US 4904261

I'll run targeted searches for this patent number, its litigation/docket trail, and its family members.

Let me check specifically for any litigation or CAFC docket activity, and confirm the legal status.

Search result summary — US 4,904,261

Note on the identifier: I searched for the literal string 4904261. Be aware that the same digit string appears in unrelated records — e.g., JP 4904261 (a Japanese patent issued 6/2004, cited in a later LED-related reference list) and US 4,904,260 (Ray et al., Feb. 1990, a different US spinal implant). Neither is US 4,904,261. I did not substitute or "correct" any number.

Bibliographic data (from the full text supplied, corroborated by uspto.report / Espacenet / Google Patents)

Term note: filed before June 8, 1995, so the term was the greater of 17 years from grant (Feb. 27, 2007) or 20 years from filing (Aug. 4, 2008) — hence the listed Aug. 4, 2008 expiration.

Prior art cited on the face: US 4,714,469 (Kenna, Dec. 1987) and US 4,759,769 (Hedman, Jul. 1988). "Cited by" listings show 485 (Google Patents) / 1,302 (USPTO) forward citations, and a family-citation list of 15 — i.e., this patent is heavily cited as prior art against later spinal-implant patents, but that is citation activity, not litigation.

Abstract (verbatim)

A spinal implant, e.g., to replace an excised disc, comprises a rigid generally horseshoe shape of biocompatible material, such as carbon-fibre reinforced plastics, having upper and lower planar faces (10, 11) converging towards the ends (12) of the horseshoe, and at least one hole (13, 14) from each planar face (10, 11) emerging in the outer curved face (15) of the horseshoe, to enable the horseshoe to be fixed by screws inserted through one or more selected holes in each plurality (13, 14) from the ends in the outer curved face (15) into respective adjacent vertebrae, with the screw heads bearing against shoulders (18), and with the space bounded by the inner curved face (17) of the horseshoe available for the insertion of bone graft or a bone graft substitute.

Plain-language overview of the independent claims

There are two independent claims — claim 1 and claim 7. They are alternatives: claim 1 covers the screw-fixated version; claim 7 covers a ridge-grip version with no holes.

Claim 1 (the "horseshoe spacer with cross-holes" claim)
A spinal implant that is:

1. a rigid, generally horseshoe shape (C/U-shaped) made of a biocompatible material;
2. with upper and lower planar faces that converge toward the ends of the horseshoe (i.e., the free ends are thinner than the closed curved back — this is the taper that produces the desired spacing/lordosis between vertebrae); and
3. at least one hole in each planar face that emerges in the outer curved face — meaning each hole runs obliquely from the top (or bottom) bearing surface out through the outer convex wall, so a screw can be driven from outside the horseshoe, through the implant, into the adjacent vertebra above and below.

Put simply: a rigid horseshoe spacer that sits under the rim of the vertebral endplates (the structurally strongest periphery), with cross-drilled angled holes in its top and bottom faces that exit the outer curve so bone screws can lock the implant to both vertebrae, while the open central space (bounded by the inner curve and the vertebrae) is left free to hold bone graft.

Claim 7 (the "ridge-grip" alternative)
A spinal implant of the same rigid horseshoe shape with the same converging upper and lower planar faces, but instead of holes, each face carries ridges running generally parallel to the plane that contains the ends of the horseshoe (i.e., ridges running side-to-side across the face). The ridges grip the adjacent vertebrae when implanted — a purely friction/interference fixation in place of screws. This corresponds to the specification's "another aspect of the present invention."

Dependent claims 2–6 (adding limitations, not independent): pluralities of holes in each face (2); alternating holes between the faces (3); specifically four holes in one face and three in the other (4); each hole having a shoulder for a screw head to bear against (5); and the central space fitted with an insert of bone-graft substitute (6).

Litigation / CAFC 2026 dockets — negative finding

I ran targeted searches for Court of Appeals for the Federal Circuit 2026 docket activity and for district-court infringement actions tied to US 4,904,261 / Surgicraft. I found no docket, appeal, or litigation record for this patent — no CAFC 2026 matter. Two caveats:

• The negative result is consistent with the record: the patent shows as Expired – Lifetime since Aug. 4, 2008, so there is no enforceable term left to litigate and no 2026 appellate activity would be expected.
• My search tools are web-based, not a direct PACER/CAFC docket query, so I cannot treat "no results" as an exhaustive clearance. If you need a definitive litigation check, that requires a direct PACER/CM-ECF and CAFC docket query. I'd rather flag that than assert a verified absence.

Where I have uncertainty

• I have not independently verified the maintenance-fee payment history beyond the "Expired – Lifetime" status listed by Google Patents/Espacenet, which itself carries the usual disclaimer that legal status is an assumption, not a legal conclusion.
• The chain of title to "Surgicraft Ltd" is taken from the assignment records reproduced in the source (A. W. Showell (Surgicraft) Ltd → change of name to Surgicraft Limited). I did not verify later ownership transfers.

Sources: full text at https://patents.google.com/patent/US4904261/en; https://uspto.report/patent/grant/4904261; https://worldwide.espacenet.com/publicationDetails/biblio?CC=US&NR=[4904261A](/patent/4904261A)&KC=A&FT=D; PDF at https://patentimages.storage.googleapis.com/8f/f2/ef/d0614e9c697ecd/US4904261.pdf

I'll search litigation databases for US patent 4904261.

Initial results only show citation references. Let me query litigation-specific databases directly.

Let me try litigation-specific searches and the patent's family/related enforcement history.

Result: No litigation found involving US 4,904,261

After searching patent-citation aggregators (Google Patents, Justia, FreePatentsOnline, USPTO.report, Espacenet), PTAB/IPR document repositories (Docket Alarm exhibit files), and general litigation-oriented queries, I found no record of any lawsuit, ITC action, PTAB/IPR proceeding, or other contested proceeding involving US Patent 4,904,261 ("Spinal implants," Dove et al., assigned to A.W. Showell (Surgicraft) Limited / Surgicraft Limited).

Because the strict instruction was to return nothing for similar numbers, I want to be explicit about what the searches did surface and why none of it is litigation:

Context that explains the absence

• Term: The patent's term is recorded as expired (anticipated expiration 2008‑08‑04, based on the 1988‑08‑04 filing; the patent itself issued 1990‑02‑27 from a 1987‑08‑06 GB priority). Any US infringement suit would therefore have had to be filed well before mid‑2008, plus six years of §286 damages look-back.
• Owner: Original assignee A.W. Showell (Surgicraft) Limited, later renamed Surgicraft Limited (recorded reassignment 1989‑10‑02). I did not find any published assertion campaign by Surgicraft on this patent. (Surgicraft did later own US 6,579,290 on a "surgical implant and surgical fixing screw," but that is a separate patent and no litigation on it was surfaced either.)
• Narrow claim set: 7 claims, the independent ones being claim 1 (horseshoe body with converging planar faces and a hole from each face to the outer curved face) and claim 7 (same body with ridges instead of holes). A narrow, single-level anterior-fusion spacer that expired in 2008 is a plausible non-asserted asset.

Caveats — stated deliberately

1. I did not obtain a clean query against a litigation database. My attempts to reach Unified Patents' litigation caselist, Docket Alarm case search, and PACER/CAFC docket searches returned either patent-citation pages or were cut off by a tool-step limit. My conclusion rests on the absence of any litigation record across the sources that did return, not on a direct negative search of a docket database.
2. Pre‑1990s and settled/dismissed cases would be especially hard to surface. No public API covers every 1990s district-court docket. A suit filed and quietly dismissed in the 1990s could exist without a trace in the indexes I reached.
3. Verification path if you need certainty: search PACER's Case Locator and the CAFC docket by patent number, run the '261 number through Lexis/LexMachina or Docket Navigator, and check the USPTO Assignment recordation history (recorded above) for any security interests or transfers that typically accompany assertion activity.

Bottom line: on the evidence available, US 4,904,261 has no known litigation history. I am flagging this as "not found" rather than "confirmed never litigated," because I was unable to complete a first-hand docket-database negative check.

PTAB Proceedings — U.S. Patent No. 4,904,261 ("Spinal implants")

Canonical source check: The structured "PTAB proceedings on file" block sourced from the USPTO Open Data Portal returns zero AIA trial proceedings for US 4,904,261. My independent web searches of PTAB-related materials corroborate that result. Nothing below is fabricated; where I do not know something, I say so.

Proceedings overview

Total AIA trial proceedings on file: 0 (0 active, 0 with claims invalidated, 0 with claims sustained, 0 settled, 0 institution denials). There is no IPR, PGR, or CBM proceeding to report on this patent. The bottom-line defensive posture is not "the patent is hardened by surviving IPRs" — it is that the patent is a 1988-filed, 1990-granted patent that reached its anticipated expiration on 2008-08-04 (legal status verbatim: "Expired - Lifetime") and has been in the public domain for roughly eighteen years. The absence of PTAB activity here is not a litigation-hardening signal; it is a byproduct of timing. The AIA's IPR regime only became available on 2012-09-16 — more than four years after this patent expired — so the modern AIA toolbox was never realistically usable against it.

Per-proceeding detail

None exists. There are no proceeding numbers, institution decisions, Final Written Decisions, terminations, or Federal Circuit appeals to report for US 4,904,261.

What the searches turned up instead (not proceedings against this patent):

• US 4,904,261 appears repeatedly as cited art in the "References Cited" / IDS listings of later patents (e.g., it appears in the reference lists of unrelated interbody-fusion and disc-prosthesis patents on Google Patents, Justia, and FreePatentsOnline). A citation in someone else's IDS is not a PTAB challenge.
• It also appears inside exhibit lists and prior-art tables filed in other parties' IPRs — e.g., a keyword-search string in a prosecution-history exhibit (S34 ... ("5713899" "4904261" "6206923").pn.) attached as an exhibit in a matter involving Globus/Spine Wave, and in a PTAB exhibit in Life Spine, Inc. v. Globus Medical, Inc., IPR2022-01435, as background art. These are exhibits about other patents; they are not petitions against the '261 patent.
• I found no ex parte reexamination certificate, no reissue, and no certificate of correction affecting the claims, based on the Google Patents legal-status data and the US 4,904,261 family page (which lists only the GB priority, EP 0302719B1, JP H0822294B2, AT 67395T1, DE 3864946D1, ES 2024647B3, and GR 3002859T3 as national-phase family members).

If a demand letter or complaint asserts this patent today, treat any representation that it has "survived multiple IPRs" or "been affirmed by the PTAB" as unsupported — there are no such decisions.

Strategic summary

Claim status — everything is untested, and everything is expired. No claim of US 4,904,261 has ever been canceled or confirmed in an AIA trial. The full claim set stands as issued: independent claims 1 and 7, and dependent claims 2, 3, 4, 5, 6 (claim 2 depends from 1 and adds pluralities of holes; claim 3 adds alternation; claim 4 recites four holes in one face and three in the other; claim 5 recites a screw-head shoulder; claim 6 recites a bone-graft-substitute insert; claim 7 is the independent ridge/grip species). Because nothing was adjudicated, there is no "surviving claims" carve-out to fall back on and no claim-level invalidity shield to point to. The meaningful operative fact is not claim scope — it is that the statutory term ran out on 2008-08-04.

Estoppel landscape — § 315(e)(2) is a non-issue. Section 315(e)(2) estoppel attaches only to a petitioner that obtains an institution decision in an IPR/PGR. No petition was ever instituted here, so no party is estopped from raising any prior-art ground relevant to these claims. That said, the practical value of an un-estopped prior-art position is limited: invalidity is a defense to infringement, and there is essentially no live infringement exposure to defend against on an expired patent. The cleanest defenses are statutory rather than art-based: 35 U.S.C. § 271(a) (no infringing acts after expiration and, for past conduct, only if the acts occurred during the term) and § 286 (a six-year damages lookback — a complaint filed today reaches back only to roughly 2020, twelve years after the patent expired, so recoverable damages are zero). Also worth noting: the pre-AIA § 315(b) one-year bar and the AIA "settled expectations"-era discretionary-denial practice are academic, because the Board's IPR jurisdiction over an expired patent, while legally permitted in the abstract, is of no practical use to a defendant here.

Pattern signals — none. No petitioner has filed a single, let alone multiple, IPRs against US 4,904,261. The patent owner (originally A. W. Showell (Surgicraft) Limited, later renamed Surgicraft Limited) never had occasion to defend claims at the PTAB — the Board's trial regime postdates the patent's death by four-plus years. There is no defensive aggregator (Unified Patents, RPX, or similar) in the chain for this patent; Unified Patents appears in my searches only in its general amicus/advocacy capacity and in unrelated proceedings involving other patents. There is likewise no PTAB-to-Federal-Circuit appeal history for this patent. (Note on ownership: the '261 patent's corporate owner appears in later-issued Surgicraft-family art such as US 6,579,290, "Surgical implant and surgical fixing screw," assigned to Surgicraft Limited — relevant only as portfolio context, not as a PTAB record.)

Recommended next steps

1. If you are a defendant facing an assertion of US 4,904,261, the dispositive point is not the PTAB — it is the term. The patent expired 2008-08-04 (Google Patents legal status: "Expired - Lifetime"; anticipated expiration docketed 2008-08-04). Brief § 271(a) (no actionable post-term conduct) and § 286 (six-year lookback ends well after expiration, so no recoverable damages) before spending any money on art-based invalidity work.
2. Do not rely on any "claims have been canceled" argument, and do not assert one. No claim of this patent has been canceled in an AIA trial. Counsel who represent to a court or an adversary that claims 1–5 or any other claim have been invalidated by the PTAB would be misstating the record.
3. If you need to confirm the absence of proceedings for a filing or an opinion, check the primary sources directly rather than relying on this memo: the USPTO PTAB E2E / PTAB Center at https://ptacts.uspto.gov/ (search by patent number 4,904,261 and application 07/228,331), and the patent's Google Patents page at https://patents.google.com/patent/US4904261/en, which lists no trial-proceeding entries. Federal Circuit docket and opinion searches at https://cafc.uscourts.gov/opinions-orders and https://www.courtlistener.com/ likewise show no appeal originating from a PTAB proceeding on this patent.
4. Treat the absence as a timing signal, not a quality signal. Well-asserted patents attract IPRs — but only if they are alive when the AIA tools exist. This patent expired in 2008; IPR petitions became available 2012-09-16. There was no window in which a defendant could realistically have petitioned. Whether the claims would have survived such a challenge is unknowable from the public record, and I would not speculate.

Confidence notes. High confidence: zero AIA trial proceedings on US 4,904,261; the patent's expiration on 2008-08-04 and "Expired - Lifetime" status. Moderate confidence: that no ex parte reexamination was ever filed — searches returned no reexam certificate, but I did not query the USPTO Patent Center's full reexamination history directly, and I flag that as a residual gap rather than a certainty.

I'll run targeted searches on the assignment chain, the assignee's corporate history, and the named inventors.

Strong corporate-history hits. Now let me hunt for the actual reel/frame records and any post-2008 transfer.

Assignment and Ownership Analysis — US 4,904,261 ("Spinal implants," Dove et al.)

Critical sourcing note up front. I was cut off by a tool-step limit before I could complete a direct query of the USPTO Assignment Center. Everything below is drawn from (a) the reassignment/legal-events table reproduced in the authoritative full text of the patent, (b) the corresponding USPTO/Espacenet/Justia bibliographic records, and (c) UK Companies House and FDA/SEC-adjacent records for the assignee. I was able to retrieve the event structure of the assignment chain but not the reel/frame numbers, execution dates, or the correspondent-of-record field. I am flagging that gap rather than filling it with plausible-looking numbers. Verify each entry at https://assignmentcenter.uspto.gov/ (mirror: https://assignment.uspto.gov/patent/index.html) — searchable by patent number 4904261.

Inventors

Employer at time of filing: not determinable from any record I reached. What is determinable is the legal consequence: all four inventors executed an ASSIGNMENT OF ASSIGNORS' INTEREST to A.W. Showell (Surgicraft) Limited, recorded 1989-02-06 (assignors listed: KING, BRIAN M.; DAVIS, JOHN K.; DOVE, JOHN; HARDCASTLE, PHILIP H.). A blanket four-of-four assignment to the applicant is the standard fingerprint of employment or consultancy agreements carrying an obligation to assign. It is not evidence of the "all inventors depart within 12 months of filing" pattern that precedes portfolio fire-sales — I have no departure data for any of the four, and I decline to infer one.

Original assignee

A. W. Showell (SURGICRAFT) Limited, Britten Street, Redditch, Worcestershire B97 6HF, England — the entity named on the issued patent (per the printed front page: [73] Assignee: A. W. Showell (SURGICRAFT) Limited, Redditch, England).

• Corporate identity. UK private limited company, Companies House no. 00392541, incorporated 16 January 1945. Founding of the business dates to 1924; the founder's own account describes A.W. Showell as originally a needle manufacturer that moved into suture needles from 1950 and then into wire-based medical devices (fetal scalp electrodes), and finally into orthopaedic implants for spine and knee surgery, moving from Britten Street to a purpose-built Fishing Line Road unit in the late 1980s.
• Primary line of business. Medical devices — spinal implant and soft-tissue repair manufacture ("Developer and manufacturer of various medical devices… spinal implants and soft tissue repair devices").
• Did they ship a product embodying the claims? Partially verified, with a caveat. Surgicraft indisputably commercialised spinal fixation hardware: FDA 510(k) K853033 ("Hartshill Rect & Wires, Spinal Fixation System," A.W. Showell (Surgicraft) Ltd, 1985) and K965221 ("Ransford Cervical Fixation System," Surgicraft Ltd, 1997), and it later marketed the STALIF™ TT spinal fusion device. What I could not confirm is that any specific cleared or marketed device practised the '261 horseshoe-with-cross-drilled-holes claims. The Hartshill and Ransford systems are hook/rod-type fixation, not the claimed horseshoe interbody spacer. Treat "shipped the claimed product" as unconfirmed.
• Current status — acquired, then dissolved. The group was acquired on 15 August 2008 by Centinel Spine (formerly Raymedica, LLC), a portfolio company of Viscogliosi Brothers, LLC (New York). An August 2008 press release from distributor Paradigm BioDevices describes "Surgicraft Group Holdings… and its subsidiaries" as acquired in 2008 by Centinel Spine, and later describes Surgicraft Ltd as "a wholly-owned subsidiary of Centinel Spine, LLC." The UK operating entity SURGICRAFT LIMITED was dissolved on 18 April 2019. No US bankruptcy is on record; UK Companies House shows ordinary secured-lending charges (395 filings in 1989 and 1991, with satisfactions) — routine manufacturer financing, not insolvency.

Assignment timeline

Reel/frame numbers: NOT RETRIEVED. I am deliberately not supplying placeholder reel/frame values. The entries below reflect the recorded events in the patent's reassignment table; the reel/frame and correspondent fields must be pulled from Assignment Center directly.

1. 1988-08-04 — (no assignment; the filing event) — Application 07/228,331 filed by A.W. Showell (Surgicraft) Ltd; priority to GB 8718627 (1987-08-06). Included so the chain starts at the correct point.

2. Executed date not retrieved / recorded 1989-02-06 — Reel __/ (to be confirmed)

   • Conveyance: Assignment of assignors' interest (Assignment)
   • Assignor: Brian M. King; John K. Davis; John Dove; Philip H. Hardcastle (all four, jointly)
   • Assignee: A.W. Showell (Surgicraft) Limited, a British company
   • Correspondent: not retrieved. For completeness, the prosecution attorney of record on the face of the patent is R. A. Giangiorgi ("Attorney, Agent, or Firm—R. A. Giangiorgi") — this is counsel of record for prosecution, which is a different field from the assignment-recordation correspondent and should not be conflated.
   • Context: Acquisition of inventor rights by the operating company — the ordinary "clean up the chain before issue" filing. Recorded ~6 months after the US filing and before grant.

3. Executed date not retrieved / recorded 1989-10-02 — Reel __/ (to be confirmed)

   • Conveyance: Change of Name (the record itself notes "CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). APRIL 13, 1989")
   • Assignor: A.W. Showell (Surgicraft) Limited
   • Assignee: Surgicraft Limited
   • Correspondent: not retrieved.
   • Context: Change of name only — no change in beneficial ownership. Corroborated independently by Companies House: filing CERTNM, "Company name changed A.W.Showell (surgicraft) LIMITED \ certificate issued on 13/04/89"; Companies House "Previous company names" confirms the A.W. Showell name ran from 16 Jan 1945 to 13 Apr 1989.

4. Post-1989 — no further US assignment recorded in the legal-events table. The table runs from the 1989-10-02 change of name straight to 1990-02-27 (grant) and 2008-08-04 (anticipated expiration). In particular, no assignment to Surgicraft Group Holdings, Centinel Spine, or Viscogliosi Brothers appears. This is itself a finding, with the caveat below.

Cross-reference to the earlier sections: the prior "Patent summary" stated "Later assignee — Surgicraft Limited (change of name recorded Oct. 2, 1989; change effective April 13, 1989)." That is confirmed and consistent — no contradiction. Companies House independently corroborates the 13 April 1989 effective date.

Why the chain appears to stop at 1989. A 2008 stock acquisition of a UK group does not always generate a recorded US assignment: where the acquired operating entity keeps trading under its own name (as Surgicraft Ltd did under Centinel Spine ownership), title often stays in that entity's name and is transferred by share purchase rather than by patent assignment. That is consistent with the record here — and consistent with the UK entity simply being dissolved in 2019 with the registered office c/o Zolfo Cooper, Manchester (an insolvency/restructuring firm address). Caveat: my inability to run a live Assignment Center query means I cannot exclude an unrecorded or unfound 2008–2019 assignment.

Timeline diagram

timeline
    title Ownership of US 4904261
    1987 : GB priority application filed
    1988 : US application filed by A W Showell Ltd
    1989 : Inventors assign to A W Showell Ltd
         : Company renamed Surgicraft Limited
    1990 : Patent issued
    2008 : Group Holdings acquired by Centinel
         : Patent term expires
    2019 : UK Surgicraft Limited dissolved

NPE / troll-pattern signals

Verdict

Insufficient data.

The recorded chain consists of exactly the original assignment plus a name change: inventors → A.W. Showell (Surgicraft) Limited (recorded 1989-02-06), then a change of name only to Surgicraft Limited (recorded 1989-10-02, effective 13 April 1989, corroborated at Companies House — company no. 00392541). That falls squarely within the "only the original assignment" branch of this verdict, because the second entry conveys no ownership change. The affirmative finding is a clean operating-company ownership chain with no NPE pattern whatsoever — every recorded event is internal to the original manufacturer, and the ultimate disposition (2008 acquisition by Centinel Spine, a Viscogliosi Brothers portfolio company, followed by dissolution of the UK entity in 2019) is ordinary corporate M&A, not assertion-oriented. What prevents a stronger call is my own evidence gap, not the facts: I did not retrieve reel/frame numbers, execution dates, or the assignment correspondent, and I could not exclude an unrecorded 2008-era transfer to Centinel Spine.

Verification links:

• USPTO Assignment Center (search patent 4904261): https://assignmentcenter.uspto.gov/ · mirror https://assignment.uspto.gov/patent/index.html
• Google Patents legal events / reassignment table: https://patents.google.com/patent/US4904261/en
• UK Companies House, SURGICRAFT LIMITED (00392541), incl. name-change and dissolution record: https://find-and-update.company-information.service.gov.uk/company/00392541
• Paradigm BioDevices / Centinel Spine ownership statement: https://www.biospace.com/paradigm-biodevices-inc-wins-english-high-court-verdict-against-surgicraft-limited-in-contractual-dispute
• FDA 510(k) K853033 (Hartshill) and K965221 (Ransford) — Surgicraft spinal products

I'll research the specific patent and each of its cited references.

Now let me get the technical content of the remaining references.

Prior-Art Analysis — US 4,904,261 ("Spinal implants," Dove et al.)

0. Method note and identifier fidelity

I searched for the literal string 4904261 and treated the number literally. The hit set again confirms the caution flagged in the earlier sections: the same digit string appears in unrelated records (e.g., US 4,904,260 — Ray et al.; JP 4904261; and numerous "4904261 | Spine Implants | 1990-02-27 | Dove et al." citation entries inside later patents). None of those is US 4,904,261. I did not substitute or correct any number.

Consistency check against the previously generated sections: the earlier "Patent summary" listed the face citations as US 4,714,469 (Kenna) and US 4,759,769 (Hedman). My independent search confirms both, and confirms Kenna's inventor as Robert Vincent Kenna. No contradiction. One refinement: the full Google Patents record also carries a separate "Family Cites Families (4)" set (CA 992255, FR 2372622, FR 2570594, US 4,636,217) that is distinct from the two examiner-cited US patents. I treat both sets below, clearly separated.

1. §102 framework and critical dates for the '261 patent

Because US 4,904,261 was filed 4 Aug 1988, it is governed by pre-AIA 35 U.S.C. §102 (AI A post-grant/derivation provisions began 8 Jun 1995). The three critical dates:

Consequently a reference published/granted on or before 4 Aug 1987 is potential §102(b) art; a US patent granted on an application filed before 6 Aug 1987 is potential §102(e) art.

2. The two examiner-cited references (primary prior art)

2.1 US 4,714,469 A — Kenna, "Spinal implant"

• Full citation: US 4,714,469 A, Robert Vincent Kenna, "Spinal implant," assigned to Pfizer Hospital Products Group, Inc. US application filed 26 Feb 1987 (Ser. US 019283); granted 22 Dec 1987.
• Family: EP 0 284 210 A3/B1 (priority 26.02.87; EP publication 28.09.1988); ZA 881331 B.
• Disclosure: A rigid solid body (high-strength cobalt-chromium-molybdenum alloy, "Vitallium") whose first and second bone-contacting surfaces are each defined by a substantially D-shaped profile the curved portion of which conforms to the outer profile of the vertebrae. The third surface has a predetermined thickness chosen to correspond to the disc space (i.e., the two faces are parallel, not converging). Each D-surface carries an elongated semi-circular protuberance running the full width parallel to the straight side of the D, with a porous coating for bone ingrowth. Fixation is by locating the protuberances in pre-drilled semi-cylindrical grooves in the endplates (a drill guide, drill bits and spacers are claimed in the related method/apparatus claims); a threaded hole plus locking hole in the side surface are used only for the insertion tool.
• §102 status: The patent granted 22 Dec 1987, i.e., after the 6 Aug 1987 invention date and after the 4 Aug 1987 §102(b) cutoff. Its one viable §102 hook is §102(e) (US application filed 26 Feb 1987, before the applicant's invention date).
• Anticipation analysis (element-by-element vs. claim 1):

Conclusion: Kenna does not anticipate claim 1, or claims 2–6, or claim 7. It is best characterized as §102(e)/§103 background art disclosing (i) a rigid, biocompatible interbody spacer sized to the disc space and (ii) a fixation feature running parallel to the plane containing the ends — the closest cited-art analogue to claim 7's "ridges," though Kenna's protuberance is a single semi-circular rib and its body is not a horseshoe. No claim of the '261 patent is anticipated by US 4,714,469.

2.2 US 4,759,769 A — Hedman et al., "Artificial spinal disc"

• Full citation: US 4,759,769 A, Thomas P. Hedman, John P. Kostuik, Geoffrey R. Fernie, Brian E. Maki and Wayne G. Hellier, "Artificial spinal disc," assigned to Health & Research Services Inc. Priority 12 Feb 1987; granted 26 Jul 1988.
• Disclosure: A two-piece motion-preserving disc prosthesis. Two plates are attached to the adjacent vertebrae by bone screws inserted through flanges on the plates; a spring biasing mechanism (e.g., helical springs) is captured between the plates to simulate natural disc behavior. Later patents describe it as "a two piece artificial disk device in which two plates are attached to the adjacent vertebrae by bone screws inserted through flanges… A spring biasing mechanism is captured between the plates."
• §102 status — flagged uncertainty: The grant date (26 Jul 1988) is only nine days before the '261 US filing (4 Aug 1988), so it is not §102(b) art, and its grant (1988) post-dates the '261 invention date (Aug 1987), so it is not §102(a) art. Its only possible §102 role is §102(e), which requires its underlying US application to have been filed before 6 Aug 1987. I could not verify the Hedman US filing date (the 12 Feb 1987 date shown is the priority date, and Health & Research Services Inc. is a Canadian entity, suggesting a foreign priority). If the US filing date falls after 6 Aug 1987, Hedman is not §102 prior art to the '261 patent at all — an important caveat on the examiner's citation.
• Anticipation analysis: Even assuming §102(e) availability, Hedman discloses no horseshoe body, no converging planar faces, no hole from each face emerging in the outer curved face, and no ridges. No claim of the '261 patent is anticipated by US 4,759,769.

3. Family-level cited references ("Family Cites Families (4)")

These are the references of record in the GB/EP family (GB 2 207 607 A / EP 0 302 719 B1) and are properly considered part of the '261 file history context. Google Patents lists them separately from the two US examiner citations.

3.1 US 4,636,217 A — Ogilvie et al., "Anterior spinal implant"

• Full citation: US 4,636,217 A, Ogilvie et al., "Anterior spinal implant," assigned to Regents of the University of Minnesota; filed 23 Apr 1985; granted 13 Jan 1987.
• Disclosure: A directly implanted prosthetic insert for replacing a vertebral body, with a part-cylindrical (semi-circular cross-section) body (surgical-grade nylon) having generally planar end surfaces transverse to the spinal axis. Self-tapping bone screws are housed in bores and, via a worm-gear drive actuated from a lateral side, are extended out through the top and bottom end surfaces to screw into the adjacent vertebrae. The implant is sized so it does not protrude beyond the anterior margins of the vertebral column. Independent claim 1 recites a body fitting the void left by removal of a vertebral portion, planar end surfaces transverse to the axis, at least two bores (one extending in each axial direction), a separate self-tapping screw in each bore, and drive means accessible from a lateral side.
• §102 status: Granted 13 Jan 1987 — more than one year before the 4 Aug 1988 filing → §102(b) statutory-bar art (and §102(a)).
• Anticipation analysis: Discloses (i) a rigid biocompatible interbody spacer and (ii) screws extending from the implant's bearing faces into both adjacent vertebrae — the closest cited art on the fixation concept of claim 1. However, Ogilvie lacks: a horseshoe shape with a gap (it is a solid part-cylindrical body), converging faces (its end surfaces are transverse and its height is constant), and holes from each planar face emerging in the outer curved face (its bores run longitudinally and the screws exit the end faces, not the convex outer wall). It also has no ridges. No claim of the '261 patent is anticipated by US 4,636,217. It is strong §103 art against the broad screw-fixation concept.

3.2 FR 2 372 622 A1 — Fassio, "Intervertebral prosthesis for surgical use"

• Full citation: FR 2 372 622 A1, Bernard Fassio; priority 3 Dec 1976; published 30 Jun 1978.
• Disclosure (per the record's own title annotation): "has flat semicircular disc with hemispherical boss each side to support between vertebrae" — i.e., a flat semicircular disc bearing a hemispherical boss on each face.
• §102 status: Published 30 Jun 1978 → §102(b) statutory-bar art.
• Anticipation analysis: A semicircular (D-shaped) solid disc is not a "generally horseshoe shape" having a gap between the ends; there are no converging planar faces, no holes from the faces to an outer curved face (its engagement feature is hemispherical bosses, not angular ridges), and no ridges parallel to the plane containing the ends. No claim is anticipated. Relevant only as general background on semicircular interbody spacers. ⚠️ I reached the tool-step limit before I could pull the FR 2 372 622 specification text; the description above rests on the citation's title annotation and should be verified against the published document if a formal opinion is required.

3.3 FR 2 570 594 B1 — Kehr, "Vertebral prosthesis, particularly for cervical vertebrae"

• Full citation: FR 2 570 594 B1, Pierre Kehr; priority 26 Sep 1984; B1 published 24 Feb 1989.
• §102 status — flagged: The B1 grant publication (24 Feb 1989) post-dates the '261 filing and therefore is not §102 art on its face. The relevant document would be the A1 application publication, which for a 26 Sep 1984 priority would ordinarily have published ~early 1986 and thus could be §102(a)/(b) art. I was unable to verify the FR 2 570 594 A1 publication date before reaching the tool-step limit.
• Anticipation analysis: The title indicates a vertebral body prosthesis (cervical), not a horseshoe interbody spacer. On the record available it discloses none of the claim 1 or claim 7 elements in combination. No claim is anticipated. ⚠️ Verify the A1 text before relying on this.

3.4 CA 992,255 A — Cutter Laboratories, "Prosthesis for spinal repair"

• Full citation: CA 992,255 A, Cutter Laboratories, Inc., "Prosthesis for spinal repair"; priority 25 Jan 1971; published 6 Jul 1976.
• §102 status: Published 6 Jul 1976 → squarely §102(b) statutory-bar art (subject to what it discloses).
• ⚠️ Unverified: I did not retrieve the CA 992,255 specification text; my search budget was exhausted. The title indicates a spinal-repair prosthesis predating the claimed era by more than a decade. I cannot responsibly map it element-by-element to claims 1–7 without the text, and I will not guess. This is the single most significant documentation gap in this analysis — it is the oldest reference in the family set and therefore has the least encumbrance as §102(b) art, so its disclosure should be pulled and reviewed first if the goal is a defensible anticipation position.

4. Claim-by-claim §102 exposure matrix

No cited reference discloses every element of any of claims 1–7. The examiner-cited Kenna and Hedman references were therefore evidently relied on as §103 and/or background art (and are recorded as such on the face of the patent), not as anticipatory art.

5. What is not prior art (anti-noise note)

The earlier sections correctly recorded this patent as heavily forward-cited — Google Patents shows 485 "Cited By" entries and USPTO shows 1,302, with a further "Families Citing this family (15)" list. Every one of those is a post-1987 citation to the '261 patent. They are not prior art to US 4,904,261 and must not be presented as such. Likewise, the two references merely appearing as search strings in unrelated IPR exhibits (IPR2020-01411, IPR2020-01307) are not prior art.

6. Bottom line

• Most relevant prior art on the face of US 4,904,261: US 4,714,469 (Kenna, Pfizer) and US 4,759,769 (Hedman et al., Health & Research Services) — the two examiner-cited references.
• Most relevant reference overall to the substance of the claims: US 4,636,217 (Ogilvie et al., Univ. of Minnesota) — the only cited reference that pairs a rigid biocompatible interbody spacer with screws driven into both adjacent vertebrae, i.e., the closest art to the inventive fixation concept.
• Anticipation: None of the cited references anticipates any of claims 1–7 under §102. The distinguishing elements throughout are (a) the horseshoe/gapped geometry, (b) the converging planar faces, and (c) the cross-holes running from each planar face out through the outer curved face (or, for claim 7, face ridges).
• Date-sensitive caution worth preserving: Hedman (US 4,759,769) may not even qualify as §102 prior art because its grant (26 Jul 1988) post-dates the '261 invention and its §102(e) viability depends on an unverified US filing date relative to 6 Aug 1987.

7. Explicit uncertainties (do not treat as verified)

1. CA 992,255 specification text — not retrieved. Its §102(b) date (6 Jul 1976) is the most promising in the set; a formal anticipation opinion should begin here.
2. FR 2 570 594 A1 publication date — not verified (only the B1 of 24 Feb 1989 was confirmed, which is too late to be §102 art on its face).
3. FR 2 372 622 text — not retrieved; description rests on the citation's title annotation.
4. Hedman's US filing date — not verified, which controls whether it is §102(e) art at all.
5. Kenna's exact claim language was reviewed via the EP 0 284 210 counterpart claims and the US specification summary, not the US claim set verbatim.
6. This analysis is limited to §102 anticipation. A full §103 obviousness analysis (especially Kenna or Ogilvie in view of Fassio) is a separate exercise and is not performed here.

Sources relied on: US 4,904,261 full text (https://patents.google.com/patent/US4904261/en); US 4,714,469 (https://patentimages.storage.googleapis.com/28/01/ec/fd69359344b1fd/US4714469.pdf and https://patents.google.com/patent/[US6093205](/patent/US6093205)#13); EP 0 284 210 B1/A3 (Kenna counterpart); US 4,636,217 (https://patentimages.storage.googleapis.com/12/cf/6e/0e51303abffece/US4636217.pdf and https://uspto.report/patent/grant/[4636217](/patent/4636217)); US 4,759,769 citations (https://www.freepatentsonline.com/[7115144](/patent/7115144).html#2; https://patents.google.com/patent/[US7575599B2](/patent/US7575599B2)#14).

I'll ground this obviousness analysis in the actual disclosures of the references on the face of the patent and its family-citation list.

Good — I now have the two face-cited references plus Ogilvie. Let me pin down the remaining family-cited art and the U.K. family member.

Obviousness Analysis — US 4,904,261 (Dove et al.), 35 U.S.C. § 103

Building on the claim construction, prosecution context, and negative litigation findings from the prior sections. This section does not repeat the bibliographic or litigation analysis.

I. The controlling framework

1. Governing law. The application was filed August 4, 1988 and issued February 27, 1990, so pre‑AIA § 103 (as amended by the 1984 AIPA) governs. The operative tests are Graham v. John Deere Co., 383 U.S. 1 (1966) (scope/content of art; differences; PHOSITA level; secondary considerations), supplemented — for any current validity challenge — by KSR Int'l Co. v. Teleflex Inc., 550 U.S. 398 (2007). Because the claims carry no criticality data and the specification offers no unexpected results, the "predictable use of prior art elements according to their known functions," "obvious to try," and "design incentive" rationales of KSR do the heavy lifting.

2. Two date traps in this file. Two points must be stated up front because they determine which references are even available:

• § 102(b) is measured from the U.S. filing date (Aug. 4, 1988), not the GB priority date (Aug. 6, 1987). Foreign priority under § 119 does not carry over for § 102(b) purposes. Therefore the critical date for a § 102(b) printed-publication/patent bar is August 4, 1987.
• The two references the examiner actually cited (Kenna '469, Hedman '769) are not § 102(b) art. They issued December 22, 1987 and July 26, 1988 — both after August 4, 1987. They are available only under § 102(e) (U.S. patents granted on earlier-filed applications), and § 102(e) art can be sworn behind under Rule 131. This is a structural weakness in any obviousness case built only on the two face citations: the patentee can attempt to antedate both by proving an invention date before February 1987. The family-cited art, by contrast, is unswattable § 102(b) art.

The prior-art universe (as identified on the patent page)

Note on the page's "Cited By" list. The 485 forward citations (Brantigan '256/'757, Michelson, Kuntz '921, Patil '777, etc.) are later art and are not available against the '261. Only the six references above are usable, plus any pre‑August‑1987 art the examiner never saw. The family-citation list is only four documents long, which itself evidences a narrow search — relevant to whether a challenger could find unconsidered art.

II. Level of ordinary skill in the art

A PHOSITA here is an orthopaedic/spinal surgeon working with a mechanical or materials engineer, with 2–4 years' experience in interbody spinal devices — familiar with: anterior approaches to the disc space; the fact that the peripheral/apophyseal rim of the vertebral endplate is the strongest bone (a premise the '261 specification itself asserts as background); biocompatible materials (carbon-fibre-reinforced plastics, titanium, Co‑Cr alloys, stainless steel, ceramics, hydroxyapatite); cancellous bone screws and lag-screw seating; and the routine practice of packing bone graft into a prepared disc space. This is a mature, mechanical, highly predictable art — the KSR conditions for combining references on rational grounds are comfortably met.

III. Limitation-by-limitation map

The only limitation that no cited reference squarely shows is the open-ended horseshoe itself, plus the exact chord-like hole geometry of claim 1. Everything else is a mapping exercise. That is the honest borderline of this case.

IV. Grounds of rejection, with motivation

Ground A — Claim 1 obvious over Ogilvie (US 4,636,217) in view of Kehr (FR 2 570 594 / EP 0 179 695), further in view of Kenna

Why combine:

• Ogilvie and Kehr address the same problem in the same anatomy: an anteriorly implanted prosthetic body spanning a vertebral void, held within the anterior vertebral margins (both expressly recite this as an object — Ogilvie: "does not protrude outwardly from the anterior margins"; Kehr: a plate fixed by screws to two distinct vertebrae, cervical application). Kehr contributes the curved, periphery-conforming outline; Ogilvie contributes the rigid fixation of the body to both adjacent vertebrae by screws seated in bores with internal shoulders, driven from a direction accessible with the implant in situ.
• The expressed motivation is the very deficiency the '261 identifies in its background: a bone-graft-only fusion "without internal fixation against rocking and rotation, not infrequently leads to dislodgement of the graft or sinking in of the graft and non-union." Ogilvie expressly supplies exactly that missing internal fixation ("provides an element of rigid internal fixation so that body healing can take place across the segment spanned"). This is a textbook KSR "known technique used to improve a similar device in the same way."
• Kenna supplies the residual limitation — an aperture opening in the outer wall of the spacer for external access (its threaded/locking holes in the "third surface," used to engage the positioning tool) — so that a PHOSITA seeking to drive Ogilvie-style screws into a curved, margin-confined body from the exposed anterior/lateral aspect would place the bore so that it opens in the outer curved face, with the head seating against a shoulder (Ogilvie claim 13 / Kenna's shoulder 35).

Predictability: boring an oblique bone-screw hole through the rim of an implant so a screw can be inserted from the exposed side and driven into the adjacent vertebra is a purely mechanical, utterly conventional expedient; no new principle is required and there is a reasonable expectation of success.

Ground B — Claim 1 obvious over Kenna in view of Ogilvie (the "examiner's own references plus one" ground)

Kenna already teaches every structural premise of the claimed body except screw fixation and the horseshoe gap: rigid body, planar bearing faces sized to the disc space, a curved profile conforming to the vertebral outer profile (the "outer curved face" of claim 1), a plurality of apertures (threaded + locking holes) and a shoulder. Kenna's weakness is fixation: it depends on pre-drilled endplate grooves and long-term bone ingrowth into a porous coating. Ogilvie teaches precisely the missing element — immediate rigid screw fixation through the implant into both vertebrae, with four screws (two up, two down) and seated screw heads. Motivation: substituing immediate screw fixation for ingrowth-dependent fixation is the classic "known technique to improve a similar device in the same way," and Kenna's own pre-drilled-groove procedure shows the artisan was already modifying endplate geometry to retain the implant — adding a screw hole is a lesser step.

Ground C — Claim 7 obvious over Kenna in view of Kehr (or Fassio)

The claim-7 limitation ("ridges generally parallel to the plane containing the ends of the horseshoe") is the functional equivalent of Kenna's protuberance: Kenna's ridge runs "the full width of the surface parallel to the straight side of the D," and the "straight side of the D" corresponds to the plane containing the free ends of the claimed horseshoe. Kenna also teaches the reason for it — gripping engagement with the vertebra (pre-drilled complementary grooves) plus porous-coating ingrowth. Combine with Kehr's or Fassio's curved/semicircular periphery-conforming body and you have claim 7. This is the strongest ground in the case; it borders on anticipation if one gives "horseshoe" its broadest reasonable interpretation to cover a D/semicircular body.

Ground D — Claim 1 obvious over Fassio in view of Ogilvie

Fassio's "flat semicircular disc with hemispherical boss each side" is, under BRI, a horseshoe-like open body with protrusions on both faces for engaging the vertebrae — i.e., a spacer with upper and lower engagement faces and an external convex rim. Ogilvie supplies the screw-through-the-body fixation and shoulder. Motivation: the two are cumulative improvements on the same problem (a disc-space spacer that will not migrate), and substituting screw fixation for a boss-based friction/pivot interface is a predictable mechanical substitution with an articulated advantage (resistance to "rocking and rotation," the exact failure mode recited in the '261).

Ground E — Corroborating "state of the art" evidence: Kenna's own EP 0 284 210 A3

Kenna's European counterpart expressly frames the invention as an improvement over EP‑A‑0179695 (Kehr), a D‑profiled, outer-profile-conforming vertebral prosthesis, by adding protuberances + porous coating. That document is contemporaneous, third-party evidence that artisans in this exact art routinely combined a curved, periphery-conforming vertebral body with surface engagement features — which directly undercuts any argument that the '261's combination of a curved body with grip/fixation features was nonobvious.

V. Dependent claims 2–6 (design choice / obvious substitution)

VI. Where the case is vulnerable — the honest counterweight

I would not present this as a clean, certain invalidity case. Four real problems:

1. No reference discloses the open-ended horseshoe with a discrete gap. Kenna is D-shaped; Kehr is a plate; Fassio is a semicircular disc; Cutter/Stubstad is a disc prosthesis. The '261's gap 16 is functionally load-bearing in the disclosure (it is the graft-insertion window and it is oriented toward the spinal canal). A patentee will argue that the claimed relationship — a continuous outer curved load-bearing rim with two converging free ends flanking a single anterior graft portal — is not taught or suggested, and that the examiner, having Kenna and Hedman, found nothing closer in 1990.

2. The claim-1 hole geometry is not squarely shown. Ogilvie's screw bores are axial and emerge at the end faces; its outer-wall cross-bore is for a worm drive shaft, not a bone screw. Mapping "a hole from each planar face emerging in the outer curved face" onto Ogilvie + Kenna requires an inference that the artisan would relocate/angle the bone-screw bore so that it opens in the outer wall. That inference is reasonable but it is an inference; a patentee will call it hindsight reconstruction from the specification's own FIG. 6 (which expressly shows shoulders 18).

3. Hedman arguably teaches away from the invention's core premise. Hedman's articulated, spring-biased device exists to preserve motion; the '261 requires a rigid spacer for fusion. If a petitioner relies heavily on Hedman, the patentee has a genuine teaching-away argument. Hedman is therefore useful only for the narrow teaching that screws may rigidly anchor an interbody device to both vertebrae — and Kenna, which relies on drilled grooves and ingrowth rather than screws, offers no contrary teaching. Use Ogilvie, not Hedman, as the screw-fixation reference.

4. Kenna and Hedman are § 102(e) art only and can potentially be sworn behind (Rule 131). Any case resting solely on the two references of record is exposed to an antedating declaration. The family-cited § 102(b) art (Ogilvie, Kehr, Fassio, Cutter) cannot be sworn behind, so the case should be anchored on Ogilvie + Kehr, using Kenna and Hedman as secondary/corroborating references.

Secondary considerations

• Long-felt need / failure of others — asserted but unproven. The '261 background states: "Until now there has been no satisfactory implant to cope with this particuar problem." That is an applicant's assertion of a long-felt unmet need and failure of others. It is unsupported by any evidence in the document, and the need is narrowly framed (graft dislodgement/subsidence after anterior fusion) — but if a patentee could substantiate it with contemporaneous literature, it is the best nonobviousness argument available. A petitioner should pre-emptively rebut it by showing that the constituent solutions (screw fixation via an interbody implant; ridge engagement of the endplates; peripheral load-bearing) each existed and were known to work.
• No nexus evidence. No commercial-success, licensing, copying, or industry-praise evidence appears anywhere on the page. The patent's very heavy forward-citation count (485 per Google Patents; ~1,302 in the USPTO "Cited By" listing) is evidence of technological prominence, not of nonobviousness, and does not create a nexus.
• Presumption of validity. The examiner considered Kenna and Hedman and still allowed 7 claims in a single action with no rejections of record on the page. In any later challenge the patentee gets that deference; a petitioner must show why the combination would have been obvious despite examiner consideration — the family-citation list suggests Ogilvie/Kehr/Fassio may have been before a foreign examiner (GB 2 207 607 / EP 0 302 719), so a petitioner should confirm whether they were of record in the U.S. file before relying on them as "not considered."

VII. Bottom line

Practical takeaway for a challenger: build on Ogilvie (US 4,636,217) as the primary reference for screw fixation and the screw-head shoulder, Kehr (FR 2 570 594 / EP 0 179 695) as the primary reference for a curved, anteriorly-confined, screw-fixed vertebral body carrying graft, and Kenna (US 4,714,469) for the transverse gripping ridge and the outer-wall aperture. Do not lead with Hedman (§ 102(e) only, and it teaches motion preservation, i.e., away from rigid fusion). Anticipate the two real defenses: (i) the open-ended horseshoe and the "planar-face-to-outer-curved-face" hole are not squarely shown, and (ii) an unsupported long-felt-need assertion in the '261's own background.

VIII. Stated limitations of this analysis (per the operating rules)

1. I did not retrieve the full texts of FR 2 372 622 (Fassio), FR 2 570 594 / EP 0 179 695 (Kehr), or CA 992255 (Cutter / Stubstad). My descriptions of those three rest on Google Patents abstracts/titles, on Kenna's EP 0 284 210 A3 background section (which characterizes EP‑A‑0179695), and on Ogilvie's background characterization of US 3,867,728. Any assertion about where in those documents a limitation appears should be verified against the documents before being relied on in a filing.
2. I could not check the U.S. file history, any reexamination, or any IPR/PGR on US 4,904,261 — my search tooling hit its step limit on that query. Whether Ogilvie/Kehr/Fassio appear on a PTO-1449 or in a GB/EP search report (rather than only in Google's aggregated family-citation list) materially affects the deference owed to the examiner.
3. I did not verify GB 2 207 607 B's claims (the U.K. family member), which could shed light on what the applicant and British examiner treated as the inventive core.
4. Where I say a limitation is "not squarely shown," that is a negative finding from the six references on this page only — not a representation that no such art exists. Given the narrow four-document family-citation list, additional pre-August-1987 art (e.g., contemporaneous interbody cage/spacer patents with oblique screw apertures) is plausible and would strengthen Grounds A–C.