Improved diagnostic imaging in joint diseases

Interrater reliability of a clinical scale to assess knee joint effusion

STUDY DESIGN

Clinical measurement.

OBJECTIVE

To determine the interrater reliability of a knee joint effusion grading scale in an outpatient orthopaedic physical therapy clinic.

BACKGROUND

Knee joint effusion may indicate joint inflammation or irritation. Therefore, objective monitoring of effusion is important to decision making regarding patient prognosis and program progression. The clinicians in the authors' clinic use a modified stroke test to assess for knee joint effusion, which is operationally based on a 5-point grading scale.

METHODS

Seventy-five patients (44 male, 31 female) receiving outpatient physical therapy for a unilateral knee problem, for whom effusion assessment was indicated, were tested. The subjects ranged from 16 to 65 years of age. Pairs of therapists graded the knee joint effusion using the clinical grading scale. A contingency table was constructed and analyzed using Cohen kappa values to establish interrater reliability. Percent agreement was also calculated.

RESULTS

The kappa value was 0.75, observed as a proportion of the maximum possible kappa, and the percent agreement was 73%. Fifty-four of 75 pairs of tests had perfect agreement. Only 5 had disagreement of 2 grades, and there were no disagreements of greater than 2 grades.

CONCLUSION

These findings provide evidence to support the proposed clinical effusion grading scale as a reliable method to assess knee joint effusion between therapists in an outpatient orthopaedic physical therapy clinic in patients with unilateral knee dysfunction. Only 5 of 75 ratings resulted in disagreement that could result in different clinical decisions being made by the therapists.

Sonography detection threshold for knee effusion

The aim of this study was to determine the threshold for detecting knee effusion by ultrasound (US). Five knee specimens from embalmed cadavers were studied. Intra-articular injection of saline, blood and synovial fluid was performed under ultrasound control and methylene blue dye instillation. The smallest amount of fluid detectable by US in the knee was 7.4 ml for synovial fluid, 10.1 and 10.4 ml for saline solution and 9.7 for blood. The threshold for detecting knee joint effusion by US in cadaver specimens was 10 ml for saline and blood and 7 ml for synovial fluid.

Distribution of joint effusion in patients with traumatic knee joint disorders: MRI assessment

One hundred forty-five knee magnetic resonance imaging examinations with joint effusions were reviewed to clarify the usual distribution of joint fluids in patients with traumatic knee joint disorders. Almost all knees (99%) had effusions in the central portion, and most knees (76%) had effusions in the suprapatellar pouch. Effusions were rarely found in the posterior femoral recess (9%) or subpopliteal recess (2%). However, this difference was considered to be only a reflection of anatomic communications. Effusions were occasionally found around posterior cruciate ligaments (36%), but were less frequently seen around anterior cruciate ligaments (18%).