Aims. Radiostereometric analysis (RSA) is considered the gold standard for in vivo migration analysis, but CT-based alternatives show comparable results in the shoulder and hip. We have previously validated a CT-based migration analysis method (CTMA) in a knee phantom compared to RSA. In this study, we validated the method in patients undergoing total knee arthroplasty (TKA). Our primary outcome measure was the difference in maximum total point motion (MTPM) between the differing methods. Methods. A total of 31 patients were prospectively studied having undergone an uncemented medial pivot knee TKA. Migrations were measured up to 12 months with marker-based and model-based RSA, and CT-RSA. Results. Mean precision data for MTPM were 0.27 mm (SD 0.09) for marker-based RSA, 0.37 mm (SD 0.26) for model-based RSA, and 0.25 mm (SD 0.11) for CTMA. CTMA was as precise as both RSA methods (p = 0.845 and p = 0.156). At three months, MTPM showed a mean of 0.66 mm (95% CI 0.52 to 0.81) for marker-based RSA, 0.79 (95% CI 0.64 to 0.94) for model-based RSA, and 0.59 (95% CI 0.47 to 0.72) for CTMA. There was no difference between CTMA and marker-based RSA (p = 0.400), but CTMA showed lower migration than model-based RSA (p = 0.019). At 12 months, MTPM was 1.03 (95% CI 0.79 to 1.26) for marker-based RSA, 1.02 (95% CI 0.79 to 1.25) for model-based RSA, and 0.71 (95% CI 0.48 to 0.94) for CTMA. MTPM for CTMA was lower than both RSA methods (p < 0.001). Differences between migration increased between the methods from three to 12 months. Mean effective radiation doses per examination were 0.016 mSv (RSA) and 0.069 mSv (CT). Imaging time for performing RSA radiographs was 17 minutes 26 seconds (SD 7 mins 9 sec) and 4 minutes 24 seconds (SD 2 mins 3 sec) for CT. Conclusion. No difference in precision was found between CTMA and marker- or model-based RSA, but CTMA shows lower migration values of the tibial component at 12 months. CTMA can be used with low effective radiation doses, and CT image acquisition is faster to perform than RSA methods and may be suitable for use in ordinary clinical settings. Cite this article: Bone Joint J 2025;107-B(2):173–180

Ligament releases are necessary for contemporary non-conforming femoral-tibial articulations. Most total knee arthroplasty prostheses are designed to be non-conforming at the articulation between the femoral and tibial components. This design is chosen on the arthroplasty principle that “constraint causes loosening” and conforming surfaces have been considered constrained. To provide stability the ligaments are adjusted so that tension in the ligament can provide stability for the total knee replacement. Ligament releases are NOT necessary for contemporary conforming femoral-tibial articulations. Through the majority of the range of motion, the normal human knee is not stabilised by ligament tension. Rather, it is the geometrical conformity of the femur and tibia, especially on the medial side, that provides stability. The ligaments are present and ready to restrain the knee from excess varus-valgus or anterior-posterior loads. In a knee design that is congruent, ligaments may be left intact as in the normal knee, ready to provide restraint but not necessarily to provide stability except when excess loads are applied to the knee. When designing and using the ADVANCE Medial Pivot total knee, the author has left ligaments in the toe-region of the stress-strain curve rather than releasing and tensioning the ligaments. Patient satisfaction survey data at routine follow-up visits for patients at 7–15 years after arthroplasty with this type of reconstruction indicate high satisfaction despite medial and lateral opening (on valgus and varus stress) that would be considered “mid-flexion instability” for non-conforming joints that require careful ligament releases and tensioning

Introduction. In total knee arthroplasty, the aim is to relieve pain and provide a stable, functional knee. Sagittal stability is crucial in enabling a patient to return to functional activities. Knee implants with a medial pivot (MP) design are thought to more accurately reproduce the mechanics of the native joint, and potentially confer greater antero-posterior stability through the range of flexion than some other implant designs. Aim. This study aims to compare the sagittal stability of four different total knee arthroplasty implant designs. Method. Comparison was made between four different implant designs: medial pivot (MP), two different types of cruciate retaining (CR1 and CR 2) and deep dish (DD). A cohort of 30 Medial Pivot (MP) knees were compared with matched patients from each of the other designs, 10 in each group. Patients were matched for age, body mass index and time to follow up. Clinical examination was carried out by an orthopaedic surgeon blinded to implant type, and sagittal stability was tested using a KT1000 knee arthrometer, applying 67N of force at 30˚ and 90˚. Results. The MP knee was more stable than the CR1 knee at both 30º (mean movement: 1.37mm vs 2.48mm, p=0.037) and 90º (1.68mm vs 2.37mm, p=0.030). The MP knee was more stable than the CR2 knee at 30º (0.98mm vs1.33mm, p=0.013). The MP knee also demonstrated less movement at 90 º (0.98mm vs 1.33mm), but this was not statistically significant (p=0.156). The MP knee was more stable than the DD knee at 30 º (0.48mm vs 1.33mm, p=0.03) and 90 º (0.67mm vs 1.15mm, p=0.048). Overall the medial pivot design was more stable than all non-medial pivot designs at 30 º (0.8mm vs1.66mm, p=0.003) and 90 º (1.1mm vs 1.61mm, p= 0.008). Conclusion. Overall, the medial pivot design demonstrated significantly greater antero-posterior stability than all other design types included in this study. Correlation with patient reported outcome scales will allow insight into whether these statistically significant differences are also clinically significant

Background. In recent literatures, medial instability after TKA was reported to deteriorate early postoperative pain relief and have negative effects on functional outcome. Furthermore, lateral laxity of the knee is physiological, necessary for medial pivot knee kinematics, and important for postoperative knee flexion angle after cruciate-retaining total knee arthroplasty (CR-TKA). However, the influences of knee stability and laxity on postoperative patient satisfaction after CR-TKA are not clearly described. We hypothesized that postoperative knee stability and ligament balance affected patient satisfaction after CR-TKA. In this study, we investigated the effect of early postoperative ligament balance at extension on one-year postoperative patient satisfaction and ambulatory function in CR-TKAs. Materials & Methods. Sixty patients with varus osteoarthritis (OA) of the knee underwent CR-TKAs were included in this study. The mean age was 73.6 years old. Preoperative average varus deformity (HKA angle) was 12.5 degrees with long leg standing radiographs. The knee stability and laxity at extension were assessed by stress radiographies; varus-valgus stress X-ray at one-month after operation. We measured joint separation distance (mm) at medial compartment with valgus stress as medial joint opening (MJO), and distance at lateral compartment with varus stress as lateral joint opening (LJO) at knee extension position. To analyze ligament balance; relative lateral laxity comparing to the medial, varus angle was calculated. New Knee Society Score (NKSS) was used to evaluate the patient satisfaction at one-year after TKA. We measured basic ambulatory functions using 3m timed up and go test (TUG) at one-year after surgery. The influences of stability and laxity parameters (MJO, LJO and varus angle at extension) on one-year patient satisfaction and ambulatory function (TUG) was analyzed using single linear regression analysis (p<0.01). Results. MJOs at knee extension one-month after TKA negatively correlated to patient satisfaction (r=−0.37, p<0.01) and positively correlated to TUG time (r=0.38, p<0.01). LJOs at knee extension had no statistically significant correlations to patient satisfaction and TUG. The extension varus angle had significant positive correlation with patient satisfaction (r=0.40, p<0.01). Discussions. In our study, we have found significant correlations of the early postoperative MJOs at extension to postoperative patient satisfaction and TUG one-year after CR-TKA. Our results suggested that early postoperative medial knee stabilities at extension were important for one-year postoperative patient satisfaction and ambulatory function in CR-TKA. Other interest finding was that postoperative patient satisfaction was positively correlated with extension varus angle. This finding suggested that varus ligament balance; relative lateral laxity to medial stability, was beneficial for postoperative patient satisfaction after CR-TKA. Intra-operative soft tissue balance had been reported to significantly affect postoperative knee stabilities. Therefore, with our findings, surgeons might be better to manage intra-operative soft tissue balance to preserve medial stability at extension with permitting lateral laxity, which would enhance patient satisfaction and ambulatory function after CR-TKA for varus type OA knee. Conclusion. Early postoperative medial knee stability and relative lateral laxity would be beneficial for patient satisfaction and function after CR-TKA

Aims

The outcome of total knee arthroplasty (TKA) is not always satisfactory. The purpose of this study was to identify satisfaction and biomechanical features characterising the gait of patients who had undergone TKA with either an anatomical single radius design or a medial pivot design. We hypothesised that the latter would provide superior function.

Most total knee prostheses are designed to have limited congruence between the femoral and tibial components to reduce constraint, based on the widely accepted principle that “constraint causes loosening”. Studies of the normal knee, however, indicate that stability under axial load occurs mostly by the geometric conformity of the surfaces. When moving in the plane of flexion-extension, the ligaments contribute little to stability because the ligaments are in the “toe-region” of their force-displacement curve. When an “out-of-plane” load is applied (i.e., load outside the plane of flexion-extension), ligaments are “recruited” for stability by being stressed into the elastic portion of the curve to resist the load. For the traditional total knee prosthesis, because of the lack of geometric congruity, the ligaments must provide all stability by being “balanced”, i.e. tensioned into the elastic portion of the force-displacement curve. Further, they must remain in that tensioned state indefinitely, with no stretching or migration of the implant. The medial pivot knee design has a fully conforming medial “ball-in-socket” articulation that provides stability to the knee through the geometric conformity. Ligaments need not be tensioned into the elastic region of the force-displacement curve but can be left in the toe-region to be recruited for out-of-plane loads. Clinical follow-up results in patients with a medial pivot prosthesis indicate that, based on Knee Society and WOMAC scores, patients report greater than 90% satisfaction with pain and function. Further, the most satisfied patients are those who, during physical examination, display medial and lateral opening that might be classified as “mid-flexion instability” for prostheses that depend on ligament tensioning for stability

INTRODUCTION. The purpose of TKA is to restore normal kinematics and functioning to diseased knees. The purpose of this study was to determine whether intraoperative kinematic data are correlated with minimum one-year outcomes following primary TKA. METHODS. We reviewed data on 185 consecutive primary TKAs in which sensor-embedded tibial trials were used to evaluate kinematic patterns following traditional ligament balancing. Procedures were performed by two board-certified arthroplasty surgeons. The same implant design and surgical approach was used for all knees. Contact locations on the medial and lateral condyles were recorded for each patient at 0°, 45° and 90° of flexion, and full flexion. Vector equations were created by contact locations on the medial and lateral sides and the vector intersections determined the center of rotation between each measurement position. Center of rotation was calculated as the average of vector intersections at 0 to 45°, 45 to 90°, and 90° to full flexion. If the average center of rotation was between 16 and 1000 mm of the contact location on the medial side it was considered a medial pivot knee. Knees were also classified as medial (16 to 200 mm on medial side), lateral (16 to 200 mm on lateral side), translating (> 200 mm medially or laterally), and other (< 16 mm on both medial and lateral sides). The new Knee Society Scoring System (KSSO objective score, KSSS satisfaction score, KSSF function score), the EQ-5D™ Health Status Index, and the University of California Los Angeles (UCLA) Activity Level Score were measured preoperatively and at minimum one-year follow-up (average 20.4 months). RESULTS. Thirty-three TKAs were excluded to eliminate potential bias due to sensor device malfunction, atypical hardware, unresurfaced patella, surgery at a non-study hospital, or early postoperative infection, revision due to aseptic loosening, ipsilateral hip disease, and subsequent neurologic disease or death unrelated to the index TKA, resulting in a final sample size of 152 knees. Twelve (7.9%) patients were lost to follow-up, and two were excluded due to outlier values for average center of rotation. Seventy-five percent of the final sample was female. Mean age and BMI were 63.6 years 33.9, respectively. Average center of rotation ranged from −1017 to 1562 mm with negative signifying the lateral side. Medial pivot knees comprised 40% (55) of the total sample. Sex, age, height, surgeon, implant side, and implant type were unrelated to pivot classification. Patient weight (100.2 vs. 90.9 kg; p = 0.012) and BMI (35.5 vs. 32.8; p = 0.044) were greater in medial pivot knees. Controlling for BMI, KSSO, KSSF, KSSS, EQ5D, UCLA, and pain scores at latest follow-up did not differ in medial and non-medial pivot knees (p ≥ 0.151). The amount of improvement in outcomes from preoperative baseline also did not differ in medial and non-medial pivot knees (p ≥ 0.161). Outcomes did not vary among knees with translating medial, lateral, and other pivots (p ≥ 0.065). DISCUSSION. Our results suggest that a medial pivot kinematic pattern may not be a substantial governor of clinical success

Backgrounds. Most of in vivo kinematic studies of total knee arthroplasty (TKA) have reported on varus knee. TKA for the valgus knee deformity is a surgical challenge. The purposes of the current study are to analyze the in vivo kinematic motion and to compare kinematic patterns between weight-bearing (WB) and non-weight-bearing (NWB) knee flexion in posterior-stabilized (PS) fixed-bearing TKA with pre-operative valgus deformity. Methods. A total of sixteen valgus knees in 12 cases that underwent TKA with Scorpio NRG PS knee prosthesis operated by modified gap balancing technique were evaluated. The mean preoperative femorotibial angle (FTA) was 156°±4.2°. During the surgery, distal femur and proximal tibia was cut perpendicular to the mechanical axis of each bone. After excision of the menisci and cruciate ligaments, balancer (Stryker joint dependent kinematics balancer) was inserted into the gap between both bones for evaluation of extension gap. Lateral release was performed in extension. Iliotibial bundle (ITB) was released from Gerdy tubercle then posterolateral capsule was released at the level of the proximal tibial cut surface. If still unbalanced, pie-crust ITB from inside-out was added at 1 cm above joint line until an even lateral and medial gap had been achieved. Flexion gap balance was obtained predominantly by the bone cut of the posterior femoral condyle. Good postoperative stability in extension and flexion was confirmed by stress roentgenogram and axial radiography of the distal femur. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibial tray using a 2-dimentional to 3-dimensional registration technique. Results. The average flexion angle was 111.3°±7.5° in weight-bearing and 114.9°±8.4° in non-weight-bearing. The femoral component demonstrated a mean external rotation of 5.9°±5.8° in weight-bearing and 7.4°±5.2° in non-weight-bearing (Fig.1). In weight-bearing, the femoral component showed medial pivot pattern from 0° to midflexion and a bicondylar rollback pattern from midflexion to full flexion (Fig2). Medial condyle moved similarly in non-weight-bearing condition and in weight-bearing condition. Lateral condyle moved posterior in slightly earlier angle during weight-bearing condition than during non-weight-bearing condition (Fig.3). Discussion. Numerous kinematic analyses of a normal knee have demonstrated greater posterior motion of the lateral femoral condyle relative to the medial condyle, leading to a mean external rotation and a bicondylar rollback motion with progressive knee flexion. A kinematic analysis of valgus knee was reported to show a different kinematic pattern from a physiological knee motion. Many valgus knees showed paradoxical anterior translation from extension to mid-flexion and greater posterior translation in the medial condyle than in the lateral condyle. Kitagawa et al. reported that this non-physiologic pattern wasn't completely restored after TKA using medial pivot knee system. In the present study, we showed kinematic patterns of the TKA performed on the valgus knee to be similar to the normal knee for the first time, even though the magnitude of external rotation was small. Conclusions. We conclude that the medial pivot pattern followed by posterior rollback motion can be obtained in TKA with modified gap balancing technique for the preoperative valgus deformity

Purpose. The purpose of this study was to compare the clinical and radiological results after total knee arthroplasty(TKA) with PCL sacrificing (PCS) Medial Pivot Knee (MPK) and PCL Substituting (PS) Nexgen® LPS. Materials and Methods. One hundred twenty knees in 80 patients after TKA with PCS ADVANCE® MPK (Group I) and 116 knees in 85 patients with PS Nexgen® LPS (Group II) were retrospectively evaluated. All the patients were followed up for more than 6 years. The evaluations included preoperative and postoperative range of motion (ROM), tibiofemoral angle, Knee Society (KS) knee and function score, Hospital for Special Surgery (HSS) knee score, WOMAC score and postoperative complications. Results. For group I, the ROM increased from a mean flexion contracture of 7.6° and further flexion of 115.1° to 1.3° and 120.5° respectively and for group II, from 9.4° and 124.8° to 1.3° and 129.7°, respectively. For group I, KS knee and function scores increased from 46 and 38 to 87 and 82 respectively, and for group II, from 49 and 43 to 88 and 81, respectively. Hospital for Special Surgery (HSS) knee score improved from preoperatively 48.3 to postoperatively 84.2 for group I and 44.6 to 82.3 for group II. WOMAC score was improved preoperatively 54.8 to postoperatively 18.3 for group I and 57.4 to 17.4 for group II. For group I, tibiofemoral angle changed from varus 4.6° to valgus 5.8° and for group II, from varus 5.8° to valgus 5.2°. The complications were 2 cases(1.7%) of periprosthetic patellar fracture and 1 case(0.8%) of early failure of the tibial component and 1 case(0.8%) of osteolysis and loosening in group I, and 1 knee (1.0%) with early femoral component failure and 1 knee with arthrofibrosis (1.0%) in group II. Conclusion. The minimum 6-year follow-up results of PCS ADVANCE® MPK TKA without box cut were comparable to those of PS Nexgen®LPS

Postoperative stiffness is a relatively uncommon issue in total knee arthroplasty (TKA). However, it can be a debilitating complication when it occurs. Manipulation under anesthesia (MUA) is commonly used as the primary treatment modality following failed physiotherapy. The ADVANCE® Medial Pivot Knee (Wright Medical Technology) was created in an effort to prevent stiffness postoperatively and increase range of motion. The EVOLUTION® Medial Pivot Knee is a second generation design that builds upon the technology of the ADVANCE® knee. We performed a retrospective review of prospectively collected data on 881 primary medial pivot knees (592 ADVANCE® knees, 289 EVOLUTION® knees). We theorized that the design changes made to the EVOLUTION® knees might contribute toward reducing the need for MUA. We found that the EVOLUTION® knees required significantly fewer manipulations under anesthesia (p = 0.036). The design modifications made to the EVOLUTION® knees may have contributed to the lower rate of MUA

In order to emulate normal knee kinematics more closely and thereby potentially improve wear characteristics and implant longevity the Medial Pivot type knee replacement geometry was designed. In the current study the clinical and radiographic results of 50 consecutive knee replacements using a Medial Pivot type knee replacement are reported; results are compared to the Australian Orthopaedic Associations National Joint Replacement Registry. The patients' data were crossed checked against the registry to see if they had been revised elsewhere. After a mean follow-up of 9.96 years results show that the Medial Pivot Knee replacement provides good pain relief and functional improvement according to KSS and Womac scores and on subjective patient questionnaires. There was one minor revision; insertion of a patella button at 6.64 years FU. There were no major revisions; all implants appeared to be well fixed on standard radiographic examination. While the revision rate for the Medial Pivot knee according to the Australia Joint Registry results is higher compared to all other types of knee replacements in the registry, and to what is reported in the literature on the medial pivot knee, it is not in the current series. Revision rate was similar to what is reported on in the literature, but after a longer follow-up period. However, long term follow-up is required to draw definitive conclusions on the longevity of this type of implant

Distal femoral fractures in elderly patient occurred with lower energy injury due to preexisting osteoporosis. Gonarthrosis is frequently accompanied in these patients, and which is difficult to treatment and hard to restore function. Traditionally, the fractures in osteoarthritic knee are treated by open reduction and internal fixation (ORIF) and total knee arthroplasty (TKA) for osteoarthritis is considered after bone union of the prior fractures. However two-stage procedure makes some problems when TKA is performed following long immobilization, previous scar, implant removal, prolonged hospital stay, and increased cost. Several authors have reported acceptable results of primary TKA with concomitant ORIF using long stem with hinged, constrained type or posterior stabilized prosthesis, but which generally need substantial bone removal for notch preparation and is disadvantageous for the fractured extremity. We report 5 patients who were treated with primary TKA with concomitant ORIF for osteoarthritic knee accompanied by distal femoral fracture using ADVANCE Medial Pivot knee (Wright Medical, Arlington, TN) in which prosthesis stem extension can be used without notch cutting. All patents were women with mean age of 79 (69–87 years). There was 1 case of medial femoral condylar fracture, 2 cases of supracondylar fractures and 2 cases of supracondylar/intercondylar femoral fractures. Fracture is well reduced in all cases and well united. The range of motion was good (mean 1–112, flexion contracture 0–5, maximal flexion 90–130) at mean follow-up of 12.6 months (range, 5–33 months). We believe that one-stage primary TKA using medial pivot knee is a reasonable alternative treatment for osteoarthritic knees accompanied by distal femoral fractures if a surgeon is experienced in fracture management and arthroplasty

Total Knee Artroplasty (TKA) is becoming more and more popular, even in the younger active age group. In this age group however the results are not that reproducible as in the older age group. People are more limited in their activities of daily living and complain more about pain, stifness and swelling. At the end and in general the younger age group is less satisfied than the older patients. The last decade minimal invasive solutions with modified instruments, Gender Knees, the use of navigation in TKA, ligament-based techniques, fast rehab protocols etc have all been introduced to make the results of TKA better. These are all elements that indeed can make the patient better. However the most important on the short term and the long term is the use of the correct implant size and the correct implantation of the prosthetic components. Since January 2011 we routinely use patient specific instruments in TKA patients under 60y that are very active or in older less active patients with important anatomic malformations. A CT-based system that scans the hip-knee-ankle is used. The data are sent to an engineer and a digital proposal is sent back to the surgeon that can approve the different measurements performed. Once approved the patient specific cutting blocks are sent to the surgeon. In our department we use the Advance Medial Pivot Knee System as our standard knee system since its introduction thirteen years ago. Since then more than 2000 implantations have been performed. This experience has made it possible to critically evaluate the patient specific cutting block technique. The first results are very satisfying. During surgery less ligamentous releases had to be performed, there was in all cases an optimal patellofemoral tracking without any release, there was less blood loss and surgery time was decreased. At all times during surgery we were very satisfied how we could verify all surgical steps and this is in our opinion very important. During the first postoperative days the patients experienced less pain (routine VAS recorded), there was a faster return to full ROM and patients asked to go home earlier. After two months patients are routinely followed up and they undergo a clinical and radiographic exam. All prosthetic components were implanted the way we had planned it. The overall axes were restored and up till now no complications were noticed. All patients experienced a fast recovery with full ROM at 2 months, no complaints about pain or swelling and very interestingly no residual intra-articular swelling which is often seen in these active and younger patient group. Patients are also asked to fill in a patient-based outcome measurements (KOOS) questionnaire. In our opinion it is a very easy and promising system for the experienced surgeon. Younger and less experienced surgeons however should be warned that they cannot blindly trust the system. We surgeons have to control what the engineer has proposed before and during surgery

Background: Knee prosthesis design is being constantly altered in a bid to imitate kinematics of the normal knee. It is hoped that this will improve the wear characteristics and performance of the implant. The ‘Medial Pivot’ knee has a characteristic geometry and is expected to lower contact stresses on the tibial surface and ease rehabilitation while providing greater stability. We conducted a study comparing the midterm outcome of the Medial Pivot knee (MP) to the Posterior Stabilised (PS) knee. Materials and Methods: Over a 3 year period, 312 knee replacements were carried out of which 124 were MP and 188 were PS. 100 patients from each of the 2 groups were called for review. Demographic data, age at operation, time since surgery and ASA grading were noted. Postoperative knee function was assessed using the American Knee Society (AKS) and Oxford Knee (OK) scores and the scores were compared between the 2 groups. Individual functional parameters were also compared. Results: 38 patients with 42 replaced knees in the MP group and 43 patients with 52 replaced knees in the PS group were reviewed. The 2 groups were comparable in terms of gender of patients and age at operation and were followed up to a mean 31 months. For the MP group the mean AKS knee assessment score was 77/100, AKS function score was 75/100 and OK Score was 23/60. For the PS group the corresponding values were 81/100, 77/100 and 22/60. The differences in scores between the groups were not statistically significant. Only active and passive knee extension was better following MP Arthroplasty than PS arthroplasty (p< 0.05). Although the mean flexion was better following the PS arthroplasty, this was not statistically significant. Conclusion: Our study has shown that the midterm outcome for the Medial Pivot knee system did not show any distinct advantage over the Posterior Stabilised knee system in terms of knee pain & function

Introduction: It is difficult to measure the knee kinematics after TKA, navigation system can measure the knee kinematics during TKA operation. The purpose of this study is to describe the knee kinematic analysis in TKA using navigation system. Patients and methods: TKA kinematics was measured in 24 patients (7 men and 17 women) 27 knees (7 rheumatoid arthritis knees and 20 osteoarthritis knees) in this study. Mean age was 72.8 (55–81). The TKA implant was Vanguard PS (Biomet, Warsaw) and navigation system was Vector Vision Knee ver. 1.6 (BrainLab Inc). All patients were operated using navigation system. This system was CT-based navigation system. We cut the bone independently and released medial collateral ligament, joint capsule and other tight structures to equal the joint balance. Femoral component was implanted parallel to clinical epicondylar line. Kinematic Analysis: We measured the joint gap (mm), coronal alignment (degree), antero-posterior translation (mm) and femoral rotation angle (degree) using navigation workstation just after all prostheses implantation and closure of joint capsule. The patient’s leg was held by operator and moved passively. All joint kinematic data were recorded at every 10 degrees in full range of motion (0 to 130 degrees). The joint gap is the distance between proximal tibial cut surface and that of distal femur (extension range: 0–40) and posterior femur (flexion range: 50–130). Medial and lateral distances were measured. Results: In extension range, medial joint gap was 21.7mm at 0 degrees and decreased to 15.2mm with knee flexion. Lateral joint gap was 22.1mm at 0 knee extension, slightly decreased up to 40 degrees. Coronal alignment was 0.47 varus at 0 deg. and increased to 6.64 varus at 40 flexion. In flexion range, medial and lateral joint gap were increased 20.7 to 25.3, 17.2 to 31.2mm. Coronal alignment was c hanged from 4.94 valgus (60 flexion) to 8.94 varus (130 full flexion). Regarding to AP translation, femoral component was once moved 7.4 mm forward in early knee flexion and 15.2mm backward with flexion. Femoral components were rotated internally to 50 degrees flexion and then rotated externally with flexion. Conclusion: The balance of TKA was still varus alignment after soft tissue release. Femoral components were moved backward and external rotation. Our results demonstrated that femoral rollback movement and medial pivot knee motion were recognized. The limitation of this study was the situation of under anesthesia and no muscle strain were loaded during the measurement of knee kinematics. However navigation system is available not only for the accurate implantation but also the measurement of intra operative knee kinematics

We compared the short term follow-up clinical and radiological results after PCL substituting (PS) Medial Pivot Knee and Nexgen. ®. LPS total knee arthroplasty (TKA). Seventy knees in 48 patients after TKA with PS ADVANCE. ®. Medial Pivot Knee (Group I) and sixty seven knees in 45 patients after TKA with Nexgen. ®. LPS (Group II) were evaluated retrospectively from March 2004 to May 2006. The mean follow up period was 31 months (range: 24–43 months) in group I and 32 month (range: 24–46 months) in group II. All the knees were operated by one surgeon. The evaluations included the preoperative and postoperative range of motion (ROM), Knee society score (KSS), tibiofemoral angle, and postoperative complications. In group I, ROM increased from preoperative mean flexion contracture of 6.3° and further flexion of 116° to postoperative mean flexion contracture 1.9° and further flexion 121°, KS knee score increased from 46 to 87, KS function score increased from 37 to 83, and tibiofemoral angle changed from preoperative varus 4.0° to postoperative valgus 5.5°. In group II, ROM increased from preoperative mean flexion contracture of 13° and further flexion of 118° to postoperative mean flexion contracture 0.9° and further flexion 123°, KS knee score increased from 50 to 87, KS function score increased from 48 to 83, and tibiofemoral angle changed from preoperative varus 4.1° to postoperative valgus 5.3°. The complications were two periprosthetic patellar fracture and one failure of tibial component in group I, and one early failure of femoral component and one arthrofibrosis in group II. There was no statistical difference in radiological and clinical results between the two groups. Minimum 2-year follow-up result of PS Medial Pivot Knee TKA was comparable to that of Nexgen. ®. LPS TKA and longer term follow-up would be necessary

In order to eliminate the “conflict” that can occur with physiological roll back of the femur on the tibia, most modern knee arthroplasty prostheses are designed to have little conformity between the femoral and tibial surfaces. However, a consequence of this design is paradoxical anterior sliding of the femur on tibia, which can result in clinically significant gait abnormalities. Recent studies show that during movement of the knee, the medial side remains very nearly stable like a ball-in-socket joint, whilst the lateral side moves front to back, rotating around the centre of the medial side. A total knee joint prosthesis designed with these same kinematics may therefore be advantageous. The objective of this study was to investigate the hypothesis that the increased constraint of a medial pivot knee promotes earlier loosening of the prosthesis. METHODS: This was a retrospective radiographic cohort study. Using our unit’s knee arthroplasty database, all patients with a Freeman-Samuelson 1000 knee arthroplasty (medial pivot design) or a Freeman-Samuelson Modular knee arthroplasty with a minimum follow-up of 2 years were identified, and matched as closely as possible for age, length of follow-up and pre-operative diagnosis (Osteoarthritis, Rheumatoid arthritis or Post-traumatic arthritis). This was a single surgeon series using a standard surgical approach with a posterior cruciate sacrificing technique. Standardised anteroposterior and lateral radiographs taken postoperatively, at 6 months, 1 year and then at yearly intervals, were examined systematically and independently of the senior surgeon (GS). Component migration and radiolucent line scores were allocated as recommended by the Knee Society. RESULTS: Group 1 (n=55),–Freeman Samuelson Modular design, mean age–70.3 years, mean length of follow-up–4.5 years. Group 2 (n=48),–Freeman Samuelson 1000 design (Medial pivot), mean age–70.4 years, mean length of follow-up–4.3 years. There were no failures in group 1. There was one failure requiring revision of the femoral component in group 2. Radiolucent lines were more prominent and frequent in the tibia, particularly under the medial and lateral plateau’s (KSS zone 1 and 6). There was no significant difference in the overall radiolucent line scores between the two groups (p=0.39, Mann Whitney U test). Similarly we found no difference between radiolucent line progression in the specific tibial zones (1–6 KSS system). Radiolucent lines in the femur were infrequent and insignificant. CONCLUSION: We found no statistically significant difference between the two designs of knee prosthesis in terms of either total radiolucent line score or rate of radiolucent line progression. The increased constraint of the medial pivot knee prosthesis does not appear to result in an increased incidence of radiographic loosening

Introduction: Restoration of predictable and normal knee kinematics after a TKR can improve the patient’s function. Traditional designs exhibit grossly abnormal kinematics with the femur subluxing posteriorly in extension and a paradoxical forward slide in flexion. In addition, the kinematics are very variable. Newer designs were intended to overcome these problems, owing to their ability to provide ‘guided motion’ of the components. The medial pivot knee uses a specifically designed articulating surface constraining the femoral component to externally rotate about an axis through the medial compartment. This study assesses the functional in vivo kinematics of Advanced Medial Pivot (AMP) TKR and compares it to kinematics of the normal knee. Methods: Thirteen patients with pre-operative diagnosis of primary osteoarthritis, who had undergone a knee replacement with the AMP knee at least one-year prior were recruited in this study. All had an excellent clinical outcome (as assessed by AKSS) and underwent fluoro-scopic analysis whilst performing a step up activity. Knee kinematics were assessed by analysing the movement of the femur relative to the tibia using the Patella Tendon Angle (PTA) through the range of knee flexion. This data was compared to that of thirteen normal knees. Results: The PTA for the normal knee has a linear relationship with knee flexion. The PTA is 14 degrees in full extension and decreases to -10 degrees at 100 degrees knee flexion during a step-up exercise. Between extension and 60 degrees of knee flexion, no significant difference was found between the PTA for the normal knee and for the AMP. The PTA for AMP is significantly higher for values of knee flexion exceeding 60 degrees. The standard deviation for different values of knee flex-ion is similar to that seen in the normal knee. Conclusions: In extension, the PTA is near normal but in flexion PTA is higher than normal suggesting that the femur is too anterior. The variability of the kinematics for AMP TKR is similar to that of the normal knee and is better than that of most other knee designs that we have studied in the past, indicating that it is a stable TKR

The long-term survival of total knee arthroplasty (TKA) has been well established; however, functional outcome remains inconsistent. More normal postoperative TKA kinematics have been shown to produce better knee function. Improved kinematics can be obtained by using implants with optimised surface geometry. Hence a TKA with an appropriate surface geometryis likely to provide superior long-term functional outcome. The Advance-Medial Pivot TKA (Wright Medical) is a fixed bearing prosthesis with a conforming medial compartment and a non-conforming (flat on flat) lateral compartment. This surface geometry is designed with the intention of replicating the normal knee motion of sliding or pivoting medially and rolling back laterally. Aim: To investigate the sagittal plane kinematics of Advanced Medial Pivot Knee and compare with those of “flat on flat” fixed bearing TKA and normal knees. 18 patients who had undergone primary TKA for osteoarthritis were recruited at an average of 18 months post operation. These patients performed flexion and extension exercises against gravity and a step up exercise. Video fluoroscopy of these activities was used to obtain the patellar tendon angle (PTA). This is a previously validated method for assessing sagittal plane kinematics of a knee joint. The kinematic profile of the Advance Medial Pivot Knee was compared to the profile of 14 normal knees and 30 flat on flat, fixed bearing TKA’s. The sagittal plane kinematics of the Advance TKA differed from the normal knees. However, similarly to normal knees, a linear relationship was observed between PTA and knee flexion angle throughout knee flexion range. The kinematics of the Medial Pivot Knee were similar to normal when the knee was in a highly flexed position. Functional plane kinematics of the Advance Medial Pivot TKA appear to meet the design criteria in that a linear relationship between PTA and flexion angle is maintained. Further work is required to establish if these improved sagittal plane kinematics translate into improved functional outcome