4.4 Post-operative management:
All horses were checked during three days p.o. for clinical signs of surgical complications such as fever, heart and respiratory rate, oedema of scrotum or prepuce, wound swelling, disruption or -drainage and judgement of post-operative posture and behaviour indicating possible discomfort or pain.
4.5 Statistical analysisData were tested for normal distribution using Kolmogorov-Smirnov Test.
Possible correlations between SAA, age and weight of removed tissue was tested either using the variance analysis for normal distributed data, or using the non-parametric Jonckheere-Terpstra-test for not normal distributed data. Possible cross correlations were tested using Spearman Rho test. Significance of differences between the resulting mean SAA values from this study and the mean SAA values derived from literature for field castrations was tested using a paired T-test. The effect size statistic Cohen’s d was calculated as a measure of relevance of the tested differences in third day SAA between the closed inguinal castration and the field castrations reported in the literature. Where applicable, significance was tested two-sided at significance level P<=0.05.
Results.
48 Horses tested negative (SAA< 3mg/l) pre-operatively. Two ponies and one Standardbred showed a pre-operative SAA level of 5mg/l, 7mg/l and 75mg/l respectively. 50 Patients recovered from surgery without showing clinical signs of surgical complications. One horse showed a unilateral incisional infection three days after surgery.
P.o. SAA values ranged from 0 (<3) mg/l to 1150 mg/l (Fig 3). The mean value of p.o. SAA is 94 mg/l. The results are separated in three groups of horses based on the value of SAA (Table 1),Negative : SAA 0-2mg/l (26 horses, 51%), Moderate : SAA 3-100 mg/l (17 horses, 33%) and High : SAA >100mg/l (8 horses,16%). Four horses in the High-group (8%) showed a SAA value over 500mg/l (Table 2), which strongly influence the calculated mean, being 27 mg/l without these values.
The data for age (Fig.2) and p.o. SAA (Fig.3) did not fulfil the criteria for a normal distribution. The weight of removed tissue (Fig.4) showed an acceptable normal distribution. Comparison between p.o. SAA and age and removed tissue weight (Fig.5, Fig.6 and Fig.7) showed a moderate but significantly (P=0,015) higher p.o. SAA in older horses. No statistical significance was shown between p.o. SAA and weight of removed tissue (P= 0,531). A not very surprising significant (P=<0,002) correlation was found between age and weight of removed tissue (larger reproductive organs in mature horses). All other possible correlations did not prove statistically significance.
The third day p.o. SAA data using the closed inguinal approach was tested highly significant lower (P<0,001) than the data recorded in the four previously referred different field castration studies (Table 3). This is true for each of eight groups of horses described in the field castration studies (2 groups in each study). Calculated Cohen’s d ranged from 1.11 to 2.75 (Table 3)
Conclusion.
The results support the hypothesis that the third day p.o. value of SAA after castration using the closed inguinal approach is significantly and relevantly (Cohen’s d >>0.8) lower than the third day p.o. values of SAA after field castrations, indicating that the closed inguinal castration is a significant and relevant less traumatic surgical procedure than a field castration.
Discussion.
The inflammatory response to a surgical procedure is caused by trauma and infection and determines the quality and duration of the p.o. healing process. For this reason, modern equine surgery relies on minimal invasive techniques whenever possible. Since Valdez et al. (1979) presented a minimal invasive inguinal approach for cryptorchidectomy (Turner and McIlwraight 1989, Adams and Fessler 2000) it was a logic step to develop an inguinal approach for normal castrations over unilateral cryptorchids (Sedrish and Leonard 2001). Although the advantages of an inguinal approach have been presented (Keller et al. 1996, Sedrish and Leonard 2001, Riemersma 2005, Kummer et al. 2009) a scrotal approach is still the standard in field castrations. The closed inguinal castration is a minimal invasive surgical procedure. Despite the renounce of anti-inflammatory medication, the inflammatory response of the closed inguinal castration, applied in this study, quantifies to be 5 to 7.5 times less than in field castrations; 51% showing no elevation in SAA at all (Table 1). The four horses showing extreme values, comparable with average field castrations (>500 mg/l) in this study may have suffered additional trauma (Table 2). There may be arguments to exclude these patients from the study, but the high impact on the mean value could be considered to bias the objective results. It is also possible that comparable patients may have been included in the reported field studies.
Apart from a significant lower contamination under acceptable surgical conditions, the inguinal approach also provides, in comparison with the scrotal approach, a more secure ligation on the proximal vaginal process, which is thinner on this site than the more distal parts, where the developing of the Plexus pampiniformis increases vascular complexity and tissue diameter (Fig.1).
The closed inguinal approach by its technique therefore eliminates the two main sources of complications in field castrations being contamination and insecure ligation. Apart from this advantage, there is also a strong indication that the closed inguinal approach is less traumatic. Although it remains to be proven whether the third day p.o. SAA level solely depends on non-septic inflammatory causes, it is feasible that at least a considerable influence of traumatic origin will contribute to these SAA values. Love et al. (2009) showed that field castrations in ponies resulted in altered behaviour indicating p.o. pain first day after surgery. This indicates an inflammatory response to trauma, since most infections become usually clinically significant some days after surgery (Kilcoyne 2013b), especially when p.o. treated with antimicrobial and anti-inflammatory medication. Whereas p.o. oedema of Scrotum and Prepuce is common after field castrations (Kilcoyne 2013b), it is extremely rare (<1%) after the castration by a closed inguinal approach (Riemersma, 2005). Less trauma may have its origin in the better surgical conditions under general anaesthesia, but may additionally depend on the difference in technical approach being either inguinal or scrotal and the difference between a true closed procedure or a procedure in which the vaginal tunic is opened, entering the peritoneal cavity. The results of this study show no correlation between the SAA and the mass of removed tissue, representing the size of the reproductive organs. This implies that retrieval of the complete vaginal process does not contribute to the SAA level regardless of the size of the organs and will therefore be minimal invasive. It has been stated that some haemorrhage (a possible source of inflammation) is normal in field castrations (Kilcoyne 2013b), but it is extremely rare in the inguinal approach (Fig.1). This is explained by not disturbing significant vascular supply while the vaginal process is surrounded by the loose connective tissue of the Tunica dartos. Even disruption of the vascular supply of the Gubernaculum remnant does not cause haemorrhage in the fast majority of cases. The only remaining trauma would be from the small skin incision over the outer inguinal area and the blunt separation of the fat containing loose connective tissue to reach the vaginal process. The closed inguinal approach additionally represents a true closed procedure and prevents any blood spilling or other contamination into the peritoneal cavity, which is known to be a source of peritoneal inflammation (Schumacher et al. 1988). The absence of a potentially irritating intraperitoneal ligature may be another advantage of the closed inguinal approach.
Although the scrotal incision provides an easy access to the Testis, the site of ligation of the more proximal located vaginal process may require some more dissection to be reached, and may therefore result in increased tissue trauma. This could be truer in colts and stallions with larger Testes, which may explain a correlation between Testis size and complication rate for scrotal castrations (Birrell et al. 2020). Each additional handling of tissues may also increase the risk of intra-operative contamination, which is the actual reason for omitting a wound closure in field castrations. The larger diameter of the distal vaginal process may hamper the proper application of an emasculator in closed fashion in many occasions (Rutgers and Merkens 1983, Kilcoyne 2013b), especially in combination with an intra-testicular anaesthesia, which results in enlargement and stiffening of the distal tissues. Therefore, using a scrotal approach often requires opening the vaginal process and pulling the internal organs (Testis, Epididymis, Plexus pampiniformis) and mesenteries distally prior to intra- or extra-vaginal ligation of testicular vascularisation (Rutgers and Merkens 1983). The vaginal process may be closed consecutively (Rutgers and Merkens 1983, Kilcoyne 2013b) but this will not prevent contamination of the peritoneal cavity with blood or tissue or the irritation of an intra-peritoneal ligature, initiation a non-septic peritonitis (Schumacher et al. 1988). These additional inflammatory responses may explain an increase in SAA value in field castrations.
The closed inguinal approach has the advantage over a field castration to be a minimal invasive castration technique without opening the peritoneal cavity. The routine intra- or p.o. medication can be omitted in the closed inguinal approach which may show the public the responsible professionalism of veterinarians in terms of preventing antibiotic resistance (Bowen, 2013). Return time to full training after a closed inguinal castration is less than 7 days, instead of several weeks after field castrations, which is highly appreciated by professional trainers. The closed inguinal approach is a fast procedure, requiring about 45 minutes from induction to recovery and an actual time in surgery of about 20 minutes. The inguinal procedure may not even be more expensive than a field castration which requires travelling, on site preparations and p.o. patient checks and treatments, which encourages many local practitioners to refer castrations of mature horses to the authors clinic.
An inguinal approach may be applied in practice as well, and has been practiced by the first author, if recumbent restraint and intra-operative contamination can be controlled. An inguinal approach will technically be impossible or extremely complicated in the standing horse, which leads to the recommendation that the standing castration should only be applied after full consent of the owner concerning a significant more traumatic surgery (this paper) associated with a considerable higher complication rate than a recumbent castration (Mason, 2015).