Introduction L’instabilité patellaire est une pathologie multifactorielle. Elle nécessite une évaluation précise de ses facteurs, en particulier d’une patella alta. Les index patellotibiaux de mesure de la hauteur patellaire, comme l’index de Caton-Deschamps, ont l’inconvénient de leur référence au tibia. Les index patellotrochléens paraissent plus adaptés, mais ils ne tiennent pas compte de la flexion du genou variable lors des imageries par résonance magnétique (IRM). Objectif L’objectif de cet article est la validation d’une nouvelle mesure IRM patellotrochléenne, l’index d’engagement patellaire en extension (EPE), qui soit reproductible et qui mesure la hauteur patellaire par rapport à la trochlée indépendamment de la flexion du genou lors de l’IRM. Matériel et méthodes Étude rétrospective sur 77 IRM (37 patients instables avec antécédent de luxation patellaire, 40 témoins, avec lésion méniscale). L’index EPE est le ratio entre la longueur de l’engagement de la patella sur la trochlée cartilagineuse et la longueur du cartilage patellaire, sur un genou virtuellement ramené en extension. Quatre mesures, faites sur plusieurs coupes sagittales, ont permis le calcul de l’index EPE. Résultats Le coefficient de corrélation intraclasse (ICC) interobservateurs était excellent (0,79). La moyenne de l’EPE était de 0,22 pour l’ensemble des genoux. L’EPE moyen était plus élevé (p=0,034) dans le groupe instable (0,26) que dans le groupe témoin (0,19). La flexion moyenne des genoux sur les IRM était 11° (−8° à 25°). Discussion L’index EPE est reproductible. C’est un index anatomique, il permet de classer patella alta une patella qui n’atteint pas la trochlée genou en extension (Index EPE égal à zéro ou négatif). C’est aussi un index fonctionnel, avec une valeur moyenne de 0,19 dans le groupe témoin. Conclusion L’Index EPE a permis de mesurer l’engagement patellaire sur la trochlée en tenant compte de la flexion du genou de l’IRM. Il peut guider une éventuelle indication chirurgicale d’abaissement patellaire et quantifier la correction à apporter. Niveau de preuve III; étude rétrospective comparative.

Anterior tibial tuberosity osteotomy is a well-described therapeutic option for the treatment of patellar instability. External torsion of the anterior tibial tuberosity can be one of several factors that adversely affect the patellofemoral joint and its stability. The Anterior Tibial Tubercle Internal Torsion Osteotomy (ATTITO) allows the correction of excessive external torsion of the tibial tuberosity in a safe and reproducible manner. LEVEL OF EVIDENCE: V.

INTRODUCTION:Patellar instability is a multifactorial pathology requiring precise evaluation of its contributing factors, particularly patella alta. Patellotibial height measurement indexes, such as the Caton-Deschamps index, have the disadvantage of being referenced to the tibia. Patellotrochlear indexes are more appropriate but fail to account for variable knee flexion during magnetic resonance imaging (MRI). OBJECTIVE:This study aims to validate a new MRI-based patellotrochlear measurement, the extension patellar engagement (EPE) index, which is reproducible and measures patellar height relative to the trochlea independently of knee flexion during MRI. MATERIALS AND METHODS:A retrospective study was conducted on 77 MRIs (37 unstable patients with a history of patellar dislocation, 40 controls with meniscal injury). The EPE index is the ratio between the patellar engagement length on the cartilaginous trochlea and the patellar cartilage length, measured on a knee virtually extended. Four measurements on multiple sagittal slices were used to calculate the EPE index. RESULTS:The inteobserver intraclass correlation coefficient (ICC) was excellent (0.79). The mean EPE index's value for all knees was 0.22. It was significantly higher (p = 0.034) in the instability group (0.26) compared to the control group (0.19). The average knee flexion during MRI was 11 ° (range: -8 ° to 25 °). DISCUSSION:The EPE index is reproducible. It is an anatomical index to classify patella alta when the patella does not reach the trochlea in knee extension (EPE index ≤0). It is also a functional index, with a mean value of 0.19 in the control group. CONCLUSION:The EPE index measures the patellar engagement on the trochlea taking into account the knee flexion during MRI. It may guide surgical decision-making for patellar distalization and quantify the required correction. LEVEL OF EVIDENCE:III; retrospective comparative study.

Introduction: A new factor for patellofemoral instability-external torsion of the tibial tubercle-has recently been described. The primary aim of this biomechanics study was to analyze the consequences of internal torsion tibial tubercle osteotomy (TTO) on an experimentally unstable patella. We hypothesized that internal TTO can stabilize an experimental patellar instability. Materials and Methods: This in vitro study was conducted on six fresh anatomical specimens. The knees were flexed to 25 degrees. The patella was destabilized by transecting the patellar retinaculae and the vastus medialis tendon and by applying continuous oblique traction on the quadriceps tendon. A 3D stereovision system was used to record patellar displacement and tilt and to determine whether patellar dislocation occurred. The measurements were done before the osteotomy then repeated on the same knee after a triangular internal torsion 30 degrees TTO was completed, without medialization. Results: There was a significant difference in the patellar displacement and tilt before and after the osteotomy (p < 0.05). Patellar dislocation, which was induced by traction on all the knees before osteotomy, did not occur after the osteotomy was performed. Discussion: Internal torsion of the tibial tubercle improves patellar stability, confirming our hypothesis. These findings confirm the stabilizing effect of placing the tibial tuberosity in internal torsion. Although a knee without instability factors is not the perfect model for patellar instability, our findings suggest that tibial tubercle torsion influences patellar stability. Internal TTO may be justified as a surgical treatment of patellofemoral instability. (C) 2020 Elsevier Masson SAS. All rights reserved.

Un nouveau facteur de l’instabilité patellaire, la torsion externe de la tubérosité tibiale antérieure (TTA) a été récemment décrit. L’objectif principal de cette étude biomécanique était d’analyser les conséquences d’une ostéotomie de torsion interne de la TTA sur une patella rendue instable. L’hypothèse était que l'ostéotomie interne de la TTA peut stabiliser une patella rendue instable. L’étude in vitro a été effectuée sur 6 pièces anatomiques fraîches. Les genoux étaient fléchis à 25°. La patella était rendue instable par section des rétinaculums patellaires, du tendon du vaste médial et par traction oblique continue sur le tendon quadricipital. Un système de stéréovision 3D enregistrait le déplacement et la bascule patellaire, ainsi que la survenue d’une luxation. Les mesures étaient effectuées avant ostéotomie, puis répétées sur le même genou, après une ostéotomie triangulaire de torsion interne de la TTA de 30°, sans médialisation. Les mesures avant et après ostéotomie retrouvaient une différence significative (p < 0,05) du déplacement et de la bascule latérale de la patella. La luxation patellaire, déclenchée par la traction sur tous les genoux avant ostéotomie, ne se reproduisait plus sur les genoux ostéotomisés. Ces résultats confirment le pouvoir stabilisant de la seule torsion interne de la TTA. Même si un genou sans facteur d’instabilité n’est pas un modèle d’instabilité patellaire parfait, ils montrent que la torsion de la TTA stabilise la patella rendue instable. Dans le traitement chirurgical de l’instabilité patellaire, la correction de cette malposition de la TTA pourrait être justifiée.

Introduction: External torsion of the anterior tibial tubercle (TT), defined as external rotation around a craniocaudal axis with respect to the posterior femoral condylar plane, may induce patellar instability. To our knowledge no studies have focused on this parameter. The present study aimed to perform an MRI analysis of TT torsion. The study hypothesis was that TT torsion correlates with patellar instability and with 3 of its components: tibial tubercle-trochlear groove (TT-TG) distance, axial engagement index of the patella (AEI), and patellar tilt. Material and methods: Four observers performed MRI measurements for 2 groups: 37 patellar instability patients (PI group) with history of at least 2 patellar dislocations, and 50 control patients with meniscal lesion but free from patellofemoral pathology. All measurements were taken from 2 axial slices with the posterior condylar plane as reference. Results: The intra-class correlation coefficient (ICC) was 0.88. TT torsion correlated with patellar instability, with a mean 5.8 degrees in controls and 17.9 degrees in the PI group (P < 0.001). There were also excellent correlations between TT torsion and TT-TG distance, patellar tilt and patellar lateralization (measured by AEI), with correlation coefficients greater than 0.85. Discussion: TT torsion is a reproducible measurement, with excellent ICC. It is significantly correlated with patellar instability, with a discrimination threshold of 11.5 degrees, and correlations with all 3 components of instability. These statistical correlations enable TT torsion to be added to the list of patellar instability factors. Further studies should determine its biomechanical role and assess the contribution of associating TT derotation to medialization or distalization procedures. Level of evidence: III; case-control study. (C) 2017 Elsevier Masson SAS. All rights reserved.

La torsion externe de la tubérosité tibiale antérieure (TTA), définie par une rotation externe selon un axe cranio-caudal par rapport au plan bi-condylien fémoral postérieur, est potentiellement un facteur d'instabilité patellaire. Aucune étude n'a, à notre connaissance, été publiée sur cette mesure. Ce travail avait pour objet une étude IRM de la torsion de la TTA. L'hypothèse était qu'elle était corrélée à l'instabilité patellaire et à trois de ses paramètres : la distance tubérosité tibiale antérieure — Gorge Trochléenne (TA-GT), l'index d'engagement patellaire axial (IEA) et la bascule patellaire. Quatre observateurs ont fait les mesures sur les IRM de deux groupes : un groupe « Instabilité patellaire (IP) » de 37 patients ayant présenté au moins deux luxations patellaires, un groupe « Témoin » de 55 patients porteurs d'une lésion méniscale et exempts de pathologie fémoro-patellaire. Toutes les mesures ont été effectuées sur deux coupes axiales avec pour référence le plan bi-condylien postérieur. Le coefficient de concordance intra-classes (ICC) était de 0,88. La torsion de la TTA était corrélée à l'instabilité patellaire, avec une valeur moyenne de 5,8° pour le groupe « Témoin » et de 17,9° pour le groupe « IP » (p < 0,001). Il existait également une excellente corrélation entre la torsion de la TTA et la distance TA-GT, la bascule patellaire et la latéralisation de la patella (évaluée par l'IEA), avec des coefficients supérieurs à 0,85. La mesure de la torsion de la TTA est reproductible avec une excellente concordance inter-observateur. Elle est statistiquement liée à l'instabilité patellaire, avec un seuil de discrimination de 11,5°. Elle est corrélée aux trois paramètres de l'instabilité. Ces liens statistiques permettent d'ajouter la torsion de la TTA à la liste des facteurs d'instabilité patellaire. Des études ultérieures sont souhaitables pour déterminer son rôle biomécanique et évaluer l'utilité d'un éventuel geste associé de dérotation de la TTA lors d'une médialisation ou abaissement de la TTA. Niveau 3. Étude cas-témoins.

INTRODUCTION:Patella alta is one of the primary factors of patellofemoral instability and its importance lies in the reduced engagement between patella and trochlea during the early degrees of flexion. The evaluation of patellar height is based on conventional x-rays, CT scan and, more recently, MRI. The objective of this multicentric prospective study is to describe a novel index to assess in the sagittal plane the functional engagement between patella and trochlea. MATERIALS AND METHODS:One hundred and thirty-five patients with objective patellar dislocation were prospectively enrolled between April 2010 and September 2011 and were compared with a second group of 45 controls. All patients underwent a standard MRI and a complete radiographic study. Sagittal engagement was measured as the ratio between the articular cartilage of the patella and the trochlear cartilage length measured on two different MRI slices. RESULTS:The mean Sagittal Patellofemoral Engagement (SPE) index was 0.43 ± 0.18 and ranged from 0.02 to 0.913 in the Objective Patellar Dislocation group versus 0.42 ± 0.11 range 0.22 to 0.55 in controls. In the Patellar Dislocation group the mean Caton-Deschamps index was 1.18 ± 0.21 (range 0.71 to 1.91). There were 58 patients with patella alta, in whom the mean SPE was 0.39 ± 0.18 (range 0.02 to 0.87). Sagittal engagement was significantly higher when compared with patients in the Patellar Dislocation group who had no patella alta (mean 0.46 ± 0.16, range 0.1-0.913). DISCUSSION:The present study introduces a new method to measure the SPE with the use of MRI. The evaluation of the functional engagement of the patella with the femoral trochlea in the sagittal plane can serve as a supplementary tool to the existing methods of evaluating patellar height, and may help to better identify the cases where inadequate engagement is recorded despite the absence of patella alta, so that the need for tibial tuberosity osteotomy may be re-assessed.

La patella alta est un des facteurs principaux de l’instabilité fémoro-patellaire. Son importance est liée à un engagement réduit de la patella dans la trochlée pendant les premiers degrés de flexion. L’évaluation de la hauteur patellaire est basée sur des radios conventionnelles, sur le scanner et plus récemment sur l’IRM. L’objectif de ce travail multicentrique prospectif est de décrire un nouvel index pour évaluer l’engagement sagittal fonctionnel de la patella dans la trochlée. Cent trente-cinq patients avec une luxation patellaire objective ont été prospectivement inclus dans une étude entre avril 2010 et septembre 2011. Ils ont été comparés à un groupe témoin de 45 patients. Tous les patients ont eu une IRM standard et un bilan radiographique complet. L’engagement sagittal était mesuré en établissant un ratio entre les surfaces articulaires patellaire et trochléenne mesurée sur 2 coupes IRM différentes. L’engagement sagittal moyen de la patella était de 0,43 ± 18. Il allait de 0,02 à 0,91 dans les instabilités patellaires objectives contre 0,42 ± 11 (0,22 à 0,55) dans le groupe témoin. Dans le groupe de luxation patellaire objective, l’index de Caton-Deschamps moyen était de 1,18 ± 21 (0,71 à 1,91). Il y avait 58 patients avec une patella alta dont l’index sagittal d’engagement était de 0,39 ± 18 (0,002 à 0,87). L’engagement sagittal était significativement plus haut dans le groupe de luxation patellaire objective qui n’avait pas de patella alta (0,46 ± 16) (0,1 à 0,91). Cette étude introduit une méthode pour quantifier l’engagement sagittal de la patella en utilisant l’IRM. L’engagement fonctionnel de la patella avec la trochlée dans le plan sagittal peut être un instrument supplémentaire aux méthodes de mesure de hauteur patellaire. La mesure combinée de la hauteur et de l’engagement permettront d’affiner les indications d’abaissement de la tubérosité tibiale. II, étude prospective non randomisée.

INTRODUCTION:The aim of this study was to define a new index to measure lateral patellar displacement (LPD) using nuclear magnetic resonance imaging (MRI), an axial index of engagement of the patella (AEI) obtained from two different axial MRI views then to validate its use in a prospective series of patients presenting an objective patellar instability (OPI).MATERIALS AND METHODS:One hundred and thirty-five patients with OPI and no history of surgery of the patella were included in a prospective study organized by the French Society of Arthroscopy performed between June 2010 and August 2012. All patients underwent axial and sagittal MRI. The AEI was obtained by projecting predefined patellar and trochlear landmarks (cartilaginous landmarks) on 2 different axial MRI views (one trochlear and one patellar). The results were compared with a series of controls (n=45).RESULTS:The preoperative AEI of the patella was 0.94 ± 0.09 for the control group and 0.84 ± 0.16 for OPI group (P=0.000016). The AEI could be obtained in 100% of the cases if it was measured on 2 MRI views while it could not be measured in 38.5% of the cases if the measurement was only obtained from one MRI view or whenever the widest part of the patella was not across from the femoral trochlea. The AEI did not significantly depend on dysplasia or the presence of a supratrochlear spur. The lowest AIE values were associated with trochlear dysplasia with a supratrochlear spur (P=0.0023) and a more prominent trochlea (P=0.0016). The AEI was correlated with patellar tilt (P<0.000001) and TT-TG on MRI (P<0.000001).DISCUSSION:AEI is a new index to measure LPD. It can be obtained in all cases because it is obtained from two different MRI views. The normal value is close to 1. It can be used to measure patellar instability on the axial plane in patients with OPI, especially in the most severe cases.

The aims of this article were to report the objective results of revision ACL reconstruction and to assess the influence of an associated lateral extra-articular tenodesis on knee stability and IKDC score.

The purpose of this multicenter retrospective study was to analyze the causes for failure of ACL reconstruction and the influence of meniscectomies after revision. This study was conducted over a 12-year period, from 1994 to 2005 with ten French orthopaedic centers participating. Assessment included the objective International Knee Documenting Committee (IKDC) 2000 scoring system evaluation. Two hundred and ninety-three patients were available for statistics. Untreated laxity, femoral and tibial tunnel malposition, impingement, failure of fixation were assessed, new traumatism and infection were recorded. Meniscus surgery was evaluated before, during or after primary ACL reconstruction, and then during or after revision ACL surgery. The main cause for failure of ACL reconstruction was femoral tunnel malposition in 36% of the cases. Forty-four percent of the patients with an anterior femoral tunnel as a cause for failure of the primary surgery were IKDC A after revision versus 24% if the cause of failure was not the femoral tunnel (P = 0.05). A 70% meniscectomy rate was found in revision ACL reconstruction. Comparison between patients with a total meniscectomy (n = 56) and patients with preserved menisci (n = 65) revealed a better functional result and knee stability in the non-meniscectomized group (P = 0.04). This study shows that the anterior femoral tunnel malposition is the main cause for failure in ACL reconstruction. This reason for failure should be considered as a predictive factor of good result of revision ACL reconstruction. Total meniscectomy jeopardizes functional result and knee stability at follow-up.

La chirurgie de révision des reconstructions du ligament croisé antérieur suit l’accroissement du nombre de chirurgies primaires. Leur fréquence et les problèmes spécifiques qu’elle pose ont fait l’objet d’une étude multicentrique au sein de la Société Française d’Arthroscopie.

Displaced meniscus tears generally result from bucket handle tears with subsequent migration of the meniscal fragment into the intercondylar notch. More rarely, the fragment may move into the meniscal recesses. In this situation, the displaced fragment may be difficult to individualize arthroscopically, so preoperative imaging is crucial. Several studies have demonstrated the reliability of magnetic resonance imaging (MRI) for the diagnosis of meniscus injury with fragment displacement in the intercondylar notch. There have been few studies devoted to fragment displacement into the collateral capsuloligamentary structures. The purpose of this study was to describe MRI findings of medial meniscus tears with displaced fragment in the meniscal recesses.This prospective study was conducted over a 22-month period (May 2003 - February 2005). During this period, we selected 39 patients whose knee MRI displayed a meniscal fragment within the medial collateral recesses. These 39 patients accounted for 15% of knees with MRI-diagnosed meniscal tears (n=272) and 2% of the knee MRI examinations performed during the study period (n=2239). One the MRI series, we studied fragment migration and morphological anomalies of the injured meniscus. For 16 knees, MRI findings could be compared with arthroscopy findings.For 25 knees (65%), the meniscal fragment had migrated downward along the medial tibial plateau and generally (64%) medially to the collateral tibial ligament. For 14 knees (35%) the meniscal fragment had migrated upward, along the medial femoral condyle in 93%, anteriorly to the medial collateral tibial ligament. For 95%, the MRI demonstrated rupture along the free border of the posterior segment and/or the mid segment of the medial meniscus or a decreased height of the posterior segment of the medial meniscus. For 14 of 16 cases, arthroscopy confirmed the meniscal tear and the localization of the displaced fragment. For two knees, arthroscopy confirmed the presence of the meniscal tear but could not identify the displaced meniscal fragment.Meniscal tears with fragment displacement into the meniscal recesses has been associated with displacement of a horizontal fissuration which flap tears described arthroscopically by DJ Dandy. Other authors consider these tear flaps as oblique fissurations. In our study, it was sometimes difficult to determine the exact site and orientation of the initial meniscal tear so it is quite likely that meniscal tears with a displaced fragment in the meniscal recesses could correspond to complex predominantly horizontal or oblique meniscal fissurations. The common feature is the presence of an unstable meniscal flap susceptible to migrate. Our findings are in agreement with the literature. Regarding the two cases where the MRI findings could not be confirmed arthroscopically, the MRI visualized a characteristic image of a meniscal fragment displaced downwardly, lying between the medial tibial plateau and the collateral tibial ligament. Arthroscopy visualized the meniscal tear but failed to visualize the displaced fragment. This might be because mobile meniscal fragments return into the joint interspace when the meniscus is manipulated arthroscopically. Small meniscal fragments might also be inaccessible arthroscopically.

Purpose of the study Displaced meniscus tears generally result from bucket handle tears with subsequent migration of the meniscal fragment into the intercondylar notch. More rarely, the fragment may move into the meniscal recesses. In this situation, the displaced fragment may be difficult to individualize arthroscopically, so preoperative imaging is crucial. Several studies have clemonstated the reliability of magnetic resonance imaging (MRI) for the diagnosis of meniscus injury with fragment displacement in the intercondylar notch. There have been few studies devoted to fragment displacement into the collateral capsuloligamentary structures. The purpose of this study was to describe MRI findings of medial meniscus tears with displaced fragment in the meniscal recesses.Material and methods This prospective study was conducted over a 22-month period (May 2003 - February 2005). During this period, we selected 39 patients whose knee MRI displayed a meniscal fragment within the medial collateral recesses. These 39 patients accounted for 15% of knees with MRI-diagnosed meniscal tears (n = 272) and 2% of the knee MRI examinations performed during the study period (n = 2239). One the MRI series, we studied fragment migration and morphological anomalies of the injured meniscus. For 16 knees, MRI findings could be compared with arthroscopy findings.Results For 25 knees (65%), the meniscal fragment had migrated downward along the medial tibial plateau and generally (64%) medially to the collateral tibia] ligament. For 14 knees (35%) the meniscal fragment had migrated upward, along the medial femoral condyle in 93%, anteriorly to the medial collateral tibial ligament. For 95%, the MRI demonstrated rupture along the free border of the posterior segment and/or the mid segment of the medial meniscus or a decreased height of the posterior segment of the medial meniscus. For 14 of 16 cases, arthroscopy confirmed the meniscal tear and the localization of the displaced fragment. For two knees, arthroscopy confirmed the presence of the meniscal tear but could not identify the displaced meniscal fragment.Discussion Meniscal tears with fragment displacement into the meniscal recesses has been associated with displacement of a horizontal fissuration which flap tears described arthroscopically by DJ Dandy. Other authors consider these tear flaps as oblique fissurations. In our study, it was sometimes difficult to determine the exact site and orientation of the initial meniscal tear so it is quite likely that meniscal tears with a displaced fragment in the meniscal recesses could correspond to complex predominantly horizontal or oblique meniscal fissurations. The common feature is the presence of an unstable meniscal flap susceptible to migrate. Our findings are in agreement with the literature. Regarding the two cases where the MRI findings could not be confirmed arthroscopically, the MRI visualized a characteristic image of a meniscal fragment displaced downwardly, lying between the medial tibial plateau and the collateral tibial ligament. Arthroscopy visualized the meniscal tear but failed to visualize the displaced fragment. This might be because mobile meniscal fragments return into the joint interspace when the meniscus is manipulated arthroscopically. Small meniscal fragments might also be inaccessible arthroscopically. Key words: Magnetic resonance imaging, knee, meniscus, arthroscopy.