Periprosthetic Fractures

Introduction

By 2030, the demand for primary total knee arthroplasties (TKAs) is expected to grow by 673% to 3.48 million procedures annually. Revision TKAs are projected to increase by 601% between 2005 and 2030. As the volume of these procedures increases, the number of periprosthetic fractures that occur intraoperatively and postoperatively is also expected to increase. In a 2011 review of the entire Mayo Clinic series to date, Abdel and Berry found an intraoperative periprosthetic femoral fracture rate of 0.3%, compared with a postoperative rate of 1.1% (unpublished data). During revisions, the intraoperative fracture rate increased by fivefold to 1.6%, whereas the postoperative fracture rate increased to 2.0%.

To accurately diagnose, discuss, and manage fractures occurring with TKAs, classification schemes are required. The most fundamental system designates periprosthetic fractures according to anatomic location (femur, tibia, or patella), but many classification systems exist for each type of periprosthetic fracture. Treatment approaches for periprosthetic total knee fractures often are based on these systems.

Classification

The ideal classification scheme (1) enables adequate communication between clinicians, (2) includes only relevant variables, (3) guides management, (4) has prognostic capabilities, and (5) is simple to apply. Fracture classifications are based on location and direction of the fracture, the quality of the alignment, the fixation of the implant, and the status of the bone and soft tissues around the knee.

Sisto and colleagues devised one of the original systems for classification of the femur ( Table 29A.1 ). Cases were classified as nondisplaced, displaced, or comminuted. Neer and co-workers subsequently classified fractures based on fracture displacement, stability, and comminution. In this system, group I fractures are undisplaced (<5 mm of displacement and/or 5 degrees of angulation), and group II fractures are displaced (>1 cm of displacement). Group IIA fractures have lateral femoral shaft displacement, and group IIB fractures have medial femoral shaft displacement. Group III fractures are displaced and comminuted.

DiGioia and Rubash modified the Neer classification, defining group I fractures as those that are extraarticular and undisplaced (<5 mm of displacement and <5 degrees of angulation). Group II fractures encompass extraarticular and displaced fractures (>5 mm of displacement or >5 degrees of angulation). Group III fractures are severely displaced or comminuted and may include intercondylar or T-shaped components. Chen and associates simplified this system by using only two categories: type I (nondisplaced) and type II (displaced and/or comminuted).

Lewis and Rorabeck modified the classification for periprosthetic femur fractures to include the integrity of the implant. This is our preferred system. Type I periprosthetic fractures are undisplaced fractures, and the prosthesis is intact. Type II periprosthetic fractures are displaced, but the prosthesis remains intact ( Fig. 29A.1 ). Type III fractures may or may not be displaced, and the prosthesis is loose or failing.

Kim and colleagues and Parvizi and associates used a system that takes into account the total amount of bone in the distal fracture fragment, the position and fixation status of the component, and the reducibility of the fracture. Type I fractures occur in patients with good bone stock and a fixed, well-positioned prosthesis. Type IA fractures are nondisplaced or easily reducible, and type IB fractures are irreducible. Type II fractures are reducible with adequate distal bone, but they have a malpositioned or loose component. Type III fractures are severely comminuted fractures with inadequate distal bone for fixation or conventional component support.

Introduction

Although they are less common than periprosthetic femoral fractures, periprosthetic tibial fractures do occur and require prompt diagnosis and appropriate management. The incidence of periprosthetic fractures seems to be increasing. In a 2011 review of the entire Mayo Clinic series, Abdel and Berry reported an intraoperative periprosthetic tibial fracture rate of 0.12% (unpublished data). Postoperative periprosthetic tibial fractures were diagnosed in 0.4% of patients. During revisions, the intraoperative fracture rate increased by tenfold to 1.4%, and the postoperative periprosthetic tibial fracture rate was 1.1%.

Classification

The Mayo classification scheme for periprosthetic tibial fractures is shown in Figure 29B.1 . The ideal system enables adequate communication between clinicians, includes only relevant variables, guides management, has prognostic capabilities, and is simple to apply.

Periprosthetic tibial fractures occur less commonly than femoral fractures, and there are also fewer classification systems. The most widely accepted is that of Felix and colleagues, and it is our preferred classification system for fractures occurring about the tibial component. The classification incorporates the anatomic location of the fracture, prosthesis stability, and timing of the fracture ( Table 29B.1 ). In their study of 102 periprosthetic tibial fractures, Felix and co-workers identified 61 type I fractures, 22 type II fractures, 17 type III fractures, and 2 type IV fractures. The four types were subcategorized as A (well-fixed prosthesis), B (loose prosthesis), or C (intraoperative fracture) (see Table 29B.1 ). Most fractures (83 of 102) occurred postoperatively and were subtype A or B.

These fractures were most commonly seen before the development of stemmed and keeled tibial components, and they were frequently encountered in conjunction with a loose tibial component as a part of abnormal stresses on the bone. Felix and colleagues found that 56 of 61 fractures occurred in the medial plateau. Of these, 50 were type IB and were associated with a loose prosthesis, whereas 11 were type IC and occurred intraoperatively. Type 2 fractures occur adjacent to the tibial stem but do not extend to the implant interface. These fractures occur distal to the stem of the prosthesis, usually at the metaphyseal-diaphyseal junction. Most are the result of trauma. Of the 22 type II fractures, 4 were type IIA, 11 were type IIB, and 7 were type IIC. Type III fractures occur well distal to the prosthesis. Fifteen of 17 were associated with a well-fixed prosthesis. Type IV fractures involve the tibial tuberosity and have a discontinuity of the extensor mechanism.