A Modified Lateral Skin Incision Reduces Wound Complications and hospital stay in Obese patients undergoing Total Knee Arthroplasty: A Propensity-Matched Cohort

Technical Summary: Modified Lateral Skin Incision in Obese TKA Patients

Problem Statement
Morbid obesity (BMI ≥ 40 kg/m²) significantly increases the risk of wound complications, including infection and dehiscence, following Total Knee Arthroplasty (TKA). These risks are attributed to soft-tissue ischemia, hypovascularity, and increased mechanical stress on the surgical site. Historically, the standard longitudinal midline incision is used, but it traverses the dominant medial cutaneous vasculature and risks injury to the infrapatellar branch of the saphenous nerve, leading to anterior knee hypesthesia and kneeling difficulties. While a lateral skin incision theoretically preserves medial angiosomal blood supply and avoids the nerve, its efficacy in the specific high-risk population of morbidly obese patients had not been rigorously evaluated using propensity-matched comparative methodology.

Methodology
This prospective cohort study, enhanced by 1:1 propensity score matching (PSM), evaluated 124 morbidly obese patients (BMI ≥ 40 kg/m²) undergoing primary unilateral TKA. The study compared two surgical approaches performed by a single senior surgeon:

• Study Group (n=62): Modified curved lateral skin incision, placed laterally to circumvent the anterior soft tissue envelope over the patella, followed by a standard medial parapatellar arthrotomy.
• Control Group (n=62): Standard longitudinal midline skin incision.

Patients were matched based on age, BMI, sex, preoperative smoking status, and deformity direction. All patients followed a standardized Enhanced Recovery After Surgery (ERAS) protocol.

Key Contributions and Findings
The study provides evidence that the modified lateral approach offers specific advantages over the midline approach in morbidly obese patients without compromising operative efficiency or long-term function:

1. Reduction in Wound Complications: The lateral group demonstrated a significantly lower overall wound complication rate compared to the midline group (3.2% vs. 19.4%; p = 0.016). All complications in the lateral group were minor (superficial erythema or delayed healing managed non-operatively), whereas the midline group included major complications (full-thickness necrosis and dehiscence) requiring operative debridement. No deep periprosthetic joint infections (PJI) occurred in either group.
2. Hospital Stay: Patients in the lateral group had a statistically shorter length of hospital stay (3.02 days vs. 3.48 days; p = 0.021).
3. Sensory Preservation and Kneeling: The lateral incision resulted in a markedly smaller area of anterior knee hypesthesia (3.25 cm² vs. 12.48 cm²; p < 0.001). Consequently, kneeling ability was significantly better at 3 months postoperatively in the lateral group (VAS 3.00 vs. 6.95; p < 0.001). However, by one year, kneeling ability scores equalized between groups.
4. Operative Metrics: There was no significant difference in operative time (74.97 min vs. 73.26 min) or incision length between the two groups.
5. Functional Outcomes: Long-term functional outcomes, measured by Knee Society Scores (KSS) and range of motion, were statistically equivalent between the two groups at final follow-up.

Statistical Analysis of Predictors
Multivariable logistic regression identified the lateral curved incision as an independent protective factor against wound complications (Odds Ratio [OR] 0.094; 95% CI 0.014–0.643), reducing the odds of complications by approximately 90%. Conversely, smoking status was identified as the strongest independent risk factor (OR 48.95). For the area of hypesthesia, the lateral incision was the dominant predictor, associated with a 9.218 cm² reduction in the affected area.

Significance and Claims
The authors conclude that for morbidly obese patients undergoing TKA, a modified curved lateral skin incision is a superior strategy compared to the standard midline approach. The study claims that this technique significantly reduces wound morbidity, shortens hospitalization, and minimizes early sensory deficits and kneeling difficulties. The authors assert that these benefits are achieved without increasing operative time or compromising long-term functional recovery. The study suggests that preserving the medial angiosomal blood supply and avoiding the infrapatellar nerve branch are critical mechanisms for these improvements.

Limitations
The authors acknowledge that the study is single-center and single-surgeon, which may limit generalizability and introduce proficiency bias. As a non-randomized study, residual confounding cannot be entirely excluded despite PSM. Additionally, the sample size may be insufficient to detect rare events like deep PJI, and the one-year follow-up does not address long-term implant survivorship. The study utilized systemic BMI rather than localized subcutaneous fat measurements for risk stratification.