Automatic Bone Screw Inspection and Measurement with VisionGauge®

VisionGauge® for Orthopedic Screw Inspection

Orthopedic reconstructive and reparative procedures commonly use medical bone screws as fixation devices. Among other applications, they are employed for bone-to-bone fixation. The bone heals better and faster if the fractures are pressed together firmly by orthopedic screws. The advantage of these screws is that they reduce the gap between the bones, and, consequently, decrease the stress. Another common use of medical bone screws is to attach various implants, such as plates, to the bone. Medical bone screws are also utilized for a variety of other general anchorage and fixation purposes.

The VisionGauge® Digital Optical Comparator is widely used by medical device manufacturers for automated inspection and measurement of orthopedic/medical bone screws.

Bone screw teeth verification with the VisionGauge® “Tooth Checker™” tool

Patented CAD-Auto-Align™, CAD-Auto-Pass/Fail™ & Tooth Checker™ tools are perfect for locating the teeth crests and/or roots and checking the part’s profile

X-ray showing fracture after stabilization with dynamic hip screw with long plate

X-ray showing fracture after stabilization with dynamic hip screw with long plate

Benefits of Bone Screw Inspection with VisionGauge® Digital Optical Comparators

VisionGauge® introduces several unique benefits in its application to the measurement and inspection of medical bone screws, including:

Proprietary CAD-Auto-Align and CAD-Auto-Pass/Fail tools for bone screw measurement

  • Compare bone screws directly to their CAD part design data.
  • The system checks screws 100% automatically in any orientation using its proprietary, patented CAD Auto-Align™ and CAD Auto-Pass/Fail™ tools.
  • The patented VisionGauge® Tooth Checker™ inspects the screw thread profile automatically, to verify all the peaks and valleys respect their specified tolerance band, regardless of the screw’s clocking.
  • Removes all operator subjectivity!
  • Automatically collects all result data for a complete device inspection history, including measurements, statistics, images, and more.
  • An extended depth-of-field permits the entire screw to be in focus - even at the helix angle, so there is no need for constantly refocusing!
  • Measure all of the screw's characteristics to very high accuracy, completely automatically:  Major/minor diameters, spacing and tooth pitch, runout, and other characteristics...
  • As an option, the system supports a rotary stage for very accurate, automated measurement of the helix angle.
  • The system is perfectly suited for bone screw inspection and measurement directly from the shop floor.
CAD Auto Pass/Fail and CAD Auto-Align tools on the VisionGauge Digital Optical Comparator inspecting threads and other features of interest on bone screws.

Check all the features of interest, quickly and to very high accuracy.

Multiple bone screws ready for automated inspection on the VisionGauge Digital Optical Comparator

Load multiple screws onto the system to have them all checked completely automatically

Features and Supported Bone Screw Measurements with VisionGauge®

Bone screw nomenclature for measurements

Orthopedic bone screws are made up of different features, with the principal features comprised of the head, thread, and tip. Different requirements apply to each feature to ensure proper overall performance of the screw. These diverse requirements can considerably complicate the inspection of bone screws. However, VisionGauge® can easily check 100% of the features over the entire screw, including its threads, head, and tip.

The importance of proper inspection of medical bone screws, both during the manufacturing process and at final inspection, cannot be overstated. Proper inspection allows bone screw manufacturers to ensure correct performance, conformance to specifications, and reduced variability of the final product. Furthermore, real-time inspection and measurement with VisionGauge® allows medical manufacturers to optimize the manufacturing process, reduce overall manufacturing costs, improve process control and enable process & part improvement. VisionGauge®'s statistics, data collection & exchange, and reporting provide manufacturers with product traceability and device history.

Automatic thread inspection: Automatically detect crests and roots in major/minor diameters of teeth or screw threads with VisionGauge®’s Patented “Tooth Checker™”.

VisionGauge®'s patented Tooth Checker™ is a fundamental feature for this optimal inspection of bone screw threads. The tool is easy-to-use, and it imposes no limits on the part geometry. It can quickly ensure that the thread peaks and valleys are all located within the specification's tolerance band, regardless of the screw's clocking. This powerful, unique tool represents a dramatic advance for bone screw inspection technology. For medical bone screw manufacturers, an accurate thread profile is critical since a number of the screw's properties (e.g., its pull-out strength...) directly depend on the screw thread profile. These manufacturers will appreciate the completely operator-independent results and many other drastic improvements presented by VisionGauge®'s patented Tooth Checker™ tool compared to the traditional optical comparator and overlay charts approach historically used to control screw threads.

VisionGauge® is capable of measuring 100% of the screw’s critical dimensions and features, including:

  • Major diameter
  • Minor diameter
  • Helix angle
  • Thread pitch
  • Pitch Diameter
  • Lead/trailing flank angles
  • Root radii
  • Lead
  • Taper
  • Circularity
  • and more...
Automatic inspection and measurement of threads and other dimensions of a bone screw

Automatically check screw dimensions

Bone screw head measurements

Check all of the features on the head

Finally, a dedicated complete dual-rotary assembly, designed specifically for the fully automated inspection and measurement of bone screws, is also available. It allows the full rotation of the screw (to check run-out, for example), its orientation at the helix angle, etc... This package also includes dedicated workholding (either pneumatic or manual) compatible with bone screws that have a thru hole as well as those without. When fitted with a pneumatic chuck, this dedicated dual-rotary assembly allows VisionGauge® to be used in a fully-automated bone screw manufacturing cell, with robot loading and unloading, for complete "lights out" operation.

Additional Information About Orthopedic Screws

There exists a wide range of orthopedic screws and they are often named after the type of bones in which they are inserted during the surgery. A few common types include:

  • Cortical screws that are designed for anchoring a cortical bone and have threads with a very fine pitch. Cortical bones are dense and compact.
  • Cancellous screws have coarser threads that are smooth, with unthreaded portion that allows the screw to act as a lag screw. A cancellous screw is longer than a cortical screw. Cancellous bones are also termed as spongy bones since they are a bit softer than the cortical bones. Examples of such bones include the ribs and pelvic bones.
  • Cannulated screws, that have a hollow shaft.
  • Herbert orthopedic screws are a variable pitch cannulated screw that are designed for fractures in small articular bones, such as the carpals. These screws are used mainly where a standard screw would affect adjacent tissue, such as in the case of the treatment of scaphoideum or osteoarticular fractures.
  • And many others as well...

With its wide range of measurement tools and great flexibility, VisionGauge® is the perfect tool for inspecting and measuring 100% of the features on all of the different types of bone screws.

variety of surgical screws

VisionGauge® includes complete inspection and measurement toolsets for checking and verifying a wide variety of surgical screws.

Thoracic lumbar vertebra pedicle screws

Thoracic lumbar vertebra pedicle screws.

Orthopedic screws can be made of different materials and have a wide range of coatings. Titanium, stainless steel and bio-absorbable materials, that get absorbed by the body over time, are the most common types of materials for bone screws. By design, bone screws require hard-to-machine materials. This only compounds the difficulties involved in machining their complex threads. This further increases the importance of complete and proper inspection and measurement of bone screws throughout their manufacturing process, for proper control. With its flexible illumination modules and powerful adaptive measurement tools, VisionGauge® has no problem accommodating any of the variations in bone screw material and finish.

X-ray of wrist fracture stabilized with plate and bone screws

For inspection and measurement of orthopedic screws on the VisionGauge® Digital Optical Comparator, some manufacturers use horizontal configurations, while others use a vertical configuration. The decision to use one or the other is generally based on fixturing considerations. The hard chrome plated stage, made from hardened tooling steel, has industry standard dual dovetail grooves that make it compatible with existing mounting fixtures, and a drop-in replacement for traditional optical comparators. Rotary stages are also an option that can be added to these systems.

The VisionGauge® Digital Optical Comparator is the new standard in measuring and controlling the geometry of medical/orthopedic bone screws. Screw manufacturers can ensure their product has good dimensional accuracy and surface finish while also significantly reducing inspection times and overall cost. Operator-to-operator variation is entirely eliminated with this system, and manufacturers are capable of automatically collecting accurate screw dimensions and inspection result data, computing process statistics, and automating complete inspection reports. The VisionGauge® Digital Optical Comparator is an invaluable tool for process control and quality improvement, and it represents a significant advantage in modern competitive medical markets for bone screw manufacturers.

Download a .pdf version of this VisionGauge® Digital Optical Comparator Application Note.


Machine Vision Products Application Bulletins: