Anthropometric Measurement of Caucasian and Asian Knees, Mismatch with Knee Systems?

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Background:Positioning and fit of the knee prostheses in patients determines functional outcome. For that matter anthropometric differences between knee joints of patients, will affect function. Since most total knees implant systems are designed for caucasians, discrepancies in matching to Asian patients might exist, with consequently less optimal fit of the implant. The aim of this study was to evaluate differences in anthropometric dimensions between Caucasian and Asian knees of patients eligible for total knee arthroplasty.Materials and Methods:134 patients were included for radiographic anthropometric measurements on distal femurs, proximal tibia and patellar dimension were measured of 67 Caucasian and 67 Asian patients. Patient groups were age and gender matched. All radiographs were obtained preoperatively prior to total knee arthroplasty at two different centers, Jakarta and Leiden. The radiographic measurements were widest anteroposterior (AP) and widest mediolateral (ML) dimensions, aspect ratio (ML/AP), patellar length and patellar tendon length, patellar tendon/patella ratio. Sizes of eight knee implant designs (Vanguard, Genesis II, Persona -standard and narrow-, GK Sphere, Gemini, Attune and Sigma PFC) were collected from manufactures brochures and compared to the anthropometric measurements. Chi-Square test, student t-test and Bayesian statistics were used to compare differences between the two populations.Results:The mean age of the Caucasian group was 68 ± 7.1 years and the Asian patients were 67 ± 7.8 years. Both groups included 14.9% males and 85.1% females. The Dutch patients had a height of 166cm (sd 8.1 cm) the Indonesian patients 156 cm (sd 8.0 cm), the Dutch being 6.4% taller. Preoperative deformities in the Asians was predominantly into varus, while the Dutch patients had a slight valgus alignment; 90% of the KL scores were grade 3 and 4, comparable in both groups. In AP and ML the Caucasian femur is larger than the Asian femur (male-AP 12%, female-AP 15%, male-ML 6%, female-ML 9%). The Caucasian tibia is larger in AP and ML dimensions compared to the Asian patient’s tibia. The ML/AP aspect ratios were significantly different (p<0.0001) between Asian and Caucasian patients, with the ML/AP aspect ratio of both the femur and the tibia being larger in Asian patients 1.4 (sd 0.10) compared to Caucasians 1.3 (sd 0.10) for the femur. As for the tibia the aspect ratio in Asian patients is 1.5 (sd 0.11); Caucasians 1.3 (0.11). The Asian patients have a relative patella baja compared to the Caucasians. Good matching to the tibial aspect ratios (ML/AP) of Dutch and Indonesian patients appeared to present to the eight knee systems but to only three knee systems matched well to the femoral aspect ratios (ML/AP).Conclusion:Absolute and relative differences of knee dimensions exist between Caucasian and Asian knees. Caucasian has larger AP and ML for both tibial and femoral but smaller in aspect ratio for both tibia and femur compared to Asian patients. With respect to the fit of the implant to the natural knee, total knee arthroplasty remains a compromise to nature