Emir Benca

The effect of simulated metastatic lesions on the biomechanical behavior of the proximal femur

Pathologic fractures of femora in patients with metastatic cancer are associated with high morbidity and mortality. Prediction of impending fractures is based on unspecific clinical criteria or past clinicians experience, which leads to underestimation or overtreatment. The aim of this study was to investigate the effect of the site of metastatic lesions on biomechanical behavior of the proximal femur. Sixteen pairs of human femora were scanned with quantitative computed tomography (QCT) to asses bone mineral density. One femur of each pair remained intact while a defined lesion was reamed out in either the superolateral or inferomedial portion of the femoral neck of the contralateral femur. All femora were loaded in a mechanical test setup mimicking one‐legged stance and stiffness, failure load, and fracture location were determined. In the biomechanical experiments the superolateral lesion and the inferomedial lesion caused a stiffness reduction of 19% and 66%, respectively. The average failure load was 40% and 75% lower for specimens with the superolateral (4.53 ± 1.56 kN) and inferomedial (1.89 ± 1.73 kN) lesions, respectively, compared to intact specimens (7.66 ± 3.34 kN). Lesions in the femoral neck led to reduction in both stiffness and failure load of the proximal femur. Furthermore, the site of the lesion had a large effect on the magnitude of the reduction in biomechanical properties. The presented data emphasize the importance of differentiating between locations of the lesion in pathologic fracture prediction of the metastatic femur and underline the insufficient accuracy of current predictive guidelines.

Combined Medial and Lateral Anatomic Ligament Reconstruction for Chronic Rotational Instability of the Ankle Joint

The acute ligament rupture in the ankle joint still falls within the domain of conservative therapy. Therapy recommendations diverge strongly, and no standardized protocol exists. Chronic ligament instability primarily resulting from acute ligament ruptures occurs with an incidence of 20% to 60% depending on the study. The treatment for chronic instability involves various techniques. Direct ligament repair has not resulted in highly successful outcomes. The prevalent reason for this is the weak caliber of the lateral ligaments, both the anterior talofibular ligament and the calcaneofibular ligament, both of which seem to be inadequate for a direct suture repair because of their structure. In the past, tenodesis-type stabilization techniques (Anderson, Hintermann) were widely used. In contrast, anatomic reconstructions using local structures are in widespread use today and are less invasive. The most common technique used today is the modified Broström method. Here, we present a surgical method using the retinaculum extensorum inferius for stabilization similar to the Broström method. Arthroscopy of the ankle joint is performed before stabilization, for diagnostic purposes and to treat accompanying pathologies within the ankle.

Biomechanical evaluation of two methods of fixation of a flexor hallucis longus tendon graft

Aims The traditional transosseus flexor hallucis longus (FHL) tendon transfer for patients with Achilles tendinopathy requires two incisions to harvest a long tendon graft. The use of a biotenodesis screw enables a short graft to be used and is less invasive, but lacks supporting evidence about its biomechanical behaviour. We aimed, in this study, to compare the strength of the traditional transosseus tendon‐to‐tendon fixation with tendon‐to‐bone fixation using a tenodesis screw, in cyclical loading and ultimate load testing. Materials and Methods Tendon grafts were undertaken in 24 paired lower‐leg specimens and randomly assigned in two groups using fixation with a transosseus suture (suture group) or a tenodesis screw (screw group). The biomechanical behaviour was evaluated using cyclical and ultimate loading tests. The Students t‐test was performed to assess statistically significant differences in bone mineral density (BMD), displacement, the slope of the loaddisplacement curves, and load to failure. Results The screw group showed less displacement (loosening) during cyclical loading, which was significant during 300, 500, 600, 700, 800, 900, and 1000 cycles (p < 0.05: other cycles: 0.079 < p < 0.402). Compared with the suture group, the screw group had higher mean ultimate load values (133.6 N, SD 73.5 vs 110.1 N, SD 46.2; p = 0.416). Conclusion Fixation of the FHL tendon with a tenodesis screw enables a less invasive procedure to be undertaken and shows similar biomechanical behaviour and primary strength compared with fixation using a transosseus suture.

The role of the subchondral layer in osteonecrosis of the femoral head: analysis based on HR-QCT in comparison to MRI findings:

Background Non-traumatic avascular osteonecrosis of the femoral head (ONFH) is a severe disease causing destruction of the hip joint, often necessitating total hip arthroplasty (THA) even in young patients. Magnetic resonance imaging (MRI) is commonly used for diagnosis of ONFH, but provides limited insight into the subchondral bone microstructure. Purpose To analyze routine MRI findings in comparison to high-resolution quantitative computed tomography (HR-QCT) with a special focus on the subchondral layer and to estimate the importance of differences determining the indication for THA. Material and Methods Twelve patients with ONFH were included before THA. Preoperative MRI and HR-QCT of the retrieved femoral heads were aligned using a registration algorithm. Pathological findings and trabecular bone parameters in matched areas were analyzed by two readers. McNemar, marginal homogeneity test, and Pearson’s correlation coefficient were used for comparison. Results Subchondral delamination was found in nine cases on HR-QCT, but missed or underestimated in all but one case on MRI (P = 0.016). Chondral discontinuity was found in all cases on HR-QCT and in two cases on MRI (P = 0.016). Areas of complete bone resorption on HR-QCT were linked to high signal intensity on 3D gradient-echo MRI sequences with water-selective excitation, while there was no correlation between trabecular bone parameters and MRI signal intensities in other areas (P = 0.304). Conclusion Subchondral delamination, subchondral resorption, and chondral discontinuity are found frequently in advanced stages of ONFH. These lesions tend to be underestimated on conventional MRI. Our results support the importance of CT imaging in the evaluation of ONFH.