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Postoperative Periprosthetic Fractures in Total Hip Arthroplasty
Introduction
Periprosthetic hip fractures include injuries along the proximal femur and surrounding the acetabulum. They may range from relatively simple fractures with a stable implant to major injuries with components that require revision. Management of such fractures requires a surgeon to borrow and blend principles for fracture treatment with concepts and “rules” of hip arthroplasty. These two disciplines often have conflicting ideas for treating a postoperative periprosthetic fracture, but it is truly an art to blend concepts from both subspecialities to provide optimal outcomes for our patients.
With an increasing number of people undergoing hip arthroplasty, a longer projected lifespan and more active/demanding patients, the number of periprosthetic fractures continues to rise. At our own institution, we have seen an increase in the number of revisions for periprosthetic fracture from 6.2% to 7.2% over the last 10 years. Some studies have projected the prevalence of periprosthetic fractures to increase an average of 4.6% over the next 30 years (which is similar to the rate seen at the authors’ home institution). , This is in part attributed to the aforementioned factors coupled with the growing worldwide trend toward cementless total hip arthroplasty. In the last decade, there has been substantial research regarding the significant morbidity and mortality of these injuries, spurring an influx of new research looking at predictive measures based on patient anatomy and implant design using clinical data and finite element analysis (FEA). The ultimate goal is to potentially identify particular implants that will have lower risks based on anatomic variations that exist. Modern technologies such as machine learning, edge detection software, and FEA hold promise to shed some light on predictive measures with associated solutions for lowering the rates of postoperative periprosthetic fracture. Preventive measures remain paramount, as the financial burden of periprosthetic fractures could result in a tidal wave of costs in the upcoming years. ,
The remainder of the chapter will focus on the epidemiology, diagnosis, classification, management, and outcomes of these fractures for both the femur and acetabulum. It is important to understand the following concepts not only for the treatment of these fractures but to also recognize at-risk cases that may be managed prior to a fracture occurring. By remaining vigilant in the aspects of diagnosis and evaluation, we may be able to achieve an “ounce of prevention.” Similarly, when necessary, working in a timely manner, optimizing modifiable factors and meticulous surgical technique can ensure the best outcomes in these difficult cases.
Periprosthetic Femur Fractures
Epidemiology
For the reasons mentioned previously, the incidence of postoperative periprosthetic fractures (PPF) is expected to follow suit, particularly in the femur. A true prevalence has been difficult to establish, yet numerous global joint registries approximate the incidence of PPFs of the femur to range between 0.1% and 2.6%. Frenzel et al. estimated about a 20% increase in the number of PPF cases over a 5-year span. The complications associated with femoral PPF pose a significant financial burden on health care systems worldwide. This is due to the greater costs attributed to increased surgical time, length of stay, and manifestations of perioperative complications. Further, timely management of these injuries is paramount, as Scott et al. recently found an increased risk of medical complications, surgical complications, and 90-day risk of prosthetic joint infection if revision for a PPF is delayed for more than 48 hours.
Preoperative Risk Factors
It is essential to recognize which patients are at higher risk for femoral PPF in order to intervene early and possibly prevent these complications from occurring. In general, risk factors for a postoperative PPF can be broken down into patient-related factors (age, body mass index [BMI], physiologic age, and so on) and surgical factors (planning, surgical technique, implants utilized, and the like). Furthermore, it is important to consider the differences associated with an early versus late PPF of the femur. There are numerous unique relationships and findings that are more related to late periprosthetic fractures, particularly those occurring years after the index procedure. A summary is shown in Table 23.1 .
TABLE 23.1
Risk Factors for Femoral Periprosthetic Fractures
Patient-Related Factors
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Surgical Factors
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Late PPF Risk Factors
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While the focus of this chapter centers around postoperative fractures, it is important to recognize that many early PPFs are thought to be missed intraoperative injuries. One explanation for a “missed” intraoperative fracture is the advent of minimally invasive or “new” surgical approaches in THA. With such procedural changes, the surgical field continues to diminish in size, giving limited line of site during the operation. Further, an approach-specific learning curve must be mastered, and early signs of fracture are often not readily detected on routine imaging. For these reasons, it is crucial to remain hyper-vigilant when inserting a femoral stem through any surgical approach.
Patient-Related Factors
For femoral PPFs, female patients and those over the age of 65 years are known to be at higher risk than the general population for these injuries. Additionally, those with systemic metabolic bone disease, neuromuscular deficits, inflammatory arthritis, osteoporosis, and proximal femoral deformities are at higher risk. , , Concerns for long-term bisphosphonate use and atypical PPFs of the femur have been realized, described in the literature and must be a consideration after a total hip arthroplasty.
Intraoperative Risk Factors
Surgical technique and planning can also influence whether a patient is at risk for sustaining a perioperative prosthetic femur fracture. When preparing the femoral canal during a primary or revision THA, it is imperative to minimize eccentric reaming (make sure that you are lateral prior to initiating reaming) and avoid perforation of the cortex (particularly anteriorly or laterally), as both events have been identified as significant contributors to an early PPF. Surgical approach, implant type, and means for fixation (cemented vs. cementless) have been implicated as surgical factors associated with potential fracture. The likelihood of a PPF within the first 30 days after surgery is up to 10 times greater in uncemented versus cemented THA. , Thinner distal cortices and a decreased meta-diaphyseal taper are anatomical roadblocks that must be managed to prevent a PPF after a cementless primary THA. Berend et al. suggest that anatomic characteristics also give rise to a higher chance of a PPF when using the anterolateral approach.
Compared with primary THA, there is an increased risk of up to 4% of PPF in revision THA cases. , Younger patients with a more active lifestyle are at risk of suffering a PPF after revision THA. More specific to revision surgery, it is crucial to be mindful when removing hardware or retained cement, as this could result in a stress riser from thin cortices or a frank perforation of the femur. Such areas of concern should be accounted for during preoperative planning so that you are prepared during surgery to bypass such defects and minimize the potential contribution to a postoperative PPF. The typical rule of thumb is to utilize a longer femoral stem, twice the bone diameter, to prevent a PPF. , , , Additionally, proximal femoral remodeling (occurs in ∼20%–40% of revision cases) should be assessed during the planning stage, as this can be associated with an occult fracture, as well as fracture when trying to remove the in situ femoral component.
Postoperative Risk Factors for Late Periprosthetic Fractures
While the elderly female patients and those with osteoporosis are also likely to suffer from a late PPF, there are several additional aspects that distinguish these cases from early fractures. Patients with long-term indwelling prostheses face a greater threat of incurring a PPF over time due to bone adaptations, greater risk for injury, and wear-related complications. Lindahl et al. analyzed 1049 patients from the Swedish National Hip Arthroplasty Register over a 3-year span. They found that late PPFs were the third most common cause for revision surgery, with most patients demonstrating signs and symptoms of loosening prior to the injury.
Osteolysis and mechanical loosening are commonly recognized as two of the biggest risk factors associated with late PPF. The relationship between the two was previously thought to be in large part due to failures in cement fixation. However, further studies have shown that peri-implant osteolysis may result in aseptic loosening with subsequent PPF. Trunnion and metallic debris (from wear or component impingement) can also spark the initiation of an adverse local tissue reaction in both cemented and uncemented arthroplasty. , ,
Diagnosis and Evaluation
Diagnosis of a PPF of the femur is often easy to make. However, it is important to complete a thorough evaluation that includes a detailed history, physical examination, and assessment of radiographs (of adjacent and contralateral joints, when possible). Often, the initial presentation occurs in relation to a low-energy trauma, such as a fall from level height. Beals and Tower found in their study that only 8% of PPFs occurred as a result of a spontaneous fracture. In up to 50% of cases, patients may report antecedent upper thigh pain before the actual traumatic incident.
Surveying serial radiographic images (if available) is paramount in evaluating a suspected PPF complication. At a minimum, there should be a standard series of radiographs obtained to include anteroposterior (AP), frog-lateral, shoot-through lateral, and AP pelvis views of the affected extremity. Imaging studies should be carefully analyzed for eccentric polyethylene wear, cement mantle fracture, metallic shedding, component loosening, areas of osteolysis, and bony defects. If any of these factors are present, close monitoring is warranted to prevent a future PPF. In addition, this knowledge may direct the management of a current injury. Appropriate counseling on activity levels, management of osteoporosis, and prompt treatment of loose components can help prevent a PPF. A long-term monitoring program set up to track patients over time is imperative in order to accurately assess and avoid PPF complications. Haddad et al. have advocated for routine follow-up with operating surgeons, as they are more familiar with the subtleties of each individual case.
In the setting of an obvious PPF, it is rare to need higher-level imaging studies. However, when the fracture is subtle or occult, metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) or a technetium bone scan may be warranted to make the diagnosis. Computed tomography (CT) scans can be used to assess peri-implant bone defects but are typically not required to make the diagnosis of a PPF. A detailed review of femoral bone loss classifications are out of the scope of this chapter. However, the authors would be remiss if this was not acknowledged as part of the assessment of a PPF. Routinely, the Paprosky classification for femoral bone defects is followed to help guide management of the revision portion of treating a PPF.
In all instances of a painful THA, whether for fracture or not, it is important to make sure there is not an underlying periprosthetic joint infection (PJI). This can be ruled out by obtaining the appropriate tests as outlined by the Musculoskeletal Infection Society (MSIS) criteria. The presence of a PPF, like any acute fracture, may alter inflammatory marker levels; careful assessment must be followed with a low threshold for performing a joint aspiration. Furthermore, the specific criteria for ruling out infection may vary with an underlying PPF. Van den Kieboom et al. investigated different serum marker thresholds in the setting of a PPF. They found that a white blood cell (WBC) count of 4552 cells/μL, polymorphonuclear (PMN) percentage of 79.5%, erythrocyte sedimentation rate (ESR) of 45.5 mm/h, and C-reactive protein (CRP) of 16.7 mg/L were the optimal threshold levels for detecting a PJI in the setting of a PPF. If revision surgery is required for a concurrent PJI and PPF, then utilizing a two-stage technique with a spacer and fracture fixation, followed by reimplantation when the infection is cleared, may be prudent. Further laboratory testing (metal levels, allergy testing, and so on) is often not necessary in the setting of an acute postoperative periprosthetic fracture, as it will not likely impact the decision-making for treatment and may delay prompt management of the injury.
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