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ОглавлениеMetacarpals (-tarsals) two and four
Gustave E. Fackelman
6.4 Postoperative considerations
6.1 Description
During axial loading of the limb, the proximal one-third of the second metacarpal bone is subjected to torsional strain.
Postoperative pain is common following fixation of the proximal portion of the “splint” bone to the major metacarpal.
The fractures of the minor metapodeal bones for which internal fixation is indicated are those located in the proximal third. These are caused either by direct trauma or by strain during normal locomotion. Research has shown that the proximal one-third of the second metacarpal bone is subjected to torsional strain during axial loading [1], due probably to the unique characteristics of the proximal (carpometacarpal) articular facets (Fig. F6A), and the strong attachment of the middle third of the bone to the third metacarpal. Typically, there is a fusiform exostosis just below the carpus (Fig. S6A), mild to moderate lameness, and pain on direct palpation. The exposed locations of the fourth metacarpal and metatarsal bones make them prone to open fracture due to direct trauma. Such fractures have been treated by resection, either of the infected portions [2], or of the entire bone [3, 4]. Here, the bony proliferation may be extreme, the lameness more marked, and a draining tract present. Cosmetic results following radical resections are not consistent, and a potential complication is luxation of the remaining short proximal fragment through the surgical incision. Efforts to avoid this complication and improve the postoperative appearance by screw fixation of the fragment to the third metacarpal (Fig. F6B) have failed due to postoperative pain at the surgery site (Fig. X6A) [5]. This appears to mimic a condition seen in humans when the syndesmosis of the distal fibula is traversed by a lag screw [6].
Fig. F6A: The proximal end of the second metacarpal bone (left) bears a joint surface, part of which is inclined caudomedially. Axial loading of the bone results in torque forces tending to twist it caudolaterally.
Fig. S6A: The exostosis that forms in response to fractures in the proximal one-third of the bone is typically fusiform, and located just below the carpus.
Fig. F6B: Following radical resection the fragment was drilled (above), and a fixation screw (thread hole in both bones) was placed to confer stability, while not disturbing the alignment of the proximal articular surface (below).
6.2 Surgical anatomy
The important landmarks are the proximal end of the fractured bone, the fracture site itself, and the axis of the distal portion of the “splint”. The first two landmarks may be obscured by bony callus, in which case it is helpful to mark the level of the carpometacarpal joint with a 20 g hypodermic needle, and plan the operation relative to this marker. Later, resection of the callus will reveal the level and direction of the fracture, facilitating the placement and orientation of the implants. Measurement on radiographs determines at what level the synostosis between the minor and the major metacarpal begins.
Fig. X6A: a) An old infected fracture—distal portion of bone resected. b) Fixation screw used to stabilize fragment and prevent luxation. c) Satisfactory healing at 6 weeks. d) Sterile bony lysis painful at 20 weeks, necessitating removal.
6.3 Surgical procedure
(Video 31022)
The first two screws are placed eccentrically away from the fracture plane, to effect axial compression.
The incision is made from the level of the carpometacarpal joint distally to include the region of osseous union between the minor and the major metacarpals. After subcutaneous hemostasis has been achieved, the thickened periosteum is incised, and, using a sharp periosteal elevator, it is reflected from the underlying callus (Fig. F6C). In older fractures, extensive “sculpting” may be necessary to restore contours that approximate normalcy (Fig. S6B). When such satisfactory contours have been attained, and the location and direction of the fracture plane noted, a one-third tubular plate is shaped to match, and the preoperative plan is executed (Fig. X6B). Usually the first two screws are placed in their holes eccentrically at a distance from the fracture, providing axial compression, after which a lag screw is placed across the fracture plane if possible (Fig. X6C). The remaining screws are then placed in a neutral position. Proximal to the synostosis it is important to place screws within the “splint” bone only, and not to invade the interosseous space (Fig. X6D). Excess periosteal tissue is resected, and the remainder is closed over the plate (Fig. F6D). Closure is in layers, attempting to eliminate as much dead space as possible. Usually, a stent bandage is oversewn to relieve tension on the primary skin sutures, and to exert gentle pressure over the most critical portion of the surgical site.
Video 31022: Fixation of a proximal splint bone fracture (with a 6-hole 3.5 mm one-third tubular plate).
Fig. F6C: a) Minimize trauma by the use of a sharp periosteal elevator. b) The periosteum is reflected to expose the fractured bone.
Fig. S6B: The extensive callus (above) extends almost halfway down the metacarpus. The white stent (right side) indicates the more normal external contours achieved by de-bulking the callus.
Fig. X6B: Despite extensive resection there may still be greater-than-normal bone stock in the operative area (case shown in Fig. S6B 12 weeks postoperatively— healed fracture, no new callus).
Fig. X6C: Use a lag screw to bridge fracture sites wherever possible, as here in an area of comminution just below the articular surface.
Fig. F6D: Callus removal results in redundant periosteum. Resect the excess tissue and suture the remainder snugly over the repair site.
The tips of the screws should not invade the space between the major and minor metacarpal bones.
Fig. X6D: a) The fracture occured just above the area of synostosis. b) Screws proximal to the synostosis should not engage the third metacarpal bone. c) Cosmetic healing occurred and the plate remained in place for 8 years, after which the patient was lost to follow-up.
6.4 Postoperative considerations
Intolerance to cold, with resultant pain and lameness, may necessitate implant removal.
A pressure bandage is applied postoperatively to aid in the prevention of seroma formation. The administration of perioperative antibiotics is continued for 24 hours. The horse is stall rested for 10 days until the skin sutures can be removed. Elastic bandaging is continued for 3 weeks. Controlled exercise is begun 1 month postoperatively, while exercise at will at pasture is discouraged for a full 12 weeks. Training is resumed at 4–6 months postoperatively, depending on soundness and radiographic healing. Typically, these fractures heal cosmetically, without the recurrence of the preoperative exostosis.
6.4.1 Complications
The only complication encountered with this surgery has been the need for implant removal due to intolerance to cold (Fig. S6C, Fig. X6E) Although this has been reported anecdotally for other fixations, the problem seems greater in this area of little skin and hair cover, with a relatively large surface area of metal lying subcutaneously. Owners should be made aware of this, since it alters the time frame for a return to training. It is recommended that strenuous exercise be postponed until the screw holes have filled in with bone, which can take up to 90 days.
Fig. X6E: At 8 months postoperatively (a), the horse was back in work but showed occasional pain, especially in cold weather. The plate was removed (b), and training successfully resumed 60 days later (c).
Fig. S6C: The tangential view and the straight AP view show good cosmetic healing 3 months postoperatively in this open jumper.
6.5 Results
The results of this treatment have been uniformly successful, even when used in older fractures (Fig. X6F). Infected fractures also respond positively to fixation, since the stability conferred is rigid (Fig. S6D), expediting the resolution of infection and enhancing healing. Antibiosis is begun preoperatively based upon appropriate culture and sensitivity testing.
Fig. X6F: This series of films shows healing at 3 days (b), 3 months (c), 5 months(d), and 2 years (e). The horse raced for 5 years with the plate in place before being lost to follow-up.
Fig. S6D: Thoroughly debride infected fractures, and remove any callus that has formed prior to the application of the plate.
6.6 References
1. Jann HW, Fackelman GE, Pratt G (1986) Strain patterns in the second metacarpal bone and their surgical significance. Vet Surg; 15:124.
2. Harrison LJ, May SA, Edwards GB (1991) Surgical treatment of open splint bone fractures in 26 horses. Vet Rec; 28:606–610.
3. Baxter GM, Doran RE, Allen D (1992) Complete excision of a fractured fourth metatarsal bone in eight horses. Vet Surg; 21:273–278.
4. Botz R (1993) Total amputation of the fourth metatarsal bone after fracturation in a horse. Prakt Tierarzt; 74:918.
5. Bowman KF, Fackelman GE (1980) Comminuted fractures in the horse. Comp Cont Educ Pract Vet; 2:98.
6. Müller ME, Allgöwer M, Schneider R, et al. (1977) Fractures of the lateral malleolus. In: Müller ME, Allgöwer M, Schneider R, et al., editors. Manual of Osteosynthesis. Heidelberg:Springer Verlag, 267.
6.6.1 Online references
See online references on the PEOS internet home page for this chapter: http://www.aopublishing.org/PEOS/06.htm
