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Discusses the evolution of the electronic knee prosthesis. Development of a fully instrumented tibial component of a total knee prosthesis; History of the use of a total knee prosthesis with a telemetric implant; Measurement of in vivo tibiofemoral compressive forces; Implications for knee-replacement design, rehabilitation and assistive devices such as lower-extremity braces, orthotics and shoes.

Studies the risks and prevention of venous thromboembolism (VTE). Role of congenital and acquired thrombophilic disorders in potentiating the risk of VTE associated with clinical risk factor; Levels of thromboembolism risk in surgical patients without prophylaxis; Prevalence of deep vein thrombosis in neurosurgical patients.

Background: Prosthetic impingement due to poor positioning can limit the range of motion of the hip after total hip arthroplasty. In this study, a computer model was used to determine the effects of the positions of the acetabular and femoral components and of varying head-neck ratios on impingement and range of motion.Methods: A three-dimensional generic hip prosthesis with a hemispherical cup, a neck diameter of 12.25 millimeters, and a head size ranging from twenty-two to thirty-two millimeters was simulated on a computer. The maximum range of motion of the hip was measured, before the neck impinged on the liner of the cup, for acetabular abduction angles ranging from 35 to 55 degrees and acetabular and femoral anteversion ranging from 0 to 30 degrees. Stability of the hip was estimated as the maximum possible flexion coupled with 10 degrees of adduction and 10 degrees of internal rotation and also as the maximum possible extension coupled with 10 degrees of external rotation. The effects of prosthetic orientation on activities of daily living were analyzed as well.Results: Acetabular abduction angles of less than 45 degrees decreased flexion and abduction of the hip, whereas higher angles decreased adduction and rotation. Femoral and acetabular anteversion increased flexion but decreased extension. Acetabular abduction angles of between 45 and 55 degrees permitted a better overall range of motion and stability when combined with appropriate acetabular and femoral anteversion. Lower head-neck ratios decreased the range of motion that was possible without prosthetic impingement. The addition of a modular sleeve that increased the diameter of the femoral neck by two millimeters decreased the range of motion by 1.5 to 8.5 degrees, depending on the direction of motion that was studied.Conclusions: There is a complex interplay between the angles of orientation of the femoral and acetabular components. Acetabular abduction angles between 45 and 55 degrees, when combined with appropriate acetabular and femoral anteversion, resulted in a maximum overall range of motion and stability with respect to prosthetic impingement.Clinical Relevance: During total hip arthroplasty, acetabular abduction is often constrained by available bone coverage, while femoral anteversion may be dictated by the geometry of the femoral shaft. For each combination of acetabular abduction and femoral anteversion, there is an optimum range of acetabular anteversion that allows the potential for a maximum range of motion without prosthetic impingement after total hip arthroplasty. These data can be used intraoperatively to determine optimum position. [ABSTRACT FROM AUTHOR]

Develops in vitro and in vivo models of cartilage injury. Percentages of apoptotic cells in full-thickness bovine and human explants; Effect of the presence of subchondral bone on cartilage response; Increase in the levels of apoptotic cells after injury; Implications of mechanical injury in inducing chondrocyte death in the form of apoptosis.

Examines the influence of cartilage injury in inducing chondrocyte apoptosis. Loss of chondrocyte viability after mechanical injury; Tendency of chrondrocytes to undergo apoptosis in response to wounding compression; Development of an in vitro model to determine the effect of mechanical injury on chondrocyte viability and matrix degradation; Occurrence of cell death as apoptosis or necrosis.

Determines the efficacy of several apoptosis inhibitors in preventing chondrocyte apoptosis after mechanical injury. Comparison of the levels of apoptotic cells; Increase in the percentage of cells undergoing apoptosis after injury; Prevention of apoptosis through caspase inhibition in both bovine and human cartilage; Reduction of the associated increase in glycosaminoglycan release.

The menisci are important biomechanical components of the knee. We developed and validated a finite element model of meniscal replacement to assess the effect of surgical fixation technique on contact behavior and knee stability. The geometry of femoral and tibial articular cartilage and menisci was segmented from magnetic resonance images of a normal cadaver knee using MIMICS (Materialise, Leuven, Belgium). A finite element mesh was generated using HyperWorks (Altair Inc, Santa Ana, CA). A finite element solver (Abaqus v6.9, Simulia, Providence, RI) was used to compute contact area and stresses under axial loading and to assess stability (reaction force generated during anteroposterior translation of the femur). The natural and surgical attachments of the meniscal horns and peripheral rim were simulated using springs. After total meniscectomy, femoral contact area decreased by 26% with a concomitant increase in average contact stresses (36%) and peak contact stresses (33%). Replacing the meniscus without suturing the horns did little to restore femoral contact area. Suturing the horns increased contact area and reduced peak contact stresses. Increasing suture stiffness correlated with increased meniscal contact stresses as a greater proportion of tibiofemoral load was transferred to the meniscus. A small incremental benefit was seen of simulated bone plug fixation over the suture construct with the highest stiffness (50 N/mm). Suturing the rim did little to change contact conditions. The nominal anteroposterior stiffness reduced by 3.1 N/mm after meniscectomy. In contrast to contact area and stress, stiffness of the horn fixation sutures had a smaller effect on anteroposterior stability. On the other hand suturing the rim of the meniscus affected anteroposterior stability to a much larger degree. This model emphasizes the importance of the meniscus in knee biomechanics. Appropriate meniscal replacement fixation techniques are likely to be critical to the clinical success of meniscal replacement. While contact conditions are mainly sensitive to meniscus horn fixation, the stability of the knee under anteroposterior shear loads appeared to be more sensitive to meniscal rim fixation. This model may also be useful in predicting the effect of biomaterial mechanical properties and meniscal replacement shape on knee contact conditions.

A nonlinear viscoelastic finite element model of ultra-high molecular weight polyethylene (UHMWPE) was developed in this study. Eight cylindrical specimens were machined from ram extruded UHMWPE bar stock (GUR 1020) and tested under constant compression at 7% strain for 100 sec. The stress strain data during the initial ramp up to 7% strain was utilized to model the "instantaneous" stress-strain response using a Mooney-Rivlin material model. The viscoelastic behavior was modeled using the time-dependent relaxation in stress seen after the initial maximum stress was achieved using a stored energy formulation. A cylindrical model of similar dimensions was created using a finite element analysis software program. The cylinder was made up of hexahedral elements, which were given the material properties utilizing the "instantaneous" stress-strain curve and the energy-relaxation curve obtained from the experimental data. The cylinder was compressed between two flat rigid bodies that simulated the fixtures of the testing machine. Experimental stress-relaxation, creep and dynamic testing data were then used to validate the model. The mean error for predicted versus experimental data for stress relaxation at different strain levels was 4.2%. The mean error for the creep test was 7% and for dynamic test was 5.4%. Finally, dynamic loading in a hip arthroplasty was modeled and validated experimentally with an error of 8%. This study establishes a working finite element material model of UHMWPE that can be utilized to simulate a variety of postoperative arthroplasty conditions.

Aim: Development of antithrombotic compounds has traditionally been performed in patients undergoing total hip and knee replacement surgery. A high number of asymptomatic deep-vein thromboses are radiologically detectable, and bleeding and other adverse events (AE) are easy to observe. However, standardization of study procedures and endpoints in early proof-of-concept studies and late pure clinical endpoint studies has been lacking. This has made comparison between studies difficult, economic analyses speculative and potential benefits of applying the drug regimen in non-selected patients uncertain. In this paper, the International Surgical Thrombosis Forum proposes a strategy for the clinical investigation of new pharmacological agents for the prophylaxis of postoperative thrombotic events., Methods: First, dose titration safety studies of short duration, in highly selected patients using objective venographic endpoints are recommended. Bleeding should be divided into the quantified volume of surgical bleeding and other adjudicated clinical bleeding events. The number of AE should be described for each dose step and classified according to International Coding of Diagnoses (ICD). Second, a dose confirmatory study of moderate exposure period and sufficient follow-up time is recommended. The exclusion criteria should be restricted to contraindications of the compared drugs and technical procedure., Results: The efficacy, bleeding and AE should be similar to those used in dose-titration studies. In addition, the failure rate of the drug to exert its effect and the net clinical benefit should be calculated., Conclusion: Finally, trials with simple clinical endpoints and long follow-up should be conducted to evaluate the potential benefits of the drug-regimen in non-selected populations.

Background: Prophylaxis is recommended following total joint replacement because of the high risk of venous thromboembolism (VTE). Postoperative low-molecular-weight heparin (LMWH) reduces the incidence of venographically detected deep vein thrombosis (DVT) to about 10-15% in total hip replacement (THR) patients. Ximelagatran is a novel, oral direct thrombin inhibitor that selectively and competitively inhibits both free and clot-bound thrombin. We compared the efficacy and safety of ximelagatran with those of enoxaparin for the prevention of VTE in patients undergoing THR., Methods: This was a prospective, randomized, multicenter, double-blind study conducted principally in the USA and Canada. Patients received fixed-dose oral ximelagatran 24 mg bid or subcutaneous enoxaparin 30 mg bid and matched placebo for 7-12 days; both regimens were initiated the morning after surgery. The incidence of VTE (by postoperative day 12) included thrombosis determined by mandatory venography of the leg on which surgery was performed and symptomatic, objectively proven DVT or pulmonary embolism (PE). VTE and bleeding events were interpreted by an independent central adjudication committee for primary analysis., Results: Of the 1838 patients randomized, 1557 had either adequate venography or symptomatic, proven VTE (efficacy population). Overall rate of venography acceptable for evaluation was 85.4%. Overall rates of total VTE were 7.9% (62 of 782 patients) in the ximelagatran group and 4.6% (36 of 775 patients) in the enoxaparin group, with an absolute difference of 3.3% and a 95% confidence interval for the difference of 0.9% to 5.7%. Proximal DVT and/or PE occurred in 3.6% (28 of 782 patients) in the ximelagatran group and 1.2% (nine of 774 patients) in the enoxaparin group. Major bleeding events were observed in 0.8% (seven of 906) of the ximelagatran-treated patients and in 0.9% (eight of 910) of the enoxaparin-treated patients (P > 0.95). Non-inferiority of ximelagatran 24 mg bid based on a prespecified margin of 5% was not met, resulting in superiority of the enoxaparin regimen., Conclusions: Both ximelagatran and enoxaparin decreased the overall rate of VTE compared with that reported historically. However, in this study, enoxaparin 30 mg bid was more effective than ximelagatran 24 mg bid for prevention of VTE in THR. Oral ximelagatran was used without coagulation monitoring, was well tolerated, and had bleeding rates comparable to those of enoxaparin. Further refinement by testing a higher dose of ximelagatran in the patients undergoing THR is warranted.

This study compared the efficacy and cost of radiation therapy with indomethacin in the prophylaxis of heterotopic ossification following total hip replacement. Twenty-two patients received a radiation dose of 10 Gy in five fractions, 28 patients 8 Gy in one fraction, and 27 patients 25 mg oral indomethacin three times a day for either 7 or 21 days. Patients at higher risk for heterotopic ossification were more likely to receive radiation therapy than indomethacin. At a mean follow-up of 2 years, there were no differences in failure rates between the high-risk patients treated with radiation and the low-risk patients treated with indomethacin. Currently, the patient-billed cost of radiation is $1400 whereas the cost for indomethacin is approximately $100. Indomethacin appears to be as effective as radiation therapy in patients at low to moderate risk for heterotopic ossification and offers significant cost savings.

Increased conformity at the tibiofemoral articulation increases contact area and reduces contact stresses in total knee arthroplasty. Malalignment, however, can increase polyethylene contact stresses. The effect of knee alignment and articular conformity on contact stresses was evaluated in a finite element model. The polyethylene insert and femoral component were modeled in high- and low-conformity conditions. An axial tibial load of 3000 N was applied across the tibiofemoral articulation at different knee positions ranging from 0 degrees, to 90 degrees, flexion, 0 to 10 mm anteroposterior translation, 0 degrees to 10 degrees axial rotation, and coronal plane angulation (liftoff). Increased conformity significantly reduced contact stresses in neutral alignment (by 44% at 0 degrees flexion and 36% at 60 degrees and 90 degrees flexion). Liftoff significantly increased contact stresses in low- and high-conformity conditions, but to a lesser degree in the high-conformity condition. Malalignment in rotation was most detrimental especially with the high-conformity insert design. Overall, increasing articular conformity reduced stresses when the knee was well-aligned. However, malalignment in axial rotation was detrimental. Mobile-bearing knee designs with increased articular congruity may result in lower contact stresses, especially the rotating-bearing designs that theoretically minimize rotational malalignment.

Venous thrombosis continues to be a major risk after total knee arthroplasty. Without prophylaxis, the prevalence of deep vein thrombosis is as high as 84%, with proximal occurrence as high as 20%. Of more concern is the occurrence of pulmonary embolism as high as 7%, with fatal pulmonary embolism as high as 0.7%. This high prevalence mandates that prophylaxis for thromboembolic disease be used for patients undergoing total knee arthroplasty. Low molecular weight heparin has been studied extensively and is safe and effective prophylaxis after total knee arthroplasty. Low molecular weight heparins have a predictable dose response, offer high bioavailability at low doses, and produce linear pharmacokinetics. It has a half-life of approximately 4.5 hours providing effective dosing every 12 to 24 hours with rapid antithrombotic action. Routine pharmacologic prophylaxis with low molecular weight heparin seems to be effective in decreasing the occurrence of venous thromboembolism. However, venographic prevalence of deep vein thrombosis among patients undergoing total knee arthroplasty and receiving prophylaxis remains substantial at 30.6%. Prophylaxis with low molecular weight heparin beyond hospitalization may be indicated with decreased hospital stays, although studies have not been convincing that extended outpatient prophylaxis for more then 7 to 10 days is necessary.

Objective: The effect of mechanical injury on chondrocyte viability and matrix degradation was studied. It was proposed that mechanical injury to human cartilage explants results in chondrocyte apoptosis with associated loss of glycosaminoglycans., Design: Full thickness human cartilage explants, 5 mm in diameter were subjected to a single static mechanical stress of 14 MPa for 500 ms under radially unconfined compression. Glycosaminoglycan (GAG) release and percentage of cells undergoing apoptosis were measured at 96 h after injury. To establish the time course of apoptosis, explants were subjected to 30% strain and cultured for varying intervals up to 7 days after injury. A group of loaded explants were also treated with the broad spectrum caspase inhibitor z-Vad.fmk after injury., Results: Internucleosomal DNA fragmentation as one indicator of apoptosis was observed in 34% (S.D.+/-11) of chondrocytes at 96 h in response to mechanical loading at 14 MPa, compared to 4% (S.D.+/-2) in the non-loaded explants. Evidence for cell death induction via apoptosis was also obtained by electron microscopy and caspase cleavage of cytokeratin. GAG release was also higher for the loaded explants, mean 1.9% (S.D.+/-0.14) of total GAG content, compared to control explants, mean 0.8% (S.D.+/-0.28). The percentage of apoptotic cells also correlated with the level of GAG release into the culture media. The percentage of apoptotic chondrocytes demonstrated a progressive increase from 6 h to 7 days post-injury. When loaded explants were cultured in z-Vad.fmk after injury, a 50% reduction in apoptosis rates was seen., Conclusions: These results demonstrate that mechanical injury induces chondrocyte apoptosis and release of GAG from the matrix. The time course suggests that a therapeutic window may exist where apoptosis could be inhibited. This potentially identifies a new approach to chondroprotection., (Copyright 2001 OsteoArthritis Research Society International.)

A six-station knee wear simulator was used to test a posterior cruciate-retaining total knee arthroplasty design. Six implants each were tested in three groups; low intensity, high intensity, and malalignment using kinematic inputs from normal gait data, more severe loading conditions, and 3 degrees varus malalignment, respectively. For each group, gravimetric wear of the polyethylene inserts was measured for 5,000,000 cycles. Knee wear testing showed significantly different results for the three groups. Low intensity group inserts had mean wear rates of 3.1 (+/- 1.2) mg per million cycles. High intensity group inserts had significantly higher mean wear rates of 7.4 (+/- 2.7) mg per million cycles. Malalignment group inserts had the highest wear rates of 9.2 (+/- 3.3) mg per million cycles. The wear generated in the knee simulator seems to be dependent on the relative motions and loads at the articulating surface. The high intensity groups were subjected to motions that included reciprocating anteroposterior translations and a higher peak axial load than the low intensity group. This resulted in increasing the amount of wear. Varus malalignment also increased the total wear significantly. These results may explain some of the wide variations in wear seen in retrieved knee implants.

Knee prosthetic designs that increase quadriceps moment arm can reduce quadriceps tension and patellofemoral compressive forces. Six knees from cadavers were tested on the Oxford knee rig, which simulates closed chain knee extension under load. Three conditions were tested sequentially for each knee: Normal, Control (implanted with the Osteonics 7000 knee design), and Scorpio (implanted with the Osteonics Scorpio design). The center of flexion-extension of the Scorpio design was 10 mm posterior to that of Control that served to lengthen the quadriceps moment arm. An electromagnetic tracking system measured dynamic knee kinematics, and a uniaxial load cell measured quadriceps tension. The Scorpio design reduced quadriceps tension when compared with the Normal or Control knee ranging from 5% to 20%. This was statistically significant at flexion angles greater than 50 degrees. In three knees, the patellar component was instrumented with a triaxial load cell that measured patellofemoral forces. Patellofemoral forces were lower with the Scorpio design compared with the Control. Increasing quadriceps lever arm reduces quadriceps forces and can facilitate activities of daily living and enhance patient rehabilitation. Reduced quadriceps forces may result in reduced patellofemoral forces that can have a beneficial effect on anterior knee pain, patellar component wear, and loosening.

Background: Up to one third of patients who undergo total knee replacement develop deep vein thrombosis after surgery despite receiving low-molecular-weight heparin prophylaxis. Ximelagatran is a novel direct inhibitor of free and clot-bound thrombin., Methods: We performed a randomized, parallel, dose-finding study of 600 adults undergoing elective total knee replacement at 68 North American hospitals to determine the optimum dose of ximelagatran to use as prophylaxis against venous thromboembolism after total knee replacement. Patients received either ximelagatran twice daily by mouth in blinded fixed doses of 8, 12, 18, or 24 mg or open-label enoxaparin sodium, 30 mg, subcutaneously twice daily, starting 12 to 24 hours after surgery and continuing for 6 to 12 days. We measured the 6- to 12-day cumulative incidence of symptomatic or venographic deep vein thrombosis, symptomatic pulmonary embolism, and bleeding., Results: A total of 594 patients received at least 1 dose of the study drug; 443 patients were evaluable for efficacy. Rates of overall venous thromboembolism (and proximal deep vein thrombosis or pulmonary embolism) for the 8-, 12-, 18-, and 24-mg doses of ximelagatran were 27% (6.6%), 19.8% (2.0%), 28.7% (5.8%), and 15.8% (3.2%), respectively. Rates of overall venous thromboembolism (22.7%) and proximal deep vein thrombosis or pulmonary embolism (3.1%) for enoxaparin did not differ significantly compared with 24-mg ximelagatran (overall difference, -6.9%; 95% confidence interval, -18.0% to 4.2%; P=.3). There was no major bleeding with administration of 24 mg of ximelagatran twice daily., Conclusion: Fixed-dose, unmonitored ximelagatran, 24 mg twice daily, given after surgery appears to be safe and effective oral prophylaxis against venous thromboembolism after total knee replacement.

Chondrocytes undergo apoptosis in response to mechanical injury in vitro. The current clinical study correlates arthroscopic and magnetic resonance imaging results with biopsy specimens of cartilage from patients with knee injury. Twenty patients were evaluated at a mean 2.7 months after acute knee injury. The mean age of the patients was 32 years and the mean weight was 83 kg. Cartilage lesions were graded separately on magnetic resonance images and arthroscopy in a blinded manner. During arthroscopy, a 1.8 mm diameter biopsy specimen was obtained from the edge of cartilage lesion. The biopsy specimen underwent histologic examination by safranin O staining and detection of chondrocyte apoptosis by the presence of deoxyribonucleic acid fragmentation. There was a positive correlation in 50% (10 of 20) when the presence or absence of cartilage lesions by magnetic resonance imaging was correlated with arthroscopy. All cases of partial thickness or full-thickness cartilage loss that were seen by arthroscopy also were detected by magnetic resonance images. Apoptotic cells were significantly more numerous in biopsy specimens from lesions compared with control biopsy specimens. The findings of reduced cell viability attributable to apoptosis may have profound implications for cartilage repair. This opens potential therapeutic avenues for the treatment of posttraumatic cartilage lesions through apoptosis prevention.

Posttraumatic arthritis is one of the most common causes of secondary osteoarthritis. The contribution of cell death to matrix degradation has not been characterized fully. The current study was designed to determine the effect of mechanical injury on chondrocyte viability and matrix degradation. Full-thickness bovine and human cartilage explants, 5 mm in diameter were subjected to mechanical loads representative of traumatic joint injury. Glycosaminoglycan release and percent apoptotic cells were measured. Unilateral patellas in eight anesthetized rabbits were subjected to an impact load. Rabbits were euthanized at 96 hours after injury and patellar cartilage was harvested for analysis. The effect of a pan-caspase inhibitor, z-VAD.fmk [benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethylketone] in preventing chondrocyte apoptosis in human articular cartilage explants was determined. A significant increase in the number of apoptotic cells was observed in response to mechanical loading. The mean in vivo apoptotic rates were 1% in control rabbits and 15% in impacted patellas. Caspase inhibition reduced chondrocyte apoptosis from 34% to 25% after mechanical injury and was associated with reduction in glycosaminoglycan release. Mechanical injury induces chondrocyte apoptosis that is sensitive to pharmacologic inhibition. This identifies a new approach to limit traumatic cartilage injury and the subsequent development of secondary osteoarthritis.

Patellar components come in onset and inset designs. Kinematic differences between these designs were studied in a cadaver model of closed kinetic chain knee extension. Seven frozen knees were implanted with a standard posterior cruciate-retaining design. Each knee first was tested with the inset design, followed by the onset design in the Oxford Knee Rig. Three-dimensional tracking of the femur, tibia, and patella was performed using an electromagnetic system during active knee extension under load. No statistically significant differences were seen in knee kinematics between the 2 designs. The inset patella tended to shift laterally and tilt laterally more than the onset patella. This difference may be clinically significant.

Outcome of the acetabular component in 90 consecutive primary noncemented total hip arthroplasties (THAs) was prospectively studied. The acetabular cup consisted of a hemispherical titanium alloy shell with a titanium fiber-mesh porous coating and a modular polyethylene liner (Harris-Galante Porous-1, Zimmer, Warsaw, Ind). The cup was implanted using line-to-line reaming with adjunctive dome screw fixation. The femoral component consisted of a titanium alloy stem with titanium fiber-mesh porous coating and a 28-mm cobalt-chrome modular head. Mean patient age was 53 years (range: 27-75 years); male:female ratio was 48:42; and mean follow-up was 6 years (range: 4.5-8 years). One acetabular component was revised for aseptic loosening. Of 81 unrevised hips available for follow-up, mean Harris hip score was 57 preoperatively and 96 at final follow-up (72% excellent, 15% good, 1 3% fair, and none poor). Of 61 unrevised hips with adequate radiographic follow-up, radiographic failure (complete periprosthetic radiolucency) was evident in 3 (4.9%) and periacetabular osteolysis in none. Radiographic failure did not correlate with poor clinical outcome. Linear polyethylene wear rate (mean: 0.13 mm/year) did not correlate with age, gender, weight, outcome, or cup abduction angle, but did correlate with the presence of femoral periprosthetic osteolysis (0.18 mm/year with femoral osteolysis versus 0.11 mm/year without; P= .01). This series of porous-coated hemispherical cups demonstrated excellent intermediate-term clinical and radiographic outcome, comparable with similarly favorable results reported by the prosthesis designers. A potentially adverse effect of polyethylene wear on the longevity of a THA was supported by a positive correlation between polyethylene wear rate and femoral osteolysis.

Increasing tibiofemoral articular conformity theoretically increases articular contact area and reduces contact stresses in total knee arthroplasty. Fixed-bearing knee designs possess relatively low tibiofemoral conformity, in part to allow tibiofemoral rotation without generating excessive stresses at the articulation or the implant-bone interface. This study analyzed knee kinematics of mobile-bearing designs in a closed chain dynamic knee extension model in posterior cruciate-retaining design with high- and low tibiofemoral conformity and posterior cruciate-substituting designs with and without rotational constraint. Overall, for all conditions, the mobile-bearing insert rotated with the femur in the presence of tibiofemoral axial rotation. In addition, the correlation of bearing rotation with femoral rotation was stronger for the high-conformity and rotationally-constrained designs than for the low-conformity designs and strongest for the posterior cruciate-retaining high-conformity condition. Changes in conformity or rotational constraint did not appear to affect femoral roll back, tibiofemoral axial rotation, or varus-valgus angulation. The results suggest that mobile-bearing inserts rotate with the femur and increasing conformity or rotational constraint in mobile-bearing design knee prostheses does not affect knee kinematics adversely, at least under closed chain knee extension conditions in vitro.

Rotating platform mobile bearing knee implants allow for increased tibiofemoral articular conformity without restricting axial rotation. In the current study, the effect of rotating platform knee replacement with and without posterior cruciate ligament substitution on knee kinematics was investigated. Five knees were implanted sequentially implanted with standard (fixed) bearings and then with rotating platform prostheses, each in posterior cruciate retaining and substituting designs. Three-dimensional kinematics for all knees were measured in an Oxford Knee Rig, which simulates dynamic quadriceps-driven closed kinetic chain knee extension under load. Rotating bearings did not significantly change knee kinematics when compared with fixed bearings. In this in vitro model, the cruciate retaining designs stayed more anterior, and had greater net femoral roll back and tibiofemoral valgus angulation with flexion than cruciate substituting designs.

A total of 108 consecutive Press-Fit Condylar total knee arthroplasties were performed in 94 patients. All patients had implantation with a cemented posterior cruciate-retaining design, which included resurfacing of the patella. Mean age at surgery was 70 years (range, 35-87 years). Patients were followed for a mean of 9 years (range, 8-10 years) with follow-up for all surviving patients. The average postoperative functional knee score was 96 points. Nonprogressive radiolucent lines were present in 59%. One patellar component was radiographically loose. Five knees underwent revision procedures, none for aseptic loosening. Survivorship was 93.4% at 9 years with revision for any reason as the endpoint and 98.7% with aseptic loosening as the endpoint. This knee arthroplasty shows excellent results at 8 to 10 years with no patients lost to follow-up.

With the aging population and improved methods of emergency transport, the number of surviving stroke and brain injury patients continues to increase. Aggressive rehabilitation of appropriate candidates is justified. In the period of spontaneous recovery, efforts are made to prevent fixed contractures using passive mobilization, splinting, nerve blocks, and electrical stimulation. If deformity persists and the patient is no longer recovering, operative management can help alleviate the functional and hygiene problems associated with these limb deformities.

Thirty-eight oblong bilobed noncustom uncemented, porous-coated titanium acetabular components were used to reconstruct failed hip arthroplasties with large superior segmental acetabular bone deficiencies. No structural bone grafts were used. All patients were followed up for 2 to 5 years (mean, 3 years) after the operation. One patient (whose socket rested primarily on a structural bone graft from a previous procedure) had revision surgery for acetabular loosening. No other patients have had revision surgery or had another ipsilateral hip operation. At latest followup, 35 patients had no or mild pain and two patients had moderate pain. Two implants migrated more than 2 mm in the first year, then stabilized. On the latest radiographs, two implants had bead shedding, but there was no measurable migration or change in position. For selected patients with large superolateral acetabular bone deficiencies, this implant facilitated a complex reconstruction, provided good clinical results, and showed satisfactory stability at early to midterm followup in most patients.

Background: Venous thromboembolic disease in the form of deep venous thrombosis and pulmonary embolism is a major risk after a total hip arthroplasty. Enoxaparin, a low-molecular-weight heparin, has been shown to reduce the prevalence of deep venous thrombosis after total hip arthroplasty. Warfarin, an orally administered anticoagulant, has been used historically to reduce the risk of deep venous thrombosis after total hip arthroplasty., Methods: We compared enoxaparin and adjusted-dose warfarin with respect to their safety and their efficacy in the prevention of clinically important venous thromboembolic disease, defined as distal or proximal deep venous thrombosis or pulmonary embolism, or both, during hospitalization after total hip arthroplasty. We also evaluated the prevalence of complications and mortality from venous thromboembolic disease within three months after discharge., Results: Three thousand and eleven patients at 156 centers were randomly assigned to prophylactic treatment with injection of enoxaparin or oral administration of adjusted-dose warfarin during hospitalization. During the study, fifty-five (3.6 percent) of the 1516 patients who were managed with enoxaparin and fifty-six (3.7 percent) of the 1495 patients who were managed with warfarin had venous thromboembolic disease. Twenty-one patients (0.7 percent), which included four (0.3 percent) of those managed with enoxaparin and seventeen (1.1 percent) of those managed with warfarin (p = 0.0083), had venous thromboembolic disease during hospitalization. After discharge from the hospital, venous thromboembolic disease developed in ninety patients (3.0 percent): fifty-one (3.4 percent) of those managed with enoxaparin and thirty-nine (2.6 percent) of those managed with warfarin. One patient who had been managed with enoxaparin died because of a pulmonary embolism, which was confirmed at autopsy. Three additional patients (one who had been managed with enoxaparin and two who had been managed with warfarin) died, and the deaths were attributed to venous thromboembolic disease; however, no autopsies were performed. Twenty-six patients (0.9 percent) (eighteen managed with enoxaparin and eight managed with warfarin) had clinically important bleeding., Conclusions: Inpatient programs providing treatment with either enoxaparin (thirty milligrams every twelve hours) or adjusted-dose warfarin for a mean of 7.3 days afforded protection against venous thromboembolic disease, with overall rates of morbidity and mortality of 3.7 and 0.6 percent, respectively, and a very low rate of major bleeding complications (0.9 percent) for three months after total hip arthroplasty. During hospitalization, the patients managed with enoxaparin had a lower rate of venous thromboembolic disease than those managed with adjusted-dose warfarin (p = 0.0083). This benefit was lost after the medication was discontinued, with no difference in the prevalences of venous thromboembolic disease between the two groups at three months after discharge from the hospital.

Outcomes of the first 60 noncemented Omnifit-HA total hip arthroplasties in 56 patients were studied prospectively for 2 to 5 years. The femoral prosthesis had a proximal third circumferential hydroxyapatite coated surface treatment. The acetabular component was a hemispheric modular, porous, nonhydroxyapatite press fit cup, supplemented with screw fixation. One cup was revised for recurrent dislocation, with no femoral revisions. The mean Harris hip score was 54 (range, 20-76) before surgery and 96 (range, 83-100) at final followup, with all patients having an excellent or good outcome. Mild thigh pain occurred in 6% of hips. Subsidence occurred in 9% of hips (range, 1-2.8 mm); in all cases, subsidence was nonprogressive after 1 year. Stable bone ingrowth fixation was evident at the hydroxyapatite coated portion in 100%. A sclerotic reactive line adjacent to the nonhydroxyapatite portion of the stem occurred in 81% but was not adjacent to the hydroxyapatite coated portion of any stem. Endosteal condensation occurred in 90% and correlated with a higher Harris hip score (mean score, 96 with, 91 without). Endosteal lysis adjacent to or distal to the hydroxyapatite coating did not occur. Lytic lesions at the calcar occurred in 19% and correlated with a greater linear acetabular polyethylene wear rate (mean, 0.30 mm/year with lytic lesions, 0.17 mm/year without). This noncemented stem with proximal third hydroxyapatite coating showed excellent short term clinical and radiographic outcome. Absence of distal endosteal lysis, along with correlation of calcar erosion to polyethylene wear, suggests that early circumferential bony ingrowth afforded by hydroxyapatite coating prevents distal endosteal access to polyethylene debris at short term followup.

One hundred ninety-nine patients who underwent primary total hip arthroplasty and used in hospital pneumatic compression stockings and aspirin as thromboembolic prophylaxis were screened for deep venous thrombosis using duplex ultrasonography on the fourth postoperative day. Of the initial 98 patients, 21 underwent noncemented arthroplasty, maintained touchdown weightbearing for 6 weeks after surgery, and then began progressive partial weightbearing. Of the subsequent 101 patients, 28 underwent noncemented arthroplasty and began progressive weightbearing immediately after surgery. All other patients underwent hybrid arthroplasty and began weightbearing to tolerance immediately after surgery. After duplex screening examination, patients with proximal deep venous thrombosis were given anticoagulation therapy, and patients with negative study results were observed clinically. The relative risk of proximal deep venous thrombosis after noncemented arthroplasty using delayed weightbearing was compared with that after noncemented arthroplasty using immediate progressive weightbearing. Of patients with noncemented arthroplasty, the prevalence of proximal deep venous thrombosis was significantly lower in those using progressive weightbearing immediately after surgery (none) than in those using delayed weightbearing rehabilitation (19%). This study showed that patients undergoing noncemented total hip arthroplasty with delayed weightbearing rehabilitation risk greater potential for deep venous thrombosis after hospital discharge. This study suggests consideration for continued thromboembolic prophylaxis or routine deep venous thrombosis surveillance, or both measures, after hospital discharge, unless more rapid progression of weightbearing is allowed.

Postoperative duplex ultrasonography screening after total hip arthroplasty has been shown to identify patients who may require treatment or additional monitoring for venous thromboembolic disease. The potential for manifestation of venous thromboembolic disease subsequent to screening remains a concern. The objective of this study was to determine the prevalence of symptomatic venous thromboembolic disease after total hip arthroplasty and after inhospital prophylaxis, inhospital screening with negative results for proximal deep venous thrombosis, and no posthospitalization venous thromboembolic disease prophylaxis. One hundred fifty patients undergoing primary hybrid total hip arthroplasty and using pneumatic compression stockings and aspirin as prophylaxis against venous thromboembolic disease were screened for deep venous thrombosis with duplex ultrasonography on the fourth day after surgery. Duplex ultrasonography screening revealed 17 (11.3%) patients with asymptomatic proximal deep venous thrombosis. In response to duplex ultrasonography screening, these patients with proximal deep venous thrombosis received therapeutic anticoagulation. Of 133 patients with a duplex screen with negative results for proximal deep venous thrombosis, 131 (98.5%) continued to have no symptoms of venous thromboembolic disease and two (1.5%) began to have symptoms for venous thromboembolic disease (one with proximal deep venous thrombosis, one with nonfatal pulmonary embolism) during 12 months of clinical followup after total hip arthroplasty. The overall prevalence of venous thromboembolic disease requiring anticoagulation was 19 of 150 (12.6%) patients. The remaining 131 (87.4%) were not exposed to the risks of postoperative anticoagulation and did not have subsequent symptomatic venous thromboembolic disease.

A common assumption among orthopedic surgeons is that cemented/hybrid total hip arthroplasty (THA) results in lower transfusion requirements than noncemented THA. The hypothesized mechanism to account for transfusion differences is that cement application, after polymerization, decreases perioperative blood loss. To evaluate this theory, a retrospective matched-pair study was performed to quantify perioperative, intraoperative, postoperative blood loss, and transfusion requirements among patients undergoing cemented/hybrid and noncemented THA. Twenty-five THA procedures were either cemented or hybrid and 25 were noncemented. Patients were matched with respect to age, gender, weight, and diagnosis. Six patients in the noncemented group and 10 in the cemented/hybrid group received autologous blood in the Post Anesthesia Care Unit. Among this subgroup, those in the cemented/hybrid group received a significantly greater volume of transfused blood (519.20 mL, versus 291.67 mL in the noncemented group, P < .017). After stratifying patients by gender, additional analysis revealed a greater total blood loss in the male population than in females (1848 mL versus 1464 mL, P < .004). Males also had a greater drain volume (548 mL versus 414 mL, P < .02). The female population utilizing hormone replacement therapy (HRT) was found to have a lesser blood loss (810 mL versus 1209 mL, P < .0107) and received a smaller amount of transfused blood (1164 mL versus 1377 mL) than those who were not on HRT. Other significant findings included a shorter length of stay in the cemented/hybrid group (6.85 versus 7.56 days, P < .012). Based on this matched-pair retrospective analysis of blood requirements, there is no indication that cemented/hybrid and noncemented THA procedures result in different blood requirements. However, differences were found in several areas when the population was stratified by gender. The information obtained from this study is important in its ability to solidify a foundation from which blood management decisions can be made.