Objective To compare the biomechanical characteristics of the less invasive stabilization system (LISS) and the dynamic condylar screw (DCS) in the fixation of subtrochanteric fractures of the femur so as to provide theoretical basis for choosing internal fixator in clinical application. Methods Twelve cadaveric human femurs (35-50 years old) were selected with similar proximal femur, excluding deformities, fractures, and other lesions. The twelve femur specimens were randomly divided into 2 groups, 6 specimens per group. An 1 cm gap of osteotomy model was made in the proximal femur up to 1 cm below the lesser trochanter to simulate a comminuted subtrochanteric fracture of femur, and the distal end was embedded with denture acrylic and liquid for denture acrylic. Fracture was fixed by LISS in group A, and was fixed by DCS in group B. The specimens were fixed on Instron-8874 servo-hydraulic mechanical testing machine in a single-leg standing position, and the axial compression test and dynamic fatigue test were carried out to compare the compressive strength and the strain distribution at both sides of the fracture line. Results Axial compression test: the strain values of the 2 strain gauges in group A were significantly smaller than those in group B (P lt; 0.01); the vertical down displacement of the femoral head in group A was significantly smaller than that in group B (P lt; 0.01) under the same load; when the load was 600 N, the axial rigidity of group A was (209.06 ± 18.63) N/mm, which was significantly higher than that of group B [(65.79 ± 7.26) N/mm] (t=3.787, P=0.004). Dynamic fatigue test: the vertical down displacement of the femoral head in group A was significantly smaller than that in group B in the same cyclic loading cycle (P lt; 0.01); when the vertical down displacement of the femoral head was 0.5 mm, the force and the cyclic loading cycles in group A were significantly larger than those in group B (P lt; 0.01). Conclusion LISS, which has good mechanical stability, can meet the requirements for subtrochanteric fracture of femur fixation in biomechanics and anatomical structures. It can be proven that the LISS internal fixator is firmer than the DCS internal fixator by biomechanical comparison.
To investigate the therapeutic effects and the related factors during operation of the less invasive stabilization systemdistal femur（LISSDF）for Types 33A3, C2 and C3 fractures classfied on the criteria by Association of Orthopedics (AO). Methods From August 2004 to December 2005, 26 patients with distal femoral fractures were surgically treated by LISSDF, including 9 patients with Type 33A3, 11 with Type 33C2, and 6 with Type 33C3. There were 15 males and 11 females, aged 3272 years (average, 55 years). The fractures occurred on the left side in 16 patients and on the right side in 10 patients. The fractures resulted from a road traffic accident in12 patients, a fall from the height in 9, and a crush injury in 5. Of the 26 patients, 3 had an open fracture (2 Gustilo Type Ⅰ,1 Gustilo Type ⅡA), with the mean time between the injury and the operation of 4 days (range, 6 h16 d).The operation through a lateral parapatellar incision and a transarticular retrograde plate of osteosynthesis (TARPO) was performed on 17 patients for Type33C2 and 33C3 fracture of the distal femur. The locking head screw (LHS) insertion through the stab incisions and monocortical fixation was performed on 9 patients for Type 33A3 fracture. Results The followup of all the patients for 12-26 months averaged 14.5 months revealed that the bone union was completed in all the 26 patients, 1 of whom had a delayed bone union. The X-ray films showed that the time for the bone union was 1136 weeks averaged 16.1weeks, and the time for the full weight loading was 1326 weeks averaged 17.6 weeks. Superficial infection developed in 1 patient, and the infection was curedafter the dressing changes. The internal fixator attachment was performed on 5 patients 613 months after operation, who had a serious pain in the lateral part of the distal femur. No deep infection，loosening of the internal fixation，breakage or failure of the implants was found in all the patients. Evaluated by the Merchant score system for the knee joint, of the 26 patients 13 achieved an excellent result, 11 achieved a good result, and 2 achieved a fair result, with 92.3% excellent and good results. Based on the Rasmussen criteria for the fracture reduction, the 26 patients had standard scores of 1219 with an average of 17.6; of the 26 patients, 16 had an excellent result, 9 had a good result, and 1 had a fair result. Conclusion The LISS is consistent with the principles of biological osteosynthesis on the design, and the system offers a new and effective internal fixation method for treatment of AO Types A3, C2 and C3 fractures. However, its operation indications and operating instructions should be strictly followed.
Objective To study the clinical outcome of comminuted factures at distal femur and proximal tibia treated with AO less invasive stabilization systems (LISS). Methods The clinical data of 14 cases of distal femoral fracture and proximal tibial fracture from September 2003 to May 2005 were analyzed retrospectively. The injury was caused by traffic accident in 9 cases, by fall in 3 cases and by slipping in 2 cases. Of 14 cases, there were 5 open fractures and 9 close fractures, including 5 cases of distal femoral comminuted fracture and 9 cases of proximal shaft comminuted fractures. According to AO/OTA classification, the fractures were classified as 33C2 in 3 cases，33C3 in 2 cases,41A2 in 2 cases，41A3 in 2 cases，41B2 in 3 cases and 41C2 in 2 cases. All patients were treated by the internal fixation with LISS-distal femur or with LISS-proximal tibia. Healing of wounds, the X-ray films before and after operations, and therecovery of joint function were observed. Results The patients were followed up from 1 month to 20 months (11 months on average). Twelve cases achieved solid osseous unions from 3 months to 5 months postoperativly; 2 cases had a good reduction and recovered smoothly 2-3 months postoperatively. The results were excellent in 10 cases, good in 3 cases and fair in 1 case according to Johner-Wruhs knee scoring. The range of knee flexion-extension was 110-130° in 11 cases, 100° in 2 cases and 80° in 1 case. Conclusion LISS is an effective method of internal fixation for treating comminntedfracture of distal femur or proximal tibia. It has the advantages of less injury, satisfied reduction and reliable fixation.