Fracture of the acetabulum can result in damage to the articular surface that ranges from minimal to catastrophic. Hip arthroplasty may be required for more severe injuries due to marked articular surface damage, post traumatic degenerative changes, persistent malunion or nonunion, or occasionally avascular necrosis and destruction of the femoral head. These problems may be seen following both closed and open fracture treatment, but prior open reduction and internal fixation often makes subsequent THA more difficult due to soft tissue scarring and retained hardware. In select acute acetabular fracture cases with severe initial comminution of the joint, open reduction and fixation can be technically impossible or so clearly destined to early failure that initial fracture treatment with combined limited fixation and simultaneous THA is the best option, especially in osteoporotic elderly fracture patients.

Problems which may be encountered during any THA in a patient with a prior acetabular fracture include: difficult exposure due to soft tissue defects and scarring, presence of heterotopic ossification, and nerve palsy from the original fracture or subsequent osteosynthesis. Retained hardware can present significant challenges and frequently is left in place or removed in part or completely, when intraarticular in location or blocking preparation of the acetabular cavity and placement of the cup. Additional potential problems include residual deformity and malunion, persistent pelvic dissociation or nonunion of fracture fragments, cavitary or segmental bone loss from displaced or resorbed bone fragments, and occasionally occult deep infection.

Preoperative assessment and planning should include careful consideration of the most appropriate surgical approach, which may be impacted by the need for hardware removal. Screening laboratory studies and aspiration of the hip may prove helpful in excluding associated deep infection. Intraoperative sciatic nerve monitoring may be of assistance in patients with partial residual nerve deficits or where extensive posterior exposure and mobilization of the sciatic nerve is needed for hardware removal or excision of heterotopic ossification. Metal cutting tools to allow partial removal of long plates and adjunctive equipment for removal of broken or stripped screws should be routinely available during these cases. Careful preoperative planning regarding implant and reconstructive options can also ensure availability of proper components and equipment. Often implants and techniques developed for revision surgery for management of major bone deficiencies are needed.

Reported results suggest that surgery is frequently prolonged, can be associated with greater blood loss and may result in increased risk of post-arthroplasty heterotopic ossification when compared to routine primary procedures. Bone stock and fracture union may be better in patients with prior internal fixation than in those with nonoperative treatment of major displaced acetabular fractures. Available long-term results document more durable results with lower rates of aseptic loosening with uncemented acetabular fixation compared to cemented acetabular components. These patients are at higher risk of revision and failure than patients undergoing THA for simple osteoarthritis, though initial short-term results are comparable to conventional hip arthroplasty patients, as long as early wound healing problems and deep infection can be avoided, which is a greater risk for acute THA for initial fracture care. The application of newer implant designs, highly porous ingrowth materials, and methods for management of acetabular bone deficiency developed for revision THA have helped improve results in this challenging subset of primary THA patients.

Total knee replacement is one of the most successful procedures in orthopaedic surgery. Although originally limited to more elderly and less active individuals, the inclusion criteria have changed, with ever younger, more active and heavier patients receiving TKA. Currently, wear debris related osteolysis and associated prosthetic loosening are major modes of failure for TKA implants of all designs.

Initially, tibial components were cemented all polyethylene monoblock constructs. Subsequent long-term follow-up studies of these implants have demonstrated excellent durability in survivorship studies out to twenty years. Aseptic loosening of the tibial component was one of the main causes of failure in these implants. Polyethylene wear with osteolysis around well fixed implants was rarely (if ever) observed. Cemented metal-backed nonmodular tibial components were subsequently introduced to allow for improved tibial load distribution and to protect osteoporotic bone. Long-term studies have established that many one-piece nonmodular tibial components have maintained excellent durability. Eventually, modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-80s mainly to facilitate screw fixation for cementless implants. These designs also provided intraoperative versatility by allowing interchange of various polyethylene thicknesses, and also aided the addition of stems and wedges. Since the late 1980's, the phenomena of polyethylene wear and osteolysis have been observed much more frequently when compared with earlier eras. The reasons for this increased prevalence of synovitis, progressive osteolysis, and severe polyethylene wear remain unclear, but there is no question that it was associated with the widespread use of both cementless and cemented modular tibial designs.

Mayo Data: Modular versus All Polyethylene Tibial Components in Primary TKA

The study population included 10,601 adult (>18 years) patients with 14,524 primary TKA procedures performed at our institution between 1/1/1988 and 12/31/2005. Mean age was 68.7 years and 55% were female. Overall revision rates and revisions for loosening, wear/osteolysis were compared across different designs using Cox proportional hazards regression models adjusting for age, sex, calendar year and body mass index (BMI). Over an average 9 years follow-up, a total of 865 revisions, including 252 tibia revisions were performed, corresponding to overall survival of 89% (Confidence intervals (CI): 88%, 90%) at 15 years. In comparison to metal modular designs, risk of tibial revision was significantly lower with all-poly tibias (HR 0.3, 95% CI: 0.2, 0.5). Overall, posterior cruciate-retaining (CR) designs performed better than the posterior-stabilised (PS) designs (p=0.002). With any revision as the endpoint, there were no significant differences across the 18 designs examined. Similarly, there were no significant differences across the 18 designs when we considered revisions for aseptic loosening, wear, osteolysis. Among patient characteristics, male gender, younger age, higher BMI were all significantly associated with higher risk of revisions (p<0.008).

Summary: Available data support the use of nonmodular tibial designs in TKA in order to prevent or reduce the chance of backside wear, third body particles from resulting metallic debris and associated polyethylene induced osteolysis. In all patients, (not just older individuals) use of an all polyethylene tibial component is an attractive and more cost effective alternative, and is associated with the best survivorship and lowest risk of revision.

Total knee replacement is one of the most successful procedures in orthopaedic surgery. Although originally limited to more elderly and less active individuals, the inclusion criteria for TKA have changed, with ever younger, more active and heavier patients receiving TKA. Initially, tibial components were cemented all polyethylene monoblock constructs. Subsequent long-term follow-up studies of these implants have demonstrated excellent durability in survivorship studies out to twenty years. Aseptic loosening of the tibial component was one of the main causes of failure in these implants. Polyethylene wear with osteolysis around well fixed implants was rarely (if ever) observed. Cemented metal-backed nonmodular tibial components were subsequently introduced to allow for improved tibial load distribution and to protect osteoporotic bone. Long-term studies have established that many one-piece nonmodular tibial components have maintained excellent durability.

Eventually, modularity between the polyethylene tibial component and the metal-backed tray was introduced in the mid-80s mainly to facilitate screw fixation for cementless implants. These designs also provided intraoperative versatility by allowing interchange of various polyethylene thicknesses, and to also aided the addition of stems and wedges. Other advantages included the reduction of inventory, and the potential for isolated tibial polyethylene exchanges as a simpler revision procedure. However several studies have documented the high failure rate of isolated polyethylene exchange procedures, probably because technical problems related to the original components are left uncorrected. Since the late 1980's, the phenomena of polyethylene wear and osteolysis has been observed much more frequently when compared with earlier eras. The reasons for this increased prevalence of synovitis, progressive osteolysis, and severe polyethylene wear remain unclear, but there is no question that it was associated with the widespread use of both cementless and cemented modular tibial designs.

Mayo Data: Modular versus All Polyethylene Tibial Components in Primary TKA. The study population included 10,601 adult (>18 years) patients with 14,524 primary TKA procedures performed at our institution between 1/1/1988 and 12/31/2005. Mean age was 68.7 years and 55% were female. Overall revision rates and revisions for loosening, wear/osteolysis were compared across different designs using Cox proportional hazards regression models adjusting for age, sex, calendar year and body mass index (BMI). Over an average 9 years follow-up, a total of 865 revisions, including 252 tibia revisions were performed, corresponding to overall survival of 89% (Confidence intervals (CI): 88%, 90%) at 15 years. In comparison to metal modular designs, risk of tibial revision was significantly lower with all-poly tibias (HR 0.3, 95% CI: 0.2, 0.5). Overall, posterior cruciate-retaining (CR) designs performed better than the posterior-stabilised (PS) designs (p=0.002). With any revision as the endpoint, there were no significant differences across the 18 designs examined. Similarly, there were no significant differences across the 18 designs when we considered revisions for aseptic loosening, wear, osteolysis. Among patient characteristics, male gender, younger age, higher BMI were all significantly associated with higher risk of revisions (p<0.008).

Available data support the use of nonmodular tibial designs in TKA in order to prevent or reduce the chance of backside wear, third body particles from resulting metallic debris and associated polyethylene induced osteolysis. In most patients, but particularly in older patients use of an all polyethylene tibial component is not only more cost effective, but is associated with the best survivorship and lowest risk of revision.

Over the past 40 years information from large institutional total joint registries have aided in patient clinical care and follow-up efforts, have helped drive improvements in clinical practice, and have been a powerful tool for generating research studies on large well documented populations of patients. Still, these efforts are limited in that they are expensive, usually reflect a single institutional experience, and results can be biased by the larger volumes or experience at the typically large academic centers which have such registries in place.

National registry efforts in other countries including Scandinavia, Australia, and the UK have resulted in improved outcomes and a decreased number of revision procedures by a combination of early identification and withdrawal of poorly performing implants, altered surgical techniques, implant choices and behaviors by surgeons, changes in practices by hospitals, and modification in requirements and incentives by payors and regulatory agencies.

The American Joint Replacement Registry (AJRR) is a collaborative multi-stakeholder, independent, not-for-profit 501 c3 organisation established in 2009 for data collection and quality improvement initiatives relating to total hip and knee arthroplasty. AJRR is a national registry effort with the goal of enrolling more than 90% of the over 5,000 hospitals performing nearly 1 million hip and knee arthroplasties each year in the US. AJRR is supported by contributions from the American Academy of Orthopedic Surgeons (AAOS), the American Association of Hip and Knee Surgeons (AAHKS), the Hip Society, the Knee Society, Health Insurers, Medical Device Manufacturers, and individual orthopaedic surgeons via designated contributions through the Orthopedic Research and Education Foundation (OREF).

The overarching goal of AJRR is to improve arthroplasty care for patients through the collection and sharing of data on all primary and revision total joint replacement procedures in the U.S. The mission of the registry is to enhance patient safety, and improve the value of arthroplasty care. This will be accomplished by providing national benchmarks for implant, surgeon and hospital performance which serves to modify behaviors thereby decreasing the revision burden, improving outcomes and reducing costs.

From the time of incorporation in 2009 up to October 2013 the AJRR has secured the participation of 218 hospitals in 47 different states in the formal enrollment process, and have level one data submission from more than 100 institutions on over 63,000 hip and knee procedures.

In addition to publicly available annual reports, confidential specific individual reports for hospitals, surgeons and manufacturers will be available by subscription with an option for future confidential online direct data queries by an individual or entity regarding their own individual performance compared to national benchmark values.

In summary, registry studies have provided a rich source of information for improving arthroplasty care over the past four decades, with the emergence and increasing interaction of national registries a major factor in current efforts to increase both the quality and value of the health care of entire populations. The development, support and continued expansion of a national registry in the US must remain a central focus if we wish to improve as much as possible the arthroplasty care provided to all patients in our country.

The amount of bone loss due to implant failure, loosening, or osteolysis can vary greatly and can have a major impact on reconstructive options during revision total knee arthroplasty. Massive bone loss can threaten ligamentous attachments in the vicinity of the knee and may require use of components with additional constraint to compensate for associated ligamentous instability. Classification of bone defects can be helpful in predicting the complexity of the reconstruction required and in facilitating preoperative planning and implant selection. One very helpful classification of bone loss associated with TKA is the Anderson Orthopaedic Research Institute (AORI) Bone Defect Classification System. This system provides the means to compare the location and extent of femoral and tibial bone loss encountered during revision surgery. In general, the higher grade defects (Type IIb or III) on both the femoral and tibial sides are more likely to require stemmed components, and may require the use of either structural graft or large augments to restore support for currently available modular revision components. Custom prostheses were previously utilised for massive defects of this sort, but more recently have been supplanted by revision TKA component systems with or without special metal augments or structural allograft.

Options for bone defect management are as follows: 1) fill with cement, 2) fill with cement supplemented by screws or K-wires, 3) Morsellised bone grafting (for smaller, especially contained cavitary defects), 4) Small segment structural bone graft, 5) Impaction grafting, 6) Large prosthetic augments (cones), 7) Massive structural allograft-prosthetic composites (APC), 8) Custom implants.

It is very helpful for revision surgeons to have a variety of reconstructive options available, even despite a well thought-out preoperative plan. Preoperative planning is important but the plan that results may require alteration during the course of the surgery to accommodate bone defects which are either less or more severe than thought pre-operatively, and to adjust to variable quality and extent of host bone remaining, as this provides the mechanical platform for the reconstruction. Maximising support on intact host bone is a fundamental principle to successful reconstruction and frequently requires extending fixation to the adjacent diaphysis.

Bone defect management during revision total knee arthroplasty can provide a wide range of challenges from relatively trivial problems with small defects manageable with cement or small amounts of cancellous graft to massive deficiencies that may defy reconstruction except with allograft prosthetic components or large segmental replacing tumor-type implants. The more common Type II deficiencies increasingly seen in the context of particulate driven osteolysis demand a wide range of implant and bone graft options so that an individualised reconstruction can be accomplished for that particular patient based on bone defect size, location, quality of bone remaining, ligamentous status, and anticipated patient demands.

Introduction

Recurrent instability after total hip arthroplasty remains a serious and somewhat frequent problem. Constrained implants have proven effective to manage instability. This has led to a liberal utilization of these devices. However, sporadic mechanical failures have been reported. This report analyzes the failures of a single constrained device at our institution.