90 Troublesome Lunate Facet: Treatment with Microvascular Techniques
90.1 Patient History Leading to the Specific Problem
This 26-year-old man was seen 4 months after sustaining a distal radius fracture in a bike accident. The fracture had been operated and a volar plate plus an external fixator was applied. An ulnar approach was also carried out in order to tackle the ulnar styloid fracture. Nevertheless, he complained of pain, diminished grip strength (59%), no extension (0 degrees), and no supination (20 degrees; ▶Fig. 90.1).
Preoperative imaging was taken (▶Fig. 90.2). Notice that there is no evidence of subchondral bone in the sunken area that could make one consider repositioning a malunited fragment. Whether those fragments were removed at the initial surgery is unknown. There is also a radially displaced fracture of the ulnar styloid including the fovea, with pain at that level.
Fig. 90.1 (a–d) Preoperative range of motion.
Fig. 90.2 (a–c) Preoperative X-rays and CT scan.
90.2 Anatomic Description of the Patient’s Current Status
The information gathered from the radiological workup was very valuable. Virtually, all the lunate facet was destroyed and through the different slices on the CT scan neither the lunate nor the sigmoid notch was recognizable. On the other hand, although the pictures of the lunate hanging in the void looked frightening, they were encouraging as far as the possibility of reconstruction was concerned: when the cartilage does not rub against bony irregularities, it will remain in pristine condition for months. Another positive finding was that the scaphoid fossa and scaphoid bone were not damaged.
90.3 Recommended Solution to the Problem
For several years, we have been using the base of the third metatarsal as a vascularized osteochondral graft to replace major articular defects on the radial articular surface. The base of the third metatarsal has a principal facet that we use for reconstructing the radial articular surface, and an accessory facet to the fourth metatarsal, which is invaluable to reconstruct the sigmoid notch provided the contralateral side is harvested (▶Fig. 90.3). The operation requires microsurgical expertise, but allows patients to maintain a painless range of motion.
It should be stressed that when dealing with malunions of the radius, the decision-making process is complicated and multiple issues should be considered (▶Fig. 90.4). In most cases the author treats, the author first carries out a diagnostic arthroscopy, and then—in the same operation—select the procedure to perform. Depending on whether the cartilage is healthy in radius and carpals or not, one of the following procedures is opted: an intra-articular osteotomy, a osteochondral graft, a resection arthroplasty, or a partial fusion. As shown in the algorithm, the vascularized osteochondral graft is reserved for the scenarios in which the damage is limited to the radius and the cartilage of the carpals is preserved. Some allowances on the cartilage quality can be accepted, but bare bone or major cartilage damage on the opposing carpal will lead to failure.
In this case, the unfeasibility of osteotomy was clear as the lunate fossa was “gone,” and the option of replacing the area by the graft was the best one. Only a major cartilage loss would have contraindicated the operation and that was very unlikely due to the fact that the lunate was “hanging in the void.”
90.4 Technique
At the time of planning, one has to take into account that if the sigmoid notch needs to be reconstructed, the contralateral third metatarsal should be used. Otherwise, the smaller facet to the second metatarsal will face the ulna offering a poor match (▶Fig. 90.5).
Fig. 90.3 Proximal to distal view of the base of a left base of the third metatarsal.
Fig. 90.4 Algorithm showing the decision-making process for dealing with malunion of the radius.
Fig. 90.5 Notice how in a left-side defect the right side is the one that matches the defect.
The operation is usually performed under regional anesthesia and the recipient site is prepared first. The lunate facet was approached through a longitudinal dorsal midline incision. The extensor pollicis longus was released from the third extensor compartment, and the second and fourth extensor compartments were dissected from the radius subperiosteally. The posterior interosseous nerve was identified and divided. The affected area of the distal radius was removed with an osteotome, sagittal saw, or rongeur as needed. This excision included the metaphyseal bone in order to create a three-dimensional defect to allow for placement of the flap. At this point, corrective osteotomies are usually performed for any salvageable malpositioned fragment (usually the anterior fragments), although in this case this was not needed. Notice at the completion of this part of the operation that the cartilage of the lunate is of good condition and that the head of the ulna is exposed (▶Fig. 90.6). The skin was closed temporarily with staples, a soft bandage applied, and the tourniquet released.
Attention is directed to the foot. Again it is important to stress that the flap is to be raised from the contralateral foot. In our anatomic study, we noticed that the vascular supply is variable. There is a competitive situation to supply the periosteum of the third metatarsal between the distal lateral tarsal artery (DLTA) and the arcuate artery (AA), both branches of the dorsalis pedis artery (DPA). Depending on the actual size at surgery, only one or both arteries (the DLTA and AA) pedicled on the dorsalis pedis are harvested (▶Fig. 90.7).
The foot was approached though a zigzag incision in the cleft between the extensor hallucis longus and the extensor digitorum longus. The extensor hallucis brevis (EHB) was cut and retracted laterally together with the extensor digitorum longus. This maneuver exposed the blood supply to the dorsum of the foot (▶Fig. 90.8). In this case, a periosteal arcade was formed between a well-developed arcuate and distal lateral tarsal arteries that crossed the base of the third metatarsal. During this dissection, a perforator to the skin was located and a skin flap was raised on it as a skin monitor.
