Canine hip dysplasia

The basics
Assessment of the coxo femoral joint (hip joint) for its congruity, conformity and the contoural landmarks of
Dr. TN Ganesh
the femoral head and acetabulum through a radiographic view of the hip is called ‘Hip Scoring’. Based on the phenotypic expression of the polygenetic genes responsible for manifesting Canine Hip Dysplasia (CHD), further aggravated by the environmental factors such as diet, exercise intolerance, stress on the hip joints etc, the disease progress to damage of bone ends i.e. degenerative joint disease (DJD). Radiography is the confirmative tool to diagnose CHD. Scores are assigned to different criteria of the joint and are later summed up to reveal the hip scores. These scores in turn are helpful in arriving at a threshold score, in order to classify hip dysplastic dogs and differentiate from good hip joints.
The hip scores can be subjective or objective in nature. From the year 1930, all around the world, many methods of hip scoring procedures are practiced, of which, some renowned scoring schemes are Orthopaedic Foundation for Animals (OFA) method in the USA, BVC/Kennel Club method practiced in common wealth countries, Federation Cynologique Inernationale (FCI), Penn Hip (Pennsylvania Hip Improvement Program) method, etc.
OFA method
The most commonly used radiographic grading system for CHD, was established by the OFA. One function of the OFA is to provide a service for the diagnosis and registry of hip status for all canine breeds.
Here, under sedation, the patient in dorsal recumbency (lying in back) in standard hip extended view radiograph is taken and the coxofemoral joints are evaluated for the following factors:

• Congruity of the femoral head (ball) and the acetabular (cup) margin.
• Amount of coverage of the femoral head by the acetabular rim, as defined by the intersection of the femoral head physeal scar with the dorsal acetabular rim (at least 50 percent of the femoral head should be covered by the acetabulam). Remodeling (bone changes) and flattering of the femoral head.

Based on the criteria mentioned below, the coxofemoral joints are given one of the seven grades. In German Shepherds, evaluation of CHD by the OFA radiographic method has reliability for correct diagnosis of 69.9 percent at 12 moths, and 95.4 percent at 24 months.
Penn HIP method (Quantitative Radiography)

The Pennsylvania Hip Improvement Program (Penn HIP) method is a stress radiographic method intended to provide a quantitative means of determining laxity (looseness) before the dog is 24 months of age. By correlating joint laxity with subsequent incidence and severity of CHD, this method can provide optimum predictive value.
The stress – radiographic method requires deep sedation or general anesthesia. The patients are positioned in dorsal recumbency, with the coxofemoral joints in a neutral flexion – extension angle to allow maximum lateral displacement of the femoral head. The neutral positioning avoids spiral tensioning of the fibrous elements of the joint capsule and hydrostatic influences that decrease hip laxity.

A compression view and a distraction view are obtained via the Penn HIP compression – distraction device. The distance between the centre of the acetabulum and the centre of the femoral head is measured on both views via templates or gauges. The distance is divided by the radius of the femoral head, a numerical value between 0 and 1 is determined (the distraction index). The index quantitates the relative displacement of the femoral head from the acetabular center.
In addition, the compression view delineates the articular surfaces and provides information concerning acetabular depth, thickness of articular carticular, and the center of rotation of the joint.
The distraction index quantitates passive joint laxity. Dogs with an index less than 0.3 rarely develop radiographic evidence of DJD. Hips with a distraction index of greater than 0.3 are considered to be susceptible to DJD.
Thus, the Penn HIP method shows promise for detecting susceptibility of CHD in dogs as early as 16 weeks of age.

Treatment of canine hip dysplasia
The aims of treatment of CHD are alleviating pain, arresting secondary degenerative changes, and producing maximum joint function.
The treatment schedule for canine hip dysplasia should be based on:

• age and health
• clinical severity of the disease
• radiographic appearance of the joint
• intended function of the dog, and
• financial constraints of the owner.

Medical therapy and management
The aim of medical therapy is oriented towards reducing pain and slowing the deterioration of the coxofemoral joint. Medical therapy should be reserved for patients with mild or intermittent clinical signs. Monetary considerations may prompt the client to choose medical therapy alone.
Exercise – the activity should be restricted to a level that the dogs can tolerate without signs of pain or exercise intolerance.

• Short leash walks initially followed by gradual increase to maximum level of function does not cause pain or lameness.
• Non-weight bearing activities (e.g. swimming) are excellent means of exercise and it avoids concussive trauma to the joints.
• Severe exercise restriction results in increased exercise intolerance, loss of muscle mass and tone, decreased range of motion and exacerbation of cartilage (soft bone) destruction.

Weight – the patient weight must be maintained in the optimum range for the age and breed.

• Obese patients should loose weight.
• Diet control is a must by adapting to low caloric diet or maintenance – type dog food. Conservative therapy, consisting of exercise restriction and weight control, is effective in controlling pain and lameness in a significant number of dogs with CHD.

Anti–inflammatory and analgesic agents – anti-inflammatory and analgesic therapy using appropriate drugs is an adjunct in medically managed patients.
Surgical management
A hip dysplastic case which has progressed to osteoarthritis (damaged bones of joint) warrants a surgical management for effective pain reduction. The various surgical techniques adopted for the management of CHD are briefed as follows:
Pectineal myectomy: Pectineal myectomy (cutting the muscle) is proposed to relieve muscle spasm and the associated pain.

• The pain relief has been attributed to release of muscle tension, reduced stress on the joint capsule and increased abduction resulting in articular alterations.
• This procedure is performed bilaterally.

Triple Pelvic Osteotomy (TPO): Triple Pelvic Osteotomy (cutting bone in three places & joining after correction) is a surgical procedure designed to correct the biomechanical imbalances in a dysplastic hip, early in progression of CHD.

• Hence, correction takes place before skeletal maturity and also before secondary degenerative changes to occur.
• The goals of TPO are correction of femoral head subluxation and restoration of the coxofemoral weight – bearing surface area.

Femoral Head and Neck Excision Arthroplasty (FHNE): Femoral Head and Neck Excision Arthroplasty (cutting ball portion of bone) is a salvage procedure.

• Joint function and pain are eliminated by FHNE and only a fibrous pseudo joint (false joint) exists. The pseudo joint is less stable than normal, and the range of motion is reduced.

Total Hip Replacement (THR): Total Hip Replacement (artificial joints) is a salvage procedure that can produce a functionally normal joint, eliminate secondary degenerative changes, and alleviate joint pain.

• The candidate should be skeletally mature and have pain and/or lameness attributable to coxofemoral disease.
• Here the affected joint is replaced with artificial (prosthesis) joint.

On a concluding note
The limited success in reducing the prevalence of CHD even in countries where hip scoring is routinely done and registries are made is due to insensitivity of detection methods, lack of parents or progeny considerations, and owner or breeder willingness to breed dogs with less than phenotypically excellent hips. Hence, routine hip scoring and breeding only those dogs achieving an excellent OFA rating at two years of age or dogs that have a Penn Hip DI of less than 0.3 at four months of age is indicated to control Canine Hip Dysplasia.

(The author is professor of surgery, Madras Veterinary College, Chennai and senior lecturer in Veterinary Surgery, Faculty of Medical Sciences, The University of The West Indies, Trinidad).