Although fractures of the tibial diaphysis respond well to intramedullary pinning, if a pin inserted retrograde into the proximal tibia emerges from the tibial plateau within the stifle joint, the pin end can interfere with joint motion.
Retrograde insertion of the intramedullary Steinmann pin into the tibia usually results in emergence of the proximal end of the pin in the stifle joint, with resultant interference with limb extension, as well as possible degenerative joint disease and refracture after pin removal. Early postoperative use of a fractured limb enhances bone healing through improved circulation, and decreases muscle wasting and osteoporosis. Interference with stifle joint function can be avoided by antegrade pin insertion just medial to the insertion of the patellar tendon, then bending the pin craniad with the chuck and severing it close to the tibia.
Fractures of the tibial diaphysis respond well to intramedullary pinning if rotational stability is maintained. This is especially true in cats and small dogs, which have a relatively narrow medullary canal. The medullary cavity of the tibia is comparatively straight and uniform in diameter, unlike that of the femur, and there is good cancellous bone at either end in which to seat the pin. However, a pin inserted retrograde into the proximal tibia emerges from the tibial plateau within the stifle joint. Here the pin end can interfere with joint motion, limiting full extension and limb function. Its presence can also lead to degenerative joint disease of the stifle. A further possible sequela is impaired healing of the original tibial fracture through prolonged disuse of the limb.
The following 3 case reports illustrate this problem. Two of the animals had a refracture after removal of the pin, and the fracture in the third took 24 months to heal. An alternative method of pin placement, bypassing the stifle joint, is also presented.
A 3-year-old female domestic shorthaired cat was treated for a transverse, midshaft tibial fracture with an intramedullary Steinmann pin. There was excellent reduction and good stability at the fracture site, but the pin was cut off so that the proximal end protruded into the stifle joint (Fig. 1). The ct did not use the leg postoperatively, but the fracture appeared healed on radiographs 5 months later, when the pin was removed (Fig. 2).
The tibia refractured 3 months later and the leg was placed in a cast for 2 months but did not heal. The animal was referred to the author for treatment. Another pin was placed antegrade, from a point extraarticularly on the tibial crest distad, into the distal metaphysic, without surgically exposing the new fracture site (Fig. 3). The cat started to walk on the leg shortly after surgery. The patient was not returned for radiographs for 5 months, at which time the fracture was not only healed, but the bone appeared to be of better quality than on earlier views (Fig. 4). Though it would have been desirable to remove the pin, it was left in place since it was not interfering with limb function.
A 7-month-old Sheltie was presented for a transverse fracture of the distal third of the tibia. An intramedullay Steinmann pin was used to reduce and stabilize the fracture (Fig. 5). Again, the proximal end of the pin protruded inoto the stifle joint. The pin was removed 7 weeks later, at which time the leg developed a valgus deformity at the fracture site. The animal was referred for correction of the deformity, which was accomplished with a 4-pin Kirschner-Ehmer splint, with the bars placed mediad and laterad (Fig. 6). The fracture healed in 6 weeks, and the K-E apparatus was removed. The dog was bearing weight on the leg during the healing period after the second procedure.
A middle-aged domestic shorthaired cat was treated for a segmented fracture of the distal third of the tibia with an intramedullary Steinmann pin and 2 full-cerclage wires. Reduction and stability were excellent, but the proximal end of the pin remained within the stifle joint near the patella. The cat did not use the leg postoperatively, and sequential radiographs revealed a delayed union that took 24 months to heal (Fig. 7). A chip fracture of the patella, where the proximal end of the pin contacted the patella, became evident 10 months after the original fracture (Fig. 8).
In all of these cases, fracture reduction was very good. There was no loss of fixation or failure of any of the implants; in Case 3, the cerclage wires did not loosen. This means the fracture remained stable throughout the prolonged healing time. In Case 2 there was some osteolysis around the pin (Fig. 5), denoting loosening, but there was no loss of fixation or deviation until after the pin was removed. In that young dog (less than a year old), with a relatively atraumatic fracture, one would have expected the fracture to have healed within 6-8 weeks.
The one common denominator in these 3 cases is interference of stifle joint function by the proximal end of the pin and subsequent disuse of the limb during healing. Studies in animals and people have shown that early postoperative use of a fractured limb enhances healing. Studies in rats showed more rapid, stronger union when the rats were allowed to use their pinned femurs than in those in which use was prevented by casts. Tibial fractures in people healed faster when cast bracing rather than full casts were used. The former allows early weight bearing on the fracture ends. Early postoperative function promotes improved circulatory status and blood supply, decreased muscle wasting, and decreased osteoporosis. Stress on the fracture ends from weight bearing may even promote healing through stimulation of osteogenesis.
It might be argued that the pin in Case 1 may have been too large, filling the entire medullary canal and, therefore, not allowing revascularization of the medullary blood supply until after the pin was removed. However, flutes or gaps between the implant and the cortex are all that are needed to allow regrowth of the vessels that promote healing. The periosteal blood supply also hypertrophies, assisting fracture healing. In addition, the leg refractured 3 months after the pin was removed, when there had been adequate time for medullary revascularization.