Why One Equivalent Device Is Often Not Enough

Written by HATEM RABEH, MD, MSc Ing

Your Clinical Evaluation Expert And Partner

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Most manufacturers assume that demonstrating equivalence means finding one single equivalent device that matches their own. This assumption shapes entire clinical evaluation strategies. It also creates vulnerabilities that Notified Bodies identify immediately.

The reality is more complex. Full equivalence to a single device is the ideal scenario, but it is not always achievable. When it is not, manufacturers must consider partial equivalence across multiple devices.

This is not a workaround. It is a legitimate regulatory pathway explicitly recognized in the MDR framework. But it requires careful justification, systematic documentation, and clear reasoning.

Here is what happens in practice, why partial equivalence matters, and how to structure it properly.

What Partial Equivalence Actually Means

Partial equivalence occurs when no single device on the market matches your device across all technical and clinical characteristics. Instead, you demonstrate equivalence by combining data from multiple devices, each contributing a portion of the equivalence argument.

For example, one device may share the same material composition and surface treatment. Another device may share the same anatomical site and intended use. A third device may share the same mechanism of action or clinical application.

Together, these devices cover the full scope of technical and clinical characteristics required to support your equivalence claim.

The MDR does not prohibit this approach. MDCG 2020-5 acknowledges that equivalence may be based on more than one device. But it sets clear expectations: the combined data must demonstrate equivalence to the same level of rigor as a single-device equivalence claim.

This is where many submissions fail.

Why Manufacturers Struggle With Multiple Equivalent Devices

The first issue is logical structure. When you introduce multiple devices, the equivalence argument becomes harder to follow. Reviewers must trace which characteristics are covered by which device. If the logic is not clear, the argument appears incomplete or inconsistent.

The second issue is overlap. Sometimes manufacturers select devices with overlapping characteristics but fail to explain why multiple devices are needed. If two devices cover the same characteristic, reviewers question whether one of them is redundant or whether the equivalence claim is being artificially inflated.

The third issue is gaps. Manufacturers assume that combining several devices automatically covers all characteristics. But when you map the characteristics systematically, gaps often appear. No device in the combination covers a specific material interaction, or a specific patient population, or a specific duration of use.

These failures are not about the devices themselves. They are about how the equivalence argument is structured and communicated.

How to Structure Partial Equivalence Properly

Start with a systematic equivalence matrix. This matrix must list all technical and clinical characteristics of your device in one column. In adjacent columns, list each equivalent device and mark which characteristics it covers.

The matrix should show complete coverage. Every characteristic must be addressed by at least one device. If a characteristic is not covered, you must either add another device or justify why that characteristic does not require equivalence demonstration.

This is the foundation. Without it, partial equivalence becomes speculative.

Next, justify why multiple devices are necessary. Explain why no single device on the market matches your device across all characteristics. This is not a theoretical exercise. You must show that you conducted a systematic literature search, identified candidate devices, and evaluated them against your technical and clinical characteristics.

If one device comes close but does not fully match, explain the gap. If combining two or three devices provides complete coverage, explain how each device contributes.

Then, for each device in the combination, provide full equivalence demonstration. This means technical comparison, clinical data analysis, and justification of differences. The standard of evidence does not change because you are using multiple devices.

Each device must meet the equivalence criteria individually for the characteristics it covers. You cannot lower the threshold because you are combining data.

What Reviewers Look for in Partial Equivalence Claims

Reviewers assess whether the combination is logical. They check if the devices selected actually address the claimed characteristics. They verify that the combination does not introduce new risks or uncertainties.

One common question: Are the devices clinically compatible? If you combine data from a device used in one patient population with data from a device used in a different population, reviewers will challenge whether the combined clinical profile is valid for your intended use.

Another question: Are there contradictions in the clinical data? If one device shows a specific adverse event profile and another device shows a different profile, reviewers will ask which profile applies to your device. If the data conflict, the equivalence argument weakens.

Reviewers also assess whether you have considered the cumulative uncertainty. Each equivalence demonstration carries some level of uncertainty. When you combine multiple devices, uncertainties may accumulate. If you do not address this, reviewers may conclude that the equivalence claim is too uncertain to support market access.

These are not arbitrary requirements. They reflect the principle that equivalence must provide the same level of confidence as clinical investigations.

When Partial Equivalence Is Justified and When It Is Not

Partial equivalence is justified when your device represents a specific combination of existing technologies or applications that no single marketed device replicates. For example, a vascular graft made from a specific polymer used in one device and designed for a specific anatomical site addressed by another device.

It is justified when the combination reflects genuine clinical practice. If clinicians already use data from multiple devices to inform treatment decisions for similar applications, partial equivalence mirrors that reasoning.

It is not justified when you are simply trying to avoid gaps in your clinical data. If your device introduces a novel characteristic that no marketed device addresses, partial equivalence does not solve that problem. You must generate new clinical evidence.

It is also not justified when the combination creates more complexity than it resolves. If you need four or five devices to cover all characteristics, reviewers will question whether equivalence is the right pathway. At that point, the accumulation of devices and data sources undermines confidence rather than building it.

How This Affects PMCF and Long-Term Evidence

Partial equivalence has implications for post-market surveillance. If your equivalence claim relies on multiple devices, your PMCF plan must address whether the combined clinical profile remains valid over time.

This means monitoring whether the clinical data for each equivalent device evolves. If new safety signals emerge for one of the devices in your combination, you must assess whether that signal applies to your device. If a device is withdrawn from the market or subject to a field safety corrective action, you must evaluate the impact on your equivalence claim.

PMCF for partial equivalence is not just about confirming your device’s performance. It is about maintaining confidence that the combined equivalence argument remains robust.

This is rarely addressed in initial CERs. Manufacturers focus on demonstrating equivalence at the time of submission. They do not plan for how equivalence will be maintained over the product lifecycle.

This becomes a compliance risk during surveillance audits and periodic safety update reports.

What This Means for Your Clinical Evaluation

Partial equivalence is not a shortcut. It is a structured regulatory pathway that requires the same rigor as single-device equivalence, with additional justification for the combination.

If you use multiple devices, your clinical evaluation report must explicitly explain the rationale, demonstrate complete coverage of technical and clinical characteristics, and address the cumulative uncertainty.

It must also plan for long-term evidence generation that accounts for changes in the clinical data for each device in the combination.

When done properly, partial equivalence is a defensible and efficient pathway. When done poorly, it creates more regulatory risk than relying on limited clinical data from your own device.

The key is recognizing when partial equivalence is appropriate and structuring the argument so that reviewers can follow the logic without hesitation.

Peace,
Hatem
Clinical Evaluation Expert for Medical Devices
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