[attachment=13288]
Abstract
Introduction.
Proximal tibial bony deficienciesare frequent conditions in primary and revision total kneearthroplasty. Modular tibial metal augmentations wereintroduced to address these deficiencies hoping that they arebetter than other methods of reconstruction (cementreinforced with screws or structural bone graft).
Material and Methods.
During Jan 2000-Jul2009, 407 total knee arthroplasty were performed in ourdepartment. 24 patients had a varus alignament of the kneemore than 25°. For replacement we have used the samepostero-stabilised prosthesis. The surgical exposure wasstandard in all cases. We have used for ligament balancingthe basic principles. For bony reconstruction we have used ametal medial wedge protected with a stem with or withoutoffset in 9 cases. The stem lenght was 80 mm or 155 mm,according to bone quality and in all cases was uncemented.pressfit. In all cases we have used a metal wedge of 10mmfor reconstruction the bone defect after we have done thestandard tibial cut. The follow-up of all patients is one year.All cases were followed radiographically and clinicallywith KSS scoreResults. Postoperatively, the functional scoreimproved from 33 to 88 points. The results were excellentin 80% of the cases and good in 20% of the cases. Therewere no complications and / or reoperations. Thepostoperative range of motion was 95° (85°-110°). Theheight of joint line was restored and it was no case of patellabaja.Conclusions. The technique of modular tibialmetal augmentations should be considered as an effectivesolution in severe proximal tibial bony deficiencies. Thetechnique is easy and fast, it allows a fast recovery of thepatient with immediate weight bearing. The wedge allowsto do a proper tibial cut and it helps in restoring the normaljoint line.
Key words: tibial wedge, augmentation, total kneearthroplasty, varus, patella baja
I. INTRODUCTION
Proximal tibial bony deficiencies arefrequent conditions in primary and revisiontotal knee arthroplasty. The surgicaltreatment of these lesions depends on thesize and location of the defect. The patient’sage and bone quality are other importantfactors in choosing the type ofreconstruction. In primary knee replacementthe most frequent bone defect is locatedpostero-medially on tibial plateau and isalways associated with an important varusdeformity of the knee. Due to different sizesand shapes of these defects a lot of surgicaltechniques have been developed to restorethe tibial plateau’s shape and integrity. Theaim of this reconstruction is to have a tibialplateau as strong as possible to support thetibial component of the knee prosthesis. Forthe long term survivalship of the implant it isessentially to have a uniform loaddistribution of the forces on tibial bone andthe implant should be fully supported by thebone. There are several causes leading tothese defects in primary knee replacement: aneglected advanced osteoarthritis with varusor valgus more than 25°, fractures,rheumatoid arthritis, avascular necrosis orfailed tibial osteotomy. Techniquesfrequently used in surgical practice includefilling minor defects with cement,augmentation of cement with screws, wiresor mesh, bone grafting (structural ormorselized) or metal augmentation withblocks or wedge.In primary knee replacement we have toevaluate the tibial defect first on preoperativeplanning. We have to be able to measure thesize of it from normal joint line, tibialtuberosity and peroneal head. Theseinformation even if not being exact cansuggest the surgeon the necessity of tibialplateau reconstruction with one of thesurgical techniques above mentioned. Thefinal decision should be taken after primarytibial cut which should be at 8mm from thehealthiest tibial side. After sizing the defectwe can do an additional cut of 2-4mm. It ispossible to eliminate the bony defect or todiminish it, and to obtain from a majordefect which needs reconstruction a minordefect which can be reconstructed with cement. When we decide to eliminate thetibial defect with a deep cut we have to bevery careful not to be under the peronealhead and also not to reduce too much thetibial size. It can be possible to finish thetechnique with a mismatch between femoraland tibial components. Also if we resect toomuch from proximal tibia, the bone strengthdecreases as being shown in numerousbiomechanical studies. This may lead tosinking the tibial component in spongiousbone and early loosening. So if it’s notpossible to exclude safely the defect,it isbetter to reconstruct it. When we proceedwith reconstruction we have to differentiatebetween cavitary and structurally defects.The cavitary defects remain contained bycortical rim and are reconstructed with bonegrafting or cement with good long termsurvivalship. The bone chips should be takenfrom femoral and tibial cuts. When thecortical rim of tibia is breeched the defect isstructural and the tibial plateau is no moresupportive. In these cases the reconstructiveoption are challenging.