[Mid-Term to Long-Term Results of Revision Total Hip Arthroplasty Using the Oval-Shaped Acetabular Cup - TC Type]

INTRODUCTION The purpose of our paper is to evaluate the mid-term to long-term results and to confirm the basic criteria of a high-quality revision implant: safe bridging of bone defects, achievement of reliable primary fixation of revision acetabular cup, achievement of good secondary stability with documentable osteointegration of cup and demonstration of remodelling of transplanted bone tissue in the area of defects and in spaces between the implant ribs. MATERIAL AND METHODS Altogether 36 patients (38 cups) were evaluated who had undergone revision hip arthroplasty in the period from 2004 to 2010. The mean follow-up was 8.2 years (5.1-11.6 years after the reimplantation, more than 10 years in 16 patients who underwent surgery). The position and osseointegration of the implant were assessed by digital radiography, the remodelling of transplanted bone tissues in the area of defects and between the implant ribs by computed tomography with reducing artefacts around the metal implant (Aquilion 64 - Toshiba Medical Systems), and for the clinical outcomes the Harris Hip Score was used. RESULTS Preoperatively, the condition of the hip joint based on the Harris Hip Score was in 30 cases evaluated as poor, in 8 patients as satisfactory. At the time of final evaluation, 8 patients achieved excellent results, in 19 patients the condition of the joint was very good (in 2 patients bilaterally), in 6 patients it was considered satisfactory and in 3 patients poor. The mean value for HHS increased from 39.5 to 84.5. Based on the radiography evaluation, in 27 patients (in 2 patients bilaterally) the osseointegration of the revision cup was good, in 8 cases with a radiolucent line of 2-4 mm in width in DeLee zone III, in one case proximal migration of the cup occurred caused by deep infection. The informed consent form for pelvic CT was signed by 25 patients of our cohort. Remodelling of bone tissue in the space between the ribs of the implant was always detected, the presence of bone cysts was not reported, the bone defects following the application of autologous spongioplasty in the monitored patients were healed. In 6 patients, an ingrowth of fibrous tissue of 2-4 mm in width in the convexity of the cup was detected. The mean survival of the revision oval-shaped cup - TC type with a follow-up of 8.2 years after the reimplantation based on Kaplan-Meier analysis was 91.4 %. DISCUSSION The number of revision total hip arthroplasties due to a younger age of patients who undergo alloplasty keeps growing. The choice of a revision implant should always match the intraoperative finding and the bone tissue quality. The standard uncemented implants with osteoactive surface can be opted for when anterior and posterior column of the acetabulum are intact (IIA and IIB according to Paprosky). Starting from type IIC, also the proximal part of acetabulum shall be considered. At our department, preference is given to the revision cup - TC type. The oval shape facilitates a lower degree of bone resection and easier restoration of the anatomical centre of rotation. Careful debridement of granulating and necrotic tissue, thorough treatment of bone defects and osteoactive surface of implants in case of adequate primary fixation of the cup substantially contribute to the quality of its osseointegration. Greater rigidity of fixation verified by pull-out tests enables to insert angular stable screws into the gaps in the proximal part of the cup. There is still room for improvement in treating the bone defect. The application of allogenic bone grafts into the defects and spaces between the ribs of the TC cup is more challenging than the use of augmentation in the systems with trabecular titanium. Based on the evaluation of CT scans, remodelling of the transplanted bone occurs, therefore the defect zone is reduced. CONCLUSIONS The oval-shaped uncemented cup - type TC meets the requirements placed on a state-of the art revision implant, moreover its specific construction helps improve the conditions where another re-operation of acetabulum is necessary. By evaluating mid-term to long-term results of non-homogenous group of 36 patients (38 cups) we have obtained data on joint function comparable to similar groups with revision uncemented implants presented in our and foreign literature. Key words: revision oval-shaped cup, bone remodelling, pull-out tests, angular stable screws, computed tomography.