NotchPass

Retrograde femoral nail and TKR notch compatibility

v2 · 4 sources

Knee replacement (femoral component)

Retrograde nail

Nail diameter

Overream the canal by

Gerow et al. note a frequent need to overream 1–1.5 mm above nail diameter.

Intended purpose & limitationsA reference aid for qualified surgeons — it does not replace clinical judgement. Tap to read before use.

Intended purpose

NotchPass presents published dimensions of total knee replacement femoral components and retrograde femoral nails, and compares them arithmetically, so that a qualified health professional can consider whether a given nail may pass through a given component’s intercondylar notch during preoperative planning.

It is an interactive presentation of information already published in the peer-reviewed literature and in manufacturers’ technique guides. It does not diagnose, does not assess a patient, does not process images or data from any medical device, and does not specify or recommend a treatment for any individual patient.

How it reaches its answers

Every figure is attributed to a named published source, shown in the “What each source says” panel with each result.
The arithmetic is stated in full: the widest instrument (opening reamer, canal reamer or driving end) is compared with the narrowest reported intercondylar width. “How the check works” sets out each category.
Where sources disagree, both are shown and the more cautious answer is given. Nothing is hidden behind proprietary logic, and no artificial intelligence is used to generate any result.
Every source is linked, so any output can be independently verified against the original document.

Limitations

Published data are incomplete. No source maps notch width to every individual component size; most give a range or the narrowest size only. Some rows carry no dimensions at all.
Figures for the same implant differ between sources, and some published verdicts have been corrected since first publication.
Notch width alone does not determine feasibility. The position of the component on the femur, how far posterior the box sits, femoral morphology, cement within the notch and the condition of the bone all matter, and none of them can be assessed here.
Nail sizes within a listed range are assumed to step by 1 mm. Some opening reamer and driving-end figures are not published and are inferred, as each result states.
Implant designs change. A figure that was correct when last reviewed may not describe the implant in front of you.

Disclaimer

This tool supports, and does not replace, the clinical judgement of the treating surgeon. All dimensions must be confirmed against the current manufacturer technique guides and, where compatibility is uncertain, by imaging and intraoperative assessment before use in a patient. No warranty is given as to the accuracy or completeness of the data. The author accepts no liability for any clinical decision, outcome or loss arising from its use. It is not intended for use by patients or by anyone who is not a qualified health professional.

Developed and maintained by Dr Siddharth Padmanabhan, Brisbane, Australia · Corrections and errors: info@notchpass.app · Last reviewed: 28 September 2026.

Every nail in this knee

Each system at its 10 mm size (or nearest). Tap one to load it.

Browse knees against this nail

Nail dimensions

Driving end = the distal end the insertion jig threads into. “First screw” = distance from the distal tip of the nail to the first interlocking hole — shorter helps in very distal fractures. Radius of curvature = the nail’s anterior bow; a smaller radius means a more curved nail. Sources: Gerow 2022 Table 2, Richards 2026 Table 1, manufacturer technique guides.

Nail	Nail Ø	Driving end	Opening reamer	First screw	Distal bend	Radius of curvature	Guide

How the check works

Everything that goes through the notch has to fit: the opening reamer, the canal reamers (nail + overream), and the nail’s driving end. The widest of these is compared with the narrowest intercondylar distance any source reports for that knee.

Clears — at least 0.5 mm to spare at the smallest size.
Tight fit — fits, with under 0.5 mm to spare.
Use caution — the numbers fit, but a source flags this knee–nail combination (usually larger nails in smaller component sizes, or a posterior notch).
Depends on size — only larger component sizes are wide enough, or only the smallest width is published.
Sources disagree — at least one source rates the knee compatible and another rates it not compatible. Treat as not compatible until you’ve confirmed the implant on imaging or with the manufacturer.
Won’t pass — wider than the notch at every reported size.
Not compatible — closed box, stemmed revision component, box too far posterior, or every source that rates it says no.

Where published widths differ by more than 0.5 mm, the check uses the narrowest and says so. Richards 2026 rates fit on nail diameter alone (it doesn’t count the driving end or opening reamer), so a knee it calls compatible can still fail this check.

Technical tips

Planning

Plan around the widest instrument, not the nail: a 12 mm driving end typically needs a 13.5 mm opening reamer, even for the smallest nails (Gerow). Reamers over 12.5 mm were the ones that failed in narrow knees (Richards).
Notch position is often more limiting than width. A box placed far posterior forces a posterior start point and an extension deformity (Richards, Jones).
Nails with small opening reamers and driving ends — RFN-Advanced, Phoenix, T2 Alpha — fit the widest range of knees; Trigen Meta, Centronail and T2 A/R the narrowest range (Richards).
The DePuy Synthes RFN-Advanced comes in a standard bend and a periprosthetic bend (9–12 mm only), reported by Richards as 5° and 10°. Choose the periprosthetic bend when the box opening sits posteriorly. Its periprosthetic wire guide matches the nail’s distal end and can be test-fitted in the open box, and an 11.2 mm drill is provided for narrow boxes.
A nail with a 10° distal bend gave better sagittal alignment than conventional nails in periprosthetic fractures (Kerr 2023, cited by Richards).
Where compatibility is borderline, a metal-cutting burr can open the component (Richards). Sigma PS: remove the polyethylene plug from the box (Honig & Sciadini 2025).
If unsure a box is open, a caudal-to-cranial notch view on fluoroscopy shows the lucent opening; CT is unreliable because of metal artefact (Honig & Sciadini).
A 10 mm reamed nail showed no difference in union versus larger nails in femoral shaft fractures (Gerow).

Set-up and entry

Supine on a radiolucent table, triangles under the distal femur at ~30° flexion; C-arm from the contralateral side.
2 cm transtendinous or parapatellar incision from the inferior patellar pole; lateral parapatellar if planning nail–plate.
The start point is often posterior to Blumensaat’s line; nails with a 4–5° distal anterior bend allow this.
If the guide wire won’t pass because of cement in the notch, drill a small pilot hole; reaming clears the rest.

Reduction

Extension deformity: anterior condylar traction pin, towel bump under the apex, flexion moment on the jig, and blocking screws or 2.4 mm Schanz pins anterior to the guide wire.
Proximal shaft caught over the anterior flange: lever it back with a Cobb through a small anterior incision, with traction and knee flexion. An AP Schanz pin joystick helps but pulls out easily in osteoporotic bone.
Coronal deformity: move the foot-end traction toward or away from the other leg; blocking screws or Schanz pins as needed.

Locking and finishing

Check that distal locking screws miss the component pegs with a perfect-circle view; bury or rotate the nail if they don’t.
Match rotation to the other side’s anteversion before proximal locking.
Stress in varus/valgus; if the nail toggles, add medial and lateral blocking screws.
Protect the polyethylene and femoral component while reaming — have a spare insert available.
Weight-bearing as tolerated immediately after surgery.

Terms of useOwnership, permitted use, disclaimers and privacy. Last updated 28 September 2026.

1. Who may use NotchPass

NotchPass is provided for qualified health professionals for preoperative planning. It is not intended for patients or for anyone who is not a qualified health professional. By using it you confirm that you are a qualified health professional and that you accept these terms.

2. What NotchPass is, and is not

NotchPass presents dimensions of total knee replacement femoral components and retrograde femoral nails that have been published in the peer-reviewed literature and in manufacturers' technique guides, and compares those figures arithmetically. It supports, and does not replace, the clinical judgement of the treating surgeon. It does not diagnose, does not assess any patient, does not process images or data from any medical device, and does not specify or recommend a treatment for any individual patient. Responsibility for every clinical decision remains with the treating clinician.

3. Accuracy of the data

The published sources are incomplete and in places inconsistent, and implant designs change. Figures may be superseded, mistaken or inapplicable to the implant in front of you. Every dimension must be confirmed against the current manufacturer technique guide, and compatibility confirmed by imaging and intraoperative assessment, before use in a patient. No warranty is given that the data are accurate, current or complete.

4. No warranty

NotchPass is provided “as is” and “as available”, without warranty of any kind to the extent permitted by law. No guarantee is given that it will be available, uninterrupted, or free from error. Certain guarantees under the Australian Consumer Law cannot be excluded; nothing in these terms excludes, restricts or modifies any right or remedy that cannot lawfully be excluded.

5. Limitation of liability

To the maximum extent permitted by law, the developer is not liable for any loss, damage, injury, cost or expense, whether direct or indirect, arising from the use of or reliance on NotchPass, including any clinical decision or outcome. Where liability cannot lawfully be excluded, it is limited to resupplying the app or the cost of resupply.

6. Ownership

NotchPass, including its text, design, code, structure and the compilation of data it presents, is the copyright of Siddharth Padmanabhan © 2026. All rights reserved. The underlying measurements remain the work of their original publishers and are cited throughout. NotchPass is not open-source software and no licence is granted beyond the permitted use in clause 7.

7. Permitted use

You are granted a personal, non-exclusive, non-transferable licence to use NotchPass for your own clinical practice, including installing it on your own device for offline use. You may share the web address with colleagues. You may not copy, republish, redistribute or sell the app or its content; incorporate it into another product, publication or service; extract or scrape its data in bulk; or remove or alter the attribution, copyright or disclaimer notices. Requests for any other use are welcome via the contact address below.

8. Links to other sites

NotchPass links to manufacturers' technique guides and published articles hosted by others. Those sites are not controlled by the developer, and no responsibility is taken for their content or availability.

9. Privacy

NotchPass requires no account and collects no personal information. Your last used knee, nail, size and reaming settings are stored on your own device so the app can restore them, and that information is never transmitted. If analytics or advertising are ever introduced, this page and a privacy policy will be updated before they are.

10. Changes

The app and these terms may be changed at any time. The app footer shows the current version and the date the data were last reviewed. If you are using an offline copy, check the version against the live site at notchpass.app.

11. Governing law

These terms are governed by the laws of Queensland, Australia, and you submit to the non-exclusive jurisdiction of the courts of that State.

12. Contact

Developed and maintained by Dr Siddharth Padmanabhan, Brisbane, Australia. Questions, corrections and permission requests: info@notchpass.app.