Assessment of registration accuracy during computer-aided oncologic limb-salvage surgery.

PURPOSE: Computer-aided surgery is used in musculoskeletal tumor procedures to improve the surgeon's orientation to local anatomy during tumor resection. For the navigation system to function correctly, preoperative imaging (e.g., CT, MR) must be registered to the patient in the operating room. The goals of this study were (1) to directly quantify registration accuracy in computer-aided tumor surgery and (2) to validate the "system reported error" (SRE) of the navigation system. METHODS: Registration accuracy was evaluated in eight bone sarcoma cases by determining the location of the anatomical paired-points used for registration following surface matching. Coordinates of specific intraoperative post-registration points were compared with the corresponding coordinates in preoperative CT scans to determine the measurement error (ME). RESULTS: The mean difference between post-registration points and planned registration points was 12.21±6.52 mm significantly higher than the mean SRE (0.68 ± 0.15 mm; p = 0.002; 95 % CI 6.11-16.96 mm). The SRE poorly correlated with the calculated ME (R(2) = 0.040). Anatomical paired-point registration with surface matching results in a substantial shift in the post-registration coordinates of the same paired-points used for registration, and this shift is not represented by the SRE. CONCLUSION: The SRE of a surgical navigation system was poorly correlated with direct measurements obtained in musculoskeletal tumor surgery. Improvement in registration accuracy is needed to better navigate tumor boundaries and ensure clear margins while maximally preserving the unaffected tissues and reducing operative morbidity.

Whole body vibration increases area and stiffness of the flexor carpi ulnaris tendon in the rat.

Whole body vibration (WBV) has been extensively studied as an anabolic stimulus for bone and muscle. Therapeutic WBV delivers low magnitude, high frequency vibrations to tissues, eliciting biological and structural responses. This study investigated the effect of 0.3G (Peak-to-Peak), 30Hz sinusoidal vibration on intact flexor carpi ulnaris tendons in rats. Experimental rats were subjected to twenty minutes of WBV daily for five days a week for a total of five weeks. The tendon cross-sectional area and the structural properties of the muscle-tendon-bone unit under tensile loading to failure were evaluated. Initial body weights were similar between the groups and the mean change in body weight of the animals of each group did not differ. The cross-sectional area of the tendons of the vibrated animals was found to be 32% greater (P<0.05) than the controls and the structural stiffness of the vibrated tendons was found to be 41% greater (P<0.05) than the controls. For specimens that failed in the midsubstance of the tendon, a trend (P=0.087) for increased ultimate load was observed in the vibrated tendons compared to the controls. No differences in material properties were observed except for the strain to ultimate load, which was reduced 22% in the vibrated group. These initial findings suggest that vibration may serve as an anabolic stimulus to tendon similar to its effects on bone and muscle. These findings are important as they open the potential that low magnitude, high frequency vibration might serve as a means to accelerate tendon healing.

Rat tibial osteotomy model providing a range of normal to impaired healing.

The purpose of this study was to develop an inexpensive and easily implemented rat tibial osteotomy model capable of producing a range of healing outcomes. A saw blade was used to create a transverse osteotomy of the tibia in 89 Sprague-Dawley rats. A 0.89 mm diameter stainless steel wire was then inserted as an intramedullary nail to stabilize the fracture. To impair healing, 1, 2, or 3 mm cylindrical polyetheretherketone (PEEK) spacer beads were threaded onto the wires, between the bone ends. Fracture healing was evaluated radiographically, biomechanically, and histologically at 5 weeks. Means were compared for statistical differences by one-way ANOVA and Holm-Sidak multiple comparison testing. The mean number of "cortices bridged" for the no spacer group was 3.4 (SD ± 0.8), which was significantly greater than in the 1 mm (2.3 ± 1.4), 2 mm (0.8 ± 0.7), and 3 mm (0.3 ± 0.4) groups (p < 0.003). Biomechanical results correlated with radiographic findings, with an ultimate torque of 172 ± 53, 137 ± 41, 90 ± 38, and 24 ± 23 N/mm with a 0, 1, 2, or 3 mm defect, respectively. In conclusion, we have demonstrated that this inexpensive, technically straightforward model can be used to create a range of outcomes from normal healing to impaired healing, to nonunions. This model may be useful for testing new therapeutic strategies to promote fracture healing, materials thought to be able to heal critical-sized defects, or evaluating agents suspected of impairing healing.