Problem Fractures of the Hand and Wrist
In the past decade there has been a trend moving away from a predominantly mechanical understanding of fracture healing toward a more biologic interpretation and treatment of fractures. Clinical experience has shown that the mechanical explanation of fracture healing does not account for the variability in fixation healing under different conditions. Even with internal fixation, the rate of fracture healing differs under different mechanical influences. A rigid fracture fixation with absolute stability in the fracture gap leads to direct or primary bone healing. Without fixation indirect, or secondary, bone healing occurs, which is characterized by callus formation. Both types of fracture healing lead to the restitution of integrity.1
Applying rigid internal fixation may cause injury to bone and surrounding tissue.3 Surgical trauma to the vascular supply to the fracture may be responsible for the slow rate of healing associated with internal fixation. This vascular damage is probably not important on a fracture exposed to minimal forces. If, however, motion occurs at the fracture site after internal fixation, resorption may result and a nonunion may occur.2 Nonunion is actually the result of 2 influences on bone tissue: mechanical forces (strain) and the lack of vascular supply. The difference between motion in the fracture gap, which induces callus formation followed by secondary bone healing, and too much motion, which leads to nonunion, is extremely small. The optimal amount of mechanical force is not defined, and we can only observe retrospectively whether the strain in the fracture gap was too great or just right to promote fracture healing. An excessive amount of motion in the fracture gap causes a decrease of vascularity and leads directly to the second cause of disturbed fracture healing: vascular damage. The vascular damage from the initial trauma may indeed be the source of the nonunion.
Clinical experience teaches that moderate motion at the fracture gap results in undisturbed fracture healing. In fact, the rate of fracture healing is fastest in this situation (Fig 1). This clinical example shows that for the optimal combination of an undisplaced and stable fracture without disturbance of axial alignment under nonrigid conditions, fast and reliable fracture healing can be observed.
Until recently, the amount of motion necessary had not been quantified. Data now are available that will indicate how much motion (strain) a fracture can tolerate.4 It seems that a few cycles of motion per day (in an experimental model 10 cycles/day) enhances callus formation whereas after 10,000 cycles per day callus formation stops and a nonunion is generated (personal communication, Hente R, MD 1991).
The current study underscores 3 principles of ideal fracture healing. Internal fixation should be stable enough to permit fracture healing, allow for some micro motion permitting endosteal and periosteal callus formation, and minimize further damage to an already impaired bed of tissue. Obviously, these conditions are not only difficult to achieve but are likely to be unpredictable. This is especially true for complex fractures of the hand for which early functional rehabilitation is mandatory and 9 considerably higher forces such as passive movement of the joints are used by the occupational therapist.
The surgeon can minimize vascular damage by carefully exposing the fracture site without extensive dissection. The newer, smaller implants assist the surgeon by minimizing dissection. These implants are sufficiently stable to permit less dissection. One tool is percutaneous screw fixation of certain fractures in phalanges whereby a device is inserted through a small stab incision to reduce the fracture and a small screw is applied for fixation (Fig 2). Minimal tissue damage is achieved by avoiding dissection of the fracture site and adequate stability is obtained by the insertion of screws so that immediate postoperative functional rehabilitation can be started.
This philosophy of minimal dissection and use of small implants can be transferred to the reconstruction of joints (Fig 3A). Minimal internal fixation combined with a bone graft allows immediate postoperative free motion (Fig 3B). The implant holds the bone graft and the joint surface in place. Undisturbed bone healing and restoration of the joint occurs (Fig 3C).
Clinical experience supports the claim that internal fixation of the hand should be as rigid as possible, permitting very little or no motion at the fracture gap. In addition, the surgeon must minimize vascular trauma to the fracture site and the surrounding periosteal envelope. Newer fixation techniques such as the use of percutaneous screws and low profile implants permit internal fixation without violating these principles. However, further research is required to understand the nature of motion at the fracture site and optimal methods of fixation fully. This will provide data for more optimal and biologic handling of bone tissue.
1. Brennwald J: Bone healing in the hand. Clin Orthop 214:7-10, 1987.
2. Brennwald J, Perren SM, Stadler J: Bone resorption in internal fixation induced experimentally. Eur Surg Res 10:66-67, 1978.
3. Gautier E, Rahn BA, Perren SM: Effect of steel versus composite plastic plates on internal and external remodeling of intact long bones. Orthop Trans 10:391, 1986.
4. Hente R, Cheal EJ, Hagerty T, Perren SM: Differentiation of repair tissue under controlled strain gradients. Orthop Trans 15:520-521, 1991.