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Anterolateral Mini-incision Hip Replacement Surgery: A Modified Watson-Jones Approach

Bertin, Kim, C*; Röttinger, Heinz

Section Editor(s): Hanssen, Arlen D MD, Guest Editor

Clinical Orthopaedics and Related Research: December 2004 - Volume 429 - Issue - p 248-255
doi: 10.1097/01.blo.0000150294.81825.8c
SECTION I: SYMPOSIUM: Papers Presented at the Hip Society Meeting 2004

Mini-incision total hip replacement seeks to eliminate some complications of traditional extensile exposure and also attempts to facilitate more rapid rehabilitation of patients after surgery. Different surgical approaches historically have been used to do hip replacement surgery. Anterior or anterolateral approaches have often been selected to decrease the risk of posterior dislocation. Traditional anterolateral approaches have divided the anterior portion of the gluteus medius and minimus and potentially jeopardized the superior gluteal nerve. These disadvantages have been associated with abductor weakness, prolonged limp and decreased patient satisfaction. To overcome these problems, a mini-incision approach was developed using the intermuscular plane between the gluteus medius and the tensor fascia lata. This intermuscular interval through a small incision provides good exposure for total hip replacement and preserves muscle integrity so that rehabilitation can be rapid and the posterior capsule remains intact so that posterior dislocation is less of an issue. The surgical technique for this new innovative approach is described in this article.

From the *Utah Hip and Knee Center, Salt Lake City, Utah; and the †Orthopädische Chirurgie München, München, Germany.

Both authors have received funding from Zimmer, Inc.

Correspondence to: Kim C. Bertin, MD, 5323 South Woodrow Street, Suite 202, Salt Lake City, UT 84107. Phone: 801-713-0606; Fax: 801-713-0609; E-mail: KBertin@UtahHipandKnee.com.

Mini-incision total hip replacement (THR) has been pursued by various surgeons to decrease the perioperative complications associated with larger and more extensile approaches and to speed the recovery of patients after THR.5,6,7,13,37 Larger incisions and surgical approaches have been associated with larger blood loss, greater need for perioperative transfusion, use of more postoperative analgesics, a longer hospital stay, and a slower recovery.34 In the process of developing less invasive approaches for hip replacement, both anterior24 and posterior approaches have been used.6,7 This has been accomplished by progressively shortening the length of incisions used for surgical exposure. Additionally, an innovative two-incision approach for hip replacement has been described.5

Experience with these approaches has helped surgeons recognize some of the limitations and disadvantages of each approach. Therefore, to circumvent the problems of dislocation associated with a posterior approach and abductor weakness and delayed recovery associated with a direct lateral approach, a mini-incision modification of the Watson-Jones approach to the hip through an intermuscular interval was developed. The interval initially described by Sayre in 189420 and later modified by Watson-Jones,35 which is anterior to the abductors and posterior to the tensor fascia lata, was selected. Using this interval, the abductor muscle function could be maintained and the posterior capsule could be left intact. With the prosthesis inserted through this intermuscular approach, rapid rehabilitation could be instituted and the risk for posterior dislocation could be minimized. The surgical technique for this new approach is described.

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Surgical Technique

The surgical approach was initially developed by one of the authors, (HR) as a modification of the classic Watson-Jones anterolateral approach. Further developmental work was done to standardize the technique, and it is now used for primary hip replacement.

The patient is positioned on the operating table in the lateral position with the affected side up. The pelvis and torso are firmly secured to the operating table with a rigid stabilization system. An important part of the operative procedure is to use a table that allows the posterior half of the table distal to the pelvis to be removed during the operation (Fig 1). This is ½ of the leg section of the table. This can be accomplished using a Jupiter Table (Trumpf Inc., Charleston, SC) or by attaching an extension onto an existing table that is approximately 20 or 25 inches wide to allow the contralateral leg to be supported on the anterior half of the table while the posterior half of the leg portion is open and free for positioning of the top leg during exposure of the femur.

Fig 1.

Fig 1.

The hip is prepped and draped using contemporary techniques that would allow the affected leg to be draped free and to be mobile during the surgical procedure. A draping system with a sterile bag on the back side of the leg portion is required. If the draping system itself does not have this bag available, a cloth or plastic bag can be formed and used to maintain sterility of the leg when the affected limb is extended, externally rotated and adducted during femoral exposure. At this time, the foot can be inserted into the bag and then brought back up onto the table during the trial reduction and final reduction.

The skin incision is made on a line beginning at the anterior tubercle of the greater trochanter extending towards the anterior superior iliac spine. This incision extends approximately 6 to 7 cm in length. One fourth of the incision is over the trochanter and the rest is proximal (Fig 2). Subcutaneous tissue and fascia are divided in line with the skin incision. The anterior borders of the gluteus medius and minimus are palpated at their insertion on to the greater trochanter and the intermuscular plane posterior to the tenser is developed from the trochanter proximally. This interval is opened best by inserting a finger along and deep to the gluteus minimus over the anterior and superior femoral neck. Modified Hohmann retractors are placed superior and then inferior to the femoral neck overlying the hip capsule (Fig 3). A third retractor can be placed over the anterior rim of the acetabulum. Improved observation is accomplished using a light source attached to the first two retractors. Care is taken in retracting the anterior border of the glutei to avoid excessive retraction. A retractor with rounded edges of medium width helps protect these muscle fibers. At this point in the operation, the insertion of the capsule along the intertrochanteric line anterior and superior to the neck is developed. This division between the capsule and the gluteus minimus is easier at this point of the operation than later.

Fig 2.

Fig 2.

Fig 3.

Fig 3.

A U-shaped capsulotomy is made with the flap based medially. The proximal margin is near the anterior rim of the acetabulum. The superior margin is as far lateral on the femoral neck as can be achieved and the lateral margin is at the capsular insertion at the intertrochanteric line. As this capsulotomy is made, the retractors on the inferior and superior aspects of the neck are moved from an extracapsular to an intracapsular position (Fig 4).

Fig 4.

Fig 4.

The femoral head and neck are removed in two segments using two separate osteotomies. Both bone cuts are made with the hip externally rotated. The first osteotomy is made at the junction of the femoral head and neck (Fig 5). When the first osteotomy is completed, an osteotome is placed in the bone cut and the distal fragment is elevated anteriorly. The femur then further is externally rotated. This better exposes the remaining femoral neck, and the second osteotomy is made at a level determined by preoperative planning. Its orientation is parallel to the first osteotomy. This creates a cylindrical neck fragment that can be extracted using a threaded Steinmann pin (Fig 6A). The proximal-distal orientation of the distal osteotomy line is best made referencing the junction of the neck into the greater trochanter. This area usually will need to be notched distally slightly to allow the neck cut to be at the correct orientation and to produce the proper leg length postoperatively. It is important that this notching be made in a straight distal fashion, not laterally into the trochanter. The lesser trochanter is difficult to see at this point in the operation. When the femoral side is being prepared, it is easier to see or palpate the lesser trochanter. After the second osteotomy is complete, a threaded Steinmann pin is inserted through the neck and the neck fragment is removed (Fig 6B). A second pin then is inserted into the head fragment and the head removed.

Fig 5.

Fig 5.

Fig 6.

Fig 6.

With the femoral head and neck removed, the acetabulum can be observed (Fig 7). Two Hohmann retractors are placed to see the acetabulum well. One is placed at about 5 o’clock and the other at about 7 o’clock. The posterior retractor will displace the femur posteriorly. The anterior retractor will keep the capsule and medial musculature retracted. If desired, a third retractor can be placed on the anterior acetabular rim. This third retractor improves the view but decreases the space available for the insertion of acetabular reamers. It can be removed and replaced as the need arises. The leg is kept externally rotated during acetabular preparation. Distal traction on the leg may help exposure.

Fig 7.

Fig 7.

The acetabulum then is prepared by removing any labrum that is present. The capsule that obstructs the view can be excised. Any excessive soft tissue can be removed and the acetabulum then can be reamed. Low-profile reamers make acetabular preparation easier. Straight reamer handles are helpful in some patients, whereas in others, an angled, offset reamer handle provides the best approach to the acetabulum. Typically the acetabulum is underreamed by 2 mm and a press-fit acetabular prosthesis is inserted. The acetabulum is inserted using positioning guides to obtain the optimal cup position. Typically, an abduction angle of 40 to 50° is desired and anteversion of approximately 20° is desired. The tendency in cup positioning is to put the cup in with excessive abduction or excessive anteversion. Good positioning is best assured with a good cup positioner and secure patient stabilization on the operating room table. Final cup position can be compared with the native acetabular anatomy and if desired, an xray can be obtained to confirm cup position. Screws are used to augment acetabular fixation at the discretion of the surgeon. Screw holes in the cup routinely are placed to take advantage of the thicker bone in the ilium that is located posteriorly and superiorly. The acetabular trial insert or final prosthesis can be inserted at this point. If there is any uncertainty about the configuration of acetabular liner to be used, the trial can be inserted now and the final implant can be inserted later. If the surgeon is confident in the design of the liner to be inserted, this can be implanted before femoral preparation.

The femur is prepared by putting the foot and leg in a pocket on the posterior aspect of the patient. This is achieved with the hip in approximately 30° of extension, 30° of adduction and 30° of external rotation (Fig 8). To observe the cut surface of the femoral neck, an elevating retractor is placed posterior and medial to the femoral neck. This retractor then levers the femur out of the wound. A second Hohmann-type retractor is placed to retract the gluteus medius and minimus. It is stabilized at the posterior corner of the greater trochanter and then gently levers the abductors out of the field of work (Fig 9). If necessary, another retractor can be placed along the medial neck to retract the soft tissues in that area. Lighted retractors again are a helpful adjunct for this portion of the operation. Any residual capsule at the margin of the lateral femoral neck is removed so that the femoral preparation can begin in direct line with the shaft of the femur. Residual lateral femoral neck is removed and a box osteotome is used to help remove this lateral portion of the femoral neck so that the broach is not in varus or valgus positioning. A sharp pointed awl followed by a sequence of rasps then prepares the femur to the appropriate size. If reamers are desired for the prosthesis selected, these can be used to cylindrically ream the femur. If needed, the calcar of the neck can be reamed smooth to allow a collared prosthesis to sit completely.

Fig 8.

Fig 8.

Fig 9.

Fig 9.

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.

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DISCUSSION

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

With the mini-incision modification of the Watson-Jones approach35 described in this article, none of the musculature around the hip is disrupted. This should lead to a faster and more complete recovery. Injury to the superior gluteal nerve supply to the tenser is unlikely because of the proximal location of the nerve and the limited distal opening in the interval between the tenser and the medius. Additionally, because of the fact that the posterior capsule usually is not disrupted, the incidence of posterior dislocation should be considerably less than with posterior approaches.

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.

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Acknowledgments

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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