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Keywords:

  • horse;
  • proximal sesamoid bone;
  • fracture;
  • racehorse

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

Reason for performing study: Analysis was performed to examine a method for refining the preoperative prognosis for horses that had surgery to remove apical fractures of the proximal sesamoid bones (PSBs).

Objectives: To determine if: 1) there was a difference in size or configuration of apical fractures between the different anatomical locations of the PSBs, which have been shown to affect the prognosis; and 2) the size or configuration could predict the prognosis for racehorses with these fractures.

Methods: The study included 110 weanlings and yearlings and 56 training racehorses that underwent surgery to remove apical PSB fractures. Radiographs of the fractures were used for measurement of the abaxial and axial proportion and the abaxial to axial ratio, and race records were used to determine average earnings per start (AEPS) and total post operative starts. Analysis of variance and regression statistics were used to compare the fragment sizes between the specific PSBs on each of the limbs and compare size and configuration of the fractures to prognosis.

Results: There was a significantly larger abaxial to axial ratio (more transverse fracture) for the forelimb medial sesamoids than for all other sesamoids in untrained racehorses (P = 0.03). There were no other significant differences in size. There was no relationship between fracture size or configuration and AEPS nor total post operative starts.

Conclusions: Apical fractures in weanlings and yearlings tend to be more transverse in the forelimb medial PSBs than the other PSBs. Apical fracture size and geometry does not determine prognosis for apical sesamoid fractures.

Potential relevance: Horses that undergo surgery to remove larger apical fractures of the PSBs do not have a worse outcome than those horses with smaller fractures.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

Fractures of the proximal sesamoid bones (PSB) are the most common fracture of the equine forelimb, and apical fractures are the most common type of PSB fracture (Dyce et al. 2002; White and Moore 1998). Apical fractures occur in the proximal 30% of the PSB and cause a partial disruption of the insertion of the suspensory ligament (Woodie et al. 1999). The differential trabecular bone density has been described to predispose the PSB to an apical location of the fracture in training racehorses (Young et al. 1991). In these young racehorses, the porosity of the mid-body of the PSB greatly decreases as training is increased while the apical portions of the PSB do not see this dramatic increase in mineralisation (Young et al. 1991). Training also tends to increase the strength of the suspensory ligament causing an increased likelihood of a PSB fracture rather than a soft tissue injury in racehorses (Bukowiecki et al. 1987).

A previous study showed that fracture geometry varies between fractures of the medial and lateral PSBs. When all types of PSB fractures were studied, lateral PSB bones were more likely to have oblique fracture while medial sesamoid bones were more likely to have complete transverse or split transverse simple fractures (Anthenill et al. 2006).

The prognosis for horses with apical PSB fractures depends on a multitude of factors. Clinical data has found that horses return to athletic function more often with surgical removal of the apical fragment as opposed to non-surgical treatment (Spurlock and Gabel 1983; Fretz et al. 1984). Sesamoiditis, suspensory desmitis, the extent of suspensory ligament insertion involvement, the degree of metacarpo- or metatarso-phalangeal joint involvement, and the anatomic location of the PSB involved determine the prognosis for return to and the level of athletic activity after surgery (Spurlock and Gabel 1983; Fretz et al. 1984). A study on Standardbred racehorses showed no difference in prognosis between medial and lateral apical PSB fractures after arthroscopic removal (Woodie et al. 1999). Larger studies on Thoroughbred racehorses found that there was a difference in prognosis between medial and lateral apical PSB fractures in the forelimb but not in the hindlimb (Schnabel et al. 2006, 2007). Horses with medial PSB fractures of the forelimb were less likely to race post operatively when compared to those with lateral PSB fractures of the forelimb (46% [13/28] and 100% [13/13], respectively) or fractures of either the medial or lateral hind sesamoids (85% [67/79] and 86% [71/83], respectively) (Schnabel et al. 2006, 2007). Those horses with medial forelimb sesamoid fractures that did race had significantly lower earnings and average earnings per start when compared to those horses with lateral forelimb PSB fractures that raced. This raises the question of whether the geometry of the fracture or simply the anatomical location of the fractured sesamoid was afactor in the difference in prognosis between the different affected sesamoids. It is possible that the size or geometry of the fragments determines the prognosis, and those certain sesamoid bones, such as the medial sesamoids in the front limb, are predisposed to larger fractures than other sesamoid bones.

The purpose of this study was to compare the size and geometry of naturally occurring apical sesamoid fractures of young horses and training racehorses, compare the size and geometry of these fractures among each of the sesamoid bones and to correlate the size and geometry of apical PSB fracture fragments with the race record of Thoroughbred racehorses with these injuries to determine if size or geometry of the fracture define the prognosis for the injured horses, and therefore could be used preoperatively to determine the prognosis.

The hypotheses tested were: 1) there is a difference in the size or geometry of the fractures between the various sesamoids; and 2) the size and geometry of the fracture fragment has a determining effect on the prognosis for racing of the affected horses.

Materials and methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

Subjects

The medical records and radiographs of Thoroughbred horses that underwent arthroscopic surgery for removal of an apical PSB fragment at Rood and Riddle Equine Hospital between January 1994 and December 2002 were examined. Training Thoroughbreds were presented for lameness and were diagnosed by the attending or referring veterinarian to have an apical sesamoid fracture as the cause of the lameness. Weanlings and yearlings (untrained racehorses) were diagnosed with an apical PSB fracture on survey radiographs and were treated to eliminate the potentially lameness causing fracture before beginning training. All horses had a 30° dorsolateral palmaromedial and a 30° dorsomedial palmarolateral oblique radiograph taken upon presentation and were confirmed to have a fracture of the proximal 1/3 of the PSB (as the definition of an apical sesamoid fracture determined by Schnabel et al. 2006, 2007). The study included 110 untrained racehorses and 56 training racehorses.

All PSB apical fracture fragments were arthroscopically removed using a standardised technique and perioperative care described by Schnabel et al. (2006).

Measurements

To determine the size and configuration of the sesamoid fracture fragments, a standard set of measurements to determine absolute and relative dimensions of the fracture in relation to the parent bone were made (Fig 1). A dorsolateral-palmaromedial oblique radiograph was used for measurement of fractures to the lateral PSB while a dorsomedial-palmarolateral radiograph was used for the medial PSB. The total abaxial length (measurement A) and abaxial fragment length (measurement B) measured from the most proximal point of the fragment to the most distolateral point of the PSB and to the most distolateral point of the fragment defined measurement A and B.

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Figure 1. Radiograph showing measurements taken for data analysis. Measurements are defined as Line A (total abaxial length), Line B (abaxial fragment length), Line C (the total axial length), Line D (axial fragment length), and Gap 1 and 2 (G1 and G2, gaps between the fragment and the body of the affected PSB).

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The total axial length (measurement C) and axial fragment length (measurement D) were measured from the most proximal point of the fragment to the most distal point of the PSB and the most distal point of the fragment on the axial surface, respectively.

Gaps between the fragment and the body of the affected PSB (measurements G1 and G2) were subtracted from the total abaxial and axial length. The ratio of the fragment abaxial or axial length over the abaxial or axial length of the PSB was then used to determine the percentage of the bone dimension lost to the fragment.

The measurements were used to determine: 1) the percentage of the abaxial surface involvement of the PSB lost to the fracture (where the suspensory ligament inserts into the bone), 2) the percentage of the axial height of the PSB lost to the fracture (the articular component), and 3) a ratio of the abaxial surface involvement to the axial surface involvement was then calculated to determined the geometry of the fragment. These measurements were then compared to the race record to determine if any affected the post injury/post treatment prognosis.

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For comparison of the consistency of the fracture size among the 4 pairs (front/rear, medial/lateral) of different sesamoid bones, the measurements were then broken into 5% increments for the percentage of the total dimension lost to the fracture and the number of fractures in each 5% increment recorded. The results were compared graphically for untrained and trained horses as well as for combined groups to determine if the fracture size varied among groups (Figs 3–5).

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Figure 3. The percentage of horses with fragments with abaxial surface involvement divided into 5% increments. Data are compared between the untrained, trained and combined groups of racehorses.

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Figure 4. The percentage of horses with fragments with axial surface involvement divided into 5% increments. Data are compared between the untrained, trained and combined groups of racehorses.

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Figure 5. Abaxial to axial fragment ratio (showing the geometry of the fragment) divided into size groups. Data are compared between the untrained, trained and combined groups of racehorses.

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Racing records and statistics

Racing records for the horses were obtained through Equibase.com1. The average earnings per start (AEPS) and total number of starts after apical PSB removal were determined for each animal, and their normalised log values used for the comparisons.

The fragment sizes and proportions were compared between the different limbs using descriptive statistics and factorial analysis of variance (ANOVA) using statistical software (Statistix 9.0)2. The size to AEPS or total number of post operative starts was correlated using regression analysis (Statistix 9.0). For all values, P (2-tailed) <0.05 was considered significant.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

PSB fragment sizes for untrained horses (weanlings and yearlings)

The sesamoid fractures of 110 pretraining horses were examined to compare the fragment involvement of the axial and abaxial surfaces of the PSB. The percentage of parent bone involvement and statistical analysis are listed in Table 1. The average PSB fragment size varied from 19.8–26.8% of either the total axial or total abaxial dimension. Fragments ranged from oblique, where the fragment occupied the same proportion of the axial and the abaxial surface, to transverse, where the abaxial fragment size was significantly larger than the axial size of the fragment. The average abaxial surface involvement was greatest in the right front lateral PSB, followed by the left front medial, right hind lateral, left hind medial, right hind medial, left hind lateral and right front medial PSBs (Table 1). The average axial surface involvement was greatest in the left hind medial PSB, followed by the right hind lateral, right front lateral, left front medial, right hind medial, right front medial and left hind lateral PSBs, respectively. No data were available for the left front lateral sesamoid as none of the subjects suffered this fracture. Differences in size between the medial and lateral front and hind PSB fragments were not significant (P = 0.56 and P = 0.70 for abaxial and axial measurements, respectively). No significant difference in size was found between those fractures in the front medial PSBs and all other PSBs (P = 0.24 and P = 0.91 for abaxial and axial measurements, respectively).

Table 1. A comparison between the mean and standard deviation of the abaxial size, axial size, and abaxial to axial proportion for PSB fragments between different locations in the untrained racehorse
Untrained fractured PSBNMean abaxial (%) ± s.d.Mean axial (%) ± s.d.Mean abaxial: axial ratio ± s.d.
Left fore medial523.9 ± 8.823.7 ± 101.11 ± 0.41
Right fore lateral126.823.81.13
Right fore medial219.8 ± 1222.4 ± 120.86 ± 0.11
Left hind lateral1519.9 ± 6.921.6 ± 7.90.98 ± 0.24
Left hind medial3521.9 ± 3.824.7 ± 4.20.89 ± 0.11
Right hind lateral3222.8 ± 5.624.6 ± 6.50.96 ± 0.21
Right hind medial2021.4 ± 4.723.4 ± 4.70.92 ± 0.13

PSB fragment sizes for horses in training

Similar measurements were made for 56 horses aged ≥2 years at the time of surgery (Table 2). Average abaxial or axial surface involvement ranged from 17.4–28.3%. The average abaxial surface involvement was greatest for the left front medial PSB, followed by the right front lateral, right hind medial, right hind lateral, right front medial, left hind lateral, left front lateral and left hind medial PSBs, respectively (Table 2). The average axial surface involvement was greatest for the left front medial PSB, followed by the right hind medial, right hind lateral, right front lateral, left hind medial, right front medial, left hind lateral and left front lateral PSBs, respectively (Table 2). There was no statistical difference in size between the medial and lateral forelimb and hindlimb PSB fragments (P = 0.83 for both abaxial and axial measurements), nor between those in the front medial and all other PSBs (P = 0.40 and P = 0.54 for abaxial and axial measurements, respectively) (Table 2).

Table 2. A comparison between the mean and standard deviation of the abaxial size, axial size, and abaxial to axial ratios for PSB fragments between different locations in the training racehorse
Training fractured PSBNMean abaxial (%) ± s.d.Mean axial (%) ± s.d.Mean abaxial: axial ratio ± s.d.
Left fore lateral318.2 ± 1119.0 ± 120.95 ± 0.07
Left fore medial626.9 ± 1828.3 ± 140.89 ± 0.20
Right fore lateral326.1 ± 1026.4 ± 9.21.02 ± 0.29
Right fore medial522.6 ± 9.024.6 ± 8.40.90 ± 0.12
Left hind lateral1422.3 ± 8.823.2 ± 9.30.99 ± 0.17
Left hind medial517.4 ± 8.225.2 ± 5.70.69 ± 0.24
Right hind lateral1123.1 ± 8.826.5 ± 7.50.88 ± 0.29
Right hind medial923.5 ± 6.826.7 ± 5.80.89 ± 0.21

Comparing the PSB surface involvement of the fragment with AEPS and total post operative starts

Regression analysis was performed to determine if there was a relationship between the amount of abaxial or axial involvement and the AEPS and total number of post operative starts. Abaxial and axial measurements were plotted against the log transformation of AEPS and the log transformation of the total post operative starts. An example graph is in Figure 2. The slope of the regression and the P-values are listed in Table 3. The slope describes the overall distribution of the values with a negative slope suggesting decreased AEPS and post operative starts with increasing fracture size and a positive slope suggesting and increased AEPS and post operative starts with increasing fracture size. As all P-values were insignificant, the slope of the lines is not significantly different from 0 and therefore the AEPS and total post operative starts have no relation to the abaxial or axial surface involvement.

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Figure 2. Linear regression analysis of untrained horses relating the fragment's abaxial surface involvement (as a fraction of the entire abaxial length) to AEPS. The linear regression equation is listed below the graph. The abaxial surface involvement did not have a significant effect on the AEPS (P = 0.23).

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Table 3. Linear regression slope and P values for PSB fractures in untrained and trained horses. Data is listed for the abaxial proportion of the fracture, the axial proportion of the fracture, and the ratio of the abaxial to the axial proportions
 AEPS slopeAEPS P valueStarts slopeStarts P value
Untrained horse abaxial regression−3.340.23−1.110.24
Untrained horse axial regression−0.760.76−0.670.43
Untrained horse abaxial/axial regression−0.810.31−0.090.74
Training horse abaxial regression1.070.63−0.080.92
Training horse axial regression−0.590.81−1.160.22
Training horse abaxial/axial regression1.180.220.610.09

Examination of fracture fragment geometry

A bar graph was used to plot the number of fragments into different size groups of the categories abaxial percentage, axial percentage, or abaxial proportion to axial proportion ratios (Figs 3, 4). PSB fractures as a percentage of the total bone length occurred in a near bell shaped curve centred at 20–25% of the length of the abaxial and axial surface for untrained horses and in a near bell shaped curve centred at 25–30% for trained horses. These data confirm that clinical fractures occur around one-quarter to one-third of the distance from the apex to the base in an area of the bone hypothesised to be less responsive to stress during training (Young et al. 1991). However, similar distribution occurred in both the trained and the untrained groups.

The abaxial to axial fragment ratio tended to be <1 in both age groups (Fig 5, Tables 1, 2). Therefore the abaxial fragment proportion was generally smaller than the axial proportion. This was accentuated in untrained horses as the mode was the group with 80–90% abaxial to axial ratio while the mode was the 90–100% group for trained horses. There was no significant difference in the abaxial to axial fragment ratio for untrained or trained horses (P = 0.23 and P = 0.32, respectively) when comparing each sesamoid to one another. There was a significant difference when comparing both of the forelimb medial sesamoids to all the other sesamoids (P = 0.03) for the untrained group. The fore medial sesamoids had a greater abaxial to axial ratio than the other sesamoids. The trained group had no significant difference in this comparison (P = 0.90).

Using regression analysis, the abaxial to axial fragment ratio was not a determinant of AEPS (P = 0.31 and P = 0.22 for untrained and trained horses, respectively), nor for total post operative starts (P = 0.74 and P = 0.09 for untrained and trained horses, respectively) (Table 3).

The first hypothesis (that there was a difference in the size or configuration of the fractures in the various sesamoids) was accepted only in the fact that the untrained forelimb medial sesamoid fractures tended to be more transverse than fractures in all other sesamoids. Otherwise there was no significant size difference in any of the measurements. The second hypothesis (that the geometry of the sesamoid fracture fragment would affect the prognosis) was rejected.

Discussion

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

This study had established that when fractures of the proximal sesamoid bones of Thoroughbred horses prior to and in race training occur, they are predisposed to fracture the proximal quarter of the sesamoid from the distal three-quarters of the bone in all sesamoids in the horse. Fractures consistently occur at approximately 20–30% of the distance from the proximal end of the PSB on both the abaxial and axial margins. The apex of a normal curve of the fracture location plot occurs in a similar location in trained or untrained horses (Figs 3 and 4). The fracture occurs in a predictable location in the bone regardless of the age or training status of the horse.

The data indicate that measuring the abaxial or axial length of the fracture or calculating the percentage of the length of the fractured bone cannot predict the prognosis for apical fractures of the PSBs in Thoroughbred racehorses. Although a fragment with a greater abaxial percentage of bone loss has been thought to be more detrimental to the suspensory apparatus, this did not have a demonstrable effect on prognosis in these 2 groups of horses with fractures of the apical one-third of the bone. There was a nonsignificant trend in the data for less success as the fragment enlarges, but within the group of apical fractures, the individual size was not significant. Therefore, within the group of apical sesamoid fractures, size does not refine the prognosis. Horses in our data set with fractures with even the largest abaxial and axial percentage raced successfully. Presumably there is a size that will begin to affect the prognosis for racing, and the trend to decreasing success would support this, but the threshold was not identifiable in this group of naturally occurring apical sesamoid fractures confined to the proximal 25–33% of the bone volume.

The obliquity of the fracture does not affect prognosis. A more transverse fracture or a fracture with a larger abaxial component than axial would appear to compromise more of the suspensory ligament insertion, but no ill effects were seen on race record when it was examined in this group of fractures. As the forelimb medial sesamoids had a significantly more transverse fracture (greater abaxial to axial ratio), and since these horses with forelimb medial fractures had a poorer prognosis in previous studies, there appeared to be an association. However, this is disproven by the regression analysis, which shows no tendency for significance between the degree of obliquity and AEPS nor total post operative starts. Therefore, measurement of the apical sesamoid fracture does not predict success at the racetrack.

When comparing this study to previous work done by Woodie et al. (1999) on Standardbred racehorses, the proportion of the abaxial surface of the PSB was smaller on average in our study than that study. The average abaxial involvement in Woodie et al. (1999) was 36% as compared to 22% for untrained horses and 24% for trained horses in this study. Measurements were taken slightly differently in Woodie et al. (1999) as a separate abaxial surface measurement was taken for both the fragment and the remaining PSB instead of the entire PSB with the gap measurement subtracted as in this study. This may account for some variation, but it is more likely that the distribution may be different between the Thoroughbred and Standardbred breeds and their different gaits. The abaxial surface involvement of the fragment was found to be insignificant in its association with post operative racing success in Standardbred horses in Woodie et al. (1999), and the result was similar in the Thoroughbred horses in our study of apical sesamoid fractures.

The only consistent tool for prediction of prognosis in the Thoroughbred racehorse is the anatomical location of the affected sesamoid. As Schnabel et al. (2006, 2007) showed, 100% (13/13) of lateral PSB fractures of the forelimb and 85% (162/190) of all hindlimb fractures started a race after injury and surgical treatment. Only 46% (13/28) of all horses with medial PSB fractures of the forelimbs started a race. Furthermore, the AEPS was greatly reduced when fractures of the medial forelimb sesamoid bone were compared to fractures at all other locations. For untrained horses, the AEPS was only $999 for medial forelimb fractures in comparison to $6145 for all other fractures. For trained horses, AEPS for medial forelimb fractures was $1977 and $3755 for all other fracture locations (Schnabel et al. 2006, 2007).

The size of the apical PSB fragment within the definition of an apical sesamoid fracture of up to one-third of the bone volume does not appear to determine the prognosis in the Thoroughbred racehorse. The consistent predisposition for fracture configuration and location, as determined by the analysis of this group of apical fractures, appears to create a tolerable injury in all sesamoids in the Thoroughbred racehorse after surgical removal, with the exception of the medial sesamoid of the front limb. It is not the size of the fragment that lowers the prognosis in the medial sesamoid of the forelimb, but some other anatomic or physiological biomechanical attribute of that bone.

Other factors including sesamoiditis as seen on radiographic examination or suspensory desmitis on ultrasound examination carry more weight in determining prognosis than does the size of the fragment (Spike-Pierce and Bramlage 2003; Schnabel et al. 2006, 2007).

Within the definition of an apical sesamoid fracture, up to approximately one-third the volume of the bone, measuring the size or the geometry of the fractured fragment cannot further refine the prognosis. Common sense would seem to tell us that the larger the surface involvement of the apical fracture the worse the prognosis, but this does not appear to be the case when less than the proximal one-third volume of the bone is involved.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

Our thanks to Dr Noah Cohen for his advice on the data analysis.

Manufacturers’ addresses

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References

1 Jockey Club Information Systems, Lexington, Kentucky, USA.

2 Statistix Analytical Software, Tallahassee, Florida, USA.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Materials and methods
  5. Results
  6. Discussion
  7. Acknowledgements
  8. Manufacturers’ addresses
  9. References
  • Anthenill, L.A., Stover, S.M., Gardner, I.A., Hill, A.E., Lee, C.M., Anderson, M.L., Barr, B.C., Read, D.H., Johnson, B.J., Woods, L.W., Daft, B.M., Kinde, H., Moore, J.D., Farman, C.A., Odani, J.S., Pesavento, P.A., Uzal, F.A., Case, J.T. and Ardans, A.A. (2006) Association between findings on palmarodorsal radiographic images and detection of a fracture in the proximal sesamoid bones of forelimbs obtained from cadavers of racing Thoroughbreds. Am. J. vet. Res. 67, 858-868.
  • Bukowiecki, C.F., Bramlage, L.R. and Gabel, A.A. (1987) In vitro strength of the suspensory apparatus in training and resting horses. Vet. Surg. 16, 126-130.
  • Dyce, K.M., Sac, W.O. and Wynsing, C.J.G. (2002) Textbook of Veterinary Anatomy, 3rd edn., W.B. Saunders, Philadelphia.
  • Fretz, P.B., Barber, S.M., Bailey, J.V. and McKenzie, N.T. (1984) Management of proximal sesamoid bone fractures in the horse. J. Am. vet. med. Ass. 185, 282-283.
  • Schnabel, L.V., Bramlage, L.R., Mohammed, H.O., Embertson, R.M., Ruggles, A.J. and Hopper, S.A. (2006) Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age ≥2 years. Equine vet. J. 38, 446-451.
  • Schnabel, L.V., Bramlage, L.R., Mohammed, H.O., Embertson, R.M., Ruggles, A.J. and Hopper, S.A. (2007) Racing performance after arthroscopic removal of apical sesamoid fracture fragments in Thoroughbred horses age <2 years. Equine vet. J. 39, 64-68.
  • Spike-Pierce, D.L. and Bramlage, L.R. (2003) Correlation of racing performance with radiographic changes in the proximal suspensory bones of 487 Thoroughbred yearlings. Equine vet. J. 35, 350-353.
  • Spurlock, G.H. and Gabel, A.A. (1983) Apical fractures of the proximal sesamoid bones in 109 Standardbred horses. J. Am. vet. med. Ass. 183, 76-79.
  • White, N.A. and Moore, J.N. (1998) Current Techniques in Equine Surgery and Lameness, W.B. Saunders, Philadelphia.
  • Woodie, J.B., Ruggles, A.J., Bertone, A.L., Hardy, J. and Schneider, R.K. (1999) Apical fracture of the proximal sesamoid bone in Standardbred horses: 43 cases (1990–1996). J. Am. vet. med. Ass. 214, 1653-1656.
  • Young, D.R., Nunamaker, D.M. and Markel, M.D. (1991) Quantative evaluation of the remodeling response of the proximal sesamoid bones to training-related stimuli in Thoroughbreds. Am. J. vet. Res. 52, 1350-1356.