Risk factors in treatment of periprosthetic fractures
Although primary total hip replacement (THR) has, in general, excellent long-term outcomes, periprosthetic femoral fracture (PPFF) after THR is a serious complication. The treatment of PPFF is clinically challenging with high mortality, morbidity, and associated costs. In recognizing the risk factors in treatment of PPFF, surgeons can try to optimize the treatment and contribute to society with efficient and effective patient care. In this article, the general risk factors in treating PPFF patients are discussed along with the ways to ameliorate them.
THR has become one of the most successful orthopedic interventions over the last decades. The excellent results have led to an expanded indication to include both younger and more elderly adults . Younger patients tend to be more active and more elderly patients tend to have poorer bone quality and increased comorbidity; such factors result in the increased probability of implant loosening and increase the chance of PPFF [2–4]. Meanwhile, with the increasing longevity of the population in general, patients with hip replacement can also be expected to live longer, which means that the implants will be in service for longer, and therefore have an increased likelihood of failing [1, 5]. This has been demonstrated by data from a Swedish registry; in the Scottish and Finnish populations this has been less clear [5–7].
Concerning such discrepancies in different epidemiological studies, Cao Li, president of the Chinese Hip Society and director of the First Affiliated Hospital Xinjiang University, Urumqi, China, reminds us that, "Epidemiological studies are empirical studies. Many of them may be simply too small to give us a definitive answer. Currently, studies on intraoperative risk factors of periprosthetic acetabular fractures are still lacking."
How does the outcome of revision THR compare with primary THR?
When compared with primary THRs, the risk of suffering a PPFF is much higher in revision THR, although not many studies have directly compared the incidences of PPFF between primary and revision THR. Lindahl et al reported an incidence of 0.4% in primary and 2.1% in revision THR, and Kavanagh estimated the incidence to be 1% after primary total hip arthroplasty (THA) and 4.2% after revision THA [3, 8]. In assessing 32,644 primary and 5,417 revision THR cases from 1969 to 2011 in the United States, Abdel et al showed a large increase in the incidence of intraoperative fractures in revision THR: from 1.7% for primary THR to 12.3% for revision THR. In the same study, the cumulative probability of suffering a PPFF was 0.8% for primary THR and 3.8% for revision THR at five years [1, 9] (Table 1). Meek et al came to similar results using data from a Scottish national database between 1997 and 2008 (52,136 primary THR, 8,726 revision THR); they reported a hazard ratio of revision THR being 4.4 times more likely to end in a PPFF than primary THR .
The mortality following surgical treatment for PPFF ranged widely from 3.3% to 34% at one year [10–13].
PPFFs often (75–84%) occur after minor trauma or ground-level falls, compared to “spontaneous” fracture (8–18%) after primary THR (the incidence of the latter can be as high as 37–50% after revision THR) [14, 15]. In a study by Bethea et al, it was shown that 75% of the patients treated for PPFF had prefracture radiographic evidence of loosening. The authors explained that, “As loosening progresses, a fibrous layer develops between the bone and the cement, increased movement at this interface results in further bone resorption.” 
While the fracture itself is easy to diagnose, component loosening often remains unrecognized. The history the preinjury symptoms and the knowledge of the mechanism of failure may shed light on the condition of the implants; both are therefore important for treatment decision-making. For example, spontaneous fractures in the early postoperative period should raise clinical suspicion for an unrecognized intraoperative fracture, whereas late spontaneous fractures are often associated with underlying osteolysis . In case of low-energy trauma events, patients often do not provide any traumatic history but describe a gradually increasing pain [16–18]. A prodrome of thigh pain, especially start-up pain, is suggestive of a loose femoral component that may have been a contributing factor to the fracture.
What are the risk factors?
Surgical management of PPFF is technically demanding, requiring skills in both arthroplasty and trauma. Implant loosening, compromised surgical bed, osteolysis, osteoporosis, and concurrent infection are some of the challenges that often confront the surgeons. Understanding and identifying the perioperative risk factors is a key step towards reducing complications and will help with the treatment decision.
Patient-related risk factors
Gender, age, and comorbidity
The treatment algorithms for PPFF are complex and can lead to relatively long operations and periods under anesthesia, greater blood loss, and unexpected incidents during surgery in comparison to native hip fractures. Advanced age, higher comorbidity, and lower body mass index at the time of surgery have been shown to be significant risk factors for postoperative mortality following surgical treatment of PPFF [19, 20].
In revision as in primary THR, the female gender has been shown to carry a higher risk for increased intraoperative risk of femoral fracture (Table 2). In the same study, age > 65 years was also a statistically significant risk factor (odds ratio [95% CI] of 2.5 [2.1 to 3.0]) for intraoperative fracture, but only in primary THR [1, 9].
In contrast, there was no difference in the risk of late postoperative fracture according to gender, although others have reported an increased risk of PPFF for female patients five (4.6% and 3.5% for female and male patients, respectively) and ten (6.6% and 5.6% for female and male patients, respectively) years after revision THR [5, 9].
Implant-related risk factors
Not all implants are created equal, and much research has been devoted to studying the performance of cemented versus uncemented implants, as well as different stem designs. Although there is no consensus on the optimal surgical technique and stem design for revision surgery, surgeons should be precautious when selecting an implant appropriate to meet specific patient needs.
Cemented versus uncemented implants
Berry et al reported that in primary THA an incidence of 0.3% in 20,859 with cemented and 5.4% in 3,121 with uncemented implants. In revision surgery, the incidences of fracture were higher: 3.6% during cemented and 20.9% during uncemented procedures . This increased risk of uncemented stems has been attributed to the increased force and hoop stresses placed on them from broaching or inserting an uncemented stem [22–24]. Recently, by summarizing a registry data of 40 years, Abdel et al observed an incidence of fractures of 5.8% in cemented stems versus 18.6% in uncemented stems in 5,417 revision THRs [1, 9]. Dale et al observed that in women, the risk of revision associated with uncemented THA increased with age in comparison to cemented THA. The situation was particularly extreme within one year after surgery: a 19-fold increase in revision due to PPFF was observed in women with uncemented THR compared to cemented THR (Table 3). Dale et al concluded that uncemented THA probably should not be used in women older than 55 years .
The usage of uncemented THA is nevertheless on the rise. We asked Cao Li how he handles the situation, "I have used uncemented THA in almost all my patients whether in primary or revision cases. The main considerations are both age and bone quality, ie, the cemented designs should be used in elderly patients with severe osteoporosis. In younger patients with good bone stock, however, a longer-term perspective is necessary. It is important to remember that revision of an uncemented stem is easier than a cemented one. Of course, one key surgical technique in implantation of an uncemented THA is to avoid intraoperative fracture. Young surgeons should pay more attention when performing an uncemented THA the first several times."
In treating PPFF, due to the suspicion that cement leakage may impede fracture healing, as well as the reported high rate of nonunion, early loosening, and higher refracture rate in cemented stems, exploration into cementless stems, and uncemented, extensive porous-coated long femoral stems have been reported to achieve good outcomes in patients with Vancouver B2 and B3 fractures [26–29]. More recently, fluted, tapered stems (modular or monoblock) have also been used to treat Vancouver B2 and B3 periprosthetic and shown good results [30–32]. With these results, the current trend has moved toward using uncemented stems in revision, especially in younger patients. Aside from having the adequate bone stock for stable distal fixation to prevent subsidence, cementless stems also preserve the bone stock in case of future revision .
How can surgeon-related risk be reduced when treating PPFF?
It was mentioned earlier that the treatment of PPFF is demanding and surgeons skillful in both arthroplasty and trauma management are required. For example, minimally invasive technique has the advantage of preserving the periosteal blood supply due to minimal soft-tissue stripping, which reduces the risk of nonunion, but it is a demanding treatment . Aside from better surgical techniques, in-depth knowledge of the Vancouver classification system is an essential tool for surgeons to reduce risk when treating PPFF.
Vancouver classification system
You may have heard that Vancouver type B1 fractures have a higher risk of failure than other Vancouver subtypes. Is this true? And what can we do about it? As Spina et al had commented in a recent publication, “Although most orthopedic surgeons use it (the Vancouver system) as a reference, few are those who strictly respect it.”  Maybe Spina et al are exaggerating slightly with this comment, but as has been discussed previously, the treatment algorithm of PPFF is complex. To ensure a correct treatment decision, a surgeon should first understand the Vancouver system of fracture classification and then be made aware of diagnostic pitfalls.
The Vancouver system provides a reproducible, validated framework to guide treatment decisions and has been widely used in the literature [35–38]. It characterizes fractures based on the location of the fracture, the stability of the implant, and the quality of the surrounding bone stock. Briefly, type A fractures involve the trochanteric region and are subdivided into AG (fractures around the greater trochanter) and AL (fractures around the lesser trochanter). Type B fractures involve the diaphysis and are subdivided into B1 (stable stem with adequate cement mantle, if applicable, and adequate bone stock), B2 (loose stem with deficient cement mantle, if applicable, and adequate bone stock), and B3 (loose stem and poor bone stock). Based on this classification, the general management principles involve the assessment of fracture location, implant stability, and the quality of bone stock and strength [22, 24, 32, 33, 35, 39]. More management details are also found in Part II and Part III of this series of articles [9–12].
Around the implant
Loose implant without
Loose implant with
Below the implant
Vancouver type A fractures
Since type A fractures occur at a low incidence, there is little in the published literature about them. Baochao Ji from the First Affiliated Hospital of Xinjiang Medical University, Urumqi, Xinjiang, China tells us, “There are pitfalls that surgeons should look out for. For example, late AG fractures are frequently associated with osteolysis, so x-rays should be carefully inspected for concomitant osteolytic lesions at the acetabular side and proximal femur. This is especially true for patients who had conventional polyethylene liner in their index surgery.” Further, “Late AG fractures tend to be low-energy fractures with minimal displacement in an elderly population. Surgical management should aim at addressing the underlying problem, that is, eliminating the particle generator (polyethylene liner exchange) and treating osteolytic lesions with bone grafting procedures. If none of the above is found, subsequent revision of the entire prosthesis may be difficult to avoid.”
The fractures that occur in the lesser trochanter with a stable stem can be managed conservatively, except when it involves a variable amount of the proximal medial femoral cortex (ie, “pseudo Vancouver A(LT)” fracture) leading to the destabilization of the stem. Such fractures really should be classified as Vancouver B2 fractures . Preoperative close inspection of x-rays is therefore vital to ensure that the fracture only occurred around the lesser trochanter. Otherwise subsidence, fracture propagation, and ultimately, stem loosening, may follow.
In case of a pseudo Vancouver A(LT) fracture, Baochao Ji advises that the standard treatment should be stem revision to a long, diaphyseal-engaging stem (Figure 1).
Vancouver B1 fractures
In theory, the management of Vancouver B1 PPFF, ie, around a stable stem, may seem straightforward. Assuming simple fracture type, type B1 fractures with stable stems can be treated with open reduction and internal fixation (ORIF) . In practice, diagnosing a stable stem can be very challenging.
It has been suggested that preoperative x-rays may not be reliable and it was recommended that the stability of fixation of the prosthesis should be checked intraoperatively [41, 42]. Corten et al reported that 20% of the type B1 fractures (classified based on preoperative x-rays) were found to involve unstable stems during the operation, leading to a change in the management plan .
Multiple authors have highlighted that B1 fractures had a higher risk of failure than other Vancouver fracture (sub)types [22, 44]. According to the analyses of outcomes of PPFF, 1,049 patients from the Swedish National Hip Arthroplasty Register, type B1 fractures had a significantly increased risk of failure in comparison to other types of fractures . The authors suspected that the misinterpretation and classification of type B2 fractures as type B1 led to the treatment of these fractures with plate fixation without stem revision. In summary, the unfavorable results of the type B1 fracture treatment may be caused by the misinterpretation of type B2 as B1 fractures, leading to suboptimal treatment [45, 46].
Surgeon-related risk: Unidentified periprosthetic joint infection
Cao Li emphasizes the peril of missed periprosthetic joint infection (PJI), "once the PJI is missed and broken out in patients who have already accepted the reconstruction operation for PPFF, then the catastrophic results that patients face are not just nonunion of fractures, but a threat to life. Therefore, the identification and treatment of the infection is of paramount importance in treating PPFF." In addition, "low-grade virulence infection may be the reason for looseness of the prosthesis, which may result in subsequent painful falls".
Although inflammatory laboratory markers may help in diagnosing PJI, the predictive value is still not encouraging . Data from the Mayo Clinic showed that, while a true infection was diagnosed at 11.6%, an elevation in white blood cell count was at 16.2%; in erythrocyte sedimentation rate, 33.3%; and in C-reactive protein, 50.5% . Therefore, patients should be thoroughly evaluated for symptoms that may suggest underlying infections (history of prior infection, wound drainage, redness and warmth around the surgical site, night pain). When facing a periprosthetic fracture with high suspicion of underlying infection, an aspiration with cell count and culture should be obtained preoperatively. Baochao Ji suggests, "Take at least six samples during the operation and perform sonication for culture postoperatively, then start a broad-spectrum intravenous antimicrobial regimen and maintain the coverage until definitive microbiological results have been obtained. The definitive oral antibiotic treatment then should be selected according to the antibiogram." Alternatively, intraoperative frozen sections have also shown reasonable sensitivity and positive predictive value in total knee and hip replacement surgeries [48, 49]. And more recently even intraoperative synovial tests to rule out infection, such as leukocyte esterase have proven to be effective and easy to use .
Postoperative risk factors
Reduced ambulatory capability is common among postoperative PPFF patients, and it is particularly detrimental for older patients [51, 52].
The PPFF patients are oftentimes older with a mean age in the mid-70s [3, 53]. Some of them are multimorbid patients and many naturally suffer from cardiovascular diseases and chronic respiratory disorder. At the same time, as mentioned before, the surgical treatment of PPFF can be complex and may involve copious blood loss and long surgical time. Both factors make the postoperative period particularly challenging for patients, and the postoperative phase often involve bedrest and mobility restriction of the affected hip.
Research results nevertheless tells us that, to avoid secondary complications, early mobilization of the patient should be encouraged . In a prospective study of 243 consecutive community-dwelling patients with hip fractures, the best predicator for mortality within 12 months after operation was the inability to standup or sit down at two weeks postoperatively (hazard ratio for inability to standup was 4.64 [95% CI 2.11–10.18, p < .001]; inability to sit down, 4.52 ([95% CI 2.10–9.72, p < .001]) .
In order for patients to achieve safe early mobilization, Cao Li suggests that an optimal rehabilitation program should involve a multidisciplinary team of rehabilitation professionals. In the early stage of rehabilitation, reduction of edema, prophylaxis of decubitus, pneumonia and deep venous thrombosis should be performed. The upper extremities can then be trained by elastic bands, and physiotherapy with a special emphasis on knee extension should prescribed for the preparation of future safe gait and stable standing. If the condition allows, a passive mobilization of the hip joint can be carried out with the help of a CPM knee rail. If walking on forearm supports is not possible, the first steps should be started on a high walker.
The treatment of periprosthetic fractures is complex and clinically challenging. Orthopedic surgeons should carefully evaluate the patient status, injury history, identify potential infections, and x-rays. Intraoperatively, avoid the pitfalls in accessing stem stability and fracture location. And lastly, design an optimum rehabilitation program to allow early mobilization and ensure the best outcome.
This series of articles was created with the support of the following specialists (in alphabetical order):
This issue was written by Maio Chen, AO Innovation Translation Center, Clinical Science, Switzerland.
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