2015 ISAKOS Biennial Congress ePoster #310

The Validation of a Novel Indentation Sensor for Arthroscopic Measurement of Cartilage Stiffness

Yuki Kitta, MD, Tokyo JAPAN
Takeo Nagura, MD, PhD, Tokyo JAPAN
Yoshimori Kiriyama, PhD, Tokyo JAPAN
Kengo Harato, MD, PhD, Tokyo JAPAN
Yasuo Niki, MD, PhD, Tokyo JAPAN
Yasunori Suda, Prof, Yaita-Shi, Tochigi Prefecture JAPAN
Yoshiaki Toyama, MD, PhD, Shinjyuku JAPAN

Department of Orthopedic Surgery, Keio University, Tokyo, JAPAN

FDA Status Cleared

Summary: VENUSTRON system is useful tool to measure the stiffness of cartilage under arthroscopic control

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Abstract:

Introduction

Evaluation of mechanical properties of the articular cartilage is essential to identify physiological and pathological condition of the joint. Several devices have been developed and used to measure the stiffness of cartilage under arthroscopic control in adults. Uchio et al (2002) reported the cartilage stiffness of the femoral condyle and patella using an ultrasonic tactile sensor. However, there have been limited data on the material properties of cartilage especially in children who are in growth period. A novel indentation sensor was developed to evaluate mechanical property of the articular cartilage during surgery. In this study, we have evaluated validation of the arthroscopic indentation sensor.

Methods

VENUSTRON system (Axiom, Sendai, Japan) is an indentation sensor system to measure the stiffness of the cartilage under arthroscopy. The system consists of 4mm sensor with 8mm outer guide.
1) Validation of stiffness measurement and repeatability;
The Stiffness of a material with known material properties (PE light, Young’s module 0.43±0.1MPa) was measured by the VENUSTRON system. The maximum displacement and pressure to calculate Young’s module of the material were set at 1.0mm and 450gram. The stiffness of PE light was measured at thickness of 2mm to 10mm with a 2mm interval. The measurement were repeated for 3 times at each thickness, to evaluate repeatability.
2) Effect of angle and contact in device placement
The Stiffness of articular cartilage of the medial and lateral femoral condyles of three human cadaveric knees was measured by the VENUSTRON system. VENUSTRON was inclined from 0 to 20 degrees with 1 degree interval. A custom made device holder was used which is able to alter indentation angle. Also, indentation was evaluated with two contact modes; shallow and deep contacts with the cartilage, respectively.

Results

1) Young’s module of the material (PE light) were 1.15-1.24 (mean 1.20) MPa. There were no difference in the measured Young’s module with the material due to the difference of thickness between 2-10mm. Inter-class correlation coefficients (ICCs) in repeated measurements using the material were 0.83-0.99.
2) The force-displacement curves were constant among 0 to 20 degrees of device inclinations with shallow touching to the articular cartilage. On the other hand, the curves reached the pressure limit before 1.0mm displacement with deep contact to the cartilage.

Discussion

Since the VENUSTRON system is manually held during the measurement, there is a concern for validity and repeatability to assess material properties of the cartilage. The limitation of measuring the stiffness of articular cartilage was to avoid deep contact with the cartilage while it was highly repeatable when we contact the device gently with non-vertical position until 20 degrees. Regarding the difference and high repeatability (ICCs 0.83-0.99), the VENUSTRON system is an useful tool to measure material property of the articular cartilage under arthroscopy.