Comparison of torsional strength of humeral intramedullary nailing: a cadaveric study

Computed Tomography-Based Humeral Templating for Uncemented Elbow Arthroplasty

BACKGROUND

Intramedullary (IM) screw insertion into the distal humerus provides fixation for a novel, uncemented elbow arthroplasty. A multitude of screw sizes is required to accommodate variable humeral morphology. The goal of this study was to use computed tomography (CT) for IM screw sizing and to validate this templating by inserting screws into three-dimensionally (3D) printed models.

METHODS

Computed tomography humerus scans for 30 patients were reformatted in the plane of the distal IM canal. Screw size was templated by measuring the canal diameter at 3 locations corresponding to the lengths of the screws being tested. Interrater and intrarater reliabilities of the measurements were assessed. Three-dimensional models of 5 humeri were printed, and IM screws were placed to achieve a secure endosteal fit.

RESULTS

We identified combinations of body components and IM screw length and diameter for all patients to seat this uncemented elbow arthroplasty. The measurements and screw width determinations were reliable. Canal diameter correlated with age but was unrelated to sex. Screws were inserted into five 3D-printed models which matched the templates and demonstrated mechanical and radiographic evidence of secure fit.

CONCLUSIONS

This study characterizes distal humerus anatomy in the context of IM screw fixation. Humerus CT scans of 30 patients were able to be templated, and validation via implantation of IM screws into 3D models was successful. Computed tomography templating will allow surgeons to predict the optimal screw size prior to implantation. A broad range of screw lengths and diameters is critical for implantation of this novel elbow arthroplasty.

[Therapy of Humeral Shaft Fractures]

Humeral shaft fractures are a rare but challenging entity of injuries of the upper extremity. Despite all advances in the past decades - including improved imaging, adjusted surgical techniques and new implant designs - the treatment of humeral shaft fractures and especially the treatment choice remains challenging. Treatment options need to be evaluated individually under consideration of fracture morphology, soft tissue and potential neurological damage as well as patient-specific factors (i.e., age, comorbidities). Moreover, the risk of common complications such as radial nerve palsy, infection, non-union and malrotation needs to be evaluated in order to facilitate the best possible therapy for each patient. The regular available treatment options include conservative (cast, brace, etc.) and surgical measures (ante- and retrograde nailing, angle-stable plate osteosynthesis). Furthermore, (temporary) external fixation remains an option in emergency and complicative cases. However, none of the aforementioned options have proven a superior gold standard. This review evaluates the currently available treatment options and their individual advantages as well as the probability of possible complications and is aiming to supply a guide for individual treatment choice.

Biomechanical comparison of humeral nails with different distal locking mechanisms: Insafelock nails versus conventional locking nails

Objective

The aim of this study was to compare the biomechanical resistance to rotational and axial forces of a conventional locking nail with a newly designed intramedullary humeral nail developed for humeral shaft fractures with a secure locking mechanism through the distal part of the nail.

Methods

InSafeLOCK humeral nail system (group 1, TST, Istanbul, Turkey) and Expert humeral nail system (group 2, DePuy Synthes, Bettlach, Switzerland) of the same size (9 × 300 mm) were examined. In total, 24 fourth-generation humerus sawbones were used in the experiment. Osteotomy was performed at the humerus shaft, and a defect was created by removing 1 cm of bone. After pre-loading 5000 cycles at a frequency of 2 Hz and a force of 50–250 N for axial loading and 5000 torsion torques between 0.5 Nm and 6.5 Nm at a 2 Hz frequency for torsional loading, the failure load values of each load were recorded. Distal interlocking was performed with an endopin in group 1, while a double cortex screw was used in group 2.

Results

All samples successfully passed the cyclic loading. The initial and final stiffness values were similar between the groups after axial loading (p = 0.873 and p = 0.522, respectively). The mean axial failure load values in groups 1 and 2 were 2627 ± 164 N and 7141 ± 1491 N, respectively. A significant difference was found in the axial failure load values (p = 0.004). Significant differences were observed between the initial and final torsional stiffness between the two groups (p = 0.004 and p = 0.004, respectively). No significant difference was found in the failure load values after torsional loading (11791 ± 2055 N.mm and 16997 ± 5440 N.mm) (p = 0.055).

Conclusion

These results provide a biomechanical demonstration of the adequate stability of both nails after axial and rotational loading. The reliability of the newly developed InSafeLOCK humeral nail system, which does not require fluoroscopic control and an additional incision for distal locking, supports its use in the clinic.

Proximal versus distal screw placement for biceps tenodesis: a biomechanical study

PURPOSE

To assess the maximum and end torque of a fourth-generation composite humerus model with no screw inserted or with a screw inserted in the distal (subpectoral) position or proximal (suprapectoral) position.

METHODS

24 large-size, fourth-generation composite humeri were randomised to the control (n=8), proximal (n=8), or distal (n=8) group. For the latter 2 groups, an 8-mm-head interference screw (7x25 mm) was inserted at 1 cm proximal and 1 cm distal to the superior aspect of the insertion of the pectoralis major tendon, respectively. The maximum and end torque of each humerus was assessed.

RESULTS

Respectively for the control, proximal, and distal groups, the maximum torque was 81.8, 78.7, and 74.3 Nm, and the end torque was 80.7, 78.6, and 71.8 Nm; only the difference between control and distal groups was significant (p=0.005 for maximum torque and p=0.033 for end torque). All fractures in both control and proximal groups involved the distal 1/3 humerus. In the distal group, the fractures involved either the distal 1/3 humerus (n=6) or the screw-hole (n=2); the difference between the 2 types of fracture was not significant in terms of maximum torque (75.7 vs. 70.0, p=0.086) or end torque (75.3 vs. 61.4, p=0.40).

CONCLUSION

Compared with proximal placement of an interference screw, distal placement decreased the maximum torque (though not significantly) and may increase the risk of proximal humeral fracture.

Computed modeling of humeral mid-shaft fracture treated by bundle nailing

Elastic bundle nailing is a method for simple humeral mid-shaft fracture osteosynthesis. The aim of our subsequent numerical simulations was to find out torsional and bending stiffness of an elastic bundle nailed humerus. Parametrical 3D numerical model was developed. The diameter of nails was the varying parameter of 1.8, 2.5, 3 and 4 mm. From our results can be seen that the bending stiffness in bundle nailing technique does not depend on nail diameter. On the contrary the torsional stiffness does highly depend on nail diameter. The dependency of the maximal stress on a nail diameter during bending and torsion of the humerus is non-linear. It can be seen that the higher diameter is used the higher stress occurs. Achieved results allow us for the recommendation of optimal nail diameter for this method, which lies between 2 and 3 mm.

Torsional Fracture of the Humerus after Subpectoral Biceps Tenodesis with an Interference Screw: A Biomechanical Cadaveric Study

BACKGROUND

Humeral fracture following subpectoral biceps tenodesis has been previously reported; however, there are no published biomechanical studies reporting the resulting torsional strength of the humerus. Our purpose was to determine if there is an increased risk of humerus fracture after subpectoral biceps tenodesis with an interference screw and to determine if screw size is also a factor. We hypothesized that limbs receiving the procedure would have reduced failure torque and rotation under external rotation compared to untreated controls and that the larger screw size would result in inferior mechanical properties compared to the smaller.

METHODS

Twenty matched pairs of embalmed cadaveric humeri were subjected to subpectoral biceps tenodesis using either a 6.25 or 8.0mm interference screw, with the untreated contralateral limb serving as a control. Each humerus was mechanically tested in torsional external rotation to failure.

FINDINGS

Maximum torque and rotation to failure were reduced in the tenodesis group compared to controls; however, there was no difference between screw sizes. When both screw sizes were combined into a single group, paired t-tests also showed similar differences.

INTERPRETATION

Based on our experiment, there is an increased risk for humerus spiral fracture when subjected to torsional external rotation after subpectoral biceps tenodesis with an interference screw compared to an intact humerus; however, there is not a significant difference between a 6.25mm and 8.0mm screw. Surgeons may elect to use alternative fixation methods in patients at high risk (e.g., overhead throwing athletes, etc.) for torsional loads and fracture.

Biomechanical Measurements of Stiffness and Strength for Five Types of Whole Human and Artificial Humeri

The human humerus is the third largest longbone and experiences 2–3% of all fractures. Yet, almost no data exist on its intact biomechanical properties, thus preventing researchers from obtaining a full understanding of humerus behavior during injury and after being repaired with fracture plates and nails. The aim of this experimental study was to compare the biomechanical stiffness and strength of “gold standard” fresh-frozen humeri to a variety of humerus models. A series of five types of intact whole humeri were obtained: human fresh-frozen (n = 19); human embalmed (n = 18); human dried (n = 15); artificial “normal” (n = 12); and artificial “osteoporotic” (n = 12). Humeri were tested under “real world” clinical loading modes for shear stiffness, torsional stiffness, cantilever bending stiffness, and cantilever bending strength. After removing geometric effects, fresh-frozen results were 585.8 ± 181.5 N/mm2 (normalized shear stiffness); 3.1 ± 1.1 N/(mm2 deg) (normalized torsional stiffness); 850.8 ± 347.9 N/mm2 (normalized cantilever stiffness); and 8.3 ± 2.7 N/mm2 (normalized cantilever strength). Compared to fresh-frozen values, statistical equivalence (p ≥ 0.05) was obtained for all four test modes (embalmed humeri), 1 of 4 test modes (dried humeri), 1 of 4 test modes (artificial “normal” humeri), and 1 of 4 test modes (artificial “osteoporotic” humeri). Age and bone mineral density versus experimental results had Pearson linear correlations ranging from R = −0.57 to 0.80. About 77% of human humeri failed via a transverse or oblique distal shaft fracture, whilst 88% of artificial humeri failed with a mixed transverse + oblique fracture. To date, this is the most comprehensive study on the biomechanics of intact human and artificial humeri and can assist researchers to choose an alternate humerus model that can substitute for fresh-frozen humeri.

Revision with plates of humeral nonunions secondary to failed intramedullary nailing

PURPOSE

The objective of this study was to evaluate the results achieved after revision with plates of humeral nonunions secondary to failed intramedullary nailing.

METHODS

We retrospectively evaluated 32 patients with humeral nonunions secondary to failed intramedullary nailing, treated by internal fixation with plates between 1998 and 2012. Nonunions were diaphyseal in 19 cases, they were located in the proximal humeral metaphysis in nine cases, and in the distal humeral metaphysis in four cases. There were 11 atrophic nonunions and 21 oligotrophic nonunions. Initial treatment was performed with static locked nails in 12 cases, nails with expansive locking systems in 11 cases, and using thin elastic nails in nine cases. The nails were placed antegrade in 18 cases and retrograde in 14 cases. Time between initial surgery and revision surgery averaged 14.5 months. In seven diaphyseal nonunions, the intramedullary nail was left in-situ. Bone graft was added in 25 cases.

RESULTS

Follow-up averaged 35 months. Union was achieved in all cases, after an average of 3.8 months. Disabilities of the Arm, Shoulder and Hand (DASH) score at last follow-up averaged 14 points, and Constant's score averaged 82 points. The analogue scale of pain averaged 0.8 points. Out of seven patients with radial nerve compromise, six recovered completely and one needed tendon transfers.

CONCLUSIONS

Revision with plates after failed intramedullary humeral nailing achieved union and good predictable objective and subjective results in all cases. Adequate implant selection and meticulous surgical technique are necessary to achieve successful osteosynthesis and bony union.

The biomechanical effect of torsion on humeral shaft repair techniques for completed pathological fractures

In the presence of a tumor defect, completed humeral shaft fractures continue to be a major surgical challenge since there is no "gold standard" treatment. This is due, in part, to the fact that only one prior biomechanical study exists on the matter, but which only compared 2 repair methods. The current authors measured the humeral torsional performance of 5 fixation constructs for completed pathological fractures. In 40 artificial humeri, a 2-cm hemi-cylindrical cortical defect with a transverse fracture was created in the lateral cortex. Specimens were divided into 5 different constructs and tested in torsion. Construct A was a broad 10-hole 4.5-mm dynamic compression plate (DCP). Construct B was the same as A except that the screw holes and the tumor defect were filled with bone cement and the screws were inserted into soft cement. Construct C was the same as A except that the canal and tumor defect were filled with bone cement and the screws were inserted into dry cement. Construct D was a locked intramedullary nail inserted in the antegrade direction. Construct E was the same as D except that bone cement filled the defect. For torsional stiffness, construct C (4.45 ± 0.20 Nm/deg) was not different than B or E (p > 0.16), but was higher than A and D (p < 0.001). For failure torque, construct C achieved a higher failure torque (69.65 ± 5.35 Nm) than other groups (p < 0.001). For the failure angle, there were no differences between plating constructs A to C (p ≥ 0.11), except for B versus C (p < 0.05), or between nailing groups D versus E (p = 0.97), however, all plating groups had smaller failure angles than both nailing groups (p < 0.05). For failure energy, construct C (17.97 ± 3.59 J) had a higher value than other groups (p < 0.005), except for A (p = 0.057). Torsional failure always occurred in the bone in the classic "spiral" pattern. Construct C provided the highest torsional stability for a completed pathological humeral shaft fracture.

Retrograde nailing of a femoral supracondyle

Because standard femoral supracondylar nails have certain disadvantages, they are often replaced by traditional femoral or tibial locked nails. The purpose of this study was to make a biomechanical comparison between both types of traditional locked nails to determine which technique was more suitable for treating unstable femoral supracondylar fractures. Fourteen left Sawbones femurs (Pacific Research Laboratories, Vashon, Washington) were osteotomized in the femoral supracondylar area. One centimeter of the medial cortex in the proximal fragment was obliquely removed to simulate an unstable fracture without shortening. Seven specimens were treated with traditional retrograde dynamic femoral locked nails, and the other 7 with traditional retrograde dynamic tibial locked nails. All specimens were tested with a servohydraulic materials testing machine to compare their relative stability. Static compression, dynamic cyclic compression, and static compression to failure were tested. An extensometer was used to measure the displacement of fragments. Displacement between the fragments increased following the increment in loads in both nails. The load-displacement curve was nearly linear up to 1000 N for both nails. The femoral nail had a greater stiffness compared with the tibial nail at 100 and 200 N (P=.02 and P=.04, respectively) in static compression and at 700 to 1000 N (P=.01 in each case) in dynamic cyclic compression, as well as larger loads in static compression to failure (8663 vs 7547 N, respectively; P<.001). Clinically, a traditional femoral locked nail may be more suitable to replace a standard femoral supracondylar nail in a retrograde fashion to treat an unstable femoral supracondylar fracture.

Biomechanical measurements of axial crush injury to the distal condyles of human and synthetic femurs

Few studies have evaluated the ‘bulk’ mechanical properties of human longbones and even fewer have compared human tissue to the synthetic longbones increasingly being used by researchers. Distal femur fractures, for example, comprise about 6% of all femur fractures, but the mechanical properties of the distal condyles of intact human and synthetic femurs have not been well quantified in the literature. To this end, the distal portions of a series of 16 human fresh-frozen femurs and six synthetic femurs were prepared identically for mechanical testing. Using a flat metal plate, an axial ‘crush’ force was applied in-line with the long axis of the femurs. The two femur groups were statistically compared and values correlated to age, size, and bone quality. Results yielded the following: crush stiffness (human, 1545 ± 728 N/mm; synthetic, 3063 ± 1243 N/mm; p = 0.002); crush strength (human, 10.3 ± 3.1 kN; synthetic, 12.9 ± 1.7 kN; p = 0.074); crush displacement (human, 6.1 ± 1.8 mm; synthetic, 2.8 ± 0.3 mm; p = 0.000); and crush energy (human, 34.8 ± 15.9 J; synthetic, 18.1 ± 5.7 J; p = 0.023). For the human femurs, there were poor correlations between mechanical properties versus age, size, and bone quality (R2 ≤ 0.18), with the exception of crush strength versus bone mineral density (R2 = 0.33) and T-score (R2 = 0.25). Human femurs failed mostly by condyle ‘roll back’ buckling (15 of 16 cases) and/or unicondylar or bicondylar fracture (7 of 16 cases), while synthetic femurs all failed by wedging apart of the condyles resulting in either fully or partially displaced condylar fractures (6 of 6 cases). These findings have practical implications on the use of a flat plate load applicator to reproduce real-life clinical failure modes of human femurs and the appropriate use of synthetic femurs. To the authors’ knowledge, this is the first study to have done such an assessment on human and synthetic femurs.

Diaphyseal humeral fractures and intramedullary nailing: Can we improve outcomes?

While intramedullary nailing has been established as the treatment of choice for diaphyseal fractures of the femur and tibia, its role in the management of diaphyseal humeral fractures remains controversial. The reasons include not only the complicated anatomy and unique biomechanical characteristics of the arm but also the fact that surgical technique and nail designs devised for the treatment of femoral and tibial fractures are being transposed to the humerus. As a result there is no consensus on many aspects of the humeral nailing procedure, e.g., the basic nail design, nail selection criteria, timing of the procedure, and the fundamental principles of the surgical technique (e.g., antegrade/retrograde, reamed/unreamed, and static/dynamic). These issues will be analyzed and discussed in the present article. Proposals aiming to improve outcomes include the categorization of humeral nails in two distinct groups: "fixed" and "bio", avoidance of reaming for the antegrade technique and utilization of "semi-reaming" for the retrograde technique, guidelines for reducing complications, setting the best "timing" for nailing and criteria for selecting the most appropriate surgical technique (antegrade or retrograde). Finally, suggestions are made on proper planning and conducting clinical and biomechanical studies regarding the use of intramedullary nailing in the management of humeral shaft fractures.

Structural properties of a novel design of composite analogue humeri models

BACKGROUND

Mechanical analogue composite bone models have been used as cadaveric bone substitutes in a wide variety of biomechanical tests. The objective of this study was to compare the structural properties of two types (Third- and Fourth-Generation) of commercially available composite analogue humeri.

METHODS

Eighteen of each generation composite analogue humeri were evaluated for flexural rigidity, torsional rigidity, and failure strength. Three tests were performed: medial-lateral four-point bending, anterior-posterior four-point bending, and external rotational torque.

RESULTS

The Fourth-Generation analogue humeri performed more closely to the biological average with respect to failure strength, flexural rigidity, and torsional stiffness when compared to the Third-Generation humeri. Both the Third- and Fourth-Generation analogues were within the range of published human bone values. There was a statistically significant difference in strength in all modes of testing between the Fourth-Generation humeri and the Third-Generation humeri.

CONCLUSION

These composite analogue humeri are ideal for standardization in biomechanical analyses. The advantage of these humeri is that their variability is significantly lower than that of cadaveric specimens for all loading regimens. The widely varying results observed when comparing composite analogue humeri to cadaveric humeri might be derived from the use of different ranges of applied load, varied test methodologies, and diverse methods of computing the stiffness. Mechanical validation of whole Fourth-Generation humeri bone models would be an appropriate follow-up to this study with a direct comparison to cadaveric humeri.

CLINICAL RELEVANCE

This study validated and advanced our overall understanding of the capacity of composite analogue humeri to model the structural properties of human bone.

Antegrade humeral nailing through the rotator cuff interval: a new entry portal

The conventional approach for antegrade intramedullary nailing (AIN) of humerus fractures is associated with persistent pain and compromised shoulder function. Damage to the critical hypovascular zone of the rotator cuff near its insertion on the humerus and/or irritation of the subacromial space by prominent hardware are the factors believed to be responsible for poor shoulder function after AIN of the humerus. This study describes a new entry portal through the rotator interval that minimizes iatrogenic damage to the rotator cuff at its insertion. This approach offers a solution for the disappointing postoperative shoulder function and pain scores associated with conventional antegrade nailing techniques. This study consisted of 33 patients with 34 humeral fractures followed for an average of 34 months. The overall satisfaction rate was more than 90%, according to the ASES (American Shoulder and Elbow Society) score. The mean Constant Score was 84 (SD, 14; range, 17 to 98), and primary bone union was achieved in 32 of the 34 cases.

Intramedullary Nailing of Humeral Head and Humeral Shaft Fractures

There is an increasing interest in intramedullary nailing for humeral fractures. Starting with diaphyseal fractures, now also proximal metaphyseal fractures of the humerus can be nailed with satisfying results. Basic ideas for humeral nailing are less invasive approaches to the humerus, less soft tissue damage, e.g. lower rates of radial nerve palsy, closed reduction and the biomechanical aspects of a central implant with elastic fixation properties. Nailing of diaphyseal humeral shaft fractures is an equivalent alternative to plating; nailing of proximal metaphyseal humeral fractures is still new and needs more reliable scientific data to clear its advantages compared to other fixation techniques. Nailing of distal metaphyseal humeral fractures is no serious option at the moment. Angular stable interlocking systems show better fixation qualities for proximal fractures or fracture components. Although in very osteoporotic bone cutouts are registered. Static interlocking is advisable. High torsional stability of the fracture fixation has to be achieved, since significant torsional load occurs during the usual movement of the upper limbs. As there is an important learning curve, possible complications of intramedullary nailing have to be kept in mind and avoided by a careful operation technique.

Compression-locked nailing of the humerus: a mechanical analysis

BACKGROUND

In the treatment of humeral fractures, reamed nailing and compression have been reported to give higher stability. In this cadaver study, we compared the Unreamed Humeral Nail (UHN) with the (reamed) Telescopic Locking Nail (TLN) to find out whether any differences exist concerning bending and rotational stability, both with and without compression.

METHODS

Nails were tested in a paired set-up with 8 pairs of fresh frozen cadaveric humeri. The nail-bone constructs were submitted to axial distraction to test compression, four-point bending and torsion. After creating a bone defect simulating an unstable fracture, bending and torsional tests were run again

RESULTS

After cyclic loading, distraction under compression with the TLN was significantly less than with the UHN: 0.10 (SD 0.06) vs. 0.31 (SD 0.18) mm (difference = -67%, 95% CI = -84% to -37%; p = 0.01). In bending, the constructs with TLN under compression were stiffer than those with the UHN: 0.96 (SD 0.25) vs. 0.80 (SD 0.25) kN/mm (difference = 0.16, 95% CI = 0.07 to 0.25; p = 0.01). In torsion and with a bone defect, no significant differences were found.

INTERPRETATION

Both nails are capable of resisting physiological forces acting on the humerus. The constructs with the TLN under compression are more stable in bending. Compression with an axial set screw is the more stable option.

Evaluation and improvement of the efficiency of the Seidel humeral nail by numerical-experimental analysis of the bone-implant contact

Seidel intramedullary humeral nail is locked distally by a spreading device and proximally by transverse cross locking screws. The main problems found in its use are: the loosening of the distal anchorage, even after X-ray verification of the correct expansion of the device; the formation of distal fractures, occurring even 1 month after the operation; the system's low stability. The problems noted can be ascribed to the behaviour of the spreading device for distal fixing. The present study, therefore, was directed at analysing the contact between the spreading mechanism and the medullary canal in relation to the geometric parameters of the mechanism itself. The main objective was to define the correct regulation of the expansion in the operating theatre, and to delimit the more appropriate conditions of use, allowing the surgeon to evaluate the suitability of this particular device for the type of fracture under treatment. Numerical and experimental techniques were used to perform an analysis of the implant behaviour. This investigation, referred to immediate post-operative condition, allowed to evaluate the stability to traction of the system, to define the typology and properties of the bone-implant contact zone and to quantify the stresses produced, all as a function of the parameter on which the surgeon intervenes in the operating theatre: the number of turns used to tighten the spreading screw. The results obtained confirm and explain the disadvantages associated with the distal expansion system: the bone-implant contact turns out to be inefficient, as revealed by the distribution of the pressure on the inner wall of the medullary canal. On the basis of the results, it is possible to define the optimal conditions of use of the nail, and to formulate a simple solution for the improvement of its performance.

Rotational stability of Seidel nail distal locking mechanism

The intramedullary distal locking mechanism in the Seidel nail uses interference fit, avoiding the need of a screw traversing soft tissue and the risk of neurovascular injury. However, there is concern for its rotational stability. This study was designed to test the rotational stability of the distal locking mechanism under the least stable conditions. A transverse osteotomy was performed 10 cm proximal to the trochlea in 10 cadaveric humeri, followed by insertion of a 9 mm diameter Seidel nail and distally locked. The proximal humeral segments were removed. Rotational test to failure was performed with a material testing machine. The initial medullary diameter and the amount of flange spread measured 9.95 mm and 11.28 mm, respectively. Most of the flanges were found to be incompletely deployed. Failure occurred by slippage of the flanges. The average failure torque and torsional stiffness of the nail bone construct tested were 0.262 N m and 0.070 N m/ degrees . The Seidel nail distal locking mechanism has low rotational stability on mechanical testing. However, the low failure torque tested in vitro does not always preclude successful fracture healing and a good clinical outcome. Whether the presence of rotational micro motion would be beneficial to bone healing would need further investigation.

Bending and torsional stiffness in cadaver humeri fixed with a self-locking expandable or interlocking nail system: a mechanical study

OBJECTIVES

This study was designed to gain data about a new expandable, noninterlocked intramedullary nail's capacity to stabilize unstable transverse humeral shaft fractures without the need for interlocking, thus making nail implantation simpler and to prove our goal hypothesis: that in a midshaft osteotomy of the humeral shaft the expandable humeral nail will show the same bending and torsional stiffness as an interlocked humeral nail, when implanted correctly according to the manufacturer's instructions.

DESIGN

Pair randomization.

SETTING

Mechanical laboratory testing.

PARTICIPANTS

Eight pairs of freshly harvested cadaveric humeri.

INTERVENTIONS

Fracture model was a midshaft transverse osteotomy, gapped to 3 mm. Each humerus pair received an expandable humeral nail (Fixion) or an interlocked humerus nail (Synthes) through a retrograde approach. The humeri were fixed in polymethylmethacrylate cylinders and tested in a servo-pneumatic material-testing machine.

MAIN OUTCOME MEASUREMENTS

Torsional stiffness and bending stiffness of the nail-bone-construction.

RESULTS

Expandable nails (interlocked nails) showed a lateral bending stiffness of 0.73 +/- 0.14 (0.63 +/- 0.1) KN/mm (P = 0.026) and a frontal bending stiffness of 0.67 +/- 0.18 (0.58 +/- 0.09) KN/mm (P = 0.084). Torsional stiffness values were 0.13 +/- 0.19 (0.43 +/- 0.09 Nm/degrees) (P = 0.012). Lower torsional stiffness in the expandable nail group was observed in humeri with a funnel shaped proximal intramedullary canal.

CONCLUSIONS

The nail systems showed similar characteristics for frontal bending (P = 0.084), but not for lateral bending (P = 0.026). For lateral bending, the Fixion nail showed significantly more stiffness than the UHN nail (P = 0.026). There was significantly lower torsional stiffness with expandable nails compared with interlocked nails. Clinical correlation would suggest that in rotationally unstable fractures (A2 and A3 diaphyseal fractures), interlocked nails would provide increased stability over expandable nails.

Failure of reamed nailing in humeral non-union: an analysis of 26 patients

The use of an intramedullary nail in the treatment of humeral non-unions remains controversial. This study evaluated the treatment of humeral delayed and non-unions with reamed nailing and compression. In a retrospective analysis of prospectively gathered data from 26 cases all treated with the Telescopic Locking Nail (TLN), the healing rate after the first intervention for non-union was 58%. After one or more re-interventions combined with an external cancellous bone graft at some time during follow-up, 90% of the 21 patients with complete follow-up eventually healed after a mean of 22 months. A total of 49 procedures with a mean of 1.9 per patient were needed. After a mean follow-up of 65 (range 24-88) months, we conducted a study to assess the functional results in the shoulder and elbow. Twelve patients were suitable for inclusion. We used the Neer and Morrey score for shoulder and elbow function, respectively. For the Neer score the median was 91 points and for the Morrey score 94 points. The outcome suggests that simple reamed nailing of humeral non-union is insufficient. Reamed interlocked nailing is feasible, provided that the primary intervention for non-union is combined with an external cancellous bone graft.

Humeral torque in professional baseball pitchers

BACKGROUND

Spontaneous fracture of the humeral shaft in throwers is a rare but well-known phenomenon. Although it has been hypothesized that the biomechanics of the throw cause such fractures, it is not clear how or when the fractures occur in the pitching motion.

METHODS

The torque acting about the long axis of the humerus was calculated in 25 professional baseball pitchers throwing in game situations.

RESULTS

Peak humeral axial torque reached a mean value of 92 +/- 16 Nm near the time of maximum shoulder external rotation at the end of the cocking phase. This torque tended to externally rotate the distal end of the humerus relative to its proximal end. The direction of the torque was consistent with the external rotation spiral fractures of the humerus noted to occur in throwers. The magnitude of the peak humeral torque averaged 48% of the theoretical torsional strength of the humerus, suggesting that repetitive stress plays a role in humeral shaft fractures.

CONCLUSIONS

Fractures are most likely to occur near the time of maximum shoulder external rotation when humeral torque peaks. Pitchers whose elbows were more extended at stride foot contact tended to have lower peak humeral torques.

Plating of humeral shaft fractures--has the pendulum swung back?

We reviewed 49 patients following plate osteosynthesis of humeral shaft fractures. There were no complications as a result of surgery. Union occurred in 47 patients (96%) at a mean of 9 weeks. Two patients required secondary procedures to achieve union. All patients had full range of motion in the elbow and shoulder joints following union. In the light of the popularisation of intramedullary nailing techniques in the last decade, with recognised complications of iatrogenic radial nerve injury, inadequate rotational stabilisation, non-union and shoulder impingement, we advocate plating of humeral shaft fractures as the surgical treatment of choice.

Complications of locked nailing in humeral shaft fractures

BACKGROUND

The purpose of this study was to investigate the complications of humeral locked nailing.

METHODS

Between 1994 and 2000, 161 humeral shaft fractures (98 acute fractures and 63 delayed unions or nonunions) in 159 patients treated with humeral locked nails were followed up for an average of 25.4 months. There were 89 men and 70 women, with an average age of 53.5 years. Acute fractures included 68 closed, 18 type I, 8 type II, 3 type IIIA, and 1 type IIIB open fractures. Thirty-six nonunions had previous operations. In general, acute fractures were treated with closed nailing and nonunions were treated with open nailing with bone grafting. Since 1998, interfragmentary wiring has been added in nonunions to compress the fracture.

RESULTS

In total, 30 patients had 31 significant complications. Nine of them were persistent nonunions, six from acute fractures and three from nonunions. Fracture gap was associated with a significantly higher risk of nonunion. The risk of operative comminution was significantly higher in retrograde nailing, and operative comminution resulted in a significantly higher risk of nonunion. Seven of the nine nonunions underwent revisional nailing and achieved eventual union. Removal of the protruded screws was performed in two cases. Other complications included shoulder impairment, elbow impairment, angular malunion, and post-nailing radial nerve palsy.

CONCLUSION

Many complications of humeral locked nailing can be prevented by improving the implant design or surgical techniques. The patients with persistent nonunion can be reliably treated by revisional nailing and bone grafting.

Recent advances in the treatment of gunshot fractures of the humeral shaft

The increase in violent crime has lead to an increase in gunshot-induced fractures in the United States. Injuries to the upper extremity are common. The treatment of gunshot injuries depends on the extent of soft tissue disruption and the type and location of fracture. Most of these injuries are a result of low-energy gunshot wounds that may be treated conservatively under the appropriate conditions. Low-energy fractures that require operative stabilization may be done with predictable results for achieving union with intramedullary fixation or compression plating. Complex open fractures from gunshot wounds associated with neurovascular injuries present a therapeutic challenge to the orthopaedic surgeon. The fractures associated with these injuries often are comminuted and unstable. Bone loss is common. Soft tissue disruption plays a more important role in high-energy gunshot-induced fractures. In these cases, external fixation is the treatment of choice for stabilization. Recent advances in the use of external fixation have led to quick fracture stabilization, stability for vascular repair, and access to the wound for debridement and subsequent soft tissue surgery.

Locked nailing with interfragmentary wiring for humeral nonunions

OBJECTIVE

Locked nailing for humeral nonunions is threatened by residual fracture gap and fracture motion. This article describes the clinical experience of using interfragmentary wiring to solve these problems.

METHODS

Interfragmentary wiring was used in 21 consecutive humeral nonunions treated with humeral locked nails. The average age of patients was 49.5 years, with an average nonunion duration of 14.4 months. Eighteen patients had previous operations. Nonunions were located at the proximal third in 4, the middle third in 10, and the distal third in 7. Antegrade nailing was used in 11 and retrograde nailing in 10. Sixteen nonunions were nailed with 8-mm nails and five with 7-mm nails. Interfragmentary wiring was applied to either the posterior or the lateral cortex of humeri in a figure-of-eight configuration. Bone grafting was performed in all and average follow-up time was 22 months.

RESULTS

With a single operation, all patients achieved osseous union in, on average, 18.3 weeks. One patient with segmental nonunion suffered acute renal failure 4 months after operation, but fracture healing was not affected. Wire infection occurred in one patient with preoperative infection at the nail entry site and was treated by implant removal. Other complications including two transient radial nerve palsies and one brachial artery injury did not affect the final outcome. At follow-up, all but four patients had complete recovery of shoulder flexion and abduction. The average postoperative Neer score (91.1 points) was significantly better than the average preoperative score (65.5 points). All but three patients had complete recovery of elbow motion.

CONCLUSION

Interfragmentary wiring, a safe procedure if properly performed, could effectively decrease the residual fracture gap and fracture motion in locked nailing of humeral nonunions. Further biomechanical studies and prospective, randomized, controlled studies are warranted.

Functional outcome after intramedullary nailing of humeral shaft fractures: comparison between retrograde Marchetti-Vicenzi and unreamed AO antegrade nailing

BACKGROUND

We compared anesthesia time, complications, fracture healing, as well as shoulder and elbow function after retrograde and antegrade nailing of humeral shaft fractures or impending fractures.

METHODS

Thirty retrograde Marchetti-Vicenzi nails (MVN) and 22 antegrade locked AO unreamed humeral nails (AO-UHN) were inserted in 52 patients. Forty-three fractures were followed up until healing, and three required reoperation for nonunion (two MVN, one AO-UHN). Nineteen MVN and 17 AO-UHN patients were evaluated according to Constant's shoulder score and HSS elbow score after an average of 2 years (0.5-3.4 years).

RESULTS

Anesthesia time did not differ significantly in both groups. Differences in Constant's shoulder score between healthy and affected side were more important in the AO-UHN group due to limitation in ROM and loss of abduction power. Differences in HSS elbow score were similar in both groups, although four supracondylar fractures occurred in the MVN group.

CONCLUSION

The retrograde approach to the humeral medullary cavity using a MVN resulted in better shoulder function and similar elbow function compared with the antegrade approach using an AO-UHN.

A biomechanical comparison of Schuhli nuts or cement augmented screws for plating of humeral fractures

Schuhli locking nuts can be used in poor quality cortical bone to enhance fixation stability as an alternative to cement augmented screws. This study compared the fixation strength and stability of plate constructs using Schuhli locking nuts with standard screws and cement augmented screws for fixation of simulated humeral shaft fractures in a test model with osteoporosis. The constructs were tested in axial compression, 4-point bending, and torsion to determine fixation stability. The humeri were cycled in torsion (4.5 Nm) for 1000 cycles to simulate upper extremity use during the early postoperative period and retested for stability. The Schuhli locking nuts and cement augmented screws had significantly greater fixation stability than the standard screws before (range, 6-14 times greater) and after cycling in torsional loading (range, 3-3.6 times greater). Although cement augmented screws and Schuhli augmentation showed increased fixation stability compared with the standard screws in axial and 4-point bending before cycling (range, 1.3-1.4 times greater), this was not significant. Compared with Schuhli fixation, cement augmented screws showed no significant difference in fixation stability in all loading modes before and after cycling. Schuhli locking nuts offer the stability of cement augmentation while avoiding its potential adverse effects on fracture healing with extravasation and thermal necrosis.

Treatment of humeral shaft delayed unions and nonunions with humeral locked nails

OBJECTIVE

To report experience with use of humeral locked nails in treating humeral delayed unions and nonunions. The following techniques yielded encouragingly good results: static locking, short-to-long segment nailing, bone grafting, fracture compression, and minimal surgical trauma.

DESIGN AND METHODS

A total of 41 consecutive patients with 13 delayed unions and 28 nonunions were treated with humeral locked nails. Delay from trauma to surgery averaged 4.2 months for delayed union and 15.5 months for nonunion. The average age of patients was 50.2 years; average follow-up time was 23.2 months. There were 7 proximal-third fractures, 21 middle-third fractures, and 13 distal-third fractures. The antegrade approach was used for 13 fractures and retrograde for 28. Open nailing was performed in 39 fractures and closed nailing in 2. If the fracture motion was still present after nail insertion, axial compression of the fracture site was specially applied. Bone grafting was performed in the fractures with open nailing. Thirty-four fractures were nailed with 8-mm nails, and 7 fractures were nailed with 7-mm nails.

RESULTS

With a single operation, all but two patients achieved osseous union in, on average, 5.6 months. One of these two patients eventually gained union after another surgery with fracture compression along the original nail and concurrent bone grafting. The second patient, undergoing hemodialysis for chronic renal failure, had persistent nonunion. At follow-up, for patients with antegrade nailing, all but four patients had less than 20 degrees limitation of shoulder abduction. For patients with retrograde nailing, all but two had less than 10 degrees limitation of elbow motion. Only the patient with persistent nonunion had continual pain and significant impairment of arm function.

CONCLUSIONS

Humeral locked nailing seems to be effective for humeral delayed unions or nonunions. It may be an acceptable alternative for fractures unsuited for plate fixation, such as those with comminution, osteoporosis, or a severely adhered radial nerve.

Antegrade locked nailing for humeral shaft fractures

Treatment results of antegrade locked nailing of acute humeral shaft fractures, including union rate and recovery of shoulder function, have been inconsistent. This led the current authors to hypothesize that implant design and surgical techniques might account for this inconsistency. In the current study, 47 fractures (38 acute; nine pathologic) in 47 patients achieved union with the techniques of closed nailing, short to long segment nailing, and fracture compression. Satisfactory recovery of shoulder function occurred because of minimal surgical trauma, prevention of impingement by the nail or locking screws, and prevention of axillary nerve injury or comminution of the humeral head. Forty-seven patients with 38 acute fractures and nine pathologic fractures were treated with humeral locked nails. Mean followup time was 21.4 months. With a single operation, all 38 acute fractures proceeded to eventual union; the average time to union was 7.8 weeks. Thirty-five patients had excellent or satisfactory recovery of shoulder function. Complications included slipout of the proximal screw, nail breakage, fragment displacement, and transient postoperative radial nerve palsy. All nine patients with pathologic fractures had substantial pain relief and increased arm function after surgery. The current study shows the reliability of antegrade locked nailing for proximal and middle third fractures of the humeral shaft.

Biomechanical comparison of bending and torsional properties in retrograde intramedullary nailing of humeral shaft fractures

OBJECTIVE

To establish whether the bending and torsional stiffness of an implanted nail are influenced by nail design and nail-bolt interface, this study compared two implanted retrograde nail systems: the AO/ASIF unreamed humeral nail (UHN) and the Russell-Taylor (RT) nail.

DESIGN

Pair randomization.

SETTING

Mechanical laboratory testing.

SPECIMENS

Twelve pairs of freshly harvested cadaveric humeri.

METHODS

Transverse fractures were simulated with a standardized midshaft osteotomy and a three-millimeter gap. Both nails were proximally and distally interlocked. The RT nail has a single interlock at its base and tip. The UHN has double interlocking both proximally and distally. The screw hole design of the RT nail features slots, whereas the UHN has round screw holes.

MAIN OUTCOME MEASURES

Anteroposterior and mediolateral bending stiffness and torsional stiffness.

RESULTS

The RT nail showed higher bending stiffness in anteroposterior and mediolateral bending. Large differences were seen in the torsional characteristics: for the first 30 degrees, the RT nail showed a much lower resistance against torsion than the UHN. Analysis of variance of stiffness at four, six, and eight newton-meters showed statistical significance (p < 0.0001). Torsional stiffness, defined as the slope of a straight line approximated to between 75 and 100 percent of the maximum torque, was very similar in both nails.

CONCLUSION

The torsional differences between the two nail systems are attributable to the nail-bolt interface of the RT nail. This dynamic system allows a clinically relevant degree of movement. The greater resistance to rotatory forces of the UHN is explained by the fact that the interlocking at its tip and base creates a static rather than a dynamic system.

Schuhli augmentation of plate and screw fixation for humeral shaft fractures: a laboratory study

OBJECTIVES

Schuhli locking nuts provide a mechanism to lock 4.5-millimeter bone screws to a standard dynamic compression plate (DCP plate). It has been proposed that Schuhlis can provide increased fixation stability in areas of a proximal cortical defect or osteopenic bone and may keep screws from loosening and backing out from the plate. A biomechanical study was performed to investigate the effect of Schuhli augmentation of a ten-hole broad DCP plate for fixation of a simulated humeral shaft fracture versus standard DCP plate fixation.

DESIGN

Biomechanical cadaver study.

INTERVENTION

Six pairs of cadaveric humeri from elderly individuals were tested in offset axial loading, torsion, and four-point bending to obtain load versus deformation curves and baseline mechanical properties. Each pair of humeri was then instrumented with a ten-hole broad DCP plate on one side and a DCP plate augmented with Schuhlis at each screw hole on the contralateral side. All screws were placed in cortical bone. The constructs were retested in all three modalities. The humeri were then cycled in torsion for 1,000 cycles and retested in all three modalities. Each humerus was then loaded to failure in torsion to determine the ultimate load and rotational displacement.

MAIN OUTCOME MEASUREMENTS

Resistance to displacement was determined from the load versus deformation curves in each testing modality before and after cycling; these data were normalized to the intact values determined prior to instrumentation. Paired Student's t tests were performed to determine statistically significant differences between the two modes of fixation.

RESULTS

There were no significant differences in stability between the two fixation techniques in all three testing modalities both before and after cycling. However, the Schuhli augmented constructs sustained significantly greater loads and rotational deformations prior to failure.

CONCLUSIONS

In this model of humeral shaft fractures in the elderly, the addition of Schuhlis did not significantly change the mechanical stability of plate and screw fixation. However, load and angular deformation at failure were significantly greater in the Schuhli augmented specimens.

Treatment of humeral shaft fractures with humeral locked nail and comparison with plate fixation

OBJECTIVE

To report the experience of a newly devised humeral locked nail in treating acute humeral shaft fractures and to compare its effectiveness with that of plate fixation.

DESIGN AND METHODS

Data were collected on 48 acute humeral shaft fractures in 48 consecutive patients treated with humeral locked nails and compared with retrospective data on 25 fractures in 25 other patients treated with dynamic compression plates. The operation time, amount of blood transfusion, time to union, complications, and functional recovery were recorded and compared. The average follow-up time was 20.5 months for the nail group and 33.3 months for the plate group. Student's t test and Fisher's Exact Test were used for statistical analyses.

RESULTS

Locked nailing had significantly shorter operation time and less blood transfusion than did plate fixation, 68 versus 93 minutes and 0 versus 102 mL, respectively. Eventual union was achieved among all in the nail group and among all but one in the plate group. Union rate and time to union were not significantly different. In the plate group, three fractures had complications: one with implant loosening and nonunion, one with deep infection, and one with postoperative radial nerve palsy; the nail group had no complications. The difference in complication rates was statistically significant. In the nail group, one varus malunion and one intraoperative comminution occurred, without adverse consequences. Functional recovery was essentially the same in both groups for uncomplicated fractures.

CONCLUSIONS

Humeral locked nailing offered a less invasive surgical technique and more favorable treatment results than did plate fixation. Correct nailing direction, precise surgical techniques, less bulky hardware, and stable transfixing screws are the keys to a successful treatment. Further prospective, randomized comparative study is warranted.

Fractures below the end of locking humeral nails: a report of three cases

We report three cases of fracture of the humerus that occurred at the tip of interlocking humeral nails inserted previously for humeral shaft fractures. The fractures occurred at 8, 10, and 26 weeks postoperatively, and all occurred through the distal interlocking screws after the patient sustained a rotational force to the arm. All three patients had further surgery, two subsequently healed their fractures, and one is still in active treatment. Orthopaedists should be aware of this complication when choosing interlocking humeral nails for the treatment of humeral shaft fractures.

Humeral shaft nonunion treated by a Seidel interlocking nail with a supplementary staple

Thirty-two adult patients with humeral shaft nonunions were treated with Seidel interlocking nails, and 6 of these 32 patients required an added staple. The indication for inserting a staple was rotational instability, despite use of a distal spreading screw. All 6 patients with nonunions were followed for at least 1 year (median, 1.5 years), and all experienced a solid union. The union period was a median of 5 months, with a range of 3 to 7 months. No complications were noted. The author believes that all humeral shaft nonunions may be treated by a Seidel interlocking nail with or without a staple supplementation and cancellous bone graft. The technique is simple, and its results are satisfactory. Predrilling the cortices of both fragments is key to successful insertion of a staple.

The rationales of interlocking nailing of the femur, tibia, and humerus

Interlocking nailing has been increasingly used to treat acute and chronic afflictions of long bones. Although the interlocking construct is similar, regardless of the anatomic area of application, the results and complications of this type of fixation in the femur, tibia, and humerus differ. This review compares the anatomy, biologic response to injury, and functional expectations of these 3 distinct long bones with respect to interlocking nailing. Final results seem related more closely to the bony anatomy and soft tissue injury than to any inherent success of interlocking techniques.