Periprosthetic and Peri-implant Fractures Workup

Updated: Feb 11, 2021
  • Author: Steven I Rabin, MD, FAAOS; Chief Editor: Murali Poduval, MBBS, MS, DNB  more...
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Workup

Laboratory Studies

No special laboratory studies are required for most periprosthetic fractures. A sedimentation rate and a complete blood count (CBC) with differential are useful if infection is suspected. 

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Imaging Studies

Radiographs of the entire bone are required to assess the condition of the joint above and below the fracture, the condition of the implant, the presence of any deformity or lesions that may influence surgical options, and the axial alignment of the bone. Two views perpendicular to each other, most often an anteroposterior (AP) view and a lateral view of the bone, are always required.

Careful attention to the condition of the cement mantle (for cemented prostheses) is important for determining the stability of the prosthesis. [8, 5] Stem subsidence and osteolysis imply loosening. [5]

Standard computed tomography (CT) and magnetic resonance imaging (MRI) are of limited utility because of scatter artifact caused by the metallic implant; however, CT with metal artefact reduction algorithms can identify subsidence and osteolysis more reliably than standard x-rays can. [5]

Bone scans are not specific.

For uncemented stems, the location of the periprosthetic fracture predicts loosening. Different prosthetic designs achieve fixation at different sites on the implant and bone. For example, in straight stems that have proximal fixation, the stem will be loose with a metaphyseal fracture, whereas in tapered stems with distal fixation, the stem will be loose with a diaphyseal fracture. This diagnosis of a loose stem is important, in that it may not be apparent on imaging but is crucial in determining classification and best treatment. [5]

For cemented stems, the type of prosthetic design determines stability. Shape-closed (eg, composite-beam) designs have rigid fixation at the stem-cement interface that is lost with any disruption of the cement mantle. Force-closed (eg, polished-taper) stems maintain stability because the stem subsides a short distance within the cement mantle and no bond is required between the stem and cement. Therefore, the stem is considered loose in these prostheses only when the cement-bone interface is disrupted but well fixed if the cement-implant interface is preserved. [5]

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Procedures

Aspiration of a failed joint replacement may help if infection is suspected.

Biopsy at the time of surgery is indicated if pathologic fracture or infection is suspected.

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Classification

There are different classification systems for different fracture sites, but the Unified Classification System discussed below now provides a standardized classification for all bones and implants.

For periprosthetic fractures around a total hip replacement, the most commonly used system has been the Vancouver classification of Duncan and Masri, [46] which provides information concerning the site of fracture, the stability of the prosthesis, and the quality of the bone. This classification specifies the following types:

  • Type A fractures are fractures of the greater (AG) or lesser (AL) trochanters
  • Type B fractures involve the femoral diaphysis and/or metaphysis around the femoral stem and are subdivided into three types: B1 fractures, which are associated with a stable stem; B2 fractures, which are associated with a loose stem but good bone stock; and B3 fractures, which are associated with a loose stem and significant bone loss
  • Type C fractures are well distal to the tip of the femoral stem [17, 46, 47, 5]

The Vancouver classification has high reliability, validity, and usefulness in guiding treatment, according to most authors. [47, 14] However, data from a Swedish hip registry showed that as many as 47% of stems thought to be stable were found to be loose at surgery; these findings underscored the need for a careful preoperative evaluation. [5]

The Unified Classification System has been suggested for pelvis and femur fractures around a total hip replacement [48]  and has been expanded to include additional sites in both the upper and the lower extremities as an extension of the Vancouver system. [49, 50] The fractured bone is specified by its Arbeitsgemeinschaft für Osteosynthesefragen (AO)/Orthopaedic Trauma Association (OTA) code number, the joint involved is specified as a modifier in square brackets, and the fracture type is then identified on the basis of its location relative to the implant. [50]

This system specifies the following types [17, 48, 49, 50] :

  • Type A is apophyseal (including greater or lesser trochanter of the femur, iliac spines or ischial tuberosity, greater or lesser tuberosity or distal epicondyles of the humerus, olecranon, poles of the patella, tibial tuberosity or malleoli)
  • Type B is in the bed of the implant (or close to it), with B1 around a well-fixed stem, B2 around a loose stem, and B3 around a loose stem with poor bone or bone defect (eg, for the acetabulum, B1 is a fracture of the acetabular lip/wall/floor that does not affect stability, B2 has a loose acetabular component but with adequate bone stock, and B3 has a loose component with severe bone loss)
  • Type C fractures are distant from the implant
  • Type D is an interprosthetic fracture between two implants (eg, between a hip and knee prosthesis or in the pelvis between two hip replacements)
  • Type E involves both bones supporting the implant (eg, acetabulum and femur for a hip replacement)
  • Type F is a fracture of a bone articulating with a hemiarthroplasty (eg, acetabulum after a hemiarthroplasty of the hip) [17, 48, 49, 50]

As an example of the Unified Classification System, a spiral fracture around a femoral implant of a total hip arthroplasty (THA) with loosening of the implant but good bone stock would be coded 32A1[IVB2]. [50]  An advantage of this system is that it is phrased in such a way that it can be applied to other prostheses besides total hip replacements. [17]

De Meo et al and Fan et al reported that the Unified Classification System is as reliable and valid as the Vancouver classification for periprosthetic femoral fractures. [49, 51]

Videla-Cés et al proposed a classification system for peri-implant femoral fractures, using nomenclature similar to that of the Vancouver classification summarized above. [52] Peri-implant fractures were classified according to whether the implant was a nail, a screw, or a plate, as well as according to the location of the fracture in relation to the original implant and the affected femoral segment. Further studies would be required to determine the utility and applicability of this system.

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