Cyril Boeri

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.

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.

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.

Coronal alignment of the lower limb

Background The coronal alignment of the lower limb is important for knee reconstruction procedures. However, normal alignment is hard to define because of its wide variation among normal individuals. Our hypothesis was that the variation in the normal anatomy as assessed by radiography is greater than commonly accepted. Methods We performed anteroposterior long-leg radiographs on 100 Caucasian patients without any known knee abnormality, to determinate the femorotibial angle, coronal orientation of the distal femoral condyles, and coronal orientation of the proximal tibial condyles. All measurements were performed by the same experienced knee surgeon. Result The mean values observed were close to the values commonly described in the Caucasian population. However, only 15–20% of the cases met the mean values of Moreland et al. (1987) for the individual items, and only 2 cases had the exact normal values. There was a wide variation for all angles measured, with a standard deviation higher than the mean value. Interpretation The variation in the lower limb axes is wider than commonly believed. There is a need for individual knee reconstruction which takes the specific knee axes of the patient to be operated into account.

Total Knee Prosthesis Implantation With a Non-Image-Based Navigation System: Rationale, Technique, Case-Control Comparative Study With a Conventional Instrumented Implantation

Summary A navigation system should improve the quality of a total knee prosthesis implantation in comparison to that obtained with the classic, surgeon-controlled operative technique. The authors implanted 100 total knee prostheses with an infrared navigation system (Orthopilot, Aesculap, Tuttlingen, Germany). The quality of implantation was studied on postoperative long leg coronal and lateral x-rays, and compared with a control group of 100 matched-paired patients operated on with a total knee prostheses implanted using a classic, surgeon-controlled technique. An optimal mechanical femorotibial angle (177–183°) was obtained in 93 cases in the study group and 75 cases in the control group (P <0.05). Similar differences were seen for the coronal and sagittal orientations of both tibial and femoral components. Globally, 67 cases in the study group and 31 cases in the control group were implanted in an optimal manner for all studied criteria (P <0.001). The used navigation system allows significant improvement in the quality of implantation of a total knee prosthesis in comparison to that obtained with classic, surgeon-controlled instrumentation, and long-term outcome might consequently be improved.

Agreement between pre-operative and intra-operative bacteriological samples in 85 chronic peri-prosthetic infections

BACKGROUND Whether pre-operative microbiological sampling contributes to the management of chronic peri-prosthetic infection remains controversial. We assessed agreement between the results of pre-operative and intra-operative samples in patients undergoing single-stage prosthesis exchange to treat chronic peri-prosthetic infection. HYPOTHESIS Agreement between pre-operative and intra-operative samples exceeds 75% in patients undergoing single-stage exchange of a hip or knee prosthesis to treat chronic peri-prosthetic infection. MATERIAL AND METHODS This single-centre retrospective study included 85 single-stage prosthesis exchange procedures in 82 patients with chronic peri-prosthetic infection at the hip or knee. Agreement between pre-operative and intra-operative sample results was evaluated. Changes to the initial antibiotic regimen made based on the intra-operative sample results were recorded. RESULTS Of 149 pre-operative samples, 109 yielded positive cultures, in 75/85 cases. Of 452 intra-operative samples, 354 yielded positive cultures, in 85/85 cases. Agreement was complete in 54 (63%) cases and partial in 9 (11%) cases; there was no agreement in the remaining 22 (26%) cases. The complete agreement rate was significantly lower than 75% (P=0.01). The initial antibiotic regimen was inadequate in a single case. DISCUSSION Pre-operative sampling may contribute to the diagnosis of peri-prosthetic infection but is neither necessary nor sufficient to confirm the diagnosis and identify the causative agent. The spectrum of the initial antibiotic regimen cannot be safely narrowed based on the pre-operative sample results. We suggest the routine prescription of a probabilistic broad-spectrum antibiotic regimen immediately after the prosthesis exchange, even when a pathogen was identified before surgery. LEVEL OF EVIDENCE IV, retrospective study.

Navigated non-image-based registration of the position of the pelvis during THR. An accuracy and reproducibility study

The precise recording of the position of the pelvis is a prerequisite for total hip replacement (THR). The anterior pelvic plane is an accepted reference for determining the 3D pelvic orientation. We hypothesized that cutaneous palpation of this plane was accurate and reproducible. Ten consecutive navigated implantations of THR prostheses were studied. In each case, four palpations of both anterior iliac spines and the pubic symphysis were performed with a navigated stylus. The first palpation was made on actual bone contours through a skin puncture and was considered as the reference. The other three palpations were made over the intact skin as a normal intra-operative procedure. There was no significant difference between the pelvic orientations measured by the three cutaneous palpations, or between the orientations measured by transcutaneous palpation and the mean result with cutaneous palpation. Cutaneous palpation can be considered as a reliable technique for the definition of pelvic orientation during THR with the non-image-based system employed.