Removal of well-fixed cementless metal-backed patellar components

Cementless Total Knee Arthroplasty: Is it Safe in Demineralized Bone?

There is concern for cementless total knee arthroplasty (TKA) in patients with decreased bone mineral density (BMD) due to the potential increase in complications, namely failed in-growth or future aseptic loosening. Some data suggest that advances in cementless prostheses mitigate these risks; however this is not yet born out in long-term registry data. It is crucial to expand our understanding of the prevalence and etiology of osteoporosis in TKA patients, survivorship of cementless implants in decreased BMD, role of bone-modifying agents, indications and technical considerations for cementless TKA in patients with decreased BMD. The purpose of this study is to review current literature and expert opinion on such topics.

The Evolution, Current Indications and Outcomes of Cementless Total Knee Arthroplasty

Total knee arthroplasty (TKA) has been performed by orthopedic surgeons for decades, but the cementless TKA has only recently gained much interest in the world of arthroplasty. Initially, early designs had multiple complications, particularly with aseptic loosening due to osteolysis and micromotion. However, modifications have shown good outcomes and excellent survivorship. Over the last several decades, changes in implant designs as well as implant materials/coatings have helped with bone in growth and stability. Furthermore, surgeons have been performing TKA in younger and more obese patients as these populations have been increasing. Good results from the cementless TKA compared to cemented TKA may be a better option in these more challenging populations, as several studies have shown greater survivorship in patients that are younger and have a greater BMI. Additionally, a cementless TKA may be more cost effective, which remains a concern in today's healthcare environment. Overall, cemented and cementless TKA have great results in modern times and there is still a debate as to which implant is superior.

How to address the patella in revision total knee arthroplasty

Patellar issues need to be carefully addressed during any revision TKA and the surgeon often faces the question of what to do with the patella at the time of revision. The choice of treatment is often made by balancing what is technically feasible with the risk of potential complications and takes into account the reason for the revision, the type of implant (i.e., metal-backing or all-polyethylene), the duration of implantation, the fixation, the stability, the sterilization technique, the wear, the presence of osteolysis, the compatibility with the femoral component, and most importantly the remaining bone stock. The various treatment options then include retention of the patellar component, revision of the patellar component, removal of the component with retention of the patellar bony shell (patelloplasty or resection arthroplasty), excision of the patella (partial or total patellectomy), secondary resurfacing, and reconstruction/augmentation of the patellar bone stock. Isolated patellar revision is associated with a high complication rate and recurrent failure when poor patellar tracking, incongruent designs and malalignment of the femoral and tibial components exist. Retention of a well-fixed all-PE (non-oxidized) patella is advocated where possible and revision of metal-backed patella is recommended (unless well fixed with poor bone stock). In the situation of a deficient patella, patelloplasty, augmentation procedures and very rarely patellectomy are other viable options.

Management of the deficient patella in revision total knee arthroplasty

There are a number of options available to manage the patella when revising a failed total knee arthroplasty. If the previous patellar component is well-fixed, undamaged, not worn, and compatible with the femoral revision component, then it can be retained. When a patellar component necessitates revision and is removed with adequate remaining patellar bone stock, an onlay-type all-polyethylene cemented implant can be used. Management of the patella with severe bony deficiency remains controversial. Treatment options for the severely deficient patella include the use of a cemented all-polyethylene biconvex patellar prosthesis, patellar bone grafting and augmentation, patellar resection arthroplasty (patelloplasty), performing a gull-wing osteotomy, patellectomy, or the use of newer technology such as a tantalum (trabecular metal) patellar prosthesis. Severe patellar bone deficiency is a challenging situation because restoration of the extensor mechanism, proper patellar tracking, and satisfactory anatomic relationships with the femoral and tibial components are critical for an optimal clinical outcome.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

A stepwise approach to revision total knee arthroplasty

Successful revision total knee arthroplasty requires detailed preoperative planning and then a meticulous, stepwise execution of the predetermined plan. Critical factors in revision total knee arthroplasty include the choice of skin incision, type of surgical approach, and component removal without removal of substantial additional bone. The surgeon must then assess the degree of bone loss and ligamentous stability and the position of the current joint line, and then determine the type of bone graft, prosthetic components, and fixation methods required to correct the intraoperative deficiencies. Accurate restoration of flexion-extension gap balance is imperative to ensure long-term successful results.

Removing well-fixed total knee arthroplasty implants

Revision total knee arthroplasty requires the removal of one or all of the prior knee components. Thoughtful and careful removal of well-fixed total knee components can preserve host bone stock and facilitate subsequent reconstructive efforts. The tools and techniques for knee component removal include simple osteotomes, saws, extraction devices, ultrasonic devices, and frequently a combination of some or all of the above. It is the unique nature of each revision arthroplasty, which presents the surgeon with such challenge. Each of the techniques discussed in this review reflects the anecdotal experience acquired in over 800 revision total knee arthroplasties performed at our center. We review our empiric bias regarding the individual applicability of these techniques.

LEVEL OF EVIDENCE

Therapeutic studies, Level V (expert opinion). See Guidelines for Authors for a complete description of Levels of Evidence.

Removal of solidly fixed implants during revision hip and knee arthroplasty

The removal of solidly fixed implants during revision hip and knee arthroplasty is a technically challenging procedure with the potential for a large amount of bone loss during component removal. This bone loss may compromise the subsequent reconstruction. Careful preoperative planning is essential before undertaking removal of solidly fixed implants. The surgeon should determine the type and size of the implants and be familiar with any specialized removal equipment that may be available. For both the hip and knee, extensive exposure is often necessary. Removal of a well-fixed femoral component often requires an extended trochanteric osteotomy. The most difficult component to remove from the knee is a well-fixed cementless patellar component. The primary goal in removing well-fixed components is to minimize loss of surrounding bone, which requires effective planning and often access to specialized tools and techniques.

Treatment of an intraoperative patellar fracture during revision total knee arthroplasty

An intraoperative vertical patellar fracture occurred through a central osteolytic defect during removal of a metal-backed patellar component. The fracture was treated successfully with cerclage wire fixation and implantation of a cemented patellar component.