Follow-Up Magnetic Resonance Imaging of Sagittal Groove Disease of the Equine Proximal Phalanx Using a Classification System in 29 Non-Racing Sports Horses

Abstract

Evolution of magnetic resonance imaging (MRI) findings in horses with sagittal groove disease (SGD) of the proximal phalanx is relatively sparsely described. This retrospective, descriptive, longitudinal study describes the findings of sequential low-field MRI fetlock examinations in horses with SGD of the proximal phalanx using a classification system. Twenty-nine horses were included, predominantly warmbloods used for show jumping (79%). For 29 limbs re-examined during the initial rehabilitation period, classification remained constant (n = 18), increased (n = 2), decreased (n = 7), and fluctuated (n = 2). Notably, two limbs with initial classification 4b (bone oedema-like signal with subchondral microfissure) and one with 4c (bone oedema-like signal with subchondral demineralisation) progressed to classification 5 (incomplete macrofissure/fracture), highlighting their potential as prodromal or imminent fissure pathology. Following conservative (n = 28) and surgical (n = 1) treatment, 86% of the horses re-entered full training and competition with a mean ± sd recovery time of 9.4 ± 4.4 months. In total, 20% of horses in the study subsequently presented for repeat MRI due to recurrent lameness after resuming full work, with classification that was the same (n = 2), increased (n = 2), or decreased (n = 2) compared with the last scan. This study underscores the variability in progression of SGD MRI findings, emphasising the need for further larger-scale research into patterns of progression.

Keywords: MRI; P1; bone fatigue; bone stress; fissure; horse; subchondral bone.

Figure 1

Flow chart overview of the number of horses and limbs with sagittal groove disease (SGD) included in the study, with green and orange boxes representing those included in the initial and subsequent periods.

Figure 2

Line graph showing evolution of sagittal groove disease (SGD) MRI classification from initial MRI examination for 29 horses with SGD (32 limbs) during the initial rehabilitation period. Overall, throughout the initial period, eighteen limbs maintained the same classification, two increased, seven decreased and two fluctuated. Three limbs were not re-examined in the initial period. Notes. Each plotted circle represents the results of one MRI examination, with different colours representing different horses (colours consistent across both charts). Lines join the sequential examinations for each limb (initial examination, t = 0). Lettered labels A–D indicate bilateral forelimbs of the same horse. Coloured arrows on the y-axis indicate limbs of horses that were at rest for 2–3 months prior to the initial MRI examination; the remainder of horses were in full work until more recently. Red squares indicate the timing of an MRI examination just before CT-guided surgical treatment was pursued.

Figure 3

Line graph showing evolution of sagittal groove disease (SGD) MRI classification from initial MRI examination for 6 horses (8 limbs) that re-presented for MRI after recurrence of lameness following a period in full work. Notes. Each plotted circle represents the results of one MRI examination, with different colours representing different horses (colours consistent across both charts). Lines join the sequential examinations for each limb (initial examination, t = 0). Numbered labels 1–6 indicate horses as referred to in Table 3. Lettered labels A, C, D indicate horses with bilateral forelimbs scanned. Red stars indicate a repeat MRI examination due to recurrence of lameness following a period in full training and competition. A coloured arrow on the y-axis indicates a limb in a horse that was at rest for 2–3 months prior to the initial MRI examination; the remainder of horses were in full work until more recently. Red squares indicate the timing of an MRI examination just before CT-guided surgical treatment was pursued.

Figure 4

From left, dorsal T1W GRE, dorsal STIR FSE, sagittal T1W GRE and sagittal T2 GRE images of the left hindlimb fetlock of a horse with decreased sagittal groove disease (SGD) MRI classification between (A) the initial examination (classification 5) and (B) repeat examination 6 months later, at the end of the rest period of the rehabilitation program (classification 4b). The extent of bone oedema-like signal associated with the sagittal groove has markedly reduced, and a faint linear hyperintense microfissure persists in the subchondral bone plate but is no longer extending into the trabecular bone. There is concurrent osteophytosis of the fetlock joint and densification and bone oedema-like signal in the dorsal aspect of the sagittal ridge of the third metatarsus. Notes. T1 GRE, T1-weighed gradient recalled echo; STIR FSE, short tau inversion recovery fast spin echo; T2 GRE, T2-weighted out of phase gradient recalled echo (T2*oW).

Figure 5

From left, dorsal T1W GRE, dorsal T2 GRE, dorsal STIR, sagittal T1W GRE and sagittal STIR images of the left forelimb fetlock of a horse with increased SGD MRI classification between (A) repeat presentation for MRI following a period in full work (classification 4c) and (B) 3.5 months later during the rest period of the rehabilitation program (classification 5). There is an increase in bone oedema-like signal and development of a visible proximodistally oriented tripartite macrofissure, which is associated with the previously identified demineralisations in the subchondral bone plate of the SG. There is concurrent osteophytosis of the fetlock joint and densification of the dorsal aspect of the sagittal ridge of the third metacarpus. Notes. T1 GRE, T1-weighed gradient recalled echo; T2 GRE, T2-weighted out of phase gradient recalled echo; STIR FSE, short tau inversion recovery fast spin echo (T2*oW).

Figure 6

From left, dorsal T1W GRE, dorsal T2 GRE, dorsal STIR and sagittal STIR, images of the right hindlimb fetlock of a horse with static SGD MRI classification between (A) initial examination (classification 5) and (B) 3 months later during the rest period of the rehabilitation program (classification 5). Despite there being no change in classification, there are signs of healing as there is almost complete resolution of the bone oedema-like signal associated with the SG and the macrofissure line is only faintly appreciated. Notes. T1 GRE, T1-weighed gradient recalled echo; T2 GRE, T2oW/, T2-weighted out of phase gradient recalled echo; STIR FSE, short tau inversion recovery fast spin echo.