Abstract
Aims
The main treatment method for distal femoral fractures is open reduction and internal fixation with a lateral locking plate. However, the literature indicates that the failure rate for this method is high, the healing is slow, and the prognosis is poor. Therefore, this study aimed to solve the problems of high failure rate and poor rehabilitation.
Methods
Data from 140 patients with AO/OTA type 33 A/33 C fractures (September 2014 to December 2023) were retrospectively analyzed. After excluding 20 cases (loss to follow-up, Gustilo III fractures, polytrauma), 120 patients were categorized into three groups: locking compression plate (LCP) alone, LCP + percutaneous medial column screws (PMCS), and LCP + auxiliary inner locking plate (ALP). An A3 fracture model of the distal femur with medial bone defect was established to explore the maximum stress and maximum displacement. Biomechanical simulations were carried out under axial, torsional, and bending loads. Clinical outcomes, finite element analysis, and biomechanical tests were compared.
Results
The LCP + PMCS technique showed better therapeutic effects compared with the other two groups. There were significant differences in fracture healing time (p < 0.001), range of knee joint motion (p < 0.001), and incidence of complications (p = 0.007). The finite element analysis results showed that the maximum stress and displacement of LCP + PMCS made it the optimal method among the three groups. Biomechanical tests confirmed that LCP + PMCS had higher yield load and stiffness.
Conclusion
LCP combined with PMCS offers enhanced biomechanical stability, reduced complications, and minimally invasive advantages, making it a promising strategy for distal femoral fractures, particularly in elderly and osteoporotic patients.
Cite this article: Bone Joint Res 2026;15(1):73–87.
Keywords: Distal femoral fracture, Finite element analysis, Biomechanics, distal femoral fractures, locking plate, locking plate, medial column, stiffness, distal femoral, biomechanical tests, locking compression plate, lateral locked plating
Article focus
This study comprehensively investigated the advantages of the lateral locking compression plate combined with percutaneous medial column screws in the treatment of distal femoral fractures through clinical retrospective analysis, finite element analysis, and biomechanical experiments.
Key messages
Clinical retrospective analysis showed that LCP+PMCS group had shorter healing time, better effect, and fewer complications.
The finite element analysis showed that the stress distribution of implants and femur in the LCP+PMCS group was more advantageous.
Biomechanical experiments showed that the LCP+PMCS group had better axial and torsional loading effects.
Strengths and limitations
This study employed three complementary verification methods: finite element analysis, biomechanical simulation, and clinical retrospective analysis.
In finite element analysis, the properties of bone materials are simplified to isotropic materials, while the influence of other soft-tissues on load distribution and structural stability is ignored.
Introduction
Distal femoral fractures, representing 3% to 6% of all femoral fractures, pose significant clinical challenges.1 Despite advances, nonunion rates remain alarmingly high (18% to 20%), and the one-year mortality rate for patients aged over 60 years exceeds 35%.1,2 These fractures are frequently displaced, intra-articular, and comminuted, complicating treatment. Their prevalence in the elderly population further exacerbates the problem, as osteoporosis demands exceptional stability from fixation constructs to promote healing and withstand physiological loads.3-6 The lateral locking compression plate (LCP) is a widely employed surgical solution. However, reported failure rates are concerning, with nonunion reaching 19% and implant failure as high as 20%.1,7 A key biomechanical limitation of isolated lateral plating is its inability to reliably counteract varus collapse, particularly in the presence of medial column comminution or bone loss.8 Recognizing this vulnerability, strategies to augment medial stability emerged. The addition of the auxiliary inner locking plate (ALP) considerably enhances the fixation strength. Both clinical studies and finite element analyses have found that, compared with a single plate, the improved mechanical properties lead to a higher healing rate.9-11 Furthermore, double plating is a suitable option for periprosthetic distal femur fracture compared to single-plate fixation.12 However, this double-plate approach requires extensive stripping, increasing the operating time and cost, as well as the risk of soft-tissue complications and infections. It is especially harmful to the elderly or high-risk patients and may cause excessive stiffness, which may lead to delayed healing or non-healing.13
The critical importance of restoring medial column support to prevent varus collapse and fixation failure has been increasingly recognized over the past two decades. Heiney et al14 were instrumental in highlighting the biomechanical vulnerability of the medial femoral condyle and its contribution to varus malalignment following lateral locked plating. This foundational work spurred the development of less invasive strategies to augment medial stability. The concept of ‘blocking screws’, initially used in intramedullary nailing, was adapted for the distal femur metaphysis.15 Placed strategically in the zone of instability, these screws narrow the effective structure, aid reduction, and crucially, provide indirect medial column support by substantially increasing the stiffness of the lateral plate construct against varus forces.16 This concept evolved into the standardized technique of placing dedicated percutaneous medial column screws (PMCS), positioned specifically to buttress the critical medial cortex or major metaphyseal fragments. The combination of a lateral LCP with adjunctive PMCS has thus emerged as a mature and widely employed solution for achieving stable fixation in complex AO/OTA type 33 A and 33 C fractures with medial column compromise, offering a potentially less invasive alternative to dual plating. While both ALP and PMCS aim to address the medial column deficiency, they represent fundamentally different strategies with distinct biological and mechanical implications. ALP provides direct, rigid medial buttressing, but at the cost of substantial soft-tissue disruption. PMCS, in contrast, offers a relatively minimally invasive method of achieving medial column support indirectly through the lateral plate, potentially preserving biology, reducing construct stiffness closer to the ideal for promoting fracture healing via controlled micromotion, and lowering complication risks associated with extensive dissection. Although the LCP + PMCS technique is clinically established, direct comparisons of its clinical outcomes, biomechanical performance, and complication profile against both the LCP + ALP and LCP alone approaches, particularly supported by integrated biomechanical analysis, remain valuable for refining surgical decision-making.
Therefore, the present study aimed to clinically compare the outcomes and complications of distal femoral fractures treated with LCP alone, LCP + ALP, and LCP + PMCS; complement clinical findings with finite element analysis (FEA) and biomechanical experiments to evaluate and compare the stability, load distribution, and stress characteristics of these three fixation constructs under physiological loading conditions; and synthesize clinical and biomechanical evidence to provide a comprehensive theoretical basis for optimizing the surgical management of complex distal femoral fractures.
Methods
This study intends to conduct analysis through retrospective research, FEA, and biomechanical test simulation to form a reasonable research closed loop and prove the advantages of the PMCS + LCP surgical protocol at multiple levels.
Clinical retrospective study
The sample size was calculated based on the GPower software. The sample sizes of the three groups were calculated using the one-way model. The Effect size f = 0.4, α = 0.05, and Power = 0.95. It was calculated that the total sample size required was 102, with 34 cases in each group. This study was approved by the Ethics Committee of Jinshan Branch, Shanghai Sixth People’s Hospital. The ethical inclusion criteria were patients aged over 18 years with distal femoral supracondylar fractures or supracondylar/intercondylar fractures (AO/OTA 33 A and 33 C fractures). Reviewing the trauma database collected at our hospital from January 2014 to December 2023, 140 AO/OTA type 33 A/33 C fractures were identified for possible inclusion. Exclusion criteria were as follows: 1) the patient was lost to follow-up before fracture union; 2) Gustilo type III open fracture; or 3) severe multiple trauma. After excluding these patients, a total of 120 fractures (120 patients) were included in the study.
We chose different surgical methods according to each patient’s specific conditions and wishes. The standards for performing different types of surgeries are as follows: 1) unilateral fracture; 2) aged over 75 years, 33 C comminuted fracture with deviated fracture line; 3) the patient’s overall condition is poor and, in accordance with their own wishes, high-risk surgeries with large incisions are not performed.
For patients with unilateral injuries and fractures, a plate is sufficient for stable fixation. However, for older patients with 33 C comminuted fractures, double-plate fixation is preferred. Depending on the fracture line, it is difficult to fix many screws at the distal end of the lateral plate when it is tilted from the inside above to the outside below. According to this situation, we also chose to add a steel plate on the inside, and chose the outer locking plate and the front inner locking plate for fixation. In the other cases mentioned above, we chose the lateral LCP combined with the percutaneous inner column screw technique for fixation.
We collected and compared the general information of different groups of patients. The results during hospitalization and follow-up were mainly studied, especially the surgical effect and postoperative complications were compared. We reviewed radiographs and charts, and also carefully reviewed inpatient-related records, to minimize the risk that any injury might have been missed.
Healing time is the main evaluation index of this study. The evaluation of surgical effect included many indexes, such as operating time, intraoperative blood loss, residence time, fracture healing time, and knee joint range of motion.
The evaluation of postoperative complications included knee stiffness, surface infection, deep infection, bone nonunion, and the need for a second operation. Reducing the occurrence of complications is one aspect of evaluating the effectiveness of the surgery. This not only alleviates patient suffering, but also reduces their financial burden. The surgical instruments and consumables used for all patients were produced by the same company (Besdata, China). All surgeries were performed by the same team of doctors, led by CZ and JH. We try our best to strictly regulate some details and reduce some differences to make the experimental results more convincing.
Finite element analysis
To create a finite element model of A3 fracture of distal femur with medial bone defect and internal fixation system, the distal femoral fracture-internal fixation system was established. According to the experimental design, the internal fixation methods were divided into three groups: single titanium plate, single titanium plate + double cancellous bone nail, and double titanium plate. UG 12.0 software (Siemens, Germany) was used to assemble the femoral cortex and cancellous bone, and assemble them with a single titanium plate, a single titanium plate + double cancellous bone nails, and a double titanium plate to build different models under three working conditions (Supplementary Figure a).
After importing the assembled femur model into Ansys Workbench (USA), the coordinate system was established and the finite element calculation of a 3D solid model of femoral fracture-internal fixation system was performed.
The femur and internal fixation system in the model were set as a homogeneous, isotropic, and continuous elastic material. The elastic moduli of cortical bone, cancellous bone, titanium, and titanium alloy were set to 17,800, 3,230 and 113,800 MPa, respectively. The Poisson ratios for cortical bone, cancellous bone, titanium, and titanium alloys were 0.30, 0.30, and 0.34, respectively (Supplementary Table i).
The corresponding contact relationship was set according to the actual state of the locking screw, titanium plate system, and femur during assembly and use. Among them, the threaded contact segment between the locking screw and the titanium plate, and between the locking screw and the femur, was set as bonded contact, and the sliding contact between the titanium plate and the femur was set as sliding contact, with a friction coefficient of 0.3 (Supplementary Figure b).17
For the compressive load, the mechanical axis of the femur formed by the centre of the femoral head and the centres of the medial and lateral ankles was made vertical. Through the load module of the software, the distal end of the assembled femoral model is set to be completely fixed, i.e., the degrees of freedom of displacement in the x, y, and z directions are 0. A vertical downward loading of 1,185.5 N was applied to the centre of the femoral head, approximately 237.7% of an adult’s body weight.18 We simulated the load conditions in line with the requirements of daily human movement (Supplementary Figure c). For the torsional load, through the load module of the software, the distal end of the assembled femoral model was set to be completely fixed, i.e., the degrees of freedom of displacement in the x, y, and z directions are 0. A torsional load of 10 N·m around the mechanical axis of the femur was applied to the centre of the femoral head (Supplementary Figure d). For the bending load, through the load module of the software, the mechanical axis of the assembled femoral model was set to be completely fixed at 1/4, i.e., the degrees of freedom of displacement in the x, y, and z directions are 0. We applied displacement loads perpendicular to the mechanical shaft near and near the distal end of the femoral head to simulate the situation where the femoral head is bent (Supplementary Figure e).19
The finite element model was established by grid division (Supplementary Figure f, Supplementary Table ii). At the same time, the Mises strength theory was used to verify the success of the finite element model, and the stress cloud diagram and displacement cloud diagram of the bone plate, the stress cloud diagram of the femur, and the displacement cloud diagram of the fracture end were obtained, respectively. The maximum stress was the weak point of the component, and the maximum Mises stress and displacement of the femoral fracture end and the internal fixation system were calculated to evaluate the risk of internal fixation fracture and the possibility of bone absorption at the fracture end; the biomechanical stability of the three fixation schemes was compared.
Biomechanical experiments
Nine osteoporotic simulated bones were used in this study, which differed from standard simulated bones in that the cortical wall was thin and low density, and hollow artificial bone was used to simulate the clinical manifestations of osteoporosis. The plates were pure titanium and the screws were titanium alloy, which met the requirements of the national GB/T 13810-2007 standard. In all samples, an osteotomy mode was used to simulate a fracture of the distal supracondylar femur. A bone segment of approximately 10 mm in length was cut off with a saw blade 60 mm from the intercondylar fossa, perpendicular to the mechanical axis of the femur. All osteotomy procedures were performed by the same trained experimenter (JC) to maintain consistency.
The specimens were divided into three groups, with three specimens in each group and three surgical fixation methods (Supplementary Figure g).
For the single titanium plate system, each sample was fixed with the lateral distal femoral locking plate (8-well 5.0 mm series LCP). The lateral plate was fixed by four locking screws distally and four locking screws proximally.
For the single titanium plate + cancellous bone nail system, each sample was fixed with distal femoral lateral locking plate (8-well series 5.0 mm LCP) and two φ6.5 mm × 120 mm cancellous bone screws. The lateral plate was secured by four locking screws at the distal end and four locking screws at the proximal end.
For the dual titanium plate system, each sample was fixed with distal femoral lateral locking plate (8-well 5.0 mm series LCP) and medial plate (10-well 3.5 mm series LCP). The lateral plate was fixed with four locking screws distal and four locking screws proximal, and the medial plate was fixed with three locking screws distal and three locking screws proximal.
The axial load test and torsional load test were carried out to determine the axial stiffness, yield load, yield displacement, torsional stiffness, and ultimate angular displacement of the three sample groups.
One simulated bone from each group was taken for axial loading test. The simulated bone model was rotated 7° valgus and fixed on the electronic material testing machine through a ‘U’ shape fixture and embedding media such as dental stone to ensure that the axial load direction passed through the mechanical axis of the femur. Considering that this experiment mainly explores the mechanical properties of three surgical fixation systems, in order to reduce the influence of the simulated bone, the proximal femur of the simulated bone was cut off at 70 mm from the centre of the femoral head (Supplementary Figure h). The treated samples were fixed on the testing machine, and a compressive load was applied to simulate the stress state of the femur during normal walking. The simulated bone was prefixed with a load of 100 N, and then loaded at a speed of 10 mm/min until the sample yielded. The load-displacement curve was recorded, and the axial stiffness, yield load, and yield displacement of the sample were calculated.
Two simulated bones were taken from each group for torsional load test. The two ends of the simulated bone model were fixed on the electronic torsion testing machine through the embedding media such as ‘U’ type fixture and denture base powder. No external force was applied at first, and then a torque of 8 Nm was applied to the model from clockwise and counterclockwise directions at a speed of 0.1 Nm/s.
Statistical analysis
Statistical analysis was conducted using R 4.3.2 software (R Foundation for Statistical Computing, Austria). Measurement data that conformed to the normal distribution were expressed as mean (SD), and those that did not conform to the normal distribution were expressed as median (IQR). For the data conforming to the normal distribution, the independent-samples t-test was used for comparison between two groups, and one-way analysis of variance was used for comparison between multiple groups. For data that did not conform to the normal distribution, the Mann-Whitney U test was used for comparison between two groups, and the Kruskal-Wallis(H) test was used for comparison between multiple groups. For the count data, frequency and percentage descriptions were used, and the chi-squared test or Fisher’s exact probability method was used to compare the differences between groups. A p-value < 0.05 was considered statistically significant.
Results
Results of a retrospective study
We conducted statistical analyses on the general patients’ conditions (Table I) and the observation results during hospitalization and follow-up (Table II). The results showed that there were no statistically significant differences in age, sex, diabetes, smoking, fracture type, prosthesis condition, etc. among the three groups of patients. However, there were statistically significant differences in healing time (p < 0.001), the range of motion of the knee joint (< 0.001), operating time (< 0.001), surgical blood loss (< 0.001), and the complications of internal fixation fractures (p = 0.007). We calculated the effect size for the primary outcome indicators (Supplementary Document 1). To avoid increasing the risk of type I errors, Bonferroni correction was performed on all p-values of the multiple tests, and no false positive results were found. For the potential confounding factors, we conducted a multivariate logistic regression analysis to separate the independent effects of the fixation technique. It was found that there was no statistically significant difference in p-values and odds ratios for each factor (Supplementary Table iii), indicating that these factors were not related to the surgical method. The healing time is a relevant indicator for evaluating the surgical effect. The range of motion of the knee joint and postoperative complications are secondary indicators for evaluation. In order to refine the healing time of the main indicator, we conducted Kaplan-Meier survival analysis on the recovery time of the three groups of patients, and found a statistically significant difference (p < 0.001) (Supplementary Figure i).
Table I.
Patient general condition between groups.
| Variable | Overall (n = 120) | Surgical methods for distal femoral fractures | Statistic | p-value | ||
|---|---|---|---|---|---|---|
| LCP n = 38 (32%) | LCP + ALP n = 48 (40%) | LCP + PMCS n = 34 (28%) | ||||
| Sex, n (%) | 0.07 | 0.967* | ||||
| Female | 84 (70.00) | 26 (68.42) | 34 (70.83) | 24 (70.59) | ||
| Male | 36 (30.00) | 12 (31.58) | 14 (29.17) | 10 (29.41) | ||
| AO/OTA 33 A/33 C, n (%) | 4.72 | 0.094* | ||||
| 33 A | 73 (60.83) | 23 (60.53) | 34 (70.83) | 16 (47.06) | ||
| 33 C | 47 (39.17) | 15 (39.47) | 14 (29.17) | 18 (52.94) | ||
| Median age, yrs (IQR) | 68.00 (61.00 to 74.25) | 66.50 (56.25 to 72.75) | 68.00 (61.00 to 75.50) | 70.00 (63.25 to 78.00) | 2.21 | 0.332† |
| TKA prosthesis, n (%) | 0.426‡ | |||||
| No | 111 (92.50) | 35 (92.11) | 46 (95.83) | 30 (88.24) | ||
| Yes | 9 (7.50) | 3 (7.89) | 2 (4.17) | 4 (11.76) | ||
| Type 2 diabetes, n (%) | 0.07 | 0.964* | ||||
| No | 90 (75.00) | 28 (73.68) | 36 (75.00) | 26 (76.47) | ||
| Yes | 30 (25.00) | 10 (26.32) | 12 (25.00) | 8 (23.53) | ||
| Obesity (BMI > 30 kg/m2), n (%) | 0.759‡ | |||||
| No | 111 (92.50) | 34 (89.47) | 45 (93.75) | 32 (94.12) | ||
| Yes | 9 (7.50) | 4 (10.53) | 3 (6.25) | 2 (5.88) | ||
| Smoking, n (%) | 0.454‡ | |||||
| No | 106 (88.33) | 34 (89.47) | 44 (91.67) | 28 (82.35) | ||
| Yes | 14 (11.67) | 4 (10.53) | 4 (8.33) | 6 (17.65) | ||
| Open fracture, n (%) | > 0.999‡ | |||||
| No | 110 (91.67) | 35 (92.11) | 44 (91.67) | 31 (91.18) | ||
| Yes | 10 (8.33) | 3 (7.89) | 4 (8.33) | 3 (8.82) | ||
Pearson’s chi-squared test.
Kruskal-Wallis (H) test.
Fisher’s exact test for count data with simulated p-value (based on 2,000 replicates).
ALP, auxiliary locking plate; LCP, locking compression plate; PMCS, percutaneous medial column screws.
Table II.
Patient outcomes during hospitalization and at follow-up among the groups.
| Variable | Overall, n = 120 | Surgical methods for distal femoral fractures | Statistics | p-value* | ||
|---|---|---|---|---|---|---|
| LCP n = 38 (32%) | LCP + ALP n = 48 (40%) | LCP + PMCS n = 34 (28%) | ||||
| Median fracture healing time, mths (IQR) | 4.60 (4.00 to 5.80) | 6.00 (5.23 to 6.80) | 4.30 (3.88 to 4.80) | 4.25 (3.90 to 4.85) | 39.81 | < 0.001* |
| Median knee range of motion, ° (IQR) | 134.25 (125.95 to 145.35) |
126.95 (123.65 to 130.20) |
142.25 (131.18 to 147.85) |
142.45 (132.20 to 149.85) |
30.56 | < 0.001* |
| Median operating time, mins (IQR) | 79.70 (72.10 to 86.18) |
71.20 (63.03 to 77.03) |
86.45 (82.15 to 92.10) |
77.85 (72.55 to 82.90) |
55.92 | < 0.001* |
| Mean intraoperative blood loss, ml (SD) | 73.57 (14.52) | 64.20 (13.13) | 80.00 (13.25) | 74.96 (12.38) | 16.00 | < 0.001† |
| Median length of stay, days (IQR) | 6.90 (6.00 to 7.63) | 6.95 (6.10 to 8.00) | 6.95 (6.30 to 7.70) | 6.40 (5.80 to 7.28) | 4.08 | 0.130* |
| Implant failure (loosening), n (%) | 0.009‡ | |||||
| No | 113 (94.17) | 32 (84.21) | 47 (97.92) | 34 (100.00) | ||
| Yes | 7 (5.83) | 6 (15.79) | 1 (2.08) | 0 (0.00) | ||
| Bone nonunion or internal fixation of fracture, n (%) | > 0.999‡ | |||||
| No | 117 (97.50) | 37 (97.37) | 47 (97.92) | 33 (97.06) | ||
| Yes | 3 (2.50) | 1 (2.63) | 1 (2.08) | 1 (2.94) | ||
| Superficial infection, n (%) | > 0.999‡ | |||||
| No | 115 (95.83) | 36 (94.74) | 46 (95.83) | 33 (97.06) | ||
| Yes | 5 (4.17) | 2 (5.26) | 2 (4.17) | 1 (2.94) | ||
| Deep infection, n (%) | 0.768‡ | |||||
| No | 117 (97.50) | 37 (97.37) | 46 (95.83) | 34 (100.00) | ||
| Yes | 3 (2.50) | 1 (2.63) | 2 (4.17) | 0 (0.00) | ||
| Planned bone grafting was performed in the second stage, n (%) | 0.887‡ | |||||
| No | 113 (94.17) | 35 (92.11) | 46 (95.83) | 32 (94.12) | ||
| Yes | 7 (5.83) | 3 (7.89) | 2 (4.17) | 2 (5.88) | ||
| Stiffness of the knee, n (%) | 0.365‡ | |||||
| No | 113 (94.17) | 35 (92.11) | 47 (97.92) | 31 (91.18) | ||
| Yes | 7 (5.83) | 3 (7.89) | 1 (2.08) | 3 (8.82) | ||
Kruskal-Wallis H test.
One-way analysis of variance.
Fisher’s exact test for count data with simulated p-value (based on 2,000 replicates).
In addition to the above data, we also used medical imaging data to demonstrate the effect of LCP + PMCS surgery. We studied patients with LCP (Supplementary Figure j) and found that nonunion of bone and implant fractures were prone to occur (Supplementary Figure k). The LCP + ALP autologous bone transplantation surgery was successful in typical cases (Supplementary Figure l). For patients with supracondylar compression of the distal femur (Supplementary Figure m), LCP + PMCS led to a faster recovery time (Supplementary Figure n).
Based on the above analysis, we believe the LCP + PMCS surgical approach to be superior.
Results of finite element analysis
We simulated the compressive load on the models of three internal fixation methods and obtained the stress distribution of the femur (Figure 1a). The maximum stress of the single titanium plate method was 154.25 MPa, the maximum stress of the single titanium plate + double cancellar bone nail method was 129.85 MPa, and the maximum stress of the double-plate method was 123.46 MPa. Likewise, we simulated the torsional load on the models of the three internal fixation methods and obtained the stress distribution of the femur (Figure 1b). The maximum stress of the single titanium plate method was 103.06 MPa, the maximum stress of the single titanium plate + double cancellous bone nail method was 75.89 MPa, and the maximum stress of the double-plate method was 58.06 MPa. Finally, we simulated the bending load on the models of the three internal fixation methods and obtained the femoral stress distribution, thereby enabling us to simulate the three scenarios under normal human physiological conditions (Figure 1c). The maximum stress of the single titanium plate method was 1,009.9 MPa, the maximum stress of the single titanium plate + double cancellar bone nail method was 1,318.4 MPa, and the maximum stress of the double-plate method was 1,108.4 MPa.
Fig. 1.
Diagrams of femoral stress distribution in different fixation systems. a) The stress distribution of the femur under a) compressive load, b) torsional load, and c) bending load.
In addition to femoral stress, we also conducted research on implant stress. We simulated the compressive load on the models of three internal fixation methods and obtained the stress distribution of the implants (Figure 2). The maximum stress of the single titanium plate method was 998.82 MPa, the maximum stress of the single titanium plate + double cancellous bone nail method was 325.42 MPa, and the maximum stress of the double titanium plate method was 364.72 MPa. Then, we simulated the torsional load on the models of the three internal fixation methods and obtained the stress distribution of the implants (Figure 3). The maximum stress of the single titanium plate method was 525.86 MPa, the maximum stress of the single titanium plate + double cancellous bone nail method was 161.91 MPa, and the maximum stress of the double titanium plate method was 378.19 MPa. Finally, we simulated the bending load on the models of the three internal fixation methods and obtained the stress distribution of the implants (Figure 4). The maximum stress of the single titanium plate method was 956.42 MPa, the maximum stress of the single titanium plate + double cancellous bone nail method was 1,035.5 MPa, and the maximum stress of the double titanium plate method was 1,039.6 MPa.
Fig. 2.
Stress distribution diagrams of implants in different fixation systems under compressive loads. a) Single titanium plates. b) Single titanium plate and double cancellous bone screws. c) Double titanium plates.
Fig. 3.
Stress distribution of implants in different fixation systems under torsional load. a) Single titanium plates. b) Single titanium plate and double cancellous bone screws. c) Double titanium plates.
Fig. 4.
Stress distribution of implants in different fixation systems under bending loads. a) Single titanium plates. b) Single titanium plate and double cancellous bone screws. c) Double titanium plates.
We exported the data of displacement and load in the three internal fixation mode models of the compressed load model and drew the load-displacement curve graph, calculating the system compression stiffness for each method (Figure 5a). The compression stiffness of the single titanium plate method was 82 N/mm, that of the single titanium plate + double spongy bone nail method was 394 N/mm, and that of the double titanium plate method was 349 N/mm. Then, we exported the data of torsion angle and torque in the three internal fixation mode models of the torsional load model and drew the torque-torsion angle curve graph (Figure 5b), calculating the system compression stiffness for each method. The torsional stiffness of the single titanium plate method was 5.63 N·m/°, the torsional stiffness of the single titanium plate + double cancellar bone nail method was 210 N·m/°, and the torsional stiffness of the double titanium plate method was 824 N·m/°. Finally, we derived the data of displacement and load in the three internal fixation mode models in the bending load model and drew the load-displacement curve graph (Figure 5c), calculating the yield load and bending stiffness for each method. The yield load of the single titanium plate scheme was 4,869 N and the bending stiffness was 491 N/mm. The yield load of the single titanium plate+ double cancellar bone nail method was 4,079 N and the bending stiffness was 827 N/mm. The yield load of the double titanium plate scheme was 3,971 N and the compressive stiffness was 834 N/mm.
Fig. 5.
Comparison of mechanical properties under different surgical fixation methods. a) Load-displacement curves of different fixed systems under compressive load. b) Torque-torsion angle curves of different fixed systems under torsional load. c) Load-displacement curves of different fixed systems under bending loads.
FEA was conducted on the example of a single titanium plate + double cancellous bone nail under compressive load to verify the influence of mesh size on the calculation results (Supplementary Table iv). During the process of grid encryption, the maximum stress was almost the same, and the relative deviation did not exceed 5%. The calculation results of each example converged. Comprehensively considering the accuracy of the calculation results and the calculation speed, the mesh size of the fixed system within all the example models was set at 1.0 mm for calculation.
According to the simulation results, under the same boundary conditions, the maximum stress of the single titanium plate method occurred at the connection between the screw and the plate, the risk of screw head thread failure was higher, and the risk of local fracture was higher. In terms of stress, the local stress exceeded the yield stress, and the material entered the yield stage, resulting in the load ultimately failing to reach the preset 1,185.5 N, which is approximately 237.7% of an average adult’s body weight. The method involves a level of displacement which is unacceptable in clinical practice. Therefore, the performance of the single titanium plate method could not meet the use requirements. The single titanium plate + double cancellous bone nail method and the double titanium plate method demonstrated statistically significant improvements in femoral stress and strain, implant stress, and overall displacement compared with the single titanium plate method.
Results of biomechanical experiments
We conducted axial load tests on the samples of three surgical fixation methods and recorded the load-displacement curves (Figure 6), then calculated the relevant indicators such as the axial stiffness, yield load, and yield displacement of the sample, and made comparisons (Supplementary Table v). To verify the predictive accuracy of the finite element model, we conducted a correlation analysis and Bland-Altman analysis on the load-displacement curves of the simulation and the experiment (Supplementary Document 2). The stiffness and yield load of the single titanium plate + spongy bone nail system were the highest, and the axial bearing capacity was the best. The stiffness and yield load of the double titanium plate system were second only to those of the single titanium plate + spongy bone nail system, and the yield displacement is the smallest, followed by the bearing capacity. The single titanium plate system was the weakest in terms of stiffness, yield load, and yield displacement, and had the weakest load-bearing capacity. In addition, compared with the double titanium plate system, the single titanium plate + cancellar bone nail system generated less displacement during yield, and the overall stability of the internal fixation system was better. The experimental results are consistent with the finite element results in terms of trend.
Fig. 6.
Results before and after compression tests of the three surgical fixation methods. a) Clockwise (left) and counterclockwise (right) compression test of the sample of the single titanium plate system. b) Load-displacement curve of single titanium plate system. c) Clockwise (left) and counterclockwise (right) compression test of the sample of the single titanium plate + cancellous bone nail system. d) Load-displacement curve of single titanium plate + cancellous bone nail system. e) Clockwise (left) and counterclockwise (right) compression test of the sample of the double titanium plate system. f) Load-displacement curve of the double titanium plate system.
Similar to the axial load model, we conducted torsional load tests on samples of three surgical fixation methods and recorded the torque-angle curves (Figure 7). Then, we calculated the torsional stiffness and ultimate angular displacement and other relevant indicators of the specimens and made comparisons (Supplementary Table vi). Finally, we found that the torsional bearing capacity of the double titanium plate system was slightly better than that of the other two fixation schemes, and there was not much difference in torsional bearing capacity between the single titanium plate system and the single titanium plate + spongy bone nail system.
Fig. 7.
The changes and results before and after torsion tests of the three surgical fixation methods. a) Clockwise (left)/counterclockwise (right) torsion test of the sample of the single titanium plate system. b) Torque-torsion angle curves of the clockwise (left)/counterclockwise (right) torsion test of the single titanium plate system. c) Clockwise (left)/counterclockwise (right) torsion test of the sample of the single titanium plate + cancellous bone nail system. d) Torque-torsion angle curves of the single titanium plate + cancellous bone nail system for clockwise (left)/counterclockwise (right) torsion test. e) Clockwise (left)/counterclockwise (right) torsion test of the sample of the double titanium plate system. f) Torque-torsion angle curve of the dual titanium plate system for clockwise (left)/counterclockwise (right) torsion test.
To summarize, compared with the double titanium plate system, the single titanium plate + spongy bone screw system has significantly improved mechanical properties. Considering that axial compression is the main load-bearing method, the single titanium plate+ spongy bone screw system is the most recommended surgical fixation method, followed by the double titanium plate system. The single titanium plate system has a relatively high risk of failure.
Discussion
The management of distal femoral fractures, particularly in osteoporotic bone or highly comminuted patterns, remains challenging due to the significant risk of mechanical failure associated with conventional lateral LCP, which often struggles to counteract medial column instability.20,21 Our integrated clinical and biomechanical analysis robustly demonstrates that augmenting LCP with PMCS creates a biomechanically superior construct. PMCS functions as an essential internal strut, effectively converting the inherently unstable cantilever system of a lone LCP into a load-sharing framework. In recent years, retrograde intramedullary nail (rIMN) fixation of has shown great potential.22-24 Ziranu et al25 discovered that retrograde intramedullary nails can be used as an effective method for treating aseptic distal femoral nonunion. However, in cases of metaphyseal comminution, joint involvement, or osteoporotic fractures, LCP + PMCS provides superior angular stability and helps to directly reduce joint fragments, which is consistent with current guidelines and tends to highly comminute or fracture plates around the joint.26,27 PMCS can enhance the screw extraction strength of osteoporotic bone, which is a key advantage that rIMN cannot achieve. The PMCS reinforcement method is inherently designed for the fixation of steel plates. Its biomechanical advantage of increasing the fixation strength of the epiphyseal bone cannot be directly transferred to rIMN, making LCP the logical platform for this study. While rIMN demonstrates excellent outcomes in select cases, recent meta-analyses indicate plating may increase the range of motion of the knee joint.28 Additionally, rIMN carries risks of knee sepsis (0.5% to 4%) and anterior knee pain (10% to 40%).29,30
Although LCP + PMCS has significant therapeutic advantages for complex distal femoral fractures, its surgical difficulty, learning curve and cost-effectiveness should be emphasized. Crucially, the efficacy and safety of the LCP + PMCS technique are highly dependent on surgical precision. Optimal PMCS placement requires meticulous attention to trajectory: screws must parallel the articular surface in the coronal plane and maintain ≤ 10° anterior angulation in the sagittal plane. Absolute avoidance of posterior deviation is paramount to prevent catastrophic popliteal neurovascular injury.31,32 This is reliably verified by mandatory lateral fluoroscopy ensuring screw tips remain definitively anterior to the posterior cortical line. While this technique has a steep learning curve, our data and experience suggest that focused training is highly effective: specialized navigation training has been proven to reduce most of the trajectory errors.33 Mastery of this technique allows the LCP to transcend its inherent load-bearing limitations, evolving into a balanced and robust fixation system. Although PMCS implants incur an initial cost premium of 15% to 20% compared to standard LCP constructs alone, our analysis, supported by Medicare data, demonstrates compelling long-term cost-effectiveness.34 This arises primarily from the prevention of revision surgeries – a single avoided fixation failure saves approximately 22 times the initial implant cost. However, with ALP fixation, type IIIB open fractures of the distal femur can re-expose the medial soft-tissues, posing a high risk of surgical complications, such as popliteal artery injury.
While our findings strongly position LCP + PMCS as a paradigm shift for complex distal femoral fractures, this study has inherent limitations. The clinical component is retrospective, and our FEA, while informative, employed necessary simplifications. The properties of bone materials were modelled as uniform and simplified into isotropic materials. Additionally, the crucial influence of the surrounding ligaments, muscles, and other soft-tissues on the load distribution and construction stability was ignored. These FEA limitations highlight areas for more sophisticated future modelling. Nevertheless, the strong concordance observed between our biomechanical predictions (enhanced stability, reduced varus risk) and the improved clinical outcomes supports the validity of the core findings. Future prospective, randomized trials are essential to definitively quantify long-term construct survivorship, refine optimal trajectory-safety parameters across diverse fracture patterns and patient anatomies, and further validate the cost-benefit profile in real-world settings.
Author contributions
J. Chen: Conceptualization, Formal analysis, Writing – original draft
J. Chen: Data curation, Investigation, Writing – review & editing
R. Lu: Data curation, Writing – review & editing
Y. Liu: Data curation, Writing – review & editing
J. Huang: Funding acquisition, Project administration
C. Zhang: Funding acquisition, Project administration, Writing – review & editing
Funding statement
The author(s) disclose receipt of the following financial or material support for the research, authorship, and/or publication of this article: this work was supported by the National Natural Science Foundation of China (81974330, 32271384) and Shanghai Pujiang Program (21PJD052).
ICMJE COI statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
Data sharing
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
Acknowledgements
Thanks to Shanghai no. 6 People's Hospital, Jinshan Branch for providing the relevant data. Special thanks to Decans Biomechanics Testing Center for the finite element analysis and biomechanical experiments. Zhang Chi and Huang Junwu are co-corresponding authors. Chen Jiahao, Chen Jialu, Lu Renjie and Liu Yi contributed equally. All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors, and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
Ethical review statement
Ethical approval for this study was obtained from the Ethics Committee of Jinshan Branch, Shanghai Sixth People's Hospital (jszxyy202443).
Open access funding
The open access fee for this article was self-funded.
Supplementary material
Details of finite element analysis and biomechanical simulation, as well as specific clinical cases.
© 2026 Chen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives (CC BY-NC-ND 4.0) licence, which permits the copying and redistribution of the work only, and provided the original author and source are credited. See https://creativecommons.org/licenses/by-nc-nd/4.0/
Data Availability
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.