Dynamics of an epidemic model with relapse over a two-patch environment.

In this paper, with the assumption that infectious individuals, once recovered for a period of fixed length, will relapse back to the infectious class, we derive an epidemic model for a population living in a two-patch environment (cities, towns, or countries, etc.). The model is given by a system of delay differential equations with a fixed delay accounting for the fixed constant relapse time and a non-local term caused by the mobility of the individuals during the recovered period. We explore the dynamics of the model under two scenarios: (i) assuming irreducibility for three travel rate matrices; (ii) allowing reducibility in some of the three matrices. For (i), we establish the global threshold dynamics in terms of the principal eigenvalue of a 2×2 matrix. For (ii), we consider three special cases so that we can obtain some explicit results, which allow us to explicitly explore the impact of the travel rates. We find that the role that the travel rate of recovered and infectious individuals differs from that of susceptible individuals. There is also an important difference between case (i) and (ii): under (ii), a boundary equilibrium is possible while under (i) it is impossible.

Dynamic analysis of the recurrent epidemic model.

In this work, an SIRS model with age structure is proposed for recurrent infectious disease by incorporating temporary immunity and delay. We formulate the model as an abstract non-densely defined Cauchy problem and derive the conditions for the global stability of disease free equilibrium, the local stability of endemic equilibrium, and the existence of Hopf bifurcation. Both non-periodic and periodic behaviors are possible when the disease persists in population, where time delay plays an important role. Numerical examples are provided to illustrate our theoretical results.

Patient-specific instrumentation does not improve accuracy in total knee arthroplasty.

Patient-specific instrumentation (PSI) has been introduced as a tool to increase the accuracy of total knee arthroplasty (TKA) compared with conventional instrumentation (CLI). However, previous studies have shown inconsistent results. The authors conducted a meta-analysis to compare the performance of PSI to CLI in TKA. PubMed, EMBASE, and Cochrane Central Register of Controlled Trials electronic databases were systematically searched to identify eligible trials published between 2000 and March 2014. Two reviewers independently assessed methodological quality according to the Cochrane Handbook. Subgroup analyses were performed based on the different study designs (randomized, controlled trial [RCT] vs non-randomized, controlled trial [non-RCT]), preoperative magnetic resonance imaging vs computed tomography, and systems of PSI to explore the source of heterogeneity. Fourteen studies (7 RCTs and 7 non-RCTs) involving 1906 patients were included. There were no statistical differences with respect to the outliers of mechanical axis, coronal femoral component, sagittal femoral component, femoral component rotation, operative time, blood loss, and length of hospital stay between PSI and CLI groups. The number of outliers in coronal tibial components (odds ratio, 2.29; 95% confidence interval, 1.20 to 4.35; P=.01) and sagittal tibial components (odds ratio, 1.67; 95% confidence interval, 1.16 to 2.42; P<.01) was significantly lower in the CLI group than in the PSI group. Based on the numbers available, the use of PSI compared with CLI was not likely to improve the accuracy of component alignment and treatment effects of TKA. Further high-quality RCTs are warranted to confirm the authors' results.

Does immobilization after arthroscopic rotator cuff repair increase tendon healing? A systematic review and meta-analysis.

INTRODUCTION: To determine whether immobilization after arthroscopic rotator cuff repair improved tendon healing compared with early passive motion. MATERIALS AND METHODS: A systematic electronic literature search was conducted to identify randomized controlled trials (RCTs) comparing early passive motion with immobilization after arthroscopic rotator cuff repair. The primary outcome assessed was tendon healing in the repaired cuff. Secondary outcome measures were range of motion (ROM) and American Shoulder and Elbow Surgeons (ASES) shoulder scale, Simple Shoulder Test (SST), Constant, and visual analog scale (VAS) for pain scores. Pooled analyses were performed using a random effects model to obtain summary estimates of treatment effect with 95% confidence intervals. Heterogeneity among included studies was quantified. RESULTS: Three RCTs examining 265 patients were included. Meta-analysis revealed no significant difference in tendon healing in the repaired cuff between the early-motion and immobilization groups. A significant difference in external rotation at 6 months postoperatively favored early motion over immobilization, but no significant difference was observed at 1 year postoperatively. In one study, Constant scores were slightly higher in the early-motion group than in the immobilization group. Two studies found no significant difference in ASES, SST, or VAS score between groups. CONCLUSION: We found no evidence that immobilization after arthroscopic rotator cuff repair was superior to early-motion rehabilitation in terms of tendon healing or clinical outcome. Patients in the early-motion group may recover ROM more rapidly. LEVEL OF EVIDENCE: Level II; systematic review of levels I and II studies.

[Problems and solutions in minimally invasive process of posterior discectomy for lumbar disc herniation].

OBJECTIVE: To analyze the problems and complications of posterior discectomy for lumbar disc herniation. METHODS: From January 2005 to June 2010, 497 patients with lumbar disc herniation were treated by posterior discectomy, which data were analyzed retrospectively. There were 395 males and 102 females,ranging in age from 20 to 78 years with an average of 43.7 years. Among them, 405 cases were in single gap, 86 cases were in double gaps and 6 cases were in three gaps. The complication of operation and solution was analyzed. RESULTS: The mean operative time was 70 min (from 45 to 210 min), and the mean hospitalization was 10 d (from 5 to 20 d). Forty-seven cases suffered operative complications. There were 16 cases of wrong location of segments (14 cases occurred in operation and 2 occurred after operation), 15 cases of less alleviation or aggravation of nerve symptoms (12 cases were poor alleviation and 3 cases were aggravation), 10 cases of urinary retention, 5 cases of cerebrospinal fluid leakage and 1 case of infection. CONCLUSION: Minimally invasive process of posterior discectomy in treating lumbar disc herniation may complicate with many problems. The operative effects can be improved and the complication can be decreased if the ability of location is improved,surgical indications is correct and the operation is exactly performed.