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Research Papers

# MRI-Based Characterization of Bone Anatomy in the Human Knee for Size Matching of a Medial Meniscal Implant

[+] Author and Article Information
Jonathan J. Elsner1

Research & Development Center, Active Implants Corporation, Netanya 42505, Israeljon.elsner@activeimplants.com

Sigal Portnoy, Avi Shterling, Eran Linder-Ganz

Research & Development Center, Active Implants Corporation, Netanya 42505, Israel

Farshid Guilak

Duke University Medical Center, Durham, NC 27710

http://www.oai.ucsf.edu/(Data set O.A.2)

1

Corresponding author.

J Biomech Eng 132(10), 101008 (Oct 01, 2010) (11 pages) doi:10.1115/1.4002490 History: Received June 24, 2010; Revised August 17, 2010; Posted September 01, 2010; Published October 01, 2010; Online October 01, 2010

## Abstract

Allograft or synthetic menisci have been suggested as a means to restore contact pressures following meniscectomy. However, when the natural meniscus is severely damaged/absent, the necessary size cannot be determined according to the recipient size and there is a need to estimate it from magnetic resonance imaging (MRI) of the contralateral knee or the injured knee bones. The use of the contralateral-knee for size matching is problematic due to economic and practical reasons. Hence, there are significant advantages for a sizing algorithm based only on the candidate knee geometry. The aim of this study is to characterize midrange values and variability of knee dimensions and to develop a set of mathematical relations representing knee dimensions using a minimum of imaging-based bone measurements. Tibia, femur, and meniscus measurements were taken in 118 MRI scans and used to develop a representative parametric knee model in which all dimensions are expressed using tibia plateau width. The model was verified by comparing the predicted values to direct MRI measurements for 20 additional subjects by means of the Pearson correlation and Bland and Altman (1986, “Statistical Methods for Assessing Agreement Between Two Methods of Clinical Measurement,” Lancet, 1, pp. 307–310) plot. Anatomical parameters in the male knee were significantly larger $(∼17%)$ compared with corresponding female measurements. However, most relations between tibia, femur, and meniscus measurements (43/56) were not significantly different between male and female populations $(p≥0.05)$, indicating that differences between male and female joints are generally related to scaling and not shape. Dimensions predicted by the knee model were in a good agreement with dimensions measured directly from the MRI $(R2>0.96)$ and the Bland and Altman plot indicated that $∼95%$ of data points were well within the ±2 standard deviation lines of agreement. The model proposed in this study is advantageous in being able to describe typical knee proportions for a given tibial width and can be used to predict the dimensions of a candidate knee based on a single measurement. The anatomical/anthropometric data presented in the study can be utilized in a sizing algorithm for artificial meniscal implants or in the design of artificial meniscus prostheses.

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## Figures

Figure 1

Description of (a) Z and X axes and (b) Y-axis orientations defined for the tibia and femur compartments

Figure 2

Description of the anatomical coordinate system and measurement planes used for (a) femur and (b) tibia compartments

Figure 3

Examples of (a) coronal, (b) sagittal, (c) femur condyles area, (d) tibial plateau area, and (e) meniscus measurements

Figure 4

Comparison of tibia measurements in male and female; total and medial tibial plateau width, measured in middle (TPW and MW), anterior (TPWA and MWA), and posterior (TPWP and MWP) planes of the tibia, as well as medial length measured in middle (ML), medial (MLM), and lateral (MLL) planes compared; significant difference was found in all measures (p<0.05)

Figure 5

Comparison of femur measurements in male and female; total and medial femur width measured in middle (FCW and FW), anterior (FCWA and FWA), and posterior (FCWP and FWP) planes of the femur, as well as medial length measured in middle (FL), medial (FLM), and lateral (FLL) planes compared; significant difference was found in all measures (p<0.05)

Figure 6

Comparison of medial meniscus measurements in male and female; medial meniscus width measured in middle (MMW), anterior (MMWA), and posterior (MMWP) planes of the tibia, as well as medial meniscus length measured in middle (MML), medial (MMLM), and lateral (MMLL) planes compared; significant difference was found in all measures (p<0.05)

Figure 7

Comparison of tibia, femur, and medial meniscus projected area measurements in male and female; total (TA) and medial (TMA) tibial plateau area, total (FA) and medial (FMA) femur condyles area, and medial meniscus area (MMA) were compared; significant difference was found in all measures (p<0.05)

Figure 8

Verification of the predicted dimensions (resulted from the parametric model) against direct measurements from MRI scans conducted in 20 independent subjects: (a) predicted dimensions calculated by the parametric model plotted versus the direct measurements taken from MRI scans separated to male and female groups. The unity line, indicating a theoretical perfect agreement between the two measurement systems, is depicted as a dashed line. (b) Average-difference plot (Bland and Altman) depicts the agreement between predicted dimensions calculated using the parametric model and direct measurements from MRI scans.

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