Evaluation Of Total Knee Arthroplasty Research Articles

Development of Multibundle Virtual Ligaments to Simulate Knee Mechanics After Total Knee Arthroplasty.

Preclinical evaluation of total knee arthroplasty (TKA) components is essential to understanding their mechanical behavior and developing strategies for improving joint stability. While preclinical testing of TKA components has been useful in quantifying their effectiveness, such testing can be criticized for lacking clinical relevance, as the important contributions of surrounding soft tissues are either neglected or greatly simplified. The purpose of our study was to develop and determine if subject-specific virtual ligaments reproduce a similar behavior as native ligaments surrounding TKA joints. Six TKA knees were mounted to a motion simulator. Each was subjected to tests of anterior-posterior (AP), internal-external (IE), and varus-valgus (VV) laxity. The forces transmitted through major ligaments were measured using a sequential resection technique. By tuning the measured ligament forces and elongations to a generic nonlinear elastic ligament model, virtual ligaments were designed and used to simulate the soft tissue envelope around isolated TKA components. The average root-mean-square error (RMSE) between the laxity results of TKA joints with native versus virtual ligaments was 3.5 ± 1.8 mm during AP translation, 7.5 ± 4.2 deg during IE rotations, and 2.0 ± 1.2 deg during VV rotations. Interclass correlation coefficients (ICCs) indicated a good level of reliability for AP and IE laxity (0.85 and 0.84). To conclude, the advancement of virtual ligament envelopes as a more realistic representation of soft tissue constraint around TKA joints is a valuable approach for obtaining clinically relevant kinematics when testing TKA components on joint motion simulators.

Comparison of weight-based versus standard dosing of tranexamic acid for blood loss and transfusion amount in knee arthroplasty without tourniquet.

The aim of the study is to compare weight-based versus standard dosing of intravenous (IV) tranexamic acid (TXA) for blood loss and transfusion amount in total knee arthroplasty (TKA) without a tourniquet. A total of 99 patients were divided into two groups: Group 1 (standard): 1 g of IV TXA 30 min before skin incision, and 1 g at postoperative 30 min and 3 h. Group 2 (weight-based): 10 mg/kg IV TXA 30 min before the skin incision, and 10 mg/kg at postoperative 30 min, and 3 h. Hemoglobin levels, before, and 1, and 2 days after the operation, postoperative amount of decrease in hemoglobin levels, and amount of erythrocyte transfusion were recorded. Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Knee Society Score (KSS) were applied in the evaluation of TKA results preoperatively, and at 1., 3., 6., and 12. months, postoperatively. In both study groups, hemoglobin levels in male patients dropped significantly more deeply than female patients. Also, in both study groups, hemo- globin levels were significantly lower in patients with comorbid illnesses. A statistically significant difference was not detected between both groups in terms of pre- and postoperative WOMAC scores, KSS knee scores, and KSS function scores. Our study showed that standard and weight-based dosing of IV TXA treatments were similar in efficacy and safety. Both treatments reduce blood loss and the need for transfusion. Also, there was no significant difference in terms of reliability between two groups.

Total knee arthroplasty radiographic evaluation via a Bayesian belief network. A pilot study

In an attempt to standardize the X-ray analysis and to create relevant correlations between it and the functional results, we present a pilot model of an artificial neural network based on a Bayesian belief network (BNN) designed for the automatic analysis of anteroposterior X-ray of the knee following total knee arthroplasty and more precisely the analysis of the tibial component. A prospective analysis was conducted in which 30 patients were analyzed and two groups resulted: the first was made up of 12 cases considered “normal” by the examiners (optimal positioning and cementation) and the second one, which was considered “pathological” (incorrect positioning or cementation) and included 16 cases. Based on 22 points established on the tibial component several geometric sizes (calculated parameters) were computed. Several parameters were compared and the results were up to 75% accuracy, 81.25% sensitivity, and 66.7% specificity. BBNs can be a solution for X-ray evaluation of total knee arthroplasty and can improve the understanding of its evolution. It needs confirmation in time, its accuracy rising with the number of patients introduced in the analysis algorithm.

Combined use of virtual monochromatic images and projection-based metal artifact reduction methods in evaluation of total knee arthroplasty.

To evaluate the effect of the combined use of virtual monochromatic imaging (VMI) and projection-based metal artifact reduction (PB-MAR) methods on further artifact reduction and image quality in total knee arthroplasty (TKA) patients. Fifty-seven knee joints from 36 patients who had a previous history of TKA for bilateral or unilateral knee joints were included in this study. Four sets of images were compared between non-MAR, PB-MAR, VMI, and VMI + PB-MAR. For quantitative analysis, the area, mean attenuation, artifact index (AI), and contrast-to-noise ratio (CNR) were calculated for each protocol. Regarding qualitative analysis, overall artifact and depiction of soft tissue and bony structure were compared using relative visual grading analysis. In the femoral region, the VMI + PB-MAR protocol showed the best MAR performance in quantitative measures including area, mean attenuation, and AI (p < .001). However, MAR protocols with VMI showed significantly lower CNRs than did the protocols without VMI in the tibial region (p < .001). On qualitative analysis, VMI + PB-MAR also showed fewer overall artifacts than did the other two MAR protocols. Soft tissue was best depicted in VMI + PB-MAR protocol, and PB-MAR showed the best performance for the depiction of bony structure (p < .001). The combined use of VMI and PB-MAR showed better MAR performance than did PB-MAR or VMI alone. In areas with severe metal artifacts, the VMI + PB-MAR and PB-MAR protocols were useful for the evaluation of soft tissue and bone structure, respectively. • The combination of artifact reduction methods is effective in reducing metal artifacts in CT. • Soft tissue was best depicted in the combined protocol of projection- and dual-energy-based methods, and projection-based protocol showed the best performance for the depiction of bone structure in case of severe metal artifacts.

Feasibility of Magnetic Resonance Imaging Monitoring of Postoperative Total Knee Arthroplasty without Metal Artifacts: A Preliminary Study of a Novel Implant Model.

Background Although magnetic resonance imaging (MRI) can provide superior detailed images of tissues without ionizing radiation, the imaging evaluation of total knee arthroplasty (TKA) complications and posttherapy changes can be limited because of abundant artifacts on MRI scans due to metallic implants and endoprosthesis in limb salvage and fracture fixation. This study aimed to develop a novel model of TKA using a polyetheretherketone- (PEEK-) on-highly cross-linked polyethylene (HXLPE) implant and to investigate its feasibility for MRI monitoring of peri-implant bone formation, the healing process, signs of infection, and tumor recurrence after TKA. Methods Three skeletally mature goats underwent TKA with the PEEK-on-HXLPE implant. Radiographic and MRI examinations were performed at 4 weeks postoperatively. Images were analyzed for the existence of artifact interruption and postoperative changes in the bone and peripheral soft tissue. Results The results showed that PEEK and HXLPE were invisible, but the metal wires were clearly visualized on X-rays. On MRI scans, PEEK and HXLPE materials showed a low signal intensity, fine metal wires generated no obvious metal artifacts on MRI scans, and the marrow and soft tissue showed a continuous signal intensity without artifact interruption. Conclusions This preliminary study introduced a novel model using PEEK-on-HXLPE knee implant for in vivo MRI monitoring of the region around the implant without metal artifacts. This novel model may be used to apply MRI to observe bone formation and the healing process around the prosthesis and the signs of infection and tumor recurrence after TKA. This model may be used to improve the diagnostic accuracy of postoperative complications of TKA clinically.

Improved walking distance and range of motion predict patient satisfaction after TKA.

The focus in the evaluation of total knee arthroplasty has shifted from objective measures of implant position and knee function, to patient-reported outcome measures (PROMs). The relation between these two measures was investigated and the possibility of prediction of the patient satisfaction level was evaluated by defining thresholds for improvement of (1) range of motion (ROM), (2) 6-min walk test (6MWT), (3) sit-to-stand test (STS) and (4) quadriceps force after TKA? Fifty-seven patients were prospectively tested at preoperative and 6 months postoperative intervals. The ROM, 6MWT, STS-test and quadriceps force were evaluated. Two clusters were created based on the postoperative KOOS, OKS and the satisfaction subscore of the new KSS, cluster 1 consisted of patients with good to excellent PROMs, cluster 2 of patients with poorer PROMs. Patients in each cluster were more similar to each other than to those in the other cluster. Receiver operating characteristic (ROC)-curve analysis was used to identify thresholds for the functional outcomes that established cluster allocation. Multiple logistic regression was used to define a model to predict cluster allocation. Patients with high postoperative PROMs (cluster 1 allocation) showed higher postoperative functional outcomes (p < 0.05). Thresholds for the improvement of ROM (≥ 5°, OR 6.3, 95% CI 1.23-31.84), 6MWT (≥ 50m, OR 8.2, 95% CI 1.61-42.18) STS (≥ 1.05s, OR 3, 95% CI 0.56-16.07) and normalized Q4 force (≥ 1.5N/BMI, OR 2.5, 95% CI 0.49-12.89) were found to be predictors of cluster allocation. A model to predict the cluster allocation contained gender, ROM improvement and 6MWT improvement (sensitivity 91.1%, specificity 75%). Thresholds for improvement of functional parameters can predict the patient satisfaction cluster. Patients, who are male, improve on the 6-min walk test with 50m or more and have an increased range of motion of 5° or more, compared to the preoperative situation, are 6-8 times more likely of being satisfied after TKA. These tests are easy to use in clinical practice and can predict the level of patient satisfaction after TKA. Level II, prognostic study.

3X-Knee: A Novel Technology for 3D Preoperative Planning and Postoperative Evaluation of TKA Based on 2D X-Rays.

This chapter introduces a solution called "3X-knee" that can robustly derive 3D models of the lower extremity from 2D long leg standing X-ray radiographs for preoperative planning and postoperative treatment evaluation of total knee arthroplasty (TKA). There are three core components in 3X-knee technology: (1) a knee joint immobilization apparatus, (2) an X-ray image calibration phantom, and (3) a statistical shape model-based 2D-3D reconstruction algorithm. These three components are integrated in a systematic way in 3X-knee to derive 3D models of the complete lower extremity from 2D long leg standing X-ray radiographs acquired in weight-bearing position. More specifically, the knee joint immobilization apparatus will be used to rigidly fix the X-ray calibration phantom with respect to the underlying anatomy during the image acquisition. The calibration phantom then serves two purposes. For one side, the phantom will allow one to calibrate the projection parameters of any acquired X-ray image. For the other side, the phantom also allowsone to track positions of multiple X-ray images of the underlying anatomy without using any additional positional tracker, which is a prerequisite condition for the third component to compute patient-specific 3D models from 2D X-ray images and the associated statistical shape models. Validation studies conducted on both simulated X-ray images and on patients' X-ray data demonstrate the efficacy of the present solution.

Subjective evaluation before and after total knee arthroplasty using the 2011 Knee Society Score

BackgroundPatient satisfaction has been recognized as an important evaluation of total knee arthroplasty (TKA). Therefore, the 2011 Knee Society Knee Scoring System (2011 KSS) was developed in order to quantify patient satisfaction, expectations, and physical activities following TKA. However, very few reports have described subjective evaluation before TKA using the 2011 KSS, as the scoring system is still relatively new. Therefore, the degree of improvement and change over time after TKA has not been evaluated. MethodsForty-nine consecutive patients (79 knees) with a mean age of 74.8±7.3years were prospectively included in the study and evaluated preoperatively and one year postoperatively. The following questions were assessed using the 2011 KSS: (1) Do patient-derived clinical scores improve after TKA? (2) Do patient-derived clinical scores before TKA correlate with those after TKA? and (3) Are there correlations among each category of the 2011 KSS score? ResultsThe majority of categories showed significant improvements after TKA. The preoperative functional activities score was positively correlated with the postoperative symptoms, functional activities, and objective score. Each category of the 2011 KSS score correlated with others postoperatively. ConclusionsAll patient-derived scores except for patient expectation significantly improved postoperatively. The more functionally active patients before receiving TKA acquired more successful objective and functional outcomes, and the postoperative knee condition was directly influenced by each subscale of the 2011 KSS.

Alterations in stress distribution and micromotion characteristics due to an artificial defect within a composite tibia used for mechanical/biomechanical evaluation of total knee arthroplasty

Artificial composite tibiae have been widely used for mechanical evaluations of total knee arthoplasty (TKA) because of their low variability and wide availability. However, little information is available about whether artificial defects created during production significantly change the distribution of stress and micromotion within composite tibiae during a mechanical evaluation for TKA. The purpose of this study was to determine the effects of artificial defects on alterations in stress distribution and micromotion in composite tibiae during a mechanical evaluation for TKA using finite element (FE) analysis. The results showed that von Mises stresses near the artificial defect were approximately 1.6-fold higher than those on the same regions of composite tibiae without artificial defects. However, the difference in von Mises stresses decreased gradually beginning 3 mm from the center of the artificial defect. Micromotion in composite tibiae with artificial defects was similar to that of tibiae without artificial defects. These findings suggest that stress/strain on the cortical bone surface should be measured at least 3 mm from artificial defect centers but that micromotion is not affected by the artificial defects during a mechanical evaluation for TKA using composite tibiae.

Descriptive analysis of the cost-effectiveness of depressed patients undergoing total knee arthroplasty: an economic decision analysis

Background Recent rising concern about the cost-effectiveness ratio of total knee arthroplasty (TKA) led us to evaluate this successful procedure from the economic perspective, thereby helping policy-makers to conduct medical resource allocation more effectively and efficiently. However, up to now no study has investigated the influence of patients' psychological factors on their evaluation of TKA’s cost-effectiveness. Therefore, we decided to determine whether and how depression, which is a common negative psychological factor in the population undergoing TKA, affects their economic evaluation of the procedure.Methods A total of 312 patients who had undergone TKA were graded into three groups based on the level of depression measured by the Center for Epidemiological Studies Depression Scale (CES-D) scores. Clinical effectiveness information was obtained using the WOMAC questionnaire; total costs related to TKA were acquired through interviews with patients and review of their medical records in the computing system.Results Patients with high-level depression (3491.9$/QALYS; 95 % CI, 3471.1–3491.9$/QALYS) had greater cost-effectiveness compared tothose with low-level (2447.1$/QALYS; 95 % CI, 2427.9–2466.3$/QALYS) and middle-level (3027.2$/QALYS; 95 % CI, 3011.0–3043.4$/QALYS) depression. We concluded there was a significant positive correlation between cost-effectiveness and the level of depression after TKA (r = 0.703, P = 0.014). Significant differences in the costs of hospital stay, medical treatment, rehabilitation, and outpatient care were detected among the three groups.Conclusions Our study might help policy-makers and clinicians identify which types of patients benefit most from TKA and then advise high-risk patients (high-level depression status in this study) about how to recovery better with limited resource allocation. Preoperative evaluation of patients’ psychological state may decrease unnecessary economic burdens and suffering during the recovery period.

Medium-term evaluation of total knee arthroplasty without patellar replacement

ObjectiveTo mid-term evaluate patients who were submitted to total knee arthroplasty without patellar resurfacing. MethodsIt was realized a retrospective cross-sectional study of patients who were submitted to total knee arthroplasty without patellar resurfacing. In all patients clinical examination was done based on the protocol of the Knee Society Scoring System, which assessed pain, range of motion, stability, contraction, knee alignment and function, and radiological evaluation. ResultsA total of 36 patients were evaluated. Of these, 07 were operated only on left knee, 12 only on right knee and 17 were operated bilaterally, totaling 53 knees. Ages ranged from 26 to 84 years. Of the 53 knees evaluated, 33 (62.26%) had no pain. The maximum flexion range of motion averaged 104.7°. No knee had difficulty in active extension. As to the alignment for anatomical axis twelve knees (22.64%) showed deviation between 0° and 4° varus. Thirty-nine (75.49%) knees showed pace without restriction and the femorotibial angle ranged between 3° varus and 13° valgus with an average of 5° valgus. The patellar index ranged from 0.2 to 1.1. ConclusionTotal knee arthroplasty whitout patellar resurfacing provides good results in mid-term evaluation.

The influence of total knee arthroplasty geometry on mid-flexion stability: An experimental and finite element study

Fluoroscopic evaluation of total knee arthroplasty (TKA) has reported sudden anterior translation of the femur relative to the tibia (paradoxical anterior motion) for some cruciate-retaining designs. This motion may be tied to abrupt changes in the femoral sagittal radius of curvature characteristic of traditional TKA designs, as the geometry transitions from a large load-bearing distal radius to a smaller posterior radius which can accommodate femoral rollback. It was hypothesized that a gradually reducing radius may attenuate sudden changes in anterior–posterior motion that occur in mid-flexion with traditional discrete-radius designs. A combined experimental and computational approach was employed to test this hypothesis. A previously developed finite element (FE) model of the Kansas knee simulator (KKS), virtually implanted with multiple implant designs, was used to predict the amount of paradoxical anterior femoral slide during a simulated deep knee bend. The model predicted kinematics demonstrated that incorporating a gradually reducing radius in mid-flexion reduced the magnitude of paradoxical anterior translation between 21% and 68%, depending on the conformity of the tibial insert. Subsequently, both a dual-radius design and a modified design incorporating gradually reducing radii were tested in vitro in the KKS for verification. The model-predicted and experimentally observed kinematics exhibited good agreement, while the average experimental kinematics demonstrated an 81% reduction in anterior translation with the modified design. The FE model demonstrated sufficient sensitivity to appropriately differentiate kinematic changes due to subtle changes in implant design, and served as a useful pre-clinical design-phase tool to improve implant kinematics.

Evaluation of Total Knee Arthroplasty Performed With and Without Computer Navigation: A Bilateral Total Knee Arthroplasty Study

Sequential bilateral total knee arthroplasty performed on 54 patients utilizing navigation (CAS-TKA) in one knee and traditional instrumentation (T-TKA) in the contralateral knee was reviewed at a mean follow-up duration of 2.5years. There were no differences with regard to KSS, ROM, postoperative anatomic alignment, mechanical axis, or tibial angle. There was a statistically significant decrease in outliers for the CAS-TKA group with respect to anatomic alignment (3.7% vs. 17.0%, P=0.024), mechanical axis (6.1 vs. 20.4%, P=0.037) and tibial component alignment (0% vs. 7.5%, P=0.042). There is no apparent benefit of CAS-TKA with regards to KSS, ROM, or alignment in the hands of fellowship-trained total joint specialists. The clinical relevance of reduced outliers in the CAS-TKA group is unknown with the current follow-up interval.

Analysis of the expectations of elderly patients before undergoing total knee replacement

The opinion of patients expressed in terms of satisfaction is extremely important in any evaluation of total knee arthroplasty (TKA) results. The primary endpoint of this study was to determine the quantitative and qualitative expectations of elderly patients before undergoing TKA. Cross-sectional study of 497 patients over 65 years was performed before TKA. Main variables collected: demographic, functioning, pain, comorbidity, depression and expectations assessed with the Hospital for Special Knee Replacement Expectation Survey. Statistical tests used were: Student's t-test, analysis of variance, Spearman's ρ and multivariate regression analysis. The means of the total and maximum expectations were 12.3 ± 1.63 and 9.5 ± 1.78 (±S.D.), respectively. Between 90 and 100% of patients referred expectations to improvement regarding pain, basic functional activities (walking, climbing stairs, knee mobility, general mobility) and general well being. There were statistically significant correlations with age ( r = −0.321), pain before operation ( r = −0.206), expected pain at 6 months ( r = −0.206), depressive symptoms ( r = −0.180) and the Barthel index (BI) ( r = 0.154). One can conclude, that the expectations of improvement among patients before TKA are high and may be classified as expectations of improvement of pain, basic functional activities and general well being. Age, pain intensity and presence of depression correlate inversely with the amount of expectations.

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Correlation between radiographic assessment and quality of life after total knee arthroplasty

The correlation between radiographic and clinical outcome was investigated for total knee arthroplasty. One hundred three total knee arthroplasties in 98 patients were investigated at an average follow-up of 10.8 years (range, 2–17 years). For radiographic evaluation the Radiographic Evaluation System of the Knee Society was used. For assessment of clinical outcome four disease-specific scores, and the Nottingham Health Profile were applied. A significant correlation was found between the extent of radiolucent lines of the tibial component and the Nottingham Health Profile (correlation coefficient: 0.61, p < 0.0001). For the disease-specific scores the correlation was low (correlation coefficient: 0.30–0.50). For the prosthetic alignment no significant correlation was found ( p < 0.05). The current results show that a correlation was found between radiological assessment and several clinical scores. We suggest that a quality-of-life score should be included in the follow-up evaluation of total knee arthroplasty.

Cost-Benefit Comparison of the Oxford Knee Score and the American Knee Society Score in Measuring Outcome of Total Knee Arthroplasty

The American Knee Society score (AKSS) and the Oxford Knee score (OKS) are validated outcome measures for evaluation of total knee arthroplasties (TKAs). We investigated whether patient self-assessment using the OKS offers a viable alternative to clinical review using the AKSS. Preoperative, 2-year, 5-year, and 10-year postoperative OKS and AKSS were reviewed from TKA patients. The scores were analyzed using the Pearson correlation. There was good correlation of OKS and AKSS at 2 years. This implies that patient self-assessment is a viable screening tool to identify which patients require clinical review, at 2 years, after TKA. However, the moderate correlation at 5 and 10 years indicates that clinical evaluation remains necessary at these time points.

Effect of variability in anatomical landmark location on knee kinematic description

Small variability associated with identifying and locating anatomical landmarks on the knee has the potential to affect the joint coordinate systems and reported kinematic descriptions. The objectives of this study were to develop an approach to quantify the effect of landmark location variability on both tibiofemoral and patellofemoral kinematics and to identify the critical landmarks and associated degrees of freedom that most affected the kinematic measures. The commonly used three-cylindric open-chain kinematic description utilized measured rigid body kinematics from a cadaveric specimen during simulated gait. A probabilistic analysis was performed with 11 anatomical landmarks to predict the variability in each kinematic. The model predicted the absolute kinematic bounds and offset kinematic bounds, emphasizing profile shape, for each kinematic over the gait cycle, as well as the range of motion. Standard deviations of up to 2 mm were assumed for the anatomical landmark locations and resulted in significant variability in clinically relevant absolute kinematic parameters of up to 6.5 degrees and 4.4 mm for tibiofemoral and 7.6 degrees and 6.5 mm for patellofemoral kinematics. The location of the femoral epicondylar prominences had the greatest effect on both the tibiofemoral and patellofemoral kinematic descriptions. A quantitative understanding of the potential changes in kinematic description caused by anatomical landmark variability is important not only to the accuracy of kinematic gait studies and the evaluation of total knee arthroplasty implant performance, but also may impact component placement decision-making in computer-assisted surgery.

Reliability Analysis of 16-MDCT in Preoperative Evaluation of Total Knee Arthroplasty and Comparison With Intraoperative Measurements

The aim of our study was to determine how consistent measurements of the distal femoral condyle on 16-MDCT are with intraoperative measurements and the reliability of 16-MDCT for the preoperative planning of total knee arthroplasty. Between August 2003 and March 2004, 33 consecutive patients (two men and 31 women; age range, 53-89 years; mean age, 71 years) presenting with osteoarthritis underwent 16-MDCT (Mx 8000 IDT) of a total of 53 knees before total knee arthroplasty. The prospective analysis included measurements of transepicondylar distance, maximum anteroposterior dimension of medial and lateral femoral condyles, and trochlear width on a Rapidia workstation. To increase reliability, we repeated the measurements on a CT workstation after 2 months and compared them with the previous values. The values measured on the CT workstation were compared with the measurements obtained in the intraoperative field. Statistical analysis was performed using kappa statistics. A p value of less than 0.05 was considered statistically significant. The mean values of transepicondylar distance, maximum anteroposterior dimension of medial and lateral femoral condyles, and trochlear width were 75, 57, 58, and 38 mm at first measurement; 76, 58, 59, and 39 mm at second measurement on the CT workstation; and 79, 57, 60, and 42 mm at intraoperative measurement, respectively. At reliability analysis between the first measurements on the CT workstation and the intraoperative measurements, kappa values were 0.84 for the transepicondylar distance, 0.81 for the maximum anteroposterior dimension of the medial femoral condyle, 0.89 for the maximum anteroposterior dimension of the lateral femoral condyle, and 0.62 for the trochlear width. The kappa values for the second measurements were 0.86, 0.77, 0.84, and 0.61, respectively. Intraoperative measurements and measured values on the CT workstation showed excellent and almost perfect agreement, and intraobserver agreement was almost perfect. Femoral sizing on a CT workstation had excellent or almost perfect correlation with intraoperative measurements. Therefore, reliable preoperative planning for total knee arthroplasty may be done with 16-MDCT and an advanced workstation.

Functional evaluation of the TKA patient using the coordination and variability of rising

A kinematic analysis of the knee function is important for the evaluation of total knee arthroplasties (TKA). We used the coordination and variability of rising from a chair as functional knee parameters. Twelve knee patients were measured prior to surgery (=pre-TKA group) and one year after surgery (=post-TKA group). A group of 15 healthy, age-matched subjects was selected as control group. The WOMAC questionnaire, frequently used by orthopaedic surgeons, was administered prior to the test. The test consisted of 10 times rising from a low chair and 10 times from a high chair. Knee and hip angles and angular velocities were measured with electrogoniometers. The relative phase (=MRP) between hip and knee was a measure for the coordination of rising and the standard deviation of the relative phase of the 10 trials (=SRP) was a measure for the variability. The coordination and variability of rising of the TKA patients were compared to the control group, and the relationship with the WOMAC questionnaire was calculated. The coordination of rising from a high chair and the variability of rising from both chair heights were significantly different for the pre-TKA group compared to the control group ( p < 0.05). The post-TKA group showed no significant differences with the control group, which indicates a functional recovery after TKA implantation. The functional parameters correlated adequately with the subjective WOMAC questionnaire. This study showed that our method is an objective measure of functionality and it will be worthwhile to use it as an additional evaluation tool.