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KNEE SOFT TISSUE TIGHTENING AND ORIENTATION IN INTACT AND PROSTHETIC KNEE IN NAVIGATED TOTAL KNEE ARTHROPLASTY: AN IN-VITRO STUDY
Presentation 0299, Knee Replacement. 8:30, Room 201ABC
S60
KNEE SOFT TISSUE TIGHTENING AND ORIENTATION IN INTACT AND PROSTHETIC KNEE IN NAVIGATED TOTAL KNEE ARTHROPLASTY: AN IN-VITRO STUDY. 1
C Belvedere1, A Leardini1, A Ensini2, L Bianchi2, F Catani2, S Giannini2 Movement Analysis Laboratory and 2Departement of Orthopaedic Surgery, Istituti Ortopedici Rizzoli, Bologna, Italy email: [email protected], web: www.ior.it
INTRODUCTION The anterior (ACL), the posterior (PCL) cruciate, the medial (MCL) and the lateral (LCL) collateral ligaments of the human knee play the important role of guiding and stabilizing the joint in full tibio-femoral extension and flexion [1]. Patellar tendon (PT) also plays an essential role as part of the extensor apparatus. Knee ligament tightening at appropriate flexion angles is one of the targets for a successful total knee arthroplasty (TKA), since slacken or tighten soft tissues can result in restricted and not natural knee motion. The aim of this in-vitro study is to identify differences in slackening/tightening patterns, between intact and prosthetic knee, by means of a navigation system during in-vitro TKA. METHODS Six fresh-frozen amputated legs with the knee free from anatomical defects and with intact joint capsule, ligaments, and quadriceps tendon were analysed using the Stryker® Knee Navigation System (Kalamazoo, MI-USA). Standard clusters with active markers were pinned on the femur and tibia. The standard pointer was used for system control, and digitations of anatomical landmarks and bone-ligament attachments. Bony landmarks were used to define the anatomical frames for the femur and tibia [2]. Series of five trials of manually driven flexions were performed and collected under condition of 10 kg on the quadriceps, with intact knee and after TKA. Bone-ligament attachments were digitised after the identification of sub-bundles attachments [3]. In the cruciate ligaments and MCL, two sub-bundles were identified: the anteo-medial (AM) and the postero-lateral (PL) in the ACL, the antero-lateral (AL) and the postero-medial (PM) in the PCL, the anterior (AB) and the posterior (PB) bundles in the MCL. Strips of points along the most anterior and the most posterior fibres in the LCL; along the most anterior and the most posterior fibres of AB in the MCL; along the most medial, central and lateral fibres in the PT were also digitized.
fibres after TKA are less vertical, 10°on average, than those in the intact knee (see figure). IF was located inside PM. No relevant differences were seen at the collaterals.
Figure: Lengthening of PCL fibers in intact and prosthetic knee. The yellow bands indicates the standard deviations. Not a real isometric fibre was detected at the LCL. In the MCL, AB and PB tighten in contrast over flexion, with PB deepest fibres being the most isometric. At the PT, fibre tightening occurs in the initial 60° flexion in the intact knee, in the initial 30° after TKA. On the sagittal plane, orientation excursion of the PT fibres was 30° on average over flexion in the intact knee, less than 5° after TKA.
The centroids of the attachments were considered as origins and insertions of single fibres that are representative for the whole ligament or sub-bundles. For each trial group, mean value and standard deviation of fibre length were calculated at each single degree of flexion by linear interpolation. Moreover, also the attachment and the length of the most isometric fibre for all ligaments and PT was considered [1].
CONCLUSIONS Ligament fibre bundles play different and important roles over knee flexion, but these were found considerably affected by TKA. Prosthesis component malpositioning can alter the natural tightening, contributing to alter mobility and stability, which can result also in knee pain. In the future, by frequently monitoring the tightening state of knee soft tissue during a standard TKA through a navigation system, those factors, altering the flexor/extensor mechanism and the effectiveness of the stabilizing effect of knee ligaments, can be recognized and corrected intraoperatively.
RESULTS AND DISCUSSION In the intact knee, AM and PL were tight only in full extension, and IF was found within AM. For the PCL, TKA results in a delay of AL tightening and in an anticipation of PM slackening. On the sagittal plane, PCL
REFERENCES 1. Zavras TD, et al. Knee Surg Sports Traumatol Arthrosc 9, 28-33, 2001. 2. Cappozzo A, et al. Clin Biomech 10, 171-178, 1995. 3. Harner CD, et al. Arthroscopy 15, 741-749, 1999.
Journal of Biomechanics 40(S2)
XXI ISB Congress, Podium Sessions, Monday 2 July 2007
S60
KNEE SOFT TISSUE TIGHTENING AND ORIENTATION IN INTACT AND PROSTHETIC KNEE IN NAVIGATED TOTAL KNEE ARTHROPLASTY: AN IN-VITRO STUDY. 1
C Belvedere1, A Leardini1, A Ensini2, L Bianchi2, F Catani2, S Giannini2 Movement Analysis Laboratory and 2Departement of Orthopaedic Surgery, Istituti Ortopedici Rizzoli, Bologna, Italy email: [email protected], web: www.ior.it
INTRODUCTION The anterior (ACL), the posterior (PCL) cruciate, the medial (MCL) and the lateral (LCL) collateral ligaments of the human knee play the important role of guiding and stabilizing the joint in full tibio-femoral extension and flexion [1]. Patellar tendon (PT) also plays an essential role as part of the extensor apparatus. Knee ligament tightening at appropriate flexion angles is one of the targets for a successful total knee arthroplasty (TKA), since slacken or tighten soft tissues can result in restricted and not natural knee motion. The aim of this in-vitro study is to identify differences in slackening/tightening patterns, between intact and prosthetic knee, by means of a navigation system during in-vitro TKA. METHODS Six fresh-frozen amputated legs with the knee free from anatomical defects and with intact joint capsule, ligaments, and quadriceps tendon were analysed using the Stryker® Knee Navigation System (Kalamazoo, MI-USA). Standard clusters with active markers were pinned on the femur and tibia. The standard pointer was used for system control, and digitations of anatomical landmarks and bone-ligament attachments. Bony landmarks were used to define the anatomical frames for the femur and tibia [2]. Series of five trials of manually driven flexions were performed and collected under condition of 10 kg on the quadriceps, with intact knee and after TKA. Bone-ligament attachments were digitised after the identification of sub-bundles attachments [3]. In the cruciate ligaments and MCL, two sub-bundles were identified: the anteo-medial (AM) and the postero-lateral (PL) in the ACL, the antero-lateral (AL) and the postero-medial (PM) in the PCL, the anterior (AB) and the posterior (PB) bundles in the MCL. Strips of points along the most anterior and the most posterior fibres in the LCL; along the most anterior and the most posterior fibres of AB in the MCL; along the most medial, central and lateral fibres in the PT were also digitized.
fibres after TKA are less vertical, 10°on average, than those in the intact knee (see figure). IF was located inside PM. No relevant differences were seen at the collaterals.
Figure: Lengthening of PCL fibers in intact and prosthetic knee. The yellow bands indicates the standard deviations. Not a real isometric fibre was detected at the LCL. In the MCL, AB and PB tighten in contrast over flexion, with PB deepest fibres being the most isometric. At the PT, fibre tightening occurs in the initial 60° flexion in the intact knee, in the initial 30° after TKA. On the sagittal plane, orientation excursion of the PT fibres was 30° on average over flexion in the intact knee, less than 5° after TKA.
The centroids of the attachments were considered as origins and insertions of single fibres that are representative for the whole ligament or sub-bundles. For each trial group, mean value and standard deviation of fibre length were calculated at each single degree of flexion by linear interpolation. Moreover, also the attachment and the length of the most isometric fibre for all ligaments and PT was considered [1].
CONCLUSIONS Ligament fibre bundles play different and important roles over knee flexion, but these were found considerably affected by TKA. Prosthesis component malpositioning can alter the natural tightening, contributing to alter mobility and stability, which can result also in knee pain. In the future, by frequently monitoring the tightening state of knee soft tissue during a standard TKA through a navigation system, those factors, altering the flexor/extensor mechanism and the effectiveness of the stabilizing effect of knee ligaments, can be recognized and corrected intraoperatively.
RESULTS AND DISCUSSION In the intact knee, AM and PL were tight only in full extension, and IF was found within AM. For the PCL, TKA results in a delay of AL tightening and in an anticipation of PM slackening. On the sagittal plane, PCL
REFERENCES 1. Zavras TD, et al. Knee Surg Sports Traumatol Arthrosc 9, 28-33, 2001. 2. Cappozzo A, et al. Clin Biomech 10, 171-178, 1995. 3. Harner CD, et al. Arthroscopy 15, 741-749, 1999.
Journal of Biomechanics 40(S2)
XXI ISB Congress, Podium Sessions, Monday 2 July 2007