Revision Hip Arthroplasty Case Title: Acetabular Augment for a Paprosky Type IIIA Acetabular Defect

Case Title: Acetabular Augment for a Paprosky Type IIIA Acetabular Defect

Demographics

 

Age: 67 years Sex: Male BMI: 23.4

 

Relevant Past Medical History

 

Principal pathologies: Bilateral developmental hip dysplasia.

Previous surgical procedures: Left total hip replacement in 1999, which was revised three years later, due to loosening and osteolysis (bone allograft and a 56 mm cup with screws). Re-revision after two months due to migration (Muller ring with a cemented socket). Right total hip replacement in 1998. Right femoral shaft fracture operated (ORIF) at the age of 45; healed with valgus and shortening deformity.

Medication: Pazolan.

History of presenting complaint: The patient was referred with left hip pain for the last two years with progressive shortening of the limb. The pain increases with walking, which has only been possible using two crutches for the

last year. Unable to bear weight and put on socks on the left side. The patient does not mention swelling or reddishness around the hip.

 

Clinical Examination

 

Symptoms: Pain with weight bearing, flexion, and rotation of the left hip. Right hip has slight pain with flexion and internal rotation. Left thigh muscle atrophy. Bilateral posterolateral surgical scars from previous surgeries.

Range of motion: Left hip: flexion 100°, extension 0°, abduction 30°, adduction 35°, internal rotation 30°, external rotation 40°. Flexion and rotation were painful.

Specific tests: Left lower limb shortening of 3 cm. Left Trendelenburg test positive.

Main disability: Unable to bear weight and walk without crutches.

Scoring: Harris Hip Score preoperatively—19.

Neurovascular evaluation: No changes.

 

Preoperative Radiological Assessment/Imaging (Figs. 19.3, 19.4, and 19.5)

 

 

 

Fig. 19.3 AP pelvis x-ray. Loose Muller ring cup with superolateral hip centre migration greater than three cm. There is a destruction of the superior rim, but the Kohler’s line is intact (Paprosky type IIIA acetabular defect). Apparently, the anterior column is deficient, but the CT scan shows that it is relatively preserved

 

 

 

 

 

Fig. 19.4 Standing AP XR of both lower extremities. Valgus and shortening deformity of the right femur (2 cm shorter than the left femur)

 

 

 

 

 

Fig. 19.5 Left hip CT scan. There is a posterior column deficiency with preservation of the anterior column and acetabular floor

Other: Blood leukocyte count and differential were normal, C-reactive protein 0.35 mg/dL, and erythrocyte sedimentation rate 12 mm/h. Left hip aspiration under x-ray control—clear fluid with a low count of leukocytes and cultures with no microbial growth.

 

Preoperative Planning

 

Diagnosis: Aseptic loosening of left Muller ring with proximal migration and loose acetabular cup on the right side. According to the Paprosky classification, this is a type IIIA acetabular defect with superior bone loss; the medial wall is relatively preserved, and the cup has migrated superolaterally (Figs. 19.3, 19.4

and 19.5).

Possible treatment options: Trabecular metal cup and augments, jumbo acetabular components, impaction bone grafting, structural allografts, acetabular cages, bilobed acetabular components, and high placement of the hip centre of rotation.

Chosen treatment method: Trabecular metal hemispherical cup in the native acetabulum and a superior augment.

Selection of implants if applicable and rational: Trabecular metal revision cup and augments. Non-cemented primary femoral stem and a distal fixation revision stem (if proximal fixation is not possible or in the case of a femoral osteotomy to remove the stem).

Expected difficulties: Poor stability of a hemispherical cup with lack of superior support. There is a high hip centre on the left side, defined as being more than 35 mm above the inter-teardrop line. We would expect difficulty in bringing the femur down and need to revise an ingrown uncemented femoral stem. A subtrochanteric shortening osteotomy may be needed if we cannot manage to bring the femur down or in case of sciatic nerve tension.

Strategies to overcome difficulties: An augment can be used to support the acetabular shell and achieve stability. Soft tissue release, a femoral revision to lower the centre of rota-

 

tion, and a subtrochanteric femoral shortening osteotomy.

Templating: In the preoperative templating, we aimed to restore the hip centre of rotation, and an augment was necessary to support the cup superiorly.

 

Surgical Note

 

Patient’s position: Right lateral decubitus. Type of anesthesia: General anesthesia. Surgical approach: Posterior approach.

Main steps: Two grams of cefazolin was given after taking intraoperative tissue cultures.

Reconstruction techniques: Progressive reaming was done in the native acetabulum until reaching the anterior and posterior columns. The intraoperative stability with a hemispherical cup was poor. A trial cup component and different trial augments were placed in the posterosuperior defect to simulate the reconstruction and access component sizes and stability. Reaming of the superior defect according to the planned size of the augment was performed. With the trial cup in place, the hemispherical trabecular metal augment was fixed with screws, and morselized fresh frozen bone allograft was used to fill the fenestrations and cavitary defects. A thin layer of cement was carefully applied in the augment-cup union to avoid extravasation of cement to the bone-implant interface. The tantalum revision cup was impacted, and additional screws were placed through the shell to enhance primary stability. The polyethylene liner was cemented. It was not possible to reduce the hip after capsular release, so the femoral stem was removed. Sciatic nerve tension was accessed after reduction with the trial femoral component and a non-cemented stem with a more profound sitting was implanted. The largest femoral head was used to reduce the risk of dislocation (Fig. 19.6).

Intraoperative Challenges

 

Unanticipated problems and solution: A possible infection, which would need a component removal, debridement, and a spacer. Trochanteric osteotomy may be necessary for stem removal and a subtrochanteric femoral shortening osteotomy if we are not able to bring the femur down or in case of sciatic nerve tension.

Thorough description of decision-making, including the reason for the final decision: The trial cup was stable in the true acetabulum with the superior augment. The hip reduction was possible with the trial stem with a more profound sitting and was stable for the tested ROM.

 

Postoperative Radiographs

(Fig. 19.6)

 

 

 

Fig. 19.6 Pelvis X-ray at 9.5 years after revision of left THR and six years after revision of right hip replacement with the same technique. There is a radiolucency in DeLee and Charnley zone 3 which has not progressed, and there is no evidence of implant migration. 2) Acetabular revision on the right hip with the same technique was carried out 4.5 years later

 

Postoperative Management

 

Chemoprophylaxis and anticoagulant treatment period: Enoxaparin 40 mg SC for four weeks

Gait/limb loading until full loading: Partial weight bearing with two crutches for twelve weeks

 

Follow-Up and Complications

 

Acetabular revision on the right hip with the same technique was carried out 4.5 years later. The high-riding trochanter raises some concern of impingement and instability. A stem with more offset could be used to decrease the risk of impingement.

Scoring: Harris Hip Score at 9.5 years follow-up—86.

 

Discussion

 

Advantages of the applied method: Most of the acetabular defects are elliptical, with the anteroposterior dimension smaller than the superior-inferior dimension. If the defect is small, reaming can be used to create a spherical cavity without compromising the anterior and posterior column support, and a standard hemispherical cup can be used. This solution can be used in the vast majority of acetabular revisions with favorable survivorship [30]. For more severe defects like the Paprosky type IIIA, the stability of the cup is questionable [11]. In this type of defect, a cementless acetabular fixation usually needs a superior buttress for primary implant stability. For segmental defects, the augment replaces part of the missing column and gives support to the hemispherical cup. This allows a lowering of the hip centre and placement of the cup in the anatomical location. With augments, it is possible to use a hemispherical revision cup in Paprosky type IIB and IIIA defects [11, 31]). There are different shapes and sizes for the augments, and their modularity is used for adaptation to the morphology and size of the defect. Another advantage is the possibility of customizing and adjusting the reconstruction intraoperatively. The use of a metal with high porosity like tantalum can increase the bone ingrowth potential, especially in cases of lim-

ited host bone contact, and the high coefficient of friction can increase primary stability [11]. The metal augments are a better option for the reconstruction of segmental defects compared to the structural allograft, with a lesser risk of fracture and bone reabsorption.

Disadvantages of the method: In the case of a cavitary defect, the bone allograft is the best option, and the use of an augment inadvisable because of the risk of wall fracture during component impaction. Cement used between the cup and the augment may penetrate the bone-implant interface interfering with the bone ingrowth. The implant should be in direct contact with host bone to allow ingrowth; this is not possible if the implant is only in contact with bone allograft. At present, it is not possible to define a minimum area of bone-implant contact to allow bone ingrowth and secondary stability. In younger patients, we should consider other techniques that restore the bone stock. The possibility of micro movements and metal wear between the cup and augment is also a concern. The longterm results of this technique are still unknown.

Alternative evidence-based techniques for the case: In uncontained defects, impaction bone grafting with rim meshes has the advantage of bone stock reconstruction, but there is a risk of bone reabsorption and cup migration in the case of massive bone loss. The revascularization and remodeling of structural bone allografts are associated with a high complication rate, with bone collapse and component loosening, mainly if they provide most of the support for the component. There is also a concern about possible disease transmission with allografts. Acetabular reconstruction cages have the advantage of bridging the ilium and the ischium and can be used if the posterior wall is missing and in the case of pelvic discontinuity. Their implantation is technically difficult, and the main disadvantage is the lack of bone ingrowth, and mechanical failure at the midterm follow-up. Other alternatives are bilobed acetabular components and high placement of the hip centre of rotation.

Why is the chosen technique better for this

case? This technique permits the restoration of the migrated hip centre, and the augment gives superior support for cup stability.

 

Indications and contraindications for your technique: When implant stability and correction of the hip center is not possible with a standard revision cup due to the absence of superior support. With the acetabular distraction technique, this type of implant can be used in the case of chronic pelvic discontinuity. In cases where press-fit fixation is impossible to achieve, even with augments, other reconstruction strategies should be used.

Learning curve and how to manage complications: The use of augments is technically less demanding than the reconstruction cages and structural allografts.

Level of evidence concerning the superiority of this method against others: Porous cups and acetabular augments have shown reliable and durable results for reconstruction in the case of major bone defects (Paprosky types II and III) at midterm follow-up [11, 12].