Accepted Article 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Prevalence, location, and symmetry of non-catastrophic ligamentous suspensory apparatus lesions in California Thoroughbred racehorses, and association of these lesions with a catastrophic injuries 2
3
4
5
1
A. E. Hill , I. A. Gardner , T. E. Carpenter , C. M. Lee , P. L. Hitchens and S. M. Stover
1*
1
J. D. Wheat Veterinary Orthopedic Research Laboratory, Department of Anatomy, Physiology, and 2 Cell Biology and the California Animal Health and Food Safety Laboratory System, University of 3 California, Davis, CA, USA; the Department of Health Management, Atlantic Veterinary College, 4 University of Prince Edward Island, Charlottetown, PEI, Canada; the EpiCentre, Massey University, 5 Palmerston North, New Zealand; and the Orthopaedic Research Center, Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA. *Corresponding author email: [email protected]
Keywords: horse; suspensory apparatus; ligament injury; risk factors
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/evj.12367
This article is protected by copyright. All rights reserved.
1
Accepted Article 18 19
Summary
20
clinical diagnosis of suspensory apparatus conditions.
21
Objective: To determine if lesions within the suspensory ligament (SL) and distal ligaments of the
22
proximal sesamoid bones (DSLs) were associated with suspensory apparatus failure or metacarpal
23
lateral condylar fracture in California Thoroughbred racehorses.
24
Study design: Cross-sectional study.
25
Methods: Suspensory apparatus specimens from 327 deceased Thoroughbred racehorses were
26
sectioned within the SL body and branches, and oblique and straight DSLs. Purple lesions ≥2 mm in
27
width were categorised as moderate and paler or smaller lesions as mild. Associations between
28
moderate lesions and age, sex, racetrack, and cause of death were evaluated using multivariable
29
logistic regression.
30
Results: Moderate lesions were evident in 16%, and milder lesions in 77% of racehorses. Moderate
31
lesions occurred with similar frequency in SL branches and oblique DSLs. Moderate lesions were
32
more likely to occur in horses that died as a result of suspensory apparatus failure (OR 4.60; 95% CI
33
1.61-13.13; and p = 0.004) or metacarpal lateral condylar fracture (OR 5.05; 95% CI 1.42-17.93; and
34
p = 0.012) compared with horses that died from non-musculoskeletal causes, and in ≥7-year-old
35
horses compared with 2-year-old horses (OR 5.33; 95% CI 1.44-19.75; and p = 0.012).
36
Conclusions Moderate lesions are common in the SL branches and oblique DSLs of racehorses, and
37
may be associated with risk for suspensory apparatus failure and metacarpal condylar fracture.
38
Monitoring health of the suspensory apparatus ligamentous structures may be a simple means of
39
assessing fatigue in, and preventing more extensive injuries to, the forelimb suspensory apparatus
40
and metacarpal condyles.
Reasons for performing study: Knowledge of the site distribution of ligamentous injuries facilitates
41
This article is protected by copyright. All rights reserved.
2
Accepted Article 42
Introduction
43
Musculoskeletal injuries are responsible for about 80% of racehorse deaths in California [1;
44
2], and are the leading cause of racehorse wastage worldwide [3-10]. Although catastrophic (result in
45
horse death or euthanasia) and severe (prevent racing for ≥6 months) injuries occur less frequently (1
46
to 8/1,000 race starts) [2; 11-14] than mild injuries (36.8/1,000 race starts) [11], many moderate and
47
severe musculoskeletal injuries in racehorses occur at the site of a pre-existing mild injury [2; 11; 15-
48
20].
49
The suspensory apparatus, comprising the suspensory (interosseous) ligament (SL), the
50
proximal sesamoid bones, and the distal ligaments of the proximal sesamoid bones (DSLs), supports
51
the metacarpophalangeal joint during weight-bearing and is a common site of injury. Twenty-one to
52
91% of catastrophic [1; 11-15], and 25 to 40% of non-catastrophic [11; 15] musculoskeletal injuries
53
involved the suspensory apparatus. An estimated 14% of actively training racehorses have a
54
palpable forelimb suspensory apparatus injury [20], and in New Zealand, 0.12 cases of suspensory
55
apparatus injury were reported per 1,000 horse training days [8].
56
Actively training or racing horses with palpable forelimb suspensory apparatus injury are at
57
increased risk of serious musculoskeletal injury [11; 15; 20; 21]. The odds of a horse with palpable
58
suspensory apparatus injury on race day having a suspensory apparatus failure during that race are
59
about 3 to 5 times that of a palpably normal horse [11; 15]. Horses with palpable suspensory
60
apparatus injury also have a significantly shorter time to injury-related training failure from suspensory
61
apparatus failure or metacarpal condylar fracture than palpably normal horses [20].
62
Though suspensory apparatus lesions are believed to be common, and palpable lesions are a
63
risk factor for more serious injury, the distribution of mild and moderate suspensory apparatus lesions
64
among racehorses, particularly within the distal sesamoidean ligaments, is unknown. Knowledge of
65
the site distribution of ligamentous injuries is critical for clinical diagnosis of suspensory apparatus
66
conditions. The objectives of the current study were to describe sites of injury in the ligamentous
67
suspensory apparatus and to determine if these injuries were associated with suspensory apparatus
68
failure and metacarpal lateral condylar fracture injuries.
69
This article is protected by copyright. All rights reserved.
3
Accepted Article 70
Materials and methods
71
Study population:
72
Bilateral forelimb specimens distal to the antebrachiocarpal joint were obtained from 327
73
horses that died between 19 November 1999 and 16 November 2002. This sample represented 53%
74
of the 621 horses necropsied by the California Animal Health and Food Safety Laboratory System
75
(CAHFS) for the California Horse Racing Board (CHRB) Postmortem Program during this time period
76
and included all carcasses with soft tissue sufficiently fresh for examination. The Postmortem
77
Program requires all horses that die or are euthanised on the property of a CHRB-sanctioned
78
racetrack (which includes all official racetracks in California) to be submitted to CAHFS for necropsy.
79
In California, Thoroughbred race training occurs at racetracks, not off site at training centres, thus the
80
Postmortem Program includes horses that die during training, those that die as a result of racing, and
81
those that die for reasons unrelated to racing or training. Horses were from 5 major California
82
racetracks (Santa Anita, Del Mar, Hollywood Park, Bay Meadows and Golden Gate Fields), 8 of 10
83
CHRB-sanctioned fair racetracks (Fairplex, Los Alamitos, Pleasanton, Sacramento, Santa Rosa,
84
Stockton, Vallejo, and Bay Meadows during the San Mateo County fair), and one CHRB-sanctioned
85
training track (San Luis Rey Downs). All horses that died during or following a race had undergone a
86
pre-race examination by the Racing Veterinarian as required by law [22] and had been passed
87
suitable to race.
88 89 90
Data collection: Horse name, age, sex, date of death, and racetrack were obtained from the official racetrack b
91
veterinarian. Age and sex were validated using official racing industry records , and adjusted to agree
92
with industry records, except where intact males were recorded as castrated by racetrack officials.
93
Racetrack where death occurred was verified using official race or workout records .
94
b
Cause of death and site of injury data were obtained from CAHFS necropsy reports. Cause
95
of death was categorised as forelimb suspensory apparatus failure, which included proximal sesamoid
96
bone fracture, SL rupture, or DSL rupture without associated metacarpal lateral condylar fracture;
97
metacarpal condylar fracture, which included those with associated suspensory apparatus failure or
98
other injuries (e.g. phalangeal fracture); other forelimb and hindlimb musculoskeletal injuries
This article is protected by copyright. All rights reserved.
4
Accepted Article 99
100 101
(OtherFMSI, HindMSI) comprising all other exercise-related forelimb and spinal, and hindlimb and pelvic musculoskeletal injuries, respectively; and non-musculoskeletal injuries (NonMSI). Suspensory apparati were removed bilaterally from the level of the carpometacarpal joint to
102
the level of the terminus of the insertion of the oblique DSLs, wrapped in saline soaked towels, frozen
103
in an anatomic orientation overnight, and then sectioned at 15, 40, 65, and 90% of the distance from
104
the carpometacarpal joint to the bifurcation of the suspensory ligament (SL) branches, at 40 and 80%
105
of the distance from the bifurcation to the apices of the medial and lateral proximal sesamoid bones
106
(medial and lateral branches (MBR and LBR)), respectively, and at 15 and 50% of the distance from
107
the base of the proximal sesamoid bones to the level of the terminus of the insertion of the oblique
108
DSLs (straight and oblique DSLs) (Fig 1).
109
Digital images were taken of all cut sections and used for lesion detection. Cut sections were c
110
placed on 1 mm grid graph paper. All digital images were produced on one photo stand at the same
111
settings, and assessed visually for evidence of lesions by one author (A.E.H.) using a single
112
computer monitor. Image colour was calibrated by setting the white point equal to that of white card
113
stock, and maximal image resolution was obtained by viewing the image at actual pixel size. Each
114
cut section was categorised using 5 lesion descriptors: colour, width, and shape; peripheral
115
proliferative tissue (yes/no); and internal circumscribed white tissue (yes/no). Colour was categorised
116
as normal (pale), pink (discrete area of increased colour paler than fresh blood), red (discrete area
117
similar in colour to fresh blood), or purple (discrete area similar in colour to oxidised blood). Lesion
118
width was measured at the widest diameter of the lesion and categorised as >0 to
Prevalence, location, and symmetry of non-catastrophic ligamentous suspensory apparatus lesions in California Thoroughbred racehorses, and association of these lesions with a catastrophic injuries 2
3
4
5
1
A. E. Hill , I. A. Gardner , T. E. Carpenter , C. M. Lee , P. L. Hitchens and S. M. Stover
1*
1
J. D. Wheat Veterinary Orthopedic Research Laboratory, Department of Anatomy, Physiology, and 2 Cell Biology and the California Animal Health and Food Safety Laboratory System, University of 3 California, Davis, CA, USA; the Department of Health Management, Atlantic Veterinary College, 4 University of Prince Edward Island, Charlottetown, PEI, Canada; the EpiCentre, Massey University, 5 Palmerston North, New Zealand; and the Orthopaedic Research Center, Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA. *Corresponding author email: [email protected]
Keywords: horse; suspensory apparatus; ligament injury; risk factors
This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/evj.12367
This article is protected by copyright. All rights reserved.
1
Accepted Article 18 19
Summary
20
clinical diagnosis of suspensory apparatus conditions.
21
Objective: To determine if lesions within the suspensory ligament (SL) and distal ligaments of the
22
proximal sesamoid bones (DSLs) were associated with suspensory apparatus failure or metacarpal
23
lateral condylar fracture in California Thoroughbred racehorses.
24
Study design: Cross-sectional study.
25
Methods: Suspensory apparatus specimens from 327 deceased Thoroughbred racehorses were
26
sectioned within the SL body and branches, and oblique and straight DSLs. Purple lesions ≥2 mm in
27
width were categorised as moderate and paler or smaller lesions as mild. Associations between
28
moderate lesions and age, sex, racetrack, and cause of death were evaluated using multivariable
29
logistic regression.
30
Results: Moderate lesions were evident in 16%, and milder lesions in 77% of racehorses. Moderate
31
lesions occurred with similar frequency in SL branches and oblique DSLs. Moderate lesions were
32
more likely to occur in horses that died as a result of suspensory apparatus failure (OR 4.60; 95% CI
33
1.61-13.13; and p = 0.004) or metacarpal lateral condylar fracture (OR 5.05; 95% CI 1.42-17.93; and
34
p = 0.012) compared with horses that died from non-musculoskeletal causes, and in ≥7-year-old
35
horses compared with 2-year-old horses (OR 5.33; 95% CI 1.44-19.75; and p = 0.012).
36
Conclusions Moderate lesions are common in the SL branches and oblique DSLs of racehorses, and
37
may be associated with risk for suspensory apparatus failure and metacarpal condylar fracture.
38
Monitoring health of the suspensory apparatus ligamentous structures may be a simple means of
39
assessing fatigue in, and preventing more extensive injuries to, the forelimb suspensory apparatus
40
and metacarpal condyles.
Reasons for performing study: Knowledge of the site distribution of ligamentous injuries facilitates
41
This article is protected by copyright. All rights reserved.
2
Accepted Article 42
Introduction
43
Musculoskeletal injuries are responsible for about 80% of racehorse deaths in California [1;
44
2], and are the leading cause of racehorse wastage worldwide [3-10]. Although catastrophic (result in
45
horse death or euthanasia) and severe (prevent racing for ≥6 months) injuries occur less frequently (1
46
to 8/1,000 race starts) [2; 11-14] than mild injuries (36.8/1,000 race starts) [11], many moderate and
47
severe musculoskeletal injuries in racehorses occur at the site of a pre-existing mild injury [2; 11; 15-
48
20].
49
The suspensory apparatus, comprising the suspensory (interosseous) ligament (SL), the
50
proximal sesamoid bones, and the distal ligaments of the proximal sesamoid bones (DSLs), supports
51
the metacarpophalangeal joint during weight-bearing and is a common site of injury. Twenty-one to
52
91% of catastrophic [1; 11-15], and 25 to 40% of non-catastrophic [11; 15] musculoskeletal injuries
53
involved the suspensory apparatus. An estimated 14% of actively training racehorses have a
54
palpable forelimb suspensory apparatus injury [20], and in New Zealand, 0.12 cases of suspensory
55
apparatus injury were reported per 1,000 horse training days [8].
56
Actively training or racing horses with palpable forelimb suspensory apparatus injury are at
57
increased risk of serious musculoskeletal injury [11; 15; 20; 21]. The odds of a horse with palpable
58
suspensory apparatus injury on race day having a suspensory apparatus failure during that race are
59
about 3 to 5 times that of a palpably normal horse [11; 15]. Horses with palpable suspensory
60
apparatus injury also have a significantly shorter time to injury-related training failure from suspensory
61
apparatus failure or metacarpal condylar fracture than palpably normal horses [20].
62
Though suspensory apparatus lesions are believed to be common, and palpable lesions are a
63
risk factor for more serious injury, the distribution of mild and moderate suspensory apparatus lesions
64
among racehorses, particularly within the distal sesamoidean ligaments, is unknown. Knowledge of
65
the site distribution of ligamentous injuries is critical for clinical diagnosis of suspensory apparatus
66
conditions. The objectives of the current study were to describe sites of injury in the ligamentous
67
suspensory apparatus and to determine if these injuries were associated with suspensory apparatus
68
failure and metacarpal lateral condylar fracture injuries.
69
This article is protected by copyright. All rights reserved.
3
Accepted Article 70
Materials and methods
71
Study population:
72
Bilateral forelimb specimens distal to the antebrachiocarpal joint were obtained from 327
73
horses that died between 19 November 1999 and 16 November 2002. This sample represented 53%
74
of the 621 horses necropsied by the California Animal Health and Food Safety Laboratory System
75
(CAHFS) for the California Horse Racing Board (CHRB) Postmortem Program during this time period
76
and included all carcasses with soft tissue sufficiently fresh for examination. The Postmortem
77
Program requires all horses that die or are euthanised on the property of a CHRB-sanctioned
78
racetrack (which includes all official racetracks in California) to be submitted to CAHFS for necropsy.
79
In California, Thoroughbred race training occurs at racetracks, not off site at training centres, thus the
80
Postmortem Program includes horses that die during training, those that die as a result of racing, and
81
those that die for reasons unrelated to racing or training. Horses were from 5 major California
82
racetracks (Santa Anita, Del Mar, Hollywood Park, Bay Meadows and Golden Gate Fields), 8 of 10
83
CHRB-sanctioned fair racetracks (Fairplex, Los Alamitos, Pleasanton, Sacramento, Santa Rosa,
84
Stockton, Vallejo, and Bay Meadows during the San Mateo County fair), and one CHRB-sanctioned
85
training track (San Luis Rey Downs). All horses that died during or following a race had undergone a
86
pre-race examination by the Racing Veterinarian as required by law [22] and had been passed
87
suitable to race.
88 89 90
Data collection: Horse name, age, sex, date of death, and racetrack were obtained from the official racetrack b
91
veterinarian. Age and sex were validated using official racing industry records , and adjusted to agree
92
with industry records, except where intact males were recorded as castrated by racetrack officials.
93
Racetrack where death occurred was verified using official race or workout records .
94
b
Cause of death and site of injury data were obtained from CAHFS necropsy reports. Cause
95
of death was categorised as forelimb suspensory apparatus failure, which included proximal sesamoid
96
bone fracture, SL rupture, or DSL rupture without associated metacarpal lateral condylar fracture;
97
metacarpal condylar fracture, which included those with associated suspensory apparatus failure or
98
other injuries (e.g. phalangeal fracture); other forelimb and hindlimb musculoskeletal injuries
This article is protected by copyright. All rights reserved.
4
Accepted Article 99
100 101
(OtherFMSI, HindMSI) comprising all other exercise-related forelimb and spinal, and hindlimb and pelvic musculoskeletal injuries, respectively; and non-musculoskeletal injuries (NonMSI). Suspensory apparati were removed bilaterally from the level of the carpometacarpal joint to
102
the level of the terminus of the insertion of the oblique DSLs, wrapped in saline soaked towels, frozen
103
in an anatomic orientation overnight, and then sectioned at 15, 40, 65, and 90% of the distance from
104
the carpometacarpal joint to the bifurcation of the suspensory ligament (SL) branches, at 40 and 80%
105
of the distance from the bifurcation to the apices of the medial and lateral proximal sesamoid bones
106
(medial and lateral branches (MBR and LBR)), respectively, and at 15 and 50% of the distance from
107
the base of the proximal sesamoid bones to the level of the terminus of the insertion of the oblique
108
DSLs (straight and oblique DSLs) (Fig 1).
109
Digital images were taken of all cut sections and used for lesion detection. Cut sections were c
110
placed on 1 mm grid graph paper. All digital images were produced on one photo stand at the same
111
settings, and assessed visually for evidence of lesions by one author (A.E.H.) using a single
112
computer monitor. Image colour was calibrated by setting the white point equal to that of white card
113
stock, and maximal image resolution was obtained by viewing the image at actual pixel size. Each
114
cut section was categorised using 5 lesion descriptors: colour, width, and shape; peripheral
115
proliferative tissue (yes/no); and internal circumscribed white tissue (yes/no). Colour was categorised
116
as normal (pale), pink (discrete area of increased colour paler than fresh blood), red (discrete area
117
similar in colour to fresh blood), or purple (discrete area similar in colour to oxidised blood). Lesion
118
width was measured at the widest diameter of the lesion and categorised as >0 to
