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RehabMeasures Instrument

Knee Injury and Osteoarthritis Outcome Score

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Atomized Content

Purpose

A 42-item self-administered assessment of five outcomes: knee-related quality of life, activities of daily living, sport and recreation function, symptoms, and pain.

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Instrument Details

Acronym KOOS

Area of Assessment

Activities of Daily Living
Pain
Quality of Life

Assessment Type

Patient Reported Outcomes

Administration Mode

Paper & Pencil

Cost

Free

Diagnosis/Conditions

  • Arthritis + Joint Conditions
  • Sports & Musculoskeletal Injuries

Key Descriptions

  • Based on the Western Ontario and Mc-Master Universities Osteoarthritis Index (WOMAC).
  • Each item is scored from 0 (no problems) to 4 (extreme problems).
  • For each subscale, the score is then normalized to a 0-100 scale with higher scores equaling better status.

Number of Items

42

Time to Administer

10 minutes

Required Training

No Training

Age Ranges

Adolescent

13 - 17

years

Adult

18 - 64

years

Elderly Adult

65 +

years

Instrument Reviewers

Initially reviewed by Jason Raad, MS in 4/2012

Body Part

Lower Extremity

ICF Domain

Body Function
Activity

Measurement Domain

General Health

Considerations

  • The KOOS is available in several languages, the American-English, Swedish, and Danish versions have been validated (); a French version (Ornetti et al., 2008); a Japanese version (Nakamura, 2011); and a Singapore English and Chinese version (Xie et al., 2006) have each had at least one validation study conducted. Visit the Koos website for a complete list of translated instruments.

  • Modified versions include:

    • FAOS: Assesses problems with the foot and ankle

    • HOOS: Assesses problems with the hip

    • RAOS: Assesses hip, knee and foot problems in patients with rheumatoid arthritis 

  • A Physical Function (KOOS-PS) is also available

  • A Children’s Version (KOOS-Child) is also available

Do you see an error or have a suggestion for this instrument summary? Please e-mail us!

Non-Specific Patient Population

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Standard Error of Measurement (SEM)

Athletes:

(Salavati et al, 2011; n = 57 patients with ACL reconstruction (39 males, 18 females); mean age = 25.6 ± 3.4 years, Athletes) 

Domain

SEM

Pain 

2.2 

Symptoms 

3.1 

ADL 

2.9 

Sports/Rec 

2.1 

QoL 

2.6

Minimal Detectable Change (MDC)

Athletes:

(Salavati et al, 2011, Athletes) 

Domain

MDC

Pain 

6.1 

Symptoms 

8.5 

ADL 

8.0 

Sport/Rec 

5.8 

QoL 

7.2 

Cut-Off Scores

Athletes/ACL Injury:

(Lohmander LS et al, 2004; n = 84; mean age = 31 (26-40) years; mean BMI = 23 (18-40) kg/m2, Athletes/ACL Injury) 

 

 

Cut-Off Score for Problematic Knee

Pain 

< 86.1

Symptoms 

< 85.7

ADL 

< 86.8

Sport/Rec 

< 85.0

QoL 

< 87.5

 

Total Knee Arthroplasty:

(Stevens-Lapsley et al; 2011; n = 39 (17 men and 22 women) mean age = 64.0 (8.2) years; mean (SD) BMI, 29.1 (5.2) kg/m2, Total Knee Arthroplasty)

 

Comparison between pre-op and post-op KOOS scores:

 

 

 

 

 

 

 

 

Pre-op

 

1-Mo Postop

 

 

3-Mo Postop

 

 

6-Mo Postop

 

Measure

Mean(SD)

Mean(SD)

p

Mean(SD)

p

Mean(SD)

p

KOOS ADL

58.33 (2.41)

69.29 (2.21)

p < 0.05

84.35 (2.74)

p < 0.05

87.92 (2.12)

p < 0.05

KOOS symptom

48.08 (2.64)

53.39 (1.99)

 

66.21 (2.72)

p < 0.05

72.37 (2.69)

p < 0.05

KOOS Sport/Rec

18.72 (3.42)

18.17 (3.46)

 

49.23 (3.42)

p < 0.05

50.53 (3.46)

p < 0.05

KOOS QOL

26.12 (2.98)

41.31 (3.01)

p < 0.05

63.30 (2.98)

p < 0.05

66.96 (3.01)

p < 0.05

KOOS Pain

48.22 (2.63)

59.19 (2.63)

p < 0.05

75.28 (2.63)

p < 0.05

80.94 (2.65)

p < 0.05

6MW (m)

430 (18)

349 (18)

p < 0.05

459 (18)

p < 0.05

473 (18)

p < 0.05

TUG (s)

9.23 (0.55)

12.15 (0.99)

p < 0.05

8.46 (0.50)

p < 0.05

7.92 (0.41)

p < 0.05

SCT (s) 

17.87 (1.72)

31.83 (3.33)

p < 0.05

16.05 (1.49)

p < 0.05

14.25 (1.29)

p < 0.05

Normative Data

Athletes:

(Salavati et al, 2011, Athletes)

 

KOOS Post-operation Baseline Norms:

 

Domain

Value: Mean (SD )

Pain

74.0 (10.2)

Symptoms

61.2 (9.3)

ADL

73.0 (8.9)

Sports / Recreation Level

51.1 (15.3)

QoL

52.9 (13.9)

 

ACL/Athletes:

(Kvist J et al, 2005; n= 62; mean age= 27 (18-37) years, ACL/Athletes) 

 

 

Men

Women

Total

Pain 

85 + 19 (n = 33) 

82 + 17 (n = 27) 

84 + 18 (n = 60) 

Symptoms 

75 + 16 (n = 34) 

74 + 25 (n = 28) 

74 + 20 (n = 62) 

ADL 

94 + 8 (n = 34) 

90 + 14 (n = 28) 

92 + 12 (n = 62) 

Sport/Rec 

64 + 23 (n = 34) 

60 + 28 (n = 28) 

62 + 25 (n = 62) 

QoL 

64 + 20 (n = 33) 

63 + 22 (n = 28) 

64 + 21 (n = 61) 

 

ACL Lesion:

(Hill GN, O’Leary ST, 2012; n=165; mean age 30.4(+ 9.7), years; 74% male; mean time to surgery following lesion 13.1(+ 20.8) months, ACL Lesion) 

  • Significant improvements in all subscales at 12 months following ACL reconstruction (p < 0.001) 
  • Improvement seen at 3 and 6 month measurements (p < 0.003) 
  • Reduced rate of recovery in Sports/rec and QoL subscales 
  • Sports/rec and QoL most sensitive to change 

 

(Ahlden M et al, 2012; = 17,794; 57.5% male; primary reconstruction n= 15,387, revision = 964; cause of injury-soccer in 1/2 of males, soccer 1/3 of females, ACL Lesion) 

  • Primary ACL Reconstruction 
    • All subscales significantly improved at 1, 2, and 5 years post-op (p < 0.001)
  • Revision 
    • Significantly improved at 1 and 2 years post-op (p < 0.05) 
    • At 5 years, only Sport/rec and QoL were improved (p < 0.002) 
  • Significantly poorer knee-related QOL in revision patients than primary reconstructions 
  • ACL reconstruction with additional intra-articular injuries 
    • Scored significantly lower on all subscales pre-op compared to ACL only (p < 0.001)

 

(von Porat A, Roos EM, Roos H, 2004; = 219; mean age 38 (range 30-56) years, Athletes/ACL Lesion) 

  • Significant differences were found in all KOOS subscales comparing ACL lesion with published reference groups

Study Group

 

 

Reference Group

 

 

Mean (SD)

95% CI

Mean (SD)

95% CI

Pain

84 (16.1)

81.9-87.1

96 (9.9)

93.7-99.0

Symptoms

76 (20.2)

72.5-79.0

94 (9.9)

92.3-96.9

ADL

90 (13.5)

88.3-92.6

96 (10.0)

93.2-98.5

Sport/Rec

63 (28.7)

58.9-68.0

90 (17.9)

85.6-95.1

QoL

60 (24.6)

56.2-63.9

92 (13.5)

88.6-95.7

 

Partial medial meniscectomy 3–5 years previously:

(Roos et al, 2005; n = 14, 10 men and 4 women; 7 participants reported at least mild functional difficulty; mean age = 45.8 (3.6) years; BML = 26.8 (2.6), Partial medial meniscectomy)

KOOS Baseline Norms:

 

Domain

Value: Mean (SD)

Pain

80 (17)

Symptoms

81 (12)

ADL

83 (17)

Sports / Recreation Level

60 (26)

QOL

68 (18)

Test/Retest Reliability

Athletes: (Salavati et al, 2011)

  • All KOOS subscales ICC higher than acceptable level of 0.70 (range=0.75-0.93) 
  • Cronbach’s alpha was higher than 0.70 in all KOOS subscales

 

Articular Cartilage Lesion: (Engelhart et al, 2012; = 54; age range 25-52 years, 67% male; 80% post-surgical repair of cartilage lesions; median BMI=27; n=33 (based on PR Functional Status Score)

KOOS: Reliability and Test-retest Reliability:

 

Domain

ICC (95% CI)

Pain

0.82

Symptoms

0.78

ADL

0.79

Sports / Recreation Level

0.80

QoL

0.82

 

Symptomatic Focal Cartilage Lesion: (Bekkers et al, 2009; = 40; mean age 35 (12) years, 70% female; cartilage lesions were the result of autologous chondrocyte implantation (n = 20) or microfracturing (n = 20); mean postoperative time was 32 months; Dutch version)

KOOS: Reliability and Test-retest Reliability

 

 

 

 

Domain

Mean KOOS (SD)

 

ICC (95% CI)

SDD

 

First

Second*

 

 

Symptoms

74 (17)

75 (17)

0.95 (0.90 - 0.97)

5

Pain

77 (15)

77 (15)

0.92 (0.86 - 0.96)

6

Function ADL

84 (14)

86 (12)

0.87 (0.77 - 0.93)

7

Sport/recreation

55 (26)

58 (25)

0.89 (0.81 - 0.93)

12

QOL

49 (23)

53 (22)

0.95 (0.91 - 0.97)

7

Total score

74 (15)

76 (14)

0.97 (0.93 - 0.98)

4

*two-day retest interval

 

 

 

 

Internal Consistency

Athletes: 

(Salavati et al, 2011, Athletes)

  • All KOOS subscales ICC higher than acceptable level of 0.70 (range = 0.75-0.93) 
  • Cronbach’s alpha was higher than 0.70 in all KOOS subscales

 

Articular Cartilage Lesion:

(Engelhart et al, 2012; = 54; age range 25-52 years, 67% male; 80% post-surgical repair of cartilage lesions; median BMI=27; n=33 (based on PR Functional Status Score, Articular Cartilage Lesion)

KOOS: Reliability and Test-retest Reliability:

 

Domain

ICC (95% CI)

Pain

0.82

Symptoms

0.78

ADL

0.79

Sports / Recreation Level

0.80

QoL

0.82

 

Symptomatic Focal Cartilage Lesion:

(Bekkers et al, 2009; = 40; mean age 35 (12) years, 70% female; cartilage lesions were the result of autologous chondrocyte implantation (n = 20) or microfracturing (n = 20); mean postoperative time was 32 months; Dutch version, Symptomatic Focal Cartilage Lesion)

KOOS: Reliability and Test-retest Reliability

 

 

 

 

Domain

Mean KOOS (SD)

 

ICC (95% CI)

SDD

 

First

Second*

 

 

Symptoms

74 (17)

75 (17)

0.95 (0.90 - 0.97)

5

Pain

77 (15)

77 (15)

0.92 (0.86 - 0.96)

6

Function ADL

84 (14)

86 (12)

0.87 (0.77 - 0.93)

7

Sport/recreation

55 (26)

58 (25)

0.89 (0.81 - 0.93)

12

QOL

49 (23)

53 (22)

0.95 (0.91 - 0.97)

7

Total score

74 (15)

76 (14)

0.97 (0.93 - 0.98)

4

*two-day retest interval

 

 

 

 

Criterion Validity (Predictive/Concurrent)

Athletes/ACL Injury:

(Lohmander LS et al, 2004, Athletes/ACL Injury) 

  • Worse KOOS score predicted for all five dimensions in ACL-injured female soccer players (p < 0.001) compared to uninjured soccer players 
    • Largest differences found in Sports/Rec and QoL (p < 0.001)

 

Construct Validity

Articular cartilage lesion:

(Engelhart et al, 2012, Articular Cartilage Lesion) 

  • Strong correlation between the following: 
    • KOOS subscales and physical outcomes of SF-36 (PF, RL, and BP) (r > 0.50) 

 

Athletes:

(Salavati et al, 2011, Athletes) 

  • Strong correlation between the following: 
    • KOOS pain and SF-36 BP (= 0.79, p < 0.01) 
    • KOOS ADL and SF-36 PF (= 0.73, p < 0.01) 
    • KOOS Sport/rec and SF-36 PF (= 0.72, p< 0.01)

Total Knee Arthroplasty:

(Stevens-Lapsley et al, 2011, Total Knee Arthroplasty) 

KOOS and 6MW Correlations:

 

 

Months

KOOS ADL versus 6MW

KOOS Pain versus 6MW

1

-0.096 (p = 0.577)

-0.272 (p = 0.108)

3

0.021 (p = 0.899)

-0.038 (p = 0.818)

6

-0.178 (p = 0.291)

-0.230 (p = 0.171)

 

 

 

6MW = 6-minute walk

 

 

Content Validity

  • Content Validity for participants with ACL and meniscus injury, and early OA a literature review was conducted, a panel of experts was consulted and a pilot study was conducted (Roos and Toksvig-Larsen, 2003)
  • In determining whether or not to have TJR, greater than 90% of patients rated all KOOS subscales (except Sport/Rec) as “extremely or very important” (Roos et al, 2003)

Floor/Ceiling Effects

Symptomatic Focal Cartilage Lesion:

(Bekkers et al, 2009, Symbtomatic Focal Cartilage Lesion)

KOOS Floor and Ceiling

 

 

Domain

Floor

Ceiling

Symptoms

0%

2.6%

Pain

0%

5.1%

Function ADL

0%

7.7%

Sport/recreation

0%

7.7%

QOL

0%

10.3%

Total score

0%

2.6%

Responsiveness

Articular Cartilage Lesion:

(Engelhart et al, 2012, Articular Cartilage Lesion)

  • Large Guyatt statistics for Sport/rec (1.06) and QoL (0.91)
  • Moderate Guyatt statistics for symptoms (0.55), pain (0.51), and ADL (0.51) 

 

 

Symptomatic Focal Cartilage Lesion:

(Bekkers et al, 2009, Symptomatic Focal Cartilage Lesion)

 

Responsiveness:

 

Domain

ES

Symptoms

0.72

Pain

0.82

Function ADL

0.70

Sport/recreation

0.98

QOL

1.32

Total score

0.91

Joint Pain and Fractures

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Minimal Detectable Change (MDC)

Osteoarthritis and Total Joint Replacement:

(Roos and Toksvig-Larsen, 2003; n = 105 patients with total knee replacements (39 males, 66 female); mean age = 71.3 (43-86) years, Osteoarthritis and Total Joint Replacement)

  • A change of 8-10 points may represent a minimal perceptible clinical improvement (MPCI)

Cut-Off Scores

Total Joint Replacement:

(Roos et al; 2003, Total Joint Replacement) 

 

 

Baseline 

6 months 

12 months 

Pain 

38 (18)

79 (20) 

83 (16) 

Symptoms 

47 (20) 

72 (18) 

84 (16) 

ADL 

41 (16) 

77 (17) 

82 (16) 

Sport/Rec 

16 (22) 

48 (33) 

46 (30) 

QoL 

19 (14) 

59 (25) 

69 (24)

Criterion Validity (Predictive/Concurrent)

Total Joint Replacement:

(Tonelli SM, 2011; = 138 women, 70 men; mean age = Women 61.92 (10.03) years, Men 61.66 (9.92) years; mean BMI = Women 35.43, Men 33.19, Total Joint Replacement) 

  • Women have worse scores than men in pain and ADL subscores prior to TKR (ppain= 0.02; pADL= 0.007)

Construct Validity

Total Joint Replacement:

(Argenson JN; = 445; mean age 71 ± 8 years; mean BMI=28 ± 4 kg/m2 ,Total Knee Replacement)

KOOS and Knee Flexion:

 

 

SUBSCALE

Pearson Coefficient

P value vs. Flexion

Pain

0.437

< 0.0001

Symptoms

0.434

< 0.0001

ADL

0.437

< 0.0001

Sport/Rec

0.212

0.0014

QoL

0.379

< 0.0001

(Roos et al, 2003, Total Knee Replacement) 

  • High correlations between SF-36 scales and KOOS scales that are designed to measure similar constructs 
    • Bodily Pain (SF-36) vs. Pain (KOOS)- rs= 0.62 
    • Physical Function (SF-36) vs. ADL (KOOS)- rs = 0.

Floor/Ceiling Effects

Total Joint Replacement:

(Roos et. al 2003, Total Joint Replacement) 

  • KOOS is better predictor of post-op improvement in comparison to WOMAC, as exhibited by lower ceiling effects in KOOS

 

KOOS Ceiling/Floor Scores

 

 

 

Pre-Op

6 months

12 months

Pain

1/0

15/0

22/0

Symptoms

0/1

3/0

12/0

ADL

0/0

8/0

11/0

Sport/Rec

0/48

16/16

9/12

QoL

0/14

11/1

17/0

Responsiveness

Total Joint Replacement:

(Roos et al, 2003, Total Joint Replacement)

  • QoL has largest effect size (2.86 @ 6 months post-op & 3.54 @ 12 months)

Osteoarthritis

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Minimal Detectable Change (MDC)

Osteoarthritis and Total Joint Replacement:

(Roos and Toksvig-Larsen, 2003; n = 105 patients with total knee replacements (39 males, 66 female); mean age = 71.3 (43-86) years, Osteoarthritis and Total Joint Replacement)

  • A change of 8-10 points may represent a minimal perceptible clinical improvement (MPCI)

Normative Data

Knee Osteoarthritis:

(Xie et al, 2006; n = 127 English and n = 131 Chinese speakers; mean age for English speakers = 65.3 (7.9), and Chinese speakers = 67.8 (7.1) years; BMI (English) 28.6 (5.4) and Chinese 27.8 (3.9);  mean duration of OA (English) 5.9 (5.6) and (Chinese) 6.1 (4.7) years; study conducted in Singapore)

Comparing knee OA between language groups:

 

 

 

Singapore English Version (n = 127)

 

 

 

KOOS Domain

Mean (SD)

Median

% Floor / Ceiling

Pain

57.0 (16.0)

58.3

0/0

Symptoms

59.8 (19.1)

60.7

0/0

ADL

60.8 (16.9)

64.7

0/0

Sport & Rec

6.6 (12.2)

0.0

66.9/0

QOL

39.6 (18.8)

43.8

3.1/0

 

 

 

 

 

Singapore Chinese Version (n = 131)

 

 

 

Pain

57.3 (12.9)

58.3

0/0

Symptoms

63.2 (17.8)

64.3

0/1.5

ADL

62.2 (13.0)

61.8

0/0

Sport & Rec

4.8 (9.4)

0.0

73.3/0

QOL

42.9 (19.4)

43.8

0/1.5

Test/Retest Reliability

Knee Osteoarthritis: (Xie et al, 2006)

 

Comparing knee OA between language groups:

 

 

Singapore English Version (n = 127)

 

 

KOOS Domain

Mean (SD)

Test-retest ICC

Pain

57.0 (16.0)

0.88

Symptoms

59.8 (19.1)

0.87

ADL

60.8 (16.9)

0.91

Sport & Rec

6.6 (12.2)

0.65

QOL

39.6 (18.8)

0.86

 

 

 

 

 

Singapore Chinese Version (n = 131)

 

 

Pain

57.3 (12.9)

0.87

Symptoms

63.2 (17.8)

0.85

ADL

62.2 (13.0)

0.84

Sport & Rec

4.8 (9.4)

0.78

QOL

42.9 (19.4)

0.60

Internal Consistency

Knee Osteoarthritis

(Xie et al, 2006, Knee Osteoarthritis)

 

Comparing knee OA between language groups:

 

 

Singapore English Version (n = 127)

 

 

KOOS Domain

Mean (SD)

Test-retest ICC

Pain

57.0 (16.0)

0.88

Symptoms

59.8 (19.1)

0.87

ADL

60.8 (16.9)

0.91

Sport & Rec

6.6 (12.2)

0.65

QOL

39.6 (18.8)

0.86

 

 

 

 

 

Singapore Chinese Version (n = 131)

 

 

Pain

57.3 (12.9)

0.87

Symptoms

63.2 (17.8)

0.85

ADL

62.2 (13.0)

0.84

Sport & Rec

4.8 (9.4)

0.78

QOL

42.9 (19.4)

0.60

Criterion Validity (Predictive/Concurrent)

Knee osteoarthritis:

(Thorund et al, 2010; n = 31; mean age = 46 (6) years; mean BMI = 26 (4) kg/m2; post surgery
21 (6) months; Danish sample, Knee osteoarthritis)

Patients versus control Knee Function:

  • Worse SF-36 Physical Functioning scores (p <0.001)
  • KOOS Activities of Daily Living score were significantly worse (p <0.001)
  • KOOS Sports Req scales were also significantly worse (p < 0.001)

Bibliography

Ahlden, M., Samuelsson, K., et al. (2012). "The Swedish National Anterior Cruciate Ligament Register: a report on baseline variables and outcomes of surgery for almost 18,000 patients." Am J Sports Med 40(10): 2230-2235. 

Argenson, J. N., Parratte, S., et al. (2008). "Patient-reported outcome correlates with knee function after a single-design mobile-bearing TKA." Clin Orthop Relat Res 466(11): 2669-2676. 

Bekkers, J. E., de Windt, T. S., et al. (2009). "Validation of the Knee Injury and Osteoarthritis Outcome Score (KOOS) for the treatment of focal cartilage lesions." Osteoarthritis Cartilage 17(11): 1434-1439.  

Engelhart, L., Nelson, L., et al. (2012). "Validation of the Knee Injury and Osteoarthritis Outcome Score subscales for patients with articular cartilage lesions of the knee." Am J Sports Med 40(10): 2264-2272. 

Hill, G. N. and O'Leary, S. T. (2012). "Anterior cruciate ligament reconstruction: the short-term recovery using the Knee Injury and Osteoarthritis Outcome Score (KOOS)." Knee Surg Sports Traumatol Arthrosc. 

Kvist, J., Ek, A., et al. (2005). "Fear of re-injury: a hindrance for returning to sports after anterior cruciate ligament reconstruction." Knee Surg Sports Traumatol Arthrosc 13(5): 393-397. 

Lohmander, L. S., Ostenberg, A., et al. (2004). "High prevalence of knee osteoarthritis, pain, and functional limitations in female soccer players twelve years after anterior cruciate ligament injury." Arthritis Rheum 50(10): 3145-3152. 

Ornetti, P., Parratte, S., et al. (2008). "Cross-cultural adaptation and validation of the French version of the Knee injury and Osteoarthritis Outcome Score (KOOS) in knee osteoarthritis patients." Osteoarthritis Cartilage 16(4): 423-428. 

Roos, E. M. and Dahlberg, L. (2005). "Positive effects of moderate exercise on glycosaminoglycan content in knee cartilage: A four‐month, randomized, controlled trial in patients at risk of osteoarthritis." Arthritis & Rheumatism 52(11): 3507-3514. 

Roos, E. M., Roos, H. P., et al. (1998). "Knee Injury and Osteoarthritis Outcome Score (KOOS)--development of a self-administered outcome measure." J Orthop Sports Phys Ther 28(2): 88-96. 

Roos, E. M. and Toksvig-Larsen, S. (2003). "Knee injury and Osteoarthritis Outcome Score (KOOS) - validation and comparison to the WOMAC in total knee replacement." Health Qual Life Outcomes 1: 17. 

Salavati, M., Akhbari, B., et al. (2011). "Knee injury and Osteoarthritis Outcome Score (KOOS); reliability and validity in competitive athletes after anterior cruciate ligament reconstruction." Osteoarthritis Cartilage 19(4): 406-410. 

Stevens-Lapsley, J. E., Schenkman, M. L., et al. (2011). "Comparison of self-reported knee injury and osteoarthritis outcome score to performance measures in patients after total knee arthroplasty." PM R 3(6): 541-549; quiz 549. 

Thorlund, J. B., Aagaard, P., et al. (2010). "Thigh muscle strength, functional capacity, and self-reported function in patients at high risk of knee osteoarthritis compared with controls." Arthritis Care Res (Hoboken) 62(9): 1244-1251. 

Tonelli, S. M., Rakel, B. A., et al. (2011). "Women with knee osteoarthritis have more pain and poorer function than men, but similar physical activity prior to total knee replacement." Biol Sex Differ 2: 12. 

Xie, F., Li, S. C., et al. (2006). "Cross-cultural adaptation and validation of Singapore English and Chinese versions of the Knee injury and Osteoarthritis Outcome Score (KOOS) in Asians with knee osteoarthritis in Singapore12." Osteoarthritis and Cartilage 14(11): 1098-1103.