The Issue of Joint Laxity and Stress Radiography

OFA does not normally respond to the various opinions expressed by individuals on Internet web sites and/or chat lines. Instead OFA maintains a web site (http://www.offa.org) to provide information that may be of value to breeders and veterinarians. However, a response to the opinions expressed by many people is prompted, as the opinions appear to have deteriorated to the point of becoming non-productive. OFA stated its position on any testing method, including PennHIP, that involved stress radiography to the breed clubs in 1994. This posting is a review of that position.

Contrary to some Internet postings, OFA, a not-for-profit organization, does support and encourage research on joint laxity and its meaning. The fact that joint laxity plays a role, but is not the only factor to be considered in development of hip dysplasia and its secondary changes of degenerative joint disease, has been recognized for over 30 years. This fact is not in dispute. The issue has been, and remains to be, the relationship of laxity that is demonstrated by forcing the heads of the femurs away from the acetabula by palpation or a fulcrum/stress device (i.e., a distraction device) to abnormal laxity (functional laxity that occurs in hip dysplasia.) Since 1972, when an independent panel of scientists classified the techniques for demonstration of joint laxity by use of an externally applied force as experimental, OFA has financially supported three research projects, recommended by external review, to answer the basic question. Dr. Belkoff, et.al. (VCOT 1: 31-36 1989) developed a device that measured the amount of force applied to the hips and noted that some dogs that demonstrated abnormal amounts of laxity were free of hip dysplasia at necropsy. These authors questioned the meaning of joint laxity as demonstrated by force. The other two projects supported by OFA are ongoing.

PennHIP is another technique for demonstration of forced (passive) laxity that is also attempting to answer the basic question of the relationship of passive laxity to functional laxity. OFA encourages their research efforts; however, OFA takes exception to the marketing techniques and claims used to promote the PennHIP testing method for clinical use, as the use of this method appears to be premature. In other words, commercialization (marketing) of the method has outreached the science.

OFA feels that general use of PennHIP as a mass screening test method for hip dysplasia is premature because:

1. The primary basis for marketing PennHIP was reported by Dr. Smith, et.al. (Am J Vet Res, July 1993) using a modification of a previously described positioning, stress/fulcrum technique. The study was a survey type involving 142 dogs (105 of which were German Shepherd Dogs). The results of the study were questioned by Dr. Susan Shott of the Biostatistical Unit, Rusk Cancer Institute (Am J Vet Res, December 1993) who challenged the analysis of the data and stated: "The data does not support the author's conclusion that the DI was the most important and reliable phenotypic factor for determining susceptibility of hips to degenerative joint disease ... and that this determination could be made with an acceptable degree of accuracy as early as 4 months of age."

2. Dr. Lust, et.al. (Dr. Smith was a coauthor) in a report involving 42 Labrador Retrievers (Am J Vet Res, December 1993) concluded that a DI of <0.4 at 4 months of age correctly predicted normal hips in 88% of the cases and a DI of >0.4 correctly predicted hip dysplasia in 57% of the cases. The authors further concluded that: "Distraction indices between 0.4 and 0.7 and at either 4 or 8 months of age were not associated strongly enough with evidence of disease to be clinically reliable in predicting, on an individual basis, the outcome for dysplastic hip conformation when the dogs were older."

3. No breeding data based on PennHIP has been reported. Dr. E. A. Leighton (JAVMA, May 13, 1997) reported on genetic progress in improving the hip quality in German Shepherd Dogs and Labrador Retrievers in the Seeing Eye closed colony of dogs. In less than 5 generations the percentage of hip dysplasia was decreased from 55 to 24% in the German Shepherd Dogs and from 30 to 10% in the Labrador Retrievers using the hip extended position and a modified OFA evaluation procedure. PennHIP DI measurements were also made but the mean DI across generations did not change. It should be pointed out that DI was considered experimental and breeding selection criteria did not include the DI. It will be interesting to see the results when DI is included as a selection criterion.

With the above reservations, plus experience with the issue of joint laxity, OFA would be remiss in its responsibility to either endorse or reject the PennHIP testing method. In other words, the jury is still out! This leaves the breeder in a dilemma as to which testing method to use, OFA or PennHIP or both, as they are entirely different test methods for the same disease.

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There is a great economic advantage to breeders for determination of the hip status at a young age and to assess the risk for development of hip dysplasia at a later age. OFA reported (Vet Clinics of No Am, May 1992) on a study of 3,369 dogs from 25 breeds. Reliability of the preliminary evaluations ranged from 71.4% in the Chesapeake Bay Retriever to 100% in the Welsh Springer Spaniel. The preliminary evaluation appeared to be breed dependent and dependent on the evaluator's experience with the skeletal development of that breed at the age of evaluation.

When faced with the problem of comparing entirely different test methods for determining dysplasia, scientists evaluate the results of reported values for false negative (probability of diagnosing a dysplastic dog as normal), false positive (probability of diagnosing a normal dog as dysplastic), specificity (probability of a normal dog receiving a normal evaluation), and sensitivity (probability of a dysplastic dog receiving a dysplastic evaluation). These values for OFA preliminary evaluations by age and hip ratings, in a different population of dogs than previously reported (Vet Clinics of No Am., May 1992) have been reported (JAVMA, November 1, 1997). The false negative and false positive values for PennHIP were reported by Dr. Smith et.al. (Am J Vet Res, July 1993). No report of selectivity or sensitivity values for PennHIP were given. There were 2,332 dogs in this OFA study and 142 dogs in the PennHIP study. The limited number of dogs resulted in a larger confidence interval for the PennHIP values. Confidence intervals (CI) are determined so that one can be 95% confident that the true value lies within the calculated range. The false negative values for OFA evaluations were 8.9% (CI=5.9 to 12.9%) at 3-6 months, 6.0% (CI=4.4 to 8.0%) at 7-12 months and 3.8% (CI=2.6 to 5.4%) at 13-18 months of age. The false negative values for PennHIP evaluations were 12% (CI=1.5 to 38.3%) at 4 months and 0% (CI=0.0 to 15.4%) at 12 months of age. It appears that the probability of retaining a dysplastic dog in the breeding pool is the same for either test method.

However, the false positive values for PennHIP were significantly greater (48% at 4 months, 57% at 6 months and 38% at 12 months) than those for OFA evaluations 17.6% at 3-6 months (CI 10.8 to 26.4%), 10.0% at 7-12 months (CI 5.7 to 15.9%) and 8.5% at 13-18 months (CI 4.8 to 13.6%). It appears that the probability for removing a normal dog from the breeding pool is less with the OFA evaluations.

Dr. Adams, et.al. (JAAHA, 1998, 34: 339-47) reported (using palpation, OFA method, PennHIP, and Norberg angle measurements) on results of a study of hip laxity, in 32 dogs from 4 breeds (12 Greyhounds, 4 Labrador Retrievers, 12 Irish Setters, and 4 hound-mix) at 6-10 weeks and 16 to 18 weeks that were compared to detection of degenerative joint disease at 52 weeks of age. Five hips with evidence of subluxation but no evidence of degenerative joint disease on the OFA type evaluation of the hip extended view were eliminated from analysis. The authors concluded that DI and Norberg Angle measurements at 6-10 and 16-18 weeks were the most reliable predictors of hip dysplasia, at 52 weeks of age, with DI being more reliable than Norberg. The OFA and palpation methods at 6-10 or 16-18 weeks were not reliable predictors. This is not surprising as reliability of OFA preliminary evaluations has been shown to increase with age of evaluation. The OFA report (JAVMA, Nov. 1997) included 380 dogs evaluated at 3 to 6 months of age. The reliability was 89.6% (CI=85.4 to 92.9%) for normal evaluations and 80.4% (CI=71.4 to 87.6%) for dysplastic evaluations. The mean age was 4.8 months (19.2 weeks) and the median age was 5 months (20 weeks) which means that over half of the dogs in the OFA study were older than in the study reported by Dr. Adams.

OFA data and PennHIP data are not representative of the general population of dogs because the programs are voluntary, most dogs are in pet homes and are not radiographed, and not all radiographs of dogs radiographed are submitted for evaluation by either program. For example; if an attending veterinarian determines a dog to be dysplastic, by either method, the radiograph(s) may not be submitted to save the owner money. PennHIP collaborators may take the hip extended view first and if the radiograph shows evidence of dysplasia the DI views may not be taken or the owner may not allow submission of an obviously large DI measurement.

Breeders are aware of the economic value of early screening of dogs for determination of the hip status. They should also be aware that both OFA and PennHIP use the radiographic evaluation of the same hip extended projection as the standard for comparing with the results of the early evaluations. The OFA standard represents the consensus of 3 independent evaluations at >24 months of age by board certified veterinary radiologists. It is not clear who evaluates a radiograph submitted for PennHIP determination, but the original study reported the standard to be Dr. Smith's evaluation. This evaluation at >24 months of age has approximately 5% false negative finding as reported by Dr. Jessen (Proceedings of a 1972 symposium on hip dysplasia) and by an internal OFA study of dogs evaluated at 24 months that were re-evaluated at an older age. This is why OFA requires the 24 month certification age. Voluntary submissions to PennHIP will provide information on the range, mean and median of the DI measurements for the various breeds. The meaning of the measurements remains unclear and will require repeat studies, on the same dogs, at >24 months of age.

Breeders must be aware of the cost, strengths, and weaknesses of the test methods available for evaluation of the hip status before making the choice of a specific testing method. Once the choice is made, it must be followed for generations before progress in improving the hip status can be evaluated. OFA data has demonstrated marked improvement of the hip status in the Portuguese Water Dog (AKC Gazette, Nov 1991) and the Chinese Shar Pei (Barker, Mar/Apr 1995). OFA data on all breeds was independently evaluated and reported by Dr. Kaneene (JAVMA, Dec 1997) an epidemiologists from the Population Medicine Center at Michigan State University. The study compared OFA evaluations on dogs born between 1972 and 1980 with dogs born between 1989 and 1992. The population consisted of 270,978 dogs. The authors, having acknowledged the fact that submissions are voluntary and that there is bias due to prior screening, concluded:

We do not believe that this is the most likely explanation, because the increase in the percentage of dogs classified as having excellent hip joint phenotype (+36% [7.82 vs. 10.64%]) was substantially larger than the decrease in the percentage of dogs classified as having canine hip dysplasia (-21.% [17.39 vs. 13.82%]). If better screening of radiographs prior to submission to the OFA was the cause of the increase in percentage of dogs classified as having an excellent hip joint phenotype, then because it is easier to differentiate dysplastic hips from hips with normal phenotypes than it is to differentiate hips with excellent, good and fair phenotypes, we would have expected that the decrease in percentage of dogs classified as having canine hip dysplasia would have been larger than the increase in percentage of dogs classified as having an excellent hip joint phenotype.

Unfortunately, PennHIP has not been available long enough to accumulate the data necessary to evaluate the effect of this test method over time.

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Elbow Dysplasia Database

Elbow dysplasia was originally described as a developmental disease manifested as degenerative joint disease (DJD) with or without an ununited anconeal process (UAP). Over time, two other inherited diseases, osteochondrosis (OCD) and fragmented medial coronoid process (FCP), were identified as part of the DJD complex collectively referred to as elbow dysplasia.

Etiology

Multiple theories on the cause of these abnormalities have been proposed. Olsson suggested a unitarian theory that UAP, OCD and FCP were all due to osteochondrosis. Osteochondrosis is a disturbance in endochondral ossification (the process by which bone is formed from a cartilage mold). Osteochondrosis results from a reduction in nutrients to the chondrocytes of the cartilage mold beneath articular cartilage. This loss of chondrocytes produces a weakened foundation under the articular cartilage, resulting in fracturing of the cartilage.

Wind suggested that asynchronous growth of the ulna and radius, or insufficient development of the ulnar trochlear notch, results in abnormal loading forces on the anconeal process or medial coronoid process.

Numerous studies suggest that the three diseases (UAP, OCD and FCP) are independent, inherited diseases.

Clinical presentation

The radiographic evidence of elbow dysplasia (ED), the presence of secondary degenerative joint disease (DJD), and the clinical presentation do not correlate directly. Grondalen reported on a population of 207 Rottweilers of which 141 were not lame. Yet 68% of the non-lame dogs had degenerative joint disease of the elbow. Another study by Read reported on serial radiographic and physical examination of 55 Rottweilers at 6 and 12 months of age. At 6 months of age the majority of lame dogs did not have radiographic evidence of ED; however, by 12 months of age the radiographic changes were apparent. But the majority of dogs remained sound.

The elbow is a complex joint with overlapping osseous structures which often makes a definitive diagnosis difficult especially when dealing with pathology involving the medial coronoid process. To increase the probability of achieving an accurate diagnosis, the routine radiographic examination of the elbow (cranial-caudal and neutral medial-lateral projections) can be supplemented with the craniolateral caudomedial oblique and an extreme flexed mediolateral projection. Even then, a definitive diagnosis can be difficult without linear tomography, computerized tomography or surgical exploration of the joint.

OFA elbow protocol

The International Elbow Working Group, (IEWG) a consortium of experts from around the world, was founded in 1989 to lower the incidence of elbow dysplasia by coordinating worldwide efforts. The OFA started its elbow database in 1990 using a modified protocol of the IEWG. The diagnosis of elbow dysplasia is based on the presence of degenerative joint disease/osteoarthrosis. Radiographically, the primary finding is sclerosis in the area of the trochlear notch and a periosteal response on the anconeal process which is best visualized on the extreme flexed mediolateral projection (Fig. 7). Although in and of itself, secondary degenerative joint disease is not an inherited disease, it is the end result found in dogs with elbow dysplasia.

Therefore, OFA requires one view of each elbow clearly labeled left and right in the extreme flexed medial-lateral position (Fig. 7). Inclusion of additional views is at the discretion of the attending veterinarian. A permanent clearance can be obtained at 24 months of age, and dogs between 5 and 24 months of age can receive a preliminary evaluation. The elbow radiographs are required to contain permanent dog identification in the emulsion. Nongrid, table top technique using high MaS and low Kvp is recommended.

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Elbow classifications

The OFA reports elbows as normal or dysplastic. While there is no subdivision classification of normal, dysplastic elbows are graded 1 through 3, with grade 3 being the most severe. Differences between dysplastic grades are based on the severity of degenerative joint disease present.

Normal  - No evidence of inherited pathologic change

Dysplastic -
    Grade 1 - mild DJD - osteophytes less than 2 mm in height
    Grade 2 - moderate DJD - osteophytes 2 to5 mm in height
    Grade3 - severe DJD - osteophytes greater than 5 mm

There can be pathology involving the medial coronoid process without a distinct fracture fragment. As seen in Fig. 8 the malformed medial coronoid process and a fissure fracture of the articular cartilage could not be ascertained from the radiographic image, but created sufficient joint instability to produce secondary degenerative joint disease (Fig. 7).

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Rationale for selective breeding

There are multiple studies supporting the theory that the various components of ED have a polygenic mode of inheritance. Further, it appears that environmental factors also contribute to expression of the disease. Selective breeding of phenotypically normal dogs has been shown to reduce the incidence of elbow dysplasia. In 1965, Corley reported on the inheritance of ununited anconeal process. Swenson reported on a study which included 4,515 dogs registered by the Swedish Kennel Club. As selective pressure was applied toward identifying and breeding dogs with normal elbows, there was a corresponding increase in the percentage of normal progeny.

There are a number of papers reporting on the inheritance of osteochondrosis and fragmented medial coronoid process. A recent report by Padgett classifies these as separate diseases that may occur alone or in combination. In this study, the initial breeding pair of Labrador Retrievers had surgically confirmed osteochondrosis and fragmented medial coronoid process in both elbows. The male dog was subsequently bred to two of his fi rst and second generation daughters. There was a total of 31 progeny produced of which 83.9% had osteochondrosis, fragmented coronoid process or both.

Table 7 illustrates the outcome of matings based on information extracted from the OFA database. A total of 13,151 progeny were identified in which both parents had elbow dysplasia evaluations. The percentages of progeny with elbow dysplasia more than doubled if either parent had ED, and more than tripled if both parents had ED, as compared to when both parents were normal. Results of selective breeding practices indicate that elbow dysplasia should be considered in the moderate to high heritability estimate category (See discussion on genetics).

Table 7: Elbow scores

Scores on 13,151 progeny from sires and dams with known elbow scores.

T = total number of progeny; D = the percentage of progeny with elbow dysplasia

Application information

The owner or agent should complete and sign the OFA application form, and the information is best obtained directly from the animal's certificate or registration papers. It is also important to record the animal's tattoo or microchip number, and registration numbers of the sire and dam. Application forms are available on request from the OFA or can be downloaded from the OFA web site (www.offa.org). The radiograph, signed application form (which should include the owner's choice of open or semi-open database), and the service fee should be mailed to: Orthopedic Foundation for Animals, Inc., 2300 E. Nifong Blvd., Columbia, MO 65201-3856. All radiographic images are retained by the OFA for research and reference purposes.

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Preliminary hip and elbow evaluations

This service is offered to evaluate the hip status of an animal as young as 4 months of age. Many owners choose to breed their animals prior to 24 months or need to know the hip status of progeny produced by a particular sire and dam before using them in a repeat breeding. The evaluation is performed by one radiologist, and the response time is usually five days. Use the same application procedure as described under "Hip Dysplasia" in Part 1.

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References

1. Bennett D: Hip Dysplasia and Ascorbate Therapy: Fact or Fancy? Seminars in Vet. Med. And Surg., Vol. 2, No. 2, 1987, p. 152-157.
2. Corley EA, Carlson W: Radiographic, Genetic, and Pathologic Aspects of Elbow Dysplasia. J Am Vet Med Assoc, 1965;147:1651.
3. Corley EA, et al: Reliability of Early Radiographic Evaluation for Canine Hip Dysplasia Obtained from the Standard Ventrodorsal Radiographic Projection. JAVMA, Vol. 211, No. 9, November 1997, pp. 1142-1146.
4. Grondalen J, Grondalen T: Arthrosis in the Elbow Joint of Young, Rapidly Growing dogs. Nordish Veterinarmedicin, 1981:33:1-16.
5. Grondalen J: Arthrosis in the Elbow Joint of Young, Rapidly Growing Dogs: Interrelation between Clinical Radiological, and Pathoanatomical Findings. Nordish Veterinarmedicin, 1982; 34:65-75.
6. Kasstrom H: Nutrition, Weight Gain, and Development of Hip Dysplasia: An Experimental Investigation in Growing Dogs with Special Reference to the Effect of Feeding Intensity. Acta Radiol. Suppl.,  Vol 344: 135-179, 1975.
7. Kealy RD, et al: Effects of Limited Food Consumption on the Incidence of Hip Dysplasia in Growing Dogs. JAVMA, Vol. 201, No. 6, 1992, p.857-863.
8. Kealy RD, et al: Effect of Diet Restriction on Life Span and Age-related Changes in Dogs. JAVMA, 2002; 220: p.1315-1320.
9. Leighton EA: Genetics of Canine Hip Dysplasia. JAVMA, Vol. 210, No. 10, 1997, pp. 1474-1479.
10. Lust G et al: Joint Laxity and its Association with Hip Dysplasia in Labrador Retrievers. AJVR, Vol. 54, No. 12, 1993, p.1990-1999.
11. Lust, G et al: Comparison of Three Radiographic Methods for Diagnosis of Hip Dysplasia in Eight-month Old Dogs. JAVMA, 2001; 219: p.1242-1246.
12. Olsson SE: Osteochondrosis in Domestic Animals. ACTA Radiologic Suppl., 358, 1978, pp.299-305.
13. Olsson SE: The Early Diagnosis of Fragmented Coronoid Process and Osteochondritis Dissecans of the Canine Elbow Joint. JAAHA, 1983:19(5):616-626.
14. Padgett GA, et al: The Inheritance of Osteochondritis Dissecans and Fragmented Coronoid Process of the Elbow Joint in Labrador Re­triever. JAAHA, 1995; 31: 327-330.
15. Read RA, et al: Fragmentation of the Medical Coronoid Process of the Ulna in Dogs: A Study of 109 Cases. J. Sm. Anim. Prac., 1990; 32(7), 330-334.
16. Reed AL, et al: Effect of Dam and Sire Qualitative Hip Conformation Scores on Progeny Hip Conformation. JAVMA, 2000; 217: 675-680.
17. Rettenmaier JL, Keller GG, et al: Prevalence of Canine Hip Dysplasia in a Veterinary Teaching Hospital Population. Vet. Rad. & Ultra­sound, Vol. 43, No. 4, 2002, p. 313-318.
18. Smith, GK et al: Coxofemoral Joint Laxity from Distraction Radiography and its Contemporaneous and Prospective Correlation with Lax­ity, Subjective Score, and Evidence of Degenerative Joint Disease from Conventional Hip-Extended Radiograph in Dogs. AJVR, Vol 54: 1021-1042, No. 7, July, 1993.
19. Swenson L, Audell L, Hedhammar A: Prevalence and Inheritance of and Selection for Elbow Arthrosis in Bernese Mountain Dogs and Rottweilers in Sweden and Benefit: Cost Analysis of a Screening and Control Program. JAVMA, 1997; 210: 215 - 221.
20. Tomlinson JL: Quantification of Measurement of Femoral Head Cover­age and Norberg Angle within and among four breeds of dogs. AJVR, 2000; 61: p.1492-1498.
21. Willis MB: Practical Genetics for Dog Breeders. H. F. & G. Witherby Ltd, Great Britain, 1992.
22. Wind A: Elbow Incongruity and Development Elbow Dysplasia in the Dog (Part 1). J Amer Anim Hosp Assoc 1986:22:711-724.

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Hip Dysplasia (cont.)

Hip joint conformation

The OFA consulting radiologists make subjective evaluations of the hip status based on criteria previously described (p.17). Although the radiologists apply the criteria subjectively, a study demonstrated good correlation between the consensus grade assigned and two objective measurements used to assess hip phenotype. These measurements are percent coverage (PC) of the femoral head within the acetabulum and Norberg angle (NA) which also estimates degree of fit. The higher the numeric value the better the degree of fit. A retrospective study of OFA hip phenotypes by Tomlinson (2000) reported a distinct difference in both percent coverage and Norberg angle values between OFA hip grades and between breeds. The following numerical values (*) for each OFA classification are averages derived from that study.

Excellent - This classification is assigned for superior hip conformation in comparison to other animals of the same age and breed. There is a deep seated ball (femoral head) which fits tightly into a well-formed socket (acetabulum) with minimal joint space width. *PC=63% NA=110

Good (Fig. 4) - The most common normal grade reported regardless of breed is slightly less than superior but a well-formed congruent hip joint is visualized. The ball fits well into the socket and good coverage is present. *PC=58% NA=108

Fair - Assigned where minor irregularities in the hip joint exist. The hip joint space is wider than a good hip phenotype. This is due to the ball slipping slightly out of the socket, causing a minor degree of joint incongruency (called subluxation). There may also be slight inward deviation of the weight-bearing surface of the socket (dorsal acetabular rim) causing the socket to appear slightly shallow. This can also be a normal finding in some breeds, such as the Chinese Shar Pei, Chow Chow and Poodle.*PC=49 NA=104

Figure 4: Good hips	Figure 5: Moderate HD

The following categories are not eligible for an OFA breed number:

Borderline - There is no clear cut consensus among the radiologists to place the hip into a given category of normal or dysplastic. There is usually more incongruency present than the minor amount found in a fair, but there are no arthritic changes present that definitively diagnose the hip joint as dysplastic. There also may be bony changes present on any of the areas of the hip anatomy that cannot be accurately evaluated as either an abnormal arthritic change or a normal anatomic variant for that individual dog. To increase the accuracy of the diagnosis, it is recommended the radiographs be repeated at a later date (usually 6 months). This allows the radiologist to compare the initial film with the most recent film and assess for progressive changes that would be expected if the dog is dysplastic. Most dogs (over 50%) with this grade that show no interval change in hip conformation receive a normal hip rating upon resubmission, usually a fair hip phenotype.

Mild Hip Dysplasia - There is significant subluxation present wherein the ball is partially out of the socket, causing an incongruent and increased joint space. The socket is usually shallow, only partially covering the ball. There are usually no arthritic changes present with this classification. If the dog has other superior traits and/or a great deal of time and investment has been placed into training, there is an option to resubmit a radiograph when the dog is older so it can be reevaluated. Most dogs will remain dysplastic, showing progression of the disease with early arthritic changes. There are a few dogs however, that show improved hip conformation with increasing age. Since HD is a chronic, progressive disease, the older the dog, the more accurate the diagnosis of HD (or lack of HD). At 2 years of age, the reliability for a radiographic diagnosis of HD is 95%, and the reliability steadily increases as the dog ages. Radiographs should definitely be resubmitted if they were initially taken during times of possible detrimental environmental effects such as periods of physical inactivity, or high hormone levels related to time of a heat cycle which could lead to a "false" diagnosis of mild hip dysplasia. *PC=40% NA=97

Moderate HD (Fig.5) - There is significant subluxation present wherein the ball is barely seated into a shallow socket, causing joint incongruency. There are secondary arthritic bone changes, usually along the femoral neck and head (termed remodeling), acetabular rim changes (termed osteophytes or bone spurs), and various degrees of trabecular bone pattern changes (called sclerosis). Once arthritis is reported, there is only continued progression of arthritis over time, and the dog may or may not be lame. The onset of lameness is unpredictable and some dogs may go most of their lives without showing any signs of lameness whatsoever. *PC=30% NA=92

Severe HD - assigned where radiographic evidence of marked dysplasia exists. There is significant subluxation present, where the ball is partially or completely out of a shallow socket. Like moderate HD, there are also large amounts of secondary arthritic bone changes along the femoral neck and head, acetabular rim changes, and large amounts of abnormal bone pattern changes. *PC=21% NA=83

In addition to assessing the dog/cat hip conformation, the veterinary radiologist reports other radiographic findings that could have familial, inherited causes, such as transitional vertebra or spondylosis. Transitional vertebra is a congenital malformation of the spine that occurs at the junctions of major divisions of the spine (usually at the thoracic and lumbar vertebral junction or the lumbar and sacral vertebral junction). Transitional vertebra take on anatomic characteristics of the two divisions of the spine between which it occurs. The most common transitional vertebra reported by OFA is in the lumbo-sacral area. Transitional vertebra are usually not associated with clinical signs and the dog/cat can be used in a breeding program, but the OFA recommends breeding to a dog/cat that does not have transitional vertebra.

Spondylosis is an incidental radiographic finding in which smooth new bone production is visualized on vertebral bodies at the intervertebral disc space margins. The new bone production can vary in extent from formation of small bone spurs to complete bridging of adjacent vertebral bodies. Spondylosis may occur secondary to spinal instability but often it is of unknown cause and clinically insignificant. A familial basis for its development has been reported. As with transitional vertebra, dogs/cats with spondylosis can be used in a breeding program.

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The effect of age and the use of preliminary radiographs for early detection of hip dysplasia

Frequently, breeders want early knowledge of the hip status on puppies/kittens in a given litter. This allows early selection of animals for use as show/performance/breeding animals or animals that would be best suited for pet homes. The OFA accepts preliminary consultation radiographs on puppies and kittens as young as 4 months of age for evaluation of hip conformation. If the dog or cat is found to be dysplastic at an early age, the economic loss from cost of training, handling, showing, etc. can be minimized and the emotional loss reduced. Preliminary radiographs are read by the OFA staff veterinary radiologist and are not sent to outside radiologists as are the 24-month-old examinations. The same hip conformation grading scheme is used.

The OFA has performed a retrospective analysis of the reliability of early radiographic evaluation for canine hip dysplasia, using information in their database obtained from the standard ventrodorsal radiographic projection. Corley (1997) reported on a population of over 2,000 dogs from the four breeds with the greatest number of OFA submissions (Labrador Retrievers, Rottweilers, German Shepherds, and Golden Retrievers). The reliability of the preliminary evaluation (3 to 18 months) was determined by comparing the initial evaluation to a follow-up evaluation (> 24 months) of the same dog. The reliability of a normal preliminary hip joint phenotype was 100% for excellent, 97.9% for good and 76.9% for fair (Table 2). The reliability of a preliminary evaluation of canine hip dysplasia was 84.4% for mild, 97.4% for moderate and 100% for severe (Table 3). Reliability of preliminary evaluations increased significantly as age at the time of preliminary evaluation increased, regardless of whether dogs received a preliminary evaluation of normal phenotype or canine hip dysplasia (Tables 4 & 5).

For normal hip conformations, the reliability was 89.6% at 3-6-months, 93.8% at 7-12 months and 95.2% at 13-18 months for the four main breeds. Pooled data comparing preliminary OFA evaluations at various ages and in various breeds with final OFA evaluations at 24 months or older resulted in a similar reliability factor for preliminary evaluations of approximately 90%. The false positive rate (defined as a preliminary evaluation of HD for a dog with a follow-up evaluation of a normal phenotype) of OFA preliminary evaluations < 6 months of age was 18%; and the false negative rate (defined as a preliminary evaluation of normal phenotype for a dog with a follow-up evaluation of hip dysplasia) of OFA preliminary evaluation < 6 months of age was 9%. This suggests that OFA preliminary evaluations of hip joint status in dogs are generally reliable. However, dogs that receive a preliminary evaluation of fair or mild hip joint conformation should be reevaluated at an older age (24 months).

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Table 2: Reliability of normal preliminary evaluations by hip grade

Norm = Normal; Dys = Dysplastic; Cl = Confidence Level

Table 3: Reliability of dysplastic preliminary evaluations by hip grade

Norm = Normal; Dys = Dysplastic; Cl = Confidence Level

Table 4: Reliability of normal preliminary evaluations by age

Norm = Normal; Dys = Dysplastic; Cl = Confidence Level

Table 5: Reliability of dysplastic preliminary evaluations by age

Norm = Normal; Dys = Dysplastic; Cl = Confidence Level

Joint laxity

Laxity is generally considered to be one of the earliest pathologic findings in HD. The fact that joint laxity plays a role, but is not the only factor, in development of hip dysplasia and its secondary changes of degenerative joint disease has been recognized for over 30 years.

Joint laxity (looseness of the joint) is a dynamic state that may not be determined by routine radiography. The joint may appear radiographically normal, but in actual use it may be loose.

Some dogs demonstrate abnormal laxity (subluxation) radiographically, but do not develop the more definitive degenerative changes of dysplasia.

Some dogs demonstrate radiographically tight hips, but later develop the degenerative changes of dysplasia.

Palpation of the hips to demonstrate looseness is not generally accepted as a single diagnostic feature of HD. Stress radiography using a fulcrum or wedge (placing an object between the thighs and bringing the stifles together to force the head of the femur out of the acetabulum) has been investigated as a technique to demonstrate the degree of radiographic subluxation that is possible. Some measurement criterion such as Norberg angle, millimeters of displacement, distraction index (DI), or dorsal lateral subluxation measurement (DLS) is usually employed to calculate the amount of displacement of the femoral head when compared to a fixed anatomic structure or to a standard radiograph taken without the fulcrum or wedge. The differences in the measurements indicate the range of possible motion or joint laxity. Different devices, measurements, and positions have been developed at the University of Pennsylvania (PennHIP®), Cornell University and Michigan State University. Use of the fulcrum technique has demonstrated that some laxity is expected in the normal joint, but that many dogs with laxity beyond a certain amount later show the more definitive characteristic radiographic changes of dysplasia. The specific degree of laxity that is acceptable at a given age, and in various breeds of dogs and cats has not been determined and represents a major unanswered question.

Table 6 is a comparison of different early screening procedures, and with the exception of palpation, all yield similar false-negative results (initially reporting a dog as normal that is later evaluated as dysplastic). There is, however, a major difference in the comparison of false-positive results (initially reporting a dog as dysplastic that is later evaluated as normal). A later publication by Lust (2001) suggested that the strength of the hip extended view (OFA view) is its specificity. Specificity refers to the ability to correctly identify dogs without hip dysplasia and this study also noted that this is dependent on the expertise of the evaluator.

Table 6: False-negative and false-positive results for dysplasia from 4 studies

1 = Reviewed by Willis; 2 = Smith et al.; 3 = Lust et al.; 4 = Corley et al.

The degree of joint laxity - as demonstrated by forcing the head of the femur away from the acetabula either by palpation or by using a fulcrum/stress device - that can be normal, and what degree is abnormal (eventually leading to degenerative joint changes) is unknown.

A primary reason this is unknown is that stress radiographic techniques measure artificially forced laxity in a non-weight bearing position. Improved accuracy using laxity as the diagnostic finding might be possible with a technique that measures dynamic laxity (laxity that occurs during normal movement).

There is currently no explanation to account for adult animals with substantial joint laxity that do not develop degenerative joint disease.

There is no pathologic evidence available to determine what processes are occurring in the hips that are lax but do not develop degenerative joint disease, or in hips that are tight yet develop degenerative joint disease. Without this information, there is a deficiency of necessary data to support breeding or treatment recommendations based on laxity alone. It is obvious that dogs with "tight" hips tend to be normal and those with markedly "loose" hips tend to be abnormal. What happens between the two extremes remains unknown. Further research using carefully controlled scientific methods is needed to understand the full implication of joint laxity.

However, breeders have a phenotypic screening method (standard hip extended radiograph) readily available that is safe, accurate, of modest cost, and effective. As an example of effectiveness, Leighton reported that while the mean DI did not change, the incidence of hip dysplasia at The Seeing Eye Inc. was dramatically reduced over five generations using the standard hip extended position and a subjective hip score similar to OFA's. That breeding program also illustrates the importance of obtaining and considering information on the hip status of siblings as well as on the dam and sire with regard to selection of potential breeding animals.

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Physical restraint or chemical restraint

Chemical restraint permits easier, and as a rule, more accurate positioning and reduces potential radiation exposure risk to the patient and veterinary personnel. The types of chemical restraint, depth of general anesthesia, or use of manual restraint only are environmental variables that can affect the radiographic evaluation.

Anesthesia has been shown to influence the evaluation, as a few dogs have been found to appear normal without anesthesia and yet demonstrate subluxation with anesthesia. This probably is due to muscular relaxation. The current belief is that a dog who appears dysplastic with anesthetic and normal without, should be considered dysplastic, or at best of questionable breeding quality. However, there are some veterinarians and a few HD control programs that do not recommend anesthesia as they feel that subluxation noted under anesthesia results in a false-positive finding.

Preliminary OFA data indicates that chemical restraint does affect the radiographic appearance of the hip joints in some dogs. Current information, observations made on large numbers of dogs, and experience with follow-up studies on large numbers of dogs, supports the recommendation that chemical restraint to the point of relaxation, or general anesthesia, be used. This appears to give a truer evaluation of the hip status, but more research is needed on this controversial subject, as there is an absence of controlled scientific data.

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Nutrition

Kasstrom, and later Kealy, reported that a higher than needed caloric intake during the rapid growth phase may result in earlier and more severe dysplastic changes when the genetic potential for dysplasia is present. Lower caloric intake may minimize or delay the evidence of dysplasia in the same dog, but will not change the genotype. Without genetic predisposition however, environmental influences alone will not create hip dysplasia.

There is no evidence in the scientific literature that megadoses of vitamin C (Bennett, 1987) or any other multi-vitamin/mineral supplement is beneficial in reducing the effects of, or preventing hip dysplasia.

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Hormonal effects

Estrus appears to affect the reliability of diagnosis in some females. Some animals in season demonstrate a degree of subluxation (laxity) that is not present when the bitch is out of season, possibly due to the relaxation effects of estrogens on the ligaments and joint capsule. Radiography of these bitches may result in a false diagnosis of HD.

It is recommended that bitches not be examined for HD when in season and radiographs should be obtained one month prior or one month following the heat cycle. In addition, following a pregnancy the OFA recommends that the bitch's radiographs be taken at least one month after weaning the offspring.

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Physical inactivity

Periods of prolonged inactivity may affect the reliability of diagnosis. A few animals exhibit subluxation after prolonged periods of inactivity due to illness, weather conditions, etc. On later examination, when the animal is in good muscular tone, the hips appear normal. Therefore, radiography is recommended when the animal is in good health and muscle tone.

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Recommendations for buyers

To verify health information when considering a purchase from a particular breeder, the buyer can obtain a pedigree of the animal in question. Health information then can be verified on the sire, dam, various siblings, and other close relatives at the OFA web site, www.offa.org. Information in the OFA's database can be used as a tool to increase the probability for obtaining a normal dog when choosing dogs for breeding, competition, or as healthy pets. Overall, if there are a substantial number of relatives that do not have OFA numbers in the pedigree, they should be assumed to be abnormal until proven otherwise. The more animals in a pedigree with OFA numbers, and the greater the percentage of their siblings with OFA numbers, the better the genetic probability for healthy animals from a given breeding. Breedings for which 2 to 3 generations of this depth and breath of information is available and normal will usually demonstrate significantly reduced incidence of HD.

It also may be helpful to consider whether the breeding in question is a repeat breeding, a line breeding, or an outcross. With repeat breedings, there may be health information available on puppies from the previous litter resulting from the same genetic combination. In the case of line breedings, experienced, knowledgeable breeders often have extensive information about the phenotypes present in their lines, and therefore can make more informed breeding choices. Longtime health conscious breeders often have greatly reduced the incidence of disease in their breeding programs, and this will be reflected in their track record (as verifiable on the OFA web site). Outcross breedings require more diligence of the breeder to fully investigate the new lines that are brought into the pedigree, and again, information available on the OFA web site may greatly aid in this effort.

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Impact of OFA hip evaluations through multiple generations of a population subset

Retrospective studies covering the period of 1972-2000 have demonstrated steady and encouraging progress as a result of the collaborative efforts of responsible breeders and the OFA. The OFA database population represents a specific subset of the general population of animals, primarily show dogs and cats, and working/hunting dogs. Accumulated data clearly illustrates the impact that the focused efforts of conscientious breeders can have on reducing the frequency of HD, and further indicates that the hip status of progeny follows that of parents (Table 1).

Success in reducing HD in a breed depends first on breeders recognizing that a problem exists. This must then be followed by a commitment to solve the problem and dedication to consistent use of a standard hip evaluation protocol.

HD has been reported in all breeds of dogs and some cat breeds that have been evaluated by the OFA. The OFA database is an important tool that can provide breeders with information regarding changes in hip status of specific breeds over time. The frequency of HD in most breeds has steadily declined. Concurrently, the percentage of animals with excellent hip conformation has steadily increased (Graph 1) in most breeds. Within the OFA population of animals with normal hip conformation, there has been a steady decrease in the percentage of fair and an increase in the percentage of excellent (Graph 2). Within the OFA population of dysplastic animals, there has been a steady increase in the percentage of mild with a corresponding decrease in the percentage of moderate dysplasia (Graph 3).

Graph 1: Percent dysplastic & excellent by birth year

Graph 2: Percent excellent vs. fair by birth year

Graph 3: Percent mild vs. moderate by birth year

While this may be surprising to some, it is also important to realize that some of the smaller sized breeds and mixed breeds have as high a percentage of HD as the larger breeds and purebreds. Generalizations that claim that dysplasia is limited to, or more common in, large dogs and pure breed dogs, are misleading.

HD appears to be perpetuated by breeder imposed breeding practices. However, when breeders and their breed clubs recognize HD as a problem and establish HD reduction as a priority, improvement of breed hip status can be accomplished without jeopardizing other desirable traits.

Although it is clear from the graphs that breeders have made steady progress toward reducing the frequency of hip dysplasia, some are concerned that this decline may reach a plateau. As with any polygenic disease, it is anticipated that HD will decline in an exponential manner. Therefore, after several generations, it may appear that progress has leveled out. This is to be expected when phenotypic data is used to place selection pressure against polygenic disease traits with moderate to high heritability estimates. However, Leighton has shown that rapid progress can be expected in the first 3 or 4 generations, and is followed by slower but continued progress in subsequent generations. In the future, a DNA based genetic test might overcome this, but meanwhile breeders can continue to make significant progress by committing to careful selective breeding practices.

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References

1. Bennett D: Hip Dysplasia and Ascorbate Therapy: Fact or Fancy? Seminars in Vet. Med. And Surg., Vol. 2, No. 2, 1987, p. 152-157.

2. Corley EA, Carlson W: Radiographic, Genetic, and Pathologic Aspects of Elbow Dysplasia. J Am Vet Med Assoc, 1965;147:1651.

3. Corley EA, et al: Reliability of Early Radiographic Evaluation for Canine Hip Dysplasia Obtained from the Standard Ventrodorsal Radiographic Projection. JAVMA, Vol. 211, No. 9, November 1997, pp. 1142-1146.

4. Grondalen J, Grondalen T: Arthrosis in the Elbow Joint of Young, Rapidly Growing dogs. Nordish Veterinarmedicin, 1981:33:1-16.

5. Grondalen J: Arthrosis in the Elbow Joint of Young, Rapidly Growing Dogs: Interrelation between Clinical Radiological, and Pathoanatomical Findings. Nordish Veterinarmedicin, 1982; 34:65-75.

6. Kasstrom H: Nutrition, Weight Gain, and Development of Hip Dysplasia: An Experimental Investigation in Growing Dogs with Special Reference to the Effect of Feeding Intensity. Acta Radiol. Suppl.,  Vol 344: 135-179, 1975.

7. Kealy RD, et al: Effects of Limited Food Consumption on the Incidence of Hip Dysplasia in Growing Dogs. JAVMA, Vol. 201, No. 6, 1992, p.857-863.

8. Kealy RD, et al: Effect of Diet Restriction on Life Span and Age-related Changes in Dogs. JAVMA, 2002; 220: p.1315-1320.

9. Leighton EA: Genetics of Canine Hip Dysplasia. JAVMA, Vol. 210, No. 10, 1997, pp. 1474-1479.

10. Lust G et al: Joint Laxity and its Association with Hip Dysplasia in Labrador Retrievers. AJVR, Vol. 54, No. 12, 1993, p.1990-1999.

11. Lust, G et al: Comparison of Three Radiographic Methods for Diagnosis of Hip Dysplasia in Eight-month Old Dogs. JAVMA, 2001; 219: p.1242-1246.

12. Olsson SE: Osteochondrosis in Domestic Animals. ACTA Radiologic Suppl., 358, 1978, pp.299-305.

13. Olsson SE: The Early Diagnosis of Fragmented Coronoid Process and Osteochondritis Dissecans of the Canine Elbow Joint. JAAHA, 1983:19(5):616-626.

14. Padgett GA, et al: The Inheritance of Osteochondritis Dissecans and Fragmented Coronoid Process of the Elbow Joint in Labrador Re­triever. JAAHA, 1995; 31: 327-330.

15. Read RA, et al: Fragmentation of the Medical Coronoid Process of the Ulna in Dogs: A Study of 109 Cases. J. Sm. Anim. Prac., 1990; 32(7), 330-334.

16. Reed AL, et al: Effect of Dam and Sire Qualitative Hip Conformation Scores on Progeny Hip Conformation. JAVMA, 2000; 217: 675-680.

17. Rettenmaier JL, Keller GG, et al: Prevalence of Canine Hip Dysplasia in a Veterinary Teaching Hospital Population. Vet. Rad. & Ultra­sound, Vol. 43, No. 4, 2002, p. 313-318.

18. Smith, GK et al: Coxofemoral Joint Laxity from Distraction Radiography and its Contemporaneous and Prospective Correlation with Lax­ity, Subjective Score, and Evidence of Degenerative Joint Disease from Conventional Hip-Extended Radiograph in Dogs. AJVR, Vol 54: 1021-1042, No. 7, July, 1993.

19. Swenson L, Audell L, Hedhammar A: Prevalence and Inheritance of and Selection for Elbow Arthrosis in Bernese Mountain Dogs and Rottweilers in Sweden and Benefit: Cost Analysis of a Screening and Control Program. JAVMA, 1997; 210: 215 - 221.

20. Tomlinson JL: Quantification of Measurement of Femoral Head Cover­age and Norberg Angle within and among four breeds of dogs. AJVR, 2000; 61: p.1492-1498.

21. Willis MB: Practical Genetics for Dog Breeders. H. F. & G. Witherby Ltd, Great Britain, 1992.

22. Wind A: Elbow Incongruity and Development Elbow Dysplasia in the Dog (Part 1). J Amer Anim Hosp Assoc 1986:22:711-724.

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