Post-traumatic avascular necrosis of the femoral head usually occurs after hip dislocation and femoral neck fracture. Recently along the development of hip arthroscopy, early stage of avascular necrosis of the femoral head can be treated rthroscopically. We hereby present two cases of post-traumatic avascular necrosis patients treated with hip arthroscopy.

Case 1

Twenty one year old female patient came to the hospital because of fall from height of 3 floors. Left acetabular fracture, both superior pubic rami fractures and severely displaced left femoral neck fracture were identified at the emergency department (Fig. 1-A). She underwent surgery at the injury day. After the repair of ruptured urinary bladder, internal fixation of the femoral neck was done. Four cannulated screws with washers were inserted for displaced femoral neck fracture, consistent with garden stage IV (Fig. 1-B). Skeletal traction of ipsilateral lower extremity was applied four weeks after the surgery for acetabular fracture. She visited us for painful limitation of motion on left hip at eight months postoperatively. Plain radiograph showed collapse of femoral head and osteophyte formation which were caused by post-traumatic avascular necrosis (Fig. 1-C,D). Femoral head was perforated by a screw. She was planned to remove the screw and resect the osteophyte arthroscopically. On arthroscopic examination, severe synovitis and folded, collapsed femoral cartilage were identified (Fig. 1-E). Screws were removed and osteophyte were also resected (Fig. 1-F). We filled the cavity caused by the screws with allogenic strut graft for structural support. After the surgery, pain was relieved and she came back to her active daily living and for six months, no other complication nor further collapse were identified postoperatively.

Case 2

Fourty year old male patient was admitted to the hospital for fall from height about fifteen feet from the ground. Left femoral neck fracture was identified on the emergency department. Previously he had underwent intramedullary nailing for the femoral shaft fracture about five years ago. Urgent internal fixation with four cannulated screws was done on the day of injury. The fixation was unsatisfactory because previously inserted intramedullary nail hindered the proper trajectory of screws. Furthermore, direction of cephalad interlocking holes of the nail were not consistent with the anteversion of femoral neck, we could not place the screws through the nail. Four months after the index surgery, collapse of femoral head and loosening of screws have occurred. MRI showed the collapse of femoral head and posttraumatic avascular necrosis. Prominent bony beak of femoral neck were identified and he complained difficulty and pain on his hip during abduction. We left two screws for secure fixation and resected the bony beak using arthroscopic burr. After the surgery, he felt free from the pain on abduction of hip.

Introduction: Electromagentic Navigation(EM) system has been introduced in total knee arthroplasty to increase the accuracy of lower limb alignment and positioning of the implant. EM navigation systems offer several potential advantages over their infrared counterparts. To our best knowledge, there have been scarce clinical results reported In order to obtain optimal results, a certain period of learning curve may be necessary. We have compared our first 100 cases of total knee arthroplasty to our last 100 cases in order to verify the clinical accuracy, efficacy and learning curve.

Methods: From July 2006 to November 2007, 138 patients underwent 200 serial primary TKA operations by a single surgeon with the assistance of Electromagnetic Navigation system. The 200 TKA cases were divided into two groups; the first 100 and the next 100 cases. We have compared the deviation in postoperative mechanical axis and angles of femoral and tibial component position(α°, β°, and γ°) in addition to the outlier percentage of post-mechanical axis between the two groups. We used the independent sample t-test to verify our results.

Results: The deviation in angle of postoperative mechanical axis was significantly lower in the last group than the first group; 2.0633 vs. 2.6944. (p=0.0145) respectively. The deviation of α° was significantly lower in the last group than the first group; 1.1597 vs. 1.6778. (p=0.005) respectively. The deviation of β ° was lower in the last group than the first group; 1.3475 vs. 1.2115, but this value was not significant. (p=0.849). The results of the value γ° proved to be more towards extension in the first group and more towards flexion in the last group, yet these values were not significant (p=0.159). The outlier percentages of postop-mechanical axis between two groups were significantly different.

Discussion and Conclusion: The navigation system most often used in studies is an optical system with an infrared camera. Many authors have reported the efficacy of optical navigation system. It has been known to increase the accuracy of lower limb alignment and positioning of the implant while decreasing the outlier percentage of postoperative mechanical axis. The large transmitter, however, for this system requires bicortical pins, which would result in stress fracture through the drill-holes in bone. In addition, another skin incision is needed for the transmitter. A new navigation technique using electromagnetic signals has been introduced with advantages including small transmitter size, although its signal is often distorted by metal devices used in the operative field. Our hypothesis was therefore that the EM system could lead to better alignment of the leg and positioning of implants than traditional method with comparable learing curve. In summary, the EM navigation system can lead to better alignment of the mechanical axis of leg and positioning of femoral implants in coronal view compared to conventional method, although it can’t prevent outliers in all case. And also our experience suggests that in order to obtain such results, however, a certain period of learning curve may be necessary. Several valuable surgical tips specific to this technology were obtained enduring our learning curve and will be presented.

Introduction: It is not uncommon situation, in a hip fracture patient treated with dynamic hip screw(DHS) system, that the hip arthroplasty should be done after removal of DHS. However multiple screw holes and postplating osteopenia under the barrel plate will be created in the proximal femur resulting adverse mechanical effects.

Purpose: The authors analysed the micromotion of femoral stem and the stress concentration of proximal femur in hip replacement performed after removal of DHS using finite element analysis.

Methods: For simulation of femoral cortical defects after removal of 4-holed DHS system, four Φ4.5 mm cortical screw holes on medial and lateral cortices of the femur and one Φ12mm lag screw. One 20mmx90mm weakened cortical bone area on lateral cortex was made for simulation of the postplating osteopenia created under the barrel plate. After meshing with eight node linear hexahedron, nonlinear contact analysis was done using ABAQUS 5.8 package system. For the postplating osteopenia we decreased the bony strength of cortical bone up to 20%.

Results: In one leg stance, the maximal micromotions at metal to bone interface were around 150& #13211; (142.3-160.6& #13211;) even in the osteoporotic femur. However, in stair climbing, it increased over 150& #13211; (170.1-191.1& #13211;) even in the non-osteoporotic intact femur. The maximal micromotions were 170.1& #13211; in intact non-osteoporotic femur and 191.1& #13211; in osteoporotic DHS removed femur in a stair climbing. The pattern of stress distribution on the surface of the femur was changed showing distal transfer of the point with maximal stress from the proximal medial area to the stem tip area. The maximal stress increased up to 89% at the lag screw hole.

Conclusion: This study suggests that the femoral stem for primary cementless hip replacement could be used in the DHS removed femur regardless of bone quality, if it is long enough to pass the screw holes and also if the post-operative rehabilitation is strictly controlled.

Introduction: Avascular necrosis (AVN) of bone is a process that is characterized pathologically by bone marrow ischemia and eventual death of trabecular bone. Following the development of the disease with the remodeling process, the microstructure and corresponding mechanical properties of the trabecular bone changes in different regions with different intensities. Eventually, the lesion leads to collapse of the femoral head and destruction of the hip joint. The most striking finding is the direct relationship between mechanical stress and the progressive collapse of the necrotic region. This study investigated the differences in the mechanical properties from the trabecular bone of the different regions in AVN of the femoral head using microfinite element models.

Materials and Methods: A 20mm cylindrical core sample was obtained from the necrotic zone of the human femoral head with pre-collapse disease throughout the overall head under the fluoroscope and then was scanned using Micro-CT. Region of interest (ROI) was determined in the necrotic, the reactive, and the sub-reactive zone respectively, which were created with the hexahedron mesh model; finite element analysis was performed.

Results: The histomorphology and FE-analysis of three zones revealed that the parameters of Tb. Th, BV/TV, reaction force, ultimated stress, and elastic modulus increase obviously in the reactive zone.

Discussion: The authors conclude that obvious increases of the parameters and the stress concentration in the reactive zone are due to the adaptive remodeling of trabeculae in the boundary zone between the necrotic and the normal zone.