Page 38 - ISAKOS 2018 Newsletter Volume 2
P. 38

ACL Evaluation with Slice Imaging: Applicability of the Porto-Knee Testing Device
Rogério Pereira, BHKin
Renato Andrade, BSc
Ricardo Bastos, MD, PhD
João Espregueira-Mendes, MD, PhD
Clínica do Dragão, Espregueira-Mendes Sports Centre–FIFA Medical Centre of Excellence, Porto, PORTUGAL
Multiplanar knee laxity beyond the physiological range of motion seems to be a hazard in several contexts. Pathological laxity often leads to comorbidities such as early osteoarthritis as well as meniscal and capsuloligamentous injuries, which may decrease the ability to perform athletic or work-related activities.
The aims of operative treatment of an anterior cruciate ligament (ACL) rupture are to restore the native arthrokinematics of the knee and to prevent comorbidities associated with the abnormal laxity.
It has been reported that ACL-reconstructed knees, even those in which the procedure is considered to have been successful, demonstrate altered kinematics, which may, under certain scenarios, impose potentially harmful amounts of stress to the ACL1. In the last few decades, however, important advances in surgical technique have led to an improvement in postoperative knee kinematics, particularly with regard to the reestablishment of knee stability in the transverse plane. Thus, it is crucial to assess multiplanar knee laxity in order to correctly classify ACL-deficient and ACL-ruptured knees in terms of their laxity profile and refine treatment indications accordingly.
Notwithstanding all of the research on objective clinical measures of joint laxity, the scientific and medical communities still maintain that there is a need for a simple and clinically applicable tool for measuring sagittal and rotatory laxity of the knee. While the Lachman test is recognized as the most sensitive and most commonly used, other clinical maneuvers, such as the anterior drawer test, are also often performed for the manual evaluation of sagittal laxity. In addition, the pivot-shift test remains the most accepted method for assessing rotatory laxity and is believed to correlate with episodes of giving way in individuals with ACL-deficient knees. However, manual examinations are subjective, lack standardization, and may be influenced by a number of variables (e.g., the extent of injury, muscle guarding, and the technique and experience of the examiner), all of which may lead to variable arthrokinematics and, as a result, limited accuracy. In light of the shortcomings and the need for a tool that will provide consistent, reproducible, and comprehensive multiplanar assessments, instrumented laxity devices continue to evolve.
Stress MRI/CT Assessment
The instrumented assessment of laxity with use of magnetic resonance imaging (MRI) or computed tomography (CT) offers new possibilities and is already a reality in daily clinical practice. This method provides insight into the anatomical structures and their association with biomechanical behavior, thereby providing an enhanced and more sensitive diagnostic workflow. As reported previously2,3, the Porto-Knee Testing Device (PKTD; Soplast, Valongo, Portugal) is a noninvasive and CT and MRI-compatible device that provides objective measurements of sagittal and rotatory laxity (Fig. 1).
Evaluation Procedures
The PKTD evaluation procedure starts by laying the patient supine on the MRI/CT table, with the lower limb placed on the PKTD. The knee is flexed to 30° and is aligned with the mechanical axis of the device. The foot rests in neutral flexion and rotation, contributing to the locking effect of the talus in the ankle mortise. The patient is instructed to remain calm and to avoid muscle guarding.

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