One-stage bilateral implantation of a calcar-guided short-stem in total hip arthroplasty

Objective One-stage bilateral, muscle-preserving, calcar-guided implantation technique through the modified minimally invasive anterolateral approach in supine position. Indications Bilateral primary/secondary osteoarthritis of the hip; bilateral femoral head necrosis; ASA I–III. Contraindications ASA IV; severe osteoporosis, other factors jeopardizing stable anchorage of cementless, calcar-guided short-stem; infection. Surgical technique Supine position. Skin incision. Opening of fascia; blunt dissection, pushing gluteal muscles dorsally with the index finger. Capsulectomy. Individual osteotomy according to preoperative plan to determine short-stem position. Remove femoral head. Prepare acetabulum. Position cup. Femoral preparation with the curved opening awl. Spare greater trochanter and gluteal muscles. Insert trial rasps in ascending sizes with “round-the-corner” technique. Select offset version, then trial reposition with intraoperative radiograph and implantation of the definitive implant. Wound closure. Consultation with the anesthesiologist to confirm a stable patient. Same procedure on contralateral hip. Postoperative management Mobilization on day 1 with immediate full weight bearing. Remove wound drains and urinary catheter (only female patients) on day 2. Intensive protocol of physiotherapy and rehabilitation. Thrombosis prophylaxis. Rehabilitation from day 7. Results Almost 500 patients have undergone surgery since 2010. First consecutive 54 patients (108 hips) prospectively evaluated. After 2 years, Harris Hip Score was 98.8; satisfaction on visual analogue scale was 9.9. Low peri- and postoperative complication rates; no implant revisions. Conclusion The muscle-sparing approach and the special “round-the-corner” technique in one-stage bilateral procedure leads to rapid mobilization and rehabilitation with excellent early clinical results and high satisfaction rates.


Introduction
A recent analysis of the Swedish hip arthroplasty registry revealed that 17% of all patients receiving primary total hip arthroplasty (THA) suffer from bilateral symptoms of osteoarthritis [6]. Onestage bilateral THA is an alternative to staged unilateral THA in those patients; however, there is still broad concern about the safety and reliability of this procedure.
Given the presence of bilateral hip osteoarthritis accompanied with bilateral corresponding symptoms, one-stage bilateral THA offers various advantages for the patients [17]. Besides the necessity of only one surgical procedure and only one anesthesia, postoperative rehabilitation can be improved [9]. Bilateral treatment, in contrast to a staged unilateral procedure, leads to early painless ambulation, without any residual symptoms of the contralateral pathological hip. The quality of rehabilitation can be enhanced and duration in total can be reduced. In addition, the recent literature implicates a complication rate comparable or even lower than in the staged procedure [1,19]. However, in order to ensure a safe procedure and high quality of postoperative function, one-stage bilateral THA needs to provide certain characteristics like short surgery duration, low blood loss and distinct muscle-sparing technique [14].
In modern THA raised consciousness in order to reduce muscle-and soft-tissue trauma has led to a widespread usage of minimally invasive approaches (MIS) [3,8,18]. Due to soft-tissue sparing techniques, some MIS approaches have been shown to possibly offer encouraging clinical results particularly in regard to early ambulation and blood loss [5,22]. Besides smaller incisions, MIS techniques aim to reduce damage especially of the abductor muscles. The continuity consequently can be preserved. One of the most common approaches used in THA is the Watson-Jones anterolateral approach performed in the supine position [15]. Over time, modifications have led to the development of a MIS approach [4,15]. It uses a muscular gap between tensor fasciae latae and gluteus medius without the necessity of any muscular transection. The gluteal muscles can be preserved. Consequently, it offers low blood loss, early recovery of hip function and excellent clinical short-term results [20,21].
However, not only the type of approach ensures the muscular continuity and reduces damage to soft tissue, but also the type of implant. Modern calcarguided short-stems have gained importance in recent years [7]. The development of new calcar-guided, metaphyseal anchoring short-stems amongst others pursues the strategy of being able to spare muscles, soft-tissue and bone [2]. They provide characteristics, making these implants well suitable for the usage in MIS techniques [15].
The key to these characteristics is a certain implantation technique which differs from conventional techniques used with traditional straight-stem designs. The heart of these implants, besides their reduced length, consists of the anatomical curvature, which has been adapted from the calcar. The positioning of the stem follows the personal anatomy alongside the calcar curve, making possible an individualized implantation ( [10], . Figs. 1 and 2). Employing a particular "round-the-corner" technique, the greater trochanter especially, together with the gluteal muscles can be distinctly protected [7].
Consequently the combination of MIS techniques accompanied with the usage of a caclar-guided short stem possibly offers distinct qualities regarding early clinical results and may support encouraging early functional outcomes [16]. Possibly the operation time and blood loss may be reduced to a low level. Several shortterm results of different types of implants support these anticipations in the early stages [2,9,12,13].
All these features taken together might be helpful especially in the demanding perioperative management of one-stage bilateral THA.
We describe the one-stage bilateral procedure of the muscle-preserving, calcar-guided implantation technique using a calcar-guided short-stem through the modified MIS anterolateral approach in supine position.

Surgical principle and objective
The main goals in modern THA especially in one-stage bilateral procedures today are the sparing of bone and soft tissue, a fast and reliable technique and excellent early clinical results with possible high postoperative activity levels. The combination of modern calcarguided short-stems using a modified MIS anterolateral approach aims to meet these requirements. The special "round-the-corner" technique of implantation without damage to the greater trochanter and the gluteal muscles is key.

Advantages
One-stage bilateral procedure 4 Only one procedure 4 Only one anesthesia 4  Results. Almost 500 patients have undergone surgery since 2010. First consecutive 54 patients (108 hips) prospectively evaluated. After 2 years, Harris Hip Score was 98.8; satisfaction on visual analogue scale was 9.9. Low peri-and postoperative complication rates; no implant revisions.
Conclusion. The muscle-sparing approach and the special "round-the-corner" technique in one-stage bilateral procedure leads to rapid mobilization and rehabilitation with excellent early clinical results and high satisfaction rates.

Schlüsselwörter
Hüfttotalendoprothese · Prothesen und Implantate · Minimal-invasive Operationsverfahren · Round-the-corner · Optimys   Fig. 3)   The joint capsule is exposed by two curved Hohmann retractors without sharp edges positioned cranial and caudal the capsule. In addition one Hohmann retractor is positioned at the anterior rim of the acetabulum, medializing vastus lateralis muscle without damage. The incision is done alongside of the femoral neck and the capsulectomy is performed. Note that no sharp dissection of any muscle, especially the gluteal muscles, is needed. From [15] Fig. 9 9 After removal of the anterior joint capsule, the femoral neck is exposed in order to perform the osteotomy by placing the two facing curved retractors intracapsular around the femoral neck. From [15] Operative Orthopädie und Traumatologie 2 · 2017 185 Fig. 10 8 (a valgus, b neutral, c varus) One of the most important steps in implanting a calcar-guided short-stem is choosing the individual height of the osteotomy in order to partly preserve the femoral neck. Consequently a preoperative templating is mandatory. The height of the osteotomy is determined intraoperatively by palpation of the lesser trochanter and the fossa piriformis. In order to position the stem in a valgus position most of the femoral neck is resected and the osteotomy is performed distally (a). If the stem is to be implanted in a varus position the osteotomy is done proximally, according to the preoperative templating, preserving most of the femoral neck (c). This way femoral offset and leg length can be reconstructed in a large bandwidth [10]. From [15] Fig. 11 8 The osteotomy is done in slight external rotation of the ipsilateral leg according to the preoperative templating using a long stiff bladed oscillating saw. From [15] Fig. 12 8 The femoral head is removed from the acetabulum using the femoral head extractor. To protect the gluteus medius a Langenbeck retractor is placed medially and pulled proximally. From [15] Fig. 13 8 During acetabular preparation a Steinmann pin is inserted in the proximal end of the acetabulum to provide optimal protection to the gluteal muscles. Two curved retractors distally and dorsally support the acetabular exposure. From [15]  Operative Orthopädie und Traumatologie 2 · 2017 187 Fig. 17 8 Using the specially curved opening awl, the proximal femur is opened alongside the calcar in the "round-the-corner" technique. The insertion is done anteriorly, not affecting posterior structures such as the greater trochanter or the gluteal muscles. From [15] Fig. 18 8 Specially curved, implant-shaped rasps are driven in gently in ascendingsizes usinga hammerinordertoprepare the proximal femurandthe femoral canal until cortical contact and a stable fit and fill is reached. A double offset minimally invasive rasp handle is available. From [15] Fig. 19 8 The insertion takes place guided by the calcar in the "round-the-corner" technique.Again, the greater trochanter accompanied by the gluteal muscles is out of reach and therefore can be optimally protected. From [15]  Special surgical considerations 4 Glove change should be performed every half hour and before switching position and starting with the second hip in regard to prophylaxis of infection. 4 Before the operation the leading symptomatic hip should be identified; it is the one to start off with. In case of complications the procedure of the contralateral hip might not be possible. 4 Intraoperative radiograph using digital image intensifier is highly recommended to verify correct trial implant positioning and to assure correct offset and leg length. Therefore intraoperative radiographs are compared to the preoperative templating and possible adjustments can be done (. Fig. 21). Errors, hazards and complications 4 Damage to the gluteus superior nerve, which supplies the gluteus medius, gluteus minimus and the tensor fasciae latae muscles. 4 After completion of the first side, further processing takes place only upon consultation of the anesthesiologist in order to confirm a stable patient. In case of complications the contralateral hip is not to be operated. 4 The implant needs sufficient fit and fill into the femoral bone with tight cortical contact in order to avoid subsidence given immediate full weight bearing. 4 Learning curve is necessary in order to avoid malpositioning of the implant.

Results
Starting in December 2010 until today the introduced calcar-guided shortstem (optimys, Mathys Ltd., Bettlach, Switzerland) has been implanted using the presented approach and implantation technique in over 4000 cases at the authors' institution. In almost 500 patients the implantation was done onestage bilaterally. The first 54 consecutive one-stage bilateral cases (108 hips) were included in a prospective observational study analyzing clinical and radiological results. The mean age at surgery was 62.7 years (standard deviation [SD] 9.0; range 36.7-76.8 years) and the mean operation time was 44.6 min (SD 16.6; range 19.0-96.0 min) for each hip. The 2-year results (mean 28.5 months), including the learning curve, have been analyzed so far and preliminary results have previously been published [9]. The follow-up was performed after 6 weeks, 6 months, 12 months and 24 months. After 6 weeks mean Harris Hip Score (HHS) and mean satisfaction on visual analogue scale (VAS) were already 87.4 (SD 9.9; range 48.0-100.0) and 9.4 (SD 1.2; range 0-10) respectively (. Figs. 25 and 26).
Initial clinical function is encouraging, allowing patients to be self-dependent a few days after surgery. After 2 years the values improved further to a mean HHS of 98.8 (SD 3.2; range 80.0-100.0) and mean satisfaction on VAS of 9.9 (SD 0.5;  Figs. 25 and 26). In the radiological follow-up after 2 years the incidence of typical radiological alterations, like stress-shielding and cortical hypertrophy in total is low, suggesting a physiological load distribution in the proximal femoral bone [11]. An analysis of the potential of reconstructing patient's anatomy showed that the technique of individualized positioning using a calcar-guided short-stem is able to reconstruct femoro-acetabular offset and leg length in a broad range [10]. The overall complication rate is low. One patient showed an intraoperative avulsion of the greater trochanter on one side, without any clinical malfunction. No therapy was required. One case of deep vein thrombosis (DVT) was reported despite regular medical prophylaxis, which could be treated successfully. In addition a prolonged seroma was documented in three cases. No postoperative joint infection occurred in any of the patients. To date, no revision surgery was needed. No signs of aseptic loosening or any other implant failure was observed. Mean drop of haemoglobin measured 5.3 g/dl. Seven patients (12.9%) needed at least one blood transfusion. However, in those patients included in the study in 2010, the usage of tranexamic acid had not been implemented yet. Thus, rates of haemoglobin drop and blood transfusion are possibly reduced further nowadays.
The muscle-sparing combination of the MIS approach and the special "roundthe-corner" technique using the calcarguided short-stem in one-stage bilateral procedure leads to extraordinary fast mobilization and rehabilitation with excellent early clinical results and distinctly high satisfaction rates. After overcoming the learning curve the implantation of a calcar-guided short-stem using the MIS anterolateral approach presents as an easy and fast technique with a low intraoperative complication rate, compared to non-curved straight-stem designs, which is favorable in regard to the usage in one-stage bilateral procedures. Mid-and long-term results are still awaited; therefore further follow-up is mandatory and will be continued.