Hip Prosthesis

Over the past few decades, many advances in hip replacement have been made and several types of prostheses are available. They may include a combination of metal and plastic (Traditional Hip) or just metal (38 Millimeter Hip).

The metals used are either cobalt-chrome alloy, or a titanium alloy. These are "super metals" initially developed for the aerospace industry and now adapted for orthopedics. The plastic used is a high-density plastic polymer called polyethylene. The type of prosthesis used for your surgery is determined by the surgeon and is based on a number of factors such as your height, weight, age, and bony structure.

Traditional Hip

A traditional total hip replacement uses a metal ball in a plastic socket for motion. While it has an excellent record for long life and durability, the plastic wears with each step and can lead to eventual loosening of the hip replacement. This process can take 10 to 20 years and is not a problem for most patients.

Traditional Hip using 28 MM ball
Traditional Hip using 28 MM ball. This prosthesis is FDA approved.

Components for Traditional Total Hip Replacement

However, younger patients may need their hip to last much longer. To specifically address this issue, we use a metal-on-metal ball and socket that dramatically reduces wear rates. In laboratory simulations, the wear rate of metal-on-metal is as much as 1000 times lower that traditional metal on plastic.

While metal-on-metal does not have the proven track record of metal on plastic, it is believed that it has the potential to last much longer than traditional hip replacements. This procedure has been used successfully for the last two years with excellent early results.

Five Year Follow Up Study - 38 Millimeter Metal on Metal Hip

38mm cup
38mm cup

Surgeons have recently begun using a larger metal-on-metal ball, which measures 38 millimeters compared to the traditional 28 millimeters ball. This larger ball has a number of advantages including a lower chance of dislocation. The surgeon performs the procedure through a much smaller incision and the result is less muscle disruption. Patients with the new ball size also have greater range-of-motion and report a more "natural" feeling to the hip.

This procedure is new, and the long-term record isn't known yet. For this reason, surgeons at Sinai are involved in a 5 year follow up study to record and provide to the public proven research on the longevity of this prosthesis and procedure. Find out more about Barry Waldman, M.D., the Sinai surgeon leading this study, here »

Minimally Invasive Total Hip Replacement

Hip replacement is one on the most successful procedures known to medicine. Wounds heal very well with little excess scarring regardless of their size.

Recently, attempts have been made to reduce the size of the incision in an attempt to shorten hospital stay and quicken the pace of rehabilitation. We believe that these heavily advertised procedures are small modifications on the basic total hip operation and afford no advantage to the patient other than a smaller incision. They also have many possible drawbacks including nerve and blood vessel damage and malalignment of the new hip.

While we seek to make our incisions as cosmetically acceptable as possible, we believe the surgery should be performed as safely as possible and with the smallest possible chance of complications.

Sinai's orthopedic department is also involved in an FDA investigation of a new metal on metal hip prosthesis called the Conserve Plus. For detailed information on this trial study, click on FDA Metal on Metal Study.