Hip Replacements, by Matthew Osso
The “pelvic girdle” is made up of two hip bones, which are each made of three main parts: the ilium, the ischium, and the pubis.
As can be seen by the figure, the upper region of the hip bone is the ilium; this section forms the sacroiliac joint. The ilium supports the sacrum on either side, which in turn supports the spine. The ishium is the bottom posterior piece of the bony hip; this is the part that humans sit on. The pubis is the bottom anterior part and the two pubic bones are connected by fibrous cartilage. This is also where the bladder rests within the human body. The large socket seen in the hip structure toward the bottom is known as the acetabulum. This socket forms the “ball and socket” joint with the femur and is a major weight-bearing joint.  Hip Replacement Surgery is usually either partial or total; the difference being how much of the hip is actually replaced during the surgery. For most partial surgeries, it is only the femoral head (the “ball”) that is replaced, with the acetabulum (the “socket”) remaining the same. The reasoning for partial instead of total would be more of an injury whereas total is typically needed for those with severe arthritis.  When looking at Total Hip Replacement Surgery there are two main types, cemented and cementless. Cemented replacements most commonly use polymethylmethacrylate as the cement and patients with such surgeries can usually move well soon after the surgery. The only issue with cemented replacements is if the cement fails and the prosthesis loosens or the bond between the cement and the bone breaks. Even so, this is generally a very reliable method. Cementless replacements are those which are directly attached to the bone without the need of cement. The surface of such implants are said to be “conductive to attracting new bone growth”. The main issue with this type of replacement is the need for very high precision in order for the bone to actually grow onto the implant. Due to this, motion directly following the procedure is usually assisted in order to allow the bone time to grow a connection with the implant. This type of implant is still being developed, but for most cases it is used in younger patients who tend to be more active and have better overall bone quality. 
In 1891, Professor Themistocles Glück developed one of the first hip implants, making the ball-and-socket joint out of ivory. This implant was then fixed to the bone of the patient using nickel-plated screws 
In 1940, Dr. Austin Moore inserted a metal replacement for a large portion of a patient’s femur that had been damaged from a “recurrent giant cell tumor”. This prosthesis was made of a Vitallium, which is a cobalt, chromium, and molybdenum alloy and is lightweight and durable. 
The first total hip replacement was successfully implemented by Sir John Charnley during the 1960’s. The socket component of the hip structure was made of Teflon, with the femur ball component being made of stainless steel. Even though the Teflon component was found to be ineffective as a prosthesis material, the form of Charnley’s prosthesis became the standard for such implants, and even today is used with some variation. 
The hip is a major weight-bearing piece of the human body and therefore, any complications with it must be seriously dealt with. Any replacements for the hip must be very sturdy, but also flexible enough to allow the day to day movement and stress the hip goes through without causing constant pain to the patient.
There are several reasons to get a hip replacement, the most common of which is arthritis. Osteoarthritis of the hip joint is the most common reason for hip replacement surgery. Other reasons why a patient may need hip replacements include: osteonecrosis, rheumatoid arthritis, bone tumors in the joint and major joint injury. Typically, alternative treatments such as physical therapy and even a cane or walker may be suggested, but if the pain continues or grows, then a hip replacement may be the solution. 
The total hip replacement implant is made up of the parts seen in the accompanying image. The acetabular shell is inserted as the “socket” part of the joint. Next, a liner (polyethylene in the shown case) is added as a cushion similar to cartilage present in a healthy joint. The stem part of the implant is inserted into the femur and the femoral head is attached to it making the “ball” portion of the joint. Once completely assembled, the implant is tested to be sure that it allows as much movement as healthy joints would.
The stem of the implant is typically made of a titanium alloy as well as a cobalt-chromium alloy. Some cobalt-chromium alloys also employ molybdenum. Cobalt-chromium alloys are also seen in the femoral head of the implant although in some cases other ceramics can be used. Finally, the acetabular shell can be made of various materials including metal, polyethylene with a very high molecular weight, or a combination of the two. The different parts of the implant all come in varying sizes and shapes and are custom made to allow for bone growth and proper fit in each patient. 
 Sanders, Tina. "The Skeletal System." Understanding Human Structure and Function. By Valerie C. Scanlon. Philadelphia: F.A. Davis, 1997. 82-107. Print.
 "Hip Implants." OrthoInfo. American Academy of Orthapedic Surgeons, Oct. 2007. Web. 04 Feb. 2013. <http://orthoinfo.aaos.org/topic.cfm?topic=A00355>.
 Gomez, Pablo F., MD, and Jose A. Morcuende, MD, PhD. "Early Attempts at Hip Arthroplasty: 1700s to 1950s." The Iowa Orthopaedic Journal (2005): 25-29. U.S. National Library of Medicine. Web. 3 Feb. 2013. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1888777/>.
 Kaminski, M., J. Baszkiewicz, J. Kozubowski, A. Bednarska, A. Barcz, G. Gawlik, and J. Jagielski. "Effect of Silicon Ion Implantation on the Properties of a Cast Co-Cr-Mo Alloy." JOURNAL OF MATERIALS SCIENCE (1997): 3727-732. Print.
 Pospula, Wieslaw. "Total Hip Replacement: Past, Present and Future." Kuwait Medical Journal (2004): 250-55. Print.
 "What Is a Hip Replacement?" National Institute of Arthritis and Muskuloskeletal and Skin Diseases. National Institutes of Health, Department of Health and Human Services, July 2010. Web. 04 Feb. 2013. <http://www.niams.nih.gov/health_info/Hip_Replacement/hip_replacement_ff.asp>.
 "The Surgical Procedure for Total Hip Replacement." Stryker. Stryker Corporation, n.d. Web. 4 Feb. 2013. <http://www.aboutstryker.com/pdfs/hip_replacement.pdf>.
 "Virtual Hip Replacement Surgery." Edheads. Zimmer, Inc., n.d. Web. 04 Feb. 2013. <http://www.edheads.org/activities/hip/glossary.shtml>.
 "Minimally Invasive Hip Surgery (MIS)." Minimally Invasive Hip Replacement. Stryker Corporation, n.d. Web. 04 Feb. 2013. <http://www.aboutstryker.com/hip/procedures/procedures-mis.php>.
 "Total Hip Replacement." OrthoInfo. American Academy of Orthapedic Surgeons, Dec. 2011. Web. 04 Feb. 2013. <http://orthoinfo.aaos.org/topic.cfm?topic=A00377>.
Images and Video
[E] Stefan Kreuzer, MD., http://www.youtube.com/watch?v=HRki3UDYa08
[F] Barry Waldman, MD., http://www.youtube.com/watch?v=-hm2ogoSc1Y