BGH “Prosthesis Control” (X ZR 41/24): When Prior Art Is Novelty-Destroying – Even Without Disclosing the Underlying Mechanism

In its judgment of 31 March 2026, the X. Civil Senate of the German Federal Court of Justice (Bundesgerichtshof, BGH) declared European Patent EP 2 445 455 for the control of a prosthesis null and void for the territory of the Federal Republic of Germany, thereby reversing the decision of the Federal Patent Court. The “Prosthesis Control” ruling confirms and sharpens one of the most practically important lines of patent law: a novelty-destroying disclosure requires only an instruction for action that, when carried out, realizes all features of the claimed subject matter — disclosure of the underlying functional mechanism is not necessary.

Key Facts of the Decision at a Glance

The judgment is strategically significant for both nullity claimants and patent proprietors, as it clarifies the threshold for an anticipatory disclosure.

The Technical Background

The patent concerns the control of a movable component of a prosthesis or orthosis, such as the motor-driven fingers of a hand prosthesis. According to the patent description, known hand prostheses had drawbacks regarding grip force; the patent therefore sought to provide control with improved grip force.

Claim 1, as upheld by the Federal Patent Court (in the version of auxiliary request 1), essentially provided the following features:

• Moving the component by means of a motor using a plurality of spaced-apart electrical motive pulses (feature 1.1′).
• Determining, by means of an electrical apparatus, when movement is arrested because the component bears against a surface (features 1.2, 1.2.1).
• Providing a plurality of electrical driving pulses to drive the motor with greater contact force (feature 1.2.2).
• Ratio of periods: each motive pulse has a period of less than one tenth of the period of each driving pulse (feature 1.2.3).

In the embodiment, the motor is driven by pulse-width modulation (PWM) at 41.6 kHz, while the low-frequency driving pulses are around 36 Hz.

The Central Issue: Anticipation by D2

The decisive prior art was reference D2 — European patent application 681 818 — concerning a method for myoelectric proportional control of a hand prosthesis. The Federal Patent Court had denied anticipation, holding that D2 did not disclose features 1.2.1, 1.2.2 and 1.2.3. The BGH disagreed and affirmed full anticipation.

A Mechanical Grip-Force Switch as an “Electrical Apparatus”

The mechanical grip-force switch described in D2 satisfies the requirement of an “electrical apparatus” (feature 1.2) because it outputs an electrical signal once a certain grip force is exceeded. The fact that grip force is measured mechanically rather than electrically is irrelevant — the claim does not require a purely electrical determination. An “electrical component” can, under ordinary understanding, even be a simple mechanical switch.

Arrest of Movement and Time Delay

A grip force necessarily presupposes that the prosthesis is already bearing against a surface — precisely the state to be determined under feature 1.2.1. It was irrelevant that the switching in D2 occurs only some time after gripping, since feature 1.2.2 is also realized when the driving pulses are provided with a time delay.

The Ratio of Periods (Feature 1.2.3)

The crux of the decision lies in feature 1.2.3: during the grip-force phase, the alternation of PWM signals (duration 100–200 ms) and intervening pauses (60 ms) additionally produces a low-frequency signal sequence with a period between 160 and 260 ms, corresponding to 3.85–6.25 Hz. The individual PWM pulses at the usual frequency of 18–40 kHz, by contrast, have a period less than one thousandth of that — so the required ratio of below one tenth is satisfied. The fact that the individual pulses themselves consist of many high-frequency single pulses does not preclude realization.

The Governing Legal Principles

The BGH formulated two official guiding principles (Leitsätze) that make the decision particularly valuable in practice.

1. An instruction for action suffices — the mechanism is irrelevant: For a novelty-destroying disclosure, it suffices that an instruction for action is given which, when carried out, realizes all features of the claimed subject matter; disclosure of the underlying functional mechanisms is not required. This confirms the line established in “Memantin” (X ZR 68/08) and “Desmopressin” (X ZR 131/09).
2. What matters is direct and unambiguous disclosure: For the question of novelty, it is not relevant whether a subject matter is disclosed as “belonging to the invention,” but only whether it is directly and unambiguously disclosed in the prior art — confirming “Aufbaupfosten” (X ZR 8/22).

Concretely: even though D2 does not reveal the relevant functional relationship (longer period = higher force), the teaching of the patent is disclosed, because the higher force is a mandatory consequence of carrying out the described method steps. It was equally irrelevant that the claims of D2 did not mandatorily provide for the low-frequency signal sequence of the embodiment.

Practical Relevance for Applicants and Litigants

The decision has direct consequences for daily work in drafting, prosecution and nullity proceedings:

• Take hidden disclosures seriously: A prior-art reference can anticipate a feature without expressly naming it, where the feature is inevitably realized when the described steps are performed.
• Secure claim wording: Anyone relying on a specific mechanism or implementation (e.g. purely electrical measurement) must expressly incorporate that limitation into the claim — in this case, the current threshold and electrical measurement found no reflection in the claim.
• Functional terms are construed broadly: A functionally defined term such as “electrical apparatus” also covers unexpected implementations such as a mechanical switch.
• Coordinate infringement and nullity proceedings: The BGH expressly referred to the correct construction of feature 1.2.3 adopted by the Regional Court (Landgericht) Mannheim in the parallel infringement dispute.

For nullity claimants, the judgment provides tailwind, as it keeps the bar for proving an anticipatory disclosure noticeably low.