Creation of a simple distal femur morphology classification system

Abstract

The purpose of this study is to propose a binary classification system based on simple measurements that summarizes individual, race, and sex-specific differences in distal femur shape. Surface models of 165 distal femurs (79 female, 86 male; 85 African-American, 80 Caucasian, 28.8 AE 7.6 years) were created with a 3-dimensional laser scanner. Surface area, width, length, curvature, and angulation were measured. Knees were classified as either type A or B within five distinct categories: (i) aspect ratio, (ii) trochlear-intercondylar width ratio, (iii) trochlear tilt, (iv) medial-lateral trochlear width ratio, and (v) trochlear sulcus shape. Correlations between these measures and surface area were calculated, and receiver-operator curves were used to select cutoff values between type A and B knees to improve differentiation of femur shapes by sex or race. The cutoff values between type A and B knees for the five categories are as follows: Category I: 0.90, Category II: 0.51, Category III: 1.02, Category IV: 0.67, and Category V: 128.7˚. Other than category IV (medial-lateral trochlear width ratio) (p ¼ 0.004, R ¼ 0.22), no categories were correlated with surface area (p > 0.25). Category I (aspect ratio, cutoff ¼ 0.90) best differentiated femurs by sex (p < 0.001, AUC ¼ 0.80), and Category V (sulcus shape) best differentiated femurs by race (p < 0.001, AUC ¼ 0.73). This system uses simple measurements to summarize important individual, race, and sex-specific differences in distal femur shape. It can be used in a clinical setting to provide insight into the relationship between sex or race differences in knee shape and mechanically influenced knee disorders ß 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:924-931, 2016.Keywords: distal femur morphology; anatomic classification system; gender differences; race differences; knee mechanicsThe shape of the distal femur is an important determinant of knee mechanics, and knee morphology is often implicated in the pathogenesis of knee disorders such as tibiofemoral osteoarthritis (OA) and patellofemoral disorders. Tibiofemoral OA pathogenesis and progression is significantly influenced by knee joint shape and alignment. [1][2][3][4][5][6][7] Regarding the tibiofemoral joint, condylar alignment is associated with knee OA and is an important factor in in femoral component positioning for total knee arthroplasty (TKA). [8][9][10] For the patellofemoral joint, trochlear shape and tilt have been associated with patellar maltracking 11 and resulting lateral patellofemoral instability, 12 chondromalacia, 13 and arthritis 14 with a clinical classification system for trochlear "dysplasia" presented by Dejour et al. 12,15 Several race or sex-specific anatomic factors are either associated with knee disorder pathogenesis or present implant design challenges for TKA. Women have a higher incidence of trochlear dysplasia and increased trochlear tilt; 14,16,17 additionally, women have a smaller average articular surface area 18 and n...

The patellofemoral morphology and the normal predicted value of tibial tuberosity-trochlear groove distance in the Chinese population

“…Lonner and Gillespie et al indicated that the overall variability of the anatomy of the distal femur should be taken into account but not sex differences [ 16 , 17 ]. According to the individual differences, Everhart et al proposed a binary classification system to describe the shape of the distal femur and five binary categories were selected based on the aspect ratio, trochlear width, trochlear tilt, the ratio of medial and lateral trochlear width, and trochlear groove angle [ 47 ]. In addition, Varadarajan et al reported that the laterally oriented proximal part and medially oriented distal part formed the intact trochlear groove, and there was a turning point to distinguish these two parts [ 48 ].…”

Three-dimensional computed tomography mapping and analysis of distal femur fractures (AO/OTA types 33A, 33B, and 33C)

“…Finally, since all the data was from a single-centered database, only patients in a regional area were included in this study. Different regions, ethnicity, and social development might be potential influence factors (27) and should be taken into consideration in future studies. Nonetheless, this is the first study that systematically described the fracture characteristics of a large number of distal femur fractures (n=217).…”

The Three-Dimensional Morphology of the Patellofemoral Joint and the Normal Predicted Value of Tibial Tuberosity-Trochlear Groove Distance In Chinese Population

“…Lonner and Gillespie et al indicated that the overall variability of the anatomy of the distal femur should be taken into account but not gender difference [19,32]. According to the individual differences, Everhart et al proposed a binary classi cation system to describe the shape of the distal femur and ve binary categories were selected based on the aspect ratio, trochlear width, trochlear tilt, the ratio of medial and lateral trochlear width, and trochlear groove angle [14]. Besides, Varadarajan et al reported that the laterally oriented proximal part and medially oriented distal part formed the intact trochlear groove, and there was a turning point to distinguish these two part [48].…”