Rule: repair any lesion that is clearly visible radiographically on a lateral or DPLMO projection.
Although it is possible for C3 slab fractures to heal with rest alone, it is advisable to repair any lesion that is radiographically evident on a lateral or DLPMO projection [3]. Radiolucent lines that are seen solely on the tangential view may involve only the subchondral bone of the proximal joint surface [4] and therefore not require internal fixation. Prognostic considerations include comminution at the joint surface, marginal osteophytes, loose fragments in the palmar-lateral joint space (an indication of comminution), size of the fragment, and degree of displacement.
5.2 Surgical procedure
Use the arthroscope to more thoroughly evaluate the joint.
Do not position the scope too close to the distal row of carpal bones.
Arthroscopy during screw fixation enables a more thorough evaluation of the entire articulation [5]. It allows a visual check of accuracy of reduction/fixation while minimizing soft tissue trauma [6]. Arthroscopic technique follows basic principles [7]. The scope is positioned between the extensor carpi radialis and common digital extensor tendons when the fracture is in its typical location in the radial facet (Fig. F5A). If the fracture is in a more frontal plane and extends into the intermediate facet, it is important not to position the scope too close to the distal row of carpal bones. Otherwise, it may be difficult to see the intermediate facet clearly. If the fracture affects the dorsolateral corner of the intermediate facet, the scope is inserted medial to the extensor carpi redialis.
Fig. F5A: An overview of the relationships of the arthroscope to the extensor carpi radialis and the common digital extensor tendons, and of the needles used to mark the C3 fragment.
Displaced slab fractures: instrument portal on the opposite side of the joint.
In displaced slab fractures, an instrument portal is made on the opposite side of the joint. If possible, the instrument portal is made exactly at the margin of the fracture so that a curette can be inserted deeply into the fracture plane for debridement. It is essential to remove all loose fragments to allow accurate reduction.
Use needles for orientation during drilling.
After debridement (with a displaced fracture) or after examining the joint (with a non-displaced fracture), a 3" (7.5 cm)18 g spinal needle is placed in the joint just above the proximal edge of the center of the slab fragment. If the position is not central, a second needle is inserted in the correct position. Additional 1" (2.5 cm) 22 g needles are inserted at the medial and lateral margins of the fracture to verify the central positioning of the spinal needle. After the central needle is positioned correctly, a 22 g needle is inserted into the carpometacarpal joint immediately distal to the first needle (Fig. F5B, Fig. F5C). A #10 scalpel blade is used to make a deep incision reaching the face of C3 after measuring proximally from the carpometacarpal needle. It is usually possible to feel the dorsal ridge in the center of the face of C3 as the overlying soft tissue is incised.
Fig. F5B: The arthroscope is inserted into the midcarpal joint between the extensor carpi radialis and common digital extensor tendons, and directed medially. A spinal needle marks the intended screw direction, while 20 g needles mark the fracture site and the carpometacarpal joint.
Fig F5C: In the lateral view, the position of the needle in the carpometacarpal joint may be better appreciated.
Verify complete penetration of the fragment arthroscopically.
Use a K-wire as a guide for the centering insert.
The alignment of the spinal needle is checked arthroscopically. A 3.5 mm hole is drilled through the slab fragment using the spinal needle to guide the direction of the drill (Fig. F5D). A general alignment aid is to keep the bit perpendicular to the long axis of MC3. This assures that the drill remains parallel to the articular surface of C3 (Fig. F5E). With displaced fractures it is easy to check arthroscopically that the glide hole has reached the fracture, since the drill can actually be seen entering the fracture gap. With nondisplaced fractures, careful measurements and/or intraoperative radiographs are necessary. After removing the 3.5 mm bit, a 2 or 3 mm K-wire is placed into the hole through the drill guide. The guide is then removed and the centering insert is positioned by sliding it down the K-wire into the glide hole (Fig. F5F). With displaced fractures, the fragment can then be manipulated with the insert and a 3 mm K-wire to further ascertain the position and completeness of the glide hole. Do not attempt to manipulate the fragment with the drill bit since the bit may break.
Fig. F5D: The glide hole is prepared in the fracture fragment by drilling parallel to the previously placed spinal needle.
Fig. F5E: Other than the spinal needle, a good directional guide for drilling is the 90° relationship to the long axis of MC3. Maintaining this positioning insures that the joint surface will not be injured.
Fig. F5F: A K-wire placed in the glide hole serves as a marker over which the centering guide can be slid into position. This saves time and avoids undue soft tissue disturbance.
Flex the carpus prior to drilling the thread hole.
For single facet fractures, use 3.5 mm × 32 or 35 mm cortex screws.
The smaller head of the 3.5 mm cortex screw is advantageous.
The carpus is flexed, aiding reduction. Accuracy is checked again arthroscopically and the thread hole is drilled (Video DBASICS). Usually, it extends only about 40 mm, but palmar penetration does not constitute a problem. After making the countersink depression, the hole is measured and tapped routinely. For fractures that involve only a single facet, a 32 to 35 mm long 3.5 mm diameter cortex screw is adequate (Fig. X5A, Video 31018). If the fracture is large, i.e., involving both facets, two or sometimes three 3.5 mm screws are used (Fig. X5B). Alternatively, 4.5 mm screws can be used; the larger screw is preferred whenever there is marked comminution along the fracture plane or whenever stability is otherwise questioned. The 3.5 mm screw is greatly preferred for sagittal fractures of the radial facet [8] because its much smaller head allows it to be placed close to the C3-C2 articulation (Fig. X5C) without