Formation free energy of an i-mer at spinodal.

In statistical mechanics, the formation free energy of an i-mer can be understood as the Gibbs free energy change in a system consisting of pure monomers after and prior to the formation of the i-mer. For molecules interacting via Lennard-Jones potential, we have computed the formation free energy of a Stillinger i-mer [F. H. Stillinger, J. Chem. Phys. 38, 1486 (1963)] and a ten Wolde-Frenkel (tWF) [P. R. ten Wolde and D. Frenkel, J. Chem. Phys. 109, 9901 (1998)] i-mer at spinodal at reduced temperatures from 0.7 to 1.2. It turns out that the size of a critical Stillinger i-mer remains finite and its formation free energy is on the order of kBT, and the size of a critical tWF i-mer remains finite and its formation free energy is even higher. This can be explained by Binder's theory [K. Binder, Phys. Rev. A 29, 341 (1984)] that for a system, when approaching spinodal, if the Ginzburg criterion is not satisfied, a gradual transition will take place from nucleation to spinodal decomposition, where the free-energy barrier height is on the order of kBT.

Formation free energies of clusters at high supersaturations.

The Helmholtz free energy of a constrained supersaturated vapor with a cluster size distribution consisting of clusters of various sizes is modeled as a mixture of hard spheres of various sizes attracting each other. This model naturally takes into account monomer-monomer and monomer-cluster interactions, so it implicitly pertains to nonideal gases, unlike prior work. Based on this model, the expressions for the equilibrium concentration and the formation free energies of clusters in a metastable supersaturated vapor have been derived. These results indicate that the widely used formula, ni = n1exp(-ßΔGi), that computes the formation free energy of a cluster does not work at high supersaturations. As an example, the formation free energies of clusters with Stillinger's physical cluster definition in metastable, highly supersaturated vapors interacting via Lennard-Jones potential are studied using these expressions. Noticeable differences have been found for both the formation free energies of clusters and sizes of the critical clusters computed from our proposed expressions vs those from the formula ni = n1exp(-ßΔGi).

Pathoanatomy and Associated Injuries of Posterior Malleolus Fracture of the Ankle.

BACKGROUND: We present a classification system that progresses in severity, indicates the pathomechanics that cause the fracture and therefore guides the surgeon to what fixation will be necessary by which approach. METHODS: The primary posterior malleolar fracture fragments were characterized into 3 groups. A type 1 fracture was described as a small extra-articular posterior malleolar primary fragment. Type 2 fractures consisted of a primary fragment of the posterolateral triangle of the tibia (Volkmann area). A type 3 primary fragment was characterized by a coronal plane fracture line involving the whole posterior plafond. RESULTS: In type 1 fractures, the syndesmosis was disrupted in 100% of cases, although a proportion only involved the posterior syndesmosis. In type 2 posterior malleolar fractures, there was a variable medial injury with mixed avulsion/impaction etiology. In type 3 posterior malleolar fractures, most fibular fractures were either a high fracture or a long oblique fracture in the same fracture alignment as the posterior shear tibia fragment. Most medial injuries were Y-type or posterior oblique fractures. This fracture pattern had a low incidence of syndesmotic injury. CONCLUSION: The value of this approach was that by following the pathomechanism through the ankle, it demonstrated which other structures were likely to be damaged by the path of the kinetic energy. With an understanding of the pattern of associated injuries for each category, a surgeon may be able to avoid some pitfalls in treatment of these injuries. LEVEL OF EVIDENCE: Level III, retrospective comparative series.

The free energy of the metastable supersaturated vapor via restricted ensemble simulations. III. An extension to the Corti and Debenedetti subcell constraint algorithm.

In order to improve the sampling of restricted microstates in our previous work [C. Nie, J. Geng, and W. H. Marlow, J. Chem. Phys. 127, 154505 (2007); 128, 234310 (2008)] and quantitatively predict thermal properties of supersaturated vapors, an extension is made to the Corti and Debenedetti subcell constraint algorithm [D. S. Corti and P. Debenedetti, Chem. Eng. Sci. 49, 2717 (1994)], which restricts the maximum allowed local density at any point in a simulation box. The maximum allowed local density at a point in a simulation box is defined by the maximum number of particles Nm allowed to appear inside a sphere of radius R, with this point as the center of the sphere. Both Nm and R serve as extra thermodynamic variables for maintaining a certain degree of spatial homogeneity in a supersaturated system. In a restricted canonical ensemble, at a given temperature and an overall density, series of local minima on the Helmholtz free energy surface F(Nm, R) are found subject to different (Nm, R) pairs. The true equilibrium metastable state is identified through the analysis of the formation free energies of Stillinger clusters of various sizes obtained from these restricted states. The simulation results of a supersaturated Lennard-Jones vapor at reduced temperature 0.7 including the vapor pressure isotherm, formation free energies of critical nuclei, and chemical potential differences are presented and analyzed. In addition, with slight modifications, the current algorithm can be applied to computing thermal properties of superheated liquids.

Is the rate of re-operation after primary lumbar microdiscectomy affected by surgeon grade or intra-operative lavage of the disc space?

STUDY DESIGN. Retrospective audit of consecutive patients. OBJECTIve. To investigate the re-operation rate following elective primary lumbar microdiscectomy and to determine whether principal surgeon grade and/or disc space lavage is a factor in recurrence. SUMMARY OF BACKGROUND DATA. Recurrent herniation of disc material following lumbar microdiscecomy surgery is one of the commonest complications of the procedure. Any reduction in the number of revision microdiscectomies performed per year would have a significant impact on patients' lives and on the health service economy. We undertook this study to ascertain whether principal surgeon grade and/or disc space lavage has an impact in reducing the re-operation rate. METHODS. We undertook a retrospective audit of patients who underwent elective primary lumbar microdiscectomy, over a 3-year period (n = 971). RESULTS. The overall re-operation rate for primary elective microdiscectomy was 3.8%, consistent with the published literature. The relative risk of re-operation in patients primarily operated by registrar surgeons was 1.2 fold the risk in patients operated by consultants (95% CI: 0.62, 2.35) although not statistically significant (p = 0.568). The risk of re-operation in the 'non lavage' group was 2.15 times the risk in the 'lavage' group (95% CI: 0.63, 7.34), but it did not reach significance (p = 0.222). CONCLUSIONS. Principal surgeon grade and intervertebral disc lavage have not been found conclusively to be factors in the rate of recurrence. This information is useful to reassure patients that their outcome from such surgery is not dependent on the grade of surgeon performing the operation. There is a possible trend towards intervertebral disc lavage reducing the rate of recurrence.

Total wrist arthroplasty using the Universal 2 prosthesis.

PURPOSE: To report outcomes of 21 total wrist arthroplasties (TWA) using the Universal 2 prosthesis. METHODS: Five men and 14 women aged 44 to 82 (mean, 62) years underwent 21 total wrist arthroplasties for rheumatoid arthritis (n=19) and post-traumatic arthritis (n=2) by a single surgeon using the Universal 2 prosthesis. Pre- and post-operative pain and function were assessed by a single surgeon using the Disabilities of the Arm, Shoulder and Hand (DASH) score and the patient-rated wrist evaluation (PRWE) score. Range of motion, stability, dislocation rate, and neurovascular status were also assessed. Radiographs were evaluated for implant alignment and fit, screw positioning, and implant loosening. RESULTS: The mean time to assessment of the range of motion was 3.1 (range, 1.8-3.9) years, and the mean time to assessment of the PRWE score was 4.8 (range, 2.1-7.3) years. The range of motion in each direction and the mean DASH and PRWE scores improved significantly following TWA. Two patients had restricted range of motion, which was treated by manipulation under anaesthetic (after 6 months in one and 8 weeks in the other). One patient underwent excision of a palmar bony bridge. One patient endured extensor pollicis longus rupture and underwent tendon transfer after 5 months. Radiographs revealed no evidence of implant loosening, migration, or malalignment. There was no sign of osteonecrosis in the remaining carpals or metacarpals. CONCLUSION: The Universal 2 TWA achieved significant improvement in range of motion and functional outcome of the wrist, with reduced rates of early joint instability, dislocation, and implant loosening, compared to previous implants. The small implant size and cementless design reduce bone loss and osteonecrosis.

Intramedullary fixation of diaphyseal clavicle fractures using the rockwood clavicle pin: review of 86 cases.

AIM: This study reports the safety, efficacy and functional and patient centred outcomes of the largest published series of patients treated with the Rockwood clavicle pin (intramedullary device) to date. PATIENTS AND METHODS: A retrospective review of case notes, radiographs and follow-up by questionnaire was conducted. 86 patients were operated upon, 70 for acute fractures (group A) and 16 for non-union (group B). RESULTS: Rate of non-union was 2 (2.9%) in group A and 0 in group B. Mean Disability of the Arm, Shoulder and Hand (DASH) scores were 5.9 for group A and 8.7 for group B. Satisfaction was rated as good or excellent in 61 (96.8%) of responders and all patients would have the procedure again. Pin prominence was the predominant complication in both groups and all patients underwent a second procedure for metalwork removal. DISCUSSION: Rockwood clavicle pins are as effective as plates in achieving union and maintaining length, however the advantages of this less invasive technique should be weighed against the common complication of pin prominence and the inconvenience of removal of metalwork in all cases.

Distal radius volar locking plates: does a variable angle locking system confer a clinical advantage?

This retrospective study compared clinical, radiological and subjective outcomes between patients with a distal radius fracture fixed with a variable angle or fixed angle volar locking plate. Radiological parameters were assessed between initial and final post-operative films. Post-operative clinical range of motion as a proportion of that in the opposite wrist was assessed clinically, and satisfaction and subjective outcomes were assessed by questionnaire. One hundred and seven patients were included in the study; 65 underwent fixation with a variable angle and 42 with a fixed angle locking plate. There were five complications and secondary operations in each group. There was no significant difference between the groups in radiological parameters measured or the proportional range of motion. Visual analogue scale, Mayo Wrist and Quick DASH scores were not significantly different between the groups. Neither the subjective nor clinical outcomes of this study demonstrated clinical superiority of either plate system.