Metal -on -metal THR has the longest clinical history of any of the curremly used available couples. Early loosening ofprostheses with a metal -on -metal bearing was initially assumed to be due to the bearing but has now bee1l recognized to be due to suboptimal implallt design, inconsistent manufacturing and surgical technique.
Patients and Methods
Over a period of 27 months, 20 patients with arthritic !zip .ioint underwent total hip replacement usillg the new generation of metal -on metal total hip replacement systems. Patients were followed-up for a mean period of 22.3 months (range 9 -30). Proper history taking with !.pecial attention to pain and functional status and examination for the range of motion and limb length discrepancy were done in every case. The pre-operative Harris Hip Score ranged from 25 to 48 with a mean of 37.6. Anteroposterior radiograph of both hips and upper femur and lateral radiograph of the affected hip were examined. The plastic ol'eriay templates were lIsed in every case before surgery.
The post-operative Harris Hip Score in the last follow -up ranged from 72 to 95 (mean 91.8). Excellent results ",'ere obtained in 11 cases (55%), good results in 6 (30%), fair results in 3 (15%) with 110 poor results. Regarding the radiological results, the acetabular llte/ination ranged from 40 -76 with a meall of 47.8 and most of the stems were neutral or in a slight valgus POSltlO1l. Radiolucellt lines appeared around the acetabular component ill 2 cases and around the femoral component in one case. These were non-progressive and did not affect the clinical outcome. There were 110 cases ofcup dislodgement or migration and there were no cases ofstem migratio1l or subsidence during the follow -lip period. Complications were infrequent a1ld post-operative dislocation was not reported in any of the cases.
Large diameter metal bearings have several advantages over conventional implants ill terms of tribology, fU1lction and clinical applications. perhaps, these bearings may become the gold standard in the course oftime.