The thing that makes joints break like a moist biscuit is their fairly small bodypart size, and that the body materials all have the same, fairly low resistance to the damage that joint hits use.
I modded them with increased joint sizes :
[BODY:HUMANOID_JOINTS]
[BP:RUA_J:right shoulder:STP][CON:RUA][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:LUA_J:left shoulder:STP][CON:LUA][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:RLA_J:right elbow:STP][CON:RLA][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:100]
[BP:LLA_J:left elbow:STP][CON:LLA][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:100]
[BP:RH_J:right wrist:STP][CON:RH][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:75]
[BP:LH_J:left wrist:STP][CON:LH][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:75]
[BP:RUL_J:right hip:STP][CON:RUL][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:LUL_J:left hip:STP][CON:LUL][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:RLL_J:right knee:STP][CON:RLL][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:LLL_J:left knee:STP][CON:LLL][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:150]
[BP:RF_J:right ankle:STP][CON:RF][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:100]
[BP:LF_J:left ankle:STP][CON:LF][JOINT][SMALL][INTERNAL]
[CATEGORY:JOINT]
[DEFAULT_RELSIZE:100]
And by increasing the tensile, torsion and bending yield and fracture rates:
[TENSILE_YIELD:11000]Joint pull damage
[TENSILE_FRACTURE:22000]
[TENSILE_STRAIN_AT_YIELD:25000]
[TORSION_YIELD:11000]Joint twist damage
[TORSION_FRACTURE:22000]
[TORSION_STRAIN_AT_YIELD:25000]
[BENDING_YIELD:11000]Joint bend damage
[BENDING_FRACTURE:22000]
[BENDING_STRAIN_AT_YIELD:25000]
So, no need to insert and adamantine joints, though that would certainly do the job as well.