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© 2004 The Journal of Bone and Joint Surgery, Inc. What's New in Hip Arthroplasty1 Department of Orthopedic Surgery, University of Texas Southwestern Medical School, 5323 Harry Hines Boulevard, Dallas, TX 75390-8883. E-mail address: michael.huo{at}utsouthwestern.edu
Specialty Update has been developed in collaboration with the Council of
Musculoskeletal Specialty Societies (COMSS) of the American Academy of
Orthopaedic Surgeons.
The discipline of total hip arthroplasty has undergone an exciting evolution over the past decade. Tremendous work has been done with regard to long-term clinical follow-up, outcome measurement, new biomaterials, improvements in surgical techniques and implant designs, recognition and treatment of complications, cost containment, epidemiology, and biomedical engineering. Over the past year (April 2003 to April 2004), sixty-four papers related to total hip arthroplasty were published in The Journal of Bone and Joint Surgery (American Volume), ninety-eight were published in the Journal of Arthroplasty, and forty-five were published in Clinical Orthopaedics and Related Research. In addition, there were 140 presentations on this topic at the annual meeting of the American Academy of Orthopaedic Surgeons (held in March 2004), thirty-eight presentations at the annual meeting of the American Association of Hip and Knee Surgeons (held in November 2003), forty-five presentations at the fall meeting of The Hip Society (held in September 2003), and forty-eight presentations at the spring meeting of the Hip Society (held in March 2004). We have organized the information selected from these 478 studies into eight sections: (1) primary total hip arthroplasty (stem), (2) primary total hip arthroplasty (cup), (3) bearing surfaces, (4) revision total hip arthroplasty (stem), (5) revision total hip arthroplasty (cup), (6) complications, (7) outcome and practice management, and (8) minimal incision total hip arthroplasty. It is our hope that this information will have a meaningful impact on the orthopaedic surgeon's daily clinical practice.
Fixation with Cement Fixation of the stem with cement has proven to be exceptionally durable. Callaghan et al.1 have continued to follow the cohort of Charnley total hip arthroplasties from the practice experience of a senior hip surgeon (Dr. Richard Johnston of Des Moines, Iowa). Three hundred and twenty-nine total hip arthroplasties were performed with use of first-generation cementing techniques between 1970 and 1972. The overall rate of mechanical failure was 16.4% for the cups and 7.6% for the stems. The overall rate of revision of the stem because of loosening was remarkably low (3.2%). Twenty-seven patients (thirty-four hips; 10.3% of the original cohort) were still alive at a minimum of thirty years after the index procedure. The revision rate in the living patients was 10%. Eighty-eight percent of the original components remained in situ at the time of the most recent follow-up or death. These data should continue to serve as the benchmark against which newer designs and surgical techniques must be judged. Multiple factors are involved in the failure of fixation of a cemented stem. Debate persists with regard to the best surface texture to use. We presented data on the early failure of cemented stems with a roughened texture or a precoating of methylmethacrylate2. Vaughn et al.3 recently reported on a nonrandomized study of 217 consecutive hybrid total hip arthroplasties that had been performed by the same surgeon with use of identical stem geometry, biomaterials, cementing techniques, and cup design. The only difference between the two groups was that 100 stems were precoated with methylmethacrylate and 117 stems were not. While the mean duration of follow-up was shorter for the group with nonprecoated stems, negative radiographic features (including debonding of the stem-cement interface) were observed in 9.1% of the hips in the group with precoated stems compared with 0.89% of those in the group with nonprecoated stems (p = 0.095). This finding may have been a reflection of the particular stem design. Lachiewicz et al. presented discrepant data to those reported by Vaughn et al., in a prospective, randomized trial involving the use of an identical cemented stem design. One hundred and fifty-three total hip arthroplasties were performed with either a precoated or a polished stem with use of third-generation cementing techniques. The hips were followed for two to five years. The quality of the cement mantle was classified as grade A in 31.1% of the hips, grade B in 51.2%, grade C1 in 16.8%, and grade C2 in 0.8%. There was no difference between the groups with regard to the cement grade, perioperative complications, or radiographic evidence of loosening. These discrepant data from two experienced surgeons who used identical stem designs in high-volume practices only continue to reflect the multifactorial nature of failure after total hip arthroplasty. In another study involving a different stem geometry and surface texture, Meneghini et al.4 reviewed the results of 102 hybrid total hip arthroplasties after a mean duration of follow-up of nine years. The stem was made of cobalt-chromium alloy and had a collar, a double-wedge geometry, and a roughened surface texture of Ra 40. Third-generation cementing techniques were used. Femoral bone geometry was classified, according to the Dorr system, as type A in 18% of the hips, type B in 68% of the hips, and type C in 14% of the hips. The quality of the cement mantle was classified as grade A in 63% of the hips, grade B in 35% of the hips, and grade C in 2% of the hips. Ninety-two percent of the stems were placed in a neutral position. Only two stems (2%) were revised because of aseptic loosening. The survival rate was 97.2% at ten years. Currently, preclinical testing of a new design or biomaterial involves biomechanical machine testing. The limitations of this type of testing include the costs of implant manufacturing, machine time, the fact that only certain modes of testing are possible, and the amount of time that is required. Stolk et al.5 proposed the use of a finite-element model for this evaluation process. They created a model on the basis of the known clinical performance of two cemented stems: the Muller stem (inferior performance) and the Lubinus stem (superior performance). The model accurately predicted damage patterns in the cement mantle and cementstem interface that were identical to the patterns that were confirmed with clinical testing and retrieval data. One major limitation, however, was that the model underestimated the quantity of the damage. It is hoped that further refinement of models such as this one will eliminate the need to manufacture prototype implants and will allow for speedy simulation testing with a variety of modes and conditions that will simulate such factors as complex muscle interaction, range of motion, and changes in bone quality.
Fixation without Cement The clinical efficacy and durability of cementless extensively-coated stems have been well documented. One of the concerns is whether smaller-diameter stems are associated with higher loosening rates. Additionally, controversy remains as to whether larger-diameter stems are associated with a greater prevalence of thigh pain. Mohan et al. analyzed 1545 total hip arthroplasties that had been performed with use of a single stem design. With regard to size, 23.5% of the stems were <12 mm in diameter, 68.4% were considered to be in the standard range (between 13.5 mm and 16.5 mm), and 8.1% were >18 mm. The fifteen-year rates of stem survival were 96.5%, 98.9%, and 97.9% for the small, standard, and large-diameter stems, respectively. The rates of mechanical failure were 15.4%, 5.1%, and 4.8% for the small, standard, and large-diameter stems, respectively. The most common site of pain reported by the patients was the greater trochanter. Overall, activity-limiting pain was reported in association with 1.6% of the small stems, 2.2% of the standard stems, and 5% of the large stems. These differences were not significant (p > 0.05). Bone remodeling around well-fixed femoral stems has been extensively studied. In the study by Knoch et al., thirty-two hips with cemented Charnley stems were compared with forty hips with cementless extensively-coated AML stems (DePuy Johnson and Johnson, Warsaw, Indiana) after fifteen to twenty years of follow-up. There was a time-dependent decrease in the amount of proximal cortical bone around both stems. The decrease in the proximal medial cortical bone was 12% for the Charnley group and 70% for the AML group. The decrease in the proximal lateral cortical bone was 9% for the Charnley group and 21% for the AML group. Proximal bone loss was significantly different between the two groups (p < 0.05). There was no difference between the groups with regard to the amount of diaphyseal bone loss (p > 0.05). In fact, there was greater decrease around the Charnley stems (range, 2% to 9%) than around the AML stems (range, 0% to 8%). There was no difference between groups with regard to expansion of the intramedullary diameter. All observed changes continued progressively over the entire observation period. The clinical relevance of micromotion between the cementless stem and the host bone has long been a focus of debate. A corollary of this issue is whether early weight-bearing after insertion of a cementless stem that results in greater micromotion is detrimental. Boettner et al. analyzed the change in stem position following forty-two cementless total hip arthroplasties with use of a radiostereometric technique. Patients were randomized to either full-weight-bearing or toe-touch weight-bearing. There was a significantly greater amount of stem subsidence in the full-weight-bearing group than in the toe-touch weight-bearing group at six weeks (0.74 mm compared with 0.024 mm; p < 0.02). This difference between the groups decreased at six months (0.84 mm compared with 0.27 mm; p = 0.10). There was a strong correlation between an increase in the amount of stem micromotion and weight-bearing (r = 0.68). The greatest amount of subsidence was observed in hips with calcar fractures, despite the use of cables or wires. It is important to recognize that the data only reflect the clinical performance of this particular type of stem geometry, surface texture, and surgical technique.
Cementless fixation of the cup remains the most popular surgical technique. One of the concerns associated with modular cementless cups is the locking mechanism of the polyethylene liner. Increased polyethylene wear and even catastrophic failure have been reported in association with cup designs having suboptimal locking mechanisms. Della Valle et al. compared the rates of polyethylene wear and periacetabular osteolysis in two groups of patients who underwent total hip arthroplasty with use of a cementless cup. In one group, the cup had a modular design with a ring-type locking mechanism. In the other group, the cup had a nonmodular design. Conventional polyethylene was used for all cups. All femoral heads were 28 mm in diameter. There was no difference between the groups with regard to the demographic characteristics of the patients. After a mean duration of follow-up of 5.7 years, there was no difference between the groups in terms of the mean amount of total polyethylene wear, periacetabular osteolysis, or calcar resorption. Additional clinical follow-up and retrieval analysis are necessary in order to conclusively determine whether cup modularity contributes to an increase in polyethylene wear.
Polyethylene Gamma irradiation has been documented to cause oxidation of polyethylene. It is expected that an accelerated wear rate as a result of progressive oxidation would be observed as the time in situ increases. However, declining physical activities associated with advancing age may lead to decreased wear. One of the most difficult clinical decisions is whether and when to recommend revision surgery because of wear. Hopper et al. evaluated the wear rate following 205 total hip arthroplasties in patients with a minimum of ten years of follow-up and at least six sets of follow-up radiographs. One hundred and twenty-seven cups had been sterilized with gamma irradiation in air, and seventy-eight cups had been sterilized with ethylene oxide. The mean wear rate did not change significantly over time. These data suggest that catastrophic wear of these particular types of polyethylene is unlikely as the duration of follow-up increases. Engh et al., from the same institution, evaluated the relationship between the amount of wear and pelvic osteolysis. Twelve patients underwent cup revision, and the polyethylene liners were retrieved and analyzed. Preoperative computerized tomographic scans were made to determine the extent of pelvic osteolysis. There was no relationship between pelvic osteolysis volume and volumetric polyethylene wear (p = 0.35). Moreover, there was also no relationship between the osteolysis growth rate and the polyethylene wear rate (p = 0.31). These data suggest that a high wear rate as measured on follow-up radiographs is not an absolute indication for cup revision. Patients with a recognized high wear rate should be followed closely, and revision surgery should be considered in the presence of impending wear-through or expanding destructive bone changes. Clinical utilization of cross-linked polyethylene has increased dramatically. Several groups recently presented clinical data that validated the superior wear characteristics of cross-linked polyethylene. Heisel et al.6 reported comparative data on twenty-four hips that had been treated with a conventional polyethylene liner and thirty-four hips that had been treated with a cross-linked polyethylene liner; the mean durations of follow-up were twenty-six and thirty-three months, respectively. Wear rates were measured with use of computer-assisted methodologies that had been previously validated. There was no difference between the two groups with regard to patient activities (as measured with an accelerometer worn at the ankle) or polyethylene thickness. The patients in the cross-linked polyethylene group were younger (p = 0.0001) and had a higher body-mass index (p = 0.006), a smaller cup size (p = 0.0001), and a smaller femoral head size (p < 0.00001). The cup position was more vertical (p = 0.007) and less anteverted (p = 0.01) in the cross-linked polyethylene group. The linear wear rate was 0.13 mm/yr for the conventional polyethylene group and 0.02 mm/yr for the cross-linked polyethylene group (p < 0.0001). The volumetric wear rates were 87.6 mm3/yr and 17.0 mm3/yr, respectively (p < 0.00001). These differences remained when adjusted for activity. Multivariate analysis demonstrated the type of polyethylene was the only factor that influenced the wear rate (p < 0.0001). Digas et al. received a research award from The Hip Society for their work on penetration rates with use of radio-stereometric analysis. Thirty-two patients underwent bilateral total hip arthroplasty with use of hybrid fixation. The patients were randomized to receive a cup with cross-linked polyethylene in one hip and a cup with conventional polyethylene in the other. The mean age was forty-eight years. The investigators analyzed the rate of head penetration at as much as two years postoperatively with the patient in both the supine and standing positions. The penetration rate was similar in the two groups at six and twelve months. At two years, there was 62% less linear penetration and 31% less three-dimensional (volumetric) penetration in the cross-linked polyethylene group (p < 0.008). Sterilization in argon gas is an established method to avoid exposure to oxygen. Polyethylene that is sterilized in this manner has been reported to be associated with reduced wear. Rothman et al. presented wear data on a group of fifteen patients who had bilateral total hip arthroplasty. Polyethylene that had been sterilized in argon was used in one hip, and cross-linked polyethylene was used in the other. After a mean duration of follow-up of two to three years, the linear wear rate was significantly lower in association with the cross-linked polyethylene (0.075 mm/yr compared with 0.14 mm/yr; p = 0.006). Moreover, the volumetric wear rate was also significantly lower in association with the cross-linked polyethylene (25 mm3/yr compared with 66 mm3/yr; p = 0.02). The authors, however, specifically cautioned that the range of the wear rates for this particular type of cross-linked polyethylene was still within the range of 0.05 to 0.1 mm/yr that has traditionally been reported in association with other non-cross-linked polyethylenes. Longer-term follow-up must be undertaken in order to fully substantiate the superior wear rate expected from cross-linked polyethylene. One purported major clinical advantage of cross-linked polyethylene is that it allows the use of a larger-diameter femoral head, which may have a clinical impact on range of motion and dislocation of the hip. Harris reported simulator-testing data on the wear rates associated with two different types of cross-linked polyethylene that were coupled with 32 and 38-mm femoral heads. All couplings were tested to 10 million cycles. The two types of cross-linked polyethylene were manufactured with use of 5 or 9.5 Mrad of radiation. With regard to the polyethylene that had been treated with 5 Mrad of radiation, the total mean weight loss was 7.2 mg in association with the 32-mm heads and 30 mg in association with the 38-mm heads. No measurable weight loss was noted in association with either head size following the tests involving polyethylene that had been treated with 9.5 Mrad of radiation. The data reflect two potentially important clinical implications: (1) there is a difference in the wear rate as a function of the manufacturing methodology, and (2) the wear rate of cross-linked polyethylene with larger-diameter head couplings remains superior to that of conventional polyethylene. Careful follow-up of patients who have received a larger-diameter head will demonstrate whether the advantages of improved hip biomechanics are balanced by the higher wear rates. The mechanical properties of polyethylene are altered by the cross-linking process, regardless of the particular methodology used. Collier et al.7 reported the results of testing of cross-linked polyethylene from six major orthopaedic implant manufacturers. Some of the major differences among the products are that (1) gamma radiation results in uniform full-depth penetration whereas electron-beam radiation results in approximately 4 cm of penetration; (2) more than twenty-four hours is required for gamma radiation, whereas minutes to hours are required for electron-beam radiation; (3) annealing after radiation facilitates further cross-linking and elimination of free radicals; (4) the temperature at which the annealing is performed varies; and (5) the dose of radiation can have different effects on the mechanical properties. Annealing at or above the melting temperature can eliminate free radicals, and the mechanical properties of cross-linked polyethylene are substantially reduced when compared with those of conventional polyethylene. Clinical surveillance and analysis of retrieved implants are necessary to determine if these alterations in biomechanical properties will have any clinical implications. One important mechanism of wear is third-body debris within the joint space. Bragdon et al.8 conducted a simulator test in which a cobalt-chromium femoral head articulated against cross-linked or conventional polyethylene in the presence of aluminum oxide (severe third-body wear) or cement (mild third-body wear) particles. There was a significant difference in the wear rate between the two types of polyethylene under the two wear conditions. In the presence of aluminum particles, the wear rate was 149 mg/million cycles for the conventional polyethylene and 37 mg/million cycles for the cross-linked polyethylene (p < 0.01). In the presence of cement particles, the wear rates were 13.5 mg/million cycles and 0.24 mg/million cycles (p < 0.001), respectively. It is hoped that the use of cross-linked polyethylene will reduce wear in the clinical setting of third-body debris from bone, cement, or metal.
Hard-on-Hard Bearings In vivo determination of joint kinematics with use of fluoroscopic gait analysis has evolved into an important research tool. Dennis et al. evaluated 195 total hip replacements with use of in vivo kinematic studies. All four types of articulation couplings were studied: metal-on-polyethylene, ceramic-on-polyethylene, metal-on-metal, and ceramic-on-ceramic. The study focused on head-cup separation during gait. Potential negative effects of such joint separation include increased wear, component loosening, instability, and even catastrophic failure of hard-on-hard bearing surfaces. Hips with a ceramic-on-ceramic coupling had the least amount of separation during the leg lift, stance, and swing phases of gait. Hips with a metal-on-polyethylene coupling had the greatest amount of separation. The authors did not provide statistical analysis. These data may be of value in laboratory hip-simulation studies in that they may allow investigators to more accurately duplicate wear mechanisms, thereby improving our understanding of the lubrication and wear characteristics of various alternative bearing surfaces.
Diaphyseal-fitting stems with an extensive porous coating frequently have been used for revision total hip arthroplasty. One of the risks of this technique is fracture, particularly in patients with femoral bone deficiencies. Meek et al.9 reported on the functional outcomes after revision procedures that were complicated by such fractures. Fractures occurred in sixty-four (30%) of 211 consecutive hips undergoing revision total hip arthroplasty with use of a diaphyseal-fitting stem. The authors identified several risk factors: (1) substantial femoral bone deficiency, (2) a low femoral cortex-to-canal ratio, (3) underreaming, and (4) large-diameter and long-stem implants. There was no difference in the fracture rate between straight and curved stems. Functional outcomes analysis demonstrated no difference between the group of patients with a fracture and the group of patients without a fracture. All but one of the stems in the patients with a fracture were judged to be stable with bone ingrowth, whereas 20% of the stems in the patients without a fracture were judged to have stable or unstable fibrous ingrowth. More than eighty fractures of femoral stems used for revision total hip arthroplasty are documented in the United States Food and Drug Administration database. This complication has been reported in association with both modular and nonmodular stem designs. Crowninshield and Maloney analyzed stresses in different simulated clinical settings of proximal femoral bone deficiency with use of finite-element analysis. Loss of proximal medial bone was predicted to increase stress within the stem by as much as 82%. An unhealed transverse femoral fracture (or osteotomy) was predicted to more than double the stress within the stem. An unhealed extended trochanteric osteotomy on the proximal-lateral side increased the stress by 50%. The authors concluded that efforts should be made to restore proximal-medial bone support and to ensure healing at the sites of proximal osteotomies or fractures and recommended that postoperative protection should be continued until there is reconstitution of structural bone support. Bourne reported six stem fractures (prevalence, 1.6%) in a series of 372 nonmodular extensively-coated revision stems that were intended for distal fixation. Five of the six fractures occurred in cases in which an extended trochanteric osteotomy was utilized.
There are no established criteria for deciding when to revise the liner and/or shell because of pelvic osteolysis. Mehin et al. used a computer-assisted quantification technique to evaluate forty-six cup revisions that had been performed because of pelvic osteolysis. Twenty-six shells were stable, and twenty were loose. The mean area of osteolysis on the anteroposterior radiograph was not different between the hips with stable and loose shells (591 mm2 compared with 630 mm2; p > 0.05). However, the mean area on the lateral radiograph was different between the groups (546 mm2 compared with 837 mm2; p = 0.05). Even more importantly, the authors noted significant differences between the groups with regard to percentage of the surface area of the shell that was in contact with the area of osteolysis. Stable shells had less contact with the area of osteolysis than did loose shells on both anteroposterior and lateral radiographs (p = 0.04 and p = 0.01, respectively). The authors recommended that revision surgery should be performed if >50% of the shell surface is in contact with an area of osteolysis.
Hemispherical Cementless Cup
Pelvic Reinforcement Cage Dennis reported his experience in association with the use of a custom-designed triflanged acetabular component. Twenty-three of the twenty-six hips were considered to have a clinically successful result after a mean duration of follow-up of 4.5 years. The principal mode of failure was insufficient fixation to the ischium. The author recommended caution when using this particular implant if there is major bone deficiency with inadequate posterior-column support. Structural graft supplemented by plate stabilization is recommended when this type of cage is used. A novel reconstructive technique is the use of modular porous metallic augments combined with a cementless cup shell. Hanssen et al. reported the early results of sixteen such reconstructions. The augments were used as segmental structural support in the defective host bone. Particulate allograft was used to fill other cavitary defects. Use of the augments was associated with improvement in the hip center location, both vertically and horizontally. One patient required rerevision because of persistent pelvic discontinuity at fifteen months. No radiolucent lines were observed between the host bone and the metallic augments, and no shell migrated.
Massive Pelvic Allograft
Complications still occur despite the improvements in total hip arthroplasty that have been made over the past four decades. Dobzyniak et al. reported their experience with 824 revision total hip arthroplasties that were performed over a fifteen-year period in a tertiary referral practice. Two hundred and ninety-seven revisions (36%) were done within the first five years after the index procedure. The reasons for early revision included aseptic loosening (38%), instability (33%), infection (14%), osteolysis (7%), painful hemiarthroplasty (4%), and periprosthetic fracture (4%). The rate of early revision because of aseptic loosening decreased progressively, from 50% from 1986 to 1991 to 36% from 1992 to 1996, and to 34% from 1997 to 2001. This finding may reflect improvements in surgical technique and implant designs.
Loosening
Infection Advances in the management of patients who have been infected with the human immunodeficiency virus (HIV) have led to an increase in the life expectancy and functional capacity of such patients. Parvizi et al.15 reviewed their experience with fifteen patients (twenty-one joint arthroplasties) after a mean duration of follow-up of more than ten years. All patients eventually died of acquired immunodeficiency syndrome (AIDS). There was unequivocal documentation of pain relief and improved functional capacity following the joint arthroplasties. Deep infection developed in six joints: four were revised, and two were treated with a permanent resection arthroplasty. It is especially important to note that four other revisions were performed for aseptic loosening at a mean of 9.3 years after the index procedure. This finding clearly underscores the need for greater implant durability and infection prevention in this patient population. The success rates associated with the use of established protocols for the treatment of infection are not consistent. Moreover, inferior results are routinely reported for patients who have an infection with a resistant organism. There is an advantage to delivering bactericidal agents locally in addition to delivering them through other routes. Bioresorbable carriers, local catheter administration with use of a reservoir, and antibiotic-impregnated bone cement are several of the currently available methods for the local delivery of antibiotics around implants. Parvizi et al. reported a novel technique involving the use of chemisorption to covalently tether vancomycin to the surface of titanium particles. The covalent bonding was acid-labile and thus was only cleaved in the presence of microorganisms. This was documented by eradication of Staphylococcus aureus colonies when incubated with the vancomycin-labeled particles. This technology holds great promise for the manufacturing of implants that can be self-protective against periprosthetic infection or that can be used for the treatment of periprosthetic infections.
Instability There is general agreement that the posterior surgical approach is associated with a higher dislocation rate. Repair of posterior soft-tissue structures has been documented by several surgeons to decrease the dislocation rate to nearly 0%. Many surgeons, however, have questioned whether the integrity of the repair persists after the patient begins mobilization. Su et al. evaluated nineteen hips with use of ultrasound at six weeks and three months after a primary total hip arthroplasty involving a posterior repair. The repair was intact in >80% of the hips at both six weeks and three months, and there were no dislocations. Yamaguchi et al.16 evaluated the physiological effects of enhanced posterior soft-tissue repair in thirteen patients with use of instrumented strength testing and compared the findings with those in sixteen patients who did not have the enhanced repair. There was no difference between the groups with regard to the preoperative or postoperative range of motion. The group that had the enhanced repair had significantly greater strength in abduction (p < 0.0001) and external rotation (p < 0.01). These two studies further support the value of enhanced posterior repair following the posterior approach to total hip arthroplasty. Peak et al. conducted a randomized, prospective study to evaluate the efficacy of using a physical therapy-based hip precaution program to decrease the rate of dislocation following total hip arthroplasty. Two hundred and seventy-five patients (303 hips) were randomized either to receive or not to receive the hip precaution program. There was only one dislocation in the cohort that received the hip precaution program, compared with none in the cohort that did not receive the program. This may, however, reflect the experience with the use of this particular surgical exposure at a tertiary high-volume center. It is well recognized that the dislocation rate is much higher following revision total hip arthroplasty than it is following primary total hip arthroplasty. Berry et al. presented the Mayo Clinic data on 4223 revision total hip arthroplasties that had been performed over a twenty-year period. The overall dislocation rate was 9.2%. The cumulative risk for a firsttime dislocation was 3.5% at two months, 6% at one year, 8.3% at five years, 10.1% at ten years, and 13.9% at twelve years. In contrast with the data that were obtained from the analysis of primary total hip arthroplasties, the risk of dislocation after revision was not correlated with age, gender, or surgical approach. There were several important findings: (1) revision for recurrent dislocation was associated with a 3.6-fold higher rate of dislocation compared with revision for aseptic loosening; (2) patients undergoing multiple revisions had higher dislocation rates than those undergoing first-time revisions (p = 0.02); (3) a smaller femoral head size was correlated with a higher dislocation rate (p < 0.0001); and (4) revision of the stem alone was associated with a greater dislocation rate than was revision of both components or revision of the cup alone (p < 0.001). These data reflect the evolution in surgical techniques, implant designs, available head sizes, and rehabilitation protocols over a long time-period. Regardless of the limitations of this information, it can be used for patient counseling and surgeon decision-making.
Thromboembolism
Heterotopic Ossification
Cost of Treatment of Complications
Surgeons have placed increasing emphasis on improvements in preoperative and postoperative management in order to realize reduced complications, lower costs, and better clinical outcomes. Several papers and presentations focused on some of these issues.
Surgeon Volume and Early Failure
Clinical Follow-up Protocol
Psychological Profile
Rehabilitation
Pain Management
Corporate Funding and Research
Controversies remain with regard to the clinical efficacy and social and financial issues related to the performance of total hip arthroplasty through one or more smaller incisions. In fact, some controversies even exist with regard to the term "minimally invasive" total hip arthroplasty. For the purpose of the present report, we have elected to use the term minimal incision surgery. Some of the concerns about the efficacy and safety of minimal incision surgery include component positioning, perioperative complications, rehabilitation, and the durability of fixation. Several surgeons have reported objective data to either substantiate or dispute some of these concerns. Dorr performed a radiographic analysis of component positioning in 105 consecutive minimal incision total hip arthroplasties and compared the data with those on fifty-nine total hip arthroplasties that had been performed with use of conventional-length incisions. No significant differences were noted with regard to cup abduction, cup anteversion, femoral offset, or leg length. He believed that proper reconstruction of the biomechanical requirements of total hip arthroplasty could be reproducibly achieved with use of minimal incision techniques. One of the proposed major advantages of minimal incision total hip arthroplasty is improved perioperative and postoperative outcome. In the study by Asayama et al., 100 consecutive hips that were scheduled to undergo total hip arthroplasty through a traditional anterolateral approach were randomized to a minimal incision group or a conventional incision group. The patients were blinded to the particular incision used. The only significant difference between the two groups was less intraoperative blood loss in the minimal incision group. There was no difference between the groups with regard to operative time, number of transfusions, blood counts, length of hospital stay, narcotic usage, component position, complications, rehabilitation goals, or discharge destination from the hospital. Berger et al. reported their experience with 100 consecutive patients who were managed with a comprehensive preoperative and postoperative multidiscipline protocol for rapid rehabilitation and recovery after minimal incision total hip arthroplasty. Ninety-seven percent of the patients met physical therapy goals and were discharged on the day of the operation, and 100% met the goals within the first twenty-three hours after surgery. The mean time to discontinuation of narcotic medication was six days. The use of walking aids was discontinued after a mean of eight days. Moreover, the mean time to driving was six days and the mean time to return to work was nine days. The mean time to walking at least a half mile was sixteen days. There were no readmissions, dislocations, or reoperations within the first three months. It is critical to recognize that these data represent the experience of the senior surgeon who developed the surgical technique and that they are from a center with the most extensive clinical experience with the use of this particular minimal incision approach. Sculco recently presented his extensive experience with the one-incision posterior approach minimal incision technique. One of the advantages of this approach is its similarity with the conventional posterior approach, allowing for easier learning and training. Four hundred and eighty-four total hip arthroplasties were performed, with a mean duration of follow-up of nearly three years. The mean length of the skin incision was 8 cm. The mean cup abduction angle was 42°. Ninety-three percent of the stems were placed in neutral alignment. A femoral cement grade of A or B was achieved in 95% of the hips. The number of complications was low, with four dislocations, one femoral fracture, two wound hematomas, and two neurapraxias. Bertin presented his experience with 223 total hip arthroplasties that had been performed with use of a one-incision anterolateral minimal incision approach without disruption of the gluteus medius. The mean operative time was sixty-one minutes, and the mean estimated blood loss was 350 mL. The risk of injury to the lateral femoral cutaneous nerve was low. Some patients exhibited clinical abductor weakness despite the fact that the abductor had not been released from the trochanter. The overall rate of complications (which included seven fractures, four dislocations, and one instance of cup migration that necessitated a reoperation) was 5.4%. White and Archibeck reported the overall experience of a large number of surgeons who had been trained to perform two-incision minimal incision total hip arthroplasty with use of the technique developed by Berger. Eighty-nine surgeons who had attended training sessions presented by the Zimmer company (Warsaw, Indiana) performed 423 total hip arthroplasties between October 2002 and September 2003, with each surgeon performing up to ten procedures. Only nineteen (21.3%) of the eighty-nine surgeons actually performed ten operations. The mean operative time decreased from 160 minutes for the first case to 127 minutes for the tenth, and the mean fluoroscopy time decreased from 146 to seventy-one seconds (p < 0.05). Complications included fracture (prevalence, 6.7%), nerve palsy (1.4%), infection (1.2%), and dislocation (0.2%). There was no correlation between the complication rate and surgeon volume. The learning curve is a challenge, as reflected by Dr. Berger's own experience. The mean operating time for that surgeon decreased from 150 to 105 minutes, and the mean estimated blood loss decreased from 700 to 250 mL. Most importantly, the prevalence of fracture decreased from 8.3% to 0.7% with increased experience. Woolson reported alarming data when the incision length was decreased, even when the procedure was performed by fellowship-trained medium-volume arthroplasty subspecialists. He reviewed the results of 171 total hip arthroplasties that had been performed by five surgeons at the same center. Eighty-one total hip arthroplasties were done with use of the minimal incision approach, and ninety were done with use of the conventional approach. The surgical dissection and implantation techniques were otherwise identical. The overall complication rate was 12% in the minimal incision group and 3% in the conventional incision group. Four (5%) of the hips in the minimal incision group had a reoperation: two hips were revised because of infection, one was revised because of trochanteric fracture, and one was revised because of mismatch of components. In addition, there were three calcar fractures and one sciatic nerve palsy in the minimal incision group. These data clearly indicate that the minimal incision approach is associated with more complications when a large number of community surgeons begin to use it. Image-guided surgical navigation has been shown to improve the accuracy of component positioning in total hip arthroplasty. Surgical navigation may be especially helpful during procedures performed with minimal incision techniques, when direct visualization may be limited. Murphy reported the cup position measurements that were obtained during ninety-three total hip arthroplasties that were performed with surgical navigation and eighty-five total hip arthroplasties that were performed without surgical navigation. Twenty-four of the procedures that were done with navigation also were done with use of a minimal incision technique. While the mean cup abduction was 41° for procedures performed with navigation and 43° for those performed without it, navigation allowed for a tighter distribution of the cup position measurements around the ideal value. It is unclear, however, whether a tighter range of cup positions will result in better function and longer durability in the clinical setting.
During 2003, the editorial staff of The Journal reviewed a large number of research studies related to total hip arthroplasty that received a Level of Evidence grade of I. In addition to articles published previously in this journal or cited already in this Update, six level-I articles were identified that were relevant to total hip arthroplasty. A list of those titles is appended to this review after the standard bibliography. We have provided a brief commentary about each of the articles to help to guide your further reading, in an evidence-based fashion, in this subspecialty area.
The major annual national meetings that focus on the clinical, research, economic, and legal issues related to total hip arthroplasty are the annual meeting of the American Association of Hip and Knee Surgeons (to be held in Dallas, Texas, in November 2004), the Hip Society Meeting (to be held on Specialty Day at the 2005 annual meeting of the American Academy of Orthopaedic Surgeons), and the annual meeting of the American Academy of Orthopaedic Surgeons (to be held in Washington, DC, in February 2005). Many excellent basic-science research papers are presented at the annual meeting of the Orthopaedic Research Society (to be held in Washington, DC, in February 2005). In addition, the American Academy of Orthopaedic Surgeons offers three to five continuing medical education courses that are focused on total hip arthroplasty each year.
Freund KG, Herold N, Rock ND, Riegels-Nielsen P. Poor results with the Shuttle Stop: resorbable versus nonresorbable intramedullar cement restrictor in a prospective and randomized study with a 2-year follow-up. Acta Orthop Scand. 2003;74:37-41. The authors randomized seventy patients into two groups to compare the clinical efficacy of a new resorbable cement restrictor with that of a traditional nonresorbable restrictor design. Similar prosthetic designs and surgical techniques were used in both groups. One major difference in the surgical technique was that the nonresorbable restrictor was placed into the femoral canal at least fifteen minutes before the injection of cement. This was necessary to allow for expansion of the restrictor in order to achieve a maximal sealing effect. The nonresorbable restrictor was placed immediately before the injection of cement. There was significantly higher prevalence of restrictor migration and cement protrusion distal to the restrictor in the group treated with the resorbable restrictor (p < 0.01). There was no significant difference between the two groups with regard to the rates of radiolucent lines, stem loosening, or osteolysis. The authors recommended against using the resorbable restrictor. One limitation of the study was the lack of quantification of the Harris cement grade between groups. The rate of stem loosening may become significantly different between the groups with longer follow-up. Honl M, Dierk O, Gauck C, Carrero V, Lampe F, Dries S, Quante M, Schwieger K, Hille E, Morlock MM. Comparison of robotic-assisted and manual implantation of a primary total hip replacement. A prospective study. J Bone Joint Surg Am. 2003;85:1470-8. An S-ROM stem was inserted with use of either the ROBODOC technique or a manual surgical technique in 154 patients. Patients were followed for twenty-four months. Patients who had been managed with the ROBODOC technique had a longer duration of surgery (p < 0.001) and more frequent dislocations (p < 0.001). However, they had better limb-length equalization (p < 0.001) and stem orientation (p < 0.001). The rate of revision for reasons other than infection in the ROBODOC group was 15%. All such revisions were performed for the treatment of recurrent dislocation. Disruption of the abductor mechanism was observed in all of the revised hips. This technology must be further refined before its wide clinical application is possible. Husted H, Blond L, Sonne-Holm S, Holm G, Jacobsen TW, Gebuhr P. Tranexamic acid reduces blood loss and blood transfusions in primary total hip arthroplasty: a prospective randomized double-blind study in 40 patients. Acta Orthop Scand. 2003;74:665-9. Three surgeons operated on eighty patients with use of an identical surgical approach, implant design, anesthesia technique, and thromboprophylaxis. The study group received an intravenous bolus injection of tranexamic acid before incision, followed by a continuous infusion for ten hours. The control group received similar quantities of saline solution. Patients who received tranexamic acid had 23% less intraoperative blood loss (p = 0.25), 45% less postoperative blood loss (p < 0.001), 34% less total blood loss (p < 0.001), and 84% fewer total blood transfusions (p = 0.04). There was no difference between the groups with regard to complications, particularly thromboembolism. Financial analysis demonstrated a lower cost for the tranexamic acid group; however, this difference was not significant. This method should be applied to larger patient populations and to cementless fixation in order to fully determine its clinical efficacy in reducing blood loss. The potential increased risk of thromboembolism must also be further studied. Kim S, Losina E, Solomon DH, Wright J, Katz JN. Effectiveness of clinical pathways for total knee and total hip arthroplasty: literature review. J Arthroplasty. 2003;18:69-74. Clinical pathways for total joint arthroplasty have been popularized over the past fifteen years with the intent of achieving improved clinical outcome and reducing costs. The authors reviewed eleven reports that had been published between 1966 and 2001 in order to compare the outcome (length of stay, cost, complications, patient-reported outcome) with and without a clinical pathway. All studies demonstrated a mean 30% reduction in the length of stay in the acute hospital. There was a mean 11% reduction in costs, ranging from $764 to $7375 per case. Among the nine studies that measured complications, four demonstrated no difference with regard to complications, four demonstrated fewer complications following institution of the clinical pathway, and one demonstrated more complications following institution of the clinical pathway. Only four studies investigated functional outcome, and one demonstrated improved function (p = 0.02). No study demonstrated an inferior outcome in association with a clinical pathway. The data from this study did not reflect greater complications in association with shorter stay; however, only one study demonstrated improved outcome. The authors concluded that additional data with a better study design must be obtained in order to more conclusively determine the efficacy of clinical pathways following total joint arthroplasty. This is a critical issue in light of the current intense interest in instituting same-day discharge programs with minimal incision surgery. O'Donnell M, Linkins LA, Kearon C, Julian J, Hirsh J. Reduction of out-of-hospital symptomatic venous thromboembolism by extended thromboprophylaxis with low-molecular-weight heparin following elective hip arthroplasty: a systematic review. Arch Intern Med. 2003;163:1362-6. Controversies persist with regard to which form and which duration of thromboprophylaxis are most effective and safe following total hip arthroplasty. This meta-analysis was designed to assess the absolute risk reduction of symptomatic venous thromboembolism in studies comparing patients with or without extended administration of low-molecular-weight heparin. Fourteen studies from 1980 to 2002 met the inclusion criteria. The absolute risk reduction was 1.56% for thrombosis, 0.36% for pulmonary embolism, and 0.09% for fatal pulmonary embolism. It appears that the previously reported added efficacy of extended prophylaxis has been overestimated. Contrast venography was uniformly utilized to document thrombosis in previous studies; therefore, the prevalences were higher. Data from this study only confirmed the relatively low prevalence of symptomatic events. The authors did not provide any guidelines as to which patients should receive extended prophylaxis. Padgett DE, Holley KG, Cummings M, Rosenberg AG, Sumner DR, Conterato D, Galante JO. The efficacy of 500 CentiGray radiation in the prevention of heterotopic ossification after total hip arthroplasty: a prospective, randomized, pilot study. J Arthroplasty. 2003;18:677-86. Fifty-nine patients with risk factors for heterotopic ossification were randomized to receive either 500 or 1000 cGy of radiation in divided doses following total hip arthroplasty. There was no difference between groups with regard to the prevalence of heterotopic ossification (p = 0.086). The rate of treatment success was 93% in the group managed with 500 cGy and 97% in the group managed with 1000 cGy. A lower dose of radiation can reduce the potential for complications with wound-healing and bone ingrowth. Moreover, the shorter time required with this protocol may be especially applicable for patients who are enrolled in an accelerated-discharge clinical pathway.
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Primary Total Hip Arthroplasty...
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