Peri-prosthetic fractures around the hip

Transcription

1 Vineet Sharma MS *, Aaron G Rosenberg MD** *Consultant, Advanced Hip and Knee Clinic, Chandigarh **Chief of Adult Reconstruction, Rush University Medical Center, 1725 West Harrison Street, Suite 1063 Chicago, Illinois ABSTRACT Periprosthetic fractures around the hip after a total hip replacement is a problem on the rise. The reason for that is an increasing number of total hips being performed and increased usage of uncemented stems and rising incidence of osteolysis. Both intraoperative and postoperative fractures present with difficult decision making problems and require proper treatment to prevent aseptic loosening or a complex revision hip replacement later. The article presents the etiology, classification and treatment options for these fractures. Keywords: Periprosthetic fractures, vancouver classification, revision total hip replacement EPIDEMIOLOGY & EXTENT OF PROBLEM As the number of hip replacements performed increases, and as the population continues to age, peri-prosthetic fractures around the hip are likely to increase in coming years. The problem may be further compounded by the rising use of uncemented stems and with the continuing problem of osteolysis 1. The rate of intra-operative fracture (with cemented or uncemented stems) has been reported as ranging from 1% and 3%-20% respectively 2-7. The exact prevalence of postoperative periprosthetic fracture is more difficult to determine but is estimated to be approximately 1% over the life of the prosthesis 8. The incidence during revision THR with cemented stems is around 6.3% and uncemented stems have been reported at 17.6% 1,9. Postoperative fractures occur in around 4% of revision cases 10,11, while the incidence with revision utilizing impaction grafting has been reported to be as low as 5% and as high as 24% 12,13. ETIOLOGY While multiple factors contribute to causation of fracture, most of these injuries are associated with a minor fall. The underlying cause in almost all cases is a decrease in mechanical strength Corresponding Author Dr. Vineet Sharma Advanced Hip and Knee Clinic, H.No.3, Sector-19A, Chandigarh. vineetsharma49@gmail.com of the host bone either due to osteoporosis, stress shielding or osteolytic lesions 8,14. Intraoperative fractures Systemic risk factors for intraoperative femur fractures during THR include those conditions which result in distorted anatomy or diminished bone quality such as osteopenia, rheumatoid arthritis, osteomalacia, Paget s disease, osteopetrosis, poliomyelitis and parkinsonism 3,15,16. Local factors include the use of press-fit cementless stems, deformity of the proximal femur, and revision surgery. Cementless stems may cause a fracture either due to the wedge effect or due to excessive force imparted to the proximal femur to achieve a stable press fit. Proximal femoral deformities, as seen due to prior fractures, DDH, prior corrective osteotomies, Paget s disease are associated with an increased risk of fracture 3,4,6, Revision THR is associated with an increased risk of intraoperative fracture for multiple reasons. These patients are usually older and have disuse osteopenia due to restricted mobility secondary to their failed arthroplasty. Femoral bone stock may also be poor due to prior surgery, infection or osteolysis. A high cortex to canal ratio is also risk factor for intraoperative fracture 20. Postoperative fractures Loosening of the femoral component is an important risk factor for postoperative fractures 22. Cortical stress risers are another important risk factor for fractures. Examples include pre-existing areas of focal femoral bone loss, screw holes, end of plates, 69

2 Sharma and Rosenberg and cortical perforation at the time of surgery. Osteolysis due to wear debris is an increasingly common phenomenon and a major risk factor for postoperative periprosthetic fractures 3,21. Impingement of a stem tip against the endosteal cortex may also create a stress riser, as a loose stem drifts into varus or a long, straight, revision cementless prosthesis impinges on the anterior cortex of normally bowed femur 22. Canal preparation during primary or revision hip replacement at the time of reaming or broaching or at the time of cement removal in revisions can cause perforation of cortex leading to postoperative fractures. The technique of controlled cortical perforation for revision of cemented femoral stems has been recommended for revisions, as it is associated with lower incidence of fractures 23. Classification There are over 10 classification systems for periprosthetic femoral fractures. Most of these are based on the location of the fracture along the femur and its relation to the prosthesis. A few of these systems take into consideration the pattern of the fracture, timing of fracture (intraoperative vs. postoperative) or the type of the implant (cemented vs. cementless). The most commonly used system, the Vancouver Classification has been reported by Masri et al. (Fig. 1 and Table 1) Intraoperative fractures The classification is based on the location of fracture in the femur 24. Type A fractures are in the proximal metaphysis and do not extend into the diaphysis. Type B fractures are diaphyseal but do not extend into distal diaphysis and can be bypassed by a standard long stem revision prosthesis. Type C fractures involve the distal diaphysis or metaphysis and cannot be bypassed by the longest revision stem prosthesis. Each of these fractures is further sub classified depending on the configuration and stability of the fracture. Subtype 1 refers to simple cortical perforation. These fractures usually occur during reaming for canal preparation or at the time of cement removal in revisions. Most of these fractures are diaphyseal (Type B1). An undisplaced linear crack is subdivided into type 2. These occur due to excessive hoop stresses in the bone either during broaching or during implant insertion (most commonly with uncemented stems) and are most common in the proximal metaphysis or diaphysis (type A2 or B2). Subtype 3 is a displaced or unstable fracture. In proximal metaphysis, type A3 fractures are either unstable trochanteric fracture or a displaced fractures of the calcar or proximal medial cortex. These usually result from forceful impaction of either the rasp or final prosthesis. Type B2 fractures occur during aggressive cement removal or reaming or can occur during forceful manipulation of the limb at the time of hip dislocation or component reduction. Type C3 fractures usually occur as a result of distal propagation of B3 fracture. Postoperative fractures The Vancouver classification for postoperative periprosthetic fractures takes into consideration fracture location, implant stability and quality of femoral bone 25. The classification system has been found to be valid with good inter and intra-observer reliability 26. Type A fractures occur proximal to the prosthesis and involve either the greater trochanter (Type AG) or the lesser trochanter (AL). Type B fractures occur around the stem or just below the tip of the prosthesis. These are further subdivided based on the stability of the implant and the quality of surrounding host bone. In type B1 fractures, the implant is well fixed and is loose in type B2 fractures. Type B3 fractures occur in severely deficient host bone stock due to generalized osteopenia, osteolysis or severe comminution, and is usually associated with a loose femoral component. The distinction between B2 or B3 fractures may be difficult on preoperative radiographs and may become apparent intraoperatively once the loose stem and cement have been removed. Type C fractures are located distal to the tip of the prosthesis. 70

3 The most common fracture pattern amongst these is the type B fracture with B2 and B3 more common than B1 25. PREVENTION As the treatment is complex, costly and fraught with complications, prevention of these fractures is extremely important. Preoperative planning The surgeon should anticipate any potential pitfalls that may be encountered intraoperatively and be prepared to manage them. A careful evaluation for any previously described systemic risk factors for periprosthetic fracture should be done in history, physical exam and review of preoperative radiographs. An assessment should be made of any scarring or adjacent joint contractures that may require special surgical techniques for surgical exposure, dislocation of the hip and manipulation of the limb during surgery. Adequate radiographic imaging to determine the location and extent of any bony deficiencies, discontinuity or deformity should be done next. If a revision procedure is being planned, decision should be made as to what components will require removal and the methods to remove them. Templating is imperative for all primary and revision procedures to determine the correct length, diameter, size and geometry of the prosthesis to be implanted to ensure correct fit and fill within the host bone. The prosthesis should be long enough to bypass any cortical defects or stress risers by at least 2 cortical diameters. Prosthesis longer than mm should be bowed to accommodate the normal curvature of femur. Intraoperative precautions Adequate surgical exposure is the key to prevention of intraoperative femoral fracture during THR. Both the surgeon and the assistants must be vigilant during manipulation of the femur and surrounding soft tissues. Extensile exposure not only helps in proper visualization but also minimizes the tethering effect of soft tissues on proximal femur. Special surgical exposures have been described for use in complex primary and revision settings 27. The commonly used osteotomy techniques are the trochanteric slide and the Extended trochanteric Osteotomy (ETO). Both these techniques help in wide exposure of acetabulum and proximal femur and also in dislocation in stiff and ankylosed hips. In addition, ETO helps in cement and component removal in revisions and also in canal preparation and correction of proximal femoral deformities 28,29. ETO is associated with a lesser incidence of intraoperative fractures and lesser surgical time in revisions 30. Periprosthetic fracture can occur during any step of THR like dislocation, canal preparation, implant insertion, cement or implant removal and hip reduction. Dislocation Protrusio, scarring, ankylosis or heterotopic ossification can all hinder dislocation of the hip. Adequate surgical exposure and soft tissue release are necessary to reduce the torsional forces on proximal femur in these cases during acetabular exposure and dislocation maneuver. Trochanteric osteotomy provides excellent exposure of the acetabulum and is extremely useful when exposure is limited by peri-articular scarring. An in situ osteotomy of the femoral neck can be used in protrusio and ankylosed hips. In revisions, dislocation should be done prior to removal of any implant or fracture fixation devices to prevent fracture through stress risers like focal osteolysis or screw holes. Implant removal and canal preparation Care should be taken during these steps to prevent any cracks or perforation in the bone. A number of manual tools, power tools and ultrasonic devices are available to aid in removal of cement as well as cemented and cementless implants. There is no substitute to cautious and appropriate use of these instruments to prevent intraoperative fractures. When the cortex is very thin, reaming with a flexible, cannulated reamer over a guide wire is recommended to prevent cortical perforation. Intraoperative fluoroscopy can be used in selected cases. 71

4 Sharma and Rosenberg Prophylactic cerclage wires can be used to prevent crack formation or propagation. ETO is an extremely helpful in implant and cement removal as well as preventing eccentric reaming and thus preventing fractures. Implant Insertion During uncemented stem insertion, surgeon should avoid underreaming distally or using a smaller size rasp in order to achieve a tighter press fit with the final prosthesis. Also using a long straight stem in a bowed femur can lead to fracture. If resistance is encountered during stem insertion, the surgeon should stop and reassess the situation to determine that the alignment and depth of insertion of the prosthesis matches that of the final broach. It is very important not to try and alter the version of the final stem as it causes high hoop stresses and can lead to proximal metaphyseal fracture. For cemented stems, extrusion of cement through the bone defects should be avoided as this can lead to subsequent fracture through unhealed stress riser. If ETO is used for exposure, it is advisable to place a cerclage wire below the terminal extent of the osteotomy to prevent fracture. In areas of weakened or absent host bone, cortical strut allografts placed beneath the cerclage wires will help dissipate the radial forces when the wires are tensioned. Reduction Fractures that occur during reduction of trial components or final components occur due to torsional forces on proximal femur. These forces are maximum when the tension in the soft tissues is increased as after excessive limb lengthening. Administration of a neuromuscular blocking agent to paralyze the muscles, minimum number of trial reductions and manipulating the prosthetic head and neck with a bone hook are other precautions to avoid fractures. Postoperative precautions These precautions aim at reducing the excessive stress on the reconstruction and limiting any of the risk factors associated with the fracture. Treatment of osteoporosis with Calcium supplements, Vitamin D and bisphosphontes is imperative. Patients with any medical or neurological problems predisposing to frequent falls should be instructed on safety and alteration of home environment to prevent falls. A close interaction between the surgeon, therapist and the patient regarding activity restrictions, weight bearing precautions and time course of rehabilitation process is important. Regular clinical and radiographic follow up helps in early detection and management of impending fractures. These situations include accelerated polyethylene wear and associated osteolysis, cortical perforation in association with extruded cement and excessive stem subsidence especially with varus malalignment. Closed reduction of a postoperative dislocation is ideally done under complete muscle relaxation to avoid any fracture during manipulation. TREATMENT OF INTRAOPERATIVE FRACTURES The treatment of intraoperative fracture depends on the location and configuration of the fracture as well as the stability of the fracture and the prosthesis. The most important principle is to define the full extent of the fracture with adequate exposure and judicious use of intraoperative radiographs. Excess soft tissue dissection should also be avoided to maintain the vascularity of the bone and enhance subsequent healing. The main goal of treating intra-operative fracture is to achieve stable, near-anatomic fixation of the fracture and secure fixation of the prosthesis in proper alignment. The surgeon should have a low threshold for aggressively treating these fractures in order to achieve these goals. Most series have shown good results when these fractures are securely fixed in proper alignment 5-7,10,17,20,30,31. Type A fracture (Proximal Metaphyseal) Cortical perforations of proximal femur (Vancouver type A1) are unlikely to compromise the fixation of prosthesis or increase the risk of postoperative fracture. Locally available bone graft, such as from acetabular reaming can be packed into the defect to promote healing and remodeling. Undisplaced cracks in the proximal femur (type A2) are typically stable and rarely compromise implant fixation. These fractures are ideally treated with a cerclage wire, preferably before stem insertion, to prevent crack propagation (Fig.2). These fractures are best identified by having an unobstructed view of the entire circumference of the calcar during stem insertion and by noting if the final prosthesis sits deeper than the trial component or by a sudden loss of firm end point during impaction. Displaced fractures of the proximal femur (Type A3) can compromise fixation of the femoral component, especially if proximally coated cementless stem is used. In addition to stabilizing the fracture with cerclage wires, it may be more appropriate to achieve distal fixation of the prosthesis by using a diaphyseal fitting extensive ingrowth prosthesis. Displaced 72

5 Cortical perforations (type C1) and undisplaced cracks (type C2), when identified intraoperatively, should be reinforced with allograft struts and cerclage wires to bypass the stress risers. The graft should be long enough to overlap the tip of the stem proximally to avoid creating another stress riser between the two. Bone graft can be packed into the perforation to improve healing of the defect. Displaced fractures of the distal femur (type C3) should be stabilized with a combination of cortical strut and plate. Fig. 2: An intraoperative type A2 fracture treated with cerclage wiring. fractures of the greater trochanter are inherently unstable and should be fixed with either cerclage wires or appropriate trochanteric fixation devices. Type B fractures (Proximal/Middle Diaphyseal) These fractures create a significant stress riser regardless of the degree of displacement. Prior to stem insertion It is recommended to place a cerclage wire just below any cortical perforation (Type B1) or undisplaced crack (type B2). Displaced, unstable fractures (Type B3) require open reduction and internal fixation to stabilize the femoral shaft. Oblique or spiral fractures can be stabilized with cerclage wires but transverse or comminuted fractures should be reinforced with fixation plates or cortical allograft struts. Once the fracture has been fixed, the revision prosthesis should be inserted to bypass the fracture. Type C fractures (Distal Diaphyseal/ Metaphyseal) Similar to type B fractures, these fracture also create significant stress risers. However, these fractures are too distal to be bypassed by even the longest stem revision prosthesis. Fractures diagnosed in immediate postoperative period. Many intraoperative fractures are first recognized in the postoperative radiographs. These must be evaluated thoroughly to determine their full extent, usually with additional radiographs. The majority of these fracture are minimally displaced, stable and do not compromise the fixation of the prosthesis and will unite with protected weight bearing and functional bracing as necessary 4,20. If the fracture pattern is unstable or the implant shows evidence of fixation instability re-operation is indicated TREATMENT OF POSTOPERATIVE FRACTURES Conservative management Nonoperative treatment of these fractures is associated with a high rate of nonunion and malunion, as high as 45% in literature. This in turn can lead to functional impairment, further fracture, early implant failure and complicated subsequent revision 22,32,33. Also prolonged recumbency required for nonoperative treatment may predispose the typical elderly patient to a number of medical complications like skin ulcers, fat embolism, pneumonia, thromboembolism and knee stiffness. At the present time, conservative management is recommended only for stable, undisplaced fractures that do not compromise the fixation of the implant. Operative treatment The options available for operative management of these fractures include internal fixation of the fracture alone, fixation of the fracture with revision of the prosthesis, and reconstruction of proximal femur with either modified impaction bone grafting or proximal femoral replacement. Cerclage wires and screw fixation Cerclage wires (either monofilament wires or multifilament cables) can be used alone to fix long, spiral fractures around the stem of a well-fixed prosthesis and for treatment of trochanteric fractures or to reinforce the femur to prevent the initiation or propagation of longitudinal cracks during canal preparation or stem insertion 34 (Figs. 3-5). However, they are 73

6 Sharma and Rosenberg Fig. 3 & 4: A type B1 fracture, the stem is well fixed and osteointegrated. Fig. 5: The above fracture treated with cerclage wiring. rarely used as isolated methods of fixation because they rarely provide enough torsional or bending rigidity. Screws in isolation can alsoact as stress risers and their purchase is usually poor in elderly osteoporotic bone. Ideally, these methods are used in combination with plate or allograft strut graft which acts as neutralization device to produce rigid fixation Plating Most periprosthetic fractures in which the femoral component remains well-fixed (type B1 and most type C) fractures can be treated with dynamic compression or locked plating. It is biomechanically advantageous to overlap the plate with the stem of the prosthesis to avoid any stress risers between the Fig. 6-8: A type B1 fracture in a well fixed uncemented stem. 74

7 two implants 35,36 (Figs. 6-10). Inserting screws trough the proximal part of the plate can be difficult in both cemented and cementless stems. Either unicortical screws or oblique screws, especially posteriorly through the thicker cortex or using cerclage cables posteriorly can avoid the problem 37. Plates are now available that allow combined use of cerclage cables and screws. Multiple studies have shown that these plates provide good biomechanical fixation 16, The newer locking compression plates have also been used for fixation of periprosthetic fractures but as would be expected data available at this time to recommend for or against their usage is limited 44,45. Minimally invasive plate osteosynthesis has also been recently used for treatment of these fractures. The advantages of this method include preservation of periosteal blood supply and thus more rapid and reliable fracture healing, less risk of infection, refracture and need for bone grafting 46. Cortical Allograft Struts Cortical onlay struts are usually obtained from either allograft femur or tibia. These grafts act as biological plates and provide initial fixation and in the long run, increase the bone stock and cortical strength. As they are more elastic than the metal plates, they are less likely to produce stress shielding, or distal stress risers. Disadvantages include prolonged and sometimes, incomplete union to the host bone, predisposing to fracture of the graft and failure of fixation. These grafts can either be used on their own or used to augment a revision prosthesis or complex femoral reconstruction as well as supplement fixation in combination with a cable plate or a compression plate. Cortical struts reliably unite to host bone via a series of processes, vascularization, followed by cancelization and finally remodeling 49. These are available freeze-dried or fresh-frozen. Although freeze-dried graft is less antigenic and equally strong in compression, it has substantially less resistance to torsional loads 47,48. Cortical stut grafts fixed with cable or wire can provide stable fixation of type B1 fractures and useful augmentation bone stock in type B2 and B3 fractures treated with revision stems. Cortical strut allografting is a technically demanding procedure and attention to detail is of utmost importance. When using 2 grafts, each graft should be approximately one third the circumference of host bone. One graft should be placed on the lateral aspect of femur and the other anteriorly. A High-speed burr should be used to shape the graft to maximize fit and to increase the contact area between the host bone and allograft. Technical pearls include: using cables rather than wires (cable tension should be high), using 3 or more cables both proximal and distal to the fracture, and using 2 struts at right angle to each other while avoiding medial soft tissue stripping to preserve vascularity 50,51. Fig. 9-10: The above fracture treated with plate with cerclage wires and screws and a cortical strut anteriorly. 75

8 Sharma and Rosenberg Revision hip arthroplasty The treatment of periprosthetic fracture with a loose femoral stem requires revision with long stem revision prosthesis 8,24. Proximally coated stems are not recommended for treatment of these fractures, as they tend to perform poorly due to poor proximal bony support 52,53. Similarly, cemented stems are associated with a high rate of failure and nonunion 32,33,53. The best results have been reported with the use of extensively porous coated stems as they function as intramedullary device and provide rigid fixation in distal diaphyseal bone 24,54 (Figs. 11&12). More recently modular tapered stems have been recommended in the patient with the very patulous diaphyseal canal. Proximally the fracture can be stabilized with cerclage cables and reinforced with cortical struts (Figs Fig. 11 : A type B2 fracture with loose femoral component. Fig. 12: The above fracture treated with revision of the stem with modular stem and cerclage wiring. Fig : A type B3 fracture, loose femoral component and poor bone stock. 76

9 Fig : The above fracture treated with revision of the femoral component with modular distal loading uncemented prosthesis, cortical strut allograft and plate fixation with cerclage wires. Proximal femoral replacement For some fractures with severe segmental bone loss proximally, reconstruction with a revision prosthesis may not be possible and proximal femoral replacement may be the only option left. Similarly, Gross has described the usage of massive proximal femoral allograft for reconstruction of the proximal femur 55,56. These constructs are best used with constrained acetabular system to reduce the dislocation risk due to abductor muscle detachment and subsequent reattachment to the prosthesis or allograft 25. SUMMARY The surgical management of periprosthetic fractures is complex and can have potential complications. Each case must be individualized. While there is no cookbook algorithm that can be applied to all cases, the Vancouver classification combines the important factors in the management of these fractures; fracture location,implant stability and bone quality and can be useful in guiding treatment. The goal is to obtain near-anatomic alignment, stable fracture fixation, and a secure and well-fixed femoral component in proper alignment which allows for early mobilization of the patient to prevent any complications associated with prolonged recumbency in old age. REFERENCES 1. Garbuz DS, Masri BA, Duncan CP. Periprosthetic fractures of the femur: principles of prevention and management. Instr Course Lect 1998;47: Garcia-Cimbrelo E, Munuera L, Gil-Garay E. Femoral shaft fractures after cemented total hip arthroplasty. Int Orthop 1992;16-1: Kelley SS. Periprosthetic Femoral Fractures. J Am Acad Orthop Surg 1994;2-3: Scott RD, Turner RH, Leitzes SM, Aufranc OE. Femoral fractures in conjunction with total hip replacement. J Bone Joint Surg Am 1975;57-4: Mont MA, Maar DC, Krackow KA, Hungerford DS. Hoop-stress fractures of the proximal femur during hip arthroplasty. Management and results in 19 cases. J Bone Joint Surg Br 1992;74-2: Schwartz JT, Jr., Mayer JG, Engh CA. Femoral fracture during noncemented total hip arthroplasty. J Bone Joint Surg Am 1989;71-8: Stuchin SA. Femoral shaft fracture in porous and press-fit total hip arthroplasty. Orthop Rev 1990;19-2: Beals RK, Tower SS. Periprosthetic fractures of the femur. An analysis of 93 fractures. Clin Orthop Relat Res : Christensen CM, Seger BM, Schultz RB. Management of intraoperative femur fractures associated with revision hip arthroplasty. Clin Orthop Relat Res :

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