An Investigation into the Postural Link Between Negative Plantar Angles and Concurrent Pathology Along the Dorsal-Myofascial Line Using Thermography
Y. Sharp
Introduction
Rationale
Studies have linked poor hind hoof balance with postural changes (Sharp and Tabor 2022) and pathology within the hind limb, with suggestions of further links into the trunk of the horse (Mannsman et al. 2010, Pezzanite et al. 2018, Clements et al. 2019). However, Pezzanite et al. (2018) and Clements et al. (2019) used diagnostic analgesia to locate isolated pathologies, suggesting the primary source of lameness, however this method is limited in recognising causation and concurrent dysfunctions. This aims of this study was to suggest areas of concurrent pathology, as areas of increased surface emissivity, using thermography, stated as clinically relevant by a specialist interpreting veterinarian, in horses presenting with negative plantar angles (NPLA) and a canted-in posture.
Hind Hoof Balance, Posture, and the Dorsal Myofascial Line
Although radiographically presenting the same as NPA, the equivalent in the hindlimbs, NPLA do not seem to present with the similar associated pathologies. Dyson et al. (2007) alluded to poor hind hoof balance being a predisposing factor in suspensory lesions, although this study did not quantify a relationship between NPLA and suspensory lesions directly, it portrayed experiential factors of its genesis, poor hoof balance and a “long toe, low heel” conformation were suggested as predispositions, especially if presenting with abnormal orientation of the distal phalanx. Mansmann et al. (2010) linked “long toe, low heel” conformation with gluteal pain, Pezzanite et al. (2019) concluded that horses with hind limb lameness localised to the distal tarsal and proximal metatarsal regions were likely to present with NPLA and most recently Clements et al. (2019) correlated NPLA with stifle pathology amongst others, with all these studies highlighting the benefits of farriery intervention (Fig.1).
Fig. 1 Historical connections between poor hind hoof balance and pathology in hind limb.
This importance of farriery intervention was quantified by Sharp and Tabor (2022) which showed limb posture was directly affected by hoof balance. The literature listed here highlights the correlation between hoof balance, posture, and pathology in the hind limb, but does not address the causation.
Clements et al. (2019) asked why the hind limbs do not present with the same pathologies as the front limbs and speculated that different ground reaction forces, shown by Hobbs et al. (2018) may be responsible for this. Hobbs et al. (2018) showed the difference in ground reaction forces in the front and hind limbs. The average force vector in the front was taller and more caudally oriented in accordance with the higher vertical and braking forces compared with the hind limbs which had a shorter and more cranially oriented average force vector due to the higher propulsive forces.
However, Sharp and Tabor (2022) suggested that static postural adaption plays a role in load transfers on both the hind hoof and higher structures and agreed with Mannsman et al. (2010), Pezzanite et al. (2018) and Clements et al. (2019) who all observed postural adaptation in their cohorts, this may be responsible for the pathophysiological/morphological cycle between the hoof, hind limb, and trunk.
Similar connections between the hoof and higher structures can be extrapolated from biomechanical studies, Hobbs et al. (2018) showed how in horses with high low front hooves, spinal stiffening and contralateral hind limb compensations were necessary for straight line propulsion and Landman et al. (2004) and Gomez – Alvarez et al. (2007) expressed the connections between lameness, spinal biomechanics, and pain in horses. These studies express dynamic relationships between hoof balance and pathology into the trunk of the horse, however research into static posture relationships between the hoof and the rest of the musculoskeletal system are limited. Considering the performance horse is stalled and/or stands for much of the day this warrants further research to outline compensatory postures’ physiological effects, on not just the hoof but the entire musculoskeletal system.
Gellman and Ruina (2022) explored the physics of abnormal compensatory posture (ACP) using mathematical models and hinted at musculoskeletal effort associated with non-vertical M3 bones. Previously, Gellman (2010) discussed neutral posture and the importance of recognition of posture as a picture of neuro-muscular system state and proprioceptive input. Gellman (2010) stated any diversion from the ideal posture pointed toward pathology, not only in the feet but it discussed the teeth and stomatognathic systems link to foot proprioception. Bowker et al. (2012) discussed the hoof as a neurosensory organ, playing a role in postural adjustments and providing stimuli for the horse to adopt appropriate postural stance. This theory was tested by Sharp and Tabor (2022) and shown to have merit, however, the mechanisms are still assumed. Postural compensations could be proven, through further research, to be a neurological response to changes in the proprioceptive input received from the hoof. While research into the relationship between hoof balance and posture is in its infancy, studies into the effects of that posture on musculoskeletal health is even more limited.
Gellman (2010) highlighted how forces acting on the hoof can be abstract. It discussed the effect of ACP on higher structures in the hind limb, pointing at ACP being a possible contributing factor in the pathogenesis of the pathologies associated with NPLA, and quantification of ACP associated with NPLA (Sharp and Tabor 2022) has begun, but quantification of the influence of these relationships on concurrent higher pathologies is limited, and could help to further elucidate the causation of this relationship. Research to find links further along the kinetic chain is therfore warranted as the interconnectivity of myofascial lines is extensive (Elbrond and Schultz 2015) (Fig.2).
Fig. 2 The superficial myofascial lines. Four lines extend all the way into the hoof. These lines show meridians of influence and anatomy directly connected by fascia. Their interconnection is extensive.
The kinetic chains and myofascial connections alluded to by Mannsman et al. (2010) have recently begun to be studied in the horse. Elbrond and Schultz (2015) studied the myofascial connections within the horse, concluding that understanding the myofascial lines would aid in unravelling the cause of locomotory issues, although quantification of this statement requires further research. Elbrond and Schultz (2015) extrapolated mechanical function of the myofascial system in locomotion and posture in the horse from human studies (Myers 2009), expressing that dysfunction within a segment could cause biomechanical disorder elsewhere. A myofascial line possibly most relevant to this study described by Elbrond and Shultz (2015) is the “superficial dorsal line” (Fig. 3) which starts in the hind hoof and extends up the hind limb, along the spine and into head.
Fig. 3 The superficial dorsal myofascial line showing the kinetic muscle chain.
This is the line expressed by Mannsman et al. (2010) as the most relevant myofascial line in the equine hind limb. Although Elbrond and Shultz (2015) showed myofascial connections extending into the hooves there is limited research into connections between them and the musculoskeletal system along these lines. Research to quantify pathophysiological relationships, resulting from ACP, connected to hoof balance, along the dorsal-myofascial line, could be useful outlining the cause of postural issues and their effect on locomotory issues.
Levin et al. (2017) expressed kinetic chains as ubiquitous across species, in agreement with Myers (2009), a statement most relevant to this study highlighted that the position and orientation of each anatomical part is a result of the loadings and functional demands of the wider system.
It could therefore be suggested that the position and orientation of the equine hind limb, could be a result of not just hoof balance (Sharp and Tabor 2022) but also the physiological state of the horse’s entirety. While abnormal position of the hind limb could create abnormal, pathological loading and musculoskeletal pathology along the dorsal-myofascial line.
Thermography
Kinetic chains are made up of multiple structures; bones, muscles, ligaments, and nerves (Levin 2017), each of which require different diagnostic modalities to assess (Dyson 2013). This creates difficulty in quantifying the kinetic chain dysfunction associated with NPLA via conventional methods, as reduction in lameness after diagnostic analgesia of a certain area suggests primary pathology. Taking into consideration the possibility of causation or concurrent issues somewhere else in the kinetic chain becomes subjective. To fully appreciate the extent of kinetic chain dysfunction a modality able to assess multiple biological tissues at once is indicated. Thermography has been shown to be useful in myofascial study (Hadad et al. 2012, Dibai-Filho et al. 2015), it has been used to assess myofascial pain syndrome (Cojocaru et al. 2015) and is used in diagnostics for the assessment of pathologies associated with a wide range of structures (Shirzadfar et al. 2018). Although thermography has not become part of mainstream equine diagnostics, due to its limitations (Soroko and Howell 2018), when used clinically it has historically been successful in indicating areas of inflammation that could account for drops in performance and detect regions of pain and musculoskeletal overload (Soroko and Howell 2018). As early as 1980 it has been shown to detect spinal pathology (Purohit and MCcoy 1980) and has been described as the most sensitive modality for the detection of equine back pain (von Schweinitz 1999). More recent studies have demonstrated its efficacy in the detection of spinal lesions (Fonseca et al. 2006, Soroko at el 2014). Although thermography provides localization and physiological information, it lacks structural specificity and cannot outline aetiology so is best used alongside other diagnostic procedures (Eddy et al. 2001). Relevant to this study, thermography’s ability to quickly and non-invasively (Raedelli et al. 2014) assess the whole horse, irrespective of system type, including both primary, secondary, and early-stage issues (Eddy et al. 2001, Soroko and Howell 2018), along a kinetic chain could be a huge benefit.
Hypothesis
A null hypothesis for this study was that there would be no correlation between the presence of ACP, NPLA and inflammatory processes along the dorsal myofascial line.
Alternative hypotheses were that horses with NPLA would present with ACP and have inflammatory processes along the dorsal myofascial line. They would have inflammatory markers in the areas linked by Mannsman et al. (2010) gluteal region, Pezzanite et al. (2018) hock region and Clements et al. (2019) stifle region, they would also present with additional concurrent inflammatory processes further into the trunk along the dorsal myofascial line. Farriery intervention to create improved hoof balance and digit proportions will affect limb orientation.
Methods
Methods for photography and farriery intervention can be found in my published paper.
Thermography protocols were exacted according to Soroko and Howell (2018) Appendix 1 and were taken in a bone scan room after a half hour equilibration period. Thermography interpretation was performed by Home - Vet IR (vet-ir.com).
Results/Discussion
A comprehensive discussion on the farriery intervention, postural changes and data can be read at the above linked paper. In this article we will be focusing on the link between hoof balance, postural changes, and thermographic findings.
The results showed a direct link between how broken back the hoof pastern axis was and metatarsal angle (Fig.4), showing that the more imbalanced the hoof, the more canted-in the horse’s posture.
Fig.4 From Sharp and Tabor (2022) showing how the changes in hoof pastern axis correlated with changes in metatarsal angle.
However, an interesting finding was that there was no significant change in hock angle (Fig.5).
Fig.5 From Sharp and Tabor (2022). (A,B,C) Results of joint angle changes and suggested further study. A is a photo showing a pre and post intervention case. Red lines denote noted changes in angle with the significant finding of the change in MA denoted by *. Measuring changes in pelvic inclination (red and green lines along buttocks) was beyond the scope of this study but is suggested for further research. (B) According to the rule of the reciprocal apparatus, the non-significant change in HA informed the assumption of a non-significant change in stifle angle, shown as 1 = 1 and 2 = 2. C shows joints for further research, to elucidate where the change in limb posture is coming from, denoted by red question marks (sacro-illiac, lumbo-sacral, hip joint). The thoracolumbar joint is also highlighted as an area for research on further links.
91% of the 12 cases had caudal thoracic inflammation, 91% had Sacro-iliac, 58% had gluteal, 58% had hamstring, 58% sciatic, 91% hock, 16% stifle and 25% had proximal metatarsal inflammation (Figs 6,7).
Fig.6 Areas of increased surface emissivity in the studies population presenting with NPLA.
Fig.7 The percentages of the study population that presented with the most prevalent areas of increased emissivity. Showing areas for further research with links to poor hind hoof balance. Note how they all follow the dorsal-myofascial line.
The insignificant changes in hock angle also suggests, due to the reciprocal apparatus, that the stifle angle was not significantly changed. This points toward the change in limb orientation coming from higher structures, likely the pelvic region. This could explain why 91% of the cases showed sacro-iliac inflammation. This sacroiliac inflammation could be a contributing factor in 58% of cases presenting with hypothermic readings in the sciatic groove as the inflammation could be creating impingement and subsequent neuropathy (Fig. 8).
Fig. 8 One of the cases showing presenting posture, radiograph, and thermographic reading and report.
Considering the preliminary finding of Tabor et al. (2018), which suggested a link between thoracolumbar extension and over-riding spinous processes, research into the effects of ACP on the thoracolumbar region could be warranted and explain the presence of caudal thoracic inflammatory markers in 91% of the studies population. Further research to measure hip extension and pelvic inclination, and the effects on the spine, associated with ACP are indicated to clarify these connections and outline pathogenesis. Importantly the findings showed multiple areas of inflammation along the dorsal myofascial line in every case (Fig 9 ).
Fig. 9 Example of Thermography readings. All the horses presented with multiple areas of increased surface emissivity along the dorsal myofascial line. Caudal thoracic, sacro-iliac and hock inflammation were the most prevalent.
The study supported the findings of Mannsman et al. (2010), finding 58% of the study population presenting with inflammatory markers in the gluteal region. This study also found 58% of the population with thermographic significance in the hamstrings, areas for further research. Our findings would seem to agree with Pezzanite et al. (2018) over Clements et al. (2019) as hock inflammation presented in 91% of the population while only 16% presented with stifle inflammation. However, this could prove to be a limitation of the screening modality or a result of different populations.
This study suggests a correlation between posture, NPLA and physiological dysfunction along the dorsal myofascial line and indicates links further into the trunk as suggested by Mannsman et al. (2010). While this study suggests the links are more extensive, and are concurrent, with posture being an important factor, more research is needed to establish causation. Future research could quantify links further along the myofascial lines and test the suggestions of Gellman et al. (2014) correlating ACP with neuro-dental and upper cervical issues. Whether the mechanisms creating ACP are purely proprioceptive or also antalgic responses to concurrent pathologies, also remains to be established.
While thermography was useful in highlighting concurrent inflammatory markers, it does not show structure and is best used as a prerequisite for further diagnostics (Eddy et al. 2001). While some of the clinical relevance of the thermographs proved to correlate with subsequent clinical findings, it was beyond the scope of this pilot study to quantify this. Further research could utilise veterinary investigations and other diagnostic modalities to establish the relevance of the findings of this study’s areas of increased surface emissivity and outline structural pathologies and confirm the existence of concurrent pathologies. However, the areas highlighted corresponded with the findings of Mannsman et al. (2010) and Pezzanite at al. (2018) and show studies further into the trunk are warranted.
Conclusion
This study suggests that the links between hind hoof balance and musculoskeletal pathology extend beyond the current associations in the hind limb, into the pelvis, sacro-illiac, and caudal thoracic regions and may also have neurological implications in the sciatic nerve. It highlights the importance of addressing hoof balance when dealing with physiological dysfunction and postural and locomotory issues following the myofascial lines.
It informs and encourages the importance of a collaboration between farriers, veterinarians, and practitioners.
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Appendix 1
Soroko and Howell (2018) Appendix. Procedures for Thermographic Examination
a. The thermographic examination should be performed indoors, in areas sheltered from the sunlight, in the absence of air drafts [9,62,63]. Normally, outdoor thermography is not recommended because the impact of the external environment will provide unreliable thermograms [13,14].
b. The temperature of the examination area should be cooler than body surface temperature, with the recommended ambient temperature ideally maintained between 21C and 26C if the local climate allows. Thermographic examination should not be performed during extreme variations in environmental temperature [13]. Ambient temperature has a significant influence on the surface temperature of the distal parts of limbs. At low-ambient temperatures, there is a decrease of blood circulation in the distal parts. At ambient temperatures above the recommended range, vasodilation causes a generalized warming of the extremities, encouraging heat loss to the environment [15]. At high ambient temperatures, contrast between the horse and background is lost, and local inflammation may be masked. Research by Mogg and Pollitt [11] has shown that for interpreting the effects of vasoconstrictor agents, the recommended air temperature is >20C, and for the study of vasodilatory agents, the ambient air temperature should ideally be <18C.
c. The minimum recommended acclimatization time for the horse before imaging is 20 minutes [13]. However, a longer period of equilibration will be required if a horse is transported from an extreme cold or hot environment [15]. According to Tunley and Henson [19], the thermographic pattern does not change significantly during acclimatization, but the time taken for stabilization of the absolute temperature of the body surface is between 39 and 60 minutes. The major factor affecting this equilibration time is the temperature difference between the original environment and that in which the images are to be obtained.
d. The ambient temperature and humidity inside and outside the examination room should be recorded. It has been reported that atmospheric pressure and humidity do not have a significant influence on distal limb temperature [64], but high humidity should be avoided.
e. The horse must have a clean, dry hair coat and skin and should be groomed at least 1 hour before the examination to eliminate artefacts arising from changes in surface emissivity.
f. Similarly, the feet should be clean, picked out, and brushed to remove external contamination.
g. Variables in winter hair coats can confuse interpretation. Clipping is not required to produce reliable thermographic images, but it is necessary that the hair coat be short, of uniform length, and lay flat against the skin to permit thermal conduction [29].
h. Blankets should be removed at least 30 minutes before thermographic examination, and any bandages should be removed at least 2 hours before imaging [62].
i. Purohit [13] recommended imaging should be performed before exercise, although sensitivity for the detection of specific pathologies (e.g., navicular disease) may be increased by subjecting the horse to an exercise stress [29,65]. The horse should not receive any physical therapy within 24 hours before the thermographic examination and should not have acupuncture in the region of the examination during the previous week.
j. Imaging should be performed before the application for the day of any necessary systemic or topical medications. Any residues should be washed off the previous day [6].
k. Unless of specific interest, avoid imaging areas of diagnostic anesthetic injections, joint block, skin lesions such as scars or blisters, or surgically altered areas. Artefacts can be produced by any material on the body surface such as dirt, thick coat, scars, and bands [62]. Anti-inflammatory medications, vasoactive drugs, regional and local blocks, sedation, and tranquilization should be avoided because of their effect on superficial perfusion [63].
l. Notes of the thermographic examination should include age, gender, and breed of the horse, type of performance and training intensity, and also information about saddle fit. A medical history is also required, including results of other veterinary examinations like radiography, ultrasonography, and palpation. This is crucial because many musculoskeletal injuries can be detected by thermography not only in the acute or chronic but also the subclinical stage of inflammation [17].
m. It is vital to take thermographic images with the correct focus, as this cannot be corrected in software after imaging. The color palette and range of temperatures included in each thermogram can usually be modified using the computer software designed for processing thermograms supplied with the thermal camera. Normally, a “rainbow” color palette allows the optimum interpretation of thermograms although alternative palettes are available [66]. The temperature range should be chosen to include the full range of temperatures encountered across the horse and should be applied to each image consistently, particularly when comparing contralateral parts of the body. Automatic settings for the temperature range, applied by the camera for each image, should be avoided as they afford no user control of the temperature scale.
n. Equal imaging distance to contralateral parts of the body recorded in separate images is crucial for the correct comparison of left and right sides. Inconsistent imaging distance may affect temperature readings due to lens aberration and differences in the number of pixels encompassing the measured area. To maintain consistent distance between camera and horse, mark the floor with the camera and horse positions to be applied. Angle of view also influences recorded temperature; wherever practicable, regions undergoing thermographic examination should be approximately orthogonal to the focal plane of the thermal camera. Westermann et al. [20] reported that thermographically determined forelimb surface temperatures were unaffected by changes in camera angle up to 20C
o. Thermographic examination of the horse for veterinary diagnosis should begin with a lateral aspect of the whole body from both sides provided the resolution of the thermal imager is high enough to provide adequate detail in the thermogram. All four limbs should be equally loaded, and the lateral and medial aspects of the distal parts of the limbs should be visible from both sides [40]. The distance between horse and camera should be about 7 m (Fig. 1). The whole-body image helps in setting the temperature scale for later images and gives the general temperature distribution of the horse. However, such an image may not be appropriate for detecting the subtle temperature differences associated with specific pathologies.
p. Images of the distal parts of the forelimbs and hindlimbs should include dorsal, palmar/plantar, lateral, and medial aspects (Fig. 2). The distance between camera and horse should be set at 1.5–2 m [50]. Contralateral limbs imaged together for palmar or dorsal aspects in one thermographic image should be positioned next to each other; the horse should stand straight with minimal lateral and medial rotation, and the limbs should be evenly loaded.
q. If there is a suspicion of musculoskeletal pathology, the thermograms should also include the lateral upper part of the thoracic and pelvic areas and also the lateral aspect of the neck, head, and trunk from both sides [45]. The distance between camera and horse for these parts of the body should be about 3 meters.
r. Thoracolumbar and sacral parts of the spine should be imaged in the dorsal aspect [18] from a height of approximately 2 m and at a distance of 1.5 m (Fig. 3).
s. Close-up images of regions of interest from different aspects can be obtained if necessary. Repeated scans of suspected areas may yield more reliable information [6].