Fig. 8.1
MRI showing torn ACL. Anterior translation of the tibia creates the “question mark sign” in the PCL that is now under less tension
Rehabilitation can take more than a year, and some dancers will never regain their previous level of achievement [27]. There is good science showing that ACL injuries can be decreased by incorporating certain exercises into an athlete’s training. The PEP program is the best known of these exercises [28]. While PEP is geared toward young female soccer players, it may be helpful in young dancers as well. ACL injury prevention in the dancer may need to be modified given the inherent training of the dancer that incorporates balance and coordination and is less focused on building strength. Perhaps most importantly, a recent meta-analysis of 14 ACL injury-prevention studies concluded that greater success in knee injury reduction in female athletes was achieved when preventive neuromuscular training commenced before the onset of neuromuscular deficits and peak knee injury incidence, optimally during early adolescence [29].
PCL Tear
Posterior cruciate ligament (PCL) tear is even less common in dancers. It typically occurs when the dancer falls on a flexed knee, striking the proximal tibia on the floor. The tibia is driven back, rupturing the PCL. Exam shows increased posterior translation of the tibia on the femur. MRI is the imaging study of choice.
Unlike the ACL, isolated PCL tears may not need reconstruction [30]. If rehabilitation results in a stable knee that does not give way, the dancer can go back to full activity without surgery or restriction. Persistent instability warrants reconstruction [31]. Prevention of falls through concentration on balance and achievement of center would be a good way to decrease these injuries.
MCL/LCL Tears
When the knee is forced medially (valgus) or laterally (varus), the medial collateral ligament (MCL) or lateral collateral ligament (LCL), respectively, can be torn. Pain and instability can prevent the dancer from dancing. Examination demonstrates varus or valgus laxity and pain. MRI will show the injury. Partial to complete MCL tears usually heal without surgery [32]. If the posteromedial corner is also damaged, a medial side repair of both is done [33]. Return to dance can take weeks to months, depending on the severity of the injury. Like the MCL, the LCL will typically heal without surgery in 6–8 weeks. Also like the medial side, if LCL and posterolateral corner are damaged, an open reconstruction is necessary [34]. In other sports, bracing helps decrease these injuries, but in dance, they are already uncommon. No special prevention strategies are known.
Meniscus Tear
When the knee is under load and twists during a landing or forced turnout, the meniscus can be squeezed and sheared, resulting in a tear. Symptoms can range from mild joint line pain to locking, where the knee cannot be fully extended. This is one of the more common injuries in dancers’ knees [11, 35].
Examination for meniscus tear involves checking range of motion and palpating the medial and lateral joint lines. Pain along either joint line should prompt the examiner to check for a McMurray sign, which is a painful snap as the knee is extended from a flexed position. In the past, physicians were told that clinical diagnosis was adequate. Unfortunately, a contusion to the femur or tibia can mimic a meniscal tear and result in an unnecessary operation. Confirmation of the diagnosis is made with the MRI (Fig. 8.2).
Fig. 8.2
MRI view of a medial meniscus tear
Treatment of meniscus tear varies. A locked knee must be treated surgically, urgently, to achieve motion and the best chance for repair [36]. Only the smallest tears can be treated non-operatively with rest and rehabilitation [37]. Most meniscus tears are treated with arthroscopic repair or partial resection. Good dance technique is the best prevention here. Knowing when you are fatigued enough to stop dancing is the key to prevention.
Patella Dislocation
A direct blow to the medial side of the patella or a landing where the knee rotates inward can cause the patella to dislocate laterally. This is especially true in dancers with hyperlaxity or a history of patella subluxation. A dislocated patella is hard to miss, as the patella sits on the outside of the knee rather than in its groove (Fig. 8.3). Acutely, the patella is reduced by straightening the knee and pushing the patella medially. Radiographs determine whether a piece of bone was knocked off, requiring surgical repair versus resection. MRI can provide details about articular cartilage damage, location of medial patellofemoral ligament (MPFL) damage, and associated bone bruises [38].
Fig. 8.3
Patella dislocation as seen in MRI axial cut
Treatment for first time dislocations is rest, bracing, and rehabilitation. Recurrent dislocation or subluxation calls for MPFL repair or reconstruction [39]. This injury is more common in dancers with hyperlaxity syndrome. They need to know that they have the syndrome and to strengthen their quadriceps, especially the vastus medialus obliquus (VMO), to decrease the likelihood of dislocation.
Fracture
In the knee, the patella, femur, and tibia can break. In the young dancer, the distal femur and proximal tibia physes can be fractured as well. Powerful trauma is required to break bones; hence, fractures are unusual in dancers. Fracture of the patella, femur, or tibia is diagnosed by radiographs. If the fracture is non-displaced, it can be treated by non-weight-bearing in a cast or immobilizer. Repeat radiographs for the first few weeks are needed to ensure the fracture remains non-displaced. Displaced fractures require open reduction and internal fixation with hardware. Fractures typically heal in 6–10 weeks.
Most injuries that result in a broken bone cannot be prevented. Bone strength can be improved, and dancers often have low bone density due to poor diet, abnormal menstrual periods, and/or an eating disorder. Teaching proper calcium, vitamin D, and protein intake should be part of every young dancer’s education. Avoiding smoking [40] and correcting disordered eating will optimize bone strength.
Micro-trauma/Overuse
With repetitive, strenuous use of a structure, breakdown occurs, leading to micro-injuries. These can be very painful and destructive over time. Most of the knee injuries sustained by young dancers are from overuse [5]. In general, overuse means too much, too soon. This can include advancing too rapidly for age, training level, conditioning, strength, or balance. It can also mean advancing too rapidly for a given environment, including studio temperature, quality of the dance floor, skill of the dance partner, or teacher’s expectations.
Overuse Knee Injuries Unique to Dancers with Open Growth Plates
Osgood–Schlatter Syndrome
Excessive traction forces on the patella tendon in dancers in their early teens can lead to stress fracture of the tibial tubercle physis (growth plate) and small tears in the tendon’s attachment fibers on the tibia. The physis can separate a bit, causing a bump at the tibial tubercle. Acute aggravation can cause additional swelling of the area. Examination demonstrates a bump at the tibial tubercle that is tender to palpation. Radiographs show widening of the tibial tubercle physis and frequently fragmentation of the apophysis.
The excess traction leading to physeal stress fracture is treated with rest. Relative rest allowing the tissues to heal should be effective. Such pain-free rest is difficult to achieve, and the pain and injury can persist. In the past, casting was employed to facilitate adequate rest [41]. Now this is rarely done; instead, a knee brace and physical therapy are prescribed. The goal is to restore knee strength and decrease traction at the tubercle through the use of strengthening and flexibility exercises. Unless the lesion becomes completely pain-free to palpation, it usually recurs. For prevention, avoid too much jumping in the immature dancer. Ensure that young dancers have excellent hamstring and quadriceps flexibility.
Sinding–Larsen–Johannson Syndrome
This problem is the same as Osgood–Schlatter, except it occurs in 10- and 11-year olds and at the patella distal pole rather than the tibial tubercle. Treatment is similar.
Common Overuse Knee Injuries in Young Dancers
Patellofemoral Pain Syndrome (PFPS)
This is the most common cause of knee pain in dancers, young and old [1–5, 7, 10]. The pain is thought to arise from the subchondral bone nerves in the patella. The cartilage has no nerves and does not contribute to the patella pain [42]. Asymmetrical overloading of the patella may cause patella deformation and pain [43]. Stairs, jumping, and grand plié are the main culprits (Fig. 8.4).
Fig. 8.4
Grand plié with deep knee flexion leads to overload and injury to the patellofemoral joint. Photo courtesy of James Koepfler
The dancer will complain of pain with any activity requiring a bent knee. This is when compressive loads on the patella are greatest. The damage can result after a single jump but more often occurs from cumulative jumps and grand pliés when the patella bone fatigues and deforms to a greater extent.
Examination consists of evaluating the patella for pain with loading. This can be done by pressing the patella into the trochlea and assessing for pain. Patella tracking is explored to determine whether changing the tracking can be used to modify forces on the damaged parts of the patella. Medial–lateral translation indicates whether hypermobility is a factor. Radiographs can determine patella tilt, patella alta or infera, and whether there is bone damage to the patella or trochlea is hypoplastic. Documenting the subtle subchondral micro-trauma has proven to be more difficult. Bone scan has been shown to indicate subchondral trauma in some patients with PFPS [44], and MRI has documented patella bone changes related to PFPS [45].
The goal of treatment of an isolated patellofemoral problem is force reduction. Depending on whether the force overload is symmetric or asymmetric, different strategies can be employed. If the force is uniform on a well-tracking patella, decreased jumping, grand plié, and overall activity will be effective. If the patella tracks laterally, a brace or taping that medializes the patella may help. Over time, strengthening the VMO and stretching the iliotibial band can relieve pain [46]. Occasionally, surgically realigning the patella is necessary.
Fat Pad Syndrome (FPS)
FPS is also known as Hoffa’s syndrome. Swollen, enlarged medial and lateral fat pads can be very painful [49]. This condition tends to occur after patellofemoral pain syndrome, or other knee pathology has existed for some time. The diagnosis is under-appreciated and frequently missed. Examination is straightforward, looking at fat pad size with the knee flexed and extended and palpating the fat pads under stress.
Since this condition occurs after another process has been present, the primary problem must be addressed first. To decrease fat pad pain and swelling, rest and oral NSAIDs are started. If ineffective, injecting the fat pad(s) with corticosteroids can be tried. Ultimately, if non-operative treatment is not successful, arthroscopic removal of the hypertrophic tissue is warranted (Fig. 8.5). As previously noted, the condition typically occurs after a long period of patellofemoral pain syndrome, so preventing PFPS is probably the best prevention for FPS.
Fig. 8.5
Fat pads can encroach anteriorly in the knee causing impingement
Plica Syndrome
The medial plica is present in most knees. These plicae can become thickened and rub against the medial femoral condyle during flexion. This is a common cause of knee pain in dancers [11]. Whether the plica or the medial femoral condyle synovium is the source of the pain is unknown. Why some plicae rub and others do not is also unknown. Some clinicians believe the rubbing results from the patella tracking laterally, pulling all medial structures laterally with it. Palpation of the plica and medial femoral condyle synovium demonstrates tenderness, making the diagnosis. An enlarged plica can be seen on MRI axial cuts and at arthroscopy (Fig. 8.6).
Fig. 8.6
Arthroscopic view of a medial plica
The goal of initial treatment is to stop the plica from rubbing against the medial femoral condyle. This may be done by medializing the patella with taping, bracing, and strengthening the VMO. In addition, the plica can be injected with corticosteroid under ultrasound guidance. If these efforts are unsuccessful, the plica can be arthroscopically excised, and if necessary, the patella can be surgically medialized. Prophylactic VMO strengthening might prevent the problem from arising.
Synovitis
Synovitis occurs when microscopic cartilage wear particles or other irritants cause the synovium to secrete macrophages and fluid to remove the irritants. The knee is symmetrically enlarged and boggy. Range of motion is limited by capsule distention.
Since synovitis occurs when something irritates the synovium, the source of irritation must be addressed. After ruling out gout, infection, and internal derangement, consider particulate debris from chondral degeneration. Determine the cause of abnormal cartilage wear, such as patella malalignment, patella overload, excessive valgus, or excessive varus. Treat the mechanical deformity causing the wear. The patella can be realigned by taping, bracing, VMO strengthening, or, as a last resort, surgical modification. Varus and valgus can be modified by bracing and possibly by technique changes. Treat underlying degenerative and inflammatory conditions to minimize knee synovitis.
Patella Subluxation and Back Knee
Young dancers have a higher incidence of hyperlaxity syndrome [16] which predisposes them to unique injury patterns. Patellar subluxation occurs when there is hyperlaxity, abnormal tracking, patellofemoral hypoplasia, or a previous dislocation. It is almost always lateral subluxation. On exam, multiple signs of hyperlaxity are present, or the patella is hypermobile from prior dislocation. The apprehension test is positive when the patella is manually translated laterally and the dancer becomes apprehensive. Sources of pain from subluxation are not well understood but may arise from abnormal patellofemoral forces when the patella is in a suboptimal tracking position.
Treatment requires determining the cause of the subluxation. It could be hyperlaxity, patella alta, severe lateral tracking, genu valgum, prior dislocation, patella and/or trochlear hypoplasia, or a combination of these. In all cases begin with taping, bracing, and VMO strengthening. If these interventions are not effective, additional measures can be employed.
The medial patellofemoral ligament can be shortened or augmented surgically [39]. In patella alta, the tibial tubercle can be surgically advanced [50]. Hypoplasia has been treated with patella and/or trochlear osteotomy to create a better capture [51]. Genu valgum can be treated with distal femoral opening-wedge osteotomy [52]. Prevention here is the same as for patella dislocation. VMO strength is critical. Preventive taping or bracing can be employed.
Back knee is the lay term for genu recurvatum, a knee that hyperextends beyond neutral (Fig. 8.7). Dancers with hyperlaxity are more prone to hyperextend. Attempts to get more turnout or a better fifth position can lead some dancers to hyperextend their knees. Back knee can lead to a stretched posterior knee capsule, pain, and a predisposition to ACL injury.
Fig. 8.7
“Back knee” hyperextension in a ballet dancer
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