Skeletal Radiol DOI 10.1007/s00256-014-1853-2
REVIEW ARTICLE
Computed tomography for preoperative planning in total hip arthroplasty: what radiologists need to know Alexander Huppertz & Sebastian Radmer & Moritz Wagner & Torsten Roessler & Bernd Hamm & Martin Sparmann
Received: 15 November 2013 / Revised: 6 February 2014 / Accepted: 17 February 2014 # ISS 2014
Abstract The number of total hip arthroplasties is continuously rising. Although less invasive surgical techniques, sophisticated component design, and intraoperative navigation techniques have been introduced, the rate of peri- and postoperative complications, including dislocations, fractures, nerve palsies, and infections, is still a major clinical problem. Better patient outcome, faster recovery and rehabilitation, and shorter operation times therefore remain to be accomplished. A promising strategy is to use minimally invasive techniques in conjunction with modular implants, aimed at independently reconstructing femoral offset and leg length on the basis of highly accurate preoperative planning. Plain radiographs have clear limitations for the correct estimation of hip joint geometry and bone quality. Three-dimensional assessment based on computed tomography (CT) allows optimizing the choice and positions of implants and anticipating difficulties to be encountered during surgery. Postoperative CT is used to monitor operative translation and plays a role in arthroplastic quality management. Radiologists should be familiar with the needs of orthopedic surgeons in terms of CT acquisition, postA. Huppertz (*) : M. Wagner : B. Hamm Department of Radiology, Charité—University Hospitals Berlin, Charitéplatz 1, 10117 Berlin, Germany e-mail:
[email protected] A. Huppertz Imaging Science Institute Charité, Robert-Koch-Platz 7, 10115 Berlin, Germany S. Radmer : M. Sparmann Proendo, Orthopedic Surgery, Berlin, Germany T. Roessler Department of Trauma and Orthopedic Surgery, Klinikum Ernst von Bergmann, Potsdam, Germany M. Sparmann Charité—University Hospital, Berlin, Germany
processing, and data transfer. The CT protocol should be optimized to enhance image quality and reduce radiation exposure. When dedicated orthopedic CT protocols and state-of-the-art scanner hardware are used, radiation exposure can be decreased to a level just marginally higher than that of conventional preoperative radiography. Surgeons and radiologists should use similar terminology to avoid misunderstanding and inaccuracies in the transfer of preoperative planning. Keywords Computed tomography . Total hip arthroplasty . 3D post-processing . Radiation exposure . Hip measurements . Modular endoprosthesis . Minimally invasive surgery
Introduction Total hip arthroplasty (THA) has evolved into a reliable and widely accepted surgical procedure for relieving pain and restoring function in patients with hip arthritis. Over 600,000 THA procedures are performed each year in Europe alone, following a tremendous increase over the last 10 years [1]. Hip replacement operations have benefited from the advent of less invasive operative techniques, the introduction of sophisticated stem and cup systems, the use of intraoperative navigation, and/or more accurate preoperative planning. Nevertheless, the rate of peri- and postoperative complications, including femoral and trochanter fractures, dislocations, false routes, neurovascular injury, muscular irritation, thromboembolic events, and infections remains high, ranging from 4 % to 10 % [2–5]. Accurate preoperative planning is crucial for the outcome of THA. Recently, two-dimensional (2D) pelvic X-ray radiographs have been replaced by three-dimensional (3D) computed tomography (CT) [6, 7]. CT avoids errors resulting from magnification and inaccurate patient positioning. Furthermore, CT enables additional assessment in the axial
Skeletal Radiol
plane, replaces projections by 3D data, and offers information on bone quality including accurate differentiation between cortical and cancellous bone. This review article is aimed at familiarizing radiologists with recent developments in minimally invasive THA and explaining what orthopedic surgeons expect from preoperative CT examinations, post-processing, and data transfer. This knowledge is essential for correct patient information, accurate planning of the CT scan, optimization of CT acquisition and reconstruction, and for avoiding misunderstanding in the communication of radiologists and surgeons. The parameters of CT acquisition protocols are discussed with a focus on optimizing image quality while reducing radiation exposure.
Surgical approach: minimally invasive hip surgery Minimally invasive hip surgery The success of THA depends on the recovery of limb function. Every injury to a muscle or its attachment impedes functional recovery by compromising muscle strength and disturbing proprioception. Minimally invasive surgery is defined as a surgical technique performed through a short skin incision without causing major injury to muscles and tendons. The advantages of minimally invasive surgery over the classic surgical technique in THA include decreased blood loss, shorter scar, less postoperative pain, faster recovery, and more rapid rehabilitation. The anterior or Smith–Petersen approach follows the principles of minimally invasive surgery (Fig. 1). It accesses the hip between the tensor fasciae muscle and the sartorius muscle, respecting the innervations and the blood supply of the medial and lateral muscle groups. The joint capsule is split and left in place. The hip joint is not dislocated, and osteotomy of the femoral neck is performed in situ. Other approaches (posterior or lateral) might be associated with muscle and/or tendon injury [8]. The benefits of small incision surgery remain controversial [2]. Patients prefer minimally invasive hip surgery: they associate smaller incisions with less body violation and better cosmetic results [9, 10]. The technique has a learning curve and requires specialized instruments. Despite being more difficult to perform, in skilled hands it is a safe procedure that does not increase complication rates, as shown by prospective, randomized studies [11–14]. In minimal incision THA, the entirety of the surgical field is not visible at any given moment. Intraoperative landmarks are different from standard surgery because less bone is visible and different references are necessary. In the early days of minimally invasive surgery, when experience with this technique was still scant, a higher percentage of acetabular component malpositioning and poor fit and fill of the femoral components was described [15].
Fig. 1 Surgical approaches to total hip arthroplasty illustrated on an axial CT slice. The anterior approach accesses the hip through the interval between the tensor fasciae latae and the sartorius muscle (ANTERIOR). It does not necessitate detachment of the tendinous insertions or retraction of muscle, thereby avoiding damage to the lateral femoral cutaneous nerve. The antero-lateral approach develops the interval between the tensor fasciae latae and the gluteus medius muscle (ANT-LAT). The lateral approach requires elevation of the hip abductors (gluteus medius and gluteus minimus muscles) to access the joint (LAT). The posterior approach accesses the joint through the back, taking the piriformis muscle and the short external rotator muscles of the femur (POST). It provides excellent access to the acetabulum and preserves the hip abductors
Biomechanical considerations Analysis of pelvic CT datasets [16] shows great variations between individuals with respect to the width and internal dimensions of bones, the centrum–collum–diaphysis (CCD) angle (Fig. 2), anteversion of the hip, and the offset distance of the femoral head (Fig. 3). Indeed, each of these variables can deviate independently of the others [17]. This means that implanting a larger prosthesis to account for one large variable may actually overcompensate for others. A decrease in the femoral head/neck offset significantly weakens the abductor muscles of the hip. A loss in hip abductor muscle strength of more than 12 % causes functional problems, such as early fatigue and limping [18]. Implanting a hip with femoral anteversion and cup anteversion cumulatively falling outside of a "safe range" of 40–60° leads to a seven-fold greater risk of postoperative dislocation [19]. A surgeon attempting to appropriately correct all of the different variables in hip geometry using standard hip replacement may be tempted to insert the hip prosthesis in a position that is optimal for the hip joint
Skeletal Radiol Fig. 2 The centrum–collum– diaphyseal (CCD) angle is measured on paracoronal maximum intensity projections (MIP, 0.75-mm slice thickness) orientated perpendicular to the longitudinal axis of the femur and to the center of the proximal femur metaphysis in different patients with osteoarthritis. a Valgus hip (more vertical neck) with 144° CCD angle in a 76year-old woman. b Neutral hip with 128° CCD angle in a 79year-old woman. c Varus hip (more horizontal neck) with 119° CCD angle in a 45-year-old man
itself, while resulting in either shortening or lengthening of the overall leg length. Postoperative leg length discrepancy of
