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Biomedical subjects

Douglas A Dennis

Publications and source records attributed to Douglas A Dennis.

At least 19 recordsLinked to original sources
PubMed2006

Evaluation of off-loading braces for treatment of unicompartmental knee arthrosis.

Two analyses were performed to assess the effectiveness of off-loading knee braces in producing condylar separation of degenerative compartments in patients with unicompartmental knee osteoarthritis. All patients were analyzed using video fluoroscopy under weight-bearing conditions. In the initial study, a single brace was analyzed in 2 dimensions and demonstrated that medial condylar separation was obtained, with corresponding pain relief, in 78% of patients. The brace was least effective in obese patients. The second study consisted of a 3-dimensional analysis of 5 subjects fitted with 5 different off-loading braces. Condylar separation in most patients was similarly observed with certain braces, whereas others demonstrated little to no condylar separation, suggesting that off-loading knee braces are not equally effective in treatment of unicompartmental knee arthritis.

Braces↗
PubMed2006

Mobile-bearing total knee arthroplasty: design factors in minimizing wear.

Premature polyethylene wear is a major cause of total knee arthroplasty (TKA) failure. It has been attributed to numerous factors including poor surgical technique, reduced polyethylene thickness, poor locking mechanisms of modular fixed bearing tibial components, gamma irradiation sterilization techniques in the presence of oxygen, and low conformity implant designs. The incidence of implantation of TKA into younger patients who have increased activity requirements and longevity expectations is increasing. This requires continued analysis of design features lessening polyethylene wear. The purpose of this manuscript is to review clinical and basic scientific studies of factors influencing polyethylene wear, focusing on the potential benefits of mobile bearing TKA which potentially reduce long-term polyethylene wear by providing increased implant conformity and reduced polyethylene contact stresses. In vivo kinematic studies have shown self-alignment of the polyethylene bearing with the femoral component typically occurs in rotating platform TKA designs which should hypothetically lessen polyethylene surface stresses, minimize stabilizing post impingement, and increase the potential for enhanced polyethylene longevity.

Humans↗
PubMed2006

The role of patellar resurfacing in TKA. Point.

While controversy persists, scientific evidence favoring patellar resurfacing in primary TKA is abundant. The literature demonstrates a substantially higher incidence of anterior knee pain and reoperation rates if the patella is not resurfaced primarily. Prospective, randomized studies have reported reoperation rates to convert unresurfaced patellas to resurfaced patellas exceed those for complications after patellar resurfacing. When resurfacing the patella, strict surgical principles are paramount to avoid complications. These include duplicating the original patella thickness, maintaining the patellar blood supply, achieving central patellar tracking, and properly positioning the femoral, tibial, and patellar components. Optimum prosthetic design features for patella resurfacing include an anatomic, asymmetric trochlear groove that is broad, extended, (distally and posteriorly) and deeper compared with first-generation designs.

Arthroplasty, Replacement, Knee↗
PubMed2006

Trends in total knee arthroplasty.

The success of total knee arthroplasty (TKA) over the past two decades of use has resulted in the implantation of TKA into younger patients who have increased functional requirements and demand increased implant longevity. Improved functional performance requires enhanced range of motion, increased motor performance, and creation of kinematic patterns that more closely resemble the normal knee. Increased longevity necessitates more durable implant fixation, improvements in bearing materials, and lower polyethylene stresses. Considerations to reduce polyethylene wear include increased cross-linking, improved femoral component surface finish, better modular tibial locking mechanisms, and the use of mobile-bearing TKA designs that allow increased implant conformity and reduced contact stresses without increasing loads transmitted to the fixation interface.

Arthroplasty, Replacement, Knee↗
PubMed2006

Patellar crepitation in the P.F.C. sigma total knee system.

Painless and painful patellar crepitation and patellar clunk syndrome represent a spectrum of peripatellar scar formation particular to posterior-stabilized knee components, although it may occur with cruciate-retaining designs as well. The formation of peripatellar inflammatory scar tissue is related to implant design and surgical technique, with microscopic and gross findings indicating varying degrees of inflammatory fibrous hyperplasia. These well recognized clinical entities have an incidence ranging between 1% and 5% in different series. The majority of patients with mildly painful or painless patellar crepitation will improve within 6 months to 1 year. In patients with more disabling symptoms such as catching, early intervention with open scar excision should be considered.

Aged↗
PubMed2005

In vivo kinematic comparison of posterior cruciate-retaining and posterior stabilized total knee arthroplasties under passive and weight-bearing conditions.

An in vivo comparison of flexion kinematics for posterior cruciate-retaining (PCR) and posterior stabilized (PS) total knee arthroplasty (TKA) was performed. Twenty patients who underwent bilateral paired TKAs were included in this prospective study. Both PCR and PS prostheses were from the same TKA series with comparable surface geometries, and all were implanted by a single surgeon. Of these 20 patients, 3-dimensional kinematics during flexion could be analyzed using a computer model fitting technique in 18 patients. The follow-up period ranged from 18 to 53 months. In the PCR TKA, an anterior femoral translation from 30 degrees to 60 degrees of flexion was observed in the weight-bearing condition. In contrast, flexion kinematics for the PS TKA was characterized by the maintenance of a constant contact position under weight-bearing conditions and posterior femoral rollback in passive flexion.

Aged↗
PubMed2005

Effect of segmentation errors on 3D-to-2D registration of implant models in X-ray images.

In many biomedical applications, it is desirable to estimate the three-dimensional (3D) position and orientation (pose) of a metallic rigid object (such as a knee or hip implant) from its projection in a two-dimensional (2D) X-ray image. If the geometry of the object is known, as well as the details of the image formation process, then the pose of the object with respect to the sensor can be determined. A common method for 3D-to-2D registration is to first segment the silhouette contour from the X-ray image; that is, identify all points in the image that belong to the 2D silhouette and not to the background. This segmentation step is then followed by a search for the 3D pose that will best match the observed contour with a predicted contour. Although the silhouette of a metallic object is often clearly visible in an X-ray image, adjacent tissue and occlusions can make the exact location of the silhouette contour difficult to determine in places. Occlusion can occur when another object (such as another implant component) partially blocks the view of the object of interest. In this paper, we argue that common methods for segmentation can produce errors in the location of the 2D contour, and hence errors in the resulting 3D estimate of the pose. We show, on a typical fluoroscopy image of a knee implant component, that interactive and automatic methods for segmentation result in segmented contours that vary significantly. We show how the variability in the 2D contours (quantified by two different metrics) corresponds to variability in the 3D poses. Finally, we illustrate how traditional segmentation methods can fail completely in the (not uncommon) cases of images with occlusion.

Algorithms↗
PubMed2005

Knee mechanics: a review of past and present techniques to determine in vivo loads.

This review article evaluates various techniques that have been used to determine in vivo loads in the human knee. Two main techniques that have been used are telemetry, which is an experimental approach, and mathematical modeling, which is a theoretical approach. Telemetric analyses have previously been used to determine the in vivo loading of the human hip and more recently evaluated in the determination of in vivo knee loads. Mathematical modeling approaches can be categorized two ways; those that use optimization techniques to solve an indeterminate system and those that utilize a reduction method that minimizes the number of unknowns, keeping the system solvable as the number of equations of motion are equal to the number of unknown quantities. More recently, we have developed an approach that relies fully on the use of in vivo data from fluoroscopy, CT scanning, magnetic resonant imaging and a revised motion analysis technique that involves only two markers on each rigid body. A review of all techniques revealed a wide range of forces at the human knee, ranging from 1.9 to 7.2 times body weight during level walking.

Algorithms↗
PubMed2005

In vivo determination of normal and anterior cruciate ligament-deficient knee kinematics.

The objective of the current study was to use fluoroscopy to accurately determine the three-dimensional (3D), in vivo, weight-bearing kinematics of 10 normal and five anterior cruciate ligament deficient (ACLD) knees. Patient-specific bone models were derived from computed tomography (CT) data. 3D computer bone models of each subject's femur, tibia, and fibula were recreated from the CT 3D bone density data. Using a model-based 3D-to-2D imaging technique registered CT images were precisely fit onto fluoroscopic images, the full six degrees of freedom motion of the bones was measured from the images. The computer-generated 3D models of each subject's femur and tibia were precisely registered to the 2D digital fluoroscopic images using an optimization algorithm that automatically adjusts the pose of the model at various flexion/extension angles. Each subject performed a weight-bearing deep knee bend while under dynamic fluoroscopic surveillance. All 10 normal knees experienced posterior femoral translation of the lateral condyle and minimal change in position of the medial condyle with progressive knee flexion. The average amount of posterior femoral translation of the lateral condyle was 21.07 mm, whereas the average medial condyle translation was 1.94 mm, in the posterior direction. In contrast, all five ACLD knees experienced considerable change in the position of the medial condyle. The average amount of posterior femoral translation of the lateral condyle was 17.00 mm, while the medial condyle translation was 4.65 mm, in the posterior direction. In addition, the helical axis of motion was determined between maximum flexion and extension. A considerable difference was found between the center of rotation locations of the normal and ACLD subjects, with ACLD subjects exhibiting substantially higher variance in kinematic patterns.

Adult↗
PubMed2005

A posterior-stabilized total knee arthroplasty shows condylar lift-off during deep knee bends.

This prospective randomized study was done to examine whether any difference in presentation of condyler lift-off exists between posterior cruciate-retaining and posterior-stabilized total knee arthroplasties. Fluoroscopic analysis of flexion kinematics under weightbearing condition was done for 18 patients who had bilateral paired total knee arthroplasties. The posterior cruciate-retaining and posterior-stabilized prostheses were from the same total knee arthroplasty series with comparable surface geometries and were implanted by one surgeon. At evaluation, five of 18 patients (28%) with posterior cruciate-retaining total knee arthroplasties had condylar lift-off, compared with 12 of 18 patients (67%) with posterior-stabilized total knee arthroplasties. Consequently, a significant difference in its incidence was seen between the groups. Condylar lift-off in posterior-stabilized knees was observed at various flexion angles, and one knee in this group had lift-off laterally and medially at different flexion angles. These findings raise concern that the higher incidence of condylar lift-off in posterior-stabilized total knee arthroplasty may lead to an increased wear rate of polyethylene associated with long-term prosthetic loosening.

Aged↗
PubMed2005

Mobile-bearing total knee arthroplasty: do the polyethylene bearings rotate?

In vivo kinematics were determined during a weightbearing deep knee bend in 39 patients implanted with four different designs of mobile-bearing total knee arthroplasty to assess polyethylene bearing mobility patterns and magnitudes. The femoral and tibial components and mobile polyethylene insert (implanted with four tantalum beads) were overlaid onto the fluoroscopic images using a three-dimensional model-fitting technique to determine bearing mobility. Three of the four designs were tested at a single time interval while one was evaluated at two postoperative intervals, (12 months apart) to assess changes in bearing mobility with time. All patients had polyethylene bearing rotation relative to the tibial tray and minimal rotation relative to the femoral component. The average maximum amounts of bearing rotation ranged from 8.4 degrees to 10.3 degrees (range, 3.0 degrees -20.1 degrees). In patients evaluated at two time intervals, the average maximum bearing rotation increased from 8.5 degrees (range, 3.4 degrees -15.5 degrees) at 3 months to 9.8 degrees (range, 48 degrees -14.1 degrees) 15 months postoperatively. The presented data demonstrates polyethylene bearing mobility occurs following mobile-bearing total knee arthroplasty and mobility is maintained during the time interval tested. The presence of bearing mobility should result in lower contact stresses reducing the potential for polyethylene wear.

Biomechanical Phenomena↗
PubMed2005

Mini-incision total knee arthroplasty can increase risk of component malalignment.

UNLABELLED: Interest in minimal-incision total knee arthroplasty has increased in recent years. We compared a group of 30 patients who had total knee arthroplasty with a mini-incision to a similar group of 30 patients who had total knee arthroplasty with a standard length incision. The minimal-incision group had some minor early advantages (less pain medication use, earlier improvement in range of motion), but these advantages dissipated by 3 months followup. Radiographic evaluations showed that four of the 30 patients with minimal incisions had tibial component varus malalignment (< 87 degrees ), whereas no patients with the standard length incision had malalignment. Although total knee arthroplasty performed using a minimal incision may provide some early advantages, minimal incisions can impede a surgeon's vision and may influence component alignment and possibly compromise long-term outcome. LEVEL OF EVIDENCE: Therapeutic study, Level III-1 (retrospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Aged↗
PubMed2005

Optimizing the femoral component cement mantle in total hip arthroplasty.

Aseptic loosening is a common cause of long-term failure of cemented femoral components in hip arthroplasty. Initiation of aseptic loosening has been associated with suboptimal cement mantle thickness and uniformity with the resultant progressive development of detrimental cement mantle defects. Long-term success is highly dependent on maintaining and protecting the integrity of the cement mantle and its interfaces primarily by decreasing cement mantle stresses. High cement stresses that initiate debonding and cement fracture can be controlled and minimized through the use of various surgical techniques that assist in creating an optimally thick, symmetric, and homogeneous cement mantle.

Arthroplasty, Replacement, Hip↗
PubMed2005

The structural allograft composite in revision total knee arthroplasty.

Although morselized cancellous autograft or allograft has been shown to be highly successful for management of smaller cavitary defects in revision TKA, structural allografts often are required for large, contained, or uncontained osseous defects. Early clinical results of revision TKA using structural allografts have been encouraging with high allograft-host union rates, as long as adequate fixation is obtained. The use of intramedullary stems with sufficient length to engage diaphyseal bone is recommended to lessen load transmission to the structural allograft and to reduce the risk of late allograft collapse or fracture. Extensive preoperative planning, meticulous operative technique, and an extended period of postoperative rehabilitation are required for optimal

Arthroplasty, Replacement, Knee↗
PubMed2005

Stability advantages of a modular total hip system.

Hip instability continues to be an infrequent, yet frustrating complication of total hip arthroplasty (THA). Restoration of normal hip anatomy and biomechanics at the time ofTHA is critical to reduce the risk of dislocation. This can be difficult in some patients due to distorted hip anatomy and wide variations in "normal" hip anatomy reported in numerous studies. Modular femoral components offer a large array of femoral offset, length, and version options which can be used independently or in combination to recreate normal osseous anatomy and a well-tensioned soft tissue envelope, which should enhance hip stability following THA.

Arthroplasty, Replacement, Hip↗
PubMed2005

Kinematics of mobile-bearing total knee arthroplasty.

In a comparison of in vivo knee kinematic patterns of mobile-bearing total knee arthroplasty with thosefrom studies of fixed-bearing total knee arthroplasty and the normal knee, no major differences in the "average" kinematic patterns of fixed- versus mobile-bearing implants was observed. However, there was less AP translation of both the medial and lateral femoral condyles during gait in patients with mobile-bearing implants. This is probably the result of the increased sagittal femorotibial conformity of most mobile-bearing implants, which reduces polyethylene shear stresses and should lessen polyethylene wear rates. In rotating-platform mobile-bearing implants, axial rotation occurs primarily on the inferior surface of the polyethylene bearing instead of on the superior surface, which reduces shear forces on the superior aspect of the polyethylene bearing, thereby lessening wear: Although the average axial rotational values after total knee arthroplasty were limited (< 10 degrees), a significant number of patients exhibited higher magnitudes of rotation (> 20 degrees), which exceeds the rotational limits of most fixed-bearing implants. Rotating-platform mobile-bearing implants may therefore be advantageous in that they can accommodate a wider range of axial rotation without creating excessive polyethylene stresses.

Arthroplasty, Replacement, Knee↗
PubMed2004

Evaluation of painful total knee arthroplasty.

Numerous conditions exist that may cause pain following total knee arthroplasty (TKA) that can be categorized into articular versus nonarticular etiologies. To critically evaluate the painful TKA, the treating physician must perform a thorough history and physical examination, as well as both laboratory and radiographic testing. Laboratory analysis is directed to differentiate septic versus aseptic etiologies of knee pain and commonly includes assessment of white blood cell count, erythrocyte sedimentation rate, C-reactive protein, and knee aspiration for cell count and cultures. Available radiographic tools include plain radiographs, stress views, arthrography, nuclear scanning, ultrasonography, and magnetic resonance imaging. In cases of unexplained pain, reoperation is unwise and frequently associated with suboptimal results. Periodic repeat evaluations are recommended until the etiology of pain is clearly determined.

Arthroplasty, Replacement, Knee↗