Purpose:The KOOS self-report questionnaire (Knee injury and Osteoarthritis Outcome Score) has 5 sub-scales, assessing knee symptoms and function, and quality of life. It is widely used as it has been found to be a valid and reliable measure. The purpose of this study was to investigate the validity, reliability and responsiveness of the Icelandic translation of KOOS.

Methods: A total of 145 were recruited for the study and in addition to answering KOOS, knee pain was rated on a visual analog scale (VAS), perception of knee function during activities of daily living on a numerical rating scale, and some were tested with the timed up-and-go test (TUG). Reliability was assessed by observing ICC-values, internal consistency with Cronbach‘s alpha, and associations between KOOS subscales and other outcome measures with Pearson‘s correlation coefficient. A one-way ANOVA was used to assess differences between groups of participants with different levels of knee dysfunction.

Results: A significant change in all KOOS subscales was found in a group of individuals seeking treatment for their knee dysfunction (p<0.001), while no change was seen in a group reporting stable knee status (ICC-values ranging from 0.825 to 0.930). Cronbach‘s alpha ranged from 0.726 to 0.966 and significant correlations were found between all KOOS sub-scales and other outcome measures (p<0.001).

Conclusion: The results indicate that the Icelandic version of KOOS is a valid and reliable measure that may be used as an outcome measure assessing knee symptoms and function of individuals with knee symptoms and impaired knee function.

Table I. Mean (SD) of participants' baseline data, by group assignment.

	No treatment (E)	Treatment (M)	Arthroplasty (L)	All
Age *	38.6 (20.1)	51.3 (16.6)	67.0 (10.1)	55.6 (18.5)
BMI †	21.5 (3.1)	25.8 (4.9)	25.3 (4.0)	24.8 (4.5)
VAS *	2.2 (1.7)	4.6 (2.3)	6.0 (2.5)	4.6 (2.7)
Self rated function *	89.8 (12.0)	61.9 (23.1)	46.6 (23.0)	64.2 (26.2)
KOOS-pain†	82.3 (9.7)	58.8 (17.9)	48.6 (15.8)	58.9 (19.9)
KOOS-symptoms‡	79.8 (10.7)	54.0 (18.6)	50.7 (17.4)	57.5 (20.0)
KOOS-ADL †	92.5 (8.2)	67.0 (18.4)	55.5 (16.7)	67.3 (21.0)
KOOS-S/R‡	65.4 (20.2)	24.7 (21.4)	18.3 (15.8)	30.6 (26.2)
KOOS-QOL †	65.1 (15.5)	41.6 (18.5)	25.6 (13.4)	39.6 (21.6)

*significant difference between all group means (p<0.001), † significant difference between all group means (p<0.01), ‡ significant difference between means of groups E and M and between means of groups E and L (p<0.001). ADL= activities of daily living, S/R= sports and recreation, QOL= quality of life.

Table II. Factors relating to reliability and internal consistency of KOOS categories.

	Pain	Symptoms	ADL	S/R	QOL
ICC-value	0.825	0.863	0.884	0.930	0.926
SEM	2.8	2.6	2.5	3.8	3.2
MDD	7.7	7.3	7.0	10.4	8.9
Cronbach‘s alpha	0.920	0.726	0.966	0.925	0.830

ADL= activities of daily living. S/R= sports and recreation, QOL= quality of life. ICC= intra-class correlation coefficient. SEM= standard error of the measurement. MDD= minimal detectable difference.

 

Figure 1. Mean (SD) scores for each of the KOOS sub-scales before and after treatment for knee dysfunction. ADL=activities of daily living. S/R=sports and recreation. QOL=quality of life. A significant difference was found between all pre- and post-treatment outcomes (p<0.001).

 

Figure 2. Test-retest scores for each of the KOOS sub-scales. ADL=activities of daily living. S/R=sports and recreation. QOL=quality of life.

 

Figure 3. Association between pain scored on a VAS (higher scores indicate worse pain) and scores on the KOOS pain sub-scale (higher scores indicate less pain).