The etiology of most periprosthetic distal femur fractures is trauma secondary to low-energy falls in older patients. Younger more active patients are more likely to encounter high-energy trauma. Restricted knee range of flexion increases the risk of periprosthetic fracture of the distal femur [18].

The most commonly used classification for periprosthetic fractures of the distal femur is by Lewis and Rorabeck which places focus on fracture displacement and knee prosthesis stability (Fig. 19.2).

Fracture location, which influences treatment decisions, is not part of this scheme.

The Su classification also takes into account fracture location (Fig. 19.3).

Pain-free function is the goal of treatment for periprosthetic fractures of the distal femur. A well-healed fracture, with appropriate coronal (±5°) and sagittal (±10°) alignment and adequate range of motion (90°), represents successful treatment. Some shortening (up to 2 cm) of the femur may be accepted [18]. Nonoperative and operative methods of treatment have been reported [2, 10, 17, 21, 22]. However, there is a paucity of high level evidence comparing different treatment options for managing this relatively rare injury. Nonoperative treatment is indicated in nondisplaced fractures or for displaced fractures without skin and soft tissue compromise in nonambulatory patients or those not likely to survive the surgical procedure because of medical comorbidities. Improvements in surgical technique and numerous studies support a trend toward operative treatment [2].

Stability of knee implant fixation is a key factor in preoperative decision making, and stability should be determined preoperatively. Proper radiographs are essential. If the prosthesis is stable, treatment can focus on appropriate reduction and stabilization of the fracture. If the femoral component is unstable and well fixed to the bone, revision of the component must accompany fracture fixation, and the possibility of using allograft or tumor-type, constrained prosthetic reconstruction should be considered. Careful assessment of fracture location, displacement, knee implant stability, and adequacy of distal femur bone stock is critical. Periprosthetic distal femur fractures carry a higher mortality risk than hip fractures [5].

The presence of a TKA implant can present problems for fracture stabilization by interfering with or precluding the use of standard fixation methods. A TKA with a narrow or closed femoral intercondylar box may limit the diameter of a retrograde nail or obviate its use [23]. Conventional nonlocking lateral buttress plating is prone to varus collapse [24, 25]. Fixed angled implants such as the 95° angled blade plate or dynamic condylar screw are difficult to employ in very distal fractures or with implants that have a deep intercondylar box. These implants can be used when adequate bone above the femoral prosthesis is available [24–26].

The indications for using locking plates have expanded, and this method is most commonly used to treat these injuries. With locked plating, there is flexibility to place multiple large diameter locking screws in the distal fracture segment, which provide a fixed angle against varus collapse. Locking plates are especially useful with extreme distal periprosthetic distal femur fractures even when associated with a deep intercondylar box. “Joysticks” and fracture reduction clamps can be used to mobilize the distal main fracture segment. There is the option to employ locking screws in the diaphysis which can be helpful when dealing with osteopenic bone [15, 27]. Assuming an acceptable reduction is achieved, the technique can be performed percutaneously with submuscular insertion of the plate proximally. The technique can be altered depending on the fracture pattern with indirect reduction and a bridge technique used for multifragmentary fractures and anatomic reduction and a compression plating technique for simple fracture patterns (Fig. 19.4). Proximal fixation is optimized with the use of relatively long plates, eight or more holes covering the proximal fragment secured with at least four screws. In order to avoid the most common problems with ORIF of these fractures (reduction in valgus), true AP radiographs are required and comparison to the contralateral limb should be employed to assure proper alignment [28].

Following stabilization of periprosthetic distal femur fractures, early rehabilitation is focused on knee range of motion and mobilization with partial weight bearing for 6–8 weeks. Touchdown weight bearing or up to 50% weight bearing is permitted if bone quality and fixation were both optimal. Transition to full weight bearing is typically made by 6–8 weeks followed by progressive resistive exercises and gait/endurance training [28, 29].

The results of locked plating of periprosthetic distal femur fractures are consistent with those of other series of locked plate fixation of native distal femur fractures suggesting that the presence of a TKA femoral component has little effect on outcomes [29]. Despite evolution of locked plating techniques and implants, nonunion continues to be a problem. Nonunion and implant failure remain a concern with rates as high as 22.2% and 8.3%, respectively, in one series [30]. Ebraheim reported an 89% union rate with 7.4% delayed unions, 3.7% nonunions, and 26% fixation failures in a series of 27 patients with periprosthetic distal femur fractures [31].

Retrograde intramedullary femoral nailing (RIMN ) is another commonly employed treatment option for periprosthetic distal femur fractures (Fig. 19.5). Advantages include the benefits of a load-sharing implant, indirect reduction, and minimal vascular disruption at the zone of injury. Challenges include the wide metaphyseal condylar fragment and inability to achieve stable distal fixation in a short osteopenic distal segment [32–34]. The distal fracture segment must also be large enough to ensure stable fixation with interlocking screws.

When RIMN is selected, it is imperative that the geometry of the femoral component accommodates the diameter of the driving end of a retrograde nail. The intercondylar distance of the posterior cruciate retaining total knee determines the size nail that can be placed. In a well-fixed posterior stabilized component, the intercondylar box blocks access to the medullary canal. A technique of opening the box with a diamond-tip metal-cutting burr to allow access to the canal has been described [23]. Reviewing operative reports, published reference lists, and radiographic total knee implant profiles should be part of the preoperative planning process [35].

Additional challenges when using this technique include maintaining fracture reduction. Even with a proper starting point, the nail can migrate to a different trajectory which can malalign the fracture. This can result in malunion particularly with an overly posterior starting point. Blocking (Poller) screws on both sides of the nail, medial and lateral to control varus/valgus, and anterior and posterior to control flexion/extension can help maintain reduction during canal reaming and nail insertion [36]. Placing as many interlocking screws as possible in multiple planes to support distal fixation in osteoporotic bone is important. A true lateral of the knee is required to confirm proper nail position relative to the knee prosthesis to avoid nail protrusion.

Early postoperative mobilization with partial weight bearing for 6 weeks is recommended. Knee range of motion is emphasized in the immediate postoperative period. Weight bearing is advanced to full from 6 to 10 weeks with an emphasis on endurance training.

Although reported union rates are favorable with this technique, the risk of malunion is high. Alignment at union is variable and this is a major challenge of treatment [37]. In a systematic review, 44 studies with 719 fractures were evaluated [38]. Pertinent outcomes considered were malunion, nonunion, and the need for secondary surgical procedures. Both locked plating and RIM N demonstrated significant advantages over nonoperative treatment. Some advantages were also observed when locked plating and RIMN were compared with conventional (nonlocked) plates. Comparison of locked plating and RIMN showed no significant differences with regard to nonunion rates or rate of secondary surgical procedures. However, RIMN demonstrated a significantly higher malunion rate when compared with locked plating [38].

To explain the healing difficulties observed in prior series of distal femur fractures treated with locking plates, Bottland et al. suggested that the high stiffness of locking plates decreases micromotion at the fracture site, thereby limiting callus formation [39]. Far Cortical Locking (FCL) plating is a recent modification of the traditional locked plating concept. FCL plating constructs have been shown to form greater amounts of callus in bovine studies when compared to traditional locking plate constructs. These results suggest that further reducing plate stiffness may increase callus and optimize healing. FCL constructs promote callus by providing a biomechanical environment and healing response for locking plates similar to that provided by external fixators [40]. Callus formation is promoted since stiffness is decreased compared with traditional locked plating and motion across the fracture site is symmetric. Clinical data with this relatively new technique is limited [39].

External fixation has also been reported as a treatment for periprosthetic distal femur fractures [41, 42]. However, the inherent risks of external fixation make it a less than optimal choice for this indication. The need to place half pins closed to the joint capsule can lead to infection, and pin placement through the quadriceps muscle can decrease motion.

Revision TKA in the face of periprosthetic fracture of the distal femur is a considerable technical challenge. Care must be taken to restore the tibiofemoral joint line and normal rotation of the femoral component. Stable patellar and tibial components can be retained if they are compatible with the design of the revised femur. Revision options depend on the bone stock of the distal femur (Fig. 19.6). As more condylar bone is lost to fracture comminution or attempts to remove the existing femoral component, allograft-prosthesis composite can be considered to replace bone loss in the distal femur. When possible, implant fixation can be obtained in the diaphysis with press-fit stems. The use of cement in the diaphysis is discouraged because it may interfere with fracture healing. Wedges or blocks allow for reconstruction of smaller defects, and bone graft should be used. As the amount of bone and soft tissue injured increases, stability becomes a major concern, and constrained or rotating hinge prostheses become a necessity. Another option in the face of severe bone loss is the use of a hinged prosthesis which can allow for immediate range of motion and weight bearing in very elderly and low-demand patients .

Mortazavi et al. reported on the use of acute distal femoral arthroplasty (DFA) for the treatment of periprosthetic fractures after TKA. They retrospectively reviewed 20 patients (22 knees) with a mean age of 69.5 years who underwent revision with DFA. Average follow-up was 58.6 months, and the mean Knee Society knee and functional scores were 82.5 and 40, respectively. There were ten postoperative complications for five patients who required additional surgery. Given the high rate of complications, the authors recommend that this procedure be limited to patients where first-line treatments are not possible [43].

A retrospective study by Chen et al. compared patients who failed primary plating procedures requiring subsequent revision to distal femoral arthroplasty to patients who underwent primary DFA. Of the 13 patients (9.2%) who failed primary ORIF, causes included nonunion (53.8%), infection (30.8%), loosening (7.7%), and refracture (7.7%). There were significantly more surgical procedures for ORIF revision to DFA, compared to primary DFA. Complications for patients who underwent primary DFA included extensor mechanism disruption (8.3%), infection (5.6%), and dislocation (2.8%) [44]. The available clinical series indicate that this is a technically demanding procedure, and given the high rate of complications, it is recommended that acute DFA be reserved for patients where first-line treatment options are not possible [44, 45].

Patients sustaining interprosthetic fractures, which occur between total hip and knee arthroplasties, are generally older and suffer from osteoporotic bone, which further increases the difficulty of treatment (Fig. 19.7). Overall, the incidence is 1.25% with ipsilateral hip and knee arthroplasties. Femur fracture s between ipsilateral hip and knee arthroplasties have less bone available for fracture fixation secondary to the presence of hardware both proximal and distal to the fracture [46].

Hou et al. reported on 13 consecutive patients with interprosthetic fracture. Four fractures occurred around a clearly loose prosthesis, which were subsequently treated with long-stemmed revisions The remaining 12 fractures were treated with a locking plate. Two of nine patients (22.2%) died before fracture union. Follow-up averaged 28 months ± 4 months, with fracture union at an average of 4.7 months ± 0.3 months. All patients returned to their self-reported preoperative ambulatory status except one who developed a loose hip prosthesis at 3-year follow-up after fracture union. Laterally based locking plates are an effective method of treatment for interprosthetic femur fractures. Bypassing the femoral implant proximally by a minimum of two femoral diameters is recommended to prevent a stress riser [47].

The incidence of periprosthetic tibial fractures is rare. The Mayo classification of periprosthetic tibial fractures is the most widely used classification system [48, 49]. Fractures are classified based on the anatomic location and proximity to the prosthesis (Fig. 19.8).