Minimally Invasive Hip Replacement
Minimally invasive hip replacement surgery has been described as keyhole hip replacement surgery. Minimally invasive surgery is quite a different philosophy and approach in the manner in which hip replacements are performed. We will discuss and describe the cutting edge technique and technology used to perform a minimally invasive surgical hip replacement (MIS hip replacement).



It is important to understand the difference between a normal hip and an arthritic hip. When two bones come together to form a joint, the surfaces that make contact are covered by cartilage. In the case of a hip joint, the socket (acetabulum) and the ball (femoral head) are covered with cartilage. The cartilage acts as a shock absorber to reduce stress and provide for a low friction surface for smooth gliding motion. The deterioration of the cartilage results in loss of the shock absorber as well as the low friction surface. This condition is called arthritis. The arthritis not only affects the femoral head and the socket, but it also affects the surrounding joint capsule, ligaments, tendons, and muscle, to produce the arthritic condition, which includes pain, swelling, and stiffness.

Essentially, arthritis is the wearing down of joint cartilage. It affects 30 million Americans and has multifactorial causes. The most common causes are previous trauma, family history (genes), and a history of being overweight. I use the analogy of a flat tire to help in understanding the condition of arthritis. Consider the cartilage of a joint like the treads of a tire. When the treads of a tire begin to wear out, the ride becomes rougher and bumpier. Eventually, the tire becomes bald, breaks down, and becomes flat, much like the natural history of an arthritic hip.

The non-operative treatments can be effective in the early stages of arthritis. However, the non-operative strategies treat the symptoms and not the cause.

The operative choices are limited for advanced hip arthritis. Hip arthroscopy has very little place in the treatment of hip arthritis. Hip arthroscopy has the ability to evaluate and diagnose a hip. However, there is a significant limitation in what a hip arthroscopy can produce. If there is a loose body or a torn labral cartilage, treatment can be obtained with hip arthroscopy. However, with advanced arthritis, because of the joint space narrowing from the loss of articular cartilage, damage can occur with attempted arthroscopy in an individual with advanced hip arthritis. The definitive treatment for advanced hip arthritis is hip replacement surgery.

Over 165,000 hip replacements were performed in the United States last year. Hip replacement is excellent at alleviating pain from arthritis. It is an important tool in the treatment of debilitating arthritis.

Indications for hip replacement include arthritis, pain which has failed non-operative treatment, and altered lifestyle, as well as deformity. Deformity can be in the form of severe bony distortion from the loss of the stress-relieving joint cartilage, or a significant leg length discrepancy.

Mobility is an important component in an individual’s lifestyle. When you are younger, there is opportunity for a greater variety of activity without restriction and pain.

As we age, for some of us the arthritis matures and the ability to move becomes significantly restricted. With a painful and the loss of mobility, independence is lost. A hip replacement can provide painless mobility and restore independence.

The three different hip replacement techniques we will discuss include the standard large incision, the minimally-invasive single incision, and the two-incision minimally invasive surgery.

The drawing demonstrates the three different approaches. The black dotted line represents the traditional approach. The mini-single incision surgery is an abbreviated approach of the traditional standard surgery. The two red dotted lines represent the two-incision minimally invasive surgery, which represents quite a different approach. This brings into question “does size matter” with surgical approach and incision in hip surgery.

Whether size matters depends on the situation. A big dog sitting side-by-side with a small dog does not seem to create a problem. The dogs appear quite compatible. In a wrestling match between a very large person compared to a small person, size does matter.

When you compare automobiles, being smaller can have advantages over the larger size car.


When it comes to hip replacement, there is a definite advantage to the size and approach of the incision. The traditional approach is 12 to 14 inches. This compares to a mini single incision of 2.5 to 3 inches and the two-incision mini incisions, which are each approximately 1 to 2 inches apiece.

Comparing the mini single incision to the traditional standard incision, you will see that the incision site is significantly smaller. The approach, however, is almost the same. The smaller incision allows for less dissection. This is felt to produce less blood loss and less pain The same high-quality traditional implants can be utilized in the mini technique as is utilized in the traditional technique. Both cemented and non-cemented type implants can be utilized with this technique.

How does one go from a 12 to 14 inch incision to a 2.5 to 3.5 inch incision? This is accomplished by specialized instruments that allow for excellent retraction. Retractors have been designed with light sources to illuminate an area of dissection. Specialized angulated inserters to place the sockets and stems have also been designed to work through small incisions.

Comparing the minimally invasive two-incision hip replacement to the traditional hip replacement, you see a significant discrepancy with the size of the incisions. However, the significant point to be made is the fact that muscles and tendons are avoided or separated in the MIS two-incision hip procedure. Whereas, in the traditional hip replacement, muscles and tendons are cut. Because the muscles and tendons are protected from being cut, there is a significant decrease in pain and blood loss, which translates into a shorter hospital stay.

The advantages of minimally invasive hip replacement surgery includes less pain, less blood loss, quicker recovery, more stability, and it is cosmetically more pleasing.

In some cases, minimally invasive hip replacement surgery is being performed as an outpatient procedure.

Several features of the surgery demonstrated are that of the ability to look down a deep wound through a small incision when utilizing the lighted retractors.

A low-profile socket reamer is passed through a small incision.

An intra-operative real-time x-ray (fluoroscope) is utilized to direct precise positioning of the reamer to perform the reaming of the socket.

The specialized socket reamer has side cut-outs to reduce the profile in order to pass this instrument through a small incision. The small raised circles of this instrument provide the cutting blades for the reaming action.

The stem is placed into the hip through a second posterior incision. The fluoroscope is utilized to determine the precise positioning of the femoral stem implant into the femur.

The post-operative dressings cover both the anterior and posterior incisions utilizing small bandages.

The cosmetic results are that of an anterior (frontal) incision where the socket was passed into the hip joint and a posterior (rear) incision where the femoral stem was passed into the hip joint.

The measurements indicate the incision to be slightly more than 1 inch.

Because of the limited amount of dissection and the fact that the muscles and tendons are separated and not cut, the stability is improved in this operative procedure. Therefore, we expect that the number of hip locations after hip replacement surgery utilizing the mini-invasive surgical techniques will decrease the complication of hip dislocation.

Who is eligible for this operative procedure? It is easier to determine eligibility based on the negative criteria. If you are overweight, which is defined as being 15 to 20% above your basal metabolic index (reference the basal metabolic index), you are not a candidate for the two-incision technique due to the limited visibility that the additional weight creates in providing exposure for this surgery. If you are too muscular, it is very difficult to retract to allow exposure to perform this surgery. If you are a large person, there is a critical number as to the top end of the size of a hip replacement that can be passed through 1 to 2 inch incisions. The bone characteristics that eliminate an individual from the two-incision mini invasive hip replacement surgery are that of poor bone quality, a wide femoral bone canal, and a low hip angle.

For the most part, overweight, large individuals are not candidates for the two-incision mini invasive surgery. However, they can be considered for single mini invasive surgical hip replacement.

The determination of the overall hip size is determined by the pre-operative x-rays. The pre-operative x-ray is templated. Within a few millimeters, the appropriate size can be determined that is required for the hip socket. If the hip socket is generally over 64 mm, the operative procedure cannot be performed.

The bone canal size is very important to determine with the pre-operative x-rays. If the femoral canal is too wide, a secure fit cannot be achieved using a non-cemented technique. A wide canal will require cement to secure the femoral implant. If this is required, a two-incision MIS cannot be performed because the cement placement cannot be properly directed with such a small incision. Therefore, only non-cemented hip replacement implants can be utilized with the two-incision MIS hip replacement surgery.

The bone quality is also an important consideration. Since the two incision MIS can only be performed with a non-cemented technique, the femoral implant needs to be press-fitted into the femoral bone canal. In order to produce this effect, the bone canal needs to be machined with drills in a precise fashion to produce a canal which is 2 mm smaller than the femoral implant. The femoral implant then has to be press-fitted utilizing aggressive impactions with a mallet in order to seat the stem into the canal. The canal bone will expand and then contract around the implant. The bone cells will then grow into the beaded implant, producing a biologic lock. With osteoporotic bone, the strength of the bone is weakened by the porosity. A very porous bone cannot withstand the press-fit impactions required to secure the implant without cement. Therefore, significantly osteoporotic bone with very thin, porous cortical bone would render an individual ineligible for this surgery. However, the minimally invasive single incision surgical technique could be performed.

The hip angle is an important consideration. The lower hip angle indicates the need for a wider incision.

The pictures indicate different widths of the femoral components.

The white lines indicate the critical distance which is required to pass the implant through a small incision.

The hip angle will determine the critical length that the implant can pass through a given incision. The lower the hip angle, the longer the incision required to pass the implant. Thus, lower hip angle, in some cases, may eliminate you from a two-incision MIS but not from a single incision MIS.

The mini incision is an abbreviated approach to the traditional incision. In the minimally invasive single incision, there is some need to cut muscles and tendons, however, to a significantly lesser degree compared to the traditional surgical technique for hip replacement surgery. The minimally invasive single incision is not limited by bone quality, size of the patient, and hip angle, as is the two-incision MIS hip replacement surgical technique.

The criteria for the minimally invasive single incision hip replacement technique requires evidence of arthritis on a hip x-ray, history of pain and failure of conservative treatment, as well as appropriate weight. An overweight individual eliminates a person from the minimally invasive single incision hip replacement technique.

The ideal candidate for the two-incision minimally invasive surgical hip replacement technique is a person with appropriate weight, good bone quality, and proper bony anatomy. The two-incision MIS hip replacement surgery offers a significant number of advantages over that of the traditional surgical technique.

If you feel that you are a candidate for hip replacement surgery and would like to learn more, please contact our office at (954) 771-3334.

Michael T. Reilly, M.D.
MTR,MD/vjl