Abstract
Background
We occasionally came across cortical atrophy of femurs with cemented collarless polished triple-taper stem in a short term period. This study aimed to estimate radiographs of cemented collarless polished triple-taper stem taken 6 months after the initial operation.
Methods
Between May 2009 and April 2011, 97 consecutive patients underwent primary total hip arthroplasty and hemiarthroplasty using SC-stem or C-stem implants. At the 6 month follow-up, a radiographic examination was performed on 70 patients (71 hips). 44 hips had Total Hip Arthoplasty, 35 had osteoarthritis, 5 had idiopathic osteonecrosis, 2 had other diseases and 27 hips had hemiarthroplasty for femoral neck fractures. The postoperative radiographs were used to estimate the cementing grade. Then the 6 month postoperative radiographs were analyzed for changes in stem subsidence, cortical atrophy and cortical hypertrophy. According to the system of Gruen- cortical atrophy and cortical hypertrophy were classified on the femoral side. We defined no cortical atrophy as grade 0, cortical atrophy less than 1 mm as grade 1, more than 1 mm and less than 2 mm as grade 2, more than 2 mm as grade 3.
Result
A cortical atrophy adjacent to the stem was found in zone II according to Gruen on grade 0 thirty-five radiographs (49%), grade 1 twenty (28%), grade 2 eleven (16%), grade 3 five (7%). in zone III grade 0 twenty-seven (38%), grade 1 thirty (42%), grade 2 ten (14%), grade 3 four (6%), in zone V grade 0 fifty (70%), grade 1 twenty (28%), grade 2 one (1%), grade 3 zero (0%), in zone VI grade 0 forty-nine (69%), grade 1 twenty (28%), grade 2 two (3%), grade 3 zero (0%). Cortical hypertrophy was only demonstrated in zone V in one case. In all cases the stem subsidence was less than 1 mm. Cortical atrophy including grade 1 was recognized in 38% of THA, and in 52% of femoral neck fractures. In one case the slight radiolucent line of the postoperative X-ray disappeared after 6 months.
Discussion
Cortical atrophy was recognized more in the femoral neck fracture group than in the THA group. And Cortical atrophy was recognized in zone 2 and zone 3 more frequently than in zone 5 and zone 6. According to the finite element analysis of SC-stem more stress is received on the medial aspect of the stem during weight bearing, so it is suspected that more cortical atrophy on the lateral aspect is associated with stem design. This is compatible with the cortical hypertrophy reported with Exeter stem in zone 5.
Conclusion
Cortical atrophy, including minor degree atrophy, occurred in 65% of cemented collarless polished triple-taper stem in short term periods after implantation. Cortical atrophy occurred in the lateral aspect of the stem more severely and more frequently than in the medial aspect. Cortical atrophy was also recognized in the femoral neck fracture group more more severely and more frequently than in the THA group.
