title: Capsulotomy Size Affects Hip Joint Kinematic Stability.
abstract: To evaluate the effect of capsulotomy size and subsequent repair on the biomechanical stability of hip joint kinematics through external rotation of a cadaveric hip in neutral flexion.
  
  
  
  Eight fresh-frozen cadaveric hip specimens were used in this study. Each hip was tested under torsional loads of 6 N·m applied by a servohydraulic frame and transmitted by a pulley system. The test conditions were (1) neutral flexion with the capsule intact, (2) neutral flexion with a 4-cm interportal capsulotomy, (3) neutral flexion with a 6-cm capsulotomy, and (4) neutral flexion with capsulotomy repair. Soft tissue was retained during all interventions. Measures indicating joint kinematics (range of motion [ROM], hysteresis area [HA], and neutral zone [NZ]) were obtained for each condition.
  
  
  
  For all hip specimens, the average ROM, HA, and NZ were calculated relative to the intact capsular state (100%) and expressed in terms of percentage (± SD). The findings for ROM were as follows: intact, 100%; 4 cm, 107.42% ± 5.69%; 6 cm, 113.40% ± 7.92%; and repair, 99.78% ± 3.77%. The findings for HA were as follows: intact, 100%; 4 cm, 108.30% ± 9.30%; 6 cm, 115.30% ± 13.92%; and repair, 99.47% ± 4.12%. The findings for NZ were as follows: intact, 100%; 4 cm, 139.61% ± 62.35%; 6 cm, 169.25% ± 78.19%; and repair, 132.03% ± 64.38%. Statistically significant differences in ROM existed between the intact and 4-cm conditions (P = .039), the intact and 6-cm conditions (P < .0001), the 4-cm and repair conditions (P = .033), and the 6-cm and repair conditions (P < .0001). There was no statistically significant difference between the intact and repair conditions (P > .99) or between the 4- and 6-cm conditions (P = .126).
  
  
  
  Under laboratory-based conditions, larger-sized capsulotomies were accompanied by increases in all 3 measures of joint mobility: ROM, HA, and NZ at time zero. Complete capsular closure effectively restored these measures when compared with the intact condition.
  
  
  
  Cadaveric models consisting of the hip joint with surrounding soft tissue were used under laboratory testing conditions to investigate potential iatrogenic joint instability resulting from expansive capsulotomies, showing that complete capsular closure leads to reconstitution of original joint stability properties at time zero.
authors.affiliation: Center for Hip Preservation, Division of Sports Medicine, New England Baptist Hospital, Boston, Massachusetts, U.S.A.
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Wuerz
authors.affiliation: Hip Preservation Center, Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Rush Medical College of Rush University, Chicago, Illinois, U.S.A.
authors.forename: Sang H
authors.initials: SH
authors.lastname: Song
authors.affiliation: Hip Preservation Center, Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Rush Medical College of Rush University, Chicago, Illinois, U.S.A.
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Grzybowski
authors.affiliation: Hip Preservation Center, Baylor University Medical Center, Dallas, Texas, U.S.A.
authors.forename: Hal D
authors.initials: HD
authors.lastname: Martin
authors.affiliation: Department of Orthopedic Surgery, Duke University Medical Center, Durham, North Carolina, U.S.A.
authors.forename: Richard C
authors.initials: RC
authors.lastname: Mather
authors.affiliation: Department of Orthopedic Surgery, University Hospitals Case Medical Center, Cleveland, Ohio, U.S.A.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Salata
authors.affiliation: Hip Preservation Center, Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Rush Medical College of Rush University, Chicago, Illinois, U.S.A.
authors.forename: Alejandro A
authors.initials: AA
authors.lastname: Espinoza Orías
authors.affiliation: Hip Preservation Center, Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Rush Medical College of Rush University, Chicago, Illinois, U.S.A.. Electronic address: Shane.nho@rushortho.com.
authors.forename: Shane J
authors.initials: SJ
authors.lastname: Nho
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D006801:Humans; D057913:Joint Capsule Release; D007593:Joint Instability / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000503:physiopathology*; D016059:Range of Motion, Articular; D012399:Rotation