title: Hip muscle weakness in patients with symptomatic femoroacetabular impingement.
abstract: OBJECTIVE
  Femoroacetabular impingement (FAI) is a pathomechanical process, which may cause hip pain, disability and early development of hip osteoarthritis (OA) in young and active adults. Patients with FAI experience functional disability during dynamic weight-bearing activities, which could originate from weakness of the hip muscles. The objective of this study was to compare hip muscle strength between patients with symptomatic FAI and healthy controls. It was hypothesized that patients would present overall hip muscle weakness compared to controls.
  
  
  METHODS
  A total of 22 FAI patients and 22 controls matched for gender, age, and body mass participated in the study. We evaluated isometric maximal voluntary contraction (MVC) strength of all hip muscle groups using hand-held and isokinetic dynamometry, and electromyographic (EMG) activity of the rectus femoris (RF) and tensor fasciae latae (TFL) muscles during active flexion of the hip.
  
  
  RESULTS
  FAI patients had significantly lower MVC strength than controls for hip adduction (28%), flexion (26%), external rotation (18%) and abduction (11%). TFL EMG activity was significantly lower in FAI patients compared with controls (P=0.048), while RF EMG activity did not differ significantly between the two groups (P=0.056).
  
  
  CONCLUSIONS
  Patients with symptomatic FAI presented muscle weakness for all hip muscle groups, except for internal rotators and extensors. Based on EMG recordings, it was demonstrated that patients with symptomatic FAI have a reduced ability to activate TFL muscle during hip flexion. These findings provide orthopedic surgeons with objective information about the amount and specificity of hip muscle weakness in patients with FAI. Future research should investigate the relationship between hip muscle weakness, functional disability and overuse injury risks, as well as the effects of hip muscle strengthening on clinical outcomes in individuals with symptomatic FAI.
authors.affiliation: Neuromuscular Research Laboratory, Schulthess Clinic, Zurich, Switzerland.
authors.forename: N C
authors.initials: NC
authors.lastname: Casartelli
authors.forename: N A
authors.initials: NA
authors.lastname: Maffiuletti
authors.forename: J F
authors.initials: JF
authors.lastname: Item-Glatthorn
authors.forename: S
authors.initials: S
authors.lastname: Staehli
authors.forename: M
authors.initials: M
authors.lastname: Bizzini
authors.forename: F M
authors.initials: FM
authors.lastname: Impellizzeri
authors.forename: M
authors.initials: M
authors.lastname: Leunig
mesh_terms: D000077:Acetabulum / Q000002:abnormalities*; D000328:Adult; D004576:Electromyography; D005260:Female; D005270:Femur Head / Q000002:abnormalities*; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D007592:Joint Diseases / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018908:Muscle Weakness / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*