Effect of acetabular labral tears, repair and resection on hip cartilage strain: A 7T MR study.

BACKGROUND: Tears of the acetabular labrum are frequently present in patients with groin pain. While it is clear that the labrum contributes to the surface area articulating with the femoral head, it is not clear whether labral repair yields different load distribution in the hip compared to labral resection. PURPOSE: Determine whether labral repair reduces cartilage strain more effectively than labral resection. METHODS: Six human cadaveric hips (mean age 37 years) were loaded in a simulated single-leg stance within the bore of a 7T MR scanner. After cartilage had reached a steady-state thickness distribution, a scan of the cartilage was acquired with a voxel size of 0.1x0.1x0.3mm. This method was repeated for each of six specimens when the labrum was intact, after a surgically simulated labral tear, after an arthroscopic labral repair and after labral resection. Cartilage thickness and strain in an anterosuperior region of interest were measured from the MR scans. A paired t-test was used to compare mean and maximum cartilage strain when the labrum was intact vs. torn, torn vs. repaired and repaired vs. resected. Three-dimensional patterns of cartilage strain distribution were qualitatively compared for the different labral conditions. RESULTS: For the number of specimens tested we found no change in mean and maximum cartilage strain, and little obvious change in the pattern of cartilage strain distribution after a simulated labral tear. Labral repair caused a 2% decrease in mean cartilage strain compared to a torn labrum (p=0.014). Labral resection caused a 4% and 6% increase in mean and maximum cartilage strain, respectively, compared to labral repair (p=0.02), and the cartilage strain distribution was elevated throughout the region of interest. CONCLUSION: Based on our ex vivo findings of increased cartilage strain after labral resection when compared to labral repair, we have demonstrated the associated consequences to the mechanical environment of the cartilage following surgical treatment of the labrum.

Pediatric and adult three-dimensional cervical spine kinematics: effect of age and sex through overall motion.

STUDY DESIGN: Cross-sectional study. OBJECTIVE: To determine the effect of age and sex on the three-dimensional kinematics of the cervical spine. SUMMARY OF BACKGROUND DATA: Spine kinematics information has important implications for biomechanical model development, anthropomorphic test device development, injury prevention, surgical treatment, and safety equipment design. There is a paucity of data of this type available for children, and it is unknown whether cervical spine kinematics of the pediatric population is different than that of adults. The helical axis of motion (HAM) of the spine provides unique information about the quantity and quality (coupling etc.) of the measured motion. METHODS: Ninety subjects were recruited and divided into 6 groups based on sex and age (young children aged 4-10 years, older children aged 11-17 years, adults aged 25+ years). Subjects actively moved their head in axial rotation, lateral bending, and flexion/extension. An optoelectronic motion analysis system recorded the position of infrared markers placed on the first thoracic vertebrae (T1) and on tight-fitting headgear worn by the subjects. HAM parameters were calculated for the head motion with respect to T1. RESULTS: HAM location in axial rotation and flexion/extension was more anterior in young females compared to adult females. Young females had a more anterior HAM location in flexion/extension compared to young males, indicating an effect of sex. For females, the HAM locations of adults were superior to those of children in flexion/extension and lateral bending whereas in males the HAM locations of adults were inferior to those of children. Age-related differences in HAM orientation were also observed in axial rotation and lateral bending. CONCLUSION.: Cervical spine kinematics vary with age and sex. The variation in spine mechanics based on age and sex found in the present study may indicate general trends that would grow stronger in even younger children (age <4 years).

The effect of donor age and low-dose gamma irradiation on the initial biomechanical properties of human tibialis tendon allografts.

BACKGROUND: Most tissue banks recover and irradiate tibialis tendon allografts from donors aged up to 65 years. It is unknown whether donor age and low-dose gamma irradiation affect the initial biomechanical properties of tibialis allografts. HYPOTHESIS: Donor age up to 65 years and low-dose gamma irradiation do not significantly affect the initial biomechanical properties of tibialis allografts. STUDY DESIGN: Controlled laboratory study. METHODS: One hundred twenty-six tibialis tendon allografts (63 pairs, 37 human donors) were divided into 3 age groups: young (<45 years), middle (46-55 years), and old (56-65 years). Within each age group, half of the paired tendons underwent tensile testing as single-strand grafts and the other half as double-strand grafts. One tendon from each donor pair was randomly assigned to undergo terminal sterilization with an absorbed dose of 1.46 to 1.80 Mrad (14.6-18.0 kGy) gamma irradiation, whereas the other tendon received no irradiation. All tendon grafts were preconditioned with a cyclic load and tested to failure in tension. RESULTS: Irradiated single-strand tendons in the old age group had a longer displacement at failure compared to the middle but not the young age group. Nonirradiated double-strand tendons in the old age group had a lower failure stress. Single-strand irradiated old tendons had a lower stiffness, and all irradiated young tendons and old double-strand tendons had a higher failure stress compared to nonirradiated tendons. CONCLUSION: Donor age up to 65 years does not significantly affect the initial failure load, stiffness, or displacement at failure of tibialis allografts. An age-related decrease in failure stress was observed among nonirradiated tendons but not in tendons subjected to irradiation. CLINICAL RELEVANCE: The results provide biomechanical evidence for use of tibialis allografts from donors up to 65 years of age. Low-dose gamma irradiation does not negatively influence the initial biomechanical properties of tibialis allografts. Further studies examining age and irradiation effects after submaximal cyclic loading conditions are recommended.