T. Muellner1, 2, L. Engebretsen1, A. Walloe1
1 Department of Orthopaedic Surgery, Oslo University Orthopaedic Clinic, 0407 Oslo, Norway
2 Univ. Clinic of Traumatology, University of Vienna Medical School, Waehringerguertel 18-20, A-1090 Vienna, Austria
The structures in and around the knee are frequently injured in children in sports as a result of chronic overuse and the special anatomic and morphologic situation in the growing adolescent. This review article will focus on common causes of knee pain in the adolescent, but will also emphasize the importance of tumors and referred pain in the diagnostic approach. Traumatic, acute disorders are not discussed in this article.
Knee pain in adolescents has many etiologies and the clinician must also rule out rare entities (e.g. tumor, referred pain) to establish a thorough diagnosis. Although meniscal injuries are less common in children than in adults, several recent reports indicate an increasing incidence of meniscal lesions in children and adolescents, especially those in competitive sports (Haus and Refior 1993, King et al. 1996, Maffulli et al. 1997). De Inocencio investigated the distribution of musculoskeletal pain in children. The knee was the most effected joint (33%), followed by other joints (e.g. ankle, wrist, elbow, in 28%), soft tissue pain (18%), heel pain (8%), hip pain (6%), and back pain (6%) (de Inocencio 1998). Symptoms were caused by trauma in 30%; overuse syndroms in 28% (eg, chondromalacia patellae, mechanical plantar fasciitis, overuse muscle pain); and normal skeletal growth variants (eg, Osgood-Schlatter syndrome, hypermobility, Sever's disease) in 18% of patients. Sources of chronic pain about the knee may include tendinitis, apophysitis, patellofemoral malalignment and maltracking, quadriceps dysfunction, hamstring contracture, neural dysfunction, vascular dysfunction, pathological plica, cartilage degeneration, meniscal tears, and also benign and malign tumors about the knee. Special consideration must be given to the possibility of a referred knee pain, e.g. slipped capital femoral epiphysis (Eilert 1993, Stanitski 1994).
Compared to adults the long bones in children are able to absorb more energy before breaking, and the presence of growth plates and apophyses for the attachment of musculotendinous structures lead to a different spectrum of injuries compared with those in adults. Both epiphyses and apophyses have physes that grow and develop by enchondral ossification. Apophyses have physes similar to epiphyses, but in contrast to epiphyses do not participate in longitudinal growth, are usually not perpendicular to the long axis of bone, are not articular, and are subjected to tension forces rather than to compression.
The reason for knee pain in children is often difficult to establish and depends on an experienced physician. The history and clinical examination are crucial as is the correct choice of additional diagnostic investigations. This paper discusses the most frequent causes of knee pain in children.
According to Sponseller and Beaty, Paget described in 1891 the clinical symptoms, which later became known as Osgood Schlatter Disease (OS) (Rang 1983, Sponseller and Beaty 1996). In 1903, Osgood (1903) and Schlatter (1903) published separate papers on the avulsion phenomena of the tibial tubercle. OS is thought to result from submaximal, repetitive, tensile stresses acting on the immature junction of the patellar tendon, tibial tubercle, and tibia, causing mild avulsion injuries followed by attempts of osseous repair (Stanitski 1994). The symptoms usually start during a rapid growth phase. In girls, the condition tends to appear at an earlier age - 11 to 13 years – than in boys who usually present it 1 to 2 years later (Kujala et al. 1985). Boys are more commonly affected than girls, but the prevalence in girls is increasing because of their increased participation in sports activity. In a group of athletic adolescents, Kujala et al (1985) found a 21% prevalence of OS, while in a group of non-athletics the prevalence was only 4.5%. Usually one side is more symptomatic and the tibial tubercle may become prominent. In 20-30% of patients both sides are symptomatic. Swelling and prominence of the tibial tubercle can be found on clinical examination, accompanied by exquisite local tenderness. The pain is usually made worse by climbing stairs, running, and jumping. Radiographs are essential to rule out a bone tumor or other rare disorders. Approximately 50% show a discrete, separate ossicle at the tibial tubercle (Krause et al. 1990). This fragment is cartilaginous initially and may ossify later. Krause et al (1990) described patients who had fragmentation of the apophysis or an abnormally shape of it at presentation, and had abnormal tibial tubercles on follow-up examination after an average of 9 years. These patients were much more likely to have chronic symptoms.
Treatment should be based on the symptoms. The immature athletes with open physes should be treated with guided activity limitations and in a few cases with partial immobilization (no casting) for a period of 6 weeks or until the tubercle apophysis is not tender. Be aware that this group may have a physeal injury in the area- a so-called Ogden lysis (Ogden 1990). In these acute traumatic avulsions of the tibial tuberosity, pain and swelling occur immediately and standing or walking is impossible. However, open reduction and internal fixation may be necessary, depending on the displacement and type of avulsion fracture (Figure 1).
For the skeletally mature patient with OS disease a treatment regimen consisting of rest, training modification, ice, and oral anti-inflammatory drugs will be helpful. Tenderness is a sign of inflammation, and with pain relief strengthening and flexibility exercises are started. Surgery may be indicated for the adult patient a with chronic OS disease, multiple ossicles, and failed conservative treatment, when excision of symptomatic ossicles may lead to pain relief. This ossicle resection can also be performed endoscopically (Klein 1996).
Sinding – Larsen - Johansson disease (Johansson 1922, Sinding-Larsen 1921) is usually seen in an active preteen boy with activity related pain (Stanitski 1994). Persistent traction on the cartilaginous junction of the patella and the patella tendon is thought to be the cause of this condition. Sometimes similar symptoms can be found at the insertion site of the quadriceps tendon into the patella.
The main symptom is usually tenderness at the involved site. Radiographs may show varying amounts and shapes of calcification or ossification near the patella apex. Medlar and Lyne (1978) identified four radiographic stages of the disease process. Differential diagnosis include a stress-fracture of the patella, a sleeve fracture and a type I bipartite patella (Figure 2). In the older adolescent, an adult type of jumper´s knee must be considered (Blazina et al. 1973). The symptoms usually resolve with progressive skeletal maturation. As in OS disease, adult patients who do not respond to conservative treatment may benefit from surgical debridement of the necrotic intratendinous tissue.
Jumper´s knee, as an adult form of the Sinding – Larsen - Johansson disease, may occur due to an acute partial tear or overuse, and usually a good medical history will detect one specific event leading to later pain. The syndrome is characterized by tenderness at the inferior pole of the patella, increasing in eccentric use of the extensor apparatus. This problem usually occurs in sports characterized by a high number of maximal jumps and sprints. Out of 47 elite division volleyball players, 25 players fulfilled the diagnostic criteria of jumper´s knee (Lian et al. 1996). The histopathological changes described include tearing of tendon fibers, myxomatous degeneration, and capillary proliferation (Ferretti et al. 1985, Karlsson et al. 1991, Roels et al. 1978). Clinically, jumper´s knee can be classified into 4 grades, originally described by Roels et al (1978) and modified by Lian et al (1996) (Table 1).
According to Ferretti (1986), the insertional tendinopathy affects, in order of frequency, the insertion of the patellar tendon into the patella in 65% of the cases, the attachment of the quadriceps tendon into the patella in 25%, and the insertion into the tibial tubercle in 15% of the cases. Treatment is conservative including eccentric exercises for at least 3 months.
If the well-supervised conservative treatment program fails, surgical excision of the necrotic part of the patellar tendon is indicated. However, only 30% (Pierets et al. 1999) to 60% (Coleman et al. 2000) of competitive athletes return to their original sporting level. Both arthroscopic and open patellar tenotomy provide symptomatic pain relief in most patients with end-stage patellar tendinopathy (Coleman et al. 2000). After open patellar tenotomy, MRI and ultrasound findings remain abnormal despite clinical recovery. Thus, clinicians ought to base postoperative management of patients undergoing patellar tenotomy on clinical grounds rather than imaging findings (Khan et al. 1999). (Figure 3)
Many of the most difficult management problems in the adult knee are a result of ill-advised surgical interventions during youth (Day 1997). Inappropriate surgery in patients diagnosed with patellofemoral malalignment is often the first episode in a series of surgical disasters. Fairbank et al (1984) found no correlation of an abnormality of Q angle, patellar height, and patella tilt in adolescents with and without knee pain. They concluded that chronic overloading, rather than faulty mechanics, is the dominant factor in the genesis of anterior knee pain in adolescent patients (Fairbank et al. 1984). Patellofemoral crepitus does not indicate knee pathology in adolescents (Stanitski 1994). Abernethy et al (1978) found asymtomatic patellofemoral crepitus in more than 60%, and only 4 (3%) having true chronic anterior knee discomfort.
The treatment of “patellofemoral dysfunction“ requires patience. More than 90% of patients can be spared a surgical procedure by using conservative treatment, and 67% of patients will have no limitations, and 25% will have minimal limitations by 6 months to 2 years (Goldberg 1997). A directed isometric progressive resistance quadriceps program with iliotibial band and hamstring stretching exercises improved consistently patients in a study of O´Neill et al (1992). The patellofemoral pain syndrome can also be caused by a deficiency in motor control. The vastus medialis muscle has been implicated because it is often underdeveloped in patients suffering anterior knee pain (Fox 1975). Further support for a neural component derives from the observation that the deficit in torque production was seen only during eccentric exercises, and that training relieves pain (Bennet and Stauber 1986).
Extensor apparatus overload is perhaps the most common cause of anterior knee pain. Pain is aggravated by activity and accompanied by mild swelling. The pain is more troubling because its chronicity than because its severity. Activities requiring increased hamstring contractions cause the characteristic anterior knee pain. Synovial thickening may be detected which was described by Eilert as the “silk sign of synovitis”.(Eilert 1993) Growth is a common factor in anterior knee pain, because rapid increase of the extremity length is not always a balanced pattern. There are no correlations between mechanical disturbances and knee pain in children. In 90% the adolescent will recover within a year and should be encouraged to live a normal life.
The frequency rate of bipartite patella has been reported to be as low as 0.05% to as high as 1.66% (Blumensaat 1932, Stucke 1950). Anatomically, bipartite patella is undistinguishable from a pseudarthrosis, with a cartilaginous bridge uniting the two fragments. In many respects it is similar to a synchondrosis. (Fulkerson et al. 1997) According to Saupe, three types of bipartite patella can be distinguished: in type I the second part is located at the inferior pole (5%), in type II - at the lateral patellar margin (20%), and in type III - at the superolateral pole (75%) (Green 1975, Stanitski 1994). Acute or chronic stress may make the junction site symptomatic. When the diagnosis of an acute fracture, a stress fracture, and of a dorsal patellar defect are ruled out, the treatment depends on the severity of the symptoms. When symptoms persist though conservative treatment, the entire fragment may be excised to eliminate the painful pseudoarticulation (Bourne and Bianco 1990, Ogden et al. 1982, Weaver 1977). Before such excision arthroscopic examination of the joint is appropriate. (Eilert 1993) If the articular cartilage is normal, the fragment may be fixed.
The disease was given its present name by König in 1877 in the belief that an inflammatory reaction to an injury is the underlying pathological process (König 1877). However, Paget called this disease “quiet necrosis” and reported on it in 1870 (Paget 1870). Mainly four theoretical explanations of OD exist: 1) Ischaemia 2) Endogenous trauma 3) exogenous trauma, and 4) the constitutional theory. OD is a process whereby a segment of hyaline cartilage, together with subchondral bone, separates from the articular surface and is most common in the knee. It occurs specifically in athletic boys between the ages of 10 and 20. The medial femoral condyle is affected in 85%, and the “classic site (i.e. lateroposterior postion of the medial femoral condyle)” in 69%. The patella is involved in approximately 5% (Aichroth 2000) (Figure 4).
The early presentation is often inconclusive with knee pain, joint effusion, and thigh atrophy. Giving way, catching, or locking suggest separation of the fragment. OD can be diagnosed on routine radiographs, but MRI arthrography can detect whether the lesion is loose (Eilert 1993).
A diagnostic test described by Wilson (1967), produces pain when the knee is extended from 90° of flexion and thereby internally rotated. The reaction is explained by abutment of the ACL from its tibial attachment with the lesion on the medial femoral condyle. The goal of treatment should be to prevent partial or complete detachment of the lesion. Important factors in the natural history of OD include among others patient´s age, and the status of physis. The natural history of OD is different in children and adults, and different in the medial and lateral femoral condyles (Garrett 1991, Hughston et al. 1984). Based on these variables patients with OD may be placed into three groups (Table 2).
Linden (1977) found no complications of OD that could be related to the original condition in 23 patients who had the condition in childhood, and were reexamined an average of 33 years later. A more recent study of another 22 knees diagnosed before skeletal maturity was not quite so positive; the follow-up was 33 years, and 32% showed moderate or severe arthritis (Twyman et al. 1991). The results were less favorable if the lesion was large and/or involved the lateral femoral condyle. Lesions in the classic area of the nonweightbearing portion of the medial femoral condyle did well with simple excision. However, there is no published evidence at present to warrant an aggressive surgical or arthroscopic approach to OD in children, with the exception of large lesions involving the lateral femoral condyle (Gross 1996).
The OD of the patella is less likely to heal than in other locations, and fixation has to be considered before total separation occurs (Eilert 1993). Separation of the fragment yields a poorer prognosis (Schwarz et al. 1988). These lesions are described to be more common in males and in patients with open epiphysis and in the lateral patellofemoral compartment (Peters and McLean 2000). In approximately 30% the trochlea is involved while in the other 60 % the osteochondritis dissecans is located on the patella. 62% out of 25 patients achieved fair or poor results at the follow-up examination (Schwarz et al. 1988). In children with a mean age of 11.4 years, de Ganzy et al reported that without any treatment in all 31 cases of osteochondritis dissecans pain had disappeared and that in 30 of the 31 the OD was not detectable on a follow-up radiograph (de Ganzy et al. 1999). Therefore they recommend no treatment for an osteochondritis dissecans in children (de Ganzy et al. 1999).
As a result of hemorrhage and fibrosis induration of the infrapatellar fat pad can cause anterior knee pain, which was described by Albert Hoffa in 1904. (Hoffa 1904) More commonly, a lesser type of synovial bit of traumatized synovium is pinched between the femur and the tibia at the margin of the joint. (Eilert 1993) The cause of the fat pad syndrome is not completely understood, most authors believe that the primary cause may be repeated traumatization of the infrapatellar fatty pad during activities that require constant repetition of maximal extension of the knee (Safran and Fu 1995). Captured between the femoral condyles and the tibial plateau, the fat pat can become injured by a direct trauma as well. The diagnosis is usually one of exclusion (Safran and Fu 1995). Usually the patient has swelling on either side of the patellar tendon tendon. The prevention of hyperextension may lead to pain relief by reducing the inflammation due to recurrent impingement. In persistent cases, the fat pat is subsequently resected on arthroscopy by exploring the anterior compartment from a superior portal (Ogilvie-Harris and Giddens 1994). Ogilvie and Harris (1994) reported on a significant improvement in the symptoms of their patients (n=11) at a mean follow up of 76 months. However, there are no randomized, controlled studies available on different treatments. The diagnosis is controversial and at least one of exclusion.
The plicae are normal synovial folds whose function is probably to assist in lubrication of the femoral condyle, such as an eyelid spreads tears over the eyeball (Eilert 1993). The symptomatic plica usually presents with a snapping or catching sensation and localized tenderness at the involved site. Synovial plicae of the knee have been suggested to be a cause of anterior pain in children and adolescents (Johnson et al. 1993). Flexion of the knee to 60° brings the plica into prominence. Inflammation and fibrosis, either from a single major incident or from repetitive microtrauma causes thickening of the plica. According to Tindel et al, the plica syndrome is an uncommon pathologic entity diagnosed far too often in the setting of concomitant pathology (Tindel and Nisonson 1992). Dorchak et al (1991) found 76 of nearly 2000 patients (4%) who underwent diagnostic arthroscopies with thickened and/or fibrotic plicae. The diagnosis of the plica as the cause of the knee pain is difficult and often one of exclusion. Conservative measures are very effective and must be emphasized before operative treaqtment. When arthroscopy is indicated, a thorough examination of the entire knee joint is necessary. When a pathological plica is found, reports are available on success after their removal (Tindel and Nisonson 1992), but again no controlled studies exist.
Persistent swelling of the knee and generalized tenderness are signs of inflammatory synovitis. In the majority of cases, the cause of the synovitis is unknown and it is therefore characterized as reactive, often after a traumatic event. In pigmented villonodular synovitis and other types of synovitis, arthroscopic synovectomy has proved to be superior to open synovectomy in adolescents because of its lower incidence of postoperative stiffness (Eilert 1993). However, pigmented villonodular synovitis reoccurs in approximately 50% (de Visser et al. 1999, Rader et al. 1995, Zvijac et al. 1999). The test for rheumatoid factor is notoriously negative in children even with confirmed juvenile rheumatoid arthritis (Eilert 1993). There are no specific laboratoty tests diagnostic for rheumatoid arthritis. Positive antinuclear antibodies are found in 25% of the children with juvenile rheumatoid arthritis, and rheumatoid factor is detected in less than 80% (Soslow 1987). Slit lamp examination of the eye for iridocyclitis is indicated if monarticular rheumatoid arthritis is suspected, as iridocyclitis is treatable and potentially very damaging (Eilert 1993). Iridocyclitis, the most severe extra-articular manifestation of juvenile rheumatoid arthritis occurs in 10% to 15% of the patients. A popliteal cyst (Baker´s cyst) may also be an early manifestation of juvenile rheumatoid arthritis (Soslow 1987).
Meniscus injuries occur in children at a much reduced rate compared to the adult (Busch 1990). The menisci assume their adult semilunar form by the 10th fetal week. During the remainder of growth, the menisci change in size but not in shape. Especially in the peripheral, the child´s meniscus is more vascular, and blood vessels have been demonstrated to penetrate the inner zones even at the age of 13 years (Clark and Ogden 1983). Most reports about the meniscus in the adolescent deal with the discoid lateral meniscus. (Aglietti et al. 1999, Bennani-Smires et al. 1998, Connolly et al. 1996, Stark et al. 1995, Washington et al. 1995) When a congenital discoid lateral meniscus becomes symptomatic during childhood, the symptoms are variable and inconsistent. The classification of Watanabe in describing the discoid meniscus is widely accepted (Watanabe et al. 1979). There are three classes: an incomplete discoid meniscus, a complete discoid meniscus, and the Wrisberg type. In a Wrisberg type of discoid meniscus (i.e. no peripheral attachment of the posterior horn except for the ligament of Wrisberg) total excision is indicated (Aichroth PM 1992). If a peripheral attachment is present, then a peripheral rim may be left. Hayashi et al. recommend a residual rim of 6 to 8 mm (Hayashi et al. 1988). A torn discoid meniscus may be exised and the meniscus reshaped to “normal” anatomy.
Out of 166 arthroscopies 17% of the patients had a meniscal injury, while cartilage lesions were found in most patients. (Lauterburg and Segantini 1994) In 92 knee arhroscopies, Maffulli et al found 10 meniscal tears in children with a mean age of 14.6 years. There is only a 56% chance of making a correct diagnosis on clinical grounds, which contrasts with an accuracy in excess of 99% with arthroscopy. (Angel and Hall 1989) Accuracy, positive predictive value, negative predictive value, sensitivity, and specificity data were much more favorable from clinical examination than from magnetic resonance imaging, and MRI diagnoses added little guidance to patient management and at times provided spurious information. (Muellner 1998, Stanitski 1998) The treatment of meniscal tears in adolescents is similar to adults, with a tendency for increased frequency of repair.
Slipped capital femoral epiphysis is a relatively common disorder in late childhood and adolescence (Figure 6). It is more common in blacks and males and there seems to be a relationship to geographic location. If the slippage is slow, and more chronic, clinical findings may be minimal and subtle. Referred pain to the medial knee via the obturator nerve is a common reason for delayed diagnosis (Bednarz and Stanitski 1998, Causey et al. 1995, Murtagh 1992, Stanitski et al. 1997). As many of 30% of patients diagnosed with a slipped capital femoral epiphysis have onset of symptoms for week to months before diagnosis (Causey et al. 1995). Left untreated the slip will often progress and stabilize when the physis closes (Oram 1953). Thus severe slips will result in severe deformity and significant early arthritis (Causey et al. 1995). Also an avascular necrosis of the femoral head - Legg Calve Perthes disease – can be the reason of knee pain and is diagnosed trough decreased rotation of the hip as well as radiographically (Tippett 1994).
The incidence of most muskuloskeletal neoplasms is highest around the knee. Nevertheless Dickinson et al report that a majority of patients with knee tumors had symptoms for around 6 months prior to initial radiographs (Dickinson et al. 1997). It is fortunate that tumors make up a small fraction of the many causes of pain and mass around the knee, but suspicion must be kept in order to avoid making an error in diagnosis that could lead to loss of a limb or even life (Gebhardt et al. 1990). Malignant bone tumors and soft-tissue sarcomas are the sixth and seventh most common causes of childhood cancer, respectively. (Young et al. 1986) Gebhardt et al reported about 199 patients, of whom 114 had bone lesions and 77 soft tissue lesions (Figures 7-9) (Gebhardt et al. 1990).
The knee is the most frequent site for osteosarcoma, probably related to the rapid growth at this location. Approximately 50% of osteosarcomas are located in the knee region (34%: distal femur, 17%: proximal tibia) (Gebhardt et al. 1990). As a cause for recurrent hemarthrosis, an intraarticular hemangioma may be found and mechanical instrumentation during arthroscopy may result in significant bleeding (Shapiro and Fanton 1993). Evaluation of a child with a suspected bone neoplasm is a complex process, but initially the most important thing is to recognize that one is dealing with a neoplastic problem. Most young patients seeking treatment for knee pain will have a traumatic, infectious, or developmental cause for the symptom (Gebhardt et al. 1990).
The vast majority of the sources of knee pain in adolescents are benign and treatable. Keep in mind that chronic cases the pain sometimes may be due “only” to a physical expression of unhappiness (Eilert 1993). But the pain of adolescence must not be underestimated since serious diseases such as tumors could be the reason. An error in diagnosis could lead to loss of limb or even life. One should remember that the incidence of most musculosceletal neoplasms is highest around the knee. Dickinson et al (1997) report that the majority of their patients had symptoms for around 6 months prior to the initial radiograph, irrespective of age or the grade of malignancy. The evaluation of history and the clinical examination are crucial in the establishment of the diagnosis and should always be performed. Radiographic imaging is the most appropriate supplemental test to be done after examination and should be done in the majority of patients with longstanding pain. The standard views of the knee (antero-posterior, lateral, tunnel, and tangential) usually provide sufficient information. To finalize the diagnosis additional tests and investigations, like magnetic resonance imaging, computed tomography, or bone scan may be necessary and should be performed when they are appropriate and needed to establish the correct diagnosis.
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