Medial Column Fusion
Thomas J. Chang
Medial column stabilization often is best achieved with medial column arthrodesis. The three medial column joints are the first metatarsal-cuneiform joint (MCJ), the navicular-cuneiform joint (NCJ) and the talonavicular joint (TNJ). This chapter focuses on the fusion of the central joint, the NCJ. There continues to be expanding literature supporting the fusion of this joint in medial column stabilization, which can be helpful in flexible flatfoot surgery.
Debate has been ongoing on the exact etiology of excessive medial column motion, and often, this has been blamed on movement of the first MCJ. Faber et al presented a prospective study to assess the contributions of the Lapidus in clinical perception of stability along the medial column. They studied 51 patients who had undergone a distal metatarsal osteotomy and 50 who had undergone a Lapidus arthrodesis. At 2-years follow-up, the feet were blinded to a neutral evaluator to assess medial column stability (1). There was no direct correlation to their findings and the procedure performed. This was very insightful and leaves room for further discussion regarding where this excessive motion actually occurs.
The TNJ provides tremendous movement within the hindfoot. Arthrodesis of this joint will result in tremendous limitation of adjacent joint movement, essentially locking up the subtalar and calcaneocuboid joints. When the posterior tibial tendon is salvageable, it is preferred to support this medial joint with realignment of the midfoot and hindfoot prior to arthrodesis. Medial fusion of the NCJ will help in this direction.
It is the author’s belief that significant medial column motion occurs at the NCJ. This is observed clinically with open kinetic chain movement at this joint and also from radiographic evidence of NCJ faulting. Evaluation of the flatfoot radiograph will often show the bisection of the talus and the first metatarsal to intersect at the NCJ. It is often noted on weight-bearing lateral radiographs that this is a common location of collapse. When the patient is placed into a hindfoot neutral position, the apex of deformity is also very evident in adapted cases. The residual supinatus/varus left within the medial column is often again noted at the NCJ level.
Kinematic studies show significant joint motion and triplanar motion at the NCJ. There are several studies showing the dramatic movement available at this joint. In 1995, Kitaoka et al (2) described 9.4 degrees of motion at the TNJ and 7.2 degrees at the NCJ and MCJ combined. Rush et al (3) in 2000 documented triplanar motion at the NCJ as well. Recently in the Journal of Biomechanics, Chris Nester from England performed some good studies evaluating the triplanar motions of all the joints in the foot and ankle and showed significant movement at the NCJ (4).
From clinical appearance, the contour of the distal navicular resembles the talar head, with the concave/convex orientation. In surgery, it is sometimes necessary to visualize the three cuneiforms in the distal portion to confirm proper anatomic position.
CRITERIA/SELECTION OF PROCEDURE/CONTRAINDICATIONS
Dr. Ted Hansen and colleagues (5) have classified this joint as “nonessential.” Arthrodesis of this joint does not overall affect the function of the foot, so the foot should function without significant stress transfer to the adjacent joints. Other nonessential joints of the foot include the calcaneocuboid joint, the medial Lisfranc joint, and the interphalangeal joints.
Fusion of the NCJ is not utilized as a “primary procedure.” It is commonly utilized to provide medial column stability in flatfoot surgery, when there is accompanying hindfoot and possibly ankle pathology. Hindfoot realignment should be used as the primary procedure (arthroereisis, calcaneal osteotomy, or hindfoot arthrodesis) followed by medial column fusion to align the forefoot to the rearfoot.
The joint contour is much like the TNJ, except for the obvious distal articulations with the three cuneiforms. In this light, it has triplanar motion and will resemble a ball-and-socket type of joint (Fig. 47.1). It is also important to be aware of the lip at the medial aspect of the joint. This will be an overhanging structure off the cuneiform, which may give the surgeon the impression the joint is directed distally. During surgery, this joint should be carefully evaluated after removing this proximal lip from the base of the cuneiform. This is easily done with a ronguer.
The joint can be prepared by either joint resection or curettage. This joint is approached by a medial incision from the first metatarsal base to the neck of the talus (Fig. 47.2A). Dissecting through subcutaneous fascia, the surgeon will encounter super-ficial nerves and the medial marginal vein. A linear incision is made through the deep fascia with care to preserve this layer for later closure (Fig. 47.2B). The anterior tibial tendon will be visualized underneath the deep fascia and can be retracted dorsally (Fig. 47.2C and D). The joint is now exposed with a vertical capsulotomy at the joint level (Fig. 47.2E). A small joint distractor can now be placed on the adjacent bones to provide good axial distraction and exposure to the joint space (Fig. 47.2F and G).