EXPERIENCES WITH MRI ON STANDING HORSES

 

Filip Vandenberghe, DVM

Equine Clinic DE BOSDREEF

Moerbeke-Waas, Belgium

 

 

Introduction

Magnetic Resonance Imaging (MRI) is, although recently introduced, already commonly used as a diagnostic tool in equine orthopaedics. Several referral clinics and universities all over the world have MRI systems installed and are scanning clinical patients on a daily basis. At this moment MRI is limited to the distal limb, skull and cranial cervical region. MRI systems can be mainly divided into two different types: high field and low field MRI. All high field and some low field systems require general anaesthesia. Since 4 years an open low field MRI scanner (Hallmarq¨) has been designed for imaging the distal limb of the standing horse. Imaging of all regions proximal of the foot require motion correction software.

 

Materials and Methods

             

Scanner

 

The Hallmarq MRI scanner consists of an open 0,27 Tesla permanent magnet, mounted on a movable frame, different sized RF-coils and a computer. The system is installed in a radiofrequency shielded room where the temperature is controlled at 20¡C.

 

 

Protocol

 

Outside the MRI room shoes and nails are removed and the horses are sedated. Sedation protocols vary  but consist in general of an α2 agonist with or without acepromazine and butorphanol. Sedation used in our clinic is romifidine (Sedivet¨) in combination with methadone (Mephenon¨) or acepromazine (Placivet¨). The romifidine sedation is repeated if necessary. Once sedated the limb is centred in the magnet with the RF coil around the selected region. The routine sequences for MRI imaging of the foot are summarized in table 1.

   

Sequences FOOT

TR

TE

Flip ¡

Slice

Gap

T1 GE sagittal, frontal

97

8

80

5

5,5

T2* GE transverse

130

13

30

5

5

STIR FSE sagittal (trans, front)

1650

23 ; 23

90

5

5,5

T1 SE transverse

500

20

90

5

5,5

T2 FSE sagittal, frontal, (transverse)

1700

30 ; 60

90

5

5,5

Table 1 : Routine protocol MRI exam of the foot.

 

 

Clinical Cases

 

In the period from October 2004 until March 2006 (18 months) 227 horses have been presented at Equine Clinic De Bosdreef for an MRI examination. 198 horses requested MRI exam of the foot, 25 horses a fetlock MRI, 3 tarsus MRI and 1 carpus MRI. The horses were mixed age, breed and use, although mainly warmblood showjumpers and dressage horses. The data of the 198 MRI exams of the foot are collected. 195 horses had forelimb lameness (158 unilateral, 37 bilateral), 3 horses hindlimb lameness (all unilateral). In all horses the pain area was localised using perineural or intra-articular anaesthesia. Radiography and ultrasonography failed to identify the exact structures responsible for the degree of lameness.

 

 

Results Foot MRI (preliminary raw data)
  

* 32 horses (16%) had multiple injuries all thought to be clinically relevant.
* DDFT lesions were seen in 29 horses (15%) as a primary lesion. Another 17 horses (8,5%) had lesions of the navicular bone and the DDFT. 15 horses with multiple lesions had DDFT lesions.
36 horses (18%) had primary navicular bone pathology. 12 horses with multiple lesions had the navicular bone involved.
* Primary desmitis of a collateral ligament of the DIP joint was seen in 11 horses (5,5%) and in another 7 horses with multiple injuries. DIP joint lesions were seen in 8 horses (4%). 8 horses (4%) had excessive synovitis of the DIP joint with tissue proliferation. 2 horses (1%) had lesions of the PIP joint.
* 15 horses (7,5%) had desmitis of the impar ligament and 20 horses (10%) had bursa problems without significant DDFT or navicular bone pathology.
* 12 horses (6%) had primary lesions of the middle or distal phalanx and 2 horses (1%) had primary laminitis.
* 4 horses (2%) had proximal collateral ligament desmitis of the navicular bone, and one horse (0,5%) distal annular ligament desmitis.
* One horse (0,5%) was violent and unable to be examined properly.

 

 

Conclusion
 

In a majority of the horses lesions of the deep digital flexor tendon (15%) and the navicular bone (18%) are diagnosed. 8,5% of the horses have lesions in both structures together. A large group of horses have multiple lesions (16%), which are all thought to be clinically relevant. These horses have a combination of lesions involving the navicular bone, DDFT, impar ligament, DIP joint, collateral ligament DIP joint, proximal collateral ligament of the navicular bone or the second or third phalanx. Lesions of the impar ligament (7,5%) and the podotrochlear bursa (10%) are also frequently seen. Primary DIP joint lesions are seen less frequently (4%) and primary significant desmitis of the collateral ligaments of the DIP joint only in 5,5% of all horses.

 

Compared to literature (Dyson et al., 2005) less DDFT lesions are seen and there is a larger equilibrium between DDFT and navicular bone lesions. There are also less horses with significant pathology of the collateral ligaments of the DIP joint. Reason for this finding can be that some irregularity at the origin of the ligament in horses with compromised conformation is not always interpret as clinically relevant and contributing to the degree of lameness. Figures in this study for the impar ligament, DIP joint, the middle and distal phalanx and horses with multiple lesions are comparable with literature. These data are preliminary and correlation with age, gender, use and outcome are still to be made.

 

 

Literature

 

á       Busoni V. et al. (2004) Magnetic Resonance Imaging of the palmar aspect of the podotrochlear apparatus : normal appearance. Vet. Radiol. And Ultrasound 45: 198-204.

á       Busoni V. et al. (2005). Magnetic Resonance Imaging findings in the deep digital flexor tendon and distal sesamoid bone in advanced navicular disease – an ex vivo study. Vet. Radiol. And Ultrasound 46: 279-286.

á       Denoix J-M et al. (1993) Magnetic Resonance Imaging of the Equine Foot. Vet. Radiol. And Ultrasound 34, 405-411.

á       Dyson S et al. (2005). Lameness associated with foot pain: results of magnetic resonance imaging in 199 horses (January 2001- December 2003) and results of treatment. Equine Vet. J. 37, 113-121.

á       Dyson S (2005). Principles of magnetic resonance imaging and interpretation in relation to the distal aspect of equine limbs. Proc. MRI meeting Bonn February 2004.

á       Mair T et al (2005). Magnetic Resonance Imaging of the distal limb of the standing horse. Equine Veterinary Education 17, 74-78.

á       Schneider P et al. (2003). What is MRI teaching us about Navicular Disease. Proc. 49th Ann. Con. AAEP, New Orleans, Louisiana.