Low heels are the most common abnormal hoof conformation seen in both the front and hind feet of horses. This conformation causes a ‘broken‐back’ hoof‐pastern axis and hyperextension of the distal interphalangeal (coffin) joint.
A low/negative or broken back hoof pastern axis in the front feet has been associated with palmar heel injuries but the significance of such angles in the hind feet has only recently received attention. A prospective case‐controlled study to investigate the association between hind foot pedal bone angle and hindlimb lameness in a UK population of horses has recently been published (Clements et al., 2020).
Horses presenting for orthopaedic investigation underwent complete lameness assessment with localisation of lameness using diagnostic nerve blocks. The hind foot pedal bone angle (PDA, the angle between a line parallel to solar surface contacting the ground and the solar margin of the pedal bone) was calculated from lateral x-rays of the foot. One hundred and eighty‐two horses were included in the study, 132 with hindlimb lameness and 50 controls. Student's t ‐tests and multivariable linear regression models were used for statistical analysis. The mean left PDA for the lame group was −1.0° compared to +1.8° for the controls. The mean right PDA for lame group was −1.1° compared to +1.4° in controls (both P<0.001).
The majority of lame horses had bilateral lameness which likely explains why the PDA did not differ significantly between the predominantly lame limb and the less lame contralateral limb. As a result of the high numbers of bilateral lameness cases, the remaining small number of unilaterally lame horses precluded a comparison between the PDA in the lame and sound feet in this unilateral hindlimb lame subset.
Lameness was most frequently localised to the stifle (59% of horses), followed by the distal tarsal joints and the proximal suspensory region. A limitation of the study was that the control group included some forelimb lame horses. It was concluded that horses with hindlimb lameness, including lameness localised to the stifle, were more likely to have negative pedal bone angles. In contrast, in the forelimb low heel confirmation and pedal bone imbalance most commonly leads to injuries to the navicular region. This difference is proposed to be due to the differing function between the front and the hind feet. The primary function of the back of the front foot are to dissipate shock and withstand a complex array of biomechanical forces, whereas the function of the back of the hind feet may be more propulsionary. Further kinematic studies are warranted to investigate this association between hind foot conformation and stifle lameness.
Clements, P.E., Handel, I., McKane, S.A. and Coomer, R.P. (2020), An investigation into the association between plantar distal phalanx angle and hindlimb lameness in a UK population of horses. Equine Vet Educ, 32: 52-59 Available HERE