ABSTRACT:The anterior cruciate ligament (ACL) fails to heal after suture repair. One hypothesis for this failure is the premature loss of the fibrin clot, or provisional scaffolding, between the two ligament ends in the joint environment. To test this hypothesis, a substitute provisional scaffold of collagen-platelet rich plasma (PRP) hydrogel was used to fill the ACL wound site at the time of suture repair and the structural properties of the healing ACLs evaluated 4 weeks after surgery. Bilateral ACL transections were performed in five 30-kg Yorkshire pigs and treated with suture repair. In each animal, one of the repairs was augmented with placement of a collagen-PRP hydrogel at the ACL transection site, while the contralateral knee had suture repair alone. In addition, six control knees with intact ACLs from three additional animals were used as a control group. No postoperative immobilization was used. After 4 weeks the animals underwent in vivo magnetic resonance imaging to assess the size of the healing ACL, followed by biomechanical testing to determine tensile properties. The supplementation of suture repair with a collagen-PRP hydrogel resulted in significant improvements in load at yield, maximum load, and linear stiffness at 4 weeks. We conclude that use of a stabilized provisional scaffold, such as a collagen-PRP hydrogel, to supplement primary repair of the ACL can result in improved biomechanical properties at an early time point. Further studies to determine the long-term effect of primary repair enhancement are needed. ß

The anterior cruciate ligament (ACL) of the knee fails to heal after primary repair. Here we hypothesize that a beneficial biologic repair response can be induced by placing a collagen-platelet rich plasma (collagen-PRP) material into a central ACL defect. A collagen-PRP scaffold was used to treat a central ACL defect in vivo. In the first experiment, the histologic response in treated and untreated defects was evaluated at 3 (n ¼ 5) and 6 weeks (n ¼ 5). In the second experiment, biomechanical testing of the treated ligaments (n ¼ 8) was performed at 6 weeks and compared with the results of biomechanical testing of untreated defects at the same time-point (n ¼ 6). The percentage filling of the defects in the treated ACLs was significantly higher at both the 3-and 6-week time-points when compared with the untreated contralateral control defects (50 AE 21% vs. 2 AE 2% at 3 weeks, and 43 AE 11% vs. 23 AE 11 at 6 weeks; all values mean AE SEM. Biomechanically, the treated ACL defects had a 40% increase in strength at 6 weeks, which was significantly higher than the 14% increase in strength previously reported for untreated defects ( p < 0.02). Placement of a collagen-PRP bridging scaffold in a central ACL defect can stimulate healing of the ACL histologically and biomechanically. ß

We used QCT scans obtained in 687 men and women, 21-97 years of age, to estimate the factor of risk for vertebral fracture, ⌽ vert , defined as the ratio of spinal loading to vertebral strength. With age, vertebral strength declined and ⌽ vert increased significantly more in women than men. Age-and sex-specific differences in ⌽ vert closely resembled previously reported vertebral fracture incidence.Introduction: Despite the high prevalence of vertebral fractures, little is known about the interaction between spinal loading and vertebral fragility. Materials and Methods:We assessed the ratio of spinal loading to vertebral strength (i.e., the factor of risk, ⌽ vert ) in an age-and sex-stratified population-based sample of 700 women and men 21-97 years of age. We measured volumetric BMD (vBMD, mg/cm

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