metal-free total hip replacement

this design responds to a patient case: dr. nyota uhura, an active 49-year-old with advancing rheumatoid arthritis whose immune system attacks the lining of her joints. after prednisone and remicade both lost effectiveness, her bloodwork (ESR 38 mm/h, WBC 30,200, anti-CCP 28 u/mL) and imaging confirmed active disease with bone erosion on the femoral head and reduced acetabulofemoral joint space, leaving her with severe morning stiffness, groin and thigh pain, and extreme discomfort when sitting. the complication that shapes the whole design is that she is allergic to most metals, ruling out a conventional metal-on-polyethylene hip implant. the goal was a total hip arthroplasty she can actually receive.

the implant replaces every metal component with a biocompatible alternative across four parts: stem, ball, liner, and socket.

• CFR-PEEK implant — carbon-fibre-reinforced PEEK is highly durable, biocompatible, and MRI compatible, with mechanical properties close to bone that reduce the risk of stress shielding.
• vitamin E UHMWPE liner — 5 mm thick for fatigue resistance and shock absorption; blending in vitamin E eliminates the free radicals UHMWPE normally produces, improving oxidation resistance and fatigue strength while keeping a low wear rate, low density, and high toughness.
• PLA and hydroxyapatite screws — the polylactic acid is bioresorbable and the hydroxyapatite is bioactive, together promoting gradual osseointegration without leaving permanent hardware.

the geometry follows the patient's anatomy: a socket with a 21.5 mm inner and 23.5 mm outer radius, a 15.5 mm ball, and a stem with an ~200 mm moment arm. screw holes in the socket and holes along the stem encourage bone growth, and a collar improves stability so the patient can bear weight sooner.

fixation was designed around an anterolateral approach chosen to minimize recovery time and muscular damage, under epidural anesthesia with propofol sedation. the femoral head is removed with a surgical saw and damaged cartilage cleared, the acetabulum is reamed to seat the cup, and the femoral component is press-fit to maximize bone growth and long-term stability. the acetabular cup is secured with the bioresorbable screws, holding it in place during osseointegration without triggering nyota's metal allergy, so the fixation hardware ultimately dissolves as her own bone takes over.