The mobile arm support

  • Published 2010

Abstract

F u n c t i o n T h e p r i n c i p l e o f t h e M o b i l e A r m S u p p o r t ( R a d u l o v i c 1978) is t o s u p p o r t t h e aff l ic ted m e m b e r w i t h a m o v a b l e sp l in t a t t a c h e d t o t h e a r m a n d h e l d in b a l a n c e b y a p n e u m a t i c s y s t e m . T h e M o b i l e A r m S u p p o r t w a s n o t c o n c e i v e d a s a p a s s i v e c r u t c h . O n t h e c o n t r a r y , i ts r o l e is t o a s s i s t w h a t e v e r a c t i v e m o v e m e n t s t h e a r m is still c a p a b l e of, w i t h o u t fighting t h e a r m ' s w e i g h t . In o r d e r f o r t h i s t o b e p o s s i b l e , t h e m u s c l e s of t h e u p p e r a r m m u s t b e r a t e d a b o u t 2 o n t h e i n t e r n a t i o n a l r a t i n g s c a l e ; t h a t is w h e n t h e m u s c l e s c a n n o t r a i s e t h e a r m , b u t c a n ac t u p o n it if i ts w e i g h t is c o u n t e r b a l a n c e d . I n th i s w a y , if t h e h a n d is u n i n j u r e d b u t t h e a r m m u s c l e s de f i c i en t , t h e h a n d c a n b e d i r e c t e d in s p a c e a n d t h u s r e n d e r e d u s a b l e d u e t o t h e m o v a b l e s u p p o r t . D e s c r i p t i o n o f the a p p a r a t u s T h e M o b i l e A r m S u p p o r t (F ig . 1) cons i s t s of t h r e e p a r t s , a h a r n e s s , a n a r t i c u l a t e d sp l in t t h a t s u p p o r t s t h e a r m a n d a p n e u m a t i c s y s t e m w h i c h r a i s e s t h e a r m a n d c o u n t e r b a l a n c e s it . 1. The harness T h e h a r n e s s is fitted t o t h e t r u n k a n d t h e sp l in t is m o u n t e d o n it . T h e f r a m e w o r k of t h e h a r n e s s is f o r m e d f r o m a l u m i n i u m , t h e t w o m a i n p a r t s of w h i c h a r e a t t a c h e d o v e r t h e s h o u l d e r s . I t is h e l d in p o s i t i o n b y a n a d j u s t a b l e be l t a n d s t r a p s . A s p h e r i c a l a r t i c u l a t i o n is a t t a c h e d t o t h e h a r n e s s a t t h e leve l o f t h e s h o u l d e r s . I t is m a d e of h a r d s t e e l a n d s e r v e s as a s u p p o r t for t h e a r m s p l i n t . T h e s u p p o r t a r t i c u l a t i o n m u s t b e l o c a t e d a s c l o s e as p o s s i b l e t o t h e a r t i c u l a r c e n t r e of t h e s c a p u l o h u m e r a l j o i n t . Fig. 1. The splint rests on a supporting spherical articulation ( A ) attached to the harness. The pneumatic system is composed of a cylinder (C) connected to a reservoir of compressed air (R) made from a simple reinforced pipe. Force is transmitted from the splint by a rod and a universal joint (U) . Two pulleys (P) connected by a cable, coordinate the movements of the elbow and shoulder 2. The supporting splint T h e s p l i n t is c o m p o s e d of t w o m e t a l p a r t s , o n e f o r t h e f o r e a r m a n d t h e o t h e r fo r t h e u p p e r a r m . T h e t w o s e g m e n t s a r e a r t i c u l a t e d a t t h e e l b o w b y a u n i a x i a l j o i n t . T h e f o r e a r m a n d u p p e r a r m of t h e p a t i e n t a r e h e l d in t h e s p l i n t b y l a r g e s e l f a d h e s i v e s t r a p s . T h e s e g m e n t a t t a c h e d t o t h e f o r e a r m is m a d e f r o m a c y l i n d r i c a l r o d w h i c h c a n t u r n o n i ts ax i s , t h u s p e r m i t t i n g p r o n a t i o n a n d s u p i n a t i o n o f t h e f o r e a r m . A s a l r e a d y m e n t i o n e d t h e s u p p o r t i n g a r m s p l i n t is f a s t e n e d t o t h e h a r n e s s b y a s p h e r i c a l a r t i c u l a t i o n w h i c h a l l o w s t h e sp l in t t o p i v o t in a n y d i r e c t i o n . 3. The pneumatic lifting system T h e p r i n c i p a l p a r t o f t h e p n e u m a t i c s y s t e m is a c y l i n d e r fixed v e r t i c a l l y t o t h e h a r n e s s a t t h e w a i s t . T h e c y l i n d e r is a t t a c h e d t o t h e h a r n e s s b y a r o b u s t u n i v e r s a l j o i n t w h i c h a l l o w s for v a r i a t i o n s i n t h e o r i e n t a t i o n o f t h e c y l i n d e r . I n s i d e t h e c y l i n d e r is a m o v a b l e p i s t o n a t t a c h e d t o a v e r t i c a l r o d . T h e r o d a c t s o n t h e p o s t e r i o r p a r t of t h e s u p p o r t i n g a r m sp l in t a n d is a t t a c h e d t o t h e s p l i n t b y m e a n s of a u n i v e r s a l j o i n t . T h i s j o i n t p l a y s t h e r o l e of t h e o r ig in of f o r c e i n t h e l e v e r s y s t e m t h a t a c t i v a t e s t h e s p l i n t ( F i g . 2 ) . T h e p n e u m a t i c s y s t e m is c o m p l e t e d b y a r e s e r v o i r o f c o m p r e s s e d a i r w h i c h is m a d e f r o m a r e i n f o r c e d , c o i l e d p i p e 1.5m in l e n g t h fixed t o t h e b a c k o f t h e h a r n e s s . T h e r e s e r v o i r is c o n n e c t e d t o t h e u p p e r p a r t of t h e c y l i n d e r . Fitting and operation T h e h a r n e s s is fitted t o t h e p a t i e n t , m a k i n g s u r e t h a t t h e s p h e r i c a l s u p p o r t a r t i c u l a t i o n is p l a c e d a s c l o s e a s p o s s i b l e t o t h e a r t i c u l a r ax is of t h e s c a p u l o h u m e r a l j o i n t . T h e a f f e c t e d a r m is t h e n a t t a c h e d t o t h e s p l i n t b y t h e s t r a p s . A i r is t h e n p u m p e d i n t o t h e r e s e r v o i r b y a s i m p l e h a n d p u m p . W h e n t h e a i r p r e s s u r e in t h e c y l i n d e r is suf f ic ien t , it a c t s o n t h e p i s t o n w h i c h is f o r c e d d o w n w a r d s a n d d r a w s d o w n t h e p o s t e r i o r p a r t o f t h e s p l i n t . A s t h e p o s t e r i o r p a r t o f t h e s p l i n t g o e s d o w n t h e a n t e r i o r p a r t of t h e sp l in t g o e s u p a l o n g w i t h t h e a r m fixed t o i t a s a r e s u l t of t h e p o s i t i o n i n g o f t h e s p h e r i c a l j o i n t . T h e p r e s s u r e in t h e r e s e r v o i r m u s t b e a d a p t e d t o e a c h p a t i e n t s o a s t o e q u a l i z e t h e p r e s s u r e b e t w e e n t h e p i s t o n a n d t h e w e i g h t of t h e a r m a n d s p l i n t . T h e p r e s s u r e r e q u i r e d for t h i s p u r p o s e u s u a l l y v a r i e s b e t w e e n 1 . 5 a n d 3 .5 b a r s . T h e r e s e r v o i r o f c o m p r e s s e d a i r a n d t h e u p p e r p a r t o f t h e c y l i n d e r is a c l o s e d s y s t e m . O n c e t h e c o r r e c t p r e s s u r e is a r r i v e d a t , it c a n n o t e s c a p e d u r i n g a r m m o v e m e n t s . T h u s t h e w e i g h t o f t h e a r m is b a l a n c e d . T h e o n e p r o b l e m t h a t r e m a i n s t o b e r e s o l v e d is h o w t o m a i n t a i n a c o r r e c t b a l a n c e w h i l e t h e a r m is s t r e t c h e d o r b e n t . If t h e e l b o w is s t r e t c h e d o u t , t h e a r m ' s c e n t r e o f g r a v i t y m o v e s a w a y f r o m t h e s h o u l d e r t h u s a d d i n g t o t h e l e v e r a r m of t h e r e s i s t a n c e ( R ) . T h e o p p o s i t e r e s u l t is p r o d u c e d if t h e e l b o w is b e n t , t h e l e v e r a r m of t h e r e s i s t a n c e d i m i n i s h e s . U n d e r t h e s e c o n d i t i o n s i t is n e c e s s a r y t o v a r y t h e p i s t o n f o r c e , m a k i n g it p r o p o r t i o n a l t o t h e r e s i s t a n c e , p r o p o r t i o n a l , t h a t i s , t o t h e e x t e n s i o n o r flexion of t h e e l b o w . T h i s c a n b e o b t a i n e d b y v a r y i n g t h e l e n g t h o f t h e l e v e r a r m s a c c o r d i n g t o t h e p o s i t i o n o f t h e e l b o w , a p r o c e s s w h i c h is d e s c r i b e d b e l o w . A p u l l e y is s i t u a t e d a t t h e l eve l o f t h e e l b o w w h i c h r o t a t e s b y t h e f l e x i o n / e x t e n s i o n m o v e m e n t s o f t h e f o r e a r m . A t t h e l eve l of t h e s h o u l d e r is a s e c o n d p u l l e y . T h e s e t w o p u l l e y s a r e s e c u r e d a n d l i n k e d t o g e t h e r b y a m e t a l c a b l e in s u c h a w a y t h a t t h e r o t a t i o n o f o n e l e a d s t o t h e r o t a t i o n o f t h e o t h e r . I t is a t t h e s h o u l d e r p u l l e y t h a t o n e finds t h e u n i v e r s a l j o i n t w h i c h t r a n s m i t s t h e p n e u m a t i c f o r c e . T h e j o i n t is p o s i t i o n e d in a n o f f se t f a s h i o n ( l ike a c a m ) s o t h a t w h e n t h e e l b o w is flexed t h e d i s t a n c e b e t w e e n t h e u n i v e r s a l j o i n t a n d t h e s p h e r i c a l s u p p o r t a r t i c u l a t i o n is r e d u c e d . O n t h e o t h e r h a n d , w h e n t h e e l b o w is e x t e n d e d , t h e d i s t a n c e b e t w e e n t h e u n i v e r s a l j o i n t a n d t h e s p h e r i c a l s u p p o r t a r t i c u l a t i o n is m a x i m a l , a b o u t t w i c e a s m u c h a s w h e n t h e e l b o w is f lexed . T h i s a r r a n g e m e n t e n s u r e s t h a t t h e a r m is in c o n s t a n t b a l a n c e w h e t h e r it is e x t e n d e d o r flexed. Fig. 2. T h e splint functions as a simple lever. (A) is the suppor t ing spherical articulation at tached to the ha rness ; (R) is the force produced by the weight of the a rm and (F) is the force t ransmit ted by the universal joint . T h e point where the force (F) is applied is fixed eccentrically on the pulley located at the level of the shou lde r and is dependen t on the movements of the forearm. T h e s y s t e m o f c o n n e c t i o n b y c a b l e a l s o h a s t h e a d v a n t a g e o f h a r m o n i z i n g t h e m o v e m e n t s of t h e s h o u l d e r a n d e l b o w . T h u s a b d u c t i o n o f t h e a r m , a l t e r s t h e p o s i t i o n o f t h e u n i v e r s a l j o i n t a n d t u r n s t h e s h o u l d e r l e v e l p u l l e y w h i c h l e a d s t o p a s s i v e flexion o f t h e e l b o w . I n d e e d , in e v e r y d a y life a b d u c t i o n o f t h e a r m a n d flexion o f t h e e l b o w a r e g e n e r a l l y p e r f o r m e d t o g e t h e r . R a n g e o f m o v e m e n t A r m m o v e m e n t s w i t h t h e a p p a r a t u s a r e m a d e p o s s i b l e by t h e s t r e n g t h of t h e p a t i e n t ' s m u s c l e s a n d t h e a r r a n g e m e n t o f t h e m e c h a n i c a l p a r t s . D u r i n g n u m e r o u s c l in ica l t e s t s , t h e pas s ive r a n g e s of m o v e m e n t p e r m i t t e d by t h e a p p a r a t u s h a v e b e e n m e a s u r e d . T h e y a r e as fo l l ows ; — s h o u l d e r a b d u c t i o n : 90° — s h o u l d e r flexion: 135° (F ig . 3 ) — s h o u l d e r a d d u c t i o n c o m b i n e d w i t h flexion: 20° — s h o u l d e r a d d u c t i o n c o m b i n e d wi th e x t e n s i o n : 35° — s h o u l d e r e x t e n s i o n : 45° — i n t e r n a l r o t a t i o n of t h e a r m : 90° — e x t e r n a l r o t a t i o n of t h e a r m : 80° — f l e x i o n o f t h e e l b o w : 120° — e x t e n s i o n o f t h e e l b o w : 0° ( c o m p l e t e ) — s u p i n a t i o n a n d p r o n a t i o n of t h e f o r e a r m : 90° ( c o m p l e t e ) T h i s g r e a t m o b i l i t y o n all l eve ls is m a d e p o s s i b l e b y t h e u s e o f t h e s p h e r i c a l s u p p o r t a r t i c u l a t i o n , i ts l o c a t i o n v e r y n e a r t h e c e n t r e of t h e s c a p u l o h u m e r a l a r t i c u l a t i o n , i ts c o n n e c t i o n w i t h t h e u n i v e r s a l j o i n t a n d , f inal ly, by t h e l o n g m o v e m e n t o f t h e c y l i n d e r p i s t o n . Cl in ica l tes ts C l i n i c a l t e s t s w e r e c a r r i e d o u t w i t h 18 p a t i e n t s . E a c h p a t i e n t h a d t o ; — h a v e a l o c a l de f i c i ency o f t h e a r m , p r e d o m i n a n t l y a t t h e s h o u l d e r o r t h r o u g h o u t t h e a r m , r e l a t e d t o p a r a l y s i s , m u s c u l a r o r r h e u m a t i c a i l m e n t s , e t c . — h a v e a m u s c u l a r r a t i n g a t t h e s h o u l d e r of a r o u n d 2 — b e a l e r t a n d if p o s s i b l e c o o p e r a t i v e . T h e 18 p a t i e n t s s u f f e r e d f r o m v a r i o u s c o n d i t i o n s ; — m y o p a t h y o f t h e s h o u l d e r g i r d l e — p a r a l y s i s o f t h e b r a c h i a l p l e x u s w i t h t h e m a j o r d a m a g e a t C 5 a n d C 6 — h e m i p l e g i a — t e t r a p l e g i a — r e f l e x s y m p a t h e t i c d y s t r o p h y of t h e a r m . T h e a p p a r a t u s u s e d for t h e s e t e s t s w a s a p r o t o t y p e fo r t h e right s i d e o n l y a n d n o t p e r f e c t l y a d a p t e d t o e a c h s u b j e c t , a fac t w h i c h l e d t o s o m e di f f icu l t ies . F o r e a c h p a t i e n t a d o s s i e r c o n t a i n i n g t h e f o l l o w i n g w a s c o m p i l e d ; — e v a l u a t i o n o f t h e h a n d i c a p p e d p a t i e n t — e v a l u a t i o n o f a c t i v e m o b i l i t y a n d t h e m u s c u l a r f o r c e fo r al l m o v e m e n t s o f t h e s h o u l d e r a n d e l b o w , first w i t h o u t a n d t h e n w i t h t h e M o b i l e A r m S u p p o r t — e v a l u a t i o n o f u s u a l m o v e m e n t s , w i t h a n d w i t h o u t t h e M o b i l e A r m S u p p o r t . R e s u l t s 1 Tolerance T o l e r a n c e t o t h e s u p p o r t w a s e x c e l l e n t . U s e o f t h e a p p a r a t u s c a u s e d n o p a i n a n d d i d n o t a g g r a v a t e t h e p a t i e n t ' s c o n d i t i o n . T h e a p p a r a t u s w a s we l l a c c e p t e d ; a f t e r fitting, t h e p a t i e n t r e q u i r e d n o t r a i n i n g in its u s e . T h e s p l i n t w a s i m m e d i a t e l y p u t i n t o a c t i o n by t h e f o r c e lef t in t h e a r m a n d t h e s u b j e c t s t e s t e d m a d e u s e o f it in t h e m o s t n a t u r a l w a y . Fig. 3. During clinical tests shoulder flexion reached 135°. 2 Gains in range of movements a S h o u l d e r m o v e m e n t s . I m p o r t a n t g a i n s w e r e n o t e d for n e a r l y all m o v e m e n t s o f t h e a r m , b u t e spec i a l l y for a b d u c t i o n a n d flexion (F ig . 4 ) . A x i a l r o t a t i o n a l m o v e m e n t s w e r e n o t a f f e c t e d b y t h e a p p a r a t u s w h i c h w a s n o t d e s i g n e d for th i s p u r p o s e . b F l e x i o n o f t h e e l b o w . F l e x i o n o f t h e e l b o w w a s i m p r o v e d in all c a s e s e x c e p t o n e ( a h e m i p l e g i c ) w h e r e n o p r o g r e s s w a s m a d e w i t h o r w i t h o u t t h e a p p a r a t u s . T h e g a i n in e l b o w flexion is e x p l a i n e d b y t w o facts . F i r s t ly , a s t h e s h o u l d e r a n d e l b o w m o v e m e n t s a r e l i n k e d by t h e a p p a r a t u s , a b d u c t i o n o f t h e a r m f a v o u r s flexion o f t h e e l b o w . S e c o n d l y , w h e n t h e a r m is a b d u c t e d a n d b e c o m e s h o r i z o n t a l , flexion of t h e e l b o w is a c c o m p l i s h e d m o r e eas i ly . c P r o n a t i o n s u p i n a t i o n m o v e m e n t s of t h e f o r e a r m . T h e y w e r e n o t a f f e c t e d by u s e of t h e a p p a r a t u s . 3 Gains in muscular strength I t w a s n o t e d w i t h s o m e s u r p r i s e t h a t m u s c u l a r s t r e n g t h w a s i m p r o v e d in o n e t h i r d of t h e c a s e s , f r o m a b o u t 1/2 t o 1 p o i n t o n t h e i n t e r n a t i o n a l r a t i n g s c a l e . I t is b e l i e v e d t h a t t h e p o s i t i o n i n g of t h e a r m a n d t h e e f fec t s o f r e s t b r o u g h t a b o u t by t h e s u p p o r t i n g sp l in t a r e r e s p o n s i b l e for th i s i m p r o v e m e n t ; o n c e t h e s u b j e c t n o l o n g e r h a s t o fight t h e w e i g h t o f h i s o w n a r m , t h e a r m m u s c l e s a r e m o r e r e l a x e d a n d c a n t h u s w o r k b e t t e r . 4 Lessening of pain I n c a s e s o f r h e u m a t i s m of t h e s h o u l d e r in w h i c h f u n c t i o n a l i n a b i l i t y is d u e l a rge ly t o p a i n , t h e s u p p o r t p r o v i d e d b y t h e sp l in t p e r m i t t e d a n i m m e d i a t e a n d p a i n l e s s r e s u m p t i o n of m o v e m e n t . I n t h e s e c a s e s t h e M o b i l e A r m S u p p o r t p r o m i s e s t o b e a usefu l i n s t r u m e n t of r e h a b i l i t a t i o n . 5 Functional improvements I m p r o v e m e n t h a s b e e n n o t e d e spec i a l l y in c a s e s o f p e r i p h e r a l n e u r o l o g i c a l c o n d i t i o n s . T h e s e p a t i e n t s c a n w r i t e b e t t e r , e a t u n a i d e d , d r e s s t h e m s e l v e s , c l e a n t h e m s e l v e s a n d u r i n a t e n o r m a l l y . T h e M o b i l e A r m S u p p o r t i m p r o v e s f u n c t i o n a l m o v e m e n t s in t h e g r e a t e r p a r t for all t h e p a t i e n t s fitted. I n p a r t i c u l a r it p e r m i t s p a t i e n t s t o c a r r y o u t a c t i v i t i e s m o r e eas i ly a n d w i t h less f a t i gue ( F i g . 5 ) . Fig. 4. Abduction of the shoulder in 10 cases of peripheral affliction. The grey area represents abduction without the support, the striped area shows the improvement produced by using the support. Fig. 5. Top, without the Mobile Arm Support a patient suffering from myopathy has to lean forward to don his spectacles. Bottom, normal action possible when using the support.

5 Figures and Tables

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@inproceedings{2010TheMA, title={The mobile arm support}, author={}, year={2010} }