Fracture Fixation of the Distal Femur: Plates or Screws?
Everyone dreads the call that tells them, Mom (or Dad) fell and broke a hip (or other bone). Fractures in older adults can be disabling and even life-threatening. The surgeon often has to use metal plates, screws, or nails to hold the bone fragments together while they heal. This treatment approach is called internal fixation.
One of the interesting challenges surgeons face is the patient with osteoporosis (decreased bone density). Putting a screw or nail through the brittle bone can cause the bone to break. The hardware can also come loose without a firm foundation of support.
Most fractures in older adults occur in the upper portion of the femur (thigh bone). Distal femoral fractures (at the bottom end of the femur) present a different type of problem. The bone is much wider at the distal end and more difficult to stabilize. Everything is even more challenging when the fracture is comminuted (broken into many little pieces).
Fixation devices (commonly referred to as hardware) range anywhere from a single nail to a complex series of screws, washers, nuts, and metal plates. The surgeon must decide which one to use for each patient. The results of this study from Germany may help with the decision-making process related to distal comminuted fracture of the femur in older patients who have osteoporosis.
Four separate fixation devices with different interlocking patterns were tested and compared. The researchers tested everything first on synthetic (manmade) bones before trying the same tests on human bones. The natural bone was from cadavers (bones preserved after death).
The four implant types put to the test included 1) a conventional locking bolt referred to as T2, 2) the Distal Femoral Nail or DFN, 3) a plate and screw model called angular stable plate or AxSOS, and 4) a Supracondylar Nail (SCN). Each one has its advantages and disadvantages.
Each fixation device was tested through repeated cycles of load until the bone was observed to deform or give five millimeters or more. Failure was defined as deformation of more than 2.5 mm. The fixation implants were tested using thousands of cycles.
The T2 is a simple bolt with two screws placed through it in. The bolt goes down through the broken bone. The screws go sideways through the bolt from one side of the broken bone to the other. The screws are slightly apart from each other and parallel to one another. The T2 design had the highest failure rate (first to fail).
The Distal Femoral Nail (DFN) is similar to the T2 in structure but one of the screws has a spiral blade design. The DFN was better than the conventional two-screw design (T2) but it had the least stability and the lowest stiffness. Bone fragments could move because there was no compression or force between the fragments.
The angular stable plate (AxSOS) had the greatest torsional stiffness. It was the third of the four implants to fail. This plate and screw design works well for bed bound patients who are not up and putting weight on the leg. The metal plate lengthwise along one side of the broken bone is held to the bone with a series of seven screws placed at different angles through the bone.
The final implant to fail was the Supracondular Nail (SCN). The SCN has a three-plane pattern of interlocking screws meaning the screws are inserted through the central bolt and bone from three different directions. This fixation device had the best strength and stability. The diagonal arrangement of the screws through the bolt gave the best fixation in the dense bone. Its use is advised for patients who are getting up and moving early after surgery for distal comminuted femoral fractures.
Studies like this one are extremely helpful to surgeons. Knowing what type of fixation devices to use based on type of fracture, biomechanical properties of each implant, rehab schedule, and bone density can help speed up recovery and prevent complications.
The supracondylar nail (SCN) is fairly new on the market with only a few studies to support its use. The results of this study suggest it has some superior advantages to the other implants available. Surgeons will want to keep an eye on this one and future study results.
Dirk Wähnert, MD, et al. Internal Fixation of Type-C Distal Femoral Fractures in Osteoporotic Bone. In The Journal of Bone and Joint Surgery. June 2010. Vol. 92-A. No. 6. Pp. 1442-1452.