Intra-individual variations in the bifurcation of the radial nerve and the length of the posterior interosseous nerve.

Anatomical literature on the radial nerve predominantly features inter-individual variations, with comparatively few studies investigating intra-individual variations. The radial nerve has a complex and variable course, particularly in relation to the location at which the nerve bifurcates to form the superficial branch of the radial nerve and the posterior interosseous nerve. Variations of the radial nerve may change the way the nerve and its branches, their blood supply and nerve transmission respond to forces. This study investigated the presence of intra-individual differences in the bifurcation point of the radial nerve and the length of the posterior interosseous nerve from the bifurcation to the radial tunnel. Eighteen embalmed human cadavers were dissected to reveal the radial nerve. Measurements were taken from the level of the lateral humeral epicondyle to the bifurcation of the radial nerve, and from the bifurcation to the radial tunnel. All cadavers presented with intra-individual variations between the left and right limbs. Significant differences were found between the left and right limbs for the measurement from the lateral humeral epicondyle to the bifurcation (median difference = 18.0 mm; p = 0.016) but not for the measurement from the bifurcation to the radial tunnel (median difference = 7.0 mm; p = 0.396). In conclusion, the location of the radial nerve bifurcation is subject to both intra- and inter-individual variations. Its specific relationship to the lateral humeral epicondyle also varies, occurring both distal and proximal to the level of the epicondyle. Clinical implications of these findings warrant further investigation.

Chronic low back pain-associated paraspinal muscle dysfunction is not the result of a constitutionally determined "adverse" fiber-type composition.

STUDY DESIGN: Investigative case control study. OBJECTIVES: To determine whether excessive paraspinal muscle fatigue in chronic low back pain results from a paucity of muscle type I fiber content. SUMMARY OF BACKGROUND DATA: Paraspinal muscle function is vital for spinal protection. Prospective studies suggest that excessive paraspinal muscle fatigability may increase risk of first-time low back pain. As contractile performance of the paraspinal muscles is governed by their constitutionally determined fiber composition, the question arises whether a constitutionally determined "adverse" composition could predispose to low back pain through impaired spinal protection. METHODS: Thirty-five male patients with chronic low back pain were compared with 32 male control patients of similar age and anthropometry. During Sorensen and 60% of maximum voluntary isometric contraction fatigue tests, median frequency declines in the paraspinal muscle surface electromyograph signal were monitored and correlated with muscle histomorphometry. RESULTS: Patients were weaker than controls during maximum voluntary isometric contractions (84.47 [28.44]vs. 98.74 [18.11] kg, respectively; P = 0.02) and more fatigable during their Sorensen tests (endurance time 105.29 [28.53]vs. 137.50 [40.38] sec, respectively; P < 0.01). There were no between-group differences in median frequency declines during the Sorensen (-0.37 [0.16]vs. -0.36 [0.12]%.sec) or 60% maximum voluntary isometric contraction (-0.42 [0.31]vs. -0.51 [0.29]%.sec) tests, for patients and controls, respectively. There were no between-group differences in the percent number of paraspinal muscle type I fibers (64 [11]vs. 64 [9]%) or the percent area occupied by type I fibers (67 [11]vs. 69 [9]%), for patients and controls, respectively. Type I and II muscle fiber narrow diameters were similar for both groups. CONCLUSION: In the patients with chronic low back pain tested, their associated paraspinal muscle dysfunction was not the result of a constitutionally determined "adverse" fiber type composition.