EQUINE VETERINARY EDUCATION Equine vet. Educ. (2020) 32 (1) 39-45 doi: 10.1111/eve.12922
Review Article Prepubic tendon rupture in the mare
S. L. Jalim Victorian Equine Group, White Hills, Victoria, Australia Corresponding author email:
sarah.jalim@victorianequinegroup.com.au
Keywords: horse; mare; prepubic tendon rupture; abdominal wall; body wall
Summary The following article discusses the clinical appearance, diagnosis, management and prognosis of abdominal wall tearing and prepubic tendon (PPT) ruptures of mares.
Introduction
Prepubic tendon (PPT) ruptures are a condition of the heavily pregnant mare. Many features of this condition overlap those of abdominal wall (AW) ruptures or hernias, often making them difficult to distinguish in the early stages. They may be categorised together as body wall defects. The conditions can be difficult to manage and constitute a high-risk pregnancy. Historically, the conditions have been given a guarded prognosis for survival of mare and foal (Hanson and Todhunter 1986).
Anatomy
The abdominal wall is made up of the external and internal abdominal oblique muscles and their aponeuroses, the transversus abdominis and rectus abdominis muscles. Any or all of these muscles may be involved in abdominal wall tearing (Hanson and Todhunter 1986). In cases of AW rupture, the intestines (and less commonly the uterus) can lie subcutaneously. The prepubic tendon extends ventrally from the brim of
the pelvis, obstructing fetal delivery in malpresentations where the fetus has its head deviated ventrally. The PPT runs along the pectin of the pelvis from one iliopubic eminence to the other (Fig 1) and is comprised of the linea alba and the insertion of the rectus abdominis muscle, which crosses such that fibres from either side of midline insert onto the PPT (Habel and Budras 1992). It is the origin of the pectineus muscle (running from iliopubic eminence to the pelvic symphysis) and the origin of the gracilis muscles, which run from the cranial end of the PPT to the inner thigh. Complete rupture of the PPT leads to complete loss of support to the ventrolateral abdominal wall (Hanson and Todhunter 1986).
Signalment
Although traumatic abdominal wall tearing is possible in any horse, PPT rupture is a syndrome only of the heavily pregnant mare. It is more common in older, multiparous mares, but will occasionally be seen in maidens. A breed predisposition has been cited in draught horses (Hanson and Todhunter 1986), and a heritable component is suspected in the Egyptian Arab (Nahachewsky et al. 2013). Suggestions have been made that Standardbreds with abdominal wall tearing may also appear to be over-represented (Ross et al. 2008), and
this appears to be true in our case population. Other commonly cited predisposing factors are the presence of twins or hydrops (Hanson and Todhunter 1986).
Clinical signs of body wall defects
Mares with abdominal wall tearing usually show signs of abdominal pain. They show a progressive ventral or ventrolateral oedema, making palpation of underlying defects in the abdominal wall difficult. Occasionally, the outline of gastrointestinal viscera can be seen directly under the skin (Fig 2). Mares with PPT are often distressed and painful. They are
reluctant to move or lie down. Tachycardia of 60–80 beats/ min and upwards is common. They often demonstrate a more severe and rapidly progressive ventral oedema, compared with mares with abdominal wall tearing. This oedema commonly extends from the forelimbs caudad to the udder. These mares develop a characteristic stance as the pelvis tips cranially without stabilisation by the abdominal wall. The flank area is poorly defined and lordosis develops with elevation of the tubera sacrale, tubera ischia and tailhead (Hendriks et al. 2007). The mammary gland will be oedematous and may have an abnormally “pulled forward” conformation with the teats pointing cranially. Blood may be seen exiting the front orifice of each teat (Fig 3). Both conditions can usually be diagnosed based on their
clinical signs. The main differential diagnosis is that of hydrops (hydroallantois or hydramnion) in which mares will also demonstrate progressive abdominal enlargement with accompanying ventral oedema (MacPherson 2012). Transrectal ultrasonography is of limited use; whilst the
prepubic tendon is palpable per rectum in nonpregnant mares, it cannot be palpated with a foal in utero. Transrectal palpation however may alert one as to the possibility of hydrops where one will palpate a severely distended uterus, and potentially an absence of fetal ballottement (Slovis et al. 2013).
Transabdominal ultrasonography may allow one to
differentiate AW tearing from a PPT rupture. In cases of abdominal wall tearing, it may be possible to visualise defects within the muscle wall (Fig 4), with accompanying haematomas or haemorrhage. Transabdominal ultrasonography will allow one to detect
underlying hydrops or (sometimes unreliably) twin pregnancies. Transabdominal ultrasonography is a key diagnostic tool in monitoring fetal viability during treatment.
Management
Decision making in these cases can be difficult, as saving both mare and fetus in advanced cases is unusual in the
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