Nikolaos Davarinos MD MSc1, Adam Hart MDCM MASc2, and John Antoniou MD PhD2 1 Orthopaedics, Bon Secours Hospital, Tralee, County Kerry, Ireland 2 Division of Orthopaedic Surgery, Department of Surgery, McGill University, Montreal, QC, Canada An anteroposterior view of both hips of our patient (Figure 34.1) and a lateral view of the left hip (Figure 34.2) are shown after a first‐stage revision THA performed elsewhere for infection. A second‐stage procedure was planned after a period of appropriate antibiotic therapy and normalization of inflammatory markers. Figure 34.1 Anteroposterior radiograph of both hips of the clinical case showing a fractured cement spacer in situ after a first stage revision left total hip arthroplasty. The goal of revising a loose acetabular component of a THA is to provide a stable construct that alleviates pain and restores lost function. Loosening of a primary acetabular component can be associated with significant periacetabular bone loss. Prior to revision, hip surgery it is of utmost importance to quantify the acetabular bone stock. Any deficiency needs to be addressed. Bone graft, reconstructive hardware, or a combination of both may be required. As such, a classification system for acetabular bone loss would facilitate preoperative planning. There is not a single accepted, standardized way to classify acetabular bone loss. The three classification systems most commonly used are: D’Antonio,1 recommended by the American Academy of Orthopaedic Surgeons (AAOS), Paprosky et al.,2 and Gross et al.3 Figure 34.2 Lateral radiograph of the left hip of the clinical case showing a fractured cement spacer in situ after a first stage revision left total hip arthroplasty. The overall quality in the literature is low. We identified one level II and three level V studies. The AAOS classification (Table 34.1) of D’Antonio is a descriptive classification.1 Table 34.1 AAOS classification. The Paprosky classification2 uses anatomical landmarks to classify the extent of bony deficiency (Table 34.2) and guides reconstruction based on available techniques. Defects can be graded as completely (type 1), partially (type 2), or non‐ (type 3) supportive. Table 34.2 Paprosky classification. * Minimum is ≤3 cm proximal to the superior transverse obturator line, and marked is >3 cm proximal to the superior transverse obturator line. ** Grade I = lateral to Kohler’s ilioischial line, grade II = to Kohler’s line, grade II+ = medial expansion of Kohler’s line into the pelvis, grade III = violation of Kohler’s line with some migration into the pelvis, and grade III+ = marked migration into the pelvis. *** Mild = minimum loss of the lateral border, moderate = complete loss of the lateral border, severe = loss of the lateral and medial borders. **** Mild = 0–7 mm distal to the superior transverse obturator line, moderate = 8–14 mm distal to the obturator line and severe ≥15 mm distal to the obturator line. Gross et al. devised a classification based on the type of bone graft required for revision (Table 34.3).3 Campbell et al. critically evaluated the reliability of these three classification systems showing inconsistency in both interobserver and intraobserver reliability among all three.4 Table 34.3 Gross classification. These classifications show limited reliability and should be considered a general guide to discern between simple and complex reconstructive scenarios. There is no clear best option. There is no consensus regarding the optimal method of reconstruction in cases of revision hip arthroplasty with severe bone loss. The major decisions regarding surgical technique for complex acetabular revision concerns the use of bone graft, cages, and cemented versus cementless components. The plethora of potential combinations of grafts and metallic devices has led to a huge diversity of reconstructive options in revision acetabular arthroplasty. This creates significant difficulty for systematic analysis of clinical literature incorporating a very heterogeneous mix of surgical techniques. Acetabular bone loss can be compensated by placing a high hip center or by using asymmetrical or bilobed acetabular components. Cementless hemispherical cups provide durable survivorship in the revision setting if initial stability and contact with sufficient host bone is possible. Cemented fixation of a polyethylene cup or liner into a supporting cage has often been the construct of choice where allograft is required to support more than 50% of the new acetabular component. Supplementary acetabular fixation may be necessary to stabilize pelvic discontinuity and protect or support bone graft and/or cups. Trabecular metal shells can be used for severe acetabular defects where bone grafting has traditionally performed poorly. The overall quality in the literature is low. Most of the evidence was level III–V with level IV being the most frequent. Basically, smaller defects (contained or cavitary) can be treated with impacted morselized cancellous allograft bone chips. Satisfactory outcomes have been reported using cementless porous hemispherical acetabular components for these defects.5–7 Noncontained, segmental defects are subdivided into those where host bone support for the implant is >50% (Paprosky 3A, Gross 2A) or <50% (Paprosky 3B, Gross 2B). Radiologically, these defects produce significant superolateral and superomedial cup migration respectively. Sporer et al. achieved 78% 10‐year survival with cementless acetabular components supported by distal femoral structural bulk allograft buttress for 3A defects.8 Paprosky et al. published a series in 2016 with a 21 year follow‐up concluding that the use of distal femoral allograft can be considered in young patients with type IIIA acetabular defects that could benefit from restoration of bone stock.9 Others have shown either good medium term survival with bulk grafts10–12 or frequent loosening with graft resorption.13,14 Options for 3B defects include placing the component high on the remaining host bone, implanting a large cementless acetabular component, using structural bone graft, or replacing lost bone with massive partial or total acetabular allograft, protected with an antiprotrusio cage, containing a cemented liner. Reconstructing the acetabulum with a high hip center has been associated with early loosening,15 although 94% survival at 10.4 years has been reported.16 Treatment of type 3B defects with cemented polyethylene cups and large allografts alone has produced poor results.17,18 The use of reconstruction cages improves their survival despite implantation difficulties and low potential for biological bone ingrowth.19 Use of porous tantalum acetabular shells, cups, and augments can address these difficulties.20–35 Brubaker et al.35 proposed specific interventions for different grades of acetabular defect based on a modification of the classification of Gross et al.,3 validated by Saleh et al.36 They calculated a prognosis for each intervention based on the available literature (Table 34.4). Kosashvili et al. reported good short‐term outcomes with the “component‐cage technique”, combining ilioischial cages with trabecular metal shells for pelvic discontinuity.30 Sculco et al. reported the evolution of the cup‐cage technique for major acetabular defects.37 Hourscht et al. discussed the reconstruction of AAOS type III and IV defects with the Ganz reinforcement ring.38 Abolghasemian et al. reported the reconstruction of massive uncontained acetabular defects using allograft with cage or ring reinforcement.39 Garcia‐Rey et al. published THA revision series using impaction allografting with mesh.40 Finally, Maruyama et al. published a new reconstruction method using a medial‐reduced cemented socket and additional bulk bone in conjunction with impaction morselized bone grafting fixed by cement.41 Conventional porous‐coated acetabular implants have proven effective in revision THA where bone stock is sufficient for stability and ingrowth, and success with these implants occurs when contact with host bone is greater than 50%.5–7 Antiprotrusio cages are recommended for host support of less than 50%, but implantation is problematic and biological bone ingrowth is not possible.19,42 Table 34.4 Modified gross classification.
34 Revision of the Acetabular Component
Clinical scenario
Top three questions
Question 1: In patients with acetabular bone loss, which classification system, compared to others, is most useful?
Rationale
Clinical comment
Available literature and quality of the evidence
Findings
Type
Description of Deficiency
IA
Segmental (Peripheral)
IB
Segmental (Central)
II
Cavitary
III
Combined
IV
Pelvic Discontinuity
V
Arthrodesis
Type of Defect
Superior Migration of Hip Center*
Medial Migration of Hip Center**
Osteolysis of Teardrop***
Osteolysis of Ischium****
I
Minimum
None
None
None
2A
Minimum
Grade I
Mild
Mild
2B
Minimum to Marked
Grade II
Mild
Mild
2C
Minimum
Grade III
Moderate or Severe
Mild
3A
Marked
Grade II+ or III
Moderate
Moderate
3B
Marked
Grade III+
Severe
Severe
Type
Description of Deficiency
I
Contained defect with intact rim and columns
IIA
Noncontained defect – minor column (>50% of host acetabulum in contact with cup
IIB
Noncontained defect – major column (<50% of host acetabulum in contact with cup
Resolution of clinical scenario
Question 2: In patients undergoing revision THA, which acetabular bone loss management techniques, compared to others, perform best in terms of outcomes?
Rationale
Clinical comment
Available literature and quality of the evidence
Findings
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