Cobalt Chromium Toxicity

Adverse local tissue responses in hip implants with dual-taper stems


Within the last two decades, modularity in hip implants became the prevalent paradigm. Modularity means prosthetic hip implant components are available in multiple segments, or parts, as opposed to a single piece (monoblock implants). Modular components generally consist of a femoral stem with an extra modular junction between the neck and stem body, known as a dual-taper stem. Dual-taper stems are popular since they allow for variations in length, shape, size, degree of offset, and rotation of the implant. Most hip replacement manufacturers have models with the modular neck design option.

However, this extra modular junction is under scrutiny for potentially causing corrosion between the neck and body stem. Studies show metal debris and adverse local tissue reactions (ALTR) secondary to taper corrosion at the head-neck junction analogous to patients with failed metal on metal hips. This study highlights patients with ALTR from modular neck-body junction corrosion.

The study involves eleven patients, eight women and three men; with a total of twelve hips (one patient had bilateral total hip arthroplasty). The patients were evaluated for ALTR secondary to modular femoral neck-body taper junction corrosion. According to the study, the patients presented with pain approximately 8 months after their initial surgery. The pain among the patients was mainly localized in the groin. However, some patients pain radiated to their buttocks, trochanters (parts of the femur), or thighs. Others experienced severe limps, weakness, and significant leg swelling. Stryker rejuvenate was among the models of implanted metal on metal hips in the patients. Patients were all implanted with hips constructed with a cobalt-chromium alloy modular neck and a titanium-alloy stem.

Before undergoing revision surgery, patients had a preoperative workup. The preoperative workup included blood tests which analyzed elevated white blood cells (checking for inflammation), erythrocyte sedimentation rate (reveals inflammatory activity), and serum metal ion levels (checking for metal sensitivity). Additionally, patients underwent a metal artifact reduction sequence (MARS) MRI to evaluate for any abnormalities.

Serum metal ion lab results demonstrated considerable elevation in serum cobalt and serum chromium levels (cobalt was worse than chromium). The MARS MRI indicated large fluid collections and hypertrophic soft-tissue reactions (pseudotumor formation) in ten of the eleven patients (90.9% of patients). Patients were later diagnosed with taper corrosion and underwent revision surgery roughly 9 months after their symptoms first appeared. Revision surgery in the patients revealed capsular hypertrophy (increased tissue growth) and necrosis (death) of the soft-tissue structures involving the hip joint. Several patients had large soft-tissue masses. The modular junction between the femoral component neck and body established marked corrosion, with taper fretting and black, flaky material deposits at the base of each hip. Microscopic testing showed obvious corrosion at the modular femoral neck-body junction in all devices along with fretting and metal debris.

This study confirms dual-taper stem designs with modular cobalt-chromium-alloy necks may cause pain and significant soft-tissue destruction and death surrounding the implanted hip eventually leading to joint failure. Adverse local tissue reactions and metal debris result from fretting and corrosion at the head-neck junction of the cobalt-chromium alloy head and cobalt-chromium alloy stem. Extensive pitting corrosion and fretting was found in many patients. Head-neck taper corrosion resulted in elevated serum cobalt and serum chromium levels. The cobalt levels were much higher than chromium in the cobalt-chromium alloy.  Blood tests also determined inflammation due to adverse local tissue responses secondary to taper corrosion. The study establishes substantial soft tissue damage from corrosion at the modular neck-body taper of a dual-taper femoral model.

Source: Adverse Local Tissue Reaction Arising from Corrosion at the Femoral Neck-Body Junction in a Dual- Taper Stem with a Cobalt-Chromium Modular Neck, The Journal Of Bone and Joint Surgery

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