Abstract
Background
Recently the taper wedged stems (TWS) are used widely in Japan because of good bone fixation and ease of the procedure. However, it is unclear how TWS get initial fixation in Japanese, especially dysplasia hip or elderly patients who had stovepipe canal. The purpose of this study is to evaluate initial bone fixation of the TWS in Japanese using computed tomography and to estimate biological bone fixation of the TWS using the Tomosynthesis.
Methods
We evaluated 100 hips underwent primary total hip arthroplasty using TWS. All patients were performed computed tomography within 2 weeks postoperatively and evaluated which part of the canal was made contact with the stem. 24 hips were male and 76 hips were female. According to the canal flare index, 9 hips were champagne flute canal, 80 hips were normal canal and 11 hips were Stovepipe canal. 10 hips were Dorr type A, 80 hips were Dorr type B and 10 hips were Dorr type C.
The initial bone fixation was classified as Medio-lateral fit (fixed at Gruen zone 2 and 7), Flare fit (fixed at zone 2 and 6), Varus 2-point fit (fixed at zone 3 and 7), Valgus 3-point fit (fixed at zone 2, 5 and 7), Distal fit (fixed at zone 3 and 5), Total fit (fixed at zone 2,3,5,6 and 7) by the stem A-P view. Moreover, we defined Medio-lateral fit, Flare fit and Total fit as Adequate fit, Varus 2-point fit and Valgus 3-point fit as Varus or Valgus fit, Distal fit as Distal fit. The stem alignment was classified as flexion, neutral and extension by the stem lateral view.
Femoral component fixation was graded as bone ingrowth, fibrous ingrowth and unstable by hip radiographs after surgery at 1 year. Spot-welds were evaluated using tomosynthesis after surgery at 6 months.
Results
47 hips were Medio-lateral fit, 7 hips were Flare fit, 9 hips were Varus 2-point fit, 12 hips were Valgus 3-point fit, 17 hips were Distal fit and 8 hips were Total fit by the stem A-P view. 63 hips were Flexion, 36 hips were Neutral and 1 hip was Extension by the stem lateral view. 62 hips were Adequate fit, 21 hips were Varus or Valgus fit and 17 hips were Distal fit. Distal fit was identified all canal shape or bone quality regardless of the Canal flare index, the Dorr classification. There was no case of adequate fit which was used larger stem.
All cases achieved bone ingrowth fixation, but there were 5 hips which we could not recognize spot-welds. 4 hips of them were classified as Distal fit.
Discussion
The study showed that initial bone fixation of the TWS exits various pattern due to femoral geometry, bone quality and stem size. Also most stems were inserted flexion by the stem lateral view. For all hips, tomosynthesis showed stable osseous fixation of the stem regardless of the type of initial bone fixation. Although it is unclear to affect long-term survivorship by the various type of initial bone fixation.
