Patent ID: 8152815

Claim:
A trialing system for use in implanting a hip prosthesis in an acetabulum and a proximal femur of a patient, the trialing system comprising: a trial head and an associated trial shell, an outer surface of said trial shell configured for receipt within the acetabulum, said trial shell having a substantially spherical bearing cavity formed therein for closely receiving said trial head during trial articulation, said bearing cavity extending beyond 180 degrees, said bearing cavity accessible via a trial shell opening in said trial shell, said trial shell opening including a head entry portion configured to allow said trial head to pass through said trial shell opening and into said bearing cavity, said head entry portion having a diameter that is less than a diameter of said bearing cavity, said trial head having a bearing portion and a rim portion, said rim portion configured to receive a femoral neck during trial articulation, said bearing portion having a substantially spherical outer bearing surface, said bearing surface having a diameter greater than said diameter of said head entry portion of said trial shell opening, a cut-out region formed in said outer bearing surface, said cut-out region having a diameter that is less than said diameter of said head entry portion of said trial shell opening, said cut-out region positioned such that when a femoral neck is disposed in said rim portion, said trial head is retained within said bearing cavity of said trial shell, whereby when said cut-out region of said trial head is aligned with said head entry portion of said trial shell opening, said trial head can pass through said trial shell opening and into said bearing cavity of said trial shell, and whereby said trial head is retained in said bearing cavity when said cut-out region is not aligned with said head entry portion, further comprising an orientation indicator on said trial head, said orientation indicator positioned to indicate alignment between said cut-out region of said trial head with said head entry portion of said trial shell, wherein an orientation groove is formed along said cut-out region between said cut-out region and said orientation indicator.