ring finger tendon attempts finger extension. Conversely, tension in the proximal belly during finger flexion would limit passive excursion in the transferred tendon to 43 cm. This is not enough excursion to allow both active wrist and finger extension, if the transferred tendon is dorsal to the wrist joint. Boyes (1960) recommended that this transfer be sutured under maximum tension. While this ensures that the transfer can provide finger extension, it will impair the function of the rest of the conjoined muscle unit because it puts the proximal muscle belly under tension in the direction of the transfer.

VOL.

16B No.

1 FEBRUARY

1991

RELEVANT

TO TENDON

TRANSFERS

Boyes used the superficialis tendon to the middle finger in his transfers for finger extension. This portion of the superficialis has an independent origin and is anatomically an independent unit. It is therefore the superficialis tendon of choice for non-synergistic transfers, if the anatomy of the transferred muscle is the only factor to be considered. References BOYES, .I. H. (1960). Tendon Transfers for Radial Palsy. Bulletin of the Hospital for Joint Diseases, 21: 2: 97-105. BRAND, P. W. Clinical Mechanics of tfik Hand, St. Louis, C. V. Mosby, 1985: 266267. THEILE, F. G. Trait& de Myologie et d’Ang&ologie. In: Valentin, G., Vogel, J., Wagner, R., and Weber, G. and E. Encyclopedic Anatomique (translated from the German by A. J. L. Jourdan). Paris, J. B. Bailliere, 1843: Vol. 3: 241.

Accepted: lOOctober 1989 Anne Hollister M.D., Division of Orthopaedic Surgery, Harbor UCLA Medical Centre, 1000 Carson Street, Torrance, CA 90509, U.S.A. 0 1991 The British Society for Surgery of the Hand

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