January 2004

I. Bone Stock Conservation and Preservation.

A. The technique preserves the anatomic femoral head and neck and normalizes the biomechanics of the hip joint.

1)  Only the pathological bone is removed.

2) Although the femoral head subchondral bone is partially removed during the femoral head preparation, the femoral trabecular bone is preserved so that the femoral neck, greater trochanter and lesser trochanter, and sub-trochanteric areas are essentially normally biomechanically loaded.  This has been confirmed by gross and sectioned microscopic anatomy, microradiographs, micro-bone and conventional densitometry.

a. Bone density of femoral neck and proximal femur has been measured in the absence of polyethylene debris with up to 21 years follow-up after hemisurface arthroplasty and is similar to the normal contralateral hip.  Manuscript in press J. of Orthopaedics.

b. Bone densitometry of femoral neck and proximal femur are generally diminished pre-operatively due to lateral displacement of the femoral head secondary to arthritis. After Conserve® Plus  metal-metal hip resurfacing the density normalizes.

c. Finite element analysis of the femoral neck and proximal femur with and without acrylic fixation of the short stem of the metal-metal hybrid surface arthroplasty demonstrated no adverse effect.

B. With the new Thin Acetabular Shell Conserve® Plus resurfacing acetabular bone stock is preserved.  Normal anatomical relationships are restored.  The proper offset is normalized, and, in general, leg lengths are equalized.

II.  Biological bone preservation and more normal joint physiology.

A. The inflammatory response to metal debris is considerably less than to polyethylene debris.

1) Incidence and magnitude of osteolysis appear insignificant at seven years.

B. Anatomic restoration and stability permits early capsular stretching to maximize range of motion

C. Range of motion is restored and occasionally is increased compared with the normal hip.

D. The metal-metal bearing itself is self-healing with no instances of runaway wear being observed.

III. Stability of the hip joint is much improved compared with stem-type devices because the head size is similar to the normal hip.

A. Component orientation is anatomic with excellent initial component stability.

B. Dislocation risk minimal in post-operative period and beyond.

C. Recurrent subluxation rare and recurrent dislocation has not been observed.

IV. Minimal morbidity.

A. General: Crutches three to five weeks. Driving two to four weeks. Return to work two to five weeks for ordinary work.  For heavy work eight to twelve weeks.

V: Revisability.

A. Since there have been no socket problems, removal is unnecessary and revision to conventional stem-type replacement if necessary is relatively simple and much like a primary joint replacement. A unipolar ball with similar metal-metal bearing tolerances can be attached to a femoral stem-type device to mate with the existing socket preserving comparable stability and range of motion to the original resurfacing.

B. Socket loosening is unlikely since the porous beaded surface is very stable. However if it is ever necessary, removal of the socket is relatively simple with minimal bone loss using concave osteotomes because there are no prominent appendages necessary for initial stability.

For more information, please e-mail us at jri@laoh.ucla.edu or call us at 213-742-1075.  Thank you for giving us the opportunity to serve you!