Brian J Sharp, Veterinary Physiotherapist
MSc(VetPhys), BSc(Phys), BSc(Biol), PGCertEd, PGDipHealthEd, MCSP, SRP, ACPAT (Cat A)

Introduction

Generalised joint hypermobility is a common phenomenon in humans, affecting between 10% and 34% of the general population. In dogs, it is recognised much less frequently, although the true incidence in this species is unknown. Maybe it occurs to a lesser extent in dogs, or perhaps it is not specifically looked for and diagnosed by veterinarians. There are no pathognomonic laboratory or radiological findings specific for this condition, and so in humans, the diagnosis is frequently made through exclusion of other disorders. The Beighton nine-point scoring system (Beighton et al 1973; Grahame et al 2000) is used for grading hypermobility in humans, but there is no such system currently available for use with dogs.

Hypermobility is generally considered to be part of a generalised connective tissue disorder that can affect all tissues and organs of the body (Bird et al 1978). It is suggested that people with hypermobility represent an extreme subset of the normal joint mobility distribution within the population (Wood 1971). Although many people have no symptoms, some individuals develop a range of musculoskeletal conditions associated with hypermobility including subluxation and dislocation of joints (Carter and Sweetnam 1958, 1960; Finsterbush and Pogrund 1982). In these cases, it is regarded as a departure from normality, and classified as one of the heritable disorders of connective tissue alongside Ehlers-Danlos and Marfan’s syndromes, and osteogenesis imperfecta. Although less severe and with no life threatening complications, it shares many of the features of these other conditions (Grahame 1999).

Over 400 mutations have been found affecting the six most common types of collagen. The mutation of specific genes results in the production of abnormal collagen, as well as in the alteration of the biological processes that regulate the assembly and organisation of connective tissue (Briggs et al 1995; Prockop and Kivirikko 1995; Jepsen et al 2002). Weakening of joint capsules in this way creates the laxity that forms the basis of hypermobility (Fredensborg and Uden 1976).

Hip joint laxity is recognised as the initial and most important element in the development of canine hip dysplasia (CHD) (Todhunter and Lust 2003), which is one of the most common orthopaedic diseases in dogs. The British Veterinary Association/Kennel Club (BVA/KC) hip-scoring scheme has been in operation since 1984 (Gibbs 1997). Radiographs are taken and assessed in accordance with the scheme, providing a score of 0 to 53 for each hip (total score 0 to 106). The scheme provides breeders with a quantitative assessment of the condition of the canine hip joint, in respect of joint subluxation and degree of degenerative change (Wood and Lakhani 2003).

Osteoarthritis (OA) is the most obvious manifestation of hip dysplasia, and the probability of developing secondary OA increases with hip joint laxity (Smith et al 1993). In humans, there is evidence of an association between hypermobility, hip dysplasia and OA (Wynne-Davies 1970; Scott et al 1979; Child 1986), but there is scant evidence that the laxity in CHD is the result of a generalised connective tissue disorder (Madsen 1997). If this were the case, it would be expected that other joints should have similar laxity. Although this is yet to be proven, dogs that have developed OA secondary to CHD, have been reported to show similar degenerative changes in various other joints, including the vertebral joints, mandible, stifle, shoulder and elbow (Olsewski et al 1983; Lust 1993).

A study investigating the relationship between hip score and range-of-motion measurements at other joints in the Labrador and Golden Retriever (MSc Veterinary Physiotherapy)

The aim of the study was to add to the body of knowledge regarding CHD, OA and hypermobility in dogs. Goniometry was used to measure joint angles to test the hypothesis that a higher hip score positively correlates with increased range-of-motion (ROM) at the elbow, carpus, stifle and tarsal joints in the dog. It was also hypothesised that intra-observer goniometry measurements of those same joints are repeatable in Labrador and Golden Retrievers.

Materials and Methods

A randomised order of testing was used in the measurement of passive flexion and extension ROM. Goniometric measurements were made of the elbow, carpus, stifle and tarsal joints of 36 Labrador and Golden Retriever dogs by a single examiner. Measurements were made in duplicate, and intra-observer repeatability determined using the British Standards Institution Repeatability Coefficient (experiment 1). Correlations were then explored between the means of these measurements and each dog’s hip score (experiment 2).

Results

Experiment 1

Experiment 2

Discussion

Experiment 1

Experiment 2

Dogs with high hip scores (11 - 106) (i.e. those more likely to have gross instability or established secondary degenerative change) were more likely to be found at the extremes of the population range (within the top or bottom 16% of the normal distribution). Younger dogs (1 – 4 years) had a greater ROM at one or several individual joints, and had a greater representation of individuals falling in the top 16%. Middle-aged dogs (5 – 8 years) were at a transition stage, with either greater or reduced range. Older dogs (9 years) had a much reduced ROM, and greater representation in the bottom 16%.

The proposed explanation for these results is that canine hip dysplasia may be just one manifestation of a more generalised hypermobility syndrome affecting several joints. In younger dogs, this is represented by a greater than average joint ROM due to hypermobility. In older dogs, a less than average joint ROM is evident due to the development of OA changes that have occurred because of the joint laxity. The transition period suggests a changeover stage when OA changes are developing. Progressive fibrosis and thickening of the joint capsule provides better stability, but less movement to the previously lax joint. The timing and severity of these changes will clearly vary depending on the environmental influences each individual dog encounters.

Conclusion

The results from this study support the theory that generalised hypermobility occurs in dogs, and that it is associated with hip dysplasia and development of osteoarthritis. Although many joints may be affected in the same way, most are under less stress than hip joints, and so the development of OA in these other joints may be less obvious. However, the presence of hypermobility has the potential to cause symptoms anywhere in the body, and the interesting preliminary findings of this research should be further investigated in a larger prospective study. An awareness by veterinarians of the existence of hypermobility in dogs may be a useful first step in preventing the early development and severity of secondary conditions such as OA. By using techniques to develop effective stabilisation of joints, the role of the veterinary physiotherapist could prove invaluable.

This research is currently being prepared for submission for publication.

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