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Knee impingement syndromes
European Journal of Radiology 27 (1998) S60 – S69
Knee impingement syndromes Carlo Faletti *, Nicola De Stefano, Giannunzio Giudice, Mauricio Larciprete Diagnostic Imaging Ser6ice, Institute for Sports Medicine, Via Filadelfia 88, 10134 Turin, Italy
Abstract Introduction: The so-called knee impingement syndromes are very frequently reported in both professional and amateur sportsmen. Purpose: The objective of our study was to classify the most frequent knee changes responsible for such syndromes considering both pathology and diagnostic work-up. Material and methods: Our patients complained of aspecific symptoms related to articular meniscal, ligament or cartilage, conditions. The site of pain was periarticular and there was no apparent sign of acute traumatic events. All individuals, aged 16–55, practised sports at different levels and women were the majority of the sample. The study was carried out from 1995 to 1997 and all the medical records presented in occasion of the sports-medicine check-up were reviewed. Results: The sites of symptom onset were divided into medial, lateral, anterior and posterior. For each of them the most frequent conditions which could be defined as impingement syndromes, were defined paying particular attention to the possible methods of diagnosis useful to classify the disorder. As for anterior syndromes, patellofemoral disorders were the most frequent findings. They were associated with either incorrect torsion movements of the lower limbs or local dysplasia. Alterations in the single skeletal and cartilage structures were reported. Always referring to anterior syndromes, Hoffa’s fat pad imflammation and the jumper’s knee were a less frequent finding. As for posterior impingement syndromes, the most frequent abnormalities involved the insertional tract of the midcalf muscle associated with bursa reaction and insertional popliteus hypertrophy. As for medial syndromes, the most frequent abnormality involved the parapatellar synovial fold whose symptoms can be often mistaken for a meniscal injury. Less frequent is the involvement of the ’pes anserinus’ tendinitis and the insertional enthesopathy of the semimembranosus muscle. As for lateral syndromes, the phlogistic involvement of the distal insertional tract of the broad fascia tensor tendon with bursa reaction is very frequently reported, while the inflammation of the popliteal tendon and of the femoral bicipital tendon is less common. Conclusions: Although less frequent than meniscal and ligament injuries, impingement syndromes must be taken into due consideration when looking for knee disorders resorting to different diagnosis methods. Diagnostic imaging is very useful in this regard as it allows a proper and correct diagnosis procedure for any single condition. © 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Diagnostic imaging techniques; Knee stress; Impingement syndromes
1. Introduction Knee stress is frequent in both professional and amateur athletes, especially those who run or jump, and with congenital changes in the femorotibial axis or patellofemoral relationships. Some athletic movements, the equipment, or the field, may also favor knee stress. All of the above, associated with repeated microtraumas or single major traumas, may lead to alterations in the joint relationships and eventually cause the so* Corresponding author. Tel.: + 39 11 354558; fax: + 39 11 325003.
called impingement syndromes where the relationships between two articular components are incongruous, with consequent friction, inflammation and/or degeneration. All articular and para-articular knee structures may be involved and thus impingement syndromes can be classified as anterior, posterior, lateral and medial according to the site of pain [1]. Diagnostic imaging techniques play a fundamental role in detecting the possible cause of patient symptoms. We will consider the main causes of impingement syndromes, classify them by site and structure involved and suggest a diagnostic work-up for more accurate diagnosis and improved cost-effectiveness.
0720-048X/98/$19.00 © 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0720-048X(98)00044-8
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
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Fig. 1. A laterolateral comparative knee radiograph shows reduced trochlear convexity on the right, indicating femoral condyle dysplasia.
Fig. 2. An axial radiograph of patellae (30°) shows reduced joint space on the right, indicating excessive patellofemoral pressure.
Fig. 3. A patellar CT shows femoral diacondylar axis intrarotation with an insufficient trochlea. The patella tends to lateralization bilaterally, with reduced external joint space for incomplete dislocation from faulty femoral axis rotation (intrarotation). An insertional calcification of the midalar ligament with reactive effusion is seen on the right.
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2. Anterior syndromes Patellofemoral disorders are an important anterior impingement syndrome which were classified clinically about 30 years ago [2] recognizing the possible predisposing factors and the different types of friction which may involve these two major skeletal structures. Both the patella, with its morphological alterations, and the relative femoral trochlear joint are involved in the biomechanical unbalance causing joint incongruence leading to (incomplete) dislocations or excessive pressure, which is most frequently external but sometimes also internal. Sports movements make such alterations apparent and sometimes even worsen them, acting on both cartilage and skeletal components and thus causing painful symptoms which are seldom related to a single trauma but rather to repeated microtraumas during sports or general activity. Even though the site of pain origin can be assessed clinically, diagnostic imaging is of fundamental importance to show both the predisposing factors and the effects of the condition itself. Conventional radiology is a major tool and telemetry of the lower limbs the only technique demonstrating the femorotibial axis variations under loading which may underlie the pathologic process. Marked femoral cervicodiaphyseal varus or valgus conditions, asymmetry of the lower limbs, or altered coxa pedis relationships, may affect the knee [3]. Some morphological changes can occur in the patella— i.e. dysplasia, bipartitism, patella alta and baja —and may lead to a joint disorder [4], but also in the femoral trochlea—i.e. condyle hypoplasia, and trochlear depth alterations. Diagnostic imaging techniques investigate such changes and their effect on intra-articular structures. If
Fig. 4. A functional MRI of the patella from various angles shows a tendency to patellar lateralization, which is clearly apparent in middle angles, with reduced external articular space.
Fig. 5. A CT arthrography of the knee at the patellofemoral level shows fissuring of the patellar lining cartilage from grade II chondromalacia in an external paramedian site.
performed correctly, standard comparative AP radiographs with the patient standing and frontal patellas, and comparative LL views with 20–30° bending with posteroinferior and axial condyle profile overlapping after Ficat (30° bending) can show such alterations [3,5]. Comparative lateral views show the altered anterior trochlear profile (Fig. 1) in trochlear dysplasia, while axial patellar views show the external patellofemoral space thinning by excessive pressure (Fig. 2). Incomplete dislocations or excessive pressure suspected on static films can be assessed on axial patellar views with the functional maneuvers of quadriceps contraction or tibial extrarotation. Such severe secondary changes as osteochondral injuries, subchondral sclerogeodetic reactions and osseous-calcific metaplasia of alar ligament attachment, can also be demonstrated. Computed tomography (CT) has been recently proposed for lower limb studies, with Dejour’s technique later modified by Lerat [6], to demonstrate the articular unbalance leading to patellofemoral conditions using scans at various levels with the limbs extended. If correctly performed, the CT technique can show femoral antiversion angle changes, tibiotarsal joint and intrinsic patellofemoral alterations with axial scans at various levels with the limbs extended or with some flexion (Fig. 3). Magnetic resonance imaging (MRI) is the latest adjunct to patellofemoral disorders studies: experimental trials are still testing its capabilities in demonstrating lower limb torsion changes, but cine-MRI exhibits great potential in depicting friction syndromes and can now be performed with dedicated, and not too expensive, equipment (Fig. 4).
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
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Fig. 6. An axial T1-weighted SPIR MRI of the knee at the patellofemoral level shows full-thickness fissuring of the patellar lining cartilage in an internal paramedian site with reactive swelling of the subchondral bone from grade IV chondromalacia.
As we said above relative to plain radiography, not only articular relationships, but also intrinsic structural alterations (for instance in the cartilage covering the skeletal heads) must be assessed. Both radiographic and CT intra-articular contrast studies have permitted us to classify chondromalacia grades on both joint aspects (Fig. 5). MRI has also proved a very useful and reliable tool thanks to particular sequences [7] showing grade I and II conditions, e.g. cartilage softening and early fissuring, and reactive subchondral bone swelling (Fig. 6). To sum up, when patellofemoral impingement is clinically suspected, the diagnostic work-up must include radiography (see above) and possibly telemetry, and then MRI or CT or CT arthrography to study the articular relationships and osteocartilagineous components. Anterior knee impingement syndromes involve the patellar tendon, which is submitted to functional overloading and consequently to dynamic stress resulting in structural changes especially at the proximal and distal attachments. During growth, this insertional condition alters the structure of the growth centers with the typical patterns of patellar (Sinding-Larsen syndrome) or tibial (Osgood-Schlatter syndrome) apophysitis. Lateral radiographs show growth center abnormalities associated with tendon thickening — a direct sign of structural changes (Fig. 7). US can be used in such cases, not to make a diagnosis but rather to assess the grade of tendon involvement, appearing as an inhomogeneously hypoechoic area because of phlogistic tissue [8]. The jumper’s knee [9] is typically found in adult athletes, especially jumpers, and involves the patellar
attachment of the lower pole of the homonymous tendon. It is caused by patellofemoral joint alterations from repeated flexion–extension movements during sports. Normal fibrous-connective tissue is more or less extensively replaced by mucoid tissue rich in fibrofatty elements, which is clearly shown with US and especially MRI, the latter depicting tendon abnormality extent and grade as well as associated injuries, if any [10] (Fig. 8). Finally, Hoffa’s fat pad inflammation [11] may result directly from compression by a single trauma or repeated microtraumas, or indirectly from hyperplasia of the pad itself. Its rich vascularization causes inflammation, which also causes several symptoms because the region is rich in nerves. Diagnostic imaging shows this abnormality very well: fat-sat MRI, in particular, depicts a smaller/bigger hyperintense area within the pad (Fig. 9).
3. Posterior syndromes Posterior impingement syndromes are less common and are mainly related to muscle attachment conditions. The most frequent abnormalities involve the insertional tract of the mid-calf muscle at the posterior aspect of the femoral condyle [12]. It is related to muscle hypertrophy or sprain and results in insertional enthesopathy sometimes associated with phlogistic distension of the relative slippage bursa. Given the deep site of this condition, MRI is more indicated than US, with axial FFE and fat-sat sequences showing attachment hyperintensity (Fig. 10).
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The syndrome from knee posterior neurovascular bundle compression by tibial distal preinsertional popliteus hypertrophy is less common. Its clinical signs are rather typical and Doppler US, or angiography, confirm the diagnosis. Stress CT or axial MRI have been recently suggested to show maximum muscle bundle hypertrophy.
4. Medial syndromes The abnormal evolution of the so-called synovial folds is the most frequent cause of medial compartment impingement. The ribbon-like, synovial-lined folds with a large implant base spread caudocranially and subdivide the joint cavity into several compartments. A medial parapatellar synovial fold is the most frequent finding (60–80% of cases). Its implant base is at the anteromedial tibial portion and the fold spreads cranially, appearing roughly as a prow sail with the top in the medial parapatellar femoral condyle. Functional
Fig. 8. A sagittal STIR MRI of the knee shows a hyperintense area at the patellar polar attachment of the homonymous tendon from high grade enthesopathy. The cartilage lining the patella and trochlea results from chondromalacia.
Fig. 7. An LL knee radiograph shows hypertrophy of the lower patellar epiphyseal growth center from apophysitis (Sinding-Larsen syndrome).
overloading or direct trauma may result in thickening and inflammation of the synovial lining [13]. Thickening decreases elasticity and erosions may consequently appear on the cartilage and on the cortical bone of the anteromedial trochlear region during knee flexion–extension. Thickening can be assessed on palpation, it causes pain on bursting. This syndrome was often suspected when medial knee pain was present, but imaging techniques now help diagnose it unquestionably. In the past, targeted conventional radiology showed medial trochlear cortical fissure and arthrography demonstrated a thickened midparapatellar strip [14], but CT and MRI now yield additional findings. Axial CT with the appropriate window depicts abnormal thickening (Fig. 11) while axial and sagittal MR images show hyperintense peripheral inflammation (Fig. 12) thanks to particular sequences enhancing reactive swelling signals.
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Fig. 9. A sagittal T2-weighted STIR MRI of the knee shows a hyperintense inflammation at Hoffa’s fat pat.
Fig. 10. An axial FFE MRI of the knee shows a hyperintense pseudocyst on the posterior profile of the midfemoral condyle at the calf muscle attachment from enthesopathy with inflammatory distension of the relative bursa.
Specific MR sequences on various planes [15] are performed when this impingement syndrome is suspected clinically because its symptoms may be mistaken for those of meniscal injury or patellar chondromalacia. The tibial insertion of the tendons of the sartorius, gracilis and semitendinosus, with the so-called anserine bursa, may be extra-articular medial sites of impingement. Altered tendon biomechanics, different tracks or equipment in such sports as long-distance running may cause attachment inflammation with tendon thickening and phlogistic distension of the slippage bursa and impingement may result [16].
Clinical suspicion is once again confirmed or disproved by diagnostic imaging, also assessing injury severity. Abnormal changes are usually missed by conventional radiology, except in chronic forms where the cortical profile at the attachment appears irregularly sclerotic, while US is very sensitive in showing enthesopathy-related hypoechoic inhomogeneity and reactive liquid distension of the slippage bursa (Fig. 13). CT and MRI may be used to rule out other conditions, but only if US is negative [17]. Semimebranosus tibial attachment impingement results from the same causes as the other medial compartment syndromes but it is more difficult to diagnose
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Fig. 13. A knee US shows an anechoic longitudinal pseudocyst on the tibial profile from anserine bursa inflammation.
Fig. 11. A CT arthrography of the knee shows a thickened midparapatellar synovial fold.
because it is often mistaken for a meniscal condition. The slippage bursa is usually represented by the anteromedial horn of the semimebranosus-gastrocnemius bursa. MRI is the most reliable imaging method: axial thin-section T2-weighted sequences, preferably with fatsat, and also radial or coronal FFE show a focal area of inhomogeneously hyperintense signal with irregular attachment of semimembranosus bundles, sometimes with subcortical bone swelling (Fig. 14). Liquid distension of the relative bursa may be associated, in which case CT can exclude meniscal involvement.
Finally, a particular knee impingement syndrome affecting the proximal attachment of the medial collateral ligament is a typical cause of pain in professional breaststroke swimmers [18] making a wrong movement at the end of the distinctive leg thrust. This results in functional overloading with enthesopathy and fibrous reaction on the medial patellar aspect involving the cartilage and synovial folds. Hoffa’s fat pad loses its normal elasticity. The consequent friction causes an impingement syndrome with the same imaging features as described above for the individual components.
5. Lateral syndromes External joint impingement may develop anteriorly at the ileotibial strip, the (pre)attachment end of the
Fig. 12. A sagittal and coronal FFE MRI shows a thickened midparapatellar synovial fold with joint effusion.
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
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Fig. 14. A radial FFE MRI of the knee. An irregular hyperintensity from semimembranosus attachment sprain is depicted on the tibial aspect of the posterior horn of the medial meniscus.
Fig. 15. A knee CT shows marked thickening of both sections of the hypodense ileotibal strip.
broad fascia tensor. It is frequent in athletes who run a lot and develops, especially, in the insertional site at Gerdy’s tubercle, where a slippage bursa is also found. Clinical examination suggests the diagnosis and imaging techniques define the involvement of each component and distinguish the adjacent meniscus, anterolateral capsular ligament and synovial [19]. US depicts the regional hyperechoic thickening and the fluid distension of the relative bursa. CT, with its panoramic and axial views, can confirm the diagnostic suspicion and show injury extent and deep joint involvement (Fig. 15). MRI is as sensitive as US and CT in depicting ileotibial strip thickening, but it also shows
the associated peripheral inflammatory reaction in the tendon and femoral cortical and subcortical bone. These findings are very important, especially in professional athletes (Fig. 16). Posterior lateral impingement involves the course and the attachments of the popliteal tendon, with its synovial sheath, and of the femoral bicipital tendon at the peroneal head. These are both uncommon findings which may be misdiagnosed as meniscal or ligamentous syndromes [20], which calls for imaging techniques to confirm or disprove the clinical suspicion. US and CT are sensitive but poorly specific in showing inhomogeneously hypoechoic tendons or fluid dis-
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Fig. 16. An axial T1-weighted and FFE MRI of the knee. The reactive area is inhomogeneously hypointense on the T1 and hyperintense on the FFE images at the cortical profile and the underlying cancellous lateral femoral condyle corresponding to the ileotibial strip friction site.
Fig. 17. An axial T2-weighted MRI of the knee shows a mild popliteal tendon structural change and the inflammation of its sheath at the lateral femoral condyle preattachment.
tension of the popliteal sheath, but MRI is more accurate and specific if we combine high morphologic quality sequences with those sensitive enough to spot even minimal signal changes of the hyperintense inflammation and reactive swelling. T1- and T2-weighted fat-sat, SPIR and FFE, especially on the axial and coronal planes, can demonstrate an abnormal popliteal tendon with inflammatory distension of its sheath and irregular cortical profile at the slippage sulcus of the tendon itself (Fig. 17). As for the biceps tendon, peroneal preattachment tendon changes and phlogistic reaction of peritendinous
tissue are reported (Fig. 18).
6. Conclusions Knee impingement syndromes are less infrequent than reported, especially in athletes. All compartments may be involved and symptoms are often not distinctive and difficult to assess clinically. Diagnostic imaging can presently support the clinician confirming or disproving his/her suspicion and demonstrating the involvement of other joints. The latest advances make imaging tech-
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
Fig. 18. An axial T2-weighted MRI of the knee at the tibial plateau. The femoral biceps tendon profile is irregular at the distal preattachment tract surrounded by hyperintense reactive tissue.
niques so sensitive that even very focal or just suspected conditions can be depicted. Radiologists should have at least the same cultural and clinical background as other specialists and should never focus on imaging alone leaving the clinics aside, to plan the best work-up relative both to diagnosis and cost-effectiveness.
References [1] Aglietti P, Insall JN, Cerulli G. Patellar pain and incongruence. I: Measurement of incongruence. Clin Orthop 1983;176:217 – 24.
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[2] Andrews JR. Overuse syndromes of the lower extremity. Clin Sports Med 1983;2:137 – 48. [3] Bodne D, Quinn SF, Murray WT. Magnetic resonance images of chronic patellar tendinitis. Skelet Radiol 1988;17:24. [4] Bourne MH, Hazel WA Jr., Scott SG. Anterior knee pain. Mayo Clin Proc 1988;63:482 – 91. [5] Dalton SE. Overuse injuries in adolescent athletes. Sports Med 1992;13:58 – 70. [6] Dejour H, Walch G, Neyret P, Jurik AG. La dysplasie de la trochlee femorale. Rev Chir Orthop 1990;76:45 – 54. [7] De Paulis F, Puddu GC. Ginocchio Ed Gnocchi, 1996. [8] Ficat P, Hungerford DS. Disorders of the Patellar Tendon. Baltimore: Williams and Wilkins, 1997. [9] Fornage BD, Rifkin MD, Touche DH, Segal PM. Ultrasonography of the patellar tendon: preliminary observations. Am J Radiol 1984;143:179 – 82. [10] Jacobson KE, Flandry FC. Diagnosis of the anterior knee pain. Clin Sports Med 1989;8:179 – 95. [11] Keskinen K, Eriksson E, Komi P. Breaststroke swimmer’s knee. Am J Sports Med 1980;8:228 – 31. [12] Kujala UM, Kvist M, Osterman K. Knee injuries in athletes. Sports Med 1986;3:447 – 60. [13] Lerat JL. Morphotypes des instabilites rotiliennes. Rev Chir Orthop 1982;68:50 – 2. [14] Maldague B, Malghem J. Le profil du genou: anatomie radiologique differentielle des surfaces articulaires. J Radiol 1986;67:725 – 35. [15] Martens M, Libbrecht P, Burssens A. surgical treatment of iliotibial band friction syndrome. Am J Sports Med 1989;17:651 – 4. [16] Masciocchi C, Barile A. RM Ginocchio Ed, Gnocchi, 1994. [17] Monetti G. Le articolazioni. In: Ecografia Ed, Gnocchi, 1994. [18] Newell SG, Bramwell ST. Overuse injuries to the knee in runners. Phys Sports Med 1984;12:80 – 92. [19] Pecina MM, Bojanic I. Overuse Injuries of the Musculoskeletal System. Boca Raton, FL: CRC Press, 1993. [20] Stoller DW. Magnetic Resonance Imaging in Orthopaedic and Sports Medicine. Philadeplhia, PA: Lippincott, 1993.
Knee impingement syndromes Carlo Faletti *, Nicola De Stefano, Giannunzio Giudice, Mauricio Larciprete Diagnostic Imaging Ser6ice, Institute for Sports Medicine, Via Filadelfia 88, 10134 Turin, Italy
Abstract Introduction: The so-called knee impingement syndromes are very frequently reported in both professional and amateur sportsmen. Purpose: The objective of our study was to classify the most frequent knee changes responsible for such syndromes considering both pathology and diagnostic work-up. Material and methods: Our patients complained of aspecific symptoms related to articular meniscal, ligament or cartilage, conditions. The site of pain was periarticular and there was no apparent sign of acute traumatic events. All individuals, aged 16–55, practised sports at different levels and women were the majority of the sample. The study was carried out from 1995 to 1997 and all the medical records presented in occasion of the sports-medicine check-up were reviewed. Results: The sites of symptom onset were divided into medial, lateral, anterior and posterior. For each of them the most frequent conditions which could be defined as impingement syndromes, were defined paying particular attention to the possible methods of diagnosis useful to classify the disorder. As for anterior syndromes, patellofemoral disorders were the most frequent findings. They were associated with either incorrect torsion movements of the lower limbs or local dysplasia. Alterations in the single skeletal and cartilage structures were reported. Always referring to anterior syndromes, Hoffa’s fat pad imflammation and the jumper’s knee were a less frequent finding. As for posterior impingement syndromes, the most frequent abnormalities involved the insertional tract of the midcalf muscle associated with bursa reaction and insertional popliteus hypertrophy. As for medial syndromes, the most frequent abnormality involved the parapatellar synovial fold whose symptoms can be often mistaken for a meniscal injury. Less frequent is the involvement of the ’pes anserinus’ tendinitis and the insertional enthesopathy of the semimembranosus muscle. As for lateral syndromes, the phlogistic involvement of the distal insertional tract of the broad fascia tensor tendon with bursa reaction is very frequently reported, while the inflammation of the popliteal tendon and of the femoral bicipital tendon is less common. Conclusions: Although less frequent than meniscal and ligament injuries, impingement syndromes must be taken into due consideration when looking for knee disorders resorting to different diagnosis methods. Diagnostic imaging is very useful in this regard as it allows a proper and correct diagnosis procedure for any single condition. © 1998 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Diagnostic imaging techniques; Knee stress; Impingement syndromes
1. Introduction Knee stress is frequent in both professional and amateur athletes, especially those who run or jump, and with congenital changes in the femorotibial axis or patellofemoral relationships. Some athletic movements, the equipment, or the field, may also favor knee stress. All of the above, associated with repeated microtraumas or single major traumas, may lead to alterations in the joint relationships and eventually cause the so* Corresponding author. Tel.: + 39 11 354558; fax: + 39 11 325003.
called impingement syndromes where the relationships between two articular components are incongruous, with consequent friction, inflammation and/or degeneration. All articular and para-articular knee structures may be involved and thus impingement syndromes can be classified as anterior, posterior, lateral and medial according to the site of pain [1]. Diagnostic imaging techniques play a fundamental role in detecting the possible cause of patient symptoms. We will consider the main causes of impingement syndromes, classify them by site and structure involved and suggest a diagnostic work-up for more accurate diagnosis and improved cost-effectiveness.
0720-048X/98/$19.00 © 1998 Elsevier Science Ireland Ltd. All rights reserved. PII S0720-048X(98)00044-8
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
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Fig. 1. A laterolateral comparative knee radiograph shows reduced trochlear convexity on the right, indicating femoral condyle dysplasia.
Fig. 2. An axial radiograph of patellae (30°) shows reduced joint space on the right, indicating excessive patellofemoral pressure.
Fig. 3. A patellar CT shows femoral diacondylar axis intrarotation with an insufficient trochlea. The patella tends to lateralization bilaterally, with reduced external joint space for incomplete dislocation from faulty femoral axis rotation (intrarotation). An insertional calcification of the midalar ligament with reactive effusion is seen on the right.
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C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
2. Anterior syndromes Patellofemoral disorders are an important anterior impingement syndrome which were classified clinically about 30 years ago [2] recognizing the possible predisposing factors and the different types of friction which may involve these two major skeletal structures. Both the patella, with its morphological alterations, and the relative femoral trochlear joint are involved in the biomechanical unbalance causing joint incongruence leading to (incomplete) dislocations or excessive pressure, which is most frequently external but sometimes also internal. Sports movements make such alterations apparent and sometimes even worsen them, acting on both cartilage and skeletal components and thus causing painful symptoms which are seldom related to a single trauma but rather to repeated microtraumas during sports or general activity. Even though the site of pain origin can be assessed clinically, diagnostic imaging is of fundamental importance to show both the predisposing factors and the effects of the condition itself. Conventional radiology is a major tool and telemetry of the lower limbs the only technique demonstrating the femorotibial axis variations under loading which may underlie the pathologic process. Marked femoral cervicodiaphyseal varus or valgus conditions, asymmetry of the lower limbs, or altered coxa pedis relationships, may affect the knee [3]. Some morphological changes can occur in the patella— i.e. dysplasia, bipartitism, patella alta and baja —and may lead to a joint disorder [4], but also in the femoral trochlea—i.e. condyle hypoplasia, and trochlear depth alterations. Diagnostic imaging techniques investigate such changes and their effect on intra-articular structures. If
Fig. 4. A functional MRI of the patella from various angles shows a tendency to patellar lateralization, which is clearly apparent in middle angles, with reduced external articular space.
Fig. 5. A CT arthrography of the knee at the patellofemoral level shows fissuring of the patellar lining cartilage from grade II chondromalacia in an external paramedian site.
performed correctly, standard comparative AP radiographs with the patient standing and frontal patellas, and comparative LL views with 20–30° bending with posteroinferior and axial condyle profile overlapping after Ficat (30° bending) can show such alterations [3,5]. Comparative lateral views show the altered anterior trochlear profile (Fig. 1) in trochlear dysplasia, while axial patellar views show the external patellofemoral space thinning by excessive pressure (Fig. 2). Incomplete dislocations or excessive pressure suspected on static films can be assessed on axial patellar views with the functional maneuvers of quadriceps contraction or tibial extrarotation. Such severe secondary changes as osteochondral injuries, subchondral sclerogeodetic reactions and osseous-calcific metaplasia of alar ligament attachment, can also be demonstrated. Computed tomography (CT) has been recently proposed for lower limb studies, with Dejour’s technique later modified by Lerat [6], to demonstrate the articular unbalance leading to patellofemoral conditions using scans at various levels with the limbs extended. If correctly performed, the CT technique can show femoral antiversion angle changes, tibiotarsal joint and intrinsic patellofemoral alterations with axial scans at various levels with the limbs extended or with some flexion (Fig. 3). Magnetic resonance imaging (MRI) is the latest adjunct to patellofemoral disorders studies: experimental trials are still testing its capabilities in demonstrating lower limb torsion changes, but cine-MRI exhibits great potential in depicting friction syndromes and can now be performed with dedicated, and not too expensive, equipment (Fig. 4).
C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
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Fig. 6. An axial T1-weighted SPIR MRI of the knee at the patellofemoral level shows full-thickness fissuring of the patellar lining cartilage in an internal paramedian site with reactive swelling of the subchondral bone from grade IV chondromalacia.
As we said above relative to plain radiography, not only articular relationships, but also intrinsic structural alterations (for instance in the cartilage covering the skeletal heads) must be assessed. Both radiographic and CT intra-articular contrast studies have permitted us to classify chondromalacia grades on both joint aspects (Fig. 5). MRI has also proved a very useful and reliable tool thanks to particular sequences [7] showing grade I and II conditions, e.g. cartilage softening and early fissuring, and reactive subchondral bone swelling (Fig. 6). To sum up, when patellofemoral impingement is clinically suspected, the diagnostic work-up must include radiography (see above) and possibly telemetry, and then MRI or CT or CT arthrography to study the articular relationships and osteocartilagineous components. Anterior knee impingement syndromes involve the patellar tendon, which is submitted to functional overloading and consequently to dynamic stress resulting in structural changes especially at the proximal and distal attachments. During growth, this insertional condition alters the structure of the growth centers with the typical patterns of patellar (Sinding-Larsen syndrome) or tibial (Osgood-Schlatter syndrome) apophysitis. Lateral radiographs show growth center abnormalities associated with tendon thickening — a direct sign of structural changes (Fig. 7). US can be used in such cases, not to make a diagnosis but rather to assess the grade of tendon involvement, appearing as an inhomogeneously hypoechoic area because of phlogistic tissue [8]. The jumper’s knee [9] is typically found in adult athletes, especially jumpers, and involves the patellar
attachment of the lower pole of the homonymous tendon. It is caused by patellofemoral joint alterations from repeated flexion–extension movements during sports. Normal fibrous-connective tissue is more or less extensively replaced by mucoid tissue rich in fibrofatty elements, which is clearly shown with US and especially MRI, the latter depicting tendon abnormality extent and grade as well as associated injuries, if any [10] (Fig. 8). Finally, Hoffa’s fat pad inflammation [11] may result directly from compression by a single trauma or repeated microtraumas, or indirectly from hyperplasia of the pad itself. Its rich vascularization causes inflammation, which also causes several symptoms because the region is rich in nerves. Diagnostic imaging shows this abnormality very well: fat-sat MRI, in particular, depicts a smaller/bigger hyperintense area within the pad (Fig. 9).
3. Posterior syndromes Posterior impingement syndromes are less common and are mainly related to muscle attachment conditions. The most frequent abnormalities involve the insertional tract of the mid-calf muscle at the posterior aspect of the femoral condyle [12]. It is related to muscle hypertrophy or sprain and results in insertional enthesopathy sometimes associated with phlogistic distension of the relative slippage bursa. Given the deep site of this condition, MRI is more indicated than US, with axial FFE and fat-sat sequences showing attachment hyperintensity (Fig. 10).
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C. Faletti et al. / European Journal of Radiology 27 (1998) S60– S69
The syndrome from knee posterior neurovascular bundle compression by tibial distal preinsertional popliteus hypertrophy is less common. Its clinical signs are rather typical and Doppler US, or angiography, confirm the diagnosis. Stress CT or axial MRI have been recently suggested to show maximum muscle bundle hypertrophy.
4. Medial syndromes The abnormal evolution of the so-called synovial folds is the most frequent cause of medial compartment impingement. The ribbon-like, synovial-lined folds with a large implant base spread caudocranially and subdivide the joint cavity into several compartments. A medial parapatellar synovial fold is the most frequent finding (60–80% of cases). Its implant base is at the anteromedial tibial portion and the fold spreads cranially, appearing roughly as a prow sail with the top in the medial parapatellar femoral condyle. Functional
Fig. 8. A sagittal STIR MRI of the knee shows a hyperintense area at the patellar polar attachment of the homonymous tendon from high grade enthesopathy. The cartilage lining the patella and trochlea results from chondromalacia.
Fig. 7. An LL knee radiograph shows hypertrophy of the lower patellar epiphyseal growth center from apophysitis (Sinding-Larsen syndrome).
overloading or direct trauma may result in thickening and inflammation of the synovial lining [13]. Thickening decreases elasticity and erosions may consequently appear on the cartilage and on the cortical bone of the anteromedial trochlear region during knee flexion–extension. Thickening can be assessed on palpation, it causes pain on bursting. This syndrome was often suspected when medial knee pain was present, but imaging techniques now help diagnose it unquestionably. In the past, targeted conventional radiology showed medial trochlear cortical fissure and arthrography demonstrated a thickened midparapatellar strip [14], but CT and MRI now yield additional findings. Axial CT with the appropriate window depicts abnormal thickening (Fig. 11) while axial and sagittal MR images show hyperintense peripheral inflammation (Fig. 12) thanks to particular sequences enhancing reactive swelling signals.
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Fig. 9. A sagittal T2-weighted STIR MRI of the knee shows a hyperintense inflammation at Hoffa’s fat pat.
Fig. 10. An axial FFE MRI of the knee shows a hyperintense pseudocyst on the posterior profile of the midfemoral condyle at the calf muscle attachment from enthesopathy with inflammatory distension of the relative bursa.
Specific MR sequences on various planes [15] are performed when this impingement syndrome is suspected clinically because its symptoms may be mistaken for those of meniscal injury or patellar chondromalacia. The tibial insertion of the tendons of the sartorius, gracilis and semitendinosus, with the so-called anserine bursa, may be extra-articular medial sites of impingement. Altered tendon biomechanics, different tracks or equipment in such sports as long-distance running may cause attachment inflammation with tendon thickening and phlogistic distension of the slippage bursa and impingement may result [16].
Clinical suspicion is once again confirmed or disproved by diagnostic imaging, also assessing injury severity. Abnormal changes are usually missed by conventional radiology, except in chronic forms where the cortical profile at the attachment appears irregularly sclerotic, while US is very sensitive in showing enthesopathy-related hypoechoic inhomogeneity and reactive liquid distension of the slippage bursa (Fig. 13). CT and MRI may be used to rule out other conditions, but only if US is negative [17]. Semimebranosus tibial attachment impingement results from the same causes as the other medial compartment syndromes but it is more difficult to diagnose
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Fig. 13. A knee US shows an anechoic longitudinal pseudocyst on the tibial profile from anserine bursa inflammation.
Fig. 11. A CT arthrography of the knee shows a thickened midparapatellar synovial fold.
because it is often mistaken for a meniscal condition. The slippage bursa is usually represented by the anteromedial horn of the semimebranosus-gastrocnemius bursa. MRI is the most reliable imaging method: axial thin-section T2-weighted sequences, preferably with fatsat, and also radial or coronal FFE show a focal area of inhomogeneously hyperintense signal with irregular attachment of semimembranosus bundles, sometimes with subcortical bone swelling (Fig. 14). Liquid distension of the relative bursa may be associated, in which case CT can exclude meniscal involvement.
Finally, a particular knee impingement syndrome affecting the proximal attachment of the medial collateral ligament is a typical cause of pain in professional breaststroke swimmers [18] making a wrong movement at the end of the distinctive leg thrust. This results in functional overloading with enthesopathy and fibrous reaction on the medial patellar aspect involving the cartilage and synovial folds. Hoffa’s fat pad loses its normal elasticity. The consequent friction causes an impingement syndrome with the same imaging features as described above for the individual components.
5. Lateral syndromes External joint impingement may develop anteriorly at the ileotibial strip, the (pre)attachment end of the
Fig. 12. A sagittal and coronal FFE MRI shows a thickened midparapatellar synovial fold with joint effusion.
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Fig. 14. A radial FFE MRI of the knee. An irregular hyperintensity from semimembranosus attachment sprain is depicted on the tibial aspect of the posterior horn of the medial meniscus.
Fig. 15. A knee CT shows marked thickening of both sections of the hypodense ileotibal strip.
broad fascia tensor. It is frequent in athletes who run a lot and develops, especially, in the insertional site at Gerdy’s tubercle, where a slippage bursa is also found. Clinical examination suggests the diagnosis and imaging techniques define the involvement of each component and distinguish the adjacent meniscus, anterolateral capsular ligament and synovial [19]. US depicts the regional hyperechoic thickening and the fluid distension of the relative bursa. CT, with its panoramic and axial views, can confirm the diagnostic suspicion and show injury extent and deep joint involvement (Fig. 15). MRI is as sensitive as US and CT in depicting ileotibial strip thickening, but it also shows
the associated peripheral inflammatory reaction in the tendon and femoral cortical and subcortical bone. These findings are very important, especially in professional athletes (Fig. 16). Posterior lateral impingement involves the course and the attachments of the popliteal tendon, with its synovial sheath, and of the femoral bicipital tendon at the peroneal head. These are both uncommon findings which may be misdiagnosed as meniscal or ligamentous syndromes [20], which calls for imaging techniques to confirm or disprove the clinical suspicion. US and CT are sensitive but poorly specific in showing inhomogeneously hypoechoic tendons or fluid dis-
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Fig. 16. An axial T1-weighted and FFE MRI of the knee. The reactive area is inhomogeneously hypointense on the T1 and hyperintense on the FFE images at the cortical profile and the underlying cancellous lateral femoral condyle corresponding to the ileotibial strip friction site.
Fig. 17. An axial T2-weighted MRI of the knee shows a mild popliteal tendon structural change and the inflammation of its sheath at the lateral femoral condyle preattachment.
tension of the popliteal sheath, but MRI is more accurate and specific if we combine high morphologic quality sequences with those sensitive enough to spot even minimal signal changes of the hyperintense inflammation and reactive swelling. T1- and T2-weighted fat-sat, SPIR and FFE, especially on the axial and coronal planes, can demonstrate an abnormal popliteal tendon with inflammatory distension of its sheath and irregular cortical profile at the slippage sulcus of the tendon itself (Fig. 17). As for the biceps tendon, peroneal preattachment tendon changes and phlogistic reaction of peritendinous
tissue are reported (Fig. 18).
6. Conclusions Knee impingement syndromes are less infrequent than reported, especially in athletes. All compartments may be involved and symptoms are often not distinctive and difficult to assess clinically. Diagnostic imaging can presently support the clinician confirming or disproving his/her suspicion and demonstrating the involvement of other joints. The latest advances make imaging tech-
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Fig. 18. An axial T2-weighted MRI of the knee at the tibial plateau. The femoral biceps tendon profile is irregular at the distal preattachment tract surrounded by hyperintense reactive tissue.
niques so sensitive that even very focal or just suspected conditions can be depicted. Radiologists should have at least the same cultural and clinical background as other specialists and should never focus on imaging alone leaving the clinics aside, to plan the best work-up relative both to diagnosis and cost-effectiveness.
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