Description of Event or Problem · 1
INTERMEDICS ORTHOPEDICS, INC. 9900 SPECTRUM DR, AUSTIN, TX 78717. THE PT IS A 39-YR-OLD MALE WHO HAD A BADLY FRACTURED ACETABULUM FROM AN ACCIDENT SEVERAL YEARS EARLIER. THE HIP WAS REVISED BY DR ALTMAN ON 2/15/96. AN EXTENSIVE ALLOGRAFT WAS PLACED INTO THE ACETABULUM. AFTER A COUPLE WEEKS, THE PT STARTED DISLOCATING AND IT WAS CONFIRMED THAT TEH ALLOGRAFT WAS NOT HOLDING THE IMPLANT IN PLACE (IT WAS SHIFTING). DR ALTMAN DETERMINED THAT THE RE-REVISION WAS NECESSARY AND ON 3/8/96 HE PERFORMED THE RE-REVISION. WHEN HE REMOVED THE SHELL FROM THE ACETABULUM, IT WAS NOTICED THAT THE TWO CANCELLOUS SCREWS HAD SHEARED OFF. THIS DID NOT HAPPEN DURING THE SURGERY, BUT DUE TO THE SHELL SHIFTING IN THE ALLOGRAFT. THE CERAMIC HEAD IS CONSIDERABLY WORN/BURNISHED. THE HOSP DOES NOT SUSPECT ANY MATERIAL DEFECTS, BUT WOULD LIKE A REPORT FOR THEIR OFFICIAL RECORDS, SINCE THIS WAS A RE-REVISION CASE. AN EXPLANTED INTERMEDICS ORTHOPEDICS, INC. (IOI) 28MM/-4MM NECK LENGTH 12/14 TAPER CERAMIC HEAD CAT #7666-44-028 AND TWO TITANIUM FULLY THREADED CANCELLOUS BONE SCREWS CAT #'S 4301-07-05 AND 4301-07-045 WERE RECEIVED AND DELIVERED TO MATERIALS TECHNOLOGY (IOI) FOR ANALYSIS. THE CERAMIC HEAD AND SCREWS HAD BEEN REMOVED DURING A RE-REVISION SURGERY NECESSITATED BY HEAD-INSERT DISLOCATION CAUSED BY SHIFTING OF ACETABULAR SHELL. SCREWS HAD APARENTLY BROKEN DURING SVC AND ONLY BETWEEN 8-9 MM OF EACH SCREW (ENCOMPASSING SCREW HEAD) WERE RETURNED TO IOI. IN ADDITION TO PERFORMING FAILURE ANALYSIS OF SCREWS, EXAMINATION OF CERAMIC HEAD WAS REQUESTED DUE TO "CONSIDERABLE BURINISHING" DETECTED ON APPROX ONE-HALF OF HEAD. THE BURNISHING OF CERAMIC DEVICE WAS DUE TO ABRASION OF HEAD AGAINST A SOFTER METALLIC MATERIAL. DEVICE WAS MFG FROM ALUMINUM OXIDE (PER ISO 6474) WHICH HAS A HARDNESS OF 91 (HARDNESS ROCKWELL R45N). APR ACETABULAR SHELL, MADE FROM TI-6AI-4V (PER ASTM F-136), HAS A HARDNESS OF APPROX 34 (HARDNESS ROCKWELL R45N). WHEN THE TWO MATERIALS ABRADE AGAINST EACH OTHER SOFTER MATERIAL WILL ALWAYS BE REMOVED AND/OR DEPOSITED ONTO HARDER MATERIAL. CONDITION OF HEAD IS NOT INCONSISTENT WITH WHAT WOULD BE EXPECTED FOLLOWING SUCH A COMPLICATION (IE, DISLOCATION). BOTH TITANIUM BONE SCREWS FAILED DUE TO SHEAR FRACTURE CAUSED BY OVERLOADING. THIS OCCURRED BECAUSE THE SHEAR STRENGTH OF MATERIAL, TI-6A1-4V (PER ASTM F-136), WAS EXCEEDED. SINCE ULTIMATE TENSILE STRENGTH OF THIS MATERIAL IS APPROX 120 KSI, PURE SHEAR STRENGTH IS AROUND 60 KSI. THEREFORE, EACH SCREW MUST HAVE BEEN EXPOSED TO SHEAR STRESSES EXEEDING THIS LEVEL. EXCESSIVE STRESS CONDITION WAS MOST PROBABLY CAUSED BY "SHIFTING OF ALLOGRAFT" DURING POST SURGERY AMBULATION. PRODUCT PACKAGING INSERT COVERS CONTRAINDICATIONS SUCH AS PTS PHYSICAL CONDITION, PREVIOUS SURGERY, INSUFFICIENT QUALITY OR QUANTITY OF BONE AND POTENTIAL ADVERSE EFFECTS SUCH AS CHANGING POSITION OF PROSTHESIS OR FISSURE OF ACETABULUM. I HAVE INCLUDED A COPY OF PACKAGING INSERT (#270003 REV D) WITH THESE AREAS HIGHLIGHTED.