Tarsometatarsal Fusions

J. Chris Coetzee

Abstract

Tarsometatarsal (TMT) fusions have always been challenging due to several reasons. The anatomy is complicated: there are always branches of the saphenous, deep, and superficial peroneal nerves that will cross the surgical field. Surgical neuromas in any of these digital nerves could severely compromise an otherwise excellent arthrodesis result. The dorsalis pedis artery also traverses from dorsal to plantar at the base of the first and second interspace. Furthermore, the TMT joints are essentially “flat-on-flat” surfaces with no inherent stability, therefore completely reliant on ligamentous structures. With the joints perpendicular to the axial force across the joints during weight-bearing, the bending force across the joint during walking predisposes it to a higher risk for nonunion. Lastly, the real estate in the cuneiforms is small, and the angle of screw placement could be challenging. Over time, arthrodesis techniques changed a little, but the fixations options expanded significantly to accommodate the challenges posed by getting the TMT joints to fuse. There is fairly informed consensus that one should not fuse the fourth and fifth TMT joints, while the first, second, and third could be fused individually or in any combination depending on the pathology. Optimum treatment still includes adequate preparation of the joints, correction of deformity in all planes, and stable fixation, followed by appropriate postoperative management to allow the fusions to consolidate.

Keywords: tarsometatarsal joints, arthrodesis, Lisfranc’s injuries

20.1 Indications

• Posttraumatic degenerative joint disease (DJD) after Lisfranc’s injuries.

• Idiopathic/primary tarsometatarsal (TMT) DJD.

• First ray hypermobility.

• Rheumatoid arthritis.

• Stable/chronic Charcot’s neuro-arthropathy or other complications of diabetes.

• Major ligamentous disruptions with multidirectional instability/dislocation of the Lisfranc joints.

• Comminuted intra-articular fractures at the base of the first or second metatarsal.

• Crush injuries of the midfoot with intra-articular fracture dislocation.

20.1.1 Pathology

• There is a wide variety of causes for midfoot arthritis.¹

• In the acute injury situation, it is most often a dislocation of the TMT joints, with or without fractures:

The ones with intra-articular, comminuted fractures usually need a primary arthrodesis.

Complete ligamentous disruptions alone still create a little controversy whether they should be fused or not.

Minor ligamentous injuries should be temporarily stabilized with screws or plates, but do not need fusions.

• Secondary DJD of the TMT joints is very common and the deformity can vary from subtle to severe with a complete collapse into valgus and extension.

• Midfoot Charcot’s neuro-arthroplasty can result in very severe deformities:

As a rule, midfoot Charcot is initially treated nonsurgically in the hope it will stabilize in a plantigrade, stable foot.

However, there are situations where one might have to do surgery early on to prevent ulcerations.² Late deformities can be difficult to correct.

20.1.2 Clinical Evaluation

• Evaluate with the patient if possible—it is most helpful to understand the severity of the deformity.

• Palpation and manipulation of the individual TMT joints will establish which joints are most affected, and also the potential for passive correction of the deformity.

• In posttraumatic cases, the soft-tissue envelope should be inspected to look for issues that could compromise healing and increase risk of infection.

• Look for second and third metatarsal overload. This is common in chronic cases and should be addressed during the correction.

• Always do a Silversköld test to see if there is an equinus contracture, which should be addressed with any midfoot arthrodesis procedure, given this will limit the torque placed across the midfoot joints and risk for nonunion.

• The hindfoot and ankle should also be examined to look for other pathology.

20.1.3 Radiographic Evaluation

• Weight-bearing anteroposterior (AP), lateral, and oblique weight-bearing views of the foot are routinely performed for evaluation of the midfoot³:

AP view: evaluation of the medial column:

Look for collapse into valgus at the TMT joint but also at the naviculocuneiform joint.

Look for relative shortening of the first ray compared to the second and third.

Oblique view: to evaluate the middle and lateral columns.

Lateral view: dorsal bossing, osteophytes, and early jointspace narrowing:

Look for collapse of the medial arch.

• Comparison to the uninvolved, contralateral foot can provide a valuable model for preoperative planning.

• For severe, complex deformities, a computed tomography (CT) scan can be very helpful in planning the correction.

20.1.4 Contraindications

• Skeletal immaturity—open physes.

• Simple, incomplete ligamentous injuries.

• Active infection.

20.2 Goals of Surgical Procedure

• To provide a stable, well-aligned midfoot which is plantigrade with normal weight distribution throughout the foot.

20.3 Advantages of Surgical Procedure

• Open debridement of arthritic changes of the midfoot.

• Allows anatomic alignment of the midfoot and reconstruction of the tripod effect of the foot.

• Improves stability of the midfoot and arch.

• Only sacrifices the “nonessential,” low-mobility TMT and intercuneiform joints.

• Allows for rigid stabilization of the medial and central columns of the midfoot.

20.4 Key Principles

• Plan incisions well, and know the anatomy. Identify and protect the neurovascular structures.

• Have a very low threshold to do two incisions. It reduces the risk of injury to the soft tissue as well as wound complications. It also allows for much better visualization of the joints.

• Reduce the deformity in all planes prior to fixation. In situ arthrodesis of a deformity is not acceptable.

• Stable fixation is essential. It could be done with screws, staples, or plate constructs.

20.5 Preoperative Preparation and Patient Positioning

• Supine, usually with a bump under the ipsilateral hip to allow easier exposure to the lateral side.

• Thigh tourniquet.

20.6 Operative Technique

20.6.1 In Situ TMT Joint Arthrodesis

• Depending on the number of TMT joints involved in the injury or arthritic process, one or two dorsal, longitudinal incisions are made:

The first incision is made over the first metatarsal, just lateral to the extensor hallucis longus. This will allow access to the first and most of the second TMT joints. Pathology involving only the medial two TMT joints can be corrected with this single incision.

• If there is any concern about the accuracy of the reduction, it is advisable to do a second more lateral incision to facilitate exposure and visualization of the joint:

The second incision is centered over the fourth metatarsal; it is much further lateral than what is appreciated (Fig. 20.1).

The most common mistake is to make the incision too far medial; incision placement may be aided by fluoroscopic guidance and identification of the intended bony targets.

The foot should be internally rotated to get an end-on view of the fourth metatarsal. If the X-ray is done with the foot in a neutral position, there is too much overlap between the third, fourth, and fifth metatarsals to accurately determine the position of the fourth ray.

• Adequately expose the joints and then remove all remaining cartilage with small osteotome and curette.

• Be very careful not to use a saw to create flat cuts. Once you start, it is difficult to get all the joint to be adequately apposed. I prefer to use an osteotome to correct minor alignment issues.

• Most critical is to remember the first TMT is about 30 mm deep. A mini-lamina spreader is invaluable to allow proper visualization down the depths of the joint:

All plantar cartilage and prominent spurs must be removed to prevent a dorsiflexion malunion.

• Meticulous bone preparation is critical to the success of the case, with a goal to expose a bleeding cancellous bone surface.

A small curved osteotome is used to microfracture the subchondral bone.

Could also use a 2-mm drill bit to perforate the surfaces.

• Bone graft is not typically required to achieve fusion:

If there is a localized defect, a cancellous graft could be harvested to fill the defect.

• Fixation is generally performed from medial to lateral and a reduction clamp is placed prior to fixation to achieve compression across the prepared joints.