Four highly cross-linked UHWMPEs except vitamin E-stabilised explants The development of both first and second generation highly cross-linked material focused on stabilizing radiation-induced free radicals as the sole precursor to oxidative degradation; however, secondary in vivo oxidation mechanisms have been identified in both conventional and highly cross-linked UHMWPE, induced by absorbed lipids and cyclic mechanical load. Retrieval studies are reporting in vivo oxidation highly cross-linked retrievals with up to ten year in vivo durations. Preclinical aging tests did not predict these in vivo material changes. With only a decade of these materials in clinical use, retrieval studies are limited to mid-term follow-up. In vitro studies face a challenge in effectively replicating the precise in vivo conditions that lead to this loss of oxidation resistance. In this study, we bypass replicating these in vivo variables by examining surgically-retrieved components, thereby testing material that has been affectively “pre-conditioned” by their in vivo service. After a preliminary post-operative analysis, we subjected retrievals to accelerated aging tests in order to predict the extent to which their oxidative stability had been uniquely compromised in vivo.Summary
Introduction
We analysed impaction bone grafting used together with cemented or uncemented fixation in acetabular revision surgery. The overall risk for re-revision did not differ between the cemented and uncemented group. However, aseptic loosening was more common in the cemented group. Several surgical techniques address bone defects in cup revision surgery. Bone impaction grafting, introduced more than thirty years ago, is a biologically and mechanically appealing method. The primary aim of this study was to evaluate the effect of bone impaction grafting when used with uncemented and cemented fixation in cup revision surgery. Uncemented cups resting on more than 50% host bone were used as controls.Summary Statement
Background
Sequentially irradiated and annealed UHMWPE hip and knee retrievals showed subsurface Highly cross-linked polyethylene was developed to improve the wear resistance of UHMWPE bearing surfaces in total hip arthroplasty. First generation irradiated and annealed polyethylene showed high oxidation Summary
Introduction
Femoral head diameter has a major influence on stability and dislocation resistance of the hip joint after Total Hip Arthroplasty (THA). Dual Mobility (DM) implants can also reduce the risk of dislocation due the large diameter mobile liner which forms the femoroacetbular articulation. However, recent studies have shown that large head prostheses can directly impinge against native soft tissues, particularly the iliopsoas, leading to anterior hip pain. Dual mobility systems have emerged as a revision option in the treatment of failed metal on metal devices because of the high incidence of post revision instability secondary to abductor loss and need for capsulectomy. We hypothesized that an Anatomically Contoured Dual Mobility (ACDM) liner could provide joint stability while better accommodating the soft tissues surrounding the hip joint. The dislocation resistance of a 44 mm ACDM implant was compared to that of a 44 mm conventional DM liner. Both implants consisted of a 28 mm inner small diameter head and the liner was abducted to be in the worst case position for dislocation (Fig. 1). The ACDM liner was based on a 44 mm sphere with smaller radii used to contour the peripheral region below the equator of the liner. MSC Adams was used for dynamic simulations based on two previously described dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal rotation of the hip and a posterosuperior directed joint force; (B) Posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction and a posteromedial force direction (Fig. 2). Impingement-free motion (motion without neck impingement against the acetabular cup) and jump distance (head separation from acetabulum at dislocation) were measured for each implant. The acetabular cup was placed at 42.5° abduction and 19.7° anteversion, while the femoral component was anteverted by 9.75° based on published data.INTRODUCTION
METHODS
While kinematic abnormalities of contemporary TKA implants have been well established, a solution has not yet been achieved. We hypothesized that contemporary TKA implants are not compatible with normal soft-tissue function and normal knee motion. We propose a novel technique for reverse engineering advanced implant articular surfaces (biomimetic surface), by using accurate 3D kinematics of normal knees. This technique accounts for surgical placement of the implants, and allows design of tibial and femoral articular surfaces in conjunction. Magnetic resonance imaging was used to create 3D knee models of 40 normal subjects (24 male, 16 female, age 29.9 ± 9.7 years), and bi-planar fluoroscopy was used to capture 3D knee motion during a deep knee bend. These data were combined to create a 3D virtual representation of an average normal knee and its motion pathway. A TKA femoral component was mounted on the average knee, and moved through its normal kinematic pathway to carve out an articular surface from a tibial template (Fig. 1 and 2). The geometry of the resulting biomimetic tibia was compared to that of the native tibia, and a contemporary TKA tibial insert that uses the same femoral component.Introduction:
Methods:
Large diameter femoral heads have been used successfully to prevent dislocation after Total Hip Arthroplasty (THA). However, recent studies show that the peripheral region of contemporary femoral heads can directly impinge against the native soft-tissues, particularly the iliopsoas, leading to activity limiting anterior hip pain. This is because the spherical articular surface of contemporary prosthesis overhangs beyond that of the native anatomy (Fig. 1). The goal of this research was to develop an anatomically shaped, soft-tissue friendly large diameter femoral head that retains the benefits of contemporary implants. Various Anatomically Contoured femoral Head (ACH) designs were constructed, wherein the articular surface extending from the pole to a theta (θ) angle, matched that of contemporary implants (Fig. 2). However, the articular surface in the peripheral region was moved inward towards the femoral head center, thereby reducing material that could impinge on the soft-tissues (Fig. 1 and Fig. 2). Finite element analysis was used to determine the femoroacetabular contact area under peak in vivo loads during different activities. Dynamic simulations were used to determine jump distance prior to posterior dislocation under different dislocation modes. Published data was used to compare the implant articular geometry to native anatomy (Fig. 3). These analyses were used to optimize the soft-tissue relief, while retaining the load bearing contact area, and the dislocation resistance of conventional implants.Introduction:
Methods:
Dual Mobility (DM) hip implants have gained popularity for the treatment and preventions of instability. In DM implants a large diameter mobile insert matches the native femoral head size. However, studies have shown that the peripheral regions of such large diameter implants overhang beyond the native anatomy and can directly impinge against nearby soft tissues, especially the iliopsoas, leading to groin pain (Fig. 1). Soft-tissue impingement can also trap the mobile DM insert, leading to damage of its peripheral rim, which secures the small diameter inner head (Fig. 2). The goal of this research was to develop an anatomically contoured soft-tissue friendly DM insert. Various Anatomically Contoured Dual Mobility (ACDM) insert designs were constructed, wherein the outer articular surface extending from the pole to a theta (θ) angle, matched that of contemporary implants (Fig. 3). However, the articular surface in the peripheral region was moved inward towards the center, thereby reducing implant volume that could impinge on the soft tissue (Fig. 1 and Fig. 3). Finite element analyses were used to determine the insert-acetabular contact area under peak in vivo loads during different activities. Finite element analysis was also used to determine resistance to extraction of the inner head. Published data was used to compare the implant articular geometry to native anatomy. These analyses were used optimize the soft-tissue relief, while matching the load bearing contact area and the resistance to extraction of the inner head in contemporary implants.Introduction:
Methods:
Large diameter femoral heads provide increased range-of-motion and reduced dislocation rates compared to smaller diameter femoral heads. However, several recent studies have reported that contemporary large head prostheses can directly impinge against the local soft tissues leading to anterior hip pain. To address this we developed a novel Anatomically Contoured large diameter femoral Head (ACH) that maintains the profile of a large diameter femoral head over a hemispherical portion and then contours inward the distal profile of the head for soft-tissue relief. We hypothesized that the distal contouring of the ACH articular surface would not affect contact area. The impact of component placement, femoral head to acetabular liner radial clearance, and joint loading during different activities was investigated. A finite element model was used to assess the femoroacetabular contact area of a 36 mm diameter conventional head and a 36 mm ACH (Fig. 1). It included a rigid acetabular shell, plastically deformable UHMWPE acetabular liner, rigid femoral head and rigid femoral stem. The femoral stem was placed at 0°, 10° and 20° of anteversion. The acetabular shell and liner were placed in 20°, 40° and 60° of abduction and 0°, 20° and 40° of anteversion. The femoral head to acetabular liner radial clearances modeled were 0.06 mm, 0.13 mm and 0.5 mm. Three loading cases corresponding to peak in vivo loads during walking, chair sit and deep-knee bend were analyzed (Fig. 2). This allowed a range of component positions and maximum joint loads to be studied.Introduction
Methods
Dual mobility (DM) implants provide increased stability and range-of-motion through the use of a large diameter mobile liner articulating against an acetabular shell. However, recent studies have reported that such contemporary large head prostheses can directly impinge against the local soft tissues leading to anterior hip pain. To address this drawback, a novel Anatomically Contoured Dual Mobility (ACDM) liner was developed that maintains the outer spherical geometry over an approximately hemispherical portion and then contours inward the distal profile of the DM liner for soft-tissue relief. The extent of the inner profile encapsulating the small diameter head is increased to provide more coverage of the head and maintain the inner head pullout force. We hypothesized that the ACDM liner for soft-tissue relief would not affect retention of the small diameter inner head or liner-acetabular load-bearing contact area. A finite element model to evaluate head retention and contact mechanics was created with a rigid acetabular shell, a plastically deformable UHMWPE DM liner, a rigid femoral head and a rigid femoral stem. For the head retention analysis, the extent of head coverage (Fig. 1) was optimized to match the inner head pullout force of a conventional DM liner. Contact mechanics of a conventional DM and ACDM liner were analyzed at the maximum joint load of three activities: gait, deep-knee bend and chair sit. One set of simulations was completed with the mobile liner and head axes aligned and another with the axes mal-aligned so that the mobile liner rim was adjacent to the femoral stem neck and the potential area of contact was away from the mobile liner apex. This allowed a broader range of potential contact to be assessed including what was determined to be a worst-case alignment.Introduction
Methods
Contemporary Posterior Cruciate Ligament (PCL) retaining TKA implants (CR) are associated with well-known kinematic deficits, such as absence of medial pivot motion, paradoxical anterior femoral sliding, and posterior femoral subluxation at full extension. The hypothesis of this study was that a biomimetic implant, reverse engineered by using healthy knee kinematics to carve the tibial articular surface, could restore normal kinematic patterns of the knee. Kinematics of the biomimetic CR and two contemporary CR implants (A, B) were evaluated during simulated deep knee bend and chair-sit in LifeModeler KneeSIM™ software. Anteroposterior motion of the medial and lateral femoral condyle centers was measured relative to a tibial origin. The implants were mounted on an average knee model created from magnetic resonance imaging (MRI) of 40 healthy knees. The medial and lateral collateral ligaments, posterior cruciate ligament, quadriceps mechanism, and the overall capsular tension were modeled. The soft-tissue insertions were obtained from the average knee model, and the mechanical properties were obtained from literature. In vivo knee kinematics of healthy subjects from published literature was used for reference.Introduction:
Methods:
Acetabular component orientation has been linked to hip stability as well as bearing mechanics such as wear. Previous studies have demonstrated wide variations of cup placement in hip arthroplasty using conventional implantation techniques which rely upon either anatomic landmarks or the use of commercial positioning guides. Enabling technologies such as navigation have been used to improve precision and accuracy. Newer technologies such as robotic guidance have been postulated to further improve accuracy. The goal of our study was to evaluate the clinical reproducibility of a consecutive series of haptically guided THR. 119 patients at 4 centers were enrolled. All patients had preoperative CT scans for the purpose of planning cup placement in lateral opening and version using proprietary software (Mako, Ft. Lauderdale, FL). All procedures were performed using a posterolateral approach. Following bone registration, acetabular preparation and component position is performed using haptic guidance. Final implant postion is ascertained by obtaining 5 points about the rim of the acetabular component and recorded. At 6 weeks, all patients had AP and cross-table lateral radiographs which were then analyzed for cup abduction and anteversion using the Hip Analysis Suite software. The goal was to determine the variability between desired preoperative plan, intraoperative measurement and postoperative results.Introduction:
Methods:
Acetabular cup position is an important factor in successful total hip arthroplasty (THA). Optimal cup placement requires surgeons to possess an accurate perception of pelvic orientation during cup impaction, however, varying pelvic anatomy and limited visual cues in the surgical field may interfere with this process. The purpose of this study was to evaluate the utility of an inertial measurement unit (IMU) in monitoring pelvic position during THA. Ten patients scheduled to undergo THA were IRB-approved and consented by four surgeons. A small IMU was placed over the patient's sacrum pre-operatively and zeroed in standing position. Pelvic orientation data was streamed and captured wirelessly throughout the procedure. Surgeons were blinded to all data throughout the study period. Prior to cup impaction, the surgeon indicated his intended cup abduction angle and the degree to which the cup impactor was manipulated to compensate for perceived AP pelvic tilt. The degree of pelvic tilt as determined by the IMU (angle β) was then recorded (Figure 1). AP-pelvis radiographs were measured in Martell Hip Analysis Suite post-operatively to calculate the cup abduction angle, which was then compared to the surgeon's intended abduction angle to determine surgeon accuracy. To predict the final cup abduction angle, the degree of pelvic tilt recorded by the IMU (angle β) was subtracted from the abduction angle of the cup impactor (angle α) that was positioned using the OR table as a reference (Figure 1). This value was then compared to the measured post-operative cup abduction angle in order to assess the accuracy of the IMU in measuring pelvic tilt. Surgeon accuracy and IMU accuracy were compared to determine if the IMU was more or less effective than surgeon perception at determining pelvic tilt.Introduction:
Materials & Methods:
Femoral head diameter has a major influence on stability and dislocation resistance after Total Hip Arthroplasty (THA). Although routine use of large heads is common, several recent studies have shown that contemporary large head prostheses can directly impinge against native soft tissues, particularly the iliopsoas which wraps around the femoral head, leading to refractory anterior hip pain. To address this, we developed a novel Anatomically Contoured large diameter femoral Head (ACH). We hypothesized that anatomical contouring of the ACH implant for soft tissue relief would not compromise dislocation resistance, and the ACH implant would provide increased stability compared to small heads. In this study the dislocation resistance of a 36 mm ACH was compared to that of 28 mm and 36 mm contemporary heads. The ACH implant was based on a 36 mm sphere with smaller radii used to contour the peripheral region below the equator of the head. MSC Adams was used for dynamic simulations based on two previously described dislocation modes: (A) Posterior dislocation (at 90° hip flexion) with internal rotation of the hip and a posterosuperior directed joint force; (B) posterior dislocation (starting at 90° flexion) with combined hip flexion and adduction and a posteromedial force direction (Fig. 1). Impingement-free motion (motion without neck impingement against the acetabular liner) and jump distance (head separation from acetabulum prior to dislocation) were measured to evaluate the dislocation risk of each implant. The acetabular cup was placed at 42.5° abduction and 19.7° anteversion, while the femoral component was anteverted by 9.75° based on published data.INTRODUCTION
METHODS
In total hip arthroplasty, the positioning of the acetabular cup, in particular, has been shown to play an important role in the survivorship of the prosthetic joint. The commonly accepted “safe zone” extends from 5–30° of anteversion to 30–50° of inclination. However, several studies have utilized a more restrictive safe zone of 5–25° of anteversion and 30–45° of inclination, a modification of the Lewinnek zone. Many attempts have been made to develop a more reliable method of positioning the acetabular component. Robotic-assisted surgery is one such method. The purpose of this study was to compare the resulting position of the acetabular component after robotic-assisted surgery with the intraoperative robotic data to determine if improved accuracy can be achieved with the robotic-assisted method. One hundred and nineteen patients received THA, at four different medical centers in the United States, using a haptic robotic arm. Pre-operative CT scans were obtained for all patients and used during the planning of the procedure, at which point the proposed component size and positioning was determined. Preparation of the acetabular bone bed, as well as impaction of the acetabular component itself, was performed using the robotic device. Using an AP Pelvis and Cross-Table Lateral radiograph, each patient's resulting acetabular inclination and version was measured using the Hip Analysis Suite software. The component position retrieved from the robot was compared to the measured values from the radiographs. The positioning data was compared to two safe zones described above.Introduction
Methods
Proper cup positioning is a critical component in the success of total hip arthroplasty surgery. A multicenter study has been initiated to study a new type of highly cross-linked polyethylene. This study provides a unique opportunity to a review the acetabular cup placement of over 500 patients implanted in the past 2 years from 13 medical centers from the U.S., Mexico, and Europe. 482 patients have received primary total hip arthroplasty using components from a single manufacturer in 5 centers in the US and Mexico and 7 centers in Europe. The acetabular anteversion and inclination were measured in post-operative radiographs. An acceptable window of cup position is defined at 5–25° of anteversion and 30–45° of inclination.Introduction
Methods
Total hip replacements using highly cross-linked polyethylene show excellent clinical outcomes, low wear, and minimal lysis at 5 years follow-up. A recent RSA study reports a significant increase in femoral head penetration between 5 and 7 years. This study is a multi-center radiographic analysis to determine whether the RSA observation is present in a large patient cohort. Six centers were enrolled for radiographic analysis of primary total hip arthroplasty for standard head sizes (26mm, 28mm, or 32mm). Radiographic inclusion criteria required a minimum of four films per patient at the following time points: 1 year; 2–4.5 years; 4.5–5.5 years; and 5.5–11 years. The Martell Hip Analysis Suite was used to analyze pelvic radiographs resulting in head penetration values. Wear rates were determined in two ways: the longest follow-up radiograph compared to the 1 year film, and individual linear regressions for the early and late periods. For both methods, average wear rates from the early period (1 to 5.5 years) and late period (>5.5 years) were compared using t-tests.Introduction
Methods
Acetabular cup positioning has been linked to dislocation and increased bearing surface wear. A previous study found correlations between patient and surgical factors and acetabular component position. The purpose of this study was to determine if acetabular cup positioning improves when surgeons receive feedback on their performance. Post-op anteroposterior (AP) pelvis and cross-table lateral radiographs were previously obtained for 2061 patients who received a total hip arthroplasty (THA) or hip resurfacing from 2004–2008. The surgeries were performed by 7 surgeons. AP radiographs were measured using Hip Analysis Suite to calculate the cup inclination and version angles. Acceptable ranges were defined for abduction (30–45 °) and version (5–25 °). The same surgeons performed a THA or hip resurfacing on 385 patients from January 2009 through June 2010. Cup inclination and version angles for this set of surgeries were compared to surgeries from 2004–2008 to determine if cup inclination and version angles improved in response to previous acetabular cup positioning studies. Improvement in accuracy was assessed by the chi-square test.Introduction
Methods
Radiation crosslinking decreases the wear of ultra-high molecular weight polyethylene (UHMWPE) and subsequent heating increases its oxidative stability. Clinical trials are showing lower femoral head penetration rate with highly crosslinked vs. conventional UHMWPE liners. Recently, a follow-up report showed a surprising increase in the femoral head penetration rate with a highly crosslinked UHMWPE, prompting us to closely analyze surgically explanted highly crosslinked UHMWPEs. Thirty-four highly crosslinked components, all irradiated (100kGy) and melted, were included in the study. The components were surgically removed from patients for non-polyethylene related reasons. Oxidation was determined at the rim immediately after explantation. After shelf storage in air for 5–77 months, oxidation and crosslink density were measured at the rim and articular surfaces. An additional retrieval (92 mos. in vivo) was tested on the hip simulator; oxidation and crosslink density were determined after simulator testing. All components showed no detectable oxidation immediately after explantation; however, surprisingly oxidation levels increased during shelf storage. Areas with increased oxidation showed a decrease in crosslink density. These changes did not correlate with in vivo duration; however, they correlated strongly with ex vivo duration. The component subjected to hip simulator testing showed no measurable wear and showed no detectable oxidation or marked decrease in crosslink density. Two mechanisms may have reduced the oxidation resistance of highly crosslinked UHMWPE upon exposure to in vivo elements and subsequent exposure to air. One mechanism is based on free radical formation during cyclic loading; the other is based on an oxidation cascade initiated by absorbed lipids. Further studies are necessary to determine the impact of these mechanisms, if any, on the stability of components during in vivo service.
There are a variety of patient and surgical factors shown to increase post-operative complication risk for a total hip arthroplasty (THA). While many studies have linked patient and surgical factors to unsuccessful outcomes post total hip arthroplasty (THA), no study has attempted to correlate the infiuence of these factors to the positioning of the acetabular cup. The purpose of this study was to determine if a correlation exists between patient and surgical factors and the anatomical position of the acetabular component. Data for 2063 patients from 2004–2008 who underwent a primary total hip arthroplasty (THA), revision THA, or Birmingham Hip Resurfacing procedure was compiled. The post- op anteroposterior pelvis (AP) and the cross table lateral digital radiographs for each patient were measured to determine cup inclination and version. Acceptable angle ranges were defined as 30–45° for abduction, and 5–25° for version. Correlations between variables and cup abduction and version angles were determined with SPSS™ statistical software. There were 1954(95%) qualifying patients. There were 1218(62%) acetabular cups that fell within the 30–45° optimal abduction range, and 1576(87%) cups in the 5–25° optimal version range. There were 921(47%) patients that had both inclination and version angles that fell within the optimal range. Regression analysis showed that surgical approach (p>
0.001), high/low volume surgeon (p<
0.001), and obesity (BMI >
30, p=0.01) were independent predictors for abduction and version combined analysis. Both surgical approach (p<
0.001) and BMI (p=0.018) were independent predictors in the individual analysis of both abduction and version. High/low volume surgeon was significant for the independent analysis of abduction (p=0.013). In the combined analysis, low volume surgeons showed a 2 fold increase (95% C.I. 1.5–2.8) in risk for cup malpositioning compared to high volume surgeons. The MIS surgical approach showed a 6 fold increase (95% C.I. 3.5–10.7) in risk for cup malpositioning compared to the posterolateral approach. Obesity (BMI>
30) showed a 1.3 fold increase (95% C.I. 1.1–1.7) in risk for cup malpositioning compared to all other body mass index groups. Posterolateral surgical approach was superior to MIS surgical approaches for independent and combined abduction and version analysis. High volume surgeons had greater accuracy for cup positioning, specifically for achieving optimal cup abduction angle. Compared to all other body mass index categories, patients that were obese (BMI>
30) displayed a greater risk for cup malpositioning for independent and combined abduction and version analysis. Further statistical analyses on patient and surgical variables and their infiuence on cup position at a lower volume medical center would provide a valuable data comparison.
The purpose of this study was to organize a multicenter radiographic study involving leading medical centers in the U.S. having the longest-term follow-up available on this type of highly cross-linked polyethylene in order to determine if the RSA observation can be confirmed in a larger study. Six academic centers agreed to contribute radiographic data to this study. All patients received primary total hip replacements with Longevity polyethylene liners (Zimmer, Warsaw, IN) coupled with 26, 28, and 32mm cobalt chrome femoral heads. The radiographic inclusion criteria required a minimum of four radiographs per patient: one at 1 year; at least one from 2 to 4.5 years; one 4.5 to 5.5 years; and at least one from 5.5 to 9 years follow-up. The Martell Hip Analysis Suit-eTM software was used for the wear analysis. All wear values were determined by calculating head penetration between the follow-up radiograph and the 1-year radiograph to remove creep, the majority of which has been shown to occur during the first year. Separate linear regressions, representing the wear rates, were computed for the early period from 1 year to 5.5 years and the late period from 5.5 years to 9 years follow-up. The Zar test was used to determine the significance of the difference between these two linear regressions. We present the completed analysis of 165 hips. When the early and late data points were combined into one data set, the second-order regression indicated an inflection point at 6.3 years with a slightly positive inflection. There were 402 film comparisons in the early time period, and the slope and confidence interval of the regression line was 4.9μm/yr (95% CI of −28μm/yr to 38μm/yr). There were 188 film comparisons in the late period, and slope of the regression line for the late period was 10.8 μm/yr (95% CI of −58μm/yr to 80μm/yr). The Zar test showed no significant difference between the two slopes (Figure 1, p=0.886). No significant increase in femoral head penetration was found for the late period after 5 years compared to the early period before 5 years follow-up in either analysis. Additionally, no significant late increase in wear was seen within individuals. While we continue to enroll patients, at this time we do not observe the increase in wear seen in the RSA study after 5 years.
Of 960 first-revision total hip replacements (THR) because of deep infection identified in the Swedish Hip Arthroplasty Registry, 16.9% were treated with a permanent implant extraction, while a staged or direct reconstruction revision protocol were employed in 56.2% and 26.9% respectively. The majority of the interventions were performed more than one year after index THR, and the dominating pathogen was coagulase negative staphylococci (CNS). We found a significant shift in types of bacteria over the years (Chi-square test, p smaller than 0.001): an increase in the CNS group and a decrease in Gram-negative aerobes. Patients treated with a permanent resection were generally older (p<
0.001), had more often a previous ipsilateral hip fracture (p<
0.001), and had more frequently Gram-negative infections (p=0.02). No systematic differences in patient characteristics or pathogens were detected between one-stage or two-stage procedures, of which the latter had a median re-implantation time of 2 (range: 0.2–62) months. Of 798 (one- or two-stage) revisions, 60 (7.5%) were revised again due to recurrent infection, with no difference between the two methods, and implying a 10-year survival of 90%; 95% confidence interval (CI95%) 88.2–93.0. Previous surgery for soft-tissue problems (RR 3.2 (CI95% 1.3–7.2)) predicted a worse outcome for one-stage procedures. The prognosis of two-staged revisions improved with increasing re-implantation interval (RR 0.8 (CI95% 0.7–1.0)) per month, and a 6 month interval carried the lowest risk of repeat revision due to infection; RR 0.1 (CI95% 0.0–0.9). Staged revisions in female patients (RR 2.3, (CI95% 0.9–5.7)) and with Staphylococcus aureus infections (RR 2.3 (CI95% 0.9–5.5)) predicted a worse outcome. Ten-year survival with repeat revision for aseptic loosening as end-point was 89% (95%CI 85.7–92.0), but decreased to 79% when all reasons for revision were taken into account (95%CI 75.0–82.3) mainly because of revision for peri-prosthetic fractures. The results suggest that direct and staged revision protocols can have a good prognosis on a national level, but efforts must be made to counteract periprosthetic fractures and the high incidence of permanent implant extraction in elderly patients.
Highly cross-linked polyethylene liners in total hip replacement (THR) have allowed the use of larger diameter femoral heads. Larger heads allow for increased range of motion, decreased implant impingement, and protection against dislocation. The purpose of this study is to report the clinical and radiographic outcomes of patients with large femoral heads with HXLPE at 5 years post-op. A group of 124 patients (132 THRs) who had a primary THR with a 36mm or larger cobalt-chrome femoral head and a Durasul or Longevity liner (Zimmer; Warsaw, IN) were prospectively enrolled in this study. 93 THRs (88 patients) had minimum 5 year follow-up. All patients received a cementless acetabular shell (Trilogy or Inter-op, Zimmer Inc, Warsaw IN) and a highly cross-linked polyethylene liner with an inner diameter of 36 or 38mm. The median radiographic follow-up was 5.6 years (range 5.0–8.0), and patients were assessed clinically by Harris Hip score, UCLA activity score, EQ-5D, and SF-36 functional scores. Femoral head penetration was measured using the Martell Hip Analysis Suite. No osteolysis was seen in the pelvis or proximal femur, and no components failed due to aseptic loosening. Four patients have questionable signs of bone changes around the acetabular shell with future CT scans scheduled to help reach a final determination. The median acetabular shell abduction and anteversion were 44° (30–66°) and 13° (3–33°) respectively. There was no evidence of cup migration, screw breakage, or eccentric wear on the liner. Regarding the femoral component, there were no episodes of loosening, migration, osteolysis, or fracture. There was no significant difference in the median penetration rate from post-op to longest follow-up between the 36mm (24 patients) and 38mm (4 patients) femoral head groups (0.056±0.10mm/yr and 0.060±0.05mm/yr respectively). Therefore, the data were pooled into one group. Using every post-op to follow-up comparison, the linear regression penetration rate of this combined group was 0.003 mm/yr which is within the error detection of the Martell method. The median femoral head penetration rate during the first post-op year measured 0.59±1.04 mm/yr. In contrast, the median steady state wear rate from the 1yr film to the longest follow-up measured -0.009±0.15mm/yr. A linear regression steady state wear rate from the 1 year film to every follow-up of −0.031 mm/yr indicated no correlation between the magnitude of polyethylene wear and time. The mid-term results on this series of patients with THRs with a 36 or 38mm femoral head articulating with highly cross-linked polyethylene showed excellent clinical, radiographic, and wear results. The lack of early signs of osteolysis with the use of these large diameter femoral heads is encouraging. Continued and longer-term follow-up is needed to provide survivorship data.
Highly cross-linked polyethylene (HXLPE) is one of the most widely utilized bearing surfaces for total hip arthroplasty (THA). The first patients to receive XLPE will be 10 years post-op as of December 31, 2008. The purpose of this study is to report the long-term clinical and radiographic outcomes of patients implanted with HXLPE. A group of 247 primary total hip replacements (224 patients) using HXLPE liners (Longevity or Durasul, Zimmer Inc.) with 22, 26, 28, or 32mm femoral heads were implanted between 1999 and 2001. Clinical evaluation measures included the Harris hip, EQ-5D, SF-36 functional scores, and UCLA activity scores. In addition to plain radiograph assessment, the computerized Martell method was used to measure head penetration over time. A matched group of 241 primary total hip replacements (201 patients) with the same head sizes using conventional polyethylene (PE) with a minimum of 7 years follow-up was used as a Martell method control group. The steady state penetration rate was defined as the slope of the linear regression line of the plot of head penetration from the 1 year film to each subsequent film to discount the early bedding-in process. A student’s t-test was used to compare wear rates between head sizes in each group, and a repeated-measures mixed model ANOVA was used to compare the groups for the 28mm head size. There were no osteolytic lesions around the cup or stem, and no revisions were performed for polyethylene wear or liner fracture. Clinical outcome scores were averaged: Harris Hip 88.1±11.97, EQ-5D 74.0±27.0, SF-36 physical activity scores 53.3±8.4, SF-36 mental score 46.9±11.1, and UCLA activity 6.4±2.1. The steady state wear of the conventional polyethylene patients increased with time for both 26 and 28mm head sizes (0.144 and 0.127mm/year, respectively). No significant difference was found between the head sizes coupled with conventional polyethylene (p=0.14). Femoral head penetration in the highly cross-linked polyethylene did not increase over time after the first year. The steady state wear rates of HXLPE liners with 28mm or 32mm femoral heads were not significantly different than a slope of zero (p=0.54 for both head sizes). Clinical follow-up results are typical of a primary THR patient population, and the radiographic results are excellent with no signs of peri-prosthetic osteolysis. Patients with PE show wear rates that are significantly different than zero indicating significant wear of the material. Conversely, patients with HXLPE display no measureable wear at 7–9 years as the wear rates were within the error detection of the Martell method. This long-term clinical and radiographic follow-up study for this new bearing material shows excellent clinical outcomes with very low in vivo wear.
A subgroup of 481 patients in the Western Region of Sweden with complete data on individual CPP (cost per patient) was selected for the health economic analysis.
For RSA, the wear rate for the 28mm femoral head group was 0.05±0.02 while the 36mm femoral head group was 0.03±0.02, p=0.13. For the Martell analysis, the average steady-state wear rate was −0.002 ± 0.01 mm per year and −0.026 ± 0.13 mm per year for 28mm and 32mm head sizes, respectively, p=0.62. There was no correlation between wear and time in situ or femoral head size for any of the clinical studies. In comparing the Martell and Devane programs, the total average wear rates were significantly different, 0.07±0.05 and 0.03±0.06mm/year respectively, p=0.01. However, when the absolute values of the Martell results were used, there was no difference, p=0.22.
In a previous report from a randomised study we reported excellent fixation and less proximal periprosthetic bone mineral loss around the Epoch design at 2 years follow-up when compared with a solid stem of similar design. We now present the 7 years follow-up. Forty consecutive patients (20 men, 10 women, mean age 57, 41–74) with non-inflammatory osteoarthritis were randomised to receive either a cementless porous-coated composite stem with reduced stiffness (Epoch) or a cementless stiff stem with a porous coating (Anatomic). Patients were followed for 7 years with repeated evaluations using radiostereometry, DXA, conventional radiography and Harris Hip Score (HHS). At 7 years 1 stem had been revised (Anatomic) due to late infection. Subsidence and stem rotations were close to zero without any difference between the two groups (p>
0,12). Median wear rates were lower than expected (0.4mm up to 7 years) for both stem designs. At 2 years loss bone mineral density was less in Gruen regions 1, 2, 6 and 7 for the Epoch stems (p<
0.04), but this difference tended to disappear with time. At 7 years only the calcar region (Gruen region 7) had significantly denser bone in the Epoch group (p<
0.001). The HHS scores did not differ (median 98, 51–100). No stem was radiographically loose. The Epoch stem achieved excellent fixation. Wear rates were low despite use of conventionally gamma-sterilised polyethylene. This low modulus stem had positive effects on early proximal bone remodeling, but this effect decreased with time.
Starting in the 1970s, long-term survivorship of total hip and knee arthroplasty has been under investigation for the Scandinavian population with the aid of implants registries. In the United States, no national arthroplasty registry currently exists. Nationwide inpatient discharge databases in the United States have proven useful when comparing the revision burden in the United States and Scandinavia. For this study, we compared the implant survivorship in the Medicare population with contemporaneous registry-based data from well-established and validated Scandinavian arthroplasty registries. The 5% systematic sample of Medicare claims from 1997 to 2004 were examined for primary and revision THA and TKA claims. The Medicare beneficiary ID was used to follow patients longitudinally between primary and revision surgery. De-identified data from the Norwegian and Swedish national hip and knee registry were also obtained for the same time period. During the 8-year study period, 30,583 and 62,878 elective primary total hip or knee replacements, respectively, were extracted from the Medicare data. In the same time period, 41,823 and 15,927 primary total hips or knees replacements were identified from the Norwegian registry. 82,037 primary total hips were identified from the Swedish registry. Survivorship was assessed by the Kaplan-Meier method, and Cox regression was used to evaluate the effect of patient attributes and cross-country comparisons. The K-M estimate showed that 8 years post-primary surgery, 93.6% of THA and 96.2% of TKA remained revision-free among the elderly Medicare population. By comparison, among Norwegians aged 65 and above, 96.0% of THA and 93.6% of TKA remained revision-free. In the US, men had a significantly higher risk of knee revision than women, but no significant gender difference among hip revision. In Norway, men had a significantly higher risk of hip revision, but no differences in knee revisions. In Sweden, men had a significantly higher risk of hip revision (5.4% vs. 3.3%). Older patients had a reduced risk of revision as compared with younger patients, in both the US and in Norway. The survival of THA is significantly better in Norway than in the US with a hazard ratio of 1.64 (p<
0.05). On the other hand, TKA had a better survival experience in the US than in Norway, with a hazard ratio of 0.55 (p<
0.05). This is the first study to evaluate the utility of Medicare as a source of THA and TKA survivorship data and to compare prosthesis outcomes in Medicare with those from Scandinavian arthroplasty registries. Unlike the Norwegian and Swedish registry data, the reasons for revision (e.g., femoral loosening) are not captured and thus greatly limited the value of the Medicare data as a tool to understand the need for revision, thereby helping to improve implant longevity and to reduce the associated cost and burden to the patient and care provider.
In this study we hypothesised that anxiety/depression, one of five dimensions in the health-related quality of life (HRQoL) measurement tool EQ-5D, could predict outcome after total hip replacement surgery. Pre-operative and one-year post-operative data from the Swedish Hip Arthroplasty Register, including 6158 patients with primary osteoarthritis of the hip, were analysed. In order to examine the association between anxiety and outcome with respect to pain and satisfaction an analysis of covariance was used. The pre-operative EQ-5D anxiety/depression dimension was a strong predictor for pain relief and patient satisfaction (p <
0.001). Orthopaedic surgeons involved in the care of patients eligible for total hip replacement surgery should be aware that mental health may influence post-operative pain and HRQoL. An appropriate assessment of mental health may enable a modification in the way these patients are managed in order to optimise the outcome after joint replacement surgery.
Periprosthetic fracture of the femur is an uncommon complication after total hip replacement, but appears to be increasing. We undertook a nationwide observational study to determine the risk factors for failure after treatment of these fractures, examining patient- and implant-related factors, the classification of the fractures and the outcome. Between 1979 and 2000, 1049 periprosthetic fractures of the femur were reported to the Swedish National Hip Arthroplasty Register. Of these, 245 had a further operation after failure of their initial management. Data were collected from the Register and hospital records. The material was analysed by the use of Poisson regression models. It was found that the risk of failure of treatment was reduced for Vancouver type B2 injuries (p = 0.0053) if revision of the implant was undertaken (p = 0.0033) or revision and open reduction and internal fixation (p = 0.0039) were performed. Fractures classified as Vancouver type B1 had a significantly higher risk of failure (p = 0.0001). The strongest negative factor was the use of a single plate for fixation (p = 0.001). The most common reasons for failure in this group were loosening of the femoral prosthesis, nonunion and re-fracture. It is probable that many fractures classified as Vancouver type B1 (n = 304), were in reality type B2 fractures with a loose stem which were not recognised. Plate fixation was inadequate in these cases. The difficulty in separating type B1 from type B2 fractures suggests that the prosthesis should be considered as loose until proven otherwise.
The purpose of this study was to compare the 2D and 3D linear and volume wear readings of the three most commonly used methods for measuring polyethylene wear: the Livermore, Devane and Martell techniques. Inter-observer variation of measurements using the techniques of Devane and of Martell on conventional radiographs was also performed. The radiographs of 80 patients (mean age 60+/−10 yrs) who had a Harris-Galante I total hip arthroplasty were measured. Nine different reviewers for the Devane technique readings including Dr Devane and eight reviewers for the Martell technique readings including Dr Martell made blinded independent wear observations for each radiograph set. One reviewer measured the 20 annual linear wear rate for all radiograph sets using the 2D Livermore technique. Inter-observer variation as a function of patient, reviewer, and total variation was statistically assessed using variance component analysis. Mean wear measured using the Livermore technique was the same as with the Devane and Martell method, but with a greater variation. Comparison of the Devane and Martell method for patient STD, reviewer STD, error STD (multiple reviews of same radiographs), total STD (randomly picked reviewer), mostly show a mean 50% lower STD with the Devane technique. Correlation (correlation coefficient of two randomly selected reviewers) is significantly better with the Devane technique.
So far 15 patients, (6 male and 9 females) with a median age of 55 years (range 42–62) have been evaluated in group 1 and 14 (9 male and 5 females) with a median age of 55 years (range 45–70) in group 2. The penetration of the femoral heads has so far been measured postoperatively (all hips supine), after 3 month (17 hips supine and standing) and after 6 month (11 hips supine and standing) using radiostereometry.
1-year follow-up on approximately 50% of the patients will be presented at the meeting.
We revised 24 consecutive hips with loosening of the femoral stem using impaction allograft and a cemented stem with an unpolished proximal surface. Repeated radiostereometric examinations for up to two years showed a slow rate of subsidence with a mean of 0.32 mm (−2.0 to +0.31). Fifteen cases followed for a further year showed the same mean subsidence after three years, indicating stabilisation. A tendency to retroversion of the stems was noted between the operation and the last follow-up. Retroversion was also recorded when displacement of the stem was studied in ten of the patients after two years. Repeated determination of bone mineral density showed an initial loss after six months, followed by recovery to the postoperative level at two years. Defects in the cement mantle and malalignment of the stem were often noted on postoperative radiographs, but did not correlate with the degrees of migration or displacement. After one year, increasing frequency of trabecular remodelling or resorption of the graft was observed in the greater trochanter and distal to the tip of the stem. Cortical repair was noted distally and medially (Gruen regions 3, 5 and 6). Migration of the stems was the lowest reported to date, which we attribute to the improved grafting technique and to the hardness of the graft.
We assessed 100 patients with a primary total hip replacement using the Harris hip score and the Nottingham Health Profile at one, three and five years after operation. They were derived from two prospective randomised series of cemented and uncemented replacements. Both scoring systems correlated highly and were each heavily influenced by the system of functional classification defined by Charnley. After five years both reflected the function of the implant and the general state of the patient. A higher degree of sensitivity is needed to show differences in the performance of an implant in the short and medium term. We do not yet have an ideal system of clinical assessment and the overall function must always be properly assessed.
We enrolled 98 patients (107 hips) with a mean age of 47 years (SD 8.6) into a prospective study of the Madreporic Lord THR; 34 hips had primary and 73 secondary osteoarthritis. After ten years, the survival rate using revision as the endpoint for failure was 70% (±9) for the cup and 98% (±0.3) for the stem. The combined clinical and radiological survival rates were 46% (±11) and 81% (±10), respectively. Osteoporosis due to stress-shielding was observed in the proximal femur. Hips with radiologically dense bone postoperatively showed the most pronounced bone loss. We recommend continued radiological follow-up of patients with this type of implant to allow revision to be performed before there is severe bony destruction of the pelvis.
