Hip Replacement (Cemented/Uncemented)
Hip Replacement (Cemented/Uncemented)
Total hip replacements are classified by how the artificial components are secured to the bone. While both methods are highly successful, the choice depends on the patient's bone quality, age, and activity level.
When You Should Consider Each Method
Cemented: Preferred for patients over 70 or those with osteoporosis whose bone may be too porous to grow into an implant.
Uncemented: Ideal for younger, active patients (typically under 65) with strong, healthy bone density.
Hybrid Approach: In some cases, a surgeon may use a cemented stem in the femur and an uncemented cup in the socket.
Revision Surgery: Often utilizes specialized versions of either method depending on the amount of remaining healthy bone.
Methods of Fixation
Cemented Fixation: Utilizing surgical-grade polymethylmethacrylate (PMMA) to create a tight mechanical interlock between the metal and the bone.
Uncemented (Press-fit) Fixation: Relying on a high-precision friction fit followed by natural bone growth into a porous metal surface.
Biological Fixation: The process where natural bone cells migrate into the "beaded" coating of an uncemented implant over 6 to 12 weeks.
Antibiotic-Loaded Cement: A variation where cement is pre-mixed with antibiotics to provide localized protection against infection.
How the Procedures Are Performed
Bone Preparation: The surgeon clears the arthritic bone and prepares the hollow center of the femur and the acetabular socket.
Grout Injection (Cemented): Wet PMMA is injected into the bone cavity immediately before the components are pressed into place.
Precision Carving (Uncemented): The bone is carved to be slightly smaller than the implant to ensure an extremely tight fit when hammered into position.
Impacting the Component: For cementless types, the metal components are impacted until they achieve a stable "friction fit" against the healthy bone.
Curing: For cemented types, the surgeon holds the implant perfectly still for 10 to 12 minutes while the cement hardens completely.
Pre-Procedure Preparation
Bone density scanning (DEXA) may be performed to determine if the bone is strong enough for an uncemented implant.
Pre-operative templating using X-rays to ensure the high-precision tools match the size of the selected uncemented components.
Evaluation of allergy history, specifically regarding the components of surgical bone cement or specific metals like Titanium.
Fasting (NPO) and standard surgical clearance for general or spinal anesthesia.
Tests Before Fixation Selection
Weight-Bearing X-rays: To assess the "fit and fill" of the femoral canal and the quality of the pelvic bone.
DEXA Scan: To provide a definitive measure of bone mineral density in the hip region.
Blood Panels: To ensure the patient is a candidate for surgery and to check for systemic inflammation.
Cardiac Clearance: Particularly for cemented procedures, to ensure the heart can tolerate potential pressure changes during cement implantation.
Life After the Procedure
Cemented Recovery: Patients can usually put full weight on the leg within hours, as the bond reaches maximum strength almost instantly.
Uncemented Recovery: Some surgeons require 4–6 weeks of "partial weight-bearing" with crutches to allow the bone to grow into the metal.
Long-term Monitoring: Uncemented implants are designed to become a permanent part of the skeleton, while cement may eventually degrade after 20–25 years.
Activity Levels: Uncemented implants are specifically designed to withstand the higher mechanical stresses of a more active lifestyle.
Benefits of Each Approach
Cemented Benefits: Provides an immediate, rock-solid foundation and allows for the localized delivery of antibiotics.
Uncemented Benefits: Preserves more natural bone and offers the potential for a longer-lasting, biological bond that does not "wear out" like cement.
Reduced Failure Rates: Both methods reduce the failure rate of hip replacements to very low levels compared to historical techniques.
Customization: Surgeons can tailor the fixation method to the specific anatomy and bone health of each individual patient.