title: Block-step asymmetry 5 years after large-head metal-on-metal total hip arthroplasty is related to lower muscle mass and leg power on the implant side.
abstract: BACKGROUND
  Metal-on-metal articulations mimic the human hip anatomy, presumably lower dislocation rates and increase the range-of-motion. This study aims to measure the muscle mass and power of both legs in patients with unilateral metal-on-metal total hip arthroplasty, and to investigate their effect on block-step test, spatio-temporal gait parameters and self-reported function.
  
  
  METHODS
  Twenty-eight patients (7 women), mean age 50 (28-68) years, participated in a 5-7 year follow-up. Patients had received one type unilateral large-head metal-on-metal total hip articulation, all of which were well-functioning at follow-up. Mean muscle mass was measured by the total-body Dual energy X-ray Absorption scans, and muscle power was measured in a leg extensor power rig. Block-step test and spatio-temporal gait parameters were measured with an inertial measurement unit. Self-reported function was assessed by the Hip Disability and Osteoarthritis Outcome Score.
  
  
  RESULTS
  We found a significant difference between the mean muscle mass of the implant-side leg and the non-implant-side leg in hip, thigh and calf areas (P<0.008) and in mean muscle power (P=0.025). Correlations between mean muscle mass and mean muscle power were significant for both the implant-side leg (r=0.45, P=0.018) and the non-implant-side leg (r=0.51, P=0.007). The difference in mean muscle power between legs correlated with block-step test asymmetry during ascending (r=0.40, P=0.047) and descending (r=0.53, P=0.006). Correlations between self-reported function and power of the implant-side leg were not significant.
  
  
  CONCLUSIONS
  Young patients have not fully regained muscle mass, muscle power and function 5-7 years after metal-on-metal total hip arthroplasty.
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark. Electronic address: mettehh20@gmail.dk.
authors.forename: M H
authors.initials: MH
authors.lastname: Hjorth
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Stilling
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark.
authors.forename: N D
authors.initials: ND
authors.lastname: Lorenzen
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark.
authors.forename: S S
authors.initials: SS
authors.lastname: Jakobsen
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark.
authors.forename: K
authors.initials: K
authors.lastname: Soballe
authors.affiliation: Department of Orthopaedics, Aarhus University Hospital, Tage-Hansens Gade 2, 8000 Aarhus C, Denmark.
authors.forename: I
authors.initials: I
authors.lastname: Mechlenburg
mesh_terms: D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D005500:Follow-Up Studies; D005684:Gait / Q000502:physiology*; D006622:Hip Prosthesis; D006801:Humans; D035002:Lower Extremity / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D015207:Osteoarthritis, Hip / Q000503:physiopathology / Q000601:surgery; D011474:Prosthesis Design
keywords: Dual energy X-ray Absorption scans; Functional motion test; Gait analyses; Metal-on-metal total hip arthroplasty; Muscle mass; Muscle power