Osteosynthesis in periprosthetic fractures: Indications, tips, and tricks
Currently, most periprosthetic femoral fractures (PPFF) are surgically managed. In treating PPFF, the first and a crucial decision facing the surgeon is: Is osteosynthesis or revision arthroplasty indicated for my patient? Although the current literature does not provide a black and white picture of which patients require stem revision and which require internal fixation only, correct assessment of the stability of the prosthetic implants greatly assists the decision-making process.
It is generally accepted that, in case of a simple fracture type with stable stem, osteosynthesis can be an effective management. However, a loose stem can easily be misdiagnosed as a stable stem, forcing the surgeon to change the treatment plans intraoperatively, since fracture fixation of a loose stem often results in a painful and unsatisfactory condition for the patient. In this article, Karl Stoffel, Chief Physician at the Bethesda Hospital, University Hospital Basel, will first focus on the process of diagnosing a loose stem in the Vancouver types of fractures and then share some general principles as well as some tips in performing osteosynthesis in PPFF. Since the Unified Classification System fracture types D, E, and F are rare, complicated, and have little supporting evidence in the literature, these will not be covered here.
The Unified Classification System (UCS) expanded upon the Vancouver Classification system and in combination with the AO/OTA Fracture and Dislocation Classification, covers all periprosthetic fractures. The UCS fracture types are:
B, Bed of the implant
C, Clear of the implant
D, Dividing the bone between two implants
E, Each of two bones supporting one joint replacement
F, Facing and articulating with arthroplasty
Screenshot from: Velkes S, Stoffel K. Periprosthetic fractures around the hip. In: Schutz M, Perka C, ed. Osteoporotic Fracture Care—Medical and Surgical Management. Stuttgart: Thieme; 2018. 461–478.
Stable or loose: How can we decide?
In deciding the stability of the implant, many factors must be considered. Among these are patient-specific factors, fracture patterns, and injury history. To ensure that all essential factors are considered, Karl Stoffel describes an algorithmic approach (Figure 1) that helps surgeons systematically evaluate the fractures using tools that are easily available, such as the patient history, nature of the fracture, stem design, and plain x-rays.
A history of thigh pain
In case of low-energy trauma, patients do not always recall the actual trauma event and cannot provide any trauma history except for the description of gradually increasing pain.
Should a patient describe increasing thigh pain on weight bearing or reduced mobility due to hip problems prior to the fracture, there is a high possibility that a loose stem is involved [1–3].
Radiographic signs of implant instability
The first question when evaluating the x-rays is, "Is the fracture comminuted?". Even when the patient has no pain but the fracture is comminuted prior to the periprosthetic fracture, the stem is likely loose . If the patient has no pain and the fracture is not comminuted, then the decision tree branches from here depending on whether the stem in place is cemented.
High-quality plain x-rays assist in the diagnosis of PPFF tremendously. Karl Stoffel shares his requirements for x-rays with us:
- AP pelvis, centered over the symphysis
- The affected hip joint in a second plane
- The whole femur in two planes. It is important that the full length of the femur is imaged
The x-rays should be closely scrutinized to fully appreciate the entire extent of the fracture, as well as the presence, status, and type of any associated knee implants. In addition, Karl Stoffel says that, nowadays, computed tomographic (CT) scans are commonly taken for PPFF patients and are standard practice in many places. CT scans could provide more accurate assessments, for example, in fracture configuration, osteolysis, and visualization of radiolucent lines around the prosthesis or cement mantle, but some radiolucency around the stem can be caused by artifact. He therefore recommends a CT with a metal artefact reduction algorithm.
Determining the stability of cementless stems
If a patient has a cementless stem in place, a careful evaluation of the x-rays of the following points can shed light on the stability of the stem .
- Time-to-fracture: Intraoperative and early postoperative (first few weeks after implantation) fractures around cementless stems should be considered as having loose stems because the stems would not have the chance to become integrated.
- Subsidence of the stem: It has been shown that early axial migration (within two years postoperatively) of cementless femoral stems has good predictive power for cementless femoral components at risk for aseptic loosening during the first and early second decades after surgery [6–9]. A cementless stem with a subsidence of greater than 3 mm may be considered loose.
- Major osteolysis: Major osteolysis can be clearly visible in x-rays; subtler osteolysis may be more evident on CT scans. In case of major osteolysis, the stem should be considered loose and must be revised [10, 11].
- Location of the fracture: If the fracture occurs at the level of stem fixation, it is most likely that at least one of the bone fragments is no longer bonded to the stem. This is often obvious on plain x-rays, but CT may help to clarify any uncertainty.
- If the fixation is achieved proximally, ie, on the metaphysis, a fracture in the metaphyseal area means the stem is loose and needs revision. Although modular stems are fixed both proximally and distally, the proximal fixation is the crucial fixation. Thus, a modular stem with a fracture around the proximal area should be considered loose and revised. By the same principle, if the fixation is achieved distally, ie, on the diaphysis, a fracture affecting the diaphyseal area means the stem is loose and needs revision.
- Fully-coated stems are fixed along the whole stem, so the stem may still be well fixed even if only the metaphyseal or diaphyseal area is affected.
- Stems with anatomical design offer stability through the metaphyseal fill and distal curve. A fracture around the metaphyseal area and distal curve probably means that the stem is loose and needs revision.
Determining the stability of cemented stems
Cemented implants can be divided shape-closed (ie, composite beam) versus force-closed (ie, polished taper) fixation. These two types of stem have a different requirement for an intact cement mantle, and therefore, are subject to different criteria in deciding whether fixation or revision is indicated.
The fixation of shape-closed stems is dependent on good stem/cement bonding. These stems are usually precoated or have matt textured surfaces so that perfect bonding between cement and stem can be achieved.
Shape-closed stems must be rigidly bound to the cement to achieve fixation. Because the stem/cement bonding can be compromised even when the cement mantle appears intact, a fracture around a composite beam stem should be revised regardless of the state of the cement mantle . An exception is in the situation of an acute fracture. In this situation, a cement mantle fracture alone is not considered diagnostic of a loose stem.
The fixation of polished taper stems is achieved through the balance of forces. Since the fixation is derived from the ability of a polished tapered stem to subside over short distances, no bonding between the stem and the cement is required. Clinical experience shows that this type of stem can provide good long-term fixation even when the stem-cement interface seems compromised [12, 13].
Therefore, in polished taper stems, one should examine for signs of failure by checking if the cement/bone interface is intact. Loss of bone stock, presence of radiolucent lines, and osteolysis all signify a failed bonding between the cement and the bone, indicating that the stem is loose and needs revision.
Testing stability intraoperatively
Even with a systematic, algorithm-based assessment in the presence of CT scans, it is still possible that a loose stem can be identified only intraoperatively [1, 5, 14, 15]. Therefore, both trauma and arthroplasty surgeons (or a surgeon with expertise in both fracture fixation and revisional arthroplasty) may need to be present or on standby.
If any doubt remains after all the above points are covered, intraoperative stem stability tests may be necessary . There are two ways to perform such tests: 1) If the distal aspect of the stem is exposed at the fracture site, one can test for instability by generating shear force along the longitudinal axis between the prosthesis and the proximal bone fragment or cement. This can be done by grasping the femur with a pointed reduction forceps and the stem tip with a Kocher forceps. 2) Another way to diagnose a loose stem is to observe the relative movement of the stem. A well-fixed stem should move with the affected leg when it is manipulated; if the leg bone is moved but not the stem, then the stem is loose.
If the above maneuver is not possible, a formal arthrotomy and dislocation may be necessary to gain adequate exposure to exclude instability. This approach, however, requires more exposure of the joint, and increases the potential for postoperative dislocation.
General management principle: Importance of surgical planning
Surgical planning of PPFF is essential and should include the plan for the upcoming procedure and for one or two backup procedures, indicated by the intraoperative findings and complications. The two main choices in PPFF treatment are fixation (reduction and osteosynthesis) or revision. Each of these procedures may demand specialist capabilities beyond that of the treating surgeon, so both trauma and arthroplasty surgeons should be present or on standby [5, 16].
Part of the preoperative planning is to verify the availability of implants for all possible primary and backup procedures. Templates should be used to determine implant type, size, and possible site of placement to maximize fixation, suitable leg length, and offset. Instruments that facilitate implant removal (cemented or cementless) should be available if there is a possibility of revision. Templating, ie, performing a virtual operation before entering the operating room is a safe way to ensure that all components are available.
General management principle: Minimally invasive approach
Open (direct) fracture reduction should be used only when a near anatomical reduction with the minimally invasive plate osteosynthesis (MIPO) technique is not possible. In case of an open reduction, the minimally invasive principles should nevertheless be adhered to, and there should be minimal soft-tissue stripping to reduce the risk of nonunion or failure [16, 17]. Locking plates, which provide absolute and relative fracture stability and potentially preserve the periosteal blood supply to the fractured bone, are frequently used in modern internal fixation. In comparison, conventional plates require more extensive soft-tissue stripping and have inadequate screw purchase in osteoporotic bone [18–20].
MIPO incorporates indirect reduction and percutaneous insertion of plates and screws, which minimize the extent of soft-tissue dissection. MIPO is indicated in minimally displaced, nondisplaced, or comminuted fractures. In minimally displaced fractures, the fracture site can be exposed with a single reduction clamp followed by a gentle traction/rotation. The reduction can be maintained by either the clamp alone, or with additional cables, wires, or plate-independent lag screws (Figure 2). Using this technique, a near anatomical reduction may be achieve with a fracture gap of less than 2 mm .
Whether MIPO technique or open reduction is used it is important that (near) anatomical reduction with correct varus/valgus positioning of the stem is achieved. As has been shown by Tadross et al, all six patients with the stem in varus position had unfavorable results . When performing fracture reduction, it is therefore important to avoid leaving the proximal fragment in varus position (Figure 3). Depending on the bone quality, either a cortical allographic strut or a second plate may be employed to provide additional medial stability .
Are some plates superior to others?
There are many different plates available on the market. We asked Karl Stoffel if some plates are superior to others. He tells us, “For the most part, no differences have been demonstrated among the different plates. In the end, the decision comes down to which plates you are more familiar and more comfortable with, and this oftentimes means sticking to the brand that you feel you receive more support for from the manufacturer". He added, "In case of osteoporotic bones, it is important to use locking plates”.
How long should a plate be?
Based on the total femoral plating concept, to prevent secondary fractures, a long plate spanning from the trochanter to the distal femur can be used. According to Karl Stoffel, “for a simple periprosthetic fracture, a 10-hole plate is considered minimum length. For a comminuted fracture, additional screw holes will be lying over the comminuted area, so the minimum length should be a 14-hole plate.” As for the optimal number of screws to be used on a locked plate, it is still a subject of debate [22, 23]. It has been recommended that at least eight (preferably ten) cortices should be engaged distally and four cortices proximally [11, 24]. Excessive use of screws close to the fracture site may cause excessive plate stiffness, leading to nonunion and plate fracture, and should be avoided . Some authors advocate that three to four screw holes should be left empty at the fracture site to increase the working length (the distance between the proximal and distal screws at the fracture site) of the plate, and thereby avoiding local stress concentration .
It is mentioned in some literature that using a long plate may require too much soft-tissue stripping. We asked Karl Stoffel how he handles the issue of soft-tissue preservation: “Plate length is not an issue; there is no fracture at the plate end and therefore some soft-tissue disruption will unlikely influence the fracture-healing process. With the newer technology of angle-stable implants, much can be done with minimally invasive plate osteosynthesis. Implants such as locking attachment plates (LAPs) compensate the mismatches between the plate and bone shape and provide sufficient fixation strength.”
How to determine the number of screws and their placement?
Under bending loads, the focused load transfer of locking plates through fixed-angle screws can increase the periprosthetic fracture risk in the osteoporotic diaphysis compared with conventional plates.
Replacing the outermost locking screw with a conventional screw reduced the stress concentration at the plate end and significantly increased the bending strength of the plating construct compared to an all-locked construct .
Disregard the number of screws to be used, if the plate ends in the diaphyseal region, a conventional screw (instead of a locking-head screw) at the most distal plate hole may be essential to avoid creation of stress risers and recurrent fractures. Additionally, the oblique position of a screw increases the fixation strength by increasing the pull-out strength [27, 28].
Since screw insertion could potentially violate the integrity of the cement mantle and cause cracks in the cement leading to the loosening of the prosthesis, monocortical screws, in comparison to bicortical screws, may reduce the risk of compromising the cement mantle [19, 23, 29]. Even then, care should be taken to avoid excessively long screws since they may push against and loosen the stem .
How to ensure rotational stability and bicortical fixation?
Although plate fixation proximally around the stem can be achieved with screws, cerclage wires, or LAPs, biomechanically, constructs using screws in combination with cerclage wires result in significantly more stable fixation than constructs with cerclages alone, presumably by providing additional rotational stability . Furthermore, biomechanical tests showed that cables or double-looped cerclage wires both provided better fixation stability compared to a single-looped cerclage .
Another option for plate fixation around an implant is the LAP, which locks into the standard long locking plate and facilitates insertion of up to four locking screws that bypass the stem anteriorly and posteriorly for bicortical purchase (Figure 4). It has been increasingly studied in recent years and has shown good clinical results [32, 33]. Biomechanically, it can be used for plate fixation around an implant and has been shown to be superior to cerclage wires and monocortical screw combination .
Although there is conventional wisdom on how to treat different types of PPFF according to the Vancouver classification of fractures, there are certain conditions that needed special attention. For example, although type B1 fractures, having well-fixed stems, are usually treated with fixation, type B1 fractures with short oblique or transverse fractures (the "problematic fractures") at the tip of a cemented stem or just above the cement plug, have been shown to have high nonunion rate or failure rate [35, 36]. Pavlou et al showed that type B1 fractures treated with plate fixation took longer time to union compared to those treated with revision (mean 12 versus 4.5 months, respectively) . Presumably, due the decreased fracture area and increased torque and high shear force in these short, oblique fractures, such fractures are inherently less stable . In addition, the secondary healing factors remain problematic for these fractures because of the vascular damage and the disrupted periosteum at the fracture site . For such "problematic fractures", both cortical onlay strut allografts (either used alone or in conjunction with a plate) or stem revision both have shown good results and are recommended (Figure 5) [36, 38, 39].
While revision with long-stemmed prostheses for all Vancouver B2 and B3 PPFF is currently advised, some recent research suggests that open reduction with internal fixation (ORIF) could lead to an equivalent outcome [13, 40, 41]. As presented in more detailed in Part 3, this concept may be sound, but more data are needed to confirm the results and identify the outcome predictors, and the application may have to be more selective .
The management of PPFF is a complex and controversial topic. Ultimately, the choice of treatment modality for PPFF depends on the patient, injury history, fracture details, existing implant, and bone characteristics. Although operative intervention generally offers the best outcome, in patients who would not be able to tolerate surgery nonoperative management may be necessary.
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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