Replacement Arthroplasty: Colwell CW

Colwell CW, Anonymous00376. · Shiley Center for Orthopaedic Research and Education at Scripps Clinic, La Jolla, California, USA. · Am J Orthop. · Pubmed #16846140 No free full text.

Abstract: More than 2 million people undergo major orthopedic surgery each year, and this rate is expected to continue rising as our population ages. Our patients are at particularly high risk for deep vein thrombosis (DVT) and pulmonary embolism. The latest guidelines from the American College of Chest Physicians recommend thromboprophylaxis for high-risk orthopedic surgery patients. Although specific recommendations vary by type of surgery, low-molecular-weight heparin, fondaparinux, warfarin, and sometimes low-dose unfractionated heparin are effective alone or with mechanical prophylaxis. Goals of treatment are to prevent proximal and distal DVT, pulmonary death, chronic pulmonary hypertension, and postthrombotic syndrome.

Colwell CW. · Shiley Center for Orthopaedic Research and Education, Scripps Clinic, La Jolla, California, USA. · Am J Orthop. · Pubmed #17948162 No free full text.

Abstract: Without prophylaxis, rates of deep vein thrombosis (DVT) after major orthopedic surgery range from 40% to 60%. Randomized clinical trials over the past 30 years have provided evidence that primary thromboprophylaxis reduces DVT, pulmonary embolism (PE), and fatal PE, and prophylaxis to prevent venous thromboembolism (VTE) in patients at risk has been ranked as the highest safety practice for hospitalized patients. Since 1986, some type of prophylaxis has been recommended for total knee arthroplasty (TKA), total hip arthroplasty (THA), and hip fracture surgery. Orthopedic guidelines published in Chest provide a current evidence-based guide for prophylaxis for TKA, THA, and hip fracture surgery. In addition to following these recommendations for routine prophylaxis, surgeons should assess patients for additional VTE risk. Patients at higher risk may need more intense prophylaxis. Data from meta-analyses and placebo-controlled, blinded, randomized clinical trials have demonstrated little or no increase in rates of clinically important bleeding with prophylaxis.

Colwell CW, Hardwick ME. · Shiley Center for Orthopaedic Research and Education, Scripps Clinic, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #17016231 No free full text.

Abstract: Low-molecular-weight heparin has been studied extensively in total knee arthroplasty (TKA) and provides highly effective and safe prophylaxis against deep venous thrombosis (DVT). Low-molecular-weight heparin received the highest rating (A1) in the American College of Chest Physicians recommendations for DVT prophylaxis after elective TKA. Prevalence of DVT with low-molecular-weight heparin prophylaxis was 33% in TKA data pooled from six randomized studies, with a proximal DVT rate of 7.1%. A metaanalysis reported a 2.4% rate of major bleeding with low-molecular-weight heparin. Low-molecular-weight heparin, given by subcutaneous injection, can be started before surgery or after surgery. A synthetic pentasaccharide (fondaparinux), which received an A1 rating in the American College of Chest Physicians recommendations, also is available. As with all treatments, the benefit must be considered against the risk when using these anticoagulants.

Gordon AC, D'Lima DD, Colwell CW. · Illinoise Bone and Joint Institution, Morton Grove, IL 60053, USA. · J Am Acad Orthop Surg. · Pubmed #16959889 No free full text.

Abstract: Although total hip arthroplasty is a common and highly successful procedure, its long-term durability has been undermined by the cellular response to polyethylene wear debris and the subsequent effects on periprosthetic bone. Research elucidating the effects of sterilization on polyethylene wear has facilitated the development of a more wear-resistant material-highly cross-linked polyethylene. Laboratory testing has demonstrated that highly cross-linked polyethylene has markedly improved wear resistance compared with conventional polyethylene under a variety of conditions. Early clinical data have supported these results. To make informed decisions about this already widely available and frequently used product, the practicing orthopaedic surgeon should have a basic understanding of the production process as well as knowledge of the most current laboratory and clinical data.

Hardwick ME, Colwell CW. · Scripps Clinic Center for Orthopaedic Research and Education, La Jolla, California, USA. · Surg Technol Int. · Pubmed #15455336 No free full text.

Abstract: Every year, approximately 2 million people experience a deep venous thrombosis (DVT). Approximately 600,000 of these people are diagnosed with a pulmonary embolism and about 10% of these die. It has been established that surgery, anesthesia, and bed rest increase the risk of DVT, and therefore, patients who undergo a major lower-extremity procedure should receive prophylaxis. During the past 10 years, the choices of pharmacological and mechanical prophylaxis have increased greatly. Warfarin is probably the most widely used prophylactic method in the U.S., but low-molecular-weight heparin (LMWH) use has increased. Also available is a synthetic pentasaccharide that acts as an anti-Xa inhibitor to decrease DVT without increase in bleeding. All but warfarin are given by subcutaneous injection and require no laboratory management to adjust the medication. Another drug in clinical trials is a direct thrombin inhibitor taken orally in a fixed dose that does not require monitoring. Non-pharmacological prophylaxis and/or stacked modalities, although used, have not shown the efficacy of pharmacological prophylaxis. With the incidence of DVT reported in the range of 41% to 85% without prophylaxis in joint replacement and hip-fracture surgery, prophylaxis is warranted in all lower-extremity joint replacement and hip-fracture patients.

Colwell CW. · Musculoskeletal Center, Scripps Clinic, La Jolla, California, USA. · Am J Orthop. · Pubmed #15195937 No free full text.

Abstract: Controlling postoperative pain following painful orthopedic procedures such as total knee arthroplasty is an ongoing challenge, as current pain management techniques often result in undermedication and/or complications. Traditional pain management strategies include opioid analgesics administered orally or via epidural catheter, patient-controlled analgesia (PCA), or intramuscular (IM) injection. This article discusses the use of PCA and the pain pump as effective modalities for the management of pain after arthroplasty. While the use of PCA has been somewhat controversial, a review of the literature supports its use over traditional IM dosing. PCA has been shown to provide more effective analgesia than IM dosing, and PCA administration is preferred over IM dosing by both patients and nurses. Continuous infusion of bupivacaine via pain pump is also an effective modality for reducing postoperative pain and decreasing postoperative consumption of opioid analgesics.

Colwell CW. · Scripps Clinic Center for Orthopaedic Research and Education, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #14646742 No free full text.

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Colwell CW. · Scripps Clinic, La Jolla, Calif 92037, USA. · Orthopedics. · Pubmed #14627117 No free full text.

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Colwell CW. · Scripps Clinic, Torrey Pines, La Jolla, Calif, USA. . · Orthopedics. · Pubmed #12597231 No free full text.

Abstract: Deep vein thrombosis and pulmonary embolism are major causes of morbidity and mortality after knee and hip arthroplasty in the United States. Although patients frequently receive prophylaxis for thromboembolism postarthroplasty, surgeons vary in their choice of modality and often use suboptimal strategies due to the possibility of provoking postoperative bleeding. This article discusses the rationale for the prevention of venous thromboembolism and offers an overview of clinical recommendations for prophylaxis in knee and hip replacement surgery. Supporting medical evidence for these recommendations is described. A summary of current prophylactic regimens and discussion of duration of therapy are also presented.

Botte MJ, Ezzet KA, Pacelli LL, Guzman MJ, Meyer RS, Meunier MJ, D'Lima DD, Colwell CW. · Division of Orthopaedic Surgery, Scripps Clinic, La Jolla California 92037, USA. · J Bone Joint Surg Am. · Pubmed #12473727 No free full text.

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Colwell CW. · Division of Orthopaedic Surgery, Scripps Clinic, La Jolla, California, USA. · Instr Course Lect. · Pubmed #12064138 No free full text.

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Colwell CW. · Scripps Clinic, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #11716391 No free full text.

Abstract: 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.

Colwell CW, Hozack WJ, Mesko JW, D'Antonio JA, Bierbaum BE, Capello WN, Jaffe WL, Mai KT. · Shiley Center for Orthopaedic Research & Education at Scripps Clinic, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #17667324 No free full text.

Abstract: Wear debris from metal-on-polyethylene articulation in conventional total hip arthroplasty can limit the implant's longevity. Modern ceramic material with high wear resistance and low fracture risk has the potential to extend the lifetime of total hip arthroplasty, which makes the procedure potentially more suitable for young, active patients. Concerns with brittle ceramic material include fracture risk, the "squeak" phenomenon, and potentially a higher dislocation rate secondary to limited neck lengths and liner options. We therefore determined the early dislocation rate in modern ceramic-on-ceramic total hip arthroplasty. In 1635 total hip arthroplasties performed over the 9-year period (1996-2005), we observed three anterior and 15 posterior dislocations (1.1%). All were treated successfully, one with a revision and 17 with closed reduction under general anesthesia. Ceramic-on-ceramic total hip arthroplasty can be a good alternative bearing surface with a low dislocation rate.

Hermida JC, D'Lima DD, Steklov N, Colwell CW. · Shiley Center for Orthopaedic Research & Education, Scripps Clinic, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #16331018 No free full text.

Abstract: Outcomes of hydroxyapatite-coated cups have not been as consistently successful as outcomes of hydroxyapatite-coated stems; therefore, we studied a newer generation acetabular design with a plasma-sprayed hydroxyapatite coating on an arc-deposited rough titanium substrate. Our objective was to determine whether clinical and radiographic outcomes would be better than reported for earlier-generation designs. Ninety consecutive hips in 85 patients implanted with this design were followed up prospectively for 2 to 5 years after surgery. Hip scores improved from a preoperative mean of 59 (+/- 12) to final followup mean of 91 (+/- 12). One hip was revised for recurrent dislocation. No hips were revised for aseptic loosening. No cup had complete continuous radiolucent lines. Incomplete lucent lines were noted on early postoperative radiographs. With followup, radiolucent line length decreased by a mean 32% and radiolucent line density increased by 9%. Mean polyethylene linear and volumetric head penetration rates were 0.17 (+/- 0.16) mm/year and 73 (+/- 70) mm/year, respectively. Head penetration rates were higher in men. No other factor (age, body weight, cup abduction, or anteversion angle) correlated with head penetration rate. Our study presents encouraging short-term results. Improvement in radiolucent lines suggests a beneficial effect of hydroxyapatite coating on osseointegration of the cup. Level of Evidence: Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

Colwell CW, Berkowitz SD, Lieberman JR, Comp PC, Ginsberg JS, Paiement G, McElhattan J, Roth AW, Francis CW, Anonymous00317. · Orthopaedic Surgery, Scripps Clinic, 11025 North Torrey Pines Road, Suite 140, La Jolla, CA 92037, USA. · J Bone Joint Surg Am. · Pubmed #16203879 No free full text.

Abstract: BACKGROUND: Warfarin, which requires coagulation monitoring, is associated with relatively high rates of thromboembolism despite providing adequate prophylaxis. This study compared an oral direct thrombin inhibitor, ximelagatran, with warfarin in order to evaluate the safety and efficacy of the medication for the prevention of venous thromboembolism in patients undergoing total knee arthroplasty. METHODS: Following surgery, patients were randomly assigned to fixed-dose oral ximelagatran (36 mg twice daily) or warfarin (target international normalized ratio, 2.5), both administered for seven to twelve days in a double-blind, double-dummy design. Warfarin was initiated on the evening of the day of surgery, and ximelagatran, on the morning after surgery. The primary efficacy end point was the incidence of asymptomatic deep-vein thrombosis determined by bilateral venography, objectively confirmed symptomatic deep-vein thrombosis or pulmonary embolism, and death from all causes during treatment. RESULTS: Adequate venograms or confirmed symptomatic events (efficacy population) were obtained for 1949 patients. Venous thromboembolism and death from all causes occurred in 22.5% (221) of 982 ximelagatran-treated patients and in 31.9% (308) of 967 warfarin-treated patients (p < 0.001). Proximal deep-vein thrombosis and pulmonary embolism were observed in 3.1% (thirty) and 0.2%, respectively, of the patients in the ximelagatran group and in 3.4% (thirty-three) and 0.4%, respectively, of the patients in the warfarin group. The six deaths from all causes included 0.3% (four) of the ximelagatran-treated patients and 0.2% (two) of the warfarin-treated patients. Major bleeding was noted in 1% (twelve) of the ximelagatran-treated patients and in 0.4% (five) of the warfarin-treated patients (p = 0.09). CONCLUSIONS: Oral ximelagatran (36 mg twice daily), administered without coagulation monitoring or dose adjustment and started the day after total knee arthroplasty, demonstrates superior efficacy compared with warfarin prophylaxis, with no wound complications and no significant difference with respect to bleeding events, although the rate of major bleeding events was greater with ximelagatran than with warfarin. LEVEL OF EVIDENCE: Therapeutic Level I.

Hardwick ME, Morris BM, Colwell CW. · Scripps Clinic, La Jolla, CA, USA. · Clin Orthop Relat Res. · Pubmed #15232456 No free full text.

Abstract: This study evaluated whether patients receiving a two-dose regime of epoetin alfa received less allogeneic blood than patients donating autologous blood before primary hip arthroplasty. Consenting patients with a hemoglobin level between 12 and 15 g/dL were randomly assigned to a two-dose administration of epoetin alfa (19 patients) or autologous donation (21 patients). Sixteen percent of the patients in the epoetin alfa group and 52% of the patients in the autologous donation group received transfusions, with a mean volume of 90 cc per patient in the epoetin alfa group and 340 cc in the autologous donation group. Hemoglobin was similar at screening; however, the epoetin alfa group achieved a higher hemoglobin (14.6 g/dL) than the autologous donation group (12.6 g/dL) before surgery. Hemoglobin remained significantly higher in the epoetin alfa group for 3 days after surgery. Administration of two doses of epoetin alfa provided patients with effective and safe reduction of allogeneic blood transfusions and decreased the necessity and difficulty of autologous donation before total hip arthroplasty.

Francis CW, Berkowitz SD, Comp PC, Lieberman JR, Ginsberg JS, Paiement G, Peters GR, Roth AW, McElhattan J, Colwell CW, Anonymous00349. · Department of Medicine, University of Rochester, Rochester, NY, USA. · N Engl J Med. · Pubmed #14585938 links to  free full text

Abstract: BACKGROUND: In a previous study of the prevention of venous thromboembolism after total knee replacement, the efficacy of ximelagatran, an oral direct thrombin inhibitor that does not require monitoring of coagulation or dose adjustment, was found to be similar to that of warfarin at a dose of 24 mg of ximelagatran twice daily. The purpose of the present study was to determine whether a higher dose of ximelagatran is superior to warfarin. METHODS: This randomized, double-blind trial compared a regimen of 7 to 12 days of oral ximelagatran, at a dose of 24 or 36 mg twice daily, starting the morning after surgery, with warfarin therapy started the evening of the day of surgery. The composite end point of venous thromboembolism and death from all causes and the incidence of bleeding were the primary outcome measures. RESULTS: Among the 1851 patients in the efficacy analysis, oral ximelagatran at a dose of 36 mg twice daily was superior to warfarin with respect to the primary composite end point of venous thromboembolism and death from all causes (20.3 percent vs. 27.6 percent; P=0.003). There were no significant differences between these two groups with respect to major bleeding (incidence, 0.8 percent and 0.7 percent, respectively), perioperative indicators of bleeding, wound characteristics, or the composite secondary end point of proximal deep-vein thrombosis, pulmonary embolism, and death (2.7 percent vs. 4.1 percent; P=0.17). CONCLUSIONS: The efficacy of oral ximelagatran, administered starting the morning after total knee replacement, was superior to that of warfarin for prevention of venous thromboembolism. Rates of hemorrhagic complications with the two drugs were similar.

Colwell CW, Berkowitz SD, Davidson BL, Lotke PA, Ginsberg JS, Lieberman JR, Neubauer J, McElhattan JL, Peters GR, Francis CW. · Scripps Clinic Center for Orthopaedic Research and Education, 11025 North Torrey Pines Road, Suite 140, La Jolla, CA 92037-1030, USA. · J Thromb Haemost. · Pubmed #14521593 No free full text.

Abstract: 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.

Francis CW, Davidson BL, Berkowitz SD, Lotke PA, Ginsberg JS, Lieberman JR, Webster AK, Whipple JP, Peters GR, Colwell CW. · University of Rochester School of Medicine and Dentistry, Rochester, New York, USA. · Ann Intern Med. · Pubmed #12379064 links to  free full text

Abstract: BACKGROUND: Warfarin is used for prophylaxis of venous thromboembolism in patients undergoing total knee arthroplasty. However, it is associated with rates of deep venous thrombosis (DVT) of approximately 38% to 55% and requires routine coagulation monitoring and frequent dose adjustment. Ximelagatran, an oral direct thrombin inhibitor, has shown promising efficacy and tolerability in patients undergoing total hip or knee arthroplasty. OBJECTIVE: To compare the efficacy and safety of ximelagatran and warfarin for prophylaxis of venous thromboembolism after total knee arthroplasty. DESIGN: Randomized, double-blind, parallel-group trial. SETTING: 74 North American hospitals. PATIENTS: 680 patients who had undergone total knee arthroplasty. INTERVENTION: 7 to 12 days of treatment with oral ximelagatran, 24 mg twice daily, starting on the morning after surgery, or warfarin (target international normalized ratio, 2.5 [range, 1.8 to 3.0]), starting on the evening of the day of surgery. MEASUREMENTS: Principal end points were asymptomatic DVT on mandatory venography; symptomatic DVT confirmed by ultrasonography or venography; symptomatic, objectively proven pulmonary embolism; and bleeding. All were assessed by blinded adjudication locally and at a central study laboratory. RESULTS: On central adjudication, incidence of venous thromboembolism was 19.2% (53 of 276 patients) in the ximelagatran group and 25.7% (67 of 261 patients) in the warfarin group (difference, -6.5 percentage points [95% CI, -13.5 to 0.6 percentage points]; P = 0.070). On local assessment, incidence was 25.4% in the ximelagatran group and 33.5% in the warfarin group (P = 0.043). In the ximelagatran and warfarin groups, respectively, major bleeding occurred in 1.7% and 0.9% of patients and minor bleeding occurred in 7.8% and 6.4% of patients. No variables related to bleeding differed significantly between the two groups. CONCLUSIONS: For prophylaxis of venous thromboembolism, fixed-dose ximelagatran started the morning after total knee arthroplasty is well tolerated and at least as effective as warfarin, but it does not require coagulation monitoring or dose adjustment.

Heit JA, Colwell CW, Francis CW, Ginsberg JS, Berkowitz SD, Whipple J, Peters G, Anonymous00251. · Division of Cardiovascular Diseases, Hematology Research, Mayo Clinic, 200 First St SW, Rochester, MN 55905. · Arch Intern Med. · Pubmed #11575978 links to  free full text

Abstract: 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.

D'Lima DD, Steklov N, Patil S, Colwell CW. · Shiley Center for Orthopaedic Research and Education at Scripps Clinic, La Jolla, CA 92037, USA. · Clin Orthop Relat Res. · Pubmed #18563502 No free full text.

Abstract: Knee forces directly affect arthroplasty component survivorship, wear of articular bearing surfaces, and integrity of the bone-implant interface. It is not known which activities generate forces within a range that is physiologically desirable but not high enough to jeopardize the survivorship of the prosthetic components. We implanted three patients with an instrumented tibial prosthesis and measured knee forces and moments in vivo during exercise and recreational activities. As expected, stationary bicycling generated low tibial forces, whereas jogging and tennis generated high peak forces. On the other hand, the golf swing generated unexpectedly high forces, especially in the leading knee. Exercise on the elliptical trainer generated lower forces than jogging but not lower than treadmill walking. These novel data allow for a more scientific approach to recommending activities after TKA. In addition, these data can be used to develop clinically relevant structural and tribologic testing, which may result in activity-specific knee designs such as a knee design more tolerant of golfing by optimizing the conflicting needs of increased rotational laxity and conformity.

Varadarajan KM, Moynihan AL, D'Lima D, Colwell CW, Li G. · Bioengineering Laboratory, Orthopaedic Surgery, Massachusetts General Hospital/Harvard Medical School, Boston, MA 02114, USA. · J Biomech. · Pubmed #18538328 No free full text.

Abstract: Analysis of polyethylene component wear and implant loosening in total knee arthroplasty (TKA) requires precise knowledge of in vivo articular motion and loading conditions. This study presents a simultaneous in vivo measurement of tibiofemoral articular contact forces and contact kinematics in three TKA patients. These measurements were accomplished via a dual fluoroscopic imaging system and instrumented tibial implants, during dynamic single leg lunge and chair rising-sitting. The measured forces and contact locations were also used to determine mediolateral distribution of axial contact forces. Contact kinematics data showed a medial pivot during flexion of the knee, for all patients in the study. Average axial forces were higher for lunge compared to chair rising-sitting (224% vs. 187% body weight). In this study, we measured peak anteroposterior and mediolateral forces averaging 13.3% BW during lunge and 18.5% BW during chair rising-sitting. Mediolateral distributions of axial contact force were both patient and activity specific. All patients showed equitable medial-lateral loading during lunge but greater loads at the lateral compartment during chair rising-sitting. The results of this study may enable more accurate reproduction of in vivo loads and articular motion patterns in wear simulators and finite element models. This in turn may help advance our understanding of factors limiting longevity of TKA implants, such as aseptic loosening and polyethylene component wear, and enable improved TKA designs.

Edwards JZ, Pulido PA, Ezzet KA, Copp SN, Walker RH, Colwell CW. · Gem City Bone and Joint, Laramie, Wyoming, USA. · J Arthroplasty. · Pubmed #18534421 No free full text.

Abstract: This preliminary prospective study to determine the rate of deep venous thrombosis (DVT) examined 277 patients undergoing total knee or total hip arthroplasty (TKA or THA) who were randomized to use a portable, continuous enhanced circulation therapy (CECT) compression device and low-molecular-weight heparin (LMWH) or to receive LMWH alone. Patients were screened for DVT using duplex ultrasound at hospital discharge and followed clinically for 3 months. In TKA, 5 DVTs (6.6%) occurred in the CECT + LMWH group compared with one pulmonary embolism and 14 DVTs (19.5%) in the LMWH group (P = .018). In THA, 1 DVT (1.5%) occurred in the CECT + LMWH group and 2 DVTs (3.4%) occurred in the LMWH group. This preliminary study demonstrated significant reduction in rate of DVT after TKA when the CECT device was combined with LMWH.

D'Lima DD, Steklov N, Fregly BJ, Banks SA, Colwell CW. · Shiley Center for Orthopaedic Research and Education at Scripps Clinic, 11025 North Torrey Pines Road, Suite 140, La Jolla, California 92037, USA. · J Orthop Res. · Pubmed #18524001 No free full text.

Abstract: We implanted an electronic knee prosthesis to measure tibial forces in vivo during activities of daily living after total knee arthroplasty. We used tibial forces and knee kinematic data collected in vivo to calculate contact stresses using finite element analysis. The polyethylene insert was modeled as an elastoplastic material, and predicted contact stresses were validated using pressure sensitive sensors. Peak contact stresses generated during walking were similar but about 18% lower than those calculated for International Standards Organization (ISO)-recommended wear simulation conditions. Stair climbing generated higher contact stresses (32 MPa) than walking (26 MPa). However, both high flexion activities (lunge and kneel) generated even higher contact stresses, with the lunge activity generating the highest stresses (56 MPa). The activities that generated high contact stresses also resulted in high equivalent plastic strain. However, the lunge activity generated dramatically higher plastic equivalent strain than the other activities. In vivo measurement of kinematics, forces, and contact stresses may be used to develop more clinically relevant wear simulator protocols. Contact stresses generated during high flexion activities were substantially higher and were largely due to the reduced contact area in deep flexion rather than due to an increase in contact forces. Our results support the use of "high flexion" designs that improve contact conditions and preserve contact area at high flexion angles.

Mündermann A, Dyrby CO, D'Lima DD, Colwell CW, Andriacchi TP. · Department of Mechanical Engineering, Durand Building 205, 496 Lomita Mall, Stanford University, Stanford, California 94305-4038, USA. · J Orthop Res. · Pubmed #18404700 No free full text.

Abstract: We examined the relationship between activity, peak load, medial to lateral load distribution, and flexion angle at peak load for activities of daily living. An instrumented knee prosthesis was used to measure knee joint force simultaneously with motion capture during walking, chair sit to stand and stand to sit, stair ascending and descending, squatting from a standing position, and golf swings. The maximum total compressive load at the knee was highest during stair ascending and descending and lowest during rising from a chair. Maximum total compressive load occurred at substantially different flexion angles ranging from 8.5 degrees during walking to 91.8 degrees during squatting. For all activities, total compressive load exceeded 2 times body weight, and for most activities 2.5 times body weight. Most activities placed a greater load on the medial compartment than the lateral compartment. Activities were grouped into three categories: high cycle loading (walk), high load (stair ascent, descent, and golf), and high flexion angle (chair sit to stand/stand to sit, and squat). The results demonstrate that the forces and motion sustained by the knee are highly activity-dependent and that the unique loading characteristics for specific activities should be considered for the design of functional and robust total knee replacements, as well as for rehabilitation programs for patients with knee osteoarthritis or following total knee arthroplasty.