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Osteoarthritis

Carl Gorman BVSc MRCVS

Key words : Laser, osteoarthritis, degenerative joint disease, analgesia, mulotimodal

 

Osteoarthritis (OA), or degenerative joint disease (DJD), is one of the commonest conditions which will be seen in practice.  It is defined as a progressive disease of joints caused by gradual loss of articular cartilage and resulting in the development of bone spurs (osteophytes) at the margins of the joints and fibrosis of the periarticular tissues.  The name osteoarthritis is derived from three Greek words meaning bone, joint and inflammation.  The condition is irreversible (given current medical capabilities), which is important to understand when considering management of the disease.  Owners must understand that this is a chronic condition which will not be cured, but needs lifelong management.

OA is as common in cats as it is in dogs, although because cats have more control over their lifestyle and exercise levels, and because they are generally smaller and more flexible than dogs, the signs of OA in cats may be missed or misinterpreted by owners, and perhaps vets.  A recent study of radiographs of cats showed that over 90% of cats over the age of 12 years had evidence of OA, most commonly in the spine, followed by the elbow and hip.   Undoubtedly, the condition is common in both our common pet species and leads to discomfort, possible behavioural changes, and alteration in the pet-owner relationship.

OA may be primary or secondary. Primary OA results from 'wear and tear' on the joint surfaces through life; in essence these are ageing changes. 

Articular cartilage consists of (amongst other materials):

  • Hyaluronic acid
  • Glycosaminoglycans (GAGs)
  • Collagen
  • Water

These are maintained and repaired by chondrocytes.  Once they can't keep up with the wear and loss of cartilage, fissures appear, exposing bone and inducing the release of degrading enzymes. (Fig 1, Fig 2)

Fig 1 Normal Cartilage Elbow

Fig 1  Normal articular cartilage, seen via arthroscopy

Fig 2 Frag Coronoid Process Damaged Cartilage

Fig 2  Damaged articular cartilage, here due to fragmented coronoid pocess

 

The enzymes and the breakdown products of cartilage cause an initially mild synovitis involving several inflammatory mediators such as interleukins and prostaglandins.  These further increase cartilage damage.  The reduced resilience of the articular cartilage leads to sclerosis (an increase in density and hardening) in the subchondral bone.  As the disease advances, osteophytes (bone spurs) develop around the joint. (Fig 3)

Fig 3 Development Of OA

Fig 3 The stages in the development of osteoarthritis

Secondary OA involves much of the same pathophysiology, but the process is accelerated or occurs at a younger age because it is a result of trauma to a joint.  Trauma may be caused by:

  • A fracture involving a joint
  • An injury to the ligaments of a joint resulting in instability (e.g. cranial cruciate ligament rupture)
  • Uneven wear through anatomical abnormalities such as bowed legs, which may be developmental or traumatic in origin
  • Developmental abnormalities causing joint incongruity (e.g. hip dysplasia or elbow dysplasia) (Fig 4)
  • Developmental abnormalities causing instability and inflammation (e.g. fragmented coronoid process)
  • Developmental disorders causing cartilage damage (osteochondritis dissecans)
  • Inflammatory diseases such as septic or autoimmune arthritis
  • Repetitive excess trauma to a joint (e.g. from excessive exercise)
  • Metabolic disorders

Fig 4 Severe OA Following HD

Fig 4 Severe osteoarthritis as a consequence of hip dysplasia

Currently we have no way of effectively reversing the changes to articular cartilage involved in OA, but much research into the area is carried out in both human and veterinary fields.  It may be that the 'holy grail' of arthritis management - a way to repair and restore articular cartilage - will be found.

Clinical signs

The clinical signs of OA relate to the discomfort caused in the affected joints, which can be very variable. OA is often described as a 'waxing and waning' disease as the severity of the clinical signs can vary from week to week.

The main sign of OA will be lameness, together with reduced exercise tolerance.  Often the lameness is worse after resting, resulting in marked stiffness when a pet gets up.  If arthritis affects both left and right limbs, lameness may be missed by owners.

Affected joints may be swollen (from osteophyte development, fibrosis or joint effusion) and have reduced range of motion.

Secondary signs may be:

  • Muscle wasting near affected joints
  • Poor coat if grooming becomes uncomfortable
  • Reduced appetite
  • Reduced interaction with owners
  • Aggression
  • Inappropriate elimination (loss of house training)

Differential diagnosis

OA should be differentiated from other causes of lameness:

  • Trauma (to bones or soft tissues such as muscle, tendon or ligament)
  • Foreign bodies
  • Joint infections
  • Autoimmune inflammatory conditions (e.g. systemic lupus erythematosis, immune mediated polyarthritis)
  • Developmental disorders such as panosteitis, hypertrophic osteodystrophy, or luxating patella (although the age group for these cases should be different to classic OA)
  • Neoplasia (e.g. osteosarcoma) (Fig 5)
  • Neurological disease (e.g. chronic degenerative radiculomyelopathy  - CDRM, spinal neoplasia)
  • Spinal disease - in particular disc disease

Fig 5 Osteosarcoma

Fig 5 Osteosarcoma in the distal femur - without xrays conditions like this can be diagnosed as arthritis in error

Diagnosis

OA is diagnosed by a combination of clinical signs, joint palpation and manipulation and radiography.

Physical signs of arthritis

  • Thickened joints (osteophytes, fibrosis) (Fig 6)
  • Effusion
  • Reduced range of movement
  • Crepitus

Fig 6 Osteophytes Causing Swelling In Carpus

Fig 6 Prominent osteophytes caused swelling of the carpus in this collie

Advanced OA is relatively easy to diagnose, as the radiographic changes will be obvious.  Osteophytes and sclerosis of the subchondral bone are seen. (Fig 7) Sclerosis presents on a radiograph as a more radiodense (whiter) area of bone. 

Fig 7 Osteophytes In An Arthrotic Elbow

Fig 7 Osteophytes in an arthritic elbow (blue arrows)

Unfortunately radiography is not very sensitive for the detection of early osteoarthritis or for an accurate assessment of the disease, as cartilage is not detected by radiography and OA is a disease of cartilage.  There is not a reliable correlation between the degree of development of osteophytes and the level of damage to the articular cartilage.  Detection of sclerosis can be a more reliable indicator of the advancement of OA. (Fig 8a and 8b)

Laser7F8

Fig 8a 

Fig 2

Fig 8b

Figs 8a and 8b Subchondral sclerosis may be the first sign of osteoarthritis seen on xrays (arrows)

Radiographic signs don't correlate well to the degree of discomfort and pain, but in general practice this will be the main method of diagnosis.

MRI Scanning and arthroscopy are the gold standard for assessing the joint surfaces and the cartilage, though it is unlikely that the cost involved in using these tools will be justified.

Management

At present, arthritis is an irreversible disease.  As such, it is a condition where management rather than treatment is the more appropriate term.  The aim is to maintain quality of life by controlling pain, enabling an acceptable level of exercise and maintaining the pet-owner relationship.  Where possible we should try to slow or halt the progression of OA.

Therapies being explored currently include joint resurfacing using cartilage grafts or artificial materials, gene therapy and stem cell therapy.

Much better results will be obtained if a multimodal approach is adopted rather than simply relying on pain relief alone.  Remember the waxing and waning nature of OA signs.  It can be hard to assess the efficacy of treatment over the short term as patients may be on the verge of a 'good' cycle when a medication or therapy is started and owners can be fooled into thinking that something is effective.  This may be why some alternative remedies are seen as efficacious by owners in spite of a lack of any real evidence.

A multi-modal approach to management of osteoarthritis:

  • Correct any underlying factors
  • Control weight
  • Manage activity
  • Lifestyle modification
  • Disease modifying therapy
  • Pain control - drugs
  • Pain control - non-drug

Correct underlying factors

Surgery to correct initiating factors is important.  Examples might be cruciate ligament surgery, removal of fragmented coronoid process or ununited anconeal process, removal of cartilage flaps in osteochondritis dissecans or correction of joint incongruity.

Joint replacement may also be appropriate.  Hip replacements are almost routine now, and elbow and knee replacements are being experimented with.

Control weight

Weight control is one of the most important features of OA management.  On the one hand dogs affected by OA will be less active and tend to gain weight unless their owners are pro-active.  On the other hand, the excess weight will add to the stress on the affected joints and make exercising more uncomfortable and difficult.

Fat tissue may also be an important source of pain and inflammatory mediators so that obese animals are more sensitive to pain and suffer more inflammation of the affected joints.

Reducing weight will make all other management modalities appear more effective and may delay the need for drugs.

Manage activity

Loss of muscle mass will lead to reduced support for arthritic joints.  This in turn results in increased pain and reduced use and movement of the joints.  Fibrosis of the tissues around the affected joints will become worse, further restricting the range of movement.  This spiral of deterioration can be hard to break out of.

Controlled exercise is invaluable in managing OA.  Excess exercise will cause further trauma to the damaged joint surfaces, so the right type and amount of exercise is important.  Pain relief is helpful in encouraging moderate exercise.

Hydrotherapy offers a low impact way to exercise and tone muscles and improve the range of motion in joints.  Referral to a veterinary physiotherapist will allow a suitable program of exercise and therapy to be constructed. (Fig 9)

Fig 9 Hydrotherapy

Fig 9 Hydrotherapy and other physical therapy can be very helpful in the management of osteoarthritis  (Photo by Aquatic Canine Therapy)

Lifestyle modification

If owners are educated about the effects of OA, they are often willing to go to extraordinary lengths to improve their pet's quality of life.  Simple changes can mean that the pet can enjoy home life and put less stress on their diseased joints.

Warm, well-padded bedding that is easy for the pet to get in and out of will improve comfort considerably.  Infra red heat lamps or heat pads can improve comfort and reduce the initial stiffness experienced when rising.  Avoid the pet having to walk on smooth (e.g. laminate) flooring by putting down carpet or rugs.  Reduce the number of times that a pet has to climb or descend stairs.  Lift them into the car or provide a ramp to avoid the concussion and pain involved in jumping in and out of vehicles.

Disease modifying therapy

Many supplements and therapies are proposed as having a disease modifying effect on OA.  Unfortunately it is rare for them to be found effective in clinical trials and their use can be disappointing if expectations are unrealistic.   It is not possible to replace lost articular cartilage, so these are best seen as mild anti-inflammatories which may improve the quality of joint fluid and help maintain and protect what cartilage remains.

                Examples of this class of therapies are:

  • Pentosan polysulphate
  • Glucosamine and chondroitin
  • Hyaluronic acid
  • N-3 fatty acids (EPA and DHA)

These may be available as injections, tablets or powders and some diets are now formulated which include some of these agents.  It should be remembered that in people, some of these therapies can seem to work well for some individuals while giving little relief to others and this may be similar for our patients.

Recently there has been interest in stem cell therapy, encouraged by techniques allowing the harvesting of stem cells from fat tissue which are then injected into the affected joint space.  As yet there is little evidence that this therapy repairs cartilage, but it does seem to exert an anti-inflammatory effect which can improve the joint health and comfort.  It is a new area which needs further assessment but may be promising.

Pain control - drugs

Control of pain and inflammation is of most importance in managing OA.  Discomfort, if of any severity and not controlled, will lead to a downward spiral of reduced mobility, loss of muscle mass and tone and reluctance to use the limbs.

The introduction of relatively safe non steroidal anti-inflammatory drugs (NSAIDs) has revolutionalised the management of OA and improved the lives of countless pets.  By interfering with the inflammatory chemical pathways these drugs reduce inflammation and pain.  Development of COX -2 (cyclooxygenase 2) specific inhibitors which 'spared' the beneficial COX-1 enzyme pathway improved the safety of these drugs.

NSAIDs must still be used with caution.  They have the potential to cause serious gastrointestinal inflammation and ulceration.  If used in hypotensive patients (for example dogs with some types of heart failure) they may cause damage to the kidneys.  Patients with impaired kidney and liver function will be less efficient at metabolising the drugs, and so the dose used will have to be modified to take this into consideration.  They may interact with other drugs which older patients are taking, so reviewing medication regularly is important, together with regular blood and urine testing.

Having said this, they are the mainstay of OA treatment and improve the lives of countless patients.

If NSAIDs are insufficient to control discomfort, then a number of additional analgesic drugs have been used in OA, including paracetamol, tramadol, amantadine and gabapentin.

Pain control - non-drug

Medications are not the only way to control pain.  In human medicine there is great interest in finding drug-free methods of pain relief, and many owners would like to explore similar opportunities for their pets.  All of the modalities listed above will improve comfort for our patients.

                Other techniques which are used include:

  • Acupunture
  • Transcutaneous  electrical nerve stimulation (TENS)
  • Extracorporeal shock wave therapy
  • Laser therapy, e.g. with the MLS laser

Therapies such as laser treatment have shown promise in reducing pain and inflammation and may allow reduction of NSAID doses in appropriate cases.  As such they can be valuable in any cases of arthritis, and may be of particular interest in patients with concurrent medical conditions which may affect their ability to use conventional pain relief.

Surgery

Surgery may be employed to treat the underlying cause of arthritis, such as fragmented coronoid process or anatomical abnormalities.  It may also be used to remove or replace an arthritic joint which cannot be managed in any other way.  Arthrodesis or joint replacement can be used. (Fig 10)

 Fig 10 Hip Replacement

Fig 10 Hip replacement in a dog with painful osteoarthritis due to hip dysplasia

Laser therapy for arthritis

It is important to correctly identify the joints affected.  The veterinary surgeon will identify these by a combination of physical examination and xrays.

Affected joints should be treated using the osteoarthritis setting on the laser unit.  As well as the joints affected, it is important to identify associated muscles and soft tissue which may be uncomfortable secondary to the joint disease.  These should be treated with a suitable setting: normally 'muscle contracture', 'chronic inflammation' and 'chronic pain' would be effective.  If trigger points are identified in the muscles associated with the joint, they should be treated with the trigger point setting.

Initial treatment should be administered two or three times a week until improvement is seen.  Then the frequency can be gradually reduced.  Many patients derive benefit from a monthly treatment in the long term, with more frequent sessions when the arthritis is aggravated.

Case example

Keira is a Rottweiler with arthritis of the right elbow.

She has her elbow treated using a point setting on points around the elbow. (Fig 11)

Fig 11

Fig 11 Laser treatment of the elbow

Scanning mode is used to treat the biceps and triceps muscles which show some contracture due to the arthritis. (Fig 12)

Fig 12

Fig 12 Treat trigger points where they are found

She has trigger points in the biceps which are treated directly using the trigger point setting. (Fig 13)

Fig 13

Fig 13 Treat muscle masses associated with the arthritic joint