# Tolerance and surface analysis of veterinary bone screws

## TL;DR

This study finds that veterinary bone screws often fail to meet quality standards, which could affect their performance in animals.

## Contribution

The study provides the first detailed dimensional and surface analysis of veterinary bone screws against engineering standards.

## Key findings

- Most screws exceeded tolerance limits for length, diameter, pitch, and thread angle.
- 40% of screws had an unacceptable surface finish.
- Deviations were observed across all manufacturers, with no single source dominating non-conformity.

## Abstract

While dimensional accuracy and surface characteristics of human orthopedic implants are extensively regulated and studied, comparable evaluations of veterinary orthopedic implants are limited. This study aimed to assess the dimensional conformity and surface finish of commercially available veterinary cortical bone screws relative to established engineering standards.

Seventy-three commercially available 2.0 mm veterinary cortical bone screws from five anonymized manufacturers were analyzed using high-magnification optical microscopy. Dimensional parameters assessed included screw length, major diameter, minor diameter, thread pitch, and combined thread angle (α + β). Measurements were calibrated using a certified micrometer scale. Dimensional conformity was evaluated using a unilateral tolerance framework based on ISO 5835 low-quality limits. Surface finish was assessed using a semi-quantitative grading system under standardized magnification.

Most screws exhibited dimensional deviations outside the defined tolerance limits. Eighty percent of screws were outside tolerance for length, 78% for major diameter, 77% for minor diameter, 98.6% for pitch, and 60% for combined thread angle. Surface finish was classified as unacceptable in 40% of screws. Tolerance deviations were observed across all manufacturers, with no single manufacturer accounting for the majority of non-conforming screws.

The findings demonstrate substantial dimensional variability and surface defects in commercially available veterinary cortical bone screws. These deviations may adversely affect screw biomechanics and the bone–implant interface, indicating suboptimal manufacturing quality. The absence of regulatory oversight for veterinary implants highlights the need for improved quality control standards to ensure consistent and reliable implant performance.