Surgical site infection and major loss of abduction negatively impact equine laryngoplasty outcomes, while breed is not a contributing factor.

Surgical site infection and major loss of abduction negatively impact equine laryngoplasty outcomes, while breed is not a contributing factor. | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 24 October 2025 V1 Latest version Share on Surgical site infection and major loss of abduction negatively impact equine laryngoplasty outcomes, while breed is not a contributing factor. Authors : M. Lahuerta , David Argüelles , Fabrice Rossignol , Manuel Iglesias 0000-0003-4448-0395 , Fernando Bulnes 0009-0001-3837-6324 , Patricia Becerra , Jose Méndez , Francisco José Vázquez 0000-0002-8712-2275 , Jorge Izquierdo-Moreno , Jorge Carmona , and Ana Velloso Alvarez 0000-0001-6526-8436 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.176131105.52645238/v1 210 views 138 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Background: Prosthetic laryngoplasty (PL) is the standard surgical treatment for recurrent laryngeal neuropathy (RLN) in horses. However, postoperative complications may compromise outcomes, and the influence of breed and anaesthetic approach remains unclear. Objectives: To identify predictors of surgical success at 3 months following PL, with a focus on postoperative complications, anaesthesia type, and breed, with special interest in Iberian baroque breeds (Andalusian and Lusitano). Study design: Multicenter retrospective cohort study. Methods: Medical records from 181 horses treated at seven equine hospitals were reviewed. Variables including breed, anaesthesia type, surgical method, and postoperative complications were analysed using chi-square tests and binary logistic regression. Results: Surgical success was achieved in 79.11% of cases. Postoperative complications occurred in 33.7% of horses and were significantly associated with treatment failure. Two independent predictors of poor outcome were identified: major loss of arytenoid abduction (OR = 0.000567; p < 0.001) and surgical site infection (SSI) (OR = 0.007; p < 0.001). Breed type and anaesthetic modality were not significantly associated with outcome. The final model demonstrated excellent predictive performance (AUC = 0.978; accuracy = 96.7%). Main limitations: Multicenter retrospective study that may be affected by selection bias and variability in practices. Conclusions: Loss of arytenoid abduction and SSI are critical determinants of poor outcome following PL. These findings underscore the importance of meticulous surgical technique and strict infection control. Breed and anaesthetic approach did not influence outcome. Identification of key risk factors supports improved surgical planning, targeted prevention, and clearer prognostic communication. Surgical site infection and major loss of abduction negatively impact equine laryngoplasty outcomes, while breed is not a contributing factor. KEYWORDS: horse, recurrent laryngeal neuropathy, prosthetic laryngoplasty, complications, risk factors, breed SUMMARY Background: Prosthetic laryngoplasty (PL) is the standard surgical treatment for recurrent laryngeal neuropathy (RLN) in horses. However, postoperative complications may compromise outcomes, and the influence of breed and anaesthetic approach remains unclear. Objectives: To identify predictors of surgical success at 3 months following PL, with a focus on postoperative complications, anaesthesia type, and breed, with special interest in Iberian baroque breeds (Andalusian and Lusitano). Study design: Multicenter retrospective cohort study. Methods: Medical records from 181 horses treated at seven equine hospitals were reviewed. Variables including breed, anaesthesia type, surgical method, and postoperative complications were analysed using chi-square tests and binary logistic regression. Results: Surgical success was achieved in 79.11% of cases. Postoperative complications occurred in 33.7% of horses and were significantly associated with treatment failure. Two independent predictors of poor outcome were identified: major loss of arytenoid abduction (OR = 0.000567; p < 0.001) and surgical site infection (SSI) (OR = 0.007; p < 0.001). Breed type and anaesthetic modality were not significantly associated with outcome. The final model demonstrated excellent predictive performance (AUC = 0.978; accuracy = 96.7%). Main limitations: Multicenter retrospective study that may be affected by selection bias and variability in practices. Conclusions: Loss of arytenoid abduction and SSI are critical determinants of poor outcome following PL. These findings underscore the importance of meticulous surgical technique and strict infection control. Breed and anaesthetic approach did not influence outcome. Identification of key risk factors supports improved surgical planning, targeted prevention, and clearer prognostic communication. 2.INTRODUCTION Recurrent laryngeal neuropathy (RLN) is a common cause of upper respiratory tract obstruction in horses. It is characterized by progressive paresis to paralysis of the arytenoid cartilage, generally left, due to loss of function of the recurrent laryngeal nerve and is recognized as a major contributor to poor performance in horses, particularly in large breeds. 1,2 Draught breeds have been reported to have a prevalence as high as 35%, which exceeds that observed in other breeds. 3,4 In horses diagnosed with left-sided RLN grade III and IV (Havermeyer grading system), 5 arytenoid cartilage abduction cannot be maintained during exercise, and during exercise, the vocal cord and arytenoid collapse into the airway, leading to inspiratory stridor and exercise intolerance. 6-8 Prosthetic laryngoplasty (PL) is considered the treatment of choice for RLN, aiming to restore passive abduction of the arytenoid cartilage and thereby improve airflow and exercise tolerance. 9 PL is often performed in combination with standing laser-assisted ipsilateral ventriculocordectomy (VeC), which has been shown to improve airway mechanics by approximately 30% in horses, enhancing arytenoid stability and reducing respiratory sound noise. 10,11 Despite its widespread use, ongoing research continues to focus on refining the surgical technique to enhance outcomes and reduce postoperative complication. The success rate of PL in racehorses remains variable ranging from 45% to 70%, 5 and complications rates of 30% to 50% have been reported. 12-15 The most common postoperative complications are loss of abduction, seroma formation, surgical site infection (SSI), persistent cough and dysphagia. 16 From a surgical perspective, success is associated with achieving ideal abduction and the absence of long-term complications. However, only 62% of horse maintain ideal abduction on the day following surgery, with significant deterioration typically occurring within the first week. 5,15-17 Previous studies have also suggested that factors that may influence successful clinical outcome are surgical approach (standing sedation versus general anaesthesia), 18 as well as surgeon technique and experience (suture placement and quality, number of sutures used or damage of the cartilage by the suture). 19-21 To date, there are no published studies documenting the prevalence of baroque horse breeds or possible complications associated to the breed. Clinical impressions suggest that certain breeds, particularly Iberian baroque types such as Andalusians and Lusitanos, may be predisposed to higher complication rates and poorer outcomes. However, objective evidence supporting these observations is limited. In this context, a comprehensive evaluation of outcome predictors is needed. The objectives of this study were to: (1) identify variables associated with a negative outcome at 3 months in horses following prosthetic laryngoplasty (PL); (2) determine whether specific factors, in particular the use of standing sedation, are associated with improved outcomes compared with general anaesthesia; and (3) assess the influence of breed on postoperative outcome. We hypothesised that Iberian baroque breeds would be more predisposed to postoperative complications, and consequently to a poorer outcome, compared with other breeds. 2. MATERIALS AND METHODS 2.1 Study design This multicentre retrospective study reviewed medical records from databases of the seven referral equine hospitals in X and Y (XXXXXXXX) between June 2014 and March 2025. Horses were eligible for inclusion if they presented respiratory noise, exercise intolerance, left RNL grade III-IV (Havermeyer grading system) confirmed via endoscopy examination, underwent prosthetic laryngoplasty (PL), had no prior surgical upper respiratory procedures, and had documented outcome data within 3 months postoperatively. 2.2 Data collection and follow-up The following variables were extracted from medical records and compiled in a Excel spreadsheet as potential risk factors influencing clinical outcomes: breed, Iberian breed, age, sex, season of the year when the surgery was performed, grade RLN (III or IV), surgical method (PL and laryngotomy or laser VeC), anaesthesia type (general or standing), surgeon, and complications (yes/no). Specific complications recorded included seroma, severe inflammation, failure of abduction (including acute sudden loss of abduction or progressive loss), dysphagia and coughing, surgical site infection (SSI) with and without prothesis infection. Additional details included whether the seroma was drainage and if it was followed by a SSI. Outcome was defined as good if performance improved or poor if initial clinical signs persisted without improvement of the performance. All the procedures were performed by seven different qualified surgeons, following the same standard surgical technique as previously described. 18 The surgeries were performed under general anaesthesia or in standing sedation with laryngotomy or ipsilateral VeC with laser . The horses that underwent PL under general anaesthesia, were positioned in right lateral recumbency, using two separate sutures as the prothesis. The VeC were performed through a laryngotomy with the horse in dorsal recumbency. The laryngeal saccules were everted with a burr and excised; the vocal folds were removed with curved Mayo scissors. The laryngotomy incision was allowed to heal by second intention. If the VeC was performed with laser, the procedure was done before general anaesthesia with sedation and local anaesthetic. The horses that underwent PL with standing sedation were positioned in stocks and firstly, a left-sided VeC was performed with a transendoscopic laser under video-endoscopic guidance. For the PL, the head was placed in a fully extended position using a headstand and stabilized in a sagittal position by an assistant and the surgical technique performed using two separate sutures as the prothesis as well. Twenty-four hours after surgery, an endoscopy was performed to assess the maintenance of the arytenoid cartilage abduction and recorded. Maintenance of the laryngoplasty abduction was semiquantitatively assessed in this study based in the table described by Dixon et al.2023. 5 Grade 1: Excessive abduction, Grade 2 and 3 : A high degree arytenoid abduction (arytenoid at circa 50–80° to sagittal plane), i.e. less than complete abduction or moderate degree of arytenoid abduction, i.e. arytenoid at circa 45° to the sagittal plane. Grade 4: A slight degree of arytenoid abduction, i.e. arytenoid is slightly more abducted than the normal resting position. Grade 5: No detectable arytenoid abduction present. During hospitalization, the complications were recorded in the clinical data of the horse. Seroma formation was defined as the presence of serosanguineous fluid accumulation at the surgical site, as detected by ultrasonographic examination. SSI involving skin or subcutaneous tissue and prothesis infection were diagnosed based on clinical signs including swelling at the laryngoplasty site, fever, purulent discharge, fistula formation, and confirmed by cytological evaluation or/and bacterial culture. Dysphagia and coughing were diagnosed when saliva or food particles were observed in the nasal passages and trachea by endoscopic examination and clinical detection of coughing sounds. Severe inflammation of the larynx was identified in cases where the horse exhibited respiratory distress necessitating temporary tracheostomy. 16 After discharge, it was recommended that the horse should not resume training between 45-60 days after surgery. The postoperative progress of the horses was assessed 1) subjectively within 3 months by telephoning the owner, trainer or referral veterinarian and 2) by endoscopic examination performed between 1-3 months postoperatively, either by the hospital or the referring veterinarian. Cases with persistent clinical signs or suffering from complications, were reassessed by endoscopic examination for the referral veterinarian or admitted to the hospitals for control check-ups. 2.3 Statistical analysis The association between the probability of success and predictor variables was investigated using JASP (version 0.95 (Intel), University of Amsterdam, The Netherlands). Descriptive statistics were used to summarize the dataset. Categorical variables, including breed (Andalusian, Lusitano, Warmblood, Crossbred, Spanish Sport Horse, Friesian, Thoroughbred), sex (stallion, mare, gelding), season of surgery (spring, summer, autumn, winter), anaesthesia type (general anaesthesia, standing sedation), surgical method (laryngotomy ventriculocordectomy with tie-back, laser ventriculocordectomy with tie-back), and postoperative complications (seroma, dysphagia, SSI, prothesis infection, severe inflammation of the larynx, loss of abduction of the arytenoid cartilage)—were presented as absolute and relative frequencies. The continuous variable, age, was summarized as mean ± standard deviation (SD), median, and interquartile range (IQR). To assess univariable associations between explanatory variables and surgical outcome at 3 months contingency tables were constructed and analysed using chi-square (χ²) tests. For 2×2 tables, continuity correction was applied when appropriate, and Fisher’s exact test was used in cases of low expected cell counts. Odds ratios (OR) with 95% confidence intervals (CI) were calculated for binary associations to estimate effect sizes. Variables with a p-value < 0.20 were considered candidates for multivariable analysis. All tests were two-sided, and statistical significance was set at p < 0.05. Binary logistic regression was performed to identify independent predictors of unsuccessful surgical outcome. All candidate variables meeting the inclusion threshold (p < 0.20) were initially entered into a full model. To minimize overfitting and address multicollinearity, a forward stepwise selection procedure was applied. Variables were retained based on their incremental contribution to model fit, evaluated by changes in the Akaike Information Criterion (ΔAIC), likelihood ratio tests, and statistical significance (p < 0.05). Model fit was evaluated using deviance, Akaike Information Criterion (AIC), and pseudo-R² indices (McFadden, Nagelkerke, Tjur, Cox & Snell). Predictive performance was assessed through accuracy, sensitivity, specificity, area under the receiver operating characteristic curve (AUC), precision, F-measure, and Brier score. Potentially influential observations were identified using standardized residuals, Cook’s distance, and DFBETAs. Odds ratios (OR) and 95% confidence intervals (CI) were calculated for all retained predictors. 3.RESULTS A total of 181 horses met the inclusion criteria (18 female, 125 stallions, 38 geldings) age range 2 to 19 years [median 6 years]). Breed distribution was as follows: Andalusians represented most horses 63% (n = 114/181) followed by Crossbred 14.4% (n = 26/181), Lusitano 7.7% (n = 14/181), Warmblood 6.6% (n = 12/181), Spanish Sport Horse 4.9% (n = 9/181), Thoroughbred 2.8% (n = 5/181) and Friesian 0.6% (n = 1/181). Regarding morphotype 70.2% (n = 127/181) horses were classified as Iberian Baroque-type (Andalusians and Lusitanos), and 29.8% (n = 54/181) as non-Baroque. Surgeries were distributed across seasons: Spring 34.8% (n = 63/181), Autumn 29.3% (n = 53/181), Winter 21.5% (n = 39/181), and Summer 14.4% (n = 26/181). The laryngeal hemiplegia grade was most frequently classified as Grade 4: 89 % (n = 161/181) and 11% (n = 20/181) showed Grade 3. All the horses had PL combined with a left unilateral ventriculocordectomy: 71.8% (n = 130/181) underwent laser VeC, while 28.2%) (n = 51/181) underwent VeC through laryngotomy. General anaesthesia was performed in 26.5% (n = 48/181) horses while standing sedation was applied in 73.5% (n = 133/181) cases. Surgical success at 3 months, defined as a good clinical outcome based on laryngeal function and respiratory performance, was confirmed in 79.1% horses (n = 144/181). Univariable analysis revealed several explanatory variables significantly associated with surgical outcome, as summarized in Table 1. Postoperative complications were strongly associated with treatment failure (p < 0.001). A total of 33.7 % of horses experienced at least one complication, and this group showed markedly lower success rates, while 66.3% (n = 120/181) horses had an uneventful recovery (Figure 1). The most frequent complication was seroma, occurring in 19.3% of horses (n = 35/181). Among these, 40% (n = 14/35) resolved spontaneously, while 60% (n = 21/35) required drainage. The presence of seroma was associated with decreased odds of success (p < 0.001). A significant association was observed between seroma drainage and the development of SSI (p < 0.001): 38.1% (n = 8/21) of drained cases developed SSI, and 9.5% (n = 2/21) subsequently developed both SSI and prosthesis-associated infection. SSI 6.6% (n = 12/181) with prosthesis-associated infection 3.3% (n = 6/181) were both significantly associated with poor outcomes (p < 0.001). A bacteriological culture was submitted in 41.6% (n = 4/12) all samples had a positive culture. The bacteria isolated were Staphylococcus spp. (25%, n = 3/ 12) and Enterococcus spp (8,3 %, n = 1/12). Three horses yielded a multidrug-resistant (MDR) Staphylococcus aureus isolates, which were susceptible to marbofloxacin, doxycycline, and trimethoprim-sulfonamide respectively. Additionally, MDR Enterococcus spp was isolated in one case, susceptible to penicillin. Six horses with prosthesis infection underwent removal within three months post-surgery. Two required complete arytenoidectomy due to arytenoid chondritis. In one case, tracheal mucosal penetration happened during suture placement through the cricoid. Despite removal of the prosthesis, thorough irrigation of the surgical site, and reinsertion of a new implant, infection still developed. Dysphagia and cough were reported in 3,9% of the horses (n = 7/181) and presented a negative effect on the outcome (p < 0.001). Three horses developed transient signs postoperatively that improved with ground feeding, likely due to gradual prosthesis relaxation, which was confirmed endoscopically. One horse developed a chronic cough despite resolution of dysphagia. Severe inflammation of the larynx was noted in 6.1% (n = 11/181) within 48 hours post-surgery. It was required to perform a temporary tracheostomy, and all of them resolved with medical treatment and tracheostomy. A major loss of arytenoid abduction, observed in 18.2% (n = 33/181) horses, was the most impactful variable (p < 0.001), with a dramatic reduction in the odds of surgical success (OR = 0.002; 95% CI: 0.000–0.010). Endoscopy evaluation at 24 hours post-surgery revealed that no cases had Dixon grade 1 abduction. The majority of horses 92,8% (n = 168/181) had a grade 2-3 relaxation, while 3,3% (n = 6/181) presented a grade 4 and 3,8% (n = 7/ 181) a grade 5. Among horses with grade 5, 57,1% (n = 4/7) horses were retired, while 28,6% (n = 2/7) underwent repeat laryngoplasty, and 14,3% (n = 1/7) had an arytenoidectomy performed. Of those reoperated, 50% (n = 1/2) failed again and subsenquently underwent arytenoidectomy. Follow-up endoscopy within the 3 months revealed progression in arytenoid relaxation in some horses: 13,6% (n = 23/168) of horses initially graded 2-3 and 50% (n = 3/6) of those with grade 4 progressed to grade 5. The remaining 50% (n = 3/6) with grade 4 achieved favourable outcomes despite reduced abduction. Additionally, surgeon´s experience was found to have an impact on reducing the likelihood of success (p = 0.007), observing less complications in the most experienced surgeons. Conversely, variables such as breed, morphotype, age group, sex, season, grade of hemiplegia, surgical method, and anaesthesia type were not significantly associated with outcome (p > 0.05). Nonetheless, variables yielding p < 0.20 were retained for subsequent multivariable analysis. A binary logistic regression model was constructed to identify predictors of surgical success at 3 months. The final model (M₁) included loss of abduction, SSI, and their interaction (loss of abduction × SSI). Model diagnostics indicated excellent fit compared to the null model (M₀), with a deviance reduction of ΔΧ² = 143.29 (df = 3, p < 0.001). The final model yielded favourable information criteria (AIC = 42.48, BIC = 55.28) and strong explanatory power across multiple pseudo R² indices: McFadden R² = 0.806, Nagelkerke R² = 0.874, Tjur R² = 0.846, and Cox & Snell R² = 0.547 (see Table 2). Regarding predictor significance, major loss of abduction was the strongest negative predictor of success (OR = 0.000567; 95% CI: 0.000–0.006; p < 0.001) (Figure 2a). SSI also significantly decreased the odds of success (OR = 0.007; 95% CI: 0.001–0.090; p < 0.001) (Figure 2b). The interaction term between these two variables was not statistically significant (p = 0.997) and showed high standard error, indicating instability. Its inclusion had negligible impact on model fit and interpretability, suggesting that the effect of co-occurrence may not be synergistic beyond the additive effects of each variable. No multicollinearity was detected (all VIFs 0.6), and the interaction term had a VIF of 1.000. Residual analysis identified one potentially influential case (case #12, standardized residual = –3.16; Cook’s distance = 0.252), but this observation did not materially alter model estimates. Model performance was excellent, with an accuracy of 96.7%, sensitivity of 98.6%, specificity of 88.6%, and a Brier score of 0.024. Discriminative ability was also high, as reflected by the area under the ROC curve (AUC = 0.978), indicating excellent separation between successful and unsuccessful surgical outcomes (Figure 3). 4. DISCUSSION This study aimed to identify predictors of surgical success at 3 months following prosthetic laryngoplasty (PL) in horses. Postoperative complications were strongly associated with treatment failure, and the final multivariable logistic regression model identified two significant predictors: loss of abduction and SSI. To the authors knowledge, this is the first study to demonstrate a correlation between clinical observations and surgical outcomes, highlighting the importance of surgical technique and postoperative care in determining clinical success and good outcome. The efficacy of PL has been evaluated in multiple studies using criteria such as owner satisfaction, race performance, and airway physiological assessments. However, differences in study design, subjective outcome assessments, and inconsistencies in postoperative follow-up contribute to the broad range of reported success rates, typically between 50% and 70% in racehorses and 73% in non-Thoroughbreds or in sports or pleasure horses. 5,16,22 The authors observed surgical success in 79.11% horses with a 66.29% complication-free recovery rate, these outcomes exceed previously reported success rates in both racehorses and non-Thoroughbreds. 16,23 The overall postoperative complications rate in our study was 33.51 % aligning with previously reported rates of 30% to 50%. 5,13,14,23 Seroma formation was the most frequently observed complication. This is likely due to the dead space created during surgery, which may increase the risk of subsequent infection. 24 Minimizing tissue disruption and closing potential spaces, especially near the cricoid cartilage can reduce occurrence. 16 Human studies have shown that closing dead space significantly lowers the incidence of seromas, which are associated with increased clinic visits, higher cellulitis risk, and increased healthcare costs. 24 In this study, drainage was performed when seromas were large, caused respiratory distress, delayed healing, or failed to resolve spontaneously. Statistical analysis showed a significant association between drainage and SSI risk. While drainage may be necessary in certain cases, it should be performed with caution. Laryngoplasty-associated infections, when detected early, can often be successfully manage with drainage, lavage, and targeted antimicrobial therapy. 16 Prosthetic laryngoplasty is classified as a clean surgical procedure, and infection rates are reported as low (0–4%) in the literature. However, in the present study, the incidence of surgical site infection (SSI) was slightly higher at 6.59%, with S. aureus and Enterococcus spp isolated from cultures. Although previous equine laryngoplasty studies have not characterized the causative organisms, our findings align with microbial patterns observed in SSIs following colic surgery. 25,26 These results highlight the importance of culture-guided antimicrobial therapy, judicious antimicrobial selection, and stringent infection-control protocols. SSI significantly compromise postoperative outcomes and are among the strongest predictors of treatment failure, underscoring the need for proactive prevention and early intervention strategies. Persistent purulent drainage from the incision after laryngoplasty should prompt early endoscopic evaluation to detect potential suture penetration into the airway, which warrants prosthesis removal to prevent ongoing contamination. In some cases, surgeons prefer to delay suture removal until 8-12 weeks postoperatively, when cricoarytenoid joint stabilization and perilaryngeal fibrosis have typically developed. 16,27 However, if early removal compromises arytenoid abduction, partial arytenoidectomy may be required to preserve airway patency. 16 In our study, tracheal mucosal penetration occurred intraoperatively in one case. Although the surgical site was flushed and a new suture reinserted, infection still developed. As there is no published evidence supporting reinsertion after decontamination, replacement with a new sterile implant is recommended, though this does not eliminate the risk of subsequent infection. These findings suggest that mucosal penetration may be a significant risk factor for prosthesis-associated infection. Dysphagia and coughing occurred in 3.8% of horses, a lower rate than previously reported (22–40% dysphagia, 43% coughing). 14 This lower incidence might be related a deeper anatomical knowledge reading the extent of the vestibulum esophagi. 28 These complications may result from seroma formation, perilaryngeal inflammation or transient neuropraxia that resolves in the first postoperative days. 29 Overall, most cases resolved or were manage conservatively, but prosthesis removal remains an option in refractory cases. 5,14,16,22 Maintenance of the laryngoplasty abduction was semiquantitatively assessed in this study based in the table by Dixon et al.2023. 5 Gradual loss of arytenoid abduction is a well-documented, typically occurring within the first six weeks postoperatively and affecting up to 76% of horses in previous reports. 16 Targeting approximately 88% of the maximal cross-sectional area for arytenoid cartilage abduction appears to be an effective surgical goal. 30 In this study, 11.9% of horses with initial Dixon grade 2–3 and 50% with grade 4, progressed to grade 5 within three months, underscoring the importance of postoperative endoscopic follow-up to enable early detection of significant loss of arytenoid abduction and to inform future management strategies and owner expectations. Interestingly, some horses grade 4 achieved favourable outcomes despite only partial abduction. This observation aligns with previous literature suggesting that even partial stabilization can result in functional improvement, particularly in non-racing horses, and may support a return to moderate levels of exercise. 16 It is not unexpected that failure to achieve or maintain arytenoid abduction emerged as the most influential predictor of poor outcome in this study. This finding reinforces the principle that sustained arytenoid abduction is critical for functional recovery following prosthetic laryngoplasty. Technical factors, including inaccurate suture placement or the application of excessive tension, may result in cartilage tearing or premature suture failure. Consequently, meticulous surgical technique is paramount. The use of a standardised intraoperative checklist , as described by Rossignol and Dixon (2021), 16 is recommended to minimise the risk of technical errors and optimise surgical outcomes. In our study, we observed that outcomes appeared influenced by surgeon, enhancing the critical role of technical expertise in optimizing postoperative results. Severe inflammation of the larynx following prosthetic laryngoplasty was observed in 6.07% of horses. To the author’s knowledge, this complication has not been frequently described in the literature. Management of these cases included the placement of a temporary tracheostomy to alleviate upper airway obstruction combined with medical treatment. Treatment was consisted into administration of dexamethasone for three days, combined with a topical laryngeal flush. 27 Regarding variables that did not affect to the outcome, seasonal variation in SSI rates, previously reported in both human and equine surgery, showed no significant association with the outcome in this cohort. 26,31 Standing sedation offers several procedures advantages, including avoidance of risks associated with the general anaesthesia (particularly in larger breeds), enhanced visualization of key anatomical landmarks, and the ability to adjust arytenoid abduction intraoperatively. 18 Despite these benefits, standing sedation did not significantly improve surgical success rates in this study. A progressive shift toward standing procedures was observed during the study, reflecting growing confidence in the technique. 25 Nevertheless, horse temperament and compliance remain critical considerations, and safety must guide the choice of anaesthetic approach. This study focused solely on the Iberian Baroque breed group, as the sample sizes for other baroque type such as Lipizzaner, Kladruber, and Friesian horses 32 were too small to allow robust statistical analysis. Although surgeons had the clinical impression that Iberian baroque breeds such as Andalusians and Lusitanos seemed to present higher complication rates after PL, our study found no significant association between breed type and surgical outcome. While anatomical differences or breed-specific traits may influence risk, any potential breed effects may have been confounded by surgical approach or institutional protocols. This study has several limitations, primarily related to its retrospective design, which restricted control over data quality, surgical standardization, and outcome assessment. Long-term follow-up was limited, with outcomes assessed at three months, potentially underestimating the evolution of clinical signs. This limitation was due to the retrospective nature of data collection and variability in long-term follow-up availability and validation, and success was defined via static endoscopy by different veterinarians, which may limit generalizability. Furthermore, the full model initially produced overfitting, with artificially perfect classification and implausible coefficient estimates, underlining the importance of model refinement. However, a major strength of this study is the statistical performance of the final model, which showed excellent discrimination (AUC = 0.965), high accuracy (96.2%), and well-calibrated fit (Nagelkerke R² = 0.824). Additionally, multicollinearity was low, and model parsimony was preserved with only three predictors, enhancing interpretability and clinical applicability. In conclusion, this is the first multicenter study to demonstrate a strong association between postoperative complications and treatment failure. Two independent risk factors for poor outcome at three months were identified: arytenoid abduction failure and SSI. In contrast, other variables such as breed type and anaesthetic modality (general anaesthesia vs. standing sedation) showed no significant effect on outcome. These findings emphasize the importance of achieving and maintaining adequate arytenoid abduction and preventing postoperative infection. Identification of these predictors enables more informed surgical planning, implementation of targeted preventive strategies, and clearer prognostic communication with horse owners, ultimately improving clinical outcomes and procedural standards. REFERENCES 1. Lane JG, Bladon B, Little DR, et al: Dynamic obstructions of the equine upper respiratory tract. Part 2: comparison of endoscopic findings at rest and during high-speed treadmill exercise of 600 Thoroughbred racehorses. Equine Vet J 38:401-407, 2006.2. 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Goulden B, Anderson L: Equine laryngeal hemiplegia part II: some clinical observations. New Zealand Veterinary Journal 29:194-198, 1981.9. Spiers V, Tulleners E, Ducharme N, et al: Larynx. In “Equine Surgery”, Ed., JG Auer, in, Vol WB Saunders Company, Philadelphia, 1992.10. Brown JA, Derksen FJ, Stick JA, et al: Ventriculocordectomy reduces respiratory noise in horses with laryngeal hemiplegia. Equine Vet J 35:570-574, 2003.11. Baldwin CM, Ireland JL, Barakzai SZ: Unilateral laser ventriculocordectomy results in increased arytenoid stability in horses with severe left sided recurrent laryngeal neuropathy. Equine Veterinary Journal 56:1149-1154, 2024.12. Fitzharris LE, Lane JG, Allen KJ: Outcomes of horses treated with removal of a laryngoplasty prosthesis. Vet Surg 48:465-472, 2019.13. Russell AP, Slone DE: Performance analysis after prosthetic laryngoplasty and bilateral ventriculectomy for laryngeal hemiplegia in horses: 70 cases (1986-1991). 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Plast Reconstr Surg 142:653-660, 2018.25. Byrne CA, Hotchkiss JW, Barakzai SZ: Variations in the application of equine prosthetic laryngoplasty: A survey of 128 equine surgeons. Vet Surg 52:209-220, 2023.26. Dziubinski N, Mählmann K, Lübke-Becker A, et al: Retrospective identification of bacterial isolates from emergency laparotomy surgical site infections in horses. Journal of Equine Veterinary Science 87:102927, 2020.27. Ducharme NG, Rossignol F: Larynx, in Auer JA, Stick JA, Kümmerle JM, et al (eds): Equine Surgery, Vol W.B. Saunders, 2019, pp 734-769.28. Brandenberger O, Martens A, Robert C, et al: Anatomy of the vestibulum esophagi and surgical implications during prosthetic laryngoplasty in horses. Veterinary Surgery 47:942-950, 2018.29. Barakzai SZ, Dixon PM, Hawkes CS, et al: Upper esophageal incompetence in five horses after prosthetic laryngoplasty. Vet Surg 44:150-155, 2015.30. Rakesh V, Ducharme NG, Cheetham J, et al: Implications of different degrees of arytenoid cartilage abduction on equine upper airway characteristics. Equine Vet J 40:629-635, 2008.31. Duscher D, Kiesl D, Aitzetmüller MM, et al: Seasonal impact on surgical-site infections in body contouring surgery: a retrospective cohort study of 602 patients over a period of 6 years. Plastic and reconstructive surgery 142:653-660, 2018.32. Radovic L, Remer V, Rigler D, et al: Y-chromosomal insights into the breeding history and sire line genealogies of two traditional Baroque horse breeds: Lipizzaner and Kladruber. J Equine Vet Sci 144:105252, 2025. TABLES Table 1. Univariable associations between explanatory variables and surgical outcome at 3 months Breed χ²(6)=9.29 0.158 – – Morphotype (Baroque) χ²(1)=1.01 0.315 0.644 0.272–1.526 Age χ²(17)=23.72 0.127 – – Sex χ²(2)=4.47 0.107 – – Season χ²(3)=3.44 0.329 – – Hemiplegia grade χ²(1)=0.27 0.603 1.406 0.388–5.091 Surgical method χ²(1)=1.43 0.231 0.580 0.236–1.426 Anaesthesia type χ²(1)=1.34 0.246 1.594 0.721–3.523 Complications χ²(1)=85.36 <0.001 0.003 0.000–0.052 Seroma χ²(1)=11.88 <0.001 0.252 0.111–0.572 Seroma drainage χ²(1)=19.90 <0.001 0.141 0.055–0.364 Loss of abduction χ²(1)=144.0 <0.001 0.002 0.000–0.010 Dysphagia χ²(1)=12.67 <0.001 0.083 0.015–0.450 SSI χ²(1)=25.53 <0.001 0.061 0.015–0.239 Prosthesis infection χ²(1)=25.89 <0.001 0.015 0.001–0.282 Inflammation χ²(1)=14.74 <0.001 0.113 0.031–0.411 Surgeon χ²(6)=17.71 0.007 – – Seroma drainage χ²(1)=19.90 <0.001 0.055 0.364 Seroma + Drainage + Infection χ²(1)=20.74 <0.001 0.056 0.011–0.282 df = Degrees of freedom. SSI= Surgical site infection. Odds ratios are presented for 2×2 comparisons. Table 2. Final binary logistic regression model for predicting surgical success at 3 months postoperatively. not-yet-known not-yet-known not-yet-known unknown Model Deviance AIC BIC df ΔΧ² p McFadden R² Nagelkerke R² Tjur R² Cox & Snell R² M₀ 177.77 179.77 182.967 180 0.000 0.000 M₁ 34.48 42.481 55.275 177 143.287 < .001 0.806 0.874 0.846 0.547 Note. M₁ includes Loss of abduction, SSI, Loss of abduction × SSI Coefficients Wald Test 95% Confidence interval(odds ratio scale) Model Estimate Standard Error Odds Ratio z Wald Statistic df p Lower bound Upper bound M₀ (Intercept) 1.428 0.188 4.171 7.589 57.591 1 < .001 2.885 6.032 M₁ (Intercept) 4.949 1.004 141.000 4.931 24.318 1 < .001 19.724 1,007.938 Loss of abduction (1) -7.474 1.244 0.000567 -6.009 36.112 1 < .001 0.000 0.006 SSI (1) -4.949 1.294 0.007 -3.825 14.632 1 < .001 0.001 0.090 Loss of abduction (1) × SSI (1) -11.092 2,662.856 0.00001524 -0.004 0.00001735 1 .997 0.000 ∞ FIGURES Figure 1: A flow chart to show complications of horses presented for the study. Figure 2. Predicted probability of surgical success at 3 months by presence of key risk factors. (A) Predicted probability of surgical success according to the presence or absence of loss of arytenoid abduction. (B) Predicted probability of surgical success according to the presence or absence of surgical site infection (SSI). Predictions were derived from the final binary logistic regression model. Both variables were strongly associated with a reduced probability of success (p < 0.001). Figure 3. Receiver Operating Characteristic (ROC) curve for the final logistic regression model. ROC curve showing the discriminative performance of the final model predicting surgical success at 3 months. The area under the curve (AUC) was 0.978, indicating excellent ability to distinguish between successful and unsuccessful outcomes. The model included loss of abduction, surgical site infection (SSI), and their interaction. Information & Authors Information Version history V1 Version 1 24 October 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Authors Affiliations M. Lahuerta Universidad CEU-Cardenal Herrera CEU Universities View all articles by this author David Argüelles Córdoba University UCO View all articles by this author Fabrice Rossignol Clinique Vétérinaire Équine de Grosbois View all articles by this author Manuel Iglesias 0000-0003-4448-0395 European University of Madrid View all articles by this author Fernando Bulnes 0009-0001-3837-6324 Córdoba University UCO View all articles by this author Patricia Becerra Universidade do Porto View all articles by this author Jose Méndez Méndez Equine Hospital View all articles by this author Francisco José Vázquez 0000-0002-8712-2275 Universidad de Zaragoza Facultad de Veterinaria View all articles by this author Jorge Izquierdo-Moreno Universidad Complutense de Madrid Facultad de Veterinaria View all articles by this author Jorge Carmona University of Caldas View all articles by this author Ana Velloso Alvarez 0000-0001-6526-8436 [email protected] Universidad CEU-Cardenal Herrera CEU Universities View all articles by this author Metrics & Citations Metrics Article Usage 210 views 138 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation M. Lahuerta, David Argüelles, Fabrice Rossignol, et al. Surgical site infection and major loss of abduction negatively impact equine laryngoplasty outcomes, while breed is not a contributing factor.. Authorea . 24 October 2025. DOI: https://doi.org/10.22541/au.176131105.52645238/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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