- 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 and Hanesworth (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.