First MPJ Arthrodesis: What The Evidence Reveals
Another common technique for arthrodesis site preparation is the utilization of power conical reamers to produce a cup to cone apposition or a ball and socket. By maintaining the contoured convex metatarsal head and concave proximal phalanx, surface contact areas for fusion increase. This allows for tri-planar “dialed in” positioning of the hallux to the metatarsal head. The optimum position is 15 to 20 degrees of dorsiflexion and 10 to 20 degrees of abduction.33 Intraoperatively, the hallux should lay parallel to the second toe with the foot fully loaded on the rigid flat surface (a basin) to simulate weightbearing and the ankle joint at 90 degrees. The hallux should also contact the surface.
Various authors have described numerous methods of internal fixation, including Kirschner wires, intramedullary Steinmann pins, staples and screws.1 The use of modern osteosynthesis constructs has decreased the non-union rate and allowed early weightbearing and a more rapid recovery.
Fusion success rates have been as great as 92 percent to 100 percent.3 Roukis and colleagues looked at three main configurations: compression screws, dorsal plate and screws, and staples.34 The authors found the overall incidence of non-union using one of these modern techniques was 5.4 percent. In another study by Dening and colleagues, a retrospective analysis of plate versus screw fixation showed MPJ fusion with single oblique lag screw fixation at 71 percent, crossing lag screws at 90 percent, a low contoured dorsal plate at 100 percent, and a dorsal plate with a plantar screw at 93 percent.35 The study authors allowed early weightbearing in all cases.
The most frequent form of osteosynthesis is low-contoured dorsal plating with or without a lag screw. Without the use of a lag screw, performing eccentric drilling of the screw hole most proximal to the joint on the metatarsal side can accomplish compression. Surgeons most often use traditional non-locking plates unless there is osteopenia. In cases of osteopenia, one can use a locking plate. If you are not using a lag screw or it is not appropriate to do so because of bone consistency, position a non-locking eccentric screw within the plate before inserting the locking screws. In cases of significant osteopenia, the surgeon can omit a compression screw. Contact of the joint surfaces with plate stabilization provides adequate fixation.
Key Considerations For Interphalangeal Joint Arthritis
Propulsive activity after first MPJ arthrodesis depends on proper positioning of the hallux in the sagittal plane and mobility of the interphalangeal joint to obtain assisted dorsiflexion in propulsion. In the presence of interphalangeal arthritis, one may avoid arthrodesis and consider implant arthroplasty.
Other options exist. One consideration is positioning the hallux in the transverse plane in 20 degrees abduction or more.33 Surgeons can also consider arthrodesis of the interphalangeal joint but this will require bone resection at the MPJ arthrodesis site to shorten the first ray, which could increase the risk of metatarsalgia.9
Could First MPJ Arthrodesis Have An Impact For Other Joint Disorders?
First MPJ arthrodesis is reportedly effective in treating many joint disorders and may also be useful in cases of revision and salvage. These conditions include joint destructive rheumatologic disorders, neuromuscular-associated hallux abducto valgus deformities, hallux abducto valgus deformity associated with osteoarthritis or severe hallux abducto valgus deformities.31,33 Other conditions are loss of both sesamoids, failed implant arthroplasty, failed hallux abducto valgus surgery, hallux varus or failed Keller arthroplasty. Finally, additional conditions include avascular necrosis, osteopenia and osteomyelitis in which significant bone loss and consistency become factors.