- Email: [email protected]
Tension in the lumbrical muscle
Tension in the Lumbrical Muscle--Graham Stack
TENSION IN T H E L U M B R I C A L MUSCLE G R A H A M STACK, London You have been reminded by Parkes (1970) that there is a limit to the extent to which the normal lumbrical muscle can be extended. This occurs in the fully flexed position of the finger, with the tip of the finger digging in to the palm. In this position the origin of the lumbrical on the profundus tendon is as far proximally in the wrist as possible, and the insertion is pulled distally over the proximal interphalangeal joint. Further elongation in the normal hand is not possible as the finger nails would dig into the skin of the palm. NORMAL LENGTH
Thus there is a normal limit to the extensibility of the lumbrical, and in the average finger this gives a lumbrical length of about nine centimetres. The muscles have a high contractile length due to the long fibre length found in the muscle, which gives a change in length on full contraction from nine centimetres to five centimetres for an average muscle. When however the flexor digitorum profundus tendon is divided distal to the origin of the lumbrical muscle, immediately it is possible for the muscle to be extended beyond its normal length, because the cut tendon carrying the muscle origin can move proximally in the wrist. LENGTH-TENSION CURVE
ill", length ---~
5cm
9cm
Fig. 1 After Eyler and Markee, Curves show tension produced by Contractile Force, Passive Stretch, and both combined. Normal values lie between "5 cm" and "9 cm". Abnormal tension can develop when the lumbrical is stretched beyond "9 cm". Eyler and Markee (1954) have illustrated the relationship between length and tension in a muscle and have applied this to the lumbricals. The diagram shown here is derived from theirs. They deduced that for high values of passive stretch a very high value of tension would be developed and they suggested that this tension would increase the force of flexion in the hand. The curve shows the tension developed in a muscle at a given length, when subjected to passive stretch, and when under active contraction. There is also a curve showing the tension developed when both factors are at work. 166
Vol. 2
No. 2
1970
Tension in the Lumbrical M u s c l e - - G r a h a m Stack
I have included in this diagram an indication of the length of the muscle in absolute figures, which demonstrates that for high normal lengths of the muscle, even when under the influence of passive stretch and active contraction the very high values of tension for increased length of the muscle are not possible. ABNORMAL LENGTH
These high values for tension may however exist under conditions of length of the lumbrical above normal, that is when the flexor digitorum profundus tendon is divided distal to the attachment of the lumbrical muscles. The proximal divided end of the tendon passes proximally towards the forearm taking the origin of the lumbrical with it, and extending the muscle. This will produce considerable extension of the lumbrical, and will produce excessive tension in the muscle, even in the absence of active contraction. When attempting to flex the finger, the lumbrical is inhibited, and therefore any increase in tension is not due to active contraction, but only to passive stretch. It is this tension acting on the insertion of the lumbrical through the extensor expansion to the base of the dorsum of the middle phalanx, which produces extension of the finger, when the subject is attempting to produce flexion. The flexor profundus has its insertion translated from the base of the volar surface of the distal phalanx, to the dorsal surface of the middle phalanx. The increased tension produced by the flexor tendon pulling on the lumbrical muscle will thus be applied on the dorsum of the finger, and produce the extension of the finger described by Parkes.
REFERENCES PARKES, A. R. (1970) The "Lumbrical Plus" Finger. The Hand 2: 164. EYLER, D. L. and M A R K E E , J. E. (1945) The Anatomy and Function of the Intrinsic Musculature of the Fingers. Journal of Bone and Joint Surgery 36a: 1. Vtd. 2
No. 2
1970
167
TENSION IN T H E L U M B R I C A L MUSCLE G R A H A M STACK, London You have been reminded by Parkes (1970) that there is a limit to the extent to which the normal lumbrical muscle can be extended. This occurs in the fully flexed position of the finger, with the tip of the finger digging in to the palm. In this position the origin of the lumbrical on the profundus tendon is as far proximally in the wrist as possible, and the insertion is pulled distally over the proximal interphalangeal joint. Further elongation in the normal hand is not possible as the finger nails would dig into the skin of the palm. NORMAL LENGTH
Thus there is a normal limit to the extensibility of the lumbrical, and in the average finger this gives a lumbrical length of about nine centimetres. The muscles have a high contractile length due to the long fibre length found in the muscle, which gives a change in length on full contraction from nine centimetres to five centimetres for an average muscle. When however the flexor digitorum profundus tendon is divided distal to the origin of the lumbrical muscle, immediately it is possible for the muscle to be extended beyond its normal length, because the cut tendon carrying the muscle origin can move proximally in the wrist. LENGTH-TENSION CURVE
ill", length ---~
5cm
9cm
Fig. 1 After Eyler and Markee, Curves show tension produced by Contractile Force, Passive Stretch, and both combined. Normal values lie between "5 cm" and "9 cm". Abnormal tension can develop when the lumbrical is stretched beyond "9 cm". Eyler and Markee (1954) have illustrated the relationship between length and tension in a muscle and have applied this to the lumbricals. The diagram shown here is derived from theirs. They deduced that for high values of passive stretch a very high value of tension would be developed and they suggested that this tension would increase the force of flexion in the hand. The curve shows the tension developed in a muscle at a given length, when subjected to passive stretch, and when under active contraction. There is also a curve showing the tension developed when both factors are at work. 166
Vol. 2
No. 2
1970
Tension in the Lumbrical M u s c l e - - G r a h a m Stack
I have included in this diagram an indication of the length of the muscle in absolute figures, which demonstrates that for high normal lengths of the muscle, even when under the influence of passive stretch and active contraction the very high values of tension for increased length of the muscle are not possible. ABNORMAL LENGTH
These high values for tension may however exist under conditions of length of the lumbrical above normal, that is when the flexor digitorum profundus tendon is divided distal to the attachment of the lumbrical muscles. The proximal divided end of the tendon passes proximally towards the forearm taking the origin of the lumbrical with it, and extending the muscle. This will produce considerable extension of the lumbrical, and will produce excessive tension in the muscle, even in the absence of active contraction. When attempting to flex the finger, the lumbrical is inhibited, and therefore any increase in tension is not due to active contraction, but only to passive stretch. It is this tension acting on the insertion of the lumbrical through the extensor expansion to the base of the dorsum of the middle phalanx, which produces extension of the finger, when the subject is attempting to produce flexion. The flexor profundus has its insertion translated from the base of the volar surface of the distal phalanx, to the dorsal surface of the middle phalanx. The increased tension produced by the flexor tendon pulling on the lumbrical muscle will thus be applied on the dorsum of the finger, and produce the extension of the finger described by Parkes.
REFERENCES PARKES, A. R. (1970) The "Lumbrical Plus" Finger. The Hand 2: 164. EYLER, D. L. and M A R K E E , J. E. (1945) The Anatomy and Function of the Intrinsic Musculature of the Fingers. Journal of Bone and Joint Surgery 36a: 1. Vtd. 2
No. 2
1970
167