Distal Tibia Tumor Resection: Two Guides Built as Geometric Counterparts

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Prof. François Sirveaux, Centre Chirurgical Émile Gallé, CHU de Nancy

Resecting a bone tumor and reconstructing with an allograft are usually described as two separate operations.

In this case they were one geometric problem. Prof. François Sirveaux, at the Centre Chirurgical Émile Gallé, CHU de Nancy, referred a chondromyxoid fibroma of the distal tibia that required a bone resection with oncological margin, followed by anatomic allograft reconstruction and osteosynthesis.

Whatever surface the resection left on the host tibia, the allograft had to reproduce in reverse. The answer was two patient-specific guides, designed as geometric counterparts of one another.

The Dual Geometric Challenge

On one side, the resection itself needed sufficient oncological safety margin. Three cutting planes were planned with a 5 mm margin, through an anterior approach. On the other side, the allograft needed to be shaped to interface precisely with the bone that would remain in the patient. The two problems could not be solved independently: any adjustment on one side of the cut required a matching adjustment on the other.

Guide Sequence and Design Logic

Planning began with tumor delineation on the patient’s MRI. It was then matched on the CT scan that was used for the resection plan with 5 mm margin for the anterior approach.

Prof. Sirveaux validated the plan: “the resection plan is adapted, 5 mm margin is sufficient, the current planning for the allograft looks good. The procedure is validated for me.”

During the review of the guide designs, Prof. Sirveaux raised an important point: does the saw blade's own thickness affect how much bone is actually removed at each cut, a detail that matters whenever two guides need to produce matching surfaces.

It's a legitimate concern for most guide designs. In this case, the cutting blocks were positioned on the portion of bone kept for both the patient and the allograft, so any material lost to the blade's kerf falls on the discarded side of the cut rather than on the retained surfaces. Blade thickness was accounted for in the geometry from the start, which is what allowed both guides to be designed as true counterparts of one another.

The resection guide sits on the distal tibia in a single fitting position, for the anterior approach. It is held by three 2.0 mm K-wires, two of them at the intersection of the cutting planes for added stability during the three-plane osteotomy. Drilling and cutting depths, precise to about 2 mm, are inscribed directly on the guide, so the surgeon can check progress against the plan while cutting.

The allograft guide is positioned on the allograft, in its own unique fitting position, and applies the complementary geometry, the same three planes, mirrored, so that the graft surface and the remaining host bone are ready to assemble. It is also held by three 2.0 mm K-wires. Both guides were designed against the same plan, which is what makes the fit optimal rather than approximate.

A Small Adjustment for a Better Fit

After the trial print, a functional check led to one modification: the allograft guide’s flange was extended slightly to improve stability and fit on the bone, while staying as thin as possible to preserve strength. The change did not affect the resection planning or the guide’s functionality, only its grip on the bone during use.

We thank Prof. Sirveaux for his trust and for the precision of his feedback throughout this case.

*Not available in the US. Allograft shaping guides are not currently 510k cleared