- Discussion:
- w/ flexion the cubital tunnel becomes taunt, and with extension the cubital tunnel becomes lax;
- sharp freee margin of aponeurosis is stretched tightly over nerve during flexion;
- volume of the cubital tunnel decreases, and extrinsic pressure increases during flexion of the elbow;
- as the elbow is flexed to 135 deg, mean cross sectional area of the tunnel decreases by about 35 %;
- this is agravated if flexion of elbow is coupled with contraction of
FCU to initiate active
wrist movement, as occurs during hammering or shoveling;
- in addition to decreases in the cross sectional area of the cubital tunnel which occur w/ flexion, there is
also a decrease in the mean cross sectional anatomy of the ulnar nerve (about 35-40%) w/ elbow flexion;
- this indicates that elbow flexion increases traction on the ulnar nerve, which is independent of any extrinsic traction;
- in the study by Toby et al 1998, w/ maximal elbow flexion a wide range of maximal strains were found (0 to 14%), and
one out of four nerves showed strain greater than 10%;
- the authors note a nerve stretch of more than 6-8% will cause a traction injury;
- the authors felt that cubital tunnel syndrome was in part a traction neuropathy;
- during extension of the elbow, the bony points of attachment come closer together, relaxing the roof of the tunnel;
- additional factor is the degree of tension in
medial ligament of elbow joint, which forms the floor of the tunnel;
Changes in intersitial pressure and cross sectional area of the cubital tunnel and of the ulnar nerve with flexion of the elbow. An experimental study in human cadavera.
RH Gelberman MD et al.
JBJS Vol 80-A. No 4. Apr 1988.
Ulnar nerve strains at the elbow.
EB Toby et al.
J. Hand Surg. Vol 23-A. 1998. p 992-997.
