Abstract
Aims
The aim of the study was to assess progression of fracture healing after locking plate osteosynthesis with hybrid fixation compared with non-hybrid fixation in the distal femur, using the modified Radiological Union Scale for Tibia (mRUST) fracture score.
Methods
A retrospective review was performed to identify patients who had operative fixation of distal femur fractures with a distal femoral locking plate. A total of 90 patients with 90 fractures (26 hybrid and 64 non-hybrid) were included for analysis. The primary outcome was to compare two constructs using mRUST score assessed on anteroposterior (AP) and lateral radiographs at six, 12, and 24 weeks, and final follow-up.
Results
Overall, 90 patients with distal femur fractures with a mean age of 53 years (SD 24.4) met the inclusion criteria. Statistically significant differences in mean mRUST scores were noted at six weeks (p < 0.001), 12 weeks (p < 0.001), and 24 weeks (p < 0.001) postoperatively, with higher mean scores in the hybrid group. However, there was no significant difference in the union rate or other complication rates between the two groups. The union rate was 100% and 97% for the hybrid and non-hybrid groups, respectively, at final follow-up.
Conclusion
This study suggests that standard locking plates with hybrid fixation form earlier bridging callus than locking plates with non-hybrid fixation. However, there were no differences in final follow-up including healing rates or complications between the two groups. Further prospective study designs are needed to compare the two constructs in distal femur fracture, which is necessary to improve the results and provide the optimal healing environment for distal femur fractures.
Cite this article: Bone Jt Open 2026;7(6):809–817.
Keywords: Distal femur fracture, Callus formation, Fracture healing, Locking plate osteosynthesis, distal femur fractures, Hybrid fixation, locking plates, locking plates, fracture healing, Distal Femoral, Tibia, lateral radiographs, prospective study, plate osteosynthesis
Introduction
Distal femur fractures account for less than 1% of all fractures and 3% to 6% of all femur fractures.1,2 There is a bimodal age distribution, with a peak in young males undergoing high-energy trauma and in elderly female patients with a low-energy mechanism.3,4
Periarticular anatomical locking plates are the most popular fixation implant due to ease of application and improved fixation in osteoporotic bone and highly complex articular fractures, when compared with blade or dynamic condylar plates.5-8 The metaphyseal area is frequently comminuted, and periarticular locking plates are commonly placed using a bridging technique relying on some degree of interfragmentary motion to stimulate osseous union. However, with periarticular locking plates, it has been shown that the construct of fixation is too stiff, and construct rigidity may delay fracture healing; clinical studies have reported fracture healing complications including delayed union, implant failure, loss of alignment, and nonunion.9-12
Locking plates have been applied with all locking screws in the proximal fragment (non-hybrid) fixation and with a combination of traditional non-locking distal in the proximal fragment and locking screws more proximal, a so-called hybrid proximal construct. Biomechanical studies suggested that hybrid proximal fixation decreased the torsional stiffness but not axial stiffness in locking plate constructs.13 In one study of distal femur fractures, locked plate constructs with all locking screws in the proximal fragment were 2.9 times more likely to result in a nonunion compared with hybrid constructs with both locking and non-locking screws in the proximal fragment.14 These studies suggest that locking plates with less stiff hybrid fixation may lead to increased callus formation and earlier signs of healing when compared with all locking constructs; however, this has not been objectively assessed in a clinical study.
The purpose of this study was to measure the timing and amount of callus formed during fracture healing by assigning modified Radiological Union Scale for Tibia (mRUST) fracture scores in hybrid compared with non-hybrid constructs of proximal fixation in distal femur fractures.9 In this study, hybrid fixation was defined as a combination between a traditional cortical non-locking screw and locking screws in the proximal fragment. Non-hybrid fixation was defined as all locking screws in the proximal fragment. We also assessed the union and complication rates between the two groups. We hypothesized that hybrid constructs would result in earlier callus formation and higher union rates.
Methods
After Institutional Review Board approval (IRBRTA 0570/2566), we identified all patients from January 2016 to December 2023 who presented with an acute distal femur fracture (AO/OTA33).15 In total, 151 patients were identified.
Patients aged at least 18 years who underwent open or closed reduction and internal fixation (ORIF or CRIF) of acute distal femur fractures (open and closed) with a laterally based locking plate using a bridged plate technique were included. Patients were excluded with: partial articular fractures (AO/Orthopaedic Trauma Association (OTA) type B fractures) (n = 12), combined medial plate constructs (n = 7), previous nonunion (n = 5), missing follow-up radiographs (n = 5), and patients with less than 24 weeks of follow-up (n = 16). After applying our exclusion criteria, 90 patients with 90 fractures (26 hybrid and 64 non-hybrid) were included for analysis.
During this period of time in our institution, distal femur fractures were fixed using combi-hole Anatomical Distal Femoral Locking Plate (DePuy Synthes, USA). There are two characteristics of proximal fixation in distal femur fractures. The first is hybrid fixation if the surgeon used a traditional cortical screw in the proximal fragment. The surgeon typically used that screw to help reduce the proximal fragment to align with the distal fragment and to move the bone to the plate. This screw usually was inserted near the fracture site skipping one hole from the fracture site. The rest of the screws were then placed as locking screws. The surgeon left the traditional cortical screw in place in the final construct. The second technique is non-hybrid fixation, for which a surgeon only used all locking screws to fix the proximal fragment. Sometimes, after a surgeon used a cortical screw to help reduce proximal fragment as described in the first technique, that screw was removed and replaced with a locking screw. The techniques depended on each surgeon’s decision intraoperatively.
All other locked plate techniques were similar between the two groups of fractures. The type of proximal fragment fixation either hybrid or non-hybrid was based on surgeons’ preference. Type A fractures, and type C fractures with a simple articular line were treated with a small distal incision for plate insertion, indirect reduction of the fracture, and percutaneous insertion of proximal shaft screws. The remaining type C fractures were treated with a medial or lateral arthrotomy with or without lag screw for fixing the articular part of the fracture, and percutaneous insertion of proximal shaft screws. The metaphyseal portion of the fracture was indirectly reduced using minimally invasive technique. Operative fixation was performed by YP and OP, who were orthopaedic trauma surgeons with Synthes’ plates (DePuy Synthes). All surgeons in our institution routinely perform spanning external fixator with initial debridement for open fractures cases, followed by delayed ORIF, as our standard operating procedure.
Standard follow-up was at two, six, 12, and 24 weeks, or until the fracture was completely clinically and radiologically healed. Clinical and physical examination was performed at each follow-up visit and recorded in the chart. All patients were made to undergo touchdown weightbearing for a period of four to eight weeks postoperatively. The exact timing of transition to full weightbearing was based on clinical and radiological findings at each follow-up. Medical records were reviewed to determine patient age, laterality, BMI, smoking status, diabetes mellitus, fracture classification, open or closed fracture, mechanism of injury, high (i.e. motor vehicle collisions, fall > ten feet, etc.) or low-energy (i.e. ground-level fall) injury, type of treatment, AO/OTA classification, fracture characteristic, osteosynthesis characteristics (working length, plate span ratio, proximal screw density; working length of a plate was defined as the distance between the first screws on either side of the fracture which was calibrated on radiographs; plate span ratio was measured with reference to the length of the plate relative to the length of the fracture zone on radiographs; proximal screw density is the quotient formed by the number of screws inserted and number of the plate holes proximal to the fracture on radiographs), time to full weightbearing, revision surgery, complications, periprosthetic fracture, and duration of follow-up. Complications were defined as implant failure (broken plate and screws), nonunion (pain with weightbearing, limp, tender to palpation at the fracture site, and the absence of fracture healing progression or bridging callus on serial radiographs), surgical site infection, revision surgery, and implant irritation.
Patient characteristics
A total of 90 patients with 90 fractures (26 hybrid and 64 non-hybrid) were included for analysis. There was no significant difference in demographic data between the hybrid and non-hybrid groups including age, sex, BMI, energy of injury, smoking status, open fracture, or diabetes (Table I).
Table I.
Demographic data.
| Variable | Average of both constructs (n = 90), n (%) |
Hybrid fixation (n = 26), n (%) |
Non-hybrid fixation (n = 64), n (%) |
p-value* |
|---|---|---|---|---|
| Mean age, yrs (SD; range) | 53.54 (24.4; 18 to 95) | 59.81 (24.23; 24 to 94) | 51.00 (24.2; 18 to 95) | 0.121 |
| Sex, n (%) | 0.893 | |||
| Male | 44 (48.89) | 13 (50.00) | 31 (48.44) | |
| Female | 46 (51.11) | 13 (50.00) | 33 (51.56) | |
| BMI, kg/m 2 , n (%) | 0.485 | |||
| ≤ 30 | 72 (80.00) | 22 (84.62) | 50 (78.13) | |
| > 30 | 18 (20.00) | 4 (15.38) | 14 (21.88) | |
| Side, n (%) | 0.352 | |||
| Left | 45 (50.00) | 15 (57.69) | 30 (46.88) | |
| Right | 45 (50.00) | 11 (42.31) | 34 (53.13) | |
| Energy of injury, n (%) | 0.630 | |||
| High | 52 (57.78) | 14 (53.85) | 38 (59.38) | |
| Low | 38 (42.22) | 12 (46.15) | 26 (40.63) | |
| Smoking status, n (%) | 0.999 | |||
| Non-smoker | 81 (90.00) | 24 (92.31) | 57 (89.06) | |
| Former smoker | N/A | N/A | N/A | |
| Current smoker | 9 (10.00) | 2 (7.69) | 7 (10.94) | |
| Fracture, n (%) | 0.686 | |||
| Closed | 65 (72.22) | 18 (69.23) | 47 (73.44) | |
| Open | 25 (27.78) | 8 (30.77) | 17 (26.56) | |
| Diabetes, n (%) | 0.500 | |||
| No | 79 (87.78) | 24 (92.31) | 55 (85.94) | |
| Yes | 11 (12.22) | 2 (7.69) | 9 (14.06) |
Chi-squared test or Fisher’s exact test; independent-samples t-test, significant if p < 0.05.
N/A, not applicable.
Radiological assessment of healing
Anteroposterior (AP) and lateral radiographs of the knee and femur were independently reviewed by two investigators (TS, YP). Their scores were averaged and the average score was used by the statistician for the comparisons. Callus formation at each cortex was evaluated and scored using the mRUST score. The mRUST score was applied to assess all four cortices as follows: 1 = no callus; 2 = callus present; 3 = bridging callus; and 4 = remodelled, fracture not visible. Low scores indicate poor fracture healing and callus formation, and high scores correlate with fracture healing and early remodelling. The mRUST score was totalled for each cortex to equal a minimum score of 4 or a maximum score of 16. mRUST scores were collected from each investigator on radiographs at six, 12, and 24 weeks and final follow-up, when available. Before radiological assessment, both investigators reviewed sample radiographs together and came to a consensus on how to apply the mRUST score to each cortex in efforts to decrease the learning curve of applying the mRUST score. In cases of obstructed visualization of the lateral cortex, our observers were instructed to use consolidation of the fracture line at the lateral cortex to best apply the mRUST score. A series of previous radiographs of the same sample were allowed to evaluate to better exemplify incremental differences in fracture healing. The type of the screw at the proximal fragment was blinded by one of our investigators (OP) before distributing to two of our investigators who scored mRUST (TS, YP), as demonstrated in Figure 1.
Fig. 1.
Non-hybrid fixation with all locking screws in the proximal fragment demonstrated in 1A. Hybrid fixation with combination of traditional non-locking distal in the proximal fragment and locking screws more proximal demonstrated in 1B. After a screw was blinded, radiographs were demonstrarted to investigators in 2A and 2B.
Fracture union was assessed for the 90 patients with 90 fractures. Union was determined by the operating surgeon as documented in the medical record, and was based on clinical history and examination findings (patient-reported absence of pain, painless ambulation, absence of limp, and no tenderness to palpation of fracture site) and evaluation of radiographs (cortical continuity, bridging cortices, and visibility of fracture line) at the time of follow-up. The radiographs of all cases documented as united in the medical record were independently reviewed by the senior author (OP) to confirm union.
Similarly, nonunion was defined by the operating surgeon as documented in the medical chart based on clinical and radiological findings. All nonunion cases were independently reviewed by one of our investigators (OP) to confirm nonunion and determine construct condition, time at nonunion, time of revision, and revision type for nonunion. The average length of follow-up for both union and nonunion cases was collected from the medical record.
Statistical analysis
The study was designed in conjunction with a statistician. All data are reported as mean with associated SD. Data analysis was performed using STATA/MP 12 software (StataCorp, USA). Group comparisons for continuous variables were analyzed using a two-samples independent-samples t-test. Chi-squared or Fisher’s exact test analysis was used to determine differences between categorical variables. Significance was defined as p < 0.05. Mann-Whitney U test was significant if p < 0.05.
Results
Demographic data
There were no significant differences in AO/OTA fracture classification or fracture characteristic including periprosthetic fractures between the two groups (Table II). There were no significant differences in working length, plate span ratio, and proximal screw density between the two groups (Table III). The mean follow-up for all patients (n = 90) was 15.99 months (6 to 55).
Table II.
Characteristic of distal femur fractures.
| Variable | Average of both constructs (n = 90), n (%) | Hybrid fixation (n = 26), n (%) | Non-hybrid fixation (n = 64), n (%) | p-value* |
|---|---|---|---|---|
| AO/OTA classification | 0.482 | |||
| 33A2 | 34 (37.78) | 10 (38.46) | 24 (37.50) | |
| 33A3 | 31 (34.44) | 8 (30.77) | 23 (35.94) | |
| 33C1 | 9 (10.00) | 1 (3.85) | 8 (12.50) | |
| 33C2 | 12 (13.33) | 5 (19.23) | 7 (10.94) | |
| 33C3 | 4 (4.44) | 2 (7.69) | 2 (3.13) | |
| Fracture characteristic | 0.508 | |||
| Simple fracture (AO/OTA 33A2 and 33C1) |
43 (47.78) | 11 (42.31) | 32 (50.00) | |
| Comminuted fracture AO/OTA 33A3, 33C2, and 33C3 | 47 (52.22) | 15 (57.69) | 32 (50.00) | |
| Periprosthetic fractures | 0.999 | |||
| No | 83 (92.22) | 24 (92.31) | 59 (92.19) | |
| Yes | 7 (7.78) | 2 (7.69) | 5 (7.81) |
Fisher’s exact test; significant if p < 0.05.
OTA, Orthopaedic Trauma Association.
Table III.
Osteosynthesis characteristics.
| Variable | Average of both constructs (n = 90) | Hybrid fixation (n = 26) | Non-hybrid fixation (n = 64) | p-value* |
|---|---|---|---|---|
| Working length,† mm 14 | 0.259 | |||
| Short (≤ 90.5) | 43 (47.78) | 10 (38.46) | 33 (51.56) | |
| Long (> 90.5) | 47 (52.22) | 16 (61.54) | 31 (48.44) | |
| Mean (SD; range) | 100.20 (47.78; 20.7 to 257.4) | 105.25 (36.32; 52.3 to 204.2) | 98.15 (51.83; 20.7 to 257.4) | 0.526 |
| Plate span ratio‡ | ||||
| Mean (SD; range) | 5.09 (2.63; 3 to 14) | 4.38 (2.26; 3 to 14) | 5.38 (2.73; 3 to 12) | 0.083 |
| Proximal screw density,§ % 14 | 0.535 | |||
| ≤ 42.2 | 37 (41.11) | 12 (46.15) | 25 (39.06) | |
| > 42.2 | 53 (58.89) | 14 (53.85) | 39 (60.94) | |
| Mean (SD; range) | 0.44 (0.11; 0.2 to 0.8) | 0.45 (0.12; 0.3 to 0.8) | 0.43 (0.11; 0.2 to 0.8) | 0.441 |
Chi-squared test or Fisher’s exact test; independent-samples t-test; significant if p < 0.05.
Working length of a plate was defined as the distance between the first screws on either side of the fracture which was calibrated on radiographs.
Plate span ratio was measured with reference to the length of the plate relative to the length of the fracture zone on radiographs.
Proximal screw density is the quotient formed by the number of screws inserted and number of the plate holes proximal to the fracture on radiographs.
Assessment of radiological callus by modified RUST score
Statistically significant differences in mean mRUST scores were noted at six weeks (p < 0.001), 12 weeks (p < 0.001), and 24 weeks (p < 0.001) postoperatively, with higher mean scores in the hybrid group (Table IV).
Table IV.
Comparison of radiological findings between hybrid and non-hybrid fixation using the modified Radiological Union Scale for Tibia (mRUST) fracture score.
| Period, wks | Average of both constructs (n = 90) (SD; range) | Mean hybrid fixation (n = 26), (SD; range) | Mean non-hybrid fixation (n = 64), (SD; range) | p-value* |
|---|---|---|---|---|
| 6 | 6.04 (1.42; 4 to 11) | 7.19 (1.55; 5 to 11) | 5.58 (1.07; 4 to 7) | < 0.001 |
| 12 | 9.57 (1.84; 6 to 16) | 11.12 (2.01; 7 to 16) | 8.94 (1.33; 6 to 12) | < 0.001 |
| 24 | 13.10 (1.90; 8 to 16) | 14.50 (1.63; 9 to 16) | 12.53 (1.71; 8 to 16) | < 0.001 |
| Final follow-up | 15.66 (1.04; 10 to 16) | 15.81 (0.63; 13 to 16) | 15.59 (1.16; 10 to 16) | 0.380 |
Independent-samples t-test, significant if p < 0.05.
Direct group comparisons of mRUST scores between high and low-energy injury, closed and open fracture were demonstrated (Table V). There were statistically significant differences between hybrid and non-hybrid fixation at six-, 12-, and 24-week follow-up, respectively, in all sub-group analysis favouring hybrid fixation with higher mean scores. There were statistically significant differences between the groups at final follow-up in low-energy injury and closed fracture sub-group analysis.
Table V.
Comparison of radiological data between hybrid and non-hybrid fixation using the modified Radiological Union Scale for Tibia (mRUST) fracture score in sub-group analysis of high versus low energy of injury and closed versus open fracture.
| Variable | Average of both constructs (n = 52), mean (SD; range) |
Mean hybrid fixation (n = 14), (SD; range) |
Non-hybrid fixation (n = 38), (SD; range) |
p-value* |
|---|---|---|---|---|
| High-energy injury | ||||
| 6 wks | 6.02 (1.36; 4 to 9) | 6.93 (1.44; 5 to 9) | 5.68 (1.19; 4 to 7) | 0.003 |
| 12 wks | 9.21 (1.74; 6 to 13) | 10.43 (2.1; 7 to 13) | 8.76 (1.36; 6 to 11) | 0.013 |
| 24 wks | 12.92 (1.87; 8 to 16) | 13.93 (1.94; 9 to 16) | 12.55 (1.72; 8 to 16) | 0.017 |
| Final follow-up | 15.71 (0.98; 10 to 16) | 15.64 (0.84; 13 to 16) | 15.74 (1.03; 10 to 16) | 0.762 |
| Low-energy injury |
Average of both constructs
(n = 38), mean (SD; range) |
Mean hybrid fixation
(n = 12), (SD; range) |
Mean non-hybrid fixation
(n = 26), (SD; range) |
|
| 6 wks | 6.08 (1.51; 4 to 11) | 7.5 (1.68; 6 to 11) | 5.42 (0.86; 4 to 7) | 0.001 |
| 12 wks | 10.05 (1.87; 7 to 16) | 11.92 (1.62; 10 to 16) | 9.19 (1.27; 7 to 12) | < 0.001 |
| 24 wks | 13.34 (1.95; 8 to 16) | 15.17 (0.83; 14 to 16) | 12.5 (1.73; 8 to 15) | < 0.001 |
| Final follow-up | 15.58 (1.13; 10 to 16) | 16 (0; 16 to 16) | 15.38 (1.33; 10 to 16) | 0.026 |
| Closed fracture |
Average of both constructs
(n = 65), mean (SD; range) |
Mean hybrid fixation
(n = 18), (SD; range) |
Mean non-hybrid fixation
(n = 41), (SD; range) |
|
| 6 wks | 6.05 (1.36; 4 to 11) | 7.06 (1.55; 5 to 11) | 5.66 (1.07; 4 to 7) | < 0.001 |
| 12 wks | 9.69 (1.83; 6 to 16) | 11.06 (2.18; 7 to 16) | 9.17 (1.37; 6 to 12) | < 0.001 |
| 24 wks | 13.18 (1.83; 8 to 16) | 14.56 (1.62; 9 to 16) | 12.66 (1.63; 8 to 16) | < 0.001 |
| Final follow-up | 15.68 (0.92; 10 to 16) | 15.94 (0.24; 15 to 16) | 15.57 (1.06; 10 to 16) | 0.028 |
| Open fracture |
Average of both constructs
(n = 25), (SD; range) |
Mean hybrid fixation
(n = 8), (SD; range) |
Mean non-hybrid fixation
(n = 17), (SD; range) |
|
| 6 wks | 6.04 (1.59; 4 to 9) | 7.5 (1.6; 5 to 9) | 5.35 (1.06; 4 to 7) | 0.001 |
| 12 wks | 9.24 (1.85; 7 to 13) | 11.25 (1.67; 9 to 13) | 8.29 (0.99; 7 to 10) | 0.001 |
| 24 wks | 12.88 (2.11; 8 to 16) | 14.38 (1.77; 12 to 16) | 12.18 (1.91; 8 to 15) | 0.012 |
| Final follow-up | 15.6 (1.32; 10 to 16) | 15.5 (1.07; 13 to 16) | 15.65 (1.46; 10 to 16) | 0.802 |
Independent-samples t-test, significant if p < 0.05.
Union rate and complications
Mean follow-up for patients with fracture union (n = 90) was 25 weeks (12 to 26). There was a significant difference with a faster time to union in the hybrid group in all sub-group analysis (high- vs low-energy injury and closed vs open fracture) if mRUST score was used as cutoff point of 10 which was defined as union (Table VI). There was no significant difference in the overall union rate at final follow-up in hybrid (100%) compared with non-hybrid (97%) constructs (p = 0.999). There were no significant differences in revision surgery, infection, implant irritation, or nonunion between hybrid compared with non-hybrid constructs (Table VII).
Table VI.
Sub-group analysis of time to union (modified Radiological Union Scale for Tibia (mRUST) fracture score of 10) comparing high- with low-energy and closed with open fracture.
| Variable | Average of both constructs, median (IQR) | Median hybrid fixation (IQR) | Median non-hybrid fixation (IQR) | p-value* |
|---|---|---|---|---|
| Energy of injury | ||||
| High | 24 (12 to 36) | 12 (12 to 32) | 24 (12 to 36) | 0.045 |
| Low | 12 (6 to 36) | 12 (6 to 12) | 24 (12 to 36) | < 0.001 |
| Closed or open fractures | ||||
| Closed | 12 (6 to 36) | 12 (6 to 32) | 24 (12 to 36) | 0.001 |
| Open | 24 (12 to 36) | 12 (12 to 24) | 24 (12 to 36) | 0.003 |
Mann-Whitney U test, significant if p < 0.05.
Table VII.
Complications from treatments.
| Variable | Average of both constructs (n = 90), n (%) | Hybrid fixation (n = 26), n (%) | Non-hybrid fixation (n = 64), n (%) |
p-value* |
|---|---|---|---|---|
| Overall complications | 7 (7.78) | 1 (3.85) | 6 (9.38) | 0.668 |
| Revision surgery | 1 (1.11) | N/A | 1 (1.56) | 0.999 |
| Nonunion | 2 (2.22) | N/A | 2 (3.13) | 0.999 |
| Infection | 3 (3.33) | 1 (3.85) | 2 (3.13) | 0.999 |
| Hardware irritation | 2 (2.22) | N/A | 2 (3.13) | 0.999 |
Fisher’s exact test, significant if p < 0.05.
N/A, not applicable.
Discussion
Anatomical precontoured locking plates have become the mainstay in treating distal femur fractures due to increased resistance to multiplanar forces around the knee and improved fixation in osteoporotic bone.6,7 Several studies indicated good to excellent results with standard locked plating, reporting union rates ranging from 80% to 100%.16-20 However, locking plates are not without fault, and healing complications occur. Several studies have reported that locking plates were too stiff and did not allow sufficient callus to form, which is necessary for secondary bone healing.10-12,21
Standard locking plates with hybrid fixation increased interfragmentary motion, and both biomechanical and clinical studies suggested that this may lead to clinical advantage through earlier and stronger fracture repair.13,14 Cui et al13 evaluated construct stiffness by comparing four diaphyseal bridge plate constructs using distal femur locking plates, all with identical locking condylar fixation. Each proximal fixation construct included all locked (AL), all unlocked (AUL), proximal unlocked (PUL), and distally unlocked (DUL) groups. They found that standard locked plating constructs with all locking (AL) or non-hybrid and distally unlocked groups (DUL) or hybrid a construct similar to what was used on our study, axial stiffness was not significantly different between the constructs but torsional stiffness was significantly decreased in the distally unlocked (DUL) or hybrid group (p < 0.05) indicating increased flexibility of the construct.13 Harvin et al14 studied in 96 patients with distal femur fractures and demonstrated that diaphyseal screw technique made a significant difference in healing rates. Hybrid technique in the proximal fragment had a higher chance of union when compared with all locking (p = 0.02). All proximal locking screw constructs were 2.9 times more likely to lead to nonunion when compared with hybrid and non-locking fixation. Other factors associated with more flexible fixation constructs such as increased working length, decreased proximal screw number, and decreased proximal screw density were not significantly associated with union in this study.14 All these were outcome measurements in the study that affect stiffness of the construct and were important to our study as we used as references to clarify in the study. Hybrid fixation is less stiff but not too unstable to allow micromotion to create a more callus formation than non-hybrid fixation. Therefore, less stiff implants could increase union rates when comparing with more stiff implants.
There have been no previous studies comparing radiological callus formation between hybrid and non-hybrid constructs. Plumarom et al22 showed that radiological callus assessment with mRUST scores had high sensitivity, specificity, and accuracy for healing of metadiaphyseal femur fractures. Our study demonstrated statistically significant differences between hybrid and non-hybrid fixation using mRUST scores at 10 as a cutoff point. There were statistically significant differences in the mRUST scores between the two groups at six, 12, and 24 weeks postoperatively. This suggests that hybrid locking constructs formed callus earlier and resulted in a faster time to union than non-hybrid locking constructs. However, there were no differences in nonunion rate, revisions, or other specific complications between hybrid and non-hybrid locking constructs.
There are several limitations to this study. The task of assigning a mRUST score to a lateral cortex is limited when it is either partly or fully obscured by the implant. As the study is a retrospective design, one limitation is uncontrolled mechanical and biological variables as potential confounders between the groups. These variables affect construct stiffness and the heterogeneity of biological propensity to heal including bone quality, quality of reduction, surgical techniques, energy of injury (high vs low), closed compared with open fracture, postoperative weightbearing protocol, degree of comminution (type A or C), and general health status. These could potentially confound the outcomes. Although our analysis indicated that the two groups were similar, systematic selection bias on how the surgeons chose cases for the two different constructs is possible. The assessment of time to union is limited by the variables inherent in making this determination in a retrospective chart review. The detection of differences in union rate is limited by the number of patients available for study. Furthermore, after inclusion and exclusion criteria were applied, there was limitation of the number of sample size of the study which might limit the power of analysis. The average length of follow is 16 months but that is not for all patients and that could affect secondary outcomes. These limitations are inherent in retrospectively assessed groups of patients.
In conclusion, in this study, standard locking plates with hybrid fixation with proximal screws that were both non-locking and locking were compared with non-hybrid all proximal locking screws in distal femur fractures. The hybrid group demonstrated significantly higher mRUST scores at six, 12, and 24 weeks postoperatively, indicating increased callus formation and likely faster time to union. However, there were no significant difference in union rate and in complications between the two groups. Further prospective study designs are needed to compare hybrid and non-hybrid fixation to improve the results and determine the optimal mechanical healing environment and, in so doing, improve the results of treatment of distal femur fractures.
Take home message
- Standard locking plates with hybrid fixation form earlier bridging callus (modified Radiological Union Scale for Tibia score) than locking plates with non-hybrid fixation.
- However, there were no differences in final follow up including healing rates or complications between the two groups.
Author contributions
Y. Plumarom: Methodology, Project administration, Writing – original draft
T. Singsuwit: Methodology, Project administration, Writing – original draft
L. Marsh: Writing – review & editing
O. Phruetthiphat: Methodology, Writing – review & editing
Funding statement
The authors received no financial or material support for the research, authorship, and/or publication of this article, other than the open access funding outlined below.
ICMJE COI statement
The authors have no conflicts of interest to disclose.
Data sharing
The datasets generated and analyzed in the current study are not publicly available due to data protection regulations. Access to data is limited to the researchers who have obtained permission for data processing. Further inquiries can be made to the corresponding author.
Acknowledgements
The authors would like to acknowledge Worarachanee Imjaijitt, MA, Office of Research Development, Phramongkutklao Hospitalm and Phramongkutklao College of Medicine, Bangkok, Thailand for statistical analysis; and Thanya Jantorn, MD, Department of Orthopedic Surgery, Phramongkutklao Hospital and College of Medicine, Bangkok, Thailand for providing sample size of surgical fixation in the current study.
Ethical review statement
Ethical approval for this study was obtained from the Institutional Review Board Royal Thai Army Department (IRBRTA 0570/2566).
Open access funding
The open access funding for this article was provided by Phramongkutklao Hospital and College of Medicine.
© 2026 Plumarom 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 generated and analyzed in the current study are not publicly available due to data protection regulations. Access to data is limited to the researchers who have obtained permission for data processing. Further inquiries can be made to the corresponding author.
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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 generated and analyzed in the current study are not publicly available due to data protection regulations. Access to data is limited to the researchers who have obtained permission for data processing. Further inquiries can be made to the corresponding author.