FORCES IN THE KNEE JOINT DURING EXERCISE OF TIlE KNEE EXTENSORS 1

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1 10 THE AUSTRALIAN JOURNAL OF PHYSIOTHERAPY FORCES IN THE KNEE JOINT DURING EXERCISE OF TIlE KNEE EXTENSORS 1 R. S. HORSFIELD, B.SC., DIP.ED. (SYD.), M.PHYS. (U.N.S.W.), M.A.I.P., M.A.C.E. What frces arise in the knee jint during the exercise f the quadriceps by extending the lwer leg weighted with a de Lrme bt? Hw d these frces cmpare with thse experienced in nrmal weight-bearing activities? These and ther questins can he answered frm a cnsideratin f the mechanics f the knee jint in different degrees f flexin frm 90 t (fully extended). EXPERIMENTAL PROCEDURE The psitin f the patient ding the knee extensr exercise is shwn in Fig. I. The nly significant frces acting n the lwer leg are the patella ligament tensin, P, the tibifemral jint reactin frce, J, and the cmbined weight f the lwer leg and exercise bt, W. When the leg is held still in any psitin between 90 0 f flexin and full extensin these three frces are in equilibrium and s have cncurrent lines f actin. It is cnvenient t determine the frces relative t the bdy weight f the patient s sme assumptin must be made cncerning the magnitude f the exercise weight, the limb weight and the patient's grss bdy weight.. Fr the purpse f this analysis it was assumed that the patient had a mass f 70 kg, the lwer leg a mass f 4 kg (Dempster, 1955) and the exercise ht a mass f 10 kg. That is, the applied exercise weight f the bt and leg is just 0.2 W. What is knwn abut the three frces is summarized in Table I where the methd f determining the unknwn characteristics f the tw frces f interest is als indicated. FIGURE 1 The three frces n the lwer leg in extensin exer.. cises using a de Lrme bt (nt t scale). lreceived Nvember, Aust.!.Physither., XXIII, 1, March, 1977 w The necessary measurements and calculatins f the knwn characteristics (as indicated by the reference letters) are as fllws: (a ) In rder t estimate the psitin f the centre f gravity f the leg, ft and ht cmbinatin sme further assumptins abut the dimensins f the lwer leg and bt must be made. The assumed dimensins which were used in the calculatins here are illustrated in Fig. 2.

FORCES IN THE KNEE JOINT DURING EXERCISE OF THE KNEE EXTENSORS 11 TABLE 1 Characteristics f the Three Frces Actin g n the Lwer Leg at Arbitrary Flexin Frce Weight j Patella Ligament Jint Reactin

20 W) using clsed vectr tri- using clsed vectr triangle fr the sum) angle fr the sum) Pint f On line between centre f Insertin f the ligament Centre f cntact area beapplicatin gravity f leg and

2 FORCES IN THE KNEE JOINT DURING EXERCISE OF THE KNEE EXTENSORS 11 TABLE 1 Characteristics f the Three Frces Actin g n the Lwer Leg at Arbitrary Flexin Frce Weight j Patella Ligament Jint Reactin Characteristic Bt and Leg Tensin Frce Magnitude 14 kg wt UNKNOWN (frm~f =0 UNKNOWN (frm};f=0 (0.20 W) using clsed vectr tri- using clsed vectr triangle fr the sum) angle fr the sum) Pint f On line between centre f Insertin f the ligament Centre f cntact area beapplicatin gravity f leg and centre in the tibial tubersity tween the tibia and the f exercise ht ~ just femur (b) anterir f the tihitalar jint (a) Line f actin Vertically dwnward at all In line frm the '''rigin'' Thrugh its pint f aptimes t the insertin f liga- plicatin and the intersecment this estimated frm tin f the lines f actin X-ray phtgraphs (c) f the ther tw frces Directin Dwnward Presumably "ut f" the Presumably "int" the (Sense) lwer leg as it extends lwer leg as it extends (b) The centre f the area f cntact between the tibia and the femur was taken as the pint f applicatin f the jint reactin frces. Measurement n a number f radigraphs f nrmal knees in varying degrees f flexin indicates that this pint mves psterirly as the degree f flexin increases.. The bservatins f Gymann and Miiller (1974) n cadaveric knees in different degrees f flexin wuld seem t cnfirm this mvement as the weightbearing areas in the knee change with flexin. 30 MM One set f calculatins was undertaken assuming this centre t remain fixed relative t the tibia during flexin, an.. ther set assuming a psterir mvement f 3 mm per 15 degrees f flexin - this mvement rate being estimated frm the radigraphs. (c) The line f actin f the patella ligament (frm the tibial tubersity t the patella surface) can he quite accurately determined frm the radigraphs fr different degrees f flexin. As the leg is mved frm full extensin (180 0 ) t 90 f flexin the angle between the patella ligament and the tibial axis changes quite markedly. This variatin has been taken int accunt in bth sets f calculatins. * t1M q20 MM--""",", K = Centre f rtatin f knee jint. J == Pint f applicatin f the jint reactin frce. P =: Insertin f the patella ligament in tibial tubersity.. CL == Centre f gravity f leg and ft. CB == Centre f gravity f bt. C = Centre f gravity f leg, ft and bt.. FIGURE 2 Assumed dimensins f lwer leg. OBSERVATIONS AND CALCULATIONS The fllwing bservatins and calculatins were made: (i) The variatin f the angle between the patella ligament and the tibial axis as a functin f flexin angle.. (ii) The magnitudes f the patella ligament tensin and the jint reactin frce (relative t bdy weight) as the leg is held in different degrees f flexin; assuming the jint reactin frce pint f applicatin t remain fixed relative t the tihial head. Aust..J.Physither., XXIII, I, March, 1977

3 12 THE AUSTRALIAN JOURNAL OF PHYSIOTHERAPY (iii) The frce magnitudes as in (ii), assuming the jint reactin frce pint f applicatin t mve psterirly relative t the tibial head as flexin increases. (iv) The femrpatellar frce fr different degrees f flexin. The quadriceps tendn tensin was taken as equal t the tensin in the patella ligament and Fig. 3 shws the assumed gemetry relating the angle between these tw tensins t the angle f flexin and insertin angle f the patella ligament flexin t full extensin. The results f ten X-ray measurements are sh,wn in Fig. 4. Angle between Patella ligament and Tibial Axis (Degrees) lto Q ANGLE OF FLEXION (DEGREES) -15 FIGURE 4 Angle f insertin f patella ligament as a functin f angle f flexin. (ii) Using the smth curve fitted t the pints in Fig. 4 the patella ligament tensin and jint reactin frce as calculated fr different degrees f flexin were bth fund t increase as the lwer leg was mved frm 90 f flexin t full extensin. The variatins f bth these frces assuming the jint reactin frce pint f applicatin t be fixed is shwn in Fig. 5 where the pint fr 90 flexin assuming the leg t be hanging withut cntractin f the quadriceps. 2.0 Frce (Multiples f Bdy Weight) 1.5 FIGURE A PATELLA LIGAMENT TENSION A JOtNT REACTiON FORCE Assumed gemetry f angles fr calculatin f femrpatellar frce in different degrees f flexin. 0.5 RESULTS (i) The angle between the tibial axis and the patella ligament was fund t increase almst linearly with the angle f flexin as the lwer leg is mved frm full Aust.l.Phrsither., XXIII, 1, March, lifo ANGLE OF FlEX(OK (DEGREES) FIGURE 5 Jint frces as a functin f flexin angle.

4 FORCES IN THE KNEE JOINT DURING EXERCISE OF THE KNEE ExTENSORS 13 (iii) 2.~ I The effect f the psterir mvement f this pint f applicatin as flexin increases was fund t be that bth the ligament tensin and jint reactin frce initially decrease mre rapidly as the leg flexes frm full extensin. The variatin f the patella ligament tensin fr the pint f applicatin f the jint reactin frce hth fixed and mv.. ing psterirly with increasing flexin is shwn in Fig. 6. A similar reductin in the jint reactin frce als ccurs. Patella Ligament Tenstn (Multiples f Bdy Weight) / /' /"/ JOWl REACTION FORce prnt OF APPLICATiON FIXED II JOINT REACTlOIi FORe!; POUiT OF APPllCAlI ON MOV INr. POSTER [ALL'f AS FLEXION I HCREASES. CONCLUSIONS AND ApPLICATIONS TO THERAPY The frces which arise in the knee jint when a patient is exercising the quadriceps by extensin f the lwer leg, using an exercise bt with up t 20% f their bdy weight added, at n time exceed abut tw and a hah times bdy weight. This is well belw the maximum frces experienced in nrmal weight-hearing activi.. ties such as climbing stairs (Frankel, 1974), walking (Mrrisn, 1970) and ismetric exercise (Smidt, 1973). In particular the finding that the femrpatellar frce reaches a maximum f j nst ver ne and a half bdy weight and drps dramatically as flexin increases t 90 0 wuld seem t indicate this t be suitable fr pstperative exercise after treatment f femrpatellar arthrsis (Bandi and Brennwald, 1974). SUMMARY 90 (iv) ~ ANGlE OF FLEXION mfgrees) I 180 FIGURE 6 Effect f mvement f jint reactin frce applicatin. The femrpatellar frce resulting frm the tw tensins was fund t increase at first and then decrease markedly as the knee is mved frm full extensin t 90 flexin. This variatin is shwn in Fig~ 7. FemrpatelJar Frce (Multiples f Bdy WeIght) The frces which arise in the knee jint during exercise f the quadriceps with a de Lnne bt are investigated. The variatin f patella ligament - tibial axis angle with varying degrees f flexin is measured frm radigraphs. These measurements are applied t a calculatin f the patella ligament tensin, tibia-femral jint reactin frce and femrpatellar frce fr the knee in different degrees f flexin (frm 90 t full ex.. tensin) with a de Lrme bt prviding an exercise lad f l/sth bdy weight. The variatin ()f the mag.. nitude f each f these frces, relative t bdy weight, are presented by means f graphs and the implicatins fr exercise therapy indicated. 1.5 lu D FIGURE 7 Variatin f femrpatellar frce with flexin angle. REFERENCES BANDI, W. and BRENNWALD, J. (1974): "The Significance f Femra-patellar Pressure in the Pathgenesis and Treatment f Chndrmalacia Patellae and Femrpatellar Arthrsis". Prceedings f the Internatinal Cnference n the Knee Jint. Eds. O. S. Ingwersen et at. Excerpta Medica, Amsterdam, p.63. DEMPSTER, W. (1955): "Space Requirements f the Seated Operatr". WADe Technical Reprt, p. 55. FRANKEL, V. H. (1974) : "Bimechanics f the Knee". Prceedings f the Internatinal Cnference n the Knee Jint. Eds. O. S. Ingwersen ee al. Excerpta Medica, Amsterdam, p. 6. Aust./.Physither., XXIII, 1, March, 1977

5 14 THE AUSTRALIAN JOURNAL OF PHYSIOTHERAPY GOYMANN, V. and MULLER, H. G. (1974): ''New Cal.. culatin f the Bimechanics f the Patellfemral Jint and its Clinical Significance". Prceedings f the Internatinal Cnference n the Knee lint. Eds. O. S. Ingwersen et ale Excerpta Medica, Amsterdam, p. 16. MORRISON, J. B. (1970): "The Mechanics f the Knee Jint in Relatin t Nrmal Walking". J. Bimechanics, 3, p SMIDT, G.. L. (1973): "Bimechanical Analysis f Knee Flexin and Extensin".. I. Bimechanics, 6, p Aust.l.Physither., XXIII, 1, March, 1977

BROCKTON AREA MULTI-SERVICES, INC. MEDICAL PROCEDURE GUIDE. Date(s) Reviewed/Revised:

BROCKTON AREA MULTI-SERVICES, INC. MEDICAL PROCEDURE GUIDE. Date(s) Reviewed/Revised: Page 1 f 6 Subject: Range f Mtin Exercises Date Develped: 4/2010 PROTOCOL FOR: All trained staff PURPOSE: Range f Mtin (ROM) exercises are very imprtant if an individual has t stay in bed r in a wheelchair.