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PubMed2006

Glenoid bone grafting with a reverse design prosthesis.

The purpose of this study was to evaluate the outcome of patients who underwent glenoid bone grafting and implantation of a reverse design prosthesis in 1 or 2 stages for the treatment of glenoid bone loss and rotator cuff insufficiency. Indications for the reverse prosthesis in this series included cuff tear arthropathy and revision arthroplasty. Nine patients were reviewed clinically and radiographically with a minimum 2-year follow-up (range, 24-41 months). Despite a low postoperative functional score (mean Constant score, 53 points [range, 22-79 points]), most patients were satisfied with their results primarily because of pain relief. (The mean pain score increased from 3 points preoperatively to 12.5 points postoperatively.) Radiographic evaluation did not demonstrate component loosening or evidence of graft failure. Six patients had radiographic evidence of an inferior scapular notch, which may be of concern in the future. Early results of this procedure are encouraging, but further clinical and radiologic assessment is necessary.

Aged↗
PubMed2000

Analysis of a femoral hip prosthesis designed to reduce stress shielding.

The natural stress distribution in the femur is significantly altered after total hip arthroplasty (THA). When an implant is introduced, it will carry a portion of the load, causing a reduction of stress in some regions of the remaining bone. This phenomenon is commonly known as stress shielding. In response to the changed mechanical environment the shielded bone will remodel according to Wolff's law, resulting in a loss of bone mass through the biological process called resorption. Resorption can, in turn, cause or contribute to loosening of the prosthesis. The problem is particularly common among younger THA recipients. This study explores the hypothesis that through redesign, a total hip prosthesis can be developed to substantially reduce stress shielding. First, we describe the development of a new femoral hip prosthesis designed to alleviate this problem through a new geometry and system of proximal fixation. A numerical comparison with a conventional intramedullary prosthesis as well as another proximally fixed prosthesis, recently developed by Munting and Verhelpen (1995. Journal of Biomechanics 28(8), 949-961) is presented. The results show that the new design produces a more physiological stress state in the proximal femur.

Adult↗
PubMed2000

Orofacial prosthesis design and fabrication using stereolithography.

The use of stereolithography for the manufacture of implantable prostheses is relatively new. Until now, its use with regard to mandibular resection has been to produce pre-operative models that allow more sophisticated planning of the contour and better preparation of the metallic framework to be implanted. This framework rejoins the sections of the mandible, returning some function, but providing no soft tissue support. Hence, the aesthetic results are not optimal. The aim of this study was to investigate the accuracy with which a stereolithographic model could be made to completely reunite both surfaces of the resected mandible and restore full contour. The design and fabrication of a mandibular prosthesis utilizing CAD/CAM technology and stereolithography is still in the early stages, but initial results indicate that with further research and better tools this could provide a new approach to mandibular resections, providing better aesthetic results.

Computer-Aided Design↗
PubMed1997

The role of implants in restorative dentistry: prosthesis design and aesthetic considerations.

When implants are used to anchor an intra-oral prosthesis, the resulting dentition should not only function well but also be aesthetically pleasing. Both aspects must therefore be carefully considered in the assessment of each case. Optimal aesthetics can be achieved only if a number of criteria, of which the amount and quality of bone present in a potential implant site are most important, are fulfilled. Collapse of the labial cortical plate is common, occurring two to three years after extraction. It can result in palatal placement of implant fixtures, leading to a poor crown emergence profile. Insertion of an implant fixture after initial socket healing but before resorption has occurred will maintain the labial contour. This technique is being used with increasing success.

Dental Abutments↗
PubMed2001

[Glenohumeral joint. Anatomical aspects and implications for prosthesis design].

Knowledge of normal anatomy and kinematics of the glenohumeral joint as well as analysis of the pathoanatomic changes that occur during the course of the disease is the condition for successful patient management. This review article critically discusses the most relevant geometrical variables. Systematically, normal anatomy, pathologic anatomy, and the implications for prosthetic design and implantation are presented. The most important aspects concerning the size and shape of the glenoid, the inclination of the articular surface in the horizontal and frontal planes, as well as the geometry of the scapular neck are discussed. The accumulated knowledge is of immediate practical use and might stimulate researchers and manufacturers to develop more adequate glenoid components.

Biomechanical Phenomena↗
PubMedDate not supplied

Toward identifying specification requirements for digital bone-anchored prosthesis design incorporating substructure fabrication: a pilot study.

PURPOSE: This paper is the first in a series that aims to identify the specification requirements for advanced digital technologies that may be used to design and fabricate complex, soft tissue facial prostheses. MATERIALS AND METHODS: Following a review of previously reported techniques, appropriate and currently available technologies were selected and applied in a pilot study. This study uses a range of optical surface scanning, computerized tomography, computer-aided design, and rapid prototyping technologies to capture, design, and fabricate a bone-anchored auricular prosthesis, including the retentive components. The techniques are assessed in terms of their effectiveness, and the results are used to identify future research and specification requirements to direct developments. RESULTS: The case study identifies that while digital technologies may be used to design implant-retained facial prostheses, many limitations need to be addressed to make the techniques clinically viable. It also identifies the need to develop a more robust specification that covers areas such as resolution, accuracy, materials, and design, against which potential technologies may be assessed. CONCLUSION: There is a need to develop a specification against which potential technologies may be assessed for their suitability in soft tissue facial prosthetics. The specification will be developed using further experimental research studies.

Biocompatible Materials↗
PubMedDate not supplied

Radiologic, mechanical, and histologic evaluation of 2 glenoid prosthesis designs in a canine model.

Aseptic loosening of glenoid components is a common problem associated with total shoulder arthroplasty. A new glenoid design aimed at improving fixation outcomes was compared with conventional keeled glenoids in weight-bearing canine shoulders. Radiographic, histologic, and mechanical tests were performed at 3 postoperative intervals (0, 3, and 6 months). The uncemented pegged glenoid achieved bone ingrowth around the peg flanges in each case. This result was confirmed histologically and radiographically. Mechanical results indicated that mean fixation strength increases significantly between 0 and 3 months after surgery and remains strong through 6 months. In contrast, conventional keeled glenoids were found to have partial or complete radiolucent lines around the keel in each instance, and mechanical testing demonstrated that mean fixation strength weakens significantly between 0 and 3 months after surgery and remains weak through 6 months. These results show that stem design changes can improve implant fixation. A cementless fluted peg stem was superior to a conventional cemented keel design in achieving osseous integration and fixation in a weight-bearing animal model.

Animals↗
PubMed1978

The mechanics of the knee and prosthesis design.

The mechanisms controlling and limiting movement and serving to transmit load between the femur and the tibia are discussed. Having accounted for the transmission of all components of force and couple across the joint and noted the load-bearing role of the menisci, some principles which might guide the design of knee prostheses are deduced. It is shown that current designs transgress some of these principles. An experimental prosthesis is then described, which incorporates analogues of the natural menisci. The possible practical application of this novel principle has been studied in cadaveric human joints and in living patients.

Biomechanical Phenomena↗
PubMedDate not supplied

Grammont reverse prosthesis: design, rationale, and biomechanics.

Combined destruction of the rotator cuff and the glenohumeral joint may lead to a painful and pseudo-paralyzed shoulder. In this situation a nonconstrained shoulder prosthesis yields a limited functional result or may even be contraindicated. Previous constrained prostheses (ball-and-socket or reverse ball-and-socket designs) have failed because their center of rotation remained lateral to the scapula, which limited motion and produced excessive torque on the glenoid component, leading to early loosening. The reverse prosthesis designed by Paul Grammont, unlike any previous reverse ball-and-socket design, has introduced 2 major innovations that have led to its success: (1) a large glenoid hemisphere with no neck and (2) a small humeral cup almost horizontally oriented with a nonanatomic inclination of 155 degrees, covering less than half of the glenosphere. This design medializes and stabilizes the center of rotation, minimizes torque on the glenoid component, and helps in recruiting more fibers of the anterior and posterior deltoid to act as abductors. Furthermore, the humerus is lowered relative to the acromion, restoring and even increasing deltoid tension. The Grammont reverse prosthesis imposes a new biomechanical environment for the deltoid muscle to act, thus allowing it to compensate for the deficient rotator cuff muscles. The clinical experience does live up to the biomechanical concept: the reverse prosthesis restores active elevation above 90 degrees in patients with a cuff-deficient shoulder. However, external rotation often remains limited, particularly in patients with an absent or fat-infiltrated teres minor. Internal rotation is also rarely restored after a reverse prosthesis. Failure to restore sufficient tension in the deltoid may result in prosthetic instability. The design does appear to protect against early loosening of the glenoid component, but impingement of the humeral cup on the scapular neck can lead to scapular notching and polyethylene wear. This is a cause for concern, especially as the notch is often more extensive than can be explained by impingement alone. Bony lysis of the scapula may also be related to a polyethylene granuloma. Further follow-up is required to ensure that loosening does not become a problem in the long term, and it has been recommended to limit its use to elderly patients, arguably those aged over 70 years. Despite these concerns, the reverse prosthesis, based on the biomechanical Grammont concept, offers a true surgical option in several situations where only limited possibilities were previously available: cuff tear arthrosis, persistent shoulder pseudo-paralysis due to a massive and irreparable cuff tear, severe fracture sequelae, prosthetic revision in a cuff-deficient shoulder, and tumor surgery. Finally, surgeons must be aware that results are less predictable and complication/revision rates are higher in revision surgery.

Biomechanical Phenomena↗
PubMed2000

The TRAC PS mobile-bearing prosthesis: design rationale and in vivo 3-dimensional laxity.

We present a posterior stabilized mobile-bearing prosthesis, TRAC PS, which has congruent contact from full extension to full flexion, allows for freedom of internal-external rotation, and has an automatic posterior shift in tibiofemoral contact on the tibia to maximize the quadriceps lever arm in flexion. TRAC PS has 2 radii of curvature in the sagittal plane, 1 for the distal femoral condyles and 1 for the posterior femoral condyles, as does the normal knee. The distal and posterior femoral condyles articulate congruently in the inner tracks or the outer tracks of the polyethylene bearing, respectively. Anterior or posterior sliding of the femoral condyles on the bearing or of the bearing on the tibial tray cannot occur, providing inherent anterior and posterior stability. Three-dimensional knee laxity testing was performed on 17 patients from 12 months to 25 months after total knee arthroplasty with the TRAC PS and on 18 healthy control subjects of similar ages. Normal ligament balancing and normal internal-external rotational laxity were achieved with the TRAC PS prosthesis. Anterior and posterior laxity in the patients with TRAC PS was significantly reduced compared with that of the control subjects.

Arthroplasty, Replacement, Knee↗
PubMed2004

Replacement of missing maxillary canines with dental implants: prosthesis design considerations.

Replacing a missing canine with a dental implant is the optimal treatment plan. The strategic roles canines play in maintaining normal function and the high visibility of these teeth, especially in the maxilla, require a restoration that provides uncompromised function and aesthetics. Eliminating lateral forces on the implant can minimize implant complications, but in young patients (ie, with steep canine guidance) achieving such a goal presents a restorative challenge. This article discusses several considerations (ie, ease of maintenance, retrievability) that will affect the design of the definitive restoration.

Adult↗
PubMed2001

Small-diameter compliant arterial graft prosthesis: Design concept of coaxial double tubular graft and its fabrication.

To minimize compliance mismatch between native artery and arterial graft prosthesis over the entire pressure regions, we proposed a coaxial double tubular artificial graft which consists of an enhanced compliant inner tube and a less compliant outer tube, both of which were fabricated using well-controlled multiply micropored segmented polyurethane (SPU) films. Double tubular grafts were coaxially assembled by inserting the inner tube into the outer tube. First, the pressure-diameter (P-D) relationship of canine common carotid arteries, which exhibited a "J" curve, was determined as a targeted artery. Two determinant variables, the pressure-induced distensibility of each tube and the intertubular space distance, were defined and formulated in several models of coaxial double tubular SPU grafts, which had various intertubular space distances, micropore densities, and wall thicknesses. The distensibility of the inner tube determined the distensibility in the low-pressure regions, which was adjusted using wall thickness and microporosity. Thinner films with higher porosities resulted in a high pressure-induced distensibility. On the other hand, a low pressure-induced distensibility in the high-pressure regions was realized using an outer tube with a thicker wall and lower microporosity. The transition point from low- to high-pressure regions was determined by the intertubular distance using the theoretical values. On the basis of these results, we presented a prototype model of a coaxial double tubular graft that exhibited well-matched compliance with canine carotid artery.

Animals↗
PubMed2001

The effect of femoral prosthesis design on cement strain in cemented total hip arthroplasty.

Finite element studies show that the highest cement stresses are located at the most proximal and distal ends of the prosthesis. In vitro biomechanical and histologic analyses of autopsy-retrieved cemented femoral components show these areas to be associated with cement-prosthesis debonding. In this study, cement strains were measured in 2 geometrically different femoral stems in paired cadaver femora: A straight, collared, moderately tapered stem (Centralign) was compared with an anatomically curved, collarless, dramatically tapered stem (Scientific Hip Prosthesis [SHP]). Results showed that the maximum strain and the overall strain profile differed between the 2 stems. The Centralign had peak strains located at the most proximal gauge positions, whereas the peak strains of the SHP were located around the middle of the femoral stem. Minimization of cement strain, especially at the crucial proximal and distal areas of the stem, by altering component design may be able to reduce cement-prosthesis debonding and improve clinical results.

Arthroplasty, Replacement, Hip↗
PubMed1993

A method of selecting the best implant prosthesis design option using three-dimensional finite element analysis.

This report presents a method for determining the optimum arrangement of implants and the optimum scheme of prosthesis splinting using biomechanics and three-dimensional finite element analysis. The three-dimensional finite element structural analysis method was used to determine the distribution of occlusal forces on teeth and dental implants. The results of the analysis showed that force distribution on occlusal surfaces does not change significantly with changes in the scheme of prosthesis splinting or implant positions. The induced stresses in bone are sensitive to the scheme of prosthesis splinting and implant positions. Induced stresses on implants for different schemes of prosthesis splinting and different implant positions varied as much as 1,000%. Therefore, the selection of implant positions and of the scheme of prosthesis splinting is critical for the longevity and stability of an implant prosthesis.

Bite Force↗
PubMed2003

Periprosthetic bone remodelling of two types of uncemented femoral implant with proximal hydroxyapatite coating: a 3-year follow-up study addressing the influence of prosthesis design and preoperative bone density on periprosthetic bone loss.

Periprosthetic bone loss is a major cause of concern in patients undergoing total hip arthroplasty (THA). Further studies are required to identify the factors determining the pattern of bone remodelling following THA and obtain improvements in the design and durability of prostheses. In this study, we monitored periprosthetic bone loss around two different types of hydroxyapatite coated femoral implant over a 3-year period to evaluate their design and investigate the relationship with the preoperative bone mineral density (BMD) at the spine, hip and forearm. Sixty patients (35 F, 25 M, mean age 63 years, range 46-75 years) undergoing THA were randomised to either the Anatomic Benoist Girard (ABG) or Mallory-Head (MH) femoral stem. Preoperative dual-energy X-ray absorptiometry (DXA) scans were acquired of the posteroanterior (PA) and lateral lumbar spine, the contralateral hip and the non-dominant forearm. Postoperative DXA scans were performed to measure periprosthetic BMD at 10 days (treated as baseline), 6 weeks, and 3, 6, 12, 24 and 36 months after THA using a standard Gruen zone analysis. Results were expressed as the percentage change from baseline and the data examined for the differences in bone loss between the different Gruen zones, between the ABG and MH stems, and the relationship with preoperative BMD. A total of 50 patients (24 ABG, 26 MH) completed the study. Three months after THA there was a statistically significant BMD decrease in every Gruen zone that varied between 5.6% and 13.8% for the ABG prosthesis and between 3.8% and 8.7% for the MH prosthesis. Subsequently, in most zones BMD reached a plateau or showed a small recovery. However, BMD continued to fall in Gruen zones 1 and 7 in ABG patients and Gruen zone 1 in MH patients. Bone loss was less in every Gruen zone in MH patients compared with ABG with the largest difference (10%, P=0.018) in Gruen zone 7. Highly significant relationships were found between periprosthetic bone loss and preoperative BMD measured at the PA spine ( P<0.001), total hip ( P=0.004) and total distal radius ( P<0.001). This study showed differences between two different designs of hydroxyapatite-coated implant that confirmed that prosthesis design influences periprosthetic bone loss. The study also showed that patients' bone density measured at the spine, hip or forearm at the time of operation was a major factor influencing bone loss around the femoral stem.

Absorptiometry, Photon↗