Broad-based disc Disc displaced between 25 \200\22350 % circumferentially beyond the edges Focal Disc displaced <25 % of the circumference Protrusion Disc material is focally displaced Extrusion Displaced disc material has a greater length than width Sequestration Disc material has lost continuity with the parent disc (a) (b) Fig. 19.5 a) Sagittal T2-weighted image showing extrusion of the L4/5 intervertebral disc. b) Axial T2-weighted image showing the full extent of this (arrowhead). A 35-year-old patient with sudden onset severe left sided sciatica. SUBASH KC/NMC-15TH/2014 276 CHAPTER 19 Musculoskeletal conditions Cord compression This is a surgical emergency secondary to compression of the spinal cord b y tumor, pus, blood, bone, or disc material. This requires decompres- sion to prevent a lon g-term neurological de \201 cit. Clinical presentation Patients complain of back pain, paralysis below the level of compress ion, urinary and fecal incontinence. Imaging Timing of imaging Urgent imaging is indicated as once complete paralysis has been p resent for > 24 hours then the chance of any reasonable recovery decreases dra- matically. However, there is no reason to scan someone in the middle of the night unless a surgeon is available who can operate immediately. It is much more appropriate to get the scan done \201 rst thing in the morning in time for the day-time emergency lists. Plain \201 lm These are helpful in showing areas of vertebral collapse or fracture but th ey cannot show what is causing the cord compression. MRI (Fig. Other imaging modalities may provide useful information about trauma and vertebra l collapse but MRI is the investigation of choice. This demon- strates what is causing the compression and over how much of a distance. Cord signal change is helpful and in trauma th e presence of blood within the cord is a bad prognostic sign. In addition this will provide detail about other abnormalities in the region and give the surgeon a road-map for any pla nned surgery. 19.6 ) CT myelography In patients who have contraindications for MRI then this is an alternative. Iodine dye is introduced into the dural sac using \202 uoroscopic control. CT is then use d to look for indirect evidence of obstruction i.e. is there a level where the dye cannot p ass through. Information for the radiologist \200 Does the patient have any known malignancy? \200 H as the patient had any recent surgery \200\224 the risk of spinal infection is much higher where there has been recent thoracic or abdominal surgery? Is the patient on any form of anticoagulation? SUBASH KC/NMC-15TH/2014 CORD COMPRESSION 277 Fig. 19.6 of the L3 vertebral body secondary to tumor replacement of the body. This is impi nging upon the cauda equina and leading to severe nerve compression. A 66-year-old male with sudden urinary incontinence. This shows collapse SUBASH KC/NMC-15TH/2014 278 CHAPTER 19 Musculoskeletal conditions Osteomyelitis Osteomyelitis is a debilitating condition with a considerable morbidity. It a ffects both children and adults, albeit differently. In children, the commonest route is by haematogenous spread. Infection typically localizes to the metaphysis with the lower limbs usually affected. The most commo n organism is Staphylococcus aureus can lead to a Brodie \200\231s abscess. . Chronic infection In adults the commonest causes are direct inoculation or pre-existing conditions such as diabetes. Staphylococcus aureus the most commonly isolated organisms. Jo int involvement is common. Chronic osteomyelitis in adulthood is usually due to a foreign b ody, chronic underlying disease, or previous trauma. and streptococci are Clinical presentation \200 Fever, malaise, lethargy, and weight loss. \200 In children, there may be a history of recent infection. \200 In adults, there may be a previous hist ory of surgery or IV drug abuse. Imaging Plain \201 lm \200 Plain \201 lms can be insensitive in the early phase (ther e has to be 50 % loss of bone before there is an appreciable radiographic change). Ill de \201 ned lucency at the site of infection. In children this is usually at the metaphysis of the bone. Periosteal elevation is seen later. \200 Chronic osteomyelitis is often characterized by necrotic bone termed a \200\230sequestrum \200\231. Bone scintigraphy \200 Osteomyelitis causes increased osteoblastic activity, which shows up as an area of increased uptake. Scintigraphy can therefore be used to con \201 rm areas of active infection and identify if there are multiple foci. CT CT is useful in identifying periosteal elevation, sequestra, or foreign bodies. MRI (Fig. \200 MRI is the modality of choice for further investigation of osteomyelitis. \200 It can identify early oedema, periosteal reaction, soft tissue collections, 19.7 ) and sequestra at the site of infection. Information for the radiologist \200 Area of concern. \200 Past history of immunosuppre ssion, chronic disease, IV drug abuse, surgery, and trauma. In \202 ammatory markers. SUBASH KC/NMC-15TH/2014 OSTEOMYELITIS 279 (a) (b) Fig. 19.7 Figures 19.7a and 19.7b are T1-weighted gadolinium axial images of the hindfoot s howing osteomyelitis of the calcaneus (arrowheads) and soft tissue pus (arrow). A 20-year-old patient admitted with red and grossly swollen hindfoot. SUBASH KC/NMC-15TH/2014 280 CHAPTER 19 Musculoskeletal conditions Discitis Discitis is infection of the intervertebral disks. It accounts for 2 \200\2234 all skeletal infection with a male:female ratio of 3:1. There are 2 distinct affected age grou ps: children and adults aged > 50. The infection may be con \201 ned to a single disc spac e or multiple levels with the lumbar spine commonly affected. The most commonly isolated pa thogen is Staphylococcus aureus always be considered. The three main routes of infection ar e: haematog- enous (commonest), direct inoculation (iatrogenic), or contiguous spread. Disc itis may progress to give vertebral body osteomyelitis. % of (60 % ) although other organisms including TB should Clinical presentation \200 Red \202 ag signs (see Box 19.1 ) for spinal pathology. \200 Acute, non-traumatic localized pain. \200 Non-speci \201 c symptoms including feve r, weight loss, and malaise. \200 Chronic illnesses such as diabetes and immunosuppressio n predispose to it. Box 19.1 Red \202 ag signs for spinal pathology Age of onset <20 or > 50 years \200 Thoracic pain \200 Fever and unexplained with loss \200 Bladder and bowel dysfunction \200 History of carcinoma \200 Ill health or previ ous medical illness \200 Progressive neurological de \201 cit \200 Disturbed gait or s addle anesthesia. Imaging Plain \201 lm \200 This is relatively insensitive for early infection. \200 L oss of disc space. \200 Indistinct end plates. \200 Chronic changes include end-plate s clerosis or collapse. \200 Gradual disc obliteration and vertebral fusion. CT \200 CT is not routinely used in the initial work-up. \200 It has a role in assessme nt of the bony anatomy, to guide biopsies, and where the patient cannot tolerate an MRI. MRI \200 MRI is the initial modality of choice. \200 Standard sequences include T1-weig hted, STIR and T1-weighted post-contrast sagittal and axial planes (Fig. 19.8 ). T1 images will show low signal intensity changes to the disc and vertebral body with loss of disc height. STIR images show high signal in the disc, adjacent vertebral end plates, and paravertebral soft tissues. SUBASH KC/NMC-15TH/2014 DISCITIS 281 Post-contrast T1 images show ring enhancement of pus and can be used to differentiate pus from oedema. Information for the radiologist \200 Predisposing factors such as recent surgery? \200 What are the in \202 ammatory markers? \200 Is there any evidence of sepsis? (a) (b) Fig. 19.8 aneurysm repair. a) Sagittal STIR image demonstrating oedema to the L4/L5 interve rtebral disc, oedema to both the L4 and L5 vertebral bodies and an epidural abscess at this level. b) T1 gadolinium image showing peripheral enhancement of the abscess. A 56-year-old patient with severe low back pain 1 month after an aortic SUBASH KC/NMC-15TH/2014 282 CHAPTER 19 Musculoskeletal conditions Psoas abscess The psoas is a retroperitoneal muscle that originates from the lateral border s of T12 to L5. It lies in close proximity to the sigmoid colon, appendix, ureters, iliac l ymph nodes, and the spine. Psoas abscesses are a result of its rich vascular supply and by conditions affecting the adjacent structures (Table 19.2). Primary psoas abscesses are comm only seen in children whilst secondary are seen in adults, commonly in IV drug abusers. Clinical presentation \200 Non-speci \201 c abdominal pain/back pain. \200 Pyrexia, ma laise, and weight loss. \200 Referred pain to the hips and femoral \202 exion. Imaging Plain \201 lm This will not demonstrate a psoas abscess but it may point to the c ause. Ultrasound UItrasound can be used to identify a psoas abscess although it may not be able t o demonstrate the underlying cause. CT \200 Post contrast-enhanced CT is the modality of choice as it can identify both a psoas abscess (a ring enhancing area) and its underlying cause. Both CT and ultrasound can be used to drain psoas abscesses percutaneously. MRI (Fig. \200 MRI \200\231s good soft tissue resolution will demonstrate these well. \200 MRI is superior to CT where there is an underlying spinal cause as it 19.9 ) will clearly show spinal and epidural extension. Information for the radiologist \200 Clinical presentation. \200 In \202 ammatory mark ers. \200 Any previous chronic diseases such as diverticulosis or history of IV drug abuse. Table 19.2 Predisposing causes for psoas abscess Disease site Conditions GI tract Diverticulitis, appendicitis, Crohns, colorectal cancer, appendiceal tumor GU tract UTI, extracorporeal shock wave lithotripsy, GU cancers Musculoskeletal infections Vertebral osteomyelitis, discitis, infectious sacro-ilitis, septic arthritis Others Endocarditis, femoral artery catheterization, endocarditis, infected abdominal aortic aneur ysm, spinal surgery SUBASH KC/NMC-15TH/2014 PSOAS ABSCESS 283 Fig. 19.9 bilateral psoas abscesses. Coronal T1 gadolinium image of the retroperitoneum demonstrating SUBASH KC/NMC-15TH/2014 284 CHAPTER 19 Musculoskeletal conditions Septic arthritis This is one of the true orthopedic emergencies where the joint requires wa shout on the same day. The reason for this is that active intra-articular infection very qu ickly results in cartilage lysis. This will then lead to prema- ture OA and even ankylosis later on. This means that any imaging should be performed in a timely manner. Clinical presentation Patients with septic arthritis usually present with a swollen painful joint that they refuse to move. They will have raised in \202 ammatory markers and may we ll have positive blood cultures. In very severe cases they may be systemically unwell. Imaging Plain \201 lm All patients will have these. Bony changes such as lysis tend to no t be visible until late on. In some joints (elbow and ankle) a joint effusion will be visib le. Further imaging Before any further imaging is undertaken the patient should be reassessed. If the diagnosis based upon the clinical and radiographic \201 ndings is de \201 nitely of a septic arthritis then the patient should go straight to theater for a washout that wil l both con \201 rm the diagnosis and treat the patient. Ultrasound This can be used to con \201 rm the presence of an effusion and where appro- pr iate be used to guide joint aspiration. MRI (Fig. This is reserved for dif \201 cult cases where the diagnosis remains in doubt or where there is concern for widespread infection and collections. 19.10 ) Information for the radiologist \200 The patient \200\231s in \202 ammatory markers, imm une status, and clotting status. \200 In addition, have they any predisposing clinical co ndition? \200 Finally what is the orthopedic plan? No intervention should be performed by radiology without appropriate senior discussion with the on-call orthopedic te am. SUBASH KC/NMC-15TH/2014 SEPTIC ARTHRITIS 285 (a) (b) Fig. 19.10 axial image at the level of the shoulder joint. The arrow points to pus within t he joint consistent with septic arthritis. b) Axial gadolinium image at the level of the mi d arm showing further pus within the soft tissues. A 9-month-old child with swollen and painful right arm. a) T1 gadolinium SUBASH KC/NMC-15TH/2014 286 CHAPTER 19 Musculoskeletal conditions Swollen diabetic foot This is a relatively common and potentially very dif \201 cult clini cal scenario to deal with. The 3 main areas of concern are: \200 Infection. \200 Trauma . \200 Charcot arthropathy. The problem is that with severe diabetes the patient may well have an insensate foot that r enders clinical examination of little use. Therefore it is essential to take a very careful history and to not be misled by the lack of painful response. Clinical presentation All of these conditions will present with a red, swollen foot. The ke y to differentiating these is the combination of the history, laboratory, and radiological tests. It is also very important to be aware that relatively trivial trauma can cause devas tating injuries in the insensate diabetic foot. Imaging Plain \201 lm (Fig. \200 These remain the key frontline investigation. In traum a they will 19.11 ) demonstrate any injury as well as act as a baseline for follow-up. \200 Charcot feet show evidence of advanced OA with destruction, disorganization, debris, dislocation, distention, and increased density. In an acute Charco t foot there will be swelling, bone resorption, and effusions. In infection there will be osteolysis, soft tissue swelling, and periosteal reactions. CT This is useful for demonstration of the bony anatomy, particularly where there is suspic ion for a fracture. MRI This is used for assessment of infection and the acute Charcot foot. Both will show sim ilar changes with in \202 ammation, effusions, and bone oedema. However on post-contrast s equences there may well be soft tissue or intra-osseous abscesses in infection. Where there are no collections the MRI \201 ndings should be taken in conjunction with laboratory te sts to distinguish between these 2 clinical conditions. Information for the radiologist In \202 ammatory markers. SUBASH KC/NMC-15TH/2014 SWOLLEN DIABETIC FOOT 287 (a) (b) Fig. 19.11 tripping over his dog. a) A dorsiplantar radiograph showing marked abnormality t o the midfoot. The lateral (b) shows that this is in fact a dislocation across the midfoot (arrowhead). The vascular calci \201 cation (arrow) is a classical \201 nding in diabeti cs. A 55-year-old diabetic presented with a painless, swollen foot after SUBASH KC/NMC-15TH/2014 288 CHAPTER 19 Musculoskeletal conditions Loose (painful) joint replacement The vast majority of joint replacements last for many yea rs, without any problems. In a small percentage they loosen either secondary to infection o r loosening of the prosthesis within the cement mantle. Clinical presentation Patients presenting with a painful joint after a prosthesis can be di vided into 2 groups. \200 Early presentation: within 18 months. These can be considered t o be infected until proven otherwise. Late presentation: after 18 months. These can either be loosening or infection. The longer the prosthesis has been infection is likely to be the cause. in situ the less likely Imaging Plain \201 lm (Fig. All patients get radiographs as part of their follow-up. Both infection and loosening show up as lysis of the cement at the bone \200\223cement interfac e. Infection tends to cause rapid changes whereas those of aseptic loosening are more gradu al. 19.12 ) Ultrasound This can be used to demonstrate joint effusions and collections. In addition it can used to guide needle aspiration where indicated. CT/MRI Both CT and MRI can be used to gain further information regarding the bony and soft tissue anatomy. Unfortunately the metalwork can signi \201 cantly degrade the image qualit y and therefore these are limited to speci \201 c cases. Fluoroscopy Surgeons will usually require con \201 rmation of infection prior to interveni ng. Fluoroscopy is a good technique to obtain a sample as not only can it be used to guide in the needle but also the images captured are solid evidence of where the sample was obtai ned. Information for the radiologist \200 When was the prosthesis put in? \200 What are the patient \200\231s in \202 ammatory markers? \200 What is the operative plan? SUBASH KC/NMC-15TH/2014