Statistical analysis of arthroplasty data: I. Introduction and background

It is envisaged that guidelines for statistical analysis and presentation of results will improve the quality and value of research. The Nordic Arthroplasty Register Association (NARA) has therefore developed guidelines for the statistical analysis of arthroplasty register data. The guidelines are divided into two parts, this one with an introduction and a discussion of the background to the guidelines, and the second one with a more technical statistical discussion on how specific problems can be handled (Ranstam et al. 2011b, see pages x-y in this issue). This first part contains an overview of implant survival analysis and statistical methods used to evaluate factors with a potential influence on this outcome

No improvement in long-term wear and revision rates with the second-generation Biomet cup (RingLoc) in young patients: 141 hips followed for median 12 years

Optimising joint reconstruction management in arthritis and bone tumour patient

The power of perturbation theory

We study quantum mechanical systems with a discrete spectrum. We show that the asymptotic series associated to certain paths of steepest-descent (Lefschetz thimbles) are Borel resummable to the full result. Using a geometrical approach based on the PicardLefschetz theory we characterize the conditions under which perturbative expansions lead to exact results. Even when such conditions are not met, we explain how to define a different perturbative expansion that reproduces the full answer without the need of transseries, i.e. non-perturbative effects, such as real (or complex) instantons. Applications to several quantum mechanical systems are presented

Inter- and intraobserver variation in staging patients with proven avascular necrosis of the hip.

Diagnosis and treatment of avascular necrosis of the hip has long been predicated on the evaluation of plain radiographs, though other modalities (such as magnetic resonance imaging) are being increasingly used to aid in this evaluation. The Ficat classification is commonly used to assess plain radiographs and to help determine what treatment is appropriate for a given patient. It also is used to help evaluate patient outcome after surgical or nonsurgical treatment. This study was designed to evaluate the adequacy of plain radiographs in the evaluation of avascular necrosis of the hip. The plain radiographs of 25 hips with avascular necrosis were analyzed on 3 occasions by 6 readers (450 total readings). A clinically significant difference in radiographic staging was defined as a Stage I or II reading of the radiographs of a given hip on 1 reading and a separate reading of the same radiographs as Stage III or IV. By this definition, interobserver variability for the first reading resulted in clinically significant differences in 10 (40%) of the 25 hips. Intraobserver variability resulted in clinically significant differences for 10 (40%) of the 25 hips as well. The most experienced readers in the study (a total joint specialist and a musculoskeletal radiologist) were consistent internally in their readings in 90% of cases, and had a clinically significant difference in only 1 case (1%); however, these same 2 readers disagreed with one another on the staging of 9 (36%) of 25 hips, with 4 (16%) of 25 hips having a clinically significant difference in readings.(ABSTRACT TRUNCATED AT 250 WORDS

Inter- and intraobserver variation in staging patients with proven avascular necrosis of the hip.

Diagnosis and treatment of avascular necrosis of the hip has long been predicated on the evaluation of plain radiographs, though other modalities (such as magnetic resonance imaging) are being increasingly used to aid in this evaluation. The Ficat classification is commonly used to assess plain radiographs and to help determine what treatment is appropriate for a given patient. It also is used to help evaluate patient outcome after surgical or nonsurgical treatment. This study was designed to evaluate the adequacy of plain radiographs in the evaluation of avascular necrosis of the hip. The plain radiographs of 25 hips with avascular necrosis were analyzed on 3 occasions by 6 readers (450 total readings). A clinically significant difference in radiographic staging was defined as a Stage I or II reading of the radiographs of a given hip on 1 reading and a separate reading of the same radiographs as Stage III or IV. By this definition, interobserver variability for the first reading resulted in clinically significant differences in 10 (40%) of the 25 hips. Intraobserver variability resulted in clinically significant differences for 10 (40%) of the 25 hips as well. The most experienced readers in the study (a total joint specialist and a musculoskeletal radiologist) were consistent internally in their readings in 90% of cases, and had a clinically significant difference in only 1 case (1%); however, these same 2 readers disagreed with one another on the staging of 9 (36%) of 25 hips, with 4 (16%) of 25 hips having a clinically significant difference in readings.(ABSTRACT TRUNCATED AT 250 WORDS

Symptoms as well as tumor size provide prognostic information on patients with localized renal tumors.

PURPOSE: T stage stratification of organ confined renal tumors is based only on tumor size. Currently T1a and T1b are defined as tumors less or greater than 4 cm. However, to our knowledge the validity of this stratification has not been determined. We determined whether symptoms could add additional prognostic information when integrated with tumor size into the TNM classification. MATERIALS AND METHODS: Patients with T1-T2N0M0 renal tumors at 6 academic centers in Europe and the United States were included in this study. T stage was defined according to the 2002 TNM classification. Age, gender, T stage, tumor size, symptoms at presentation, Fuhrman grade and cancer specific survival were determined in all cases. Survival estimates were compared using the Kaplan-Meier method and multivariate analysis of the data were performed with the Cox model. RESULTS: A total of 1,771 patients with pT1-T2N0M0 renal tumors were included in this study. There were 1,148 males and 623 females. Mean age was 59.6 years. Median tumor size was 5 cm. Of the tumors 781 (44.1%), 616 (34.8%) and 374 (21.1%) were stages T1a, T1b and T2, respectively. In 825 patients (46.6%) symptoms were related to renal cancer. T stage and symptoms strongly correlated, in that 67%, 51% and 29% of patients with T1a, T1b and T2 tumors, respectively, were asymptomatic. Symptoms increased the risk of cause specific death for each T stage level. On multivariate analysis Fuhrman grade (HR 1.46), T stage (HR 1.81) and symptoms (HR 2.98) were independent predictors of survival. Based on these results 4 groups resulting from combinations of 2002 TNM stage and symptoms with significantly different risks of death were defined, namely 1) T1a-4 cm or less without symptoms, 2) T1b-4 cm or less with symptoms and greater than 4 cm without symptoms, 3) T2a-greater than 4 cm and 7 cm or less with symptoms, and 4) T2b-greater than 7 cm with symptoms CONCLUSIONS: In this study we noted that a system combining tumor size and symptoms can accurately stratify patients for predicting survival in those with organ confined renal tumors. Our data support the idea that symptoms should be integrated in further modifications of the TNM system