Commentary on
"Improvement of the Bone-Pin Interface Strength in Osteoporotic Bone with Use of Hydroxyapatite-Coated Tapered External-Fixation Pins"
By Antonio Moroni, MD et al.

Commentary by Jesse B. Jupiter, MD*,
Massachusetts General Hospital, Boston, MA

The historical origin of external fixation of skeletal fractures has often been attributed to Malgaigne, who conceived the "griffe metallique" or metal claw designed for the treatment of fractures of the patella in 1843¹. Soon thereafter Chassin developed a similar claw-like device for the treatment of displaced fractures of the clavicle². Perhaps the first fixator that incorporated pins drilled into the cortex of the bone was that invented by Keetley in England in 1893³. Since then, numerous investigators including Lambotte⁴, Hoffman⁵, Vidal⁶, Anderson and O'Neill⁷, Agee⁸, and Pennig⁹—just to mention a few—have advanced the concept and design of external fixation frames used specifically for the treatment of fractures of the distal end of the radius. Yet, despite substantial improvements in metallurgy, design, and the understanding of the biomechanical forces acting on the external frames, the pin-bone interface has remained a major site of complications leading to failure of treatment. In fact, the early unfavorable experiences of orthopaedic surgeons using the external fixation device of Anderson and O'Neill led to the coining of the term "Seattle serum" to describe the all-too-frequent pin-related infections observed, thus tempering enthusiasm for the use of external fixation in the treatment of distal radial fractures.

As our populations age world-wide in the twenty-first century, we will witness a dramatic increase in the number of fractures associated with osteoporosis, particularly those of the distal end of the radius. With advances in technology will come new developments in external fixation devices, with some allowing multiplanar fracture reduction and others allowing active motion at the radiocarpal joint. Regardless of these advances, the pin-bone interface will remain the most critical component of the system. The biomechanical factors that influence the "rigidity" of an external fixation frame include the pin diameter; pin design; location of the pins in relationship to the fracture site as well as to each other; the location of the connecting bar and its distance from the underlying bone; and the degree of osseous contact, which influences how much of the physiologic load will be borne either by the frame alone or by the bone and frame together¹⁰. Pin loosening can also result from a number of factors including pin design and placement, bone necrosis due to surgical trauma during pin insertion, abnormal contact pressures at the pin-bone interface from unfavorable axial loading on the pins due to faulty frame design, or delay in fracture healing¹¹.

The data presented in the study by Moroni and colleagues would suggest that the pin-bone interface strength will be significantly improved by coating the pins with hydroxyapatite. Their experimental design is well-conceived and the study carefully performed. The results clearly demonstrate the beneficial effect of the hydroxyapatite coating on the results of pin fixation in osteoporotic bone. This clinical experience convincingly supports the finding of prior laboratory work performed by the same investigators and should influence physicians to request that implant manufacturers offer hydroxyapatite-coated pins for external fixation devices designed for use throughout the skeletal system.

*The author did not receive grants or outside funding in support of his research or preparation of this manuscript. He did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the author is affiliated or associated.

References

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2. Colton C. The history of fracture treatment. In: Browner B, Jupiter J, Levine A, Trafton P, editors. Skeletal trauma, Vol 1. 1st ed. Philadelphia: WB Saunders: 1992. p 20-1.
3. Keetley CB. On the prevention of shortening and other forms of mal-union after fracture by the use of metal pins passed into the fragments subcutaneously. Lancet. 1893;June 10:137-9.
4. Lambotte A. Chirurgie operatoire des fractures. Paris: Masson et Cie; 1913.
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