Total Hip Arthroplasty: Surgical Technique

Fig. 5.1

Algorithm for the evaluation of a painful total hip arthroplasty (THA). ESR Erythrocyte sedimentation rate; CRP C-reactive protein; WBC White blood cell count

5.3.2.2 Radiographic Evaluation

The radiographic evaluation includes an anteroposterior (AP) view of the pelvis and AP and lateral view of the affected hip, including the entire stem and the entire cemented area in cemented stems. Serial plain radiographs are the initial study of choice. These provide information related to the position and alignment of the prosthesis, changes in position, areas of osteolysis, stress shielding and remodeling changes, the quality of cement and interfaces, the quality of the greater trochanter, canal size, and other bone deformities. The surgeon must note the changes to the implant position and the bone, comparing it to previous films. Details that must be assessed are shown in Table 5.1 (Fig. 5.2).

Table 5.1

Data to be evaluated on preoperative radiographs

Bone references on the acetabular side – Kohler line – Isquion area – Teardrop – Superior migration of the cup	– Medial and anterior wall – Posterior column and posterior wall – Medial wall and posterior column – Acetabulum roof
Interface – Bone-implant – Cement-bone – Cement-implant
Osteolysis areas
Radiolucent lines around the implants
Quality of greater trochanter
Position of the implants
Wear polyethylene
Pelvic discontinuity

../images/479782_1_En_5_Chapter/479782_1_En_5_Fig2_HTML.png — Fig. 5.2

Bone references on the acetabular side

Criteria for cemented implant loosening were described by Harris et al. [4]. Radiographic assessment of cementless implant stability was described by Engh et al. [5] and Moore et al. [6]. All these criteria are shown in Table 5.2 [4–8].

Table 5.2

Radiographic signs of osseointegration and loosening

Definitive cemented femoral loosening

– Migration of the stem

– A continuous radiolucent line around the stem-cement interface

– A fracture of the stem

– A fracture in the cement mantle

Probable cemented femoral loosening

– A complete radiolucent line around the bone-cement interface

Possible cemented femoral loosening

– A radiolucent line extending between 50% and 100% of the bone-cement interface

Definitive uncemented femoral osseointegration: bone ingrowth

– No subsidence or stem migration

– No radiolucent line around the stem

– Presence of spot welds

Stable fibrous fixation of an uncemented stem

– No progressive subsidence

– A radiodense parallel, nonprogressive line around the stem less than 1 mm of diameter

– No other bone changes

Uncemented stem loosening

– Progressive subsidence or migration of the stem

– A radiolucent line around the stem greater than 1 mm of diameter

– A bone pedestal extending partial or completely across the intramedullary canal

– Hypertrophy cortical

Radiographic signs of osseointegration of porous coated uncemented cups

– Absence of radiolucent lines

– Presence of superolateral buttress

– Presence of medial stress shielding

– Presence of radial trabecular pattern

– Presence of inferomedial buttress

Cup loosening

– A progressive radiolucent line around the cup

– Changes in position or migration of the cup

5.3.2.3 Other Imaging Techniques

In addition to the radiographic study, in many cases it is necessary to perform other imaging techniques.

Computed tomography (CT) scan: Frequently, radiographs underestimate the size and the location of osteolysis and bone defects, and a CT scan can be especially useful to assess the quality of acetabular bone. They can also be used to diagnose infection as they can reveal fluid collections or joint distensions and, in cases of recurrent dislocation, help to more accurately assess the position of the implants.
Magnetic resonance imaging (MRI) can be used to assess the presence of pseudotumors and muscle damage in cases of metal-on-metal THA.
Nuclear medicine images: Technetium-99m (Tc-99) bone scintigraphy is frequently used to assess the stability of cemented implants, but it is not very specific because many other causes can increase the radionuclide uptake, such us infection, tumors, Paget’s disease, etc. In general, a negative or normal result excludes a diagnosis of loosening and provides more information than an abnormal scan. Tc-99 bone scans appear to be of limited usefulness in the evaluation of loosening in cementless implants.

The use of scintigraphy with gallium-67 (Ga-67), indium-111, or marked leukocyte is more sensitive for the diagnosis of infection [9].

5.3.3 Classification of Bone Defects

Once the surgeon has decided to perform a revision surgery, the following step is to classify the bone defect. Bone defects around the femur and the acetabulum will determine the reconstruction technique. Several classifications have been described to classify the bone loss around the components.

5.3.3.1 Acetabular Bone Defects

The American Academy of Orthopedic Surgeons Committee on the Hip (D’Antonio Classification) distinguishes two types of defects: segmentary, when there is a loss of the bone affecting the supporting walls or columns of the acetabulum, and cavitary, when the defect involves a volumetric loss of bone with the rim and medial wall intact [10]. Other classifications have been proposed to describe the extent of periacetabular bone loss in revision THA [11], such as Paprosky et al. [12], Saleh et al. [13], Gustilo and Pasternak [14], Gross et al. [15], Parry et al. [16], and Engh et al. [17].

One of the most used classification systems is the one described by Paprosky et al. in 1994 [12]. This is based on anatomical references (medial wall-teardrop, hip center-superior dome, Kohler line-anterior column, and ischium lysis-posterior column) and on the presence or absence of an intact acetabular rim and its ability to provide rigid support for an implanted acetabular component (Fig. 5.3). Based on the structures which are deficient, and the degree of hip center migration, Paprosky et al. offered recommendations regarding the type and amount of supplemental allograft needed for reconstruction, methods of graft fixation, and implant selection.

../images/479782_1_En_5_Chapter/479782_1_En_5_Fig3_HTML.jpg — Fig. 5.3

Paprosky classification of acetabular bone defects

Berry et al. defined pelvic discontinuity as a distinct form of bone loss, occurring in association with total hip arthroplasty, in which the superior aspect of the pelvis is separated from the inferior aspect because of bone loss or a fracture through the acetabulum [18]. It can be identified in preoperative radiographs as (1) a transverse fracture of the pelvis on the AP view, (2) a medial migration of the inferior hemipelvis related to the superior hemipelvis (a broken Kohler line), and a (3) rotation of the inferior hemipelvis in relation to the superior hemipelvis (asymmetry of the obturator foramen). Berry subclassified the AAOS type IV defects into three categories [18]: type IVa (pelvic discontinuity with cavitary or moderate segmental bone loss), type IVb (severe segmental loss or combined segmental and massive cavitary bone loss), and type IVc (previously irradiated bone with or without cavitary or segmental bone loss).

5.3.3.2 Femoral Bone Defects

To classify femoral bone defects, we can use the classification of the American Academy of Orthopedic Surgeons Committee on the Hip (D’Antonio Classification) [19] or Paprosky et al. [20], a classification system that defines femoral insufficiency based on the location of the bone loss and the degree of severity and proposes a treatment algorithm for surgical reconstruction based on these, which may allow surgeons to plan preoperatively for the type of femoral implant necessary to achieve a durable reconstruction (Fig. 5.4).

Type I: defect in which minimal metaphyseal bone loss has occurred and the proximal femoral geometry is maintained. These defects are typically seen after removal of an uncemented implant with narrow metaphyseal geometry or following removal of an implant with minimal proximal ingrowth potential. These defects can be treated with a cylindrical, extensively porous coated stem, or a tapered, proximally porous coated stem.
Type II: a defect with extensive metaphyseal bone loss and minimal diaphyseal bone in which the proximal metaphyseal bone may not be mechanically supportive for a proximally fitting implant. The entirety of the diaphysis remains intact. These defects are commonly seen after removal of a cemented femoral implant or removal of a proximally fitting stem with a wide femoral geometry. In these cases, a femoral implant that engages the diaphysis, with an ongrowth surface or a porous ingrowth surface, is typically recommended.
Type III defects are those in which the proximal metaphysis is completely unsupportive and the endosteal bone is severely deficient or absent. In Type IIIA there is more than 4 cm of intact diaphyseal bone available for distal fixation, and in Type IIIB there is less than 4 cm of diaphyseal bone available for distal fixation. The use of an extensively porous coated stem when at least 4 cm of intact diaphyseal bone was present is possible, but in Type IIIB defects, a tapered stem is preferred. Current total hip arthroplasties offer modularity, allowing for independent diaphyseal and metaphyseal fixation, with substantial intraoperative flexibility for version; limb length and offset can be also considered in these defects.
Type IV are those with severe metaphyseal and diaphyseal bone loss, typically with severe ectasia (pronounced expansion of endosteal bone with profound cortical thinning) of the femoral canal, making uncemented fixation unreliable. Reconstruction options are usually limited to proximal femoral replacements, impaction grafting with a cemented stem, and allograft prosthetic composites.