Evaluation of Cemented and Cementless Fixation of Dual-mobility Hip Prosthesis in Elderly Patients With Osteoarthritis

The Elderly Hip Patient The proportion of elderly in the Danish population is increasing and their and functional level is generally good, despite other health problems, which intensifies the demand for a primary definitive (one-stage) and safe surgical treatment in case of osteoarthritis or fragility low-energy displaced femoral neck fracture. Total hip arthroplasty (THA) is one of the most successful procedures in modern orthopaedic surgery to achieve pain relief and restore normal walking ability in a preoperative painful and stiff hip joint.

Bone Quality and THA surgical technique Osteoporosis (brittle bones) is defined as a chronic systemic skeletal disease characterized by low bone mineral density (osteopenia) and microarchitecture changes in the trabecular bone structure resulting in reduced strength and therefore increased risk of fractures. Among Danish women over 65 years of age, the prevalence of osteoporosis is 40-60%, and the prevalence among men is increasing. Much effort is put into secondary fracture prophylaxis such as vitamin D and calcium as well as medical bone anti-resorptive treatment (i.e. bisphosphonates).

When the bone is weak/osteoporotic there is a general but undocumented recommendation of cemented over uncemented THA fixation. It has been shown that uncemented hip stems migrate more than cemented components in osteopenic and osteoporotic bone wherefore cemented stem fixation is recommended. However, Danish hip surgeons favour uncemented fixation even in the fragile and osteoporotic elderly because it reduces the surgical time, minimizes the risk of intraoperative cement disease/fat embolism and dead, and makes revision surgery in case of infection or peri-prosthetic fracture easier to re-operate. In 2012, 7364 acetabular cups were inserted uncemented versus 1015 uncemented - for all indications for THA in Denmark. Reoperation of the same hips within 2 years after primary THA due to new femoral neck fracture or complications following treatment of proximal femoral fracture was 4.7 %. There is clinical conviction that cemented cups are easier to place in the correct inclination and anteversion position. However, due to the posterior-lateral overhang of dual mobility cups the postero-lateral edge-cementation is likely to be insufficient leading to micromotion and aseptic loosening. In the clinical experience this is a lesser risk with cementless cups. Compared to other Nordic countries, Denmark has the lowest incidence of aseptic cup loosening of 34.8% and respectively 47.3% and 50.4% for Norway and Sweden. The reason for revision due to dislocation is 33.5% in Denmark compared to Norway and Sweden, respectively 23.8% and 23.4% and may be related to an overall difference in surgical approach (postero-lateral approach in Denmark but antero-lateral approach in Norway and Sweden). Approximately 96% are operated with posterior approach in Denmark whereas 23.8% and 60.3% were operated by posterior approach in Norway and Sweden, respectively.

Dual-mobility articulation concept In 1974 Professor Bousquet developed the dual-mobility (DM) hip articulation concept to reduce wear, restore near-normal motion-range in the hip joint, and at the same time increase hip prosthesis stability. The dual-mobility hip articulation design consist of a large non-fixed polyethylene liner sliding freely within the metal cup-shell which is fixed into the bone, and inside the mobile liner is a second articulation with a small femoral head. The dual-articulation of the prosthetic joint prevents impingement of the femoral neck on the acetabular rim of the implant. Studies have shown that dual-mobility hip prostheses have good survival rates and reduces dislocation rates both in patients with primary osteoarthritis of the hip and a lesser compliant patient group with displaced femoral neck fractures . Clinical expectations for the dual-mobility articulation concept for treatment of displaced medial FNF are good; however, there are only a few publications available and there are no studies of implant fixation / cup migration. It is important to study both the dislocation risk as well as the mechanical stability of the bony fixation since the advantage of a low dislocation rate would be meaningless if the cups were to loosen mechanically from the surrounding bone in the mid- or longer term.

Femoral Neck Fracture and THA THA may be used as the primary treatment option for displaced medial femoral neck fractures (FNF). Compared to screw osteosynthesis, THA results in a stable fracture treatment with less post-operative pain and faster mobilization after displaced medial FNF and with fewer complications. The most common complication to THA treatment in old and perhaps memory-impaired patients is dislocation instability. At the Regional Hospital Holstebro our results with the Saturne® Dual-Mobility THA in this patient group (n>500) during the last 7 years propose the risk of THA hip dislocation in high-risk patients to be below 5%. In 2012, 10,309 patients were admitted to Danish hospitals with femoral fractures. Approximately 600 of these hip fracture patients were treated with THA. Patients with hip fractures are very resource intensive and require approximative 2.2% of all hospital bed days in Denmark. Furthermore, these elderly, with an average age of 80 years and a high co-morbidity percentage also have a high mortality risk of approximately 10% within the first 30 days after FNF. The one-year mortality is 15-25%. Reoperations frequency depends on the fracture type and operative treatment, and varies from a few per cent after insertion of THA to 25% after osteosynthesis. Often it is the acute and chronic medical conditions that cause the elderly to low energy falls resulting in hip fracture, but it may also just be accidental and related to osteoporosis.