The close union achieved between pure grade titanium and healthy bone makes dislocation a rare event. We report the case of the total avulsion of an apparently well-integrated implant from a healthy mastoid bon

O'Reilly, B. J.

Walter, C.

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The Journal of Laryngology and OtologyJuly 1991, Vol. 105, pp. 573-574Total avulsion of an osseointegrated screwB. J. O'REILLY, C. WALTER (Heiden, Switzerland)AbstractThe close union achieved between pure grade titanium and healthy bone makes dislocation a rare event. We report thecase of the total avulsion of an apparently well-integrated implant from a healthy mastoid bone.IntroductionSince Professor Branemark first reported the phenomenon ofosseointegration (Branemark et al., 1969) over 100,000 puregrade titanium screws have been implanted in the skull, mostlyintraorally. A feature of these implants is their remarkablystrong adhesion to the surrounding bone which makes rejec-tion or dislocation an exceptional event.Case reportThe patient, a 17-year-old Caucasian and a semi-profes-sional ice-hockey player, had a total agenesis of the right auri-cle. Seven years previously he had undergone an unsuccessfulotoplasty and, when offered the choice of a revision otoplastyor a bone-anchored prosthetic auricle, opted for the latter.FIG. 1Auricular prosthesis with superior fixture still attached.FIG. 2Instrument indicating site of avulsed fixture. Fixture containingsheared abutment screw arrowed.Accepted for publication: 11 March 1991.573https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0022215100116640Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 08:23:45, subject to the Cambridge Core terms of use, available at574 B. J. O.REILLY, C. WALTERFIG. 3Two replacement fixtures with cover screws.The first stage surgery was performed in October 1989 and"three 4 mm titanium screws were satisfactorily implanted bythe senior author (CW) in the standard fashion (Tjellstrom,1989) into healthy cortical mastoid bone. At the second stagesurgery, performed four months later, all three fixtures werefound to be rigid. Abutments were attached to the upper twofixtures without mishap but the abutment screw sheared withinthe lower fixture and could not be removed. Although useless,the lower fixture was left in situ and a bridge was attachedacross the two remaining abutments. A silicon rubber auricularprosthesis was fashioned around an acrylic plate with six reten-tion clips to fasten it to the bridge.The patient was delighted with his prosthesis and wore itdaily until August 1990 when, during a game of ice hockey, hewas struck by a club on the prosthesis. The inferior abutmentscrew was detached and the superior fixture was entirelyavulsed (Figs. 1 & 2).The ear was explored 10 days after the incident by whichtime a low grade infection was present around the inferior fix-ture. Despite this infection the fixture was found to be secureand a fresh abutment was attached to it. The superior fixturesite contained no remaining part of its prosthesis and the screwthreads had been entirely erased, although no fracture waspresent. Two new 4 mm titanium screws were implanted infresh sites (Fig. 3) and the wound was closed with a split thick-enss skin graft around the abutment.We intend to attach a new bridge in four months and hope topersuade the patient to remove the new prosthesis before ice-hockey games.DiscussionAlthough initially designed for intraoral use, osseointe-grated implants have been used percutaneosly since 1977 toattach auricular, nasal and orbital prostheses and boneanchored hearing aids. The success (ie integration) rateappears to be at least as high for the percutaneous as for theintraoral implants. Albrektsson et al. (1987) reported the fail-ure of only six out of 389 percutaneous implants, and five ofthese failures were in irradiated patients. Considering onlyauricular prostheses, the results are at least as good with onlytwo failures from 282 implants (Tjellstrom, 1989). The onearea of (relative) failure is the orbit where 19 out of 81 implantsfailed to integrate (Tjellstrom, 1989). However, the thin corti-cal bone available, the frequency of previous radiotherapy andthe likelihood of penetrating the frontal sinus may all militateagainst success in this area.Once osseointegration has occurred the union achievedbetween implant and bone is so close that its removal, whetherby accident or design, is extremely difficult; a torque of136 Ncm has failed to remove a well-integrated implant (Tjell-strom, 1989). Consequently where it is necessary to remove aprosthesis it is usual to remove the abutment but to leave theosseointegrated screw as a permanent subcutaneous fixture.Equally it is not surprising that traumatic dislocation of anosseointegrated screw is a rare event. Of the prosthesessecured by osseointegrated screws the auricle and the bone-anchored hearing aid are perhaps the more exposed to trauma.The bone-anchored hearing aid readily detaches from its abut-ment and there is little likelihood of dislocating its fixture. Incontrast, the retention clips of the auricular prosthesis may notbe so readily detached from the bridge which (as in our case)may act as a lever on any remaining attachment.No firm conclusions can be drawn from a single case but itwould seem reasonable to advise patients with auricular pros-theses to remove them before engaging in contact sports. Thepossibility of traumatic dislocation of the implant would beobviated by the substitution of magnets for retention clips,although these might make attachment of the prosthesis moreawkward for the patient.ReferencesAlbrektsson, T., Branemark, P. I., Jacobsson, M., Tjellstrom, A.(1986) Present clinical applications of osseointegrated percuta-neous implants. Plastic and Reconstructive Surgery, 79: 721-730.Branemark, P. I., Adell, R., Beine, U., Hansson, B. O. (1969)Intra-osseous anchorage of dental prostheses: 1. Experimentalstudies. Scandinavian Journal of Plastic and Reconstructive Sur-gery, 3: 81-100.Tjellstrom, A. (1989) Osseointegrated systems and their appli-cations in the head and neck. In Advances in OtolaryngologyHead and Neck Surgery, (Myers, E. M., ed.), Year BookMedical Publishers Inc., 3: 39-70.Address for correspondence:Squ. Ldr. B. J. O'Reilly, F.R.C.S.Ed.,Princess Mary's R.A.F. Hospital,Halton,Aylesbury,Bucks HP22 5PS.Key words: Ear, external; Osseointegrated implanthttps:/www.cambridge.org/core/terms. https://doi.org/10.1017/S0022215100116640Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 11 Jul 2017 at 08:23:45, subject to the Cambridge Core terms of use, available at

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