A new acetabular shell reamer will cut according to its designated size, with a tolerance of + 0.00 mm/ -0.50mm. After numerous surgeries, the reamer may cut undersize, in proportion to wear on the teeth. Often, the actual cut size will fall out of the specification of the lower limit of its nominally labeled size after 2-3 months of use. For example, a new 56mm shell might measure 55.7mm. With wear from 25 surgeries on its cutting teeth, it may now cut 55.2mm in the acetabulum –.30 mm below specifications. Rather than sheering a clean swath when new, worn and rounded teeth may burnish and push away on the bone to a much higher degree, deflecting the bone and the shell enough that there’s a measurable difference in cut size between a dull shell reamer versus a sharp one of the exact same physical size. One can feel this effect when reaming, with the higher push forces needed to obtain a cut. These factors together, as seen in independent studies, cause undercutting during reaming of the acetabulum by as much as 2mm in size!
“When sharpened with the chemical honing process ChemSharp™, will the shell reamer cut be even smaller?”
Acetabular shell reamers may recover some cut size after re-sharpening. OrthoGroup’s testing with dull shells which were then re-sharpened was surprising. The average cut size of the ChemSharp chemically-honed group was approximately .25mm larger. Conclusion: Some of the cut size that was lost from wear, was recovered simply by re-sharpening with ChemSharp.
“How do acetabular shell reamers wear, and how quickly?”
Acetabular shell reamer wear comes from 3 main causes: • Physical abrasion with cancellous and cortical bone. • Contact with retractors during reaming can cause wear or damage on teeth, and can come from contact with trays and other instruments and rough handling in cleaning and sterilization. • Steam sterilization itself is detrimental to sharpened edges. Wear surfaces rapidly become non-passive and subject to corrosion. An outlier size such as a 38mm may sit unused in a sterilization tray, though the tray of reamers may have gone through 30-40 surgeries. Caustic disinfecting chemicals, steam sterilization and incidental contact with other instruments will cause erosion of the original surface, even while never having gone through any acetabular cutting.
“Are we using our sets too long before replacement?”
There are many factors that lead to wear in shell reamer sets, but a good rule of thumb used frequently is, a set should be retired after 10-12 weeks of surgeries in a moderately busy environment – maybe after 30 surgeries worth of use. Often, surgeon complaints lead to the retirement of a dull set of acetabular shell reamers (and/or other cutting instruments). The surprising results of a literature search, citing references and in-house testing, reveals just how much wear can affect both cutting, performance, and surgical efficacy. This may beg the question: “Are we using our sets too long before replacement?” You be the judge, after reading the next question:
“What is the impact of using dull and worn shell reamers?”
• Surgeon Fatigue: Dull shell reamers require more forceful engagement of the reamer into the acetabulum being reamed, causing surgeon fatigue, frustration, and prolonged reaming. • Oblong cuts: Dull shell reamers will tend to “hunt” for softer bone, resulting in less precise, oblong cuts, rather than accurate, spherical cuts as intended. • Undercutting: worn shell reamers cut undersize and can compromise the fit of the acetabular component. • Burnished, less vascular reamed surfaces: Dull teeth on the acetabular shell reamer compress and burnish the exposed surfaces of the acetabulum where the acetabular component is to be seated, and can inhibit healthy bone growth into the porous coating of the acetabular cup implant. Conclusion: If you are waiting for the surgeon to complain about poor cutting performance of the acetabular shell reamers, you have waited too long to replace them.
• Surgeon satisfaction: Less frustration and fatigue – and improved accuracy – when using sharpened acetabular shell reamers. • Cutting performance: Superior cutting accuracy and vascularity following the ChemSharp process. • Significant savings: A new set of shells can average around $3,000 and take many months to arrive, especially in these modern times of supply chain disruptions. You can now resharpen your instruments in a week or less with our proven process – and save money! By employing the ChemSharp process you can save about $2000 per set and have your shells back in time for your next case. • Speeds Surgery: Faster and easier reaming with sharper instruments makes the cutting process quicker and more efficacious. Saves OR time and money! • Environmentally Green: Each time you throw away a perfectly good but dull set of acetabular shell reamers or other cutting instruments, you add to the medical waste issues plaguing the industry.