UvA-DARE (Digital Academic Repository) Characterizing scaphoid nonunion deformity using 2-D and 3-D imaging techniques ten Berg, P.W.L. Link to publication Citation for published version (APA): ten Berg, P. W. L. (2017). Characterizing scaphoid nonunion deformity using 2-D and 3-D imaging techniques General rights It is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulations If you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. UvA-DARE is a service provided by the library of the University of Amsterdam (http://dare.uva.nl) Download date: 02 Sep 2018
CHAPTER 9 Summary & Discussion Conclusion
SUMMARY & DISCUSSION INTRODUCTION The scaphoid nonunion is a common, but potentially devastating complication of a scaphoid fracture. 21 It is defined by a failure of fracture healing six months after the scaphoid injury. 20 The relatively high nonunion rate (~5 10%) reported in the literature 22,153-157 is often explained by the scaphoid s small, complex shape and tenuous blood supply. 10,19,66 Nonunions are associated with a typical humpback deformity in which the distal fragment rotates volarly resulting in a malalignment of the scaphoid fragments. 104 The natural history of untreated scaphoid nonunions describes the eventual onset of carpal osteoarthritis, showing a particular pattern of carpal collapse also known as scaphoid nonunion advanced collapse (SNAC) causing painful disabilty. 36 It is unclear how close the restored scaphoid anatomy must be to the original intact anatomy to yield a good clinical outcome and to prevent carpal osteoarthritic development. This hampers reaching consensus about the optimal reconstructive technique. 47 It is likely that this uncertainty can be explained by the less reliable use of standard 2-D imaging tools to evaluate scaphoid nonunion deformity and carpal osteoarthritis. 45,52,53,95,97 Therefore, to optimize surgical management, more reliable 3-D imaging tools are required. To this end, we deem an approach in full 3-D space independent of the viewing direction necessary, as the deformity and associated carpal collapse pattern manifest in 3-D space. 84,104 In this thesis, 3-D CT-based imaging techniques are proposed and investigated to evaluate scaphoid nonunion deformity and the associated level of osteoarthritic progression of the carpus. The following purposes are defined: 1. to objectively estimate the original anatomy of an affected scaphoid (anatomic studies); 2. to investigate how scaphoid nonunion deformity develops over time (patient study) and to improve correcting this deformity in reconstructions (experimental study); 3. to investigate how carpal osteoarthritis develops over time (patient studies). PART I: SCAPHOID ANATOMY Knowing the original anatomy of a scaphoid nonunion including the original position of the proximal and distal segments is a prerequisite for quantifying deformity, described by the maligned position of the segments. As there is a wide spectrum of scaphoid sizes and shapes among individuals, 1 a patient-specific approach in estimating the original scaphoid anatomy is required. When using the contralateral scaphoid as reference, potential anatomic variation in left-to-right differences may reduce the precision in estimating the original scaphoid anatomy. Prior cadaveric and imaging studies have shown that there are no large side-to-side differences in healthy scaphoid pairs. 66,69,158 These studies, however, 96 Chapter 9
investigated scaphoid anatomy with a physical caliper or conventional radiologic measures, which have limited reliability. 43,44,46,158,159 Moreover, estimating the original scaphoid anatomy may be more precise by using intact reference bones other than the contralateral side; a possibility that has not been investigated before. In Chapter 2, we investigated how to estimate the original scaphoid length by using anatomic measurements of intact ipsilateral bones and compared this with length estimations based on measuring the contralateral scaphoid, in order to find the most precise anatomic reference. To this end, we measured the scaphoid and capitate lengths and the distal radius width using virtual 3-D bone models obtained from bilateral CT scans of 28 healthy wrist pairs. After correlating the anatomic measurements, we found that a good ipsilateral estimate of the scaphoid length can be obtained by taking the average of the radius width and the capitate length. Nevertheless, the contralateral scaphoid was most precise in estimating the normal scaphoid length, and should therefore be considered the most appropriate reference for length restoration. In scaphoid reconstruction surgery restoring the scaphoid length alone is not sufficient, as a scaphoid nonunion deformity is not a 1-D but a 3-D problem, as previously stated. 41,42 Consequently, deformity should be corrected by realigning the distal scaphoid fragment relative to the proximal fragment in 3-D space. The goal of chapter 3 was to investigate if the normal 3-D alignment of the intact contralateral scaphoid can help quantifying fragment malalignment and, subsequently, guiding fragment realignment of a scaphoid nonunion in 3-D space. To this end, we investigated left-to-right differences in the alignment of the distal scaphoid segment relative to the proximal segment, using 3-D CT images from bilateral CT scans of 19 healthy wrist pairs. We showed that, on average, the proximal and distal segments of scaphoid pairs were symmetrically aligned, validating the use of the contralateral scaphoid as 3-D anatomic reference. Despite the high degree of bilateral symmetry, in general, side-to-side differences could be up to 2 mm or 10 in individual cases. This may result in a small discrepancy between the estimated intact alignment based on the contralateral scaphoid and the original intact alignment in a given case. Nonetheless, until more precise references become available, we recommend using the contralateral side, especially since its use is rather straightforward. PART II: NONUNION DEFORMITY Despite the increasing literature on scaphoid nonunions, it is still unclear how deformity develops over time in untreated nonunions and how to effectively correct the deformity by realigning the fragments. 21,50,51 A plausible explanation for these uncertainties is the unreliable way deformity is currently measured. In standard radiography, the projection of overlapping bones may hamper obtaining good visualization of the scaphoid. 160-164 Previous inter-observer studies 43,44,46 showed that conventional plane CT measurements, 9 Summary & Discussion 97
including the intrascaphoid angle (ISA), have limited reliability (Figure 4.3). The ISA represents the angle between the two lines perpendicular to the proximal and distal articular surface of the scaphoid, as measured in the sagittal plane. Observer variation is caused by variations in the position of the wrist during scanning, manual selection of the slice, and the measurements themselves. To improve visualization of the entire scaphoid contour in the sagittal plane, in 1988, Sanders 165 developed a CT protocol in which scan slices are along the longitudinal axis of the scaphoid with the arm in overhead position. Currenty, many radiologic workstations allow obtaining sagittal reformations in the longitudinal axis of the scaphoid. 166 Despite the availability of dedicated protocols, standard scaphoid deformity measures remain unreliable. 43,44,46 Given the fact that the contralateral side is an appropriate 3-D anatomic reference (chapter 2 and 3), we were able to quantify scaphoid nonunion deformity using 3-D CT-based imaging techniques, as demonstrated in chapter 4. To this end, in a cohort of 28 unilateral scaphoid nonunion patients, the scaphoid nonunion fragments were superimposed onto the mirrored contralateral scaphoid. We observed that a humpback deformity was generally present in which the distal fragment rotates volarly (mean 26 ). This humpback deformity, as measured with 3-D CT, however, did not correlate with the ISA (mean 8 ), which was conventionally derived from measurements in standard sagittal CT slices. It therefore seems that conventional measurements on CT slices underestimate the level of humpback deformity. Moreover, observer agreement of ISA measurements was unsatisfactory, which is consistent with previous findings. 43,44,46 In the current cohort, besides bone loss at the nonunion sites, excessive osteophytic growth on the dorsal ridge of the scaphoid was detected and quantified. The volumes of the bone losses and osteophytes were comparable in size and increased progressively over time in untreated scaphoid nonunions. In literature, little attention has been given to this phenomenon of dorsal osteophytic overgrowth, as standard reconstructive surgery is primarily focused on realigning the fragments by inserting a graft in the volar bone defect. Our finding showed that removing some part of the dorsal osteophyte may be required in addition to interpositional bone grafting in order to restore the normal scaphoid anatomy. Unfortunately, due to the retrospective design of our study, we were not able to investigate the relation between the level of deformity and clinical parameters, such as pain, range of motion and grip strength, in a consistent manner. To investigate this, a prospective study is recommended. In Chapter 5, we evaluated an experimental surgical plate fixation technique to improve anatomic restoration by guiding fragment realignment using real-sized plastic bone models of scaphoid waist nonunions, retrospectively obtained from 8 patients. Plate osteosynthesis for the scaphoid has previously shown to be useful in a subset of scaphoid nonunions, such as in cases with large bone defects where screw purchase may be compromised, or in cases with persistent nonunion after initial screw fixation. In these 98 Chapter 9
specific cases, reported union rates are around 90%. 114,115,167 In our experimental study, we investigated residual fragment malalignment after utilizing prebent plates based on a 3-D printed model of the mirrored contralateral scaphoid and compared the results with standard practice where plates are bent intraoperatively using a freehand technique. Three independent operators performed the realignment procedure using prebent and conventionally bent plates. We also compared the mismatch of the plates with the volar scaphoid surface to investigate the potential prominence or articular impingement, which are common hardware-related issues in plate osteosynthesis. 113 Our study showed that a prebent plate did not improve fragment realignment compared to the conventional plating technique. We explain this outcome by the general difficulty to find a unique fit of the plate to the scaphoid surface due to its round and smooth curvature. On the other hand, the prebent plate was better adapted to the scaphoid surface at waist level, which may reduce the risk of prominence and subsequent cartilage damage. Additional studies are needed to further improve surgical reduction techniques and assess the clinical outcomes in relation to the level of reconstructed scaphoid morphology. Instead of using adapted standard plates, another research group 51 previously described the use of 3-D printed patient-specific reduction guides to intra-operatively find the optimal fragment position as preoperatively planned. These guides consist of a prereduction guide to find the insertion points of two parallel K-wires into the proximal and distal nonunion fragments, and a subsequent postreduction guide to manipulate the paired K-wires and find the reduced fragment position. In a case series of nine scaphoid nonunion patients, 51 this technique resulted in a precise anatomic restoration. This latter technique, however, is still currently time- and resource intensive, requiring advanced planning software, and long-term follow-up data is absent. We believe that such techniques will be increasingly accessible due to the continuing development efforts for easy-to-use planning software and the availability of 3-D printers to create drilling and reduction guides in a hospital setting. This forms an interesting area for future research. PART III: CARPAL OSTEOARTHRITIS Currently, it is not clearly known whether reconstruction surgery can prevent the development of carpal osteoarthritis. 21 Moreover, it is uncertain at what level of carpal osteoarthritis the surgical decision should change from a reconstructive to a salvage procedure. 48 An important factor contributing to these uncertainties is the unreliable, qualitative assessment of the level of carpal osteoarthritis on standard radiographs. 57,58 Therefore, improving the detection of osteoarthritic changes in the wrist following a scaphoid nonunion is required. In Chapter 6, our goal was to find new radiologic features that are indicative for osteoarthritic changes in the wrist following a scaphoid nonunion, in addition to generally known features such as sclerosis and joint space narrowing. To this end, we focused on 9 Summary & Discussion 99
the intrinsic changes of other carpal bones than the scaphoid, using CT and MRI scans obtained from a retrospective cohort of 73 patients treated for a scaphoid nonunion. The uninjured scaphoid of the opposite wrist in each bilateral scan served as control. We showed that intra-osseous carpal cysts were overrepresented in the injured wrists, and that there were more cysts detectable in older nonunions. Most cysts outside the scaphoid were eccentrically located in the trapezoid (12%). We believe that the formation of trapezoid cysts are triggered by local mechanical stress of the distal scaphoid nonunion fragment, and may therefore serve as an additional radiologic parameter indicating osteoarthritic changes. In Chapter 7, we investigated the reliability in staging osteoarthritic changes using plain radiographs by evaluating the effect of providing an image of the contralateral healthy wrist and of giving an educational training. To this end, 82 fully trained surgeons rated anteroposterior radiographs of 19 patient wrists following a scaphoid nonunion based on SNAC stages 0 4, representing a radiographic classification of the general level of carpal osteoarthritis. 36 There was no significant difference in agreement between observers who rated unilateral radiographs and who rated bilateral radiographs, nor between agreement between observers who received training and who did not. This cross-sectional study showed that an additional comparison view and/or training is not clinically relevant in staging carpal osteoarthritis using standard radiographs. Overall, observer agreement was only moderate, indicating that there is still room for improvement in the way we assess carpal osteoarthritis. Instead of attempts to improve conventional, qualitative evaluation, we believe that efforts should be made to develop quantitative imaging methods to analyze osteoarthritic progression. In Chapter 8, our goal was to develop a semi-automated technique to measure radial styloid pointing in 3-D space, to provide a quantitative, rather than a qualitative measure of osteoarthritic changes. Radial styloid pointing due to spur formation is considered an early sign of radiocarpal osteoarthritis. Therefore, we compared the styloid size from the injured wrist with the healthy contralateral styloid size using 3-D CT models obtained from CT scans from 31 scaphoid nonunion patients. We compared these findings with nonunion duration and with SNAC stages 0 4, based on radiographic assessment by six independent observers. In 74% of the patients the styloid was significantly pointed. Increased styloid pointing was associated with older nonunions, and with more severe osteoarthritis as assessed radiographically. Previous research at our institute 168,169 showed that also other measures of carpal osteoarthritic changes can be quantified, including joint space distances. For example, dynamic 3-D CT wrists imaging is a promising tool in detecting altered carpal dynamics with the possibility to quantify cartilage thickness. Combining standard evaluation and advanced quantitative measurements may improve staging carpal osteoarthritis, which helps us to decide between reconstructive and salvage surgery. 100 Chapter 9
CONCLUSION In this thesis, we described the development of 3-D CT-based imaging techniques to quantify scaphoid nonunion deformity and to evaluate the level of carpal osteoarthritis. For an objective evaluation of deformity in a given case, the contralateral intact scaphoid is the best available anatomic reference (chapter 2 and 3). 70,170 Based on this concept, we showed that the ununited scaphoid has a tendency to deform in a predictable pattern over time, including the formation of osteophytes along the dorsal ridge (chapter 4). 82 Anatomic restoration of the scaphoid may require the removal of a part of the dorsal osteophyte, in addition to realigning the fragments. Nevertheless, anatomic restoration of the scaphoid remains challenging. A standard plate adapted to a 3-D printed anatomic scaphoid model is unable to correct the scaphoid deformity precisely (chapter 5). Standard qualitative radiographic evaluation of carpal osteoarthritic changes has limited reliability, regardless of the availability of a comparison view of the intact wrist or of an observer training (chapter 7). Therefore, this thesis described the development of a 3-D CT-based imaging technique to objectively analyze radial styloid pointing serving as a quantitative measure of carpal osteoarthritis (chapter 8). 171 The styloid is significantly pointed in the majority of the scaphoid nonunion wrists, with more severe pointing in older nonunions having more severe osteoarthritis. Three-dimensional styloid pointing analysis is an objective method to assess osteoarthritic progression in the wrist following a scaphoid nonunion. We believe that our proposed imaging techniques form a solid basis for future clinical studies to investigate the consequences of the reconstructed scaphoid morphology on wrist function and long-term osteoarthritic development, which eventually may lead to reaching consensus about the optimal reconstructive technique. 9 Summary & Discussion 101