A trial reduction with provisional implants now can be completed. The foot and leg are removed out of the bag and maintained sterile. The leg then is externally rotated and the trial head/neck segment applied to the femur (Fig 12). The hip is reduced, and range of motion and leg lengths are confirmed.
The provisional implants are removed from the hip by first externally rotating the lower extremity and dislocating the hip. The trial head/neck segment is removed and if the acetabular trial liner had been used, the final liner is inserted. The leg then is placed back into the bag on the posterior aspect of the table. The femoral broach is removed and the final femoral stem is inserted. The leg is retrieved out of the bag and brought back on the table and is externally rotated. The final prosthetic head is implanted on the stem and a final reduction is accomplished. During the final reduction, leg length and stability are confirmed. Leg length is estimated by tension on the capsule and by referring to the knee position of both legs with the legs adjacent to each other on the table. The wound is closed by loosely approximating the U-based capsular flap back up to the remaining capsule in the lateral aspect of the hip. If this capsule is excessively thick, it can be thinned to eliminate any impingement. A drain routinely is used. This is inserted exiting superiorly through a separate portal and the fascia then is closed. Subcutaneous tissue and skin then are closed.
It is a common part of our practice to infiltrate the various layers on closure with 0.25% marcaine with epinephrine. This is used in the capsule, fascia and skin.8 A sterile dressing is applied. The drain usually is removed 6 to 24 hours after surgery, depending on whether the patient goes home the day of surgery or stays in the hospital overnight.
The anterolateral surgical exposure for mini-incision hip replacement described in this article is one that allows THR to be done through a very small incision. This skin incision leads to an intermuscular exposure of the hip intended to cause minimal muscle damage and to facilitate rapid rehabilitation.
The posterior approaches for mini-incision hip replacement surgery still require a posterior capsulotomy and posterior dislocation of the hip to achieve a view for implantation of the prosthesis. Posterior approaches traditionally have been associated with a higher rate of postoperative dislocation.3,12,14,38,39 This complication has been postulated to be caused by division of the posterior capsule. To circumvent this problem, investigators have done a repair of the capsule and short external rotators after inserting the implants. This usually considerably has decreased the rate of dislocation,18,23,27,36 but in some series, it has been associated with no considerable change in the dislocation rate,10 and in other studies, the repair has been found incompetent by postoperative radiographic investigation.31,32 Even with the best results, posterior dislocation still occurs in some patients.
The anterior approaches to the hip have been associated with a lower risk of postoperative dislocation.12,33,38,39 These approaches have been popular for the insertion of hemiarthroplasties and THRs. Anterior approaches have provided very good exposure for the acetabulum and femur for prosthesis implantation, and a number of these approaches have been described.3,17,24,25,30 They all have in common the division of the anterior 25 to 50% in the gluteus medius and minimus or reflection of that portion of the abductors with a sleeve of vastus lateralis attached either through the fascia or bone removed from the greater trochanter. The divided abductors have then been repaired during incision closure. These lateral approaches have eliminated many of the complications associated with complete osteotomy of the greater trochanter, but they present other potential problems. Damage to the superior gluteal nerve frequently is encountered.1,2,4,22,28,29 This has been reported in up to 77% of patients at 6 weeks postoperatively and in up to 40% of patients at 52 weeks postoperatively in cases operated through a lateral approach.1 At 3 months, 52% of patients show acute injury patterns on EMG compared with baseline EMG studies done from before surgery.22 Many patients either recover or show few problems, but complete muscle denervation probably is present in 10% of hips postoperatively.4,28,29 This complication always is associated with a notable limp and compromised patient function.28 There is a safe area extending 3 to 5 cm proximal to the tip of the greater trochanter.9,11,15,16,19 If the division of the gluteus medius is limited to this area, the possibility of superior gluteal nerve injury is minimized.11 Given this normally safe area, it may, however, be impossible to eliminate this nerve injury completely because of anatomic variations seen in some patients.15 Furthermore, when the repaired gluteus medius and minimus fail to heal properly after repair, a persistent limp and positive Trendelenburg sign occur in an additional group of patients.4,32 Obrant et al26 reported an average 23% decrease in abduction strength after anterolateral exposure. Trying to minimize this muscle weakness is one of the factors that has led to the development of so many variations of this procedure. To promote healing of these reattached muscles, surgeons have prescribed the use of crutches for 6 to 8 weeks and delayed patient rehabilitation. This limited activity is directed at supporting the repaired tendons during healing.
If an anterolateral approach, which splits the vastus lateralis muscle, is used, additional bleeding often is encountered from injury to a transverse branch of the lateral circumflex femoral artery. Nerve injury to the posterior portions of the vastus lateralis also can occur because the femoral nerve enters the muscle proximally and medially. Division of the muscle can leave the posterolateral portion denervated.30
This mini Watson-Jones approach is different from the approaches done through the internervous interval between the tenser fascia lata and the sartorius. These approaches also are usually done with the patient in the supine position and additional incisions often are made to assist with instrumentation or implant insertion. This mini Watson-Jones approach is done through the intermuscular interval between the gluteus medius and the tenser fascia lata. It is done with the patient in the lateral position and uses only one incision for all intervention.
One distinct advantage of this mini-incision approach is that it accommodates any design of prosthesis. Any contemporary acetabular or femoral prosthesis can be inserted through this exposure. Fully porous coated, proximally porous coated, and grit-blasted taper stems have been used in our patients. This is valid also for cemented implants. To pressurize the cement for femoral fixation, the surgeon must make sure that a long enough pressurization nozzle is used. The exposure is adequate to accommodate most current prostheses.
This surgical approach can be used in almost all patients. For the first few patients operated on using this approach, the surgeon should choose slender patients with reasonably good range of motion and minimal deformity. In learning the approach, an incision 1 to 2 cm longer in each direction makes the exposure easier. The incision can be shortened as the surgeon’s becomes more experienced. Patients who are extremely obese or very muscular are the most difficult to achieve adequate exposure. In these patients it is often helpful to make the incision a few centimeters longer distally. Additionally, the most important structure to release to assist with exposure and minimize forced exposure is the capsule. The capsule should be cut posteriorly to the area of the piriformis insertion and inferiorly to the medial border of the femoral neck. If these soft tissues are not surgically released, the tendency is to put more pressure on the femur in adduction, extension and external rotation and this can result in femoral shaft fracture. Patients who have had previous anatomy-changing fractures or have retained internal fixation devices (sliding nail or blade plate) should be done with a larger incision.
We have used this approach in over 300 patients during the last year and think it is an excellent anterior approach without muscle damage through a small incision. One difficult aspect of this approach is consistent acetabular component positioning that is necessary to avoid anterior dislocation associated with excessive acetabular anteversion. We think this can be avoided with a good acetabular positioning device, experience with the approach, and possibly using computer guidance. Another difficulty encountered in this approach is femoral exposure. An adequate capsular division as noted above and an assistant experienced in positioning the leg are both important to resolve this issue.
Because this surgical approach is new, experience will need to be accumulated to make sure that prosthesis positioning is appropriate. Additional clinical parameters-blood loss, rate of recovery, abductor muscle function, incidence of dislocation, and others-need to be documented and reported. Because this is a new approach, it should be closely evaluated before it is used extensively.
Special thanks to Dana Mears, MD; Mauro Meyer, MD; Aldo Toni, MD; and Robert Hube, MD for constructive input during development of the technique.
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