Biomechanical evaluation of calcaneocuboid distraction arthrodesis: a cadaver study of two different fixation methods.

Calcaneocuboid distraction arthrodesis can be used to treat stage 2 posterior tibial tendon dysfunction. Nonunion, graft resorption, and implant failure have been reported after this procedure. This study compared two of the most commonly used methods for fixation of calcaneocuboid distraction arthrodesis. Twelve pairs of cadaver feet underwent simulated calcaneocuboid distraction arthrodesis. One specimen in each pair was fixed with two crossed 3.5 mm cortical lag screws. The contralateral specimen was fixed with a cervical H-plate. The calcaneus was fixed and a load was applied to the plantar aspect of the cuboid at a rate of 5 mm/minute until joint separation of 3 mm or fracture occurred. The average applied load to failure at 1.0 mm of joint separation was 30.5 +/- 11.6 N for the crossed screws and 77.7 +/- 36.4 N for the cervical H-plate (p = 0.001). The average stiffness at 1.0 mm of joint separation was 27.5 +/- 10.9 N/mm for the crossed screws and 43 +/- 21.2 N/mm for the cervical H-plate (p = 0.036). The higher stiffness and load to failure may account for the decreased nonunion rate noted anecdotally by some surgeons with H-plate fixation over crossed screw fixation for calcaneocuboid distraction arthrodesis.

Specificity of the cholesterol side-chain cleavage enzyme system of adrenal cortex.

Incubation of lanosta-8, 24-dien-3beta-o1-1,2-3H and lanost-8-en-3beta-o1-1,2-3H with an adrenocortical bovine mitochondrial acetone-dried preparation did not yield any significant (less than 0.01%) 3beta-hydroxy-4, 4, 14-trimethyl-5alpha-pregn-8-en-20-one. Under the same conditions cholesterol-1,2-3H yielded 8.3% pregnenolone. Incubation of (20S)-17alpha, 20-di-hydroxycholesterol-7-3H yielded 0.6 to 1.6% (20S,22R)-17alpha, 20, 22-trihydroxycholesterol, 1.0 to 3.2% of 17alpha-hydroxy-pregnenolone, but no significant (less than 0.02%) (20S,22S)-17alpha,20,22-trihydroxycholesterol. In another experiment incubation of cholesterol-1,2-3H yielded 5% pregnenolone, 0.5% 17alpha-hydroxypregnenolone, 0.2% (20R,22R)-20,22-dihydroxy-cholesterol, but no significant ( less than 0.01%) 17alpha-hydroxy-cholesterol, (20S)-17alpha, 20-dihydroxycholesterol or (20S,22R)-17alpha, 20,22-trihydroxycholesterol.

Exclusion of 20(22)-dehydrocholesterol as an intermediate in the biosynthesis of pregnenolone in bovine adrenocortical mitochondrial acetone-dried powder preparations.

Incubation of (22R)-(22-180)20-hydroxycholesterol with a bovine adrenocortical mitochondrial acetone-dried powder preparation in air yielded (20R, 22R)-20, (22-18O)22-dihydroxy-cholesterol. Incubation of (20S)-(20-18O)22-hydroxycholesterol yielded (20R, 22R)-(20-18O)20,22-dihydroxycholesterol. The formed glycols and the substrates reisolated at the end of the incubations had the same 18O abundance as the starting materials. No significant (20R, 22R)-20,22-dihydroxycholesterol was formed following incubation with either (E)-or (Z)-20, (22)-dehydrocholesterol. (20R,22S)-20, 22-Epoxycholesterol yielded approximately 1/5 of the amount of pregnenolone obtained in a similar incubation with cholesterol. No significant pregnenolone formation was observed with (20R, 22R)-20,22-epoxycholesterol. These results exclude a mechanism for the biosynthesis of (20R, 22R)-20,22-dihydroxycholesterol from the monohydroxylated cholesterol derivatives by way of dehydration followed by epoxidation and hydration. Similarly, the participation of an olefin and an epoxide as intermediates in the transformation of cholesterol to pregnenolone in acetone-dried powder preparations of adrenal cortex mitochondria is unlikely.

Inhibition of the conversion of cholesterol to pregnenolone in bovine adrenocortical preparations.

The inhibition of the conversion of [4-14C] cholesterol to [4-14C] pregnenolone by a number of steroids has been studied in bovine adrenocortical mitochondrial acetonedried preparations. At equimolar substrate and inhibitor concentrations (3.3 muM) the most potent inhibitors were cholesterol derivatives containing a nitrogen function at c-22, followed by derivatives containing oxygen functions at c-22 or c-20 or both. The presence of a hydroxyl group at c-17 or the replacement of the 3beta-hydroxyl group by fluorine reduced the inhibitory efficacy. In the presence of inhibitors that were also relatively good substrates of the cholesterol side-chain cleavage system, such as some cholesterol derivatives hydroxylated in the side-chain,the rate of [4-14C] pregnenolone formation increased with time as the inhibitor was consumed. (20S)-20,21-Dihydroxycholesterol exerted such an effect on the kinetics of [4-14C]pregnenolone formation, and yielded 21-hydroxypregnenolone which was identified by gas chromatography-mass spectrometry. The synthesis of (20R)-22-ketocholesterol, of (20R,22R)-22hydroxycholesterol, (20R,22S)-hydroxycholesterol, and of (20S)-desmosterol is described.