Andrew I. Spitzer
Total hip arthroplasty (THA) is one of the most successful modern surgical procedures, eliminating the debilitating pain associated with arthritis and restoring function to the disabled patient. It provides a reliable, durable, and predictable excellent result and is generally regarded as one of the most significant advances in the management of the end-stage degenerative hip by rheumatologists, orthopaedic surgeons, the general medical community, and patients alike. Since its original introduction by Sir John Charnley at Wrightington Hospital in the United Kingdom in the late 1960s, the annual number of primary total hip arthroplasties performed has steadily increased. In addition, although originally applied to a predominantly elderly population, the technology has been extended to younger and more active patients. An aging population, improved wear properties and fixation of implants, and techniques designed to provide more rapid and complete recovery of function all have combined to increase current and anticipated future demand for total hip arthroplasty.
Pathogenesis
Etiology and Epidemiology
Osteoarthritis is the most common indication for total hip arthroplasty. It afflicts an estimated 21 million adults in the United States in at least one joint and may involve the hip in as many as 1.5% of the American adult population. Osteoarthritis is either primary, without identifiable cause, or secondary, owing to another systemic disease, congenital malformation, or structural abnormality of the hip joint. Joint destruction also can result from inflammatory arthropathies and rheumatologic disease (Table 12-1).
Pathophysiology
Although the actual mechanism of articular cartilage damage differs among the various causes of the arthritic hip, the final common pathway is one characterized by destruction of the smooth articular cartilage, resulting in a high friction articulation. Bone begins to grind directly on bone, generating debris, joint effusions, and in some cases frank inflammation and synovitis. The actual source of pain is unknown but may be capsular distention, synovitis, or irritated pain receptors within the bone or surrounding tissues. Motion of the joint becomes painful, especially with weight bearing, and limits mobility and function of the patient.
Diagnosis
History and Physical Examination
Clinical Features
Patients suffering from an arthritic hip joint complain of pain located in the groin, buttock, or lateral hip, often radiating along the anterior thigh toward, but usually not beyond, the knee. The pain typically is worse with activity, although start-up stiffness followed by early relief with light activity may occur. Barometric and weather changes also affect the pain, with damp and cold weather usually exacerbating the symptoms. Although the pain may wax and wane, the clinical course is usually progressive. The pace of progression, however, is unpredictable and multifactorial.
As the arthritic symptoms worsen, patients complain of a limp, ipsilateral limb shortening, stiffness, and limitation in mobility and vocational and avocational tasks. Even activities of daily living, such as toenail care, donning and doffing socks and shoes, short-distance ambulation, rising from or assuming a seated position, negotiating stairs, and sleeping, become challenging and impaired. The impact of the arthritis often becomes overwhelming as each hip cycle, of which a normal individual experiences roughly a million per year, causes pain.
On physical examination the patient may demonstrate a depressed affect, frustration, and anger. Abductor weakness from involuntary guarding and subsequent atrophy, and from laxity of the abductor muscles from limb shortening, manifests in several gait abnormalities. The Trendelenburg gait occurs as the pelvis drops to the opposite side with ipsilateral single limb stance. The gluteus medius is unable to pull the body weight over the femoral head. Patients will compensate for this weakness with an abductor lurch, in which the body is thrust over the ipsilateral limb during single-limb stance, positioning the center of body mass
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directly over the femoral head and minimizing the lever arm and resulting torque imposed by body weight, a so-called Duchenne gait (Fig. 12-1). The gait will also typically become antalgic, with the patient minimizing the time spent weight bearing on the involved hip because of the pain. Finally, shortening of the limb because of loss of the joint space and bony collapse or penetration may also impact gait, resulting in a rise and fall of the ipsilateral shoulder with each step.
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TABLE 12-1 Causes of Degenerative Disease of the HIP |
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Additional physical findings include diminished range of motion, with hip flexion and internal rotation most commonly affected. Flexion contracture may be present. This is measured as an inability to fully extend the hip while the other hip is flexed, fixing the pelvis and preventing pelvic hyperextension to achieve hip extension (Thomas test) (Fig. 12-2). Adduction contracture, which may require correction at the time of surgery to prevent dislocation of the total hip arthroplasty, can occur as well, with an inability to passively abduct the limb. Limb-length discrepancy is common and should be accurately measured. Actual limb length is measured between two bony prominences with a fixed relationship to one another, such as the anterior superior iliac spine and the lateral or medial malleolus. Measurement between points without such a fixed relationship, such as the pubic symphysis or umbilicus and a malleolus, will result in erroneous and unreliable values that vary with pelvic obliquity and abduction of the hip. Pelvic obliquity causing apparent, accentuated, or pseudonormalized limb-length inequality should also be recognized to warn patients about what their perceptions of limb length may be postsurgery.
Finally, a thorough examination of both lower extremities and spine should be performed, including an assessment of the neurologic and circulatory status of the limbs. Other causes of pain and factors that may compromise the outcome of total hip arthroplasty should be identified.
Radiologic Features
A low anteroposterior (AP) pelvis radiograph, taken from the level of the anterior superior iliac spine to distal, will usually provide adequate visualization of the acetabulum and the length of the femur in which the prosthesis will sit. A full AP pelvis may be necessary if significant bone erosion or abnormality exists. A true lateral hip radiograph (“shoot-through'' lateral) allows evaluation of the anterior and posterior hip joint space. A frog-limb lateral (Löwenstein) will normally complete the films required for a thorough evaluation. On occasion, additional pelvic views–inlet, outlet, obturator and iliac oblique, and false profile–or longer views of the femur in multiple planes may be useful.
The hallmark of an arthritic hip is loss of the cartilage-containing joint space, with bone articulating directly against bone. An osteoarthritic hip also may demonstrate subchondral sclerosis, bony cysts, and marginal osteophytes. Inflammatory arthropathy tends to be less hypertrophic, with global joint space loss and in some cases a minimum of periarticular reaction. Avascular necrosis is characterized by prominent sclerosis and/or cysts of the femoral head, femoral head collapse, and secondary acetabular arthritic change. Residual findings from childhood disease may include persistent uncoverage of the femoral head, acetabular dysplasia, subluxation, coxa magna, and deformity of the femoral head from slipped capital femoral epiphysis. Posttraumatic deformity can assume almost any configuration.
Important factors to observe, in addition to the arthritic joint and the bony reaction, include bone quality, which may affect fixation choice, and any anatomic variants that may present challenges at the time of surgery, such as unusually tall or short stature, excessive coxa vara or coxa valga, unusually large and potentially structurally significant cysts, and extremely small or large femoral or acetabular anatomy.
Lines, angles, and measurements that may help to define the anatomic abnormalities either causing or resulting from the arthritis include Shenton's line, Klein's line, Kohler's line, the center-edge angle, acetabular index, neck-shaft (CCD) angle, and the femoral cortical index. Assessment of the radiographs with these tools may facilitate surgical planning and enhance the surgeon's appreciation of the unique reconstructive challenges of each hip.
Diagnostic Workup
Although the history, physical examination, and radiographs will be adequate to establish the diagnosis and cause of arthritis in most cases, additional studies may be necessary. An MRI may differentiate intrinsic articular pathology from periarticular soft tissue irritation and will make the
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diagnosis of early avascular necrosis (AVN) prior to radiographic findings. CT scans will define complex bony abnormalities, and three-dimensional reconstructions can improve the surgeon's three-dimensional understanding of complex deformities. Nuclear scintigraphy may be useful to assess metastatic disease when suspected or other sites of disease that may be primary sources of pain. Laboratory studies assessing inflammatory disease markers such as rheumatoid factor, anti–nuclear antibodies, lyme titers, and others can help to define systemic disease. Complete blood count, sedimentation rate, and C-reactive protein measurements may be useful to evaluate for local or systemic infection. Aspiration of the joint, when clinical suspicion for infection is present, yields fluid that should be analyzed
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with cell count and differential; glucose level; microscopic review with appropriate stains for bacteria, fungi, and acid-fast bacilli; and formal culture for these organisms as well.
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Figure 12-1 A: Normal gluteus medius function. B. Weak gluteus medius causing a positive Trendelenburg sign with the pelvis dropping on the contralateral side. C: Abductor lurch or Duchenne gait. |
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Figure 12-2 Thomas test for hip flexion contracture. |
In many arthritic patients, concurrent pain from other arthritic anatomic locations can confuse the clinical picture. The hip can be the primary pain generator but can refer pain to the knee or cause a gait abnormality that exacerbates underlying spinal disease or ipsilateral or contralateral lower-extremity arthritic joints. Despite pain in these other areas, the severely arthritic hip should be addressed primarily. For example, it is generally advisable to replace the arthritic hip before undertaking spinal surgery, because the persistent gait abnormality may compromise the results of spine surgery. Similarly, hip replacement should precede an ipsilateral knee replacement when both joints are symptomatic and arthritic, because the referred pain from the hip and hip stiffness can compromise outcome and rehabilitative efforts after knee surgery. Furthermore, the new center of rotation of the hip should be used to establish a neutral mechanical axis (a factor critical in total knee arthroplasty longevity) prior to embarking on the knee reconstruction. When a true differential diagnosis dilemma exists as to the actual source of pain, diagnostic injections of local anesthetic with or without corticosteroid may help to define the primary source of pain.
In the absence of radiographic evidence for significant arthritis, alternative sources of pain must be sought. An MRI with and without arthrography along with diagnostic aspiration and injection may be useful to distinguish intra-articular from extra-articular pathology. A further workup may include evaluation of other anatomic locations and the neurologic and metabolic status of the patient (Table 12-2). Pain that is only presumptively located in the hip is not an indication for total hip arthroplasty in the absence of proven articular pathology that warrants such a major intervention.
Treatment
Nonoperative Management
The goals for treating the arthritic hip are to eliminate pain and, when possible, to restore motion to the joint and mobility to the patient. Often this requires surgery, but conservative, nonoperative treatment should be exhausted before proceeding directly to the operating theatre. The American College of Rheumatology publishes guidelines for the management of Osteoarthritis. These guidelines can be used as a paradigm for treating the degenerative hip of any cause. Simple analgesics, nonsteroidal anti-inflammatory drugs, and disease modifying agents when available may be offered as a first line of treatment. These all may be combined with physical therapy and judicious use of adaptive aids and assistive devices for both ambulation and other activities of daily living. Intra-articular injections of corticosteroids may diminish the intensity of acute inflammatory flares in the joint. Local application of ointments and compounds are usually not useful around the hip because of the depth of the joint beneath the often robust soft tissue envelope. Other adjuncts such as the use of nutraceuticals and intra-articular injections of viscosupplements may be useful but at present have not been scientifically proven to be effective. When these modalities fail, surgical intervention becomes appropriate to consider.
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TABLE 12-2 Alternative Sources of HIP Pain |
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Operative Treatment
Indications and Contraindications
The indications for total hip arthroplasty include pain unresponsive to nonoperative management along with radiographically proven severe degenerative disease. The patient must also have a realistic expectation relative to activity level, with a willingness to minimize impact loading activities and excessive exercise. Active infection either locally, systemically, or at a distant location is an absolute contraindication to joint arthroplasty. In addition, pain about the hip without documented cause or radiographically proven degenerative disease in the absence of compelling symptoms should not be treated with hip arthroplasty.
The list of relative contraindications is more controversial. Younger males with osteoarthritis, for instance, are a cohort that has a documented higher failure rate after total hip arthroplasty, presumably because of activity level and intensity. Counseling with appropriate caution and warning must be given to these patients contemplating total hip arthroplasty. Other relative contraindications include the very elderly, those medically at risk for perioperative
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morbidity or mortality, immunocompromised status increasing risk of infection, and unwillingness or inability to comply with recommended precautions or restrictions.
Surgical Goals
The goals of total hip arthroplasty are straightforward and intuitive. The reconstruction must re-establish normal anatomy, as closely as possible, with regard to limb length and femoral offset, and preserve soft tissue tension to ensure stability. Immediate and long-term fixation of the components along with bearing surfaces that are optimized to reduce wear are critical to reliable and durable service. Perioperative complications should be minimized with careful preoperative planning and vigilant perioperative management. And, most important, the patient's pain should be relieved and mobility and function should be restored.
Preoperative Planning
The preoperative planning process helps ensure intraoperative achievement of the surgical goals of total hip arthroplasty. The process begins with a thorough medical evaluation, identifying and treating sources of infection, and optimizing the patients' cardiovascular, pulmonary, and general health status. The orthopaedic evaluation includes history, examination with an assessment of gait disorder, range of motion, limb lengths, neurovascular status and skin integrity, radiographic imaging, and, if necessary, special studies. Ideally, with an understanding of the underlying pathology, the surgeon can use templates on the radiographs to size and place the components, appreciate the biomechanical alterations of both the diseased hip and the proposed reconstruction, mentally rehearse the procedure, and anticipate pitfalls. Patient education regarding precautions and expectations facilitates postoperative rehabilitation and discharge planning. Finally, the process culminates in the operating room with choice of anesthesia and patient preparation including perioperative antibiotics, urinary bladder management, careful patient positioning, and meticulous sterile technique.
Surgical Approaches and Exposures
There are numerous surgical approaches, each with certain benefits and risks, that enable the hip surgeon to accomplish the goals of total hip arthroplasty. In addition, modifications of each of these approaches, some of which have been published and others that remain technical pearls of master hip surgeons, have evolved over time. In choosing a surgical approach, the surgeon should carefully consider familiarity, skill, and the idiosyncrasies and characteristics of each approach. There is no single best or worst methodology, but a measured analysis should reveal the right combination of surgeon, patient, and surgical approach to optimize the outcome.
Charnley first performed his low frictional torque arthroplasty through a trochanteric osteotomy, which allowed for wide exposure of the hip and offered the opportunity to adjust abductor tension when reattaching the trochanter. Unfortunately, nonunion of the osteotomy occurred in as many as 25% of patients in some series. Although still useful in complex primary and revision surgery, this approach has largely been abandoned for exposure of the straightforward primary total hip arthroplasty.
The posterior approach, which classically centers a posteriorly directed incision over the trochanter, incises the iliotibial band laterally and splits the fibers of the gluteus maximus muscle. The gluteus medius is elevated, the short external rotators are detached from their trochanteric insertion, and a posterior capsulotomy and dislocation are performed. Although this approach provides the most extensile exposure, higher dislocation rates have been reported. However, with a more truncated exposure, repair of the soft tissue, and with the use of larger bearing surfaces, that dislocation rate should be significantly reduced.
Anterolateral approaches use a vertical incision centered over the trochanter. The iliotibial band is split distally, and the fibers of the tensor fascia lata are split proximally. In the direct lateral approach, the surgeon detaches the anterior portion of the gluteus medius and a portion of the vastus lateralis as a soft tissue sleeve, sometimes with a wafer of bone attached. In the anterolateral approach, the surgeon detaches the anterior third of the gluteus medius, often with a wafer of trochanteric bone as well. Anterior capsulotomy and dislocation are performed. The acetabulum is well visualized in these approaches, and the dislocation rate has been reported to be lower. However, these exposures are not as easily extensile, often require postoperative weight bearing and activity limitations while the soft tissue/bony abductor sleeve heals, and have been associated with a higher incidence of gluteus medius weakness and limp.
The direct anterior approach uses an anterior incision along the interval between the tensor fascia lata and the sartorius muscles. Splitting this interval allows direct visualization of the anterior capsule, which can be incised, enabling anterior dislocation. Although this muscle-splitting approach provides good acetabular exposure and improved hip stability, it is not extensile, and exposure of the femur can be challenging. Management of intraoperative complications may necessitate a second, more extensile approach. In addition, the use of a specialized fracture table for patient positioning is a prerequisite.
There has been a great deal of interest recently in total hip arthroplasty performed through miniaturized incisions using so-called minimally invasive techniques. Most agree that these techniques carry with them a steep learning curve, and significant complications have been reported. Most also agree, though, that more rapid rehabilitation may be facilitated and that less invasive surgery has forced hip surgeons to refine and improve surgical technique. The critical lesson learned from this recent process is that any incision through which a total hip arthroplasty is performed should be large enough and at a suitable site to enable proper positioning of the components with a minimum of soft tissue and bony injury.
Implant Choice
The proper choice of implants requires a basic understanding of the various options available and their design features. Both cemented and cementless femoral and acetabular components are available. Multiple bearing surface options also exist and can significantly affect the longevity of the hip reconstruction.
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Acetabulum.
Although metal-backed cemented acetabular components with inner polyethylene liners have been used in the past, cemented acetabular components today consist of all-polyethylene designs of varying outer and inner diameters. The backside normally is textured to enhance fixation by promoting cement interdigitation and interlock. Although these components are generally less expensive, they have proven to have higher loosening rates than uncemented cups in most series. This is also probably owing in part to the technical demands of adequately cementing an acetabular component into a bleeding cancellous acetabular bed and the difficulty of achieving proper cement interdigitation into the bone.
Cementless acetabular components have become the implant of choice in most primary total hip arthroplasties for North American surgeons. They consist of a metal outer shell of varying diameter, which is textured on its bone-opposing surface with either sintered beads, plasma spray, fiber mesh, or tantalum to create pores of optimum size of 150 to 400 nm to promote bone ingrowth. The shape of this shell is either less than a hemisphere, hemispheric, or with a peripheral flare designed to increase the interference fit between the shell and the bone. Additional features of the metal shell include optional holes for screw fixation to bone, a locking mechanism for the inner liner, and the ability to accommodate multiple modular liners with varying offsets, lips, orientations, inner diameters, and materials, including in some cases metal, ceramic, and polyethylene. The versatility of these cups accommodates widespread application and has led to an outstanding clinical track record of excellent fixation.
Femur.
Both cemented and uncemented femoral components of successful design can produce excellent long-term results when implanted with excellent surgical technique.
There are two disparate cemented femoral stem fixation philosophies, which have influenced their respective stem designs. Both philosophies rely on proper cement technique to achieve a strong bone/cement bond. This technique is based on an understanding of bone cement not as an adhesive, but rather as a grout requiring intrusion into and interdigitation within the cancellous bone of the inner femur. The composite beam philosophy and design strives also to achieve a perfect bond of the cement to the stem, by texturing, precoating with methacrylate monomer, or otherwise roughening the surface of the stem. This bonding of prosthesis to cement and cement to bone can lead to stress shielding of the proximal bone, with most of the load transmitted through the stiffer stem, bypassing the periprosthetic bone (Fig. 12-3). Debonding from the cement or the bone can occur, which signals loosening and can cause abrasive production of wear debris and subsequent osteolysis. In contrast, the taper-slip philosophy and design strives to engage a multitapered, polished, collarless stem into the cement mantle, exploiting the viscoelastic property of cement and its ability to creep. The stem never achieves a bond with the cement, but rather continues to engage the cement, often with a small amount of subsidence. The engaging taper generates hoop stresses that are transmitted radially to the surrounding bone, favorably loading the periprosthetic bone (Fig. 12-4). Although the success of some cemented stems from both philosophies has been outstanding, problems from the loosening of rough surface stems, leading to extensive periprosthetic bone osteolysis caused by the wear particles liberated by cement abrasion, dampened enthusiasm for cemented stems in North America. Nevertheless, the taper-slip philosophy with its potential for positive bone remodeling and its proven durability has gained popularity worldwide.
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Figure 12-3 Force transmission in a composite beam cemented stem reconstruction. |
Cementless femoral stems, similar to cementless acetabular cups, rely on bone ingrowth into a textured surface to achieve durable fixation. There are a myriad of designs with variability of material, surface texture and length of coating, fixation concept (fit and fill versus taper fit), bone preparation recommendations (broached versus machined), modularity, and stiffness-reducing features such as coronal slots, and hollowed stems. Each design feature has potential distinguishing merit, but the clinical performance of many cementless stems of many designs has been outstanding. With bone ingrowth, however, comes stress shielding, to some degree, potential for thigh pain from modulus mismatch and micromotion concentration at the stem tip, intraoperative femoral fracture risk, and challenging revisions. Nevertheless, the straightforward implantation techniques, the potential for permanent biologic implant fixation, and reliability and predictability of cementless femoral stems have stimulated enthusiastic use for many patient demographic groups, particularly in the United States.
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Figure 12-4 Force transmission in a taper slip cemented stem reconstruction. |
Bearing Surface.
The choice of bearing surface has taken on extraordinary importance in recent years owing to the pervasive problem of periprosthetic osteolysis resulting from polyethylene wear in metal head on conventional high-molecular-weight polyethylene bearing surfaces. Recently cross-linking of polyethylene, which provides dramatically improved wear properties in vitro and reduced oxidation potential, has been introduced. Early critical studies demonstrate reduced wear compared with conventional polyethylenes. The mechanical properties of these new polyethylenes are moderately reduced however. The very low wear rate, the opportunity to use large femoral head sizes, and improved materials have led to renewed interest in metal against metal and ceramic against ceramic. In contrast to polyethylene bearings, where boundary lubrication predominates and where increasing the head size increases the frictional torque and volumetric wear, with hard on hard bearing couples, larger-diameter heads favor fluid film lubrication and reduce the number of wear particles while imparting the associated benefits of improved stability and range of motion.
Both commonly used hard on hard bearing couples have some potential problems. Metal on metal couples are associated with increases in serum cobalt and chromium metal ion levels. The significance of increased ion levels is unclear, and to date no major clinical problems have been identified. Carcinogenesis or distant organ toxicity remain theoretical concerns. It is advisable to avoid the use of metal-on-metal implants in women of childbearing age, patients with significant kidney disease, and those with documented metal allergy. Ceramic-on-ceramic couples carry a risk of fracture despite material improvements that reduce this risk. Ceramics are also sensitive to impingement between the femoral head and the prosthetic liner; thus accurate implant positioning is especially important for these implants. A squeaking noise may occur in a few patients with ceramic-on-ceramic bearings.
Implant Choice Summary.
In summary, the hip replacement surgeon has a vast array of implant options, most of which seem to provide at least very good short-term results. Nuances of differences, which may not emerge until long-term follow-up is available, may eventually help surgeons individualize implants to patients based on age, activity level, bone quality, expectations, longevity, and metabolic status. In the meantime, an understanding of the design principles of the various implants, along with their theoretical and proven risks and benefits must suffice to guide implant choice.
Surgical Technique
Acetabulum.
Once the surgical exposure of choice has been performed, full 360-degree visualization of the acetabulum must be achieved. To facilitate this, the remaining acetabular labrum is removed along with the transverse acetabular ligament inferiorly. The fatty remnant of the pulvinar is resected to identify the fovea and thus the usual limit of medial reaming. In some cases a large medial osteophyte will need to be removed to reveal the pulvinar remnant. In addition, capsular resection or release, based on the preoperative deformities, may be necessary to enable adequate retraction of the femur for full acetabular exposure. Retractor placement is entirely dependent on surgical approach and should be individualized to maximize visualization.
Acetabular reaming commences with medialization to the appropriate depth, followed by reaming (in the intended orientation of the actual implant) to proper size. Reamer size is increased stepwise until subchondral bleeding bone is identified in a hemispheric shape, maintaining constant vigilance to central reaming and remaining wall thicknesses.
For cementless cups, underreaming by 1 to 2 mm ensures a strong interference press fit, which should be tested with an appropriately sized trial. Depending on the appearance of the prepared acetabulum, a cup size is chosen, with or without fixation holes. Cysts or defects are bone grafted with autogenous morcellized bone graft as necessary. The actual shell is impacted into place, with screw holes positioned superoposterior to avoid the neurovascular structures at risk in the anterior hemisphere of the acetabulum. Orientation of 10 to 30 degrees of anteversion and 40 to 50 degrees of abduction should be achieved by use of either a positioner guide or intra-articular landmarks. A useful pearl is to orient the inferiormost portion of the cup at the level of the teardrop and the posterior edge of the cup at the level of the ischium. Stability of the cup is tested with the inserter in place, and full seating is verified. Screws are placed, if desired. Overhanging osteophytes that can cause impingement and dislocation are removed, especially in the
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anterosuperior and posteroinferior quadrants. A trial liner can be placed for subsequent trial reduction.
For cemented cups, line-to-line reaming is usually recommended, as the many polyethylene cups provide for a cement mantle of 1 to 4 mm. Additional cement fixation holes are drilled into the ilium, ischium, and pubis. The acetabulum is irrigated of debris, which could compromise cement interdigitation into the cancellous bone. Cement is introduced in a doughy phase and pressurized. The cup is inserted, with meticulous attention to positioning. Excess cement is removed, and the cup is held in place until the cement is fully cured.
Femur.
During the initial exposure of the hip, prior to femoral head resection, the position of the current center of rotation is identified and measured relative to other bony landmarks such as the lesser or greater trochanters. Additional aids to ensure limb-length equalization and to minimize excessive lengthening may be used at this point as well. The neck resection level and orientation is established based on preoperative templating. With the head resected, preparation of the canal commences. The Pyriformis Fossa, which is lateral and posterior, must be clearly identified. A box or round osteotome may be used to remove any retained superolateral femoral neck or any other obstructing portion of the trochanter preventing access to the Pyriformis Fossa. Vigilance is necessary to maintain a lateral position and avoid varus alignment of reamers, broaches, or actual implants.
Cement technique is critical to the success of any cemented stem. Indeed, it is useful to conceive of the femoral stem and the cement as two distinct implants that must optimally interact to achieve the best result. Therefore, the idiosyncrasies of each component must be understood. Cement itself is a grout, not an adhesive, requiring intrusion into and interdigitation with the dense cancellous bone on the endosteal surface. As it is introduced, it must be in a viscous enough phase to resist any back bleeding, which creates laminations and weakened areas in the cement, and to withstand pressurization without running out of the canal. Of course, the bony substrate must be prepared properly to accept the cement, occluding the medullary canal to enable pressurization and retaining the endosteal adjacent cancellous bony structure.
For cemented stems, the medullary canal may be opened with a canal finder but should not be reamed vigorously, which could remove the cancellous bone, burnish the endosteum, and significantly compromise the shear strength at the bone/cement interface by eliminating the cancellous structure into which cement must intrude for strength. Serial broaching establishes the size of the stem that achieves stable fixation. Calcar reaming is performed for a collared stem and may be performed for a collarless stem. Trial reduction should be performed with trial neck segments and trial heads of varying neck lengths. Range of motion, limb length, and soft tissue tension assessment should be carried out at this point, along with a careful evaluation of stability in the at-risk positions, determined by the surgical approach. Biomechanical parameters can be modified by choosing different cup liner options, such as lipped, face-changing, or extra-offset liners, or stem options including offset, neck length, and head size. Proper component orientation should be verified. A useful technique to ensure a combined cup and stem anteversion of 30 to 60 degrees is to rotate the fully extended femur until the transverse plane of the head matches the face of the acetabulum. The degree of femoral internal rotation establishes the combined anteversion angle. Limb length should also be assessed at this point, using the methodology of measuring the femoral center of rotation to a fixed anatomic landmark and comparing that with the value obtained prior to head resection as described above, or using any system or device that is reproducible for the individual surgeon.
Once the construct is satisfactory to the surgeon, the broach is removed. The canal is brushed and cleared of any loose cancellous bone. The endosteal bone covering the entrance to the lesser trochanter may be removed with a large curette without excavating the lesser trochanter to allow for cement interdigitation in that area. The canal diameter is sized for a cement restrictor, and this is placed 1 to 2 cm distal to the intended tip of the stem. The stem is assembled with any centralizers on the back table, avoiding contact of the surface of the stem with blood or other contaminants that may compromise the cement/implant interface. The canal is irrigated with pulsatile lavage and dried to provide the optimum interface for cement application. Cement is mixed, and once a doughy viscosity has been reached, is introduced in a retrograde fashion using a cement gun. Pressurization with a proximal canal occluder is held for a sustained period of time, depending on the behavior characteristics of the cement, but long enough to allow steady flow of the cement into the cancellous structure. Some advocate venting of the canal at this point to prevent the rare cardiovascular collapse reported in the literature, although most surgeons eliminate this step except in the most high risk individuals. Immediate insertion of the stem should follow release of pressurization to prevent any backflow of cement out of the interstices of the cancellous bone. Meticulous attention to alignment in the AP and medial-lateral (ML) dimensions and to proper anteversion of 10 to 20 degrees is critical. The stem, once fully seated, should be held firmly until the cement hardens, but excess cement should be removed prior to final curing. The technique for cementing a femoral stem is demanding, and each detail contributes to an ideal result.
The preparation of the canal for a cementless stem is much more idiosyncratic. The alignment issues and the methodology for lateralization and opening the medullary canal pertain to cementless stems, just as described above for cemented stems. For stems designed for fit and fill, a distal reaming process followed by a proximal reaming or broaching step establishes stable fixation. Alternatively, tapered stems may require only serial broaching, exploiting the richly vascularized cancellous bony structure, which can be compacted to support a stem in three-point fixation. Trial reduction is performed exactly as described for a cemented stem. The actual cementless stem is slightly larger than the broaches or trials; therefore, it should be inserted firmly but carefully, particularly as it begins to seat. One must resist the urge to pound harder on the implant as resistance is met. Rather, multiple lighter taps gently seat the implant while avoiding an intraoperative fracture. Circumferential inspection around the visible proximal femur is advisable.
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If a fracture is identified, the prosthesis should be removed enough to effect complete reduction. Cerclage of the intertrochanteric and, if necessary, the subtrochanteric region can restore the integrity of the proximal femur and its ability to resist the hoop stresses imparted by the implant. The implant is reinserted and stability is verified.
Once the femoral implant is inserted, a final trial reduction may be performed. Minor adjustments in the neck length can correct any soft tissue laxity or tightness resulting from the final implant seating at a location slightly different from the broach or trial. Any areas of bony or soft tissue impingement should be relieved. The actual head is then impacted over the clean and dry neck. The hip is articulated, soft tissue or bony repair is completed, depending on the chosen surgical approach, and the fascia, subcutaneous tissues, and skin are closed in a routine fashion.
Postoperative Management
Rapid mobilization has become routine. Weight bearing is usually as tolerated, unless an intraoperative complication requiring protection has occurred. Walking assistive devices such as walker, crutches, or cane are recommended for support and to avoid falls. They may be gradually discontinued over 3 to 6 weeks, and sometimes even sooner. Although some controversy exists about the utility of instructing patients in dislocation precautions, conventional wisdom suggests that patients should be warned to avoid the at-risk positions, determined by the surgical approach.
Perioperative pain management is critical to rapid mobilization. There is a general shift away from parenteral narcotics because of their associated complications, especially sedation, confusion, and postoperative nausea and vomiting. A multimodal approach is preferred by many, including elements such as regional anesthetic and block techniques, preoperative and postoperative long-acting oral analgesics, intraoperative wound infiltration, and all supplemented with immediate-release narcotics and or intramuscular or subcutaneous narcotics for breakthrough pain.
Complications
Intraoperative Complications.
Most but not all intraoperative complications or their sequelae can be eliminated by vigilance. Preoperative medical evaluation and clearance along with expert anesthesia will substantially reduce the risks associated with anesthesia. Careful surgical technique along with a thorough knowledge of the anatomy reduces risk of neurologic or vascular injury. Intraoperative fractures occurring during implant insertion should be identified and fixed as described in the technique section above. Infection is perhaps the most dreaded complication for both surgeon and patient alike. Antibiotics, usually from the first-generation cephalosporin family, administered preoperatively and continued for 24 hours postoperatively are the single most effective prophylaxis against infection. Additional interventions that may further reduce the incidence of infection include meticulous sterile technique, operating in a laminar flow environment or under ultraviolet lights, the use of body exhaust systems, Betadine-impregnated adhesive skin drapes, antibiotic irrigation, gentle handling of the soft tissues, and careful wound management.
Postoperative Complications.
Early postoperative complications are uncommon, but can dramatically impair early rehabilitation and recovery; therefore, prophylaxis is appropriate. There is a risk of deep vein thrombosis following total hip arthroplasty. Pharmacologic prophylaxis using a low-molecular-weight heparin, pentasaccharide, or Coumadin is appropriate for most patients, and usually is continued for 10 days to 3 months, depending on the chosen agent and the individual patient risk factors. Mechanical adjuncts include pneumatic compression devices, compression stockings, and rapid mobilization. Rapid mobilization enhances return of pulmonary, bowel, and bladder function and reduces complications such as pneumonia, urinary tract infection, severe constipation, and skin breakdown. Additional aids such as urinary bladder catheterization, stool softeners, pulmonary toilet, and cushioned mattresses or pressure-point protectors can be helpful. Total hip arthroplasty can be associated with two to three units of blood loss from intraoperative and postoperative bleeding. Routine blood count monitoring should continue during hospitalization, and sometimes even after discharge, to avoid anemia-related complications. In addition, perioperative use of marrow stimulants such as Erythropoietin may minimize overall exposure to blood transfusions, and autologous predonation may reduce exposure to allogeneic blood.
Long-Term Complications.
The risk of infection exists beyond the perioperative period. Any bacteremia can potentially cause infection in a prosthetic joint. Because nonsurgical treatment of infected prostheses is notoriously unsuccessful, and because the operative treatment is often associated with morbidity and even mortality, vigilant prophylaxis is mandated. Any systemic or distant infection should be treated aggressively. The choice of prophylaxis against bacteremia induced by other surgery should be guided by the organisms most likely present at the surgical site. Controversy exists regarding prophylaxis before routine dental care and other less invasive procedures such as endoscopy. Some would argue that the risk of antibiotic resistance and adverse reactions increases with prophylaxis, and therefore it should not be routine, at least after 2 years from surgery except in the immunocompromised host. However, it is the opinion of the author that the benefits of any reduction in the likelihood of infection following even these minor procedures more than outweigh the minimal risks of resistance or adverse reaction to antibiotic use, particularly in the elderly population in whom joint replacement is most common and who are more likely to be immunocompromised from chronic disease. The risk of dislocation reduces dramatically after 3 months; however, there is a lifelong cumulative risk. Wear-induced periprosthetic osteolysis is a significant long-term challenge. Modern bearing surfaces, which reduce particulate wear and its sequelae, should reduce the incidence of this periprosthetic osteolysis. Aseptic loosening is primarily related to the service life of the prosthesis. The cumulative risk of loosening increases over time, but even at 25 to 30 years of follow-up remains low at or about 1% per year total. Unfortunately, the only definite solution is surgical revision. Catastrophic failure of the implant itself is rare, because metallurgic modifications
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stimulated by fracture of early-generation prostheses have been implemented.
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