AN ISOMETRIC NORMATIVE DATABASE TO FACILITATE RESTORATION OF FUNCTION IN KNEE-INJURED ACTIVE YOUNG ADULTS Professor J Charteris* INTRODUCTION Few physiotherapists in South Africa can afford the expense of sophisticated isokinetic dynamometers for measuring muscular strength increments during rehabilitation, or the time to interpret the subtleties o f muscle dynamics revealed by these technologies. The reality o f the situation, for the vast majority of patients able to get physiotherapy at all, is that subjective clinical assessments most often determine rehabilitation steps and the termination of services to the client. At best, simple though effective isometric or isotonic testing guide these clinical judgements. For the foreseeable future in South Africa, we are facing increasing demands for medical and allied medical services, with decreasing expectation of expensive, state-of- the-art technological support. This need not necessarily be viewed with dismay; recent evidence increasingly supports the view that the older, simpler, methods o f gaining (and assessing) strength, when implemented with expertise, may be as effective as more sophisti­ cated methods1. MErHODS Thirty-five males and 35 females with no history of knee injury were selected from a group of normal active young adults. While seated, the subjects were requested to make maximal isometric efforts of knee extension and flexion against a wall-mounted steel cable, chain-linked to a precision strain-gauge (MIE system**) coupled to a micro-processor. The subject is braced in a seated position over a plinth, the knee flexed 90fi. Maximal isometric extensions (or flexions) are made in this position, putting tension on a steel cable via a suitably padded strap around the leg. Movement is impossible but muscular efforts put tension on the cable and the interfaced strain gauge reads the force produced. Since this force will vary depending on the leverage involved the perpendicular distance from the knee joint centre to the cable is carefully measured and captured on the computer. There­ after the product o f force generated and lever-arm distance is com­ puted automatically to yield torque curves for extension and flexion. For present purposes only maximal torques generated were o f inter­ est (See Table I). At the same time subjects were asked to identify their “dominant” lower extremity, in order to test their perception of “dominance” against actually measured “dominance”. For this study “dominant” was defined as the isometrically deter­ mined stronger, and “non-dominant” as the contralateral weaker limb in terms of knee extensor and flexor capability. RESULTS Neither sex showed significant isometric torque differences be­ tween right and left limbs, for either extensors or flexors. Despite there being a dominant limb in terms o f strength in each individual case, sufficient left-dominant individuals were present to obliterate a left-right difference. Thus left-right differences were within 2%, for both sexes and for extensor and flexor torques. However, when absolute strength dominance (irrespective or left-right relationship) was measured, the differences were significant (Table I). Males and females responded very similarly in respect o f these levels o f dif­ ference, suggesting that there is no sex-related factor in contralateral (Q/Q; H/H) asymmetry ratios. This is depicted in Figure 1. lO O q ----1 ---- 1 ---- 1 — | - — 88 9 0 — 88 5 0 - D N D N D N D N MALE FEMALE MALE FEMALE EXTENSORS FLEXORS FIGURE 1: Dominant/Non-Dominant Ratios for seated isome­ tric knee extensor and flexor torques. In respect of knee isometric strength in the test position (90° hip and knee flexion; seated), the less-strong (non-dominant) extensor (x 242; ± 62 Nm) produced tension at 88% of that of the stronger (dominant) extensor (x 275; ± 68 Nm) in the case of the males. There was marginally less contralateral asymmetry in the females, the level being 90%. Participation in one-sided activities may account for much of the asymmetry o f tension development routinely shown in the results of strength testing on large numbers2. Similarly, when the non-dominant flexor mean was compared with the dominant, the asymmetry level was about 91% for both sexes. These data suggest that, regardless o f sex or the muscle group under investigation, isometric contralateral asymmetries (non-domi­ nant: dominant) are close to 90% under these conditions (Table I). In all cases there were significant differences between measured (MDR) and perceived (PDR) contralateral dominance ratios, and between MDR and right/left (RL) ratios, but not between PDR and RL ratios (see Table I). In other words, since most subjects perceived their right limbs to be stronger, PDR and RL were the same. However, the limb perceived to be dominant was (in terms of isometric torque generated) actually weaker in a sufficient number of cases for there to be no congruence between PDR and MDR. The implication of the significant difference between PDR and MDR is that reliance should not be placed on patient’s reports of dominance in cases where the therapist is attempting to find out whether an injured knee is the normally stronger or weaker of the two joints. Under any test conditions normal subjects have stronger knee extensor than flexor mechanisms. This is borne out in the extensor (Q) to flexor (H), or ipsilateral quadriceps-to-hamstring ratios (Table II). These ratios are movement-speed specific7,8, but under the isometric conditions imposed here the combined-limb Q/H ratio ABSTRACT Prohibitive costs technologically advanced dynamometers need not dissuade rehabllitationists from making useful as­ sessments of musculo-skeletal performance in clinical set­ tings. The use of simple strain-gauge measures of isometric torque is demonstrated using knee flexor-extensor capacities, dominance ratios, contralateral asymmetries and sexual di­ morphism ratios. Functional restoration of knee-injured active young adults, using normative charts as a data base, is a cheap and feasible option. * Rehabilitation Research Unit, Department o f Human Movement Studies, Rhodes University ** MIE Medical Research Limited, 6 Worthey Moor Road, Leeds Bladsy 28 Fisioterapie, Mei 1993 Peel 49 no 2 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Male Female TABLE i: SEATED ISOMETRIC TORQUES (Nm) OF KNEE EXTENSORS AND FLEXORS QUADRICEPS (Q) Male Female Dominant (Nm) Non- Dominant (Nm) Right (Nm) Left (Nm) CONTRALATERAL DOMINANCE RATIOS Q/Q Measured (MDR) Perceived (PDR) Right/Left (RL) I 275 (68) 'I 242 (62) r - - - 257 (72) ---------1 260 (63) i 1.14(0.11) [88%] ii ------ 1.00(0.16) [100%] ” • 1 1 1.00(0.16) [101%] I 130 (21) ■| 117 (21) r 122 (23) ~ “1 124 (21) 1 1 1.11(0.12) [90%] ------- 1 l----------- 0.98(0.15) [102%] - " I 1 0.98(0.14) [102%] HAMSTRINGS Dominant (Nm) Non- Dominant (Nm) Right (Nm) Left (Nm) DOMINANCE RATIOS H/H Measured (MDR) Perceived (PDR) Right/Left (RL) 152 (38) 1 134 (34) \ 145 (36) 142 (36) ' 1-------- 1.13(0.06) [88%] ----1 i- 1.04(0.09) [96%] — i 1 1.02(0.09) [98%] i 72 (12) i 66 (12) r~ 70 (12) n 69 (11) 1 1 1.09(0.07) [92%] '■ i i----- 1.00(0.10) [100%] ~1 1 1.01(0.10) [99%] NOTE: Solid link (---;— ) denotes significant differences (p < 0.05) Broken-link (----- ) indicates no significant difference Standard Deviations in parentheses. Reciprocal of ratio, (%), in square brackets. (both sexes) was 1.78. Taking the reciprocal, this means that ham­ strings were 56% as strong, isometrically, as quadriceps, which is in very close agreement with values reported in recent literature7,8. While knowledge o f normal Q/H ratios is critical for therapy to be meaningfully applied, misunderstanding of the ratio is common, and potentially harmful, (see discussion). In the present study useful data on agonist/antagonist ratios were revealed which, if used correctly, are of real clinical significance. Figure 2 shows that, regardless o f sex or dominance or limb side, the flexor/extensor torques were insigni­ ficantly spread around 0.56. TABLE U S IPSILATERAL (Q :H) DOMINANCE RATIOS. Dominant Non-Dominant Right Left LI KBS COMBINED 1.65 1.75 1.77 1.63 1.76 [541] [57%] [56%] [55%] [56%] 1 .81 1.75 1.74 1.80 1.78 [551) (57%) (57%) [56%] [56%] NOTE: Reciprocal of ratio, (i.e. H/Q ratio) as t, in square brackets. Sexual dimorphism in strength expression is revealed in these results (Table III). Again the picture was consistent, whether com­ paring extensors or flexors o f either dominant or non-dominant limbs: the females were, effectively, 48% as strong as the males under these test conditions. Figure 3 shows how small the band of variability is around this sex-based differences. TABLE Ills SEXUAL DIMORPHISM (Reciprocal in Brackets) QUADRICEPS HAMSTRINGS M/F Dominant M/F Non-Dominant M/F Dominant M/F Non-Dominant r ----- 1 r n 2.12 2.07 2.07 2.06 (47.3%) (48.3%) (48.3%) (48.6%) M/F x 2 09 (47.7%) M/F X 2.07 (48.4%) QUADRICEPS HAMSTRINGS F / M O J* 00 1 1 1 l 1 r i T D N D N FIGURE 2: Deviation of mean values in H/Q Ratios Dominant (D); non-dominant (N); right (R); left (L) and combined right and left (R + L) flexor-to-extensor ratios, about the overall mean value of 56. Left-most value in each pair is male; right value in each pair is female FIGURE 3: Deviation of mean values in Sexual Dimorphism of isometric torque. Mean female/male (F/M) ratio is depicted as a horizontal band. Vertical bars show domi­ nant (D) and non-dominant (N) mean deviations for quadriceps and hamstrings. Cleariy these are insignificantly spread about the overall F/M mean o f 0.48 in the case of nor­ mal active young adults under these test conditions. A 6-sigma table of Standard Scores was constructed from the dominant and non-dominant mean and standard deviation data, for extensors and flexors of the knee and for both sexes. This provides (Table IV) a useful guide to therapists concerned in increasing strength while ensuring normal agonist/antagonist ratios and remain­ ing within acceptable contralateral asymmetry levels. 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DURBAN 4000 Tel: (031) 37-1501 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) TABLE IV : NORMATIVE (Standard Score) TABLE For Seated Isometric Knee Extensor and Flexor Torques ASSIGNED RATING STANDARD SCORE ISOMETRIC MAXIMUM TORQUE (ND) MALES FEMALES EXTENSOR FLEXOR EXTENSOR FLEXOR DOM N/D DOM N/D DOM N/D DOM N/D 100 480 427 266 236 195 182 108 103 95 459 408 255 226 189 176 104 99 EXCELLENT 90 439 390 243 216 182 169 101 96 85 418 371 232 205 176 163 97 92 80 398 353 220 195 169 156 94 89 75 377 334 209 185 163 150 90 85 GOOD 70 357 316 198 175 156 143 86 81 65 336 297 186 165 150 137 83 78 60 316 279 175 154 143 130 79 74 55 295 260 163 144 137 124 76 71 AVERAGE 50 275 242 152 134 130 117 72 66 45 254 223 141 124 124 111 68 63 40 234 205 129 114 117 104 65 60 35 213 186 118 103 ; n 98 61 56 POOR 30 193 168 106 93 104 91 58 53 25 172 149 95 83 98 85 54 49 20 152 131 84 73 91 78 50 45 15 131 112 72 63 85 .72 47 42 DEFICIENT 10 111 94 61 52 78 65 43 38 5 90 75 49 42 72 59 40 35 0 70 57 38 32 65 52 36 31 In using this scale it is important to keep in mind the sample upon which it was based, viz. normal, healthyyoung adults without history of knee injury. Thus certain patients may be so weak as not to be recordable on the standard score table. The concern of the present paper, however, is with restoration of normal knee function at a stage when the client is ready to benefit from an active-resistive exercise regimen. DISCUSSION It is sometimes implied that a particular H/Q ratio is advant­ ageous for or required by, a particular activity: e.g., that; “long distance runners need a hamstring-to-quadriceps ratio of 0.60”3. Several authors have found, in specific instances, a ratio of 0.60 for hamstring-to-quadriceps torque as Nunn and Mayhew (1988)1 suggest, but others have found ranges o f variability between 0.43 and 0.90 for the same ipsilateral muscle imbalance between hamstring and quadriceps4. In fact there is no fixed agonist/antagonist knee ratio for humans, or specific groups, or even individuals: the ham­ string-to-quadriceps (H/Q) ratio is an arithmetic calculation done on situation-specific data obtained in diverse ways and it varies with sex. age, state of training, body position, and velocity of motion.5,6,7’*’ The ubiquitous force-velocity relationship applies, such that the H/Q ratio increases as velocity increases because, while both extensor and flexor torques drop with speed increments, that of the quadriceps drops at a faster rate5,6,7. Worrell and co-workers (1990)8 demon­ strated sex-based differences in this ratio and lower H/Q values when supine than when seated, probably because of a robbed length-ten- sion relationship o f the hamstrings in the supine position9. The present results are specific to seated 90E flexion isometric knee torques. It is fundamentally naive to fix torque values, bilateral asymmetries, agonist/antagonist ratios and sexual dimorphism in­ dices, determined by any single technique, as if these were situation- exclusive. For instance, claims that H/Q ratios “are”, or “should be” some value which can be rote-learned and applied in all situations are invalid: the normal H/Q ratio is a value that alters within each individual when tested isometrically versus isokinetically (where it is clearly a speed-dependent relationship). The findings of the present study must be seen in this context: they are generalisable with caution, being relative to active young adults tested isometrically in the same seated position. Used as guidelines by the discerning therapist they should be useful in planning the on-going course o f rehabilitation or of asymmetry reduction in other­ wise unimpaired young adults who aspire to active lifestyles without undue risk of injury/re-injury of the knees. CLINICAL APPLICATION In respect o f the normative data presented in Tables I to IV the question arises whether subjects with a history o f knee impairment would be easily identified by their residual weaknesses and muscular imbalances, and whether the identified deficiencies provide gui­ delines as to what could be done to restore optimal function. Four case histories are presented to indicate the extent o f weakness or imbalance, and to suggest a plan of action for restoration of normal levels o f performance. It is clearly not the purpose of this paper to prescribe any particu­ lar rehabilitation protocol to be followed. The present concern is whether simple seated isometric test results, in the form presented, can provide sufficient feedback.to enable the therapist to achieve requisite strength increments and symmetries in knee-injured active young adults. Case Number One Subject TB (Female): Femoral Fracture (R), 12 months previously. Presenting Asymmetries This subject exhibits an essentially normal seated isometric H/Q ratio of 0.63 on the surgically-treated (right) side but not on the unaffected (left) side. This apparent anomaly is due to the fact that the extensors and the flexors on the impaired side have lost strength concomitantly, without the ratio being shifted outside normal limits (Figure 4). FIGURE 4: Clinically significant deviations in seated isometric H/Q ratios. Normal mean H/Q ratio is 0.56 ( ± 0.07) as depicted by horizontal band. Solid vertical bars depict aberrant right H/Q ratios; broken vertical bare show left H/Q ratios o f the same subjects. The H:Q ratio on the unaffected (left) side, however, is 0.46, which is more than one SD below the mean and is due to a left hamstring torque of 60 Nm which is “poor” for a dominant limb. One might conjecture that postural and locomotor strategies adopted to move about with a surgically repaired right limb may have involved extensions on the unaffected side which kept the extensors relatively Physiotherapy, May 1993 Vol 49 no 2 Page 31 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) PHYSICAL AND OCCUPATIONAL THERAPISTS Hundreds of positions available immediately, in any state — Florida, Texas, New England. . . "When I called Medical Resources International, I got a job immediately — within two days. I couldn't believe it. Especially since I had waited sever­ al months for another agency to place me." —fosee Simard M edical Resources Interna­ tional can place you in any specialty in any part of the United States — at $35,000 to $60,000 a year. And you get ser­ vices no other company provides. Your licensure and credentialing fees are fully paid. 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Main SL Fairfield, IA 52556 U.S.A. ■ Fax (515) 472-1897 Must have good com m and o f the English language R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) well conditioned while the hamstrings underwent some degree of disuse atrophy. Be that as it may, the sub-optimal H:Q ratio in this particular case does not point to the injured limb but rather to the contralateral side, suggesting that neither absolute torque values alone or agonist/antagonist ratios alone can be relied on to give the clinical picture: a general functional overview is necessary. However, the contralateral Q:Q and H:H ratios are very reveal­ ing. The normal Q:Q ratio is located between 0.85 and 1.15 with a mean essentially 1.00. Similarly the normal H:H ratio is somewhere between 0.97 and 1.13. Figure 5 shows that subject TB has a Q:Q ratio of 1.85 (left-dominant) which indicates the extent to which the deficient right knee extensors need to be rehabilitated to reduce bilateral asymmetry. This subject also exhibits an H:H ratio of 1.33 (left-dominant) indicating the extent to which the right knee flexors need strengthening. FIGURE 5: Clinically significant deviations in contralateral (Q/Q; H/H) ratios. Figure 6 indicates the “distance” the right extensors must go to be within one SD of the permissible difference: in patient TB the right quadriceps exhibit 54% of left quadriceps torque and should be over 86% as strong to be within acceptable ranges of difference. Rehabilitative Implications The above profile implies a need to strengthen the right knee extensor mechanism at a rate twice that at which the right flexor mechanism is strengthened (See Figure 6). The intervention goal is to increment strength as follows using the normative Standard Score Chart: Right quadriceps, by 46 Nm to 117 Nm; Right hamstrings, by 21 Nm to 66 Nm; Left hamstrings by 12 Nm to 72 Nm; Left quadriceps to remain essentially unaltered. The aim should be to increment strength at relative ratios o f RQ: RH: LH = 4 : 2 : 1 , per unit time. This would, in due course, result in a balanced achievement of average strength values, acceptably normal contralateral asymmetry (Q:Q; H:H) levels and normal ipsi- lateral (H/Q left; H/Q right) agonist/antagonist asymmetry ratios. Case Number Two Subject AB (Female): Bilateral Knee Surgery, 48 months previously. Presenting Asymmetries This subject has exceedingly weak knee extensors and very weak flexors and also has stronger left quadriceps and right hamstrings. Figure 4 highlights the motor impairment of this subject, in which the left H/Q ratio is an acceptable 0,67, while the right H/Q ratio is 1.09 (stronger flexors than extensors). What should be a 1.0 Q:Q ratio is in fact 1.47, but the H:H ratio is normal, even though both hamstring groups rate “poor” in abso­ lute strength (Figure 5). Rehabilitative Implications Clearly subject AB has about the same “distance” to go to bring right quadriceps and left hamstrings to within an acceptable approxi­ mation of their contralateral counterparts (Figure 6). CONTRALATERAL SYMMETRY LEVEL .____________J% )_______________ , FIGURE 6: Clinically significant defects of the weaker knee, in percent of the stronger in selected cases. Shaded bar depicts weaker quadriceps, in percent of stronger. Open bar depicts weaker hamstrings. Permissible deviations (le. normal asymmetry levels) are indicated by solid blocks on right. Width of gaps indicates extent of abnormal asymmetry. The rehabilita­ tive goal is to close these gaps. This should take precedence in the attempt to lift the absolute strength values on both sides to more acceptable levels. Using the normative Standard Score Chart (Table IV) the intervention goal is as follows: R Q : L Q : L H : RH = 2 :1 .5 : 1 : 1 , per unit time Case Number Three Subject KH (Male): Arthroscopic Meniscectory (R), 24 months previously. Presenting Asymmetries Here is a case in which, following meniscectomy (R) the Q:Q ratio, which should be 1.0, is too high at 1.21, the affected knee not having regained as much extensor strength as would be optimal. Consistent with this relatively reduced right knee extensor strength, (even though in absolute values it is “average”), the right flexor strength is too great for an optimal balance. Figure 4 shows a right H/Q ratio two SD higher than the mean for seated isometric torques, and a left H/Q ratio that is normal. In this subject, as in the previous two, a distinct imbalance exists between left and right H/Q ratios (0.52 vs 0.71). While this difference is nowhere near as great as that in the case of subject AB, it does show that, even though the score is “average” to “good” on all strength tests, there still exists a risk-increasing imbalance in H/Q ratios between the two limbs. Rehabilitative Implications This subject should concentrate on incrementing strength in the knee extensors to raise their strength by almost 20% on each side. Physiotherapy, May 1993 Vol 49 no 2 Page 33 R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) Case Number Four Subject PV (Male): Arthroscopy for Patel- lo-femoral Pathology (R), 36 months pre­ viously. Asymmetry Analysis In this case the strength score is “below average” in knee extension (X SS 43) and “poor” in knee flexions (X SS 34) bilaterally. As the subject is left-dominant for both ex­ tensors and flexors, the standard scores sug­ gest similar H/Q ratios, which in fact is the case (see Figure 4). These ratios are about 0.47 which is one standard deviation below the normal seated isometric mean. As Fig­ ure 5 attests, Q/Q and H/H ratios are within normal limits, and Figure 6 shows that the weaker (R) knee is within acceptable levels of difference from values in the stronger limb. Therefore there are no asymmetries of concern in this case, and whatever condition­ ing is needed toensureoptimal performance is restricted to a need to maintain these bal­ ances while simultaneously increasing left and right extensor and flexor strength. The suggested regimen is one which produces a 10% increment in strength of the quadriceps and a 25% increment in strength of the ham­ strings (ie. a Q:H = 1:2. 5 training ratio). Acknowledgement The meticulous contribution o f Heidi Calitz during the data collection phase o f this project is gratefully recognised. References 1. Nunn KD, Mayhew JL. Comparison of three methods of assessing strength imbalances at the knee. Journal o f Orthopaedic and Sports Physical Therapy 1988;10(4):134-137. 2. Charteris J, Goslin BR. T he Effects of position and movement velocity on isokinetic force out­ put at the knee. Journal o f Sports Medicine and Physical Fitness 1982;22(2):154-160. 3. Levinrad I. The quadriceps-hamstring ratio. SA Runner[Tri-cycling March 1991. 4. Nosse JL. Assessment of selected reports on the strength relationship. Journal o f Ortho­ paedic and Sports Physical Therapy 1982;5:78- 85. 5. Hageman PA, Gillaspie DM, Hill LD. Effects of speed and limb dominance on eccentric and concentric isokinetic testing of the knee. Jour­ nal o f Orthopaedic and Sports Physical Therapy 1988;10(2):59-65. 6. Klopfer DA, Greij SD. Examining quadri­ ceps/hamstrings performance of high velocity isokinetics in untrained subjects. Journal o f Or­ th o p a e d ic a n d S p o r t P h y sic a l T herapy 1988;10(1): 18-22. 7. Thompson Me, Shingleton PT, Kegerreis ST. Comparison of values generated during testing of the knee using the Cybex II Plus and Biodex Model B-2000 isokinetic dynamometers. Jour­ nal o f Orthopaedic and Sports Physical Therapy 1989; 11(3):108-115. 8. Worrell TW, Denegar CR, Armstrong SL et al. Effect of body position on hamstring muscle group average torque. Journal o f Orthopaedic and Sports Physical Therapy 1990;11(10):449- 454. 9. Charteris J, Goslin BR. In vivo approximations of the classic in vitro length-tension relation­ ship: an isokinetic evaluation. Journal o f Ortho­ p a e d ic a n d S p o r ts P h y s ic a l T h era p y 1986;7(5):222-231. WORK IN THE USA PHYSIOTHERAPISTS EXCELLENT JOBS We handle all licensure and visa paperwork. Minimum commitment of one year required. 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