Connections between angle of the shoulder and pain in the hooves — a contribution to diagnostics of lameness

Dr. med. vet. Hiltrud Strasser

Abstract

The body posture of a horse is defined by the positioning of the hooves and limbs, the angle of the shoulder, the height of the withers and croup and the profile of the backline.

In the horse world many faults in conformation are considered genetic and irreversible. This research demonstrates that there is a link between pain in the hooves and conformation and body posture, and the problems are, to a certain extent, reversible when the cause is removed.

The 60 documented cases illustrate the connection between hoof capsule deformation and body posture. Shoulder angles were also assessed in anatomical drawings and photographs found in farriery, veterinary and horse breeding textbooks and in naturally living, wild horses. Removing the cause of the pain in the hooves resulted in a significant change in shoulder angle, approaching what would be considered the normal range as evidenced from the textbooks and wild horses. This observation of shoulder angles is a useful diagnostic tool indicating hoof pain.

Materials and Methods

Observations over many years, which included hundreds of horses identified with locomotory problems, indicated that the angle of the shoulder was steeper before trimming hooves, with our method, than after. This suspicion resulted in the scientific documentation of 60 cases. The horses were led around and allowed to assume a comfortable position. Lateral photographs were taken at a 90° (degree) angle to the sagittal axis. (See Figure 1.) Measurement inaccuracies can be made when the angle of the photograph is not precise however consultation with statisticians confirmed that these errors become statistically insignificant due to the large number of cases.

The highest point of the wither is located and a vertical line drawn down from this point to intersect the ground perpendicularly. The frontal aspect of the point of the shoulder is then identified and a line drawn connecting this point to the highest point of the wither. A horizontal line is then drawn from the point of the shoulder to the vertical line intersecting it at 90°. The shoulder angle (a) can be determined. (Figure 1.)


Figure 1. — Determination of the shoulder blade angle




Figure 2a and b. — Comparison of shoulder angle before and after hoof treatment.

Measurements were taken from the skeletal drawings in 10 different textbooks from various countries and written in varying time periods. (See Figure 3.)


Figure 3. — Measurement of shoulder angle from textbook pictures.

Shoulder angles of patients:



Shoulder angles averaged 61.5° before trimming and 57.3° after trimming. An average reduction in the shoulder angle of 4.2° was calculated. 30 (50%) of the patients were considered higher in the quarters than at the withers before trimming. After reducing the overgrown bars half of those affected were observed to have lost this conformational deviation.

When a vertical line was drawn from the highest point of the withers to the ground it was found that this line transected the humerus in most of the patients (indicating the line was cranial of the elbow joint), however after the first treatment only 33% still exhibited this abnormality. Only 3 patients (5.0%) had vertical cannon bones before treatment. After trimming 48 (80%) of the patients had vertical cannon bones. (See Figure 2a and 2b.)

Shoulder angles assessed in

a) Anatomical textbook pictures:
1. Hickmann ............... 52°
2. Körber .................... 52°
3. Adams .................... 58°
4. Nickel/Schu/Sei ...... 52°
5. Wissdorf et al .......... 56°
6. Goody ..................... 53°
7. Gray ........................ 50°
8. Rooney .................... 54°
9. Lungwitz ................. 49°
10. Ruthe ..................... 47°
Average ....................... 52.3°

b) Photographs from a horse breeding textbook “Pferdezucht und Pferdefuetterung”:
45°
45°
51°
47°
47°
Average 47°

c) Photograaphs of Exmoor Ponies “Survival of the Fittest”:
47°
49°
Average 48°

d) Photographs from auction catalogues of champion horse:
53°
54°
51°
55°
50°
52°
Average 52.5°

It can be assumed that wild horses and top class breeding horses have good anatomical conformation and therefore optimal shoulder angles. The author has not identified a shoulder angle greater than 55° in these groups. In the older textbooks it was not possible to find a shoulder angle greater than 53° but in the newer textbooks, (Adams, Wissdorf) shoulder angles of 56-58° are common.

Results

1. The shoulder angle in healthy horses is between 45° and 55°.
2. Our patients had on average an 11° greater shoulder angle (61.5°) than what is optimal (50°).
3. Most of the patients with non vertical cannon bones before treatment had vertical cannon bones after treatment.
4. A significant number of horses assessed as high in the quarters assumed a normal body posture after treatment.

Discussion

The thorax is suspended between the shoulder blades in an elastic way by different ligaments and muscle systems. The highest point of the withers contour is a spinal process and this is connected to the other spinal processes and also to the shoulder blade by the pars cucullaris of the lig. Supraspinale (“cap of the wither”). This point is in alignment with the dorsal end of the shoulder blade and is kept this way via the connection described; consequently it can be used as a reference point. (See Figure 3.) A line from the shoulder joint to the highest point of the withers runs parallel to the spine of the scapula and m. supra spinatus and can be used to represent the angle of the shoulder blade. (See Figures 1 and 3.)

It is assumed that wild living horses and top breeding horses have optimum shoulder angles. (See figure 1.) The investigation found no shoulder angle steeper than 55° in these groups of horses. A consideration of all of the measurements in the study leads to the conclusion that there is an anatomically defined optimum shoulder angle of approximately 50° (ranging from 45° to 50°) and it can be assumed that the steeper shoulder angles commonly seen today are pathological. It is noteworthy that more recent veterinary textbooks have illustrations showing steep shoulder angles as anatomically normal. This may be caused by the (unfortunately) widespread acceptance that steep shoulders are correct.

The stay apparatus of the horse has been well documented and notable anatomy textbooks in all languages illustrate the stay apparatus with ground parallel coffin bones. A standing horse with correctly suspended, ground parallel, coffin bones exerts no energy, and does not need muscular activity, to support its body weight. (See figures 3 and 4.) It is obvious then that the muscles of a quietly standing horse are smooth and soft.

The angles between the bones in the limbs of a horse are fixed by the tension between the two tendon systems (flexor and extensor) — see Figure 4. Changing the angles of the joints from that which is optimal requires muscular activity. When the coffin bone is displaced from the ground parallel position a necessary muscular adjustment is made by the horse to regain a balance in the tendon systems – this muscular activity is not designed as a long term solution as a knowledge of histology explains. Unfortunately current attitudes ensure that this situation is ongoing, resulting in chronic muscular tension. These contracted muscles can be seen by the well trained eye as bulging and can be palpated, being hard and undeveloped. Well developed muscles, through training, may also look bulging but do not feel hard. Muscle tension in the limb of a quietly standing horse is not a healthy situation.


Figure 4.

Steepening the shoulder blade requires the action of various muscles namely m. rhomboideus, cervical part of m. serratus and the m. pectoralis profundus and it is primarily these muscles that become chronically contracted. What reasonable explanation can there be for why an animal, so well designed to operate efficiently, activates an energy consuming muscular system to steepen the shoulder?

Hundreds of observations of shoulder angles and the changes obtained from the trimming method used prove that the main cause for unphysiological muscular tension is pain in the hoof. Removing the cause of hoof pain, by trimming, results in should angle changes from the pathologically steep towards the more physiologically correct. As it is the long heels and overgrown bars that are removed it is logical to conclude that these are responsible for the pain, muscle tension and steepness of pastern and shoulder angles. (See Figure 2a and 2b.) Pain in the hoof, in most cases, is caused by long heels and overgrown bars.

There is a direct connection between the pastern angle and the shoulder angle due to the indisputable necessary balance between the opposing tendon systems. Today nearly all horses, including young horses, are trimmed with long heels consequently the sensitive internal areas of the hoof receive unphysiological pressure during weight bearing. To minimise or prevent this pain, the horse keeps the pastern steep by using fore arm, shoulder and neck muscles in order to avoid loading the area of the hoof which is being subjected to the unphysiological pressure. The horse will weight the frontal aspect of the hoof avoiding the posterior heel area which is painful. These actions result in the stance commonly seen in our patients. Rearward slanting cannon bones can be quickly identified by visually dropping a vertical line from the highest point of the withers to the ground. (See Figures 1–4.)

When the problem is unilateral lameness is obvious however when the problem is bilateral then the movement is stunted or stiffened and overt lameness is not readily identified. It is regularly observed that the paces of the problem horses we have treated improve. The lameness does not immediately disappear due to inflammation in the previously pinched areas, which takes some time to resolve depending on how severely damaged the corium is and on how chronic the situation was. The healing process will frequently involve abscessing of necrotic material that resulted from impaired circulation to the front of the coffin bone. (Pollitt video 1993 clearly shows the occlusion of the digital arteries that occurs with the elevation of the heels). This is removed by the return in blood circulation associated with ground parallel coffin bones.

Conclusion

Significant changes in conformation have been observed after trimming the bars and heels of patients presented at the Hoof Clinic. This finding has been evaluated by the scientific measurement and comparison of shoulder angles as outlined in this report. In horses with locomotory problems the angle of the shoulder can give an indication of where the pain is located however it is important to be familiar with the effects of the muscles and their synergistic relationships so that a correct diagnosis is made and appropriate treatment programme implemented.

The observation of a vertical line from the highest point of the withers to the ground can provide an initial indication of tension in the musculature of the flexor apparatus. This can be confirmed by palpation and determination of the shoulder angle. Without even lifting the hooves it is possible to diagnose whether an animal suffers from pain in the heel/bar area.

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Literature

Amirsadeghi, H., “The Arabian Horse”, British Library Cataloguing, in Publication Data, 1998
Baker, S., “Survival of the Fittest”, British Library Cataloguing, in Publication Data, 1993
Goody, P., „Horse Anatomy“, J.A. Allen, London 1976
Gray, P., “Lameness”, J.A. Allen, London, 1994
Hickmann, J., “Farriery”, J.A. Allen. London, 1983
Koch, T., “Lehrbuch der Veterinär-Anatomie”, Gustav Fischer Verlag Jena, 1960
Körber, H.-D., “Huf, Hufbeschlag, Hufkrankheiten”, Kosmos, Stuttgart, 1997
Löwe, H./Meyer, H. „Pferdezucht und Pferdefütterung“ Eugen Ulmer Verlag Stuttgart, 1979
Lungwitz, A., „Der Lehrmeister im Hufbeschlag“, G. Schönfeld's Verlagsbuchhandlung, Dresden 1896
Nickel, R./Schummer, A./Seiferle, E., „The Anatomy of the Domestic Animals“, Parey Berlin, 1986
Rooney, J.R., “The Lame Horse”, The Russell Meerdink Comp. Ltd, WI, USA, 1998
Stashak, T.S., “Adam ́s Lameness in Horses”, Lea& Febiger, Philadelphia,USA, 1989
Storch, A., „Zar Konj” („König Pferd“), Quadratisch Print Design, Moskau, 2003
Strasser, H./Kells, S. “The Hoofcare Specialist's Handbook”, Sabine Kells Publishing, Canada, 2001
Wissdorf, H./Gerhards, H./Huskamp, B. “Praxisorientierte Anatomie des Pferdes”, Verlag M&H Schaper,Alsfeld-Hannover, 1998

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