Impact of cement-augmented condylar screws in locking plate osteosynthesis for distal femoral fractures - A biomechanical analysis

Comparison of the biomechanical stability of transverse and oblique screw trajectories in retrograde intramedullary nailing of supracondylar femur fractures

BACKGROUND

The goal was to determine the effect of addition of oblique trajectory distal interlock screws to a retrograde intramedullary femoral nail on implant stability (stiffness), cycles to failure and mode of failure. The hypothesis was that addition of oblique screws would increase implant stability and number of loading cycles to failure.

METHODS

Eight matched pairs were tested; one femur implanted with a femoral nail with only transverse distal interlock screws and the other with transverse and oblique interlock screws. Axial compressive load was applied to the femoral head and the gluteal tendon was tensioned vertically to simulate standing or at 45° to the sagittal plane to simulate stair climbing. Loads were cycled to increasing amplitude until failure of fixation (10 mm displacement or 10° rotation).

FINDINGS

In simulated standing, oblique screw specimen had greater sagittal bending (bowing) than transverse only specimen. Transverse (axial) plane motion was higher in simulated stair climbing in oblique screw specimen. Oblique screw specimen had higher sagittal plane translation at 600 N of load. At 300 N, oblique screw specimen had lower internal-external rotation than transverse only specimen. A larger number of cycles to failure were observed in four oblique screw of seven paired specimen. Failure (10 mm or 10 degrees of motion) was only achieved during simulated stair climbing.

INTERPRETATION

Our hypothesis that adding oblique screws improves fixation was rejected. Activities of daily living other than standing may constitute a challenge to fracture fixation; fixation failure occurred at lower loads in simulated stair climbing than standing.

Rethinking the 10% strain rule in fracture healing: A distal femur fracture case series

Since the 1970s, the 2%-10% rule has been used to describe the range of interfragmentary gap closure strains that are conducive for secondary bone healing. Interpreting the available evidence for the association between strain and bone healing remains challenging because interfragmentary strain is impossible to directly measure in vivo. The question of how much strain occurs within and around the fracture gap is also difficult to resolve using bench tests with osteotomy models because these do not reflect the complexity of injury patterns seen in the clinic. To account for these challenges, we used finite element modeling to assess the three-dimensional interfragmentary strain in a case series of naturally occurring distal femur fractures treated with lateral plating under load conditions representative of the early postoperative period. Preoperative computed tomography scans were used to construct patient-specific finite element models and plate fixation constructs to match the operative management of each patient. The simulations showed that gap strains were within 2%-10% only for the lowest load application level, 20% static body weight (BW). Moderate loading of 60% static BW and above caused gap strains that far exceeded 10%, but in all cases, strains in the periosteal region external to the fracture line remained low. Comparing these findings with postoperative radiographs suggests that in vivo secondary healing of distal femur fractures may be robust to early gap strains much greater than 10% because formation of new bone is initiated outside the gap where strains are lower, followed by later consolidation within the gap.

Surgical Management and Outcomes following Pathologic Hip Fracture—Results from a Propensity Matching Analysis of the Registry for Geriatric Trauma of the German Trauma Society

Background and Objectives: The outcomes of patients with pathologic hip fractures remain unclear. Data from a large international geriatric trauma registry were analyzed to examine the outcomes of patients with pathologic hip fractures compared with patients with typical osteoporotic hip fractures. Materials and Methods: Data from the Registry for Geriatric Trauma of the German Trauma Society (Deutsche Gesellschaft für Unfallchirurgie (DGU)) (ATR-DGU) were analyzed. All patients treated surgically for osteoporotic or pathologic hip fractures were included in this analysis. Across both fracture types, a 2:1 optimal propensity score matching and multivariate logistic regression analysis were conducted. In-house mortality rate and mortality at the 120-day follow-up, as well as mobility after 7 and 120 days, reoperation rate, discharge management from the hospital and readmission rate to the hospital until the 120-day follow-up were analyzed as outcome parameters for the underlying fracture type—pathologic or osteoporotic. Results: A total of 29,541 cases met the inclusion criteria. Of the patients included, 29,330 suffered from osteoporotic fractures, and 211 suffered from pathologic fractures. Multivariate logistic regression analysis revealed no differences between the two fracture types in terms of mortality during the acute hospital stay, reoperation during the initial acute hospital stay, walking ability after seven days and the likelihood of being discharged back home. Walking ability and hospital readmission remained insignificant at the 120-day follow-up as well. However, the odds of passing away within the first 120 days were significantly higher for patients suffering from pathologic hip fractures (OR: 3.07; p = 0.003). Conclusions: Surgical treatment of pathologic hip fractures was marked by a more frequent use of arthroplasty in per- and subtrochanteric fractures. Furthermore, the mortality rate among patients suffering from pathologic hip fractures was elevated in the midterm. The complication rate, as indicated by the rate of readmission to the hospital and the necessity for reoperation, remained unaffected.

Cement distribution and initial fixability of trochanteric fixation nail advanced (TFNA) helical blades

INTRODUCTION

Early fixation and rehabilitation is the gold standard treatment for intertrochanteric femur fractures. To avoid postoperative complications such as cut-out or cut-through, cement augmentation with perforated helical blades has been developed. The purpose of this study was to evaluate the distribution of injected cement at the head-neck portion of proximal femur using computed tomography (CT) and to examine its initial fixability and clinical outcomes.

PATIENTS AND METHODS

Elderly patients who had intertrochanteric fractures were treated with a helical blade only (BO group) or with a helical blade and cement augmentation (CA group). After fracture reduction, trochanteric fixation nail advanced (TFNA) helical blades were inserted, aiming at the center/center position with 20 mm of tip-apex distance. In the CA group, 4.2 mL of cement was injected under an image intensifier (1.8 mL of cement was directed cranially and 0.8 mL each was directed to the caudally, anteriorly, and posteriorly). Patient demographics, radiographic parameters with CT, and post-operative clinical outcome were examined.

RESULTS

Each group included nine patients with similar demographics. Maximum penetration depth (MPD) in the CA group was significantly greater than those in the BO group for all four directions (p < 0.01). In the CA group, the anterior MPD was significantly greater than the posterior (p < 0.01) and the cranial (p = 0.02) MPD. Surface area and volume in the CA group were two-times and three-times larger than that in the BO group, respectively. Among radiographic parameters, ΔRotation angle in the CA group was significantly smaller than that of the BO group (p = 0.03). For the ΔParker score, the CA group showed less of a decrease than in the BO group (p < 0.01). Visual analog scale (VAS) for the passive range of motion (ROM) and for full-load walking in the CA group was significantly lower than those in the BO group (p < 0.01).

CONCLUSIONS

The initial fixability of the TFNA helical blade with cement augmentation demonstrated double the surface area and triple the volume. This suppressed implant micro-motion, reduced postoperative pain, and accelerated rehabilitation in the acute phase.

Boundary Conditions Matter - Impact of Test Setup On Inferred Construct Mechanics in Plated Distal Femur Osteotomies

The mechanics of distal femur fracture fixation has been widely studied in bench tests that employ a variety of approaches for holding and constraining femurs to apply loads. No standard test methods have been adopted for these tests and the impact of test setup on inferred construct mechanics has not been reported. Accordingly, the purpose of this study was to use finite element models to compare the mechanical performance of a supracondylar osteotomy with lateral plating under conditions that replicate several common bench test methods. A literature review was used to define a parameterized virtual model of a plated distal femur osteotomy in axial compression loading with four boundary condition sets ranging from minimally to highly constrained. Axial stiffness, longitudinal motion, and shear motion at the fracture line were recorded for a range of applied loads and bridge spans. The results showed that construct mechanical performance was highly sensitive to boundary conditions imposed by the mechanical test fixtures. Increasing the degrees of constraint, for example by potting and rigidly clamping one or more ends of the specimen, caused up to a 25x increase in axial stiffness of the construct. Shear motion and longitudinal motion at the fracture line, which is an important driver of interfragmentary strain, was also largely influenced by the constraint test setup. These results suggest that caution should be used when comparing reported results between bench tests that use different fixtures and that standardization of testing methods is needed in this field.

More than a reposition tool: additional wire cerclage leads to increased load to failure in plate osteosynthesis for supracondylar femoral shaft fractures

INTRODUCTION

Surgical treatment of supracondylar femoral fractures can be challenging. An additional wire cerclage is a suggested way to facilitate fracture reduction prior to plate osteosynthesis. Denudation to the periosteum remains a problematic disadvantage of this procedure. This study analyzed the effect of an additional wire cerclage on the load to failure in plate osteosynthesis of oblique supracondylar femoral shaft fractures.

MATERIALS AND METHODS

On eight pairs of non-osteoporotic human femora (mean age 74 years; range 57-95 years), an unstable AO/OTA 32-A2.3 fracture was established. All specimens were treated with a polyaxially locking plate. One femur of each pair was randomly selected to receive an additional fracture fixation with a wire cerclage. A servohydraulic testing machine was used to perform an incremental cyclic axial load with a load to the failure mode.

RESULTS

Specimens stabilized with solely plate osteosynthesis failed at a mean load of 2450 N (95% CI: 1996-2904 N). In the group with an additional wire cerclage, load to failure was at a mean of 3100 N (95% CI: 2662-3538 N) (p = 0.018). Compression deformation with shearing of the condyle region through cutting of screws out of the condylar bone was the most common reason for failure in both groups of specimens. Whereas axial stiffness was comparable between both groups (p = 0.208), plastic deformation of the osteosynthesis constructs differed significantly (p = 0.035).

CONCLUSIONS

An additional wire cerclage significantly increased the load to failure. Therefore, an additional cerclage represents more than just a repositioning aid. With appropriate fracture morphology, a cerclage can significantly improve the strength of the osteosynthesis.

Cement augmentation of an angular stable plate osteosynthesis for supracondylar femoral fractures - biomechanical investigation of a new fixation device

Background

Implant anchorage in highly osteoporotic bone is challenging, since it often leads to osteosynthesis failure in geriatric patients with supracondylar femoral fractures. Cementation of screws is presumed to prevent such osteosynthesis failure. This study aimed to investigate the effect of a newly designed, cementable fenestrated condylar screw for plate fixation in a biomechanical setting.

Methods

Eight pairs of osteoporotic cadaver femora with an average age of 77 years, ranging between 62 and 88 years, were randomly assigned to either an augmented or a non-augmented group. In both groups an instable 33-A3 fracture according to the AO / OTA classification was fixed with an angular stable locking plate. All right samples received a cement augmentation of their fenestrated condylar screws with calcium phosphate bone cement (CPC). Mechanical testing was performed at a load to failure mode by cyclic axial loading, using a servohydraulic testing machine.

Results

With a mean of 2475 N (95% CI: 1727–3223 N), the pressure forces resulting in osteosynthesis failure were significantly higher in specimen with cemented condylar screws as compared to non-cemented samples (1875 N (95% CI: 1320–2430 N)) (p = 0.024). In both groups the deformation of the constructs, with the distal screws cutting through the condylar bone, were the most frequent cause for failure. Analysis of axial stiffness (p = 0.889) and irreversible deformity of the specimens revealed no differences between the both groups (p = 0.161). No cement leakage through the joint line or the medial cortex was observed.

Conclusion

Based on the present study results, the newly introduced, cementable condylar screw could be an encouraging feature for the fixation of supracondylar femoral fractures in patients with reduced bone quality in terms of load to failure accuracy of the cement application.

[Treatment of patients with fragility fractures]

BACKGROUND

Fragility fractures are fractures in multimorbid, geriatric patients. Currently, their number is already high and is likely to increase in the future.

OBJECTIVE

This article gives an overview of the principles in the management of patients with fragility fractures.

MATERIAL AND METHODS

A selective literature review was performed to describe the epidemiology and relevance of fragility fractures. In addition, the principles of the perioperative management and surgical treatment of patients with fragility fractures are shown.

RESULTS

Due to the significant number of comorbidities, the treatment of patients with fragility fractures represents an interdisciplinary challenge. Ideally, treatment should be carried out in an interdisciplinary team under the leadership of orthopedic surgeons and geriatricians. Treatment should be based on consensus guidelines, which have been adapted to the local circumstances. Attention should be paid to some special aspects of the surgical treatment in this vulnerable patient cohort. Important are optimal soft tissue management, cement augmentation procedures and joint replacement in cases of periarticular fractures.

CONCLUSION

There is evidence that with optimal care the treatment of patients with fragility fractures can be significantly improved.

Cement augmentation of glenoid baseplate screws does not improve primary stability in reversed shoulder arthroplasty: A cadaveric study

INTRODUCTION

Cuff tear arthritis and complex proximal humeral fractures are common pathologies that are frequently addressed by the implantation of a reversed shoulder prosthesis. The present cadaveric study aimed to analyze the effect of cement augmentation of the glenoid component on the primary stability in geriatric patients.

HYPOTHESIS

Cement augmentation of glenoid baseplate screws has an influence on primary stability in reversed shoulder arthroplasty (RSA).

MATERIALS AND METHODS

Glenoid base plates (Delta Xtend, DePuy Synthes, Westchester, USA) were implanted in 6 pairs of formalin-fixated scapulae of 4 female and 2 male donors (average age 83 years). Two angle stable screws were placed at the superior and inferior position. Cement augmentation was performed with 2ml bone cement (Kyphon, Medtronic, Minneapolis, USA) per screw in right specimens. Afterwards, biomechanical testing with 600 to 1000N (100 cycles) at a 65° abduction angle was performed. Finally, a load-to-failure analysis was conducted.

RESULTS

No implant loosening was observed during cyclic tests from 600N to 1000N. In addition no difference in the plastic deformation was detected at 600N (p=0.301), 700N (p=0.522), 800N (p=0.480), 900N (p=0.521) and 1000N (p=0.748). Load-to-failure analyses revealed implant loosening at 3314N (SD 823N) in the cement-augmented implants and at 3059N (SD 974N) in scapulae with non-cemented screws (p=0.522).

DISCUSSION

Cement-augmented fixation of the glenoid component did not result in an increased primary stability in this study. Thus, the application of cement should be critically assessed considering associated risks and increased costs.

LEVEL OF PROOF

Basic science study, controlled laboratory study.