CHAPTER SYNOPSIS
The classifications and the treatment of periprosthetic knee fractures will be discussed. These fractures are difficult to manage due to the presence and type of the knee implants, fracture pattern and location, limited amounts of bone for fixation, and poor bone quality that is often encountered. The optimal method(s) of fracture fixation or revision for these difficult cases is proposed.
IMPORTANT POINTS
- 1
The majority of periprosthetic fractures require operative intervention. As a general rule, if the total knee implants are well fixed and well aligned, attempts should be made to retain the implants. The indications for surgical intervention are a displaced fracture and/or an unstable prosthesis.
- 2
The contraindication for surgical intervention is advised in medically unstable patients.
- 3
Various classification systems have been proposed for supracondylar femur fractures. We use the classification system proposed by Su et al. because it is simple and reproducible and aids in surgical management.
- 4
The classification system proposed by Felix et al. for periprosthetic tibia fractures is our preferred classification system.
- 5
Keating et al. described a classification system for periprosthetic patella fractures.
CLINICAL/SURGICAL PEARLS
- 1
The most common surgical techniques described in the literature for treatment of periprosthetic fractures are open reduction and internal fixation either with plate and screws, intramedullary nailing, and revision arthroplasty. As a general rule, a good result is defined if the patient has a minimum of 90 degrees of knee flexion, varus-valgus malalignment no greater than 5 degrees, flexion-extension malalignment no greater than 10 degrees, and fracture shortening of no greater than 2 cm.
- 2
Preoperative factors that should be ascertained are the stability of the implants, the fracture location relative to components, surrounding bone quality, the type and design of the implants, and the medical and functional status of the patient.
- 3
The most important factor in achieving a successful outcome in treating such fractures is the choice of the proper method of fixation and the preservation of blood supply to the fracture fragments.
- 4
Bone grafts are an important adjunct in acute treatment and can be obtained as either autograft or allografts.
- 5
If plate fixation is selected, long plates are recommended with locking screws if available with minimal stripping of the soft tissues or periosteum from the bone.
- 6
The mortality rate after surgical intervention of periprosthetic femur fractures is high (11%) and is similar to that after treatment for hip fractures. It is higher in patients treated by open reduction and internal fixation compared with revision arthroplasty.
CLINICAL/SURGICAL PITFALLS
- 1
Surgical complications can be avoided by proper classification and management.
- 2
Operative intervention is recommended for most fractures.
- 3
As a general rule, if the total knee components are loose prior to fracture or loosened as a result of the fracture, revision arthroplasty with a long-stemmed component should be performed.
- 4
On the other hand, if the total knee components are well fixed and there is adequate bone adjacent to the implants, the fracture can usually be stabilized by one of a variety of fixation techniques, most commonly using plates or intramedullary devices.
HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM
There are more than 400,000 total knee arthroplasty (TKA) procedures performed in the United States annually. This number is expected to double over the next decade. The incidence of knee periprosthetic fractures is expected to increase because of an increase in TKA performed, the increased survivorship of the elderly with TKAs, and the increased activity of patients after TKA.
Periprosthetic fractures can occur intraoperatively or postoperatively after TKA. The fractures include supracondylar femur fractures, proximal tibial fractures, and patellar fractures. Management of these fractures is dictated by the type and location of the fracture in relation to the total knee components and the stability of the prostheses. Methods of treatment include casting, open reduction and internal fixation, external fixation, revision arthroplasty, or arthrodesis. It is important to understand which options are most appropriate for each type of fracture pattern since no treatment option is optimal for all fractures. Early classification systems focused on displacement as a guide to operative versus nonoperative treatment; however, current surgical techniques and implants have made operative treatment the preferred choice for most of these fractures.
The incidence of supracondylar periprosthetic femur fracture after primary TKA is 0.3% to 2.5% and 1.6% to 38% after revision surgery. These occur more frequently in older patients with osteoporotic bone. Periprosthetic tibia fractures are less common than supracondylar femur or patella fractures because of the use of keeled or short stem tibial components. Felix et al. reported a 0.1% intraoperative and a 0.4% postoperative tibial periprosthetic fracture rate. The incidence of patellar fractures after total knee replacement is between 0.05% and 21%. Rates tend to be higher when the patella has been resurfaced. Overall, men have a higher rate of patellar periprosthetic fracture (1.01%) compared with women (0.40%).
INDICATIONS/CONTRAINDICATIONS
Supracondylar Periprosthetic Femur Fractures
The precise definition of what constitutes a periprosthetic supracondylar femur fracture has been evolving and increasing in the accepted distance from the knee joint line. In Neer et al.’s 1967 study, the supracondylar region was defined as the lower 3 inches (7.62 cm) of the femur. Culp et al. later specified 9 cm proximal to the knee joint line and Sisto et al. included all fractures occurring within 15 cm proximal to the knee joint line. Intraoperative fractures typically occur during total knee preparation or during knee manipulation for stiffness after TKA. The most frequent mechanism for postoperative fractures is a low-velocity fall onto the knee. The majority of these fractures are metaphyseal (intercondylar split or complete condylar fracture) or diaphyseal (anterior or anterolateral cortical penetration) within the distal 15 cm of the femur.
Risk factors for periprosthetic supracondylar femur fractures include osteopenia/osteoporosis, rheumatoid arthritis, neurologic disorders, chronic steroid therapy, anterior cortical notching of the femur, arthrofibrosis or knee stiffness, and revision knee arthroplasty. It is unclear whether osteoporosis or chronic steroid use is the underlying etiology for increased risk of these fractures in patients with rheumatoid arthritis as both conditions are common in this population. In two studies on supracondylar periprosthetic fractures, the majority of patients had rheumatoid arthritis and many were chronic corticosteroid users. Anterior cortical notching (which is cutting of the anterior femoral cortex more than 3 mm) clearly reduces the bending and torsional strength of the femur in experimental studies. However, many authors suggest that remodeling and stress redistribution around the implant occur resulting in a low clinical fracture incidence. In a series of 670 posterior cruciate retaining total knee arthroplasties, of which 180 cases (27%) had anterior cortical notching, only two patients sustained supracondylar femur fractures (one with notching, one without). When the anterior cortical femur is notched and a fracture occurs, the pattern is usually different than with unnotched femurs. Notched femurs tend to have short oblique fractures originating from the notched metaphyseal cortex, whereas unnotched femurs tended to have more of a diaphyseal fracture pattern. Although no large clinical series have shown an increased incidence of periprosthetic fracture with notching, it is intuitively preferable to avoid anterior cortical notching due to the weakened biomechanical interface between the distal femur and the femoral component. Patients with a revision total knee replacement have an approximately 2- to 3-fold increased risk (a rate of approximately 1.6%) of fracture in the supracondylar region compared with primary TKA.
Computer navigation for TKA has become increasingly popular because of its potential to improve the accuracy of placement of the femoral and tibial components. Femoral stress fractures have been reported at the pinhole site for the navigation trackers. As a result, it is recommended avoid transcortical pins which are asymmetrically placed, fully enclosed in cortical bone, and which weaken the bone more than unicortical or bicortical pins.
Tibial Periprosthetic Fractures
Tibial periprosthetic fractures are less common than supracondylar femoral periprosthetic fractures. Risk factors for these fractures include coronal malalignment (varus knee) and excessive anterior tilt of the tibial component. These fractures can occur concurrently with femoral fractures leading to injuries that have been termed a “floating prosthesis.”
Patellar Periprosthetic Fractures
Risk factors for patellar periprosthetic fractures include patellae with very thin residual bone, those with a large central peg, in cases of tibiofemoral malalignment leading to increased stresses in the patellofemoral joint, and in cases with osteonecrosis of the patella (often after lateral release).
CLASSIFICATION SYSTEM
Supracondylar Periprosthetic Femur Fractures
There are several classification systems to describe supracondylar periprosthetic fractures. The Neer classification is based on fracture displacement only.
Neer Periprosthetic Classification ( Table 29-1 )
Type I—Undisplaced (<5-mm displacement and/or <5-degree angulation)
Type II—Displaced >1 cm (a) with medial femoral shaft displacement and (b) with lateral femoral shaft displacement.
Type III—Displaced and comminuted.
| Type I | Undisplaced (<5-mm displacement and/or <5-degree angulation) |
| Type II | Displaced >1 cm |
| a | With medial femoral shaft displacement |
| b | With lateral femoral shaft displacement |
| Type III | Displaced and comminuted |
DiGioia and Rubash modified the Neer classification focusing on fracture displacement ( Table 29-2 ). Chen, Mont, and Bachner simplified the classification into two types, nondisplaced and displaced.
| Group I | Extra-articular, undisplaced (<5-mm displacement or <5-degree angulation) |
| Group II | Extra-articular, displaced (>5-mm displacement or >5-degree angulation) |
| Group III | Severely displaced (loss of cortical contact) or angulated (>10 degrees); may have intercondylar or T-shaped component |
Chen et al. Classification ( Table 29-3 )
Type I—Nondisplaced.
Type II—Displaced and/or comminuted.
| Type I | Nondisplaced (Neer type II) |
| Type II | Displaced and/or comminuted (Neer types II and III) |
Rorabeck and Lewis included prosthesis stability (loosening) in their classification and emphasized the need to consider revision arthroplasty if the implant is considered loose.
Lewis and Rorabeck Classification ( Table 29-4 )
Type I—Undisplaced fracture; prosthesis intact.
Type II—Displaced fracture; prosthesis intact.
Type III—Displaced or undisplaced fracture; prosthesis loose or failing.
| Type I | Undisplaced fracture; prosthesis intact |
| Type II | Displaced fracture; prosthesis intact |
| Type III | Displaced or undisplaced fracture; prosthesis loose or failing |
None of these classification systems are currently widely used. While they indicate which fractures are amenable to nonoperative treatment, they do not aid in choosing from among available modes of surgical intervention. Su et al. proposed a classification system that may aid the surgeon in choosing the best operative option.
Su and Colleagues Classification ( Fig. 29-1 )
Type I—Fracture proximal to the femoral component.
Type II—Fracture originating at the proximal end of femoral component and extending proximally.
Type III—Any part of the fracture line can be seen distal to the upper edge of the anterior flange of the femoral knee component.
Related posts:
Soft Tissue Balancing during Total Knee Arthroplasty
Intraoperative Complications during Total Knee Arthroplasty: How to Get Out of Trouble
Addressing Ligament Deficiency in Revision Total Knee Arthroplasty
The Infected Primary Total Knee Arthroplasty
Adjunctive Fixation in Total Knee Arthroplasty Revision: Stems and Sleeves
Surgical Exposure in Total Knee Arthroplasty
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