Minimally Invasive Orthopedic Surgery: First Results in Navigated Total Hip Arthroplasty

Abstract

Minimally invasive hip approaches decrease soft tissue damage but reduce the view of the operating field. The combination of minimally invasive approaches with navigation techniques can resolve this conflict. A modified anterolateral approach was used for minimally invasive implantation of hip endoprostheses, in combination with a navigation technique. A newly developed femoral clamp was used in the study, which allowed a secure fixation of the navigation reference frame without compromising the visibility of the small incision. The results included short skin incisions and hip joint muscle preservation, with only a moderate increase in operating times.

Conventional hip approaches cause soft tissue damage, resulting in postoperative luxations, heterotopic ossifications, and muscular insufficiencies.^1-4 Postoperative nerve damage can also occur and has a negative influence on clinical outcomes.⁵ Different minimally invasive approaches have been developed in the past few years with the goal of reducing these complications.^6-12In addition to this development, various techniques for navigated orthopedic implants have been developed to ensure an ideal, reproducible implant placement.^13-15 Because of the potentially reduced view of the operating field, the use of navigated operating techniques is more important with minimally invasive approaches than with other approaches. Thus far, few data are available on minimally invasive total hip arthroplasty (THA) using navigation.^16-18 The most significant challenge for minimally invasive, navigated THA is the fixation of the reference frames without compromising the surgical approach. Simultaneous fixation of the holders for the locators is difficult with a minimally invasive approach, and frequently, a compromise is made in the surgical approach.

This study presents the initial results after minimally invasive hip endoprostheses implantation using a modified anterolateral approach in combination with a navigated technique. The authors describe the approach, special draping, and patient positioning and also show the intraoperative data and complications in the first 19 cases. A new femoral clamp for fixation of the femoral reference frames is also part of the evaluation.

Materials and Methods

The minimally invasive approach, in combination with special draping and patient positioning used in this study, was used previously in approximately 400 manual implantations of THAs.¹² The approach is a modified conventional Watson-Jones anterolateral approach, with the patient in the supine position.

Figure 1: Modified instruments for Metha short-stem prosthesis implantation.

With the patient under general anesthesia, both legs are covered separately with a sterile double-fenestrated drape. The incision starts approximately 2 cm distal from the tip of the trochanter major and continues approximately 8 cm to 10 cm at a 20° angle toward the anterior cranial. The fascia lata is split in the same direction, between the musculus tensor fasciae latae and the musculus gluteus medius. The borderline to the musculus tensor fascia latae is displayed at the ventral limitation of the trochanter major, at the frontal edge of the musculus gluteus medius. Passing the edge of the musculus rectus femoris and the ventral boundary of the musculus gluteus medius, the hip joint capsule is approached. The ligamentum iliofemorale is split or partially resected to display the femoral head from anterolateral view, and three modified Hohmann retractors (B. Braun Aesculap, Tuttlingen, Germany) are inserted (Figure 1). To facilitate an easier removal of the femoral head, an osteotomy is performed with its lateral base at the femoral neck. Following the extraction of the bone wedge and the articular head, another modified Hohmann retractor is used for improved visualization of the acetabulum. After reaming the acetabulum with a cropped reamer, the acetabular component (Plasmacup SC, B. Braun Aesculap) is implanted in the usual manner with a double-cropped cup impactor (Figure 1). For femoral preparation, the operating table is angled at 25° on the level of the hip joint to position the operated leg in external rotation, adduction, and extension underneath the nonoperated leg. Because of this modified position, the resection plane at the femoral neck is rotated ventrolaterally into the incision. This allows a safe preparation of the femur without damaging the abductors, which would compromise the functionality of the joint. Special and modified retractors allow visualization of the femoral resection surface (Figure 1). The femoral canal can be safely prepared with cropped handles, and the femoral implant (BiContact, Metha, B. Braun Aesculap) can be implanted.

Navigation Technique and Femur Clamp

The previously described image-free navigation system, OrthoPilot THA 2.1 (B. Braun Aesculap), was used for cup and stem implantation.¹⁹ As part of this study, a specially designed clamp was developed to fixate the locator on the femur. The tension mechanism is comparable to a screw clamp. Spikes anchor themselves into the cortical bone and provide high rotational stability. The clamp is applied ventrally in 45° hip flexion on the proximal muscle and tendon-free area between the trochanter minor and the trochanter major. Therefore, the tensioned clamp is fastened on the proximal femur at a 30° distal tilt. The hook-shaped end is engaged at the calcar close to the trochanter minor, and the plane end is fixed below the tractus iliotibialis on the trochanter major.

Intraoperative Data and Complications

The operating time (from skin incision to completion of wound closure, in minutes) and the length of the skin incision were recorded. Damage to the musculus gluteus medius was quantified on a 3-stage scale. The body weight and height were determined preoperatively to calculate the body mass index (Table). For this study, only perioperative complications were recorded, including possible intraoperative or immediately perioperative fractures or fissures, nerve lesions, hematomas, luxations, and cardiac and cerebrovascular complications. Furthermore, possible complications related to the navigation technique and the newly developed femur clamps were documented.

table

Results

From February 2006 through April 2006, 19 hip endoprostheses were consecutively implanted using the minimally invasive approach with the navigated technique. The Plasmacup SC was implanted as the acetabular component. The modular Metha short-stem prosthesis was used in 8 cases, and the BiContact stem in 11 cases. The surgical indication in all cases was primary coxarthrosis. The average age was 63 years (range: 51-77 years), and 53% of the study population was female. The results are presented in the Table. Of the first 5 cases in the series, breakages of the clamp fixation screw occurred in 2 cases, and loosening of the clamp during surgery occurred in another 2 cases. In all cases, cup navigation was already completed. For each case, the stem was implanted without complications using the manual technique. The cases with breakages and loosening were excluded from evaluation. No other intraoperative or directly postoperative complications were observed. Modifications were made to the clamp, which remained stable during surgery in all 14 subsequent cases.

Discussion

Because of the reduced vision in minimally invasive operation techniques, navigation is an important tool to guarantee correct and reproducible implant positioning. With the navigation system used in this study, Lazovic and Kaib²⁰ demonstrated improved implant positioning compared with the manual implantation technique. The modified anterolateral approach for minimally invasive THA used in this study is proven to preserve the muscles surrounding the hip joint.¹² The goal of this study was to combine this minimally invasive approach with the navigated implantation technique and to evaluate the preliminary results.

Using a modified posterior approach for minimally invasive THA, DiGioia et al¹⁸ reported an incision length of 11.7 cm with a navigated technique. The authors of the study described have used a modified anterolateral approach to achieve a slightly shorter incision, with a mean length of 10.5 cm. An average incision of 9.1 cm has been documented with the manual technique.¹² The additional length of approximately 1.5 cm is caused by the clamp fixation, which requires extension of the incision in the distal direction.

Preserving the gluteus medius muscle intact was possible in most cases in this study. In 6 cases, the gluteus medius muscle was damaged up to 1 cm. Similar results were documented using the minimally invasive approach in the manual technique.¹² Leaving the hip abductors intact preserves muscular control of the joint. Active pelvic control and walking ability are not affected.

Average operating times of 120 and 150 minutes are cited in the literature for minimally invasive approaches using navigation in THA.^17,18 The average operating time in this study was 74 minutes, which is significantly lower than the averages cited in the literature. From an economic standpoint, the finding is not negligible.

An average operating time of 64 minutes was achieved in 92 patients using the minimally invasive approach.¹² Navigation, therefore, increased operating time an average of 10 minutes. We feel that reducing the operating time is possible once constraints posed by the learning curve are overcome.

Different femoral components can be implanted using this minimally invasive navigation. Presently, only a cropped handle exists for the implantation of the Metha short-stem prosthesis. The handle makes it possible to implant the short-stem prosthesis, preserving the soft tissue. A cropped handle is currently unavailable for Bicontact stems, thus implantation is difficult and imposes stress on the soft tissue. No wound-healing complications have occurred, however, and Bicontact stems could be implanted without complications in all cases. For this study, a new femur clamp was developed for the fixation of the reference frames. The clamp is fixed on the proximal femur with a 30° distal rotation, allowing the Hohmann retractor to be positioned behind the acetabulum during acetabular preparation. Surgeons can access the acetabulum through exerting pressure on the femoral neck and the greater trochanter without loading strain on the clamp. The use of cropped acetabular reamers is essential to avoid pressure on the clamp and to prevent clamp loosening. The distal rotation of the clamp leaves the operating field accessible for stem preparation, and allows the computer to easily locate the reference frames (Figure 2).

Figure 2: Left: reference frames attached to the femur and pelvis before OrthoPilot data registration. Right: operated leg positioned in external rotation.

Independent draping of both legs with a double fenestrated drape is necessary using the described approach for positioning the leg in external rotation, adduction and extension underneath the nonoperated leg. The additional extension, provided by angling the operating table downwards by 25° at the hip, is crucial for soft tissue preservation during stem preparation and implantation.

The study presents preliminary results after using a modified anterolateral approach for navigated minimally invasive THA. The newly developed clamp was modified after initial mechanical complications, and the subsequent operations could be performed without further difficulties. The results to date are promising, with a moderate increase of operating time, a short incision and preservation of the hip abductors. In the future, the evaluation of the clinical and radiologic results must be conducted on a larger patient population.

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Authors

Dr H.J. Walde is from the Department of Traumatology, Hand and Reconstructive Surgery, Nordwest-Krankenhaus Sanderbusch, Sande, Germany, and Dr T.A. Walde is from the Department of Traumatology, Plastic, and Reconstructive Surgery, University of Göettingen, Germany.