Biomechanical comparison of fixation systems in posterior wall fracture of acetabular by finite element analysis

Semi-automated finite element analyses of surgically treated acetabular fractures to investigate the biomechanical behaviour of patient-specific compared to conventional implants

BACKGROUND

In acetabular fracture surgery, understanding the biomechanical behaviour of fractures and implants is beneficial for clinical decision-making about implant selection and postoperative (early) weightbearing protocols. This study outlines a novel approach for creating finite element models (FEA) from actual clinical cases. Our objectives were to (1) create a detailed semi-automatic three-dimensional FEA of a patient with a transverse posterior wall acetabular fracture and (2) biomechanically compare patient-specific implants with manually bent off-the-shelf implants.

METHODS

A computational study was performed in which we developed three finite element models. The models were derived from clinical imaging data of a 20-year-old male with a transverse posterior wall acetabular fracture treated with a patient-specific implant. This implant was designed to fit the patient's anatomy and fracture configuration, allowing for optimal placement and predetermined screw trajectories. The three FEA models included an intact hemipelvis for baseline comparison, one with a fracture fixated with a patient-specific implant, and another with a conventional implant. Two loading conditions were investigated: standing up and peak walking forces. Von Mises stress and displacement patterns in bone, implants and screws were analysed to assess the biomechanical behaviour of fracture fixation with either a patient-specific versus a conventional implant.

RESULTS

The finite element models demonstrated that for a transverse posterior wall type fracture, a patient-specific implant resulted in lower peak stresses in the bone (30 MPa and 56 MPa) in standing-up and peak walking scenario, respectively, compared to the conventional implant model (46 MPa and 90 MPa). The results suggested that patient-specific implant could safely withstand standing-up and walking after surgery, with maximum von Mises stresses in the implant of 156 MPa and 371 MPa, respectively. The results from the conventional implant indicate a likelihood of implant failure, with von Mises stresses in the implant (499 MPa and 1000 MPa) exceeding the yield stress of stainless steel.

CONCLUSION

This study presents a workflow for conducting finite element analysis of real clinical cases in acetabular fracture surgery. This concept of personalized biomechanical fracture and implant assessment can eventually be applied in clinical settings to guide implant selection, compare conventional implants with innovative patient-specific ones, optimizing implant designs (including shape, size, materials, screw positions), and determine whether immediate full weight-bearing can be safely permitted.

Which implant is better for the fixation of posterior wall acetabular fractures: A conventional reconstruction plate or a brand-new calcaneal plate?

BACKGROUND

Increased posterior wall acetabular fractures among older adults, require precise treatment to restore stability to the joint, lower the risk of degenerative arthritis, and enhance overall functional recovery. The purpose of this study was to compare the fixation stability and mechanical characteristics of calcaneal buttress plate and conventional reconstruction plate under different loading condition.

METHODS

Typical acetabular posterior wall fractures were created on twenty synthetic hemipelvis models. They were fixed with calcaneus plate and reconstruction plate. Dynamic and static tests were performed. Displacements of fracture line and stiffness were calculated.

FINDINGS

After dynamic loading, calcaneus plate fixation has significantly less displacement than the reconstruction plate on the superior posterior wall. Under static loading condition, the calcaneus plate group has significantly less displacement than the reconstruction plate group on the inferior posterior part of the fracture. The average stiffness values of the calcaneus plate group and the reconstruction plate group were 265.16±53.98 N/mm and 167.48±36.87 N/mm, respectively and a statistically significant difference was found between the two groups.

INTERPRETATION

The calcaneal plate group demonstrated better stability along the fracture line after dynamic and static loading conditions. Especially when the fragment was on the acetabulum's superior posterior, inferior posterior, and inferior rim, Calcaneal buttress plates offer biomechanically effective choices.

The survivorship and factors affecting the outcome of the use of spring plates in multifragmentary posterior wall acetabular fractures at a single academic institution

BACKGROUND

Multifragmentary posterior wall fractures are not uncommon after posterior hip fracture-dislocation. They can be elementary but are commonly associated with transverse acetabular fractures. Specific technical challenges are encountered when managing these fracture patterns. The loss of the posterior landmarks due to the associated comminution may render achieving an anatomical reduction and stable fixation difficult. The application of spring plates can provide a good buttress with multiple anchor points and creates a new cortex for the bridging plate.

PURPOSE OF THE STUDY

-To assess the outcome and survivorship of the use of spring plates for the fixation of multi-fragmentary posterior wall fractures. -To analyse the factors affecting the outcome of the fixation of these challenging injuries.

PATIENTS AND METHODS

We retrospectively reviewed all the patients who underwent posterior wall acetabular fixation using a spring plate between December 2009 and March 2020 at our institution. Forty-seven patients had a minimum follow-up of 1 year and were included in the study with a mean age of 36 ± 10 years (range:17-60) and a mean follow-up period of 4.4 ± 3.5 years. Seventeen patients had an associated transverse acetabular fracture, and an anterior columnar screw was used for additional fixation. Functional outcome was assessed using the Oxford hip score (OHS). Radiological assessment was undertaken for the images done immediately post-operatively and at the last follow-up. Patients with advanced post-traumatic arthritis and complications such as avascular necrosis (AVN), nerve injuries, non-union, heterotopic ossification and fixation failure were identified. The hazard rate of re-operation on the native hip was estimated using the life tables. Kaplan Meier analysis was used to assess survival with THR or excision arthroplasty as an endpoint.

RESULTS

Six patients underwent a total hip replacement: secondary to AVN in four and infection in two patients. The hazard of THR was estimated at 6% (SE = 0.02) during the first three years, then decreased dramatically afterwards. The five-year survival of native hip was 83% (SE = 0.06). Native hip was expected to survive for 10.67 years (95% CI 9.49-11.83) without joint replacement. The mean OHS in our cohort was 33.66 (3-48), and 29 patients (61.70%) had an OHS of more than 30.

CONCLUSION

The use of spring plates to fix multifragmentary posterior wall fractures has excellent mid-term results, high survivorship and a low complication rate. Combining an anterior columnar screw and a posterior spring plate has shown to be a suitable fixation construct in selected patients with associated transverse acetabular fractures. A longer-term follow-up with a larger cohort using this fixation construct is needed.

Biomechanical analysis of fixation methods in acetabular fractures: a systematic review of test setups

Purpose

Optimal anatomical reduction and stable fixation of acetabular fractures are important in avoiding secondary dislocation and osteoarthritis. Biomechanical studies of treatment options of acetabular fractures aim to evaluate the biomechanical properties of different fixation methods. As the setup of the biomechanical test can influence the experimental results, this review aimed to analyze the characteristics, comparability and clinical implications of studies on biomechanical test setups and finite element analyses in the fixation of acetabular fractures.

Methods

A systematic literature research was conducted according to the PRISMA guidelines, using the PubMed/MEDLINE and Web of Science databases. 44 studies conducting biomechanical analyses of fixation of acetabular fractures were identified, which met the predefined inclusion and exclusion criteria and which were published in English between 2000 and April 16, 2021. The studies were analyzed with respect to distinct parameters, including fracture type, material of pelvis model, investigated fixation construct, loading direction, loading protocol, maximum loading force, outcome parameter and measurement method.

Results

In summary, there was no standardized test setup within the studies on fixation constructs for acetabular fractures. It is therefore difficult to compare the studies directly, as they employ a variety of different test parameters. Furthermore, the clinical implications of the biomechanical studies should be scrutinized, since several test parameters were not based on observations of the human physiology.

Conclusion

The limited comparability and restricted clinical implications should be kept in mind when interpreting the results of biomechanical studies and when designing test setups to evaluate fixation methods for acetabular fractures.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00068-022-01936-9.

Biomechanical analysis of fixation methods for acetabular fractures: A review

Acetabular fractures are known as one of the most frequent types of pelvic fractures with growing frequency among elderly people. Because of this, it is important to establish the methods of repair that will produce optimal outcomes for fracture healing and joint remobilization. Open reduction and internal fixation are considered as the "gold standard" of acetabular fracture repair; however, to the best of authors' knowledge, there is no systematic review comparing different repair methods from biomechanical point of view. As such, in this review paper, we summarize the results of English language literature biomechanically focused on acetabular fracture fixation methods in the last thirty years with the aim to create a reference for clinical decision making. The selected literature within the review is broken down into categories based on type of fracture, i.e., simple or complex, and then further grouped based on fracture line orientation. Clinical recommendations and future research possibilities are also provided.

Percutaneous fixation of acetabular fractures

The objective of surgery for acetabular fractures is to achieve precise reduction to restore joint congruence, fix internal bone fragments, avoid displacement of the fracture and allow rapid rehabilitation.Open reduction and internal fixation is the benchmark method for displaced acetabular fractures, but open reductions can increase morbidity, causing neurovascular injury, blood loss, heterotopic bone formation, infection and poor wound healing.An anatomical reduction with a gap of 2 mm or less is a predictor of good joint function and reduced risk of post-traumatic osteoarthritis.The percutaneous approach is associated with fewer complications than open techniques, but acetabular geometry makes percutaneous screw insertion a challenging procedure.The percutaneous technique is recommended for non-displaced or slightly displaced fractures, and in obese, osteoporotic and elderly patients who cannot receive total joint arthroplasty.We recommend the use of intramedullary cannulated screws.Fracture reductions are achieved by manual traction of the affected bones. If some fracture displacement remains, accessory windows can be used to introduce a ball spike pusher, a hook or a Steinmann pin which can be used as a joystick to rotate the fracture.In this paper, we describe the accessory windows for the anterior column, the quadrilateral plate and the posterior column. We detail the position, direction and kind of screws used to stabilize the anterior and posterior columns. Cite this article: EFORT Open Rev 2018;3 DOI: 10.1302/2058-5241.3.170054.