Jean-Yves Jenny

Learning curve in navigated total knee replacement. A multi-centre study comparing experienced and beginner centres

This study analyzes the OrthoPilot navigation systems (Aesculap, Tuttlingen, FRG) learning curve in beginner vs. experienced centres. We conducted a prospective, controlled, multi-centre study in 13 European orthopedic centres. Overall, 368 total knee replacements (TKR) were included in this study, with 150 TKR performed in experienced centres (control group) and 218 TKR in beginner centres (study group). The study parameters were implantation accuracy, clinical outcome, operation time and complications. No difference was found between both groups, except for operating time which was significantly longer in the study group. However, this increase in operating time disappeared after 30 implantations in all beginner centres. So, we conclude that the systems learning curve levels off at this point. Given the high accuracy of implantation when using the OrthoPilot navigation system, we believe this learning curve to be acceptably low.

Reproducibility of intra-operative measurement of the mechanical axes of the lower limb during total knee replacement with a non-image-based navigation system

Objective: The restoration of a normal mechanical axis of the lower limb following total knee prosthesis (TKP) depends on the accuracy of the intra-operative measurement of the femoro-tibial angle. We have studied the reproducibility of intra-operative measurement of the coronal mechanical femoro-tibial axis with the OrthoPilot® (Aesculap, Tuttlingen, Germany) non-image-based navigation system. Material and Methods: A consecutive series of 20 TKP (Aesculap SEARCH Evolution® prosthesis) implanted by the same surgical team of two senior orthopedic surgeons was analyzed. They used a non-image-based navigation system that allows the mechanical axes of the femur and tibia to be defined with a kinematic analysis. The operating surgeon and assistant surgeon performed the kinematic analysis twice and once, respectively, and measured coronal mechanical femoro-tibial angles in maximal extension and at 90° flexion without varus or valgus stress. Results: The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1° (SD=0.7°). The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle at 90° of knee flexion was 0.2° (SD=0.6°). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1° (SD=0.7°). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.0° (SD=0.6°). There were no significant differences and a high correlation between all paired intra- and inter-observer measurements. Conclusion: This system allows high reproducibility of the intra-operative measurement of the mechanical axes of the lower limb by a non-image-based kinematic registration of the hip, knee and ankle centers.

The rationale for navigated minimally invasive unicompartmental knee replacement.

Computer-aided systems have been developed recently to improve the precision of implantation of unicompartmental or total knee replacements. Minimally invasive techniques were eveloped to decrease the surgical trauma related to prosthesis implantation. However, there are concerns about loss of implant positioning accuracy with minimally invasive techniques. Minimally invasive instruments have been adapted for use with a typical 6-cm skin incision for unicompartmental knee replacement. We prospectively studied 60 patients who had minimally invasive navigated UKA and compared them with an earlier group of 60 patients who underwent open navigated UKA. We used an intraoperative nonimage-based navigation system. Minimally invasive navigated implantation of a UKA did not reduce the radio-graphic accuracy of the implantation compared to open navigated implantation. There were no major complications and little change from the conventional navigated operating technique. Because we do not yet know if navigation influences function and long-term survival, our conclusions need to be confirmed on a larger scale.Level of Evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Measurement of the Knee Flexion Angle With a Smartphone-Application is Precise and Accurate

We hypothesized that the measurement of the knee flexion angle measured with a specific Smartphone application was different from the reference measurement with a navigation system designed for total knee arthroplasty (TKA). Ten consecutive patients operated on for navigation assisted TKA were selected. Six navigated and 6 Smartphone measurements of knee flexion angle were obtained for each patient. The paired difference between measurements and their correlation were analyzed. The mean paired difference between navigated and Smartphone measurements was -1.1° ± 6.8° (n.s.). There was a significant correlation between both measurements. The coherence between both measurements was good. The intra-observer and inter-observer reproducibility were good. The Smartphone application used may be considered as precise and accurate. The accuracy may be higher than other conventional measurement techniques.

High Infection Control Rate and Function After Routine One-stage Exchange for Chronically Infected TKA

BackgroundMany surgeons consider two-stage exchange the gold standard for treating chronic infection after TKA. One-stage exchange is an alternative for infection control and might provide better knee function, but the rates of infection control and levels of function are unclear.Questions/PurposesWe asked whether a one-stage exchange protocol would lead to infection control rates and knee function similar to those after two-stage exchange.MethodsWe followed all 47 patients with chronically infected TKAs treated with one-stage exchange between July 2004 and February 2007. We monitored for recurrence of infection and obtained Knee Society Scores. We followed patients a minimum of 3 years or until death or infection recurrence.ResultsThree of the 47 patients (6%) experienced a persistence or recurrence of the index infection with the same pathogen isolated. Three patients (6%) had control of the index infection but between 6 and 17 months experienced an infection with another pathogen. The 3-year survival rates were 87% for being free of any infection and 91% for being healed of the index infection. Twenty-five of the 45 patients (56%) had a Knee Society Score of more than 150 points.ConclusionsWhile routine one-stage exchange was not associated with a higher rate of infection recurrence failure, knee function was not improved compared to that of historical patients having two-stage exchange. One stage-exchange may be a reasonable alternative in chronically infected TKA as a more convenient approach for patients without the risks of two operations and hospitalizations and for reducing costs. The ideal one stage-exchange candidate should be identified in future studies.Level of EvidenceLevel IV, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Diagnostic value of C-reactive protein and transthyretin in bone infections of the lower limb

In a prospective study, white and red blood cell counts, hematocrit, erythrocyte sedimentation rate (ESR), albumin, alpha-1 acid glycoprotein, C-reactive protein (CRP), and transthyretin (TTR) values were determined by serial measurements during 23 days in 80 patients with an open fracture of the lower limb. Postoperative reference profiles were defined in 74 patients without septic complications. In the six remaining patients, serum CRP and TTR concentrations were found efficient for the early diagnosis of postoperative infections: a CRP/TTR mass concentration ratio higher than 0.6 from the 8th day after surgery was sensitive (100%) and specific (93%). Variations of CRP and TTR concentrations often preceded the clinical diagnosis in patients with early infection. ESR was found unreliable with regard to postoperative infection because of its high dependence with respect to red blood cell count.

High Activity Arthroplasty Score has a Lower Ceiling Effect Than Standard Scores After Knee Arthroplasty

The tested hypothesis was following: the High Activity Arthroplasty Score has a significant lower ceiling effect than American Knee Society Score and Oxford Knee Score after total knee arthroplasty. One hundred patients operated on for total knee arthroplasty with more than one-year follow-up have been included. The ceiling effect was 53% for the American Knee Society Score, 33% for the Oxford Knee Score, and 0% for the High Activity Arthroplasty Score. High Activity Arthroplasty Score had a significantly lower ceiling effect than American Knee Society Score and Oxford Knee Score. High Activity Arthroplasty Score has the potential to detect more subtle differences in level of function than standard scoring systems among a non-selected total knee arthroplasty population.

Navigated non-image-based positioning of the acetabulum during total hip replacement

We tested the hypothesis that the non-image-based navigation system used in our department was able to measure accurately the 3D positioning of the acetabular cup of a total hip replacement (THR) and to increase the accuracy of its implantation during THR. We studied 50 consecutive navigated implantations of a THR and compared the intra-operative measurement of the cup by the navigation system to the post-operative measurement by computed tomography (CT) scan. The mean difference between the navigated and CT scan measurements for cup inclination was 2°. The mean difference between the navigated and CT-scan measurements for cup flexion was 4°. These differences were significant but considered to be clinically irrelevant in most cases. A total of 73% of the cases were within the safe zone defined prior to the study. The non-image-based system used allows a precise orientation of the cup during THR.RésuméLe but de notre étude est de mettre en évidence la possibilité de positionner de façon précise, dans les trois plans de l’espace, la cupule d’une prothèse totale de hanche et d’améliorer ainsi son implantation. Nous avons étudié 50 prothèses consécutives naviguées en comparant la mesure per opératoire de la cupule par le système de navigation et la mesure post opératoire par scanner. La différence entre les mesures faites par navigation et les mesures par scanner ne montre au niveau de l’inclinaison de la cupule qu’une différence de 2° et pour la flexion de 4°. Ces différences sont significatives mais n’ont aucune conséquence clinique dans la plupart des cas. 73% des cupules étaient dans la zone de sécurité que nous avions définie avant de mettre en route cette étude. En conclusion, le système de navigation sans image permet une orientation précise de la cupule lors d’une prothèse totale de hanche.

Difficultés et reproductibilité de la mesure radiographique de l’axe épiphysaire proximal du tibia selon la technique de Lévigne

Resume La mesure radiographique de l’axe epiphysaire proximal du tibia mise au point par Levigne a ete proposee pour differencier le varus tibial constitutionnel de l’usure osseuse. Les auteurs ont etudie la reproductibilite intra- et inter-observateur d’une telle mesure. Cinquante cliches telemetriques du membre inferieur de face ont ete realises chez 50 patients volontaires, indemnes de toute pathologie connue du genou, choisis au hasard dans une population d’operes du membre superieur. Quatre series de mesures independantes ont ete realisees par trois operateurs differents. La reproductibilite intra- et inter-observateur a ete etudiee par le calcul du coefficient de correlation intraclasse ρ.L’axe epiphysaire proximal n’a pu etre determine sur 7 a 18 des 50 cliches selon les operateurs. Les 3 observateurs n’ont ete capables de realiser toutes les mesures que pour 25 patients seulement. La reproductibilite intra-observateur etait consideree comme bonne (ρ = 0,62). La reproductibilite inter-observateur etait consideree comme moyenne (ρ = 0,41). La technique de Levigne ne semble pas pouvoir etre utilisee de facon fiable pour definir des indications chirurgicales differentes selon la morphologie de l’extremite proximale du tibia.

Diagnostic accuracy of intra-articular C-reactive protein assay in periprosthetic knee joint infection – a preliminary study

BACKGROUND Periprosthetic joint infection often raises diagnostic challenges, as the published criteria are heterogeneous. New markers for predicting periprosthetic infection have been evaluated. Here, we assessed one of these markers, C-reactive protein (CRP), in joint fluid. HYPOTHESIS We hypothesised that intra-articular CRP levels would perform better than serum CRP concentrations in diagnosing knee prosthesis infection. PATIENTS AND METHODS We prospectively included 30 patients including 10 with native-knee effusions, 11 with prosthetic-knee aseptic effusions, and 11 with prosthetic-knee infection defined using 2011 Musculoskeletal Society criteria. Serum CRP was assayed using turbidimetry or nephelometry and intra-articular CRP using nephelometry. Appropriate statistical tests were performed to compare the three groups; P values < 0.05 were considered significant. RESULTS Serum and intra-articular CRP levels were 5- to 16-fold higher in the group with periprosthetic infection than in the other two groups. Although the areas under the ROC curves were not significantly different, the likelihood ratios associated with the selected cut-offs suggested superiority of intra-articular CRP: a value > 2.78 mg/L suggested possible infection (100% sensitivity and 82% specificity) and a value > 5.37 mg/L probable infection (90% sensitivity and 91% specificity). DISCUSSION Our findings suggest a possible role for intra-articular CRP assay in diagnosing knee prosthesis infection and perhaps periprosthetic infection at any site. LEVEL OF EVIDENCE Level III, diagnostic study, development of a diagnostic criterion in consecutive patients comparatively to a reference standard.