Quality assessment of guidelines on thromboprophylaxis in orthopaedic surgery.

We evaluated the quality of guidelines on thromboprophylaxis in orthopaedic surgery by examining how they adhere to validated methodological standards in their development. A structured review was performed for guidelines that were published between January 2005 and April 2013 in medical journals or on the Internet. A pre-defined computerised search was used in MEDLINE, Scopus and Google to identify the guidelines. The AGREE II assessment tool was used to evaluate the quality of the guidelines in the study. Seven international and national guidelines were identified. The overall methodological quality of the individual guidelines was good. 'Scope and Purpose' (median score 98% interquartile range (IQR)) 86% to 98%) and 'Clarity of Presentation' (median score 90%, IQR 90% to 95%) were the two domains that received the highest scores. 'Applicability' (median score 68%, IQR 45% to 75%) and 'Editorial Independence' (median score 71%, IQR 68% to 75%) had the lowest scores. These findings reveal that although the overall methodological quality of guidelines on thromboprophylaxis in orthopaedic surgery is good, domains within their development, such as 'Applicability' and 'Editorial Independence', need to be improved. Application of the AGREE II instrument by the authors of guidelines may improve the quality of future guidelines and provide increased focus on aspects of methodology used in their development that are not robust.

Exploration and neurolysis for the treatment of neuropathic pain in patients with a sciatic nerve palsy after total hip replacement.

The purpose of this study was to establish whether exploration and neurolysis is an effective method of treating neuropathic pain in patients with a sciatic nerve palsy after total hip replacement (THR). A total of 56 patients who had undergone this surgery at our hospital between September 1999 and September 2010 were retrospectively identified. There were 42 women and 14 men with a mean age at exploration of 61.2 years (28 to 80). The sciatic nerve palsy had been sustained by 46 of the patients during a primary THR, five during a revision THR and five patients during hip resurfacing. The mean pre-operative visual analogue scale (VAS) pain score was 7.59 (2 to 10), the mean post-operative VAS was 3.77 (0 to 10), with a resulting mean improvement of 3.82 (0 to 10). The pre- and post-neurolysis VAS scores were significantly different (p < 0.001). Based on the findings of our study, we recommend this form of surgery over conservative management in patients with neuropathic pain associated with a sciatic nerve palsy after THR.

Novel use of a hip spacer to perform reconstruction following extra-articular scapula resection for sarcoma.

The shoulder is the third most common site for bone and soft tissue tumours and limb-sparing resection for tumours of the shoulder girdle remains challenging. We present a novel use of a hip spacer to perform the reconstruction following an extra-articular scapula resection for sarcoma.

A framework for predictive modeling of anatomical deformations.

A framework for modeling and predicting anatomical deformations is presented, and tested on simulated images. Although a variety of deformations can be modeled in this framework, emphasis is placed on surgical planning, and particularly on modeling and predicting changes of anatomy between preoperative and intraoperative positions, as well as on deformations induced by tumor growth. Two methods are examined. The first is purely shape-based and utilizes the principal modes of co-variation between anatomy and deformation in order to statistically represent deformability. When a patient's anatomy is available, it is used in conjunction with the statistical model to predict the way in which the anatomy will/can deform. The second method is related, and it uses the statistical model in conjunction with a biomechanical model of anatomical deformation. It examines the principal modes of co-variation between shape and forces, with the latter driving the biomechanical model, and thus predicting deformation. Results are shown on simulated images, demonstrating that systematic deformations, such as those resulting from change in position or from tumor growth, can be estimated very well using these models. Estimation accuracy will depend on the application, and particularly on how systematic a deformation of interest is.

Nonlinear elastic registration of brain images with tumor pathology using a biomechanical model.

A biomechanical model of the brain is presented, using a finite-element formulation. Emphasis is given to the modeling of the soft-tissue deformations induced by the growth of tumors and its application to the registration of anatomical atlases, with images from patients presenting such pathologies. First, an estimate of the anatomy prior to the tumor growth is obtained through a simulated biomechanical contraction of the tumor region. Then a normal-to-normal atlas registration to this estimated pre-tumor anatomy is applied. Finally, the deformation from the tumor-growth model is applied to the resultant registered atlas, producing an atlas that has been deformed to fully register to the patient images. The process of tumor growth is simulated in a nonlinear optimization framework, which is driven by anatomical features such as boundaries of brain structures. The deformation of the surrounding tissue is estimated using a nonlinear elastic model of soft tissue under the boundary conditions imposed by the skull, ventricles, and the falx and tentorium. A preliminary two-dimensional (2-D) implementation is presented in this paper, and tested on both simulated and patient data. One of the long-term goals of this work is to use anatomical brain atlases to estimate the locations of important brain structures in the brain and to use these estimates in presurgical and radiosurgical planning systems.

Further Roles of Geometry and Properties in the Mechanics of Saccular Aneurysms.

Rupture of intracranial saccular aneurysms continues to result in significant morbidity and mortality. Although it has long been thought that biomechanical factors play key roles in the genesis, growth, and rupture of these lesions, few analysis have employed realistic descriptions of the geometries and material properties. This paper presents parametric finite element studies for subclasses of elliptical and spherical lesions which complement those recently reported by Kyriacou and Humphrey. In particular, we show again that lesion shape, not size, is a primary determinant of aneurysmal wall stress. Moreover, material anisotropy and geometry can exhibit competing or synergistic effects on the stress fields - this suggests that these interactions may be important in the formulation of theories on lesion growth. Finally, we show that Laplace's equation (for spherical membranes) yields reasonable approximations for wall stress only for a very limited class of lesions. There is a need, therefore, for detailed analysis and thus more precise data on lesion geometry, material properties, and loading conditions.

Influence of size, shape and properties on the mechanics of axisymmetric saccular aneurysms.

Rupture of intracranial saccular aneurysms is the most common cause of spontaneous subarachnoid hemorrhage which, despite advances in neurosurgery, continues to result in significant morbidity and mortality. Currently, the decision to treat a diagnosed, unruptured aneurysm is based primarily on the maximum dimension of the lesion even though there is controversy over the 'critical size' (e.g. many 'large' lesions do not rupture whereas some 'small' ones do). There is a need, therefore, for improved predictors of the rupture-potential of these lesions. In this paper, we show that it is highly unlikely that saccular aneurysms expand or rupture due to a limit point instability, and suggest that a rupture-criterion should be based on local multiaxial states of stress or strain. Moreover, our results from nonlinear finite element analyses reveal important roles of lesion shape, material properties, and loading conditions, not just size, in governing the distributions of stress and strain within a sub-class of axisymmetric saccular aneurysms. For example, we find that maximum biaxial stresses and strains are most often at the fundus, where rupture tends to occur, and that maximum stresses increase markedly with increases in lesion size, the ratio of neck diameter to lesion height, and the distending transmural pressure.

The use of Laplace's equation in aneurysm mechanics.

It is widely thought that the genesis, expansion, and rupture of intracranial aneurysms are each governed, in part, by mechanical mechanisms, and consequently that continuum mechanics has an important role to play in increasing our understanding of the natural history of these lesions. Mechanical analyses must, of course, be mathematically and conceptually consistent with fundamental principles, definitions, and findings. In this note, we identify and correct fundamental errors that appear in three recent papers on the mechanics of human intracranial aneurysms. In addition, we also show that, based on a simple analysis, it is unlikely that saccular aneurysms expand or rupture due to a limit point instability, and discuss directions for future mechanical analyses of aneurysms.