The biomechanical assessment of fixation methods in periprosthetic femur fractures.

OBJECTIVE: The aim of our study was to compare the biomechanical properties of different fixation methods used in periprosthetic femur fractures. METHODS: We created sawbone models with Mallory Type 2 periprosthetic femur fractures. The periprosthetic fractures were fixed with cables, cables and strut graft, or cables and plates. The biomechanical properties of these three different fixation methods were compared with the intact femur, the intact femur with prosthesis and the femur with periprosthetic fracture without fixation. RESULTS: The periprosthetic fracture without fixation had a significantly lower yield point value than the periprosthetic fractures with fixation (p<0.05). There was no significant difference between the three different fixation methods of the periprosthetic fractures. The intact femur with a prosthesis showed statistically higher values than all three fixation methods of perioprosthetic fractures. CONCLUSION: Mallory Type 2 periprosthetic fractures should be fixed. There is no difference among the fixation methods used in the study and none of them provide a stability equivalent to that of an intact femur with prosthesis.

[Investigation of radioulnocarpal joint load distribution effects of radial shortening osteotomy for the treatment of Kienböck disease: a biomechanical study]. / Kienböck hastaligi tedavisinde kullanilan radyal kisaltma osteotomisinin radioulnokarpal ekleme binen yükler üzerindeki etkilerinin arastirilmasi: Biyomekanik çalisma.

OBJECTIVES: We evaluated the effects of radial shortening osteotomy on the radiolunate joint load distribution. MATERIALS AND METHODS: This biomechanical study used standard left wrist models made of solid foam (Sawbones, Malmö, Sweden). The radioulnocarpal joint load distribution was investigated in the normal wrist model and 2 mm and 4 mm radial shortening osteotomy models under 14 kgf and 25 kgf loads when the wrist position was neutral. RESULTS: In the normal wrist group, the comparison of the average pressure distributions under the 14 kgf and 25 kgf loads shows that the increase at the ulnocarpal joint loading and the decrease at the radiolunate joint loading were statistically significant (p=0.012, p=0.036, respectively). When we compared the respective average pressure distributions after 14 kgf and 25 kgf loading, there were no significant differences between the normal wrist and the osteotomy groups. CONCLUSION: Consequently, radial shortening osteotomy is not effective in decreasing radiolunate joint loading when the wrist is in neutral position.

The biomechanical effects of talectomy on the foot.

The biomechanical effects of talectomy on the foot were investigated in seven fresh below-the-knee amputation specimens using pressure-sensitive films placed on the facets of the calcaneus, footprints, and loading-pattern diagrams in the intact foot and after talectomy with anterior and posterior displacement of the foot. Both talectomy techniques distorted the loads carried by the facets of the calcaneus. In the intact foot, 65.6% of the loads were carried by the posterior facet of the calcaneus and 34.4% by the anterior and middle facets. After talectomy with anterior displacement of the foot, although the loads carried by the anterior and middle facets decreased significantly (P = .018), the increase in the loads carried by the posterior facet was not significant compared with the intact foot (P = .176). Similarly, the loads carried by the posterior facet decreased significantly after talectomy with posterior displacement of the foot (P = .028), but the increases in the loads carried by the anterior and middle facets were not significant (P = .735). Comparing the two types of talectomy, the loads carried by each facet changed significantly (P = .018). Talectomy with posterior displacement of the foot also changed the loading patterns and resulted in significant pronation of the foot. These results suggest that talectomy should be performed only as a salvage procedure and that talectomy with anterior displacement of the foot may be preferred when talectomy is indicated.

[Biomechanical analysis of load transmission characteristics of limited carpal fusions used to treat Kienböck's disease]. / Kienböck hastaligi tedavisinde sinirli karpal füzyonlarin yük aktarma özelliklerinin biyomekanik analizi.

OBJECTIVES: Although limited carpal fusions used in the treatment of Kienböck's disease are thought to act by decreasing the loads on the lunate, biomechanical studies show that capitohamate fusion acts oppositely to what is expected. This experimental study was designed to resolve this paradox. METHODS: In a biomechanical cadaveric study, load transmissions at the radioulnacarpal joint were investigated under 140 and 210 newtons of load with three wrist postures, namely, neutral, ulnar and radial deviations, in five intact wrists and after scaphotrapeziotrapezoid, capitohamate, and scaphocapitate fusions. RESULTS: Under 140 newtons of load, the loads imposed to the lunate decreased following scaphotrapeziotrapezoid and scaphocapitate fusions, but increased after capitohamate fusion. However, when the load was increased to 210 newtons, there were no differences between intact wrists and limited carpal fusions in respect to the loads exerted on the lunate. In all the situations, the lunate was subjected to a significantly greater load in ulnar deviation. CONCLUSION: These results suggest that limited carpal fusions do not alter load transmission characteristics of the wrist joint under 210 newtons of load. The etiology of the Kienböck's disease seems to be related to an overload in ulnar deviation and the beneficial effect of limited carpal fusions seems to be associated with restricted ulnar deviation of the wrist rather than load transmission characteristics.