[Application of bone-retaining femoral stem prosthesis in young patients with Dorr C femoral medullary cavity].

To assess the clinical efficacy of Tri-Lock bio-short prosthesis in artificial total hip arthroplasty(THA) in young patients with Dorr type C femoral medullary cavity.From January 2010 to January 2014, 35 young patients(37 hips) with in the chimney-like femoral medullary cavity received Tri-Lock BPS prosthesis of THA, including 18 males(20 hips) and 17 females with an average age of (32.2±3.0) years old ranging from 21.2 to 38.5 years old. There were 16 cases of rheumatoid hip arthritis (17 hips), 8 cases of rheumatoid arthritis (9 hips), and 11 cases of aseptic necrosis of femoral head (11 hips). All cases were complicated with different degrees of osteoporosis. According to Singh index, 26 cases were classified as Grade III and 9 cases as Grade II. Biological prostheses were used for the acetabulum, with ceramic lining and full ceramic femoral head. The proximal femoral medullary cavity was Dorr type C on anteroposterior X-ray. After replacement, X-ray examination was performed to locate the prosthesis stem. Engh and Harris criteria were used to evaluate the stability of bone-prosthesis interface and hip function, respectively. Changes of hip movement pre-operation and at last follow-up were compared.All patients were followed up for 18 to 45 months(means 33.8 months). Harris hip scores in 35 cases (37 hips) increased significantly from preoperative 61.8±3.0 (51.2 to 73.5) to 93.3±6.5 (92.5 to 98.8) points at last follow-up (t=54.745, P<0.01). The hip mobility increased from (46.5±8.0)°(0° to 55°) before surgery to(101.2±10.5)°(85° to 130°) at the last follow-up, the difference was statistically significant(t=133.091, P<0.01). Immediately after surgery, the prostheses were tightly packed with the medullary cavity. At the final follow-up, 17 hips had significant femur cortical bone thickening;12 hips had varying degrees of stress occlusal bone resorption at proximal femoral, including 9 degree I(low femur density, round and blunt) and 3 degree II(involving small rotor) hips. Meanwhile, 15 hips had significant femur cortical bone thickening without thigh pain.The cone-shaped short Tri-lock biological short-stem can fill Dorr C chimney-like medullary cavity and effectively retain good proximal femoral bone mass. Titanium microporous coating on the surface can effectively increase the friction of the prosthesis. The short-stem end in the medullary cavity can effectively avoid the occurrence of coxa varus.