Freund's adjuvant induced polyarthritis in rats has been used extensively to study pain processes of long duration. There are limitations of this model for chronic studies of pain/arthritis since the severe systemic changes provoke ethical concerns and also affect behaviour, physiology and biochemistry. Attempts to limit adjuvant-induced arthritis by plantar injection of the inoculum have been made. In this model, however, the process evolved to produce widespread polyarthritis if followed for the 6-plus-weeks necessary for chronic studies. Therefore, although it offers the researcher a reliable limited model of inflammation and nociception at the outset, for longer studies it may have all the disadvantages of the polyarthritic rat. The purpose of the present study was to produce a limited arthritic process in rats, stable over 6 weeks and suitable for behavioural and neurochemical studies of various chronic pain treatment methods. Injection (0.05 ml) of complete adjuvant containing 300 micrograms Mycobacterium butyricum in the tibio-tarsal joint produces a predictable monoarthritis, stable clinically and behaviourly from weeks 2 through 6 post injection. As revealed by clinical observations and X-ray examinations, the arthritis produced was limited anatomically, pronounced, prolonged and stable. A marked increase in sensitivity to paw pressure was seen in the affected limb. Animals gained weight and remained active, indicating little systemic disturbance as opposed to polyarthritic rats. We propose this limited model of arthritis as a suitable alternative to the polyarthritic rat for prolonged studies.

Eccentric graded exercise reduced pain and increased muscle strength in chronic tennis elbow more effectively than concentric graded exercise.

BackgroundChronic tennis elbow (lateral epicondylosis) is a common disorder. Like other chronic soft-tissue pain conditions it is often difficult to treat successfully. The effects of exercise have been discussed, but no convincing evidence has been put forward so far, and a simple protocol for exercise is lacking.Aims of the studyThis study is a randomized, controlled, clinical trial of the effect of exercise versus expectation (wait-list) on pain, muscle strength, function, and quality of life in patients with long-standing lateral epicondylosis.MethodsEighty-one subjects with tennis elbow lasting for more than 3 months were randomly allocated to an exercise group (n = 40) or a reference group (n = 41). The exercise group performed daily exercise, with weekly load increase, for 3 months. The reference group was wait-listed, but otherwise followed in the same way. Outcome measures were pain during maximum voluntary muscle contraction (Cozen's test) and pain during maximum muscle elongation with a load (modified Empty-can-test); muscle strength was measured with a Chatillon MSE 100 hand-held dynamometer, and the Disability of the Arm, Shoulder and Hand (DASH) and the Gothenburg Quality of Life questionnaires.ResultsThe exercise group had greater and faster regression of pain, both during muscle contraction and muscle elongation, than the reference group (p = 0.0005 and p = 0.0016, respectively). There was a non-significant muscle strength difference between the groups, but no differences regarding DASH scores or quality of life measures.ConclusionsExercise appears to be superior to expectation in reducing pain in chronic lateral epicondylosis.