Utilisation of joint movement range in arboreal primates compared with human subjects: an evolutionary frame for primary osteoarthritis.

OBJECTIVE

To determine whether an arboreal lifestyle required full use of movement ranges underutilised in nine joint groups in humans, because under-utilisation of available movement range may be associated with susceptibility to primary osteoarthritis.

METHODS

Utilisation of the nine joint groups was studied in two species of primate exercising in a simulated arboreal environment, using 'focal animal' observation techniques supplemented by telephoto photography and by review of archival material from other sources. Fifteen apes were observed over a total observation period of 20.2 man-hours and 152 films were analysed for utilisation of movement range.

RESULTS

With one exception, all the movement ranges reported to be under-utilised in humans were fully utilised by the apes in climbing activities. The exception, metacarpophalangeal extension, was an essential component of the chimpanzee ground progression mode of knuckle walking.

CONCLUSIONS

The underused movement range in several human joints is explicable as residual capacity from a semiarboreal lifestyle. If the correlation with primary osteoarthritis is confirmed, it suggests that the disease may reflect a disparity between inherited capacity and current need. The significance of the result lies in its implication that primary osteoarthritis may be preventable.