Biomechanical Outcomes of Bridge-enhanced Anterior Cruciate Ligament Repair Are Influenced by Sex in a Preclinical Model

Despite the well-established role of sex on the anterior cruciate ligament (ACL) injury risk, its effects on ACL surgical outcomes remain controversial. This is particularly critical when developing novel surgical techniques to treat the injury because there are limited data existing on how these procedures will respond in each sex. One such approach is bridge-enhanced ACL repair, in which primary suture repair of the ACL is augmented with a bioactive scaffold saturated with autologous blood. It has shown comparable biomechanical outcomes to ACL reconstruction in preclinical models.

We asked (1) whether sex affects the biomechanical outcomes of bridge-enhanced ACL repair; and (2) if suture type (absorbable or nonabsorbable), used to repair the torn ACL, can minimize the potential sex discrepancies in outcomes after 15 weeks of healing in a large animal preclinical model.

Seventeen (eight males, nine females) Yorkshire pigs (Parson’s Farms, Hadley, MA, USA) underwent bilateral ACL transection and received bridge-enhanced ACL repair with an absorbable suture (n = 17) on one side and with a nonabsorbable suture (n = 17) on the other side. The leg receiving the absorbable suture was randomized within each animal. ACL structural properties and AP knee laxity for each knee were measured after 15 weeks of healing. Mixed linear models were used to compare the biomechanical outcomes between sexes and suture groups.

When treated with absorbable suture, females had a lower ACL linear stiffness (females, 11 N/mm [range, 8–42]; males, 31 N/mm [range, 12–56]; difference, 20 N/mm [95% confidence interval {CI}, 4–36]; p = 0.032), ACL yield (females, 121 N [range, 56–316]; males, 224 N [range, 55–538]; difference, 103 N [95% CI, 6–200]; p = 0.078), and maximum load (females, 128 N [range, 63–332]; males, 241 N [range, 82–538]; difference, 114 N [95% CI, 15–212]; p = 0.052) than males after 15 weeks of healing. Female knees treated with absorbable suture had a lower linear stiffness (absorbable, 11 N/mm [range, 8–42]; nonabsorbable, 25 N/mm [range, 8–64]; difference, 14 [95% CI, 2–26] N; p = 0.054), ACL yield (absorbable, 121 N [range, 56–316]; nonabsorbable, 230 N [range, 149–573]; difference, 109 N [95% CI, 56–162]; p = 0.002), and maximum load (absorbable, 128 N [range, 63–332]; nonabsorbable, 235 N [range, 151–593]; difference, 107 N [95% CI, 51–163]; p = 0.002) along with greater AP knee laxity at 30° (absorbable, 9 mm [range, 5–12]; nonabsorbable, 7 mm [range, 2–13]; difference, 2 mm [95% CI, 1–4]; p = 0.034) than females treated with nonabsorbable suture. When repaired using nonabsorbable suture, the biomechanical outcomes were similar between female and male knees (p > 0.10).

Females had significantly worse biomechanical outcomes than males when the repairs were performed using absorbable sutures. However, the use of nonabsorbable sutures ameliorated these differences between males and females.

The current findings highlight the critical role of sex on the biomechanical outcomes of bridge-enhanced ACL repair in a relevant large animal model. Better understanding of the mechanisms responsible for these observations using preclinical models and concomitant clinical studies in human patients may allow for additional development of sex-specific surgical and rehabilitative strategies with potentially improved outcomes in women.