Prothèses totales de genoux. Analyse clinique et numérique des micromouvements de l'implant tibial [Total knee prosthesis. Clinical and numerical study of micromovements of the tibial implant].

INTRODUCTION: The importance of the micromovements in the mechanism of aseptic loosening is clinically difficult to evaluate. To complete the analysis of a series of total knee arthroplasties (TKA), we used a tridimensional numerical model to study the micromovements of the tibial implant. MATERIAL AND METHODS: Fifty one patients (with 57 cemented Porous Coated Anatomic TKAs) were reviewed (mean follow-up 4.5 year). Radiolucency at the tibial bone-cement interface was sought on the AP radiographs and divided in 7 areas. The distribution of the radiolucency was then correlated with the axis of the lower limb as measured on the orthoradiograms. The tridimensional numerical model is based on the finite element method. It allowed the measurement of the cemented prosthetic tibial implant's displacements and the micromovements generated at bone-ciment interface. A total load (2000 Newton) was applied at first vertically and asymetrically on the tibial plateau, thereby simulating an axial deviation of the lower limbs. The vector's posterior inclination then permitted the addition of a tangential component to the axial load. This type of effort is generated by complex biomechanical phenomena such as knee flexion. RESULTS: 81 per cent of the 57 knees had a radiolucent line of at least 1 mm, at one or more of the tibial cement-epiphysis jonctional areas. The distribution of these lucent lines showed that they came out more frequently at the periphery of the implant. The lucent lines appeared most often under the unloaded margin of the tibial plateau, when axial deviation of lower limbs was present. Numerical simulations showed that asymetrical loading on the tibial plateau induced a subsidence of the loaded margin (0-100 microns) and lifting off at the opposite border (0-70 microns). The postero-anterior tangential component induced an anterior displacement of the tibial implant (160-220 microns), and horizontal micromovements with non homogenous distribution at the bone-ciment interface (28-54 microns). DISCUSSION: Comparison of clinical and numerical results showed a relation between the development of radiolucent lines and the unloading of the tibial implant's margin. The deleterious effect of lower limbs' axial deviation is thereby proven. The irregular distribution of lucent lines under the tibial plateau was similar of the micromovements' repartition at the bone-cement interface when tangential forces were present. A causative relation between the two phenomenaes could not however be established. Numerical simulation is a truly useful method of study; it permits to calculate micromovements which are relative, non homogenous and of very low amplitude. However, comparative clinical studies remain as essential to ensure the credibility of results.

Tibial component positioning in total knee arthroplasty: bone coverage and extensor apparatus alignment.

Correct positioning of the tibial component in total knee arthroplasty (TKA) must take into account both an optimal bone coverage (defined by a maximal cortical bearing with posteromedial and anterolateral support) and satisfactory patellofemoral tracking. Consequently, a compromise position must be found by the surgeon during the operation to simultaneously meet these two requirements. Moreover, tibial tray positioning depends upon the tibial torsion, which has been shown to act mainly in the proximal quarter of the tibia. Therefore, the correct application of the tibial tray is also theoretically related to the level of bone resection. In this study, we first quantified the torsional profile given by an optimal bone coverage for a symmetrical tibial tray design and for an asymmetrical one. Then, for the two types of tibial trays, we measured the angle difference between optimal bone coverage and an alignment on the middle of the tibial tubercule. Results showed that the values of the torsional profile given by the symmetrical tray were more scattered than those from the asymmetrical one. However, determination of the mean differential angle between the position providing optimal bone coverage and the one providing the best patellofemoral tracking indicated that the symmetrical prosthetic tray offered the best compromise between these two requirements. Although the tibiofemoral joint is known to be asymmetric in both shape and dimension, the asymmetrical tray chosen in this study was found to fulfill this compromise with more difficulty.

An intramedullary alignment guide lodging within the femoral canal during total knee arthroplasty: a case report.

The usual complications of total knee arthroplasty include thrombo-embolism, infection, and loosening. We report an unusual and potentially serious complication of an intramedullary guide lodging within the femoral canal during the procedure. Considering the risk of fracture and additional exposure, the guide was not removed and was cut in situ. The rest of the operation was completed successfully and the patient made an uneventfully recovery.

Revue des arthroplasties totales de la hanche et du genou infectées--à propos de 28 cas [Review of infected total arthroplasties of the hip and knee--apropos of 28 cases]

This study is a long-term analysis of a group of patients with infected arthroplasties of the hip or the knee. We identified 28 patients with an infected arthroplasty (22 hips, 6 knees) documented by bacterial culture or on direct examination. At the time of diagnosis and on follow-up (a mean of 46 months after treatment) we evaluated the clinical picture, the radiological appearances of the articulation and the biological parameters. 19/28 patients showed a typical clinical picture, whereas in 9 others the picture was more doubtful. The treatments were 14 two-stage replacements of the arthroplasties, 7 simple resections, 5 conservative treatments and 2 one-stage replacements. On follow-up, 25 patients were considered as cured of their infection and 3 as failures. From a functional viewpoint, 9 patients showed no limitation, whereas 19 were limited in the daily activity. Half of the patients had no pain. Radiology showed that 20/26 evaluated patients had no signs of recurrence. Paraclinical examinations are important in the diagnosis of persistent low grade infections, particularly the demonstration of bacteria by pre-surgical sampling (fine needle aspiration, culture from draining sinuses). In spite of the cure of infection, the functional and painful sequellae are often considerable. As a result of our experience, we recommend a two-stage surgical procedure. Only when the general condition of the patient is poor, or when the infection is not under control, would we envisage an alternative procedure (arthrodesis, girdelstone, conservative).

Effect of tibial tray inclination on the femoro-tibial contact pattern of a mobile total knee arthroplasty

Introduction: The posterior inclination of the tibial component is an important factor that can affect the success of total knee arthroplasty. It can reduce the posterior impingement and thus increase the range of flexion, but it may also induce instability in flexion, anterior impingement between the polyethylene of postero-stabilizing knee prosthesis, and anterior conflict with the cortical bone and the stem. Although the problem is identified, there is still a debate on the ideal inclination angle and the surgical technique to avoid an excessive posterior inclination. The aim of this study was to predict the effect of a posterior inclination of the tibial component on the contact pattern on the tibial insert, using a numerical musculoskeletal model of the knee joint. Methods: A 3D finite element model of the knee joint was developed to simulate an active and loaded squat movement after total knee arthroplasty. Flexion was actively controlled by the quadriceps muscle and muscle activations were estimated from EMG data and were synchronized by a feedback algorithm. Two inclinations of the tibial tray were considered: a posterior inclination of 0° or 10°. During the entire range of flexion, the following quantities were calculated: the tibiofemoral and patello-femoral contact force, and the contact pattern on polyethylene insert. The antero-posterior displacement of the contact pattern was also measured. Abaqus 6.7 was used for all analyses. Results: The tibio-femoral and patello-femoral contact forces increased during flexion and reached respectively 4 and 7 BW (bodyweight) at 90° of flexion. They were slightly affected by the inclination of the tibial tray. Without posterior inclination, the contact pattern on the tibial insert remained centered. The contact pressure was lower than 5 MPa below 60° of flexion, but exceeded 20 MPa at 90° of flexion. The posterior inclination displaced the contact point posteriorly by 2 to 4 mm. Conclusion: The inclination of the tibial tray displaced the contactpattern towards the posterior border of the tibial insert. However, even for 10° of inclination, the contact center remained far from the posterior border (12 mm). There was no instability predicted for this movement.

Objective results at 1 year of a new ultracongruent postero-stabilized total knee arthroplasty

Introduction: A new ultra congruent, postero-stabilized total knee arthroplasty (TKA) with a mobile bearing, the FIRST knee prosthesis (Free Insert in Rotation Stabilized in Translation, Symbios SA), was designed and expected to significantly reduce polyethylene wear, to improve the range of motion and the overall stability of the knee while ensuring a physiological ligament balance. Gait analysis has proven to give really objective outcome parameters after lower limb surgery. The goal of our study was to compare the subjective and really objective results of this new TKA with two other widespread models of TKA. Methods: A clinical prospective monocentric cohort study of 100 consecutive patients (47-88 yrs) undergoing a FIRST TKA for primary osteoarthritis is currently being done. Pre- and post-operative follow-ups (6 weeks, 4 months and 1 year) were done with well-recognized subjective evaluations (EQ-5D and WOMAC scores) and semi-objective questionnaires (KSS score and radiography evaluation) as well as with a really objective evaluation using gait parameters from 6 walking trials, performed at different speeds (slow, normal and fast) with an ambulatory gait analysis system (Physilog®, BioAGM CH). The outcomes of the first 32 new TKA after one year of follow-up were compared to the results after 1 year of a randomized controlled clinical trial comparing 29 NexGen® postero-stabilized TKA (Zimmer Inc) with a fixed bearing and 26 NexGen® TKA with a mobile bearing using the same methods. Results: Subjective and semi-objective results were similar for the three types of TKA. As for the really objective parameters, the gait cycle time of the FIRST TKA was statistically significantly shorter at normal speed of walk, as well as double-support periods, as compared to both standard models. The extension (in terms of range of motion when walking) of the operated knee was significantly improved for all three types of walk in favour of the FIRST TKAs compared to both NexGen TKAs. The normal walking speed was significantly higher with faster swing speed and stride lengths for the new TKA. Significantly better coordination scores were observed at normal walking speed for the FIRST TKA as compared to the fixed-bearing TKAs. Conclusion: The FIRST TKAs showed statistically significantly better objective outcomes in terms of gait after one year of follow-up with similar subjective and semi-objective results in comparison with widespread TKA designs. These encouraging short-terms results will have to be confirmed at a 5 years follow-up of the FIRST TKAs.

Prothese totale du genou aujourd'hui: que dire a nos patients? [Total knee arthroplasty today: what should we tell our patients?]

Total knee arthroplasty (TKA) remains the preferred treatment for patients with invalidating osteoarthritis. It allows these patients to find once again a satisfactory quality of life. These results are reflected by the increasing number of interventions performed each year and in always younger patients. The objective of this review of the scientific literature was to determine the long-term quantitatively and qualitatively results of TKA and determine the parameters which could influence the long-term outcome. There does not seem to be any clear arguments in favor of one type of implant or surgical technique. One also notices that TKA in females and older patients seem to have longer lifespan, estimated to approximately 15 years. The most frequent complication remains aseptic loosening followed by infections.

A randomised controlled clinical trial and gait analysis of fixed- and mobile-bearing total knee replacements with a five-year follow-up.

This study compared the outcome of total knee replacement (TKR) in adult patients with fixed- and mobile-bearing prostheses during the first post-operative year and at five years' follow-up, using gait parameters as a new objective measure. This double-blind randomised controlled clinical trial included 55 patients with mobile-bearing (n = 26) and fixed-bearing (n = 29) prostheses of the same design, evaluated pre-operatively and post-operatively at six weeks, three months, six months, one year and five years. Each participant undertook two walking trials of 30 m and completed the EuroQol questionnaire, Western Ontario and McMaster Universities osteoarthritis index, Knee Society score, and visual analogue scales for pain and stiffness. Gait analysis was performed using five miniature angular rate sensors mounted on the trunk (sacrum), each thigh and calf. The study population was divided into two groups according to age (≤ 70 years versus > 70 years). Improvements in most gait parameters at five years' follow-up were greater for fixed-bearing TKRs in older patients (> 70 years), and greater for mobile-bearing TKRs in younger patients (≤ 70 years). These findings should be confirmed by an extended age controlled study, as the ideal choice of prosthesis might depend on the age of the patient at the time of surgery.

L'arthroplastie totale de genou: évolution et résultats actuels

Avec 95% de bons résultats à 10 ans, on peut considérer aujourd'hui que l'arthroplastie totale du genou est un traitement fiable des gonarthroses chez des patients âgés à demande fonctionnelle raisonnable. Les quatre complications potentielles principales après la mise en place d'une prothèse totale du genou sont le descellement aseptique, l'infection, le manque de flexion et les douleurs persistantes. En cas de problème avec une prothèse totale du genou, il faut toujours exclure la présence d'une infection avant d'envisager une autre raison. Les innovations actuelles en arthroplastie du genou doivent viser à améliorer les résultats chez les patients jeunes et actifs i.e. tant au niveau de la conception des nouveaux implants, voire des matériaux plus résistants, que des techniques chirurgicales elles-mêmes. Total knee arthroplasty: current advances and results With a 95% success rate at 10 years, total knee arthroplasty can be regarded today as a reliable way of treating knee osteoarthritis in elderly patients with reasonable functional demands. The four main potential complications after placing of a total knee prosthesis are aseptic loosening, infection, lack of flexion and persistent pain. If a problem arises with a total knee prosthesis, infection must always be ruled out before considering other causes. Current innovations in knee arthroplasty should be aimed at improving results in young and active patients, i.e. in regard to both the design of new implants, or tougher materials, and to the surgical techniques themselves.

Soft tissue artifact distribution on lower limbs during treadmill gait: Influence of skin markers' location on cluster design.

Segment poses and joint kinematics estimated from skin markers are highly affected by soft tissue artifact (STA) and its rigid motion component (STARM). While four marker-clusters could decrease the STA non-rigid motion during gait activity, other data, such as marker location or STARM patterns, would be crucial to compensate for STA in clinical gait analysis. The present study proposed 1) to devise a comprehensive average map illustrating the spatial distribution of STA for the lower limb during treadmill gait and 2) to analyze STARM from four marker-clusters assigned to areas extracted from spatial distribution. All experiments were realized using a stereophotogrammetric system to track the skin markers and a bi-plane fluoroscopic system to track the knee prosthesis. Computation of the spatial distribution of STA was realized on 19 subjects using 80 markers apposed on the lower limb. Three different areas were extracted from the distribution map of the thigh. The marker displacement reached a maximum of 24.9mm and 15.3mm in the proximal areas of thigh and shank, respectively. STARM was larger on thigh than the shank with RMS error in cluster orientations between 1.2° and 8.1°. The translation RMS errors were also large (3.0mm to 16.2mm). No marker-cluster correctly compensated for STARM. However, the coefficient of multiple correlations exhibited excellent scores between skin and bone kinematics, as well as for STARM between subjects. These correlations highlight dependencies between STARM and the kinematic components. This study provides new insights for modeling STARM for gait activity.

Giant extraskeletal myxoid chondrosarcoma of the thigh treated by wide extraarticular resection and reconstruction with a tumor prosthesis

Introduction: Extraskeletal myxoid chondrosarcoma (EMC) is a rare soft tissue tumour with a high risk for local recurrence and metastases. While this entity is resistant to radio- or chemo-therapy, wide resection remains the treatment of choice. Case report: A 60 year old man presented to our service with a large mass in his right thigh, slowly evolving over the past 7 years. His main complaint was the volume of his thigh. Imaging showed a 23x13x14 cm tumour in the quadriceps, eroding the cortical bone and with potential contamination of the knee joint. The risk of a pathological fracture was estimated considerable. A CT-guided core-needle biopsy revealed a FNCLCC grade 2 EMC. A thoraco-abdominal CT scan showed multiple pulmonary metastases. Due to the palliative situation with a very slow disease progression, a wide extraarticular resection of the distal femur and reconstruction with a megaprosthesis were performed. Extensive skin necrosis necessitated three revision procedures for débridement and confection of a pediculated lateral gastrocnemius muscle flap. No complementary treatment was possible for the pulmonary metastases. At 18 months follow-up, he walked without crutches, was able to do his activities of daily living. He was painfree and highly satisfied with the result. During the follow-up, slow progression of the pulmonary metastases was noted, which remained asymptomatic. Conclusion: Extraskeletal myxoid chondrosarcoma is a rare soft tissue tumour, and wide excision remains the treatment of choice. Whenever possible, limb salvage should be proposed to preserve function and quality of life.

Characteristics and outcome of knee prosthetic joint infections (PJI): A 10-year cohort study (2000-2009)

Background: Prosthetic joint infections (PJI) lead to significant long-term morbidity with high cost of healthcare. We evaluated characteristics of infections and the infection and functional outcome of knee PJI over a 10-year period. Methods: All patients hospitalized at our institution from 1/2000 through 12/2009 with knee PJI (defined as growth of the same microorganism in ≥2 tissue or synovial fluid cultures, visible purulence, sinus tract or acute inflammation on tissue histopathology) were included. Patients, their relatives and/or treating physicians were contacted to determine the outcome. Results: During the study period, 61 patients with knee PJI were identified. The median age at the time of diagnosis of infection was 73 y (range, 53-94 y); 52% were men. Median hospital stay was 37 d (range, 1-145 d). Most reasons for primary arthroplasty was osteoarthritis (n = 48), trauma (n = 9) and rheumatoid arthritis (n = 4). 23 primary surgeries (40%) were performed at CHUV, 34 (60%) elsewhere. After surgery, 8 PJI were early (<3 months), 16 delayed (3-24 months) and 33 late (>24 months). PJI were treated with (i) open or arthroscopic debridement with prosthesis retention in 26 (46%), (ii) one-stage exchange in 1, (iii) two-stage exchange in 22 (39%) and (iv) prosthesis removal in 8 (14%). Isolated pathogens were S. aureus (13), coagulase-negative staphylococci (10), streptococci (5), enterococci (3), gram-negative rods (3) and anaerobes (3). Patients were followed for a median of 3.1 years, 2 patients died (unrelated to PJI). The outcome of infection was favorable in 50 patients (88%), whereas the functional outcome was favorable in 33 patients (58%). Conclusions: With the current treatment concept, the high cure rate of infection (88%) is associated with a less favorable functional outcome o 58%. Earlier surgical intervention and more rapid and improved diagnosis of infection may improve the functional outcome of PJI.