What does it mean for a disk to rupture, and how does it happen?

The disk is composed of two parts.  The outer covering is much like a thick shell.  It is comprised of tough fibers that protect and contain the central part.  It is thinnest at the top; this thin area is located just below the spinal cord.  The central part of the disk has the consistency of thick tooth paste; it is much softer than the outer part.

When the outer shell degenerates, it allows the central part of the disk to escape.  This is called a disk rupture or a ruptured disk.  Since the shell is thinnest near the spinal cord, disk material that escapes almost always goes upward, putting pressure on the cord.  Because the spinal cord is encased within its bony canal, it cannot move away from the pressure and it becomes pinched.

Degenerative disk disease causes spontaneous degeneration of the outer part of the disk, resulting in escape of the central part.  It is not related to injury, although trauma can cause disks to rupture.  It is also not related to age.  Most dogs with degenerative disk disease are 3-7 years old.  It is just a spontaneous event that is most likely controlled by genetic factors.  Certain breeds, notably the Dachshund, Poodle, Pekinese, Lhaso Apso, and Cocker Spaniel have a high incidence of disk disease.  Other breeds, such as the German Shepherd and Doberman Pinscher, also have disk disease but with a lower incidence.  Many breeds never have degenerative disk disease.

Most owners report that a disk rupture occurred following some traumatic event, such as a relatively small jump or fall.  Although this act is frequently blamed for the disk rupture, if the disk had not already been degenerating, the rupture would not have occurred.

How does a ruptured disk affect the spinal cord?

The spinal cord is much like a telephone cable that is carrying thousands of tiny wires.  When it is crushed, transmission of information through the wires is stopped.  When the disk degenerates and ruptures, a similar event occurs.  The central part is forced upward, putting pressure on the spinal cord and/or the nerves that leave the spinal cord over the disks (i.e., spinal nerves).  Pressure on the spinal nerves results in pain; pressure on the spinal cord results in pain and/or loss of information transmission.  This results in paralysis or partial paralysis.

Most disk ruptures occur in the middle to lower part of the back.  However, they may also occur in the neck.  The former often causes paralysis without severe pain; the latter often causes severe pain without paralysis.  If paralysis affects all four legs, the disk rupture must be in the neck.  Because of the way the nerve tracts are arranged in the spinal cord, disk ruptures in the neck may affect the rear legs first or even exclusively.
How fast do disks degenerate and rupture?

Disk degeneration usually occurs relatively slowly, i.e., over several days or weeks.  The dog usually experiences pain and becomes reluctant to move.  It may lie around for a few days allowing the body to resolve the problem, often without the owner being aware that a problem existed.  However, disks may also rupture very acutely.  Some dogs will go from normal walking to total paralysis in less than one hour.

How is a disk rupture diagnosed?

A presumptive diagnosis of disk disease is made based on the dog's history of neck or back pain, incoordination when walking, or paralysis when there is no history of trauma.  The physical examination will indicate that the problem originates from the spinal cord, giving further evidence to disk disease.  Another important factor is the breed.  If the dog is one of the high incidence breeds, the diagnosis is even more likely.

In some cases, plain radiographs (x-rays) may assist the diagnosis, but they may also be normal since neither the disk nor the spinal cord are visible.  If the diagnosis is in doubt or if surgery is to be performed, a myelogram may be done.  This procedures involves injecting a special dye around the spinal cord while the dog is under anesthetic.  When radiographs are taken, the dye will be seen outlining the spinal cord.  A break in the dye column means that there is pressure on the spinal cord.

How do you know if the pressure on the spinal cord is due to a disk or something else?

It is possible that the pressure is due to a blood clot or a tumor.  Both are possible but not very common, especially when compared to disk ruptures.  If the breed of dog is correct for disk disease, there has been a sudden onset, and there has been no trauma, there is about a 95% chance that a disk rupture is causing the pressure.  However, the diagnosis is not definite until the time of surgery.

Are all disk ruptures treated with surgery?

Not necessarily.  Treatment is based on the stage of the disease.  Stage I disk disease produces mild pain and is usually self-correcting in a few days.  Stage II disk disease causes moderate to severe pain in the neck or lumbar (lower back) area.  Stage III disk disease causes partial paralysis (paresis) and results in the dog walking in staggering or uncoordinated movements.  Stage IV disk disease causes paralysis but the ability to feel is present.  Stage V disk disease causes paralysis and loss of feeling.  These stages tend to overlap in some dogs, and dogs may move from one stage to another over a period of hours to days.

Dogs with Stage II and III disease are usually treated with anti-inflammatory drugs, pain relievers, and restriction from exercise.  Surgery may be considered if the pain or uncoordination persists after 4-7 days of treatment or if the neurological status declines from one day to the next.  It is important that the dog not receive pain medication unless total confinement to a crate or cage is enforced.  If the pain sensation is taken away, the dog is more likely to progress to total rupture of the disk.  The sensation of pain is important for limiting motion.  The length of confinement will vary among different dogs.

Dogs with Stage IV disease should have surgery, although a small percentage will recover without it.  Dogs with Stage V disease should have surgery, and the sooner that surgery is done, the better the prognosis.  If at all possible, these dogs should be operated on within the first 24 hours of the onset of paralysis.

What is the purpose of surgery?

The goal of surgery is to remove pressure from the spinal cord.  If the disk rupture occurs in the lower back, a window is made in the side of the vertebral bone to expose the spinal cord.  This window allows removal of disk material and relieves pressure from the cord.  If the disk rupture occurs in the neck, a window is made in the bone exposing the spinal cord.  This may be done either from the top or the bottom, depending on the situation and the training of the surgeon.

What is the success rate for treating disk disease with and without surgery?

StageRecovery without SurgeryRecovery with Surgery

II: up to 1 week80-90%90-95%
II: past 1 week60-70%90-95%
III30-40%85-95%
IV: up to 3 days< 25%85-95%
IV: past 3 days< 20%60-70%
V: up to 24 hours< 5%50%
V: past 24 hours< 5%<20%

When will we know if the surgery is successful?

When surgery is completed, we hope to achieve two things.  First, the dog should be recovering from the anesthetic.  Secondly, the disk rupture should be located and the pressure relieved from the spinal cord.  However, the return of walking ability and relief from pain may not occur for several days, or even weeks, so success cannot be determined immediately.

When can my dog go home?

Following surgery, your dog will be hospitalized for 3-7 days.  Bladder and bowel control are often lost when the dog is paralyzed, so it is best for control of these functions to return before going home.  However, it is generally best not to extend hospitalization beyond 7 days because regaining the ability to walk partly depends on exercise and motivation.  Since motivation is such an important part of the recovery process, visitation is encouraged beginning the day after surgery.  Please ask about scheduling your visits.

If paralysis was present before surgery, your dog may not be able to walk when it is discharged from the hospital.  You will be given detailed instructions on the procedures that should be performed.  Recovery is dependent on four factors:  whether or not permanent damage was done before surgery, if the surgery was performed promptly, physical therapy performed at home, and the motivation of your dog.  You will be instructed on ways to achieve the last two.

Is it likely that my dog will be worse after surgery than before?

Dogs that have surgery on the lower back are generally no worse after surgery unless the spinal cord damage has progressed due to the disc rupture.  However, dogs that have surgery on the neck may actually have increased lameness in one or both front legs.  This is a setback due to the manipulation around the spinal cord normally associated with surgery.  The lameness may persist for a few days, but it should be temporary.  Improvement should occur steadily until the legs return to normal.

What does it mean if surgery is not successful?

Most dogs are either greatly helped and return to normal or near normal or they do not improve at all.  If walking is not regained, most dogs will also not regain control of the bladder and bowels.  This means that urine and stool incontinence will accompany paralysis.

Can my dog rupture a disk again?

The answer is "yes."  However, more than 95% of degenerated disks will heal without surgery.  So the chance of your dog needing surgery a second time is less than 5%.

What if the myelogram is normal?

The purpose of the myelogram is to identify pressure on the spinal cord.  If the myelogram is normal, there is no pressure on the spinal cord.  This has several important implications.  First, it means that surgery will generally not be appropriate because the purpose of surgery is to relieve the pressure from the cord.  Second, it means that one of the following conditions is likely to exist.

1.  Spinal Shock.  This is a temporary loss of spinal function that is generally associated with trauma.  It occurs suddenly and is somewhat like a concussion of the brain.  It may leave permanent damage, or full recovery may occur.  Recovery from spinal shock generally occurs within a few hours to a few days.

2.  Fibrocartilaginous Infarct or Embolism.  In this condition, a small amount of disk material ruptures and gets into one of the blood vessels leading to the spinal cord.  As the vessel narrows, the disk material obstructs it, depriving a certain segment of the spinal cord of its blood supply.  Without proper blood supply, that segment of the spinal cord quits working, resulting in paralysis.  Surgery will not help these dogs because there is no pressure on the spinal cord.  Often, paralysis involves only one rear leg, or one rear leg is more severely affected than the other.  Complete recovery may occur in a few days to weeks, or there may be permanent damage to a portion of the spinal cord.

Diagnosis of fibrocartilaginous infarct/embolism is based on the correct clinical signs and a normal myelogram.  Confirmation requires a biopsy of the spinal cord so the diagnosis is confirmed only with an autopsy.

3.  Degenerative Myelopathy.  This condition means that the spinal cord is slowly dying.  It results in progressive paralysis that begins with the dog dragging its rear feet as it walks.  This is called "knuckling over" and results in the toe nails of the rear feet being worn because they drag the ground with each step.  It progresses to weakness of the rear legs, then paralysis.  It generally takes several weeks before paralysis occurs, and it generally occurs in large breeds of dogs, especially German Shepherds.  Because there is no successful treatment and paralysis includes loss of urine and bowel control, euthanasia is generally recommended.

Diagnosis of degenerative myelopathy is based on the correct clinical signs, especially in a large breed of dog, and a normal myelogram.  Confirmation requires a biopsy of the spinal cord so the diagnosis is confirmed only with an autopsy.

A normal myelogram in a dog with slowly progressive paralysis is very frustrating because the two most likely diseases (numbers 2 and 3) cannot be confirmed without an autopsy. 

EUROPEAN AND AMERICAN STUDIES OF INTERVERTEBRAL DISC DISEASE

Several studies have been conducted in America and Europe over the years relating to intervertebral disc disease (IVDD) in the dachshund.  The results of those studies are presented below. Many thanks to Finnish DCA Member Silja Linko-Lindh for the information presented here and for her assistance in both translating and interpreting the results.

  In 1980, a project conducted by Havraneck & Balzaretti in Switzerland consisted of an x-ray study of 209 dachshunds between the ages of 12 and 18 months.  Of the dogs that showed calcifications, 79% got IVDD symptoms later, while dogs with clear x-rays lived without problems.  As a part of the study, some of the x-rayed dogs were bred to each other. The offspring were x-rayed at the age of 12 months, with the following results:  if both parents were free of calcifications, 30% of the offspring had calcifications; if one calcification-free parent was bred to one with calcifications, 56% of the offspring had calcifications; if both parents had calcifications, 83% of the offspring had calcifications.  This study gives strong evidence to support the theory that calcified discs tend to herniate and that calcifications are hereditary.  The connection between calcifications and paralysis seems undisputable if credence is given to this study.

 A project conducted by Ball et al in the U.S. in 1982 consisted of a pedigree-study of 536 dachshunds. There was an overall IVDD occurrence 19%.  Thirty-one of the dogs in the study were the offspring of the same afflicted stud: 61 % of them (19 dogs) had IVDD problems.

The Stigen project, conducted in Norway during the years spanning 1991-1996, consisted of x-ray studies of 327 dachshunds, ages 12-18 months.  Of them, 115 dachshunds returned for new x-rays five years later. Conclusions: dachshunds with calcifications at the age of 12 months have a four-time greater risk for problems than dogs without calcifications.  Calcifications can increase but they can also disappear.  Another conclusion of this study was that disc calcification is hereditary.
 

A short summary of the thesis written by the Danish veterinarian Vibeke Jensen (approved on September 28, 2000) to outline the results of his extensive study in this area has been provided below by Anu Lappalainen, and translated from the Finnish by Silja Linko-Lindh:

 The study was divided into 5 parts, and four of them are published or accepted for publishing in various veterinary journals.

 Part One

 Development of Intervertebral Disc Calcification in the Dachshund: A Prospective Longitudinal Radiographic Study [Journal of the American Animal Hospital Association, 7/2000]

 Dr. Jensen followed the development of calcifications in forty dogs from eleven litters by x-rays.  Four of the litters were wirehaired dachshunds, 4 litters were smooths, one litter was longhaired standards and 2 litters were longhaired miniatures (FCI breed standard). The dogs were x-rayed at the ages of  6, 9, 12, 18 and 24 months and some also at the age of three or four years.

Results:  The first calcifications were already evident at the age of 6 months but the highest number of calcifications appeared between the ages of 12 and 18 months. After 24 months new calcifications were few and appeared only in those dogs who had several calcifications.  Many of the calcifications were barely visible before the age of 24 months, but could be confirmed with certainty at that age.  Calcifications started to disappear at the age of 18 months, and that phenomenon accelerated after 24 months. The disappearance of the calcifications was more common in dogs with several calcifications.  At the age of 12 months 53% of the dogs had confirmed calcifications and 7% were suspected cases.  At the age of 24 months 80% of the dogs had calcifications (averaging approximately 3.2 calcifications per dog). Of the calcifications, 80% were in the thoracolumbar (mid-back) area.

Conclusions:  Dogs should be at least 2 years of age when x-rayed. Most calcifications can be seen at the age of 24-27 months.

 Part Two

 Occurence of Intervertebral Disc Calcification in the Dachshund [Journal of Veterinary Medicine, Series A, 47 (5): 283-296]

This was a study of the effects of mechanical phenomena (exercise, climbing stairs, hunting, running with bicycle) on the occurence of the calcifications. Forty-eight wirehaired standard dachshunds (FCI breed standard, not over 9-10 kilograms,) were elected to represent the Danish dachshunds, with offspring of imported dogs and frequently used sires being avoided.  Also avoided were females from heavily bred lines.  Dogs were 24-55 months old, clinically healthy and had not been treated for back problems.

Results:

77% of the dogs had calcifications, averaging 4.5 calcifications per dog. The connection between climbing stairs and calcifications can be considered statistically significant.  Moderate climbing decreases the number of calcifications. Running alongside a bicycle a couple of times a month increased the number of calcifications, but dogs with this kind of exercise were only 4 of the 48, so the result could also be a coincidence.  Conclusions: moderate unleashed exercise and moderate climbing of stairs have a positive effect of the health of the discs. The reason seems to be the better metabolism of the intervertebral discs. But climbing stairs is still a risk for dogs with clearly and strongly calcified discs.

Part Three

Inheritance of Intervertebral Disc Calcification in the Dachshund [Journal of Veterinary Medicine, Series A, 47 (6): 331-340]

Eight males, 16 females and 69 of their offspring (all wirehaired standards, FCI standard) were studied. Every litter in the sample was represented by at least three dogs. The offspring were between two and three years old. None of the offspring had had any symptoms of intervertebral disc disease but one of the mothers had the disease diagnosed.

 Results: 100% of the sires, 75% of the dames and 80% of the offspring had calcifications. If both parents had calcifications 91% of their offspring had calcifications. If only one parent had calcifications, 44% of the offspring had calcifications. The heredity rate, depending on the counting method for the occurence of the calcifications, is between 0.46 and 0.87. The rate is higher between dam-offspring than between sire-offspring. (That fact could be due to the effect of environmental factors associated with the dam, such as rough play with the pups, litter size, and nutrition.) Conclusion: calcification of the intervertebral discs is hereditary.  The phenomen can be controlled and significantly decreased by breeding choices.

 Part Four

Asymptomatic Radiographic Disappearence of Calcified Intervertebral Disc Material in the Dachshund [Veterinary Radiology and Ultrasound, 7/2000]

 The same 40 dogs used in the study outlined in Part One were followed with new x-rays at the age of 3-4 years.

Results: Nearly 10% of the calcifications had disappeared partly or totally. It is notable that the disappearance occurred only in those dogs who had more than 4 calcifications and more calcifications disappeared in litters where all of the dogs had calcifications. The calcifications that disappeared had been more calcified than others and had been obvious for a longer period.  This seems to indicate that calcifications disappear only from strongly degenerated discs. The mechanism of symptomless disappearance of calcifications is not known.

 Part Five

 Deformity of discs.

This study has not been published so the correct name for it is not known. The short result is that the deformity of discs seems to be hereditary but doesn't seem to have any connection with the calfications of the intervertebrals discs.

 Study #1 is credited to Jensen V & Arnbjerg J.

Study #3 is credited to Jensen V & Christensen K.

 
A line-based study in Denmark studied 126 dachshunds in 26 litters, with at least one afflicted dachshund in each litter.  Afflicted sires and grandsires were heavily represented, while dames and granddames were usually health.  (That fact may indicate that the breeders whose litters were studied knew their bitches’ lines better than they knew the lines of males they used.) The wirehaired standard sized dachshunds (80% of x-rayed dogs) had the most calcifications. The study concluded that the best time to x-ray is between the ages of one and two years. After that age the calcifications don't increase but they can disappear. The breeding committee of the Danish dachshund club recommended at the conclusion of the study that only dogs free of symptoms be used for breeding and that the health of the grandparents should be checked. If it is not possible to check the back history in the line behind the stud, then using males over 8 years of age was recommended, as most occurrences of IVDD will have occurred before that age.

 The science represented above supports what many breeders already believe:  while many factors contribute to disc disease, it is probable that the most significant of those factors is heredity.  

 If x-raying breeding stock for calcifications can indicate which animals are most likely to produce offspring who suffer from disc disease, and if that information can be used to slowly but surely lessen the occurrences of IVDD in dachshunds, then responsible breeders have a very effective tool to use in an attempt to greatly reduce the occurrence of the breed’s largest health problem.  Dachshund owners can also utilize x-rays to have an idea of whether or not a particular dog is predisposed to IVDD, and this could be a very valuable asset in determining whether or not a dog is suitable for agility training or for other activities that incorporate jumping.  It is probably quite important that the x-ray equipment be of high quality and that the dog is placed in the specified positions to facilitate reading of the x-rays.

 Thanks to Dr. Marilyn (Julie) Roane for rendering these superb drawings and for lending her veterinary expertise as a consultant in presenting the results of the studies. 

These drawings show the optimal positioning of the dachshund for taking x-rays to determine if disk calcifications are present.  Two x-rays should be taken of the dog, one with the front legs in the forward position and another with the front legs moved back, as pictured in drawings #1 and #2.

Drawing N0.2

This offers the veterinarian two views of the areas between the vertebrae; comparing the two x-rays is very helpful in making the determination as to whether or not calcifications are present. Sandbags are used to hold the legs in place and cushions are placed as pictured in order to maintain the proper alignment of the spine.

Drawing No.3 illustrates the correct separation of the rear legs with a cushion

Drawing No. 4 shows the correct angle of the x-rays as well as offering an anterior view of how the cushions should be placed.

Reprinted from the DCA Newsletter, December, 2001