Introduction

Robotics have been applied to total knee arthroplasty (TKA) to improve surgical precision in component placement and joint function restoration. The purpose of this study was to evaluate prosthetic component alignment in robotic arm-assisted (RA)-TKA performed with functional alignment and intraoperative fine-tuning, aiming for symmetric medial and lateral gaps in flexion/extension. It was hypothesized that functionally aligned RA-TKA the femoral and tibial cuts would be performed in line with the preoperative joint line orientation.

Introduction

Dislocation is a major cause of Total Hip Arthroplasty (THA) early failure and is highly influenced by surgical approach and component positioning. Robotic assisted arthroplasty has been developed to improve component positioning and therefore reduce post-operative complications.

The purpose of this study was to assess dislocation rate in robotic total hip arthroplasty performed with three different surgical approaches.

Background

Unicompartmental knee arthroplasty (UKA) patients with knee partial thickness cartilage loss have inferior functional performance compared to those with full thickness loss. Therefore, the aim of the present study was to investigate on the association between postoperative patients' joint awareness and satisfaction and preoperative radiographic osteoarthritis (OA) Ahlbäck grade in subjects undergoing robotic arm-assisted UKA.

Introduction

Robotics have been applied to total knee arthroplasty (TKA) to improve surgical precision in components’ placement, providing a physiologic ligament tensioning throughout knee range of motion. The purpose of the present study is to evaluate femoral and tibial components’ positioning in robotic-assisted TKA after fine-tuning according to soft tissue tensioning, aiming symmetric and balanced medial and lateral gaps in flexion/extension.

Introduction

Total shoulder replacement is a successful treatment for gleno-humeral osteoarthritis. However, components loosening and painful prostheses, related to components wrong positioning, are still a problem for those patients who underwent this kind of surgery. CT-based intraoperative navigation system is a suitable option to improve accuracy and precision of the implants as previously described in literature for others district.

Introduction

Robotic technology has been applied to unicompartmental knee arthroplasty (UKA) in order to improve surgical precision in prosthetic component placement, restore knee anatomic surfaces, and provide a more physiologic ligament tensioning throughout the knee range of motion. Recent literature has demonstrated high reliability of robotic-arm assisted UKA in component placement and executing a soft-tissue tensioning plan, with excellent short-term survivorship. Few studies have investigated survivorship and patients' satisfaction at longer follow-ups. Therefore, the purpose of the present study was to determine the survivorship, clinical results and patients' satisfaction of robotic-arm assisted UKAs at a mid-term follow-up, with a minimum of 5 years of follow-up.

Introduction

Unicompartmental knee arthroplasty (UKA) currently experiences increased popularity. It is usually assumed that UKA shows kinematic features closer to the natural knee than total knee arthroplasty (TKA). Especially in younger patients more natural knee function and faster recovery have helped to increase the popularity of UKA. Another leading reason for the popularity of UKA is the ability to preserve the remaining healthy tissues in the knee, which is not always possible in TKA. Many biomechanical questions remain, however, with respect to this type of replacement.

25% of knees with medial compartment osteoarthritis also have a deficient anterior cruciate ligament [1]. In current clinical practice, medial UKA would be contraindicated in these patients. Our hypothesis is that kinematics after UKA in combination with ACL reconstruction should allow to restore joint function close to the native knee joint. This is clinically relevant, because functional benefits for medial UKA should especially be attractive to the young and active patient.

Introduction

Robotic technology has been applied to unicompartmental knee arthroplasty (UKA) in order to improve surgical precision in prosthetic component placement, restore knee anatomic surfaces, and provide a more physiologic ligament tensioning throughout the knee range of motion. Recent literature has demonstrated the reliability of robotic assisted UKA over manual UKA in component placement and executing a soft-tissue tensioning plan. The purpose of this multicenter study was to determine the correlation between 3D component positioning and soft-tissue tensioning with short-term clinical results following robotic assisted medial UKA.

Background

Currently, stailess steel, titanium and carbon-fiber reinforced polyetheretherketone (CF-PEEK) plates are available for the treatment of distal radius fractures. Since the possibility to create a less rigid fixation may represent an advantage in case of ostheoporotic or poor quality bone, the aim of this study is to compare the biomechanical properties of these three materials in terms of bending stiffness with a single static load and after cyclical loading, simulating physiologic wrist motion.

Background

Implants based on the polyetheretherketon (PEEK) polymer have been developed in the last decade as an alternative to conventional metallic devices. PEEK devices may provide several advantages over the use of conventional orthopedic materials, including the lack of metal allergies, radiolucency, low artifacts on magnetic resonance imaging scans and the possibility of tailoring mechanical properties. The purpose of this study was to evaluate the clinical results at mean 24-month follow-up using a new plate made of carbon-fiber-reinforced polyetheretherketon (CFR-PEEK) for the treatment of distal radius fractures.

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.

During total knee replacement (TKR), surgical navigation systems (SNS) allow accurate prosthesis component implantation by tracking the tibio-femoral joint (TFJ) kinematics in the original articulation at the beginning of the operation, after relevant trial components implantation, and, ultimately, after final component implantation and cementation. It is known that TKR also alters normal patello-femoral joint (PFJ) kinematics resulting frequently in PFJ disorders and TKR failure. More importantly, patellar tracking in case of resurfacing is further affected by patellar bone preparation and relevant component positioning. The traditional technique used to perform patellar resurfacing, even in navigated TKR, is based only on visual inspection of the patellar articular aspect for clamping patellar cutting jig and on a simple calliper to check for patellar thickness before and after bone cut, and, thus, without any computer assistance. Even though the inclusion in in-vivo navigated TKR of a procedure for supporting also patellar resurfacing based on patient-specific bone morphology seems fundamental, this have been completely disregarded till now, whose efficacy being assessed only in-vitro. This procedure has been developed, together with relevant software and surgical instrumentation, as an extension of current SNS, i.e. TKR is navigated, at the same time measuring the effects of every surgical action on PFJ kinematics. The aim of this study was to report on the first in-vivo experiences during TKR with patellar resurfacing.

Four patients affected by primary gonarthrosis were implanted with a fixed bearing posterior-stabilised prosthesis (NRG, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. All TKR were performed by means of two SNS (Stryker®-Leibinger, Freiburg, Germany) with the standard femoral/tibial trackers, the pointer, and a specially-designed patellar tracker. The novel procedure for patellar tracking was approved by the local ethical committee; the patients gave informed consent prior the surgery. This procedure implies the use of a second system, i.e. the patellar SNS (PSNS), with dedicated software for supporting patellar resurfacing and relative data processing/storing, in addition to the traditional knee SNS (KSNS). TFJ anatomical survey and kinematics data are shared between the two. Before surgery, both systems were initialised and the patellar tracker was assembled with a sterile procedure by shaping a metal grid mounted with three markers to be tracked by PSNS only. The additional patellar-resection-plane and patellar-cut-verification probes were instrumented with a standard tracker and a relevant reference frame was defined on these by digitisation with PSNS. Afterwards, the procedures for standard navigation were performed to calculate preoperative joint deformities and TFJ kinematics. The anatomical survey was performed also with PSNS, with relevant patellar anatomical reference frame definition and PFJ kinematics assessment according to a recent proposal. Standard procedures for femoral and tibial component implantation, and TFJ kinematics assessment were then performed by using relevant trial components. Afterwards, the procedure for patellar resection begun. Once the surgeon had arranged and fixed the patellar cutting jig at the desired position, the patellar-resection-plane probe was inserted into the slot for the saw blade. With this in place, the PSNS captured tracker data to calculate the planned level of patellar bone cut and the patellar cut orientation. Then the cut was executed, and the accuracy of this actual bone cut was assessed by means of the patellar-cut-verification probe. The trial patellar component was positioned, and, with all three trial components in place, TFJ and PFJ kinematics were assessed. Possible adjustments in component positioning could still be performed, until both kinematics were satisfactory. Finally, final components were implanted and cemented, and final TFJ and PFJ kinematics were acquired. A sterile calliper and pre- and post-implantation lower limb X-rays were used to check for the patellar thickness and final lower limb alignment. The novel surgical technique was performed successfully in all four cases without complication, resulting in 30 min longer TKR. The final lower limb alignment was within 0.5°, the resurfaced patella was 0.4±1.3 mm thinner than in the native, the patellar cut was 1.5°±3.0° laterally tilted. PFJ kinematics was taken within the reference normality. The patella implantation parameters were confirmed also by X-ray inspection; discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements.

At the present experimental phase, a second separate PSNS was utilised not to affect the standard navigated TKR. The results reported support relevance, feasibility and efficacy of patellar tracking and PFJ kinematics assessment in in-vivo navigated TKR. The encouraging in-vivo results may lay ground for the design of a future clinical patella navigation system the surgeon could use to perform a more comprehensive assessment of the original whole knee anatomy and kinematics, i.e. including also PFJ. Patellar bone preparation would be supported for suitable patellar component positioning in case of resurfacing but, conceptually, also in not resurfacing if patellar anatomy and tracking assessment by SNS reveals no abnormality. After suitable adjustment and further tests, in the future if this procedure will be routinely applied during navigated TKR, abnormalities at both TFJ and PFJ can be corrected intra-operatively by more cautious bone cut preparation on the femur, tibia and also patella, in case of resurfacing, and by correct prosthetic component positioning.

A new design of total ankle replacement was developed. According to extensive prior research, the design features a spherical convex tibial component, a talar component with radius of curvature in the sagittal plane longer than that of the natural talus, and a meniscal component fully conforming to these two. The shapes of the tibial and talar components are compatible with a physiologic ankle mobility and with the natural role of the ligaments.

Within an eight-centre clinical trial, 114 patients were implanted in the period July 2003 – September 2006, with mean age 62.2 years (range 29 – 82). The AOFAS clinical score systems and standard radiographic assessment were used to assess patient outcome, here reported only for those 75 patients with follow-up longer than 6 months.

Intra-operatively, the components maintained complete congruence at the two articulating surfaces of the meniscal bearing over the entire motion arc, associated to a considerable anterior motion in dorsiflexion and posterior motion in plantarflexion of the meniscal-bearing, as predicted by the previous mathematical models. Mean 10.0 and 23.5 degrees respectively of dorsi- and plantar-flexion were measured immediately after implantation, for a mean additional range of motion of 19.2, which was maintained at follow-ups. Radiographs showed good alignment and no signs of evolutive radiolucency or loosening. The mean AOFAS score went from 40.8 pre-op to 66.2, 74.6 and 77.2 respectively at 3, 6 and 12 month follow-ups. One revision only was performed successfully three days after implantation because of a technical error.

In the score system utilized, Function and RoM sections scored better than any average previous total ankle result, Pain scored similarly. The satisfactory though preliminary observations from this novel design encourage continuation of the implantation, which is now extended over a few European countries. Instrumented gait and three-dimensional fluoroscopic analyses are in progress to quantify functional progresses.

Navigation-assisted surgery in total knee arthroplasty (TKA) is aimed at improving the accuracy with which prosthesis components are implanted in the bones, according to anatomical plane orientations. Traditional surgical techniques based on the identification of transepicondylar and intramedullary axes are replaced with those based on segmental anatomical frame definitions following anatomical landmark identification. These frames are offered on the screen to the surgeon to target in real time the alignment goal by adjusting position and orientation of the bone saw guides. However, immediately after sawing, final bone, and in case cement, preparation and component implantation is necessarily a series of actions performed manually by the surgeon. In the current study, we wanted to compare intra-operatively the final component alignments with the corresponding at the original resection planes.

In this series, 50 Scorpio PS TKAs were analyzed. The navigation system used was the Stryker Knee Navigation System (Stryker-Navigation, Kalamazoo, USA). An ‘anatomical survey’ defined anatomical frames for the femur and tibia, based on relevant anatomical landmark identification, and provided target orientations for all the relevant bone cuts. These references were targeted in all three anatomical planes, and bone cuts were made accordingly. Corresponding alignments of the bone resection planes in the frontal, sagittal and transverse planes for the femur and in the frontal and sagittal planes for the tibia were recorded, with a 0.5° resolution. Then, component implantation was performed and alignments were measured again by means of an instrumented probe. Because of the shape of the prosthesis components, only the alignments in the frontal plane for the femur and in the frontal and sagittal planes for the tibia were recorded.

The difference between the alignment of the bone cuts and the alignment of the prosthesis components, in the frontal plane of the femur, and in the frontal and sagittal planes of the tibia was larger than 2° respectively in 8%, 6%, 10% of the patients.

The present study offers a figure for the different alignment between resection planes and final implanted components, necessarily the effect of the manual procedures implied in TKA for the final implantation of the components. Considering that 1° is the claimed achievable accuracy of the navigation systems, and that the correct alignment goal was achieved at the resection planes, these figures reveal that in up to 10% of the patients the benefit obtained by navigation can be lost by the manual procedures implied in component implantation. These differences in alignment put also concerns in the postoperative statistical comparison between conventional and navigated TKAs.

Functional outcome in Total Knee Arthroplasty (TKA), as measured by means of gait analysis for kinematics, kinetics, and muscular activity around the knee shows abnormalities even in patients with excellent clinical outcome. Knee flexion during loading response phase is reduced, accompanied by co-contraction of knee extensors and flexors. Such subtle failure in knee performance during loading absorption was claimed to depend on several factors: quadriceps weakness, prosthetic design, pre-surgical pattern, proprioception disruption. It was supposed to damage the implant in time. The lack of the anterior cruciate legament seems to play a major role in the loss of control of the roll back pattern of the condyles on the tibial plateau in TKA patients. Previous works on unicondylar knee artrhoplasty (UKA) demonstrated better gait performance when anterior cruciate ligament was preserved allowing the patients to maintain normal quadriceps mechanics. The aim of the present work is to evaluate UKA patients knee function during gait compared to TKA with the hypothesis that UKA ensures more physiological knee loading response pattern of movement and a more phasic muscular activation, thus reducing the risk of failure. Twenty patients with Oxford/Exactech UKA (mean age 70 (SD 7.9), mean follow-up 2 years) were evaluated by means of a Vicon 612-8 cameras system, two Kistler forceplates and Telemg respectively for knee 3D kinematics, kinetics and muscular activity. Data of UKA were compared to those of a control population of ten healthy subjects and ten patients with TKA matched for age and follow up. Mean UKA-IKS score at the time of gait analysis was 90. Time-distance parameters evidenced a slight slow gait with reduced stride length and cadence and a symmetric longer stance phase with respect to TKA and controls. Knee kinematics on the sagittal plane showed knee flex-ion during loading response very close to controls and a reduced but phasic pattern of joint moments on the sagittal plane. Adduction moment at the knee was normal. EMG showed controversy results as some patients had a regular pattern of activation of rectus femoris and hamstrings without co-contraction whereas other patients had co-contraction. These preliminary results indicate that UKA allows in most patients a quite normal knee kinematics and kinetics, although some abnormalities persist in quadriceps activation. Further research is required to understand these findings assessing other factors which could influence quadriceps activity such as age, proprioception, and muscular strength.

Introduction: Computer navigation in total knee arthroplasty (TKA) may assist the surgeon with precise information about ligament tension and varus/valgus alignment throughout the complete range of motion, but there is only little information about how much ligament laxity is needed and how much laxity is too much. In the current study we measured the mechanical axis and opening of the joint at different time points, in different degrees of knee flexion and with varus and valgus stress during the procedure of computer navigated TKA.

Methods: Forty-nine consecutive patients underwent a MIS computer navigated TKA. With the Stryker Knee Navigation System varus/valgus alignment and distraction/compression was measured in 0°, 45° and 90° of knee flexion immediate after digitalization of the knee and after fascial closure. Values were noted in a neutral position and with maximal varus and maximal valgus stress applied. Patients with posterior stabilized implants were compared to those with cruciate retaining implants. Patients with preoperative varus malalignment or valgus malalignment were compared to patients with straight preoperative mechanical axes.

Results: At the beginning of the operative procedure the mean mechanical alignment was 1.9° varus at 0° knee flexion, 1.5° varus at 45° knee flexion and 1.5° varus at 90° knee flexion. Patients showed a mean mediolateral joint opening of 6.1° at 0° knee flexion, 5.9° at 45° knee flexion and 4.5° at 90° knee flexion. After implantation of the knee prosthesis and fascial closure mechanical alignment was 0.3° varus at 0° knee flexion, 0° varus at 45° knee flexion and 0.2° varus at 90° knee flexion. Mean joint laxity was 3.4° at 0° knee flexion, 3.1° at 45° knee flexion and 2.3° at 90° knee flexion. There was more lateral than medial joint opening postoperatively in 45° and 90° knee flexion regardless of the prosthesis type implanted. Preoperative varus and valgus malalignment could be reduced to values identical with those patients with straight preoperative mechanical axes.

Discussion: Mean varus/valgus laxity after implantation of a MIS computer navigated TKA was lower than prior to prosthesis implantation. Varus/valgus laxity of an approximate total range of 1.5°–2° can be achieved at all measured degrees of knee flexion and seems to be the ideal laxity for TKA. Computer navigation in TKA can consistently reduce preoperative varus/valgus malalignment to a level comparable to patients with preoperatively normal mechanical axes. More lateral joint opening is found before as well as after implantation of the prosthesis in 45° and 90° of knee flexion. The type of prosthesis implanted seems not to effect postoperative joint laxity.

Introduction: One of the four pillars of successful total knee arthroplasty (TKA) is restoration of the joint line. In conventional TKA the surgeon does not have a tool to control the accuracy of joint line restoration intraoperatively. The present study investigates if the preoperative joint line can be restored using an optical navigation system for TKA.

Materials and methods: Patients from two Orthopedic Centers (Istituto Orthopedico Rizzoli Bologna, 51 patients; Orthopädie Samedan, 42 patients) received computer assisted TKA (Stryker Scorpio) using the Stryker Knee navigation system. Using the software delivered with the navigation system depth of femoral and tibial medial and lateral osteotomies were recorded. After definite prosthesis implantation medial and lateral femoral condyle height as well as tibial length including polyethylene inlay were also recorded. Varus/valgus alignment was additionally recorded before and after prosthesis implantation.

Results: After femoral osteotomie varus/valgus alignment was 0 degrees (Stdv. 0.6 degrees). Lateral and medial osteotomies were performed with a depth of 8.2 and 8.8 mm respectively. Tibial osteotomie was performed with 0 degrees of varus/valgus (stdv. 0.7 degrees). Lateral and medial tibial osteotomies were performed with a depth of 7.5 and 4.8 mm respectively. After definite prosthesis implantation femoral and tibial varus/valgus alignment was 0.2 degrees of varus (stdv. 0.8 degrees) and 0.1 degrees of varus (stdv. 0.8 degrees) respectively. The femur was lengthened by 0.2 mm (stdy. 3 mm) medially and 1.1 mm (stdy. 3.1 mm) laterally. The tibia was shortened after component implantation by 1.5 mm (stdy. 3.4 mm) medially and 1.1 mm (stdv 3.1 mm) laterally.

Discussion: With the use of the Stryker Knee Navigation System, we can reconstruct the preoperative joint line with reproducible accuracy after a TKA. When prosthesis component and polyethylene inlay thickness are known, osteotomies may be performed and corrected intraoperatively to restore the joint line.

Patellar maltracking after total knee arthroplasy (TKA) introduces complications such as anterior knee pain and patellar subluxation, generally due to prosthetic component malallignment in both tibiofemoral (TF) and patellofemoral joints. It is still debated if it is necessary to resurface the patella, which would better adapt the patellar articular surface to the prosthetic femoral troclea with a prosthesis, but also result in possible bone fractures. In this study, an in-vitro analysis is presented in order to identify differences between intact and TKA patellar tracking with and without patellar resurfacing and to show how much the latter is similar to intact knee patellar tracking.

Three fresh-frozen amputated legs with knees free from anatomical defects and with intact joint capsule, collaterals and quadriceps tendon were analyzed using the Stryker knee navigation system (Kalamazoo, MI-USA). Landmark digitations were used to define anatomical frames for femur, tibia and patella. Manually driven TF flexions, from 0 to 140, were performed under conditions of no load and of 10 kg on the quadriceps, with intact knee and TKA with patella resurfaced and not. TF flex/extension, intra/extra rotation, ad/abduction were calculated according to a standard convention. Patellar flex/extension, medial/lateral tilt, rotation and shift were calculated according to a recently proposed articular convention.

Since more repeatable, results relative to trials under 10 kg are reported. Intact knee: 4 abduction; considerable intra rotation (from 16 to 4), followed by continuous extra rotation starting at 30 TF flexion; linear increase in patellar flexion (from 20 to 110); initial medial patellar rotation (from 12 to 8), followed by medial rotation starting at 60 TF flexion; initial lateral patellar tilt (from 4 lateral to 4 medial), followed by medial tilt starting at 70 TF flexion; initial 6 mm lateral patellar shifts from 0 to 80 TF flexion, followed by 4 mm medial shift. TKA knee: small differences in ad/abduction between intact and TKA knees, both with and without resurfaced patella; slight initial extra rotation, followed by continuous intra rotation starting at 20 TF flexion; linear increase in the flexion of the patella, both resurfaced and not, close to the that of the intact knee; patellar rotation more lateral than in the intact knee; patellar tilt without resurfaced patella closer to the intact knee one; 6 mm lateral patellar shift, likely accounted for the surgical technique.

Slightly more than TKA with resurfaced patella, TKA with non resurfaced patella flexes nearly like the intact knee. The closeness in values of patellar flexion and tilt represents a proof of the closeness in behavior of not resurfaced patella in TKA to the patella in the intact knee.

Tibial component loosening continues to be the most common mode of TKA failure. A debate persists on the dependence of mobilisation of this component on the equilibrium between mechanical load transfer and counterbalancing bone resistance. The aim of the present work is to study the in-vivo kinematics of TKA and to relate it with the degree of posterior slope with which the tibial component was implanted for two prosthesis designs with congruent polyethylene insert.

Twenty-three patients with osteoarthritis of the knee had TKA using a cemented prosthesis (OPTETRAK, Exactech). A cruciate retaining (CR, 10 knees) or a posterior stabilized (PS, 13 knees) implant was randomly assigned at operation. Standard pre- and post-operative antero-posterior and lateral roentgenograms of the knee were taken. Fluoroscopic analysis was performed after at least 18 and 7 months after surgery for the CR and the PS group, respectively. Patients performed stair ascending, chair rising-sitting and step up-down motor tasks. Articular contacts were assumed as the two points on the medial and lateral femoral prosthetic condyles closest to the tibial component base-plate. The spine-cam distance was calculated as the minimum distance between corresponding surfaces.

Only small differences in the position of the contacts over knee flexion angles were found among the motor tasks and between the two TKA designs. An overall posterior location of the tibio-femoral contact points was found at the medial and lateral compartments over all motor tasks, a little more pronounced for the PS patients. Statistically significant correlation over the three motor tasks analysed was found between posterior position of the tibio-femoral medial contact in maximum knee flexion and the post-operative tibial posterior slope. This is true for the PS and for the aggregated groups. Although no statistically significant, a general trend is observed of higher degree of flexion at which the cam contacts the spine as the post-operative posterior slopes increases: a 35 higher knee flexion angle for a tibial component implanted with a 5 of posterior slope. Generally, even when the correlations were statistically significant the correlation coefficients were always lower than 0.4.

The present work reports combined measurements of post-operative posterior slope and full in-vivo relative motion of the components in both CR and PS TKAs. General trends were found between posterior slope of the tibial component and positions of the tibio-femoral contacts, but a statistically significant correlation was found only for the tibio-femoral medial contact in maximum knee flexion in the PS and in the aggregated. General trends were found between posterior slope of the tibial component and degree of flexion at which the cam starts to be in contact with the spine. The nearly standard antero-posterior translation of the tibio-femoral contacts can be bigger in flatter polyethylene inserts.

Aims: Prior research has demonstrated that currently available total ankle implants fail to restore physiologic joint mobility. Most of the modern mobile-bearing designs that feature a flat tibial component and a talar component with anatomic curvature in the sagittal plane function non physiologically with the natural ligament apparatus. The aims of this investigation were a) to elucidate the natural relationship between ligaments and articular surfaces at the intact human ankle joint and b) to develop a new design of total ankle replacement able to replicate this relationship between the retained ligaments and the implanted prosthetic components.

Methods: Motion during passive flexion was analyzed in ten skeleto-ligamentous lower leg preparations including tibia, fibula, talus, calcaneus and intact ligaments. Geometry of ligament fiber arrangement and articular surface shapes was obtained with a 3D digitizer (FARO Technologies, Inc.). A sagittal four-bar linkage model was formulated as formed by the tibia/fibula and talus/ calcaneus rigid segments and by the calcaneofibular and tibiocalcaneal ligaments. To test the ability of possible new prostheses to reproduce the compatible mutual function between the articulating surfaces and the ligaments retained, non-conforming two-component and fully-conforming three-component designs were analyzed. A new total ankle replacement has been designed, prototypes manufactured and implanted in seven skeleto-ligamentous lower leg preparations, and motion was observed. A corresponding new prosthesis has been produced (Finsbury, UK), and implanted in four patients.

Results: The articular surfaces and the ligaments alone prescribed joint motion into a preferred single path of multiaxial rotation (one degree of unresisted freedom). Fibers within the calcaneofibular and tibiocalcaneal ligaments remained most isometric throughout the passive range. The four-bar linkage model well predicted the sagittal plane kinematics observed in corresponding experiments. A ligament-compatible, convex-tibia, fully-congruent, three-component prosthesis design showed the best features: complete congruence over the entire range of flexion together with an acceptable degree of entrapment of the meniscal bearing. Restoration of natural joint kinematics and ligament recruitment was observed in all replaced ankles.

Conclusions: The overall investigation is demonstrating that a profound knowledge of the changing geometry of the joint passive structures throughout the range of passive flexion (mobility) is mandatory for a successful design of joint replacements.