The u-series: A separable decomposition for electrostatics computation with improved accuracy.

The evaluation of electrostatic energy for a set of point charges in a periodic lattice is a computationally expensive part of molecular dynamics simulations (and other applications) because of the long-range nature of the Coulomb interaction. A standard approach is to decompose the Coulomb potential into a near part, typically evaluated by direct summation up to a cutoff radius, and a far part, typically evaluated in Fourier space. In practice, all decomposition approaches involve approximations-such as cutting off the near-part direct sum-but it may be possible to find new decompositions with improved trade-offs between accuracy and performance. Here, we present the u-series, a new decomposition of the Coulomb potential that is more accurate than the standard (Ewald) decomposition for a given amount of computational effort and achieves the same accuracy as the Ewald decomposition with approximately half the computational effort. These improvements, which we demonstrate numerically using a lipid membrane system, arise because the u-series is smooth on the entire real axis and exact up to the cutoff radius. Additional performance improvements over the Ewald decomposition may be possible in certain situations because the far part of the u-series is a sum of Gaussians and can thus be evaluated using algorithms that require a separable convolution kernel; we describe one such algorithm that reduces communication latency at the expense of communication bandwidth and computation, a trade-off that may be advantageous on modern massively parallel supercomputers.

Biomolecular simulation: a computational microscope for molecular biology.

Molecular dynamics simulations capture the behavior of biological macromolecules in full atomic detail, but their computational demands, combined with the challenge of appropriately modeling the relevant physics, have historically restricted their length and accuracy. Dramatic recent improvements in achievable simulation speed and the underlying physical models have enabled atomic-level simulations on timescales as long as milliseconds that capture key biochemical processes such as protein folding, drug binding, membrane transport, and the conformational changes critical to protein function. Such simulation may serve as a computational microscope, revealing biomolecular mechanisms at spatial and temporal scales that are difficult to observe experimentally. We describe the rapidly evolving state of the art for atomic-level biomolecular simulation, illustrate the types of biological discoveries that can now be made through simulation, and discuss challenges motivating continued innovation in this field.

Puncture wounds of the foot. Evaluation and treatment.

Puncture wounds of the foot are a common injury, often occurring in the warmer months. Various objects have been described as the penetrating source in these wounds; however, nails and glass are the most common cause of pedal puncture wounds. All puncture wounds should be evaluated thoroughly and treated aggressively to reduce the risk of complications. Viewing this injury lightly may cause complications, and is often a source of litigation. A systematic approach to the evaluation and treatment of puncture wounds limits complications and results in a satisfactory outcome for the patient and physician.

Off-loading techniques in the treatment of diabetic plantar neuropathic foot ulceration.

In the individual with diabetes mellitus, foot ulceration represents the single most important risk factor in lower-extremity amputation. The goal of treatment is to obtain a healed and closed wound that (1) eliminates a portal of entry for bacterial invasion and development of limb-threatening infection, and (2) allows for tissue loading. This manuscript reviews current off-loading approaches to the treatment of plantar neuropathic foot ulcers, along with advantages and disadvantages of those techniques.

Oblique medial malleolar osteotomy for the management of talar dome lesions.

The purpose of this retrospective study was to determine the efficacy of the oblique medial malleolar osteotomy for the management of medial talar dome lesions. Arthroscopy remains a viable option for the management of these lesions; however, the central and posteromedial lesions are often difficult to gain access to with arthroscopy and may require open arthrotomy. Fourteen oblique medial malleolar osteotomies were performed for the surgical management of medial talar dome lesions. Subjective data were collected through the process of questionnaire. Objective criteria consisted of radiographic evaluation and retrospective medical record review. Seven of the 14 patients related a history of trauma preoperatively. The oblique medial malleolar osteotomy demonstrated osseous union at an average of 6.6 weeks. There were no delayed unions or nonunions. None of the patients required a second operative procedure. Nine patients reported excellent postoperative results, two patients had good results, two had fair results, and one patient related a poor postoperative outcome with only 50% relief of pain. Patients greater than the age of 30 were found to have less favorable results. Follow-up ranged from 6 to 72 months, with a mean follow-up of 34 months.

Limb loss after lower extremity bypass.

BACKGROUND: Infrainguinal bypass now has a limb salvage rate approaching 90% at 10 years. This study helps elucidate the causes of limb loss despite bypass surgery. METHODS: A retrospective chart review of all patients undergoing a major lower extremity amputation after attempted bypass surgery. RESULTS: Between July 1987 and January 1997, 67 major amputations (52 below knee, 15 above knee) followed infrainguinal bypass for limb salvage in 64 patients. Of these patients, 53 (83%) were diabetic and 10 (16%) were on dialysis. The etiology of limb loss included thrombosed bypass (n = 33, 49%), lack of limb salvage despite patent bypass (n = 23, 34%), intraoperative bypass failure (n = 6, 9%), and exposed/infected bypass (n = 5, 8%). The 23 patients with patent grafts required amputations because of hindfoot necrosis (n = 6), persistent forefoot necrosis (n = 6), acute diabetic foot infection (n = 6), and various other reasons (n = 5). Using life-table analysis, survival for the whole group was 56% at 12 months and 17% at 48 months. Patients with limb loss despite a patent bypass fared the worst with survival of 21% at 2 years. CONCLUSIONS: Bypass thrombosis caused half of the amputations after limb salvage surgery. A patent bypass was functioning at the time of amputation in another third. Survival after failure of limb salvage was abysmal, especially in patients with patent bypasses.

Biological principles of bone graft healing.

Bone graft healing is a sequential process involving inflammation revascularization, osteogenesis remodeling, and incorporation into the host skeleton to form a mechanically efficient structure Successful incorporation is determined by the histocompatibility between host and donor. Although there is no antigenicity toward autografts, allogeneic bone may provoke an immune response. This response can be reduced through various bone processing techniques. Overall autogeneic and allogeneic bone transfers proceed to satisfactory results.

The Lapidus procedure.

Arthrodesis of the first metatarsal cuneiform joint has been described as a primary procedure for hallux abducto valgus repair since the early 1900s. Popularized by Paul W. Lapidus, this procedure has remained controversial since its introduction, falling in and out of vogue in the orthopedic and podiatric communities. The authors expound their experiences, using modified operative techniques and advanced internal fixation principles, with emphasis on proper patient selection and clinical results.