Failure of a metal on metal hip prosthesis presenting as a destructive soft tissue mass due to ALVAL.

We would like to draw attention to the relatively new concept of ALVAL prosthetic failure, illustrated by the following clinical case. Whilst currently very topical and familiar to orthopaedic surgeons, it may not be as familiar to rheumatologists. A 58-year-old woman underwent a successful resurfacing procedure of the right hip in September 2003. She underwent a similar procedure for the left hip in April 2007. At the time of this surgery, a dislocation of the right prosthesis occurred which hampered recovery. She presented to A and E in April 2009 with difficulty weight bearing and painful movements of the right hip. She was apyrexial, had a WBC of 19.9 and a CRP of 96.3. A radiograph showed bilateral hip prostheses. On the right, there was thinning of the inferior femoral neck and a soft tissue mass was visible in the same region (Fig. 1). An ultrasound showed pannus around the right hip joint and a collection in the right psoas bursa. An aspirate revealed white cells and no organisms, with no growth on culture. A CT scan confirmed bony erosion at the inferior aspect of the femoral neck along with the soft tissue mass. The prosthesis was successfully revised to a total hip replacement, with a ceramic on ceramic bearing in May 2009. Significant amounts of stained and necrotic tissue were removed from around the original prosthesis. Histology showed fibrovascular connective tissue with extensive dystrophic calcification, chronic inflammatory infiltrate and hemosiderin-laden macrophages. Analysis of the removed prosthesis showed excessive wear of both the acetabular and the femoral components. She was diagnosed with Aseptic Lymphocytic-Vasculitis-Associated Lesion (ALVAL). The use of large metal on metal (MoM) bearings in hip replacement has been gaining in popularity. The superior wear characteristics, improved motion and stability have attractive benefits, especially in young active patients. The materials currently used are high carbon cobalt chromium alloys. Reports of problematic painful MoM hips associated with soft tissue masses have been increasing. They can be destructive and lead to infiltration and destruction of soft tissues, pain, dislocation, nerve irritation or palsy, or cause local bone resorption leading to component loosening or fracture [1]. Willerts et al. first reported patients undergoing revision for non-infected, painful MoM implants with histological findings of diffuse perivascular lymphocytic infiltrates with accumulation of macrophages and eosinophilic granulocytes with tissue necrosis and termed it ALVAL [2]. Later reports found similar histological findings [1, 3]. The underlying cellular reaction appears similar to a type IV hypersensitivity response [2], (sometimes referred to as metal hypersensitivity), though exact causation remains unclear [4]. The trigger appears to be an increased local concentration of metal ions, to which an excessive reaction is initiated in certain patients. Blood levels of metal ions are elevated with all MoM bearings [5]. The extent appears to be related to the orientation of the components [6–8], with the resulting abnormal biomechanics in malaligned prostheses leading to focal regions of increased wear. This is especially noticeable in women, where the smaller J. R. B. Hutt (&) 6 Nevis Road, Tooting, London SW17 7QX, UK e-mail: drhutt@hotmail.com