title: Ruptured human Achilles tendon has elevated metabolic activity up to 1 year after repair.
abstract: OBJECTIVE
  Following Achilles tendon rupture, running is often allowed after 6 months. However, tendon healing is slow and the metabolic status of the tendon at this point is unknown. The purpose of this study was to investigate tendon metabolism (glucose uptake) and vascularization at 3, 6 and 12 months after Achilles tendon rupture as measured using PET and power Doppler ultrasonography (PDUS).
  
  
  METHODS
  The study group comprised 23 patients with surgically repaired Achilles tendon rupture who were investigated at 3 months (n = 7), 6 months (n = 7) and 12 months (n = 9) after surgery. The triceps surae complex was loaded over 20 min of slow treadmill walking while a radioactive tracer ((18)F-FDG) was administered prior to PET. Vascularization was measured in terms of PDUS flow activity, and patient-reported outcomes were scored using the Achilles tendon rupture score (ATRS) and sports assessment (VISA-A) questionnaire.
  
  
  RESULTS
  Relative glucose uptake ((18)F-FDG) was higher in repaired tendons than in intact tendons at all time-points (6, 3 and 1.6 times higher at 3, 6 and 12 months, respectively; P ≤ 0.001), and was also higher in the tendon core than in the periphery at 3 and 6 months (P ≤ 0.02), but lower at 12 months (P = 0.06). Relative glucose uptake was negatively related to ATRS at 6 months after repair (r = -0.89, P ≤ 0.01). PDUS flow activity was higher in repaired tendons than in intact tendons at 3 and 6 months (P < 0.05 for both), but had normalized by 12 months.
  
  
  CONCLUSIONS
  These data demonstrate that the healing process as determined by metabolic activity and vascularization continues for 6 months after injury when large loads are typically allowed on the tendon. Indeed, metabolic activity remained elevated for more than 1 year after injury despite normalized vascularization. The robust negative correlation between tendon metabolism and patient-reported outcome suggests that a high metabolic activity 6 months after the injury may be related to a poor clinical healing outcome.
authors.affiliation: Institute of Sports Medicine Copenhagen, Department of Ortopaedic Surgery, Bispebjerg Hospital, University Hospital of Copenhagen, Bldg. 8, Bispebjerg Bakke 23, DK-2400, Copenhagen NV, Denmark. pernilla.eliasson@gmail.com.
authors.forename: Pernilla
authors.initials: P
authors.lastname: Eliasson
authors.affiliation: Institute of Sports Medicine Copenhagen, Department of Ortopaedic Surgery, Bispebjerg Hospital, University Hospital of Copenhagen, Bldg. 8, Bispebjerg Bakke 23, DK-2400, Copenhagen NV, Denmark.|Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.|Musculoskeletal Rehabilitation Research Unit, Bispebjerg Hospital, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Couppé
authors.affiliation: Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: Markus
authors.initials: M
authors.lastname: Lonsdale
authors.affiliation: Institute of Sports Medicine Copenhagen, Department of Ortopaedic Surgery, Bispebjerg Hospital, University Hospital of Copenhagen, Bldg. 8, Bispebjerg Bakke 23, DK-2400, Copenhagen NV, Denmark.|Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: René B
authors.initials: RB
authors.lastname: Svensson
authors.affiliation: Metropol, School of Physiotherapy, Copenhagen, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Neergaard
authors.affiliation: Institute of Sports Medicine Copenhagen, Department of Ortopaedic Surgery, Bispebjerg Hospital, University Hospital of Copenhagen, Bldg. 8, Bispebjerg Bakke 23, DK-2400, Copenhagen NV, Denmark.|Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Michael
authors.initials: M
authors.lastname: Kjær
authors.affiliation: Department of Clinical Physiology and Nuclear Medicine, Bispebjerg Hospital, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Friberg
authors.affiliation: Institute of Sports Medicine Copenhagen, Department of Ortopaedic Surgery, Bispebjerg Hospital, University Hospital of Copenhagen, Bldg. 8, Bispebjerg Bakke 23, DK-2400, Copenhagen NV, Denmark.|Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.|Musculoskeletal Rehabilitation Research Unit, Bispebjerg Hospital, University Hospital of Copenhagen, Copenhagen, Denmark.
authors.forename: S Peter
authors.initials: SP
authors.lastname: Magnusson
mesh_terms: D000125:Achilles Tendon / Q000293:injuries* / Q000378:metabolism* / Q000601:surgery; D000328:Adult; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000493:pharmacokinetics*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D020127:Recovery of Function; D015203:Reproducibility of Results; D012421:Rupture / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000601:surgery*; D012680:Sensitivity and Specificity; D058971:Tenotomy; D014018:Tissue Distribution; D016896:Treatment Outcome
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG; ATRS; Healing; Loading; Positron emission tomography; Power Doppler ultrasonography