Evaluación dinámica en la inestabilidad femoropatelar. The quadriceps active ratio

Abstract

Patellofemoral instability (IFP, in Spanish) is defined as an abnormal movement occurring between the femoral trochlea and the patellar bone when the knee joint moves. As a result, the latter tends to escape from the natural restraints provided by the bony groove in the femoral side, generally with a lateral direction. Clinical presentation is evident around skeletal maturity; in consequence it becomes a common cause for consultation among young individuals attending knee clinics. In severe cases, the dislocation episodes can be recurrent, severely affecting the functionality of the lower limb, and thus jeopardizing the chances of these individuals to integrate in leisure and occupational activities at the same level of others in their age bracket. The cause of this condition is multifactorial. Diverse anatomic features in the joint are related to a higher incidence of IFP; the most relevant among them are a high ridding patella, a flattened or convex troclear groove and a disbalanced extensor retinaculum, especially due to an injury of the medial patellofemoral ligament. Historically, special attention has also been paid to the contributing role of muscular imbalance in the lower limb. Several other rotational or postural alterations in the femoral, tibial and foot bones are considered as risk factors, too. The list of predisposing elements is vast, including hyperlaxity, patellar morphology, knee alignment and even certain personality traits. 12 One of the most demanding challenges in IFP management is objectively defining these alterations. Traditionally, physical examination manoeuvres and imaging for this entity have been performed with the patient in a resting attitude. In such scenario, muscles are relaxed, and therefore the result of their action in the patellofemoral joint is neglected. As a consequence, knees are evaluated from an “in vitro” inspection, that may not be a reflection of the actual dynamics happening during a dislocation episode, generally associated with pivoting, jumping or cutting movements. Hence, during the last decades, several researchers have advocated for a more dynamic avenue in the study of this condition. Following this stream, a number of studies have analysed the relations in the patellofemoral joint while muscular forces are applied to the knee. These studies, with certainly diverse methodology, have allowed for a better understanding of the joint functioning, and particularly to the knowledge of why IFP is favoured in certain knee configurations. The Orthopaedic Research Institute of Queensland - The ORIQL, in Townsville (Australia) has also produced an original contribution to the field of dynamic studies: the quadriceps active ratio. I have been part of the research team in charge of developing this novel method to calculate patellar height since 2015, thanks to a Research and Clinical Fellowship in the Institute. This ratio analyses the direct contact between the articular surfaces of the patella and the femoral trochlea by means of sagittal magnetic resonance imaging, obtained during quadriceps voluntary 13 activation. A distinctive characteristic is the fact that all measurements are obtained within the patellofemoral joint, avoiding external (historically tibial) referencing. The quadriceps active ratio has been validated in a clinical study including 94 patients attending a knee clinic associated with The ORIQL. It showed a high accuracy in the detection of patients with clinically manifest IFP, superior to classic and/or current methods such as Insall-Salvati or Blackburne-Peel ratios. Moreover, the reliability during consecutive observations and among diverse evaluators was sound. Electromyographic tests also confirmed the feasibility of the voluntary muscular contraction required for this assessment. In sum, the test is reliable, reproductible and clinically applicable, with no relevant additional costs. Our contribution has been positively accepted in specialized forums where it has been presented. We obtained the Award for the Best Oral Communication in the 2019 Spanish Knee Society – Spanish Arthroscopic Association Combined Annual Meeting, and the 2019 “Doctor Jaraba” Special Research Award from the Medical Council of Las Palmas (Spain). Several distinguished authors have backed the results of our research, and thanks to these collaborations we have developed optimized image acquisition protocols to further improve our technique. In this thesis, an extensive approximation to the aetiology of IFP is displayed, as well as a wide description of clinical presentation and other aspects of practical relevance. Diagnostic techniques are thoroughly discussed, with a dedicated focus on dynamic methods, where the quadriceps active ratio is framed.