Revision Hip Arthroplasty Case Title: Cup-Cage Reconstruction for Severe Acetabular Bone Loss

Demographics

 

Age: 57 Sex: Female BMI: 28.7

 

Relevant Past Medical History

 

Principal pathologies: Hypertension

Previous surgical procedures: Right THR 1994 for mild hip dysplasia (type I)

Medication: Amlodipine, Tylenol

History of presenting complaint: No prodro-mal hip symptoms. Three-week history of sudden onset acute, severe, right-sided groin pain with radiation into the posterior buttock. Rapid deterioration from unaided ambulation to using two crutches and is unable to weight bear through the right hip. Significant nocturnal symptoms

 

Clinical Examination

 

Symptoms: Buttock and groin pain with all ROM. Severely antalgic gait

Range of motion: Flexion to 40°, no internal or external rotation—all limited by pain

Specific tests: Trendelenburg positive. Unable to assess abductor strength. Hip provocative text positive. ESR 34 and CRP <5

Main disability: Unable to weight bear through the right hip, even to transfer. Using two crutches to mobilize

Neurovascular evaluation: Intact

Preoperative Radiological Assessment/Imaging (Figs. 20.1 and 20.2)

 

 

 

Fig. 20.1 AP right hip: Loose cemented cup with iliac and ischial osteolysis

 

 

 

 

Fig. 20.2 Lateral right hip: Extent of iliac and ischial osteolysis demonstrated

 

Preoperative Planning

 

Diagnosis: Aseptic loosening of cemented acetabular cup with severe osteolysis ilium and ischium (Figs. 20.1 and 20.2)

Possible treatment options: Cup-cage reconstruction, structural allograft with rigid cage and cemented liner, CTAC (custom triflange acetabular component) and jumbo cup reconstruction

Chosen treatment method: Cup-cage reconstruction

Selection of implants if applicable and rational: (1) Zimmer trabecular metal acetabular shell—to maximize bone ingrowth where host bone contact is expected to be <50%. (2) Zimmer TM acetabular revision cage—with flanges for securing into host ilium and ischium. (3) 36 mm internal diameter 10-degree elevated rim liner. Longevity highly cross-linked polyethylene— maximising head size and rim to increase stability and highly cross-linked to minimize wear debris

Expected difficulties: (1) Severe iliac and ischial osteolysis. (2) Potential pelvic discontinuity. (3) Well-fixed monobloc stem. (4) Shortening proximally with tight abductors

Strategies to overcome difficulties: (1 and 2). Cup-cage construct. (3 and 4). Extended trochanteric osteotomy for stem removal, abductor length and function

Templating: Preoperative planning for the length of the extended trochanteric osteotomy and cup cage (Fig. 20.3)

 

Surgical Note

 

Patient’s position: Lateral decubitus.

Type of anaesthesia: General.

Surgical approach: Extended trochanteric osteotomy.

Main steps: 12 cm ETO—posterior to anterior, lateral one-third of the femur. Proximally in the interval between gluteus minimus and piriformis, bevelled distally. Stem and cement mantle excised from the femur with cement osteotomes. ETO allows excellent exposure of the acetabulum and pelvis; therefore acetabulum is addressed at this juncture. Acetabular cup and cement and

 

 

 

 

Fig. 20.3 Templating for trabecular metal shell, TM acetabular revision cage, ZMR and length of extended trochanteric osteotomy

 

fibrous tissue are completely excised. Assessment of bone defects and pelvic discontinuity before reconstruction with the cup-cage construct (see below). After acetabular reconstruction, titanium diaphyseal modular taper stem (ZMR) is used to reconstruct femur. The rationale for this stem is twofold; firstly, the ETO precludes any metaphyseal press-fit stem or cementation with pressur-ization into the proximal canal; secondly, the modularity allows accurate restoration of leg length and offset. Once definitive stem is inserted, the trial reduction was performed with trial acetabular liner, femoral body and femoral head to ensure the appropriate degree of combined inclination and version to maximize stability and fine-tuning of leg length, prior to cementation of the definitive liner. Definitive implants inserted after correction of leg length, cup version and inclination and offset are confirmed. The ETO was reduced, ensuring correct length and tension of hip abductors, and secured with three cerclage wires (Figs. 20.4 and 20.5).

 

Reconstruction techniques: This technique maximizes the host bone contact with a porous trabecular metal shell, grafts the central defect and uses a cage to stabilize the ilium to the ischium. The acetabular defect is reamed by hemispherical reamers until contact is made with the bleeding bone, any defect is filled with packed morsellized bone allograft, and an absorbable gelatin compressed sponge (e.g. Gelfoam®) may be required on the floor of the defect to contain the packed graft. The acetabular defect is sized for a trabecular metal acetabular component for adequate scratch fit and 2–3 mm of distraction if pelvic discontinuity is present. The trabecular metal cup is inserted in a more open and retroverted manner, than the native acetabulum, to allow access to the ischium and ilium for the respective flanges of the cage. At least two screws with good purchase, each aiming at the posterior column or the acetabular dome, are inserted to improve the cup stability. The cage is appropriately sized and secured to the ischium through a slot made in the ischium and to the outer table of the ilium with minimum two bicortical screws. The polyethylene liner is cemented into the cage with an appropriate degree of version and inclination to maximize stability and the cement used to interdigitate the cup-cage construct [7, 11].

 

Intraoperative Challenges

 

Challenges and solutions: After excision of the cup, cement, fibrous and osteolytic tissue, there was a pelvic discontinuity, significant central defect and uncontained superior defect (type V acetabular defect—Gross classification). The cup-cage technique allows grafting of central defects with morsellized allograft; if containment is required medially, an absorbable gelatin compressed sponge is a useful adjunct. Where proximal and anterior migration of the acetabular cup has occurred, the hip abductors can be scarred and shortened; failure to address this can lead to several potential complications—shortening leg length, an irreducible hip intraoperatively or an unstable hip. A trochanteric slide, either in isolation or incorporated into the ETO, allows accurate restoration of leg length and offset while

maintaining hip abductor function once the slide/ ETO has healed.

Thorough description of decision-making, including the reason for the final decision: Decision for ETO and its advantages for stem removal, preservation of the hip abductors, and facilitation of trochanteric slide as discussed in the preoperative planning. Additionally, it facilitates excellent exposure of the acetabulum—particularly where exposure of the ilium and ischium will be required. The cup-cage reconstruction has several advantageous aspects in this case—(1) the tantalum acetabular shell has excellent scratch-fit and bone ingrowth properties and both beneficial where host bone stock is deficient. (2) The cage secures the construct, whilst bone ingrowth occurs and is flexible enough to prevent complications associated with large, rigid constructs in the periacetabular bone loss. (3) Facilitates bone grafting of central defects.

(4) Modular system allows ‘fine-tuning’ to address individual defect encountered.

 

Postoperative Radiographs

(Figs. 20.4 and 20.5)

 

 

 

Fig. 20.4 Post-op anteroposterior radiograph: Medial allograft, cup cage and ETO with modular tapered femoral stem

 

 

 

 

 

Fig. 20.5 Post-op lateral radiograph: Flanges of the cage engaging into the ischium and secured to the ilium

 

Postoperative Management

 

Chemoprophylaxis and anticoagulant treatment period: Enoxaparin for five weeks.

Gait/limb loading until full loading: Touch-toe four weeks, 50% four weeks and then full weight bearing. This allows for osteo-integration of the trabecular metal cup and tapered femoral stem.

 

Follow-Up and Complications

 

No post-op complications. Initial thigh pain observed in first 2 weeks, related to restoration of leg length.

 

Discussion

 

Advantages of the applied method: Our preferred treatment option in a significant acetabular bone loss and/or pelvic discontinuity is the cup-cage

reconstruction. This technique incorporates elements of the acetabular distraction technique with the scratch-fit highly porous acetabular shell whilst having the added advantage of bridging the host ischium and ilium. It facilitates bone grafting of cavitary defects, and also this technique can be used with augments or structural allografts if there is an associated segmental defect.

Disadvantages of the method: Complication rates, particularly with the cage, associated with this technique were relative frequent with its early use [12]. These were, in part, owing to the technical difficulty of the procedure and lack of osseous integration of the cage. Most frequently sciatic nerve injury was associated with securing the inferior flange of the cage to the top of the ischium. This has led to the senior author (AEG) recommending slotting the inferior flange into the ischium rather than laying it on top.

Alternative evidence-based techniques for the case: Triflange reconstruction with a CTAC (custom triflange acetabular component) and jumbo hemispherical cup.

Why the is chosen technique better for this case? CTACs, by their very nature, have distinct time to manufacture and cost disadvantages, without demonstrably improved survivorship over cup-cage reconstruction [13]. Increasing the defect to accommodate a jumbo hemispherical cup has two disadvantages over the cup-cage reconstruction: firstly, reaming of host bone compounds acetabular bone loss and, secondly, raising the hip centre—which the senior author would not endorse as a basic philosophy.

Indications and contraindications for your technique: Indications—Gross classification type IV and type V acetabular defects with significant acetabular bone loss and pelvic discontinuity.

Learning curve and how to manage complications: A surgeon must be proficient in the technique of using a cage. Loosening of the construct is usually managed by a cage reconstruction with a more rigid type of cage, e.g. Burch-Schneider cage.

Level of evidence concerning the superiority of this method against others: III.