The management of proximal femoral bone loss is a significant challenge in revision hip arthroplasty. A possible solution is the use of a modular proximal femur endoprosthesis (EPR). Although the survivorship and functional outcome of megaprostheses used in tumour surgery has been well described, outcome of EPRs used in revision hip surgery has received less attention. The aim of this study was to determine the 5-year outcome following proximal femur EPR and determine factors that influence it.

This was a retrospective consecutive case series of all EPRs (n=80) performed for non-neoplastic indications, by 6 surgeons, in our tertiary referral centre, between 2005–2014. Patient demographics and relevant clinical details were determined from notes. The most common indications for the use of EPRs included infection (n=40), peri-prosthetic fracture (n=12) and failed osteosynthesis of proximal femoral fractures/complex trauma (n=11). Outcome measures included complication and re-operation rates, implant survival and assessment of functional outcome using the Oxford-Hip-Score (OHS).

The mean age at surgery was 69 years and mean follow-up was 4 (0 – 11) years. The mean number of previous hip operations was 2.4 (range: 0 – 17). Twenty-five patients sustained a complication (31%), the most common being infection (n=9) and dislocation (n=4). By follow-up, further surgery was required in 18 (22%) hips, 9 of which were EPR revisions. 5-yr implant survivorship was 87% (95%CI: 76 – 98%). Mean OHS was 28 (range: 4 – 48). Inferior survival and outcome were seen in EPRs performed for the treatment of infection. Infection eradication was achieved in 34/41 with the index EPR procedure and in 40/41 hips by follow-up.

Limb salvage was achieved in all cases and acceptable complication- and re-operation rates were seen. EPRs for periprosthetic fractures and failed osteosynthesis had best outcome. We recommend the continued use of proximal femur EPR in complex revision surgery.

Optimum component orientation in hip arthroplasty is vital in an effort to avoid dislocation and excessive wear. Computer navigation in hip arthroplasty surgery has the potential to improve accuracy in component placement. However, it has been slow to gain widespread acceptance. One of the major concerns surgeons have is the difficulty in registering pelvic landmarks.

We used a retrospective series of 200 pelvic CT scans to validate a new methodology to construct the anterior pelvic plane, using anatomical landmarks that are easily palpated with the patient positioned and draped in the lateral decubitus position. Analysis of the scans was also made in an effort to stimulate the inaccuracies of obtaining the anterior pelvic plane through soft tissue.

When comparing the new registration methodology to the anterior pelvic plane, the error in acetabular component inclination was 0.69° (SD 2.96) and anteversion was 1.17° (SD 3.53). This compares favourably to the error in acetabular component inclination of −0.92° (SD 0.26) and anteversion of −5.24° (SD 2.09) when the anterior pelvic plane is registered through soft tissue. The data also shows that using the new registration method in more than 99.6% of cases the acetabular placement is within the safe zone as described by Lewinnek.

This study appears to show that through the identification of anatomical constants we are able to construct the anterior pelvic plane from anatomical landmarks that are easily palpable in the lateral decubitus position during hip arthroplasty. These landmarks also appear to be more accurate in obese patients than registering the anterior pelvic plane.

Introduction: In a photoelasticimetric model Ondrouch suggested a correlation between stress in arthritic joints, microfractures and bone cysts. Other authors believe in a causative role of access of joint ßuid to bone in periarticular osteolysis. In our opinion mechanical stress induced by cartilage defects induces microfractures followed by cystic bone degradation. Materials and Methods: A þnite element analysis using the well described parameters for cancellous and cortical bone as also cartilage was performed. Several typical situations of localized and general cartilage pathologies were calculated in a schematic hip joint situation. Results: A signiþcant impact of cartilage defect size and resulting stress distribution correlating well to cystic lesions of patients with osteoarthritis of the hip could be shown. In localized cartilage defects max. stress was calculated at the rims of the lesions in the subchondral bone. Assuming a situation with an allready preformed cyst either in the acetabulum or the femoral head, further enlargement of the cyst will appear due to a maximal stress at the rims of the lesions. Femoral lesions have a comparable small tendency to grow, thereas acetabular lesions will grow rapidly. Discussion and Conclusion: These þndings þt very well with the clinical observations. Cartilage lesions inducing microfractures by mechanical stress may be able to explain the process of subchondral cyst formation. A process involving osteoclasts and myxomatous cells within the bone marrow seems to be a subsequent mechanism of remodelling and formation of myxomatous cyst content.