Three-dimensional corrective osteotomies of complex malunited humeral fractures using patient-specific guides

ARTICLE IN PRESS J Shoulder Elbow Surg (2016) ■■, ■■–■■

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Three-dimensional corrective osteotomies of complex malunited humeral fractures using patient-specific guides Lazaros Vlachopoulos, MDa,b,*, Andreas Schweizer, MDc, Dominik C. Meyer, MDc, Christian Gerber, MD, FRCSEd(hon)c, Philipp Fürnstahl, PhDa a

Computer Assisted Research and Development Group, Balgrist University Hospital, University of Zürich, Zürich, Switzerland b Computer Vision Laboratory, ETH Zürich (Swiss Federal Institute of Technology Zürich), Zürich, Switzerland c Department of Orthopaedics, Balgrist University Hospital, University of Zürich, Zürich, Switzerland Background: Corrective osteotomies of malunited fractures of the proximal and distal humerus are among the most demanding orthopedic procedures. Whereas the restoration of the normal humeral anatomy is the ultimate goal, the quantification of the deformity as well as the transfer of the preoperative plan is challenging. The purpose of this study was to provide a guideline for 3-dimensional (3D) corrective osteotomies of malunited intra-articular fractures of the humerus and a detailed overview of existing and novel instruments to enlarge the toolkit for 3D preoperative planning and intraoperative realization using patient-specific guides. Methods: We describe the preoperative 3D deformity analysis, relevant considerations for the preoperative plan, design of the patient-specific guides, and surgical technique of corrective osteotomies of the humerus. Results: The presented technique demonstrates the benefit of computer-assisted surgery for complex osteotomies of the humerus from a preoperative deformity analysis to the creation of feasible surgical procedures and the generation of patient-specific guides. Conclusions: A 3D analysis of a post-traumatic deformity of the humerus, 3D preoperative planning, and use of patient-specific guides facilitate corrective osteotomies of complex malunited humeral fractures. Level of evidence: Basic Science Study; Surgical Technique © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. Keywords: Three-dimensional; corrective osteotomy; patient-specific guides; humerus; capitulum; intra-articular; ramp; fan-shaped

Corrective osteotomies of malunited fractures of the proximal and distal humerus are among the most demanding orthopedic procedures.6,8,11 Osteotomies are elective proceEthics Committee approval was not necessary for this study (waiver no. 1022015 issued by the Cantonal Ethics Committee Zurich, KEK Zürich). *Reprint requests: Lazaros Vlachopoulos, MD, Computer Assisted Research and Development Group, Balgrist University Hospital, University of Zürich, Forchstrasse 340, CH-8008 Zürich, Switzerland. E-mail address: [email protected] (L. Vlachopoulos).

dures scheduled in advance, providing sufficient time for a careful diagnosis and operative planning. Computer-based methods have become popular currently, especially in hand surgery,19,20,24,28 because of the need for high performance and precision levels of complex osteotomies.9 However, the quantification of the deformity, the development of feasible surgical procedures, and the transfer of the preoperative plan to the operating room are still major challenges, requiring sophisticated techniques and profound clinical expertise.

1058-2746/$ - see front matter © 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved. http://dx.doi.org/10.1016/j.jse.2016.04.038

ARTICLE IN PRESS 2 The benefit of computer-assisted planning and patientspecific instrumentation for corrective osteotomies of the upper extremity has already been emphasized.15,18,19,21,25,26,28,30 With the increase in the experience of the computerassisted techniques during the last decade, modifications of the technique for intra-articular deformities of the distal radius have been successfully developed.20,23 However, the application of guides for corrective osteotomies of the humerus has been described only for the correction of distal extraarticular (varus and valgus) deformities. To the best of our knowledge, the application of 3-dimensional (3D) planned corrective osteotomies with patient-specific instrumentation has not been addressed for either post-traumatic deformities of the proximal humerus or intra-articular deformities of the humerus. The purpose of this study was to provide a guideline for performing, in a standardized fashion, corrective osteotomies of the humerus with 3D preoperative planning and patient-specific guides. First, we present a detailed overview of existing techniques for 3D preoperative planning and patient-specific guide design that are modified for the humeral anatomy. Second, to enlarge the toolkit and to facilitate a broad range of osteotomies of the humerus, we provide several novel instruments for 3D preoperative planning and patientspecific guide design.

Materials and methods 3D deformity analysis and preoperative planning The restoration of the normal humeral anatomy is an ultimate goal in performing corrective osteotomies of the humerus. Thus, it is crucial to assess the deformity as accurately as possible. In a templatebased approach, the bone fragments are reduced to a 3D reconstruction template.9 The contralateral healthy humerus is commonly proposed as a reliable reconstruction template.19,25,27,30 The

L. Vlachopoulos et al. most fundamental step of the deformity analysis is the generation of 3D triangular surface models of the pathologic and contralateral humerus. The models are extracted from computed tomography (CT) scans (slice thickness, 1 mm; 120 kV; Philips Brilliance 40 CT; Philips Healthcare, Eindhoven, The Netherlands) using thresholding, region growing, and the marching cubes algorithm.16 Thereafter, the models are imported into in-house–developed planning software, CASPA (Balgrist CARD AG, Zürich, Switzerland). The surface registration method, iterative closest point,1,5 is applied to superimpose the models.13,19 The key idea of the iterative closest point (ICP) algorithm is to determine the transformation (ie, the relative amount of 3D translation and rotation) necessary for superimposing the pathologic humerus to the mirror model of the contralateral and healthy humerus, such that the distance between the model surfaces is minimized. However, using the entire contralateral humerus in the registration can introduce errors associated with intraindividual side-to-side differences, especially in the torsional alignment.7,27 Instead, for proximal (or distal) reconstruction, it is probably more suitable to register only the proximal (or distal) humerus region (Figs. 1, A).17 After the registration of the pathologic humerus to the reconstruction template, the humeral shaft serves as the reference fragment (Fig. 1, A). Before a malunion of (multiple) fragments is quantified, the malunited parts must be identified and separated on the basis of the previous fracture lines by creating virtual osteotomy planes.9,10 Then, the reduction to the normal anatomy is simulated by registering the mobilized fragments to the reconstruction template (Fig. 1, B). The relative 3D rotation and the 3D translation between each fragment and the reference fragment quantify the malalignment (Fig. 1, C). In addition, it is important to incorporate clinically relevant considerations in the simulated reduction (eg, by adopting the alignment of the fragments manually). For instance, a small shortening compared with the contralateral side might be preferable when a gap between the fragments can be avoided. In other cases, a realignment of the articular surface might be indirectly possible with a less risky osteotomy. Thereafter, the ideal surgical implant and the position of fixation must be identified. Finally, patient-specific guides are designed to transfer the preoperative plan into the surgery. As

Figure 1 Deformity analysis and planned correction. A 3D model is illustrated of the pathologic humerus (orange), with the selected region (yellow) for the registration of the shaft (A) to the mirrored, contralateral humerus (green, target model). After the first registration (A), the shaft fragment serves as the reference fragment (yellow), and the proximal deformity is revealed. A second registration (B) of the humeral head fragment (orange) is performed to complete the reduction (magenta) to the target model. The relative transformation of the humeral head fragment quantifies the amount of the reduction and can be expressed in 6 degrees of freedom (ie, a rotation around a 3D axis and a translation along a 3D displacement vector) with respect to the humeral coordinate system (C). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

ARTICLE IN PRESS Corrective osteotomies of malunited humeral fractures each deformity is unique, the surgical strategy for the transfer may differ from patient to patient. Therefore, having versatile tools to realize the planned osteotomy and the reduction is crucial. The definitive position of the fragment, the position of the implant, and the osteotomy planes might have to be iteratively refined as they are mutually interdependent.9

Design of patient-specific guides Reducing a fragment in the surgery in all 6 degrees of freedom (ie, 1× rotation, 2× angulation, and 3× translation)22 is hardly possible if it is performed freehand without the help of navigation tools. In the proposed technique, patient-specific guides are designed and used to support the surgeon in the reduction task. A guide may function as a positioning guide (basic guide), an osteotomy guide, a reduction guide, or a combination of these guides.

Basic guide The basic guide is always the first guide applied to the bone. The fundamental function of the basic guide is to create a correspondence between the 3D preoperative plan and the intraoperative situation by placing the guide on the bone exactly at the position where it was preoperatively planned. In other words, the function of the guide is the registration of the preoperative plan to the intraoperative situation. For this purpose, the body of the guide is shaped in a way that it can be uniquely placed by using characteristics of the irregular-shaped bone surfaces. 9 Therefore, the undersurface of the guide body corresponds to the negative contour of the bone. To ensure that the basic guide incorporates sufficient characteristics of the bone surface, the guide fit is verified on a printout of the bone model. Whenever the identification of the intended position of the basic guide is not possible, the basic guide design has to be re-engineered. The in vivo guide fit can never be better than that on the printout because of additional potential soft tissue interference. Once the registration of the preoperative plan to the intraoperative situation is performed, the guide position is maintained by placing reference K-wires through drill sleeves connected to the guide body of the basic guide (Fig. 2, A and B). By doing so, every further step can rely on the reference K-wires. Hence, the reliability of the intraoperative identification of the planned position of the basic guide is crucial for the entire procedure and should be carefully designed. The deltopectoral approach is one of the commonly used approaches for the reduction of proximal humeral fractures,4 but it is also commonly used for corrective osteotomies.11 For this reason, we propose to design the basic guide such that it matches the outer surface of the greater tuberosity (Fig. 2, A), avoiding contact with the assumed insertion of the pectoralis major and deltoid. However, in our experience, it is necessary to incorporate an arch over the bicipital groove to improve the rotational stability of the guide (Fig. 2, A). The arch-shaped part is in contact only with the lateral border of the lesser tuberosity, leaving a place for the long tendon of the biceps (Fig. 2, A). We have incorporated an additional hook at the inferior border of the humeral head (Fig. 2, A) to avoid the guide sliding in the proximal direction. For distal humeral osteotomies, it is important that the basic guide covers the lateral or medial supraepicondylar ridge to provide rotational stability (Fig. 2, B). In addition, the guide has to be in contact

3 with the bone surface on the proximal border of the malunited fragments to define the position of the guide in the proximal/distal direction (Fig. 2, B).

Osteotomy guides Different approaches for designing an osteotomy guide are possible, depending on the surgical approach, the available space, and the type of planned osteotomy (ie, closing wedge,28 opening wedge,28 single cut, multiplanar,23 or intra-articular osteotomy23). The most compact and most versatile guide type directly integrates a cutting slit19 (Fig. 3, A, cutting slit guide) or a cutting surface (Fig. 3, B, cutting surface guide) to constrain the saw blade according to the planned osteotomy plane.10 Another possibility is a metallic inlet guide, incorporating a dedicated frame to insert a metallic inlay. The inlay contains a cutting slit to guide the saw blade (Fig. 3, C).10,13 Although the technique is accurate and eliminates the potential abrasion of the polyethylene, it is limited to certain saw blade types, and it requires more space for the frame. In intra-articular osteotomies, the so-called outside-in approach has been successfully applied to the distal radius and proximal tibia.10,23 Here, the key idea is to perform the intra-articular osteotomy without the exposition or the visualization of the joint by using the intra-articular drill guide for navigation (Fig. 3, D). The complexcurved osteotomy cut is performed by consecutively drilling holes along the cut surface (ie, spaced by 5 mm). A cannulated chisel23 is used to complete the osteotomy by inserting a K-wire into each drill hole. Alternatively, it is possible to create additional intraarticular drill guides with slightly shifted drill holes to perforate and mobilize the entire fragment. It is crucial to know the drill depth in advance to prevent accidental damage of the cartilage on the opposed articulating surface. Thereby, the lengths of the drill sleeves are matched to the length of the drill bit to ensure the correct drill depth.23 The fan-shaped guide (Fig. 3, E) is a modification of the intraarticular drill guide. The major benefit of this novel technique is that the cortex remains intact apart from a small single entry point. Moreover, it is not necessary for the bone surface to be approachable over the entire length, permitting this guide to perform a guided osteotomy in cases in which, otherwise, ligaments or tendons would have to be released. Several divergent drills fan out the osteotomy plane. These drills are predefined by drill sleeves and originate from the entry point.

Reduction guides The reduction can be performed either directly by the manipulation of the fragments or indirectly by the reduction with the implant. For the direct manipulation of the fragments, a K-wire–based reduction guide or a fragment reduction guide can be designed. For the indirect reduction with the implant, a predrill screw holes guide, a prebent plate, or a ramp guide can be used. An implant-independent reduction guide is the K-wire–based reduction guide (Fig. 4, A).19 With this technique, the fragments are directly reduced using K-wires as navigation aids. Typically, 2 parallel K-wires are placed in the fragment, and 2 further parallel K-wires are placed in the reference fragment. The angle between both sets corresponds to the angle of the deformity, indicating the completion of the reduction when the K-wires become parallel (Fig. 1, B). To place the divergent K-wires before the osteotomy, a two-part preoperative K-wire–based reduction guide is necessary. After the

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Figure 2 Basic guide. (A) The basic guide for the proximal humerus is designed to match the outer surface of the tuberculum majus. An arch over the bicipital groove (arrow) controls the rotational stability of the guide. An additional hook (arrow) at the inferior border of the humeral head limits the translation in the proximal direction. The intraoperative identified position is maintained by placing reference K-wires (arrow). Because additional divergent K-wires are placed in the humeral head, the basic guide consists of 2 parts to facilitate the removal of the guide with the K-wires in place. (B) To control the rotational stability of the basic guide on the distal humerus, the lateral supraepicondylar ridge is enclosed (arrow). In addition, for the correct proximal/distal direction, the basic guide is designed to lie on the proximal end of the malunited capitulum fragment (arrow). Note the plastic deformation of the supposed unaffected articular surface (green arrow). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

osteotomy, the postoperative K-wire–based reduction guide is used to bring the K-wires and, consequently, the fragment into the reduced position.19 When the fragments are too small to place K-wires or the K-wires might interfere during the surgical procedure, a fragment reduction guide (Fig. 4, B) is a viable option. This novel technique allows manipulation of the fragment directly, reducing it to the planned position by clamping the fragment in the guide body. For this purpose, one part of the undersurface of the guide body matches to the fragment surface in its reduced position and the other part to the reference fragment. Another option is to use an implant for the indirect reduction if the placement of a K-wire–based reduction guide is not possible.

A commonly applied method is based on a predrill screw holes guide (Fig. 4, C) for predrilling the final direction of the screws of the angular stable plate.15,18,28 After an osteotomy, the drill holes are aligned with the holes of the implant, which sometimes might be laborious and therefore might need an additional temporary fixation. Finally, the indirect reduction is performed by placing the screws into the predrilled screw holes. As a simplification of the previous technique, we introduce a new technique to perform the indirect reduction with a ramp guide (Fig. 4, D). The idea is to fix the plate with the screws to the fragment in its final position on the fragment, to perform the osteotomy, and then to reduce the fragment with the plate. For this purpose, the guide body of the ramp guide is designed to match the undersurface and

ARTICLE IN PRESS Corrective osteotomies of malunited humeral fractures

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Figure 3 Osteotomy guides. Several methods are applicable to guide the planned osteotomy. Cutting slit guides (A) and cutting surface guides (B) are the most versatile. Although the metallic inlet guide (C) is accurate, it is limited to certain saw blades and requires more space. The intra-articular drill guide (D), designed for intra-articular osteotomies, allows an outside-in approach to mobilize the fragment. With the modification of a fan-shaped guide (E), a “deep” osteotomy can be performed with a small entry point placed on the cortical surface. the screw holes of the plate. As a result, the shape of the ramp guide fully defines the final position of the plate relative to the fragment. To remove the ramp guide, leaving the reference K-wires in place, the guide is usually designed as a 2-part guide (Fig. 4, D). The printout of a humeral model in its reduced position can be useful to prebend the plate preoperatively (Fig. 4, E).13 However, the generation of a 3D model of the plate is necessary to integrate a prebent plate into the 3D preoperative plan. The bending device guide (Fig. 4, F) facilitates the preoperative bending, which is particularly helpful for angle blade plates. The guide consists of a support guide and a bending ramp. The slope of the ramp and the kink point are selected so that they match the position and the amount of necessary bending for the plate to fit to the humeral surface. The blade of the plate is fixed first between the proximal part of the bending ramp and the support guide. By bending the plate to the ramp, the planned adaptation of the plate is relatively straightforward.

Discussion Complex malunions of the proximal and distal humerus are among the most difficult orthopedic conditions to treat.6,8 The incidence of complications and unsatisfactory results of corrective osteotomies has been reported to be high.3,6,8 Nevertheless, the procedure can be effective and durable over time for younger patients, justifying the complex intervention.3,6 During the last decade, computer-assisted methods and patient-specific instrumentation have been advocated in total shoulder arthroplasties12,14,29 and for corrective osteotomies of extra-articular deformities of the distal humerus.19,21,25,26,30 In addition, modifications of the technique have been established for complex intra-articular malunions around the tibia plateau and the distal radius, with promising results.10,20,23

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Figure 4 Reduction guides. (A) K-wire based reduction guides with at least 2 K-wires in each fragment fully define the planned correction. (B) With a fragment reduction guide, the fragment is clamped and directly reduced without the need of placing K-wires into the fragment. (C) With a predrill screw holes guide, the drill holes are predrilled through the plate before the osteotomy, and the reduction is performed indirectly with the plate. (D) Using a ramp guide, the plate can be fixed, with the screws to the fragment, into its final position before the osteotomy. On the printout of the humeral models in the corrected position, the implant can be prebent (E), or a bending device guide may facilitate the task (F).

However, a description of the transfer of the technique to corrective osteotomies of the proximal humerus or intraarticular osteotomies is still lacking. In this study, we provide a guideline for 3D corrective osteotomies of complex malunited fractures of the humerus and a detailed overview of the existing and novel instruments to enlarge the toolkit for the 3D preoperative planning and intraoperative realization using patient-specific guides. The methods and tools presented are conceived as practical yet

potentially nonexhaustive guidelines. However, most of the principles are also directly applicable to further anatomies if the basic guide is thoroughly adapted because a successful, reliable procedure depends on the correct intraoperative identification of the guide position. The most versatile way to perform a reduction is to use K-wire–based reduction guides. However, especially in cases of excessive soft tissue tensioning during a reduction, the bending stiffness of the K-wires is crucial. The bending

ARTICLE IN PRESS Corrective osteotomies of malunited humeral fractures stiffness of a metallic rod changes as the fourth power of the diameter.2 Therefore, increasing the diameter of the K-wires by 50% will increase the stiffness by a factor of 5. Omori et al21 used 1.5- or 2.0-mm K-wires with a similar technique for corrective osteotomies of cubitus varus deformities and reported on accurate postoperative results. However, they assumed that for closing wedge osteotomies, the reduced position of a fragment is mostly defined by the resected wedge. Hence, we recommend using K-wires with a diameter of at least 2.5 mm for opening wedge osteotomies. Another approach is to use the implant for defining the reduction indirectly by using a predrill screw holes guide.9,10,18 By using this technique, we recently showed that more precise reductions could be achieved for closing wedge and single-cut osteotomies of the forearm.28 However, for opening wedge osteotomies with extensive lengthening, the final corrections were less accurate, probably because a precise reduction was difficult to achieve or to maintain. As the approach solely relies on the used implant, any deviation from the planned implant position or screw direction will influence the reduction. With the novel technique of using a ramp guide, the plate is fixed to one fragment with the use of the implant-specific targeting devices. After the osteotomy, the reduction is achieved more easily by aligning and fixing the shaft fragment to the plate. Another benefit is that the reduction does not depend on the insertion of the screws in the predrilled direction and therefore can be combined with variable angle screws and with angled blade plates. However, the main limitation is that the technique is not always applicable because it is required that the plate stick out of the bone or at least that it not intersect the bone in the initial configuration of the malunion. Whether the accuracy of a reduction with this technique is higher than with the predrill screw holes guide will be investigated in further studies. For intra-articular osteotomies, one of the major benefits of patient-specific guides is the possibility of performing an osteotomy with an10,23 outside-in approach10,23 by using an intraarticular drill guide. In combination with a fragment reduction guide, the osteotomy and the reduction can be performed without requiring a direct view into the joint. However, during an analysis of the deformity, it is also important to examine carefully the presumed intact intra-articular surface. For example, a 3D deformity analysis may reveal plastic deformations (Fig. 2, B) that would otherwise remain undetected if examined on plain radiographs or single CT slices. Without the consideration of plastic deformations, the performed correction would result in an intra-articular step-off, which would require additional efforts for its correction. To reduce the number of guides required per patient, a guide can combine several primary functions of a basic guide, an osteotomy guide, or a reduction guide into one guide body. Similarly, the reference K-wires can also inherit additional tasks (ie, serving as reduction K-wires or predrilling of the screw holes). For example, to avoid placing various K-wires and thereby weakening the bone, one could use the

7 K-wires first as reference K-wires. After the osteotomy, the K-wires can be reused with a K-wire–based reduction guide for the reduction task. Last, the K-wires are replaced with screws through the plate for the final fixation. Accordingly, the initial direction of the K-wires should correspond to the final direction of the screws, and the diameter of the K-wires should match the diameter of the drill bit. The main disadvantage of the presented technique is that the whole procedure depends on an accurate preoperative 3D analysis, planning, and design of the patient-specific guides. Although it is possible to design alternative guides for several scenarios, they will never tackle all potential difficulties arising during surgery. For example, it is important to anticipate the amount of available space for the guides and soft tissue interfering with the selected surgical approach (ie, insertion of tendons and ligaments) during the preoperative planning. Another potential disadvantage of patient-specific guides is that periosteal stripping is necessary to achieve a unique fitting of the basic guide for the registration of the preoperative plan. Whether this might cause a delayed union still needs to be investigated. However, the benefits of the technique for corrective osteotomies of complex malunions after humeral fractures outweigh these disadvantages.

Conclusions Complex deformities of the humerus as described in this study are rare, and the corrections by osteotomies are challenging. Each deformity is unique; therefore, the surgical strategy differs from patient to patient. The preoperative planning and the design of patient-specific guides have to be adapted to the pathologic process of the patient. However, with the proposed tool set, corrective osteotomies of complex malunited humeral fractures are probably predictable with promising results.

Disclaimer Part of the work was funded by the Swiss Canton of Zürich through a Highly Specialized Medicine (HSM2) grant. The authors, their immediate families, and any research foundation with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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