Musculoskelet Surg DOI 10.1007/s12306-014-0329-9
ORIGINAL ARTICLE
Sliding external fixator ‘‘a product design and cadaveric experiment’’ A. A. Mohammed • S. P. Frostick
Received: 26 January 2014 / Accepted: 4 March 2014 Ó Istituto Ortopedico Rizzoli 2014
Abstract Background External fixation spanning a joint like the elbow, while maintaining joint mobility, is a well-established practice, and it could be done with a variety of external fixation systems. In current systems, correct identification of the elbow center of rotation under X-ray guidance with lateral views is mandatory. If the center of rotation of the fixator is not aligned with that of the elbow joint, the assembly will not work. This new design idea aims to propagate the principle of sliding external fixation applied on the extensor side of a joint, with the limbs of the fixator being able to slide in and out during joint extension and flexion, respectively, without hindering the joint movement, without the need to use X-ray guidance to identify the center of rotation. Materials and methods A cadaveric experiment was carried on using a sliding fixator prototype applies on two cadaveric elbow specimens, which were tested though the arc of movement. Results Assembling the fixator over the intact elbows without identifying the center of rotation did not impede A. A. Mohammed (&) S. P. Frostick Royal Liverpool University, Liverpool, UK e-mail: [email protected] S. P. Frostick e-mail: [email protected] A. A. Mohammed Royal Liverpool and Broadgreen University Hospitals NHS Trust, Liverpool, UK S. P. Frostick Musculoskeletal Science Research Group, Department of Molecular and Clinical Cancer Medicine, Faculty of Health and Life Sciences, Institute of Translational Medicine, University of Liverpool, Liverpool, UK
the joint movement. Furthermore, after surgical dislocation of the elbow, the external fixator was able to keep the joint congruent, throughout the movement arc. Conclusion It was possible to apply a sliding external fixator on the extensor surface of a joint without identifying the center of rotation, and that does not seem to impede the joint movement, while can still keep the dislocated joint congruent despite attempted distraction. Keywords Elbow Dislocation External fixation Center of rotation
Introduction There are different indications to externally fix the elbow including fracture dislocations, joint instability after extensive contracture release, and distraction interposition arthroplasty [1]. Application of these devices requires accurate alignment, any off-axis alignment between the fixator hinge and the elbow axis leads on average to a 3.7and 7.1-fold increase in motion resistance for 5° and 10° mal-orientation, respectively [2]. Current treatment Fixation options include a mono-lateral fixator fixed on the lateral aspect of the joint, a circular fixator, or the Compass Elbow Hinge [3], all of which would be able to allow the joint flexion and extension only if the center of rotation of the external fixator coincides with that of the joint; if there is a mismatch, the joint would be disturbed on attempting movement as the joint and the external fixator would have different movement arcs.
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Musculoskelet Surg Fig. 1 An embodiment 10 of the invention comprises a first frame member 12 and a second frame member 22 each having a proximal end 14, 24, and a distal end 16, 26, and an axis between the two ends, the frame members being hinged together at their proximal ends at the joint level, by means of a hinge 30 formed from a first hinge portion 18 on the first frame member and a second hinge portion 28 on the second frame member, the hinge portions being adapted to interfit to form the hinge. In this embodiment, each hinge portion comprises a plurality of interfitting leaf portions 32, which act when assembled together to form a hinge that opens stably in a single plane and is resistant to torsional forces on the two frame members. The hinge is held together by a hinge pin 34, which is fitted into a central aperture 36
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Musculoskelet Surg
To be able to identify the center of rotation, repeated lateral X-rays are needed, and Orthofix on its galaxy system describes using an elbow hinge that has a central radiolucent unit with an in-built targeting cross which can be used to achieve a correct alignment, as an alternative to inserting a k wire into the center of the condyles under fluoroscopy, and only later sliding the hinge over it [4]. New design The new design provides a sliding external fixator (SEF), device (pending patent) having a first and second linearly extendible arms hinged together. Each arm has a multiholes bar (considered as a base for fixation to the bone), similar to multiple rancho cubes made into a long bar rather than cubes, and half pins are fixed into the ulna and into the humerus on the extensor surface and then held into the corresponding base, using the rancho fixation as with systems like the Taylor Spatial Frame [5]. Two or more half pins adapted to be inserted into bone in the sagittal plane of the subcutaneous border of the ulna, and then, the half pins are attached to the base. A first and a second frame members each having a proximal end and a distal end, the frame members hinged together at their ends closer to the joint, the frame members are tubular (having a cross section which accommodates the cross section of the corresponding base, and such cross section could be for example rectangular or any other configuration other than circular as that would not be able to prevent rotation between the elements themselves) having an inner surface, and the sliding base is mounted within the inner tubular space, each base comprising of fixing means adapted to fix a half pin to the base. In this way, the first base member is fixed to the humerus, and the second base member is fixed to the ulna. The device provides a hinging point that moves linearly relative to the fixing points of the device to the limb as the joint moves. When the elbow is bent, the hinge is bent (Fig. 1b–d), and the sliding bars move within the guide means away from each other and apply tension to the springs, while if the patient extends the joint, the movement is aided by tension of a spring-loaded mechanism. Ideally the spring tension level is adjustable, while the length of the frames should prevent the bars from dislodgement. Each frame member comprises guide means aligned parallel to the axis to receive a sliding base 40, 50. In this embodiment, the frame members are tubular having an inner surface 42, 52 and a sliding base, for example 40 is mounted within the inner tubular space 42 and the guide means comprises the inner surface 42 of the frame members. Each frame member has a slot 44, 54 in the side of the
frame member parallel to the axis of the hinge, extending along the axis of the frame member and through which a half pin mounted on the sliding base projects in use. In this embodiment, each frame member has matching slots on both sides parallel to the axis of the hinge as shown in Fig. 1a–e, and a collar 46, 56 mounted over the exterior of a frame member so as to strengthen it and to hold the frame member in shape. Each sliding base 40, 50 has a proximal end 48, 58 nearest the proximal end of the frame member and a distal end 49, 59, each sliding base comprising a plurality of fixing means 60 adapted to fix a half pin 72, 74, 82, 84 to the base. The embodiment further comprises two first half pins, 72 and 74, and two second half pins 82 and 84, mounted on the sliding bases. Each half pin is adapted to be fixed to the sliding base and to be inserted into bone by means of a threaded portion 76. The fixing means comprise an aperture 62 formed in the sliding base, a centering sleeve 64 sized to fit into the aperture 62 and having a central bore 66 adapted to receive the shank 68 of the half pin 74, and a grub screw 69 that fits into a threaded screw hole 63 orthogonal to the aperture 62 in order to fix the centering sleeve and the half pin in place to the sliding base. Extension springs 90, 100 are associated with each frame member, the proximal end 92, 102 of each spring is connected to the frame member adjacent to its proximal end 14, 24, and the distal end of each spring 94, 104 is connected to the proximal end 48, 58 of each sliding base. The frame members have a plurality of apertures 110 through their sides to allow access to the grub screws to allow positioning and fixing in place of the half pins. The device is illustrated in Fig. 1a–d showing progressive degrees of bending of the device. In Fig. 1a–h, the device is shown fully extended, with the sliding bases located close to the hinge. When the device is applied, on bending the sliding bases are drawn progressively further from the hinge axis, moving along the inside of the tubular frame members and extending the springs. Half pins 82, 84 move along the slot 54 and the corresponding slot on the opposite side of the frame member. Collar 56 is provided to stabilize and strengthen the frame member and in use presents a stop position for the half pin 82 as shown in Fig. 1d.
Cadaveric experiment Objectives 1.
To find out whether external fixation applied on the extensor surface of the elbow can avoid the need to identify the center of rotation.
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Musculoskelet Surg
Fig. 2 1 Application of the fixator in elbow extension. 2 Mobilization of the elbow to 90 degrees of flexion while the fixator slides. 3 Surgical dislocation of the elbow. 4 Re-application of the fixator in extension. 5 Mobilization of the re-applied fixator to a flexed position
2.
To find out whether the joint can remain congruent with this kind of fixation.
7.
8. Materials and methods A hand-made SEF prototype from basic equipments to simulate the sliding principle, it comprised of two sliding window glides, the bases of which linked with a door hinge, and on each sliding component, two 4–5 hole blocks of Rancho cubes fixed with bolts and nuts. This prototype was applied on two cadaveric elbows on scapula to fingertip specimens. The experiment involved the following steps: 1.
2. 3.
4. 5.
6.
Applying two pins in the ulna and two pins in the humerus over the extensor surface, and perpendicularly over the subcutaneous border of the ulna. Applying the SEF prototype on an intact elbow without identifying the center of rotation. Moving the intact joint through an arc of movement, from full extension to ninety degrees of flexion to find out whether the joint movement is impeded by the fixator or not. Disconnecting the fixator, while keeping the pins. Performing an open dislocation of the elbow through posterior approach, dividing the triceps tendon, medial collateral ligament, lateral collateral ligament, capsule, and brachialis insertion (Fig. 2(3)). Re-applying the fixator.
123
Testing the joint congruency through the arc of movement to find out whether the joint stays concentric or not. A posteriorly directed distracting force of fifteen Newton applied over the volar proximal aspect of the ulna to test the stability of the construct.
Results Assembling the fixator over the intact elbows with pins holding each arm of the fixator to their corresponding locations (Fig. 2(1)), without identifying the center of rotation while keeping the hinge behind the elbow about the level of the tip of the olecranon, also without using any X-ray guidance, did not impede the joint movement, and the elbow was mobilized through full range of movement with the external fixator being able to accommodate its position through the sliding mechanism on either side of the hinge which remained at the joint level (Fig. 1(2)). Furthermore, while keeping the pins in place, surgical dislocation of the elbow had been performed (Fig. 2(3)), and then on re-application of the external fixator to where it was before the dislocation, it was still able to keep the joint concentrically congruent, throughout the movement arc (Figs. 2(4, 5)). The distracting force applied in an attempt to dislocate the joint has failed to dislocate the construct.
Musculoskelet Surg
Discussion Elbow fracture dislocations happen in different age groups; however, it is more tolerated in children [6], with stiffness being a major problem in complicated situations especially when extensive internal fixation is performed; however, heterotopic ossification is also reported in closed reductions of elbow dislocation [7]. Hinged external fixation reported in literature as a treatment option for posttraumatic elbow instability [8], and also terrible triad of the elbow was reported to be treated with hinged external fixator combined with miniplate and was found to enhance postoperative stability of the elbow [9], Furthermore, open arthrolysis and monolateral hinged external fixation were reported as effective in treating posttraumatic ankylosed elbow [10], and also hinged external fixation was found as an effective rehabilitation method for improving range of motion and maintaining joint stability when treating elbow stiffness and distal humeral non-union with open arthrolysis, surgical reduction, and internal fixation in conjunction with the external fixation [11]. However, the external fixator reported in use was either mono-lateral or circular in type, and although external fixation is an established treatment option, it had not been reported in literature to be applied over the extensor surface of the elbow joint. In our product design, the principle is a start for a new thinking, trying to answer the question as what if the fixator is applied on the extensor surface, would that be possible to apply and if so would it work? After doing this experiment according to the proposed design, it was possible to apply a sliding external fixator on the extensor surface of a joint without identifying the center of rotation and without using radiological guidance. Furthermore, this external fixator did not seem to impede the joint movement, while can still keep the dislocated joint congruent. A better-manufactured prototype would include a set of multidirectional pin clamps and would make the application easier; when the pins are fixed to the bone, the fixator should be able to accommodate the pins even if they are not exactly in the same plane perpendicular to the ulnar subcutaneous border and in-line with humerus, while still
able to keep the hinge behind the elbow. Furthermore, making the spring-loaded mechanism adjustable would accommodate different demands, joint sizes and at the same time prevent collapse, while can still recoil from flexion to extension. Conflict of interest A. A. Mohammed: Patent is pending for this design, (Filing Ref No. 19020/P1/GB/Innovate, and Patent Application No. 1319419.6). S. P. Frostick: Nil.
References 1. Tan V, Daluiski A, Capo J, Hotchkiss R (2005) Hinged elbow external fixators: indications and uses. J Am Acad Orthop Surg 13(8):503–514 2. Bottlang M, O’Rourke MR, Madey SM, Steyers CM, Marsh JL, Brown TD (2000) Radiographic determinants of the elbow rotation axis: experimental identification and quantitative validation. J Orthop Res 18(5):821–828 3. McKee MD, Richards RR, King GJW et al (1997) The compass elbow hinge for complex acute elbow instability (abstract). J Bone Joint Surg 79B(Suppl I):75 4. Orthofix International (2013) Galaxy Fixation Technique. http:// intl.orthofix.com/uploads/contentUpload/GF-1101-OPT-E0.pdf. Accessed 7 Dec 2013 5. Smith & Nephew (2011) Taylor Spatial Frame. http://www. smith-nephew.com/global/assets/pdf/products/surgical/tsf.pdf. Accessed 7 Dec 2013 6. Di Gennaro GL, Spina M, Fosco M, Antonioli D, Donzelli O (2013) Dislocations of the elbow in children: long term follow up. Musculoskelet Surg 97(1 Supplement):3–7 7. Sreenivas T, Menon J, Nataraj AR (2013) Heterotopic ossification of the elbow after closed reduction and retrograde intramedullary nailing for radial neck fracture treated by anconeus interposition. Musculoskeletal Surgery. 97(3):267–271 8. Ring D, Bruinsma WE, Jupiter JB (2014) Complications of hinged external fixation compared with cross-pinning of the elbow for acute and subacute instability. Clin Orthop Relat Res. doi:10. 1007/s11999-014-3510-4 9. Yang Y, Wang F (2013) Hinged external fixator with mini-plate to treat terrible triad of elbow. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi 27(2):151–154 10. Ouyang Y, Liao Y, Liu Z, Fan C (2013) Hinged external fixator and open surgery for severe elbow stiffness with distal humeral non-union. Orthopedics 36(2):e186–e192 11. Ruan HJ, Liu S, Fan CY, Liu JJ (2013) Open arthrolysis and hinged external fixation for posttraumatic ankylosed elbows. Arch Orthop Trauma Surg 133(2):179–185
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ORIGINAL ARTICLE
Sliding external fixator ‘‘a product design and cadaveric experiment’’ A. A. Mohammed • S. P. Frostick
Received: 26 January 2014 / Accepted: 4 March 2014 Ó Istituto Ortopedico Rizzoli 2014
Abstract Background External fixation spanning a joint like the elbow, while maintaining joint mobility, is a well-established practice, and it could be done with a variety of external fixation systems. In current systems, correct identification of the elbow center of rotation under X-ray guidance with lateral views is mandatory. If the center of rotation of the fixator is not aligned with that of the elbow joint, the assembly will not work. This new design idea aims to propagate the principle of sliding external fixation applied on the extensor side of a joint, with the limbs of the fixator being able to slide in and out during joint extension and flexion, respectively, without hindering the joint movement, without the need to use X-ray guidance to identify the center of rotation. Materials and methods A cadaveric experiment was carried on using a sliding fixator prototype applies on two cadaveric elbow specimens, which were tested though the arc of movement. Results Assembling the fixator over the intact elbows without identifying the center of rotation did not impede A. A. Mohammed (&) S. P. Frostick Royal Liverpool University, Liverpool, UK e-mail: [email protected] S. P. Frostick e-mail: [email protected] A. A. Mohammed Royal Liverpool and Broadgreen University Hospitals NHS Trust, Liverpool, UK S. P. Frostick Musculoskeletal Science Research Group, Department of Molecular and Clinical Cancer Medicine, Faculty of Health and Life Sciences, Institute of Translational Medicine, University of Liverpool, Liverpool, UK
the joint movement. Furthermore, after surgical dislocation of the elbow, the external fixator was able to keep the joint congruent, throughout the movement arc. Conclusion It was possible to apply a sliding external fixator on the extensor surface of a joint without identifying the center of rotation, and that does not seem to impede the joint movement, while can still keep the dislocated joint congruent despite attempted distraction. Keywords Elbow Dislocation External fixation Center of rotation
Introduction There are different indications to externally fix the elbow including fracture dislocations, joint instability after extensive contracture release, and distraction interposition arthroplasty [1]. Application of these devices requires accurate alignment, any off-axis alignment between the fixator hinge and the elbow axis leads on average to a 3.7and 7.1-fold increase in motion resistance for 5° and 10° mal-orientation, respectively [2]. Current treatment Fixation options include a mono-lateral fixator fixed on the lateral aspect of the joint, a circular fixator, or the Compass Elbow Hinge [3], all of which would be able to allow the joint flexion and extension only if the center of rotation of the external fixator coincides with that of the joint; if there is a mismatch, the joint would be disturbed on attempting movement as the joint and the external fixator would have different movement arcs.
123
Musculoskelet Surg Fig. 1 An embodiment 10 of the invention comprises a first frame member 12 and a second frame member 22 each having a proximal end 14, 24, and a distal end 16, 26, and an axis between the two ends, the frame members being hinged together at their proximal ends at the joint level, by means of a hinge 30 formed from a first hinge portion 18 on the first frame member and a second hinge portion 28 on the second frame member, the hinge portions being adapted to interfit to form the hinge. In this embodiment, each hinge portion comprises a plurality of interfitting leaf portions 32, which act when assembled together to form a hinge that opens stably in a single plane and is resistant to torsional forces on the two frame members. The hinge is held together by a hinge pin 34, which is fitted into a central aperture 36
123
Musculoskelet Surg
To be able to identify the center of rotation, repeated lateral X-rays are needed, and Orthofix on its galaxy system describes using an elbow hinge that has a central radiolucent unit with an in-built targeting cross which can be used to achieve a correct alignment, as an alternative to inserting a k wire into the center of the condyles under fluoroscopy, and only later sliding the hinge over it [4]. New design The new design provides a sliding external fixator (SEF), device (pending patent) having a first and second linearly extendible arms hinged together. Each arm has a multiholes bar (considered as a base for fixation to the bone), similar to multiple rancho cubes made into a long bar rather than cubes, and half pins are fixed into the ulna and into the humerus on the extensor surface and then held into the corresponding base, using the rancho fixation as with systems like the Taylor Spatial Frame [5]. Two or more half pins adapted to be inserted into bone in the sagittal plane of the subcutaneous border of the ulna, and then, the half pins are attached to the base. A first and a second frame members each having a proximal end and a distal end, the frame members hinged together at their ends closer to the joint, the frame members are tubular (having a cross section which accommodates the cross section of the corresponding base, and such cross section could be for example rectangular or any other configuration other than circular as that would not be able to prevent rotation between the elements themselves) having an inner surface, and the sliding base is mounted within the inner tubular space, each base comprising of fixing means adapted to fix a half pin to the base. In this way, the first base member is fixed to the humerus, and the second base member is fixed to the ulna. The device provides a hinging point that moves linearly relative to the fixing points of the device to the limb as the joint moves. When the elbow is bent, the hinge is bent (Fig. 1b–d), and the sliding bars move within the guide means away from each other and apply tension to the springs, while if the patient extends the joint, the movement is aided by tension of a spring-loaded mechanism. Ideally the spring tension level is adjustable, while the length of the frames should prevent the bars from dislodgement. Each frame member comprises guide means aligned parallel to the axis to receive a sliding base 40, 50. In this embodiment, the frame members are tubular having an inner surface 42, 52 and a sliding base, for example 40 is mounted within the inner tubular space 42 and the guide means comprises the inner surface 42 of the frame members. Each frame member has a slot 44, 54 in the side of the
frame member parallel to the axis of the hinge, extending along the axis of the frame member and through which a half pin mounted on the sliding base projects in use. In this embodiment, each frame member has matching slots on both sides parallel to the axis of the hinge as shown in Fig. 1a–e, and a collar 46, 56 mounted over the exterior of a frame member so as to strengthen it and to hold the frame member in shape. Each sliding base 40, 50 has a proximal end 48, 58 nearest the proximal end of the frame member and a distal end 49, 59, each sliding base comprising a plurality of fixing means 60 adapted to fix a half pin 72, 74, 82, 84 to the base. The embodiment further comprises two first half pins, 72 and 74, and two second half pins 82 and 84, mounted on the sliding bases. Each half pin is adapted to be fixed to the sliding base and to be inserted into bone by means of a threaded portion 76. The fixing means comprise an aperture 62 formed in the sliding base, a centering sleeve 64 sized to fit into the aperture 62 and having a central bore 66 adapted to receive the shank 68 of the half pin 74, and a grub screw 69 that fits into a threaded screw hole 63 orthogonal to the aperture 62 in order to fix the centering sleeve and the half pin in place to the sliding base. Extension springs 90, 100 are associated with each frame member, the proximal end 92, 102 of each spring is connected to the frame member adjacent to its proximal end 14, 24, and the distal end of each spring 94, 104 is connected to the proximal end 48, 58 of each sliding base. The frame members have a plurality of apertures 110 through their sides to allow access to the grub screws to allow positioning and fixing in place of the half pins. The device is illustrated in Fig. 1a–d showing progressive degrees of bending of the device. In Fig. 1a–h, the device is shown fully extended, with the sliding bases located close to the hinge. When the device is applied, on bending the sliding bases are drawn progressively further from the hinge axis, moving along the inside of the tubular frame members and extending the springs. Half pins 82, 84 move along the slot 54 and the corresponding slot on the opposite side of the frame member. Collar 56 is provided to stabilize and strengthen the frame member and in use presents a stop position for the half pin 82 as shown in Fig. 1d.
Cadaveric experiment Objectives 1.
To find out whether external fixation applied on the extensor surface of the elbow can avoid the need to identify the center of rotation.
123
Musculoskelet Surg
Fig. 2 1 Application of the fixator in elbow extension. 2 Mobilization of the elbow to 90 degrees of flexion while the fixator slides. 3 Surgical dislocation of the elbow. 4 Re-application of the fixator in extension. 5 Mobilization of the re-applied fixator to a flexed position
2.
To find out whether the joint can remain congruent with this kind of fixation.
7.
8. Materials and methods A hand-made SEF prototype from basic equipments to simulate the sliding principle, it comprised of two sliding window glides, the bases of which linked with a door hinge, and on each sliding component, two 4–5 hole blocks of Rancho cubes fixed with bolts and nuts. This prototype was applied on two cadaveric elbows on scapula to fingertip specimens. The experiment involved the following steps: 1.
2. 3.
4. 5.
6.
Applying two pins in the ulna and two pins in the humerus over the extensor surface, and perpendicularly over the subcutaneous border of the ulna. Applying the SEF prototype on an intact elbow without identifying the center of rotation. Moving the intact joint through an arc of movement, from full extension to ninety degrees of flexion to find out whether the joint movement is impeded by the fixator or not. Disconnecting the fixator, while keeping the pins. Performing an open dislocation of the elbow through posterior approach, dividing the triceps tendon, medial collateral ligament, lateral collateral ligament, capsule, and brachialis insertion (Fig. 2(3)). Re-applying the fixator.
123
Testing the joint congruency through the arc of movement to find out whether the joint stays concentric or not. A posteriorly directed distracting force of fifteen Newton applied over the volar proximal aspect of the ulna to test the stability of the construct.
Results Assembling the fixator over the intact elbows with pins holding each arm of the fixator to their corresponding locations (Fig. 2(1)), without identifying the center of rotation while keeping the hinge behind the elbow about the level of the tip of the olecranon, also without using any X-ray guidance, did not impede the joint movement, and the elbow was mobilized through full range of movement with the external fixator being able to accommodate its position through the sliding mechanism on either side of the hinge which remained at the joint level (Fig. 1(2)). Furthermore, while keeping the pins in place, surgical dislocation of the elbow had been performed (Fig. 2(3)), and then on re-application of the external fixator to where it was before the dislocation, it was still able to keep the joint concentrically congruent, throughout the movement arc (Figs. 2(4, 5)). The distracting force applied in an attempt to dislocate the joint has failed to dislocate the construct.
Musculoskelet Surg
Discussion Elbow fracture dislocations happen in different age groups; however, it is more tolerated in children [6], with stiffness being a major problem in complicated situations especially when extensive internal fixation is performed; however, heterotopic ossification is also reported in closed reductions of elbow dislocation [7]. Hinged external fixation reported in literature as a treatment option for posttraumatic elbow instability [8], and also terrible triad of the elbow was reported to be treated with hinged external fixator combined with miniplate and was found to enhance postoperative stability of the elbow [9], Furthermore, open arthrolysis and monolateral hinged external fixation were reported as effective in treating posttraumatic ankylosed elbow [10], and also hinged external fixation was found as an effective rehabilitation method for improving range of motion and maintaining joint stability when treating elbow stiffness and distal humeral non-union with open arthrolysis, surgical reduction, and internal fixation in conjunction with the external fixation [11]. However, the external fixator reported in use was either mono-lateral or circular in type, and although external fixation is an established treatment option, it had not been reported in literature to be applied over the extensor surface of the elbow joint. In our product design, the principle is a start for a new thinking, trying to answer the question as what if the fixator is applied on the extensor surface, would that be possible to apply and if so would it work? After doing this experiment according to the proposed design, it was possible to apply a sliding external fixator on the extensor surface of a joint without identifying the center of rotation and without using radiological guidance. Furthermore, this external fixator did not seem to impede the joint movement, while can still keep the dislocated joint congruent. A better-manufactured prototype would include a set of multidirectional pin clamps and would make the application easier; when the pins are fixed to the bone, the fixator should be able to accommodate the pins even if they are not exactly in the same plane perpendicular to the ulnar subcutaneous border and in-line with humerus, while still
able to keep the hinge behind the elbow. Furthermore, making the spring-loaded mechanism adjustable would accommodate different demands, joint sizes and at the same time prevent collapse, while can still recoil from flexion to extension. Conflict of interest A. A. Mohammed: Patent is pending for this design, (Filing Ref No. 19020/P1/GB/Innovate, and Patent Application No. 1319419.6). S. P. Frostick: Nil.
References 1. Tan V, Daluiski A, Capo J, Hotchkiss R (2005) Hinged elbow external fixators: indications and uses. J Am Acad Orthop Surg 13(8):503–514 2. Bottlang M, O’Rourke MR, Madey SM, Steyers CM, Marsh JL, Brown TD (2000) Radiographic determinants of the elbow rotation axis: experimental identification and quantitative validation. J Orthop Res 18(5):821–828 3. McKee MD, Richards RR, King GJW et al (1997) The compass elbow hinge for complex acute elbow instability (abstract). J Bone Joint Surg 79B(Suppl I):75 4. Orthofix International (2013) Galaxy Fixation Technique. http:// intl.orthofix.com/uploads/contentUpload/GF-1101-OPT-E0.pdf. Accessed 7 Dec 2013 5. Smith & Nephew (2011) Taylor Spatial Frame. http://www. smith-nephew.com/global/assets/pdf/products/surgical/tsf.pdf. Accessed 7 Dec 2013 6. Di Gennaro GL, Spina M, Fosco M, Antonioli D, Donzelli O (2013) Dislocations of the elbow in children: long term follow up. Musculoskelet Surg 97(1 Supplement):3–7 7. Sreenivas T, Menon J, Nataraj AR (2013) Heterotopic ossification of the elbow after closed reduction and retrograde intramedullary nailing for radial neck fracture treated by anconeus interposition. Musculoskeletal Surgery. 97(3):267–271 8. Ring D, Bruinsma WE, Jupiter JB (2014) Complications of hinged external fixation compared with cross-pinning of the elbow for acute and subacute instability. Clin Orthop Relat Res. doi:10. 1007/s11999-014-3510-4 9. Yang Y, Wang F (2013) Hinged external fixator with mini-plate to treat terrible triad of elbow. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi 27(2):151–154 10. Ouyang Y, Liao Y, Liu Z, Fan C (2013) Hinged external fixator and open surgery for severe elbow stiffness with distal humeral non-union. Orthopedics 36(2):e186–e192 11. Ruan HJ, Liu S, Fan CY, Liu JJ (2013) Open arthrolysis and hinged external fixation for posttraumatic ankylosed elbows. Arch Orthop Trauma Surg 133(2):179–185
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