adverse reaction to metal debris ( armd ) in arthroplasty surgery of the hip is a well - known problem and has resulted in several products being withdrawn from the marketplace . complications related to the release of metal ions can be devastating for patients and represent a significant surgical challenge . although the bearing surfaces are a causative factor for metal debris to accumulate , corrosion at the head  neck or neck stem junction in a modular prosthesis has been described as a significant problem . in the absence of any reciprocal articulating surface a hemiarthroplasty however , case reports have surfaced which highlight the potential for such a complication to arise [ 35 ] . we present the case of a unipolar hemiarthroplasty requiring revision within 18 months of insertion secondary to an adverse reaction to metal debris . six months previously she had sustained a fragility fracture of her hip whilst on holiday in canada . she was treated locally with an uncemented hemiarthroplasty ( zimmer press fit ml taper titanium alloy stem , zimmer versys cobalt - chrome femoral head and neck adapter ) . the patient reported persistent groin pain and a leg length discrepancy since the time of surgery . she had a normal white cell count , esr and crp . on aspiration a turbid , green , an mri scan revealed fluid around the femoral head and neck but no evidence of soft - tissue compromise or pseudotumour formation . the injection of local anaesthetic afforded temporary relief and confirmed the hip as the source of pain . subsequently , the decision was made to revise the hemiarthroplasty to a total hip replacement . intraoperatively a large amount of the  pea - soup like fluid was again noted together with some lysis of the proximal femur . the femoral head was explanted and corrosion was seen at the head neck junction with black staining around the trunnion and on the reciprocal surface of the adapter sleeve . the femoral stem was found to be well - fixed and after cleaning the trunnion was left in situ . the area of lysis proximally was debrided and packed with reamings taken from the acetabulum . biopsies taken intraoperatively confirmed an adverse metal reaction with an alval score of 8/10 ( loss of synovial lining with attached surface fibrin , numerous perivascular lymphohistiocystic aggregates , loss of normal tissue arrangement with the presence of acellular hyalinised zones ) ( fig . 1 ) . 
 figure 1:intra - operative biopsies confirmed an adverse metal reaction with an alval score of 8/10 ( loss of synovial lining with attached surface fibrin , numerous perivascular lymphohistiocystic aggregates , loss of normal tissue arrangement with the presence of acellular hyalinised zones ) intra - operative biopsies confirmed an adverse metal reaction with an alval score of 8/10 ( loss of synovial lining with attached surface fibrin , numerous perivascular lymphohistiocystic aggregates , loss of normal tissue arrangement with the presence of acellular hyalinised zones ) a year post - operatively our patient is clinically improving and her metal ions are undetectable . the diagnosis was considered pre - operatively but only confirmed post - operatively with histological analysis . reported a similar case involving a patient who required revision surgery for armd 3 years after insertion of a hemiarthroplasty with components analogous to ours . the patient required two revisions and only improved after the cocr head was changed to ceramic . this led the authors to conclude that the trunnion mismatch between the adapter sleeve and the titanium stem caused both the initial and the on - going metal sensitivity . described two cases of patients experiencing severe trunnion corrosion and armd more than 10 years after insertion of a hemiarthroplasty . in one case the corrosion of the trunnion was so severe that the head disengaged from the stem . a further case of armd complicating hemiarthroplasty has been reported in the literature . in this case , high levels of titanium metal debris in specimens taken from the femoral - bone stem interface led the authors to conclude that armd resulted from metal release from the femoral stem itself . the prosthesis concerned consists of a titanium alloy stem ( zimmer ml taper tivanium ) and a cobalt chromium ( cocr ) femoral head and neck adapter ( zimmer versys ) . it is our belief that there were two modifiable factors that contributed to armd in this case . firstly , the torque produced by a large femoral head is sufficient to increase the risk of fretting corrosion at the head / neck junction similar to that seen in total hip replacement surgery . secondly , the neck adapter interposing the femoral head and stem is an independent risk factor for both corrosion and metal ion release . this is the first case in the literature where the patient required revision surgery within 18 months of the primary procedure . we are familiar with the presentation of armd as there has been a large cohort of metal on metal prostheses in this hospital . the fact that this was revised early meant there was less severe soft tissue damage at the time of surgery compared to similar cases in the literature [ 35 ] . we feel that armd should be considered as part of your differential diagnosis for a painful hemiarthroplasty especially if a modular prosthesis is involved . such cases should be investigated thoroughly and the pain should not be ignored even when infection has been excluded . corrosion at the head neck junction is possible in hemiarthroplasty when a modular system is used and is exacerbated by the large diameter femoral head inherent to this type of prosthesis . we feel that armd should be considered in all cases where pain and dysfunction in the presence of a hip prosthesis can not be explained by routine investigations .