Faculty Profiles - KOBAYASHI Koichi

Papers - KOBAYASHI Koichi

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Three-dimensional evaluation of lower extremity alignment during gait and standing in healthy elderly individuals: A comparative study using fluoroscopy and 3D to 2D image matching. International journal

Tatsuya Soeno, Takashi Sato, Koichi Kobayashi, Ryota Katsumi, Kazutaka Otani, Hiroyuki Kawashima

Bio-medical materials and engineering 36 ( 4 ) 257 - 266 2025.7

Language：English Publishing type：Research paper (scientific journal)

BackgroundThe differences in bony alignment of the lower extremities during gait compared to standing remain unclear.ObjectiveThis study aimed to evaluate three-dimentional (3D) lower extremity alignment in healthy elderly individuals during the stance phase of gait and compare it with static standing alignment.MethodsThirty-four knees (9 females, 8 males; mean age 73.2 years) were assessed using single-plane X-ray fluoroscopy and a 3D to two-dimensional (2D) image matching technique. Alignment during stance phase and standing was evaluated in a world coordinate system, using the direction of gravity and frontal X-ray (aligned with the gait direction) as references.ResultsCompared to standing, the femur (3.5°), tibia (3.2°) and tibial joint line relative to the floor (3.3°) exhibited increased lateral inclination during stance phase (p < 0.01). In the transverse plane, the femur showed a significant increase in external rotation during stance phase (5.0°, p < 0.01) compared to standing, with no significant difference in tibial rotation.ConclusionLower extremity alignment significantly differs between static standing and gait, making it challenging to accurately infer the alignment during gait from standing assessments. This approach offers a practical means for assessing functional lower extremity alignment, potentially improving clinical outcomes in realignment surgeries.

DOI： 10.1177/09592989251315369

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Image-free robotic-assisted total knee arthroplasty is associated with joint line distalization and improves mid-flexion instability: A prospective cohort study. International journal

Keisuke Maeda, Tomoharu Mochizuki, Shigeru Takagi, Go Omori, Noriaki Yamamoto, Koichi Kobayashi, Hiroyuki Kawashima

Journal of experimental orthopaedics 12 ( 2 ) e70239 2025.4

Language：English Publishing type：Research paper (scientific journal)

PURPOSE: Total knee arthroplasty (TKA) has demonstrated long-term durability, with a significant reduction in revisions due to polyethylene wear and component loosening. However, mid-flexion instability (MFI) is a key factor in early TKA revisions, affecting patient satisfaction and implant longevity. Recent advancements in robotic-assisted TKA (raTKA) provide precise joint line (JL) restoration and component positioning, potentially reducing MFI. This prospective study evaluated the impact of image-free raTKA on MFI and JL restoration. METHODS: This prospective cohort study included 59 knees undergoing primary TKA using the image-free robotic systems NAVIO® and CORI® and the JOURNEY II® Bi-Cruciate Stabilized knee system. Intraoperative component gap (CG) measurements at 0°, 30°, 60° and 105° of flexion were taken, and JL changes were assessed pre- and post-operatively using computed tomography (CT)-based three-dimensional (3D) models with the 3D-3D matching technique. The distal femoral JL was quantified. RESULTS: Both the medial and lateral CG at 30° and 60° were significantly smaller compared to those at 0° and 105°. Post-operative JL showed distalization of 1.5 mm at the medial femur and 2.0 mm at the lateral femur compared to preoperative JL. CONCLUSIONS: This study is the first to assess JL restoration in raTKA using CT-based bone landmarks, offering precise insights. Image-free raTKA facilitates precise JL restoration, optimizing knee kinematics and enhancing stability. These findings suggest that this technique contributes to improved post-operative joint function and greater patient satisfaction. LEVEL OF EVIDENCE: Level II, prospective cohort study.

DOI： 10.1002/jeo2.70239

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Concept and Fabrication of Beta-Type Titanium Alloy Rod with Parts Possessing Different Young’s Moduli for Spinal Fixation Reviewed

Masaaki Nakai, Kengo Narita, Koichi Kobayashi, Keisuke Sasagawa, Mitsuo Niinomi, Kazuhiro Hasegawa

Journal of the Japan Institute of Metals and Materials 88 ( 12 ) 367 - 374 2024.12

成長期における跳躍型疲労骨折に関係する脛骨の彎曲と皮質骨厚の3次元評価

青木一磨, 林智彦, 渡邉聡, 林豊彦, 齋藤大寛, 齊藤将, 森清友亮, 古賀良生, 大森豪, 小林公一

臨床バイオメカニクス 45 60 - 66 2024.10

Accuracy of an image matching technique for assessing knee alignment during the stance phase of gait using single-plane anteroposterior radiography. International journal

Koichi Kobayashi, Makoto Sakamoto, Tatsuya Soeno, Takashi Sato

Bio-medical materials and engineering 2024.8

Language：English Publishing type：Research paper (scientific journal)

BACKGROUND: Accurate measurement of bone alignment of the knee during walking provides ideal clinical information for diagnosis and treatment of knee joint disorders. To bring this ideal closer to clinical reality, we developed an image matching technique to measure the three-dimensional (3D) position of bones using anteroposterior radiography during the stance phase of treadmill walking. OBJECTIVE: To develop and validate an image matching method for evaluation of 3D knee alignment using anteroposterior radiography of artificial femoral and tibial bones. METHODS: The 3D position of each bone was recovered by minimizing the difference between the projected outline and the contour of the bone in the anteroposterior radiograph. The true value of the position was measured using a 3D coordinate measuring machine. RESULTS: The mean values ± standard deviation and root mean squares (RMS) of translation errors were within -1.6 ± 2.1 mm and 2.6 mm, respectively, for femur, and 2.1 ± 1.9 mm and 2.8 mm for tibia. The mean values ± standard deviation and RMS of errors in rotation were within 0.3 ± 0.7° and 0.7°, respectively, for femur, and -0.3 ± 0.9° and 0.9°, respectively, for tibia. CONCLUSION: Our method is suitable for evaluating 3D knee alignment on anteroposterior radiography.

DOI： 10.3233/BME-240059

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Effects of three-dimensional femur and tibia postures on the parameters of standing long-leg radiographs for osteoarthritic knees in elderly female subjects. International journal

Kazutaka Otani, Takashi Sato, Koichi Kobayashi, Tomoharu Mochizuki, Osamu Tanifuji, Ryota Katsumi, Hiroyuki Kawashima

Clinical biomechanics (Bristol, Avon) 117 106297 - 106297 2024.7

Language：English Publishing type：Research paper (scientific journal)

BACKGROUND: Long-leg frontal radiographs of the lower extremities are used to assess knee osteoarthritis. Given the three-dimensional (3D) nature of alignment changes in osteoarthritis, postural alterations in the femur and tibia extend beyond the coronal plane (in-plane) to include the transverse and sagittal planes (out-of-plane). This study investigates the impact of these out-of-plane factors on in-plane knee alignment parameters observed in frontal radiographs. METHODS: A total of 97 osteoarthritic knees in women were examined. Using a 3D-to-two-dimensional (2D) image matching technique, we evaluated the 3D postures of the femur and tibia in the standing position as viewed from frontal radiographs in the world coordinate system. Statistical analyses were conducted to explore associations between these 3D postures and 2D alignment parameters obtained from frontal radiographs under identical conditions. FINDINGS: The femur exhibited a medial inclination of 2.7°, a posterior inclination of 3.9°, and an internal rotation of 4.2°, whereas the tibia showed a lateral inclination of 6.4°, an anterior inclination of 6.7°, and an internal rotation of 6.7°. Both coronal and rotational postures of femur and tibia influenced the hip-knee-ankle angle, mechanical axis percentage, and medial proximal tibial angle. However, only coronal factors of tibia impacted tibial joint line obliquity relative to the floor. INTERPRETATION: Attention should be paid to the potential impact of the out-of-plane postures of the femur and tibia on parameters assessed in plain frontal radiographs of the lower extremities.

DOI： 10.1016/j.clinbiomech.2024.106297

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Assessment of spinal alignment in standing position using Biplanar X-ray images and three-dimensional vertebral models

Koichi Kobayashi, Makoto Sakamoto, Keisuke Sasagawa, Masaaki Nakai, Masashi Okamoto, Kazuhiro Hasegawa, Kengo Narita

Porto Biomedical Journal 9 ( 3 ) 2024.5

Publishing type：Research paper (scientific journal) Publisher：Ovid Technologies (Wolters Kluwer Health)

Abstract

We developed two methods for three-dimensional (3D) evaluation of spinal alignment in standing position by image matching between biplanar x-ray images and 3D vertebral models. One used a Slot-Scanning 3D x-ray Imager (sterEOS) to obtain biplanar x-ray images, and the other used a conventional x-ray system and a rotating table. The 3D vertebral model was constructed from the CT scan data. The spatial position of the vertebral model was determined by minimizing the contour difference between the projected image of the model and the biplanar x-ray images. Verification experiments were conducted using a torso phantom. The relative positions of the upper vertebrae to the lowest vertebrae of the cervical, thoracic, and lumbar vertebrae were evaluated. The mean, standard deviation, and mean square error of the relative position were less than 1° and 1 mm in all cases for sterEOS. The maximum mean squared errors of the conventional x-ray system and the rotating table were 0.7° and 0.4 mm for the cervical spine, 1.0° and 1.2 mm for the thoracic spine, and 1.1° and 1.2 mm for the lumbar spine. Therefore, both methods could be useful for evaluating the spinal alignment in standing position.

DOI： 10.1097/j.pbj.0000000000000256

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3D Whiteside's Line計測健常膝と変形性膝関節症膝の検討

谷藤理, 望月友晴, 小林公一, 佐藤卓, 渡辺聡, 前田圭祐, 川島寛之

日本整形外科学会雑誌 97 ( 3 ) S853 - S853 2023.3

膝前後X線像による皮質骨幅測定の精度検証

高根沢佑斗, 森清友亮, 坂上勇太, 森隆裕, 古賀良生, 望月友晴, 古賀寛, 坂本信, 小林公一, 田邊裕治, 佐々木朋裕

臨床バイオメカニクス 43 253 - 257 2022.10

コーンビームCTを用いた上下顎歯の三次元歯軸角度の特徴

石井義人, 坂本信, 坂上勇太, 亀田剛, 森清友亮, 小林公一, 坂井幸子, 遠藤英昭, 平元和彦

臨床バイオメカニクス 43 339 - 344 2022.10

コーンビームCTを用いた上下顎歯の三次元歯軸角度の特徴

石井義人, 坂本信, 坂上勇太, 亀田剛, 森清友亮, 小林公一, 坂井幸子, 遠藤英昭, 平元和彦

臨床バイオメカニクス 43 339 - 344 2022.10

Assessment of knee collateral ligament stiffness by strain ultrasound elastography

Surangika Wadugodapitiya, Makoto Sakamoto, Masaei Tanaka, Yuta Sakagami, Yusuke Morise, Koichi Kobayashi

Bio-Medical Materials and Engineering 1 - 13 2022.3

Publishing type：Research paper (scientific journal) Publisher：IOS Press

BACKGROUND: Knowledge of the biomechanics of the normal collateral ligaments is important to secure optimal stability of the knee following injury. Various in vitro methods have been described in evaluating the biomechanics of these ligaments. However, a method of direct evaluation has not been reported. OBJECTIVE: To determine the stiffness characteristics of the collateral ligaments of the knee using strain ultrasound elastography. METHODS: Strain ultrasound elastography was performed on different components of the collateral ligaments in various angles of knee flexion in 18 healthy males (36 ligaments). We measured relative stiffness of the ligaments using strain ratio (SR = target tissue strain/reference strain). A lower strain ratio indicates higher relative stiffness. RESULTS: There was moderate to excellent intra- and inter-rater agreement for strain ratio measurements in all ligament portions. Strain ratios were lowest at 0° in all three ligaments, indicating high relative stiffness. In the superficial and deep medial collateral ligaments, the strain ratio increased with increasing knee flexion, whereas in the lateral collateral ligament, stiffness showed a tendency to fluctuate. CONCLUSION: Strain ultrasound elastography is a reliable tool for monitoring relative stiffness of the collateral ligaments of the knee and is easily applied to the routine clinical setting.

DOI： 10.3233/bme-211282

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Experimental determination of static and dynamic Young’s moduli of healthy and degenerated bovine articular cartilage using the split-Hopkinson pressure bar

Takahiro MORI, Hiroto SAKURAI, Koichi KOBAYASHI, Makoto SAKAMOTO, Yuji TANABE

Mechanical Engineering Journal 9 ( 2 ) 21 - 00400 2022

コーンビームCTによる三次元歯軸の解析

坂上勇太, 坂本信, 森清友亮, 亀田剛, 小林公一, 坂井幸子, 遠藤英昭, 田邊裕治

臨床バイオメカニクス 42 79 - 85 2021.10

荷重-非荷重における大腿骨脛骨間の相対位置変化解析変形性膝関節症の進行との関連

森清友亮, 森隆裕, 古賀良生, 望月友晴, 大森豪, 小林公一, 坂本信, 田邊裕治

臨床バイオメカニクス 42 63 - 66 2021.10

膝前後単純X画像における変形性膝関節症進行度の定量的評価システムの開発と信頼性の検討

森隆裕, 坂上勇太, 望月友晴, 古賀良生, 森清友亮, 古賀寛, 大森豪, 小林公一, 坂本信, 田邊裕治

臨床バイオメカニクス 42 39 - 43 2021.10

荷重-非荷重における大腿骨脛骨間の相対位置変化解析変形性膝関節症の進行との関連

森清友亮, 森隆裕, 古賀良生, 望月友晴, 大森豪, 小林公一, 坂本信, 田邊裕治

臨床バイオメカニクス 42 63 - 66 2021.10

膝前後単純X画像における変形性膝関節症進行度の定量的評価システムの開発と信頼性の検討

森隆裕, 坂上勇太, 望月友晴, 古賀良生, 森清友亮, 古賀寛, 大森豪, 小林公一, 坂本信, 田邊裕治

臨床バイオメカニクス 42 39 - 43 2021.10

コーンビームCTによる三次元歯軸の解析

坂上勇太, 坂本信, 森清友亮, 亀田剛, 小林公一, 坂井幸子, 遠藤英昭, 田邊裕治

臨床バイオメカニクス 42 79 - 85 2021.10

In vivo stiffness assessment of patellar and quadriceps tendons by strain ultrasound elastography

Surangika Wadugodapitiya, Makoto Sakamoto, Sayaka Suzuki, Yusuke Morise, Koichi Kobayashi

Bio-Medical Materials and Engineering 1 - 10 2021.5

Publishing type：Research paper (scientific journal) Publisher：IOS Press

BACKGROUND: The patellar and quadriceps tendons are responsible for the extension mechanism of the knee joint and frequently become inflamed during sports. Diagnosis and determination of when an athlete can return to sports following these injuries are usually performed by assessing morphological features and functional outcomes. Nevertheless, mechanical properties are not being assessed. OBJECTIVE: To describe the stiffness characteristics of these two tendons over the range of knee flexion and to test the feasibility of using strain ultrasound elastography (SE). METHODS: SE with an acoustic coupler as the reference was performed for nine healthy males. Relative stiffness measurements were obtained using the strain ratio (SR = target tissue strain/reference strain) by placing the knee in five different flexion angles. Lower SR indicates higher relative stiffness. RESULTS: This study showed reliable measurement with good intra- and inter-rater agreement for SR at 30°. SR of the quadriceps tendon decreases as knee flexion increases, indicating increased relative stiffness. In the patellar tendon, no significant difference was observed between 30° and 60°. Beyond 60°, relative stiffness increased constantly. CONCLUSIONS: SE is a reproducible and feasible tool to monitor relative stiffness of the patellar and quadriceps tendons in routine clinical settings.

DOI： 10.3233/bme-206016

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Papers - KOBAYASHI Koichi