OUR ANATOMICAL DIFFERENCES

Richard Beauchamp

This is the outline of a talk given to EPTA in 1999, attempting to show why we should not treat all pupils alike, or expect them to achieve the same results with the same technical methods.

CONTENTS

• Muscles in the arm
• Intrinsic muscles of the thumb (Thenar muscles)
• Hypothenar muscles
• The other intrinsic musicles
• The fingers

Muscles in the arm

Flexor digitorum superficialis

• Normally has two heads - humero-ulnar and radial - Radial head is sometimes absent.
• Slip to little finger is sometimes absent. May be replaced by another slip from ulnar or from the hand.
• There are other variations in the tendons (such as lumbrical attachments). (Those to the ring and little finger may be joined?).

Flexor digitorum profundus

• May have accessory slips from pollicis longus or superficialis.
• Index finger usually distinct throughout, but tendon may be connected to middle finger (1 in 10) and/or flexor pollicis longus (1 in 200).

Flexor pollicis longus

• Sometimes connected to FDP, FDS or pronator teres. The interosseus attachment - and even the whole muscle may be missing.
• Tendon may be connected to FDP index (1 in 200) or even FDP medius.

Extensor digitorum

• Tendons variably deficient, but more often doubled or tripled to one or more digits - most often index or medius.
• Sometimes a slip of tendon goes to the thumb.
• Connecting tendons variable - tendon to index normally distinct, but may be connected to medius.

Extensor digiti minimi

• Usually sends a slip to ED tendon.
• May send a slip to ED ring.
• Rarely absent.
• May be fused with ED.

Extensor indicis

• Occasionally sends accessory slips to extensor tendons of other digits.
• Rarely may be interrupted by an additional muscle belly on back of hand.

Extensor pollicis brevis

• Attaches to base of proximal phalanx, but commonly attaches to distal phalanx as well (usually joining tendon of extensor pollicis longus).
• May be absent or fused completely with abductor longus.
• Its tendon sometimes unites with that of extensor pollicis longus.

Palmaris longus

One of the most variable of muscles.

• Frequently absent on one or both sides.
• A head may arise from the intermuscular septum, the humerus, the fascia of the arm or one of the muscles.
• The coronoid head is often absent or rudimentary, but may be reinforced by fibres from the ulna.
• Fasiculi may connect it with the flexor carpi radialis or FDS.
• The two heads may be completely separated.
• Both coronoid and humeral heads may be divided.
• Muscle belly may be central, distal or digastric (proximal and distal muscle belly connected by a central tendon) in position.
• It may be completely muscular from origin to insertion or only a fibrous strand.
• Either the muscle belly or tendon may be bifid or both.
• Duplication occurs rarely.
• Accessory slips may insert into abductor digiti minimi, flexor digiti minimi or antibrachial fascia. They may arise from the FDS, ulnar tuberosity and coronoid process or the radial tuberosity and the oblique line of the radius.

Much of the above information about the Palmaris Longus has been quoted from Quain's "Elements of Anatomy" and from Koo's and Roberts' paper "The Palmaris Longus Tendon".

Intrinsic muscles of the thumb (Thenar muscles)

Abductor pollicis brevis

Opponens pollicis

Flexor pollicis brevis

Adductor pollicis

Hypothenar muscles

Palmaris brevis

Abductor digiti minimi

• May be fused with flexor brevis.

Flexor digiti minimi brevis

• May be absent.
• May be fused with abductor.

Opponens digiti minimi

The other intrinsic muscles

Dorsal interossei

• The 2nd generally reaches the digital expansion and the proximal phalanx.
• The 3rd usually extends only to the digital expansion.
• The 4th may be wholly attached to the digital expansion, but often sends an additional slip to the proximal phalanx.

Palmar interossei

• Do not vary a great deal, but are occasionally reduplicated.

They contribute strongly to MCP flexion and interphalangeal extension.

Lumbrical muscles

Variations are common (45% according to Froment in 1846).

• Any may be unipennate or bipennate. When bipennate, they arise from adjoining tendons of FDP or, in the case of the first lumbrical, of FDP and FPL.
• Absence.
• Bifurcated distal insertions, terminating at adjacent fingers or in the same finger.
• Proximal insertion in FDS tendon, the interosseus membrane of the forearm, or the bones of the forearm.
• Extension up the forearm
• Lumbrical muscle present in the FPL tendon.
• Supernumerary lumbricals.
• Double insertion.

The lumbrical most frequently affected by double insertion is that of the ring finger (15% - 43% of cases). The distal insertion of the lumbrical can be seen on the ulnar side of the finger. Lumbrical muscles extended up the forearm easily produce a carpal tunnel syndrome. According to Kopsch (1898) and Reinhardt (1902) the classical arrangement of lumbricals occurs in only 39% of cases.

Lumbricals alter the balance between flexors and extensors and are important proprioceptors. the 1st lumbrical has approximately 50 neuromuscular spindles for a weight of about 3 grams.

The fingers

Index finger

Intrinsic muscles are normally independent, but in 1 in 10 cases are limited by:

• non-differentiation in muscular mass of FDP
• interdigital tendinous connections
• double origin of 2nd lumbrical (between FDP tendons of index and medius).

The FDP tendon of the index finger:

• is connected to the tendon of FPL in 1 in 200 cases
• often shares origin of FDS muscle with little finger.

The Extensor Indicis makes it possible to point this finger when the rest of the hand is in a fist. (Hence the name "index") Use of this muscle can help to lift the medius when the ring finger is flexed, thus limiting the tension between the ED connecting tendons for the medius and ring fingers.

Medius

Highly interdependent because of tendinous connections of ED tendons on back of hand, FDP connections, lack of differentiation in muscular mass of FDP, joint origins of 3rd lumbrical.

Full extension of medius limits DIP flexion in ring finger in 41% and in little finger in 11%.

(Try full extension test on DIP flexion in other fingers. Do this with great care, and do not force!)

Apparent flexion of DIP's in other fingers can be achieved by hyper extending them at the MCP, but this causes tension in the hand (Another danger of flexed finger tips?)

Ring finger

Similar to above, but exacerbated by having ED and FDP connections on both sides as well as sharing the common origins of both 3rd and fourth lumbricals.

Little finger

• FDS often missing or too weak to operate.
• In some cases there seems to be a connection between FDS of little and ring fingers, i.e. flexion of PIP can only take place if PIP of ring finger is fully flexed.

EDM makes it possible to point the little finger independently of the others, but this tendon is sometimes fused with the ED tendon and/or connected to it, or absent. Its ED tendon itself is usually only a slip branching off the tendon for the ring finger.

Raising the little finger with EDM can be a help in lifting the ring finger when the medius is flexed, as the ring finger is raised mainly by the web connection between it and the little finger, with some participation of the ED connecting tendons, and therefore communicates no tension to the other fingers. This, however, is no help at all if the EDM is absent or joined/fused to its ED tendon. It is interesting to watch the medius being helped by the EI and the ring finger being helped by the EDM in a trill with these two fingers.

The common habit of curling the little finger is a way of making the FDP act as a limiter for the other fingers (forcing them to flex slightly as they are raised and allowing them to open out as they descend) as well as aiding in the lifting of the ring finger. A pronounced curling of the little finger may be needed to achieve the right degree of limitation to the medius as the effect is conveyed across two FDP tendons. This technique is often observed in trills between the index and middle fingers. It may be unnecessary to create a limit to extension if the natural tonus of the FDP is sufficient to do so passively.

All piano teachers please memorise the following quote!

"Extrinsic muscles are said to be strong, pluriarticular, little differentiated motors, supplying mainly the force required for common power movements, without real precision. The short intrinsic muscles are said to be essentially the motors of fine movements."

Sources

©Copyright Richard Beauchamp 1999 Disclaimer