A NEW APPROACH TO NECK SPARING THA STEM

Abstract

Introduction: Architectural changes in the proximal femur after THA continue to be a problem. In an attempted, to reduce these changes some surgeon designers have advocated the concept of neck sparing stem designs.

To-date neck-sparing stems have been disappointing in their ability to maintain the calcar. A new approach was undertaken to improve load transfer and to create a tissue-sparing stem that would be simple in design, reproducible in technique and provide for fine-tuning joint mechanics while maintaining compressive loads to the calcar.

Methods: Review of previous published work was evaluated along with FEA modeling in creating a new approach to neck sparing stems for THA. The MSA^™ Stem is a simple curved stem with a unique lateral T-back designed for torsional stability, ease of preparation and insertion. The proximal design has a novel proximal conical shape designed to transfer compressive forces to the calcar.

A modular neck provides for fine-tuning joint mechanics.

Results: FEA modeling will be reviewed. Strain patterns for the MSA^™ stem demonstrated better patterns vs. long stems or the short Biodynamic stem.

Discussion: In theory neck retaining devices provide or:

• Bone and Tissue sparring

• Restoration of joint mechanics

• Minimal blood loss

• Potential reduction in rehabilitation

• Ease of revision

• Simple surgical technique

• Options for bearing surface

• Selection of femoral head diameter

• Standard surgical approach to the hip

We are encouraged and believe there are advantages in the concept of neck sparing stems. Clinical/surgical evaluation is now underway and will be reported on in the future.