The role of nuclear medicine techniques in differentiation between septic and aseptic loosening of total hip and knee arthroplasty

Jansen JA, Smit F, Pereira Arias-Bouda LM. The role of nuclear medicine techniques in differentiation between septic and aseptic loosening of total hip and knee arthroplasty. This article gives an overview of nuclear imaging techniques, which can be used to diagnose (a)septic loosening in joint replacements. The pathophysiology of loosening and the differences between septic and aseptic loosening with its therapeutical consequences are discussed. An overview is given of the advantages and limitations of frequently used techniques as triple-phase bone scanning and white blood cell scintigraphy. The additional value of SPECT/CT and the possible role of FDG PET/CT in the diagnosis of prosthetic joint infection is discussed. Tijdschr Nucl Geneesk 2012; 34(4):988-994 Introduction A growing number of total hip and knee replacements are performed annually with a very good outcome in the majority of cases giving relief of arthritic pain and improved function. In some patients though complications occur of which loosening and infection are the most common (1-3). The reason for approximately seventy percent of all reoperations in joint arthroplasty is loosening of the prosthesis. Symptoms of loosening are usually quite nonspecific with persistent pain at the arthroplasty site especially on weight bearing, and reduced mobility of the patient and the prosthesis (3,4). When prosthetic loosening is caused by infection it is classified as septic loosening, and in case of aseptic loosening it will be due to wear of the bearing surfaces (figure 1). Infections occur in 2 to 3 percent of all primary joint replacements, and in 5 to 8 percent of revision joint replacement patients (5,6). About one third of the infections are directly post-operative, about one third are early infections within a year, and about one third are late infections more than one year after surgery (7). Infections are frequently caused by staphylococci from the skin, which can cause fulminant infections with purulent discharge from the operation wound in the early stage. Late onset and low grade infections usually have less specific infective signs though, but can also cause loosening on long term as well. It can be very difficult to distinguish between septic and aseptic loosening, as both may be accompanied by similar symptoms (8). Recent improvements in tribology of bearing surfaces and prosthetic coatings have influenced the incidence of aseptic prosthetic loosening. The highly cross-linking of polyethylene inserts in acetabular cups and knee liners has diminished wear and occurrence of small particle disease. The crosslinking process has improved wear resistance of polyethylene liners without impairment of other significant material properties (9). Also through hydroxyapetite coating or plasmaporous spraying of femoral and tibial prosthetic stems bony ingrowth and early stabilization of implants can be stimulated. As an alternative to standard cobalt-chrome on polyethylene bearings also aluminium oxide ceramic bearings have been developed in order to improve performance and longevity. Alumina ceramic is entirely biostable and bioinert material with good mechanical properties. Through more precise manufacturing and contact surface geometry the fracture risk of the ceramic heads and liners has been reduced, but squeaking still remains a concern in ceramic-on-ceramic bearings (10). More recently metal-on-metal bearings have received a lot of media attention. Although these hard-on-hard FIGURES AND TABLES Jansen et al. Figure 1. Pictures of retrievals showing wear of the bearing surfaces of total hip (A) and total knee (B) prosthesis, causing wear and small particle disease that can lead to aseptic loosening. A B Figure 1. Pictures of retrievals showing wear of the bearing surfaces of total hip (A) and to al kne (B) pros hesis, causing wear and small particle disease that can lead to aseptic loosening.