Understanding The Potential Impact Of Diabetes On Bone Biology And Biomechanics

Author(s): 
By Glenn Weinraub, DPM
al., measured changes in structural and material properties of intact bone and bone with healed fractures in diabetic rats at three and four weeks.3 They concluded that the structural and material strength of femurs with healed fractures in diabetic rats are delayed by at least one week compared to the non-diabetic controls. However, a meta-analysis of closed foot and ankle fractures from the literature by Boddenberg led this author to the conclusion that diabetes itself does not pose a significant risk of delayed bone healing.4 In general, however, it is well accepted that type 1 diabetes is associated with a decrease in bone mass and delayed healing of fractures in human and animal models. In fact, a very recent paper by Kloting, et. al., showed an actual decrease of up to 80 percent in the expression of genes coding for a multitude of bone specific proteins in newly diagnosed and in well compensated diabetic rats.5 Case Study: When There Is Complete Midfoot Charcot Breakdown A 52-year-old type 1 diabetic male presented with complete midfoot Charcot breakdown and a full thickness ulceration to the plantar midfoot. Fortunately, nuclear and magnetic resonance imaging was negative for osteomyelitis. At the time of the initial debridement, the patient’s HbgA1C was 7.8. Due to the patient’s intrinsic bone healing compromise, we decided to proceed with reconstruction utilizing adjunctive external fixation and orthobiologics in the form of platelet gel concentrate (PGC), demineralized bone matrix (DBM) and internal direct current bone stimulation. Even with all the adjunctive measures, complete radiographic bone healing did not occur until 14 weeks postoperatively. Case Study: When A Patient Presents With Posttraumatic OA Of The Ankle In the second case, a 36-year-old type 1 diabetic female presented with long-term posttraumatic osteoarthritis of the ankle. The patient underwent an ankle joint arthrodesis. At that time, her HbgA1C was 7.2 and she had been a one-pack per day tobacco user for greater than 10 years. Due to both intrinsic and extrinsic bone healing compromise with this patient, we employed adjunctive measures including PGC, DBM and direct current bone stimulation. The patient achieved final consolidation at 10 weeks postoperatively. A Helpful Primer On Bone Structure Bone is classified as short (tarsals, carpals), flat (scapular, ilium) or long (tibia, fibula). The component tissues of bone include hematopoietic marrow, periosteum, cortical bone and cancellous bone. Cortical (compact) bone forms 80 percent of the mature skeleton. It is very dense with only 10 percent porosity. The compressive strength of bone is proportional to its density squared. Therefore, cortical bone may have a compressive strength 10 times greater than an equal volume of cancellous bone. Cancellous (trabecular) bone has approximately 20 times more surface area per unit volume than cortical bone. It also has about 50 to 90 percent porosity, which gives it a much higher rate of metabolic activity because of greater accessibility to adjacent cellular constituents. In long bones, there is a biomechanical interplay that takes place between the cortical and cancellous bone. This interplay may have greater consequences for the insensate diabetic patient. In long bones, the diaphyseal cortical regions will resist torsion and bending forces. Where the cortical bone thins out at the neck of the bone (the “cutback region”), it has the support of the underlying epiphyseal-metaphyseal cancellous bone. This allows for greater deformation under equal loads. This unique complex formed by articular cartilage, cancellous bone and cortical bone acts to absorb impact loads. Replacement of this complex by a joint prosthesis may eliminate shock absorption with resultant increased peak loads to the diaphyseal cortical bone. Cortical or cancellous bone may consist of woven (primary) or lamellar (secondary) bone. Woven bone consists of irregular and random oriented collagen fibrils. It is isotropic, meaning that it responds the same no matter the direction of applied forces. It is rarely present after the age of 4 with the exception of pathologic processes. Lamellar bone consists of densely packed, well-organized collagen fibrils. It is anisotropic as its mechanical properties will differ based on the direction of applied forces. Osteons form the bulk of the diaphyseal cortex.

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