Distal femoral fixation: a laboratory comparison of the 95 degrees plate, antegrade and retrograde inserted reamed intramedullary nails

Orthogonal plating of distal femur fractures: A biomechanical comparison with plate-nail and parallel plating constructs

Purpose

This study compared the biomechanical properties of orthogonal plating with plate-nail and parallel plating constructs for supracondylar distal femur fractures.

Methods

A supracondylar distal femur fracture was simulated using 15 synthetic osteoporotic femurs. Constructs included: (1) plate-nail (lateral locked distal femoral plate + retrograde intramedullary nail); (2) parallel plating (lateral locked distal femoral plate + medial 4.0 mm compression plate); and (3) orthogonal plating (lateral locked distal femoral plate + posterior one-third tubular plate). Specimens underwent nondestructive loading, fatigue loading, and loading to failure. Gapping at the fracture was measured using a three-dimensional motion capture system. Baseline torsional and axial stiffness, stiffness and strain after fatigue loading, and load to failure were determined. A case example of orthogonal plating is also presented.

Results

There was no difference in baseline torsional (p = 0.51) and axial stiffness (p = 0.53). Stiffness after fatigue loading was highest with parallel plating, with no difference between the plate-nail and orthogonal plating constructs (p = 0.84). Strain after fatigue loading was lowest in the parallel plating group (0.54 ± 0.19%), followed by the plate-nail (2.89 ± 0.83%) and orthogonal plating groups (3.04 ± 0.51%).

Conclusion

Orthogonal plating demonstrated comparable baseline stiffness to plate-nail and parallel plating constructs, and similar biomechanical performance in fatigue loading to plate-nail constructs. All specimens had ≤3% strain after fatigue loading, suggesting sufficient stability for fracture healing. The benefits of enhanced stability from dual-implant fixation may be achieved through orthogonal plating while avoiding an additional medial surgical approach, and therefore warrants further investigation as a novel alternative for distal femur fracture fixation.

Biomechanical analysis of the drilling parameters for early osteonecrosis of the femoral head

BACKGROUND AND OBJECTIVE

Core decompression is a surgical procedure commonly used to treat the early osteonecrosis of the femoral head. However, It is not known whether different drilling parameters affect postoperative biomechanical strength. This study aimed to analyze the mechanical stability of different drilling locations and diameters of core decompression using finite element analysis.

METHODS

Finite element models were established based on computed tomography images obtained from five healthy participants, including the different drilling locations (Lesser trochanter: Above, Parallel, and Below) and diameters. Biomechanical parameters including stiffness and stress were evaluated under slow running loads.

RESULTS

At the same drilling diameter, the femoral stiffness was highest (p < 0.05) in the Above group and lowest in the Below group, while the maximum equivalent stress of the entry area and the necrotic area was highest (p < 0.05) in the Below group and lowest in the Above group. With the increase of drilling diameters, the stiffness decreased and its decreased percentage comparing the preoperative: Above (1.06-8.82%), Parallel (2.51-13.61%), and Below (3.99-15.06%). The maximum equivalent stress of the entry area and necrotic area increased as the drilling diameter increased, and its increased percentage comparing the preoperative, for the entry area: Above (14.11-219.58%), Parallel (35.91-306.37%), and Below (46.12-240.98%); for the necrotic area: Above (13.64-114.69%), Parallel (29.37-187.76%), and Below (44.76-202.10%). The range of safety drilling parameters (SDP) was obtained (Below<9 mm, Parallel<11 mm, and Above<13 mm) by comparing the maximum equivalent stress of two areas and its yield strength. For patients of different sizes and normal bone mineral density (BMD), the maximum equivalent stress of the two areas did not exceed its yield strength using the range of SDP, except for the patients with abnormal BMD (Osteoporosis) or high body mass index (BMI≥28 kg/m²).

CONCLUSIONS

The biomechanical properties of early osteonecrosis of the femoral head deceased with increasing drilling diameters parameters, especially at the location below the lesser trochanter. The SDP (Below<9 mm, Parallel<11 mm, and Above<13 mm) is a suitable reference for most patients to perform slow running postoperatively, while it may be not suitable for patients with osteoporosis or obesity.

Finite element analysis of different medial fixation strategies in double-plate osteosynthesis for AO type 33-C2 fractures

OBJECTIVES

In this study, we evaluated the biomechanical characteristics of different locations of medial fixation strategies in double-plate osteosynthesis for fixing AO/ASIF type 33-C2 fractures by means of finite element analysis.

METHODS

We used 3-matic software and UG-NX software to construct AO/ASIF type 33-C2 fractures and lateral less invasive stabilization system (LISS) plates, medial plates (MPs), and medial support pads (MSPs), respectively. Then, the LISS, MP and MSP were assembled into the fracture model separately to form three fixation models: MSP+LISS, anteromedial plate (AMP+LISS), and MP+LISS. In the next procedure, we performed finite element analysis using ANSYS software after meshing the elements of the models in HyperMesh 11.0 software. Loading conditions including lateral-medial four-point bending, anterior-posterior four-point bending, axial loading, and torsional loading were applied to evaluate the biomechanical advantages among the three fixation types. We observed the peak Von Mises Stress (VMS) value, maximum displacement, bending angle in the coronal plane of the fracture, and torsional angle of the fracture to assess the degree of plate deformation and fixation stability.

RESULTS

Our results showed that in both lateral-medial four-point bending and anterior-posterior four-point bending, the calculations of MP+LISS were marginally better than those of AMP+LISS. However, with the action of axial loading and torsional loading, the deformation of MP+LISS was distinctly smaller than that of AMP+LISS, and the fixation stability of MP+LISS was also prominently better. Under lateral-medial four-point bending, the VMS on the lateral plate of MSP+LISS (59.977 MPa) was approximately half of the two double-plate models. Under anterior and posterior four-point bending, the 38.209 MPa peak VMS of MSP+LISS was still superior to the other two double-plate models. Under torsional loading, the peak VMS (347.75 MPa), the maximum torsional angle of the femoral head (7.852 °), and the torsional angle of fracture (0.036 °) of MSP+LISS preceded those of the other two models. However, under axial loading, the peak VMS (76.376 MPa) and the maximum displacement (3.1798 mm) of MSP+LISS were slightly higher than those of MP+LISS.

CONCLUSION

The MSP+LISS model showed better biomechanical performance than the double-plate models, which might be an effective solution for the treatment of comminuted distal femur fractures.

Comparison of three methods of Müller type C2 and C3 distal femoral fracture repair

Background

We compared the outcomes of three fixation techniques for Müller type C2 and C3 distal femoral fractures.

Methods

We retrospectively analyzed patients undergoing internal fixation for Müller type C2 and C3 distal femoral fractures via locking plate (Group A), lateral locking condylar plate and medial contoured reconstruction plate (Group B), and lateral locking condylar plate and anterior reconstruction plate (Group C). Knee joint functional recovery and functional outcomes were evaluated 12 months postoperatively.

Results

Patients included 34 men and 24 women aged 25 to 74 years (mean, 50.3 ± 10.73 years). Operating times were longest in Group B and similar in Groups A and C. Bleeding volume in Group A was smaller than in Group B and similar to that of Group C. Functional outcomes were excellent in 18 (31%) fractures, good in 24 (41%), moderate in 11 (19%), and poor in 5 (9%). Good-to-excellent results were achieved in 56%, 82%, and 83% of patients (Groups A, B, and C, respectively). Groups B and C's outcomes were superior to Group A's outcomes. No significant difference in postoperative complications between the groups existed.

Conclusion

Lateral locking condylar and anterior reconstruction plating was useful for complex type C distal femoral fractures.

Comparative analysis of the biomechanical behavior of anterograde/retrograde nailing in supracondylar femoral fractures

Supracondylar femoral fractures account for a noticeable percentage of the femoral shaft fractures, affecting two etiological groups: high energy trauma in young men, with good bone quality, and older women with osteoporotic femur. Surgical treatment of those kind of fractures remains controversial, with different surgical options such as plate and sliding barrel locking condylar plate, less invasive stabilization system (LISS) or intramedullary nailing, which has emerged as a new fixation choice in the treatment of that type of fractures. The present work performs a comparative study about the biomechanical behavior of anterograde and retrograde nailing in supracondylar femoral fractures type A, in order to determine the best choice of nailing and locking configuration. A three-dimensional finite element model of the femur was developed, modeling femoral supracondylar fracture and different nailing configurations, both for anterograde and retrograde nails. The study was focused on the immediately post-operative stage, verifying the appropriate stability of the osteosynthesis. The obtained results show a better biomechanical behavior for anterograde nails, providing a better stability from the point of view of global movements, lower stresses in screws, and less stress concentration in cortical bone. So, for the analyzed fractures and osteosyntheses types, anterograde nailing has demonstrated to be a better surgical option, being an excellent indication in supracondylar fractures of femur, with clear benefits compared to retrograde nailing, providing a better stabilization which enables for a more satisfactory fracture healing.

Supplementation of Lateral Locked Plating for Distal Femur Fractures: A Biomechanical Study

OBJECTIVES

To investigate the biomechanical properties of a lateral locked plate alone or in combination with a supplemental medial plate or an intramedullary nail (IMN).

METHODS

Intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C) were simulated with a standardized model in 28 synthetic femora and divided into 4 groups. Group I was instrumented with a 4.5-mm lateral locked distal femoral plate alone, group II with a lateral locked plate plus a low-profile precontoured 3.5-mm medial distal tibial plate, group III with a lateral locked plate plus a medial 3.5-mm reconstruction plate, and group IV with a lateral locked plate plus a retrograde IMN. Specimens were then axially loaded and cycled to failure or runout. Outcomes of interest were baseline stiffness, survivability, and cycles to failure.

RESULTS

Groups III and IV have a significantly higher baseline stiffness (P < 0.001) when compared with groups I and II. Furthermore, groups III and IV had a higher max load to failure (P < 0.01) when compared with groups I and II. The survivability in groups III and IV was 71% and 100%, respectively, while no specimens in group I or II survived maximum loading. There was no significant difference between group III and IV regarding stiffness, survivability, and cycles to failure.

CONCLUSION

When considering fixation for intra-articular distal femur fractures with metaphyseal comminution (OTA/AO 33-C), we found that supplementation of a lateral locked plate with a medial plate or an IMN to be biomechanically superior to lateral locked plating alone regarding stiffness, survivability, and cycles to failure. A low-profile precontoured plate did not add significantly to the construct stiffness in this study.

Double plating of intra-articular multifragmentary C3-type distal femoral fractures through the anterior approach

INTRODUCTION

In this prospective case series, we report a mean of 12-month follow-up of the utilization of a dual plating of distal femoral fractures. Our technique included a lateral distal femoral locked plate with a low-contact-locked medial plate and bone graft through an extended medial parapatellar anterior approach for the fixation of C3-type distal femoral fractures.

PATIENTS AND METHODS

Sixteen patients (11 males and 5 females) presented with supracondylar femoral fracture type C3, according to Müller long-bone classification system and its revision OA/OTA classification. These were treated using dual plating through extended anterior approach and bone grafting. Our outcomes included clinical and radiological outcomes. Secondary outcomes included postoperative complications.

RESULTS

The mean time of complete radiological union in the studied population was 6.0 ± 3.5 months with a range of 3-14 months. We have not observed postoperative varus or valgus deformity in our cohort. The majority (68.75%) of the studied patients showed significant improvement in range of motion (90°-120°) during follow-up. Eleven out of sixteen patients (68.75%) had well-to-excellent functional outcome. Poor outcome was reported in only two patients (12.50%).

CONCLUSIONS

Dual plating fixation using anterior approach for type C3 distal femoral fractures is an efficient method of management. It has several advantages such as precise exposure, easy manipulation, anatomical reduction and stable fixation. However, operative indications and instructions should be strictly followed. The surgical technique must be rigorous, and the biomechanical qualities of these implants must be understood to prevent the development of major complications.

Comminuted supracondylar femoral fractures: a biomechanical analysis comparing the stability of medial versus lateral plating in axial loading

The aim of this study was to compare the biomechanical properties of medial and lateral plating of a medially comminuted supracondylar femoral fracture. A supracondylar femoral fracture model comparing two fixation methods was tested cyclically in axial loading. One-centimetre supracondylar gap osteotomies were created in six synthetic femurs approximately 6 cm proximal to the knee joint. There were two constructs investigated: group 1 and group 2 were stabilized with an 8-hole LC-DCP, medially and laterally, respectively. Both construct groups were axially loaded. Global displacement (total length), wedge displacement, bending moment and strain were measured. Medial plating showed a significantly decreased displacement, bending moment and strain at the fracture site in axial loading. Medial plating of a comminuted supracondylar femur fracture is more stable than lateral plating.

Prospective comparative study of two methods for fixation after distal femur corrective osteotomy for valgus deformity; retrograde intramedullary nailing versus less invasive stabilization system plating

INTRODUCTION

The aim of this study was to compare the radiological and functional results of two different methods of fixation for the correction of femoral valgus deformities.

METHODS

Patients who had undergone osteotomy and correction of a valgus deformity from 2007 to 2013 were prospectively followed. Thirty three patients (20 females, 13 males) with 39 lower limbs were included in the study. Seventeen lower limbs were treated with retrograde intramedullary nailing (IMN) and 22 with less invasive stabilization system plating. Standing orthoroentgenograms of the lower limbs were taken pre-operatively and at the final follow-up. mLDFA, aLDFA, mechanical axis deviation (MAD) were measured in this orthoroentgenograms. Knee osteoarthritis outcome score (KOOS) and knee range of motion were used pre-operatively and at the final follow-up as part of the evaluation of the clinical results. All patients duration of surgery, length of hospital stay were assessed. Operations were performed by two orthopedic surgeons. The choice of correction method for each patient was determined by the surgeon. Pre-operative and post-operative values were simultaneously measured by two additional orthopedic surgeons.

RESULTS

The mean age of the patients was 26.2 years (18.0-51.0) in the plating group and 29.3 years (18.0-55.0) in the nailing group. Patients in the plating and nailing groups were followed up for 24.0 (12.0-60.0) and 27.8 (12.0-60.0) months. All patients were followed for a minimum of 12 months. No significant differences were observed between the groups in terms of age, sex, or duration of follow-up (p > 0.05) Comparison of the pre- and post-operative mLDFA, aLDFA, MAD, length of hospital stay, and duration of surgery between the plating group and nailing group, no significant difference was observed between the groups (p > 0.05). However, patients treated with retrograde IMN had significantly better post-operative results in terms of the KOOS and range of motion of the knee according to plating group (p < 0.05).

CONCLUSION

Retrograde IMN does not provide a radiological advantage over the LISS plating technique for valgus deformity but retrograde IMN and correction offered better functional results in cases of femoral valgus deformity than did the LISS plating method.

Finite element comparison of retrograde intramedullary nailing and locking plate fixation with/without an intramedullary allograft for distal femur fracture following total knee arthroplasty

PURPOSE

Periprosthetic distal femur fracture after total knee arthroplasty due to the stress-shielding phenomenon is a challenging problem. Retrograde intramedullary nail (RIMN) or locking plate (LP) fixation with/without a strut allograft has been clinically used via less invasive stabilization surgery (LISS) for the treatment of these periprosthetic fractures. However, their biomechanical differences in construct stability and implant stress have not been extensively studied, especially for the osteoporotic femur.

METHODS

This study used a finite-element method to evaluate the differences between RIMN, LP, and LP/allograft fixation in treating periprosthetic distal femur fractures. There were sixteen variations of two fracture angles (transverse and oblique), two loading conditions (compression and rotation), and four bony conditions (one normal and three osteoporotic). Construct stiffness, fracture micromotion, and implant stress were chosen as the comparison indices.

RESULTS

The LP/allograft construct provides both lateral and middle supports to the displaced femur. Comparatively, the LP and RIMN constructs, respectively, transmit the loads through the lateral and middle paths, thus providing more unstable support to the construct and high stressing on the implants. The fracture pattern plays a minor role in the construct stabilization of the three implants. In general, the biomechanical performances of the RIMN and LP constructs were comparable and significantly inferior to those of the LP/allograft construct. The bone quality should be evaluated prior to the selection of internal fixators.

CONCLUSIONS

The LP/allograft construct significantly stabilizes the fracture gap, reduces the implant stress, and serves as the recommended fixation for periprosthetic distal femur fracture.

A three-dimensional comparison of intramedullary nail constructs for osteopenic supracondylar femur fractures

OBJECTIVES

This study developed a new 6 degree-of-freedom, unconstrained biomechanical model that replicated the in vivo loading environment of femoral fractures. The objective of this study was to determine whether various distal fixation strategies alter failure mechanisms and/or offer mechanical advantages when performing retrograde intramedullary nail (IMN) stabilization of supracondylar femur fractures in osteoporotic bone.

METHODS

Forty fresh-frozen human femora were allocated into 2 groups of matched pairs: "locked" (fixed angle locking construct with both distal locking screws rigidly attached to the IMN) versus "unlocked" (conventional locking technique with 2 distal locking screws targeted through the distal locking screw holes of the IMN) and "locked" versus "washer" (fixed angle locking with the most distal screw exchanged for a bolt with condyle washers) distal fixation of a retrograde IM nails. A comminuted fracture (OTA 33-A3) was simulated with a wedge osteotomy. Bone density measurements were completed on all specimens before instrumentation. Instrumented femurs were loaded axially to failure, whereas 6 degree-of-freedom translations and angulations were measured using Roentgen stereophotogrammetric analysis.

RESULTS

Mean (± SD) load born by "locked" specimens (1609 ± 667 N) at clinical failure was 38.1% greater (P = 0.09) than the corresponding mean load born by "unlocked" specimens (1165 ± 772 N). Clinical failure for the "washer" group (1738 ± 772 N) was 29.9% greater (P = 0.07) than the corresponding mean of the "locked" counterparts (1338 ± 822 N). Failure load was most clearly related to bone density in the "unlocked" fixation group.

CONCLUSIONS

Predicting failure load based on bone density using a least squares estimate suggests that the washer construct provides superior fixation to other treatment techniques. The failure mechanism for a comminuted, supracondylar fracture cannot be analyzed accurately with a 1-dimensional measurement. The most common failure mechanism in this model was medial translation and varus angulation.

Distal femoral dome varus osteotomy: surgical technique with minimal dissection and external fixation

The results obtained when employing distal femoral varus osteotomy are variable. Our objective was to describe a surgical technique involving minimal dissection, semicircular osteotomy with external fixation for valgus angular deformities, and early weight bearing.

DESIGN

Series of cases.

SETTING

Orthopedic Referral Trauma Center.

PATIENTS

Sixteen patients with valgus angular deformities of >12°.

INTERVENTION

Wedge varus osteotomy, minimal dissection with external fixation using a standard system, multidirectional Newfix. Main outcome measurements included pain, surgical time, knee flexion and extension angles, and assessment of knee function based on the Hospital Special Surgery knee rating scale (HSSkrs).

RESULTS

Of 16 patients, 14 were evaluated to the end of the study. When we compared preoperative values with those obtained postoperatively at a mean of 24±2.1months, pain measurement was reduced from 7 to 2.1 (p=0.002), angle of flexion was reduced from 105.4±14.6° to 105.3±11.1° (p=0.06), and angle of extension, from -1.67 to -1.25° (p=0.6), while HSSkrs assessment increased from 67.5±2.7 to 79.4±5 (p=0.003). Two patients were excluded from the study, one due to infection that developed along the trajectory of a screw, and the other patient underwent complete arthroplasty of the knee, which was performed to combat the pain that was not being alleviated.

CONCLUSIONS

The technique improves function and reduces pain while facilitating early rehabilitation in 83% of cases.

Distal femur fractures of the elderly--different treatment options in a biomechanical comparison

BACKGROUND

Fractures of the distal femur, especially in the elderly patient, are an unsolved problem in orthopaedic and trauma surgery. Poor bone stock quality caused by osteoporosis often results in bad implant anchorage in the distal part with a high risk of secondary failures such as cutout. This study investigates the biomechanical characteristics of four implants with different distal locking options under quasi-static torsional and cyclic axial loading. Therefore, an osteoporotic bone model simulating severe osteoporotic conditions was used.

METHODS

Four different implants (T2 intramedullary nail, supracondylar nail (SCN), distal femoral nail (DFN) and the AxSOS angular stable plate) with different distal locking options were instrumented using an osteoporotic bone model. Five specimens per implant and per loading type (torsional and axial) were used. Mechanical testing was performed under physiologic loading conditions. First, a torsional test was performed in internal and external rotation (10 Nm), with a new specimen; a stepwise cyclic axial loading was conducted until failure of the construct.

FINDINGS

For torsional loading, the lowest range of motion (ROM) and neutral zone (NZ) was found for the AxSOS plate construct. The SCN and T2 constructs showed similar results, and the highest ROM and NZ were found for the constructs treated with the DFN. Axial stiffness was highest for SCN constructs and in the same range for DFN and T2. The lowest stiffness showed in the AxSOS plate constructs with 47% of SCN stiffness. Under cyclic axial loading, the SCN constructs showed the highest number of cycles to failure, followed by AxSOS (70%), DFN (69%) and T2 (48%).

INTERPRETATION

In conclusion of this biomechanical study, we can clinically suggest that, if, in general, torsional stability is required (e.g., for bedridden patients) the AxSOS plate will be sufficient. By contrast, the findings of this study support the fact that the SCN should be considered for mobile patients where early postoperative mobilisation for rehabilitation is desired.

Development and mechanical testing of a short intramedullary nail for fixation of femoral rotational osteotomy in cerebral palsy patients

Background

Rotational osteotomy is frequently indicated to correct excessive femoral anteversion in cerebral palsy patients. Angled blade plate is the standard fixation device used when performed in the proximal femur, but extensile exposure is required for plate accommodation. The authors developed a short locked intramedullary nail to be applied percutaneously in the fixation of femoral rotational osteotomies in children with cerebral palsy and evaluated its mechanical properties.

Methods

The study was divided into three stages. In the first part, a prototype was designed and made based on radiographic measurements of the femoral medullary canal of ten-year-old patients. In the second, synthetic femoral models based on rapid-prototyping of 3D reconstructed images of patients with cerebral palsy were obtained and were employed to adjust the nail prototype to the morphological changes observed in this disease. In the third, rotational osteotomies were simulated using synthetic femoral models stabilized by the nail and by the AO-ASIF fixed-angle blade plate. Mechanical testing was done comparing both devices in bending-compression and torsion.

Results

The authors observed proper adaptation of the nail to normal and morphologically altered femoral models, and during the simulated osteotomies. Stiffness in bending-compression was significantly higher in the group fixed by the plate (388.97 ± 57.25 N/mm) than in that fixed by the nail (268.26 ± 38.51 N/mm) as torsional relative stiffness was significantly higher in the group fixed by the plate (1.07 ± 0.36 Nm/°) than by the nail (0.35 ± 0.13 Nm/°).

Conclusions

Although the device presented adequate design and dimension to fit into the pediatric femur, mechanical tests indicated that the nail was less stable than the blade plate in bending-compression and torsion. This may be a beneficial property, and it can be attributed to the more flexible fixation found in intramedullary devices.

Biomechanical Characterization of an Osteoporotic Artificial Bone Model for the Distal Femur

The treatment of osteoporotic distal femur fractures is still an unsolved problem of trauma surgery. The poor bone stock often leads to secondary loss of reduction and implant failure. Therefore, the development of new implants and their biomechanical testing is essential. In a previous study, we developed and initially characterized an artificial osteoporotic bone model of the distal femur. This follow-up study was performed to characterize this model in a biomechanical comparison. We investigated two different artificial bones: five foam cortical shell (Sawbones) and 10 custom-made artificial femoral condyles. Additionally, eight human femora were used for comparison. For biomechanical testing, two intramedullary nails (distal femur nail (DFN) and supracondylar nail (SCN)) were cyclically axial loaded in an AO 33 C2 unstable distal femoral fracture model. In our testing, the artificial bone showed a decrease in the axial stiffness of 27% for the SCN and 28% for the DFN compared to the human results. Also the number of cycles for a deformation of 2.5 mm was reduced by 55% (SCN) and 62% (DFN). This decrease was homogenous and caused by the relative high bone mineral density of the human specimen used. The modes of failure showed no difference between the artificial and human bones. Our customized artificial bone provides suitable results. In relation to the human bones classified as mildly osteoporotic, we assume that the biomechanical properties match to serve as an osteoporotic bone. Yet, we suggest to check transferability of the results with human material.

Internal fixation of type-C distal femoral fractures in osteoporotic bone

BACKGROUND

Fixation of distal femoral fractures remains a challenge, especially in osteoporotic bone. This study was performed to investigate the biomechanical stability of four different fixation devices for the treatment of comminuted distal femoral fractures in osteoporotic bone.

METHODS

Four fixation devices were investigated biomechanically under torsional and axial loading. Three intramedullary nails, differing in the mechanism of distal locking (with two lateral-to-medial screws in one construct, one screw and one spiral blade in another construct, and four screws [two oblique and two lateral-to-medial with medial nuts] in the third), and one angular stable plate were used. All constructs were tested in an osteoporotic synthetic bone model of an AO/ASIF type 33-C2 fracture. Two nail constructs (the one-screw and spiral blade construct and the four-screw construct) were also compared under axial loading in eight pairs of fresh-frozen human cadaveric femora.

RESULTS

The angular stable plate constructs had significantly higher torsional stiffness than the other constructs; the intramedullary nail with four-screw distal locking achieved nearly comparable results. Furthermore, the four-screw distal locking construct had the greatest torsional strength. Axial stiffness was also the highest for the four-screw distal locking device; the lowest values were achieved with the angular stable plate. The ranking of the constructs for axial cycles to failure was the four-screw locking construct, with the highest number of cycles, followed by the angular stable plate, the spiral blade construct, and two-screw fixation. The findings in the human cadaveric bone were comparable with those in the synthetic bone model. Failure modes under cyclic axial load were comparable for the synthetic and human bone models.

CONCLUSIONS

The findings of this study support the concept that, for intramedullary nails, the kind of distal interlocking pattern affects the stabilization of distal femoral fractures. Four-screw distal locking provides the highest axial stability and nearly comparable torsional stability to that of the angular stable plate; the four-screw distal interlocking construct was found to have the best combined (torsional and axial) biomechanical stability.

FIXATION OF SUPRACONDYLAR FEMORAL FRACTURES: A BIOMECHANICAL ANALYSIS COMPARING 95° BLADE PLATES AND DYNAMIC CONDYLAR SCREWS (DCS)

Objective: To determine, by means of comparative biomechanical tests, whether greater compressive load resistance and flexion is presented by 95° angled blade plates or by dynamic condylar screws (DCS), and to correlate the failure type presented during the tests with each type of plate. Methods: Sixty-five porcine femurs were subjected to 1 cm medial wedge osteotomy, in the metaphysis, to simulate an unstable supracondylar femoral fracture. Osteosynthesis was performed on these pieces: 35 were fixed using 95° lateral blade plates and 30 with DCS plates. Another variable studied was the failure type presented in each group, in an attempt to correlate this with the type of plate. Results: There were no statistically significant differences in biomechanical resistance between the two types of plates, or between the failure type and the plate type used for the osteosynthesis. Conclusion: The two types of plate behaved in a similar fashion. However, the angled blade plate proved to be superior to the DCS in the flexion test. No statistical difference in failure type or type of plate used was observed.

Temperature influence on DXA measurements: bone mineral density acquisition in frozen and thawed human femora

BACKGROUND

Determining bone mineral density (BMD) with dual-energy x-ray absorptiometry (DXA) is an established and widely used method that is also applied prior to biomechanical testing. However, DXA is affected by a number of factors. In order to delay decompositional processes, human specimens for biomechanical studies are usually stored at about -20 degrees C; similarly, bone mineral density measurements are usually performed in the frozen state. The aim of our study was to investigate the influence of bone temperature on the measured bone mineral density.

METHODS

Using DXA, bone mineral density measurements were taken in 19 fresh-frozen human femora, in the frozen and the thawed state. Water was used to mimic the missing soft tissue around the specimens. Measurements were taken with the specimens in standardized internal rotation. Total-BMD and single-BMD values of different regions of interest were used for evaluation.

RESULTS

Fourteen of the 19 specimens showed a decrease in BMD after thawing. The measured total-BMD of the frozen specimens was significantly (1.4%) higher than the measured BMD of the thawed specimens.

CONCLUSION

Based on our findings we recommend that the measurement of bone density, for example prior to biomechanical testing, should be standardized to thawed or frozen specimens. Temperature should not be changed during measurements. When using score systems for data interpretation (e.g. T- or Z-score), BMD measurements should be performed only on thawed specimens.

Polyaxial locking plate fixation in distal femur fractures: a biomechanical comparison

OBJECTIVES

Uniaxial, first-generation locking plates have become increasingly popular for fixation of supracondylar femur fractures. Polyaxial plates are currently available, which allow for variable-angle screw insertion; however, the biomechanical integrity of these new locking constructs is yet unproven. This study compares the mechanical stability of a conventional locking plate with that of a new polyaxial design.

METHODS

A comminuted supracondylar femur fracture (AO/OTA33-A3) gap model was created in fourth-generation synthetic composite bones. Fixation was obtained with 2 different plate constructs: (1) a conventional locking plate (uniaxial screw heads threading directly into plate) and (2) a polyaxial locking plate (screw heads are captured and "locked" into a fixed angle using locking caps). Eight specimens of each type were then tested in axial, torsional, and cyclic axial modes on a material testing machine.

RESULTS

The mean axial stiffness for the polyaxial locking plate was 24.4% greater than the conventional locking plate (168.2 vs 127.1 N/mm; P < 0.0001). The mean torsional stiffness was also greater for the polyaxial plate (2.78 vs 2.57 Nm/degree; P = 0.0226). Cyclic axial loading caused significantly less (P = 0.0034) mean irreversible deformation in the polyaxial plate (5.6 mm) than in the conventional plate (8.8 mm). The mean ultimate load to failure was significantly higher (P = 0.0005) for the polyaxial plate (1560 N) than for the conventional plate (1337 N).

CONCLUSIONS

The tested plate construct with its polyaxial locking screw mechanism provides a biomechanically sound fixation option for supracondylar femur fractures. The frictional locking mechanism allows maintenance of angular stability while affording the option of variable screw placement.

The biomechanics of ipsilateral intertrochanteric and femoral shaft fractures: a comparison of 5 fracture fixation techniques

OBJECTIVES

The aim of the present study was to examine biomechanically 5 different construct combinations for fixation of ipsilateral intertrochanteric and femoral shaft fractures.

METHODS

Twenty-five fresh-frozen adult human femora (age range = 58-91 years, average age = 75.4 years) were tested in physiological bending and in torsion to characterize initial bending and torsional stiffness and stiffness following fixation of combined intertrochanteric and femoral shaft fractures. Five fracture fixation device constructs were assessed-construct A: long dynamic hip screw (long DHS); construct B: reconstruction nail; construct C: DHS plus low-contact dynamic compression plate; construct D: DHS plus retrograde intramedullary nail; and construct E: long intramedullary hip screw. Axial stiffness, torsional stiffness, and axial load-to-failure were the main measurements recorded.

RESULTS

There were no differences between constructs in terms of axial stiffness (P = 0.41), external rotation stiffness (P = 0.13), and axial load-to-failure (P = 0.16). However, there was a borderline statistically significant difference in internal rotation stiffness between the constructs (P = 0.048). Specifically, construct C was significantly stiffer than construct E (P = 0.04).

CONCLUSIONS

All constructs showed no statistical differences when compared with one another, with the exception of construct E, which provided the least torsional stiffness. However, the current in vitro model did not simulate fracture healing or support offered by soft tissues, both of which would affect the stiffness and load-to-failure levels reached.

The biomechanics of human femurs in axial and torsional loading: comparison of finite element analysis, human cadaveric femurs, and synthetic femurs

To assess the performance of femoral orthopedic implants, they are often attached to cadaveric femurs, and biomechanical testing is performed. To identify areas of high stress, stress shielding, and to facilitate implant redesign, these tests are often accompanied by finite element (FE) models of the bone/implant system. However, cadaveric bone suffers from wide specimen to specimen variability both in terms of bone geometry and mechanical properties, making it virtually impossible for experimental results to be reproduced. An alternative approach is to utilize synthetic femurs of standardized geometry, having material behavior approximating that of human bone, but with very small specimen to specimen variability. This approach allows for repeatable experimental results and a standard geometry for use in accompanying FE models. While the synthetic bones appear to be of appropriate geometry to simulate bone mechanical behavior, it has not, however, been established what bone quality they most resemble, i.e., osteoporotic or osteopenic versus healthy bone. Furthermore, it is also of interest to determine whether FE models of synthetic bones, with appropriate adjustments in input material properties or geometric size, could be used to simulate the mechanical behavior of a wider range of bone quality and size. To shed light on these questions, the axial and torsional stiffness of cadaveric femurs were compared to those measured on synthetic femurs. A FE model, previously validated by the authors to represent the geometry of a synthetic femur, was then used with a range of input material properties and change in geometric size, to establish whether cadaveric results could be simulated. Axial and torsional stiffnesses and rigidities were measured for 25 human cadaveric femurs (simulating poor bone stock) and three synthetic "third generation composite" femurs (3GCF) (simulating normal healthy bone stock) in the midstance orientation. The measured results were compared, under identical loading conditions, to those predicted by a previously validated three-dimensional finite element model of the 3GCF at a variety of Young's modulus values. A smaller FE model of the 3GCF was also created to examine the effects of a simple change in bone size. The 3GCF was found to be significantly stiffer (2.3 times in torsional loading, 1.7 times in axial loading) than the presently utilized cadaveric samples. Nevertheless, the FE model was able to successfully simulate both the behavior of the 3GCF, and a wide range of cadaveric bone data scatter by an appropriate adjustment of Young's modulus or geometric size. The synthetic femur had a significantly higher stiffness than the cadaveric bone samples. The finite element model provided a good estimate of upper and lower bounds for the axial and torsional stiffness of human femurs because it was effective at reproducing the geometric properties of a femur. Cadaveric bone experiments can be used to calibrate FE models' input material properties so that bones of varying quality can be simulated.

Biomechanical considerations in plate osteosynthesis: the effect of plate-to-bone compression with and without angular screw stability

OBJECTIVE

We compared the biomechanical stability of bone-plate constructs using a compression plate (CP), an internal fixator (IF), and a combination plate (CP/IF).

METHODS

Standardized simulated shaft fractures with a segmental defect in composite bones (n=60) and intraarticular distal femur fractures with a comminuted supracondylar zone in fresh frozen cadaveric femurs (n=36) were stabilized by CP, IF, and CP/IF. Construct stiffness, plastic deformation, and fixation strength were measured under axial compression and torsion using a biaxial testing machine.

RESULTS

The experimental results indicate for the distal femur fracture model that IF has less loss of reduction by plastic deformation under axial load compared to CP (IF 61% of CP). Under torsion, the CP showed significantly (P<0.05) decreased plastic deformation compared to the IF (CP 51% of IF). The combination (CP/IF) of the 2 fixation principles generally resulted in a higher load to failure under axial compression and torsion (145% failure load of CP and 118% of IF under axial compression, 88% of CP and 109% of IF under torsion). Results were similar between the 2 fracture models.

CONCLUSIONS

Under compression, IF provides similar fixation in comminuted fractures and was better than the CP for avoiding loss of reduction, whereas under torsional loading, CP was more important for stiffness, plastic deformation, and load to failure than IF. However, combination (CP/IF) fixation seems advisable in intraarticular and extraarticular fractures of long bones with a metaphyseal comminution. These data may be utilized by surgeons to build a more specific treatment plan in patients with these fracture types.

Biomechanical analysis of distal femur fracture fixation: fixed-angle screw-plate construct versus condylar blade plate

OBJECTIVE

The objective of this study is to establish the relative strength of fixation of a locking distal femoral plate compared with the condylar blade plate.

METHODS

Eight matched pairs of fresh-frozen cadaveric femurs were selected and evaluated for bone density. A gap osteotomy model was used to simulate an OTA/AO A3 comminuted distal femur fracture. One femur of each pair was fixed with the blade plate; the other, with a locking plate. After 100 N preload and 10,000 cycles between 100 N and 1000 N, total displacement of each specimen was assessed. After completion of cyclic loading, maximum load to failure was tested.

RESULTS

Significantly greater subsidence (total axial displacement) occurred with the blade plate (1.70 +/- 0.45 mm; range, 1.21-2.48 mm) than with the locking plate fixation (1.04 +/- 0.33 mm; range, 0.67-1.60 mm) after cyclic loading (P = 0.03). In load-to-failure testing, force absorbed by the locking plate before failure (9085 +/- 1585 N; range, 7269-11,850 N) was significantly greater than the load tolerated by the blade plate construct (5591 +/- 945 N; range, 3546-6684 N; P = 0.001). Variability in bone mineral density did not affect the findings (fixed angle distal femoral plate r = 0.1563; condylar blade plate r = 0.0796).

CONCLUSIONS

The locking screw-plate construct proved stronger than the blade plate in both cyclic loading and ultimate strength in biomechanical testing of a simulated A3 distal femur fracture. Although differences were small, the biomechanical performance of the locking plate construct over the blade plate may lend credence to use of the locking plate versus the blade plate in the fixation of comminuted distal femur fractures.

Retrograde nailing versus fixed-angle blade plating for supracondylar femoral fractures: a randomized controlled trial

BACKGROUND

A variety of devices have been used in the treatment of supracondylar femoral fractures. The condylar blade plate relies on the principles of open reduction, absolute stability and interfragmentary compression to achieve union. The technique of retrograde nailing uses indirect reduction of the metaphyseal fracture component, offering relative stability and a less invasive approach. Randomized comparison of these common methods of fixation has not been reported.

METHODS

Twenty-two patients with 23 supracondylar femur fractures were recruited from two regional trauma centres over a 26-month period and randomized to receive either a retrograde intramedullary nail fixation (IM group, 12 fractures) or a fixed-angle blade plate fixation (BP group, 11 fractures). The groups were followed for 12-36 months. The primary outcome measures were revision surgery and general health.

RESULTS

Three patients in the IM group required revision surgery for the removal of implant components. No reoperations occurred in the BP group. There was a trend towards greater pain in the IM group, although there was no statistically significant difference in the scores for any of the SF-36 domains.

CONCLUSION

Both distal femoral nailing and blade plating give good outcomes. There is a trend for patients undergoing retrograde nailing to complain of more pain and to require revision surgery for removal of implants.

The effect of plate rotation on the stiffness of femoral LISS: a mechanical study

OBJECTIVE

Malposition of the femoral Less Invasive Stabilization System (LISS) plate may alter its biomechanical behavior. This study compares the mechanical stability of "correctly" affixed LISS plates matching the slope of the lateral femoral condyle to "incorrectly" placed LISS plates fixed in external rotation relative to the distal femur.

METHODS

A fracture gap model was created to simulate a comminuted supracondylar femur fracture (AO/OTA33-A3). Fixation was achieved using two different plate positions: the LISS plate was either placed "correctly" by internally rotating the plate to match the slope of the lateral femoral condyle, or "incorrectly" by externally rotating the plate relative to the distal femur. Following fixation, the constructs were loaded in axial, torsional, and cyclical axial modes in a material testing machine.

MAIN OUTCOME MEASUREMENT

Stiffness in axial and torsional loading; total deformation and irreversible (plastic) deformation in cyclical axial loading.

RESULTS

The mean axial stiffness for the correctly placed LISS constructs was 21.5% greater than the externally rotated LISS constructs (62.7 N/mm vs. 49.3 N/mm; P = 0.0007). No significant difference was found in torsional stiffness between the two groups. Cyclical axial loading caused significantly less (P < 0.0001) plastic deformation in the correct group (0.6 mm) compared with externally rotated group (1.3 mm). All the constructs in the incorrect group failed, where failure was defined as a complete closure of the medial fracture gap, prior to completion of the test cycles.

CONCLUSION

Correct positioning of the LISS plate for fixation of distal femur fractures results in improved mechanical stability as reflected by an increased stiffness in axial loading and decreased plastic deformation at the bone-screw interface.

Supracondylar femoral fractures in elderly patients treated with the dynamic condylar screw and the retrograde intramedullary nail: a comparative study of the two methods

INTRODUCTION

The objective of this study is to present the results of surgical management of supracondylar fractures of the femur (types A and C according to the AO/ASIF classification) in elderly patients with the use of two different methods of fixation: the mini open dynamic condylar screw fixation (DCS) and the closed retrograde intramedullary nailing (RIN).

MATERIALS AND METHODS

Eighty patients with supracondylar fractures of the femur were treated from January 1994 to June 2000 and 72 of them followed up completely. There were 25 (34%) men and 47 (65%) women with a median age of 73.2 years (range 60-88 years). In patients with the same type of fracture, the chosen method was random, one after the other (alternately). RIN was used in 35 patients, and DCS was used in 37. The mean operative time for the DCS fixation group was 145 min (range 115-180 min), whereas for the RIN group it was 92 min (range 76-110 min) (p<0.001) with an average estimated blood loss of 310 cc (range 120-450 cc) and 118 cc (range 90-165 cc), respectively (p<0.001). The mean follow-up was 28 months (range 18-42 months).

RESULTS

According to the criteria set by Schatzker and Lambert, excellent results were recorded in 18 (51%), good in 11 (31%), moderate in 3 (9%), poor in 3 (9%) patients with RIN and excellent in 19 (51%), good in 11 (30%), moderate in 4 (11%) and poor in 3 (8%) patients with DCS (p>0.05). The complications that occurred in the RIN group were 2 (6%) stiffness of the knee (mean flexion 80 degrees), 2 (6%) non-unions, 2 (6%) varus deformity and in the DCS group 2 (5%) haematomas, 4 (11%) stiffness of the knee (mean flexion 73 degrees) and 2 (5%) non-unions.

CONCLUSION

Although the two methods appear to have the same percentage of excellent results and same time to bony union, RIN is preferable to DCS in terms of less blood loss and shorter operating time.

Minimally invasive percutaneous plating of distal femoral fractures using the dynamic condylar screw

BACKGROUND

In distal femoral fractures, conventional open reduction and internal fixation causes complications because of excessive soft-tissue stripping. To prevent this, minimally invasive percutaneous plating was performed in distal femoral fractures.

METHODS

Sixteen supracondylar or intercondylar femoral fractures were treated by minimally invasive percutaneous plating with the dynamic condylar screw without bone graft. Five (31%) were open fractures.

RESULTS

All fractures healed except one. The average time for fracture healing was 17 weeks (range, 14-22 weeks). Complications included one nonunion related to early full weight bearing. No patient showed malunion or deep infection. Results were evaluated by modified Neer rating, and all patients had excellent or good results. Intra-articular fractures showed less favorable range of motion and clinical scores than extra-articular fractures.

CONCLUSION

Minimally invasive percutaneous plating with the dynamic condylar screw can provide favorable results in the treatment of distal femoral fractures.

Biomechanical evaluation of the less invasive stabilization system, angled blade plate, and retrograde intramedullary nail for the internal fixation of distal femur fractures

OBJECTIVE

To evaluate the stability of the retrograde intramedullary nail (IMN), angled blade plate (ABP), and a locked internal fixator (Less Invasive Stabilization System [LISS], Synthes, Paoli, PA) for internal fixation of distal femur fractures.

DESIGN

Destructive biomechanical testing of matched pairs of fresh-frozen human cadaveric bone-implant constructs.

SETTING

Biomechanical laboratory.

METHODS

A fracture model was created to simulate an AO/OTA33-A3 fracture. Forty-eight matched pairs of specimens were used. Six groups of 8 pairs each were tested to failure: LISS versus ABP and LISS versus IMN (axial, torsional, and cyclical axial).

MAIN OUTCOME MEASUREMENT

Load to failure, mode of failure, energy to failure, displacement at the load to failure, and stiffness.

RESULTS

Fixation strength (load/moment to failure) of the LISS constructs was 34% greater in axial loading (P = 0.01) and 32% less in torsional loading (P = 0.05) compared with ABP constructs and 13% greater in axial loading (P = 0.35) and 45% less in torsional loading (P < 0.01) compared with IMN constructs. Loss of distal fixation in axial loading occurred in 1 of 16 cases with the LISS, in 3 of 8 cases with the ABP, and in 8 of 8 cases with the IMN. Cyclical axial loading demonstrated significantly less plastic deformation for the LISS construct compared with ABP constructs (P < 0.01) and similar plastic deformation compared with IMN constructs (P = 0.98).

CONCLUSIONS

All 3 fixation devices (LISS, ABP, and IMN) offer sufficient torsional stability and sufficient proximal fixation that withstands axial loading without failing. The LISS provides improved distal fixation, especially in osteoporotic bone, at the expense of more displacement at the fracture site.

A mechanical study of gap motion in cadaveric femurs using short and long supracondylar nails

OBJECTIVE

To determine the relative stability achieved in unstable supracondylar femur fractures treated with long (36 cm) and short (20 cm) retrograde intramedullary nails using 1 or 2 proximal locking bolts. We hypothesized that longer nails would reduce fracture site motion compared with short nails and that 2 proximal locking bolts would improve stability compared with 1 proximal locking bolt.

DESIGN

Nine pairs of matched human cadaveric femurs were instrumented with 20-cm and 36-cm retrograde intramedullary nails (all 12-mm diameter, Biomet, Warsaw, IN) following reaming to 13 mm. Transverse supracondylar gap (6 mm) osteotomies were created. The femurs were mounted and cyclically tested separately in coronal plane bending and sagittal plane bending on a materials testing system. Fracture site translation was measured using a digital caliper in the respective plane.

SETTING

Orthopaedic biomaterials laboratory.

RESULTS

With 2 proximal locking bolts, average sagittal translation was 7.2 mm and 1.8 mm, respectively, for the 20-cm and 36-cm nails. Coronal translation was 6.3 mm and 4.3 mm, respectively. With a single proximal locking bolt, average sagittal translation was 7.6 mm and 2.2 mm, respectively, for the 20-cm and 36-cm nails. Coronal translation was 13.6 mm and 4.4 mm, respectively. A statistically significant difference in fracture site translation was found in each pairing by Student t test (P < 0.005), except coronal translation with 2 proximal locking bolts (P = 0.056). Free-body analysis predicts higher local stresses at the proximal interlocks of the shorter nail.

CONCLUSIONS

Longer nails provide improved initial fracture stability when compared with short retrograde nails for supracondylar femur fractures due to a more stable mechanical interaction between the femoral diaphysis and the nail. A second proximal locking bolt in the long nail provides no additional stability.

Retrograde fixation of distal femoral fractures: results using a new nail system

OBJECTIVES

To investigate the management and outcome of distal femur fractures treated with retrograde nailing.

DESIGN

Prospective.

SETTING

Unfallkrankenhaus Berlin, level I trauma center.

PATIENTS

A consecutive series of 47 patients with 48 fractures of the distal femur (37 fractures AO type A and 11 fractures type C) operated on between May 1999 and June 2000.

OUTCOME MEASURES

Outcome was assessed by using standard radiographic criteria of time to union, incidence of infection, malunion, and knee function (Leung score).

RESULTS

After an average time of 33 months (range 12-37 months), 44 patients were reexamined. Three patients were lost to follow-up. The average age was 44 years (range 17-92 years). Of patients, 19 sustained polytrauma, and 10 had associated soft tissue damage. A total of 34 patients underwent primary definitive osteosynthesis within 12 hours after trauma. All fractures healed after an average of 12.6 weeks (range 9-17 weeks). Seven complications were noted-three related to severity of injury (one deep venous thrombosis, two leg length shortenings of 1.5 cm and 2.5 cm) and four related to the operation (insufficient counterboring of the nail in two patients, one malreduction, one iatrogenic fracture of femur shaft). There was no relevant difference between type A and type C fractures in functional, clinical, or radiographic outcomes.

CONCLUSIONS

Retrograde nailing is recommended as an alternative method to plate osteosynthesis in stabilizing distal femoral fractures, particularly in type C fractures.

Orthopedic management of vertebral and long bone fractures in patients with osteoporosis

Because of the evolving demographics of the world's population, fracture surgeons must become experts in the treatment of fractures in osteoporotic bone. Toward this end, fracture surgeons are learning to modify the classic techniques of internal fixation to adapt them to the elderly population. Screws should be placed into the best quality of bone available, which, in most cases, is an opposing cortex. Screw fixation can be augmented using acrylic cement. When using plate fixation, stable bone contact at the fracture site is the most important factor in reducing strain in the plate. Shortening of the affected bone is advisable to achieve this contact in comminuted fractures. Plates should not be used to bridge areas of comminution in osteoporotic bone. Plates should generally be as long as is compatible with the affected bone, with screws placed as close to and as far away from the fracture site as possible. When confronted with diaphyseal fractures or fractures with metaphyseal-diaphyseal comminution, locked intramedullary nails can be used. Angled blade plates are applicable to osteoporotic metaphyseal fractures but should be used as tension band plates, which require stable load-sharing contact opposite the plate. Antiglide plating and use of tension band wires are also effective strategies for osteoporotic fractures. Finally, to reduce the morbidity of bone graft harvest and to ensure adequate volumes of graft, the use of bone graft substitutes is particularly applicable in elderly patients. All patients with evidence of osteoporosis should be started on a medical regimen to combat further bone loss that includes calcium supplementation with a prescription for antiresorptive agents, including bisphosphonates, calcitonin, or hormone replacement therapy.

Internal fracture fixation in patients with osteoporosis

Because of the decreased holding power of plate-and-screw fixation in osteoporotic bone fractures, internal fixation can have a high failure rate, ranging from 10% to 25%. Screws placed into cortical bone have better resistance to pullout than do those placed into adjacent trabecular bone. Plates should not be used to bridge unstable regions of bony comminution in osteoporotic patients. Fixation stability is optimized by securing stable bone contact across the fracture site and by placing screws both as close to and as far from the fracture as possible. Intentional shortening can improve stability and load sharing of the fracture construct. Structural bone graft or other types of fillers can be used to fill voids when comminution prevents stable contact. Load-sharing fixation devices such as the sliding hip screw, intramedullary nail, antiglide plate, and tension band constructs are better alternatives for osteoporotic metaphyseal locations. Proper planning is essential for improved fracture fixation in this high-risk patient group.

Indirect reduction and bridge plating of supracondylar fractures of the femur

Between October 1995 and December 1998, 16 patients with A-O type A3, C2 or C3 supracondylar femoral fractures were treated by open reduction and internal fixation using indirect reduction and bridge plating. Seven (44%) patients had open fractures. The patients were followed for a mean of 46 months (range 24-71). All fractures healed. The average time for fracture healing was 18.5 weeks (range 12-28). Four primary bone grafts and three secondary bone grafts were performed. By using the modified Schatzker rating scale, the result of 13 patients (81%) were rated as excellent or good. Complications included two implant failures that were due to full weight bearing before bone healing, and one superficial delayed wound healing. No deep infections were found in this series. The open fracture group needed longer time to heal and had a higher rate of receiving bone grafts. We conclude that indirect reduction and bridge plating with a 95 degrees dynamic condylar screw (DCS) or condylar blade plate can produce favourable results for complex distal femoral fractures. We suggest primary bone grafts or early secondary bone grafts for comminuted open fractures using an indirect reduction technique.

Knee fractures in the athlete

Sports-related fractures of the knee, although uncommon, do occur during athletic participation. The assessment and management of each fracture type have been emphasized in this article to provide a guideline for treating these acute knee injuries to a successful return to sports-specific competition. Anatomic fracture reduction is necessary to have optimal joint function in the knee as well as stability of fracture for early joint motion, promote bone healing, and avoid traumatic arthritis. This is especially crucial to the injured athlete, as residual deficits of the knee can greatly affect performance. Selection of low-profile implants at the time of surgery to prevent soft tissue irritation and possible implant removal must also be considered with the return to athletic activity.

Supracondylar femur fracture fixation: mechanical comparison of the 95 degrees condylar side plate and screw versus 95 degrees angled blade plate

The best way to stabilize supracondylar femur fractures remains debatable. Previous studies have compared internal fixation to intramedullary fixation, but none have compared the stiffness characteristics and strength of the 95 degrees angled blade plate (ABP) with the 95 degrees condylar side plate and screw (DCS). 14 synthetic femora were cut in half and the proximal pole of the distal fragment was made secure. A 1 cm gap was made parallel to the femoral condylar weight-bearing surface to create an extraarticular supracondylar femur fracture (OTA 33-A3). 7 femora were stabilized with an ABP and 7 with a DCS. Using an MTS compression/torsion servohydraulic testing machine, each femur was tested in 7 modes of loading: (1) axial compression; (2) anterior compression; (3) posterior compression; (4) medial compression; (5) lateral compression; (6) torsion in external rotation; and (7) torsion in internal rotation. The stiffness of the construct in each mode, the "maximum load in axial compression", and the fatigue characteristics in axial compression were measured. The DCS showed a statistically significant greater stiffness in axial compression and average maximal load than the ABP. The fatigue tests revealed no evidence of permanent deformation or loosening of either construct.

Distal femoral fractures and LISS stabilization

In recent years, the technique of surgical stabilization in the distal femur has changed. This change decreased the number of non unions and the need for bone grafting. Minimally invasive surgical techniques with a submuscular plate placement have replaced the emphasis on anatomical reduction in the shaft area. Reconstruction of complex articular injuries has been simplified by more direct visualization of the articular surface with the lateral peripatellar approach. Problems remaining are surgical technique and implant considerations. The Less Invasive Stabilization System (LISS) simplifies the surgical technique for percutaneous plate osteosynthesis. An insertion guide is used to insert monocortical, self-tapping screws through a stab incision. A thread in the plate provides the angular stability for the anchoring of these screws. In extra-articular fractures and simple intra-articular fractures, the distal femoral nail permits intramedullary stabilization. A spiral blade improves fixation of the distal femoral condylar block. Despite the enhanced surgical technique and implant possibilities, a great number of patients show a functional deficiency. These are particularly patients with complex intra-articular fractures. The 'fatigue failure' of the osteoporotic implant-bone construct is a problem in elderly patients. The LISS represents a good option to avoid the addition of bone cement to an osteosynthesis.

Biomechanical evaluation of the less invasive stabilization system for the internal fixation of distal femur fractures

OBJECTIVE

Comparison between a Less Invasive Stabilization System (LISS) using monocortical screws with angular stability and two conventional plate systems Condylar Buttress Plate (CBP) and Dynamic Condylar Screw (DCS) for the treatment of distal femoral fractures with respect to biomechanical properties.

DESIGN

Biomechanical study using paired cadaver femurs. In Test Configuration 1 (distal test), a ten-millimeter gap at the diaphysis-metaphysis junction simulates a supracondylar femoral fracture. Test Configuration 2 (proximal test) has the same configuration, but the gap was cut in the isthmic region. Proximal and distal plate ends were fixed to corresponding cortical bone fragments in both tests. Optical displacement transducers served to quantify the system's ability to withstand a stepwise increased load. Reversible (deflection) and irreversible deformation (subsidence) of the bone-plate construct was investigated.

RESULTS

In Test Configuration 1, LISS showed less irreversible deformation in 72 percent of the left-right comparisons. No correlation between bone mineral density, cross-section area of bones and the measured response of the construct under load was found between pairs. In Test Configuration 2, 83 percent of the left-right comparisons showed less permanent deformation but a higher elastic deformation for LISS.

CONCLUSIONS

These results suggest an enhanced ability to withstand high loads when using the monocortical screw fixation technique with angular stability. A higher elastic deformation of LISS compared with conventional plating systems in distal femoral fractures can be explained by the lower bending stiffness caused by different design and material properties.

Mechanical comparison of endosteal substitution and lateral plate fixation in supracondylar fractures of the femur

OBJECTIVE

To assess for improved rigidity with the addition of a medial endosteal plate to laterally plated supracondylar femoral fractures.

DESIGN

A randomized paired study in a supracondylar femoral fracture model comparing two fixation methods tested cyclically in axial and torsional loading.

METHODS

One-centimeter supracondylar gap osteotomies were created in twenty synthetic femurs approximately six centimeters proximal to the knee joint. Ten were stabilized with a lateral eight-hole buttress plate alone, and ten were secured by a similar lateral buttress plate plus a medial endosteal eight-hole dynamic compression plate. Group 1 (n = 5; lateral plate alone) and Group 2 (n = 5; lateral and endosteal plates) were axially loaded up to 700 newtons through a materials test system for three cycles. A displacement transducer detected movement at the medial fracture gap. Group 3 (n = 5; lateral plate alone) and Group 4 (n = 5; lateral and endosteal plates) were tested in torsion. A rod-and-pulley system created an external rotation torque up to twenty Newton-meters for three cycles. A rotary potentiometer measured angular displacement.

RESULTS

Lateral buttress plating with endosteal substitution showed statistically significant decreased motion at the fracture site in torsional (p < 0.004) and axial loading (p < 0.0001) versus lateral buttress plating alone using Student's t test.

CONCLUSION

The addition of a 4.5-millimeter endosteal plate to a lateral buttress plate provides significantly increased stability, as compared with lateral plating alone in a femoral supracondylar fracture model during simulated axial and torsional loading. Neither fixation construct, however, restored the torsional stability of the distal femur to its preinjury (intact) level.

Stress analysis of the distal locking screws for femoral interlocking nailing

In femoral locked nailing, the distal locking screws are vulnerable to mechanical failure. Biomechanical studies have shown that the stress on these screws is substantially affected by the fit of the nail in the medullary canal. In this study, a "closed form" mathematical model based on elastic beam-column theory was developed to investigate how the nail-cortical contact, which was simulated by a linear elastic foundation, affected the stress on the distal locking screws. Providing data for the model was a construct of a fractured femur with an intramedullary locked nail loaded by an eccentric vertical load. The stress on the locking screw was analyzed as a function of the distance from the fracture to the locking screw in the distal fragment under two situations: with and without nail-cortical contact in the distal fragment. With nail-cortical contact, the screw stress decreased as the length of nail-cortical contact and the distance between the distal locking screw and the fracture site increased, but this stress contrarily increased when the nail reached the femoral region at which the screw length increased. The screw stress was much higher without nail-cortical contact than with contact and continued to increase as the nail was inserted further. The mathematical model developed here can be a convenient means of rapid stress evaluation and parametric analysis for locked femoral nailing. It may be used to improve the design of interlocking nails and surgical technique.

Mechanical comparison of a distal femoral side plate and a retrograde intramedullary nail

OBJECTIVE

To compare quantitatively the axial and torsional stiffness of a retrograde intramedullary nail and a fixed angle screw side plate in treating a supracondylar femur fracture in osteopenic femora. To determine the modes of failure of an intramedullary nail and a side plate under axial loading.

DESIGN

Matched pair cadaveric study.

SETTING

Orthopaedic biomechanics laboratory.

PATIENTS AND OTHER PARTICIPANTS

Eleven matched pairs of preserved human femora were selected. The cadaveric specimens were harvested from relatively elderly donors with an average age of 75.6 years, which represents the principal population at risk for poor fracture fixation.

INTERVENTION

The eleven matched pairs were osteotomized to simulate segmental structural defects in the supracondylar region. One femur of each matched pair was fixed with an intramedullary nail, and the contralateral femur was fixed with a side plate.

MAIN OUTCOME MEASURES

Axial and torsional stiffness values. Axial modes of failure.

RESULTS

The intramedullary nail axial stiffness was 14 percent (p = 0.04) less and torsional stiffness was 17 percent (p = 0.05) less than that provided by the side plate. The axial failure of the intramedullary nail occurred distally, allowing the hardware to protrude into the articular space. The side plate also failed distally by displacing the condylar screw into a varus angulation.

CONCLUSION

The mechanical advantages favor the use of the side plate if fixation stiffness is essential. The axial mode of failure occurs distally for both fixation devices.

New technique for treatment of unstable distal femur fractures by locked double-plating: case report and biomechanical evaluation

BACKGROUND

A comminuted, intra-articular distal femur fracture was surgically treated by the authors with a locked, double-plating technique because fixation stability could not be initially achieved by using a standard double-plating technique. The purpose of this study was to determine biomechanically whether a locked double-plate construct would enhance fixation stability compared with a nonlocked double-plate construct.

METHODS

Six matched pairs of mildly osteopenic femurs were selected and all had a reproducible intra-articular fracture pattern created. Each pair underwent fixation with either a double-plating construct or a locked, double-plating construct that was randomly assigned. The instrumented femurs were then mechanically tested in several loading modes to determine fixation stability. After initial testing, specimens were cyclically loaded and retested for stability.

RESULTS

The locked, double-plating construct provided significantly greater fixation stability than the standard double-plating construct in precycling and postcycling biomechanical testing.

CONCLUSION

The technique described is particularly applicable for severely comminuted fractures of the distal femur and fractures in osteopenic bone with poor screw purchase. It offers a simple alternative for enhancing fixation stability, which avoids the potential complications of methylmethacrylate-enhanced screw fixation.

The supracondylar intramedullary nail in elderly patients with distal femoral fractures

From February 1994 until July 1997, a prospective study of all elderly patients with a displaced distal femoral fracture, who were treated with an intramedullary supracondylar nail, was made. The outcome of 31 fractures in 30 elderly patients was studied. The average age was 82 years (55-98). Two-thirds of the patients had had previous ipsilateral femoral pathology. Average acute hospital stay was 17 days. All patients were reviewed at 6 months and all cases have been followed for over 1 year. More than 90% of surviving fractures had healed within 6 months of the operation. Outcome scores were; 22 (85%) excellent or satisfactory, 2 (7.5%) unsatisfactory and 2 (7.5%) failures. The mortality rate was 17% at 6 months and 30% at 1 year, which is similar to patients with a fractured neck of femur. This nail is recommended for its versatility and favourable outcome scores in this age group.

Internal fixation of supracondylar femoral fractures: comparative biomechanical performance of the 95-degree blade plate and two retrograde nails

OBJECTIVE

The biomechanical stability of supracondylar femoral fractures fixed with a condylar blade plate (plate), a Green Seligson Henry nail (GSHN), or a new retrograde unreamed supracondylar femoral nail (new nail) based on the AO unreamed femoral nail were compared.

DESIGN

A standardized simulated comminuted supracondylar femoral fracture (segmental defect) in fresh frozen paired cadaveric femora was stabilized with one of the implants. The interfragmentary fracture site stiffness in three directions and axial strength of the fixator-bone construct were compared (pairwise).

RESULTS

The plate versus the new nail was (a) axially 10 percent as stiff and 50 percent as strong (ultimate strength), (b) as stiff in A/P bending, and (c) five times more stiff in torsion. Varus angle at failure under axial load was significantly greater for the plate than for the new nail. There were no statistical differences in axial stiffness and ultimate strength between the new nail and the GSHN, but the new nail was 50 percent and 30 percent as stiff in A/P bending and torsion, respectively. The magnitude of deformation at failure under axial loading was similar.

CONCLUSIONS

In fixation of extraarticular comminuted supracondylar distal femur fractures, results indicate that (a) the new nail provides equal or greater stability than does the plate, except when large torsional loads are anticipated, and (b) the new nail provides stability equal to the GSHN for axial loading and lesser stability against off-axis loads. As is evident in this and other studies, intramedullary implants are less torsionally stiff than are plates. The torsional stiffness of the new nail is expected to be sufficient because it is comparable to many available nails, and low torsional moments are expected for healing femoral supracondylar fractures.

Distal femoral fixation: a biomechanical comparison of the standard condylar buttress plate, a locked buttress plate, and the 95-degree blade plate

OBJECTIVES

This biomechanical cadaver study was performed to compare the fixation stability of a standard lateral condylar buttress plate with a similar condylar buttress plate with the distal screws locked to the plate. Then the study was repeated with six additional matched femoral pairs to compare the locked plate with a standard 95-degree blade plate.

DESIGN

Six matched pairs of mildly osteopenic femurs were selected, and each side was assigned randomly to fixation with either a standard lateral condylar buttress plate or a modified lateral condylar buttress plate with locked distal screws. The experiment was repeated with six additional matched pairs of femurs instrumented with either a modified lateral condylar buttress plate with locked distal screws or a standard 95-degree blade plate.

INTERVENTION

The femurs were instrumented, and a gap osteotomy was created at the distal femoral metaphysis. The instrumented femurs were then mechanically tested in axial compression and bending/torsional loading to determine fixation stability; then they were loaded at 1,000 newtons for 10(5) cycles and retested for stability.

MAIN OUTCOME MEASUREMENT

The displacement across the osteotomy gap at 100-newton and 1,000-newton axial loads was measured directly for each specimen before and after cycling. In addition, resistance to displacement in bending/torsional loading (newtons/centimeter) was determined from load/displacement curves, before and after cycling.

RESULTS

The locked buttress plate provided significantly greater fixation stability than the standard plate both before and after cycling in axial loading. The locked buttress plate also proved significantly more stable in axial loading than the blade plate both before and after cycling.

CONCLUSION

A condylar buttress plate with locked screws is a valid concept for improving fixation stability.