CARPAL BONE ALIGNMENT MEASUREMENT

▪︎ The  following  are  the  most  frequently used  measurements  to  define  carpal  bone  alignment- 

1) LC  angle :  This  is  helpful  to  quantify  midcarpal  misalignment. 

• A  normal  LC  angle  should  be  0  ±  15  degrees  with  the wrist  in  neutral . 

2) SL angle : one  of  the  major  determinants  of  SL  dissociation.

• Normal  values  range  from  30  to  60  degrees  (average, 47 degrees).

•Although  angles  greater  than  80  degrees  indicate  SL  ligament  disruption,  lower  readings  do  not  rule  out this  pathology. Values  less  than  30  degrees  are  not  unusual for  patients  with  STT  joint  osteoarthritis.

3) RL  angle :  This  gives  objective  evidence  of  the  dorsal  or palmar  tilt  of  the  lunate.  

•The  normal  RL  angle  should  be  0 ±  15  degrees.

4)  Ulnar Variance : Ulnar  variance  is  usually  measured  on  standard  PA  radiographs,  although  lateral  radiographic  projections  also  offer very accurate readings.  

• When  the   ulna  is  shorter  than  the  radius,  the  ulnar  variance is  negative,  and  when  longer,  it  is  positive.   

5) Carpal Height Ratio :  This  is  another  parameter  in  the  evaluation  of  carpal  collapse.

6) Ulnar  translocation  ratio :  In  some  instability  conditions, there  is  an  ulnar  shift  of  the  carpal  bones.  The  amount  of translocation  can  be  quantified  using  a  variety  of  techniques. 

Very commonly used  technique measures the perpendicular distance from the center of the head of the capitate to a line from the radial styloid, which extends distally and parallel to the longitudinal axis of the radius. The carpal translocation ratio (calculated as the ratio of this distance to the length of the third metacarpal) in normal wrists is 0.28 ± 0.03.