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Biomedical subjects

Harry E Rubash

Publications and source records attributed to Harry E Rubash.

At least 37 records · Page 2Linked to original sources
PubMed2005

In vivo kinematics of the ACL during weight-bearing knee flexion.

No study has investigated the three-dimensional morphological changes of the anterior cruciate ligament (ACL) during functional activities in vivo. The purpose of this study was to analyze the elongation, rotation (twist), and orientation of the ACL during weight-bearing flexion in five human subjects using dual-orthogonal fluoroscopic images and MR image-based computer models. The ACL consistently decreased in length with flexion. At 90 degrees , the length decreased by 10% compared to its length at full extension. The ACL twisted internally by only 20 degrees at 30 degrees of flexion. The ACL was oriented more vertically (approximately 60 degrees ) and slightly laterally (approximately 10 degrees ) at low flexion angles. These data on in vivo ligament elongation demonstrate that the ACL plays a more important role in lower flexion angles than at higher flexion angles during weight-bearing flexion. These data also suggest that successful ACL reconstruction should not only restore the ligament's elongation behavior, but also its rotational and orientation characteristics, so that normal ACL biomechanics are restored.

Adult↗
PubMed2005

Anterior tibial post impingement in a posterior stabilized total knee arthroplasty.

Despite the numerous long-term success reports of posterior stabilized (PS) total knee arthroplasty (TKA), recent retrieval studies of various PS TKA designs revealed wear and deformation on the anterior side of the tibial post. This study investigated the mechanisms of anterior impingement of the post with the femoral component. Seven cadaveric knees were tested to study kinematics and tibial post biomechanics during simulated heel strike using an in vitro robotic testing system. Intact knee kinematics and in situ anterior cruciate ligament (ACL) forces were determined at hyperextension (0 degree to -9 degrees) and low flexion angles (0 degrees to 30 degrees) under the applied loads. The same knee was reconstructed using a PS TKA. The kinematics and the tibial post contact forces of the TKA were measured under the same loading condition. The ACL in the intact knee carried load and contributed to knee stability at low flexion angles and hyperextension. After TKA, substantial in situ contact forces (252.4 +/- 173 N at 9 degrees of hyperextension) occurred in the tibial post, indicating anterior impingement with the femoral component. Consequently, the TKA showed less posterior femoral translation compared to the intact knee after the impingement. At 9 degrees of hyperextension, the medial condyle of the intact knee translated 0.1 +/- 1.1 mm whereas the medial condyle of the TKA knee translated 5.6 +/- 6.9 mm anteriorly. The lateral condyle of the intact knee translated 1.5 +/- 1.0 mm anteriorly whereas the lateral condyle of the TKA knee translated 2.1 +/- 5.8 mm anteriorly. The data demonstrated that anterior tibial post impingement functions as a substitute for the ACL during hyperextension, contributing to anterior stability. However, anterior post impingement may result in additional polyethylene wear and tibial post failure. Transmitted impingement forces might cause backside wear and component loosening. Understanding the advantages and disadvantages of the tibial post function at low flexion angles may help to further improve component design and surgical techniques and thus enhance knee stability and component longevity after TKA.

Aged↗
PubMed2005

Ex vivo wear of conventional and cross-linked polyethylene acetabular liners.

Explanted highly cross-linked polyethylene acetabular liners show third-body scratching. It was suggested that this surface damage could increase the wear rate of highly cross-linked polyethylene. We investigated the wear behavior of surgically explanted highly cross-linked and conventional acetabular liners using a hip simulator. Highly cross-linked explants showed no weight loss. The scratches and original machine marks of the highly cross-linked liners present at explantation remained during testing; the wear rates of these liners were 1.1 +/- 2.3 mg/million cycles, representing weight gain. In contrast, conventional liners showed wear rates of -12.9 +/- 1.4 mg/million cycles, representing weight loss. Wear was associated with rapid surface polishing and scratch elimination. After testing, the liners were melted to trigger shape memory and recover plastic deformation-induced surface changes. Highly cross-linked liners showed substantial recovery of original machining marks after melting, indicating that the scratches were a result of plastic deformation and not wear. None of the conventional polyethylenes showed any recovery after melting. The wear resistance of the highly cross-linked polyethylene studied was not compromised by surface changes that occurred during the first year of in vivo service.

Acetabulum↗
PubMed2005

Acetabular anatomy and transacetabular screw fixation at the high hip center.

A quadrant system that defines the safe acetabular locations for screw placement exists for the anatomic hip center. We wanted to develop a similar system for the high hip center. The purposes of our study were to identify the anatomic structures at risk during placement of transacetabular screws in the high hip center, to identify maximum bone depth for screw purchase, and to determine if a high hip center quadrant system could be validated to guide placement of screws during acetabular arthroplasty. For this cadaver study of nine pelves, an acetabulum was reamed superiorly into the high hip center a distance equal to (1/2) of the native acetabular diameter. Screws exiting the acetabular bone by 15 mm were inserted before a computed tomography scan and a precise anatomic dissection were done. Structures at risk of penetration by screws include the external iliac vessels, the obturator nerve and vessels, the superior gluteal nerve and vessels, and the sciatic nerve. We found that a quadrant system at the high hip center can demarcate safe zones for screw placement. At the high hip center, only the peripheral (1/2) of the posterior quadrants are safe for screw placement.

Acetabulum↗
PubMed2005

In vivo articular cartilage contact kinematics of the knee: an investigation using dual-orthogonal fluoroscopy and magnetic resonance image-based computer models.

BACKGROUND: Quantifying the in vivo cartilage contact mechanics of the knee may improve our understanding of the mechanisms of joint degeneration and may therefore improve the surgical repair of the joint after injury. OBJECTIVE: To measure tibiofemoral articular cartilage contact kinematics during in vivo knee flexion. STUDY DESIGN: Descriptive laboratory study. METHODS: Orthogonal fluoroscopic images and magnetic resonance image-based computer models were used to measure the motion of the cartilage contact points during a quasi-static lunge in 5 human subjects. RESULTS: On the tibial plateau, the contact point moved in both the anteroposterior and the mediolateral directions during knee flexion. On the medial tibial plateau, flexion angle did not have a statistically significant effect on the location of the contact points. The total translation of the contact point from full extension to 90 degrees of flexion was less than 1.5 mm in the anteroposterior direction, whereas the translation in the mediolateral direction was more than 5.0 mm. In the anteroposterior direction, the contact points were centered on the medial tibial plateau. On the lateral tibial plateau, there was a statistically significant difference between the location of the contact point at full extension and the locations of the contact points at other flexion angles in the anteroposterior direction. No significant difference was detected between the location of the contact points at other flexion angles. The overall range of contact point motion was about 9.0 mm in the anteroposterior direction and about 4.0 mm in the mediolateral direction. The contact points were primarily on the inner half of the medial and lateral tibial plateaus (the half closest to the tibial spine). The contact points on both femoral condyles were also on the inner half of the condyles (near the condylar notch). CONCLUSIONS: The tibiofemoral contact points move in 3 dimensions during weightbearing knee flexion. The medial tibiofemoral contact points remained within the central portion of the tibial plateau in the anteroposterior direction. Both the medial and lateral tibiofemoral contact points were located on the inner portions of the tibial plateau and femoral condyles (close to the tibial spine), indicating that the tibial spine may play an important role in knee stability. CLINICAL RELEVANCE: The results of this study may provide important insight as to the mechanisms contributing to the development of osteoarthritis after ligament injuries.

Adult↗
PubMed2004

Function of the anterior cruciate ligament after unicompartmental knee arthroplasty: an in vitro robotic study.

The objective of this study was to investigate the role of the anterior cruciate ligament (ACL) in the anterior-posterior (AP) stability of the knee after unicompartmental knee arthroplasty (UKA). AP tibial loads were applied to human cadaveric knee specimens using a robotic testing system. After UKA, the knee exhibited tibial translations similar to that of the native knee, and the forces in the ACL were also similar to those seen in the native knee. The ACL-deficient knee after UKA exhibited significantly greater anterior tibial translations than the native knee and the knee after UKA with an intact ACL. These data suggest that medial UKA does not alter the anterior stability of the knee, but a functional ACL is necessary to ensure normal stability after UKA.

Aged↗
PubMed2004

Osteoblast proliferation and maturation by bisphosphonates.

Aseptic loosening and osteolysis are currently the most common causes of failure of total joint replacements. Osteolysis is initiated by a macrophage response to wear debris, resulting in localized, osteoclastic peri-implant bone loss. We have previously inhibited osteoclast-mediated bone resorption in a canine total hip arthroplasty model using oral bisphosphonate therapy. Based on serendipitous observations from our canine study, we hypothesized that bisphosphonates have an anabolic effect on osteoblasts, in a manner distinct from their inhibitory effect on osteoclastic bone resorption. We studied the anabolic effects of two FDA-approved bisphosphonates (alendronate and risedronate) on two in vitro models: a primary human trabecular bone cell culture and the MG-63 osteoblast-like cell line. Following treatment with bisphosphonates at varying concentrations and time periods, cells were assayed for proliferation effects and results were quantified using the methods of direct cell count, and the colorimetric MTT (3-dimethylthiazol-2,5-diphenyltetrazolium bromide) assay at 24, 48, and 72 h. The effect of bisphosphonates on the maturation of osteoblasts were tested with alkaline phosphatase bioassay and reverse transcription-polymerase chain reaction for markers of osteoblast differentiation. Results from both the primary human trabecular bone cell culture and the MG-63 osteoblast-like cell line showed that both bisphosphonates significantly increased the cell number over controls, attaining peak levels at a concentration of 10(-8)M. Alkaline phosphatase activity was also increased, representing earlier commitment of osteoprogenitor cells towards the osteoblastic phenotype. Bisphosphonates also enhanced gene expression of BMP-2, Type I collagen and osteocalcin. In summary, bisphosphonates, aside from their role as inhibitors of osteoclastic bone resorption, are promoters of osteoblast proliferation and maturation.

Adaptation, Physiological↗
PubMed2004

In vivo tibiofemoral contact analysis using 3D MRI-based knee models.

This paper quantified the motion of the tibiofemoral contact points during in vivo weight bearing flexion using MRI- based 3D knee models and two orthogonal fluoroscopic images. The contact points on the medial and lateral tibial plateau were calculated by finding the centroid of the intersection of the tibial and femoral cartilage layers and by using the bony geometry alone. Our results indicate that the medial femoral condyle remains in the central portion of the tibial plateau and the lateral condyle translates posteriorly with increasing flexion. Using the bony contact model increased the total translation of the medial and lateral condyles by 250 and 55%, respectively, compared to the cartilage contact model. These results suggest that using the bony geometry alone may not accurately represent the articular surfaces of the knee. Articular cartilage geometry may have to be used to accurately quantify tibiofemoral contact.

Adult↗
PubMed2004

Kinematics of the knee at high flexion angles: an in vitro investigation.

Restoration of knee function after total knee, meniscus, or cruciate ligament surgery requires an understanding of knee behavior throughout the entire range of knee motion. However, little data are available regarding knee kinematics and kinetics at flexion angles greater than 120 degrees (high flexion). In this study, 13 cadaveric human knee specimens were tested using an in vitro robotic experimental setup. Tibial anteroposterior translation and internal-external rotation were measured along the passive path and under simulated muscle loading from full extension to 150 degrees of flexion. Anterior tibial translation was observed in the unloaded passive path throughout, with a peak of 31.2+/-13.2 mm at 150 degrees. Internal tibial rotation increased with flexion to 150 degrees on the passive path to a maximum of 11.1+/-6.7 degrees. The simulated muscle loads affected tibial translation and rotation between full extension and 120 degrees of knee flexion. Interestingly, at high flexion, the application of muscle loads had little effect on tibial translation and rotation when compared to values at 120 degrees. The kinematic behavior of the knee at 150 degrees was markedly different from that measured at other flexion angles. Muscle loads appear to play a minimal role in influencing tibial translation and rotation at maximal flexion. The results imply that the knee is highly constrained at high flexion, which could be due in part to compression of the posterior soft tissues (posterior capsule, menisci, muscle, fat, and skin) between the tibia and the femur.

Biomechanical Phenomena↗
PubMed2004

In situ forces of the anterior and posterior cruciate ligaments in high knee flexion: an in vitro investigation.

The function of the anterior and posterior cruciate ligaments (ACL and PCL) in the first 120 degrees of flexion has been reported extensively, but little is known of their behavior at higher flexion angles. The aim of this investigation was to study the effects of muscle loads on the in situ forces in both ligaments at high knee flexion (>120 degrees). Eighteen fresh-frozen human knee specimens were tested on a robotic testing system from full extension to 150 degrees of flexion in response to quadriceps (400 N), hamstrings (200 N), and combined quadriceps and hamstrings (400 N/200 N) loads. The in situ forces in the ACL and PCL were measured using the principle of superposition. The force in the ACL peaked at 30 degrees of flexion (71.7 +/- 27.9 N in response to the quadriceps load, 52.3 +/- 24.4 N in response to the combined muscle load, 32.3 +/- 20.9 N in response to the hamstrings load). At 150 degrees, the ACL force was approximately 30 N in response to the quadriceps load and 20 N in response to the combined muscle load and isolated hamstring load. The PCL force peaked at 90 degrees (34.0 +/- 15.3 N in response to the quadriceps load, 88.6 +/- 23.7 N in response to the combined muscle load, 99.8 +/- 24.0 N in response to the hamstrings load) and decreased to around 35 N at 150 degrees in response to each of the loads. These results demonstrate that the ACL and PCL carried significantly less load at high flexion in response to the simulated muscle loads compared to the peak loads they carried in response to the same muscle loads at other flexion angles. The data could provide a reference point for the investigation of non-weight bearing flexion and extension knee exercises in high flexion. Furthermore, these data could be useful in designing total knee implants to achieve high flexion.

Aged↗
PubMed2004

Economic evaluation in total hip arthroplasty: analysis and review of the literature.

We performed a bibliographic search of MEDLINE databases from January 1966 to July 2002 to identify English language articles that contained either "cost" or "economic" in combination with "total hip arthroplasty" (THA) in the abstract or title. Each study was then critically reviewed for content, technique, and adherence to established healthcare economic principles. Only 81 of the 153 studies retrieved contained actual economic data. Only 6% of studies adhered to established criteria for a comprehensive health care economic analysis. Although the number of publications regarding economic evaluation of THA is on the rise, the methodologic quality of many of these studies remains inadequate. Future studies should employ sound healthcare economic techniques to properly evaluate and assess the true social and economic value of THA.

Arthroplasty, Replacement, Hip↗
PubMed2004

Long-stem cemented calcar replacement arthroplasty for proximal femoral bone loss.

Revision total hip arthroplasty with accompanying bone defects may require calcar replacement prostheses to restore hip stability and function. Twenty-nine hips in 27 patients were followed for a mean of 41 months (range, 24-101 months). The average Harris Hip Score increased from 34 to 82 points. Acceptable cement mantles (A, B, C1) were present in all cases. Three femoral components (10.3%) were re-revised as a result of aseptic loosening. Two others (6.9%) were loose by radiographic criteria. Thus, 24 (82.8%) of the 29 index femoral components were rigidly fixed according to radiographic criteria, whereas 26 (89.7%) still were in place at the time of review. The results of this study suggest that long-stem cemented calcar-replacement prostheses with modern cementing technique are a reasonable option in femoral revision arthroplasties involving proximal bone loss.

Aged↗
PubMed2004

The painful total hip replacement.

Total hip replacement is one of the most common and successful orthopaedic procedures. However, evaluation and treatment of the painful total hip replacement is one of the most difficult challenges for the arthroplasty surgeon. The differential diagnosis includes causes that are intrinsic and extrinsic to the hip. A thorough history and physical examination provide the basis for a focused, efficient workup of the painful total hip replacement. The temporal onset, duration, severity, site, and character of the pain all provide important clues in determining the cause of the painful total hip replacement. The physical examination should focus on tests and maneuvers that reproduce the patient's symptoms. Laboratory tests and radiographic evaluation are used selectively as indicated by the history and physical examination findings. With a careful and thorough evaluation, the cause of the painful total hip replacement can be determined in most patients, and the appropriate treatment can be initiated.

Algorithms↗
PubMed2004

Proprioception, kinesthesia, and balance after total knee arthroplasty with cruciate-retaining and posterior stabilized prostheses.

BACKGROUND: The effect of total knee arthroplasty on proprioception, kinesthesia, and postural control remains controversial. It is argued that retaining the posterior cruciate ligament may help to preserve these sensorimotor functions and improve the longevity of the prosthesis and the functional outcome. We performed a prospective, randomized study to assess proprioception, kinesthesia, and balance following total knee arthroplasty with cruciate-retaining and posterior stabilized prostheses. METHODS: Twenty patients scheduled to undergo total knee arthroplasty were randomly assigned to receive either a cruciate-retaining or a posterior stabilized prosthesis. Joint-position sense, the threshold to detect joint motion, and the subject's ability to balance on an unstable platform were assessed prior to and at least six months after the operation. Paired two-tailed t tests (with a level of significance of p < 0.05) were used to assess the effect of the arthroplasty on the preoperative measures for all subjects. Analysis of covariance was performed to identify the effects of prosthetic design. RESULTS: Following total knee arthroplasty, patients detected motion significantly faster and reproduced joint position with less error. The balance index also improved significantly from the preoperative to the postoperative evaluation. The group treated with the posterior stabilized prosthesis more accurately reproduced joint position when the knee was extended from a flexed position. CONCLUSIONS: Total knee arthroplasty results in mild improvements in proprioception, kinesthesia, and balance. These changes may result from the retensioned capsuloligamentous structures and reduced pain and inflammation. Retention of the posterior cruciate ligament does not appear to significantly improve proprioception and balance compared with those functions in patients with a posterior stabilized total knee design.

Aged↗
PubMed2004

Knee kinematics with a high-flexion posterior stabilized total knee prosthesis: an in vitro robotic experimental investigation.

BACKGROUND: An analysis of contemporary total knee arthroplasty reveals that, on the average, patients rarely flex the knee beyond 120 degrees. The biomechanical mechanisms that inhibit further flexion after total knee arthroplasty are unknown. The objective of the present study was to investigate the capability of a single design of a fixed-bearing, high-flexion posterior stabilized total knee arthroplasty system (LPS-Flex) to restore the range of flexion to that of the intact knee. METHODS: Thirteen cadaveric human knees were tested, with use of a robotic testing system, before and after total knee arthroplasty with the LPS-Flex prosthesis. The passive path and the kinematics under an isolated quadriceps force of 400 N, under an isolated hamstring force of 200 N, and with these forces combined were determined. Posterior femoral translation of the lateral and medial femoral condyles and tibial rotation were recorded from 0 degrees to 150 degrees of flexion. RESULTS: The medial and lateral condyles of the intact knee translated posteriorly from full extension to 150 degrees, reaching a mean peak (and standard deviation) of 22.9 +/- 11.3 mm and 31.9 +/- 12.5 mm, respectively, under the combined muscle forces. Following total knee arthroplasty, the amount of posterior femoral translation was lower than that observed in the intact knee. At 150 degrees, approximately 90% of the intact posterior femoral translation was recovered by the total knee replacement. Internal tibial rotation was observed for all knees throughout the range of motion. The cam-spine mechanism engaged at approximately 80 degrees and disengaged at 135 degrees. Despite the absence of cam-spine engagement, further posterior femoral translation occurred from 135 degrees to 150 degrees. CONCLUSIONS: The tibiofemoral articular geometry of the intact knee and the knee after total knee arthroplasty with use of the LPS-Flex design demonstrated similar kinematics at high flexion angles. The cam-spine mechanism enhanced posterior femoral translation only at the mid-range of flexion. The femoral component geometry of the LPS-Flex total knee prosthesis may improve posterior tibiofemoral articulation contact in high flexion angles.

Aged↗
PubMed2003

Macrophage response to cross-linked and conventional UHMWPE.

To prevent wear debris-induced osteolysis and aseptic loosening, cross-linked ultra-high molecular weight polyethylene's (UHMWPE) with improved wear resistance have been developed. Hip simulator studies have demonstrated very low wear rates with these new materials leading to their widespread clinical use. However, the biocompatibility of this material is not known. We studied the macrophage response to cross-linked UHMWPE (XLPE) and compared it to conventional UHMWPE (CPE) as well as other clinically used orthopaedic materials such as titanium-alloy (TiAlV) and cobalt-chrome alloy (CoCr). Human peripheral blood monocytes and murine macrophages, as surrogates for cells mediating peri-implant inflammation, were cultured onto custom designed lipped disks fabricated from the test materials to isolate cells. Culture supernatants were collected at 24 and 48h and analyzed for cytokines such as IL-1alpha, IL-1beta, TNF-alpha and IL-6. Total RNA was extracted from adherent cells and gene expression was analyzed using qualitative RT-PCR. In both in vitro models, macrophages cultured on cross-linked and conventional polyethylene released similar levels of cytokines, which were also similar to levels on control tissue culture dishes. Macrophages cultured on TiAlV and CoCr-alloy released significantly higher levels of cytokines. Human monocytes from all donors varied in the magnitude of cytokines released when cultured on identical surfaces. The variability in individual donor responses to TiAlV and CoCr surfaces may reflect how individuals respond differently to similar stimuli and perhaps reveal a predisposed sensitivity to particular materials.

Animals↗
PubMed2003

Femoral rollback after cruciate-retaining and stabilizing total knee arthroplasty.

Limited data comparing the kinematics of posterior cruciate ligament-retaining or substituting total knee arthroplasty with its own intact knee under identical loadings is available. In the current study, posterior femoral translation of the lateral and medial femoral condyles under unloaded conditions was examined for intact, cruciate-retaining, cruciate ligament-deficient cruciate-retaining and posterior-substituting knee arthroplasties. Cruciate-retaining and substituting total knee arthroplasties behaved similarly to the cruciate-deficient cruciate-retaining total knee arthroplasty between 0 degrees and 30 degrees flexion. Beyond 30 degrees, the posterior cruciate-retaining arthroplasty showed a significant increase in posterior translation of both femoral condyles. The posterior cruciate-substituting arthroplasty only showed a significant increase in posterior femoral translation after 90 degrees. At 120 degrees, both arthroplasties restored approximately 80% of that of the native knee. Posterior translation of the lateral femoral condyle was greater than that observed in the medial condyle for all knees, indicating the presence of internal tibial rotation during knee flexion. The data showed that the posterior cruciate ligament is an important structure in posterior cruciate-retaining total knee arthroplasty and proper balancing is imperative to the success of the implant. The cam-spine engagement is valuable in restoring posterior femoral translation in posterior cruciate-substituting total knee arthroplasty.

Aged↗