Isometry Measurements in the Knee With the Anterior Cruciate Ligament Intact, Sectioned, and Reconstructed

Abstract

When assessing isometry during anterior cruciate ligament surgery, it is assumed that points determined to be isometric remain so after reconstruction. We sought to evaluate if isometric measurements vary with the status of the anterior cruciate ligament. A computerized electronic isometer was used to measure the magnitude and pattern of change in separation distance between a constant point in the tibial insertion of the anterior cruciate ligament and five positions within the femoral insertion with the anterior cruciate ligament intact, sectioned, and reconstructed. For the center position, the magnitude and pattern of the change in separation distance was physiologically isometric in all conditions (maximal length change, 3.0 mm). For the posterior position, the isometry pattern remained physiologic in each condition, and the magnitude of the separation distance was nearly isometric in all conditions (maximal length change, 3.7 mm). The superior and inferior positions had similar isometric measurements in the intact and sectioned conditions but significantly different measurements after anterior cruciate ligament reconstruction. Intraoperative assessment of isometry at positions in the center or posterior portion of the anterior cruciate ligament's femoral insertion provides useful information that is not altered by reconstruction. For superior and inferior positions, however, points found to be isometric in the anterior cruciate ligament-deficient knee did not remain isometric after reconstruction.

Anatomic anterior cruciate ligament reconstruction: the two-incision technique

“…This point corresponding to the most isometric point [12,19,23], consequently, the most anterior fibres of AM band are the most isometric [13,18,19,29]. The PL band of the ACL represents the bulk of ligament and its fibres are the most inferior and posterior.…”

A isometricidade do ligamento cruzado posterior

“…In the Ortiz et al 14 study, simulating in laboratory situations of muscular contraction corresponding to daily life activities, the localization of the PCL isometric point is so much modified that it remains outside the ligament femoral insertion. The very absence of the PCL produces alterations in isometry, since the absence of primary restriction on the posterior displacement of the tibia allows it to stay in a more posterior position during all the arch of movement of the knee, similarly to what occurs with isometry when the ACL is absent (Amis and Jakob 2 , Covey et al 5 , Furia et al 7 ).…”

“…No estudo de ORTIZ et al 14 , simulando em laboratório algumas situações de contração muscular que correspondem a atividades de vida diária de uma pessoa, a localização do ponto isométrico do LCP se modifica tanto que fica fora da inserção femoral do ligamento. A própria ausência do LCP acarreta alterações na isometricidade, pois a ausência do restritor primário do deslocamento posterior da tíbia permite que ela se encontre em posição mais posterior durante todo o arco de movimento do joelho, análogo ao que ocorre com a isometricidade do LCA quando de sua ausência 2,5,7 .…”

“…O conhecimento da isometricidade do ligamento cruzado posterior (LCP) é considerado fundamental para se reconstruir o LCP, e é estudada por vários autores com diferentes modelos experimentais, tais como o uso de fio inextensível conectando os pontos ou através de cálculo trigonométrico (3,4,5,6,7,8,9,11,12,13,14,15,16) . Neste estudo objetivamos resumir as informações obtidas na literatura referentes à isometricidade do ligamento cruzado posterior.…”

Femoral tunnel placement in anterior cruciate ligament reconstruction: rationale of the two incision technique

“…At level of femur, the attachment of AM bundle is anterior and proximal, just behind the top of the intercondylar notch roof. This point is corresponding to the most isometric point [19,20]. Consequently, the most anterior fibers of AM bundle are the most isometric [21,22].…”