title: The envelope of passive motion allowed by the capsular ligaments of the hip.
abstract: Laboratory data indicate the hip capsular ligaments prevent excessive range of motion, may protect the joint against adverse edge loading and contribute to synovial fluid replenishment at the cartilage surfaces of the joint. However, their repair after joint preserving or arthroplasty surgery is not routine. In order to restore their biomechanical function after hip surgery, the positions of the hip at which the ligaments engage together with their tensions when they engage is required. Nine cadaveric left hips without pathology were skeletonised except for the hip joint capsule and mounted in a six-degrees-of-freedom testing rig. A 5 N m torque was applied to all rotational degrees-of-freedom separately to quantify the passive restraint envelope throughout the available range of motion with the hip functionally loaded. The capsular ligaments allowed the hip to internally/externally rotate with a large range of un-resisted rotation (up to 50±10°) in mid-flexion and mid-ab/adduction but this was reduced towards the limits of flexion/extension and ab/adduction such that there was a near-zero slack region in some positions (p<0.014). The slack region was not symmetrical; the mid-slack point was found with internal rotation in extension and external rotation in flexion (p<0.001). The torsional stiffness of the capsular ligamentous restraint averaged 0.8±0.3 N m/° and was greater in positions where there were large slack regions. These data provide a target for restoration of normal capsular ligament tensions after joint preserving hip surgery. Ligament repair is technically demanding, particularly for arthroscopic procedures, but failing to restore their function may increase the risk of osteoarthritic degeneration.
authors.affiliation: Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, Unitrd Kingdom.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: van Arkel
authors.affiliation: Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, Unitrd Kingdom; Musculoskeletal Surgery, Department of Surgery and Cancer, Imperial College London, Charing Cross Hospital, London W6 8RF, United Kingdom.
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amis
authors.affiliation: Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, Unitrd Kingdom. Electronic address: j.jeffers@imperial.ac.uk.
authors.forename: Jonathan R T
authors.initials: JR
authors.lastname: Jeffers
mesh_terms: D000368:Aged; D001182:Arthroscopy; D002102:Cadaver; D006621:Hip Joint / Q000502:physiology*; D006801:Humans; D017746:Joint Capsule / Q000502:physiology*; D008023:Ligaments, Articular / Q000502:physiology*; D008297:Male; D016059:Range of Motion, Articular; D012399:Rotation; D019415:Torque
keywords: Capsule; Hip; Ligaments; Range of motion; Slack