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Mechanical asymmetry during articulation of tibial and femoral cartilages: local and overall compressive and shear deformation and properties.

ABSTRACT: During knee movement, femoral cartilage articulates against cartilage from the tibial plateau, and the resulting mechanical behavior is yet to be fully characterized. The objectives of this study were to determine (1) the overall and depth-varying axial and shear strains and (2) the associated moduli, of femoral and tibial cartilages during the compression and shearing of apposing tibial and femoral samples. Osteochondral blocks from human femoral condyles (FCs) characterized as normal and donor-matched lateral tibial plateau (TP) were apposed, compressed 13%, and subjected to relative lateral motion. When surfaces began to slide, axial (-E(zz)) and shear (E(xz)) strains and compressive (E) and shear (G) moduli, overall and as a function of depth, were determined for femoral and tibial cartilages. Tibial -E(zz) was approximately 2-fold greater than FC -E(zz) near the surface (0.38 versus 0.22) and overall (0.16 versus 0.07). Near the surface, E(xz) of TP was 8-fold higher than that of FC (0.41 versus 0.05), while overall E(xz) was 4-fold higher (0.09 versus 0.02). For TP and FC, -E(zz) and E(xz) were greatest near the surface and decreased monotonically with depth. E for FC was 1.7-fold greater than TP, both near the surface (0.40 versus 0.24MPa) and overall (0.76 versus 0.47MPa). Similarly, G was 7-fold greater for FC (0.22MPa) than TP near the surface (0.03MPa) and 3-fold higher for FC (0.38MPa) than TP (0.13MPa) overall. These results indicate that tibial cartilage deforms and strains more axially and in shear than the apposing femoral cartilage during tibial-femoral articulation, reflecting their respective moduli.

SUBMITTER: Wong BL

PROVIDER: S-EPMC2882527 | biostudies-literature | 2010 Jun

REPOSITORIES: biostudies-literature

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Mechanical asymmetry during articulation of tibial and femoral cartilages: local and overall compressive and shear deformation and properties.

Wong Benjamin L BL Sah Robert L RL

Journal of biomechanics 20100415 9

During knee movement, femoral cartilage articulates against cartilage from the tibial plateau, and the resulting mechanical behavior is yet to be fully characterized. The objectives of this study were to determine (1) the overall and depth-varying axial and shear strains and (2) the associated moduli, of femoral and tibial cartilages during the compression and shearing of apposing tibial and femoral samples. Osteochondral blocks from human femoral condyles (FCs) characterized as normal and donor ...[more]

PMID: 20394929

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Project description:BACKGROUND:The mobile Oxford unicompartmental knee arthroplasty (UKA) implant has been widely used with an intramedullary guide for femoral preparation. We modified the femoral guide technique based on the tibial cut first and spacer block technique. This study was performed to determine the radiographic accuracy and early clinical outcomes of the extramedullary method. METHODS:We retrospectively evaluated 50 consecutive patients who underwent UKA using the extramedullary technique. An equal number of patients who underwent UKA with the conventional technique were matched as the control group. Clinical outcomes were evaluated in terms of the operating time, blood loss, range of motion, and Hospital for Special Surgery score. Radiographic accuracy was evaluated by the implant position and alignment in the coronal and sagittal planes. RESULTS:The mean follow-up period was 39.76 ± 5.77?months. There were no differences in the postoperative Hospital for Special Surgery score, range of motion, or hip-knee-ankle angle between the two groups. The operating time in the extramedullary group was shorter than that in the conventional group (54.78 ± 7.95 vs. 59.14 ± 10.91?min, respectively; p = 0.025). The drop in hemoglobin after 3?days was only 12.34 ± 4.98?g/L in the extramedullary group which was less than that in the conventional group (p = 0.001). No significant differences were found in the postoperative coronal and sagittal angles between the two groups. Acceptable radiographic accuracy of the implant alignment and position was achieved in 92% of patients in the extramedullary group and 96% of patients in the conventional group. CONCLUSIONS:The radiographic and clinical results of the extramedullary technique were comparable with those of the conventional technique with the advantage of no intramedullary interruption, less blood loss, a shorter operating time, and more rapid recovery. As the technique depends on the accurate tibial cut and overall alignment, we do not recommend it to surgeons without high volume experiences. TRIAL REGISTRATION:Retrospectively registered LEVEL OF EVIDENCE: IV, retrospective study.

Project description:Adhesion formation after flexor tendon repair remains a clinical problem. Early postoperative motion after tendon repair has been demonstrated to reduce adhesion formation while increasing tendon strength. It is hypothesized that during mobilization, tendon cells experience mechanical shear forces that alter their biology in a fashion that reduces scar formation but also activates key genes involved in tendon healing. To test this hypothesis, primary intrinsic tenocyte cultures were established from flexor tendons of 20 Sprague-Dawley rats and sheared at 50 rpm (0.41 Pa) using a cone viscometer for 6 and 12 hours. Total RNA was harvested and compared with time-matched unsheared controls using cDNA microarrays and Northern blot analysis. Microarray analysis demonstrated that mechanical shear stress induced an overall "antifibrotic" expression pattern with decreased transcription of collagen type I and collagen type III. Shear stress down-regulated profibrotic molecules in the platelet-derived growth factor, insulin-like growth factor, and fibroblast growth factor signaling pathways. In addition, shear stress induced an overall decrease in transforming growth factor (TGF)-beta signaling pathway molecules with down-regulation of TGF-beta2, TGF-beta3, TGF-RI, and TGF-RII expression. Moreover, sheared tendon cells increased expression of matrix metalloproteinases and decreased expression of tissue inhibitors of metalloproteinase, an expression pattern consistent with an antifibrotic increase in extracellular matrix degradation. However, up-regulation of genes implicated in tendon healing, specifically, vascular endothelial growth factor-A and several bone morphogenetic proteins. Interestingly, the known mechanoresponsive gene, TGF-beta1, also implicated in tendon healing, was differentially up-regulated by shear stress. Northern blot validation of our results for TGF-beta1, TGF-beta2, TGF-beta3, and collagen type I demonstrated direct correlation with microarray data. Groups of assays that are related as part of a time series. Computed

Dataset Information

Mechanical asymmetry during articulation of tibial and femoral cartilages: local and overall compressive and shear deformation and properties.

Publications

Mechanical asymmetry during articulation of tibial and femoral cartilages: local and overall compressive and shear deformation and properties.

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