Hemispheric, porous-ingrowth revision acetabular components (generally with multiple screw fixation) have demonstrated versatility and durability over 25 years. Jumbo cups (minimum diameter of 62mm in women, 66mm in men, or 10mm larger than the normal contralateral acetabulum) are utilised in the majority of revisions with acetabular bone loss, with or without bone grafting, or other augmentation. The popularity of jumbo cups is due to their relative ease of use and the reliability of the result. With up to 20-year follow-up, and failure defined as cup revision for aseptic loosening or radiographic evidence of loosening, implant survival was 97.3% (95% confidence interval, 89.6% to 99.3%) at ten years and 82.8% (95% CI, 59% to 97.6%) at fifteen years. Twenty-year survivorship with 88% free from aseptic loosening of the metal acetabular component has been reported. Instability is decreased in association with larger diameter bearings. Revisions associated with wear of non-crosslinked polyethylene increased in the second decade. Crosslinked polyethylene and ultra-porous materials will likely increase both the durability and the utility of jumbo cups.

Loosening is generally the most common reason for revision TKA. In the AOA NJR, the rate of revision varies depending on fixation. Cemented fixation has a lower rate of revision than cementless fixation; 6.7% vs. 8.2% at 14 years. Loosening does occur more frequently in younger patients and in males. Tibial component loosening is the most common. There is an opportunity for improvement. More durable fixation can be achieved through improved cement technique, rather than going cementless.

De-bonding of the tibial baseplate from the cement is the mechanism of failure in up to 2.9% of total knee arthroplasties. Among seven surgeons at one center, there was a 6.4 fold range (0.7%-4.5%) in the occurrence of such loosening with the same prosthesis. This surgeon-related variability in tibial component de-bonding indicates that surgical technique influences loosening. In a laboratory study, earlier application of cement to metal increases bond strength (p<0.01) while later application reduces bond strength (p<0.05). Fat contamination of the tibial tray-cement interface reduces bond strength, but application of cement to the underside of the tibial tray prior to insertion substantially mitigates this (p<0.05).

Age is often used as a surrogate for activity. However, it has been demonstrated that BMI has a stronger correlation to post-operative activity than age. The fundamental exercise in choosing a bearing is maximizing the benefit-to-risk ratio. The following question should be addressed on a patient by patient basis: what available bearing is most likely to meet the needs of this patient, with an acceptable risk of revision surgery during their lifetime, is accepted in my community, and with a justifiable cost?

The risk of ceramic fracture is very low with Biolox® Delta, and that risk decreases with increasing head size. However, concerns of taper corrosion, not wear and osteolysis, have driven the increase in utilization of ceramic heads. More research is needed into the etiology of taper corrosion, especially surgeon variability in taper assembly.

Crosslinked polyethylene has substantially reduced wear, osteolysis, and revision rates compared to non-crosslinked polyethylene, regardless of the countersurface. In the AOA National Joint Replacement Registry, ceramic/ceramic, metal/XLPE, ceramic/XLPE, and ceramicised metal/XLPE are the most commonly used bearing surfaces. With 12–15 year follow-up, there is no difference in the cumulative percent revision of these four bearings in patients aged <55.

Ceramic heads are variably more expensive. The ability to recoup the increased cost of ceramic heads through a diminished lifetime revision cost is dependent on the price premium for ceramic and the age of the patient. A wholesale switch to ceramic bearings regardless of age or cost differential could result in an economic burden to the health system.

One measure of “standard” is simply “the most frequently used”. In this regard, market data alone makes the determination of “standard” without regard to clinical or economic outcomes. However, longer follow-up, including financial data, is necessary to better assess the relative value (benefit-to- risk ratio) of all the available bearing couples.

Both the patient and the surgeon want hip and knee arthroplasties to last a lifetime. As a result, many patients have been told to defer arthroplasty as long as possible. After arthroplasty, many patients have been advised to limit physical activity. Such management strategies prioritise longevity but compromise lifestyle. Given that the technical aspects of the arthroplasty are satisfactory, modern total hip and knee prostheses have demonstrated remarkable durability. Quantitative studies of patient activity have measured up to 48 million cycles in-vivo, with impact, without evidence of loosening, osteolysis, or other impending failure. These data suggest that with current technology, an active lifestyle is compatible with implant longevity.

Introduction

The benefits of femoral head-neck modularity in hip surgery have been recognized for decades. However, reports of head/neck taper fretting & corrosion has led to research being conducted, yet the clinical effect of these processes remains unclear. Whilst femoral head size, material and the characteristics of the taper have been a focus of research, potential contributing variables such as in vivo head-neck assembly technique on the performance of these connections is not clear. We performed an observational study to investigate variation in femoral head-neck taper assembly during surgery, with the initial focus being the number of head impactions.

Intentionally crosslinked polyethylene has improved the survivorship of total hip replacement and is the current standard bearing material for total hip arthroplasty. Regardless of the manufacturing method and counter-surface, the wear rates have been reduced on the order of 90% compared to historical materials, with a substantial reduction in the occurrence of osteolysis. Squeaking is not an issue. The wear of crosslinked polyethylene bearings has not shown the position sensitivity of hard-on-hard bearings. Liner fracture and dissociation have been reported, most commonly in association with malposition, and their occurrence has been decreased by improved modularity. Further, the consequences of a fractured polymeric bearing are substantially less than those of a fractured ceramic bearing. In most markets, there is a cost-differential favoring crosslinked polyethylene. A clinical advantage of ceramic-ceramic must be demonstrated, not theorised, before declaring it to be the new standard.

As a generic technology, intentionally crosslinked polyethylene has improved the durability of total hip replacement. Regardless of the manufacturing method, the wear rates have been reduced on the order of 90% compared to historical materials, with a substantial reduction in the occurrence of osteolysis. Most of the data is with 28 and 32 mm bearings. Larger diameter bearings have been shown to reduce the occurrence of dislocation. However, there is clinical evidence that volumetric wear is increased with larger diameter crosslinked polyethylene bearings, and this may increase the occurrence of osteolysis. Further, modular liner fracture is more likely with larger diameter bearings (thinner liners), which is generally associated with increased cup abduction angle and/or increased anteversion. Contemporary polymers are better than their predecessors, but there is always opportunity for improvement.

There are numerous benefits of femoral head/neck modularity in both primary and revision surgery. Taper corrosion necessitating revision surgery was recognised decades ago, and there are concerns that the incidence is increasing. Variables in design, manufacturing, biomechanics, and modular head assembly have all been implicated. While the incidence of clinically significant taper corrosion is unknown, the adverse local tissue reaction (ALTR) does not appear to occur absent a cobalt chromium interface.

The utilization of ceramic heads has increased in recent years. Domestically, more than 50% of femoral heads are now ceramic. This is due, at least in part, to a reduction in patient age at the time of surgery. A stronger influence, however, may be the concern for an adverse local tissue reaction (ALTR) due to taper corrosion with a cobalt chromium femoral head. Ceramic heads have a small risk of in-vivo fracture and cost more. Compared to cobalt chromium alloy, ceramic femoral heads wear less against UHMWPE, although the reduction may not be clinically significant when paired with a crosslinked polyethylene. In the Australian National Joint Replacement Registry, of the five bearing combinations with 14-year cumulative percent revision (CPR) data, the lowest is metal femoral heads with crosslinked polyethylene (5.4%).

In-vivo taper assembly technique is variable and can play a role in clinical success or failure, regardless of the head material: taper corrosion with cobalt chromium heads, or fracture of ceramic heads. Standardization of head-neck taper assembly is desirable.

There is increased awareness of the health benefits of regular exercise, and quantifying daily activity has become popular. Consequently, there are an increasing number of devices for measuring physical activity. Healthcare professionals and the general public should know the accuracy and limitations of these devices to better determine which ones suit their needs.

Ten devices were tested: one ankle-based device, StepWatch™ Activity Monitor (SAM); two wrist-based devices, FitBit Force™ and Nike+ Fuelband SE; seven waist-based devices, Omron HJ-321 Pedometer, Sportline 340 Strider Pedometer, FitBit One™, Samsung Galaxy S4 utilizing the two most popular applications (Runtastic and Noom Walk), and the iPhone 5 utilizing the two most popular applications (Runtastic and ARGUS). Thirty healthy volunteers, mean age 25.6 years (range 20–30) and mean body mass index 23.5 (range 17.3–29.0), completed the following protocol: (1) walk briskly around a 400-M track simulating community ambulation (2) jog around a 400-M track (3) walk slowly for 10-M, approximating household or workplace pace (4) ascend 10 steps, and (5) descend 10 steps. Each subject completed 3 trials for each task. Manual count was the gold standard (Champion Sports Tally Counter). Accuracy and mean percent error were calculated to demonstrate overall performance and any tendencies for over or undercounting. An Aggregate Accuracy Score was calculated using the mean accuracy of each activity and multiplying by a corresponding weighted value for a prototypical person: 400-M walk represents community ambulation, weighted 40%; 10-M walk represents household and workplace ambulation, weighted 30%; 400-M jog represents jogging or running, weighted 20%; Stair Ascent and Descent represent community and household stair use, weighted 5% each.

Device rank based on the Aggregate Accuracy Score was #1 FitBit One™ (98.0%), #2 Omron HJ-321 (97.0%), #3 StepWatch™ Activity Monitor (93.3%), #4 Runtastic Google App (92.7%), #5 Runtastic iPhone App (89.5%), #6 Fitbit Force™ (88.2%), #7 Argus iPhone App (87.2%), #8 Sportline 340 Strider (85.7%), #9 Nike Fuelband (76.1%), #10 Noom Walk Google App (75.9%). The FitBit One™ was 99.5%, 97.8%, 96.7%, 94.3%, and 96.9% accurate in the 400-M walk, 10-M walk, 400-M jog, 10 stair ascent, and 10 stair descent, respectively. The Omron HJ-321 was 99.3%, 94.9%, 97.9%, 92.2%, and 91.3% accurate, respectively. The SAM performed well (>95% accurate) in all activities except one, consistently undercounting the 400-M jog by about 25% (95% CI: −27.2% – −23.9%). The FitBit ForceTM and Nike+ Fuelband SE wrist devices were ≥90% accurate in the 400-M walk and 400-M jog, but ≤83% accurate for all other activities. Three of the 4 smartphone applications were >97% accurate in the 400-M walk, 1 of 4 was 97.3% accurate in the 400-M jog, but all devices performed poorly (≤90% accurate) for all other activities.

Smartphones are very popular, but current technology is less accurate for measuring overall daily activity. The relatively inexpensive FitBit One™ and Omron HJ-321 pedometer are highly accurate for quantifying a variety of activities, including running. The StepWatch™ Activity Monitor performs well in lower cadence, but consistently undercounted jogging. Wrist-based activity devices are not as accurate as waist-based. Next generation technologies, including smartphones, should undergo accuracy testing before recommending them for daily use.

Loosening is generally the most common reason for revision TKA. In the AOA NJR, the rate of revision varies depending on fixation. Cemented fixation has a lower rate of revision than cementless fixation; 6.7% vs. 8.2% at 14 years. Loosening does occur more frequently in younger patients and in males. Tibial component loosening is the most common. There is an opportunity for improvement. More durable fixation can be achieved through improved cement technique.

De-bonding of the tibial baseplate from the cement is the mechanism of failure in up to 2.9% of total knee prostheses. Among seven surgeons at one center, there was a 6.4-fold range (0.7%-4.5%) in the occurrence of such loosening with the same prosthesis. This surgeon-related variability in tibial component de-bonding suggests that surgical technique influences loosening rates. In a laboratory study, earlier application of cement to metal increases bond strength (p<0.01) while later application reduces bond strength (p<0.05). Fat contamination of the tibial tray-cement interface reduces bond strength, but application of cement to the underside of the tibial tray prior to insertion substantially mitigates this (p<0.05).

Both the patient and the surgeon want hip and knee arthroplasties to last a lifetime. As a result, many patients have been told to defer arthroplasty as long as possible. After arthroplasty, many patients have been advised to limit physical activity. Such management strategies prioritise longevity but compromise lifestyle. Given that the technical aspects of the arthroplasty are satisfactory, modern total hip and knee prostheses have demonstrated remarkable durability. Quantitative studies of patient activity have measured up to 48 million cycles in vivo, with impact, without evidence of loosening, osteolysis, or other impending failure. These data suggest that with current technology, an active lifestyle is compatible with implant longevity.

Patients, and their femurs, come in all shapes, sizes, and types. Fortunately, so do cementless femoral stems! A simple approach is to separately consider A) the part inside the bone and B) the part outside the bone. The inner-cortical geometry (Dorr type), bone density, and presence of any deformity, influence selection of stem shape, length, and extent of ingrowth surface (the part inside the bone). Restoration of limb length and offset is a function of the neck angle and length (the part outside the bone). Clinical data indicates that undersizing of cementless stems increases the risk of revision for aseptic loosening while restoration of limb length and offset favorably affects patient satisfaction and function.

As a generic technology, intentionally cross-linked polyethylene has improved the durability of total hip replacement. Regardless of the manufacturing method, the wear rates have been reduced on the order of 90% compared to historical materials, with a substantial reduction in the occurrence of osteolysis. Most of the data is with 28mm and 32mm bearings. Larger diameter bearings have been shown to reduce the occurrence of dislocation. However, there is clinical evidence that volumetric wear is increased with larger diameter cross-linked polyethylene bearings, and this may increase the occurrence of osteolysis. Further, modular liner fracture is more likely with larger diameter bearings (thinner liners), which is generally associated with increased cup abduction angle and/or increased anteversion. Contemporary polymers are better than their predecessors, but there is always opportunity for improvement.

Outcomes in arthroplasty have 3 general sources of variability: the patient, the prosthesis, and the medical-surgical-rehab. services. There are numerous factors that can contribute to earlier-than-usual clinical failure of a TKA (failure = need for revision). There are intense debates regarding design and material factors. There are technical factors such as misalignment, soft tissue imbalance, and inadequate fixation. The greatest source of variability in the outcome equation is, however, the patient.

In cohort studies, the amount and type of patient activity influences the longevity of TKA. Quantitative studies have demonstrated >45-fold variation in the number of steps per day. Semi-quantitative data and survey studies show variability in the types of recreational activities and in the intensity. Age is often used as a surrogate, but BMI has a better correlation with activity than age. There is no formula, however, that can predict the longevity of an arthroplasty in a specific patient. For this reason, activity recommendations following arthroplasty continue to be debated. Which do you prioritise; lifestyle or longevity? More importantly, which does the patient prioritise?

Hemispheric, porous-ingrowth revision acetabular components (generally with multiple screw fixation) have demonstrated versatility and durability over 25 years. Jumbo cups (minimum diameter of 62mm in women, 66mm in men, or 10mm larger than the normal contra-lateral acetabulum) are utilised in the majority of revisions with acetabular bone loss, with or without bone grafting, or other augmentation. The popularity of jumbo cups is due to their relative ease of use and the reliability of the result. With up to 20 year follow-up, and failure defined as cup revision for aseptic loosening or radiographic evidence of loosening, implant survival was 97.3% (95% confidence interval [CI], 89.6% to 99.3%) at ten years and 82.8% (95% CI, 59% to 97.6%) at fifteen years. Instability is decreased in association with larger diameter bearings. Revisions associated with wear of non-crosslinked polyethylene increased in the second decade. Crosslinked polyethylene and ultra-porous materials will likely increase both the durability and the utility of jumbo cups.

In the Registry Era, in the Information Age, and with a competitive and expanding marketplace, the focus has been on the prosthetic joint devices. However, a distinction should be made between mechanical failure of a device, failure of an arthroplasty, and the limitations of technology. The patient and the surgeon play central roles in the majority of revisions (failure of an arthroplasty). Analysis of a large United States database indicates that the most common causes of revision are instability/dislocation (22.5%), mechanical loosening (19.7%), and infection (14.8%). Acetabular component position has been linked to higher wear and instability. Increased odds of component mal-position were found with lower-volume surgeons and patients with a higher body mass index. Medical co-morbidities significantly increase the risk for revision within 12 months of surgery. Patient demographics and pre-operative status have been shown to be more important than implant factors in predicting the presence of thigh pain, dissatisfaction, and a low hip score. The most predictive factors were ethnicity, educational level, poverty level, income, and a low pre-operative WOMAC score or pre-operative SF-12 mental component score.

The elements of my routine pre-operative planning include skin and scar assessment, the limb length (physical exam and radiographic assessments), the socket type, the stem type, and radiographic templating. Blood management is rarely an issue for primary total hips today and I generally do not recommend pre-operative autologous donation. I currently use a low molecular weight heparin for venous thromboembolic prophylaxis for most all patients. All of my patients have pre-operative medical clearance from a hospital intensivist.

A press-fit modular cementless socket is my “workhorse”, although I occasionally use supplemental fixation with spikes (low bone density) or screws (shallow or otherwise deficient hemisphere). Cemented fixation is reserved for hips with radiation necrosis. I use a dual-offset tapered cementless stem in most cases but will use a modular stem in dysplastic, post-traumatic, or severely osteoporotic femurs.

I template every case. My goals are to determine component sizes - “the part inside the bone” and improve the biomechanics of the hip – “the part outside the bone”. Sizing is relatively straightforward. For the socket, I use the teardrop and the superior bony edge as landmarks for size and position. I use a Johnson's lateral view radiograph to assess socket version and anterior osteophytes. With a tapered stem, proximal fit on the AP radiograph is the goal and the stem does not need to be canal filling. For the neck resection, I reference off the lesser trochanter.

Medialisation of the hip center of rotation (COR) decreases the moment arm for body weight; increasing the femoral off-set lengthens the lever arm for the abductor muscles. These changes in hip biomechanics have a double benefit: a reduction in required abductor forces and lower joint reaction forces. There is accumulating clinical evidence that such favorable alterations in biomechanics can improve clinical outcomes and reduce wear. Higher femoral offset has been associated with greater hip abduction motion and abductor muscle strength. In two independent studies, higher femoral offset has been associated with a significant reduction in polyethylene wear.

The traditional arthroplasty goal has been to re-create the offset of the operated hip. In an analysis of 41 patients with one arthritic hip and one clinically and radiographically normal hip (Rolfe et al., 2006 ORS), we found that the horizontal femoral offset of the arthritic hip was, on average, 6mm less than that of the normal, contralateral hip. Considering this, and with medialisation of the COR, is it reasonable to make the femoral offset a few millimeters greater than that pre-op. With modular trial components, final offset and limb-length adjustments are made intra-operatively by assessing soft tissue tension, joint stability and range of motion.

Applying these principles in a consecutive series of 40 hips, the hip center of rotation was medialised by 5.6mm and the horizontal femoral offset was increased by an average of 9.5mm, being larger than the normal, contralateral hip by an average of 5.2mm. This combination increased the net biomechanical advantage (NBA) of the diseased hip to an average of 12.5% more than the normal, contralateral hip. The increase in femoral offset is compensated for by medialising the center of rotation. The average lateralisation of the proximal femur of 3.9mm did not cause trochanteric bursitis or other pain. When the offset is right, soft tissue tension can be maintained without over-lengthening. In this series, 2.9mm average lengthening resulted in the reconstructed limb being an average of 1.1mm shorter than the normal side.

Hemispheric, porous-ingrowth revision acetabular components (generally with multiple screw fixation) have demonstrated versatility and durability over 25 years. Jumbo cups (minimum diameter of 62mm in women, 66mm in men, or 10mm larger than the normal contra-lateral acetabulum) are utilised in the majority of revisions with acetabular bone loss, with or without bone grafting, or other augmentation. The popularity of jumbo cups is due to their relative ease of use and the reliability of the result. With up to 20 year follow-up, and failure defined as cup revision for aseptic loosening or radiographic evidence of loosening, implant survival was 97.3% (95% confidence interval [CI], 89.6% to 99.3%) at ten years and 82.8% (95% CI, 59% to 97.6%) at fifteen years. Instability is decreased in association with larger diameter bearings. Revisions associated with wear of non-crosslinked polyethylene increased in the second decade. Cross-linked polyethylene and ultra-porous materials will likely increase both the durability and the utility of jumbo cups.

Questions/purposes:

What factors influence tibial tray-cement interface bond strength? We developed a laboratory model to investigate this issue with the goal of providing technical recommendations to mitigate the risk of tibial tray-cement loosening.

Adverse local tissue reactions (ALTR), such as so-called pseudotumours associated with metal-metal bearings, can also occur secondary to corrosion products from modular tapers where at least one side is composed of cobalt alloy. In 1988, Svensson et al. reported a fulminant soft-tissue pseudotumour following a cementless, metal-on-polyethylene total hip. This case had all of the features of ALTR that were subsequently observed in association with contemporary large diameter metal-metal bearings, having the same histological characteristics that Willert and colleagues termed ALVAL in 2005.

There is a documented increased risk of femoral taper corrosion in association with larger diameter (>32 mm) metal-metal bearings. There may be a generic increase in the risk of taper corrosion with larger diameter bearings, regardless of acetabular bearing type. Other variables include the design and manufacturing tolerances of the taper and head, the stiffness of the neck, implantation time, and possibly in vivo assembly. Head and neck moment arm and neck length have not been demonstrated to be independent risk factors for taper corrosion or fretting. Retrieval analyses indicate that fretting and corrosion tend to be higher on the head than on the stem. ALTR has similarly been described in association with corrosion of the modular neck-stem junction. Taper corrosion is the probable explanation for elevated ion levels and ALTR in association with well-positioned metal-metal total hip bearings and low bearing wear. Whole blood or serum metal levels are elevated with a greater elevation of cobalt compared to chromium. Ion analyses are now relatively accessible and reliable and should be obtained in the evaluation of a painful total hip without an obvious cause. Cross-sectional imaging, such as a MARS MRI scan, can demonstrate associated changes in the periprosthetic tissues and secure the diagnosis.

Treatment recommendations are similar to those established for hips with metal-metal bearings and ALTR. Removal of the modular cobalt alloy head and/or neck component is recommended. At this time, there are no established criteria for the degree of “acceptable” femoral taper damage. The dilemma faced by the revising surgeon is whether to expose the patient to the potential morbidity associated with revision of a well-fixed femoral stem, particularly a distally-fixed, extensively porous-coated stem, in the setting of mild-to-moderate fretting and corrosion of the femoral taper. Several manufacturers offer ceramic heads with a titanium alloy taper sleeve inside the head specifically for mating to previously used femoral tapers. It is not recommended to put a ceramic head taper directly onto a used femoral taper. Surface damage of the used femoral taper can create high localised stresses in the ceramic head and predispose to head fracture. The same principles can be applied to corrosion of a stem-neck taper. If the modular neck is made of cobalt alloy, it is preferable to exchange it for one made of titanium alloy (if available). Again, there are no established criteria for the degree of “acceptable” femoral taper damage. The paucity of reported experience with such revisions inhibits further comment at this time.

It is prudent to be suspicious of “taperosis” considering that the majority of heads used over the past 5 years are cobalt alloy and >36 mm in diameter, many contemporary stems have narrower, and hence more flexible necks, some tapers are smaller (shorter), more variable in vivo assembly secondary to “minimally invasive” surgical techniques, and the risk of taper corrosion increases with time in situ. Additional studies are needed to determine the incidence of clinically significant taper corrosion. There are more than 30 different head-stem tapers worldwide and the incidence of clinically significant taper corrosion is likely variable for different head-stem combinations. Similar to ALTR that occur with metal-metal bearings, some cases of ALTR secondary to taper corrosion may be asymptomatic.