APPROACHES

Mini-Posterior (Mini-Posterolateral)

Because more than 60% of THAs in the United States are performed via the posterior approach, it is logical that many orthopedic surgeons will start minimally invasive THA using some modified version of a posterior approach. Because the mini-posterior approach meets the needs of most patients, many surgeons may not need to learn additional minimally invasive surgical approaches for THA.

One commonly used technique for mini-posterior THA is the one described by Dorr and colleagues.³ Briefly, the patient is placed in the lateral decubitus position and an approximately 8-cm skin incision is made along the posterior border of the trochanter extending from the tip of the greater trochanter to the level of the vastus tubercle on the femur. A fascial incision is then made extending proximally in line with the fibers of the gluteus maximus (Fig. 65-1). Finger dissection is then used to find the plane between the gluteus medius and the minimus. An L-shaped incision of the capsule and external rotators is made that parallels the inferior border of the gluteus minimus, is carried to the piriformis fossa, then is turned distally to incise the external rotators from the greater trochanter ending at the proximal edge of the quadratus femoris. The hip is then dislocated and the femoral neck cut is made in accordance with preoperative planning. The acetabulum is visualized with a minimal anterior capsulectomy. Curved reamers and/or computer navigation can be used to assist in acetabular reaming. The real acetabular component is then inserted. The osteotomized femur is delivered through the incision, and specialized retractors are placed near the femoral neck to facilitate femoral preparation and insertion of the trial stem and then the real stem. The posterior capsule and external rotators are repaired either through drill holes in the greater trochanter or by using a soft-tissue repair that approximates the external rotators and capsule to the inferior edge of the gluteus minimus and the cut edge of superior hip capsule. The overlying fascia and skin are then closed.

FIGURE 65-1 Mini-posterior approach to the hip. Fascia between tensor fasciae latae (TFL) and gluteus maximus is incised to expose the external rotators, which are then incised to access the posterior hip capsule.

A distinct advantage of the minimally invasive posterior approach is its familiarity for most reconstructive surgeons. This approach can be easily converted to a standard posterior approach if visualization proves suboptimal or if a complication develops. The technique involves less muscular dissection than the standard posterior approach, which may decrease intraoperative blood loss and postoperative pain and may facilitate more rapid rehabilitation and hospital discharge. A recent cadaver study showed that the mini-posterior approach caused less muscle damage than the two-incision minimally invasive technique for THA.⁴

The major disadvantage of the minimally invasive posterior approach has been suboptimal component position. Woolson and associates demonstrated in a comparative study that the acetabular component was malpositioned twice as often and the femoral component was malpositioned three times as often in patients who underwent a minimally invasive posterior approach versus patients who underwent a standard posterior approach.⁵ The acetabular component tends to be placed in an excessively vertical position. The femoral component tends to be placed in a flexed position owing to a posterior starting point in an attempt to avoid injuring the skin at the proximal end of the incision. Subsequent studies by Sculco and colleagues and others^6,⁷ showed a lower prevalence of malposition and attributed the earlier findings of Woolson to the learning curve of the surgeons involved in the study. A second disadvantage is that the proximal skin of the incision is at risk for abrasion during femoral broaching, and the surgical team must be diligent to protect this skin. Woolson’s study demonstrated an increased prevalence of wound complications in patients treated with a minimally invasive posterior incision when compared with those treated with a standard incision.

Recent randomized studies have compared the standard posterior approach to the minimally invasive posterior approach. Chimento and colleagues demonstrated an advantage with the mini-posterior technique for patients with a body mass index of less than 30.⁸ These patients had less intraoperative blood loss, less total blood loss, and less limping at 6 weeks after surgery. However, there was no difference detected in functional outcomes at 1 and 2 years. Larger studies have suggested little benefit of the mini-posterior approach over the standard posterior approach. Ogonda and colleagues demonstrated no significant difference in postoperative hematocrit, blood transfusion requirements, pain scores, or analgesic use in two groups of patients randomized to standard posterior incision versus minimally invasive posterior approach.⁹ Moreover, there was no functional difference in early walking ability or length of inpatient hospitalization. The functional outcome scores 6 weeks postoperatively were the same. A comprehensive gait analysis study by this same group of investigators showed no difference between patients who received the minimally invasive approach versus the standard posterior approach.^10,¹¹ Specifically, there was no difference in gait velocity, ease of transfers, stair climbing, and the use of gait aids at 2 days and at 6 weeks.

Wenz and colleagues studied the patients who had a mini-posterior approach and retrospectively compared their outcomes with patients who underwent THA via a traditional direct lateral approach.¹² The mini-posterior incision group required less operative time, had less blood loss, and required fewer intraoperative blood transfusions. The prevalence of intraoperative and postoperative complications was not significantly different between the two groups. Postoperatively, the mini-posterior incision group required fewer blood transfusions. Radiographic analysis showed adequate component position and cement mantle in both groups. The only difference noted was a slight tendency toward valgus placement of the femoral stem in obese patients in the mini-posterior incision group. Early functional outcomes favored the mini-posterior incision group, with more patients able to ambulate on postoperative day number 1 and fewer patients requiring assistance from physical therapy. Fewer mini-posterior incision patients required skilled nursing care after hospital discharge. There was, however, no decrease in length of hospital stay.

Mini-Anterolateral

To minimize the risk of dislocation, an anterolateral approach has been advocated by many for THA. A modification of this approach has been developed for minimally invasive THA.¹³ Briefly, with the patient in the lateral position a 3-inch incision is made, angled 25 to 30 degrees anterior to the femur from posterosuperior to anteroinferior direction centered inch distal to the tip of the greater trochanter. The fascia is incised; the anterior 25% of the gluteus medius is then divided at the junction of the anterior and superior trochanter. The gluteus minimus is then transected in an L-shaped fashion (Fig. 65-2). The leg is then slightly externally rotated as the anterior abductors are detached from the trochanter. This exposes the capsule, and its anterior portion is excised. The hip can then be slowly dislocated without the remaining abductors being damaged. A provisional femoral neck cut is made to better visualize the lesser trochanter, and then a definitive femoral neck cut can be made based on preoperative templating.