An STL model of the equine uterus

Keywords: model, 3D, STL, equine, uterus.

The author has used a stereolithographic (STL) file to view and print equine uteruses and pelvic structures in 3D.

NEW: This, small file can even be downloaded on a cell phone. Pay no attention to dialog alluding to processing of the file. Go ahead and download it. With the App "Fast STL viewer" (see Google play store) already downloaded on your phone, click on this downloaded file (not the App itself!) and the uterus will appear on your phone as shown in the thumbnail above. Incidentally, the same file can be downloaded and viewed on your laptop. 

Viewing the model:

For STL viewing alone on your laptop the author suggests that you download this file. Click on it and your laptop (PC or Apple) will bring up a suitable program for viewing. An example of  such an interface is shown below. 

Printing the model:

Custom STL printing can be done through Axis Prototypes in Montreal after contacting the author.  Axis holds the right to a digitally engineered model of the tract and pelvis that is ready for printing. High quality prints such as those seen here are not inexpensive.  Printing a 25 cm model (caudal to cranial) printed from STS nylon will cost approximately $600 Can. ($460 US). 

Manipulating the model:

In the absence of a real uterus or a printed tract, this digital model serves to remind one of many practical aspects of equine reproduction  A short list comes to mind immediately. Some may wish to print this list so that it can be referred to as the model is manipulated. Better still, manipulate the model on a cell phone while reading the learning points on a laptop.

1.Rotate the tract for a view of the vulva lips and clitoris. Be reminded of its "winking" appearance often, but not exclusively, seen during estrus. Note the importance of the clitoris in diagnosis of CEM and the conformation of the vulva lips in infertility. 

2.Enter the vagina and move cranially until the external urethral orifice is encountered. Note that the hymen is normally found just cranial to the orifice but is absent here because this tract was modeled from that of a pluriparous mare. At this point, one should also contemplate the potential problem of urine pooling in the cranial vagina in older mares due to splanchnoptosis.

3.Traveling further cranial in the vagina, one can see the opening of the cervix, showing its dorsal frenulum. Consider the simple nature of the equine cervix compared to that in other species i.e. there are no transverse cervical rings and the cervix is easily dilated for artificial insemination, embryo collection and is even distensible enough to remove fetuses that are three or four months old. The same distensibility is certainly not encountered in ruminants and other domestic animals.

4.Turning to the left and right at a point just caudal to the cervix, one should be reminded that the vagina lies completely within the peritoneal cavity at this point. This is important because it permits one to penetrate the cranial vagina for standing ovariectomy in mares. It also means that if the cranial vagina is torn during foaling, evisceration can occur from this site.

5.Withdraw from the vagina and rotate the model so that the cervix is visible from within the peritoneal cavity. Note that the cranial portion of cervix is firmly suspended between the ilial shafts on either side, by the mesocervix i.e. the caudal portion of the mesometrium. This is significant because the cervix of a mare cannot be grasped, elevated and manipulated as it can in a cow.

6.Rotate and tilt the model so that the mesometrium, containing the uterine artery (middle uterine artery) can be seen clearly. Be reminded that a uterine artery can be forced back against the shaft of the ileum during foaling, rupturing the vessel, causing severe hemorrhage within the mesometrium. Unlike the situation in cows, there is no fremitus in this artery during pregnancy.

7.Rotate the model so that the attachment of the mesometrium the uterus along its lateral borders can be appreciated. Note in turn, how the mesometrium is attached to the abdominal wall on either side. This firm attachment affords substantial stability to the equine uterus and explains in part why uterine torsion is less common in mares than it is in cows. It also means that the equine uterus cannot be retracted during palpation as is done in cattle.

8.Rotate the uterus so that the intercornual ligament is visible. Although it is fairly well-developed. It is never used to retract the uterus  for reasons just mentioned.

9.Tilt the uterus so that its dorsal surface is visible, showing how the bifurcation of the uterine horns provides a T-shaped structure instead of the Y-shape characteristic of the bovine uterus.

10.Rotate the uterus up and down on it's transverse axis, noting the length of the uterine body in a mare compared to the very short body in ruminants. This has many implications. For example, in cattle is very important to enter a particular uterine horn for insemination or embryo collection. In mares by contrast, the long uterine body means that semen is simply deposited anywhere in the body and during embryo collection, the embryo is collected from the uterine body.

11.Rotate the tract and pan in and out over the ovaries, noting their large size in comparison to those of cows. Be reminded that although equine corpora lutea are three or four times the diameter of bovine corpora lutea, they cannot be detected by transrectal ovarian palpation. This is because equine  ovaries are surrounded by thick tunica albugineae, disguising the presence of corpora lutea. Therefore, to determine if a mare is ovulating (in the absence of progesterone assay) one must use ultrasonography

12. Noticeably absent from this model are the ovarian bursae. The author apologizes for that oversight and time allowing, will add that in his next life.

3D tangible, intangible and ghost tracts

Keywords: ghost, 3D, scanning, STL, model, teaching, client, education

To explore the value of three dimensional modeling in teaching and client education, the author scanned a frozen equine rectum and reproductive tract using a photographic 3D modeling program (3DSOM). The same process was used to scan an equine pelvis. 

Image size: 1417 x 1224px

After the mesh model of the rectum, anus, tract and pelvis had been built, it was re-modeled into a smoothed version of the scanned tissues using the 3D modeling program 3DSMax, being careful not to change basic anatomy. In this manner the tract, rectum and pelvis were re-created in an accurate, true-to-life, true scale representation. Using the resulting 3D mesh, the model was also converted into a stereolithographic (.stl) file which some readers will recognize as being a common file type used for 3D printing.  Using a tough and slightly flexible nylon polymer and selective laser sintering (SLS), several models of the tract were printed. See below.

Image size: 1696 x 1022px

Parts of the 3D model have been used for video production such as this entry in LORI or stationary images while the large model has been used for student and client education. 

Most recently, the author used the same model to create another potentially useful image for educational purposes. It is shown below.

Image size: 1590 x 803px

Finally, when the model is manipulated so that the SLS printing thickness in minimized, it takes on a radiograph-like appearance (see below). This makes lumens and internal structures such as the cervix and urethra visible; also structures that were modeled to scale. This provides the viewer with a unique perspective of the reproductive tract. 

Image size: 1233 x 781px

As mentioned, the author has printed several models of the tract and pelvis for teaching use. The tracts in the image below are about 30 cm long. Although it is possible to print in several colors, it is less expensive to paint the model as desired. To interact with a 3D STL model of this equine uterus and pelvis, click here. Please contact Dr Lofstedt at: lofstedt@upei.ca to report errors in the way this model functions.

Image size: 1152 x 1164px

Finally, to examine the possibility and potential value of creating 3D models for education, visitors may wish to view this video. 

A model to explain foaling

Keywords: equine, education, model, foaling

Image size:1478 x 813 px

The author uses this model frequently, especially during the foaling season when students participate in foal watches and when owners require instructions on what to expect during foaling and when to intervene. The model can be used to demonstrate the diffuse nature of equine placentation and how readily this may detach from the endometrium in cases of dystocia; far more rapidly than in ruminants. They are informed that this (in large part) accounts for the high death rate in equine dystocia. It is emphasized that second stage foaling is also very rapid and that the foal is likely to die unless the first responder has basic knowledge of how to respond during foaling. This is why the teaching model has proven valuable and why the author encourages others to build similar models.

With an assistant holding the red velvet allantochorion stationary within an imaginary uterus, the author demonstrates how the allantochorion remains attached to the endometrium after it has ruptured at the site of the cervical star. At this point, the author usually digresses, showing how the allantochorion can become detached from the endometrium, even before it has ruptured at the cervical star. In that case, it would move caudally and appear at the vulva lips instead of the amnion. This  serves to introduce the subject of premature placental separation (red bag) and the importance of rapid intervention should that occur.

Progressing in the vein of a normal foaling, the author shows how the amnion appears at the vulva lips with the forelimbs and muzzle of the foal visible through the amnionic membrane. The translucent polyester material used for the model allows this to be demonstrated clearly. There is an elasticized opening in the amnion. This opening shows where an attendant would cut the amnion or where it would rupture spontaneously. The author notes the possibility of asphyxiation in foals caused by an intact amnion remaining over the foal's muzzle after birth and consequently, stresses the need to transect or rupture the amnion when it first appears at the vulva lips.

At this time (before the simulated second stage is complete) the author may pull the model apart so that it is clear that the umbilical cord has two distinct parts; the intra-amnionic cord and the extra-amnionic cord. It is emphasized that this anatomy is distinctly different from that in ruminants where the amnion is attached to the chorion and there is no extra-amnionic cord. Furthermore, the author continues, it is that difference in anatomy that prevents the amnion from leaving the vulva lips and suffocating the newborn ruminant. In horses by contrast, the amnion is shown (in the model) to be free of the chorion, tethered to it only by the extra-amnionic cord. This allows the amnion to be born without rupturing, making neonatal asphyxiation a significant reality in horses; hence the need for amnionic rupture by the attendant.

At this time as well, for students of veterinary medicine or animal science it is useful to show a major difference in the anatomy of the intra- and extra-amnionic umbilical cords i.e. the presence or absence of the urachus. In the model, a yellow-colored string on the intra-amnionic umbilical cord represents the urachus. The urachus is shown to leave the umbilical cord where leaves the amnion and emerges into the allantois. This is used to demonstrate how allantoic fluid (predominantly urine) accumulates within the allantoic cavity. If the model is re-assembled at this point, it is possible to demonstrated how the allantoic fluid escapes when the allantochorion ruptures at the cervical star. The author adds that this is the first major discharge of fluid that occurs during foaling; before the rupture of the amnion and the discharge of amnionic fluid.

With the model re-assembled and the elasticized opening of the amnion at the vulva lips, the author emphasizes the need for immediate examination of fetal presentation, position and posture. Noting those conditions under which foaling is unlikely to proceed without specialized assistance (wry-neck, shoulder flexion, breech posture etc), the author turns to basic obstetrical mutations, especially carpal flexion and the need to repel the foal to obtain space for mutation. With the current model, the stuffed toy has short limbs that make it difficult to demonstrate malposture. A longer limbed toy would be preferable.

With the toy foal in normal position and posture, one can suggest to the student or owner that with a live foal, this is a time when one could contemplate leaving the stall, to observe the completion of foaling from a distance. Alternatively, if progress appears to have stalled, to intervene as necessary.

Once the toy foal has been "delivered", it is easy to demonstrate how the placenta can be expelled inside out or in its normal anatomical situation. The author usually takes this opportunity to mention that the placenta should be kept for inspection to ensure that placental fragments have not been retained and that there are no signs of placental pathology. This is also a convenient time to introduce the idea of time limits for placental expulsion and suckling (~3 hours in both cases).

Having used this model for many years, the author can attest to its value in teaching students and preparing horses owners for foaling.