3.14 Periprosthetic fractures around the knee
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1 Introduction
Periprosthetic fractures around the knee (PPKFs) present a difficult clinical scenario for the following reasons:
They mostly affect older adults and are complicated by the increased prevalence of comorbidity, cognitive and functional impairments seen in this population; these nonoperative factors need to be addressed in order to maximize outcomes.
They are associated with a higher risk of morbidity and mortality; definitive treatment must allow for early mobilization.
Operative management of periprosthetic fractures is inherently associated with increased infection risk due to open operative history.
Antecedent pain and/or a poorly functioning implant prior to periprosthetic fracture may indicate the need for an infection workup.
They are complicated by the presence of a total knee arthroplasty (TKA) and the wide spectrum of components, implant wear status, and surrounding bone stock.
The overall mechanical alignment must be evaluated prior to definitive treatment.
Total knee arthroplasty components may be stable or unstable, in good or poor alignment, and with or without good surrounding bone stock.
The wide variety of TKA components also adds difficulty, especially if revision is indicated. Some may be obsolete and no longer available.
A concomitant proximal hip prosthesis or implant is not uncommon, adding further difficulty and frequently requiring alternative fixation strategies.
There is no consensus on the ideal mode of fixation and/or treatment, and thus, several options exist.
Periprosthetic fractures around the knee require careful planning in order to achieve the goals of early mobilization, fracture healing, and continued long-term implant survivorship (ie, a stable implant rendering revision arthroplasty unnecessary). Treatment strategy depends on surgeon experience, skill level, and preference, but should also fall in line with several principles in order to achieve a desired clinical result. This chapter presents a comprehensive and pragmatic approach to the management of periprosthetic fractures around the knee, along with some helpful tips and tricks to avoid pitfalls and complications.
2 Epidemiology and etiology
The incidence of PPKF approaches 2.5% following primary TKA, with even higher rates following revision TKA [1–4]. The following patient factors contribute to the incidence of periprosthetic fractures [3]:
Younger age (< 60 years) and older age (> 80 years) groups are at higher risk for PPKF.
Comorbidities that lead to falls [5].
Dementia, limited ambulatory status, or other neurological conditions.
Bone quality is poor.
Changes in bone quality secondary to altered femoral stress and strain following TKA have been reported to be important. Studies have noted significantly decreased bone mineral density about the distal femur following primary TKA [3, 6].
In a more recent finite element analysis, Sun et al [7] noted a high concentration of stress located just proximal to the femoral implant, which may explain why supracondylar periprosthetic fractures are the most common fractures seen after total knee replacement [3, 6].
Femoral notching of the anterior femoral cortex with the bone cuts for the femoral component has been implicated as a potential cause for subsequent supracondylar fracture. However, in large cohort studies, a correlation between femoral notching and periprosthetic fracture has not been identified [8, 9].
3 Diagnostics
Periprosthetic fractures following TKA are associated with morbidity and mortality rates comparable to those in hip fracture patients, and medical optimization must begin immediately upon admission [10]. A thorough history and physical examination along with the appropriate imaging modalities must be performed to formulate a treatment plan. Issues of frailty and potential problems with the original knee prostheses need to be considered.
3.1 Imaging
3.1.1 Plain x-rays
Plain x-rays are the primary imaging modality for diagnosis and in guiding operative treatment. Adequate preimaging pain management including femoral nerve blockade, utilizing cross-table views to obtain the laterals, manipulating the uninjured extremity, and gently propping up the injured extremity helps to obtain the desired imaging. The following views help achieve this:
True AP and lateral views along with oblique views are essential.
Full-length orthogonal view of the ipsilateral femur and tibia to examine the proximal and distal extent of the fracture lines and to provide an estimate of overall alignment as well as the existence of any preexisting hardware. Some centers can only obtain long leg x-rays with patients standing. A CT scanogram can be a helpful method of obtaining this imaging with patients supine.
A low AP view of the pelvis helps to judge overall leg lengths, especially if a hip implant is present.
For those fractures extending well into the femoral diaphysis, contralateral x-rays may also be valuable in recreating appropriate femoral rotation. This can be done by taking a perfect AP view of the knee, moving up to the ipsilateral femur and taking an AP of the hip. The profile of the lesser trochanter (LT) can be used to match the version on the injured side.
Previous serial x-rays of the affected implant should be acquired, whenever possible. Analyzing previous serial x-rays offers the best insight into potentially loose components (aseptic or septic). If serial x-rays are unavailable, at the very least, try and obtain the most recent follow-up x-ray, as it provides the most recent component alignment prior to fracture.
3.1.2 Computed tomography
Advances in software may provide even more information out of computed tomographic (CT) scans than previously realized ( Case 1: Fig 3.14-1 ) [11–13].
CASE 1
Patient
A 63-year-old man was struck by a car as he stepped off a curb sustaining a closed injury to his right knee. This happened 3 years after a total knee arthroplasty of the right knee.
Comorbidities
Hypertension
Treatment and outcome
The right lower extremity was neurovascularly intact. The AP ( Fig 3.14-1a ) and lateral ( Fig 3.14-1b ) x-rays of the knee exhibited a periprosthetic fracture about the tibial component. Further workup with computed tomography denoted a multiplanar fracture about the implant ( Fig 3.14-1c–f ) with a notable coronal plane fracture across the tibial tubercle ( Fig 3.14-1f ). A dual incision approach utilized the previous midline incision, distally extended to fix the tubercle component ( Fig 3.14-1g–h ), followed by a laterally based incision over Gerdy′s tubercle to assess the lateral tibial plateau. Orthogonal plate placement was performed, with a long lateral plate utilized to disperse the deforming forces inherent in a proximal third tibial fracture. The patient went on to uneventful healing ( Fig 3.14-1i–j ). Here, key points are not only to restore proper component alignment in relation to the femur, but similar to the setting of a primary total knee arthroplasty (TKA), the final examination of TKA stability and tracking should be performed. Assuming the gaps were properly balanced prior to the fracture, lack of needing to upsize or downsize the liner is a crude measure of appropriate fracture reduction.
Despite metal artifact (ie, distortion of image quality caused by metal interference during scanning), conventional CT can offer:
Better fracture characterization than plain x-rays in regard to the extent of fracture and degree of comminution.
Reconstructed images in different planes to better assess specific fracture line locations.
Highly sensitive and specific information regarding osteolytic pockets about the implant when combined with standard metal artifact reduction protocols [13].
Compiled 3-D reconstructions can also provide improved fracture pattern visualization. Dual-energy CT (DECT), a relatively new technology, has proven especially useful in reducing beam-hardening artifact created by metal implants [11, 12]. Ferrara et al [11] utilized DECT in order to reduce metal artifact and calculate TKA component position with subsequent clinical correlation. The authors reported DECT as a highly reproducible and accurate tool to assess TKA component position. Pessis et al [12] utilized the technology to recreate the DECT images into virtual monochromatic spectral images. In other words, images similar to plain x-rays were recreated but with a significantly higher degree of characterization, with information obtained from the DECT, and with additional metal artifact subtraction. While this new technology is on the cutting edge, its clinical availability and application needs further investigation.
3.1.3 Magnetic resonance imaging
Similar to CT, advances in magnetic resonance imaging (MRI) software and design sequences have provided greater ability to suppress metal artifact and characterize surrounding soft tissue and osteolysis about a TKA [14–16].
In the setting of periprosthetic fractures, however, MRI plays a limited role, mostly due to difficulty in performing the study in acutely unstable fracture patients. Subjecting an older patient to a confined loud area for a relatively long period is not a pragmatic approach to care, especially when the information obtained is comparable to that of CT [11]. Suspected ligamentous instability should be examined and addressed intraoperatively for TKA and does not typically require advanced imaging.
4 Classification
The purpose of classification systems is not only to help properly diagnose the injury but more important to help in guiding the optimal treatment choice. While some classification systems rarely do both, the most commonly applied systems for periprosthetic fractures about the femur are generally consistent in guiding the appropriate treatment based on the proper diagnosis. While some have attempted to classify periprosthetic fractures involving tibial and patellar components, these systems are largely not used in the clinical setting [17–20]. In general, proper treatment for periprosthetic fractures around the femoral, the tibial, and the patellar components are based on implant stability, the quality of the surrounding bone stock, and for the fractures about the patella, the status of the extensor mechanism.
4.1 Su classification
The Su classification [21] focuses primarily on fracture location in relation to the femoral component, which potentially aids in dictating treatment, but does not address implant stability and/or bone stock:
Type I: Fracture is proximal to the femoral component.
Type II: The fracture extends proximally with the origin at the proximal extent of the femoral component.
Type III: Includes any fracture line seen within the femoral component.
In general, intact implants with fracture lines originating and/or extending proximally from the upper end of the femoral component can be treated with open reduction and internal fixation (ORIF), while a loose implant or fractures that are within the body of the femoral component should be considered for revision. However, while a general treatment algorithm can be applied, specific circumstances can yield different operative strategies.
4.2 Unified Classification System (UCS)
This classification system aims to unify classification systems used for periprosthetic fractures around various joint replacement components (eg, hip and knee) into a single system that can be universally applied to any periprosthetic fracture [22]:
Type A: This is a fracture of an apophysis or protuberance of bone, eg, tibial tuberosityor greater trochanter in hips.
Type B: This involves the bed supporting an implant, eg, fracture of the femoral shaft around an arthroplasty stem or fracture of the patella that has been resurfaced. This group can be subdivided into:
B1: Implant is well fixed.
B2: Implant is loose.
B3: Implant is loose and bone bed is poor quality because of osteolysis, comminution, or osteoporosis.
Type C: Fracture is in the bone containing the implant but is distant from the implant.
Type D: Fracture affects one bone that supports two replacements, eg, femur following hip and knee replacement ( Case 2: Fig 3.14-2 ) or tibia following knee and ankle replacement.
Type E: Involves two bones supporting one replacement, eg, fracture of femur and tibia after knee replacement (“floating knee replacement”).
Type F: Involves a joint surface that is not replaced but is directly articulating with an implant, eg, patellar fracture when the patella has not been resurfaced or acetabular fracture after hip hemiarthroplasty.
CASE 2
Patient
A 73-year-old woman sustained low-energy falls 7 years and 5 years after a right total hip arthroplasty and total knee arthroplasty, respectively.
Comorbidities
Morbid obesity
Hypertension
Hyperlipidemia
Type 2 diabetes mellitus
Treatment and outcome
Initial workup and x-rays revealed a long, spiral, interprosthetic fracture (Unified Classification type D) between the two implants ( Fig 3.14-2a–b ). Decision making for definitive fixation relied heavily on early mobilization and immediate weight bearing. Lag screw fixation with lateral plate, along with a lateral plate alone was contemplated. However, due to the long extent of the fracture, the aforementioned options would not allow for immediate weight bearing. Thus, the decision was made to proceed with a combined retrograde nail and lateral locking plate combination that would allow for immediate weight bearing ( Fig 3.14-2c–h ). To allow for more stability without absolute rigidity, the reamed intramedullary nail was linked to the plate via the proximal and distal locking holes, forming a linked construct. The patient was made weight bearing as tolerated, and eventually there was uneventful healing ( Fig 3.14-2i–j ).
5 Decision making
For effective decision making, the basic treatment principles are as follows:
Obtain as much information as possible about the articular design of the present implant. This will, for example, enable the surgeon to know when a posterior stabilized knee replacement will permit access for intramedullary fixation or not. Useful reference guides for this purpose have been published [23].
Careful tissue handling and less invasive techniques should be performed whenever possible. Specific tools are available and helpful.
Operative strategy must aim to achieve a stable construct. This includes spanning the entire femur to avoid stress risers and to distribute forces along a longer length.
For fragility fracture patients (FFPs), there is no alternative to immediate mobilization with full weight bearing (FWB) and no external splints hindering mobility (see chapter 1.8 Postoperative surgical management).
Assess the stability of the prosthetic joint replacement prior to surgery. In the absence of clear radiological evidence of loosening the concept of a “happy knee replacement” can be employed. If the patient had no preinjury problems with the knee replacement, and the x-rays do not show obvious loosening, then it is fairly safe to assume that the knee prosthesis is stable enough to be retained. An “unhappy knee replacement” (eg, pain, swelling, stiffness, poor function) should be regarded as possibly loose or unstable, and should be considered for revision. Here, this decision can be made intraoperatively by assessing the overall stability of the implant.
Contingency plans need to be agreed preoperatively. Occasionally, despite good preoperative assessment, new information may become apparent during the procedure and the operative strategy needs to be adapted. For example, a presumed well-fixed implant may be identified as loose during surgery. A surgeon experienced in both trauma and arthroplasty would be well prepared to manage such a scenario if conversion from a fixation strategy to a joint replacement revision strategy is required ( Case 3: Fig 3.14-3 ). Many trauma surgeons need to ask for assistance from arthroplasty colleagues in such a scenario.
Orthogeriatric care involves assessment of comorbidities and frailty that will help guide management and shared decision making with the patient and families [24, 25]. Frail older patients usually have delicate soft tissues and are prone to soft-tissue complications. Careful tissue handling and less invasive techniques are often required. The specifics are discussed in chapter 1.2 Principles of orthogeriatric surgical care.
5.1 Operative treatment
With few exceptions, periprosthetic fractures around the knee are managed operatively. The UCS classification can be used to outline, in general terms, the treatment options for periprosthetic fractures around the knee.
Type A: if the apophysis or protuberance is displaced and is important to the function of the joint then it cannot be ignored and will require operative treatment. This is usually the case with avulsion of the tibial tuberosity or the poles of the patella.
Type B: Management is usually determined by subtype:
Type B1 fractures can often be treated with fracture fixation techniques.
Type B2 fractures often require revision of the loose component often combined with fixation of the fracture using techniques such as long stem implants and cerclage fixation.
Type B3 fractures may require complex arthroplasty reconstruction techniques.
Type C: the implant can often be “ignored” and fracture fixation performed using the principles outlined below.
Type D: the fractures can be further analyzed by using a “block out analysis”. In a fracture between a hip and a knee replacement, for example, block out the hip and assess the type of fracture present just for the knee. Ask it is a B or C type fracture. Repeat the process blocking out the knee and assessing the hip fracture. Then formulate a treatment plan following the general principles for whatever type of fracture is identified for each aspect of this “block out analysis”.
Type E: follow the same logic of a “block out analysis” as described for type D.
Type F: if displaced, the fracture of an unsurfaced patella will usually require operative fixation.
5.2 Plate, nail, or revision arthroplasty?
Surgeons should remember that these techniques aim to employ relative stability and indirect fracture healing. Fixation should also enable early FWB. Initial assessment of the fracture location can aid in determining if fixation is possible. Very low fractures that run below the anterior flange are often associated with loose components and revision components should be on hand as backup. Frequently, component stability assessment is difficult to assess preoperatively and needs to be made intraoperatively. In periprosthetic TKA fractures, however, there is a lower incidence of needing revision as most fixation strategies are amenable to healing. Revision TKA or even distal femoral replacement (DFR) is reserved for the settings of obvious severe bone loss and/or lysis.
CASE 3
Patient
A 78-year-old woman sustained a low-energy fall 16 years after a left total knee arthroplasty.
Comorbidities
Hypertension
Osteoporosis
Treatment and outcome
The x-rays revealed a periprosthetic fracture about both the femoral and tibial components ( Fig 3.14-3a–b ). Initially seen and evaluated at an outside institution, the treating surgeon, who was trauma trained but without an arthroplasty background, stabilized the distal femoral fracture in a good position to allow for healing ( Fig 3.14-3c–d ). Further questioning revealed symptoms of loosening prior to fracture, and on closer examination of the injury images, areas of osteolysis and loosening were likely the stress risers that caused an insufficiency fracture about the tibial component. Following stabilization, the patient was then referred to our senior author. Upon healing, the patient noted continued pain with weight bearing, and was revised on both the femoral and tibial sides with a retained lateral plate (albeit distal screws were removed). Five years following revision, the patient remains pain free, with full range of motion, and walking with a cane ( Fig 3.14-3e–f ).
In regard to fixation, deciding between an intramedullary (IM) nail or a plate can be based on surgeon preference, the TKA design (posterior stabilized versus cruciate retaining), and preinjury range of motion (ROM). If the patient has limited ROM prefracture, reamed IM nailing may actually cause a malreduction since the appropriate starting point will not be possible. Fractures that are above the level of the metadiaphyseal junction are typically more amenable to either anterograde or retrograde IM nailing. At the level of the metaphyseal junction, surgeon preference usually can dictate plating or reamed IM nailing (if amenable).
5.3 Nonoperative treatment
Nonoperative treatment may be more appropriate for severely ill patients, those that have advanced dementia, are suffering from profound frailty and sarcopenia, and for patients who are chronically nonambulatory. Even in these patients, however, operative stabilization may be helpful for pain control, protecting soft tissues, and facilitating easier transfer and hygienic care; for the extremely frail patients, a definitive spanning external fixator can offer reasonable results.
6 Therapeutic options
6.1 Initial treatment in the emergency department
As with all FFPs, close attention to preoperative hydration, blood loss, and pain control is necessary. Assessment of nutrition, functional and cogntive status, and goals of care are important. Discharge planning should also be performed on admission. Preoperative optimization aims to achieve safe operative treatment, but is also important for achieving postoperative mobilization and avoidance of in-hospital complications (see chapter 1.4 Preoperative risk assessment and preparation). Pain control techniques should include careful use of analgesic medication in patients prone to adverse effects, the use of regional anesthetic techniques, and appropriate preoperative immobilization strategies (see chapter 1.12 Pain management). Traction is not usually required for PPKF but may be of benefit when the femur is shortened or severely displaced. With any immobilization, padding and protection of the skin to prevent pressure ulceration is critical.
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