Berry and colleagues examined whether femoral head diameter and operative approach changed the long‑term risk of dislocation after primary total hip arthroplasty.
Mayo Clinic series of 21,047 primary hips in 17,168 patients (1969 to 1999), each asked specifically about dislocation at set intervals for up to 30 years.
Key Findings
Dislocation risk was lowest with 32‑mm heads and highest with 22‑mm heads under every approach. After adjustment, 22‑mm heads carried 1.7 times the risk (95% CI 1.3 to 2.1) and 28‑mm heads 1.3 times (1.0 to 1.6).
Head size mattered most with the posterolateral approach: 10‑year dislocation was 12.1% with 22‑mm, 6.9% with 28‑mm and 3.8% with 32‑mm heads. The gradient was small anterolaterally (3.8% to 2.4%) and transtrochanterically (3.5% to 2.8%).
The posterolateral approach carried 2.3 times the adjusted risk of the anterolateral approach. These hips predate routine posterior capsular repair, which appears to reduce early dislocation.
First‑time dislocations kept accruing: cumulative risk was 2.2% at 1 year, 3.8% at 10 years and 6.0% at 20 years. Late first dislocations occurred with all three head sizes.
Compared with osteoarthritis, arthroplasty for hip fracture (1.8), osteonecrosis (1.6) or inflammatory arthritis (1.4) independently raised dislocation risk, as did age 70 or older (1.2) and female sex (1.2).
Head size tracked era: 22‑mm heads were used more in the 1970s, 32‑mm in the 1980s and 28‑mm in the 1990s. Head diameter is not the same as head‑to‑neck ratio, which was not studied.
Authors' conclusion
In total hip arthroplasty, a larger femoral head diameter was associated with a lower long-term cumulative risk of dislocation. The femoral head diameter had an effect in association with all operative approaches, but the effect was greatest in association with the posterolateral approach.
Berry and colleagues examined whether femoral head diameter and operative approach changed the long‑term risk of dislocation after primary total hip arthroplasty.
Mayo Clinic series of 21,047 primary hips in 17,168 patients (1969 to 1999), each asked specifically about dislocation at set intervals for up to 30 years.
Key Findings
Dislocation risk was lowest with 32‑mm heads and highest with 22‑mm heads under every approach. After adjustment, 22‑mm heads carried 1.7 times the risk (95% CI 1.3 to 2.1) and 28‑mm heads 1.3 times (1.0 to 1.6).
Head size mattered most with the posterolateral approach: 10‑year dislocation was 12.1% with 22‑mm, 6.9% with 28‑mm and 3.8% with 32‑mm heads. The gradient was small anterolaterally (3.8% to 2.4%) and transtrochanterically (3.5% to 2.8%).
The posterolateral approach carried 2.3 times the adjusted risk of the anterolateral approach. These hips predate routine posterior capsular repair, which appears to reduce early dislocation.
First‑time dislocations kept accruing: cumulative risk was 2.2% at 1 year, 3.8% at 10 years and 6.0% at 20 years. Late first dislocations occurred with all three head sizes.
Compared with osteoarthritis, arthroplasty for hip fracture (1.8), osteonecrosis (1.6) or inflammatory arthritis (1.4) independently raised dislocation risk, as did age 70 or older (1.2) and female sex (1.2).
Head size tracked era: 22‑mm heads were used more in the 1970s, 32‑mm in the 1980s and 28‑mm in the 1990s. Head diameter is not the same as head‑to‑neck ratio, which was not studied.
Authors' conclusion
In total hip arthroplasty, a larger femoral head diameter was associated with a lower long-term cumulative risk of dislocation. The femoral head diameter had an effect in association with all operative approaches, but the effect was greatest in association with the posterolateral approach.