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    Femoral Head-Stem Dissociation Secondary to Severe Trunnion Corrosion

    An 81-year-old male patient was doing well 11 years after an uncomplicated primary THA – until he felt a “pop” in the hip accompanied by pain and an inability to bear weight.

    Authors

    Christopher Bechtel, MD, and John A. Abraham, MD

    Disclosures

    The authors have no disclosures relevant to this article.

    Introduction

    Modular femoral heads are ubiquitous in total hip arthroplasty (THA), as they allow surgeons to accurately restore patients’ hip offset, leg length, and soft tissue tension, as well as facilitate exposure during revision THA. 

    Although the positives of these heads abound, the most common complication seen from their use is corrosion at the modular head-stem interface. The etiology for this corrosion is likely multifactorial and likely includes implant-specific and patient-specific factors: [1-4]

    • Angular mismatch of the trunnion taper and femoral head
    • Modular surface area contact
    • Trunnion diameter
    • Neck angle
    • High offset stems
    • Dissimilar metals
    • High body mass index (BMI)
    • Increased activity level following surgery

    Furthermore, technical factors such as improper seating, inappropriate impaction forces, and damage to the modular surfaces can also contribute to corrosion of the trunnion. [1-4] Severe trunnion corrosion can also lead to femoral head dissociation from the stem and result in catastrophic implant failure. [5-10]

    Fortunately, these events are exceedingly rare, with an estimated prevalence of 0.052%. [5] Although no definitive risk factors can be ascertained from published case reports, the commonalities seen thus far include: [5,9,10]

    • Male gender
    • Height above 5 feet, 10 inches
    • Weight greater than 80 kg
    • Large cobalt-chromium heads (36 mm or 40 mm) with increased offset

    The aim of this report is to illustrate another case of femoral head-stem dissociation related to severe trunnionosis.

    Case Presentation

    A 70-year-old male patient underwent an uncomplicated right THA with a 58-mm Trident acetabular shell, highly cross-linked polyethylene liner, size 4 lateral-offset Accolade TMZF stem, and 36+0 cobalt-chromium head (Stryker Orthopaedics, Mahwah, New Jersey).

    After 11 years of excellent function and pain relief, he felt a sudden “pop” in his right hip as he was exiting his car. He had immediate pain and inability to bear weight on his right lower extremity.

    He presented to the emergency department and was found to have dissociation of the femoral head from the stem, as well as significant tapering of the trunnion (Figure 1). He was transferred to our institution for definitive care and revision surgery.

    Figure 1. Preoperative AP pelvis (top) and hip (bottom) radiographs demonstrating acute femoral head-stem dissociation with significant tapering of the stem’s trunnion. The femoral stem and acetabular shell appear to be well fixed, with no evidence of osteolysis, loosening, fracture, or subsidence.

    Of note, the patient has a medical history of coronary artery disease with stents, abdominal aortic aneurysm repair, and atrial fibrillation for which he was taking warfarin (Coumadin). He denies having any pain, instability, fevers, chills, or systemic symptoms prior to this incident. He also denies vision or hearing loss, difficulty ambulating, loss of balance, vertigo, or neuropathy. He does not use an assistive walking device.

    Physical Examination

    • Height: 6 feet, 2 inches
    • Weight: 240 pounds
    • BMI: 32.0 kg/m2
    • Temperature: 98.0F
    • Heart rate: 67 and irregular
    • Blood pressure: 126/64
    • Respiratory rate: 18 bpm
    • Oxygen saturation: 95% on room air
    • Right lower extremity shortened and externally rotated
    • Well-healed incision over the right hip without signs of infection
    • Pain with any attempted right hip passive or active range of motion
    • Tenderness to palpation about the right hip and groin
    • No tenderness to palpation about any other bony prominence
    • Full range of active and passive motion throughout all other joints
    • 2+ peripheral pulses in bilateral lower extremities
    • Sensation intact to light touch
    • Motor function normal in the sural, saphenous, deep/superficial peroneal, and tibial nerve distributions

    Laboratory Tests

    • Hemoglobin: 10.4 g/dL  (normal range 14-17g/dL)
    • International normalized ratio (INR): 2.1 (normal range 0.8 – 1.2)
    • Partial thromboplastin time: 39 seconds  (normal range 27 – 37 seconds)
    • Prothrombin time: 23.3 seconds (normal range 8.9 – 13.1 seconds)
    • Erythrocyte sedimentation rate (ESR): 66 mm/hour (normal range 0 – 15 mm/hour)
    • C-reactive protein (CRP): 2.50 mg/dL  (normal range 0 – 0.8mg/dL)

    Diagnosis

    • Acute right hip femoral head-stem dissociation with significant trunnion corrosion

    Treatment

    The patient was scheduled for a revision THA, with complete revision of the femoral component, acetabular liner exchange, and extensive soft tissue debridement of metallosis.

    Surgical Details

    • The patient was medically optimized for surgery, including vitamin K administration to reverse his elevated INR.
    • He underwent preoperative right hip aspiration, given the preoperative elevated ESR and CRP levels. The fluid was black with significant debris. The total nucleated cell count was 9000/mcL, but a differential could not be performed because of significant cell necrosis.
    • Using the patient’s old incision, the hip was exposed utilizing a standard posterolateral approach.
    • Capsulotomy revealed 30 mL of blackened fluid. Extensive metallosis involving the entire synovium and intra-articular space was observed (Figure 2).
    • After 3 sets of cultures were taken and sent for aerobic, anaerobic, mycobacterial, and fungal cultures, a thorough synovectomy was performed to reduce the burden of metallosis.
    • The femoral head was easily removed and found to have evidence of corrosion.
    • The femoral stem and acetabulum were both noted to be well fixed and well positioned. 
    • Extensive tapering and corrosion of the trunnion was noted, however, necessitating removal of the femoral stem (Figure 3). This was accomplished without significant bone loss using a combination of osteotomes and a burr. 
    • The femur was prepared and revised to a diaphyseal-engaging, tapered, fluted, modular prosthesis.
    • The acetabular liner was exchanged and a ceramic 36-3 mm head was impacted on the stem.
    • The hip was reduced, with reestablishment of offset, soft tissue tensioning, and leg lengths, as well as excellent stability.
    • A total of 9 liters of antibiotic-impregnated irrigation was used.
    • The posterior capsule and external rotators were reattached through bone tunnels and the hip was closed in layers over a superficial drain.

    Figure 2. Representative sample of extensive metallosis and staining of the synovium.

    Figure 3. Intraoperative photo revealing the extent of trunnion corrosion and tapering.

    Postoperative Follow-Up

    The patient was transferred in stable condition to the post-anesthesia care unit and then to the orthopedic floor. He was made weight-bearing as tolerated with posterior hip precautions.

    He received 48 hours of intravenous antibiotics. All cultures came back negative for infection. In addition, he received warfarin for deep vein thrombosis prophylaxis given his significant cardiac history and baseline use of warfarin for atrial fibrillation.

    At the 3-week follow-up visit, the patient was doing well. He had no complaints regarding his right hip. He had minimal pain and remained weight-bearing as tolerated.

    The patient denied fevers, chills, nausea, vomiting, paresthesias, chest pain, shortness of breath, or difficulty breathing. His incision was well healed without erythema, edema, ecchymosis, drainage, or wound necrosis.

    Radiographs demonstrated a well-fixed, well-positioned implant with no signs of fracture, dislocation, loosening, or subsidence (Figure 4).

    Figure 4. Three-week postoperative radiographs: AP pelvis (top), AP hip (middle), and lateral hip.

    Surgical Pearls

    • The stem used in the primary THA (Accolade TMZF) is composed of beta titanium (titanium, molybdenum, zirconium, and fluoride). This particular alloy has 25% greater flexibility compared with the standard Ti-6Al-4V-alloy. Because of the lower modulus of elasticity, it is possible that the normal forces of gait caused plastic deformation of the titanium trunnion within the cobalt-chromium femoral head, leading to wear and corrosion.
    • During revision for metallosis, thorough debridement of the metallic-stained soft tissues should be performed. Osteolysis can occur and should be treated accordingly. Occasionally, it may be necessary to perform a repeat irrigation and debridement, as further tissue necrosis may occur over time.
    • Unlike metallosis from metal-on-metal THA, cases of femoral head-stem dissociation inevitably have plastic deformation of the trunnion that mandates revision of the femoral prosthesis. We recommend revision utilizing a ceramic femoral head to minimize any additional causes of metallosis and taper corrosion.
    • In hindsight, it would have been interesting to have obtained a baseline cobalt and chromium level; however, given the acuity of his femoral head-stem dissociation, as well as the lack of symptoms suggestive of cobaltism or metal poisoning, we did not feel it necessary to have the laboratory values before revision surgery.

    Author Information

    Christopher Bechtel, MD, is an orthopaedic surgery fellow at The Rothman Institute at Thomas Jefferson University. John A. Abraham, MD , is an associate professor at The Rothman Institute and Director of the Musculoskeletal Oncology Center at Thomas Jefferson University Hospital and the Kimmel Cancer Center.

    Adult Reconstruction Section Editor, Rothman Institute Grand Rounds

    Antonia F. Chen, MD, MBA

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