What are Phalanx and Hoof Angles?
By Esco Buff, PhD, APF-I, CF
The word phalanx derives from the Greek term for a military formation where it can appear as if the bones are arranged side-by-side (as in a human hand), like an army formation.1,2 Phalanx (plural: phalanges or phalanxes) in equines refers to three bones found in the horse’s foot and lower leg. Between each of these three bones is a joint, known as a phalangeal joint, that allows the joint to be used for flexion or extension.1
The three phalanx bones are named based on their position relative to the rest of the body.1 Distal means furthest from the body and proximal means closest to the body.
The phalanx bones have several names. They are:
Coffin Bone or P3 or Distal Phalanx Bone, Short Pastern Bone or P2 or Middle Phalanx Bone, and Long Pastern Bone or P1 or Proximal Phalanx Bone.
The joints in between each of the phalanx bones also have several names. They are:
Coffin Joint or Distal Interphalangeal Joint, Pastern Joint or Proximal Interphalangeal Joint, and Fetlock Joint or Metacarpophalangeal Joint.3
Phalanx Angle refers to the alignment of the three phalanx bones when a line is drown through the center of rotation of each joint of the phalanx bones. 4 Phalanx Angle alignment can only be done with a correctly taken radiograph. Several studies have shown that straight phalangeal alignment is the ideal and poor bone alignment can predispose a horse to negative pathology or structural and functional changes. 4,5,6,7,8,9,10,11
Hoof Pastern Axis (HPA) refers to the alignment between the hoof and the pastern when a line is drawn through the middle of the pastern and compared to the angle of the hoof wall.4,9,10,11,12 It is a visual external assessment.
Hoof Pastern Axis (HPA) and Phalanx Angle are not the same. They are two different ways of assessing angles in the limb. Sometimes they can be very different from each other and the same at other times. One requires radiographs (phalanx angles) and one does not (hoof pastern axis).
When referring to phalanx angles and hoof pastern axis, there are three types of alignments: broken back, ideal or straight, and broken forward.
Straight phalanx angle and straight hoof pastern axis is when the angle of alignment is a straight line.
As written previously, studies have shown that straight phalangeal alignment is the ideal and poor bone alignment can predispose a horse to negative pathology or structural and functional changes.4,5,6,7,8,9,10,11 Therefore, the goal is to try and maintain a more ideal alignment. This can be done by the farrier in multiple ways depending on numerous variables.
This article will help you understand the terminology associated with phalanx angles and hoof pastern axis in order to enhance your knowledge and understanding when the farrier is discussing these terms with you.
References and Resources
1. Phalanx. The Biology Dictionary. Last updated April 28, 2017. https://biologydictionary.net/phalanx/
2. Phalanx. Merriam-Webster Dictionary. Last updated May 3, 2022. https://www.merriam-webster.com/dictionary/phalanx
3. Al-Agele, R. et al., 2019, 'The Anatomy, Histology and Physiology of the Healthy and Lame Equine Hoof', in C. S. Rutland, V. Kubale (eds.), Veterinary Anatomy and Physiology, IntechOpen, London. 10.5772/intechopen.84514.
4. The Truth About Hoof Pastern Angle. The Truth about Hoof Pastern Axis (theequinedocumentalist.com).
5. Dorner, Cristobal & Fueyo, Pablo & Olave, Rodrigo. (2017). Relationship between the Distal Phalanx Angle and Radiographic Changes in the Navicular Bone of Horses: A Radiological Study. Global Journal of Medical Research. 17. 7-13. 10.17406/GJMRG.
6. Weaver M, Shaw D, Munaiwa G, Fitzpatrick D, Bellenger C. 2009.Pressure distribution between the deep digital flexor tendon and the navicular bone, and the effect of raising the heels in vitro.Vet. Comp. Orthop .Traumatol. 22, 278-282.
7. Waguespack and Hanson, 2010, Navicular Syndrome in Equine Patients: Anatomy, Causes and Diagnosis, https://www.vetmed.auburn.edu/wpcontent/uploads/2015/01/PV1110_waguespack_Surgical.pdf.
8. Ruff, K.C., Osborn, M.L. and Uhl, E.W. (2016), Analysis of Forces Acting on the Equine Navicular Bone in Normal and Dorsiflexed Positions. The FASEB Journal, 30: 923.4- 923.4. https://doi.org/10.1096/fasebj.30.1_supplement.923.4.
9. Moleman, M., Van Heel, M.C.V., Van Weeren, P.R. and Back, W. (2006), Hoof growth between two shoeing sessions leads to a substantial increase of the moment about the distal, but not the proximal, interphalangeal joint. Equine Veterinary Journal, 38: 170- 174. https://doi.org/10.2746/042516406776563242.
10. O’grady, SE. The Negative Palmer Angle. Equine Therapeutic Farriery | Dr. Stephen O'Grady, veterinarians, farriers, books, articles (equipodiatry.com).
11. 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. https://doi.org/10.1111/eve.13186.
12. Hoof Pastern Axis – Influential Factors. Hoof Pastern Axis - Influential Factors (theequinedocumentalist.com).
