Understanding Minimally Invasive Hip Replacement Surgery

 In the last 3-4 years there has been a lot of talk and publicity concerning “minimally invasive” hip replacement.  There is great confusion amongst patients regarding the definition of minimally invasive surgery and how it may or may not benefit them.

What are the differences in hip replacement procedures? What qualifies as minimally invasive surgery?  What are the risks and benefits of these procedures? 

Methods for Total Hip Replacement
Common approaches to total hip arthroplasty in the western region of the United States include the well-known posterior approach, which likely represents some 80-90% of hip replacements.  The anterolateral (Harding) surgical approach represents the majority of the remaining procedures.  Both of these techniques can be implemented using smaller incisions, which limit the amount of muscle split on the lateral side of the hip; however, they do not significantly change or limit the muscles released during the deeper dissection.    These approaches should be referred to as "mini approaches".

The two-incision approach is a novel minimally invasive surgical technique, combining an anterior incision and a superoposterior incision to avoid muscle detachment, but it does split the gluteus maximus muscle during the second incision.  Furthermore, there are other technical limitations which restrict the approach to a certain subset of patients and implant types.

The anterior approach has some variants (Smith-Peterson, Hueter) and is much less commonly used in the United States, especially on the West Coast.  In fact, the anterior is more frequently utilized in Europe.  When used as a Hueter variant, and with a special orthopedic table, it is a valid minimally invasive approach, thus avoiding muscle detachment (or muscle splitting) and allowing access for excellent component positioning.  Unlike the two-incision approach, the anterior approach is applicable to nearly all patients presenting for primary hip replacement and allows the vast majority of implant types, cement less and cemented, to be used. This is my current approach for nearly all primary hip replacements.

What is Minimally Invasive Hip Replacement Surgery?
A minimally invasive approach is considered “valid” when it significantly decreases recovery time and increases early function by minimizing deep and superficial tissue trauma.  It must also be able to retain all the principles of bone-implant fixation and preserve the long-term results of traditional approaches.

Minimally invasive approaches accomplish the above definition by avoiding or limiting the detachment of muscles and ligaments from bone and also limiting the splitting of muscles during the surgery.  The basic principles of hip replacement must remain the same; these include: fixation, stability and maintenance of leg length.

These procedures also employ small incisions–between three and five inches–as larger incisions are no longer necessary.  It should be emphasized that the size of the incision has little to do with how “minimally invasive” the procedure is.  A surgical procedure is classified as “minimally invasive” by what is done subcutaneously, or under the skin.  The avoidance of muscle detachment or muscle splitting is what allows the patient to enjoy the benefits of facilitated rehabilitation and a speedy return to normal activities

What Is Not Considered Minimally Invasive Hip Replacement Surgery
“Small incision,” or “mini incision,” hip replacement is not minimally invasive surgery.  Again, the emphasis in minimally invasive surgery is on the deeper dissection and what is being effected beneath the skin that allows patients the postoperative benefits of this type of surgery.  The length of the skin incision does not determine the patient’s postoperative recovery time, pain, function or limitations.

Benefits of Minimally Invasive Hip Replacement:
     Decreased pain
     Decreased physical therapy
     Minimal motion restrictions
     Decreased hospital stay
     Early return to function
     Improved stability
     Precise leg length analysis
     Decreased limp

Other Potential Benefits:
     Decreased blood loss
     Decreased use of extended care facilities
     Decreased use of home care, home physical therapy and adaptive equipment

Risks of Minimally Invasive Hip Replacement:
     Lower surgeon familiarity and experience with procedures
     Procedure is more difficult to perform
     Greater potential for intraoperative mechanical complications

Summary of Minimally Invasive Anterior Approach:
An incision is positioned anywhere from 3.5-4.5 inches over the anterior aspect of the hip.  The thin fascia over the fascia lata muscle is opened and the interval between sartorius medially and tensor fascia lata laterally is developed. The interval between rectus femoris medially and gluteus medius laterally is developed to reach the anterior hip capsule.  The capsule is excised to expose the hip joint.  No repair of capsule or muscles is required upon closure.

Benefits of the Anterior Approach:
     It is applicable to the vast majority of patients.
     It allows the use of cemented or cement less implants.
     No muscle releases or muscle splitting are necessary,
     There is a low incidence of lateral-sided hip pain.
     There is no abductor weakness
     There are no significant motion restrictions.
     The dislocation rates thus far are approximately 0-2%.
     There is a very fast return to function and normal gait.
     There is significantly less pain.
     There are no strengthening limits.
     No abductor pillows are used.

Limitations of this procedure:
     A special operating room table is required to keep the incision 3.5-4.5” and to access the femur without releasing posterior muscles.
     There is risk of thigh numbness from lateral femoral cutaneous nerve palsy.
     The use of intraoperative X-ray is common―on average, 20-30 seconds.