The Journal ofArthroscopic and Related Surgery 8(3):311-319 Published by Raven Press, Ltd. 0 1992 Arthroscopy Association of North America
Arthroscopy:
Videoarthroscopy:
Review and State of the Art
Summary: Since the introduction of videoarthroscopy, there has been rapid technological advancement. The charged couple device (CCD) has become the standard small pickup unit for the present cameras. The video signal processing and transfer has been modified and improved. New Y/C or super VHS and red, green, blue (RGB) systems have been associated with improvements in monitors, video recorders, and video printers. Measurements of video quality such as resolution, signal-to-noise ratio, pixels, and contrast have been confusing to clinicians evaluating these new systems. Equipment compatibility and the weak-link theory is important to understand when selecting new equipment. This review article presents an update for the clinician who wants more information to differentiate among the new video arthroscopic systems. Key Words: Videoarthroscopy-Y/C-RGB-Video recorders-Video printers. _
Videoarthroscopy has become the standard for orthopedic surgeons to visualize and perform intraarticular procedures. It allows increased sterility over direct visualization and is conducive to a more comfortable position for the surgeon. The monitor allows the assistant and/or nurse to observe and participate in the intraarticular surgery. This enhances and makes their assistance more effective. Similarly, with the monitor, video recorders, and printers it improves medical education for the resident or fellow. Patients also are able to see and more thoroughly understand their intraarticular pathology. Video recorders and printers also enhance scientific presentations and documentation. The standard videoarthroscopy system includes arthroscope, light source and cord, camera, monitor, and video recorder. Within the past few years, the video components have undergone significant changes (l-4). These technological advances and changes in equipment may be confusing to surgeons
who are looking to upgrade their present video system. The purpose of this review is to discuss recent improvements and changes in technology and, one hopes, assist in the selection process of new video equipment. There are certain concepts common to all the video components in the system. These concepts include picture quality and methods of measurements, video formats, system compatibility, and weak-link theory.
BASIC VIDEO THEORY The video system converts light energy into electrical energy and then back into light energy again. The camera consists of two units: a camera head with a sensor, and a control unit with electronic circuitry to generate a transmittable signal. Presently, the sensor used is a solid state unit or chip called a charged coupled device (CCD) (Fig. 1). In the past, vacuum chamber pick-up tubes (Vidicon and Saticon) and other solid state units, e.g. mental oxid semiconductor (MOS) and charged primary device (CPD), were used. The CCD has better sensitivity, resolution, signal-to-noise ratio, and improved dynamic range. The CCD sensor within the
From the Garland Orthopaedic Clinic, Garland, TX (J.M.W.), and Southern California Center for Sports Medicine. Long Beach, California, U.S.A. Director, Southern California Center for Sports Medicine (D.W.J.). Address correspondence and reprint requests to Dr. Douglas W. Jackson at 2760 Atlantic Avenue, Long Beach, CA 90806, U.S.A.
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AND D. W. JACKSON playback mode, a magnetic circuit is completed as a magnetic tape moves across the pickup head recreating the electronic signal. PICTURE QUALITY AND ITS MEASUREMENTS
FIG. 1. A charged coupled device, “chip”
camera is made up of many small picture elements (pixels). In the absence of light, these pixels are nonconductive; in the presence of light, they are conductors (electron emitters). Each pixel has a filter that is capable of sensing either red, green, or blue light to render color information. The picture being taken is transformed into a matrix that is made up of these conductive and nonconductive pixels. This matrix is then scanned systematically at a rate of 525 lines/frame, 30 frames/s, which generates a signal frequency. The scanning rate is standardized by the National Television Systems Committee (NTSC) guidelines and is the same even with Y/C and red, green, blue (RGB) formats. This signal frequency is then transmitted to a monitor, video recorder, video printer, and/or video floppy recorder. In the monitor, the signal is converted back to light, again using the NTSC standard of 525 lines/frame of video information. Using a cathode ray tube, an electronic gun directs a beam to the picture tube, which is a fluorescent screen (raster). Scanning by the beam can produce light at all points on the scan raster, thus giving a picture on the tube. The raster is made up of red, green, and blue dots and pixels. The intensity of each color dot varies proportionally with the strength of the electronic beam. Various nuances of color are created by differing the various brightness of these red, green, and blue pixels (Fig. 2). A video tape recorder takes the electronic signal and, with varying current passing to the recording heads, the tape is magnetized as it passes. In the
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Discussion about picture quality most commonly centers around resolution. Many people think that to judge video equipment, all they need to understand is resolution. Resolution specifications are most commonly listed as horizontal resolution. Horizontal resolution is the horizontally resolvable detail in a picture. Horizontal resolution measurements are the number of distinct vertical lines that can be seen in a picture. Vertical resolution is expressed as the number of distinct horizontal lines that can be seen in a picture and is measured in the same manner as horizontal resolution. The higher the resolution, the sharper and clearer the picture. Resolution is measured using a resolution chart (Fig. 3). Using this chart, the camera is aimed and zoomed in until the outermost markings on the chart fall at the edge of the view finder. The wedged lines are followed in until they are too blurred to be counted. The number next to this blurred area is the resolution. Due to NTSC standards, it is limited to ~525 lines, as this is the standard for the screening system. In practice, it is less than that, as not all of the 525 scannable lines are usable. It is dependent on the number of pixels in a camera, the capability of the electronics and the video system to carry and process the signal, and the number of pixels in the monitor. phosphor dots electron beam
ube ace FIG. 2. Variation of red, green, and blue dots or picture elements used to make the color seen on the picture tube.
VIDEOARTHROSCOPY:
REVIEW
Pixel numbers are occasionally used in place of a measure of resolution. This is easy to understand as the more picture elements or pixels in video equipment, the more detail you are able to pick up or show. This is shown diagrammatically in Fig. 4. The next most commonly used measurement of picture quality is the signal-to-noise ratio. In simplistic terms, it is the ratio of the measurement of the highest signal obtained to the noise produced in electronic frequency or signal. Noise is the undesirable electronic disturbance produced in an electronic circuit. The higher the signal-to-noise ratio, the better. As seen diagrammatically in Fig. 5 in a low signal-to-noise circuit, a signal has a tendency to get lost, With a lower signal-to-noise ratio in a video system, you get a grainier, coarser picture, the effect often being described as “picture snow.” It would be easy to choose equipment if this were all there were to judging picture quality. But, un-
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fortunately, there are many other things that go into making a quality picture, for example, color quality. Specifications for resolutions and signal-to-noise ratio are usually only given as black and white, not as color measurements. These measurements can be made for color, but judging color quality is a very subjective matter and is not totally dependent upon these measurements. More important than color quality for picture quality, are contrast and edge enhancement. This is because the human eye is much more sensitive to the black and white parts of a picture than to the color portions. Contrast is the ratio between the maximum and minimum brightness in a picture. For example, a high contrast picture would have intense blacks and whites, whereas a low contrast picture would only have various shades of gray. Edge enhancement is the highlighting or darkening of the edges of objects to give them high contrast. Increased edge enhance-
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PIXEL
E
E
FIG. 4. The more picture elements seen.
(pixels), the more detail
VIDEO FORMATS
ment in a picture gives a much sharper and clearer picture, which we need for video arthroscopy. This is because our eyes are more sensitive to black and white changes, and most of the pathology seen arthroscopically is more black and white than color. With all these factors going into make up picture quality, some people like to talk about “apparent This is distinguished from measured resolution”. resolution in that it is the subjective evaluation of the picture quality in total. For example, comparing two systems side by side may show a clearer, sharper picture (apparent resolution) even though the measured resolution is the same. In our experience, the camera with the highest resolution that we have tested on specification sheets did not actually have the picture we preferred the most. Another problem with trying to rely on resolution and signal-to-noise ratio specifications to pick video equipment is that measurements are done by the manufacturers and are not certified by independent testers. The conditions under which measurements are done and how they are done can be manipulated no noise
noise
signal
signal in noise
high signal to noise
low signal to noise
FIG. 5. The higher the signal-to-noise ratio, the easier it is to differentiate the signal from the background noise.
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in such a way that, for example, a monitor’s resolution, measured by two different companies, can differ by > 170 lines. So how do you judge which video system produces the best quality picture? You can use the measurements of signal-to-noise ratio and resolution as a general guide, but, in the end, the only way to judge is by direct comparison, Ideally, it would be best to compare systems in an operating room (OR), using the same arthroscope and light source, and switch back and forth from one system to another to allow your eyes to determine which system has the best apparent resolution or picture quality for your purposes.
As confusing as evaluating picture quality can be for a busy orthopedic surgeon, there is probably more confusion when it comes to discussing video formats. Formats are simply the manner in which electronic signals produced by a camera carry their color and brightness information. There are different formats presently available. The three most commonly used in the United States are NTSC, RGB, and Y/C. The standard video format in the United States, Canada, Japan, and most of South America and Asia is NTSC. It was established by the NTSC as a format to be used for broadcast purposes. Transmission had to be within a limited band width assigned to each television station, which resulted in certain limitations. And, in order to best utilize this limited band width and allow for easy broadcast, the committee decided that all information should be carried on one signal. This is termed “composite video”. Both color and brightness information are carried on the same signal (Fig. 6). SECAM and PAL are similar composite systems that are the standards in other parts of the world. They differ in frequency and scanning rates and are not compatible with NTSC video equipment. The primary advantage to the NTSC format is that it is standard. As such, almost all equipment, even if it is capable of Y/C and/or RGB formats, will also have a NTSC format available for system compatibility. There are several problems, however, its limited band width allows limited information to be transmitted. This is especially noticeable in video recorders as NTSC recorders have limited resolution. The combination of both color and brightness information on one signal also causes several prob-
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AND STATE OF THE ART
Standard Video Format FIG. 6. The standard video format NTSC with color and brightness on the same line.
mmmmC()LOR
mm
Bi!
TNESSmmm
lems. As the camera processes color and brightness separately, an encoding process is required to combine these signals into one, and the result is an increased signal noise. The combination of the two results in cross talk or interference between the two, also again increasing the noise. Both of these factors result in decreased signal-to-noise ratios. Also, as the color and brightness information must alternate in one signal, color or brightness flicker may result if not properly handled. Y/C system is the next most commonly available system. Y stands for the luminants or brightness signal and C stands for the chromants or color signal. This is more commonly referred to as Super VHS or SVHS, which only refers to the taping system that made this format popular. In this component signal, video information is carried on two different signals: Y and C (Fig. 7). This system has the advantage of not requiring the encoding or having problems with the cross talk or flicker inherent in the NTSC format. Handling the brightness signal separately allows for higher contrast in the images. This higher contrast is seen as a sharper picture with higher apparent resolution or picture quality. The primary advantage of the Y/C format is its video recorders. With this format, video recorders, such as SVHS, Beta, and high band 8 mm, allow for significantly higher resolution than is available with the NTSC format. Similarly, Y/C produces clearer pictures on hard copy producers. The disadvantage
of this system include the requirements of more expensive monitors and recorders to obtain its benefits. Also, it is a poor transmission format, as the luminants and color frequency travel at different speeds. Over longer cord distances, they will be out of synchronization and must be remanipulated to bring them back into phase, requiring extra electronic circuits, and thereby decreasing some of the advantages. RGB is the third most commonly used video format and is also a component system. With it, video information is separated into red, green, and blue signals and carried separately (Fig. 8). Brightness is generated as a percentage of these colors (30% of red, 59% of green, and 11% of blue). There are several advantages to this system. As it requires less electronic processing than do NTSC and Y/C, there is increased signal-noise-ratio due to less noise production. It has a wider band width, allowing more information to be transmitted. The result is an exceptionally sharp picture with distinct color separation for use with monitors and hard copy printers. It is also the format of choice for computer interfacing, which may become more important in the future. The disadvantages include the increased expense for RGB video equipment. Video taping is possible with the RGB format, but presently available equipment for recording on the RGB format is prohibitively expensive. Other disadvantages include the fact that the three signals must be pre-
Super - VHS Format FIG. 7. Y/C or Super VHS video format with color and brightness on separate lines.
mmmmmmmm
mmmmmm
COLORmmmmmmmm
BRwB
TNESS
mmmmmm
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RGB Video Format
FIG. 8. RBG video format with red, green, and blue signals carried on different lines; brightness is generated as a percentage of red colors.
cisely synchronized, which is difficult to attain and maintain. Also, the color in the monitor cannot be adjusted because the format system renders the hue knob oq a monitor inoperable. Although, with the equipment we had available for evaluation, Y/C and RGB seemed to be far superior to the NTSC format, the differences seemed fairly small. Even in the NTSC system format, the new systems that we have been evaluating, with their improved CCD units and electronic circuitry, are a definite improvement over the older models. Several cameras have NTSC, Y/C, and RGB formats available. With these cameras switching to the Y/C and RGB formats, we have seen improvements in picture quality over the NTSC format in that same camera. Which of these two systems is better is subjective and it is difficult to get orthopedists to agree on their preference.
SYSTEM COMPATIBILITY With three different formats available, system compatibility becomes a problem. As discussed earlier, the standard that most video equipment is capable of handling is the NTSC system. Y/C and RGB formats require special equipment, as the Y/C uses two cables and the RGB uses three cables to transmit information. For example, in order for an SVHS recorder to get the improved resolution of which it is capable requires a camera with the component system of a Y/C to produce it. Furthermore, to play an SVHS tape back also requires an SVHS recorder. Similarly, to get the advantages of a Y/C or RGB format camera on the monitor, the monitor must be capable of handling these component signals. Arthroscopy,
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THE WEAK LINK THEORY This video concept is that no integrated system is any stronger than its weakest link. For example, if you have a camera with a resolution of only 300 lines and use a monitor with 600 lines, the system will only produce 300 lines of resolution (Fig. 9). The monitor will thus be underutilized. The camera and monitor numbers could be reversed, with the same results. Video recorders and hard copy printers, when substituted, have the same results. More importantly, apparent resolution or true picture quality could be substituted with similar results. A picture will be no better than the quality produced by the poorest performing component of that video system. INDIVIDUAL COMPONENTS Camera In the OR, the picture produced on a monitor is dependent on the placement and positioning of the arthroscope, inflow/outflow, portal placement, extremity positioning, light source, camera, and monitor. Assuming adequate surgical technique and a good arthroscope and light source, the poorest performing or weakest link in the system is the camera, thus making the camera the most important component of the video purchase. As discussed earlier, cameras should be compared, ideally, side by side, in order for surgeons to judge their preference for the best picture quality (apparent resolution). The signal-to-noise ratio and measured resolution are useful guides, with certain limitations, as discussed earlier. New cameras have been further decreased in size and weight for easy handling. The CCD or chip has increased sensitivity and the camera control unit has improved electronic circuitry for additional improvements in picture quality. As far as formats are concerned, all cameras are capable of NTSC’s format even if they have available Y/C or RGB formats. Some cameras even _..__~ I
FIG. 9. Weak link theory, system resolution.
VIDEOARTHROSCOPY:
REVIEW
come with an all three format capability. A camera with NTSC and either Y/C or RGB is going to allow for better picture quality either on a monitor or with a hard copy printer. Y/C format is required to get the added benefits of a Y/C type video recorder. RGB format cameras give the added advantage of improved computer interfacing. Three-chip cameras are just coming on the market. These cameras have three CCD units within them with increased pixels or sensing units. The three-chip camera is the standard for broadcast that, theoretically, offers the best picture quality due to its increased sensitivity. It has its best applications with the RGB format where each chip can be used to pick up a different color. To work properly, it requires exact alignment, which is difficult to attain and maintain. It also, of course, is bigger than a single-chip camera, and costs more. A singlechip camera with RGB and/or Y/C may be only several thousand dollars more expensive than a camera with a standard NTSC; a three-chip camera is approximately double the price. The only three-chip camera that we tried did not give us enough of a subjectively improved picture to justify the additional cost. Camera head controls are another new development. Many cameras now have buttons to control white balance, sensitivity boost, starting and stopping the VCR, and taking hard copy prints, as well as having other remote control functions. These allow the surgeon added control and free OR personnel for other details. Other systems use a separate hand-held remote control device to allow the same control with more functions available. These additional controls may exceed the “gadget tolerance” of some surgeons, and a button occasionally is pushed inadvertently. It takes a while to adjust to the additional controls. A problem that many of the new cameras address is fog control. There are multiple new ways to han-
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dle this problem. Options include O-rings, sapphire lenses, glass-on-glass, water seals, age systems, and heaters. Which will ultimately be incorporated as the most desired and practical, only time will tell. Videoscopes are a new camera/arthroscope variation. Instead of connecting to a coupler, which then connects to a camera head, the arthroscope attaches directly to the camera without a coupler (Fig. 10). By removing the coupler, you get a slight improvement in light and optical transmission to the camera. By connecting the scope and camera with a screw-in design as opposed to the typical coupler clamp, there is also a tighter fit, potentially decreasing fogging problems. When buying a videoscope, the price, compared to that of a typical scope, camera, and coupler, is actually less. This is due to the fact that you are not buying the coupler. There are, however, disadvantages with the videoscope. The camera and scope must be bought together as a unit due to their special connection. Most also are more difficult to sterilely bag due to their screw-in design, although one company has a special snap-tit design, called “collet-coupler”, which does allow easy sterile bagging. Monitors Almost all monitors presently available outperform the cameras. Discrimination in this purchase is less important than in the camera. Again, resolution and signal-to-noise specifications can be used as criteria, but only by direct A-to-B comparisons can you decide if one monitor has better picture quality or apparent resolution than another. Monitors by different manufacturers may have different picture qualities related to the design of their picture tubes. Some, as they are primarily designed for home entertainment viewing, have softer colors and less sharpness for a warmer picture. Monitors with a sharper picture and increased edge enhancement and contrast with true color reproduction are more
FIG. 10. A: A normal setup with arthroscope attached to left comer of black coupler. B: A videoscope with a camera and arthroscope directly attached without the coupler seen in A.
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appropriate for the OR. Monitors differ from televisions in that they are capable of receiving video input only through direct cable inputs; they are not able to accept broadcast signals. Some monitors are combined monitor/televisions and are able to accept both, but this has no advantages in the OR. If one is going to use a camera or video recorder with Y/C or RGB, the monitor must be able to handle these formats. Video recorders Video recorders most commonly in use presently include Umatic, VHS, and 8 mm format recorders. When video recorders are included in the video system, they become a weak link, as shown by their resolution quality (Table 1). They are usually outperformed by most new cameras. The new super VHS ED beta and high band beta significantly increase not only measure resolution but also the signal-to-noise ratio, apparent resolution, and picture quality in general. This system requires a Y/C format camera to benefit from the improvements, however. There is only one medically available and that is the SVHS recorder, which is also approximately twice as expensive as the typical VHS recorder. Those used to the 8 mm lose the advantage of decreased tape size and the resulting decreased storage requirements. Tapes recorded in SVHS mode require an SVHS machine to play them back and a Y/C-type monitor to obtain their added benefits. This becomes a problem when tapes are played back where these are not available. As discussed earlier, RGB recorders are available but, presently, are prohibitively expensive. Eight millimeter, high band recorders are also available but have not been brought to the medical market. Hard copy printers An excellent review of hard copy printers was published by Dr. Charles H. Brown (5). Printers offer several exciting advantages. By allowing qualresolution of various video recording systems
TABLE 1. Approximate
System
VCR Resolution (lines)
ED Beta Super VHS High Band 8 mm W Umatic 8mm VHS Beta
450 400 400 280 225 200 200
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ity instant prints at a push of a button for recording arthroscopic pathology, they can be used instead of video tapes for documentation and patient education. Print images produced can also easily be stored in patient charts, which prevents the storage problems of video tapes. The video print would also be available for viewing during discussions with patients at postoperative follow-ups without the difficulties and time involved in reviewing tapes. Also, at any time in the future they would be available in the patient’s chart for easy review. There are two basic types of video printers: thermal and photographic. Thermal video printers take a video signal and a push of a button to capture a single video frame, storing it in memory while a print is made. This is then produced on a heatsensitive paper. The resolution produced is -NO600 television lines and requires -90 s between exposures. The photographic video printer offers several advantages, with resolution increasing to 60& 700 television lines with increased color accuracy. But the quality is still not quite that of a 35 mm camera mounted directly to an arthroscope. It also allows production of conventional slides or prints, and some models allow as many as nine separate pictures to be taken on each print, slide, or picture. Both types have models that accept Y/C and RGB for improved picture quality. Both types have models in the $3,000 range, with the more expensive, higher quality photographic model costing more than twice that. The cost for thermal prints is -$l.OO a print, with photographic prints costing anywhere from $1.30 to $2.00. With a photographic video printer, conventional prints and slides can be made at an even lower cost. Still video floppy recorders Still video floppy recorders are another new option in the video system. During a procedure, a video floppy recorder can be used to store up to 50 still images from a video signal. At any subsequent time, the images can be reproduced on a monitor and reviewed. Prints of slides can be made from them on a thermal or photographic printer. The still video floppy recorder sells for -$2,000 and discs cost -$20. THE HUMAN FACTOR Before we started evaluating new video equipment for purchase, we had been very happy with the video equipment that we had been using for the
VIDEOARTHROSCOPY:
REVIEW
last several years. Although there is definitely improved resolution and picture quality with the new equipment, we are not actually seeing any pathology that we weren’t seeing with our old equipment. Most arthroscopic pathology is fairly obvious and seeing it is more dependent on the surgical technique than on differences in the equipment presently available. The only area in which improved picture quality is helping is that of evaluating subtle changes in articular cartilage, such as hairline cracks and superficial fibrillation. These subtle findings will rarely change the treatment or improve the quality of care given. An important unanswered question is: what price is one going to pay to improve their system? This is especially significant in today’s medical economic environment. Another important consideration in choosing a new video system is the company and its representative. Even the best equipment will be of less value without a good representative who is available for inservicing, trouble shooting, and quick replacement service. THE FUTURE In the future, we will see further improvements and increasing complexity in video equipment. Technological refinements of the equipment we have available today will be seen over the next few years. The next major steps in the video system will be the high definition television, or HDTV. HDTV, by changing the way in which a camera scans a picture and a monitor scans the raster, will increase the scanning lines in both, giving major improvements in resolution and overall picture quality. IDTV, or improved definition television, is presently available for some monitors and is an intermediate step towards HDTV. Digital video, which makes information easier to deal with, is also another major step. In a digital system, information is converted into a string of l’s and O’s, unlike the
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analog signals presently used, which are constantly variable. Once information is digitalized, converting it to l’s and O’s, it can be manipulated with less difficulty. Digital signals also take up less space than do analog signals, which means more information can be fitted into a given amount of wire or radio frequency. Unfortunately, neither digital video nor HDTV will be available for several years, and so one should not hold off purchases waiting for their appearance. SUMMARY When one is choosing video equipment today, there are many choices. The equipment available today is vastly superior to video systems that are only a few years old. When choosing equipment, it is more helpful to compare one system to another by direct viewing than to check specifications alone. Resolution and signal-to-noise can be used as guides. New systems with Y/C format allow for improved video recording. Y/C and RGB formats allow for improved pictures on monitors and video printers. Video printers and floppy disc storage systems offer new ease in recording and keeping video pictures. What equipment is best for you can only be determined by determining your needs, trying the equipment, and judging it for yourself in the OR. REFERENCES 1. Jackson DW. Videoarthroscopy: A permanent medical record. Am J Sports Med 1978:6:213-6. 2. Jackson DW, Strizak AM. Present status of videoarthros-
copy. Conremp Orrhop 1980;2:521-t. 3. Thayer JL, Jackson DW. Videoarthroscopy:
What an orthopaedist should know about video equipment. Contemp Orrhop 1983;6:51-8. 4. Yates C, Grana WA. Equipment and advantages in videoarthroscopy: In: Update in arthroscopic techniques. Baltimore: University Park Press, 1984:17-23. 5. Brown CH. Producing still images in arthroscopy. Arthroscopy 1989;5:87-92.
Arthroscopy, Vol. 8. No. 3, 1992
Arthroscopy:
Videoarthroscopy:
Review and State of the Art
Summary: Since the introduction of videoarthroscopy, there has been rapid technological advancement. The charged couple device (CCD) has become the standard small pickup unit for the present cameras. The video signal processing and transfer has been modified and improved. New Y/C or super VHS and red, green, blue (RGB) systems have been associated with improvements in monitors, video recorders, and video printers. Measurements of video quality such as resolution, signal-to-noise ratio, pixels, and contrast have been confusing to clinicians evaluating these new systems. Equipment compatibility and the weak-link theory is important to understand when selecting new equipment. This review article presents an update for the clinician who wants more information to differentiate among the new video arthroscopic systems. Key Words: Videoarthroscopy-Y/C-RGB-Video recorders-Video printers. _
Videoarthroscopy has become the standard for orthopedic surgeons to visualize and perform intraarticular procedures. It allows increased sterility over direct visualization and is conducive to a more comfortable position for the surgeon. The monitor allows the assistant and/or nurse to observe and participate in the intraarticular surgery. This enhances and makes their assistance more effective. Similarly, with the monitor, video recorders, and printers it improves medical education for the resident or fellow. Patients also are able to see and more thoroughly understand their intraarticular pathology. Video recorders and printers also enhance scientific presentations and documentation. The standard videoarthroscopy system includes arthroscope, light source and cord, camera, monitor, and video recorder. Within the past few years, the video components have undergone significant changes (l-4). These technological advances and changes in equipment may be confusing to surgeons
who are looking to upgrade their present video system. The purpose of this review is to discuss recent improvements and changes in technology and, one hopes, assist in the selection process of new video equipment. There are certain concepts common to all the video components in the system. These concepts include picture quality and methods of measurements, video formats, system compatibility, and weak-link theory.
BASIC VIDEO THEORY The video system converts light energy into electrical energy and then back into light energy again. The camera consists of two units: a camera head with a sensor, and a control unit with electronic circuitry to generate a transmittable signal. Presently, the sensor used is a solid state unit or chip called a charged coupled device (CCD) (Fig. 1). In the past, vacuum chamber pick-up tubes (Vidicon and Saticon) and other solid state units, e.g. mental oxid semiconductor (MOS) and charged primary device (CPD), were used. The CCD has better sensitivity, resolution, signal-to-noise ratio, and improved dynamic range. The CCD sensor within the
From the Garland Orthopaedic Clinic, Garland, TX (J.M.W.), and Southern California Center for Sports Medicine. Long Beach, California, U.S.A. Director, Southern California Center for Sports Medicine (D.W.J.). Address correspondence and reprint requests to Dr. Douglas W. Jackson at 2760 Atlantic Avenue, Long Beach, CA 90806, U.S.A.
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AND D. W. JACKSON playback mode, a magnetic circuit is completed as a magnetic tape moves across the pickup head recreating the electronic signal. PICTURE QUALITY AND ITS MEASUREMENTS
FIG. 1. A charged coupled device, “chip”
camera is made up of many small picture elements (pixels). In the absence of light, these pixels are nonconductive; in the presence of light, they are conductors (electron emitters). Each pixel has a filter that is capable of sensing either red, green, or blue light to render color information. The picture being taken is transformed into a matrix that is made up of these conductive and nonconductive pixels. This matrix is then scanned systematically at a rate of 525 lines/frame, 30 frames/s, which generates a signal frequency. The scanning rate is standardized by the National Television Systems Committee (NTSC) guidelines and is the same even with Y/C and red, green, blue (RGB) formats. This signal frequency is then transmitted to a monitor, video recorder, video printer, and/or video floppy recorder. In the monitor, the signal is converted back to light, again using the NTSC standard of 525 lines/frame of video information. Using a cathode ray tube, an electronic gun directs a beam to the picture tube, which is a fluorescent screen (raster). Scanning by the beam can produce light at all points on the scan raster, thus giving a picture on the tube. The raster is made up of red, green, and blue dots and pixels. The intensity of each color dot varies proportionally with the strength of the electronic beam. Various nuances of color are created by differing the various brightness of these red, green, and blue pixels (Fig. 2). A video tape recorder takes the electronic signal and, with varying current passing to the recording heads, the tape is magnetized as it passes. In the
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Discussion about picture quality most commonly centers around resolution. Many people think that to judge video equipment, all they need to understand is resolution. Resolution specifications are most commonly listed as horizontal resolution. Horizontal resolution is the horizontally resolvable detail in a picture. Horizontal resolution measurements are the number of distinct vertical lines that can be seen in a picture. Vertical resolution is expressed as the number of distinct horizontal lines that can be seen in a picture and is measured in the same manner as horizontal resolution. The higher the resolution, the sharper and clearer the picture. Resolution is measured using a resolution chart (Fig. 3). Using this chart, the camera is aimed and zoomed in until the outermost markings on the chart fall at the edge of the view finder. The wedged lines are followed in until they are too blurred to be counted. The number next to this blurred area is the resolution. Due to NTSC standards, it is limited to ~525 lines, as this is the standard for the screening system. In practice, it is less than that, as not all of the 525 scannable lines are usable. It is dependent on the number of pixels in a camera, the capability of the electronics and the video system to carry and process the signal, and the number of pixels in the monitor. phosphor dots electron beam
ube ace FIG. 2. Variation of red, green, and blue dots or picture elements used to make the color seen on the picture tube.
VIDEOARTHROSCOPY:
REVIEW
Pixel numbers are occasionally used in place of a measure of resolution. This is easy to understand as the more picture elements or pixels in video equipment, the more detail you are able to pick up or show. This is shown diagrammatically in Fig. 4. The next most commonly used measurement of picture quality is the signal-to-noise ratio. In simplistic terms, it is the ratio of the measurement of the highest signal obtained to the noise produced in electronic frequency or signal. Noise is the undesirable electronic disturbance produced in an electronic circuit. The higher the signal-to-noise ratio, the better. As seen diagrammatically in Fig. 5 in a low signal-to-noise circuit, a signal has a tendency to get lost, With a lower signal-to-noise ratio in a video system, you get a grainier, coarser picture, the effect often being described as “picture snow.” It would be easy to choose equipment if this were all there were to judging picture quality. But, un-
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fortunately, there are many other things that go into making a quality picture, for example, color quality. Specifications for resolutions and signal-to-noise ratio are usually only given as black and white, not as color measurements. These measurements can be made for color, but judging color quality is a very subjective matter and is not totally dependent upon these measurements. More important than color quality for picture quality, are contrast and edge enhancement. This is because the human eye is much more sensitive to the black and white parts of a picture than to the color portions. Contrast is the ratio between the maximum and minimum brightness in a picture. For example, a high contrast picture would have intense blacks and whites, whereas a low contrast picture would only have various shades of gray. Edge enhancement is the highlighting or darkening of the edges of objects to give them high contrast. Increased edge enhance-
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PIXEL
E
E
FIG. 4. The more picture elements seen.
(pixels), the more detail
VIDEO FORMATS
ment in a picture gives a much sharper and clearer picture, which we need for video arthroscopy. This is because our eyes are more sensitive to black and white changes, and most of the pathology seen arthroscopically is more black and white than color. With all these factors going into make up picture quality, some people like to talk about “apparent This is distinguished from measured resolution”. resolution in that it is the subjective evaluation of the picture quality in total. For example, comparing two systems side by side may show a clearer, sharper picture (apparent resolution) even though the measured resolution is the same. In our experience, the camera with the highest resolution that we have tested on specification sheets did not actually have the picture we preferred the most. Another problem with trying to rely on resolution and signal-to-noise ratio specifications to pick video equipment is that measurements are done by the manufacturers and are not certified by independent testers. The conditions under which measurements are done and how they are done can be manipulated no noise
noise
signal
signal in noise
high signal to noise
low signal to noise
FIG. 5. The higher the signal-to-noise ratio, the easier it is to differentiate the signal from the background noise.
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in such a way that, for example, a monitor’s resolution, measured by two different companies, can differ by > 170 lines. So how do you judge which video system produces the best quality picture? You can use the measurements of signal-to-noise ratio and resolution as a general guide, but, in the end, the only way to judge is by direct comparison, Ideally, it would be best to compare systems in an operating room (OR), using the same arthroscope and light source, and switch back and forth from one system to another to allow your eyes to determine which system has the best apparent resolution or picture quality for your purposes.
As confusing as evaluating picture quality can be for a busy orthopedic surgeon, there is probably more confusion when it comes to discussing video formats. Formats are simply the manner in which electronic signals produced by a camera carry their color and brightness information. There are different formats presently available. The three most commonly used in the United States are NTSC, RGB, and Y/C. The standard video format in the United States, Canada, Japan, and most of South America and Asia is NTSC. It was established by the NTSC as a format to be used for broadcast purposes. Transmission had to be within a limited band width assigned to each television station, which resulted in certain limitations. And, in order to best utilize this limited band width and allow for easy broadcast, the committee decided that all information should be carried on one signal. This is termed “composite video”. Both color and brightness information are carried on the same signal (Fig. 6). SECAM and PAL are similar composite systems that are the standards in other parts of the world. They differ in frequency and scanning rates and are not compatible with NTSC video equipment. The primary advantage to the NTSC format is that it is standard. As such, almost all equipment, even if it is capable of Y/C and/or RGB formats, will also have a NTSC format available for system compatibility. There are several problems, however, its limited band width allows limited information to be transmitted. This is especially noticeable in video recorders as NTSC recorders have limited resolution. The combination of both color and brightness information on one signal also causes several prob-
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AND STATE OF THE ART
Standard Video Format FIG. 6. The standard video format NTSC with color and brightness on the same line.
mmmmC()LOR
mm
Bi!
TNESSmmm
lems. As the camera processes color and brightness separately, an encoding process is required to combine these signals into one, and the result is an increased signal noise. The combination of the two results in cross talk or interference between the two, also again increasing the noise. Both of these factors result in decreased signal-to-noise ratios. Also, as the color and brightness information must alternate in one signal, color or brightness flicker may result if not properly handled. Y/C system is the next most commonly available system. Y stands for the luminants or brightness signal and C stands for the chromants or color signal. This is more commonly referred to as Super VHS or SVHS, which only refers to the taping system that made this format popular. In this component signal, video information is carried on two different signals: Y and C (Fig. 7). This system has the advantage of not requiring the encoding or having problems with the cross talk or flicker inherent in the NTSC format. Handling the brightness signal separately allows for higher contrast in the images. This higher contrast is seen as a sharper picture with higher apparent resolution or picture quality. The primary advantage of the Y/C format is its video recorders. With this format, video recorders, such as SVHS, Beta, and high band 8 mm, allow for significantly higher resolution than is available with the NTSC format. Similarly, Y/C produces clearer pictures on hard copy producers. The disadvantage
of this system include the requirements of more expensive monitors and recorders to obtain its benefits. Also, it is a poor transmission format, as the luminants and color frequency travel at different speeds. Over longer cord distances, they will be out of synchronization and must be remanipulated to bring them back into phase, requiring extra electronic circuits, and thereby decreasing some of the advantages. RGB is the third most commonly used video format and is also a component system. With it, video information is separated into red, green, and blue signals and carried separately (Fig. 8). Brightness is generated as a percentage of these colors (30% of red, 59% of green, and 11% of blue). There are several advantages to this system. As it requires less electronic processing than do NTSC and Y/C, there is increased signal-noise-ratio due to less noise production. It has a wider band width, allowing more information to be transmitted. The result is an exceptionally sharp picture with distinct color separation for use with monitors and hard copy printers. It is also the format of choice for computer interfacing, which may become more important in the future. The disadvantages include the increased expense for RGB video equipment. Video taping is possible with the RGB format, but presently available equipment for recording on the RGB format is prohibitively expensive. Other disadvantages include the fact that the three signals must be pre-
Super - VHS Format FIG. 7. Y/C or Super VHS video format with color and brightness on separate lines.
mmmmmmmm
mmmmmm
COLORmmmmmmmm
BRwB
TNESS
mmmmmm
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RGB Video Format
FIG. 8. RBG video format with red, green, and blue signals carried on different lines; brightness is generated as a percentage of red colors.
cisely synchronized, which is difficult to attain and maintain. Also, the color in the monitor cannot be adjusted because the format system renders the hue knob oq a monitor inoperable. Although, with the equipment we had available for evaluation, Y/C and RGB seemed to be far superior to the NTSC format, the differences seemed fairly small. Even in the NTSC system format, the new systems that we have been evaluating, with their improved CCD units and electronic circuitry, are a definite improvement over the older models. Several cameras have NTSC, Y/C, and RGB formats available. With these cameras switching to the Y/C and RGB formats, we have seen improvements in picture quality over the NTSC format in that same camera. Which of these two systems is better is subjective and it is difficult to get orthopedists to agree on their preference.
SYSTEM COMPATIBILITY With three different formats available, system compatibility becomes a problem. As discussed earlier, the standard that most video equipment is capable of handling is the NTSC system. Y/C and RGB formats require special equipment, as the Y/C uses two cables and the RGB uses three cables to transmit information. For example, in order for an SVHS recorder to get the improved resolution of which it is capable requires a camera with the component system of a Y/C to produce it. Furthermore, to play an SVHS tape back also requires an SVHS recorder. Similarly, to get the advantages of a Y/C or RGB format camera on the monitor, the monitor must be capable of handling these component signals. Arthroscopy,
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THE WEAK LINK THEORY This video concept is that no integrated system is any stronger than its weakest link. For example, if you have a camera with a resolution of only 300 lines and use a monitor with 600 lines, the system will only produce 300 lines of resolution (Fig. 9). The monitor will thus be underutilized. The camera and monitor numbers could be reversed, with the same results. Video recorders and hard copy printers, when substituted, have the same results. More importantly, apparent resolution or true picture quality could be substituted with similar results. A picture will be no better than the quality produced by the poorest performing component of that video system. INDIVIDUAL COMPONENTS Camera In the OR, the picture produced on a monitor is dependent on the placement and positioning of the arthroscope, inflow/outflow, portal placement, extremity positioning, light source, camera, and monitor. Assuming adequate surgical technique and a good arthroscope and light source, the poorest performing or weakest link in the system is the camera, thus making the camera the most important component of the video purchase. As discussed earlier, cameras should be compared, ideally, side by side, in order for surgeons to judge their preference for the best picture quality (apparent resolution). The signal-to-noise ratio and measured resolution are useful guides, with certain limitations, as discussed earlier. New cameras have been further decreased in size and weight for easy handling. The CCD or chip has increased sensitivity and the camera control unit has improved electronic circuitry for additional improvements in picture quality. As far as formats are concerned, all cameras are capable of NTSC’s format even if they have available Y/C or RGB formats. Some cameras even _..__~ I
FIG. 9. Weak link theory, system resolution.
VIDEOARTHROSCOPY:
REVIEW
come with an all three format capability. A camera with NTSC and either Y/C or RGB is going to allow for better picture quality either on a monitor or with a hard copy printer. Y/C format is required to get the added benefits of a Y/C type video recorder. RGB format cameras give the added advantage of improved computer interfacing. Three-chip cameras are just coming on the market. These cameras have three CCD units within them with increased pixels or sensing units. The three-chip camera is the standard for broadcast that, theoretically, offers the best picture quality due to its increased sensitivity. It has its best applications with the RGB format where each chip can be used to pick up a different color. To work properly, it requires exact alignment, which is difficult to attain and maintain. It also, of course, is bigger than a single-chip camera, and costs more. A singlechip camera with RGB and/or Y/C may be only several thousand dollars more expensive than a camera with a standard NTSC; a three-chip camera is approximately double the price. The only three-chip camera that we tried did not give us enough of a subjectively improved picture to justify the additional cost. Camera head controls are another new development. Many cameras now have buttons to control white balance, sensitivity boost, starting and stopping the VCR, and taking hard copy prints, as well as having other remote control functions. These allow the surgeon added control and free OR personnel for other details. Other systems use a separate hand-held remote control device to allow the same control with more functions available. These additional controls may exceed the “gadget tolerance” of some surgeons, and a button occasionally is pushed inadvertently. It takes a while to adjust to the additional controls. A problem that many of the new cameras address is fog control. There are multiple new ways to han-
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dle this problem. Options include O-rings, sapphire lenses, glass-on-glass, water seals, age systems, and heaters. Which will ultimately be incorporated as the most desired and practical, only time will tell. Videoscopes are a new camera/arthroscope variation. Instead of connecting to a coupler, which then connects to a camera head, the arthroscope attaches directly to the camera without a coupler (Fig. 10). By removing the coupler, you get a slight improvement in light and optical transmission to the camera. By connecting the scope and camera with a screw-in design as opposed to the typical coupler clamp, there is also a tighter fit, potentially decreasing fogging problems. When buying a videoscope, the price, compared to that of a typical scope, camera, and coupler, is actually less. This is due to the fact that you are not buying the coupler. There are, however, disadvantages with the videoscope. The camera and scope must be bought together as a unit due to their special connection. Most also are more difficult to sterilely bag due to their screw-in design, although one company has a special snap-tit design, called “collet-coupler”, which does allow easy sterile bagging. Monitors Almost all monitors presently available outperform the cameras. Discrimination in this purchase is less important than in the camera. Again, resolution and signal-to-noise specifications can be used as criteria, but only by direct A-to-B comparisons can you decide if one monitor has better picture quality or apparent resolution than another. Monitors by different manufacturers may have different picture qualities related to the design of their picture tubes. Some, as they are primarily designed for home entertainment viewing, have softer colors and less sharpness for a warmer picture. Monitors with a sharper picture and increased edge enhancement and contrast with true color reproduction are more
FIG. 10. A: A normal setup with arthroscope attached to left comer of black coupler. B: A videoscope with a camera and arthroscope directly attached without the coupler seen in A.
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appropriate for the OR. Monitors differ from televisions in that they are capable of receiving video input only through direct cable inputs; they are not able to accept broadcast signals. Some monitors are combined monitor/televisions and are able to accept both, but this has no advantages in the OR. If one is going to use a camera or video recorder with Y/C or RGB, the monitor must be able to handle these formats. Video recorders Video recorders most commonly in use presently include Umatic, VHS, and 8 mm format recorders. When video recorders are included in the video system, they become a weak link, as shown by their resolution quality (Table 1). They are usually outperformed by most new cameras. The new super VHS ED beta and high band beta significantly increase not only measure resolution but also the signal-to-noise ratio, apparent resolution, and picture quality in general. This system requires a Y/C format camera to benefit from the improvements, however. There is only one medically available and that is the SVHS recorder, which is also approximately twice as expensive as the typical VHS recorder. Those used to the 8 mm lose the advantage of decreased tape size and the resulting decreased storage requirements. Tapes recorded in SVHS mode require an SVHS machine to play them back and a Y/C-type monitor to obtain their added benefits. This becomes a problem when tapes are played back where these are not available. As discussed earlier, RGB recorders are available but, presently, are prohibitively expensive. Eight millimeter, high band recorders are also available but have not been brought to the medical market. Hard copy printers An excellent review of hard copy printers was published by Dr. Charles H. Brown (5). Printers offer several exciting advantages. By allowing qualresolution of various video recording systems
TABLE 1. Approximate
System
VCR Resolution (lines)
ED Beta Super VHS High Band 8 mm W Umatic 8mm VHS Beta
450 400 400 280 225 200 200
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ity instant prints at a push of a button for recording arthroscopic pathology, they can be used instead of video tapes for documentation and patient education. Print images produced can also easily be stored in patient charts, which prevents the storage problems of video tapes. The video print would also be available for viewing during discussions with patients at postoperative follow-ups without the difficulties and time involved in reviewing tapes. Also, at any time in the future they would be available in the patient’s chart for easy review. There are two basic types of video printers: thermal and photographic. Thermal video printers take a video signal and a push of a button to capture a single video frame, storing it in memory while a print is made. This is then produced on a heatsensitive paper. The resolution produced is -NO600 television lines and requires -90 s between exposures. The photographic video printer offers several advantages, with resolution increasing to 60& 700 television lines with increased color accuracy. But the quality is still not quite that of a 35 mm camera mounted directly to an arthroscope. It also allows production of conventional slides or prints, and some models allow as many as nine separate pictures to be taken on each print, slide, or picture. Both types have models that accept Y/C and RGB for improved picture quality. Both types have models in the $3,000 range, with the more expensive, higher quality photographic model costing more than twice that. The cost for thermal prints is -$l.OO a print, with photographic prints costing anywhere from $1.30 to $2.00. With a photographic video printer, conventional prints and slides can be made at an even lower cost. Still video floppy recorders Still video floppy recorders are another new option in the video system. During a procedure, a video floppy recorder can be used to store up to 50 still images from a video signal. At any subsequent time, the images can be reproduced on a monitor and reviewed. Prints of slides can be made from them on a thermal or photographic printer. The still video floppy recorder sells for -$2,000 and discs cost -$20. THE HUMAN FACTOR Before we started evaluating new video equipment for purchase, we had been very happy with the video equipment that we had been using for the
VIDEOARTHROSCOPY:
REVIEW
last several years. Although there is definitely improved resolution and picture quality with the new equipment, we are not actually seeing any pathology that we weren’t seeing with our old equipment. Most arthroscopic pathology is fairly obvious and seeing it is more dependent on the surgical technique than on differences in the equipment presently available. The only area in which improved picture quality is helping is that of evaluating subtle changes in articular cartilage, such as hairline cracks and superficial fibrillation. These subtle findings will rarely change the treatment or improve the quality of care given. An important unanswered question is: what price is one going to pay to improve their system? This is especially significant in today’s medical economic environment. Another important consideration in choosing a new video system is the company and its representative. Even the best equipment will be of less value without a good representative who is available for inservicing, trouble shooting, and quick replacement service. THE FUTURE In the future, we will see further improvements and increasing complexity in video equipment. Technological refinements of the equipment we have available today will be seen over the next few years. The next major steps in the video system will be the high definition television, or HDTV. HDTV, by changing the way in which a camera scans a picture and a monitor scans the raster, will increase the scanning lines in both, giving major improvements in resolution and overall picture quality. IDTV, or improved definition television, is presently available for some monitors and is an intermediate step towards HDTV. Digital video, which makes information easier to deal with, is also another major step. In a digital system, information is converted into a string of l’s and O’s, unlike the
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analog signals presently used, which are constantly variable. Once information is digitalized, converting it to l’s and O’s, it can be manipulated with less difficulty. Digital signals also take up less space than do analog signals, which means more information can be fitted into a given amount of wire or radio frequency. Unfortunately, neither digital video nor HDTV will be available for several years, and so one should not hold off purchases waiting for their appearance. SUMMARY When one is choosing video equipment today, there are many choices. The equipment available today is vastly superior to video systems that are only a few years old. When choosing equipment, it is more helpful to compare one system to another by direct viewing than to check specifications alone. Resolution and signal-to-noise can be used as guides. New systems with Y/C format allow for improved video recording. Y/C and RGB formats allow for improved pictures on monitors and video printers. Video printers and floppy disc storage systems offer new ease in recording and keeping video pictures. What equipment is best for you can only be determined by determining your needs, trying the equipment, and judging it for yourself in the OR. REFERENCES 1. Jackson DW. Videoarthroscopy: A permanent medical record. Am J Sports Med 1978:6:213-6. 2. Jackson DW, Strizak AM. Present status of videoarthros-
copy. Conremp Orrhop 1980;2:521-t. 3. Thayer JL, Jackson DW. Videoarthroscopy:
What an orthopaedist should know about video equipment. Contemp Orrhop 1983;6:51-8. 4. Yates C, Grana WA. Equipment and advantages in videoarthroscopy: In: Update in arthroscopic techniques. Baltimore: University Park Press, 1984:17-23. 5. Brown CH. Producing still images in arthroscopy. Arthroscopy 1989;5:87-92.
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