Periprosthetic osteolysis-bone loss in the vicinity of a prosthesis-is the most serious problem limiting the longevity of artificial joints. It is caused by bone-resorptive responses to wear particles originating from the articulating surface. This study investigated the effects of graft polymerization of our original biocompatible phospholipid polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) onto the polyethylene surface. Mechanical studies using a hip-joint simulator revealed that the MPC grafting markedly decreased the friction and the amount of wear. Osteoclastic bone resorption induced by subperiosteal injection of particles onto mouse calvariae was abolished by the MPC grafting on particles. MPC-grafted particles were shown to be biologically inert by culture systems with respect to phagocytosis and resorptive cytokine secretion by macrophages, subsequent expression of receptor activator of NF-kappaB ligand in osteoblasts, and osteoclastogenesis from bone marrow cells. From the mechanical and biological advantages, we believe that our approach will make a major improvement in artificial joints by preventing periprosthetic osteolysis.

Surface grafting of artificial joints with a biocompatible polymer for preventing periprosthetic osteolysis

Malposition of the acetabular component is a risk factor for post-operative dislocation after total hip replacement (THR). We have investigated the influence of the orientation of the acetabular component on the probability of dislocation. Radiological anteversion and abduction of the component of 127 hips which dislocated post-operatively were measured by Einzel-Bild-Roentgen-Analysis and compared with those in a control group of 342 patients. In the control group, the mean value of anteversion was 15 degrees and of abduction 44 degrees. Patients with anterior dislocation after primary THR showed significant differences in the mean angle of anteversion (17 degrees), and abduction (48 degrees) as did patients with posterior dislocation (anteversion 11 degrees, abduction 42 degrees). After revision patients with posterior dislocation showed significant differences in anteversion (12 degrees) and abduction (40 degrees). Our results demonstrate the importance of accurate positioning of the acetabular component in order to reduce the frequency of subsequent dislocations. Radiological anteversion of 15 degrees and abduction of 45 degrees are the lowest at-risk values for dislocation.

Reducing the risk of dislocation after total hip arthroplasty: THE EFFECT OF ORIENTATION OF THE ACETABULAR COMPONENT

Background: It has been postulated that use of a larger femoral head could reduce the risk of dislocation after total hip arthroplasty, but only limited clinical data have been presented as proof of this hypothesis

Methods: From 1969 to 1999, 21,047 primary total hip arthroplasties with varying femoral head sizes were performed at one institution Patients routinely were followed at defined intervals and were specifically queried about dislocation The operative approach was anterolateral in 9155 arthroplasties, posterolateral in 3646, and transtrochanteric in 8246 The femoral head diameter was 22 mm in 8691 of the procedures, 28 mm in 8797, and 32 mm in 3559

Results: One or more dislocations occurred in 868 of the 21,047 hips The cumulative risk of first-time dislocation was 22% at one year, 30% at five years, 38% at ten years, and 60% at twenty years The cumulative ten-year rate of dislocation was 31% following anterolateral approaches, 34% following transtrochanteric approaches, and 69% following posterolateral approaches The cumulative ten-year rate of dislocation was 38% for 22-mm-diameter femoral heads, 30% for 28-mm heads, and 24% for 32-mm heads in hips treated with an anterolateral approach; 35% for 22-mm heads, 35% for 28-mm heads, and 28% for 32-mm heads in hips treated with a transtrochanteric approach; and 121% for 22-mm heads, 69% for 28-mm heads, and 38% for 32-mm heads in hips treated with a posterolateral approach Multivariate analysis showed the relative risk of dislocation to be 17 for 22-mm compared with 32-mm heads and 13 for 28-mm compared with 32-mm heads

Conclusions: In total hip arthroplasty, a larger femoral head diameter was associated with a lower long-term cumulative risk of dislocation The femoral head diameter had an effect in association with all operative approaches, but the effect was greatest in association with the posterolateral approach

Level of Evidence: Therapeutic Level III See Instructions to Authors for a complete description of levels of evidence

Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty.

Numerous factors influence total hip arthroplasty (THA) stability including surgical approach and soft tissue tension, patient compliance, and component position. One long-held tenet regarding component position is that cup inclination and anteversion of 40° ± 10° and 15° ± 10°, respectively, represent a “safe zone” as defined by Lewinnek that minimizes dislocation after primary THA; however, it is clear that components positioned in this zone can and do dislocate. We sought to determine if these classic radiographic targets for cup inclination and anteversion accurately predicted a safe zone limiting dislocation in a contemporary THA practice. From a cohort of 9784 primary THAs performed between 2003 and 2012 at one institution, we retrospectively identified 206 THAs (2%) that subsequently dislocated. Radiographic parameters including inclination, anteversion, center of rotation, and limb length discrepancy were analyzed. Mean followup was 27 months (range, 0–133 months). The majority (58% [120 of 206]) of dislocated THAs had a socket within the Lewinnek safe zone. Mean cup inclination was 44° ± 8° with 84% within the safe zone for inclination. Mean anteversion was 15° ± 9° with 69% within the safe zone for anteversion. Sixty-five percent of dislocated THAs that were performed through a posterior approach had an acetabular component within the combined acetabular safe zones, whereas this was true for only 33% performed through an anterolateral approach. An acetabular component performed through a posterior approach was three times as likely to be within the combined acetabular safe zones (odds ratio [OR], 1.3; 95% confidence interval [CI], 1.1–1.6) than after an anterolateral approach (OR, 0.4; 95% CI, 0.2–0.7; p < 0.0001). In contrast, acetabular components performed through a posterior approach (OR, 1.6; 95% CI, 1.2–1.9) had an increased risk of dislocation compared with those performed through an anterolateral approach (OR, 0.8; 95% CI, 0.7–0.9; p < 0.0001). The historical target values for cup inclination and anteversion may be useful but should not be considered a safe zone given that the majority of these contemporary THAs that dislocated were within those target values. Stability is likely multifactorial; the ideal cup position for some patients may lie outside the Lewinnek safe zone and more advanced analysis is required to identify the right target in that subgroup. Level III, therapeutic study.

/pdf/what-safe-zone-the-vast-majority-of-dislocated-thas-are-3jv0nbhn8q.pdf

What Safe Zone? The Vast Majority of Dislocated THAs Are Within the Lewinnek Safe Zone for Acetabular Component Position.

Background: Hemiarthroplasty and total hip arthroplasty are commonly used to treat displaced intracapsular fractures of the femoral neck, but each has disadvantages and the optimal treatment of these fractures remains controversial.

Methods: In the present prospectively randomized study, eighty-one patients who had been mobile and lived independently before they had sustained a displaced fracture of the femoral neck were randomized to receive either a total hip arthroplasty or a hemiarthroplasty. The mean age of the patients was seventy-five years. Outcome was assessed with use of the Oxford hip score, and final radiographs were assessed.

Results: After a mean duration of follow-up of three years, the mean walking distance was 1.17 mi (1.9 km) for the hemiarthroplasty group and 2.23 mi (3.6 km) for the total hip arthroplasty group, and the mean Oxford hip score was 22.3 for the hemiarthroplasty group and 18.8 for the total hip arthroplasty group. Patients in the total hip arthroplasty group walked farther (p = 0.039) and had a lower (better) Oxford hip score (p = 0.033) than those in the hemiarthroplasty group. Twenty of thirty-two living patients in the hemiarthroplasty group had radiographic evidence of acetabular erosion at the time of the final follow-up. None of the hips in the hemiarthroplasty group dislocated, whereas three hips in the total hip arthroplasty group dislocated. In the hemiarthroplasty group, two hips were revised to total hip arthroplasty and three additional hips had acetabular erosion severe enough to indicate revision. In the total hip arthroplasty group, one hip was revised because of subsidence of the femoral component.

Conclusions: Total hip arthroplasty conferred superior short-term clinical results and fewer complications when compared with hemiarthroplasty in this prospectively randomized study of mobile, independent patients who had sustained a displaced fracture of the femoral neck.

Level of Evidence: Therapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.

Total hip arthroplasty and hemiarthroplasty in mobile, independent patients with a displaced intracapsular fracture of the femoral neck. A randomized, controlled trial.

Background: A widely variable prevalence of dislocation after total hip arthroplasty has been reported, partly because of varying durations of follow-up for this specific end-point. The effect of demographic factors on the long-term risk of dislocation as a function of time after total hip arthroplasty is not well understood. The purpose of the present study was to determine the risk of dislocation as a function of time after Charnley total hip arthroplasty and to investigate the demographic factors that influence the cumulative risk of dislocation.

Methods: Six thousand six hundred and twenty-three consecutive primary Charnley total hip arthroplasties were performed in 5459 patients at one institution between 1969 and 1984. The patients included 2869 female patients and 2590 male patients with a mean age of sixty-three years. All procedures were performed with a 22-mm femoral head, and all femoral and acetabular components were fixed with cement. The patients were followed at routine intervals and were specifically queried about dislocation. The cumulative risk of dislocation was calculated with use of the Kaplan-Meier method.

Results: Three hundred and twenty hips (4.8%) dislocated. The cumulative risk of a first-time dislocation was 1% at one month and 1.9% at one year and then rose at a constant rate of approximately 1% every five years to 7% at twenty-five years for patients who were alive and had not had a revision by that time. Multivariate analysis revealed that the relative risk of dislocation for female patients (as compared with male patients) was 2.1 and that the relative risk for patients who were seventy years old or more (as compared with those who were less than seventy years old) was 1.3. Three underlying diagnoses—osteonecrosis of the femoral head, acute fracture or nonunion of the proximal part of the femur, and inflammatory arthritis—were associated with a significantly greater risk of dislocation than osteoarthritis was.

Conclusions: The cumulative long-term risk of dislocation after total hip arthroplasty is considerably greater than has been reported in short-term studies. The incidence of dislocation is highest in the first year after arthroplasty and then continues at a relatively constant rate for the life of the arthroplasty. Patients at highest risk are female patients and those with a diagnosis of osteonecrosis of the femoral head or an acute fracture or nonunion of the proximal part of the femur.

Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.

The Cumulative Long-Term Risk of Dislocation After Primary Charnley Total Hip Arthroplasty

Background: Some patients have a dislocation for the first time many years after a total hip arthroplasty, but little is known about the risk factors and outcomes associated with late dislocation. The purposes of this study were (1) to determine the prevalence of late dislocation after total hip arthroplasty, (2) to characterize demographic and other factors associated with such late dislocations, and (3) to report the outcomes of such late dislocations.

Methods: Between 1969 and 1995, 19,680 primary total hip arthroplasties were performed in 15,964 patients at our institution. According to a prospective surveillance protocol, the patients were followed routinely at regular intervals and were specifically queried at each time-point about whether (and, if so, when) the hip had dislocated. First dislocations that occurred five years or more after the operation were defined as late dislocations.

Results: Five hundred and thirteen (2.6%) of the 19,680 hips dislocated. Of the 513 hips, 165 (0.8% of the entire cohort; 32% of the dislocated hips) first dislocated five or more years after the primary arthroplasty. The median time until the occurrence of these late dislocations was 11.3 years (range, five to 24.9 years) after the operation. Late dislocation was more frequent than early dislocation in women (p = 0.03), and late dislocation was associated with a younger age at the time of the primary total hip arthroplasty (median, sixty-three years) than was early dislocation (median, sixty-seven years) (p = 0.02). Clinical factors associated with late dislocation included previous subluxations without dislocation in twenty patients, a substantial episode of trauma in eleven patients, and onset of marked cognitive or motor neurologic impairment in eleven patients. Radiographically, the late dislocation occurred in association with polyethylene wear of >2 mm in eighteen hips, with implant loosening with migration or a change in position in eight, and with initial malposition of the acetabular implant (anteversion of 30d or abduction of >55d) in thirty. Late dislocation recurred in ninety (55%) of the 165 hips and was treated with a reoperation in fifty-five hips (33% of the hips with late dislocation; 61% of the hips with recurrent dislocation).

Conclusions: Late dislocation is more common than was previously thought. Several separate processes, some distinct from those associated with early dislocation, can lead to late dislocation. Late dislocation can occur in association with a long-standing problem with the prosthesis that manifests late (such as malposition of the implant or recurrent subluxation), it can occur in association with a new problem (such as neurologic decline, an episode of trauma, or polyethylene wear), or it can occur in association with any combination of these factors. The likelihood of the first late dislocation recurring is high.

Late dislocation after total hip arthroplasty.

https://onlinelibrary.wiley.com/doi/pdf/10.1016/j.orthres.2003.08.013

The effectiveness of polyethylene versus titanium particles in inducing osteolysis in vivo.

Background: The hip joint is a common location for metastatic disease. Actual as well as impending fractures at this site are frequently due to mechanical instability after tumor invasion and are usually treated surgically with hip arthroplasty. The objective of this study was to analyze survival and influences on survival after hip arthroplasty for metastatic hip disease. Methods: Two hundred and ninety-nine patients who had undergone a total of 306 hemiarthroplasty or total hip arthroplasty procedures for treatment of a pathologic or an impending pathologic hip fracture between 1969 and 1996 at our institution were included in this study. Data that had been acquired prospectively within the total joint registry of our institution were reviewed retrospectively. Results: The median duration of survival after the arthroplasty was 8.6 months. The duration of survival was significantly associated with the site of the fracture, location of the primary tumor, and time from the diagnosis of the primary tumor to the surgery for the fracture (p ≤ 0.05). The time from the diagnosis to the arthroplasty was a significant independent predictor of survival. Conclusions: Patients undergoing hip arthroplasty for metastatic disease have a limited life expectancy, with only 40% (120) of the 299 patients in our series still alive at one year after the surgery. By identifying prognostic factors regarding life expectancy, this study provides surgeons and oncologists with information with which to weigh risks and benefits of hip arthroplasty for individual patients preoperatively. Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.

Marius von Knoch

Papers

Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty.

The Cumulative Long-Term Risk of Dislocation After Primary Charnley Total Hip Arthroplasty

Late dislocation after total hip arthroplasty.

The effectiveness of polyethylene versus titanium particles in inducing osteolysis in vivo.

Patient survival after hip arthroplasty for metastatic disease of the hip.