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Bipolar Arthroplasty

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        - Total Hip Replacement Menu:
        - International Bipolar News

- Discussion:
    - Gilberty & Bateman in 1974, reported use of bipolar prosthesis;
    - rationale was that erosion and protrusion of acetabulum would be less because motion is present between metal head & polyethylene socket (inner
             bearing), as well as between metallic cup & acetabulum (outer bearing), since cup is not fixed in bone;
    - theory that distribution of shear forces between the inner and outer bearings will spare acetabular surface from wear and erosion;
             - acetabular wear is diminished through reduction of total amount of motion that occurs between the acetabular cartilage and metallic outer shell
                    by the interposition of a second low-friction interbearing within the implant;
    - because of compound bearing surface, bipolar designs provide greater overall range of motion than either unipolar designs or conventional THR;
    - made available with a 22 or 32 mm diameter head;
    - recent modifications:
             - axis of metallic and polyethylene cups are now eccentric so that with loading of hip, metallic cup rotates laterally than medially, and thus avoids
                    fixation in varus position and avoids impingement of head on edge of cup, which causes frx of poly bearing insert and dislocation;

- Indications:
    - femoral neck fracture:    
           - due to the risks of osteolysis, many orthopaedist are reluctant to insert bipolar components and instead insert unipolar componenets:
    - salvage procedure in revision THR surgery:
           - indications:
                  - massive acetabular deficiencies which do not permit secure fixation of the acetabular component;
                  - hip instability from deficiency of abductors is a relative indication because bipolar component is intrinsically more stable than fixed component;
                  - if patient has no abductor musculature, bipolar implant provides added stability against dislocation compared w/ THR;

- Relative Contra-indications:
    - DDH:
           - further technical point is that a bipolar prosthesis may not do well if the acetabular souricil angle is greater than 15 deg;
                  - most dysplastic acetbuli will have a high sourcil angle;
           - in these cercumstances the acetabulum should be reamed deeply, and if necessary bone grafted superiorly;

- Complications:
    - degree of inner bearing motion decreases over time;
    - acetabular migration:
           - bipolar implants in revision acetabular surgery usually migrate, especially in soft bone such as that in rheumatoid arthritis or against bone graft;
           - migration and pain are occasional problems with bipolar implants in young patients requiring total hip replacement;
    - osteolysis:
           - this is any especially prevelant complication due to the thinness of the polyethylene bearing surface (between the inner and out components);
           - bipolar components shed twice as many polyethylene particles as are found in fixed acetabular components;
           - young active patients are at high risk for osteolysis, and in these patients a 22 mm head should be used

Transcervical fractures of the hip treated with the Bateman bipolar prosthesis.

Fractures of the femoral neck treated with a bipolar endoprosthesis.

Ten Common Problem Fractures--Symposium: The Displaced Femoral Neck Fracture: Internal Fixation versus Bipolar Endoprosthesis. Results of a Prospective, Randomized Comparison.

Bateman bipolar hemiarthroplasty for displaced intracapsular femoral neck fractures. Uncemented versus cemented.

Component motion in bipolar cemented hemiarthroplasty.

Use of bipolar endoprosthesis and bone grafting for acetabular reconstruction.

Bipolar hip arthroplasty for recurrent dislocation after total hip arthroplasty. A report of three cases.

Fractures of the femoral neck treated with a bipolar endoprosthesis.

The displaced femoral neck fracture. Internal fixation versus bipolar endoprosthesis. Results of a prospective, randomized comparison.

Bipolar hemiarthroplasty for fracture of the femoral neck. Clinical review with special emphasis on prosthetic motion.

Transcervical fractures of the hip treated with the Bateman bipolar prosthesis.

Comparison of bipolar implants with fixed-neck prostheses in femoral-neck fractures.

The long-stem bipolar prosthesis in surgery of the hip.

Experience with bipolar prosthesis in femoral neck fractures in the elderly and debilitated.

Bateman bipolar hip arthroplasty for femoral neck fractures. A five- to ten-year follow-up study.

Bipolar hemiarthroplasty in degenerative arthritis of the hip. 100 consecutive cases.

Long-term results of bipolar arthroplasty in osteoarthritis of the hip.

Failure of the Polyethylene after Bipolar Hemiarthroplasty of the Hip. A report of five cases.

Acetabular osteolysis and migration in bipolar arthroplasty of the hip: five- to 13-year follow-up study.