title: Temporal healing in rat achilles tendon: ultrasound correlations.
abstract: The purpose of this study was to explore whether a new ultrasound-based technique correlates with mechanical and biological metrics that describe the tendon healing. Achilles tendons in 32 rats were unilaterally transected and allowed to heal without repair. At 7, 9, 14, or 29 days post-injury, tendons were collected and examined for healing via ultrasound image analysis, mechanical testing, and immunohistochemistry. Consistent with previous studies, we observe that the healing tendons are mechanically inferior (ultimate stress, ultimate load, and normalized stiffness) and biologically altered (cellular and ECM factors) compared to contralateral controls with an incomplete recovery over healing time. Unique to this study, we report: (1) Echo intensity (defined by gray-scale brightness in the ultrasound image) in the healing tissue is related to stress and normalized stiffness. (2) Elongation to failure is relatively constant so that tissue normalized stiffness is linearly correlated with ultimate stress. Together, 1 and 2 suggest a method to quantify mechanical compromise in healing tendons. (3) The amount and type of collagen in healing tendons associates with their strength and normalized stiffness as well as their ultrasound echo intensity. (4) A significant increase of periostin in the healing tissues suggests an important but unexplored role for this ECM protein in tendon healing.
authors.affiliation: Department of Orthopedics and Rehabilitation, University of Wisconsin, 1111 Highland Ave., 5059 WIMR, Madison, WI 53705, USA.
authors.forename: Connie S
authors.initials: CS
authors.lastname: Chamberlain
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Duenwald-Kuehl
authors.forename: Gregory
authors.initials: G
authors.lastname: Okotie
authors.forename: Sabrina H
authors.initials: SH
authors.lastname: Brounts
authors.forename: Geoffrey S
authors.initials: GS
authors.lastname: Baer
authors.forename: Ray
authors.initials: R
authors.lastname: Vanderby
mesh_terms: D000125:Achilles Tendon / Q000000981:diagnostic imaging* / Q000293:injuries / Q000503:physiopathology*; D000818:Animals; D001696:Biomechanical Phenomena; D001698:Biomedical Engineering; D015815:Cell Adhesion Molecules / Q000378:metabolism; D024042:Collagen Type I / Q000378:metabolism; D024061:Collagen Type III / Q000378:metabolism; D007150:Immunohistochemistry; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors; D014463:Ultrasonography; D014945:Wound Healing / Q000502:physiology*
chemical_list: D015815:Cell Adhesion Molecules; D024042:Collagen Type I; D024061:Collagen Type III; C512836:Postn protein, rat