Blocking screws: an adjunct to retrograde nailing for distal femoral shaft fractures

Current Concepts in Management of Distal Femur Fractures

Recent studies report the overall incidence of distal femur fractures as 8.7/100,000/year. This incidence is expected to rise with high energy motor vehicle collisions and elderly osteoporotic fractures in native and prosthetic knees keep increasing. These fractures are more common in males in the younger age spectrum while females predominate for elderly osteoporotic fractures. Surgical treatment is recommended for these fractures to maintain articular congruity, enable early joint motion and assisted ambulation. Over the last two decades, development of minimally invasive and quadriceps sparing surgical approaches, availability of angle stable implants have helped achieve predictable healing and early return to function in these patients. Currently, laterally positioned locked plate is the implant of choice across all fracture patterns. Retrograde with capital implantation of intramedullary nails with provision for multiplanar distal locking is preferred for extra-articular and partial articular fractures. Even with these advancements, nonunion after distal femur fracture fixation can be as high as 19%. Further recent research has helped us understand the biomechanical limitations and healing problems with lateral locked plate fixation and intramedullary nails. This has lead to development of more robust constructs such as nail-plate and double plate constructs aiming for improved construct strength and to minimise failures. Early results with these combination constructs have shown promise in high risk situations such as fractures with extensive metaphyseal fragmentation, osteoporosis and periprosthetic fractures. These constructs however, run the risk of being over stiff and can inhibit healing if not kept balanced. The ideal stiffness that is needed for fracture healing is not clearly known and current research in this domain has lead to the development of smart implants which are expected to evolve and may help improve clinical results in future.

Biomechanical comparison of distal femoral fracture fixation: Polyaxial vs. uniaxial locking screws with different blocking screw configurations in retrograde femoral nailing

INTRODUCTION

Clinical studies have indicated reduced reliance on blocking screws with the introduction of polyaxial locking nails, yet the biomechanical superiority of polyaxial locking over blocking screws remains unverified, specifically for distal dia-metaphyseal femur fractures.

HYPOTHESIS

We hypothesized that the combination of multiaxial locking using three screws and parallel locking reinforced by two blocking screws would result in superior outcomes compared to utilizing only parallel locking with two screws and one blocking screw.

MATERIALS AND METHODS

Third-generation custom-made femur models representing AO/OTA 32 A1.2 dia-metaphyseal comminuted oblique fractures were divided into four groups (n=10/group). Group A employed distal fixation with three 4.5-mm polyaxial screws. Group B used two parallel locking screws and two blocking screws, Group C used two parallel locking screws and one blocking screw, and Group D used only two parallel screws. Specimens underwent axial and torsional load testing to assess fatigue strength, ultimate strength, axial stiffness (N/mm), torsional stiffness (N/mm/deg), axial load to failure (N), torsional load to failure (N/mm), coronal and sagittal angulations, and fracture site collapse.

RESULTS

Group C exhibited statistically superior torsional stiffness compared to Groups B and D (p=0.039 and p=0.034, respectively). Axial load to failure was highest in Group B and lowest in Group D (p=0.032). Group C demonstrated the highest torsional strength, while Group B exhibited the lowest (p=0.006). Coronal displacement was greatest in Group B, while Group A showed the highest resistance (p=0.009). Group A demonstrated the greatest resistance to fracture site collapse, with the weakest specimens observed in Groups B and C (p=0.01).

DISCUSSION

The performance of a single laterally positioned blocking screw is comparable to using two blocking screws. Medial positioning of a second blocking screw is unnecessary for stability enhancement. Multiaxial locking prevents fracture site collapse and coronal plane angulation more effectively than other methods. Multiaxial locking and/or parallel screws with a single laterally positioned blocking screw provide superior stiffness and stability for treating unstable dia-metaphyseal distal femoral fractures.

LEVEL OF EVIDENCE

N/A.

Optimal blocking screw placement for retrograde IM nail fixation of distal femur fracture: a standardized biomechanical study of "osteoporotic" synthetic bone

PURPOSE

Intramedullary (IM) nail use for metaphyseal fracture management is problematic in long bones like the femur because the larger medullary cavity allows increased fracture motion and potentially increased implant failure and malunion/nonunion risk; Achieving effective distal femur fracture fixation is even more difficult in osteoporotic bone. Blocking screws to control IM nail movement are known to be effective for tibia fracture management. Few studies have evaluated IM nail and blocking screw use efficacy for distal femur fracture fixation in osteoporotic bone.

METHODS

This study used an osteoporosis simulation synthetic bone model to evaluate retrograde IM nail fixation of a standardized non-comminuted, extra-articular distal femur fracture with and without blocking screws. The hypothesis was that use of one or two blocking screws would increase IM nail fixation stability as evidenced by greater peak IM nail load and lesser movement. A servohydraulic device under displacement control collected loading force versus movement deflection data. Shapiro-Wilk tests confirmed data normality. One-way analysis of variance and Tukey post hoc tests were used to compare condition specific loading force and movement differences.

RESULT

In the coronal plane, blocking screw conditions displayed greater loading ranges (38.3 ± 2 vs. 19.1 ± 2 N, 100.5% difference) (p < 0.0001) and lesser movement (2.0 ± 0.3 vs. 6.86 ± 0.4 mm, 243% difference) (p < 0.0001). In the sagittal plane, the two blocking screw condition displayed a significantly greater loading magnitude (29.9 ± 6 vs. 20.8 ± 2.3 N, 43.8% difference) than the identical control condition without blocking screws (p = 0.018); however, movements were comparable (p = 0.82). Long-axis rotational loading failed to reveal load magnitude differences (p = 0.28); however, two different blocking screw conditions displayed decreased movement (1.32 ± 0.2 vs. 2.05 ± 0.3 mm, 53.8% difference) compared to other conditions (p ≤ 0.018).

CONCLUSIONS

Use of one or two blocking screws on the medial and lateral sides of the IM nail decreased coronal plane movement in the intramedullary canal. Combining retrograde IM nail implantation with blocking screws reduced medial-lateral IM nail movement and increased fracture stability. These characteristics may help prevent fixation failure, malunion, and even nonunion in patients with a distal femur fracture in osteoporotic bone.

Factors Predictive of Blocking Screw Placement in Retrograde Nailing of Distal Femur Fractures

OBJECTIVES

(1) Identify factors that predict blocking screw placement in the treatment of a distal femur fracture with retrograde nail fixation and (2) determine whether acceptable alignment and stability were achieved in fractures that received blocking screws.

DESIGN

Retrospective Comparative Study.

SETTING

Level I Trauma Center.

PATIENTS/PARTICIPANTS

Between 2011 and 2017, we identified 84 patients with distal third femur fractures treated with a retrograde femoral nail. Data were analyzed according to those who did (BLOCK, n = 30) and did not (NO BLOCK, n = 54) receive blocking screws. Patients in both groups were treated by orthopaedic trauma surgeons; postoperative weight-bearing radiographs were obtained of every patient.

INTERVENTION

Fixation using a retrograde femoral nail with or without blocking screws. Blocking screws were placed at the discretion of the treating surgeon to reduce malaligned fractures or improve stability.

MAIN OUTCOME MEASUREMENTS

(1) Demographics, radiographic apparent bone gap (RABG), space available for the nail (SAFN), and distal segment length [as a ratio of bicondylar width (BCW)]; and (2) post-operative alignment and stability (change in alignment over time).

RESULTS

Patients treated with blocking screws had a higher body mass index (BMI) (BLOCK: 29.0, NO BLOCK 25.7, P = 0.03). In addition, the BLOCK group had larger RABGs (BLOCK: 8.2 mm, NO BLOCK: 3.6 mm, P = 0.02), more SAFN (BLOCK: 51.4 mm, NO BLOCK: 39.8 mm, P = 0.02), and shorter distal segments (BLOCK: 1.7 × BCW, NO BLOCK: 2.0 × BCW, P = 0.01). In a multivariable logistic regression, the combination of these factors was significantly predictive of blocking screw placement with a large effect size (R = 0.36, P < 0.01). A distal segment length ≤ ×2 BCW was 77% sensitive for blocking screw placement, and a BMI ≥25 kg/m was 70% sensitive. Negative predictive values for blocking screw placement were distal segment length > ×2 BCW (79%), BMI <25 kg/m (77%), RABG <4 mm (76%), and SAFN <50 mm (71%). Patients that received blocking screws had acceptable postoperative alignment and stability, similar to fractures that did not receive blocking screws (P > 0.05).

CONCLUSIONS

This retrospective study of distal femur fractures treated with retrograde nails identified several factors that can be used to predict when blocking screw placement may be useful for increasing stability and maintaining alignment in distal third femur fractures treated with retrograde IM nails. Patients treated with blocking screws had a higher BMI, greater cortical bone loss, more SAFN, and shorter distal segments. There was no difference in postoperative alignment or stability between the 2 groups.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Blocking Screw-assisted Intramedullary Nailing Using the Reverse-rule-of-thumbs for Limb Lengthening and Deformity Correction

Introduction

Historically, blocking screws have been used to assist in acute reduction of fractures during intramedullary (IM) nailing. The reverse-rule-of-thumbs (RROT) for blocking screws was introduced to facilitate internal lengthening nail use in deformity correction and limb lengthening. Our study investigated the ability of blocking screws, using same principle, to accurately correct long-bone deformity with and without lengthening and to prevent lengthening-induced deformity.

Materials and methods

This is an institutional review board (IRB)-approved retrospective study on 86 patients who had IM nail-assisted limb reconstruction of femur or tibia with blocking screws. Surgeries were performed for deformity correction, limb lengthening, or deformity correction and limb lengthening. Data on the following variables were collected: number of blocking screws, distance of each blocking screw to osteotomy, distance of osteotomy from joint line, and amount of lengthening. Mechanical axis deviation (MAD) and joint alignment parameters were measured preoperatively and at the final postoperative follow-up. The primary outcome was the ability to obtain desired MAD and joint orientation angles. Accuracies were reported as postoperative measurements relative to goal. Association for the Study and Applications of the Methods of Ilizarov (ASAMI) scores were collected.

Results

The accuracy of deformity correction was within 6 mm from goal, while joint orientation was corrected to within 1.5° of goal. Number of blocking screws did not significantly impact accuracy. Distance of blocking screw to osteotomy and amount of lengthening did not affect accuracy. In femurs, osteotomies greater than 10 cm from the joint line were more accurate in MAD goal (p = 0.017). This result was not replicated in tibias. ASAMI scores were excellent or good.

Conclusion

Using RROT configuration, blocking screws were effective in correcting deformities of lower extremity long bones and in preventing deformity during limb lengthening. If positioned correctly, number of screws and their distance to osteotomy did not affect accuracy. Amount of lengthening did not impact accuracy. Distal femoral osteotomy less than 10 cm from knee joint may be challenging even with using blocking screws.

How to cite this article

Dabash S, Zhang DT, Rozbruch SR, et al. Blocking Screw-assisted Intramedullary Nailing Using the Reverse-rule-of-thumbs for Limb Lengthening and Deformity Correction. Strategies Trauma Limb Reconstr 2019;14(2):77–84.

Effect of Blocking Screws on Union of Infraisthmal Femur Fractures Stabilized With a Retrograde Intramedullary Nail

OBJECTIVE

To investigate the effect of blocking screws (BS) on the union rate and stability of infraisthmal femur fractures treated with retrograde intramedullary nail (RIMN) insertion.

DESIGN

Retrospective cohort study.

SETTING

A single level 1 trauma center.

PATIENTS/PARTICIPANTS

All patients with an infraisthmal femur fracture treated with a RIMN from 2005 to 2012 were included.

INTERVENTION

All fractures were treated with a RIMN. BS were used at the discretion of the treating surgeon.

MAIN OUTCOME MEASUREMENTS

(1) Radiographic time to union, (2) initial postoperative sagittal and coronal angulation, and (3) final sagittal and coronal angulation.

RESULTS

Neither the average time to union (BS 21.1 weeks vs. 21.8 weeks), nor union rates (BS 61% vs. 77%) were statistically different between BS and non-BS constructs. No significant alignment differences existed whether BS were used or not.

CONCLUSIONS

In this study, we were not able to verify our hypothesis. In fact, we did not find any significant advantages when BS were added to a RIMN construct for distal femur fractures with respect to union time, union rate, or improvements in alignment. Additional studies are needed to determine the actual benefit of BS in the treatment of infraisthmal femoral shaft fractures treated with retrograde intramedullary nailing.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.