Component Positioning and Stable Fixation in Total Hip Arthroplasty

Introduction

Total hip arthroplasty (THA) is one of the most successful and cost-effective surgical treatments performed within the field of orthopaedics and across all surgical specialties. The main goal of THA is to provide patients with a stable joint that is enduring and painless. In order to achieve such results, it is imperative to obtain adequate fixation of both the femoral and acetabular components in the proper position at the time of index surgery.

Malpositioning and unstable fixation of components are known risk factors for instability, accelerated wear, construct failure, and limb length discrepancy. ^, Postoperatively, each of these complications may lead to poor outcomes, decreased patient satisfaction, increased morbidity, and, potentially, mortality.

Diligent preoperative planning may mitigate the risks of instability and malpositioning. However, intraoperative complications and difficulties are likely to occur. Therefore, it is crucial that the adult reconstructive surgeon be aware of potential problems that may be encountered at the time of surgery and have the ability to formulate and implement a timely and effective treatment strategy.

In this chapter, we will briefly review some of the most commonly encountered difficulties and complications as they pertain to component position and stable fixation in total hip arthroplasty. We aim to provide some history and insight into the prevention and successful management of these scenarios when they are inevitably encountered throughout the career of an adult reconstructive surgeon.

Preoperative Considerations

Initial Evaluation

The importance of preoperative planning for THA cannot be understated. This starts at the level of the history and physical examination and should take into consideration patient-specific factors and conditions that may affect the morphology and version of the native hip. For example, patients with developmental dysplasia of the hip or a history of avascular necrosis of the femoral head tend to have increased native anteversion ( Fig. 18.1 ) . Femoroacetabular impingement and slipped capital femoral epiphysis patients may have increased native retroversion of the hip. All of these diagnoses may also result in migration of the native hip center, which—along with restoration of leg length—is critical when considering correct component positioning. Preoperative radiographs should be scrutinized to identify deformity, bone loss, and bone quality. These factors may have implications on which approach and which implants will be utilized at the time of surgery.

Fig. 18.1, Anteroposterior pelvic radiograph demonstrating avascular necrosis of the left femoral head with a dysplastic acetabulum. This patient’s increased native femoral anteversion and proximally migrated hip center were accounted for during preoperative planning for total hip arthroplasty.

Templating

Templating should be routinely performed on all patients prior to THA. A proper template creates a visual guide for restoration of hip center, re-creation of femoral offset, and equalization of leg lengths. Multiple studies have also shown that sizing of both the acetabular and femoral components can be estimated with accuracy based on a preoperative template. ^, Implant type may also be influenced, for example, in a patient with Dorr A proximal femoral bone or a small proximal femoral metadiaphysis; smaller or micro implant sizes may be templated in order to optimize fit. Placement of the most appropriate implant of correct size plays a critical role in obtaining stable fixation in acceptable alignment intraoperatively. The senior author recommends displaying templates in the operating room at the time of surgery. An example can be seen in Fig. 18.2 , in which the operative hip was templated and implant specifications, neck cut length, and preoperative leg lengths are clearly displayed.

Fig. 18.2, Templated right total hip arthroplasty displayed in the operating room at the time of surgery.

Implant Options

Surgeons must possess thorough knowledge and understanding of the different types of implants at their disposal when performing THA. Based on patient anatomy and bone quality, certain implants may be more indicated than others to achieve appropriate positioning and stability. Currently in the United States, the majority of primary THAs are performed using cementless femoral and acetabular components. Thus, we will mainly focus our discussion on the design and indications for these types of implants. ^,

Cementless Femoral Components

Khanuja et al. describe six general types of cementless femoral stems based off of their geometry, which dictates where fixation occurs. Understanding the shape and biomechanics of each stem can help to ensure adequate stability and positioning when used in the proper setting. In general, there are wedged designs that obtain fixation in the femoral metaphysis. There are tapered stems of slightly varied shape that obtain fixation at the metaphyseal/diaphyseal junction, and sometimes in the proximal diaphysis. Long cylindrical stems obtain fixation in the diaphysis; modular stems, which have two components prepared separately, can obtain fixation in the diaphysis as well as the metaphysis of the proximal femur.

Understanding the shape and points of fixation of these different stems allows the surgeon to preoperatively plan and template the implant that will give the best chance for optimal fixation and proper component positioning at the time of surgery. Multiple studies have demonstrated excellent intermediate and long-term survivorship of wedged stems that obtain fixation in the metaphysis when used on both old and young patients. These are the stems most commonly utilized for routine THA across the United States.

In patients that present with poor bone quality, dysplasia, or otherwise abnormal anatomy of the proximal femur, implants that achieve more distal fixation are often required. The use of tapered, long cylindrical, and modular stems that bypass the proximal femoral metaphysis and obtain their fixation in the distal metadiaphyseal and diaphyseal regions have been used with great success in complex THA ( Fig. 18.3 ). These implants allow for avoidance of dysplastic and nonsupportive bone while enabling solid initial fixation distally. These implants also allow for correction of leg length, version, and offset as necessary. The surgeon should have knowledge of specific sizes, neck shaft angles, and offset options for each implant that may be utilized. Multiple studies have demonstrated excellent intermediate to long-term survivorship of these stems when utilized in complex hip arthroplasty in patients with abnormal proximal femoral anatomy.

Fig. 18.3, Postoperative anteroposterior hip radiograph status post right total hip arthroplasty demonstrating use of a short conical stem. This implant achieved adequate initial stability in the distal metadiaphyseal region of the proximal femur in appropriate position in the setting of dysplastic proximal femoral anatomy and a narrow proximal femoral intramedullary canal.

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