Thigh pain, subsidence and survival using a short cementless femoral stem with pure metaphyseal fixation at minimum 9-year follow-up.

BACKGROUND

Short femoral stems designed to spare bone stock and improve load transfer at the proximal femur level have been introduced in recent years. However, little is known on the long-term outcomes of these stems.

HYPOTHESIS

Short cementless stems have low rate of thigh pain and subsidence as well as few revision needs at mid-term follow-up.

MATERIALS AND METHODS

We prospectively followed 64 patients (72 hips) undergoing total hip arthroplasty with a femoral stem designed to achieve a pure metaphyseal fixation. Patients with hip fracture, femoral neck deformity and osteoporotic bone were excluded. Clinical evaluations were performed annually until the last follow-up, a minimum of 9 years after surgery. At each follow-up, implant positioning was assessed on conventional plain films with a computer assisted radiographic evaluation.

RESULTS

The Harris hip score improved from 43 points (range 19-50) before surgery to 88 points (range 73-100) at the final follow-up (P=0.001), and the Womac score averaged 47 points (range 35-56 points) preoperatively and 76 points (range 63-84) at the last follow-up (P=0.001). Thigh pain was reported by five patients (8%) at the 2-year follow-up, but only in two (3%) was still present, and related to the prosthesis, at last follow-up. Computer assisted radiographic analysis showed a neutral alignment of the stem in 56% of cases, a varus-valgus alignment less than 5° in 36% and equal to 5° in 8%. Stem subsidence was observed in 12 hips but was less than 4mm in all cases (range 0-3mm). Calcar height remained unchanged over time. Adaptive bone remodelling, including proximal bone resorption and distal cortical hypertrophy were not observed at follow-up. No patients had aseptic loosening of the stem nor were radiolucent lines detectable at the level of the porous coating. Survivorship analysis showed a 100% survival rate of the stem at nine years.

DISCUSSION

This study showed that a femoral stem designed to achieve a pure metaphyseal fixation may obtain, in a selected group of patients with adequate bone quality, satisfactory clinical outcomes without compromising implant stability. The limited periprosthetic bone remodelling observed after a minimum of 9 years follow-up suggests that this type of implant may improve mechanical stresses on host bone compared with standard stems requiring diaphyseal fixation.

LEVEL OF EVIDENCE

Level IV. Historical series.