Abstract
Background:The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading. We hypothesized that following total hip arthroplasty (THA), the reduced femoral head size impairs this protective biomechanical function.Methods:In cadavers, THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. Eight hips were examined. Capsular function was measured by rotating the hip in 5 positions. Three head sizes (28, 32, and 36 mm) with 3 neck lengths (anatomical 0, +5, and +10 mm) were compared.Results:Internal and external rotation range of motion increased following THA, indicating late engagement of the capsule and reduced biomechanical function (p < 0.05). Internal rotation was affected more than external. Increasing neck length reduced this hypermobility, while too much lengthening caused nonphysiological restriction of external rotation. Larger head sizes only slightly reduced hypermobility.Conclusions:Following THA, the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion. The posterior capsule was the most affected, indicating that native posterior capsule preservation is not advantageous, at least in the short term. Insufficient neck length could cause capsular dysfunction even if native ligament anatomy is preserved, while increased neck length could overtighten the anterior capsule.Clinical Relevance:Increased understanding of soft-tissue balancing following THA could help to prevent instability and improve early function. This study illustrates how head size and neck length influence the biomechanical function of the hip capsule in the early postoperative period.
Highlights
The hip joint capsule passively restrains extreme range of motion, protecting the native hip against impingement, dislocation, and edge-loading
Following total hip arthroplasty (THA), the capsular ligaments were unable to wrap around the reduced-diameter femoral head to restrain extreme range of motion
M any surgical approaches for total hip arthroplasty (THA) aim to maximize capsule preservation[1,2,3,4,5,6,7,8,9,10] and/or repair capsule incisions[1,2,3,4,5,6,7,8,9], while others excise the capsule to improve exposure, as it is considered of little consequence[11,12]
Summary
THA was performed through the acetabular medial wall, preserving the entire capsule, and avoiding the targeting of a particular surgical approach. The hips were mounted into a 6degrees-of-freedom testing rig (Fig. 2) using an established protocol[24]. This rig adopted the International Society of Biomechanics coordinate system[25] and allowed either for flexionextension or abduction-adduction torques to be applied through pulleys with hanging weight couples, or for these axes to be fixed at specific angular positions with screw clamps[19,22]. Internal-external rotations were applied using the rotating axes of a dual-axis servohydraulic materials testing machine (model 8874; Instron) equipped with a 2-degrees-of-freedom (tension-torque) load-cell, allowing the passive restraint to hip rotation from the capsular ligaments to be measured. Internal-external rotations were applied using the rotating axes of a dual-axis servohydraulic materials testing machine (model 8874; Instron) equipped with a 2-degrees-of-freedom (tension-torque) load-cell, allowing the passive restraint to hip rotation from the capsular ligaments to be measured19,22. e94(3) Name Position Rationale
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
