Standardising the clinical assessment of coronal knee laxity

Abstract

Clinical laxity tests are used for assessing knee ligament injuries and for soft tissue balancing in total knee arthroplasty. This study reports the development and validation of a quantitative technique of assessing collateral knee laxity through accurate measurement of potential variables during routine clinical examination. The hypothesis was that standardisation of a clinical stress test would result in a repeatable range of laxity measurements. Non-invasive infrared tracking technology with kinematic registration of joint centres gave real-time measurement of both coronal and sagittal mechanical tibiofemoral alignment. Knee flexion, moment arm and magnitude of the applied force were all measured and standardised. Three clinicians then performed six knee laxity examinations on a single volunteer using a target moment of 18 Nm. Standardised laxity measurements had small standard deviations (within 1.1°) for each clinician and similar mean values between clinicians, with the valgus laxity assessment (mean of 3°) being slightly more consistent than varus (means of 4° or 5°). The manual technique of coronal knee laxity assessment was successfully quantified and standardised, leading to a narrow range of measurements (within the accuracy of the measurement system). Minimising the subjective variables of clinical examination could improve current knowledge of soft tissue knee behaviour.

The dynamic nature of alignment and variations in normal knees

“…The use of such attachments has been validated in previous studies using same method, and the use of bony attachments is not viable in the setting of normal volunteers. [19][20][21] One previous study recorded inter-and intra-registration measurement errors of this system, finding errors of up to 1°, 19 which is why this minimum difference was used in the power calculation. We did not measure the intra-registration measurement error in this study, and as the system is operator dependent, the degree of error may differ from that recorded in previous studies.…”

“…[25][26][27] This study used a similar infra-red based computer navigation system to measure FTMA, with a method that had previously been validated. [19][20][21] This method of measurement has a number of potential advantages over other measurement systems. The immediate generation of real-time onscreen coronal and sagittal FTMA angles enables dynamic measurements of alignment to be made on weight-bearing, with immediate visualisation of angular displacement.…”

“…In each patient the FTMA was measured with a validated method using an infrared-based navigation system (Orthopilot, B Braun, Tutlingen, Germany), with reference arrays attached to the patient using fibroelastic straps [19][20][21] (Figs 1 and 2). All measurements were taken by a single surgeon who had experience of > 1000 navigated arthroplasties (KD) and who travelled to each centre to take the measurements.…”

The measurement of medial knee gap width using ultrasound

“…Clinically, valgus laxity is typically assessed via the valgus stress test in which the knee is slightly flexed, abduction is applied to the limb, and the size of the joint opening is estimated in order to grade injury severity. However, such approaches can be highly subjective; scoring systems depend on the perception of millimeters of differences in joint opening [14, 15], which may actually exceed the discriminating capacity of human judgment [16, 17]. In one study, the overall agreement between five clinicians in their assessment of mediolateral instability was reported to be only moderate [18, 19].…”

Non-invasive, non-radiological quantification of anteroposterior knee joint ligamentous laxity

“…A non-invasive adaptation of this technology using software algorithms identical to those used in a commercially available image-free navigation system has been validated to quantify lower limb mechanical and coronal knee laxity in early flexion. 20,21 Using the same fabric strap method, a pilot study on six embalmed cadaveric lower limbs gave acceptable reliability, precision and agreement with a conventional image-free navigation system measuring AP translation in early flexion. 22 …”