Introduction. A bicruciate retaining (BCR) TKA is thought to maintain a closer resemblance to the native knee kinematics compared to a posterior cruciate retaining (CR) TKA. With BCR TKAs retainment of the anterior cruciate ligament (ACL) facilitates proprioception and balance which is thought to lead to more natural knee kinematics and increased functional outcome. The aim of this study was to quantify and compare the kinematics of a BCR and CR TKA during functional tests. Materials and Methods. In this patient-blinded randomized controlled trial, a total of 40 patients with knee osteoarthritis were included, 18 of them received a BCR TKA (Vanguard XP, Zimmer-Biomet) and 22 received a CR TKA (Vanguard CR, Zimmer-Biomet). Fluoroscopic analysis was done 1 year post-operatively. The main outcome was posterior femoral rollback (i.e. translation of the femorotibial contact point (CP)) of the BCR and CR TKA during a step-up test. Secondary, the kinematics during a lunge test were quantified as anterior-posterior (AP) translation of the femorotibial CP. Independent student t-tests (or non-parametric equivalent) were used to analyze the effect of BCR versus CR TKA on these measures, to correct for the multiple testing problem post-hoc Bonferroni-Holm corrections were applied. Results. The mean AP CP for the BCR implant was not significantly different from the CR implant in the medial compartment (Figure 1, left). However, laterally the BCR implant shows a more posterior CP during late extension i.e. from 30° flexion to 0° extension (Figure 1, right). Figure 2 shows the AP CP during the final extension phase (30° flexion to 0° extension) of the step-up task for both implants on the tibia plateau. While the CR TKA remains mostly stable throughout this phase, the BCR TKA shows tibial internal rotation from 30° to 10° and tibial external rotation in the final extension phase: a kinematic pattern comparable to the natural knee's screw home mechanism. The lateral AP CP of the BCR TKA is more posterior compared to the CR TKA during the whole lunge task (Figure 3, right) the medial CP is more anterior in the 0–30° flexion (Figure 3, left). The main differences between the implants during the lunge task are observable in the early flexion phase, which is in line with ACL function. Conclusion. These preliminary results suggest that the kinematics of the BCR implant reproduces the natural screw-home mechanism in early flexion/late extension. The difference between the BCR and CR implants is mostly visible in the flexion phase in which the ACL is effective, which is in congruency with the absence of the ACL in CR TKAs. For any figures or tables, please contact the authors directly

Introduction. Better functional outcomes, lower pain and better stability have been reported with knee designs which restore physiological knee kinematics. Also the ability of the TKA design to properly restore the physiological femoral rollback during knee flexion, has shown to be correlated with better restoration of the flexor/extensor mechanism (appropriate flexor/extensor muscle lever arm, sufficient quadriceps force to extend the knee under load and limited patello-femoral force), which is fundamental to the function of the human knee. The purpose of the study is to compare the kinematics of three different TKA designs, by evaluating knee motion during Activities of Daily Living. The second goal is to see if there is a correlation between the TKA kinematics and the patient reported outcomes. Methods. Ten patients who are at least 6 months after their Total Knee Replacement are included in this study. Seven satisfied and 3 dissatisfied patients are selected for this design. In this study 5 different movements are being analysed: flexion/extension; Sitting on and rising from a chair, Stair climbing, descending stairs, Flexion and extension open chain and squatting. These movements will be captured with a fluoroscope. The 2D images that are obtained, are matched with the 3D implants. (see figure 1 and 2.) This 3D image is processed with custom-made software to be able to analyse the movement (figure 3.). Tibio-femoral contactpoints of the medial and lateral condyles, tibio-femoral axial rotation, determination of the pivot-point are analysed and described. After this analysis, a correlation between the kinematics and the KOOS and KSS is investigated. Results. Currently 6 patients underwent the fluoroscopic analysis and completed the questionnaires. At this moment the movements are being analysed and a correlation between the TKA kinematics and the patient reported outcomes will be investigated. Conclusion. Patient satisfaction is determined by several variables. In this study we hope to be able to conclude that the kinematics of a TKA are also an important variable. The results of this first group will be ready in july 2015

Aim: To compare the kinematic profile of two types of TKRs – a single-axis design Vs a polyradial design, with that of the normal knee. Methodology: An in-vivo fluoroscopic analysis was carried out as part of a four-armed prospective randomised trial comparing the clinical outcome of two commonly used types of TKRs each with posterior cruciate retaining -CR and sacrificing –CS models. The kinematic profile was obtained by measuring patella tendon angle at specific angles of knee flexion using an established fluoroscopic method whilst the patients performed close and open chain exercises. The data was compared with the kinematic profile of the normal knee. Results: Fifty-five patients who had undergone TKR at least one year prior, were invited to take part in this ethically approved study. They were matched for age and gender and had a similar clinical outcome. The kinematic profile of single axis design TKR was closer to normal especially near extension. During mid-flexion, abnormal anterior femoral translation was noticed with the polyradial design. No significant difference was noted between CR and CS designs. Conclusions: Kinematics after a TKR differed from that of a normal knee. Reproducible differences were found between the two designs, which may predict mode of failure and longevity

Introduction

Better functional outcomes, lower pain and better stability have been reported with knee designs which restore physiological knee kinematics. Also the ability of the TKA design to properly restore the physiological femoral rollback during knee flexion, has shown to be correlated with better restoration of the flexor/extensor mechanism, which is fundamental to the function of the human knee. The purpose of the study is to compare the kinematics of three different TKA designs, by evaluating knee motion during Activities of Daily Living. The second goal is to see if there is a correlation between the TKA kinematics and the patient reported outcomes.

Functional outcome after patellofemoral joint replacement (PFA) for osteoarthritis remains inconsistent. It is believed that functional outcome for joint replacement is dependent upon postoperative joint kinematics. Minimal disruption of the native joint, as in PFA, should produce more normal kinematics and improved outcome. No previous studies have examined joint kinematics after isolated PFA.

Aim: To investigate the sagittal plane kinematics of patellofemoral replacement and compare with the normal knee.

Twelve patients who had undergone successful PFA at least two years previously were recruited. Patients performed flexion/extension against gravity, and a step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), the angle between the long axis of the tibia and the patella tendon, as a function of knee flexion. This is a previously validated method of assessing sagittal plane kinematics of a knee joint. The kinematic profile of the PFA joints was compared to the profiles for fourteen normal knees.

Overall, the kinematic plot obtained for PFA reflected similar trends to that for normal knees; but the PTA was slightly but significantly increased throughout the entire range of flexion (two degrees). This is equivalent to an average displacement of the lower pole of the patella of 1.5mm.

Sagittal plane knee kinematics after PFA are much more normal than after TKR and this should give improved functional outcome. The observed increase in PTA through range may result from increased patella thickness or a shallow trochlear groove and may influence patellofemoral contact forces.

Aim: To study the sagittal plane kinematics of the Avon patello-femoral replacement (Stryker-Howmedica), PTA.

Introduction: Replacement of the patello-femoral joint for end stage osteoarthritis has previously been associated with inconsistent results. Retention of the cruciate ligaments is likely to be important in maintaining normal kinematics and hence improved functional outcome.

Methodology: Twelve patients who had undergone Avon PFR least two years previously were recruited following ethical approval. American Knee Society, Bristol and Oxford knee scores were obtained. Patients performed open chain flexion and extension against gravity, in addition to closed chain step up. Video fluoroscopy of these activities was used to obtain the Patellar Tendon Angle (PTA), which is the angle between the long axis of the tibia and the patella tendon, at specific angles of knee flexion. This is a previously validated method of assessing the kinematic profile of a knee joint. These measurements were used to determine the kinematic profile of each knee and they were then compared to a group of twelve normal knees.

Results: A one way ANOVA revealed no significant differences between the kinematic profile following Avon PFR and that of the normal knee. All patients had good or excellent knee scores.

Conclusion: The kinematic profile after Avon PFR is similar to that of the normal knee. In contrast all TKRs we have studied have abnormal kinematics, which are associated with abnormal patello-femoral joint loading. This suggests that isolated PFR should have a functional advantage over TKR.

Numerous papers present in-vivo knee kinematics data following total knee arthroplasty (TKA) from fluoroscopic testing. Comparing data is challenging given the large number of factors that potentially affect the reported kinematics. This paper aims at understanding the effect of following three different factors: implant geometry, performed activity and analysis method. A total of 30 patients who underwent TKA were included in this study. This group was subdivided in three equal groups: each group receiving a different type of posterior stabilized total knee prosthesis. During single-plane fluoroscopic analysis, each patient performed three activities: open chain flexion extension, closed chain squatting and chair-rising. The 2D fluoroscopic data were subsequently converted to 3D implant positions and used to evaluate the tibiofemoral contact points and landmark-based kinematic parameters. Significantly different anteroposterior translations and internal-external rotations were observed between the considered implants. In the lateral compartment, these differences only appeared after post-cam engagement. Comparing the activities, a significant more posterior position was observed for both the medial and lateral compartment in the closed chain activities during mid-flexion. A strong and significant correlation was found between the contact-points and landmarks-based analyses method. However, large individual variations were also observed, yielding a difference of up to 25% in anteroposterior position between both methods. In conclusion, all three evaluated factors significantly affect the obtained tibiofemoral kinematics. The individual implant design significantly affects the anteroposterior tibiofemoral position, internal-external rotation and timing of post-cam engagement. Both kinematics and post-cam engagement additionally depend on the activity investigated, with a more posterior position and associated higher patella lever arm for the closed chain activities. Attention should also be paid to the considered analysis method and associated kinematics definition: analyzing the tibiofemoral contact points potentially yields significantly different results compared to a landmark-based approach

Background. The overall goal of total knee arthroplasty (TKA) is to facilitate the restoration of native function following late stage osteoarthritis and for this reason it is important to develop a thorough understanding of the mechanics of a normal healthy knee. While there are several methods for assessing TKA mechanics, these methods have limitations that make them prohibitive to both replicating physiological systems and evaluating non-implanted knees. These limitations can be circumvented through the development of mathematical models that use anatomical and physiological inputs to computationally simulate joint mechanics. This can be done in an inverse or forward manner to solve for either joint forces or motions respectively. The purpose of this study is to evaluate one such forward model and determine the accuracy of the predicted motions using fluoroscopy. Methods. In vivo kinematics were determined during flexion from full extension to 120 degrees for ten normal, healthy, subjects using fluoroscopy and a 3D-to-2D registration method. All ten subjects had previously undergone CT scans allowing for the digital reconstruction of native femur and tibia geometries. These geometries were then input into a ridged body forward model based on Kane's system of dynamics. The resulting kinematics determined through fluoroscopy and the mathematical model were compared for all of the ten subjects. Results. The three kinematic parameters evaluated for this study were the initial positioning and translation of the medial and lateral condylar contact point in addition to the axial position and rotation of the femur with respect to the tibia. The model simulations demonstrated an average of −2.16mm of medial condyle translation, −14.03mm of lateral condyle translation, and 20.09°of axial rotation. Through fluoroscopy, subjects demonstrated an average of −3.63mm of medial condyle translation, −16.02mm of lateral condyle translation, and 15.65°of axial rotation. Comparing these two methods the model predicted on average an additional 1.47mm of medial condyle translation, 1.98mm of lateral condyle translation, and 4.44° less axial rotation compared to the fluoroscopic analysis of the same ten subjects. Conclusion. In comparing the simulation kinematics to the that of the fluoroscopic assessment, the results are comparably similar demonstrating a forward model can be a viable assessment of knee kinematics in the future. By validating mathematical simulation as a feasible means of mechanical assessment, it becomes possible to evaluate mechanics using inputs to reflect extraordinary and theoretical instances such as trauma patients and congenital deformities unable to be assessed by other methods. The nature of the model also allows for a seamless transition to assess TKA mechanics, creating a more efficient means of evaluating both device design and surgical technique

Aims

The aim of this study was to compare a bicruciate-retaining (BCR) total knee arthroplasty (TKA) with a posterior cruciate-retaining (CR) TKA design in terms of kinematics, measured using fluoroscopy and stability as micromotion using radiostereometric analysis (RSA).

Orthopaedic surgeons and their patients continue to seek better functional outcomes after total knee replacement, but TKA designs claim characteristic kinematic performance that is rarely assessed in patients. The objectives of this investigation is to determine the in vivo kinematics in knees with Cruciate Retaining TKA using Patient Specific Technology during activities of daily living and to compare the findings with previous studies of kinematics of other CR TKA designs. Four knees were operated by Triathlon CR TKA using Patient Specific Technology and a fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during three motor tasks. 3D fluoroscopic analysis was performed at 4-month follow-up. The range of flexion was 90°(range 5°–95°) during chair-rising, 80°(range 0°–80°) during step up and 100° (range 0°–100°) during leg extension. The corresponding average external rotation of the femur on the tibial base-plate was 7.6° (range +4.3°; +11.9°), 9.5° (+4.0°; 13.5°) and 11.6° (+4.5°; +16.1°). The mean antero-posterior translations between femoral and tibial components during the three motor tasks were +4.7 (−3.7; +1.0), +6.4 (−3.8; +2.6) and +8,4 (−4.9; +3.5) mm on the medial compartment, and −2.5 (−7.1; −9.6), −3.6 (−6.1; −9.7), −2.6 (−7.7; −10.3) mm on the lateral compartment, respectively, with the medial condyle moving progressively anterior with flexion, and the medial condyle moving progressively posterior with flexion. We compared Triathlon CR PSI TKA results from this study with Genesis II CR TKA, with Duracon CR TKA, with Triathlon CR TKA and with the healthy knee kinematics. The results of this study showed no screw home mechanism. The internal rotation of the tibia with knee flexion is close to normal, better than Genesis II, Duracon and Triathlon CR TKA operated with standard surgery. The medial condyle is characterized by the same pattern of the other implants, with a paradoxical anterior translation of 5 mm. The lateral condyle shows a posterior rollback better than Triathlon CR operated with standard surgery. For the first time is demonstrated that the surgical technique can modify the tibio-femoral kinematics

Introduction. Previous fluoroscopy studies have been conducted on numerous primary-type TKA, but minimal in vivo data has been documented for subjects implanted with revision TKA. If a subject requires a revision TKA, most often the ligament structures at the knee are compromised and stability of the joint is of great concern. In this present study, subjects implanted with a fixed or mobile bearing TC3 TKA are analyzed to determine if either provides the patient with a significant kinematic advantage. Methods. Ten subjects are analyzed implanted with fixed bearing PFC TC3 TKA and 10 subjects with a mobile bearing PFC TC3 TKA. Each subject underwent a fluoroscopic analysis during four weight bearing activities: deep knee bend (DKB), chair rise, gait, and stair descent. Fluoroscopic images were taken in the sagittal plane at 10 degree increments for the DKB, 30 degree increments for chair rise, and at heel strike, toe off, 33% and 66% cycle gait and stair descent. Results. The average weight bearing maximum flexion for the fixed bearing TKA group was 104 degrees (SD = 18.2 degrees). The average medial and lateral anterior-posterior (AP) translation for these subjects from full extension to maximum weight-bearing flexion was −6.74 mm and −8.0 mm in the posterior direction, respectively. The average femorotibial axial rotation was 1.27 degrees from full extension to maximum flexion. The average medial and lateral AP translations respectively from full extension to maximum flexion are shown in Figures 1 and 2 and the corresponding average femorotibial axial rotation pattern is shown in Figure 3. Subjects implanted with a mobile bearing device are presently being analyzed. Discussion. The fixed bearing device, on average, does not allow for much axial rotation when compared to less constrained or mobile bearing TKA designs. Previous studies have mobile bearing rotating platform primary posterior stabilized devices have documented that the bearing does rotate with the femur. Therefore, it is assumed subjects having a mobile bearing TC3 TKA may achieve greater axial rotation. Subjects having the fixed bearing TC3 TKA did achieve posterior femoral rollback of both condyles, revealing that a fixed bearing revision TKA may act more like a hinged device

Purpose of the study: Comprehension of total knee arthroplasty (TKA) kinematics is primordial for improving the functional outcome and longevity of these prostheses. Several methods are available for evaluating knee kinematics. The purpose of this study was to determine the accuracy of the 2D fluoroscopic method in vitro, taking optoelectronic analysis as the gold standard. Material and methods: In order to compare these two techniques, a posterior stabilised prosthesis was implanted on dry bones. The lateral ligaments were modellised with two elastic bands. Thirty flexion movements were imposed consecutively. The kinematics of this prosthetic model were recorded simultaneously using the fluoroscope and a computer-assisted surgery system. The technique used for the fluoroscopic analysis was based on the detection of the contours and projective geometry algorithms. The statistical analysis measured differences and correlations between the two systems using the root mean square (RMS) method and interclass coefficients of correlation (ICC) in addition to Bland and Altman analyses. Results: Three hundred thirty six relative implant positions were analysed for 30 flexions from −8 to 132 degrees. The objective RMS were to the order of one degree for flexion, varus and tibia rotation. Conversely, there was a difference of 2.43±3.17 mm for the mediolateral distance (ML). Similarly the ICC were to the order of 0.9 for the six degrees of freedom of the model with the exception of ML displacement where the ICC was 0.106. These analyses were confirmed by the Bland and Altman analysis which revealed an underestimation of the ML distance by the fluoroscopic method in greatest internal rotation. Discussion: This study is the first using a realistic model to evaluate the kinematic data provided by 2D fluoroscopy in comparison with conventional navigation data. The results show a good agreement between the two techniques and a small difference in measures excepting for the ML plane. The results are less satisfactory than those reported in the literature where data were obtained from computer simulations. Conclusion: 2D fluoroscopy of the TKA kinematics provides precise data. Nevertheless, the limits and inaccuracies of this technique should be recognized. This study is a prerequisite for in vivo 2D fluoroscopy

Introduction. Previous fluoroscopic studies compared total knee arthroplasty (TKA) kinematics to normal knees. It was our hypothesis that comparing TKA directly to its non-replaced controlateral knee may provide more realistic kinematics information. Using fluoroscopic analysis, we aimed to compare knee flexion angles, femoral roll-back, patellar tracking and internal and external rotation of the tibia. Material and methods. 15 patients (12 women and 3 men) with a mean age of 71.8 years (SD=7.4) operated by the same surgeon were included in this fluoroscopic study. For each patient at a minimum one year after mobile-bearing TKA, kinematics of the TKA was compared to the controlateral knee during three standardized activities: weight-bearing deep-knee bend, stair climbing and walking. A history of trauma, pain, instability or infection on the non-replaced knee was an exclusion criteria. A CT-scan of the non-replaced knee was performed for each patient to obtain a 3-D model of the knee. The Knee Osteoarthitis Outcome Score (KOOS) was also recorded. Results. Active flexion was significantly higher in the TKA group with a weight-bearing flexion averaging 103.4° and a passive flexion 133°, and respectively 96.4° and 135° for the contro-lateral knee. Twelve TKA patients out of 15 showed a higher flexion than their contro-lateral knee. The extension was also singificantly higher in the TKA group than in their contro-lateral knee (−4.8° versus −1.8) (p=0.0095). The axial rotation was significantly higher in the non-replaced knees than in the TKA group with respectively 18.7 ° versus 8.9° (p=0.0005). The position of the femorotibial contact point during the arc of flexion was significantly more posterior for the non-replaced knees compared to the TKA. The tracking of the patella showed significantly less lateral tilt for the TKA. KOOS scores were comprised between 70 and 100 but none of the patient did consider the replaced knee as a forgotten knee. Discussion and conclusion. The results of our study demonstrated that TKA may restore the arc of flexion with a better patellar tracking even if kinematics parameters of TKA are not directly comparable to the contro-lateral knees. This kinematics differences may explain why despite very good specific quality of life and functional score, none of the patient considered his/her replaced knee as a forgotten knee

Introduction: In conjunction with a bilateral randomised control trial comparing the clinical outcome of two total knee arthroplasties (TKA), we carried out an in-vivo fluoroscopic analysis of both knees in the trial. Knee A, is a new mobile bearing posterior cruciate retaining TKA and Knee B, an established fixed bearing posterior cruciate retaining TKA. Method: In an ethically approved study, video fluoroscopy was taken of both knees of seven patients performing three exercises; extension against gravity, flexion against gravity and a step up exercise. Ten images at ten-degree intervals over the flexion range were frame grabbed and digitised. The relationship of patella tendon angle (PTA) to knee flexion angle (KFA) was assessed using a newly developed computer system. Five normal knees in fit volunteers were also fluoroscoped and assessed. Results: A similar pattern of results was obtai ed for all three exercises. Knee A behaved in a linear, more consistent fashion than Knee B, which behaved non-linearly. Analysis of variance showed this difference was significant for all three exercises (p < 0.039). Conclusions: This bilateral study provides a powerful way of assessing the kinematics of two different knee implants. Knee A behaves in a linear predictable fashion that is nearer normal than Knee B. These results will be used in conjunction with a clinical outcome study and an RSA study to provide a complete assessment of a new TKA

Introduction: Mobile bearing total knee arthroplasty (TKA) has been developed to theoretically provide a better, more physiological function of the knee and produce less polyethylene (PE) wear. The theoretical superiority of mobile bearing TKA’s over fixed bearing devices has not yet been proven in clinical studies. The objective of the present study was to analyze in vivo the knee joint kinematics in the sagittal plane in a patient population that had received either a fixed or a mobile TKA in a prospective, randomized, patient- and observer-blinded, clinical study. Methods: 31 patients were evaluated by means of fluoroscopy during unloaded flexion and extension against gravity, as well as during step-up and step-down with full weight bearing. In these 31 patients, 22 fixed bearing TKAs, 16 mobile-bearing TKAs and 19 natural knee joints were included. All patients had been operated in a prospective, randomized, patient- and observer-blinded, clinical study, and had received either fixed or a mobile bearing, cruciate retaining Genesis II TKA for primary osteoarthritis. Fluoroscopic radiographs were evaluated by measuring the „patella tendon angle” as a measure of antero-posterior translation as well as the “kinematic index” as a measure of reproducibility. Results: During unloaded movement, fluoroscopic analysis did not show a significant difference between both types of prosthesis designs and the natural knee. In the weight-bearing movement, both types of TKA designs did not show the typically arched but a more linear patellar tendon angle curve, with a greater angle in extension and in flexion than the natural knees. This means that the femur glides anteriorly under load near extension and does not show the natural roll-back in flexion. In the mobile-bearing group, inter-individual deviations from the mean during weight-bearing movements were significantly less than in the fixed-bearing group. Conclusions: In the present study, no functional advantage of mobile bearing TKA over fixed bearing devices could be found. Both TKA designs showed the typical kinematics of an anterior instability. Long-term follow-ups are necessary to elucidate the possible influence of lower PE wear on the incidence of aseptic loosenings

Kneeling is one of important motion in Asians culture, also there were teachers of tea or flower ceremony who sit seiza routinely. But also, people in the Middle East need deep flexion keeling when they pray. At the symposium with the title of “A Challenge of deep flexion after TKA”, held at the 33rd Annual Meeting of Japanese Society of Reconstructive Arthroplasty in 2003, it was agreed that the definition of post-operative deep flexion to be more than 130 degrees of flexion. Four hundred and seventy two patients treated with a total of 598 consecutive primary total knee arthroplasties were performed and 480 knees were followed for 4.1 to 10.6 years(mean, 7.2 years). Preoperatively, the mean Hospital for Special Surgery knee score was 45.8 points. At the time of latest follow-up, the mean knee score was 88.5 points. The mean preoperative and postoperative ranges of flexion were 116 and 134 degrees, respectively. No knee developed osteolysis, aseptic loosening. A revision operation was performed in 3 knees because of infection. Achieving deep flexion is multi-factorial, such as preoperative planning, surgical procedure, prosthesis design, and postoperative rehabilitation. About surgical tips for deep flexion, posterior positioning of femoral component will increase the femoral posterior offset and decrease the anterior patello-femoral pressure. Through osteophyte removal will increase the posterior clearance and avoid the bone-polyethylene impingement. The flexion gap should be balanced after creating a balanced extension gap, since preparation of the flexion gap affects the extension gap in TKA. Based upon studies of the healthy knee in deep flexion, it was hypothesized that deep flexion would require tibial internal rotation greater than 20 degrees, greater posterior translation of the lateral femoral condyle than the medial condyle, and subluxation of the articular surfaces in terminal flexion. However, as the results of our fluoroscopic analysis of kinematics during deep flexion kneeling after fixed bearing PS TKA, tibial internal rotation increased with greater knee flexion, but there was high variability about the trend line. Patients with deeply flexing fixed bearing PS knee arthroplasty showed two phases of condylar translation with deep flexion. Interestingly, these two-phase translations are dictated by the design of the cam/post mechanism and serve to maintain the condyles within the posterior articular surfaces of the tibia plateau. Surface separation of both medial and lateral condyles was observed in terminal flexion. At least direct edge wear by the femoral condyle in maximum flexion is denied from this phenomenon. However, potential problems of TKA that allows for deep flexion are considerable such as dislocation, polyethylene wear, and anterior knee pain. In TKA using PS type of implant, the risk of insert damage also exists in factors other than deep flexion motion, such as cam/post or notch/post. Surgeons must confirm carefully not to set implants loose, or not to leave remnants of osteophytes during surgery and to pay attention not to raise the activity level of patients too high after surgery

Aim: This study was designed to investigate the nature and extent of tibial translation (TT) during open kinetic chain (OKC) and closed kinetic chain (CKC) activity; recent reports have suggested that the anterior cruciate ligament (ACL) may be strained to an equal amount during CKC and OKC exercise. Method: Fifteen unilaterally ACL deficient (ACLD) patients and six control subjects underwent fluoroscopic assessment while performing a passive extension exercise, an OKC resisted extension exercise, and a weight-bearing CKC exercise designed to reflect knee motion experienced during dynamic daily activity. Measurements of the patella tendon angle (the angle between the long axis of the tibia and the patella tendon) were obtained to calculate relative TT. Results: The results show that in ACL intact (ACLI) knees the CKC exercise caused greater anterior TT than the OKC exercise from 0 to 60° of knee flexion (p< 0.05). No difference between ACLI and ACLD knees was detected during the CKC exercise. Maximum weight-bearing (CKC) TT was 8±3 mm. The ACLD tibia during the OKC exercise translated more than the ACLI tibia, and to the same extent as the CKC exercise at 10 to 200 of knee flexion. The ACLI tibia during OKC exercise translated to a maximum of 3±4 mm at 1 0° knee flexion. Summary: This study has demonstrated that fluoroscopic analysis may be used to detect differences in the kinematics of ACLI and ACLD limbs during activity. It validates recent data demonstrating that the ACL may be strained during CKC exercise to an equal or greater amount than during OKC exercise, and shows that the ACLD knee kinematics are similar to the ACLI knee during CKC exercise. Factors other than the ACL may control the extent of maximal TT during weightbearing activity. This has important consequences for the development of rehabilitation regimes after ACL reconstruction. The commonly held assumption that CKC exercise will protect an ACL graft may not be valid

Both backside and articular surface wear have been linked to osteolysis after total knee arthroplasty (TKA). Prostheses with cementless fixation, screw holes in high load regions, and thin polyethylene are susceptible to backside wear. Factors associated with articular wear are similarly well defined. Micromotion at the modular polyethylene interface has been reported for many prostheses, but the relevance of such data compared to articular motions and wear are difficult to appreciate. This study compares in vivo motions and wear occurring at the backside and articular surfaces after TKA. Contemporary PCL-retaining prostheses from one manufacturer were implanted by one surgeon using cement fixation. The polyethylene inserts were > 6mm thick with a full peripheral rim capture and anterior wire locking mechanism. Femoral condylar motions were measured in 20 knees using fluoroscopic analysis during stair and gait activities. All patients had good to excellent clinical outcomes at one year follow-up. Articular and backside surface damage was evaluated on 32 polyethylene inserts retrieved after 27 months (1 to 71) months in-situ for infection (9), autopsy (6), patellar resurfacing (4), patellar loosening (4), tibial loosening (3), osteolysis (2), and other (4). Femoral condylar translation over the polyethylene articular surface ranged from 5-10 mm, which is substantially larger than the reported 50-500 micron range of backside interface micromotion measured in vitro. Damage covered < 33% of the backside surface and appeared as a cast impression of the opposed metal tibial component without scratches associated with micromotion. In contrast, damage consisting predominantly of scratching, burnishing and tractive striations covered 46% of the articular surface. Different locking mechanisms for modular polyethylene inserts result in different degrees of backside wear. No significant backside wear was observed these retrieved inserts with a wire-supplemented peripheral capture. Given the abrasive wear mechanisms and particulate debris shed during femoral condylar sliding, efforts to control motions at the articular surface appear warranted

Aims:Understanding total knee replacement mechanics and their influence on patient mobility requires accurate analysis of both operated joint accurate kinematics and full body kinematics and kinetics. The main aim of this study is to perform these two analyses conjointly, as never been reported previously. An innovative graphic-based interface is also pursued aimed at supporting quantitative functional assessment of these patients during the execution of daily living motor tasks in a single synchronized view. Methods: Three-dimensional fluoroscopic and gait analysis were carried out on eleven patients with PCL-retaining mobile bearing (Interax ISA, Stryker / How-medica / Ostetonics) and on ten posterior stabilized fixed bearing (Optetrak PS, Exactech) knee prostheses. Patients performed three trials of stair ascent twice on the same day: first in the radiology department for fluoroscopy acquisition and later in the Movement Analysis Laboratory, utilizing an identical staircase. Three-dimensional fluoroscopic analysis entails reconstruction of absolute and relative positions and orientations of the two metal components in space by analyzing series of fluoroscopic images of the operated knee and utilizing knowledge of the 3D cad models of these components. Conventional stereophotogrammetry and dynamometry were used to calculate kinematics and kinetics of the trunk, pelvis and of the major joints of the lower limb. An advanced computer-based interface was developed (MULTIMOD, EU-funded project: IST-2000-28377) to show together a) original video of the patient tasks, b) 3D graphical representation of bony segment motion, c) original fluoroscopic images, d) 3D reconstruction of prosthesis component relative motion, and e) graphical transverse plane representation of the contact areas at the base-plate of the replaced knee. All these were registered in space and synchronized in time. Results: No significant statistical differences on clinical data were found between the two patient populations. Observations at the interface allowed distinct identification of the most critical phases of the task and of the most common compensatory mechanisms utilized by these patients. Statistically significant correlation was found between knee flexion at foot strike and the position of the mid-condylar contact points, and between maximum knee adduction moment and corresponding lateral trunk tilt. Conclusions: A more complete and powerful assessment of the functional performances of different TKR designs is obtained by combining gait and fluoroscopic in-vivo analyses, which provide correlated and synergic quantitative information

Introduction: Total knee replacement (TKR) is a common treatment for end stage osteoarthritis of knee. The best knee replacement is one in which the kinematics of the normal knee are reproduced. Amongst several factors affecting kinematics, variation in surface geometry and the retention/ sacrifice of the PCL are considered especially important. It is not known which of these two factors is most influential for establishing optimum joint kinematics after TKR. Method: Four groups of patients who had undergone TKR at least one year previously were recruited. Two groups of patients had undergone replacement with a single axis design (Scorpio, Stryker Howmedica) in both PCL retaining (Scorpio CR, n=15) and PCL sacrificing (Scorpio CS, n=15) variants. The other two groups had undergone replacement with the traditional polyradial design prosthesis (Sigma, Depuy, Johnson & Johnson), again with both PCL retaining (Sigma CR, n=14) and PCL sacrificing (Sigma CS, n=13) variants. An in-vivo fluoroscopic analysis was carried out on all patients. Patients were asked to perform closed chain step up and open chain extension and flexion against gravity. The kinematic profile of each knee was obtained by measuring patella tendon angle (PTA) at specific angles of knee flexion (KFA) using an established fluoroscopic method. The data was also compared with the kinematic profile of normal knees. American Knee Society, Oxford and Patella Scores were recorded for all patients. Results: All groups were comparable in terms of age and gender. In addition, no significant difference was found between groups in clinical outcome. PTA results for a step-up exercise are shown in the figure. A one way ANOVA between groups revealed that knee kinematics after total knee replacement is different to that for normal knees. No differences were found between groups when the data was analysed using CR/CS as the independent variable. The only differences between groups were found when surface geometry was used as the independent variable. It was shown that the kinematic profile of the single axis Scorpio design (in both CR & CS ) was closer to normal, especially near extension, than the traditional polyradial design (Sigma CR & CS). Conclusions: Kinematics after a total knee replacement differ from that for a normal knee. Differences in surface design between knee replacements appear to have greater influence on kinematics than the presence or absence of the PCL