Back to basics: Hoof pastern conformation and its role in development of pathology within the coffin joint

Warmbloods and Warmblood cross-breeds make up a high proportion of sports horses in active competition work in the Western world. As a breed, Warmbloods often have small feet relative to their body size and weight, resulting in proportionally increased load on structures within the hoof capsule. This may predispose to some patterns of pathology, resulting in lameness that can be localised to within the foot. The paper by Carrozzo et al. (2025) presents an uncommon variation of a common pathology, namely osteoarthritis of the distal interphalangeal joint (DIP), in a small number of Warmblood horses all working competitively at a high level within the showjumping industry.

The propensity for many horses to be ‘broken back’ in hoof pastern conformation, with a long toe and low heel conformation extends the point of breakover further dorsal relative to the long axis of the distal limb and places greater loading forces onto the dorsodistal aspect of the middle phalanx and the extensor body and extensor process of the distal phalanx. Therefore, a ‘broken back’ conformation as well as a high workload may explain why lameness clinicians routinely see modelled articular margins, new bone formation and areas of sclerosis (radiographs and MRI) or abnormal fluid accumulation (‘oedema’ on MRI) within the trabecular bone of the dorsal aspect of these osseous structures within the dorsal recess of the DIP joint (Figure 1), rather than modelling within the palmar recess of the DIP joint.

A ‘broken back’ hoof pastern conformation also results in the palmar flexor compacta of the navicular bone becoming liable to greater compressive force from the deep digital flexor tendon, with pathology we might expect to see on MR images including abnormal increased fluid/necrosis signal within the navicular spongiosa and focal concavities in contour representative of erosive lesions extending within the flexor compacta (Figure 2).

Increased compressive forces between the two adjacent articular surfaces of the palmar distal aspect of the middle phalanx and the dorsal margin of the navicular bone due to increased load from proximal, perhaps secondary to repeated jumping effort rather than solely due to increased shearing forces secondary to DDFT compression may be a contributing cause of the relatively rare occurrence of osteoarthritis primarily within the palmar recess of the DIP joint reported in the accompanying paper. The authors note the need for further research investigating conformation as a potential cause of increased forces between the articular surfaces of the middle phalanx and the navicular bone.

It is interesting to note that in the three cases presented there appears to be little evidence of modelling within the dorsal recess of the DIP joint despite the extensive changes described within the palmar recess. It is interesting to consider what other factors may be contributing to a primary increased compressive load on the navicular bone and the changes consequently seen on the images shown.

Considering the findings reported, we should consider whether the comparatively common observation on MR images of thickening of the dorsal endosteal margin of the navicular bone (Figure 3) should be viewed as a precursor to the more advanced changes described in this paper and make note of the implications of this milder feature when summarising the potential relevance of imaging findings in clinical records.

Even with advanced multiplanar imaging modalities such as CT and MRI, it remains difficult to reliably diagnose cartilage loss antemortem in clinical cases until this pathology is advanced (McKnight & Posh, 2012; Rovel et al., 2019). Recent research by Baker et al. (2023) validated a pulse sequence for T2 mapping of cartilage within the DIP joint using low-field MRI and illustrates the need to continue to develop technologies which facilitate diagnosis of cartilage damage at earlier stages, if treatment options are to have more chance of being successful in restoring a functional level of soundness to affected horses.

This paper provides useful guidance for clinicians interpreting images from all forms of diagnostic imaging modalities and is a reminder to pay close attention to structures juxtaposed within the palmar recess of the DIP joint, to increase likelihood of detection of the development of pathologies in this area at earlier stages than are presented in the accompanying paper. It is important to check critically the positioning of slice set up and the orientation of resulting images obtained from multiplanar imaging modalities, such as CT and MRI, and to avoid dismissing the appearance of potentially less common pathology as being due to slice obliquity or limb positioning (Case 1). Case 3, illustrated in Figure 2 is additionally interesting as the MR images show a more symmetric pattern of abnormal low signal within the palmar lateral and palmar medial aspects of P2, which might also be overlooked for reasons of symmetry.

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