The primary indication for TMT arthrodesis is primary or post-traumatic arthrosis resulting in pain, deformity, or both. The fusion construct may include one or more joints based on the extent of the pathology. Typically when there is single ray involvement, especially the second or third, there is minimal deformity. On the other hand, post-traumatic deformity of the medial and middle rays can present with complex malalignment involving multiple planes, as can Charcot neuroarthropathy.

Isolated first TMT arthrodesis is commonly performed for the treatment of advanced hallux valgus deformity, with or without first ray hypermobility (Fig. 6.3) [3]. Although substantial controversy surrounds the exact indications for the modified Lapidus in the setting of hallux valgus, this procedure is widely recognized and commonly performed in bunion surgery. The powerful corrective potential also makes the modified Lapidus an excellent option for recurrence or salvage of prior failed hallux valgus procedures [17].

Isolated first TMT fusion is occasionally used in complex flatfoot reconstruction, in lieu of a medial cuneiform plantarflexion osteotomy (Cotton osteotomy), when there is concurrent first TMT arthrosis or hypermobility in addition to pes planus [5, 6]. First TMT fusion has also been described for the correction of severe plantarflexion deformity in pes cavus reconstruction [4].

TMT arthrodesis can be performed for the treatment of an acute unstable ligamentous Lisfranc injury [1] or acute bony Lisfranc with substantial comminution (Figs. 6.4, 6.5, and 6.6) [2]. Although controversial, some authors also advocate primary arthrodesis of purely ligamentous Lisfranc injuries with multidirectional instability [1]. Proponents of fusion contend that compared with arthrodesis, open reduction and internal fixation (ORIF) for ligamentous Lisfranc injuries has a high incidence of loss of reduction, increased rates of symptomatic hardware, and early degenerative changes with transarticular constructs [1, 18, 19]. Additional arguments reason that if the hardware is not removed, bridge plate and transarticular constructs effectively create a functional arthrodesis of the involved joints, and given the minimal physiologic motion in the medial three rays, little function is lost with arthrodesis. Yet another controversy arises over primary arthrodesis for complex intra-articular bony Lisfranc injuries. Advocates contend that severe articular damage ubiquitously progresses to early arthritic changes and patients are better served with primary fusion of the medial one to three rays [2].

Major counterpoints against primary arthrodesis include the observation that radiographic evidence of post-traumatic arthritis is frequently asymptomatic. Furthermore, acute fusion can be technically challenging, especially with substantial comminution, and require larger exposures than ORIF. This can potentially cause additional damage to the already traumatized soft tissues. Also, many surgeons routinely remove hardware following ORIF, with the hope that some degree of physiologic motion will return after the acute injury has healed.

Neuropathic arthropathy frequently affects the midfoot and presents unique challenges to health-care providers and surgeons alike. The mainstay of treatment is accommodative casting and bracing. Operative intervention is usually avoided during the earlier inflammatory phases of the disease, and fusion surgery typically involves large rigid constructs.

The dorsal midfoot has a very thin subcutaneous layer and soft tissue compromise is an absolute contraindication for fusion. Burns and soft tissue loss must be addressed prior to surgery, and the often profound swelling associated with acute midfoot trauma should be temporized until the edema subsides and surgery can be performed safely. Lisfranc injuries occasionally present with the skin at risk from TMT subluxation, and temporary spanning external fixation or provisional percutaneous fixation may be necessary.

In diabetic patients , blood glucose control should be optimized prior to elective surgery. The American Diabetic Association recommends a target hemoglobin A1c of <7.0% [20], and orthopedic complications , especially infection, are known to increase with higher A1c levels [21, 22]. When vascular insufficiency is suspected, ankle brachial indices (ABI) , toe pressure measurements, and/or transcutaneous oxygen levels (TCO₂) should be performed. ABI and toe pressures greater than 0.45 mm Hg, as well as TCO₂ levels greater than 30 mm Hg, are generally considered the minimum threshold for predictable wound healing. It is important to note that blood vessel compliance may be altered in patients with diabetes or peripheral vascular disease, falsely elevating ABIs. If there is concern about perfusion, vascular surgery intervention should precede any orthopedic procedures .

Nonunion rates in smokers undergoing foot and ankle fusions range from 18.6% to 27% [23, 24]. As such, many surgeons will require that patients stop smoking prior to surgery. Some will test for serum nicotine and cotinine levels and delay elective surgery until smoking cessation has been confirmed. In the setting of trauma, patients are extensively counseled on the detrimental effects of smoking and encouraged to quit.

Active infection is another contraindication to surgery. When infection status is unclear, we will obtain basic inflammatory labs including a white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). If these parameters are elevated, and the diagnosis is still in question, a bone scan or potentially open bone biopsy can be performed.

Thorough preoperative evaluation and management of concurrent medical problems is crucial for successful surgery. As outlined above, particular detail must be paid to perfusion, diabetes, and smoking. Overall foot alignment should be assessed both clinically and with weight-bearing radiographs; in complex deformity imaging of the contralateral side may be helpful. Hindfoot deformity , such as pes cavus, can lead to lateral column overload and should be addressed at the time of surgery. Gastrocnemius contracture especially can place undue pressure through the midfoot and has been identified in up to 78% of patients with primary midfoot osteoarthritis [25].

Determination of which joints within the TMT complex are truly symptomatic can be a challenging endeavor. Radiographic evidence of disease is frequently diffuse, yet the lateral column is often asymptomatic despite the presence of arthritis on x-ray [16, 26]. Careful clinical examination with correlation to radiographic findings is imperative, and selective image-guided injections may be used when the diagnosis is in question. Advanced imaging techniques such as CT are helpful to better evaluate the joints. If the viability of a joint within the medial or middle columns is questionable, the authors believe it is preferable to include it in the arthrodesis.

Meticulous joint preparation sets the stage for a successful fusion. An important technical aspect is to adequately visualize and expose the deep (plantar) aspect of the joints. The first TMT is nearly 30 mm deep and the plantar aspect is difficult to see without joint distraction. Liberal use of distractors such as lamina spreaders and Hintermann distraction forceps greatly aid visualization. The authors prefer a smooth lamina spreader as a fast and effective way to distract the joint; toothed retractors are avoided as they can crush the subchondral surface. Curved curettes and ¼-inch curved osteotomes are very effective at reaching the plantar-most lip of the TMT joints. Ideally the TMT plantar capsule will be maintained; the intact plantar soft tissue can serve as a tension band and is especially useful if planning dorsal plate fixation. Similarly the intercuneiform, and occasionally intermetatarsal, joints require preparation if being incorporated into the fusion mass. In trauma situations, care is taken to prevent excessive soft tissue stripping from comminuted articular fragments while the cartilage is denuded.

The subchondral plate is important for construct stability and maintaining the length of the first ray. Biomechanically, constructs which retain the subchondral plate have higher loads-to-failure and bending moments, thus enhanced stability, compared to constructs which remove the subchondral plate such as is performed with a flat cut [27]. The reciprocal contoured joint surfaces also have superior resistance to rotational and shear forces [27], and when transarticular screw constructs are used, the subchondral plate resists dorsal migration of the screws with physiologic loading [27]. Additionally, retaining the subchondral plate prevents inadvertent over-shortening of the first ray [6]. Flat cuts with a saw, while very efficient, run the risk of iatrogenic first ray over-shortening and, if not carefully executed, malposition of the TMT given the significant angulatory power of first TMT arthrodesis. If the situation requires resection of the subchondral plate, consideration should be given for additional screw or plate fixation.

Fenestration of the subchondral plate exposes cancellous bone and creates hematoma and channels for potential vascular ingress [6]. The authors prefer to use a small drill so that the bone debris generated can be packed into the joint as local bone graft. Alternatively, a small burr can be used; if a burr is selected, we reduce the speed to 20,000 revolutions per minute and generously irrigate the bone to prevent thermal necrosis. When a Kirschner wire is used, the cancellous bone within the channel is impacted, theoretically limiting blood flow to the arthrodesis site.

First TMT fusion , especially when performed for hallux valgus, often requires realignment of the coronal, sagittal, and occasionally axial planes of the first ray. Plantar gapping of the first TMT due to cantilever loading is a well-known phenomenon. The deep aspect of the TMT must be properly denuded to avoid hyperextension deformity of the first ray with subsequent overload of the adjacent metatarsals. Conversely, overcorrection of the first ray into plantar flexion can lead to sesamoid pain or a hallux cock-up deformity [5]. Persistent varus deformity of the first TMT is not uncommon in bunion surgery, and periodically small laterally based wedges are osteotomized off the medial cuneiform to allow the metatarsal head to swing laterally and reduce the MTP joint. Typically no more than a few millimeters is required and the authors use this technique judiciously. Scrutiny of preoperative radiographs may reveal an intermetatarsal facet on the first metatarsal [7], and this may block first TMT reduction and therefore need to be resected (Fig. 6.2). The authors prefer to position the first TMT with the foot in a simulated weight-bearing position. A stack of towels or a flat instrument tray lid held under the plantar surface of the foot works well. When correcting hallux valgus, lateral pressure on the first MTP allows for manipulation in the coronal plane. The joint is then provisionally pinned into place with Kirschner wires or guide wires from a cannulated screw set. Even in experienced hands, we recommend multiplanar fluoroscopy to critically evaluate joint position and articular congruity.