Early Diagnosis of Pending Failures of Total Hip Arthroplasty With Hard to Hard Bearings

During last 6 years approximately 10.000 ceramic balls and 5.000 ceramic liners have been implanted in the region Emilia-Romagna in Italy (4 million Every single year approximately 60.000 hip prostheses are implanted in Italy. Quality of life of patients after surgery is very good, as widely demonstrated in the literature. On the basis of data produced by the only complete hip register in Italy that is run in our Lab (RIPO, Register of Orthopedic Implants in the Region Emilia-Romagna) survival rate of primary total hip prosthesis is 95.6% at 9 years. Reasons for revision are mainly aseptic loosening of one or both components (40% of the total) and dislocation (26%), being the latter much more frequent in the first two years. Less frequently revision is due to sepsis (7% of the total),bone fracture (11%), prosthesis fracture (3%) or pain (3%). Revision is relates, among the others, to prosthesis-related factors, such as fixation to bone and articular coupling. In our experience, during the last ten years 32% of implants had both articular component in ceramic , 34% had metal head and plastic liner, 24% ceramic head and plastic liner, 10% both components in metal.

Each solution has strengths and weakness and they have been identified and clinically applied in order to overcome step by step limitations observed in the previous one. The most recent are the hard-on-hard bearings, that is ceramic on ceramic and metal on metal. These two solutions, beside very promising results on wear resistance, show some peculiar failures: respectively fracture of the ceramic component and hypersensitivity induced by metal ions.

Aim of research proposal is to investigate two uncommon and less investigated early symptoms of failure:

• 'noising hip' in ceramic on ceramic total hip arthroplasty
• pain without radiographic signs of loosening in metal on metal total hip arthroplasty These two situations are extremely relevant, as they prelude to a failure of the prosthesis. If clearly identified they could represent a powerful tool in early diagnosis of pending failure To reach this goal our patients wearing hard-on-hard total hip arthroplasty, suffering for described symptoms will undergone a specific diagnostic procedure.

The first group will be studied through CT scan of the patients to evaluate impingement or instability of the prosthesis, and a needle aspiration for synovial fluid. The fluid will be examined to identify ceramic wear debris, according to a method of separation and analysis in scanning electron microscopy that was set in our Lab.

Sound will be recorded by means of a wearable sensor set capable of recording the articular noise produced during level walking. This instrumentation will be coupled to motion analysis technology.

This would make possible a diagnostic approach able to correlate the involved factors to clinical occurrences, on the basis of the recorded frequencies.

-Second group will be studied through the dosage of circulating ions, deriving from the articular surfaces and through the histological classification of vasculitis in periimplant tissues. There is increasing evidence, indeed that locale release of submicron particles worn out from articular surfaces can release metal ions (mainly Chromium and Cobalt) responsible for lymphocyte local infiltration. In particular CD20 positive B lymphocyte and CD3 positive T lymphocyte and sometimes CD68 positive plasma cells are present. The cells could justify the development of pseudotumors in metal-on metal hip prosthesis.

Data collected from patients matched to in vitro results will allow us to to avoid or at least propose a more appropriate timing for revision surgery.