Vaishnav Rajgopal
Douglas D. R. Naudie
Total hip arthroplasty (THA) is extremely successful for the restoration of function and relief of pain resulting from arthritic conditions of the hip. However, complications can and do occur after THA. This chapter reviews the major complications associated with THA, which include (but are not limited to) the following: infection, neurovascular injury, thromboembolism, instability, heterotopic ossification, leg-length discrepancy, component fracture or failure, and the possibility of systemic complications. Each of these complications will be reviewed and methods of prevention and management will be discussed.
Infection
Infection in the setting of THA has a major impact on patient satisfaction, morbidity, and mortality and places a large financial burden on the healthcare system. The incidence of infection after THA has remained relatively constant, 1% to 2%, for primary THA and 3% to 5% for revision THA. The development of a periprosthetic infection depends on the number and virulence of the bacteria, the status of the wound environment, and the host's ability to eliminate the bacteria. Staphylococcus aureus and Staphylococcus epidermidis account for >50% of the pathogens in patients with a THA infection; Gram-negative aerobic and facultative organisms for 11% of pathogens, and anaerobic bacteria 12% of pathogens. Pathogens that cause infection originate from the patient's skin (most frequent), blood, or the operating room environment. The wound environment is important and often suboptimal in patients who have advanced vascular disease, a history of multiple operative procedures, extensive scarring, or a history of wound infection. Increased risks of infection have been shown to occur in patients with rheumatoid or psoriatic arthritis, those on immunosuppressive medication, or those with diabetes mellitus, hemophilia, obesity, and malnourishment.
Classification
Periprosthetic infections around a THA are classified based on mode and timing of presentation (Table 13-1). Acute postoperative infections(type I) may be caused by wound colonization, infected hematomas, or superficial infections spreading to the periprosthetic space and usually present during the first postoperative month. Late chronic infections (type II) originate at the time of surgery, but owing to either a small inoculum or low virulence of the organisms, onset of presentation is often delayed to between 1 and 24 months. Acute hematogenous infections (type III) are the least common and characterized by deterioration in a previously well-functioning joint; these may be associated with a history of an acute illness or recent dental work. Positive intraoperative cultures (type IV) was added as a fourth type to include patients with two out of five positive intraoperative cultures without any other features of obvious infection.
Prevention
The factors that are important in the prevention of periprosthetic THA infection include proper identification of risk factors, surgical technique, and operating room environment. Prophylactic antibiotic use is the most important factor for reducing the incidence of deep periprosthetic
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infection. The optimal time for its administration is just before the skin is incised, and current recommendations are that systemic antimicrobial prophylaxis be given 30 to 60 minutes before the skin incision is made. Prolonged procedures require an additional intraoperative dose of antibiotic. Other measures designed to reduce the incidence of infection include the use of body exhaust suits, laminar flow (vertical laminar airflow units generally reduce airborne contamination better than horizontal units), ultraviolet lights (which destroy airborne bacteria), proper sterilization of instruments, careful preparation of the operative site, the use of double gloves, and reduction of traffic flow in the operating room. Characteristics of the prosthesis have also been found to predispose a patient to infection: cobalt-chromium surfaces have been found to be more conducive to infection than titanium surfaces; porous surfaces have been found to be more conducive to infection than polished surfaces.
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TABLE 13-1 Classification of Infected Total Joint Replacements |
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Postoperative urinary tract infections occur in approximately 7% to 14% of patients. No correlation has been found, however, between bacteria isolated from urine and those isolated from deep infections. Late hematogenous (type III) infections have been reported following dental, gynecologic, urologic, and gastroenterologic procedures. Streptococcus viridans is the predominant bacteria in the human oral flora but accounts for a low percentage of late infection around prosthetic joints. Dental procedure prophylaxis (associated with gingival hemorrhage) includes amoxicillin 2 g PO (or clindamycin 300 mg PO) administered 1 hour prior to procedure. The American Society of Colon and Rectal Surgeons and the American Society for Gastrointestinal Endoscopy do not recommend prophylactic antibiotics for colonoscopy, sigmoidoscopy, or endoscopy.
Diagnosis
Infection should be suspected in the presence of a warm, erythematous, swollen wound with persistent drainage, unremitting pain, and an irritable range of motion. Night or rest pain is also worrisome. Radiographic evidence of early failure should also raise concern for septic loosening. Investigations to rule out infection include erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), aspiration, frozen section, and intraoperative cultures.
Management
Treatment options for an infected THA include suppressive antibiotics, irrigation and debridement with prosthetic retention, prosthetic exchange (one- or two-stage), resection arthroplasty, arthrodesis, and very rarely amputation. Management is ultimately dictated by timing of the diagnosis, medical presentation, and patient comorbidities. The goals of treatment are eradication of infection and restoration of function of the affected limb. Antibiotic therapy and operative debridement remain the mainstays of treatment. Cephalosporins are the most commonly used antibiotics in the setting of THA infection and have a broad spectrum of activity against the most common pathogens involved in THA infection. They also have low toxicity to patients and high soft tissue and bone concentrations. Since the late 1990s, however, several strains of resistant bacterial flora have emerged.
The presence of a foreign body (implant) makes the eradication of infection without operative debridement almost impossible. In addition, bacteria can adhere to the surface of a biomaterial and form a biofilm, or glycocalyx, that protects the bacteria from antibiotics and host defenses. Surgical debridement should include excision of all infected and necrotic tissue and the removal of cement, wires, cables, plates, screws, nonabsorbable sutures, and prostheses. Patients who present with an acute (type I or III) infection can be treated with surgical debridement, polyethylene liner exchange, and component retention (if well fixed) followed by intravenous antibiotics. The optimal treatment for patients with chronic infections (type II) is surgical debridement, removal of components, insertion of an antibiotic spacer, and administration of intravenous antibiotics under the direction of an infectious disease specialist (usually about 6 to 8 weeks). The use of a PROSTALAC (prosthesis of antibiotic-loaded acrylic cement) offers the advantages of better mobilization, control over limb-length discrepancy, and antibiotic delivery.
Reimplantation should be considered depending on wound healing, antibiotic effectiveness, soft tissue and bone quality, and potential for rehabilitation. Antibiotic suppression is reserved for those patients who are too sick or refuse surgery, when the organism is identifiable and sensitive to an appropriate oral antibiotic, the prosthesis is well fixed, and there are no signs of systemic sepsis. Long-term suppression is reported to have about a 30% success rate, with
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the outcome being retained implants. In select patients who may not be able to tolerate a second surgery, a one-stage exchange can be used with the advantages of a single hospitalization and avoidance of interim instability, disuse atrophy, and limb shortening. Two-stage exchange with the use of antibiotic-loaded cement has the lowest overall reinfection risk and a success rate approaching 90%. Resection arthroplasty is an uncommon salvage procedure for an infection around a THA and is most indicated for patients who are not candidates for staged reimplantation or who are unable to comply with postoperative rehabilitation protocols. Arthrodesis is recommended in young patients with unilateral hip infections. Disarticulation of the hip is performed only in the face of life-threatening infection, severe loss of soft tissue and bone stock, and vascular injury.
Neurovascular Injury
Neurologic and vascular injuries are among the most distressing complications of THA for both patient and surgeon. The prevalence of nerve palsy after THA has been reported as between 0.6% and 3%; this incidence increases up to around 5% for revision THA or for THA done for congenital dysplasia. The sciatic, femoral, obturator, and gluteal nerves can be injured. The prevalence of vascular injury is extremely rare, ranging from 0.2% to 0.3%. Nonetheless, vascular injuries to the iliac, femoral, obturator, and gluteal arteries have been described. The proposed causes of nerve or vascular injury include direct trauma, traction or pressure from retractors, extremity positioning, excessive tensioning (often from lengthening the extremity), ischemia, thermal injury from cement, constriction by wire or suture, or dislocation of the components. The placement of acetabular screws into major intra-abdominal vascular cavities has also been reported with catastrophic results.
Prevention
A thorough knowledge of the neurovascular structures about the pelvis helps the surgeon to avoid injury to these vital structures. Extreme care must be undertaken during surgical dissection, retractor placement, insertion of acetabular screws, and the passing of cerclage wires. Preoperative angiography may be indicated for high-risk situations, such as those involving intrapelvic migration of a failed acetabular component or intrapelvic extravasation of cement. Anatomic studies have defined four acetabular quadrants created by the intersecting lines from the anterior and posterior iliac spines (Fig. 13-1). The posterior-superior quadrant has been shown to be the safest area for the placement of acetabular screws. Placement of screws in the anterior-superior or anterior-inferior quadrants should be avoided because of risk of vascular injury to the iliac vessels.
Management
In instances of significant intraoperative bleeding, the anesthetist and nursing staff should be immediately informed so as to have appropriate blood and instruments (vascular clips) available. All vascular injuries should be treated with prompt identification, application of pressure, proximal and distal control of the vessel, and hemostasis with direct repair, shunting, clipping, or ligation of the vessel. A vascular surgeon may be required for major vascular injuries. In instances of postoperative neurovascular compromise, a surgical exploration is warranted if there has been passage of cerclage wires around the femur, excessive lengthening of the extremity has occurred, or a large postoperative hematoma is diagnosed or suspected.
A knee immobilizer should be worn in patients with a femoral nerve injury to prevent knee buckling. Patients with sciatic or peroneal nerve injury should have the foot splinted postoperatively to prevent equinus deformity.
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Figure 13-1 Diagram of the four acetabular quadrants created by two intersecting lines from the anterior and posterior superior iliac spines. (Reproduced with permission from Wasielewski RC, Cooperstein LA, Kruger MP, et al. Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg Am. 1990;2[4]:501–508. ) |
Thromboembolism
Thromboembolism (TE) is the most common complication following THA and is the leading cause of postoperative morbidity. Abnormalities in coagulation that occur following THA can be related to the Virchow triad of venous stasis, endothelial damage, and hypercoagulable state. Venous stasis occurs as a result of leg positioning during the
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procedure, localized postoperative swelling, and postoperative immobility. Venous endothelial injury occurs with local dissection, thermal injury from cautery or bone cement, and during limb positioning for component insertion. Hypercoagulability results from the intraoperative stimulus of the clotting cascade and because blood loss can result in reduction in antithrombin III and inhibition of the fibrinolytic system. The presence of a factor V Leiden mutation (activated protein-C resistance), antiphospholipid antibody syndrome, protein C and S deficiency, and genetic abnormalities related to antithrombin III increase the risk of TE. Previous TE and active malignancy are the other most potent risk factors for postoperative TE. Use of hormone replacement or oral contraceptive therapy, pregnancy, advanced age, obesity, smoking, poor mobilization, and lengthy duration of surgery are less potent risk factors for TE.
Prophylaxis of TE disease
Without either mechanical or pharmacologic prophylaxis, asymptomatic deep vein thrombosis (DVT) will develop after 40% to 60% of THAs, proximal DVT will develop after 15% to 25% of THAs, and a fatal pulmonary embolism (PE) will develop after 1% to 3% of THAs. Prophylaxis of TE disease was recommended by the National Institutes of Health (NIH) consensus in 1986. The American College of Chest Physicians (ACCP) currently recommends the use of fractionated heparin, warfarin (target INR [international normalized ratio] 2.0 to 3.0), or fondaparinux (Table 13-2). This prophylaxis should occur even if the patient has been discharged. The ACCP also recommends that patients at high risk of TE (active malignancy, obesity, bilateral surgery) should receive extended prophylaxis for 28 to 35 days. The ACCP recommends against the use of acetylsalicylic acid (ASA), dextran, low-dose unfractionated heparin, graduated compression stockings, intermittent compression stockings, or venous foot pumps as the only method of prophylaxis. Under the influence of current prophylaxis, 85% to 90% of all DVTs following THA occur in the calf, and 17% to 23% of these distal thrombi extend to more proximal veins in the thigh. After 7 to 10 days of prophylaxis, the frequency of symptomatic TE within 80 days of surgery is between 2% and 3%, symptomatic nonfatal PE is 0.6%, and fatal PE is 0.06%.
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TABLE 13-2 ACCP Grade 1A Recommendations for Thromboembolism Prophylaxis in Total HIP Arthroplasty |
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Anesthetic Considerations
The use of regional anesthesia has been shown to reduce the occurrence of DVT by 40% to 50%. The proposed mechanism is probably related to a sympathetic blockade resulting in increased lower extremity blood flow mitigating the effects of stasis. The use of short-acting unfractionated heparin given intravenously following component insertion has also been found to significantly inhibit fibrin formation. Patients who receive autologous blood have demonstrated lower rates of DVT (9%) and PE (0.3%) compared with those patients who received banked blood (DVT of 13.5% and PE of 0.7%).
Pharmacologic Methods
Warfarin is the most commonly used agent for prophylaxis of TE disease following THA and exerts its anticoagulant effect by inhibiting the hepatic production of vitamin K–dependent clotting factors II, VII, IX, and X. Warfarin is administered orally but requires regular monitoring of the INR. Unfractionated heparin exerts its anticoagulant effect through a high binding affinity for antithrombin III, thereby accelerating the inhibition of thrombin, factor IX, and Xa. Fractionated low-molecular-weight heparins (LMWH) differ in their molecular weights and exert their anticoagulant effect through the inhibition of factor Xa. These offer several advantages over unfractionated heparin because they have better bioavailability, prolonged circulating half-life, and a lower frequency of development of thrombocytopenia. However, in 1997 the United States Food and Drug Administration (FDA) issued a public health advisory on the use of fractionated heparin with epidural or spinal anesthesia. This was owing to reports of epidural and spinal hematomas causing permanent neurologic injury following the use of neuraxial anesthesia and LMWH. Fondaparinux is a synthetic pentasaccharide that acts as a specific inhibitor of factor Xa with no direct inhibition of thrombin. Although an effective prophylactic agent, it causes an irreversible change to the binding site for factor Xa and has been associated with an increased risk of a major bleeding episode if
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administered within 6 hours of surgery. Aspirin limits platelet aggregation by inhibiting thromboxane A2 and offers the advantages of low cost, ease of administration without monitoring, and few bleeding complications. However, the PEP (Pulmonary Embolism Prevention) trial found that aspirin did not reduce the risk of symptomatic DVT following THA, and therefore, it is not recommended as the only means of prophylaxis.
Mechanical Modalities
External pneumatic compression devices (EPCDs) increase venous return, decrease stasis, and enhance endothelial-derived fibrinolysis without bleeding risk. Calf and thigh sleeves have been associated with a reduction in distal calf DVT but a greater prevalence of high-risk proximal DVT after THA compared with warfarin. EPCDs alone have not been shown to be more effective than pharmacologic prophylaxis after THA but may offer an advantage when used in combination.
Diagnosis
Detection of TE may be clinically obvious or subtle. The presence of calf tenderness (the Homan sign), low-grade fever, fatigue, tachycardia, and diaphoresis may or may not be present. Patients with proximal DVT may have pain or swelling in their thigh. The classic presentation of PE, consisting of shortness of breath, pleuritic chest pain, mental status changes, tachycardia, and tachypnea, is rarely present. Ascending contrast venography is the most reliable and sensitive method for detection of asymptomatic and nonocclusive venous thrombi in the THA patient; however, this is expensive, invasive, and has been associated with complications including contrast-induced nephropathy, limb edema, and contrast allergy. Doppler ultrasound is a noninvasive technique that allows visualization of venous channels but is not sufficiently sensitive for routine postoperative surveillance of the THA patient. The ACCP guidelines recommend against the routine use of Doppler ultrasound screening at the time of hospital discharge in asymptomatic patients following THA. A chest radiograph in conjunction with an electrocardiogram and ventilation-perfusion (V/Q) scan can help in the diagnosis of PE; however, PE can be more accurately diagnosed with spiral CT, MR, or pulmonary angiography.
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TABLE 13-3 Risk Factors Considered to Relate to Dislocations after Total HIP Arthroplasty |
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Management of Established TE Disease
Continuous intravenous heparin administration or high-dose fractioned LMWH followed by oral anticoagulation with warfarin for 3 months is recommended for isolated cases of proximal DVT and 6 months in cases of PE. Anticoagulation prevents further thrombus formation while allowing the fibrinolytic system to dissolve clots that have already formed. An inferior vena cava filter is reserved for circumstances where full anticoagulation is absolutely contraindicated or with recurrent PE despite therapeutic anticoagulation.
Instability
Dislocation is among the most frequent and distressing complications for a patient following THA. The incidence of dislocation after THA varies widely (0.3% to 9%) with most large series averaging 2% to 3% for primary THA. Many variables can predispose to dislocation, including disease and patient, surgical, and rehabilitation factors (Table 13-3).
Risk Factors
Many risk factors for THA dislocation have been identified; however, not all studies support all risk factors. Disease conditions such as developmental dysplasia of the hip, prior hip surgery, and nonhealed fracture and disease states such as rheumatoid arthritis and prior sepsis have been identified as risk factors for dislocation following THA. Gender has also been recognized to influence the likelihood of dislocation, with dislocation reported to occur twice as frequently in females as in males in some studies. Age was not found to be important as a risk factor for THA instability in many studies; however, two studies have shown that older patients have higher dislocation rates. Factors that may decrease the patient's ability to control the hip, such as alcoholism or
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neuromuscular disease, also have been shown to increase dislocation rates.
The surgical approach has been shown to influence the rate of dislocation, with the lateral and anterolateral approaches showing lower dislocation rates than the posterior approach. More recently, however, enhanced soft tissue closure after posterior approach has shown significantly reduced dislocation rates. The orientation of the acetabular component has also been related to dislocation, with retroverted components predisposing to posterior dislocation and excessively anteverted components predisposing to anterior dislocation. Vertical orientation of the acetabular component (>55 degrees) has also been considered a risk factor for dislocation (Figs. 13-2 and 13-3). Femoral head size and the avoidance of re-enforcement at the base (a “skirt'') have also been studied as possible factors in dislocation, and it is believed that enlarging the size of the femoral head and avoiding the use of a skirt improves hip stability. When head size is increased and skirts are avoided, the head-to-neck ratio is increased, the range of motion required for intra-articular impingement increases, and dislocation decreases. A similar benefit can be gained by decreasing the femoral neck diameter for a given head diameter or by using a neck trunnion with a narrow anterior-posterior profile. The use of acetabular outside diameters >62 mm have also been shown to have greater dislocation rates than when components <60 mm were used. Elevated rim and lipped liners have also been shown to improve stability, provided they are used to maximize restoration of femoral offset and avoid impingement. Finally, surgeon experience influences the dislocation rate, with less experienced surgeons having a higher dislocation rate than experienced surgeons.
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Figure 13-2 A: Anteroposterior radiograph of a dislocated total hip arthroplasty demonstrating a vertically positioned acetabular component and resultant hip dislocation. B: Anteroposterior radiograph of the same patient after revision total hip arthroplasty in which the cup was revised and repositioned and the femoral head was upsized to a 32-mm-diameter head. |
A recent randomized, prospective controlled trial evaluated the role of postoperative functional restrictions on the prevalence of dislocation. This study found removal of commonly used restrictions (extremes of range of motion, abduction pillows, elevated toilet seats and chairs) did not increase the prevalence of dislocation, but conversely promoted lower costs and a higher level of patient satisfaction. The postoperative time frame of dislocation has also been shown to be important in predicting future dislocations. The greatest risk of dislocation occurs within the first 3 months after surgery. Dislocations that occur beyond 5 weeks have been shown to have a higher rate of recurrent dislocation than those in patients who had their initial dislocation within the first 5 weeks.
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Figure 13-3 Schematic diagram illustrating the safe zone of 45 ± 10 degrees vertically and 15 ± 10 degrees of anteversion as the range of acetabular component position that will provide the highest stability. α angle represents cup anteversion; β angle represents cup abduction. (Reproduced with permission from Lewinnek GE, Lewis JL, Tarr R, et al. Dislocation after total hip-replacement arthroplasties. J Bone Joint Surg Am. 1978;60[2]:217–220. ) |
Classification
The direction of dislocation of a THA is usually posterior, with anterior dislocation being much less frequent. Dorr and associates have proposed a classification system based on increasing severity of the cause: Type I dislocations can be attributed to malposition of extremity, Type II dislocations are caused by soft-tissue imbalance, and Type III by component malposition.
Prevention and Management
The best prevention of instability following THA is to recognize all of the contributing factors that can lead to dislocation and avoid them. When a dislocated THA is encountered, the immediate treatment is closed reduction with either conscious sedation in the emergency department or general anesthesia in the operating room. The usual method of reduction is longitudinal traction with the hip in slight flexion. Care must be taken not to dislodge or dissemble a well-seated, modular component. Postreduction immobilization in the form of a brace and reinforcement of motion precautions can be used to avoid redislocation. For recurrent hip instability, the underlying cause of dislocation should be addressed (Fig. 13-3). Operative management should focus on correcting the cause of the dislocation, and surgical planning should include all possible revision options: modular liner and head exchange, trochanteric advancement, use of a constrained acetabular liner, or revision of one or both components. Patients should also be counseled regarding expectations as the results of revision surgery for recurrent instability are mixed.
Heterotopic Ossification
Heterotopic ossification (HO) in the soft tissues surrounding the hip joint is a frequent complication of THA, with a reported incidence between 0.6% and 61.7%. The extent of HO may vary from slight to complete bony ankylosis (Fig. 13-4). The cause and pathogenesis of HO are not clear but are related to the duration of the surgical procedure and to the amount of soft tissue dissection. HO is associated with such conditions as ankylosing spondylitis, Forestier disease, posttraumatic arthritis, and in some males with considerable bilateral osteophytic osteoarthritis. Surgical approach may also increase the risk of HO after THA, with anterior and anterolateral approaches demonstrating an increase in the possibility of HO compared with the transtrochanteric and posterior approaches.
Classification
The most commonly used classification is that described by Brooker (Fig. 13-5): Grade 0 has no ossification, grade I represents one or two isolated areas of ossification each <1 cm in diameter, grade II represents more widespread isolated areas of ossification along the proximal femur or acetabular rim, grade III ossification covers more than half of the distance between the femur and pelvis but does not bridge the entire distance, and grade IV ossification bridges the entire distance between the femur and pelvis.
Prevention
The identification of patients at risk for HO should be a priority. Various treatment modalities have been developed to reduce the incidence of HO following THA. Low-dose radiation has been shown to help in the prevention of HO. Various radiation protocols have been described including a single preoperative or postoperative (800 cGy) dose. If irradiation is chosen for prophylaxis postoperatively, it is recommended that cementless porous implants should be adequately shielded or a cemented implant be used. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit prostaglandin synthesis and may interfere with the inflammatory response and subsequent development of heterotopic bone. Indomethacin has been used successfully. Bisphosphonates have the ability to prevent mineralization of osteoid but have no inhibitory effect on the formation of osteoid matrix itself, and clinical trials have not shown a significant benefit in the prevention of HO formation from this treatment.
Diagnosis
HO is usually painless and rarely requires removal; however, some patients may develop local signs of inflammation such as erythema, effusion, tenderness, and loss of motion. Assessment of the extent and severity of HO is made on radiographic analysis. HO may become visible as early as 3 to 4 weeks postoperatively.
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Figure 13-4 Anteroposterior (A) and lateral (B) radiographs of a patient several years after left total hip arthroplasty demonstrating severe heterotopic bone formation in the soft tissues adjacent to the left total hip arthroplasty. |
Management of Established Heterotopic Ossification
Once HO becomes visible on radiographs, only surgical excision will eradicate it. If surgical excision is warranted because of limitation of motion, the procedure should be delayed until about 6 to 12 months after the index arthroplasty to permit maturation of the HO and the development of a fibrous capsule (which allows for more precise dissection of planes and reduces the amount of trauma to the surrounding tissues).
Leg-Length Discrepancy
Limb-length discrepancy (LLD) is a potential complication following THA and can adversely affect an otherwise excellent outcome. Patient dissatisfaction from this complication is the most common cause of litigation against the orthopaedic community. The true prevalence of postoperative LLD is difficult to quantify because of marked variation in reporting methods and in the interpretation of its clinical significance.
Prevention
The frequency of LLD can be reduced by conducting careful preoperative templating from standardized radiographs and by taking intraoperative measurement of limb-length differences and offset with various measurement methods.
Management
When faced with a patient who has symptomatic postoperative LLD, it is important first to determine if the LLD is a true discrepancy or an apparent discrepancy secondary to a flexion or abduction contracture of the hip. In many cases, patients have a postoperative abduction contracture of the hip, which gives them a pelvic obliquity, resulting in an operated leg that seems too long. When these patients stand with the feet close together, the contralateral normal
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hip will be in an adducted position and will feel shorter than the leg on the operated side. These patients should be asked to stand with their feet widely separated so that both hips are equally abducted; in doing so the pelvis becomes level and the legs then seem equal in length. For these patients, an appropriate program of abductor muscle strengthening often is helpful.
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Figure 13-5 Schematic diagram outlining the Brooker classification of heterotopic bone formation around a total hip arthroplasty (Reproduced with permission from Brooker AF, Bowerman JW, Robinson RA, et al. Ectopic ossification following total hip replacement: incidence and a method of classification. J Bone Joint Surg Am. 1973;55:1629–1635. ) |
When a true limb-length discrepancy exists because of overlengthening, it is important to determine the amount of true lengthening. This can be accomplished with the use of osseous landmarks or blocks under the foot. It is also important to discuss with the patient the reason for dissatisfaction and his or her expectations of treatment. Revision to correct a substantial postoperative LLD is seldom indicated because the procedure is fraught with the possibility of postoperative hip instability. As a result, although patient dissatisfaction may be great, surgery to correct true overlengthening is not frequently performed. LLD that is not associated with back or hip pain, sciatica, or recurrent dislocation should almost always be treated nonoperatively by placing a shoe lift on the short side. Revision arthroplasty is considered to be the last course of action in patients with ongoing symptoms of instability, gait dysfunction, and low back pain, and one recent study has reported success with revision for true overlengthening (although this was performed for less than one half of 1% of total hip surgery performed at their institution).
Periprosthetic Fracture
With the increasing number of THAs performed each year and an aging population, the rates of revision THA have been increasing. Revision THA can be undertaken for any reason, but commonly occurs as a result of periprosthetic fracture, wear, or osteolysis.
Periprosthetic Acetabular and Femoral Fractures
Periprosthetic fractures around the acetabular or femoral components of a THA are complications that a reconstructive surgeon must be able to manage. These fractures can occur intraoperatively or postoperatively. The incidence of intraoperative acetabular periprosthetic fracture has been reported to be <0.2%. The acetabulum can fracture from impaction forces incurred while employing a press-fit technique into an acetabulum that has been underreamed by 1 or 2 mm in relation to the acetabular component. Other contributing factors include osteopenia and Paget disease. Postoperative periprosthetic acetabular fractures usually occur as a result of bone loss from osteolysis but can also occur because of traumatic fracture.
Periprosthetic femoral fractures occur more frequently and can also occur intraoperatively or preoperatively. A review of the Mayo clinic joint registry demonstrated an intraoperative femoral periprosthetic fracture rate of 1% in primary THA and 7.8% in revision THA. These fractures are more common when the femoral component is inserted without cement at the time of primary THA. A similar increased prevalence of fracture with cementless femoral stems is seen in the revision setting. Revision THA with impaction grafting is associated with a higher incidence of intraoperative and postoperative fractures. Postoperative periprosthetic fractures of the femur occur in from 0.1% to 2.1%.
Classification
Callaghan described a classification system of intraoperative periprosthetic acetabular fractures that includes those occurring around the anterior wall, transverse, inferior lip, and posterior wall fractures. Peterson and Lewallen classified postoperative periprosthetic acetabular fractures into two types: Type I is a clinically and radiologically stable acetabular component, and type II is an unstable acetabular component. The Vancouver classification is the one most commonly used for periprosthetic femur fractures and considers three important factors: the site of the fracture, the stability of the implant, and the quality of the surrounding bone stock. For those that occurintraoperatively, type A fractures are proximal metaphyseal (not extending into the diaphysis), type B fractures are diaphyseal (not extending into the distal diaphysis and therefore not precluding diaphyseal long-stem fixation), and type C fractures are distal fractures extending beyond the longest extent of the longest revision stem and can include the distal metaphysis (Table 13-4). Each type is subclassified into subtype 1, representing a simple cortical perforation, subtype 2, representing a displaced linear crack, and subtype 3, representing a displaced, or unstable fracture.
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TABLE 13-4 Vancouver Classification of Intraoperative and Postoperative Femur Fractures |
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For those that occur postoperatively, type A fractures occur around the trochanteric region and can be subclassified into AG (greater trochanter) and AL (lesser trochanter). Type B fractures occur around or just distal to the femoral stem and can be subclassified into B1fractures in which the femoral implant is well fixed, into B2 fractures in which the femoral implant is loose but bone stock is good, and into B3 fractures in which the implant is loose and there is a severe loss of bone stock. Type C fractures occur distal to the stem and can be treated independently of the arthroplasty above (Fig. 13-6).
Prevention and Management
Intraoperative acetabular fractures should be assessed for stability. Stable fractures can be treated conservatively whereas unstable fractures require fixation and postoperative weight-bearing restrictions. Early postoperative acetabular fractures are treated according to their pattern. Patients with stable, minimally displaced acetabular fractures, in whom a cementless component has been augmented with screw fixation, can be treated conservatively with union expected in most cases. Late postoperative acetabular fractures are usually associated with significant osteolysis and often warrant operative intervention.
Intraoperative femoral fractures that are diagnosed at the time of surgery should be addressed at that time with simple bone grafting (type A1), cerclage wiring (type A2), or with the use of wires, cables, cortical strut grafts, trochanteric claw plates, and a diaphyseal-fitting stem (types A3, B1, B2, and B3). Diaphyseal fractures should be bypassed by at least two cortical diameters with a diaphyseal-fitting stem. If the fracture occurs distal to a well-impacted femoral stem (type C), the stem should be retained and the fracture should be treated with extramedullary strut and cable augmentation or formal open reduction and internal fixation. Intraoperative fractures that are identified in the immediate postoperative period should be evaluated fully with radiographs to determine extent. Most of these fractures are stable, minimally displaced, do not compromise the fixation of the prosthesis, and will unite successfully without complication.
Postoperative periprosthetic femoral fractures are treated using the Vancouver classification. Type AG fractures are usually stable and can be treated with protected weight bearing and avoidance of abduction for 6 to 12 weeks. Internal fixation is considered if the greater trochanter has displaced >2.5 cm or if the patient has pain, instability, and abductor weakness. Type AL fractures are rare, but if they involve a large portion of the calcar femorale, they may result in loss of implant stability and therefore revision THA is necessary. Type B1 fractures should be treated with open reduction and internal fixation with or without cortical strut grafts. B2 fractures are treated with revision to a longer femoral stem and fracture fixation with cerclage wires with or without cortical strut grafts. Patients with B3 fractures often require structural allograft replacement of the proximal femur with an allograft-prosthetic-composite revision, tumor prosthesis, or a custom implant. Patients with type C fractures are treated with standard open reduction and internal fixation.
Wear and Osteolysis
Patients with polyethylene wear and pelvic osteolysis following total hip arthroplasty present a difficult problem because patients are usually asymptomatic and satisfied with the function of their existing hip replacement (Fig. 13-7). The problem becomes more difficult because there is a reported morbidity and risk of complications associated with surgical revision for polyethylene wear and osteolysis, and the long-term outcomes of surgical procedures done to address these problems are unknown.
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Figure 13-6 Anteroposterior (A) and lateral (B) radiographs of a patient with a Vancouver C periprosthetic fracture. Postoperative anteroposterior (C) and lateral (D) radiographs of the same patient following internal fixation with a locking condylar plate. |
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Figure 13-7 Anteroposterior radiograph of a 46-year-old woman demonstrating eccentric wear of the acetabular polyethylene component and severe periprosthetic osteolysis. |
Prevention and Management
Although eccentric head position is an indication of wear, it is not by itself a reason for revision. Revision is indicated only when polyethylene wear is extensive and complete wear-through is imminent. For stable acetabular cups, exchange of the polyethylene liner is recommended. Even if the acetabular component and the locking mechanism have a bad track record with significantly increased revision rates, strong consideration should be given to cementing a polyethylene liner into the retained well-fixed shell. Revision of the acetabular shell is indicated if it is unstable or nonmodular, if hip stability cannot be achieved, or if the thickness of the replaced polyethylene liner is <6 mm thick. Modular femoral heads should be exchanged if possible when the stem is retained in a revision procedure as the degree of surface roughness of the femoral head may influence future wear and subsequent osteolysis. The rationale behind the surgical treatment of excessive wear is twofold: to prevent complete wear-through that could damage the inside of the metal shell, and to replace the debris-producing bearing surfaces with surfaces that wear less.
The decision to operate on a patient with extensive osteolysis is based on the likelihood of the patient developing complications related to the osteolysis (such as cup loosening) during his or her lifetime. An operation usually is indicated if the lesion is rapidly increasing in size or if the lesion is eroding away cortical support of the cup. Treatment is determined on a case-by-case basis; in general, revision is indicated in most but not all symptomatic patients and some but not all asymptomatic patients. Although some morbidity is associated with liner exchange (particularly instability), concern revolves around the bone loss associated with a full cup revision and uncertainty as to whether the revised cup will gain bone in-growth.
Systemic Complications
THA can result in morbidity related to pulmonary, cardiac, gastrointestinal, renal, or postoperative mental status changes. These are best prevented through careful preoperative assessment (often in conjunction with an internist and anesthesiologist) to identify any modifiable risk factors. Management of these problems involves addressing the system involved. Rarely, THA can result in mortality. Death from cardiac arrest during THA has been described in association with insertion of a cemented long-stem femoral component. When faced with this scenario, excessive pressurization of the cement should be avoided, consideration should be given to placement of a venting hole distal to the femoral isthmus, and invasive hemodynamic monitoring should be used.
References
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Instability
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P.107
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Heterotopic Ossification
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Neurovascular Injury
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Periprosthetic Fracture
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Systemic Complications
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Wear and Osteolysis
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