SPONTANEOUS INJURY OF THE ACCESSORY LIGAMENT OF THE SUPERFICIAL DIGITAL FLEXOR TENDON (PROXIMAL CHECK LIGAMENT): A NEW ULTRASONOGRAPHIC DIAGNOSIS Jean-Marie Denoix, DVM, PhD; Soufiane Yousfi, DVM
SUMMARY This study points out the spontaneous injury occurrence of the accessory (proximal check) ligament of the equine superficial digital flexor tendon (AL-SDFT). This injury was identified and documented ultrasonographically in 45 horses. This paper also presents the normal ultrasonographic appearance of the AL-SDFT. Ultrasonography is an adequate technique for AL-SDFT evaluation. Indications include carpal canal syndrome and proximal superficial digital flexor tendonitis.
INTRODUCTION Ultrasonography has become a very useful technique for evaluation of tendons, joints and associated structures in the horse. Injuries of these structures are common in sport and racehorses and were described and documented in the carpal area? Accessory (proximal or radial check) ligament of the superficial digital flexor tendon (ALSDFT) strain was only reported in one horse based on clinical and radiographic findings.Z AL-SDFT desmotomy has been reported as an effective SDFT tendonitis treatment. 3 Recently in a retrospective study, 23 cases of ALSDFT desmopathy were presented. 4
Authors' address:Clinique equine - INRA- Laboratoire d'Anatomie.
Ecole NationalV6t~rinaired'AIfort, 7 Avenuedu G6n6ralde Gaulle.94704 Maisons-AlfortCedex, France. Fax +33 (1) 43 96 31 62. Acknowledgements:This study was supported by the INRA (National Institute of Agronomic Research) and the Service des Haras (French National Horse Breeding Department of the AgricultureMinistry).
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Figure 1.
Medial aspect of the left carpus in the horse. 1) Radius; 2) Medial collateral ligament of the carpus; 3) Flexor carpi radialis muscle; 4) Flexor carpi ulnaris muscle; 5) Superficial digital flexor muscle; 6) AL-SDFT; 7) Superficial digital flexor tendon; 9) Deep digital flexor tendon; 9) Carpal palmar common ligament.
The purpose of this study is to report spontaneous injury of the AL-SDFT and present its ultrasonographic appearance. Normal reference ultrasound images are presented.
MATERIALS AND METHODS Seven sound, adult horses without history of lameness were used to obtain normal transverse and longitudinal (frontal and sagittofrontal) ultrasound scans of the distal
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ULTRASOUND UPDATE antebrachium; these scans were compared to transverse and longitudinal anatomical sections of seven normal frozen injected limbs and four dissected specimens. Ultrasound scans were made with a mobile machine a or a non portable machine b and 7.5 MHz linear or a 10 MHz sector probes. They were recorded on 3/4 inch U-marie videocassettes c to allow retrospective analysis. Within the last four years, carpal canals were examined uhrasonographically in lame horses because of abnormal findings obtained during physical and dynamic examination and/or positive antebrachial or proximal metacarpal nerve blocks; in 45, abnormal findings in the AL-SDFT were found.
RESULTS
Figure 2, Transverse anatomical section of the left carpus in the horse, proximal aspect. 1) Radius; 2) Flexor carpi radialis muscle; 2') Tendon sheath of the flexor carpi radialus muscle; 3) Flexor carpi ulnaris muscle; 4) Lateral ulnar muscle; 5) Superficial digital flexor muscle; 6) ALSDFT; 7) Deep digital flexor muscle; 8) Flexor retinaculum; 9) Carpal canal; 10) Median artery; 11 ) Radial distal artery; 12) Median vien; 13) Collateral ulnar artery and vein; 14) Cephalic vein; 15) Medial nerve; 16) Ulnar nerve; 17) Antebrachial fascia; 18) Skin.
Comparison between distal antebrachium ultrasound scans of sound horses, dissected specimens, and anatomic sections was performed; it established reference AL-SDFT ultrasound images (Figs. 1-4). The proximal part of this ligament is located between the flexor carpi radialis tendon medially and the deep digital flexor muscle body laterally. It forms the medial wall of the proximal carpal sheath. Caudomedially to the AL-SDFT are the median artery, veins, and nerves. The distal part of the AL-SDFT is located under the antebrachial fascia and flexor retinaculum, medially. Craniomedially to the AL-SDFT is the distal tendon of the flexor carpi radialis muscle. Caudomedially to it are the median artery, veins, and nerve. This distal part of the superficial digital flexor muscle body is found caudolaterally to it. Among the carpal canals which were examined, abnormal AL-SDFT findings were identified in 45 horses. They included thickening, hypoechoic images and fiber pattern alteration (Figs. 5,6). Most injured patients were race and sport horses; four were pleasure or instruction horses. aSonoline LM SIEMENS AG, Medical Engineering Group, Erlangen, Germany. bALOKA SSD 2000, ALOKA CO., LTD. 6-22-1 Mute, Mitaka-shi, Tokyo 181, Japan. cVideocassette Recorder VO, 7630 Sony, Paris, France.
Figure 3. (left) Transverse ultrasound scan of a sound carpal area in the horse. 1) Radius; 2) Flexor carpi radialis muscle; 3) Flexor carpi ulnaris muscle (FUC); 4) Superficial digital flexor muscle; 5) AL-SDFT (LA); 6) Deep digital flexor muscle; 7) Flexor retinaculum (RF); 8) Carpal canal; 9) Median artery; 10) Radial distal artery; 11) Cephalic vein; "t2) Median nerve; 13) Skin; 14) Accessory carpal bone (AC).
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Figure 4. Frontal ultrasound scan of a sound carpal area in the horse, 1) Skin; 2) Subcutaneous tissue; 3) Antebrachial fascia; 4) Radial artery (AR); 5) Flexor retinaculum; 6) Medial artery (AM); 7) AL-SDFT (LA).
Figure 6. Frontal ultrasound scan of the carpal area in the horse with an injury of the AL-SDFT. 1) Skin; 2) Subcutaneous tissue; 3) Antebrachial fascia; 4) Radial artery; 5) Flexor retinaculum; 6) Medial artery; 7) AL-SDFT (LA). Deep to the medial artery, the AL-SDFT looks thickened and hypoechogenic with some evidence of fibers disruption. and fourteen were normal. Abnormal caudal distal radius profile was found or suspected in four cases. In one case osteochondroma of the distal radius was previously removed and one case had remodeling at the proximal ALSDFT insertion.
DISCUSSION
Figure 5. Transverse ultrasound scan of the carpal area in the horse with an injury of the AL-SDFT. 1) Radius; 2) Flexor carpi radialis muscle; 3) Flexor carpi ulnaris muscle; 4) Superficial digital flexor muscle; 5) AL-SDFT (LA); 6) Deep digital flexor muscle; 7) Flexor retinaculum; 8) Carpal canal; 9) Medial artery; 10) Radial distal artery; 11) Cephalic vein; 12) Median nerve. On this clinical case with a right forelimb lameness, the AL-SDFT is terribly thickened and hypoechogenic. These findings are indicative of an accessory desmopathy. Injury of the AL-SDFT was accompanied by abnormal findings involving one or several structures of the carpal canal (synovial effusion within the carpal sheath, superficial digital flexor tendonitis, retinaculum flexorum distension or thickening, flexor carpi radialis tenosynovitis, proximal third interosseous muscle injury). Eighteen horses were also examined radiographically
Volume 16, Number 5, 1996
This study determined the precise location and anatomical relationships of the AL-SDFT as well as the normal ultrasonographic aspect (shape and echogenicity). These data are of great interest for clinical evaluation of the ligament. Spontaneous AL-SDFT injuries have been rarely reported in the literature. A radiographic diagnosis of an injury at its radial attachment was made by Lingard z in a 5year-old Arabian stallion. In a retrospective study of 45 horses examined ultrasonographically, Denoix and Audigi63 reported seven AL-SDFT desmopathies. Recently, a retrospective study and the follow-up of 23 clinical cases with spontaneous AL-SDFT injury has been reported 4 and showed that this lesion was found in young or adult horses with high levels of physical activity. Ultrasonography allowed accurate diagnosis of spontaneous AL-SDFT injuries, documentation of concomitant injuries as well as follow-up examination of these lesions. This technique was essential for differential diagnosis of carpal canal syndrome, or for the lesional diagnosis after positive proximal metacarpal or antebrachial nerve blocks
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without radiographic carpal abnormalities or metacarpal ultrasonographic injuries.
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REFERENCES 1. Denoix JM, Audigie F: Examen echographique du carpe du chevah Lesions identifiees sur 45 cas cliniques. Practique Veterinaire Equine 1993;25(3):193-203. 2. Lingard TR: Strain of the superior check ligament. J Am Vet Med Assoc 1966;148(4):364-366. 3. Bramlage LR: Superior check desmotomy as a treatment for superficial digital flexor tendonitis: initial report. Proc 32nd An Cony AAEP 1986;365-369. 4. Denoix JM: Ultrasonographic diagnosis of spontaneous injury of the accessory ligament of the superficial digital flexor tendon (proximal check ligament) in 23 horses. Proc AAEP 1995; 142-143.
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This study demonstrated that spontaneous A L S D F T may occur in sport and racehorses. Ultrasonography is an adequate diagnostic technique for this rarely described lesion. Desmopathy of the A L S D F T must be suspected in horses presenting a carpal canal syndrome and a proximal S D F T tendinopathy.
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P R O C E E D I N G S O F T H E 1996 DUBAI INTERNATIONAL EQUINE SYMPOSIUM Edited by Norman W. Rantanen, and Michael L. Hauser The Equine Athlete: Tendon, Ligament and Soft Tissue Injuries The completeproceedingsof this three-day symposium,with 29 papers on tendon, ligament and soft tissue injuries of the equine athlete. Authors represented are: Julia Wilson; JeanMarie Denoix; Roger K. Smith; Allen E. Goodship; Roy R. Pool; Dan 1. Hawkins; Joc Mayhew; Norman W. Rantanen; Tracy A. Turner; Ted S. Stashak; Ronald L. Genovese; Sue Dyson; W. Rich Redding; lan M. Wright; C. Wayne Mcllwraith: Barrie D. Grant; Alan J. Nixon; Leo B. Jeffcott; William Moyer;Joe it. Cannon; Carlos C. Cervantes;Michael L. Hauser; Larry R. Bramlage; Mimi Porter; Milos Chvapil; William M. Davis; Carol Gillis, and Virginia Reef. Symposium date: March, 1996. Handsomely bound, size 9 X 11,430 pp.
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