modular total hip arthroplasty system are now widely used , as these components increase the flexibility during primary and revision total hip arthoplasty . but this modularity itself associated with some risk of intraoperative and postoperative complications . we report a case of late disassembly of a primary total arthroplasty in a 42 years old patient five years after the replacement surgery where the femoral head remained in the acetabular socket . femoral head should be solidly impacted onto the stem and confirm that it has been assembled correctly before reduction . modular total hip arthroplasty system now widely employed , that offer the advantage of increase flexibility in components selection during the surgery , but it introduce the risk of intraoperative errors in matching and disassembly of the components postoperatively1 
 2 . we report a unusually late separation of a modular femoral head from the neck of a primary total hip arthroplasry . a 42 years old man , who had osteoarthritis of right hip ( fig 1 ) , had an uncemented total hip replacement done through posterolateral approach . a porus coated , metal backed acetabular component with metal liner and a taper - locked modular femoral head with hydroxyapatite coated femoral stem were used . initial results was excellent , the patient had no pain and could walk without supportive aids . the patient was regularly followed up to about five years and all the x - rays of those period were normal and had no abnormalities ( fig . preoperative x - ray , showing osteoarthritis of hip joint . showing radiographs at various intervals , a- immediate postoperative , bone month post surgery and c - one year post surgery radiograph of hip joints at three years after surgery . five years after postoperatively , while the patient was rising from a chair , the patient experience a sudden click and followed by complete functional disability and impossibility to bear the weight . standard radiograph showed disassembly of femoral neck and head while the head of prosthesis remained inside the acetabular socket . all the femoral and acetabular components visible in the x - ray are normal in appearance . there are no fracture lines in any components or complete fracture of any components or any other extra , abnormal sized or shaped metal piece visible in the x - ray ( fig . open reduction was performed , same head was assembled onto the neck and the head was reduced into the acetabular socket . there was no evidence of visible corrosion of the interface between modular head and neck of femoral components . intra - operative images are not available as that were not taken during the surgical procedure . the modular femoral head disassembled from the stem and remained in the acetabular socket postoperative period was uneventful and a quick functional recovery was achived . modularity in total hip arthroplasty has been benefit in term of allowing inventory reduction , while provide surgeon versatility intraoperatively and thus allowing optimal joint reconstruction 3 , but it also introduce the risk of failure at the interfaces . modular femoral head may disassemble during close reduction of a dislocated prosthesis or during normal activity 1 such as in case report of current study . we suspect that the mechanism of this disassembly of femoral head was the sealed air that pushes back the stem neck and unlocks the taper lock . it is also possible that the head was not impacted adequately onto the stem intraoperatively . as a result of this experience , certain recommendation can be made to prevent this type of complication . the taper should be neatly clean and completely dry before the implantation of femoral head onto it . it is advised to use second blow as it may disengage the head if it was not placed centrically onto the taper , otherwise this second blow solidly lock the taper lock mechanism in a centrally placed head . always confirm that , the head has been assembled correctly by applying manual distraction forces to femoral head . disassembly of modular total hip arthroplasty system after surgery is rare , but it can occur in any case . therefore , whenever using such type of arthroplasty system , all the precautionary measures should be taken during surgery which are necessary to prevent such type of complication .
introduction : modular total hip arthroplasty system are now widely used , as these components increase the flexibility during primary and revision total hip arthoplasty . but this modularity itself associated with some risk of intraoperative and postoperative complications.case report : we report a case of late disassembly of a primary total arthroplasty in a 42 years old patient five years after the replacement surgery where the femoral head remained in the acetabular socket.conclusion:femoral head should be solidly impacted onto the stem and confirm that it has been assembled correctly before reduction .