Three-dimensional assessment of lower limb alignment: Reference values and sex-related differences.

BACKGROUND: Three-dimensional (3D) preoperative planning and assisted surgery is increasingly popular in deformity surgery and arthroplasty. Reference ranges for 3D lower limb alignment are needed as a prerequisite for standardized analysis of alignment and preoperative planning in 3D, but are not yet established. METHODS: On 60 3D bone models of the lower limbs based on computed tomography data, fifteen parameters per leg were assessed by standardized validated 3D analysis. Distribution parameters and differences between sexes were evaluated. Reference values were generated by adding/subtracting one standard deviation from the mean. RESULTS: Women had a significantly lower mean mechanical lateral distal femoral angle compared with men (86.4 ±â€¯2.1° vs. 87.8 ±â€¯2.0°; P < .05) and significantly lower mean joint line convergence angle (-2.5 ±â€¯1.4° vs. -1.3 ±â€¯1.2; P < .01), but higher mean hip knee ankle angle (178.9 ±â€¯1.9° vs. 177.8 ±â€¯2.3°; P < .05) and mean femoral torsion (18.2 ±â€¯9.5° vs. 13.2 ±â€¯6.4°; P < .05), resulting in a tendency towards valgus alignment and vice versa for men. Differences in mean medial proximal tibial angle were not significant. The mean mechanical axis deviation from the tibial knee joint center was 6.9 ±â€¯7.3 mm medial and 1.4 ±â€¯16.1 mm ventral without significant differences between sexes. CONCLUSIONS: We describe total and sex-related reference ranges for all alignment relevant axes and joint angles of the lower limb. There are sex-related differences in certain alignment parameters, which should be considered in analysis and surgical planning.

Three-dimensional assessment of lower limb alignment: Accuracy and reliability.

INTRODUCTION: Three-dimensional (3D) surgical planning and patient-specific implants are becoming increasingly popular in orthopedics and trauma surgery. In contrast to the established and standardized alignment assessment on two-dimensional (2D) long standing radiographs (LSRs) there is neither a standardized nor a validated protocol for the analysis of 3D bone models of the lower limb. This study aimed to create a prerequisite for pre-operative planning. METHODS: According to 2D analysis and after meticulous research, 24 landmarks were defined on 3D bone models obtained from computed axial tomography (CT) scans for a 3D alignment assessment. Three observers with different experience levels performed the test three different times on three specimens. Intraobserver and interobserver variability of the landmarks and the intraclass correlation coefficient (ICC) of the resulting axes and joint angles were evaluated. RESULTS: Overall, the intraobserver and interobserver variability was low, with a mean deviation <5 mm for all landmarks. The ICC of all joint angles and axis deviations was >0.8, except for tibial torsion (ICC = 0.69). All knee joint angles showed excellent ICC (>0.95). CONCLUSIONS: Using the defined landmarks, a standardized 3D alignment assessment with low intraobserver and interobserver variability and high ICC values for the knee joint angles can be performed regardless of examiner's experience. The described method serves as a reliable standardized protocol for a 3D malalignment test of the lower limb. Three-dimensional pre-operative analysis might enhance understanding of deformities and lead to a new focus in surgical planning.

Finite element analysis of the ovine hip: development, results and comparison with the human hip.

OBJECTIVES: The ovine hip is often used as an experimental research model to simulate the human hip. However, little is known about the contact pressures on the femoral and acetabular cartilage in the ovine hip, and if those are representative for the human hip. METHODS: A model of the ovine hip, including the pelvis, femur, acetabular cartilage, femoral cartilage and ligamentum transversum, was built using computed tomography and micro-computed tomography. Using the finite element method, the peak forces were analysed during simulated walking. RESULTS: The evaluation revealed that the contact pressure distribution on the femoral cartilage is horseshoe-shaped and reaches a maximum value of approximately 6 MPa. The maximum contact pressure is located on the dorsal acetabular side and is predominantly aligned in the cranial-to-caudal direction. The surface stresses acting on the pelvic bone reach an average value of approximately 2 MPa. CONCLUSIONS: The contact pressure distribution, magnitude, and the mean surface stress in the ovine hip are similar to those described in the current literature for the human hip. This suggests that in terms of load distribution, the ovine hip is well suited for the preclinical testing of medical devices designed for the human hip.