Abstract
Background
We occasionally come across cortical atrophy of the femur with cemented collarless polished triple-taper stem, a short time after the operation. This study aimed to estimate the radiographs of cemented collarless polished triple-taper stem taken at three, six, twelve, and twenty-four months after the initial operation.
Methods
Between May 2009 and April 2011, 97 consecutive patients underwent primary total hip arthroplasty and hemiarthroplasty using a SC-stem or C-stem implant. During the 24 month follow-up, radiographic examination was performed on a total of 95 patients (98 hips). Out of those 95 patients, 52 hips had total hip arthroplasty, 45 had osteoarthritis, 5 had idiopathic osteonecrosis, there were two 2 other cases and 46 hips had hemiarthroplasty for femoral neck fractures. The cementing grade was estimated on the postoperative radiographs. The 24 month postoperative radiographs were analyzed for changes in stem subsidence, cortical atrophy and cortical hypertrophy. According to the Gruen zone, 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, and more than 2 mm as grade 3. We defined Grade 1 as 1 point, Grade 2 as 2 points, and Grade 3 as 3 points. The points in every zone were calculated, and the average per zone was determined.
Result
The mean points of the cortical atrophy adjacent to the stem was 1.19 in THA, and 1.58 in BHA in zone II, 0.98 in THA, and 1.15 in BHA in zone III, 0.34 in THA, and 0.6 in BHA in zone V, and 0.63 in THA, and 0.93 in BHA in zone VI. Statistical significance was found between the two groups (THA and BHA). Stem subsidence slightly increased with time. During the following 2 years there was not a single case with over 1.5mm of stem subsidence. The average stem subsidence after 24 months was 0.72 in THA, and 0.78 in BHA. Cortical hypertrophy was only demonstrated in 5 cases.
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 the 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. These findings are compatible with the cortical hypertrophy reported with Exeter stem in zone 5.
Conclusion
Cortical atrophy (cancellizaton) was recognized in 70% of THA group, and in 80% of BHA group, 2 years after the operation. Cortical atrophy in most cases was recognized in Gruen Zones 2 & 3 (P<0.01). Cortical atrophy was found more severely and more frequently in the femoral neck fracture group than the THA group (P<0.01).
