hello everybody this is scott solomon with board Preppers and today i'm going to be talking about how to simplify concave versus convex rules now generally speaking this is not all that difficult but it is very easily confused or mixed up people flip them over so I'm going to show you an easy way to keep it straight so when you're getting ready for your board exam around the board exam you're able to not let one of these simple questions get you mixed up so with that being said the first thing we have to do is identify what is concave what is convex and I have some drawings on the board that we'll use so here you'll see let's just call it the glenoid fossa and then the humerus so every joint when referring to con the concave or convex rule has two surfaces involved so we're going to use this as an example so the glenoid fossa is a concave surface and the head of the humerus is a convex surface right so now that we got to generally cleared out let's then talk about the upper extremity versus lower extremity and then in that case really the upper extremity and the lower extremity are the same so we don't need to really do both we'll just do one and because the upper extremity is here I'll just use it so the next thing we have to do is identify the joints we have three of them and each has two surfaces all right the shoulder the elbow and the wrist the hip knee ankle they're the same as far as convex concave so now let's look at it the shoulder is made up of two surfaces one of the glenoid fossa we've already identified that as a concave surface and we'll people use an eight because for simplification and the head of the humerus is convex where we'll use an X to represent that in the elbow to distal end of the humerus is convex the proximal end of the forearm is concave the distal end of the four are made up of the styloid creates a concave surface and then the cuboidal bones of the carpals make up a convex surface so there are your letters right I'm axe convex concave concave convex that's the pattern it's the same for the lower extremity so now let's just bring it over and set it up so the board is going to take this now and apply it to open chain versus closed chain activities right so let's put open versus closed let's then transpose these letters into the two columns a X X a a X we'll do it again a X X a a X and now open chain versus closed open chain says that the proximal end is fixed in the distal end is moving therefore the moving bone makes the rule in this case the distal bone so distal distal distal now the moving bone makes the rule right so in the closed chain now the distillate becomes fixed and the proximal end becomes mobile so now the proximal bone is making the rule so here you go shoulder hip open chain convex closed chain can be a concave elbow and knee open chain concave closed chain compacts wrist and ankle open chain convex closed chain concave rule that's how you do it if it's just as simple as remembering a x xax doing it twice doing it like this draw it on your whiteboards that give you plenty of them set it off to the side and then if the question ever presents itself you have that easy access you don't waste any extra energy trying to go through and keep it straight in your mind you've already done it again this is Scott Solomon with bored Preppers I do appreciate your time I look forward there's more of these coming out so I look forward to speaking to you soon have a great day and thanks again