Can A Reamer System Improve First MPJ Fusions?
There are many methods you can use to prepare the first metatarsophalangeal joint (MPJ) for arthrodesis. One of those techniques involves using a cup and cone reamer system. Using this system can be helpful, especially when there has been some trauma to the joint surface, when you’re dealing with an extremely arthritic joint with hypertrophy or when the patient has a square metatarsal head. These conditions could potentially prohibit an exact coaptation of the opposing bones.
However, the cup and cone reamer system (Howmedica) is designed to take advantage of the convexity of the first metatarsal head and the concavity of the base of the proximal phalanx, which yields solid contact between two opposing surfaces for arthrodesis.1 The Howmedica system contains five matching barrel reamers as well as proximal and distal bits that are 10, 12, 14, 16 and 18 mm in diameter.
Insightful Step-By-Step Tips
When it comes to the first MPJ arthrodesis, begin by making a dorsal-medial incision. Dissect through the tissue layers to the capsule. You may commonly encounter significant synovial fluid and osteophytes, which you can debride with a rongeur. You can achieve chondroplasty with the small joint reamer system or with another technique of your choice. I have found a rotary burr to be quite sufficient for this job.
Proceed to place a 0.062-inch smooth Kirschner wire axially through the first metatarsal head and make sure it is securely within the shaft. Occasionally, you may need to use the barrel reamer to yield a cylindrical distal metatarsal. You can attach it to a Jacobs chuck and trauma drill, and then guide the entire assembly over the K-wire.
Perform reaming until you’ve obtained a smooth cylindrical surface. (You may omit this portion of the technique since the concave and convex surface reamers are often sufficient to prepare the arthrodesis site.) Attach the cannulated proximal reamer (concave in appearance) to a trauma drill/reamer via a Jacobs chuck and then place the entire assembly over the Kirschner wire so it sits flush with the metatarsal head.
Perform reaming until the subchondral plate is denuded and you see bleeding bone. Remove the Kirschner wire and place it axially through the base of the proximal phalanx. Use the convex reamer in the same fashion to prepare the phalangeal surface. The result is a surgically induced cup and cone. I prefer to drill with a 2-mm drill bit on both surfaces at this point.
A Few More Pearls About Reaming
Reaming through the subchondral plate is absolutely necessary if you wish to obtain consistent union of any arthrodesis site. Inadequate preparation of the bone surface is one of the most common surgical causes of failure of arthrodesis second to improper fixation. Other causes for delayed union or non-union include patient factors such as non-compliance with weightbearing restrictions and smoking.
Using the “ream” setting on the trauma drill is necessary because of the lower RPM and torque differential when compared to the “drill” setting. I have found the drill setting to be too aggressive.
Adequate soft tissue exposure and retraction is necessary in order to avoid damage to delicate structures by the reaming process.
Addressing Final Positioning Of The Hallux
One topic of discussion among many surgeons is the final positioning of the hallux on the metatarsal. The literature can be rather vague with respect to exact angles.2,3 Much of this depends on the type of patient you are treating. Obviously, a female patient who is adamant about continuing to wear high-heeled shoes would dictate one position while an inactive male might require another position.