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The Paediatric Knee
Introduction
Knee injuries in children and adolescents are common. , There has been a significant increase in sport participation among young athletes in recent years, and overuse and traumatic injuries about the knee in young patients often prompt medial evaluation. , Many injuries mirror those seen in the adult population; however, there are some unique considerations in the treatment of children and adolescents with knee injuries. Children can have distinct pathological conditions, often related to their growth and development. In addition, surgical outcomes in kids have often been described as different from their adult counterparts. In this chapter we highlight some of the most common knee injuries that children and adolescents sustain and discuss the unique aspects of treatment of these injuries in this population.
Growth-Related Considerations
Skeletal immaturity introduces a challenge to the management of paediatric knee injuries. The growth plates, or physes, around the knee are among the fastest growing in the body and as such are subject to metabolic or mechanical insult that can lead to growth disturbances or angular deformities. Injury to the physis can occur from injury alone but can also be iatrogenic, and surgical treatment of skeletally immature patients requires careful attention to physeal status to minimise the chance of iatrogenic injury. Normal physeal ossification and closure occurs after puberty in adolescents. Girls generally grow 2 years after the onset of menses, typically until age 14.5, and boys have slightly delayed maturation and grow until age 16.5. Historically, assessment of the level of physiological maturity was done with the Tanner staging system, which assesses the presence or absence of secondary sex characteristics. More recent literature, however, has suggested that Tanner staging is not reliably reproducible among orthopaedic surgeons, with significant variations in inter- and intrarater reliability. Thus the most predictable assessment of skeletal maturity is with a bone age posteroanterior (PA) radiograph of the left hand. Bone age can be determined by comparing this radiograph to a series of maturation standards, as depicted in the Greulich and Pyle Atlas. In 2013 a short hand bone age assessment was developed and validated, and this system offers easy and ready use in an office setting ( Fig. 36.1 ).
In addition to physeal development and maturation, injury to the physis should be considered and ruled out with any traumatic injury to the knee in young patients. Because of the lack of mineralisation of this area in the growing child, the physis serves as a weak point in the system, surrounded by stronger bone, ligaments and the joint capsule. Salter-Harris fractures can occur through the physis, and the hypertrophic zone of the physis is the most often affected because this zone particularly lacks collagen and calcification. Although paediatric patients can certainly sustain injuries to ligaments and other intraarticular structures, ruling out a physeal fracture is an important step in the management of knee injuries in young patients.
Paediatric Knee Assessment
Physical Examination
A comprehensive knee physical examination has been described in a previous chapter, and this should be referenced, because a thorough physical examination of the lower extremity should be performed in children presenting with knee pain. Assessing swelling, areas of tenderness, range of motion, strength, ligamentous stability and provocative manoeuvres as described are key to honing in on a proper diagnosis. Given the propensity for physeal fractures in children, careful attention should be paid to palpating for bony tenderness about the distal femur or proximal tibia. In addition, we recommend examining the hip for any child or adolescent presenting with knee pain because a slipped capital femoral epiphysis (SCFE) can often present with knee pain as the chief complaint. Pain with range of motion or axial loading of the hip and obligate external rotation of the hip with flexion should prompt further radiographic evaluation of the hips with anteroposterior (AP) pelvis and frog-leg lateral radiographs of the hips.
The presence of a knee effusion is abnormal in a child or adolescent, and intraarticular pathology conditions should be suspected if an effusion is noted. The most common cause of a knee effusion in a child is acute hemarthrosis as a result of trauma. However, infectious, rheumatological, haematological and oncological processes can also cause knee effusions in a child and should be considered and ruled out. High rates of patellar dislocations, anterior cruciate ligament (ACL) tears, and meniscal injuries were reported in paediatric and adolescent patients (10 and 18 years) undergoing knee MRI for traumatic knee effusions. These conditions may require surgical intervention, and an accurate diagnosis is critical. A high index of suspicion and more advanced workup should be considered in young patients with knee effusions.
Infectious causes of pain and swelling should also be significantly considered in the differential diagnosis of children with knee pain. Lack of trauma or the presence of only minor trauma in the setting of increasing pain, swelling/effusion, painful or limited range of motion or limping may suggest underlying osteomyelitis or septic arthritis. Hematogenous bacterial seeding of bones and joints is more common in children than in adults. Systemic symptoms such as fever, chills, or malaise often accompany pain complaints in the setting of infection; however, in the very early, or alternatively very chronic, stages, these findings may not be present. Treating physicians should have a low threshold to order testing for inflammatory markers, including complete blood cell count (CBC), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) if an infectious pathological condition is suspected based on history and examination.
Ligamentous laxity is also more common in paediatric patients compared with adults, and this may have implications for treatment of certain pathological conditions of the knee, including patellar dislocations and ACL tears. Generalised laxity or hypermobility can be assessed using the Beighton Hypermobility Score ( Fig. 36.2 ) , which measures flexibility at the thumbs, small fingers, elbows, knees and flexion of the trunk. A score higher than 6 suggests hypermobility, and this may inform future prognosis or surgical decision making. Young age and female sex have been associated with hyperlaxity, and teenage girls can be a particularly at-risk population.
Physical examination of the child or adolescent can be challenging for a number of reasons. Young age can make cooperation and compliance with examination difficult, particularly in the setting of pain or discomfort. There can be significant anxiety in young patients about moving the injured extremity, and this can limit the provider’s ability to adequately and confidently evaluate the knee. Examination under anaesthesia may be the most reliable way to obtain an unbiased examination in a young patient, and this should be considered as an important step in surgical management.
Imaging
As described in previous chapters, knee imaging is a critical component of diagnosis. In children, plain radiographs of the knee can be very helpful in identifying fractures, avulsions, physeal abnormalities or osteochondral injuries about the knee. For many paediatric knee injuries, radiographs alone can inform the proper treatment course, and this is the case for many fractures. Complex or intraarticular fractures can be further defined and understood with computed tomography (CT) scans; however, minimising radiation in children, when possible, is preferable.
Skeletal maturity is most accurately assessed with a PA bone age radiograph of the left hand. Other valuable radiographic studies include standing long-leg alignment films, which can help assess for genu varum or genu valgum. This can be particularly helpful in skeletally immature patients with ACL tears to assess and document preoperative alignment or assess alignment in patients with patellar instability or osteochondritis dissecans lesions of the lateral or medial femoral condyles. In patients with open physes, there is an opportunity to use guided growth procedures as an adjunct to surgical procedures about the knee to correct malalignment without requiring osteotomies.
Magnetic resonance imaging (MRI) is the gold standard for diagnosing most intraarticular injuries of the knee, such as ligament tears, patellar dislocations, chondral or meniscal injuries and occult injuries, or better defining osteochondral injuries and evaluating osteochondritis dissecans lesions. Traumatic knee effusions in children and adolescents are associated with higher rates of ACL tears, meniscal injuries and patellar dislocations, and MRI should be strongly considered in young patients with knee effusions in the absence of plain radiograph abnormalities.
Anterior Cruciate Ligament Ruptures
Unique Concerns in the Paediatric Population
ACL tears and reconstructions in children and adolescents significantly increased over the past 20 years. , Once thought to be a rare injury among skeletally immature patients, paediatric ACL tears are becoming routine in sports medicine offices across the United States. Appropriate management of ACL tears in children and adolescents depends on an accurate assessment of the level of skeletal maturity to help inform treatment options. Multiple studies have shown increased risk of secondary chondral or meniscal injuries with delayed treatment of ACL tears in young patients, and surgical stabilisation of the knee with ACL reconstruction should be strongly considered in paediatric patients with unstable ACL tears unless there are significant medical, psychological, or social deterrents or barriers for surgery.
Decision making for young athletes with ACL tears can be challenging. Preoperative alignment and skeletal maturity need to be taken into account because iatrogenic physeal injury can occur with surgical intervention in skeletally immature patients. Some animal studies show disruption of even a small percentage of the cross-sectional area of the physis (4% of the tibial physis, 7% of the femoral physis) can cause growth disturbances. , Physeal-respecting and physeal-sparing surgical techniques have been described as options for younger patients. These include transphyseal reconstructions, partial transphyseal reconstructions, all-epiphyseal reconstructions and combined physeal-sparing intraarticular/extraarticular reconstructions using iliotibial band autograft. These techniques are described in detail in the next section. Multiple treatment algorithms have been proposed for surgical treatments based on age and level of maturity. Fig. 36.3 was published by DeFrancesco et al. in 2018 and is a helpful, graphic representation that summarises the surgical options available, based on the level of maturity.
In addition to deciding on the appropriate surgical procedure, attention must also be directed towards choosing an appropriate graft for the reconstruction. Use of allograft in young patients has consistently shown higher failure rates in young patients and should be avoided if possible. , Common soft tissue autografts used for paediatric ACL surgery include the hamstring and quadriceps tendons and iliotibial band. Bone–patellar tendon–bone grafts are also commonly used in adolescents approaching skeletal maturity and in those already skeletally mature; however, it is prudent to avoid this graft in skeletally immature patients with significant growth remaining because of the risk of the bony plugs crossing the physis and leading to the creation of a bony bar that can result in growth disturbance.
Surgical Treatment Options
Surgical treatment of ACL tears is becoming the standard of care in young patients and has yielded excellent surgical results, , minimising the risk of further chondral injury resulting from the risk secondary instability exposures. Multiple surgical techniques can be employed, depending on the age and maturity of the patient, with preoperative decision making in this age group being a crucial step. Surgical priorities include avoiding iatrogenic injury to the physes, which can be mitigated by physeal-sparing or physeal-respecting techniques, using soft tissue autografts and employing fixation constructs that do not cross the physis. Fig. 36.4 summarises the types of reconstructions that can be performed in skeletally immature patients.
Physeal-Sparing Iliotibial Band Reconstruction
Technique
Initially described by Kocher, Garg, and Micheli, , physeal-sparing iliotibial band reconstruction can be effectively used in skeletally immature patients with significant growth remaining. The initial series of patients were Tanner stages 1 and 2. No tunnels are drilled with this technique and there is all-suture fixation, which minimizes iatrogenic risk to the physis. The iliotibial band (ITB) is harvested proximally, leaving it attached to Gerdy’s tubercle. The ITB is then wrapped around the lateral femoral condyle in the over-the-top position, passed through the femoral notch, underneath the intermeniscal ligament and is secured to the proximal tibial periosteum distal to the tibial physis ( Fig. 36.4A ). The graft is secured proximally to the lateral femoral condyle periosteum and the intermuscular septum using heavy suture in a position of 90 degrees of knee flexion and neutral rotation of the foot to avoid overconstraint of the knee. Distally, full-thickness periosteal flaps are developed and the graft is folded into the periosteum and secured with nonabsorbable suture in a position of full extension or slight knee flexion, depending on surgeon preference for tibial sided fixation.
Outcomes
This technique has demonstrated favourable results with low revision rates in paediatric patients and no reported cases of growth disturbance. , , In the initial series of 44 patients with an average age of 10.3 years, Kocher et al. reported a 4.5% revision rate, with high International Knee Documentation Committee (IKDC) and Lysholm knee scores. A follow-up study included 237 patients (240 knees) with a mean age of 11.2 and a mean follow-up of over 2 years. Graft rupture occurred in 6.6% of knees, and patients continued to report high Pedi-IKDC, Lysholm and Tegner scores. Two surveys of surgeons in the Pediatric Research in Sports Medicine (PRISM) Society showed that this technique is being used with regular frequency across the country for skeletally immature patients with ACL tears. ,
Biomechanically, multiple studies have found that the ITB reconstruction has demonstrated superior results, despite being a nonanatomical reconstruction. This technique has been reported to better restore anteroposterior and rotational stability to the knee compared with other physeal-sparing reconstructions. , In addition, no implants or tunnels are used in this procedure, and thus more options are available to the surgeon if a revision surgery is required. Kocher et al. noted that thigh asymmetry from ITB harvest was the most commonly observed complication in their patient cohort, but only 1.6% of patients reported symptoms related to this.
The physeal-sparing ITB technique is the authors’ preferred method of ACL reconstruction in a skeletally immature patient with significant growth remaining (boys with bone age younger than 13, girls with bone age younger than 12). There is a low revision rate, favourable biomechanical profiles and patient outcomes and no cases of reported growth disturbance, and it optimises options for revision surgery if needed.
All-Epiphyseal Reconstruction
Technique
All-epiphyseal ACL reconstructions have also been endorsed for skeletally immature patients with significant growth remaining. These techniques involve tunnels or sockets that remain entirely within the epiphyses of the distal femur and proximal tibia to minimise injury to the physes ( Fig. 36.4B ). The original technique was described by Anderson; however, since then, multiple modifications have developed. Various graft types (typically hamstring or quadriceps tendon) and fixation options have been described with this all-epiphyseal technique, including suspensory fixation, interference screw within the epiphyses and distal post fixation below the level of the physis.
Outcomes
All-epiphyseal reconstructions have also shown high scores in patient-reported outcomes regarding knee function and return to sport rates. , , , , Revision rates in these studies have ranged from 4% to 15%.
All-epiphyseal reconstructions can be technically challenging, particularly in very young patients who may have narrow epiphyses and in whom it should be performed with intraoperative fluoroscopy or CT scan to minimise the chance of iatrogenic injury to open physes. , Cases of growth disturbance and leg overgrowth have been reported in association with this technique in the literature, some of which were subclinical, but others required corrective surgery. , ,
Although this technique is a more anatomical reconstruction of the ACL in paediatric patients, biomechanical testing suggests it does not restore knee stability to the same extent as the ITB reconstruction. ,
Partial Transphyseal and Transphyseal Reconstructions
Technique
Partial or conventional transphyseal reconstructions have been advocated by many as appropriate for the treatment of paediatric patients with ACL tears. The authors recommend considering these techniques in older adolescents with less than 2 years of growth remaining (boys 13 to 16, girls 12 to 14) because they involve violating the physis. In a typical partial transphyseal reconstruction ( Fig. 36.4C ), the femoral graft and fixation is intraepiphyseal, and a tibial tunnel is drilled through the physis, with fixation preferably kept away from the physis. With a conventional transphyseal technique ( Fig. 36.4D ), tunnels are drilled through both the femoral and tibial physes. The chance of iatrogenic growth plate injury can potentially be mitigated by using smaller, more vertically positioned tunnels to avoid oblique or large tunnels, which can affect more cross-sectional area of the physis, using soft tissue grafts and maintaining fixation away from the physis.
Outcomes
Many studies have reported good clinical outcomes with transphyseal reconstructions, and no cases of growth disturbance or angular deformity. In fact, a recent French survey found increased popularity with transphyseal techniques, even in prepubertal children. However, it is very important to minimise injury to the physes around the knee. MRI studies have shown damage to physes with transphyseal drilling. , One recent study of partial transphyseal reconstructions showed a high rate of growth disturbance (16.7%) among patients; however, most of these did not require surgical correction.
Cordasco et al. found that adolescents with transphyseal soft tissue reconstructions had higher failure rates and lower return to sport rates compared with younger patients with all-epiphyseal reconstructions and older adolescents with patellar tendon autograft. In addition, there is some evidence that augmenting small hamstring grafts with allograft for transphyseal reconstructions may lead to increased failure rates. ,
Postoperative Concerns – Reinjury and Revision Surgery
Young, active patients continue to be the most at-risk population for ACL graft failure and contralateral ACL tear. This is concerning for young patients with high activity demands, many of whom have aspirations for high-level sports participation at the college or elite levels. Paterno et al. found a 30% rate of secondary ACL injury (20.5% contralateral, 9% ipsilateral) among adolescents who underwent ACL reconstruction. Complications and revision rate do not seem to significantly differ when all-epiphyseal patients were compared with transphyseal adolescents. In addition, younger skeletally immature patients were found to have similar reoperation and early revision rates compared with more skeletally mature adolescents. There is still much debate over timing of return to sports, and more high level studies are needed to identify predictive parameters for safe return to sport.
In terms of revision surgery for paediatric patients, outcomes have mirrored adult studies showing lower patient reported outcomes and return to sport rates. Christino et al. reported a 20% revision graft reinjury rate and contralateral ACL injury rate in adolescents undergoing revision, and 55% of patients returned to sport at the same level. Ouillette et al. found similar revision graft failures (21%), but only a 27% rate of return to sport after revision. In addition, allograft revisions had higher failures rate than autograft revisions in their study (27% versus 11%), but this result was not statistically significant.
Summary
ACL tears in skeletally immature patients are common injuries. Careful attention should be directed towards surgical decision making and avoiding iatrogenic growth disturbance with injury to the physes around the knee. Physeal-sparing and transphyseal reconstructions can safely be performed in young patients, based on the level of skeletal maturity, with good expected outcomes. Young patients continue to be the most at risk for subsequent ACL injury, and exploring ways to decrease this risk should be the focus of continued research.
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