- Email: [email protected]
A biomechanical knee scoring system
The Knee 1994; 1: 75-78
A biomechanical
knee scoring system
I A C Lennox’, D Williams*,
R Wytch*
‘Glasgow Western Infirmary, Glasgow, UK, *Department University, Aberdeen, UK
of Biomedical
Physics, Aberdeen
Summary This paper reports new measurements for parameters of knee function in both normal and osteoarthritic subjects. These values are used to devise a totally objective system for assessing knee function, based on four measurements: range of movement, quadriceps strength, step length and walking cadence. This test is simple to perform, noninvasive and reproducible. The system can be used to quantify any increase in function produced by treatment of a knee condition using parametric data upon which statistical analysis can be performed. The system has been used to calculate the knee score of 14 patients with symptomatic osteoarthritis and the scores are compared with subsequent intra-operative grading. (The Knee 1994; 1: 75-78) Key words: Osteoarthritis, knee, score, biomechanics
Introduction In order to assess a particular treatment, or compare different treatments for a knee condition, the severity of that condition must be measured both before and after treatment. This has previously been done by a method of pain scoring’; in order to improve these scoring systems, a functional questionnaire has been added as well as some objective knee function measurements2,“. These knee scoring systems have become increasingly complicated, but are still heavily weighted towards pain, and are therefore essentially subjective. The scales for subjective data are non-linear and not transferable between patients, which makes scientific analysis very difficult. These authors have devised an objective method of assessing knee function to quantify the benefits of treatment and monitor the natural history.
Methods The parameters of knee function included the following:
which were measured
- range of movement: flexion, lag, varus strain, valgus strain,
extension, extension physiological valgus
Accepted: January 1994 Correspondence and reprint requests to: Mr Iain Lennox, Infirmary, Glasgow, UK @ 1994 Butterworth-Heinemann 096%0160/94/0207544
Ltd
- walking: distance walked on a treadmill, speed, step length - quadriceps: strength, girth.
cadence,
The instruments used were calibrated and the techniques tested for accuracy and repeatability. The measurements were then performed on volunteers and on 14 patients with unilateral osteoarthritis (OA), subsequently proven at arthroscopy. The volunteers had an average age of 26 years (range 22-49 years) and were all asymptomatic, fit and healthy. The patients had an average age of 66 years (range 33-86 yearsg; there were six men and eight women. Each measurement was tested to see if the range of values was significantly different in the OA and ‘normal’ groups (P < 0.05). This was true of four measurements only: total range of movement, quadriceps strength ratio, cadence and step length (adjusted for height). These four measurements were expressed as a percentage of normal. The normal values were derived from the average values of the fit volunteers, or in the case of quadriceps, strength from the patient’s other knee. An average percentage of these four measurements was used to determine the ‘knee function score’ as a percentage of the expected normal. This score was an objective score upon which statistical analysis could be performed:
c/o Victoria
/ knee score =
R,
R,
Q,
~ +Q”+C”+z
C
S \
)- x
100 4
76
The Knee 1994; 1: No 2
where R, is the range of movement of the symptomatic knee, R, is the ‘normal’ range of knee movement, Q, is the quadriceps strength of the symptomatic knee, Q, is the quadriceps strength of the asymptomatic knee, C is the walking cadence, C,, is the normal cadence, S is the walking step length/height and S, is the normal step length/height. Instrumentation Range
with a long-arm
goniometer
with the
Gait analysis The gait pattern of the subjects was observed using a video vector system described by Begg et a14. Analysis of the videotape allowed walking speed, cadence (number of steps per minute) and step length measurements to be calculated.
of movement
The measurement of knee range of movement was recorded using a Penny & Giles electrogoniometer (Blackwood, UK). The measuring element is based on strain gauge technology and is housed within a spring which lies between two sliding end blocks. Movement of one end block relative to the other gives an output on the angle display unit. The electrogoniometer was attached laterally to the midline of the thigh and the leg using adhesive tape whilst the volunteer was standing erect. Tubigrip bandage sleeves were then applied over the end blocks. The subject was seated in an adjustable chair and the maximum range of active extension/ flexion was recorded. Penny & Giles electrogoniometers are pre-calibrated, but the accuracy and reproducibility of this device was confirmed by comparison with a plastic hand-held goniometer. Muscle
and was measured subject standing.
strength
Muscle strength was recorded using an MIE myometer (MIE Medical Research Ltd, Leeds, UK). A modified orthopaedic examination couch was used to seat the patient and to support the myometer. The couch had an adjustable backrest to accommodate all sizes and a seatbelt harness to restrain the subject from flexing at the hips, by restricting trunk movement. Velcro straps were attached to its rear legs and to the load cell beneath the couch, with the other end of the load cell attached to an ankle plate. With a subject seated on the couch, the backrest adjusted to give maximum support, and the ankle plate fitted to the front of the tibia, the subject extended his or her knee with maximum effort. This value was recorded on the digital myometer. All measurements were recorded on three occasions and the mean value calculated; adequate recovery time was allowed before starting each measurement. The system was calibrated before use according to the manufacturer’s instructions using standard masses (5 kg and 10 kg). Quadriceps
girth
The quadriceps girth was measured with the subject standing. A circumferential measurement 6 cm proximal to the patella was taken using a purpose-designed orthopaedic tape measure. Physiological
valgus
The physiological valgus angle of the knee is the angle the line of the femur makes with the line of the tibia
Results Range of movement The knee range of movement tests were performed on 18 normal healthy volunteers (Table 1). Ten were reassessed to confirm reproducibility (inter-observer error) of results and all values for flexion/extension were found to be within 5% of the original recordings. The values for extension lag were found to be within 3” of the original recordings, and the values for varus and valgus strains were found to be within 2” of the original recordings. There was no statistically significant difference between right and left legs (paired t-test, P < 0.05). The range of flexion/extension for 14 patients with unilateral OA of the knee (Table 1) showed that their movement was significantly less than normal, with a mean of 85” compared with 110” for the normal group (P < 0.05). The range of recordings for extension lag and varus/ valgus strains were not significantly different between the 14 OA patients and the normal volunteers. These tests were, therefore, not included in the subsequent knee function scoring system. Physiological valgus Physiological valgus in the normal group varied from 5” to lo”, with no measurable asymmetry; the higher values of 8”-10” were recorded with female subjects. This range of values agreed with the current literature5. In 14 patients with OA, three instances of asymmetry were observed, with a higher physiological valgus in the symptomatic knee but with a normal valgus angle in the asymptomatic knee. Quadriceps girth The quadriceps girth of 12 volunteers ratios of right/left calculated. On
was recorded reassessment
and the
Table 1. Flexion/extension
Control Number Average value (9 Standard deviation Range
18 110 3.5 103-118
OA 14 85 21.5 27-107
Lennox et al.: A biomechanical
values were found to be within 5% of the original recordings. The quadriceps girth ratio of the patient group with ‘symptomatic knee/asymptomatic knee’ had a similar mean but a greater range. However, the range of values was not significantly different between normal and OA subjects and this measurement was therefore not included in the knee scoring system.
Quadriceps
knee scoring system
77
Table 2. Quadriceps strength ratio
Number Average
Standard Range
deviation
Control
OA
27 1 0.1 0.82-I .I 3
14 0.61 0.3 0.08-I .o
strength
quadriceps strength test was carried out on 27 volunteers (Table 2). Ratios were taken of right/left leg to account for any drift within the load cell and display meter. Thirteen volunteers were subsequently reassessed and all ratios were found to be within 8% of the original recording. The quadriceps strength ratios for the patients with symptomatic knee/asymptomatic knee showed that the symptomatic knee strength is significantly reduced (P < 0.05), the OA group having a mean ratio of 0.61.
The
Table 3. Step length/height
and cadence
Number Step length/height Average Range Standard deviation Cadence (steps/min) Average Range Standard deviation
Control
OA
10
12
0.45 0.39-0.51 0.04
0.21 0.10-0.41 0.1
104 94-l 25 8.7
79 30-I 00 28
Gait analysis
Video vector recordings were made on 10 volunteers (seven male and three female) and their step length and cadence were determined (Table 3). Five volunteers were subsequently reassessed and their ‘step length/ height’ and cadence were found to be within 6% of the original recordings. The step length/height values given in Table 3 show that the value for the OA group was significantly lower than normal, with a mean of 0.21 compared with 0.45 for the normal group. Cadence was greatly reduced in the OA group, with a mean value of 79 compared with a normal mean value of 104 (P < 0.05). To verify this method of calculating step length and cadence from video recordings, five volunteer subjects were allowed 3 minutes on a treadmill and walking speeds were obtained for both methods. Walking speeds were found to differ by not more than 5%.
Discussion The 14 OA patients underwent arthroscopy of their symptomatic knee. At this time the diagnosis was confirmed and the OA was graded by a consultant orthopaedic surgeon who had no knowledge of the patients’ symptoms or knee scores. The knees were graded as: - mild: wear of articular cartilage - severe: destruction of the articular bone.
cartilage
to
Table 4 demonstrates that there is good correlation between the knee score and subsequent intra-operative grading of the arthritis. This correlation between knee score and joint pathology is not absolute, as that would not allow for improvement of knee score with treatment, for a given knee pathology. Patients with bilateral knee pathology will have bilateral quadriceps
Table 4. Correlation operative
between
objective
Average
knee score
knee score and
grade
Grade Normal Mild (n = 9) Severe (n = 5)
100 81 51
Range 92.4-l 07.6 65.5-93.3 22.9-64.8
deficiency and thus their quadriceps ratio and consequently their knee score will be higher than those of a patient with unilateral pathology. However, improvement can be measured in patients with bilateral pathology and this improvement can be compared with that seen in patients with unilateral pathology; absolute scores, however, cannot be compared. The quadriceps strength measurement is a comparison with the other side and so is age- and sexindependent. The step length measurement is divided by body height and so is sex-independent. Cadence is sex-dependent, but using a correction factor to compensate for female cadence resulted in such a small difference to the final knee score that it was not considered worthwhile. Total range of knee movement in a healthy asymptomatic knee is not age-dependent. The normal value is defined as that expected in a young fit arthritis-free adult and is used as a standard against which patients can be judged, not as a goal for treatment. The absolute knee score will give an idea of how disabled the patient is, but the real value of the system is in looking at the improvement of knee score with treatment. When calculating the percentage improvement, each patient acted here as his or her own control and thus reasons for a poor knee score other than knee disease such as hip and foot pathology are eliminattd.
78
The Knee 1994; 1: No 2
Conclusion
References
A simple
1
and reproducible method of assessing knee function has been devised, relying on only four objective measurements. The knee score produced can be used to measure improvement in knee function and
assess various forms of treatment in patients, without the inherent difficulties of using non-linear scales and subjective measurements. The cost of the instrumentation to measure these parameters is reasonably modest. This knee score has been used to evaluate unilateral OA but there is no reason why it cannot be used to assess a range of knee pathologies.
Crosby EB, Insall J. Recurrent dislocation of the patella. J Bone Joint Surg [Am] 1976;
2
3
%A: 9-12
Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on the use of a scoring scale. Am J Sports Med 1982; 10: 1.50-4 Aichroth PM, Freeman MAR, Smille IS, Souter WA. A knee function assessment chart. J Bone Joint Surg [Br] 1978; 60B: 308-9
4
5
Begg RK, Wytch R, Major RE. A microcomputer based video vector system for clinical gait analysis. J Biomed Eng 1990; 12(5): 383-8 Kapandji IA. The Physiology of the Joints, Vol. 2.
Edinburgh:
Churchill Livingstone,
1987: 66-70
Electronic submission on disk In response to technical advances and in recognition of the widespread use of computers for text
origination, the Publishers and Editors of The Knee are encouraging submissions on disk. Use of your disk will retain the integrity of the text, minimize the introduction of literal errors during typesetting, and thus reduce the time needed to proofread the material.
L!
Submit to the Editor only the final accepted version of both the manuscript and the electronic version on disk. All amendments or revisions made during the refereeing process should be incorporated. The hard copy and electronic files must match exactly.
The text should be saved as a word processor file in IBM compatible MSDOS or Macintosh format. If you have the facility to save as ASCII file(s), please also make a copy in this format.
Present your manuscript as simply as possible. Complex formatting will take up more of your time and will also complicate and delay the production process.
For further information and full guidelines, please contact: Ihe Knee, c/o Medical Journals Group, Butterworth-Heinem, Linacre House, Jordan Hill, Oxford OX2 SDP, UK. Tel: +44 (0)865 310366. Fax: +44 CO)865 310898.
A biomechanical
knee scoring system
I A C Lennox’, D Williams*,
R Wytch*
‘Glasgow Western Infirmary, Glasgow, UK, *Department University, Aberdeen, UK
of Biomedical
Physics, Aberdeen
Summary This paper reports new measurements for parameters of knee function in both normal and osteoarthritic subjects. These values are used to devise a totally objective system for assessing knee function, based on four measurements: range of movement, quadriceps strength, step length and walking cadence. This test is simple to perform, noninvasive and reproducible. The system can be used to quantify any increase in function produced by treatment of a knee condition using parametric data upon which statistical analysis can be performed. The system has been used to calculate the knee score of 14 patients with symptomatic osteoarthritis and the scores are compared with subsequent intra-operative grading. (The Knee 1994; 1: 75-78) Key words: Osteoarthritis, knee, score, biomechanics
Introduction In order to assess a particular treatment, or compare different treatments for a knee condition, the severity of that condition must be measured both before and after treatment. This has previously been done by a method of pain scoring’; in order to improve these scoring systems, a functional questionnaire has been added as well as some objective knee function measurements2,“. These knee scoring systems have become increasingly complicated, but are still heavily weighted towards pain, and are therefore essentially subjective. The scales for subjective data are non-linear and not transferable between patients, which makes scientific analysis very difficult. These authors have devised an objective method of assessing knee function to quantify the benefits of treatment and monitor the natural history.
Methods The parameters of knee function included the following:
which were measured
- range of movement: flexion, lag, varus strain, valgus strain,
extension, extension physiological valgus
Accepted: January 1994 Correspondence and reprint requests to: Mr Iain Lennox, Infirmary, Glasgow, UK @ 1994 Butterworth-Heinemann 096%0160/94/0207544
Ltd
- walking: distance walked on a treadmill, speed, step length - quadriceps: strength, girth.
cadence,
The instruments used were calibrated and the techniques tested for accuracy and repeatability. The measurements were then performed on volunteers and on 14 patients with unilateral osteoarthritis (OA), subsequently proven at arthroscopy. The volunteers had an average age of 26 years (range 22-49 years) and were all asymptomatic, fit and healthy. The patients had an average age of 66 years (range 33-86 yearsg; there were six men and eight women. Each measurement was tested to see if the range of values was significantly different in the OA and ‘normal’ groups (P < 0.05). This was true of four measurements only: total range of movement, quadriceps strength ratio, cadence and step length (adjusted for height). These four measurements were expressed as a percentage of normal. The normal values were derived from the average values of the fit volunteers, or in the case of quadriceps, strength from the patient’s other knee. An average percentage of these four measurements was used to determine the ‘knee function score’ as a percentage of the expected normal. This score was an objective score upon which statistical analysis could be performed:
c/o Victoria
/ knee score =
R,
R,
Q,
~ +Q”+C”+z
C
S \
)- x
100 4
76
The Knee 1994; 1: No 2
where R, is the range of movement of the symptomatic knee, R, is the ‘normal’ range of knee movement, Q, is the quadriceps strength of the symptomatic knee, Q, is the quadriceps strength of the asymptomatic knee, C is the walking cadence, C,, is the normal cadence, S is the walking step length/height and S, is the normal step length/height. Instrumentation Range
with a long-arm
goniometer
with the
Gait analysis The gait pattern of the subjects was observed using a video vector system described by Begg et a14. Analysis of the videotape allowed walking speed, cadence (number of steps per minute) and step length measurements to be calculated.
of movement
The measurement of knee range of movement was recorded using a Penny & Giles electrogoniometer (Blackwood, UK). The measuring element is based on strain gauge technology and is housed within a spring which lies between two sliding end blocks. Movement of one end block relative to the other gives an output on the angle display unit. The electrogoniometer was attached laterally to the midline of the thigh and the leg using adhesive tape whilst the volunteer was standing erect. Tubigrip bandage sleeves were then applied over the end blocks. The subject was seated in an adjustable chair and the maximum range of active extension/ flexion was recorded. Penny & Giles electrogoniometers are pre-calibrated, but the accuracy and reproducibility of this device was confirmed by comparison with a plastic hand-held goniometer. Muscle
and was measured subject standing.
strength
Muscle strength was recorded using an MIE myometer (MIE Medical Research Ltd, Leeds, UK). A modified orthopaedic examination couch was used to seat the patient and to support the myometer. The couch had an adjustable backrest to accommodate all sizes and a seatbelt harness to restrain the subject from flexing at the hips, by restricting trunk movement. Velcro straps were attached to its rear legs and to the load cell beneath the couch, with the other end of the load cell attached to an ankle plate. With a subject seated on the couch, the backrest adjusted to give maximum support, and the ankle plate fitted to the front of the tibia, the subject extended his or her knee with maximum effort. This value was recorded on the digital myometer. All measurements were recorded on three occasions and the mean value calculated; adequate recovery time was allowed before starting each measurement. The system was calibrated before use according to the manufacturer’s instructions using standard masses (5 kg and 10 kg). Quadriceps
girth
The quadriceps girth was measured with the subject standing. A circumferential measurement 6 cm proximal to the patella was taken using a purpose-designed orthopaedic tape measure. Physiological
valgus
The physiological valgus angle of the knee is the angle the line of the femur makes with the line of the tibia
Results Range of movement The knee range of movement tests were performed on 18 normal healthy volunteers (Table 1). Ten were reassessed to confirm reproducibility (inter-observer error) of results and all values for flexion/extension were found to be within 5% of the original recordings. The values for extension lag were found to be within 3” of the original recordings, and the values for varus and valgus strains were found to be within 2” of the original recordings. There was no statistically significant difference between right and left legs (paired t-test, P < 0.05). The range of flexion/extension for 14 patients with unilateral OA of the knee (Table 1) showed that their movement was significantly less than normal, with a mean of 85” compared with 110” for the normal group (P < 0.05). The range of recordings for extension lag and varus/ valgus strains were not significantly different between the 14 OA patients and the normal volunteers. These tests were, therefore, not included in the subsequent knee function scoring system. Physiological valgus Physiological valgus in the normal group varied from 5” to lo”, with no measurable asymmetry; the higher values of 8”-10” were recorded with female subjects. This range of values agreed with the current literature5. In 14 patients with OA, three instances of asymmetry were observed, with a higher physiological valgus in the symptomatic knee but with a normal valgus angle in the asymptomatic knee. Quadriceps girth The quadriceps girth of 12 volunteers ratios of right/left calculated. On
was recorded reassessment
and the
Table 1. Flexion/extension
Control Number Average value (9 Standard deviation Range
18 110 3.5 103-118
OA 14 85 21.5 27-107
Lennox et al.: A biomechanical
values were found to be within 5% of the original recordings. The quadriceps girth ratio of the patient group with ‘symptomatic knee/asymptomatic knee’ had a similar mean but a greater range. However, the range of values was not significantly different between normal and OA subjects and this measurement was therefore not included in the knee scoring system.
Quadriceps
knee scoring system
77
Table 2. Quadriceps strength ratio
Number Average
Standard Range
deviation
Control
OA
27 1 0.1 0.82-I .I 3
14 0.61 0.3 0.08-I .o
strength
quadriceps strength test was carried out on 27 volunteers (Table 2). Ratios were taken of right/left leg to account for any drift within the load cell and display meter. Thirteen volunteers were subsequently reassessed and all ratios were found to be within 8% of the original recording. The quadriceps strength ratios for the patients with symptomatic knee/asymptomatic knee showed that the symptomatic knee strength is significantly reduced (P < 0.05), the OA group having a mean ratio of 0.61.
The
Table 3. Step length/height
and cadence
Number Step length/height Average Range Standard deviation Cadence (steps/min) Average Range Standard deviation
Control
OA
10
12
0.45 0.39-0.51 0.04
0.21 0.10-0.41 0.1
104 94-l 25 8.7
79 30-I 00 28
Gait analysis
Video vector recordings were made on 10 volunteers (seven male and three female) and their step length and cadence were determined (Table 3). Five volunteers were subsequently reassessed and their ‘step length/ height’ and cadence were found to be within 6% of the original recordings. The step length/height values given in Table 3 show that the value for the OA group was significantly lower than normal, with a mean of 0.21 compared with 0.45 for the normal group. Cadence was greatly reduced in the OA group, with a mean value of 79 compared with a normal mean value of 104 (P < 0.05). To verify this method of calculating step length and cadence from video recordings, five volunteer subjects were allowed 3 minutes on a treadmill and walking speeds were obtained for both methods. Walking speeds were found to differ by not more than 5%.
Discussion The 14 OA patients underwent arthroscopy of their symptomatic knee. At this time the diagnosis was confirmed and the OA was graded by a consultant orthopaedic surgeon who had no knowledge of the patients’ symptoms or knee scores. The knees were graded as: - mild: wear of articular cartilage - severe: destruction of the articular bone.
cartilage
to
Table 4 demonstrates that there is good correlation between the knee score and subsequent intra-operative grading of the arthritis. This correlation between knee score and joint pathology is not absolute, as that would not allow for improvement of knee score with treatment, for a given knee pathology. Patients with bilateral knee pathology will have bilateral quadriceps
Table 4. Correlation operative
between
objective
Average
knee score
knee score and
grade
Grade Normal Mild (n = 9) Severe (n = 5)
100 81 51
Range 92.4-l 07.6 65.5-93.3 22.9-64.8
deficiency and thus their quadriceps ratio and consequently their knee score will be higher than those of a patient with unilateral pathology. However, improvement can be measured in patients with bilateral pathology and this improvement can be compared with that seen in patients with unilateral pathology; absolute scores, however, cannot be compared. The quadriceps strength measurement is a comparison with the other side and so is age- and sexindependent. The step length measurement is divided by body height and so is sex-independent. Cadence is sex-dependent, but using a correction factor to compensate for female cadence resulted in such a small difference to the final knee score that it was not considered worthwhile. Total range of knee movement in a healthy asymptomatic knee is not age-dependent. The normal value is defined as that expected in a young fit arthritis-free adult and is used as a standard against which patients can be judged, not as a goal for treatment. The absolute knee score will give an idea of how disabled the patient is, but the real value of the system is in looking at the improvement of knee score with treatment. When calculating the percentage improvement, each patient acted here as his or her own control and thus reasons for a poor knee score other than knee disease such as hip and foot pathology are eliminattd.
78
The Knee 1994; 1: No 2
Conclusion
References
A simple
1
and reproducible method of assessing knee function has been devised, relying on only four objective measurements. The knee score produced can be used to measure improvement in knee function and
assess various forms of treatment in patients, without the inherent difficulties of using non-linear scales and subjective measurements. The cost of the instrumentation to measure these parameters is reasonably modest. This knee score has been used to evaluate unilateral OA but there is no reason why it cannot be used to assess a range of knee pathologies.
Crosby EB, Insall J. Recurrent dislocation of the patella. J Bone Joint Surg [Am] 1976;
2
3
%A: 9-12
Lysholm J, Gillquist J. Evaluation of knee ligament surgery results with special emphasis on the use of a scoring scale. Am J Sports Med 1982; 10: 1.50-4 Aichroth PM, Freeman MAR, Smille IS, Souter WA. A knee function assessment chart. J Bone Joint Surg [Br] 1978; 60B: 308-9
4
5
Begg RK, Wytch R, Major RE. A microcomputer based video vector system for clinical gait analysis. J Biomed Eng 1990; 12(5): 383-8 Kapandji IA. The Physiology of the Joints, Vol. 2.
Edinburgh:
Churchill Livingstone,
1987: 66-70
Electronic submission on disk In response to technical advances and in recognition of the widespread use of computers for text
origination, the Publishers and Editors of The Knee are encouraging submissions on disk. Use of your disk will retain the integrity of the text, minimize the introduction of literal errors during typesetting, and thus reduce the time needed to proofread the material.
L!
Submit to the Editor only the final accepted version of both the manuscript and the electronic version on disk. All amendments or revisions made during the refereeing process should be incorporated. The hard copy and electronic files must match exactly.
The text should be saved as a word processor file in IBM compatible MSDOS or Macintosh format. If you have the facility to save as ASCII file(s), please also make a copy in this format.
Present your manuscript as simply as possible. Complex formatting will take up more of your time and will also complicate and delay the production process.
For further information and full guidelines, please contact: Ihe Knee, c/o Medical Journals Group, Butterworth-Heinem, Linacre House, Jordan Hill, Oxford OX2 SDP, UK. Tel: +44 (0)865 310366. Fax: +44 CO)865 310898.