MIS Bunion Surgery System Study Notes

MIS Bunion Surgery System

Accutrack Screws

  • Current screws, like Accutrack threes, are used for MIS due to their length (up to 60mm) providing necessary lever arm.
  • Surgeons typically use a standard size for the big lever arm, a mini for the medial screw, and a micro for the Akin osteotomy.

Purpose-Built System

  • Executive team's challenge: create a system specifically for MIS bunion surgery.
  • Goal: all instrumentation in one box, including MIS-helpful tools like a burr, elevators, and disposable instrumentation.
  • Disposable instrumentation benefits:
    • Sales team can offer more bunion surgeries at surgery centers.
    • Acts as a force multiplier.

Screw Options

  • Beveled (compressive) screws will be included.
  • Some surgeons prefer non-compressive screws, while others are okay with compression, accounting for it in their correction.
  • A version of the metacarpal nail with extended increments will be created for beveled options (both Accutrack and Innate).
  • This provides options for compressive or non-compressive treatment, equivalent in length range and diameters to current options.

Compression Considerations

  • Dr. Felipe prefers non-compressive screws but acknowledges manual compression during correction.
  • In modern MIS, the head is moved significantly (close to 100%), potentially negating the need for compression.
  • Traditional osteotomies rely on bony contact for biomechanical support, which is often absent in MIS.
  • Compression may not be necessary in MIS due to minimal bony contact.
  • Arthrex initially used compressive implants but moved to non-compressive ones.

Screw Design

  • Most screws have a conical design but aren't truly compressive because the thread distance doesn't change like Accutrack screws.
  • The solution should offer both compressive and non-compressive options.
  • Some customers successfully use Accutrack for MIS, while others prefer non-compressive screws.

Alternative Screws

  • Dr. uses OsteoMed screws (Stryker StramiFix) for open Chevron and smaller sizes for lesser toes.
  • Surgeons often perform bunion and toe corrections together.
  • Having options for the entire procedure (bunion and toes) is beneficial.

New Accutrack Screws

  • New Accutrack screws have a 2.0mm front and 2.4mm tail.
  • The 2.4mm tail is suitable for the second and third toes but less ideal for the fourth and fifth.
  • Lengths up to 40mm are available; up to 50mm needed for the second and third metatarsals.

Screw Choice

  • When performing a hammertoe correction, both fully threaded Accutrack and partially threaded headless screws are options.
  • Availability is a key factor in the choice.
  • The stability required for toes is less than for other procedures, and significant compression isn't needed.
  • Resection arthroplasty and fusion yield similar clinical outcomes; ease of insertion and removal is important.

Bevel Importance

  • The second screw is crucial; the first screw grabs two cortical bones.
  • The second screw goes into the mid-shaft of the metatarsal.
  • Sinking a regular screw too much can cause loss of purchase in the medial cortical bone.
  • The bevel design ensures maximum purchase of the cortical bone, especially in older patients with thinner cortical bone.
  • Some surgeons use only one screw, which can be an Accutrack screw, sunk into the proximal metaphysial or epiphysial bone.
  • Adding more screws improves biomechanical strength.
  • Cortical bone is only 2-3mm thick, so even a few threads of purchase matter.
  • Removing bone spikes near the distal screw can loosen it if it lacks good purchase.

Compression Challenges

  • Excessive compression can cause the head to move proximally.
  • The second screw primarily serves as an anti-rotational device, enabling earlier weight-bearing.
  • Compression against soft metaphysical bone in the head is less effective.
  • In older patients (e.g., 75-year-old women), compression is unlikely to be achieved due to soft bone.
  • Accutrack screws achieve compression effectively when used with two cortical bones.
  • Compression is not achieved in soft talar joints due to insufficient calcaneal bone density.
  • Some surgeons use headed screws or clamps for compression in such cases.

MIS Bunion Cases

  • Dr. Felipe performs 60-70% of bunion surgeries MIS.
  • Dr. Ortiz performs 100% of bunion surgeries MIS.

Open Surgery Indications

  • Open surgery is indicated for mild deformities with sagittal issues or arthritis requiring joint decompression.
  • Conditions like hallux rigidus may necessitate open surgery.

Screw Sizes

  • Three screw sizes will be offered.
  • 2.5mm for Akin osteotomy.
  • 4.0mm (proximal) and 3.5mm (distal) screws.
  • Proximal and distal screws available in sizes from 26mm to 60mm.
  • Most commonly used sizes: 34-46mm (proximal) and 46-54mm (distal).
  • Shorter screws (two furrows, 40mm) needed if using two furrows technique.

Screw Placement

  • The kit will include instrumentation for three screws.
  • Pin size is 1.1mm (0.04 inch).
  • The pin can be too flexible.

Guide Pin Issues

  • 1. 1mm guide pin is too flexible, making it hard to position correctly; can cause "sky-ing" (incorrect trajectory).
  • Suggests using a 1.4mm pin initially for guidance, then switching to the 1.1mm pin after the first screw is placed.
  • NovaStep uses a 1.3-1.4mm pin for its 4.0mm screw.

K-Wire Innovations

  • Competitors have increased guide wire diameter.
  • InFrame K-wire has a thicker diameter.
  • Dual diameter K-wire (thicker proximally, thinner distally) could be a good option.
  • Procedure: insert larger diameter wire, then pull it out the other side to stabilize. Slide screw over it.
  • Cobalt chrome wires offer increased stiffness even at 1.1mm diameter.

K-Wire Criticality

  • Proper K-wire placement is a game-changer for MIS bunion surgery.
  • Getting the K-wire right is the most challenging part of the procedure.
  • Thicker, stiffer K-wires offer a significant advantage.

Accessory Pack

  • Accessory Pack will include:
    • Disposable elevator.
    • Burr.
    • Joystick K-wires (2.0mm and 1.6mm).

Measurement Device

  • A special gauge will be needed to measure the bevel depth.

K-Wire Technique

  • The device is placed in the perfect position measure then put it all the way through, and then you can put your screw in.
  • An extra option is to use auxiliary instruments if primary K-wire instrumentation fails rather than going all the way through every case.
  • A sharp tip is useful, especially for the second screw in contact with cortical bone.

Material Concerns

  • Accutrack: titanium alloy.
  • Innate: stainless steel.
  • Concerns over revisions are expected due to similar recurrence rates between MIS and open techniques, so stainless steel could be better to remove versus titanium.

Combining Materials

  • Using one Accutrack screw and one Innate screw should not lead to galvanic corrosion.
  • Patients may prefer titanium due to its association with advanced technology, not because of medical issues.
  • There's no technical reason to avoid combining different materials.

Micromotion

  • Micromotion from stainless steel is not a concern, unlike in leg fractures where it aids fusion.
  • Stiffer materials are preferred for immediate weight-bearing.
  • Long-term effects of micromotion need further study.

Screw Integrity

  • Smaller screws (3.5mm) need good grab to avoid stripping, and the 4.0 screw looks fine.
  • The worry is that a smaller guide pin could cause issues for the 3.5 screw.
  • Some only use the 4.0 screw to cut procedural time and mitigate a risk of loosening of screw 2.

Power & Burrs

Note: The following section discusses power tools (handpieces and burs) used during surgery

  • Burs are frequently utilized.
  • Different burs are needed for different procedures.
  • For a hammertoe, a shorter bur is preferred (2.0mm).
  • For calcaneal osteotomy, a longer bur (3.0mm) is preferred.
  • For bone removal, a straight 3.0 mm burr is used.
  • For MIS from the forefoot to the hindfoot, need some different options for burs (4 or 5 options).

Power Unit Evaluation

  • Two power units were tested: NSK and Amadeo.
  • The NSK unit has 6 newton centimeters, the Amadeo unit runs at 6.5.
  • Dr. Felipe felt the NSK machine was better because it cut bone more easily.
  • Dr. Ortiz felt the Amadeo machine because it also has two ports and offers sagittal saws and osteotomy blades.
  • Both machines were very similar.
  • Long-term torque maintenance is a key factor to consider, they have similar torque in parts.

Sterile Kits

Note: Discussion about the cost and benefits of sterile kits

  • Sterile kit with appropriate screw/implant, power and burs would be helpful.
  • May be cheaper than resterilizing instruments, when considering storage, manpower, and risks of instrument failure.
  • Sterile kits ensure having backups available for quick procedures like MIS.
  • Sterile kits could be a possibility for the international market.
  • The upfront cost of power units is high (~$10,000-$15,000).

Sterilization Costs

  • Sterilization costs range from $35 to $100 per set, depending on the facility and wrapping method.

Beaver Blade

  • Beaver blade is mandatory for MIS.
  • It has a round handle with a rectangular blade that is sharp on the end and one side.
  • The beaver blade allows 2mm incisions.
  • The beaver blade is often provided because big hospitals took years to adopt the blade.
  • Reusable handles are used, and blades are replaced.
  • Several blades are needed for a high profusion.

Chevron Cut

  • People think a chevron cut is more stable, but if you're translating a 100%, there is no reason for a chevron.
  • They move virtually 100%, there's no reason for a chevron unless that a chevron osteotomy is preferable from the vascularity point of view.
  • The French company prescribes an augment shell mass.

Translation Instrumentation

  • A translation instrumentation is needed to to provide thick Ky to fracture the bone.
  • If the K wire is like a hemostat with a little bit of curvature to bring K wire against the head, there is less cooling up.
  • For the best results it would be best to keep them perfectly parallel.
  • Perfectly parallel are often not done.
  • The targeting devices are not that effective.

Benefits of a Guide

  • Less experienced surgeons like the guide, they feel more confident to beginner.
  • Young doctors who have only worked with MIS are comfortable with it.
  • For a better grip you get a better stiffness with whatever you end up using to set this all up.
    This is a good composition/Feel, and we can do another competition to test the better grip.