Overview
ISO 7206-13:2016 defines a laboratory method to determine the torque required to loosen the head fixation of stemmed femoral components used in partial and total hip joint prostheses. It applies when the femoral head and neck/stem (the cone) are separate components joined by a locking conical taper or other mechanical means, and covers metallic and non‑metallic materials. The standard focuses on static torque testing under specified conditions; it does not prescribe specimen handling or clinical inspection procedures.
Key topics and technical requirements
- Test principle: Apply a steadily increasing static torque to the head/cone assembly until breakaway (rotation) occurs or a defined maximum is reached.
- Sample size: A minimum of five test specimens per cone unit.
- Assembly and fixation: Assembly follows ISO 7206-10 procedures. Head fixation for torque application can be achieved by:
- Flattening the head equator to two parallel planes (perpendicular distance 30–70% of head diameter; remaining wall ≥ 2.0 mm). Example: for a 28 mm head, 19.0 mm ± 0.5 mm is suitable.
- Gluing the head into a metal calotte covering at least 140° of the hemisphere (bond breakaway torque must exceed expected head/cone torque).
- Embedding the head in cast resin (embedding/bond strength must exceed expected torque).
- Loading rates and limits:
- Torque loading rate: 20 Ncm/s ± 4 Ncm/s, or rotation rate 0.05°/s ± 0.01°/s.
- Termination criteria: load peak and decrease, torque limit 50 Nm, or angle limit 20°.
- Apparatus requirements: Testing machine compliant with ISO 7500-1, able to apply axial compressive force for assembly and torque with 1% accuracy; angular displacement measurement to ±0.5°.
- Alignment: Axis alignment and degrees of freedom are required to avoid biased results (fixture ideally allows 5 DOF).
- Performance criteria and reporting:
- Acceptance criteria are defined by the customer (often relative to clinically successful assemblies) and should include mean and per-sample lower limits.
- Test report must reference ISO 7206-13 and include specimen identities, fixation method, loading rates, maximum torque/angle at rotation, termination reasons, and observable damage.
Applications and who uses it
- Implant manufacturers - design verification, quality control of modular taper connections and femoral head fixation strength.
- Test laboratories - standardized procedures for reporting breakdown torque and generating comparative data.
- Regulatory bodies and notified bodies - evidence of mechanical stability for conformity assessment and pre‑market submissions.
- R&D and failure analysis teams - development of taper geometries, material pairings, and assembly processes to reduce fretting and micromotion.
Related standards
- ISO 7206 series (e.g., ISO 7206-1, ISO 7206-10) - dimensions and static load procedures for femoral heads.
- ISO 7500-1 - verification and calibration requirements for testing machines used in this test.
Keywords: ISO 7206-13:2016, hip joint prostheses, torque resistance, head fixation, stemmed femoral components, taper connection, implant testing, femoral head torque test.
Open preview (PDF)Implants for surgery — Partial and total hip joint prostheses — Part 13: Determination of resistance to torque of head fixation of stemmed femoral components