Intra-articular pressure profile of the knee joint in a spectrum of inflammatory arthropathies

Objectives—The intra-articular pressure (IAP) rises significantly after isometric quadriceps contraction in patients with rheumatoid synovitis, a process that may temporarily impede synovial blood flow and cause oxidative injury. In acute traumatic knee eVusions (ATE) pressure rises are trivial. This study compared the IAP profiles of patients with ATE with three diVerent populations—an acute synovitis on the background of a chronic inflammatory arthropathy, a chronic low grade inflammatory arthropathy, and an acute intermittent inflammatory arthropathy. The study objective was to discover if the pressure profiles observed in these groups reflect an influence of the inflammatory process or time or both. Methods—Thirty three patients were studied. These were divided into four subgroups; group 1:five acute traumatic knee eVusions (ATE); group 2: acute eVusions on the background of a chronic inflammatory arthropathy: seven rheumatoid arthritis (RA),five psoriatic arthritis (PsA); group 3: seven osteoarthritis (OA) and group 4: acute eVusions on the background of an intermittent inflammatory arthropathy: seven pyrophosphate arthropathy (PA), one amyloid (AA), one Behcet’s (B). IAP was measured (mm Hg) at rest and during isometric quadriceps contraction using the hand held portable 295-1 intra-compartmental pressure monitor system (Stryker UK).The volume of synovial fluid aspirated was recorded. Results—Expressed as medians (interquartile range). Resting IAP was; ATE 6 (2‐12), RA 8 (5‐47), PsA 18 (11‐31), OA 17 (7‐21), PA 25 (9‐29), AA 14, and B 12. IAP increased in all subjects during isometric contraction; ATE 9 (7‐16), RA 56 (33‐150), PsA 52 (43‐85), OA 56 (20‐116), PA 53 (41‐ 65), AA 47, B 57 and the IAP rise was significant (p 0.05). The volume of synovial fluid aspirated in groups 2, 3, and 4 correlated significantly with the magnitude of the IAP change (r = 0.45, p < 0.05). Conclusion—The IAP rise during isometric quadriceps contraction is a feature of all patients with an inflammatory based eVusion irrespective of the duration of the eVusion. This is not the case in patients with an ATE. In inflammatory synovitis the rise in intra-articular pressure with isometric quadriceps contraction relates to eVusion volume.It is concluded that the inflammatory process prevents reflex muscle inhibition, a locally protective mechanism that minimises the potential for intermittent ischaemia/oxidative injury. (Ann Rheum Dis 1997;56:686‐689)