Im­age That!

Learn how high-tech imag­ing op­tions can take the mys­tery out of your horse’s foot-re­lated lame­ness.

Horse & Rider - - News - By Barb Crabbe, DVM

Learn how high-tech imag­ing op­tions can de­mys­tify your horse’s foot- re­lated lame­ness.

Step into my time ma­chine so we can travel back to 1989. We see you and your horse with the vet­eri­nar­ian ex­am­in­ing the horse for lame­ness. Nerve blocks show the prob­lem lies in your horse’s heels, but his X-rays look just fine. “He’s got navicular,” the vet says. “It’s just not bad enough to show up on X-rays yet.” It’s a dev­as­tat­ing blow. You treat your horse with cor­rec­tive shoe­ing and anti-in­flam­ma­to­ries for years. You even in­ject his cof­fin joints. Un­for­tu­nately, he’s never re­ally right, and his X-rays never change. “There must be some­thing there,” you think. “I wish there was a way to look inside his feet and see what’s re­ally wrong.”

Fast-for­ward a cou­ple of decades. New horse, same prob­lem. Your horse is lame, and nerve blocks con­firm the pain is com­ing from his heels. “Not this again!” you think. “Isn’t there some­thing more that we can do?”

Thanks to ad­vances in imag­ing, yes! Here I’ll ex­plain how ad­vanced imag­ing op­tions like nu­clear scintig­ra­phy (bone scan), mag­netic res­o­nance imag­ing (MRI), and com­puted to­mog­ra­phy (CT) have changed the world of equine lame­ness di­ag­no­sis— es­pe­cially in­volv­ing your horse’s feet. You’ll see why neb­u­lous an­swers like “navicular dis­ease” or even “bi­lat­eral heel pain” have be­come ob­so­lete, and how you can get an ac­cu­rate and spe­cific di­ag­no­sis in­stead. You’ll also learn how hav­ing a spe­cific di­ag­no­sis can greatly im­prove your horse’s chances for a suc­cess­ful recovery.

Hoof Ba­sics

Your horse’s foot is com­pli­cated. Add to that the many lame­ness prob­lems that orig­i­nate from the foot, and you’ll un­der­stand why it’s so im­por­tant to be able to cre­ate ac­cu­rate images of the area.

Thirty years ago, vet­eri­nar­i­ans fo­cused most of their at­ten­tion on the navicular bone—a small, wing­shaped bone in the back of the foot that dis­trib­utes stress and as­sists the func­tion­ing of lig­a­ments that both sup­port your horse’s limbs on the ground and pro­duce move­ment. If your horse was lame, a nerve block (dead­en­ing of the nerves that sup­ply a cer­tain area of the leg) might con­firm the pain orig­i­nates from his heels or foot. In the vast ma­jor- ity of cases, the navicular bone was blamed, and a di­ag­no­sis of “navicular dis­ease” was made. Ra­dio­graphs were taken. Some­times the bone looked dam­aged; some­times it didn’t. Some­times your horse im­proved; some­times he stayed lame for the rest of his life.

Now we know that those “navicular” horses likely had one of a wide va­ri­ety of dif­fer­ent, spe­cific in­juries, rang­ing from chronic de­gen­er­a­tion of the bone it­self to an acute in­jury of one of the many small ten­dons or lig­a­ments within the foot. And through ad­vances in tech­nol­ogy, imag­ing tech­niques can iden­tify spe­cific in­juries, which means that treat­ments can be more tar­geted and ef­fec­tive, and you’ll have a more ac­cu­rate pic­ture of your horse’s chances for recovery when a di­ag­no­sis is made.

Imag­ing Op­tions

Vet­eri­nary medicine has made ma­jor ad­vance­ments since those years of di­ag­nos­ing so many horses with navicular dis­ease. Th­ese five imag­ing op­tions play a large part in those en­hance­ments to our di­ag­nos­tic tool­box. →


An X-ray ma­chine passes a beam of ra­di­a­tion through your horse’s body to­ward a plate that de­tects the ra­di­a­tion, and then con­verts that in­for­ma­tion into an im­age to make a ra­dio­graph. Ar­eas of the body that ab­sorb more ra­di­a­tion ap­pear white (thick bone), while ar­eas that ab­sorb less ra­di­a­tion ap­pear dark (less thick bone or soft tis­sues). More mod­ern sys­tems (known as dig­i­tal ra­di­og­ra­phy or DR) are fully com­put­er­ized, re­sult­ing in more de­tailed images that can be ma­nip­u­lated with a computer to help with in­ter­pre­ta­tion.

Pros: They pro­vide a good over­all as­sess­ment of the bones in your horse’s feet, in­clud­ing the navicular bone, and are es­pe­cially use­ful for iden­ti­fy­ing frac­tures or bone de­gen­er­a­tion. In some cases they show ab­nor­mal­i­ties where soft tis­sues at­tach. Com­par­ing ra­dio­graphs taken sev­eral years apart can show how sig­nif­i­cantly bones can change over time.

Cons: Ra­dio­graphs don’t pro­vide much in­for­ma­tion about soft tis­sues. Even when it comes to bone, ra­dio­graphs are less sen­si­tive than other imag­ing modal­i­ties such as MRI or CT. Stud­ies have shown that there can be a great deal of bone in­flam­ma­tion present even though ra­dio­graphs ap­pear nor­mal. The ma­chine passes sound waves through your horse’s body parts to make an im­age. The waves are ab­sorbed by or pass through tis­sues de­pend­ing on tis­sue den­sity, and a tiny mi­cro­phone de­tects the waves that “bounce back” as echoes to de­velop and an im­age. Less-dense ma­te­ri­als (like fluid) al­low sound waves to pass com­pletely through them and ap­pear darker or “more black,” while dense tis­sues (like bone) will bounce back all of the waves and ap­pear lighter or “more white.”

Pros: Ul­tra­sound can pro­vide ac­cu­rate and de­tailed images of soft-tis­sue struc­tures and joint sur­faces. It’s es­pe­cially use­ful to mon­i­tor heal­ing of an in­jury through­out re­ha­bil­i­ta­tion.

Cons: Ac­cu­racy de­pends on the op­er­a­tor’s skill. Ul­tra­sound of the foot is par­tic­u­larly dif­fi­cult to per­form, in part be­cause the hoof wall in­ter­feres with the pas­sage of the sound waves. To get an ac­cu­rate di­ag­no­sis, the ul­tra­sonog- ra­pher must be very ex­pe­ri­enced and have spe­cial­ized equip­ment. And un­like other imag­ing modal­i­ties like ra­di­og­ra­phy and MRI, images can’t be re­li­ably sent to out­side ex­perts for re­view.

Mag­netic Res­o­nance Imag­ing (MRI)

MRI sub­jects a part of your horse’s body to a very strong mag­netic field that im­pacts the align­ment of tiny par­ti­cles (called pro­tons) within his cells.

The mag­netic field is ma­nip­u­lated us­ing short bursts of ra­dio waves that cause the pro­tons to change their align­ment. Pro­tons in dif­fer­ent types of tis­sues have char­ac­ter­is­tic re­sponses, and send off unique sig­nals that are de­tected and con­verted to an im­age.

There are two op­tions for ob­tain­ing an MRI. High-field (the mag­net is very strong) MRI gives the most de­tailed, ac­cu­rate re­sults but re­quires that your horse be put un­der gen­eral anes­the­sia. Low-field (the mag­net is not as strong) MRI may lack some im­age qual­ity, but can be done with your horse stand­ing and se­dated, avoid­ing the risk of anes­the­sia. As equip­ment has im­proved, images of the foot ob­tained with low-field MRI are of­ten good enough to pro­vide a di­ag­no­sis.

Pros: MRI pro­vides a very de­tailed, spe­cific im­age of all parts of your horse’s foot. High-field MRI is the most sen­si­tive of all of the avail­able imag­ing tools, and will de­tect ab­nor­mal­i­ties that can’t be seen on ra­dio­graphs or aren’t clear on ul­tra­sound. MRI is the only way to iden­tify bone edema, or fluid ac­cu­mu­la­tion within the bone, that of­ten ac­com­pa­nies lame­ness.

MRI has only been avail­able since the late 1990s, and is of­ten rec­om­mended for horses with a lame­ness that’s been iso­lated to the foot but shows no ab­nor­mal­i­ties on ra­dio­graphs or ul­tra­sound. His­tor­i­cally a last re­sort for horses that have re­sponded poorly to early treat­ment, MRI is now rec­om­mended ear­lier in the lame­ness workup. An MRI that gives you an ac­cu­rate early di­ag­no­sis can go a long way to­ward mak­ing good treat­ment and man­age­ment de­ci­sions, and will im­prove the chances your horse will fully re­cover.

Cons: High-field MRI re­quires anes­the­sia, so risks must be con­sid­ered if low-field MRI is un­avail­able or im­age qual­ity is ques­tion­able. It takes a long time to cre­ate an MRI im­age, so it’s best if the source of lame­ness has been ac­cu­rately lo­cated prior to imag­ing. MRI is best for soft-tis­sue in­juries, and may not be as ac­cu­rate as CT for iden­ti­fy­ing some bone ab­nor­mal­i­ties. MRI doesn’t al­low for eval­u­a­tion of blood flow.

Com­puted To­mog­ra­phy (CT Scan)

Just like ra­dio­graphs, a CT scan passes ra­di­a­tion through your horse’s body

to­ward a plate that then de­tects the amount of ra­di­a­tion spread through the tis­sues to cre­ate an im­age. In­stead of a sin­gle beam, the CT scan­ner passes many small beams from dif­fer­ent an­gles, cre­at­ing slices of in­for­ma­tion that com­bine to pro­duce a very de­tailed im­age. The X-ray tube ro­tates around the pa­tient, as well as “slides” along its length, which elim­i­nates any loss of in­for­ma­tion about a spe­cific struc­ture be­cause it’s ob­scured by another struc­ture. CT scans pro­vide very de­tailed images of both bone and soft-tis­sue struc­tures.

Pros: CT scans are much more sen­si­tive for de­tect­ing bone le­sions than ra­dio­graphs, and com­pare fa­vor­ably to low-field MRI for many soft-tis­sue in­juries. They also al­low for eval­u­a­tion of blood flow, which can’t be done with MRI. It takes much less time to pro­duce an im­age us­ing CT com­pared with MRI, meaning larger ar­eas are eas­ier to eval­u­ate and pre­cise lo­cal­iza­tion of the source of lame­ness isn’t as crit­i­cal.

Cons: The ma­jor­ity of feet CT scans re­quire anes­the­sia, so risks must be con­sid­ered. Stand­ing CT of the head and neck is pos­si­ble, how­ever, and work is be­ing done to al­low for stand­ing CT scans of the feet in the near fu­ture. CT is typ­i­cally not as ac­cu­rate as high-field MRI for di­ag­nos­ing soft-tis­sue in­juries, and it will not iden­tify bone edema.

Nu­clear Scintig­ra­phy (Bone Scan)

Nu­clear scintig­ra­phy in­volves in­ject­ing your horse with a ra­dioac­tive sub­stance that cir­cu­lates through­out his blood­stream. A gamma cam­era cre­ates images by de­tect­ing ar­eas of in­creased ra­dioac­tiv­ity, in­di­cat­ing in­creased blood flow—a sign of in­flam­ma­tion.

Pros: A bone scan iden­ti­fies ar­eas of ac­tive in­flam­ma­tion and is of­ten com­bined with other imag­ing modal­i­ties to de­ter­mine if the anatomic ab­nor­mal­i­ties iden­ti­fied are sig­nif­i­cant. It can be help­ful for lo­cal­iz­ing a source of lame­ness where re­sults from a clin­i­cal lame­ness exam are un­clear. Bone scans can also help iden­tify ar­eas of sub­clin­i­cal in­flam­ma­tion—prob­lems that are brew­ing but might not yet cause lame­ness. This allows for early man­age­ment be­fore in­juries be­come se­vere.

Cons: Images ob­tained with a bone scan do not pro­vide good anatomic de­tail. Ad­di­tional imag­ing, in­clud­ing ra­dio­graphs, ul­tra­sound, MRI, or CT, are nec­es­sary to ac­cu­rately di­ag­nose the pre­cise cause of lame­ness.

Case in Point

Is it im­por­tant to iden­tify the cause of lame­ness so specif­i­cally? In some cases, ab­so­lutely! Here’s one case I en­coun­tered.

Scooter is a 14-year-old Paint mare used for breed-show-level com­pe­ti­tion. She’d shown some foot sen­si­tiv­ity over the years, and per­forms bet­ter if shod with pads. Last fall, af­ter a hard sum­mer of show­ing, she started balk­ing. Then one day, she be­came very lame.

Dur­ing her exam, Scooter was quite lame on the left front foot, and was un­com­fort­able when the lower joints of both fore­limbs were flexed. With a nerve block to her left front heel and sole, Scooter be­came slightly lame on the right front foot. When we blocked her right front heel, she moved bet­ter than she had in years. There were no ab­nor­mal­i­ties seen on ra­dio­graphs of her front feet.

Scooter im­proved quite a bit within a week of her sud­den lame­ness, and her own­ers were given the op­tion of treat­ing her cof­fin joints with in­jec­tions to re­duce in­flam­ma­tion in many struc­tures within the foot. If suc­cess­fully treated, Scooter might be able to con­tinue to work—and still make it to the fall shows. Al­ter­na­tively, they could pur­sue a more spe­cific di­ag­no­sis with an MRI.

They chose the MRI, which re­vealed that Scooter had edema in both navicular bones and ex­ces­sive fluid in her cof­fin joints. The most sig­nif­i­cant find­ing, how­ever, was a tear in her deep dig­i­tal flexor ten­don at the level of the navicular bone. In other words, she had some ev­i­dence of in­flam­ma­tion that most likely ex­plained her chronic low­grade foot sore­ness and a sig­nif­i­cant soft-tis­sue in­jury that was most likely the cause of her acute lame­ness.

Scoot­ers’s cof­fin joints were in­jected with steroids and hyaluronic acid to re­duce in­flam­ma­tion. She was also ad­min­is­tered Til­dren, a med­i­ca­tion that in­hibits os­teo­clasts—cells that are in­volved with bone de­gen­er­a­tion— and is es­pe­cially ef­fec­tive for treat­ing bone edema. Af­ter sev­eral months of rest, she was put into a very care­ful re­ha­bil­i­ta­tion pro­gram to al­low the

ten­don in­jury to heal. Af­ter a full year off, Scooter was sound and back in the com­pe­ti­tion ring.

Had Scooter’s own­ers taken the op­tion of treat­ing her cof­fin joints and keep­ing her in work, it’s likely she’d have been sound for a pe­riod of time. How­ever, the deep dig­i­tal flexor ten­don in­jury could’ve wors­ened and had a sig­nif­i­cant im­pact on her long-term sound­ness. In fact, she might’ve be­come per­ma­nently lame. Be­cause her own­ers ob­tained an ac­cu­rate di­ag­no­sis, they were able to treat her ap­pro­pri­ately, give her ad­e­quate time to heal, and im­prove the chances that their horse would stay sound for the long haul.

TOP: Ra­dio­graphs pro­vide a good over­all eval­u­a­tion of the bones in your horse’s feet, but pro­vide limited in­for­ma­tion about soft­tis­sue struc­tures. MID­DLE: MRI is the most sen­si­tive of all of the imag­ing op­tions, and pro­vides de­tailed in­for­ma­tion about both bone and soft-tis­sue struc­tures. BOT­TOM: A bone scan will iden­tify ar­eas of ac­tive bone in­flam­ma­tion, but does not give de­tailed in­for­ma­tion about anatomic struc­tures.

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