Fractures of the carpal bones

The use of open wedge high tibial osteotomy (HTO) to correct varus deformity of the knee is well established. However, the stability of the various implants used in this procedure has not been previously demonstrated. In this study, the two most common types of plates were analysed (1) the Puddu plates that use the dynamic compression plate (DCP) concept, and (2) the Tomofix plate that uses the locking compression plate (LCP) concept. Three dimensional model of the tibia was reconstructed from computed tomography images obtained from the Medical Implant Technology Group datasets. Osteotomy and fixation models were simulated through computational processing. Simulated loading was applied at 60:40 ratios on the medial:lateral aspect during single limb stance. The model was fixed distally in all degrees of freedom. Simulated data generated from the micromotions, displacement and, implant stress were captured. At the prescribed loads, a higher displacement of 3.25 mm was observed for the Puddu plate model (p<0.001). Coincidentally the amount of stresses subjected to this plate, 24.7 MPa, was also significantly lower (p<0.001). There was significant negative correlation (p<0.001) between implant stresses to that of the amount of fracture displacement which signifies a less stable fixation using Puddu plates. In conclusion, this study demonstrates that the Tomofix plate produces superior stability for bony fixation in HTO procedures.

Finite element analysis of Puddu and Tomofix plate fixation for open wedge high tibial osteotomy

Periprosthetic fracture fixation of the femur following total hip arthroplasty: A review of biomechanical testing - Part II.

Displaced supracondylar fractures of the humerus in children.

Computer assisted reconstruction of complex proximal humerus fractures for preoperative planning.

Purpose The hypothesis of this study was that more stable fixation of acute scaphoid fractures may be achieved by a screw placed perpendicular to the fracture plane than along the long axis of the scaphoid, as previously suggested. We examined this assumption on different fracture patterns using a finite element analysis model. Methods A computed tomography scan of an intact scaphoid of a young man provided the data set for all fracture models. We used semiautomatic segmentation to create 3-dimensional computer models of the 3 simple fracture configurations: oblique, transverse waist, and proximal fractures, according to the Herbert classification. Each fracture type was analyzed, using finite elements, for its biomechanical response to 2 types of virtual fixation: a screw placed either perpendicular to the fracture plane or centrally along the long axis of the scaphoid. We measured motion at the fracture plane (in millimeters) and strain in the screw threads (in millipascals). Results Considerably less motion was measured at the fracture plane with the perpendicular screw compared with the long axis screw, especially in the oblique-type fractures: (1) Herbert-type B1 oblique fracture mean motion of 0.05 mm (±0.03) for the perpendicular screw versus 0.28 mm (±0.05) for the long axis screw; (2) B2 transverse waist fracture mean motion of 0.06 mm (±0.03) for the perpendicular screw versus 0.18 mm (±0.06) for the long axis screw; and (3) B3 proximal fracture mean motion of 0.07 mm (±0.01) for the perpendicular screw versus 0.28 mm (±0.011) for the long axis screw. Higher strains were measured on the screw placed perpendicular to the fracture. Conclusions According to this model, higher fixation stability is achieved when the scaphoid is fixated perpendicular to the fracture. In transverse waist fractures, a centrally placed screw will also be perpendicular to the fracture, which explains the results of previous models.

Optimal fixation of acute scaphoid fractures: finite element analysis.

Purpose Acute scaphoid fractures are commonly fixed with headless cannulated screws positioned in the center of the proximal fragment. Central placement of the screw may be difficult and may violate the scaphotrapezial joint. We hypothesize that placement of the screw through the scaphoid tuberosity will achieve perpendicular fixation of an oblique waist fracture and result in more stable fixation than a screw in the center of the proximal fragment. Methods We designed oblique osteotomies for 8 matched pairs of cadaver scaphoids and fixed each specimen with a headless cannulated screw. In 1 specimen, we positioned the screw at the center of the proximal fragment; we placed its matched pair perpendicular to the fracture. The perpendicular screw was directed through the scaphoid tuberosity. We placed the specimen under the increasing load of a pneumatically driven plunger. We compared stiffness, load, distance at failure, and mechanism of failure between the central and perpendicular screw groups. Results We found no difference between groups. Stiffness was identical in both groups (131 N/mm) and load to failure was similar (central screw, 137 N vs perpendicular screw, 148 N). Conclusions In this biomechanical model of an unstable scaphoid fracture, we found that similar stability of fixation had been achieved with a screw perpendicular to the fracture plane with entry through the tuberosity, compared with a screw in a central position in the proximal fragment. This study suggests that placing the screw through the tuberosity, perpendicular to a short oblique fracture, will not impair fixation stability. Clinical relevance Percutaneous fixation of scaphoid fractures has become popular although it is technically challenging. An easier distal approach through the tuberosity, without violating the scaphotrapezial joint, may not impair the fixation stability of an oblique fracture.

Optimal fixation of oblique scaphoid fractures: a cadaver model.

Purpose
Understanding acetabular orientation is important in many orthopaedic procedures. Acetabular orientation, usually described by anteversion and abduction angles, has uncertain measurement variability in adult patients. The goals of this study are threefold: (1) to describe a new method for computing patient-specific abduction/anteversion angles from a single CT study based on the identification of anatomical landmarks and acetabular rim points; (2) to quantify the inaccuracies associated with landmark selection in computing the acetabular angles; and (3) to quantify the variability and symmetry of acetabular orientation.

Acetabular orientation variability and symmetry based on CT scans of adults

Intramedullary nailing is the most commonly used technique for fixing femoral shaft fractures. Use of a fluoroscopy based computerised navigation system can improve the nailing technique by locating the entry point of the nail, inserting locking and Poller screws and providing accurate nail and screw measurements. These tasks then can be performed with markedly reduced radiation exposure. However, fracture reduction in vivo has not been achieved by computerised navigation systems, since dynamic imaging of two separate anatomic sites, such as fracture fragments, has not yet proved feasible. Open reduction can result in higher rates of infection and non-union. Several techniques have been suggested to accomplish closed reduction, such as the use of the femoral distractor, percutaneous Schanz screws to manipulate the fragments, and tourniquet. These solutions rely exclusively on fluoroscopy thus exposing both the patients and the surgeons to a significant amount of radiation.

Eran Peleg

Papers

Optimal fixation of acute scaphoid fractures: finite element analysis.

Optimal fixation of oblique scaphoid fractures: a cadaver model.

Acetabular orientation variability and symmetry based on CT scans of adults

Computerised navigation for closed reduction during femoral intramedullary nailing

A short plate compression screw with diagonal bolts--a biomechanical evaluation performed experimentally and by numerical computation.