A Closer Look At Beaming The Columns In The Charcot Diabetic Foot
- Volume 27 - Issue 3 - March 2014
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The question arises as to whether one should lock the medial and lateral columns with fusion of the subtalar joint or with a subtalar implant. The subtalar implant is the senior author’s preference because it limits any subtalar motion that is abnormal without completely eliminating inversion and eversion. Accordingly, there can be some mobile adaptation of the foot to the supporting surface on which it ambulates and, at the same time, the two columns can now serve to support each other.
It has been the senior author’s experience that of the two columns, the medial column is vastly more important in Charcot reconstruction. If one removes the medial column beam due to infection or other complications, the loss of the Charcot correction will be inevitable unless the patient has had arthrodesis. Similarly, a broken medial column beam will result in a significant loss of correction. The lateral column beam only serves to prohibit plantar dislocation of the cuboid. If the lateral column is completely stable prior to surgery, the lateral column beam is not really necessary.
It is important to recognize that the purpose of beams is not to compress the fusion sites but only to act as support structures for the diseased ligaments and bones of the foot. Grant and coworkers clearly showed evidence that a frame with tension and compression and parallel fixation produced superior compression than other methods of fixation.14
Further Pointers On The Beaming Technique
The fluoroscope is requisite for the correct placement of beams. One can place the guide pin via a plantar approach to the first metatarsal by dorsiflexing the toe or a dorsal approach by plantarflexing the toe. One should center the tip of the pin in the metatarsal head. Drive the pin through the long shaft of the metatarsal until it exits its base centrally as one can see in the photo on the right. Similarly, the guide pin should traverse the center of the medial cuneiform, the body of the navicular and the head and neck of the talus. This may take some practice.
Generally speaking, a 115 mm cannulated screw is necessary for the medial column. It should be made out of stainless steel, not titanium, because stainless steel has a 240,000 PSI versus only 180,000 PSI for titanium. Use the largest diameter screw you can find. The heads of commercial hip screws have a tendency to be very hard on the metatarsal head so carefully countersink the screw head — whether you drill or not — to protect it from splintering and collapsing.
At this time, if one decides to place a lateral column beam, advance the guide pin. Typically, it is necessary to enter the foot just proximal to the sulcus between the third and fourth toes, and transverse the soft tissues of the forefoot with the guide pin. The guide pin should be virtually horizontal as it enters between the bases of the third and fourth metatarsals. Elevate the cuboid into its anatomically correct position as the guide pin passes through the cuboid into the body of the talus.
Place the medial column beam under direct fluoroscopic guidance. The threads of the screw at the tip are the weakest point of the screw and they are at the area of the highest bending moment. The screw threads should be as far away from the talonacivular joint as possible, buried as deep as possible in the talus. The lateral column screw should have its head interdigitating between the bases of the fourth and fifth metatarsals, and not compress through the bases. This is perhaps the best evidence that the purpose of beaming isn’t to compress segments for arthrodesis, it is to load share.