The purpose of this study was to describe the intra- and inter-observer variability of the registration of bony landmarks and alignment axes on a Computed Axial Tomography (CT) scan. Six cadaver specimens were scanned. Three-dimensional surface models of the knee were created. Three observers marked anatomic surface landmarks and alignment landmarks. The intra- and inter-observer variability of the point and axis registration was performed. Mean intra-observer precision ranks around 1 mm for all landmarks. The intra-class correlation coefficient (ICC) for inter-observer variability ranked higher than 0.98 for all landmarks. The highest recorded intra- and inter-observer variability was 1.3 mm and 3.5 mm respectively and was observed for the lateral femoral epicondyle. The lowest variability in the determination of axes was found for the femoral mechanical axis (intra-observer 0.12 degrees and inter-observer 0.19 degrees) and for the tibial mechanical axis (respectively 0.15 degrees and 0.28 degrees). In the horizontal plane the lowest variability was observed for the posterior condylar line of the femur (intra-observer 0.17 degrees and inter-observer 0.78 degrees) and for the transverse axis (respectively 1.89 degrees and 2.03) on the tibia. This study demonstrates low intra- and inter-observer variability in the CT registration of landmarks that define the coordinate system of the femur and the tibia. In the femur, the horizontal plane projections of the posterior condylar line and the surgical and anatomical transepicondylar axis can be determined precisely on a CT scan, using the described methodology. In the tibia, the best result is obtained for the tibial transverse axis.

Only 57% of the patients with a pathological TT-TG distance (≥20 mm) had lateralization of the tibial tubercle in relation to the posterior cruciate ligament. The TT-PCL distance is an alternative method for determining the position of the tibial tubercle.

A comparative kinematics study was conducted on six cadaver limbs, comparing tibiofemoral kinematics in five conditions: unloaded, under a constant 130 N ankle load with a variable quadriceps load, with and without a simultaneous constant 50 N medial and lateral hamstrings load. Kinematics were described as translation of the projected centers of the medial (MFT) and lateral femoral condyles (LFT) in the horizontal plane of the tibia, and tibial axial rotation (TR) as a function of flexion angle. In passive conditions, the tibia rotated internally with increasing flexion to an average of À168 (range: À12/À208, SD ¼ 3.08). Between 0 and 408 flexion, the medial condyle translated forwards 4 mm (range: 0.8/5.5 mm, SD ¼ 2.5 mm), followed by a gradual posterior translation, totaling À9 mm (range: À5.8/ À18.5 mm, SD ¼ 4.9 mm) between 40-1408 flexion. The lateral femoral condyle translated posteriorly with increasing flexion completing À25 mm (range: À22.6 to À28.2 mm, SD ¼ 2.5 mm). Dynamic, loaded measurements simulating a deep knee bend were carried out in a knee rig. Under a fixed ankle load of 130 N and variable quadriceps loading, tibial rotation was inverted, mean TR Keywords: knee; kinematics; muscle loading; anterior cruciate ligament Knee kinematics are complex and intriguing and have been studied extensively. 1 The deduced model describes posterior translation of the femoral condyles relative to the tibia with increasing flexion. This translation is greater on the lateral than on the medial side, leading to relative internal tibial rotation. However, different methods reveal different patterns, and existing literature is not unanimous in describing ''normal'' knee kinematics. Differences can be attributed to intrinsic and extrinsic factors. Intrinsic factors relate to the interindividual differences. Most studies included small numbers of specimens, patients, or volunteers, so bias cannot be excluded, even with a normal distribution of anatomic features or kinematic patterns. Extrinsic factors include the experimental setup with differences in quadriceps force, hamstrings cocontraction, triceps surae cocontraction, loads, and mechanical constraints imposed on the joint. Also, the mathematical model used for describing knee kinematics will influence the results. [2][3][4][5] Studies describing passive or unloaded knee kinematics 6-12 should be differentiated from studies describing loaded kinematics. Loaded in vitro experiments typically use load frames, knee simulators, or robots where controlled loads are applied to the joint. [13][14][15][16][17][18][19][20][21][22][23][24][25] These experiments can use a feedback loop between ankle load and applied quadriceps force, but are arbitrary when it comes to cocontraction of important muscle groups. Loads exerted by cocontraction of hamstrings and triceps surae remain uncertain, which is reflected in the large range of applied loads use in kinematic experiments. 14,16,20,21,24,25 Loaded in vivo research uses MRI imaging, 10,26,27 roentgen stereophotogram...

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The aim of this study was to quantify the effects of understuffing and overstuffing UKA on bone stresses, load distribution and ligament strains. For that purpose, a numerical knee model of a cadaveric knee was developed and was validated against experimental measurements on that same knee. Good agreement was found among the numerical and experimental results. This study showed that, even if a medial UKA is well-aligned with normal soft tissue tension and with correct thickness of the tibia component, it induces a stiffness modification in the joint that alters the load distribution between the medial and lateral compartments, the bone stress and the ligament strain potentially leading to an osteoarthritic progression.