**Background:** Poor wound healing after abdominal surgery, such as incisional hernia and wound dehiscence, remains a common complication. Sutures provide mechanical support but also act as foreign materials that can exacerbate inflammation. Surgeons often overestimate tension requirements and use larger sutures, potentially increasing tissue reactivity. This study aimed to compare biomechanical stability and tissue reactivity after suturing canine midline abdominal incisions with different suture sizes (USP 2-0, 3-0, and 4-0 PGA).
**Methods:** The study comprised two parts. (1) Ex vivo biomechanical testing: 14 samples of canine abdominal skin and fascia/muscle were collected from dogs weighing 5–15 kg. Tissue blocks (3×10 cm) were incised along the midline and sutured with one of six combinations: simple interrupted or continuous pattern with USP 2-0, 3-0, or 4-0 PGA sutures. Each combination was performed four times. Uniaxial tensile testing was conducted using an LLOYD LR10K plus machine with a 1,000 N load cell. Stress at 10%, 20%, 30%, 40%, 50% strain and maximum tensile force were recorded. (2) In vivo animal experiment: 27 adult beagles (mean weight 13.4±1.48 kg) underwent three 3-cm midline incisions (starting 3 cm posterior to xiphoid, spaced 1–2 cm apart). Each incision was closed with one of the six suture combinations (each performed four times). Skin samples were collected at 1, 7, and 14 days; linea alba samples at 1, 7 days, and 3 months. mRNA expression of IL-1β, IL-6, and TNF-α was measured by RT-PCR; protein levels by ELISA. Histological evaluation (H&E staining) used a semi-quantitative scoring system per ISO10993, assessing inflammation (polymorphonuclear cells, lymphocytes, plasma cells, macrophages, giant cells, necrosis) and tissue reactivity (inflammation score×2 + neovascularization + fibrosis + fat infiltration). Statistical analysis used Fisher's exact test, Mann–Whitney U test, and Wilcoxon test (p<0.05).
**Key Results:**
- Biomechanical: For skin, no significant stress differences below 30% strain among groups. At 40% strain, USP 4-0 showed significantly lower stress. Maximum tensile strength for USP 4-0 sutured skin was 92.5 N (minimum 56.3 N, 1.03 MPa), significantly lower than USP 2-0 and 3-0, but still exceeding general canine abdominal wall requirements. For muscle, no significant differences below 50% strain; maximum tensile strength and stress were similar across groups. Failure endpoints: larger sutures caused tissue tearing; smaller sutures caused suture breakage. Continuous sutures had higher suture breakage; interrupted sutures more tissue rupture.
- Tissue reactivity: No wound dehiscence, infection, or incisional hernia occurred. USP 2-0 and 3-0 groups showed more redness and scab formation at 1–2 weeks. mRNA and protein levels of IL-1β, IL-6, and TNF-α were significantly higher in USP 2-0 vs USP 4-0 at all time points in skin and at 1 and 7 days in muscle. At 3 months, no significant differences in muscle. Simple interrupted sutures caused higher IL-1β mRNA at 7 days in muscle compared to continuous. Histological scores (inflammation and tissue reactivity) were significantly higher for USP 2-0 vs USP 4-0 at 1, 7, and 14 days in skin and at 1 and 7 days in muscle.
**Clinical Implications:** USP 4-0 PGA sutures provide sufficient biomechanical stability for canine abdominal wall closure (skin and linea alba) while significantly reducing early inflammatory response compared to larger sutures. Surgeons should select the smallest suture size that meets tension requirements to minimize foreign material implantation and tissue trauma, potentially improving wound healing and reducing complications. Continuous suturing may offer advantages over interrupted suturing in terms of lower inflammation in muscle tissue. These findings support using finer sutures in routine low-tension abdominal closures in dogs.