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At least 973 records · Page 54Linked to original sources
PubMed2005

A novel method for assessing variations in visual acuity after the blink.

A novel instrument was developed to assess the visual acuity in correlation with time after blink. The method uses an optical blink detector which triggers the display of a random target symbol on a computer monitor. The delay time between blink and symbol display varies randomly from blink to blink, the exposure duration is fixed at 100 ms. The subject has to identify the correct symbol, a score is kept of the correct responses in correlation to delay time. The recovery of visual acuity after blink was measured for subjects wearing two types of bifocal contact lenses and a control group of non-contact lens wearers. All groups required between 200 and 500 ms to achieve their best visual acuity. Subjects wearing the translating bifocal lenses recovered their vision significantly faster than the subjects wearing no lens or the simultaneous vision bifocal lens.

Adult↗
PubMed2004

Primary stability of a robodoc implanted anatomical stem versus manual implantation.

OBJECTIVE: To assess the initial stability of anatomical stems implanted in manually broached femoral cavities compared with that assessed in cavities milled with the robodoc system. DESIGN: The bone-prosthesis interface motion was measured in matched pairs of cadaveric femora to assess the initial stability of anatomical stems implanted with two different implantation techniques. BACKGROUND: The high costs of surgical robots and the increased perioperative efforts associated with their use can only be justified if measurable benefits for patients can be achieved. Increased initial stability of the stem as an early indicator for better bone ongrowth would be such a benefit. METHODS: Seven pairs of fresh frozen human cadaveric femora were used. One femur of each pair was randomly assigned to receive the robotic milling method; the other femur underwent manual broaching by an experienced surgeon. Initial micromotions of the anatomical stems were measured during simulated gait cycles with loads of < or =1500 N, and both groups underwent matched-pair analysis. Results. High motion of the prostheses was found for both implantation techniques. CONCLUSIONS: The robodoc system did not enhance the primary stability of the anatomical prosthesis compared with the manual broaching method.

Adult↗
PubMed2005

The impact of the CCD-angle on range of motion and cup positioning in total hip arthroplasty.

BACKGROUND: Biomechanical analysis and clinical experience reveal that offset total hip stems increase soft tissue tension and reduce the risk for dislocation in total hip arthroplasty. Most of these stems have a smaller neck-shaft-angle to increase the offset. This study investigates if changing the neck-shaft-angle has an impact on how cup and stem should be positioned with regard to range of motion. METHODS: A mathematical model of a total hip arthroplasty was developed to analyze range of motion until impingement between cup and neck. Range of motion was determined for each combination of neck-shaft-angles and additional parameters like cup inclination, cup anteversion, stem antetorsion, head/neck ratio and design of the cup opening. RESULTS: A maximized range of motion is achieved for neck-shaft-angles between 125 degrees and 131 degrees . Reducing the neck-shaft-angle by one degree requires reducing the cup anteversion by about 2 degrees and increasing the cup inclination by 0.45 degrees . Stems with neck-shaft-angles more than 135 degrees are not recommended when the head/neck ratio is 2.3 or less. INTERPRETATION: Stems with a reduced neck-shaft-angle for an increased offset should be coupled with cups that are inclined slightly higher and less anteverted as compared to a standard stem. Precise recommendations for optimal component positioning can only be given for a specific prosthesis system regarding all parameters.

Arthroplasty, Replacement, Hip↗
PubMed2005

Bilateral symmetry of the human metacarpal: implications for sample size calculations.

OBJECTIVE: The aim of this study was to assess the three-dimensional mechanical symmetry of the human second metacarpal and provide sample size estimates for future mechanical intervention studies of the metacarpal. DESIGN: Bone densitometry and digital image analysis were used to assess the morphometric, geometric and densitometric symmetry of the second human metacarpal. BACKGROUND: An assessment of the left-right mechanical symmetry of the human metacarpal is important in considering the suitability of using the contralateral metacarpal as a control and in providing sample size calculations for future studies involving a mechanical intervention to the metacarpal such as implantation of a metacarpophalangeal prosthesis. METHODS: Metaphyseal sectional areas, diaphyseal cortical sectional areas, second moments of area, average periosteal and medullary radii and bone densities were measured at nine transverse levels for each of seven pairs of index metacarpals using computed tomography and bone densitometry. Polar Fourier regression was used to assess the morphometry of sectional periosteal and endosteal boundaries. Differences between clinically important left-right parameters were assessed. RESULTS: Mean differences between clinically important left-right parameters were small (<3%) and similar to the degree of experimental precision. There were strong significant left-right correlations for the morphometric, geometric and densitometric parameters considered, indicating a high degree of bilateral mechanical symmetry. CONCLUSIONS: The contralateral bone is a suitable control for mechanical intervention studies of the human metacarpal, and the use of bilateral pairing results in an important reduction in sample size. RELEVANCE: Responses to mechanical interventions on the human metacarpal, such as implantation of a metacarpophalangeal prosthesis, are generally unknown. The degree of left-right mechanical symmetry in the human metacarpal provides a measure of the advantage of using paired design studies to address these questions.

Anatomy, Cross-Sectional↗
PubMed2006

Patient-prosthesis mismatch does not affect survival following aortic valve replacement.

OBJECTIVE: Patient-prosthesis mismatch (PPM) has been reported to increase perioperative mortality and reduce postoperative survival in patients undergoing aortic valve replacement (AVR). We analysed the effect of PPM at values predicting severe mismatch on survival following AVR in our unit. METHODS: Prospectively collected data on 1481 consecutive patients who had undergone AVR with or without coronary artery revascularisation between 1997 and 2005 were analysed. Projected in vitro valve effective orifice area (EOA) and geometric prosthesis internal orifice area (GOA) were evaluated and values were indexed to body surface area (cm(2)m(-2)). PPM was defined as EOAi<0.6 and/or GOAi<1.1. Long-term survival data were obtained from the National Institute of Statistics. RESULTS: One thousand four hundred and eighteen patients were identified. 67/1418 (4.7%) patients had GOAi<1.1; 122/1418 (8.6%) had EOAi<0.6 and 38 (2.6%) patients exhibited both forms of mismatch. One thousand two hundred and sixty-seven patients (89%) demonstrated no mismatch (reference group). There were 75 in-hospital deaths (overall mortality 5.3%) with no significant difference between the mismatch and the reference groups. Survival data were available for up to 8 years (median 36 months, IQR 6-60 months). There were 160 late deaths (13/143 PPM group vs 147/1198 reference group). The 5-year survival estimate was similar for both groups (83% PPM group; 81% reference group; p=0.47). Cox-hazard analysis identified advanced age as the only predictor of reduced survival (age>80, RR 2.13, 95% CI 1.38-4.586, p=0.004). CONCLUSIONS: Severe patient-prosthesis mismatch was predicted in 4-10% of patients undergoing AVR but this did not affect in-hospital mortality or mid-term survival.

Adult↗
PubMed2006

Patient prosthesis mismatch affects short- and long-term outcomes after aortic valve replacement.

OBJECTIVE: The aim of this study was to evaluate the impact of patient prosthesis mismatch (PPM) and additional risk factors on outcome after aortic valve replacement (AVR). METHODS: Four thousand one hundred and thirty-one patients who were operated between May 1996 and April 2004 were evaluated. One thousand eight hundred and fifty-six patients received bileaflet mechanical AVR and 2275 stented xenograft AVR. PPM was defined as severe if manufacturers effective orifice area (EOA) divided by body surface area (BSA) was <0.65 cm(2)/m(2) and as moderate in the range of 0.65-0.85 cm(2)/m(2). PPM, age, gender, EOA index, emergency indication for surgery (within 24h), EuroSCORE as well as requirement for additional procedures were tested. Univariate (Fisher's exact test) and multivariate logistic regression analysis as well as survival analysis (Kaplan-Meier) were performed. RESULTS: Severe PPM was present in 97 (2.4%) and moderate PPM in 1103 (26.7%) patients. PPM occurs more frequently with xenograft AVR. In-hospital mortality was 5.2% for severe, 10.6% for moderate and 6.9% with no PPM (p=0.018, OR 1.4). Moderate PPM was independently predictive for short- and long-term mortality. Further analysis revealed patient age >70 years (n=1589, p=0.002, OR 1.85), emergency indication (n=374, p<0.001, OR 4.4), EuroSCORE >10 (n=494, p<0.001, OR 4.7) and additional cardiac procedures (n=2049, p<0.001, OR 2.0) as predictors for adverse outcome after AVR. CONCLUSION: Severe PPM is rare; moderate PPM is present in a quarter of patients. PPM has a significant impact on short- and long-term mortality after AVR.

Aged↗
PubMed2006

Accidental sizing of patent foramen ovale during atrial septal defect sizing for device.

A 21 year old lady with a 22 mm secundum atrial septal defect with adequate rims, and thin septum at the region of the fossa ovalis, but no additional atrial septal defect by transthoracic and transoesophageal echocardiogram was taken up for ASD sizing with a view to device closure. Initially, the ASD was sized to only 8 mm. However, the distal balloon was not fully opened out, and seemed to be conical with restricted opening. Inadvertent passage of sizing balloon through a patent foramen ovale (PFO) was immediately confirmed by transthoracic echocardiogram. The ASD was then recrossed and sized to 24 mm with normal opening out of the distal balloon. This was confirmed by transthoracic echocardiogram. A 28 mm ASD device was deployed across the ASD under transthoracic echocardiographic guidance with no residual flow.

Adult↗
PubMed2006

Endoscopically guided placement of prefabricated cochlear implant electrodes in a common cavity malformation.

OBJECTIVE: To devise a safe and effective method of optimal customized electrode placement in the common cavity of children with cochleovestibular malformations. METHODS: Specialized electrodes were manufactured on the basis of three-dimensional data obtained from the high resolution computed tomography (HRCT) scans of the temporal bones of these two children. Electrode positioning was achieved with direct endoscopic view of the cavity utilizing a three-hole common cavity technique. RESULTS: Optimal electrode positioning in apposition to the medial neuroepithelium in the common cavity was verified visually intraoperatively. Postoperatively, minimal stable electrical current levels were found to be required. CONCLUSIONS: Custom-designed electrodes have the potential to offer improved results in children with common cavity malformations. Intraoperative direct positioning may further improve these results.

Cochlea↗
PubMed2005

Impact of valve prosthesis-patient mismatch on pulmonary arterial pressure after mitral valve replacement.

OBJECTIVES: We sought to determine the impact of valve prosthesis-patient mismatch (PPM) on pulmonary arterial (PA) pressure after mitral valve replacement (MVR). BACKGROUND: Pulmonary arterial hypertension is a serious complication of mitral valve disease, and it is a major risk factor for poor outcome after MVR. We hypothesized that valve PPM might be a determinant of PA hypertension after MVR. METHODS: Systolic PA pressure was measured by Doppler echocardiography in 56 patients with normally functioning mitral prosthetic valves. Mitral valve effective orifice area (EOA) was determined by the continuity equation and indexed for body surface area. RESULTS: Thirty patients (54%) had PA hypertension defined as systolic PA pressure >40 mm Hg, whereas 40 patients (71%) had PPM defined as an indexed EOA < or =1.2 cm(2)/m(2). There was a significant correlation (r = 0.64) between systolic PA pressure and indexed EOA. The average systolic PA pressure and prevalence of PA hypertension were 34 +/- 8 mm Hg and 19% in patients with no PPM versus 46 +/- 8 mm Hg and 68% in patients with PPM (p < 0.001). In multivariate analysis, the indexed EOA was by far the strongest predictor of systolic PA pressure. CONCLUSIONS: Persistent PA hypertension is frequent after MVR and strongly associated with the presence of PPM. The clinical implications of these findings are important given that PPM can largely be avoided by using a simple prospective strategy at the time of operation.

Aged↗
PubMed2005

Acromion-fixation of glenoid components in total shoulder arthroplasty.

Successful design of components for total shoulder arthroplasty has proven to be challenging. This is because of the difficulties in maintaining fixation of the component that inserts into the scapula; i.e., the glenoid component. Glenoid components that are fixated to both the glenoid and acromion (a long process extending medially on the dorsal aspect of the scapula) have the possible advantage of greater stability over those that are fixated to the glenoid alone. In this study, a finite element analysis is used to investigate whether or not acromion fixation is advantageous for glenoid components. Full muscle loading and joint reaction forces are included in the finite element model. Reflective photoelasticity of five scapulae is used to obtain experimental data to compare with results from the finite element analysis, and it confirms the structural behaviour of the finite element model. When implanted with an acromion-fixated prosthesis, it is found that high unphysiological stresses occur in the scapula bone, and that stresses in the fixation are not reduced. Very high stresses are predicted in that part of the prosthesis which connects the acromion to the glenoid. It is found that the very high stresses are partly in response to the muscle and joint reaction forces acting at the acromion. It is concluded that, because of the relatively high forces acting at the acromion, fixation to it may not be the way forward in glenoid component design.

Acromion↗
PubMed2005

A novel acetabular alignment guide for THR using selective anatomic landmarks on the pelvis.

This paper presents a novel approach for acetabular alignment during the implant of a prosthetic hip joint in a natural pelvis. The alignment instrument uses selective anatomic bony landmarks on the pelvis, which are accessible in surgery, to guide the placement of the acetabular component in the appropriate orientation. A closed form solution, involving both a forward and reverse analysis, is presented to relate the parameters of the device with the abduction and anteversion angles. Using mathematical models, this device should allow the surgeon to place the acetabular component with an orientation between 10.9 degrees and 19.1 degrees anteversion and 35.7 degrees and 44.3 degrees abduction with 95% confidence in a male/left specimen for the commonly accepted target of 15 degrees anteversion and 40 degrees abduction. This device is currently being used successfully by one of the authors in THR surgery.

Acetabulum↗
PubMed2006

Geometry of human ribs pertinent to orthopedic chest-wall reconstruction.

Orthopedic reconstruction of blunt chest trauma can aid restoration of pulmonary function to reduce the mortality associated with serial rib fractures and flail chest injuries. Contemporary chest wall reconstruction requires contouring of generic plates to the complex surface geometry of ribs. This study established a biometric foundation to generate specialized, anatomically contoured osteosynthesis hardware for rib fracture fixation. On human cadaveric ribs three through nine, the surface geometry pertinent to anatomically conforming osteosynthesis plates was characterized by quantifying the apparent rib curvature C(A), the longitudinal twist alpha(LT) along the diaphysis, and the unrolled curvature C(U). In addition, the rib cross-sectional geometry pertinent to intramedullary fixation strategies was characterized in terms of cross-section height, width, area, and cortex thickness. The rib surface exhibited a curvature C(A) ranging from 3.8 m(-1) in the anteromedial section of rib seven to 17.3 m(-1) in the posterior section of rib three. All ribs had in common a longitudinal twist alpha(LT), ranging from 41-60 degrees. The unrolled curvature C(U) decreased gradually from ribs three to five, and increased gradually with reversed orientation from rib six to nine. The cross-sectional area remained constant along the rib diaphysis. However, the medullary canal increased in size from 29.9 mm(2) posteriorly to 41.2 mm(2) in anterior rib segments. Results of this biometric rib characterization describe a novel strategy for intraoperative plate contouring and provide a foundation for the development of specialized rib osteosynthesis strategies.

Bone Plates↗
PubMed2005

Exercise hemodynamics of bovine versus porcine bioprostheses: a prospective randomized comparison of the mosaic and perimount aortic valves.

OBJECTIVE: This prospective randomized study compares a porcine with a bovine bioprosthesis in the aortic position with regard to hemodynamic performance during exercise. METHODS: Between August of 2000 and December of 2002, 136 patients underwent aortic valve replacement with the porcine Medtronic Mosaic (n = 66) or the bovine Carpentier-Edwards Perimount (n = 70) bioprosthesis. Transthoracic echocardiography was performed to assess hemodynamic and dimensional data preoperatively and 10 months postoperatively; the latter follow-up included stress echocardiography with treadmill exercise. RESULTS: At rest and during exercise (25 and 50 W), there was a significant difference in mean pressure gradient between the bovine and the porcine valves with labeled sizes 21 and 23, with superiority of the Perimount prosthesis. There was no difference in effective orifice area and incidence of patient-prosthesis mismatch among all sizes. The left ventricular mass index decreased significantly within 10 months postoperatively in the size 23 bovine group and the size 25 porcine group. CONCLUSIONS: Our data show a significant superiority of pressure gradients for the bovine bioprosthesis, especially with small valve sizes, when compared with the porcine device, which is more distinctive during exercise.

Aged↗