Table 1.

UCS Classification and periprosthetic fractures treatment algorithm.

JOINT	BONE
Shoulder Elbow Wrist Hip Knee Ankle	1: Humerus 14: Glenoid/scapula 2: Radius/ulna 3: Femur 4: Tibia 34: Patella 6: Acetabulum/pelvis 7: Carpus/metacarpals 8: Talus
FRACTURE TYPE	TREATMENT
A Apophyseal or extraarticular/periarticular Subtypes A1: Avulsion of (e.g. greater trochanter) A2: Avulsion of (e.g. lesser trochanter)	Depends on displacement and importance of soft tissue attached, e.g.: greater trochanter, tibial tuberosity, greater humeral tuberosity: surgical treatment lesser trochanter, coracoid process: conservative treatment
B Bed of the implant or around the implant Subtypes B1: Prosthesis stable, good bone B2: Prosthesis loose, good bone B3: Prosthesis loose, poor bone or bone defect	B1: Lower limb: reduction and fixation, LCP and if possible MIPO technique preferred. B1: Upper limb: depends on displacement, conservative treatment preferred. B2: Revision surgery. B3: Revision surgery that may require complex reconstruction (megaprosthesis, allograft/stem composite). Depends on the bone loss and age/activity of the patients.
C Clear of or distant to the implan	Same management as no-periprosthetic fracture.
D Dividing the bone between two implants or interprosthetic or intercalary	Decision-making depends on “block-out analysis”*. Subtype A (both prostheses stable): reduction and fixation Subtype B (one stable and one loose): revision surgery Subtype C (both loose):both joint revision surgery, total replacement
E Each of two bones supporting one arthroplasty or polyperiprosthetic	Decision-making depends on “block-out analysis”* (e.g. separate assessment of femoral fracture with stem of THA and acetabular fracture with cup)
F Facing and articulating with a hemiarthroplasty	Depends on displacement, conservative treatment preferred.

^*Block-out analysis= to analyze separately PF in relation with two joints.