Measurement of stiffness in the metacarpophalangeal joint: the effects of physiotherapy

THE ROLE OF NEGATIVE INTRA-ARTICULAR PRESSURE IN STABILIZING THE METACARPOPHALANGEAL JOINT

Negative intra-articular pressure (IAP) is a passive stabilizer during joint movement. In contrast to that of large joints, the IAP within the metacarpophalangeal (MCP) joint has not been well studied. The objective of this study was to evaluate the biomechanics of the MCP joint in terms of load–displacement relation and IAP during the application of long-axis distraction to fresh cadaver specimens. Nine fresh MCP joints specimens from four hands were used. A long-axis distraction load of 16 kg was applied to the cadaver MCP joint before and after venting of the joint capsule. In addition to load–displacement data, a pressure transducer was used to measure the IAP of the MCP joint during loading. After venting the capsule, significant increases were found in displacement at a load of 16 kg (4.60 ± 0.80 mm in an intact MCP joint and 5.22 ± 0.97 mm in a vented MCP joint) and in displacement at the cross-point (3.44 ± 0.82 and 4.01 ± 0.81 mm). No significant difference was found in the displacement difference between a load of 16 kg and the cross-point (1.16 ± 0.26 and 1.20 ± 0.33 mm) as well as stiffness at the terminal range under both the intact and venting conditions (12.59 ± 2.53 and 12.28 ± 2.70 kg/mm). The IAP decreased dramatically during the 5% to 10% total distraction of load. It was found that negative IAP of the MCP joint contributes significantly to initial stability.

The Contribution of Different Tissues to Stiffness of the Wrist Joint

Passive articular stiffness is not only a function of articular tissues, but also tissues associated with movement, such as muscles and tendons. Allowance has been made for the relative contribution of these extra-articular tissues in comparing the resting stiffness of normal subjects and patients with rheumatoid arthritis. In addition, the stiffness of the muscle-joint complex with agonist/antagonist muscles co-contracting has been measured. Significant muscle wasting was found in rheumatoid arthritis (forearm muscle cross-sectional area for normals: 30.9 cm2, for rheumatoid arthritis: 22.7 cm2, p = 0.002). Allowing for this, there was a significant difference in resting stiffness between normals and rheumatoid arthritis subjects (adjusted resting stiffness normals: 90.8 × 10-3Nm/deg, rheumatoid arthritis: 120.3 × 10-3Nm/deg, p = 0.015). There was no difference between the groups in terms of the relationship between stiffness and grip at different levels of muscle co-contraction, suggesting the muscles are qualitatively normal in rheumatoid arthritis.

Relationship between weakness and muscle wasting in rheumatoid arthritis

OBJECTIVE

To relate weakness of grip to loss of forearm muscle bulk, hand joint deformity, and hand joint tenderness in patients with rheumatoid arthritis (RA).

METHODS

Using anthropometric data we have estimated the anatomical cross-sectional area (CSA) of forearm muscles in 100 subjects with RA compared with 100 aged and sex-matched normal subjects. We also recorded hand joint tenderness using a modification of the Ritchie articular index, and a simple index of hand joint deformity.

RESULTS

We found a significant reduction in anatomical CSA in RA (forearm CSA in normal subjects 29.7 cm2 and in RA 25.9 cm2; p = 0.002). In simple linear regression we found that 46.3% of the variation in grip strength in normal subjects was explained by variation in muscle CSA; in RA this figure decreased to 33.4%. Adding terms for joint deformity and pain in a multiple regression model improved the amount of variation explained to 37.9%.

CONCLUSIONS

Although there is significant muscle wasting in RA, it is likely that reduction in strength is also attributable to joint deformity and pain leading to inhibition of grip directly and, indirectly, by arthrogenous muscle inhibition. Doubts remain about the quality of muscle in RA.

Treating arthritis with locally applied heat or cold

The scientific for the treatment of arthritis with locally applied heat or cold is reviewed. Experimental studies in vitro, in animals, in healthy subjects, and in patients are considered. Results of investigations of the effects of locally applied heat or cold on the deeper tissues of joints and on joint temperature in patients are not consistent. In general, locally applied heat increases and locally applied cold decreases the temperature of the skin, superficial and deeper tissues, and joint cavity. Most studies dealing with the effects of heat and cold on pain, joint stiffness, grip strength, and joint function in inflamed joints report beneficial effects. In vitro studies show that higher temperatures increase the breakdown of articular cartilage and tissues that contain collagen. Therefore, one goal of physical therapy should be to decrease intraarticular temperature in actively inflamed arthritic joints.

Bioengineering aspects of rehabilitation

This paper discusses the development of bioengineering in the field of human joints and its particular relevance to rehabilitation.

Biodynamics of the wrist in rheumatoid arthritis--the enigma of stiffness

The wrist has been moved rhythmically in the horizontal plane by sinusoidal torques provided by a printed motor. Measurements have been made on normal subjects and subjects with rheumatoid arthritis. Both groups exhibited a resonance, the oscillations being greatest when the applied torque was of certain frequency. In both groups the resonant frequency fell to approximately the same constant value when the torque was raised. While the main relationships were similar a somewhat lower torque resulted in the lowering of resonant frequency in the patients. The relationship between applied torque and peak velocity at resonance was also studied. For a given torque the motion was greater in the patients. No objective signs of increased viscous or elastic stiffness were demonstrable at the wrist in patients with rheumatoid arthritis.