Revision rates of hip resurfacing arthroplsty(HRA) have been reported to be higher than primary total hip arthroplasty (THA) and in most national registries accounts to be 3.5% over 15 years.  Revision of HRA is associated with a major risk of 5- year re-revision of 11%, which is much higher than the 2.8% revision risk of a primary THA  .It seems logic as HRA mostly indicated in younger age group who are characterized by higher level of both daily and sport activities. This is in addition to the specific design of the prosthesis .
In our study we aim at restoring the daily and sport activities of the patients for which they underwent their HRA surgery.
the most common indications for revision are Femoral neck fracture (incidence range 0.9-1.1%) owing to osteoporosis or notching of the femoral neck during surgery[2,9], component loosening, infection and metallosis with adverse local soft tissue reaction. 
Other risk factors that may propose to HRA failure and the need for revision include: age, Gender and implant factors. Increased age accompanied by poor bone quality which subject the patient to complications as femoral neck fractures, osteoporosis of femoral neck and aseptic loosening. Many studies emphasized that patients above 55 years had increased risk of complications. [8, 11, 22]. female gender is a risk factor for implant failure, with revision rates in females significantly increased compared to males (5.7 vs 2.6 %, p < 0.001). Many studies have shown that survival rate of HRA may reach 95 to 98 % at 10 years in male patients . The previous study's factors are compatable with our study with some deviation owing to the small number of the series.
Implant factors that exaggerate risk Challenges of revision include malposition which is associated with increased incidence of aseptic loosening and increased metal ion release. This is due to increased edge loading of the prosthesis and loss of fluid film lubrication . Also; many studies have emphasized that decreased femoral component size is associated with increased release of metal ions with subsequent the incidence of failure for every 4 mm decrease in femoral component diameter
Component loosening in our study involved 4 patients. In 3 cases both components were loose and revised while in one case only the femoral component affected and isolated femoral revision with retention of the acetabular shell has been done. The technique is less time consuming less technically demanding, minimizes risk of dislocation owing to use of large diameter femoral head and maintenance of residual acetabular bone stock . The only drawback of this procedure concerned with conflicts about the use of metal on metal bearing surface total hip arthroplasty and corrosion-related complications. Recent studies utilized femoral component with dual mobility femoral head though the Food and Drug Administration (FDA) has not approved the use of that [6, 21]
Sandiford NA et al.  declared that. Complete revision of both acetabular and femoral components to a THA would minimize the potential sources of cobalt and chromium ions and consequently could produce good short-term clinical outcomes.
In the setting of metallosis which explored intraoperatively in 3 cases, proper understanding of the characteristics and anatomic relationships is essential as this soft tissue contamination can distort normal surgical landmarks. Thorough debridement of metal debris and inflammatory soft tissue was performed. Any cystic or lytic osseous lesions were packed with bone graft. Extensive osteolysis may require the use of bone grafting along with supplemental fixation. Patients with these presentation had been revised by ceramic on ceramic bearing couplewith functional outcomes similar to those of Willert et al. 
Advantges of conversion of hip resurfacing to THA include avoidance of implant mismatch awareness, elimination of cobalt or chromium ions source if titanium-alloy femoral and acetabular components, or ceramic femoral heads are utilized.  However; some shortcomings may limit the prevalence of this strategy namely minimizing bone stock owing to bone loss on removal of hip resurface implants and concern of stability due to use of smaller femral head in THA compared with that of hip resurfacing implants
The targets to be achieved in this study are relief of pain and returning back of patient daily and sport activities. In last follow-up all patients (except one) returned back to their daily activities and sports. One patient has moderate reduction in range of motion owing to hetertropic ossification. .
Clinical outcomes of conversion of HRA to total hip arthroplasty had been assessed via some studies. Su et al.  declared that clinical outcomes of this conversion was related to the indication of revision and the highest postoperative outcome observed in patients who underwent conversion for femoral neck fracture or implant loosening. The worst outcomes were seen in patients who underwent revision for unexplained pain or metal sensitivity.
In our study the average highest outcome according to Oxford, Harris, WOMAC and UCLA activity hip scores observed in patients revised for femoral neck fractures with values at last visit of 39.5, 98,8, 7.4 and 9.3 respectively. The worst outcome observed in cases revised for unexplained pain with values of 38. 38.6, 4, 12.3 and 4 respectively. Our study outcome is comparable with many studies as Su et al. .
Revision of a single component of HRA, with retention of the remaining components, has been associated with mixed clinical results. In a study comparing 21 patients undergoing conversion of HRA to THA to patients undergoing primary THA, found that in the 18 patients who underwent femoral-sided revision only there was no clinical difference at a mean 46-month follow-up with regard to the mean Harris hip score; WOMAC and UCLA activity score . The results could not be compared with those of our study as we have no comparative cohorts of primary THA (a limitation in our study).
Many studies emphsized that on revising resurfacing hip arthroplasty due to causes related to femoral component, the decision to change the femoral component only or both femoral and acetabular depends largely on the orientation of the acetabular component.[2,15]
In our study we follow similar strategy that if the lateral acetabular opening angle was greater than sixty degrees, we changed both acetabular and femoral components because some vertical orientation of the cup may be compatible with femoral component in resurfacing arthroplasty but this position is difficult to be compatible with fixed angle of the stemmed metal on metal THA prosthesis and lateral sublaxation mostly occur.
on the other hand; cases with lateral acetabular opening angle of resurfacing prosthesis near forty degree so during revision the fixed angle of the stemmed metal femoral component usually becomes compatible with the previous metal acetabular cup so in these cases we revised only femoral component.
Revision of both acetabular and femoral components of HRA to THA has varying clinical outcomes reported across multiple studies. A registry study of 882 HRA revision emphasized that no difference in re-revision rates and clinical outcome between the acetabular-sided, femoral-sided, or combined acetabular and femoral-sided cohorts.  This finding correlated with the results of the prior study by Su et al.  Similar findindings have been illustrated in our study (Table5) with no marked differences in clinical outcome between both component revision and isolated femoral component revision regarding Oxford, Harris, WOMAC and UCLA activity hip scores. A small difference in outcome noticed in our study regarding the indication for revision with worst outcome in patients revised for component loosening, unexplained pain and component wear. Table(5)
Sandiford,et alin a review of 25 patients undergoing conversion of surface arthroplasty to THA, found significant postoperative increases in Oxford, Harris, and WOMAC hip scores, with clinical results similar to revision THA .
Reports on clinical outcomes following HRA revision for complications associated with metal wear are mixed, with some studies touting midterm clinical success rates as high as 97 %, while other data shows that revision for implant wear is associated with a significantly worse outcome when compared with revision for mechanical etiologies [21, 24]. These reports outcomes support our results regarding worse outcomes of revised cases for implant wear relative to those of femoral neck fractures ( 10 cases) or femoral neck thinning ( 3 cases). Table ( 5)
Limitations of the study
our study presents some limitations, namely small number of patients, follow-up period is somewhat short relatively and lacking of comparative study. The technique itself has some limitations owing to the concerns of metal on metal coupling in hip arthroplasty. Furthermore systematic approach to revision of hip resurfacing arthroplasty to total hip arthroplasty is necessary to ensure optimal clinical results.