Sampling plan for orthopedic implant - Process Validation


I am working as a process validation engineer in Europe. Our notified body recommended us to perform process validation when the output cannot be verified at 100%.
The recent changes in standards (for example ISO 19227 for the validation of cleaning process of orthopedic implants, ...) ask to use "statistical techniques with rationale for sample sizes". And i have difficulties to define a statistical rationale because:
- we have very small lot (the batch size is between 10 and 100 pcs around)
- we have no process history
- all my processes are outsourced and my subcontractor are really bad in quality field, they have never validated a process and I am new in process validation field too

I have attributes data (GO/NO GO) and variable data (length for example).

1) Attribute
For the attributes, i need to choose an AQL and a LTPD. For priority, we are focusing on validating all the critical output (TOC, THC, cytotoxicity, ...). For that, we have a defined an AQL of 0.25% (no process history, no rationale) and for the LTPD, I do not know how to choose it...

2) Variable
We plan to perform a capability study and plan to prove that the process is capable (Pp and Ppk > 1.33). However, after that, i do not know how to choose my sampling... Do i have to the ppk to a LTPD and an AQL?

Do you know how to choose LTPD and AQL acceptable for critical default (sterility, cleanliness, critical dimensions, ....) when the lot size is really small (orthopedic implants, ...)?


all my processes are outsourced and my subcontractor are really bad in quality field, they have never validated a process and I am new in process validation field too
IMHO, you cannot succeed with these prerequisites.

Without diving into specifics:
  • in case you a running short of actual product for your validations, can you define and build worst-case (dummy) products, in sterilization often referred to as "PCD (Process challenge device)" that represent you actual products in the relevant process characteristics?
  • In case you are planning to use standard sterilization methods (such as irradiation or ethylene oxide), the related standards are pretty specific about required sample sizes.

Hi Gerhard,

I have no issue for the processes like the gamma sterilization because the standard is very clear on the methodology and the sampling.
However, it is not the case for the machining, laser marking, packaging processes where no sampling plan is described.

It is asked to use "statistical techniques with rationale for sample sizes ". I do not know which AQL and LTPD to use for my critical characteristics. And which sampling to use for small batch production...
Hello, a little bump since I began some testings...

Context: It is very difficult to explain the necessity of validation to our supply so we do not have a solid OQ (meaning no identification of critical parameters such as speed, ...). I just have a machine capability performed on a complex and aluminum product using all the axes (8 or 9) of one equipment. As all the equipment are of the same brand, we decided to accept this "OQ".

I am currently performing a performance qualification of CNC equipments. They are used for the manufacturing of orthopaedic implants (screws, rods, nuts, ...). We have decided to manufacture for each kind of product (based on their physical dimensions) at least three batches representative of the routine. We already identified for each of them critical dimensions and critical aspect. Most of them are measured but few of them are controlled by a GO/NO test or visual aspect.

we agreed with the supplier for the three first batches of each product reference to control and record:
- 100 measures for each dimension per batch --> my aim was to have enough data to perform a capability study and calculate the lower bound of capability index with a confidence level of 95%. I saw that 100 measures are a good sampling to have relevant confidence in the capability indexes (and i will have 300 measures if there are no variation inter lot). But i did not find relevant sources.
- 100% of control GO/NO GO and 100% for the visual aspect. honestly, the production was launched without ending the protocol writting so we decided to have the maximum of values. but I do not know if I have to write a rationale with an approach of LTPD/AQL for critical defauts or do i need to also perform a capability study (with minitab). How can i justify this sampling in my protocol?

The aim is to validate the manufacturing process by showing that:
- for the dimensions measured, the process is stable and have a pp/ppk lower bound at 95% of confidence > 1.33. After that, should I calculate the Z score, calculate the %ppm and link to the AQL/LTPD too?
- for the characteristics controlled by visual inspection or GO/NO GO controls, i do not know if i i have to use capability studies too or claim a NQA/LTPD %...

Thanks for your help,

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