Hip Arthroplasty & Spacer: Beating Infection, Boosting Recovery

Comprehensive Introduction and Patho-Epidemiology

Resection arthroplasty followed by the insertion of an antibiotic-loaded spacer remains the gold standard for the surgical management of chronic, deep periprosthetic joint infection (PJI) of the hip. Historically, deep periprosthetic infections were managed by resection arthroplasty alone (Girdlestone procedure), which reliably eradicated infection but left the patient with a profoundly shortened, unstable, and functionally debilitating lower extremity. The advent of the two-stage exchange arthroplasty revolutionized the management algorithm. The discussion in this chapter pertains primarily to the diagnosis, operative technique, and postoperative management of late chronic infection. Acute infection, whether postoperative or hematogenous, presents with a drastically different clinical picture and is managed via a distinct algorithm, typically involving aggressive irrigation and débridement with component retention (DAIR).

The pathogenesis of chronic periprosthetic infection is fundamentally tied to the formation of a bacterial biofilm. Planktonic bacteria adhere to the inert surface of the prosthesis and rapidly secrete an exopolysaccharide glycocalyx, enveloping themselves in a highly protective biofilm. This biologic shield renders the bacteria metabolically indolent and highly resistant to both host immune responses (macrophages, antibodies) and systemic bactericidal antibiotics. Chronic infections generally present in a delayed manner, usually months or occasionally years after the index arthroplasty. In many instances, the indolent infection has been present since the original procedure. Due to the low virulence of the infecting organism—most commonly coagulase-negative Staphylococcus (CoNS) or Cutibacterium acnes—the classic systemic signs of infection, such as fever, erythema, and profound swelling, are entirely lacking. Often, an insidious, unrelenting hip pain is the only presenting symptom.

It is critical for the arthroplasty surgeon to recognize that chronic infections also include missed or delayed diagnoses of acute infections. A missed acute postoperative infection or a delayed diagnosis of an acute hematogenous seeding event must be treated as a chronic infection once the biofilm is established; it can no longer be managed with simple débridement and component retention. The natural history of untreated chronic periprosthetic infection is a trajectory of progressive pain, functional disability, and catastrophic joint destruction. The severity of symptoms depends on an interplay between the virulence of the organism, the host’s systemic immunocompetence, and the status of the periprosthetic soft tissue envelope. Low-virulence organisms present with chronic, dull pain, whereas highly virulent organisms (e.g., methicillin-resistant Staphylococcus aureus or Enterococcus) or immunocompromised hosts may present with fulminant sepsis, chronic draining sinuses, and rapid physiological decline.

Untreated patients face severe systemic and local risks. Systemically, there is an ever-present risk of bacteremia seeding other native joints, heart valves, or concurrent total joint arthroplasties. The precise incidence of cross-seeding is unknown but is markedly elevated in hosts with multiple medical comorbidities. Locally, the chronic inflammatory response driven by the infection, combined with the innate immune system's frustrated attempts at phagocytosis, leads to profound osteolysis. This infection-mediated bone loss, compounded by the mechanical loosening of the implants, critically compromises the structural integrity of the proximal femur and acetabulum, drastically increasing the risk of periprosthetic fracture and complicating eventual reconstructive efforts.

Detailed Surgical Anatomy and Biomechanics

A profound understanding of the surgical anatomy of the hip is paramount when undertaking a resection arthroplasty and spacer insertion, as the normal tissue planes are often obliterated by dense scar tissue, chronic inflammation, and heterotopic ossification. The pertinent anatomy of the lateral and posterior aspects of the hip must be meticulously navigated to achieve safe exposure and thorough débridement. The fasciae latae robustly cover the musculature of the lateral hip. Distally, these fascial fibers condense to form the iliotibial band, which inserts onto the lateral aspect of the proximal tibia at Gerdy’s tubercle. Proximally, the fascia splits to envelop the gluteus maximus, innervated by the inferior gluteal nerve, and the tensor fascia lata, innervated by the superior gluteal nerve.

Deep to the fascia lata, over the lateral aspect of the hip, lie the major abductors: the gluteus medius and the gluteus minimus, both innervated by the superior gluteal nerve. Preserving the integrity of the abductor mechanism is critical during spacer insertion to prevent profound postoperative limp and instability. More posteriorly, situated deep to the gluteus maximus, are the short external rotators. From proximal to distal, these include the piriformis (receiving branches from S1 and S2), the superior gemellus (nerve to the obturator internus), the obturator internus (nerve to the obturator internus), and the inferior gemellus (nerve to the quadratus femoris). Slightly deeper and more anterior is the obturator externus (innervated by the posterior branch of the obturator nerve), and distally lies the quadratus femoris (nerve to the quadratus femoris).

The sciatic nerve, the most critical neurovascular structure in the posterior approach, typically emerges from the greater sciatic foramen at the lower border of the piriformis and courses posterior to the short external rotators. When approaching the hip posteriorly, identifying and tagging the short rotators, then reflecting them posteriorly over the sciatic nerve, provides a crucial protective barrier during the extensive retraction required for implant extraction. Surgeons must also be acutely aware of the ascending branch of the medial femoral circumflex artery, which courses over the posterior aspect of the quadratus femoris. This vessel is frequently encountered during the distal extent of the posterior capsular release and can produce substantial, difficult-to-control bleeding if not preemptively identified and coagulated.

Anteriorly, the anatomy is equally unforgiving. Anterior to the hip capsule lies the iliopsoas tendon, upon which the femoral nerve rests as it crosses under the ilioinguinal ligament to enter the anterior thigh. When placing retractors over the anterior acetabular wall to gain exposure for cup removal, the retractor tips must be placed directly on bone, subperiosteally, to avoid catastrophic compression or laceration of the femoral nerve. From a biomechanical perspective, the insertion of a spacer restores soft tissue tension, which is vital for preventing profound myostatic contracture of the abductors and iliopsoas. Spacers can be broadly grouped into articulating spacers and nonarticulating (static) spacers. Articulating spacers resemble either a total hip replacement (with antibiotic-loaded implants on both sides) or a hemiarthroplasty, providing an articulating surface that allows for limited range of motion and weight-bearing. Static spacers are non-mobile blocks or dowels of antibiotic-loaded polymethylmethacrylate (PMMA) placed into the acetabulum and femoral canal, serving primarily to deliver high-dose local antibiotics and maintain dead space.

Exhaustive Indications and Contraindications

The decision to proceed with a two-stage exchange arthroplasty utilizing an antibiotic spacer is dictated by the chronicity of the infection, the virulence of the pathogen, the integrity of the soft tissue envelope, and the physiologic reserve of the host. The primary indication for resection arthroplasty and spacer insertion is a confirmed late chronic deep periprosthetic infection. This procedure is also strictly indicated in cases of acute infections where the implants are found to be grossly loose, or in acute infections caused by highly virulent or multidrug-resistant organisms (e.g., MRSA, VRE, or fungal species) where biofilm eradication via simple débridement is impossible.

Contraindications to a two-stage exchange are relatively few but carry significant weight. Absolute contraindications include a medically unstable patient who cannot tolerate the physiologic insult of a major explantation surgery, or a patient with a terminal illness where the surgical morbidity outweighs the potential benefits. In such extreme scenarios, chronic suppressive antibiotic therapy or a definitive resection arthroplasty (Girdlestone) without reimplantation may be considered. A relative contraindication is the presence of a massively compromised soft tissue envelope that precludes primary closure; in these instances, coordination with plastic surgery for rotational or free flap coverage must be planned prior to the index resection.

Patient Selection and Timing

Differentiating between an acute and chronic infection is the fulcrum upon which the surgical decision rests. Acute infections, if diagnosed early (typically within 3 to 4 weeks of the index procedure or an acute seeding event), can often be managed with aggressive open débridement, copious irrigation, exchange of modular components (head and liner), and retention of the well-fixed osseointegrated implants. However, if the diagnosis of an acute infection is delayed, the biofilm matures, rendering the bacteria impervious to both systemic antibiotics and mechanical lavage. At this juncture, the infection must be reclassified as chronic.

Pre-Operative Planning, Templating, and Patient Positioning

Thorough preoperative planning begins with a meticulous clinical history and physical examination, which often provide the first diagnostic clues of a chronic PJI. Patients frequently recount a history of poor wound healing, prolonged postoperative drainage, extended courses of oral antibiotics, or prior superficial surgical débridements. These narratives strongly suggest a missed or failed treatment of an acute postoperative infection. Another distinct subset of patients presents solely with unremitting pain, often dating back to the initial arthroplasty. This pain is typically distinguishable from classic mechanical or aseptic loosening; it is often constant, present at rest, and described as a deep, dull ache, rather than the sharp, start-up pain associated with mechanical failure.

The physical examination in the setting of chronic infection is notoriously nonspecific but requires systematic evaluation. Findings can range from a nearly normal exam with only mild pain at the extremes of motion, to overt signs of sepsis including erythema, induration, and a chronically draining sinus tract (which is pathognomonic for deep infection). The surgeon must observe the patient's gait pattern, noting any antalgic limp or a positive Trendelenburg sign, which may indicate abductor insufficiency, deep pain, or superior gluteal nerve pathology. The soft tissue envelope must be critically assessed for thickness, compliance, and previous surgical scars. Poor tissue compliance may compromise wound closure and necessitate advanced reconstructive flap coverage. Furthermore, passive range of motion, straight-leg raising, and a comprehensive neurovascular examination must be documented to establish a preoperative baseline.

Imaging and Laboratory Investigations

Radiographic evaluation is mandatory to exclude other causes of aseptic failure and to template for eventual reconstruction, though radiographs often appear normal in early chronic infections. In long-standing cases, plain films may reveal a periosteal reaction, which is highly suggestive of a deep infection, or rapid, aggressive focal osteolysis. Rarely, mature sinus tracts extending through the cortical bone may be visualized.

Laboratory investigations form the cornerstone of the diagnostic algorithm. The erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are the most useful initial screening tests. An ESR > 30 mm/hr and a CRP > 10 mg/L are strong indicators of potential infection. However, the sensitivity of these markers diminishes in the setting of indolent, low-virulence organisms. If both values are strongly negative, deep infection is highly unlikely. Peripheral white blood cell (WBC) count is rarely elevated in chronic PJI and is not a reliable diagnostic tool.

If there is any clinical suspicion or elevation of inflammatory markers, a fluoroscopically or ultrasound-guided hip aspiration is strictly indicated. Crucially, any systemic antibiotics must be discontinued for a minimum of 2 to 3 weeks prior to aspiration to mitigate the risk of false-negative cultures. The aspirate must be sent for synovial fluid cell count and differential, as well as aerobic, anaerobic, fungal, and mycobacterial cultures. A synovial WBC count > 2000 cells/µL or a polymorphonuclear leukocyte (PMN) percentage > 65% is highly suggestive of infection. Intraoperatively, a frozen section of the most inflamed periprosthetic tissue is invaluable; a finding of > 5 PMNs per high-power field (HPF) correlates strongly with active infection. Conversely, intraoperative Gram stains have extremely poor sensitivity for late chronic infections and should not be relied upon to rule out PJI.

Differential Diagnosis

The differential diagnosis for a painful total hip arthroplasty must be systematically evaluated. Intrinsic causes include aseptic loosening, failure of fibrous ingrowth in uncemented implants, polyethylene wear with aggressive macrophage-induced synovitis, modulus mismatch (thigh pain from stiff stems), tendinitis (e.g., psoas tendon impingement on an overhanging acetabular shell), greater trochanteric bursitis, abductor avulsion, heterotopic ossification, and periprosthetic stress fractures. Extrinsic causes of referred pain must also be ruled out, including lumbar spinal pathology (such as L2 or L3 nerve root radiculopathy), aortoiliac vascular claudication, inguinal or femoral hernias, and lateral femoral cutaneous nerve impingement.

Step-by-Step Surgical Approach and Fixation Technique

The surgical management of chronic periprosthetic hip infection via a two-stage exchange demands meticulous technique, beginning with the complete removal of all implants, cement, and foreign material. The patient is typically positioned in the lateral decubitus position. The previous incision is utilized whenever possible, excising previous scar tissue and any draining sinus tracts en bloc. Deep exposure is generally achieved via an extensile posterior or direct lateral approach. The joint is dislocated, and the modular head is removed to facilitate exposure of the acetabulum and femoral stem.

Implant extraction can be technically demanding and fraught with complications. Well-fixed cemented stems require the use of flexible osteotomes, high-speed burrs, and ultrasonic cement removal tools to clear the mantle without perforating the cortex. For fully porous-coated or extensively ingrown uncemented stems, an extended trochanteric osteotomy (ETO) is frequently required. The ETO provides direct access to the diaphyseal fixation, allowing for controlled disruption of the bone-implant interface using pencil burrs and Gigli saws, while simultaneously providing unparalleled exposure of the acetabulum. Acetabular components must be carefully explanted using curved explant blades (e.g., Explant system) to minimize collateral damage to the remaining pelvic bone stock.

Radical Débridement and Spacer Fabrication

Once the implants and all foreign materials are removed, a radical, oncologic-style débridement of the joint space is performed. All devitalized bone, infected granulation tissue, and compromised soft tissue must be aggressively excised until healthy, bleeding margins are achieved. The medullary canal is reamed and vigorously brushed, followed by pulsatile lavage using several liters of normal saline, often augmented with dilute betadine or chlorhexidine solutions.

The fabrication and insertion of the antibiotic-loaded spacer is the critical final step of the first stage. Spacers serve a dual purpose: they deliver a massive local concentration of antibiotics directly to the infected bed (far exceeding minimum inhibitory concentrations) while maintaining soft tissue tension and dead space. High-dose antibiotic cement is prepared by hand-mixing (to increase porosity and enhance elution) 3 to 4 grams of heat-stable powdered antibiotics (typically a combination of Vancomycin and Tobramycin or Gentamicin) per 40-gram bag of PMMA.

Articulating spacers can be constructed using commercially available molds or fabricated intraoperatively by coating a smaller, smooth femoral stem with antibiotic cement and mating it with an all-polyethylene cemented acetabular component. Alternatively, a hemi-articulating spacer can be created by molding a large cement head over a central endoskeletal rod. If the bone loss is too severe, or the abductor mechanism is entirely deficient, a static spacer is utilized. Static spacers consist of block-like dowels of cement placed into the femoral canal and the acetabular void, completely immobilizing the joint to allow soft tissue healing and maximize local antibiotic delivery.

Complications, Incidence Rates, and Salvage Management

The management of chronic PJI is fraught with potential complications, both systemic and local. The physiological toll of the infection, combined with the massive surgical insult of explantation, places these patients at high risk for perioperative morbidity. Locally, the use of antibiotic spacers carries its own unique set of mechanical and biological risks. Dislocation is a frequent complication of articulating spacers, occurring in up to 15-20% of cases, driven by compromised abductor musculature, altered joint biomechanics, and the lack of a true capsular restraint.

Spacer fracture is another significant complication, particularly in patients who are non-compliant with weight-bearing restrictions or when the spacer is fabricated with an insufficient endoskeletal structural core. The addition of high doses of powdered antibiotics to PMMA profoundly weakens the mechanical properties of the cement, making it brittle. If a spacer fractures or dislocates, it can cause catastrophic damage to the remaining bone stock, potentially converting a contained defect into a massive structural void. Systemically, the elution of high doses of aminoglycosides and vancomycin from the spacer can lead to acute kidney injury (AKI), necessitating close monitoring of renal function, particularly when concurrent systemic intravenous antibiotics are administered.

Salvage Management

In cases where the two-stage exchange fails to eradicate the infection, the surgeon is faced with a challenging salvage scenario. Options include a repeat two-stage exchange, which carries a significantly lower success rate than the primary attempt. If the patient's bone stock is completely exhausted or their physiological reserve is depleted, a

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