Biomechanical Research of Three Parallel Cannulated Compression Screws in Oblique Triangle Configuration for Fixation of Femoral Neck Unstable Fractures

OBJECTIVE

Surgical treatment with internal fixation, specifically percutaneous fixation with three cannulated compression screws (CCSs), is the preferred choice for young and middle-aged patients. The mechanical advantage of the optimal spatial configuration with three screws provides maximum dispersion and cortical support. We suspect that the spatial proportion of the oblique triangle configuration (OTC) in the cross-section of the femoral neck isthmus (FNI) may significantly improve shear and fatigue resistance of the fixed structure, thereby stabilizing the internal fixation system in femoral neck fracture (FNF). This study aims to explore the mechanical features of OTC and provide a mechanical basis for its clinical application.

METHODS

Twenty Sawbone femurs were prepared as Pauwels type III FNF models and divided equally into two fixation groups: OTC and inverted equilateral triangle configuration (IETC). Three 7.3 mm diameter cannulated compression screws (CCSs) were used for fixation. The specimens of FNF after screw internal fixation were subjected to static loading and cyclic loading tests, respectively, with five specimens for each test. Axial stiffness, 5 mm failure load, ultimate load, shear displacement, and frontal rotational angle of two fragments were evaluated. In the cyclic loading test, the load sizes were 700 N, 1400 N, and 2100 N, respectively, and the fracture end displacement was recorded. Results were presented as means ± SD. Data with normal distributions were compared by the Student's t test.

RESULTS

In the static loading test, the axial stiffness, ultimate load, shear displacement, and frontal rotational angle of two fragments were (738.64 vs. 620.74) N/mm, (2957.61 vs. 2643.06) N, (4.67 vs. 5.39) mm, and (4.01 vs. 5.52)° (p < 0.05), respectively. Comparison between the femoral head displacement after 10,000 cycles of 700N cyclic loading and total displacement after 20,000 cycles of 700-1400N cyclic loading showed the OTC group was less than the IETC group (p < 0.05). A comparison of femoral head displacement after 10,000 cycles of 1400N and 2100N cycles and total displacement after 30,000 cycles of 700-2100N cycles showed the OTC group was less than another group, but the difference was not significant (p > 0.05).

CONCLUSION

When three CCSs are inserted in parallel to fix FNF, the OTC of three screws has obvious biomechanical advantages, especially in shear resistance and early postoperative weight-bearing, which provides a mechanical basis for clinical selection of ideal spatial configuration for unstable FNF.

Gamma Nail Combined with One Cannulated Compression Screw Fixation for Treating Pauwels Type III Femoral Neck Fractures in Young and Middle-Aged Adults: Clinical Follow-Up and Biomechanical Studies

OBJECTIVE

Recently, some clinical studies have reported the use of an intramedullary nailing system for treating unstable femoral neck fractures or femoral neck fractures combined with femoral shaft fractures in young adults, and the results have indicated certain advantages. However, no study has investigated the mechanical properties of this method. We aimed to evaluate the mechanical stability and clinical efficacy of the Gamma nail combined with one cannulated compression screw (CCS) fixation for treating Pauwels type III femoral neck fracture in young and middle-aged adults.

METHODS

This study consists of two parts: a clinical retrospective study and randomized controlled biomechanical test. Twelve adult cadaver femora were used to test and compare the biomechanical properties among three fixation methods: three parallel CCS (group A), Gamma nail (group B), and Gamma nail combined with one cannulated compression screw (group C). The single continuous compression test, cyclic load test, and ultimate vertical load test were used to evaluate the biomechanical performance of the three fixation methods. We also conducted a retrospective study of 31 patients with Pauwels type III femoral neck fractures, including 16 patients with fractures fixed with three parallel CCS (CCS group) and 15 patients with fractures fixed with Gamma nail combined with one CCS (Gamma nail + CCS group). The patients were followed up for at least 3 years, and all were evaluated for surgical time (from skin incision to closure), surgical blood loss, hospital stay, and the Harris hip score.

RESULTS

In mechanical experiments, we have found that the mechanical advantages of Gamma nail fixation are not as good as those of conventional CCS fixation. However, the mechanical properties of Gamma nail fixation combined with one cannulated screw perpendicular to the fracture line are much better than those of Gamma nail fixation and CCS fixation. No significant difference was found in the incidence of femoral head necrosis and nonunion between the CCS and Gamma nail + CCS groups. Moreover, there was no statistically significant difference in the Harris hip scores between the two groups. One patient in the CCS group showed significant withdrawal of cannulated screws at 5 months after surgery, whereas in the Gamma nail + CCS group, all patients, including those with femoral neck necrosis, showed no loss of stability of the fixation.

CONCLUSION

Among the two fixation methods evaluated in this study, Gamma nail combined with one CCS fixation showed better biomechanical properties and may reduce complications associated with unstable fixation devices.

Biomechanical Properties of Bionic Collum Femoris Preserving Hip Prosthesis: A Finite Element Analysis

OBJECTIVE

Compared with total hip replacement, conventional collum femoris preserving prosthesis has a better bone retention effect. However, damage to the trabecular bone of the proximal femur leads to inevitable abnormal stress distribution, which leads to increased risks of femoral neck bone absorption, periprosthetic fracture, prosthesis loosening, rotation, and sinking. Thus, we compare the biomechanical properties of collum femoris preserving (CFP) and bionic collum femoris preserving (BCFP) hip prostheses.

METHODS

The Sawbone digital model (#3503, left, medium) was selected as the research object. We used the Mimics 21.0 software to reconstruct the digital model of the femur and the SolidWorks 2019 software to build and assemble the three-dimensional models of CFP and BCFP prostheses. With the ANSYS Workbench 2021R1 software, the models were meshed and assigned values to simulate the load of a single foot under slow walking. We measured the mechanical distribution of the whole model and obtained the stress nephogram.

RESULTS

For CFP prosthesis, the peak stresses of the medial interface of the stem neck, the lateral interface of the stem neck, and the end of the stem were 64.894, 32.199, and 8.578 MPa, respectively; the peak stresses of the medial surface of the femoral shaft, the lateral surface of femoral shaft, the medial femoral neck bone-prosthesis interface (osteotomy interface), the lateral femoral neck bone-prosthesis interface (basal area), the lateral femoral neck bone-prosthesis interface (osteotomy interface), and the greater trochanter area were 28.093, 24.790, 14.388, 5.118, 4.179, and 8.245 MPa, respectively; the valley stress of the greater trochanter area was 1.134 MPa. For BCFP prosthesis, the peak stresses of the medial interface of the stem neck, the lateral interface of the stem neck, and the end of the stem were 47.015, 26.771, and 47.593 MPa, respectively; the peak stress of tension screw was 15.739 MPa; the peak stresses of the medial surface of the femoral shaft, the lateral surface of femoral shaft, the medial femoral neck bone-prosthesis interface (osteotomy interface), the lateral femoral neck bone-prosthesis interface (basal area), the lateral femoral neck bone-prosthesis interface (osteotomy interface) and the greater trochanter area were 28.581, 25.364, 15.624, 6.434, 4.986, and 8.796 MPa, respectively; the valley stress of the greater trochanter area was 1.419 MPa; the peak stress of bone-metal interface between the tension screw and the lateral surface of the femur was 5.858 MPa.

CONCLUSION

Compared with the CFP prosthesis, the design of the BCFP prosthesis is based on the lever balance theory. With the bionic reconstruction of tension trabeculae, BCFP prosthesis makes up for the defects of CFP prosthesis design, optimizes the stress distribution, and reduces the stress shelter effect of the proximal femur, which has better biomechanical properties.

Hollow-bone-graft dynamic hip screw can fix and promote bone union after femoral neck fracture: an experimental research

BACKGROUND

Delayed bone union, nonunion or osteonecrosis often occur after femoral neck fractures in young adults. Secondary bone healing requires strong internal fixation, intramedullary pressure reduction and early functional exercise.

OBJECTIVE

To compare bone healing of femoral neck fractures treated with hollow-bone-graft dynamic hip screws (Hb-DHS) and standard dynamic hip screws (DHS) in an animal model.

DESIGN

Testing of specifically designed fixation devices in a pig animal model.

INTERVENTIONS/METHODS

We designed Hb-DHS and DHS devices appropriate to the femoral neck and head of experimental animals and used them in eight pigs (4-month-old, male or female, 30-40 kg/each). Under anesthesia, we induced medium neck type, Garden III type femoral neck fractures in each pig with fracture gaps of 0.5 mm and then fixed each left femur with Hb-DHS and each right femur with DHS. We assessed the animals radiographically and by postmortem visual appraisal of evidence of bone healing 8 and 16 weeks postoperatively.

RESULTS

There were significant differences in radiographic and general findings between the Hb-DHS and DHS groups at weeks 8 and 16 postoperatively. We found statistically significant differences between the Hb-DHS and DHS groups in bone healing scores, trabecular bone volume percentage and bone mineral density as assessed on plain radiographs and computed tomography images (P < 0.05). There were also significant differences between the Hb-DHS and DHS groups in postmortem visually assessed indicators of bone healing at both 8 and 16 weeks postoperatively.

CONCLUSIONS

The Hb-DHS device promotes femoral neck bone union, stimulates trabecular bone formation, increases BMD and has advantages over DHS for internal fixation of femoral neck fractures. This animal experiment will contribute to developing optimal treatment for femoral neck fractures in young adults.

Use of the patellar-pubic percussion test in the diagnosis and management of a patient with a non-displaced hip fracture

This case report describes the diagnosis and subsequent medical and physical therapy management of a 68-year-old patient with an undiagnosed non-displaced hip fracture. Initial plain film radiographs and a computed tomography (CT) scan of the involved hip were both interpreted as negative. One of the findings on the physical examination included a positive patellar-pubic percussion test (PPPT). This finding in a female patient of this age raised the suspicion of an occult hip fracture and she was referred back to her primary care physician. Repeat radiographs revealed a non-displaced hip fracture and the patient was treated surgically. The PPPT is an easy-to-implement clinical examination tool that may be extremely useful in physical therapy practice to guide the decision-making process for patients with suspected hip fractures. The utilization of the PPPT by the treating physical therapist for the patient in this case report contributed to a timely diagnosis, potentially preventing the disabling sequelae associated with a displaced femoral fracture.