Subluxation of the patella
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Summary
Subluxation of the patella may produce pain and instability in young people. However its classification, diagnosis and treatment are controversial. We have used computerized tomography (CT) to measure the amount of lateral shift of the patella and the angle of tilt to the femur in patients with subluxation. The mean lateral shift was 31.4% and the angle of tilt 31.8 degrees. These values are significantly greater than those obtained from conventional axial radiographs or in arthrographic axial views.
We have obtained interesting evidence that the rate of lateral shift apparently increased on voluntary contraction of the quadriceps muscle (Q-contracted). With the quadriceps contracted, the mean rate of the lateral shift in the affected knees showed a significant increase (+ 27.7%) compared to that in normal knees (+ 14.0%).
We have reviewed 40 knees treated by operative realignment with a mean follow-up of 27 months. The mean rates of lateral shift measured from CT-image in the knees before operation improved significantly to the normal range at follow-up, both with the quadriceps relaxed and contracted. The results evaluated by Insall's criteria were “excellent” in 13 knees; “good” in 22; “fair” in 3 and “poor” in 2. The satisfactory group (those with excellent and good results) revealed an improvement in lateral shift when the quadriceps was contracted, while the unsatisfactory group (fair and poor results) did not.
Key words
Patella Subluxation Computerized tomographyRésumé
La subluxation de la rotule peut entraîner chez les sujets jeunes des douleurs et une instabilité. Cependant, la classification, les critères du diagnostic et le traitement sont sujets à controverse. Nous avons utilisé la tomodensitométrie (TDM) pour mesurer l'importance du déplacement externe de la rotule et son inclinaison par rapport au fémur dans un groupe de malades présentant une subluxation. La déviation moyenne était de 31,4% et l'angle d'inclinaison de 31,8 degrés. Ces chiffres étaient significativement-plus élevés que ceux obtenus à partir de radiographies conventionnelles ou d'arthrographies axiales.
Nous avons montré que le déplacement externe de la rotule augmente lors de la contraction volontaire du quadriceps. Lorsque le quadriceps est contracté, la déviation augmente de 27,7% sur les rotules subluxées contre 14% dans les genoux normaux.
Nous avons revu 40 genoux traités par une opération de réalignement, avec un recul moyen de 27 mois. Le taux moyen de déviation externe, mesuré par TDM, s'est amélioré significativement jusqu'à des chiffres normaux, que le quadriceps soit relâché ou contracté. Les résultats, évalués selon les critères d'Insall, sont «excellents» pour 13 genoux, «bons» pour 22, «assez bons» pour 3 et «mauvais» pour 2. Le groupe des résultats satisfaisants (excellents et bons) présente une diminution du déplacement de la rotule même lors de la contraction du quadriceps, contrairement au groupe des résultats «assez bons» et «mauvais».
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