We hypothesized that interindividual variations in the teardrop, which represents the volar projection of the lunate facet of the distal radius, cause unsatisfactory fitting of the volar locking plate to the bone. This can cause flexor tendon ruptures. Herein, we conducted a cross-sectional study and measured the ratio of teardrop height and the teardrop inclination angle as parameters of teardrop configuration for 200 standardized lateral radiographs (average age of the patients, 51 years). We also quantified the influence of the teardrop morphology by analyzing the fit of three locking plates to three radii with differing teardrop inclination angles using a three-dimensional computer-aided design system. The average ratios of the teardrop height and teardrop inclination angle were 0.42( 0.30-0.56˚) and 28.8˚(9.9-44.9˚), respectively. The teardrop inclination angle was moderately correlated with age in men but not in women. In the plate-to-bone fit analyses, the fit of all the plates was significantly different between bones, with the configuration of the radius with the lowest teardrop inclination angle being the closest approximation to that of each plate. We demonstrated the interindividual variation in the shape of the teardrop and its influence on the fit of the volar plate, highlighting the importance of careful plate selection for achieving osteosynthesis of bones with a high teardrop inclination angle. Keywords: distal radius fracture; locking plate; plate-to-bone fit; teardrop morphology; three-dimensional computer-aided designThe treatment of distal radius fractures, including those in osteoporotic patients, has improved remarkably with the use of volar locking plates for osteosynthesis. The plates are installed on the anterior surface of the distal radius, which is concave and palmarly directed, and the ulnar distal end of the slope has a steep projection. As it has a U-shaped outline on lateral radiographs, it is called a teardrop, and it functions as a mechanical buttress for subluxation of the lunate. 1 This projection is higher on the ulnar side, where the flexor tendons are in close proximity to the bone compared to the radial side; therefore, to avoid flexor tendon injury, locking plates should not be placed distal to the watershed line, which Orbay called the distal ridge of the pronator fossa on the palmar surface. 2 Most available locking plates for the distal radius are precontoured to its standard morphology. However, the plates do not always fit well to the bone surface. Therefore, it became apparent that there are interindividual differences in the bony configuration of the distal radius, especially in the height and inclination of the slope to the teardrop. These interindividual differences have not been discussed in the anatomical description of the distal radius. [2][3][4][5] The discrepancy between the shape of the plate and the configuration of the teardrop leads to insufficient plate contact in some cases, which in turn causes complications such as flexor tendon injuries....

Almost all of the currently available fracture fixation devices for metaphyseal fragility fractures are made of hard metals, which carry a high risk of implant-related complications such as implant cutout in severely osteoporotic patients. We developed a novel fracture fixation technique (intramedullary-fixation with biodegradable materials; IM-BM) for severely weakened long bones using three different non-metallic biomaterials, a poly(l-lactide) (PLLA) woven tube, a nonwoven polyhydroxyalkanoates (PHA) fiber mat, and an injectable calcium phosphate cement (CPC). The purpose of this work was to evaluate the feasibility of IM-BM with mechanical testing as well as with an animal experiment. To perform mechanical testing, we fixed two longitudinal acrylic pipes with four different methods, and used them for a three-point bending test (N = 5). The three-point bending test revealed that the average fracture energy for the IM-BM group (PLLA + CPC + PHA) was 3 times greater than that of PLLA + CPC group, and 60 to 200 times greater than that of CPC + PHA group and CPC group. Using an osteoporotic rabbit distal femur incomplete fracture model, sixteen rabbits were randomly allocated into four experimental groups (IM-BM group, PLLA + CPC group, CPC group, Kirschner wire (K-wire) group). No rabbit in the IM-BM group suffered fracture displacement even under full weight bearing. In contrast, two rabbits in the PLLA + CPC group, three rabbits in the CPC group, and three rabbits in the K-wire group suffered fracture displacement within the first postoperative week. The present work demonstrated that IM-BM was strong enough to reinforce and stabilize incomplete fractures with both mechanical testing and an animal experiment even in the distal thigh, where bone is exposed to the highest bending and torsional stresses in the body. IM-BM can be one treatment option for those with severe osteoporosis.

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