Rationale and Expectations

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CHAPTER SYNOPSIS

This chapter presents a technique for performing minimally invasive total hip arthroplasty by using a posterior mini-incision as well as current evidence supporting this procedure. Minimally invasive total hip arthroplasty has propelled changes in the process of total hip arthroplasty such as modifications in anesthetic and postoperative pain control protocols and the use of computer navigation. The benefits of minimally invasive total hip arthroplasty, and the resulting change in the process of this procedure, include decreased postoperative pain and improvements in early postoperative function. The chief benefit of minimally invasive total hip arthroplasty is its potential for significant improvements in patient satisfaction.

IMPORTANT POINTS

1

Minimally invasive total hip arthroplasty involves modified approaches that allow component placement with minimal soft tissue injury. It is not simply conventional total hip arthroplasty performed through a smaller incision.
2

When performed by surgeons with adequate experience and training, minimally invasive total hip arthroplasty is a safe and reproducible procedure.
3

Minimally invasive total hip arthroplasty, combined with modified anesthetic and pain control programs, allows significant improvements in early postoperative recovery.
4

Computer navigation provides optimal placement and positioning of components, even with the reduced exposure associated with minimally invasive surgical techniques.

CLINICAL/SURGICAL PEARLS

1

Formal preoperative education shapes patient expectations, reduces anxiety, and improves postoperative recovery.
2

Incisions in the iliotibial band and gluteus maximus tendons are avoided, and the quadratus femoris is left intact, as is the piriformis in some cases.
3

The hip capsule is incised, not excised.
4

Specialized curved retractors and reamers are used to minimize soft tissue tension.
5

Impingement must be avoided. This is accomplished by appropriate implant selection and positioning, including the use of the largest diameter femoral head possible.
6

Early activity is encouraged, with full weight bearing as early as 4 hours after surgery.

CLINICAL/SURGICAL PITFALLS

1

The use of general anesthesia and parenteral narcotics should be avoided. Adverse side-effects, including nausea, urinary retention, and confusion, interrupt rehabilitation activities and interfere with patient satisfaction.
2

Fixed retractors, such as a Charnley retractor, increase soft tissue tension and prevent the use of smaller incisions as “mobile windows.” Instruments with long handles and curved instruments and tools must be used.
3

Native acetabular geometry is not a reliable guide for acetabular cup placement. Cups placed to mirror the position of the native acetabulum may have too much vertical inclination and too little anteversion.
4

The size of the skin incision should not compromise component placement or fixation. If necessary, the skin incision must be increased and the approach modified to provide appropriate exposure.

HISTORY

The introduction of minimally invasive surgical techniques for total hip arthroplasty has generated controversy within the orthopedic community. Minimally invasive surgery (MIS) total hip arthroplasty (THA) is defined by the length of the skin incision, limited to 10 to 12 cm or less, accomplished by either anterior or posterior approaches. Advocates for MIS have cited the potential for limited incisions to improve the cosmetic result, decrease operative time and blood loss, reduce postoperative pain, and speed postoperative recovery. Critics emphasize the increased difficulty in performing MIS procedures and suggest that limited exposure will result in malpositioned or poorly fixed components as well as undue soft tissue traction, increasing the risk of neurovascular injury or injury to muscle. Some studies have reported these complications. Critics have cautioned against the broad acceptance of minimally invasive THA until the benefits and safety margin of MIS have been documented.

Minimally invasive THA is not simply conventional THA performed through a smaller incision. Rather, the approaches have been modified to allow component placement with a minimum of soft tissue disruption. Specialized retractors have been devised to facilitate exposure, and curved instruments have been designed for the purposes of reaming and placing acetabular components. Substantial evidence, including multiple prospective randomized trials, now shows that minimally invasive THA can be accomplished safely, when performed by surgeons with adequate training and experience with MIS techniques.

The techniques for minimally invasive THA have evolved concurrently with modifications in anesthesia and postoperative pain management protocols. Anesthesia is accomplished with an epidural block, avoiding inhalational anesthetics and parenteral narcotics. Local pain control is augmented by the injection of the joint capsule and muscles with a cocktail containing ropivacaine, methylprednisolone, and morphine. By avoiding parenteral narcotics, adverse effects, including nausea, vomiting, hypotension, confusion, and urinary retention, can be reduced or eliminated. This has allowed the full realization of the benefits expected with minimally invasive THA, including early mobilization and rehabilitation, with earlier return to function. With these protocols hospital stay has significantly decreased, and same-day discharge has become possible for an increasing number of patients.

INDICATIONS

Minimally invasive THA is indicated for patients who want a smaller incision. The patient should understand that the skin incision will be of an appropriate length to accomplish the procedure safely and effectively, which may require lengthening it as needed. With severely obese patients, a small incision may not be possible. Similarly, the length of the incision may be influenced by the presence of a preoperative deformity requiring an extended exposure.

TECHNIQUE

The author routinely uses a posterior mini-incision. The technique has been published, as have its results. Others have used anterior or two-incision approaches. The patient is placed in the lateral decubitus position, and a skin incision of approximately 8 to 10 cm is made along the posterior border of the greater trochanter, from the tip of the trochanter to the vastus tubercle. Deep dissection involves an incision of the gluteus maximus muscle over the posterior border of the greater trochanter. Neither the iliotibial band nor the gluteus maximus tendon is incised. The short external rotators and posterior capsule are incised simultaneously between the piriformis and quadratus muscles (4 cm) ( Fig. 20-1 ). The quadratus femoris is not elevated or incised, and the piriformis insertion may remain intact in certain cases. Dislocation of the hip allows a femoral neck cut, which is determined by measuring distally from the head-neck junction the distance measured from the preoperative radiograph. After the femoral head is removed, retractors are placed to expose the proximal femur ( Fig. 20-2 ). After femur preparation the acetabulum is exposed by a posterior-superior retractor and an anterior-superior retractor that pulls against the greater trochanter and retracts the femur anteriorly. Exposure is completed with an incision through the medial hip capsule, including the posterior ischial femoral ligament. This allows retraction for the femur completely anterior to the acetabulum ( Fig. 20-3 ).

A number of important differences exist between the posterior mini-incision approach and the standard posterior approach. The iliotibial band is not incised. The incision through the gluteus maximus is only 6 cm, and the tendon is not incised from the femur. The hip capsule is incised in two places, posterior and medial, but not excised. The quadratus femoris muscle is preserved, as is the piriformis in flexible hips. Reduced disruption of hip tissue may reduce postoperative pain. Avoidance of capsular excision, combined with repair of the posterior capsule, contributes to improved stability.

Complete acetabular exposure is obtained by specialized instrumentation. Avoiding the use of fixed retractors such as a Charnley retractor is important during the procedure because fixed retractors increase skin tension and decrease the mobility of the incision. Specialized curved retractors and reamers have been designed to minimize soft tissue tension with smaller wounds ( Fig. 20-4 ). Retractors equipped with fiber optic lighting give improved visualization. Instruments for cup implantation have a curved design to allow appropriate orientation without interference of anteroinferior soft tissues.