Search

The transition of oligonucleotides from the B to the A conformation has been studied by the use of simple geometric calculations aimed at finding possible hydration sites which could stabilize these conformations. The method involves the classification of equally spaced grid points, surrounding the oligonucleotide, into groups depending on whether a water molecule, so placed, could form single, multiple or nil contacts to polar oligonucleotide atoms. The occurrence of the multiple, and therefore bridging, sites is more extensive for the 'A' than the 'B' conformation. Thus, more general evidence is presented in support of the economy of hydration hypothesis in which phosphate groups, in the low humidity 'A' form, have been seen to be bridged by single water molecules. Similar calculations for the 'Z' DNA conformation show a different preference for multiple bridging sites.

Radiolucent lines at the bone-cement interface beneath the tibial components were assessed in 91 consecutive Oxford meniscal knee replacements in 78 patients. Of 80 knees in which radio-opaque cement was used, a radiolucent line was observed in 77, with a radiodense line in the bone immediately adjoining. Radiolucent lines developed in the majority of patients within one year after operation. In 11 knees fixed with radiolucent cement (which precluded assessment of the radiolucent line) a radiodense line was observed beneath the lucent cement in all cases. Histological examination of the interface obtained from secure tibial components showed the lucent zone to be composed of fibrocartilaginous connective tissue and the radiodense line to be a thick lamella of bone. It is suggested that the living bone under a rigid prosthesis requires a layer of relatively compliant fibrocartilaginous material at its interface to accommodate load-bearing. Attention is drawn to the importance of the radiodense line: its presence may constitute positive evidence that healing at the level of bone section is complete and that equilibrium is established; its absence at a mature interface may indicate disequilibrium and impending failure.

Unicompartmental knee arthroplasty is an attractive concept, but some reports on its use are unfavorable. A meniscal bearing prosthesis has many advantages in this mode of arthroplasty. The authors present preliminary results of 25 unicompartmental knee replacements done with the Oxford Meniscal knee, with a follow-up period of 12-54 months (mean, 21 months). They discuss the scientific basis of unicompartmental knee arthroplasty, which they conclude may be the most appropriate treatment for selected cases of degenerative arthritis of the knee.

Monte Carlo computer simulation techniques may be used to predict structural properties of solvent networks in helical fragments of nucleic acids, provided that suitable potential functions are available to describe the interactions between nucleic acid atoms, water and counterions. Previous studies have shown that simple non-bonded and point charge parameters are adequate for mononuclear ions such as sodium and calcium. In this study a model interaction potential for the polynuclear ammonium ion is evaluated. The parameters used take account of the distribution of charge over the constituent atoms in the ion. Simulations are carried out on the ammonium salt of a small nucleic acid crystal hydrate and a comparison is made between the predicted and experimental results. It is shown that the simulated structure is in reasonable agreement with experiment. It is therefore feasible to use this potential in studies of ammonium-containing bimolecular systems.

A detailed knowledge of structural and energetic aspects of water-nucleic acid interactions is essential for understanding the role of solvent in stabilizing the various helical forms of nucleic acids. In this study, computer simulation techniques have been used to predict structural properties of solvent networks in small nucleic acid crystal hydrates. A detailed comparison of predicted and experimental results on the structure of the solvent networks is presented and includes an analysis of both the local environment and hydrogen bond pattern of each water molecule. A correlation between the environment of each unique water molecule and its energetic properties (such a dipole moment and binding energy) is seen. As in the previous studies on small amino acid hydrate crystals, non-pair additive (cooperative) effects are found to be non-negligible. It is concluded that the potential functions used in this initial study lead to simulated solvent networks in reasonable agreement with experimental data. Thus, it is now feasible to use them in studies of hydration of larger helical fragments of nucleic acids of more direct biological interest.

Three cases of osteotomy for osteoarthritis of the hip which demonstrate the ability of cartilage to resurface previously eburnated areas are presented. These cases support the claim that cartilage regeneration of the femoral head after osteotomy does take place. Histologically, this new surface consists of fibrocartilage.

A knowledge of structural and energetic aspects of water- and ion-nucleic acid interactions is essential for the understanding of the role of solvent and counterions in stabilising the various helical forms of nucleic acids. In this study, Monte Carlo computer simulation techniques have been used to predict structural properties of solvent networks in small nucleic acid crystal hydrates containing the ions sodium, ammonium and calcium. Appropriate parameters to describe the interaction potentials of the ions are added to those previously developed for water and nucleic acid atoms. A comparison is made between the predicted and experimental results and it is concluded that the potential functions used lead to simulated solvent structure in reasonable agreement with experimental data, at least in the cases of sodium and calcium. It is now feasible to use these functions in studies of hydration of larger helical fragments of nucleic acids of more direct biological interest.

A case is reported of spontaneous subluxation of C.3 on C.4 in a 6-year-old boy due to an upper respiratory infection after surgical treatment for muscular torticollis.