Minimal incision surgery (MIS) has improved the surgical outcomes of many types of surgery. For example, in laproscopic surgery a minimal incision approach has a number of short term benefits including decreased infection rates, shorter hospital stays and faster return to activities for patients. Laproscopic MIS also has the additional long term benefit of preservation of the abdominal wall. Use of multiple small incisions compares favorably to one larger incision by preventing abdominal hernias and abdominal wall weakness.
In foot and ankle surgery, the size of the incision used to perform a surgery is dictated by the technique used to perform a surgery. Traditional ‘open’ foot and ankle surgeries that involves cutting bone and placing fixation require an adequate length of incision to accomplish the following -
- Provide necessary visualization of bone and soft tissue structures
- Provide adequate room for instrumentation, retraction or fixation
- Decrease tension on skin, arteries and nerves from retraction
When you begin surgical planning for a bunionectomy, you have to ask the question - what’s better – a smaller incision or a better long term outcome? Are the two complimentary or mutually exclusive?
Is there a benefit to a smaller incision in bunion surgery?
Let’s take a quick look at the current options available for minimal incision bunion surgery and then compare the pros and cons of these surgical techniques. Current techniques use to perform minimal incision bunion surgery all have a smaller incision, but the differences in the procedures lie in the type of fixation used and the orientation of the osteotomy (cut in the bone). Be sure to follow these links for video and technical information of the individual companies and techniques.
Screw fixation only
- ProsStep from Wright Medical, Memphis TN, uses a chevron, or V shaped osteotomy (cut in the bone) to correct the bunion. Correction is held in place while multiple screws are used for fixation.
- Arthrex, Naple FL, has developed a MIS bunion technique that uses a transverse osteotomy with dual screw fixation.
- NovaStep PECA bunionectomy with performed with a transverse osteotomy and percutaneous screw fixation of the osteotomy.
Screw and plate systems
- NovaStep, based out of Orangeburg, NY, developed an intramedullary locking plate called Centrolock Guided Transverse Osteotomy System. This bunionectomy technique uses a transverse osteotomy with a locking plate that resides within the bone (medullary canal) to reduce space.
- CrossRoads Mini Bunion technique uses a transverse osteotomy and intamedullary screw and plate fixation.
- Wright Medical also provides a locking plate MIS technique called ISO (Intraosseous Sliding Osteotomy) Plate with POCKETLOCK™ Technology. This technique uses a transverse osteotomy.
Bunionectomy and bone healing - what is primary and secondary bone healing?
In almost all bunionectomy procedures, one of the key steps in correcting the bunion is to cut the first metatarsal bone and displace the bone into a corrected position. The bone is then stabilized in that corrected position while it heals. Ideally, the surgical fracture (osteotomy) is well aligned and well apposed and stable. If these three precursors of fracture healing are met, healing typically proceeds uneventfully. Good apposition, good alignment and stable fixation all leads to the optimal kind of bone healing called primary bone healing.
But what if the osteotomy is unstable, poorly aligned and displays motion at the fracture site? Healing will not take place by primary bone healing. The surgical osteotomy will heal by secondary bone healing. The clinical findings of secondary bone healing include swelling specific to the osteotomy, clicking and popping and pain.
What is the difference between primary and secondary bone healing?
When your doctor orders a post op x-ray following your bunionectomy, what he/she is doing is assessing primary vs secondary bone healing. Primary bone healing will show minimal gapping at the osteotomy on x-ray and no surrounding proliferation of bone surrounding the fracture. In secondary bone healing, we’ll often see a fracture line and proliferative formation of bone surrounding the fracture. This proliferation of bone is an attempt by your body to stabilize the fracture. When there’s good alignment, good apposition and stability at the fracture site, bone healing occurs directly across the surgical osteotomy. Not so in secondary bone healing. In secondary bone healing, your bone is actively working to find a way to stabilize the fracture. Primary bone healing is optimal but secondary bone healing can indeed heal. Secondary bone healing usually takes longer to heal and has a greater propencity for delayed union or non-union at the osteotomy site.
Does minimal incision bunionectomy heal by primary or secondary bone healing?
Remember our prior mention of osteotomy and fixation for each of these MIS bunion procedures? In a perfect world, every osteotomy has great apposition and alignment and will heal by primary bone healing. But in MIS surgery, we sometimes have to push the limits of the surgery to accomplish our MIS goals. If you reread each of the procedure descriptions above, only the Prostep from Wright medical uses an osteotomy that preserves apposition of bone through the use of a chevron osteotomy. All of the other procedures use a transverse osteotomy. A transverse osteotomy is a straight cut across the bone with limited apposition and alignment. A transverse osteotomy is inherently unstable.
In addition to apposition and alignment, we also said that the third factor that needs to be present for primary bone healing is stable fixation. One of the axioms in bone plating and fixation is that there needs to be at minimum two point fixation. In each of the three procedures described above that use screw fixation only, two screws are placed across the osteotomy. Remember, I said two screws at minimum.
The remaining three MIS bunionectomy systems use a plate and screw system to stabilize the surgical osteotomy. In each of these cases, the fixation used is a plate and screw combination that is placed in an intramedullary fashion (within the bone).
What are the pros and cons of traditional vs MIS bunionectomy
Using minimal incision approaches to perform bunionectomy procedures is not new to foot and ankle surgery. Thirty years ago, minimal incision surgery was performed on a regular basis in office based practices, but the results were less than optimal. Due to consistently poor outcomes, the MIS procedures of the 1970’s fell to the wayside. But there’s been a resurgence over the past two years to bring MIS bunionectomy surgery back.
Issues to consider when contemplating MIS bunion surgery
The issues that are important to consider when contemplating MIS bunionectomy are –
- Surgeon skill and training
- Stability of the osteotomy
- Reliability of the fixation
- Patient expectations
A traditional bunionectomy is a bread and butter procedure for a foot and ankle surgeon. Each surgeon may have their favorite techniques but most importantly, we do them on a regular basis. MIS bunionectomy on the other hand is not a procedure done with frequency and therefore presents as a challenge for most foot and ankle surgeons regardless of level of training. My impression is that Companies like CrossRoads, Wright and Arthrex take this issue very seriously. Training for MIS bunionectomy is readily available to surgeons. Reps are present for cases and often the reps will present for follow-up on cases.
Why is the orientation of the osteotomy important? We talked earlier about the orientation of the osteotomy and how that orientation dictates apposition, alignment and stability. Transverse osteotomies are inherently unstable. A transverse osteotomy does not provide adequate apposition and stability, regardless of fixation type. In traditional, open bunionectomies, the surgeon relies on the apposition and alignment of the osteotomy and not the fixation. MIS bunionectomy procedures rely heavily on fixation, not apposition and alignment of the bone. Reliance on fixation alone in bone fixation is a known pathway to poor outcomes.
Knowing that in most cases, apposition and alignment of MIS bunionectomies is tenuous at best, we really put a lot of faith in the fixation techniques used in these procedures. And as I mentioned before, it’s the apposition and alignment of the bone, not the fixation that heals the osteotomy. The two point screw fixation techniques are a minimal standard in the science of bone healing. The plate and screw systems may be better at stabilizing the bone, but again, these fixation techniques will often result in secondary bone healing.
What really seems to drive the decision making in MIS bunionectomy is patient expectations. Patients are interested in cosmetic outcomes that will allow for return to low cut shoes and sandals. When vanity weighs as heavy in the pre-operative planning and choice of procedures, I start to get cold feet.
As a foot surgeon, do I plan to do a lot of MIS bunionectomies?
So let me get this straight – we’re contemplating performing a bunionectomy that is inherently unstable due to the orientation of the osteotomy, fixation is minimal which may lead to secondary bone healing and the surgical decision making is being driven by inflated patient expectations. Many surgeons would explain the inherent disadvantages of MIS bunionectomy away by saying, “the success of the procedure is all in the patient selection.” For my practice, I’m just not sold on the virtues of MIS bunionectomy.
The advantages for certain MIS procedures, like laproscopy, are quite clear. In foot and ankle surgery, MIS techniques in ankle arthroscopy have truly revolutionized ankle surgery even within the course of my career. MIS bunionectomy is still struggling to find a home in my tool box. I’m going to sit on the sidelines with this procedure until I can see clear and definitive advantages to the procedure.
Follow this link to join the discussion surrounding minimal incision bunionectomy.