The primary prosthetic components for hip and knee surgery are:

Hip Components


The shell fits into the hip joint socket and needs to be fixed in place. The materials used for the shell are crucial to enable the implant to be fixed to the hip socket effectively.

Shells are made from metal. For the last twenty years cobalt chrome or titanium alloys have been the most popular materials. However, recent advances using porous metals have significantly improved the ability of the bone to grow quickly into the outer surface of the shell.

The shells are made from pure titanium or tantalum with pores in the metal that mimic coral. This helps the living bone to grow into the coral-like porous metal. These two materials are highly bio-compatible, but at the same time they are strong and flexible and are ideal for revision hip surgery.


The liner is fixed inside the shell. It acts as a bearing surface for the head or ball which is attached to the stem. Movement causes friction between the lining and the head. Therefore, the materials that form the lining are crucial to reduce wear to a minimum. The articulating surfaces must be exceptionally smooth but also very hard-wearing.


The head or ball articulates with the liner and can be manufactured from metal or ceramic. The head is inserted on the morse taper at the top of the stem.


The stem is fixed into the thigh bone (femur).

A cemented stem is held in place by a type of acrylic cement that acts as a grout, filling the bone marrow space between the metal stem and the bone.

A cementless prosthesis has a fine mesh, beaded or porous surface which abuts against living bone. Bone grows into these uneven depressions on the surface of the implant. Surface coatings such as hydroxyapatite (HA) may also be applied to the irregular surface of cementless stems.

Knee Components


The femoral component is metal and replaces the end of the femur, the groove where the kneecap slides. The femur is commonly called the thighbone. It is the largest bone in the body.

Plastic Insert & Tibial Base Plate

The tibial component replaces the end of the tibia—commonly called the shinbone. The tibial component is made up of the plastic spacer which provides a weight-bearing surface and the metal tibial tray that is fitted directly onto the bone. The plastic used is very tough and very slick – so slick and tough that you could ice skate on a sheet of the plastic without much damage to the plastic

Patella Component

The patellar component replaces the surface on bottom of the patella. The "top" of the kneecap is the part you can feel through your skin. The "bottom" is the on the other side, and slides up and down in the femoral groove when you bend or straighten your leg.


Stems improve the mechanical stability of tibial components in total knee replacement (TKR), but come at a cost of stress shielding along their length. Their advantages include resistance to shear, reduced tibial lift-off and increased stability by reducing micromotion. Longer stems may have disadvantages including stress shielding along the length of the stem with associated reduction in bone density and a theoretical risk of subsidence and loosening, peri-prosthetic fracture and end-of-stem pain. These features make long stems unattractive in the primary TKR setting, but often desirable in revision surgery with bone loss and instability. In the revision scenario, stems are beneficial in order to convey structural stability to the construct and protect the reconstruction of bony defects.


A femoral augment, or set of augments, for use with a knee joint prosthesis, where the femoral augment includes a main body portion, an aperture formed within the main body portion and extending in a generally distal/proximal direction, and a pair of legs extending outwardly from said main body portion in a generally posterior direction.


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