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5.1 Definition of the Injury

Acute quadriceps injuries are those affecting the quadriceps femoris musculature and its tendons. The quadriceps femoris is comprised of four distinct muscles: the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius, which act as the major extensor apparatus for the knee. The rectus femoris also imparts hip flexion activity to the quadriceps due to its origin on the pelvis. Some authors argue for the definition of a fifth quadriceps muscle, the vastus medialis obliquus, which is thought to have a horizontal orientation to its muscle fibers and help to medially stabilize the patella, but it is typically described as simply part of the vastus medialis [5, 23, 52].

5.1.1 Anatomy

The quadriceps muscles are found in the anterior compartment of the thigh along with the femoral artery and nerve. All four muscles of the quadriceps converge to form a common tendon insertion which attaches on the patella. The quadriceps tendon itself has three distinct layers. The most superficial layer is derived from the rectus femoris, the middle layer from the vastus lateralis and medialis, and the deepest layer from the vastus intermedius. The rectus femoris originates on the ilium and is the most superficial of the four muscles. Its anterior position, superficial to the other three quadriceps muscles, makes it more susceptible to blunt force trauma, and, henceforth, it is the most often injured. The three deep components, from lateral to medial, are the vastus lateralis, the vastus intermedius, and the vastus medialis, all of which have their origins on the femur [53].

5.1.2 Function

The quadriceps muscles, patella, and patella tendon make up the extensor mechanism of the knee. Tension produced in the quadriceps is transmitted down through the patella, which acts as a pivot point to lever the force, through the patella tendon and to the tibial tubercle. The quadriceps muscles work together to control knee stability and minimize impact forces during loading of the knee joint and are critical in active movements of the lower limb including walking, running, jumping, and cutting [32, 52]. This is in addition to the patella stabilizing activity of the vastus medialis during normal gait and the hip flexion activity of the rectus femoris which helps swing the leg forward when taking a step [18].

Forces in the quadriceps tendon vary depending on the degree of knee flexion. Patella and quadriceps tendon forces are equal at 50° of flexion, while at 30° of flexion, the force experienced by the quadriceps tendon is 30 % less than that in the patellar tendon. This change in forces shifts the patellofemoral contact area to a more distal point on the patella which gives the quadriceps tendon a mechanical advantage during late knee extension. Conversely, when the knee is flexed to 90° and beyond, the force in the quadriceps tendon is 30 % greater than the patella, and the patellofemoral contact area is more proximal on the patella giving the patellar tendon a mechanical advantage during early knee extension [20, 21]. The quadriceps muscles can contract both concentrically and eccentrically, although higher forces are generated during eccentric contractions when the majority of quadriceps injuries occur [46]. Pain models, reported by Torry et al. and Henricksen et al., reported reduced quadriceps activation and decreased early stance knee flexion, which demonstrated the effects of quadriceps dysfunction on knee biomechanics [19, 50, 52].

5.1.3 Injury Mechanism

There are several common injuries which affect the quadriceps musculature. The most common is a quadriceps contusion, usually the result of a direct blow to the anterior thigh, commonly seen in contact sports such as football, basketball, ice hockey, and soccer [25]. Colloquially referred to as “Charlie Horses” in the United States, quadriceps contusions result from forces sufficient to cause tissue damage and disrupt the vasculature leading to two types of injury. The first injury is an intermuscular hematoma that is contained within the fascia and is more likely to spread out causing an ecchymosis. The second is an intramuscular hematoma that takes longer to heal and can lead to myositis ossificans and other complications [23, 25].

The quadriceps are the most common site for muscle contusion in the body, likely due to their anterior position in the lower limb and the fact that the quadriceps muscles are adjacent to the femur, making them highly susceptible to compressive forces and injuries from direct trauma. Interestingly, the quadriceps muscles are most resistant to impact injuries when they are struck while maximally contracted. Contraction decreases the compression of the muscle against the bone and protects the muscle fibers from more severe compression. Muscle contusions usually occur deep in the muscle belly and tend to cause less disability than strains, which are usually confined to the superficial muscle layers [12, 16, 23, 52, 53].

Quadriceps strains occur most commonly at the musculotendinous junction, the weakest point of the musculotendinous unit, and are due to indirect trauma from an excessive stretch [6, 16, 22, 54]. A quadriceps strain, commonly referred to as a “pulled muscle,” typically takes place following a single major active extension activity such as sprinting or jumping where the patient did not properly warm up to prevent injury due to tensile overload [22]. Several components of the quadriceps muscles place them at a higher risk for strains and tears: higher constitution of fast-twitch (type II) muscle fibers, extension of the musculotendinous unit across two joints, eccentric action (lengthening during contraction), and shape (fusiform has the highest risk) [5, 16, 46, 54]. Because the rectus femoris is the only one of the quadriceps muscles that crosses two joints, it is the most commonly strained of the four quadriceps muscles [5].

Other injuries to the quadriceps include tendinopathy, tendon tears, and fascial ruptures leading to muscle hernias. Quadriceps tendinopathy (Fig. 5.1) is significantly less common than patellar tendinopathy due to the superior vascularity, strength, and mechanical advantage of the quadriceps tendon compared to the patellar tendon [52]. Quadriceps tendinopathy tends to be the result of an overload/overuse injury in runners and endurance athletes. It most commonly occurs at the distal attachment on the patella [33]. Tendon ruptures (Fig. 5.2) are seen mostly in the middle-aged and elderly population and are often associated with systemic illnesses such as diabetes, gout, rheumatoid arthritis, and kidney disease [23]. Quadriceps tears typically occur when a patient is attempting to regain their balance to avoid a fall. Rapid eccentric contraction against the falling body weight while the knee is partially flexed imparts maximum tensile stress on the quadriceps tendon. In younger patients, tears are usually the result of forced contraction or blunt trauma [22, 23].

Fig. 5.1
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Sagittal view T2 MRI of a knee demonstrating increased signal at the distal insertion of the quadriceps tendon (yellow arrow) secondary to quadriceps tendinopathy

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Fig. 5.2
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Sagittal view T2 (a) and T1 (b) MRIs of a knee demonstrating complete disruption of the quadriceps tendon above the patella (yellow arrows)

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Quadriceps muscle hernias have been found to occur most often in soccer, basketball, and rugby and result from a portion of the muscle protruding through a focal fascial defect. Fascial defects commonly occur following muscle hypertrophy and increased compartmental pressure at weak areas within the fascia, such as portions where blood vessels penetrate the fascia [34, 47].

5.2 Symptoms and Signs

5.2.1 Quadriceps Contusions

The typical history includes a direct trauma from an object or person to the anterior, medial, or lateral thigh, for example, a hockey player who blocks a hard shot of the puck with his thigh. The impact from the puck causes bleeding into the quadriceps muscles and a contusion [3, 25]. A study from the West Point Military Academy reported that the most common activities leading to quadriceps contusions were sports including football, hockey, wrestling, and baseball; however, quadriceps contusions can also result from simple accidents, falls, car crashes, and crush injuries [44].

Patients who have suffered a quadriceps contusion will typically complain of swelling and tightness in the thigh, difficulty walking, local tenderness to palpation, tenderness with straightening, decreased range of motion, and occasionally a palpable mass in the muscle body depending on the severity of their injury. Rarely, patients can suffer femoral nerve damage from the impact, due to either the direct impact or resultant swelling in the anterior compartment after the injury [3]. Although the mechanism of injury is a forceful impact, quadriceps contusions are rarely accompanied by fractures of the underlying femur. Hemorrhaging is common due to local capillary disruption and tissue edema, and a major trauma causing a large contusion can lead to compartment syndrome [25]. This is a rare occurrence, typically only seen with large contusions resulting from a major trauma, but due to its severe consequences (necrosis, fibrosis, and contractures), practitioners should remain mindful of it. Symptoms of compartment syndrome include pain out of proportion to the injury, paralysis, paresthesia, pallor, and a palpable pulse (the “5 Ps”). Since the anterior compartment houses the femoral nerve, compartment syndrome can often be ruled out with normal testing of the femoral cutaneous nerves.

Quadriceps contusions can be assessed using a variety of tests, including direct palpation described by Brukner and Khan, a firmness rating and thigh circumference described by Bull, passive knee flexion ROM described by Jackson and Feagin, and the brush-swipe and tap tests described by Ryan to determine the presence of knee effusion. Of these, only the reliability of the thigh circumference measurements has been verified [24, 56].

Inspection of the affected area may demonstrate ecchymosis, deformity, or swelling depending on the extent of the injury. Strength testing may show deficits in resisted knee extension and hip flexion compared to the uninjured side, and patients may also have limited knee flexion. Straight leg raises should be normal, unless there is concurrent damage to the extensor mechanism. The patient’s gait might also be altered in more severe contusions [50]. Knee effusion can be present in any grade, as can increased thigh circumference on the affected side [27, 56].

Based on the clinical exam findings, Jackson and Feagin described an initial classification system for quadriceps contusions in 1973, which was later modified by Ryan et al. in 1991 (Table 5.1). This classification system has been shown to be useful in predicting disability times associated with each grade of contusion. Mild contusions have an average disability time of 13 days, 19 days for moderate contusions, and 21 days for severe contusions [24].

Table 5.1 Quadriceps contusion clinical classification system and typical symptoms at presentation
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5.2.2 Quadriceps Strains

Quadriceps strains are a common injury encountered in sporting events which require rapid cutting movements, kicking, or jumping. The typical history of a quadriceps strain will reveal a patient who attempted to jump, kick, or suddenly changed directions while running. An excessive tensile force rapidly acting on the muscle strains the fibers past their ability and causes a tear near the musculotendinous junction; however, recent imaging-based studies have demonstrated tears proximal in the rectus femoris (Fig. 5.3), which is the muscle most often injured [12]. Fatigue has been reported to be a major factor in this type of injury, so injuries often occur toward the end of sporting events [16, 48].

Fig. 5.3
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Coronal (a) and axial view (b) MRIs of an anterior thigh demonstrating a partial tear of the rectus femoris muscle (yellow arrows)

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The affected patient will often be immediately aware that they have suffered some sort of injury and will report a sharp, tearing pain in their anterior thigh. The pain may have a delayed onset, but the patient will typically experience rapid loss of function. Pain can be felt anywhere down the quadriceps muscle but is most commonly located toward the musculotendinous junction of the rectus femoris. An obvious deformity may be seen following the injury which can be palpated along the anterior thigh (Fig. 5.4). Strength testing of hip flexion and resisted knee flexion may elicit pain and demonstrate loss of strength/function. Passive stretching and direct palpation will also cause pain. The clinical grading system for quadriceps strains is based on pain, strength, and palpable muscle defects detected during physical examination (Table 5.2) [27].

Fig. 5.4
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Photograph of an obvious deformity in the anterior left thigh as the result of a mid-substance rectus femoris muscle tear (yellow arrow)

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Table 5.2 Quadriceps strain clinical classification system
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The incidence of myositis ossificans has been reported to be between 9 and 17 %. Myositis ossificans should be suspected if symptoms worsen after 2–3 weeks accompanied by loss of knee flexion and persistent swelling [4].

5.2.3 Quadriceps Tendon Tears

Tears of the quadriceps tendon are a rare occurrence, but they are more common than tears of the patellar tendon. Patients who have suffered a complete or partial tear of the quadriceps tendon are typically older (>40 years old) and often have conditions that can lead to degeneration in the tendon (gout, obesity, rheumatoid arthritis, diabetes, infections, etc.) [48]. Other patients who are at risk for quadriceps tendon tears are those that use performance-enhancing substances such as anabolic steroids and creatine. These drugs lead to increased muscle strength, and steroids have been reported to weaken tendons, change collagen fibril structure, and decrease tendon elasticity in animal studies. The combination of amplified muscle strength and a potentially weakened tendon increases the likelihood of suffering a tendon rupture. Quadriceps tendon tears can also be the result of repeated microtraumas and strong, sudden decelerations [41].

The common mechanism of injury in quadriceps tendon tears is a sudden eccentric contraction of the quadriceps muscle with the foot planted and the knee partially flexed (typically more than 60°). This is typically the result of a fall or missed step but can also be due to a direct blow, laceration, or iatrogenic causes (following total knee replacement, anterior cruciate ligament reconstruction, meniscectomy, or steroid injections).

If seen in the acute phase, the patient will usually present with a painful, swollen knee with loss of function following a fall or buckling of the knee. Younger patients often have a history of activity-dependent pain above the patella. A careful history is critical in these patients to understand the underlying mechanism or disease which contributed to the tendon tear. Ambulation will be difficult, if not impossible, for the patient, and they will likely have tenderness and swelling above the patella with ecchymosis. With complete tears, the patella can be low-lying, and there will be a palpable defect or gap above the patella [23].

Extensor strength testing in full active extension against gravity in supine and flexed positions will reveal the degree of tear and retinaculum damage based on the amount of extension lag. Patients with complete tears will be unable to complete a straight leg raise or maintain a passively extended knee position. Patients with a partial tear can have some degree of extension intact but will be unable to maintain extension against force and will demonstrate an extensor lag. In addition, partial ruptures may demonstrate full extension in supine position, while being limited from the flexed position. Flexion should be intact in both complete and partial tears and should be compared to the contralateral normal side to rule out bilateral tears [23].

Patients with a delayed presentation or chronic tear of the quadriceps tendon may have the gap in their tendon filled in with fibrotic tissues or a hematoma. These patients will still have weakness in extension and an antalgic gait [23, 28, 44].

5.2.4 Quadriceps Tendinopathy

Quadriceps tendinopathy has been classified as a variant of “jumper’s knee” because it has a propensity for affecting athletes involved in jumping sports such as volleyball and basketball. Those affected patients complain of anterior knee pain at the superior pole of the patella. Compared to the sharp or deep pain associated with other common quadriceps ailments, the pain of quadriceps tendinopathy is dull and often described as “achy.” The onset of pain is slow and activity dependent [9, 11, 13, 33].

Physical examination will reveal tenderness to palpation at the suprapatellar pole. The stability of the patella and knee should be normal, but patients may demonstrate hamstring and/or quadriceps tightness. Patients will usually have a full range of motion of their knee, although there may be joint effusion [9, 11, 13].

Jumper’s knee is classified into four different stages based on the timing and duration of symptoms. The classification of jumper’s knee is seen in Table 5.3 [9].

Table 5.3 Jumper’s knee classification system
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5.2.5 Quadriceps Muscle Hernia

Quadriceps muscle hernias usually occur at the anterior mid-thigh region where a previous injured area of fascia has become weakened. Fascial weakening can be the result of muscle overuse or hypertrophy and commonly occurs at the structurally weak points where vessels and nerves penetrate the fascia. The typical history for quadriceps hernias is a sudden forceful kick followed by a bulge at the site of the herniation. Muscle hernias are common in professions where a high demand is placed on the legs such as athletes and members of the military. A soft mobile mass can be palpated at the site, and it becomes more prominent and solid when the quadriceps muscles are contracted [47]. When the quadriceps are relaxed, sometimes a fascial defect can be palpated. Most muscle hernias do not cause symptoms, but with prolonged activity some cramping and pain can develop. The defect can lead to nerve entrapment or incarceration of the muscle tissue, which can cause substantial pain and discomfort [7, 47].

5.3 Imaging

5.3.1 Quadriceps Contusions

Imaging of quadriceps contusions is typically limited to ruling out other complications of the injury. Radiographs of the femur can be obtained to rule out a fracture and the development of myositis ossificans. Magnetic resonance imaging (MRI) can be used to obtain information about the early phases of healing in contusions; however, MRI is typically only used to evaluate patients who are not responding to therapy and those whose diagnosis is in doubt. MRI is also widely used to assess the degree of injury in professional athletes [27, 30].

The appearance of a quadriceps contusion on MRI varies depending on the extent and severity of the lesion. A “feathery,” infiltrative signal intensity on STIR (short-tau inversion recovery) and T2-weighted images is indicative of focal edematous changes in the muscle and can have a similar appearance to grade I strains [12]. Contusion-induced hematomas are typically found deeper in the muscle belly as compared to those caused by muscle strains, and while increased muscle girth may be noted, discontinuity of the fibers or major disruption of the muscle architecture should not be present. As the lesion heals, it will demonstrate lower-signal intensity as hemosiderin deposits within the healing hematoma. Compared to ultrasound of a contusion, which is initially echobright before becoming echopoor as it liquefies and then echobright again as the clot organizes, MRI allows for the identification of muscle atrophy, fibrotic muscle tissue, and any heterotopic bone formation as the lesion heals [1, 12, 16, 30].

Myositis ossificans is a relatively uncommon complication encountered following a single or repeated muscle contusion. This condition most often affects young male athletes who engage in contact sports such as football, basketball, ice hockey, and wrestling. Following some contusions, heterotopic bone formation occurs in the soft tissues of the affected muscle or tendon. Bone formation can also been seen in the fascia and can be attached to the periosteum, causing it to be confused with a parosteal osteosarcoma in some cases [36]. To differentiate between the two conditions, the patient history is important because sarcomas will typically not have a significant history of trauma to the affected limb. If the diagnosis remains in doubt, an excisional biopsy may be warranted to confirm the pathology and direct the proper treatment course [4, 27, 31, 36].

Thus far, the cause of myositis ossificans is not yet understood, but animal studies have suggested the cause to be mesenchymal connective tissue cells undergoing trauma and/or osteogenic protein-induced metaplasia to osteoblasts and fibroblasts. The osteoblasts and fibroblasts deposit cancellous, osteoid material which eventually matures into lamellar bone around the edges of the lesion. The lesion formed is typically solitary and well defined and will often regress without treatment [4].

The risk of developing myositis ossificans was defined by Jackson and Feagin in 1973 and then again by Rothwell in 1982 [43]. With mild (grade I) contusions, the risk of developing myositis ossificans was reported to be between 0 and 9 %, with a moderate (grade II) or severe (grade III) contusion the risk jumped to 17–72 %, and with recurrent quadriceps contusions the risk was between 54 and 100 % [24, 27].

Ultrasound and MRI are both highly sensitive for diagnosing myositis ossificans. Ultrasounds can differentiate myositis ossificans from bony tumors and will reveal an oval hypoechoic mass without infiltrative borders. Early signs of myositis ossificans on ultrasound are a center of less echogenicity accompanied by an outer hyperechoic peripheral rim. Calcifications may be seen in mature myositis ossificans lesions leading to distal acoustic shadowing [1, 30, 31].

The MR appearance of early (immature) myositis ossificans lesions typically shows a heterogeneous, high T2 signal and an enlargement of the tissues where the mass is growing. There may be a rim of low-signal intensity surrounding the mass. The addition of intravenous gadolinium will result in an intense heterogeneous enhancement of the lesion(s). Older myositis ossificans lesions (weeks or months following the initial injury), which have had the chance to begin to mature, will show a different appearance on MR imaging. A low-signal rim can be appreciated which corresponds to mature cortical bone. The same heterogeneous, high T2 signal lesion will still be appreciated, along with persistent edema surrounding the lesion. Further imaging as the lesion matures will show decreased edema in and around the lesion and can show signals mimicking fat tissue located centrally within the lesion which likely represents marrow fat [31].

5.3.2 Quadriceps Strains

Quadriceps strains are classified via MRI based on the amount of disruption to the muscle fibers and muscle architecture. First-degree strains can show the same “feathery” appearance on MRI as contusions, indicating edema and hemorrhage in the fibers and musculotendinous junction; however, strains will show at least a minimal amount of fiber disruption. Second-degree strains will show a partial tear that has not retracted back into the muscle. Fluid collections around the fascia and hematomas are often observed in conjunction with the tear. Complete rupture of the muscle fibers is seen in third-degree strains, and the muscle will typically retract from the site of the tear [5, 12]. MRI is usually only utilized for preoperative planning to assess the degree of muscle retraction [16, 30].

5.3.3 Quadriceps Tendon Tears

Complete tears of the quadriceps tendon are typically diagnosed clinically and confirmed by ultrasound or less expensive modalities than MRI. However, magnetic resonance imaging is the best choice for an imaging study if there is any remaining doubt regarding the diagnosis. T2-weighted MR images will clearly demonstrate clear, full, and continuous disruption of all three layers of the tendon if a complete rupture has occurred. Characteristically, with complete tears, the proximal remnant will retract, as well as giving the patellar tendon a “wrinkled” appearance [8, 30]. Heterogeneous signal intensity on T1-weighted images often indicates the presence of an accompanying hematoma. When looking at the entire extensor mechanism on MRI, an undulating outline of the patellar tendon should not be considered diagnostic for a complete tear because it can also be the result of knee hyperextension and is therefore not diagnostic. Partial tears will have single layers that are discontinuous, but the remaining layers will be intact which will rule out a complete tear. Partial tears are often confined to the anterior rectus femoris tendon fibers at the insertion on the patella [5, 30]. This makes MRI quite useful for differentiating complete from partial quadriceps tendon tears.

5.3.4 Quadriceps Tendinopathy

Although it occurs less often, quadriceps tendinopathy has a similar appearance to that seen in patellar tendinopathy on MRI. Quadriceps tendinopathy will reveal fusiform thickening of the tendon and altered signal intensity, most commonly at the insertion of the distal quadriceps tendon to the patella. The normal lamellated architecture of the tendon will be lost, and indistinct changes can be appreciated within the fatty tissue planes. If extension strength is normal, MRI may demonstrate signs of degeneration at the posterior insertion of the quadriceps tendon [9, 11, 13, 33].

MRI is quite sensitive for detecting tendinopathies in both symptomatic and asymptomatic athletes, and symptomatic tendons can have the appearance of being normal. To prevent false-positives, it is very important that physicians order MRIs for quadriceps tendinopathy in the face of positive clinical findings and not as a routine screening test. Older patients suffering from quadriceps tendinopathy may exhibit degenerative changes, including tendon calcification or bony spurs on the superior pole of the patella [9, 11, 13, 18].

When evaluating an MRI for signs of tendinopathy, one should be aware of a phenomenon known as the “magic angle,” which affects tissues composed of well-ordered collagen fibers, seen in hyaline cartilage, menisci, and tendons. When exposed to a magnetic field, these tissues can appear hyperintense when the fibers are oriented at a so-called magic angle of approximately 55° to the static field of the magnet. The hyperintense artifact this creates can be easily mistaken for tendinopathy or other forms of pathology. The magic angle phenomenon can be avoided with an echo time of 37 ms or more on T2-weighted sequences [39].

Ultrasound examination is quite sensitive to diagnose and demonstrate the extent of tendinopathy. Signs of chronic tendinopathy include a quadriceps tendon thickness greater than 6.1 mm, erosion of the superior pole of patella, patellar osteophytes, and tendinous calcification. Ultrasound imaging of quadriceps tendinopathy can also reveal hypoechoic areas masking the normal fibrillar appearance of the tendon [11, 13].

5.3.5 Quadriceps Muscle Hernia

Ultrasound and MRI are both valuable tools to detect or confirm muscle hernias. MRI can often show the fascial defect through which the muscle is protruding. While most hernias can be diagnosed based on clinical signs, MRI is very useful in confirming the diagnosis, preoperative planning, and postoperative monitoring if necessary [34].

5.4 Treatment

5.4.1 Nonoperative

5.4.1.1 Quadriceps Contusions

If possible, a patient who has suffered a quadriceps contusion should immediately have the knee put in 120° of flexion for approximately 10 min. This has been reported to compress the injury to limit hemorrhage and muscle spasm. Research has shown that patients who are put in 120° of flexion immediately following a quadriceps contusion return to normal range of motion more quickly than those who do not and have a lower chance of developing myositis ossificans [2–4, 27]. If the leg is left extended, the quadriceps can start to heal in a shortened position which makes for a more difficult recovery [3].

The use of a hinged brace or a compression wrap is helpful to maintain the leg in 120° of flexion, and ice and compression should be actively employed during the first 24 h. Twenty-four hours following the initial injury, patients should discontinue immobilization at 120° of flexion and begin electrical stimulation and/or passive stretching, still accompanied by icing and compression [2]. Active pain-free quadriceps stretching and strengthening should be performed several times a day. Patients should apply ice for approximately 20 min every 2–3 h to reduce swelling and inflammation. Crutches may be needed for more severe contusions. Typically, patients will be able to return to sports following a mild contusion within a week or two. More severe contusions can cause disability lasting up to 3–4 months but typically resolve within 3 weeks [24, 27]. Development of myositis ossificans or compartment syndrome will significantly increase the length of disability, especially if surgery is indicated.

Contusions that do not receive immediate medical attention and already have limited knee flexion due to intramuscular bleeding should be managed differently. The patient should be kept in the prone position, and the knee should be positioned in the maximum amount of flexion without experiencing pain. In the flexed position, the patient should isometrically contract the quadriceps muscles until the patient feels fatigued. This fatiguing contraction should relax the spastic muscle and allow the practitioner to passively stretch the muscle further. This entire process is repeated approximately three more times, and then the patient is immobilized in their maximum amount of pain-free flexion and placed on crutches. This process should be repeated twice daily until 120° of flexion is achieved, at which time the crutches may be discontinued once the patient can ambulate without a limp [2].

The use of nonsteroidal anti-inflammatory drugs (NSAIDs) is not recommended for mild contusions, but their use is thought to prevent the development of myositis ossificans following severe or repeated contusions based on studies in hip replacement patients [14, 35]. Myositis ossificans should be suspected if symptoms worsen 2–3 weeks following the initial injury or in patients with persistent knee swelling [4].

To return to sports, players should have no pain and be able to flex the knee to 120° with the hip extended, in addition to being able to complete functional field testing without limitations. Players with myositis ossificans can still compete in sports, but they may experience a limited range of knee motion and some occasional pain and/or swelling.

Surgical excision of heterotopic bone should not be performed until the bone has matured (typically 12–24 months). Surgical excision of immature bone should not be attempted because it has been reported to lead to a more severe local recurrence of the bone formation.

5.4.1.2 Quadriceps Strains

Treatment goals for muscle strains are aimed at minimizing the bleeding and hematoma formation following injury to the muscle. There is a scarcity of literature on the specific treatment of muscle injuries, including strains. Because of this, the treatment protocols have not changed drastically in recent years. Acute treatment for strains complies with the PRICE (Protection, Rest, Ice, Compression, and Elevation) protocol for the first 24–72 h following an injury. Ice and compression should be used for approximately 10–20 min at a time in hour-long intervals [10]. Grade 2 and 3 strains may require crutches to allow proper rest and immobilization of the quadriceps. Protection and rest are aimed to prevent further damage to the muscle, while ice decreases blood flow, bleeding, and inflammation at the damaged area. The use of ice following acute muscle injuries has been shown to be effective in decreasing pain caused by the injury, but as of yet there is no definitive proof that it leads to faster healing and a quicker return to sports [10, 17, 25, 37]. Compression and elevation both aid in decreasing blood flow and swelling in the injured area.

The use of NSAIDs can help to reduce pain and facilitate earlier to sports, but the long-term effects on strains is unknown, so a short course (between 3 and 7 days) is only recommended by some centers. Some centers believe that NSAIDs should be contraindicated due to the increased risk of local bleeding and the potential for slower healing of the injury. Therefore, their use is controversial [35].

Following acute treatment with the PRICE protocol, active management of a quadriceps strain should begin 3–5 days following the injury. Active management consists of stretching, strengthening, range-of-motion exercises, cardiovascular fitness, proprioceptive exercises, and functional training to restore function of the injured muscle [12].

Cross et al. reported a 4-stage active management phase to return athletes to sports that involved sport-specific exercises, combined with intense physiotherapy focused on soft tissue therapy with stretching and strengthening exercises. They allowed athletes to perform staged running drills once they had achieved full pain-free passive knee range of motion and could complete single leg hops with three sets of ten repetitions while pain free. Athletes were not allowed to run on consecutive days because this was considered to be potentially harmful. When players were able to successfully complete all four of the stages, they were slowly integrated back into team practices [12].

Stretching should be performed to the point where it becomes uncomfortable but should not cause pain. Passive, active-passive, dynamic, and proprioceptive neuromuscular facilitation stretching are all acceptable forms of stretching, but ballistic stretches should not be used because they risk re-injuring the healing muscle fibers.

Strengthening exercises should include isometric, isotonic, isokinetic, and functional exercises and should be conducted through a pain-free range of motion. There is not an established set of guidelines to safely return to sports after a quadriceps strain; however, athletes should have restored knee range of motion and normal or close to normal strength compared to the uninjured side while being pain free. Performance on functional tests is also helpful to gauge readiness to return to sports, and isokinetic muscle strength testing may be useful for assessing strength and preventing re-injury [37].

The time required to return to play following a quadriceps strain is not only dependent on the severity or grade but also the location of the strain. Cross et al. reported that strains affecting the rectus femoris took significantly longer to heal (9–27 days) compared to those occurring in the vastus muscles (4–5 days), especially those that affect the central tendon, known as the “bull’s eye lesion” [12, 37].

5.4.1.3 Quadriceps Tendon Tears

Incomplete or partial tears of the quadriceps tendon can often be managed nonoperatively. The patient’s knee should be immobilized in full extension for a period of up to approximately 6 weeks depending on the size of the tear. Use of the PRICE protocol has yielded positive results, and reports have indicated that hemarthrosis evacuation, which is common after a quadriceps tendon tear, can aid in reducing pain and speeding recovery [10]. It has been reported that even small knee effusions can affect quadriceps strength, which further supports the need for early and aggressive knee effusion treatment [26, 50]. The effect of early hematoma evacuation has not been studied to determine its possible benefits; however, evacuation is thought to be useful to reduce pain and may allow for earlier recovery. It should be noted that hematoma evacuation, if attempted, should be done early on, prior to consolidation, which would make evacuation more difficult [3]. Practitioners should attempt to avoid prescribing anti-inflammatory medications for patients with quadriceps tendon tears because they have been shown to impair tendon healing. Patients can be allowed to discontinue immobilization once their ability to perform a straight leg raise has been restored, and they can begin progressive knee range of motion and strengthening exercises.

Surgical intervention may be required if patients fail conservative management. The choice of surgical procedure is typically dependent on the degree of the tear and how many tendon layers have been ruptured. If one of the three tendon layers remains intact, repairs can proceed with removal of scar tissue and side to side-to-side closure of the tendon; however, if the majority of the tendon is torn off the bone, suture anchors or sutures placed through the patella may be necessary to reattach the tendon [28, 29, 40, 45].

When a complete quadriceps tendon rupture occurs, patients will require surgical repair or reconstruction to reestablish function of the extensor mechanism because conservative treatment most often results in poor outcomes. Early interventions (between 24 h and 1 month) for complete tears are desirable to prevent tendon retraction, patella baja, and muscle atrophy, which can lead to poor outcomes. Several different techniques have been described for surgical repair of quadriceps tendon ruptures. The most commonly used technique involves a transosseous suture repair through vertical patellar drill holes, although other surgeons recommend positioning the transosseous suture through the patella with a transverse drill hole. To anchor the quadriceps tendon, a locking or figure-of-eight suture technique is used, and repair of the medial and lateral retinaculum should be performed when necessary. Ruptures that occur more proximally with part of the tendon remaining intact can sometimes be repaired with end-to-end sutures. Ruptures occurring at the insertion on the patella will often have bony avulsion fragments still attached to the tendon which should be retained to allow for improved bone healing. Another repair technique uses a circumferential suture placed with the knee at 30° of flexion, which aims to protect the repair and add additional strength to allow for early postoperative mobilization. Alternative repair techniques involved the use of wire cerclages, screw augmentation, or suture anchors [28, 29, 41, 42, 45, 55].

Studies have reported that early postoperative mobilization results in improved tendon healing and earlier return of joint motion. As a result, passive flexion to between 30° and 90° is typically initiated on postoperative day one [55]. Most surgeons recommend partial or non-weight-bearing for the first 6 weeks following surgery [25, 28, 29].

Chronic quadriceps tendon ruptures are typically more difficult to treat due to scarring and retraction of the tendon which can prevent direct repairs. The tendon must be mobilized by elevating the quadriceps muscles off of the femur and adhesions must be released. Once the tendon is released, improved outcomes are reported if the tendon can be reapproximated to the patella. If reapproximation is not possible, the tendon will require reconstruction, typically with an autologous hamstring graft. Alternatively, a procedure to lengthen the quadriceps tendon, described by Scuderi, can be used when direct repair is not possible. This procedure entails cutting a full-thickness inverted “V” in the proximal quadriceps tendon stopping approximately 2 cm proximal to the rupture. A triangular flap can then be turned down and attached to the patella. The portion of the tendon where the flap was cut can then be repaired in a side-to-side manner [28, 29, 41, 42].

5.4.1.4 Quadriceps Tendinopathy

Conservative therapy is the treatment of choice for quadriceps tendinopathy and should include rest with activity modification and a physiotherapy program aimed at aggressive hamstring strengthening. Ice, massage, ultrasound, iontophoresis, and phonophoresis have also been used with positive results [25]. NSAIDs and local steroid injections around the tendon are relatively safe and can be a helpful addition to conservative treatment [35]. As a patient’s pain decreases, the intensity of physical activity can be gradually increased [9, 11, 13].

Platelet-rich plasma (PRP) treatment is based on the premise that growth factors in concentrated plasma can aid in tendon healing. The use of serial injections of platelet-rich plasma into an injured tendon has been reported to improve outcomes, especially in refractory cases of quadriceps tendinopathy [15].

Sclerosing agents, if properly injected, can obliterate the hypervascularity associated with tendinopathy. Improved results have been reported when ultrasound is used to find a “feeder” vessel, which is obliterated by injection of a sclerosing agent leading to a decrease in the vasculature surrounding the affected tendon. Serial injections of sclerosing agents have been reported to yield significant reductions in pain and disability [11, 38].

Surgery to treat quadriceps tendinosis is not often needed and is typically only considered in patients who have failed various modalities of conservative therapy and steroid injections. Following MRI, the degenerative tissue and calcifications in the affected tendon can be surgically removed. If a large portion of the tendon is affected and requires excision, reattachment to the patella may be necessary [11, 13].

5.4.1.5 Quadriceps Muscle Hernia

Quadriceps muscle hernias typically do not meet the criteria for surgery and only present an aesthetic problem. For those that become strangulated and require repair, fasciotomy with a simple closure of the fascial defect has reported good results [47].

5.4.2 Operative Treatment and Findings at Surgery

5.4.2.1 Quadriceps Contusions

Surgical intervention for quadriceps injuries is typically only indicated for hematoma removal, compartment syndrome, complete muscle ruptures, quadriceps tendon tears, and, rarely, muscle hernias. Occasionally, with the development of myositis ossificans following a contusion, surgery will be necessary to restore knee movement or relieve pressure on a nerve or blood vessel [27].

Operative findings for muscle contusions treated with fasciotomy typically show increased compartmental pressures with a large hematoma confined within the anterior compartment of the thigh. Published reports have not reported any occurrences of necrotic muscle, fibrosis, or loss of function. Rarely, contusions can cause muscle tears which can be appreciated upon operation [27].

Myositis ossificans can be excised, but surgical excision of the ectopic bone is typically reserved for cases in which symptoms have progressed or remained debilitating over a period of 12 months despite physical therapy and pain management. Reports suggest that excision of the mass should be held until the bone has fully matured, typically within 1 year of symptom onset and with a negative uptake on a bone scan [4].

Operative findings for myositis ossificans vary depending on the location of the lesion. In the thigh, one will typically see an osseous mass extending from the muscle itself. One type commonly seen is the stalk type with a thin bony stalk connecting the femur to the overlying ossified bone. Another is the periosteal type, where a larger region of the ossified muscle contacts the underlying bone. The third common type shows no connection between the ossified muscles and bone beneath [4].

5.4.2.2 Quadriceps Tendon Tears

Quadriceps tendon tears can be complete or partial and tend to occur either mid-substance or near the insertion on the patella. Operative findings can be as simple as a torn tendon or can show signs of degenerative changes which are common in quadriceps tendon ruptures. Grossly degenerative or friable tissue should be removed to allow for the fresh end of the tendons to be repaired [22, 23]. Biopsies taken from 22 operative cases reported evidence of degenerative changes, including organized scar tissue, calcifications, neovascularization, chondrogenic metaplasia, and severe mucoid collagen structure changes in all cases [51]. Inflammatory changes, such as granulation tissue and damaged collagen, should be expected when repairing a torn tendon and are not indicative of degeneration but rather the inflammatory process occurring after the initial rupture. In older patients, signs of collagen degeneration are expected and are likely a cause of the increased incidence of tendon rupture in the older population. A lack of signs of tendon degeneration is common in younger patients with a tendon rupture. Hematomas are a common finding during operative repair of a torn quadriceps tendon, and Hardy et al. reported that nearly 80 % of patients with a complete quadriceps rupture also had a patellar osteophyte typically located on the anterior superior patellar pole [18, 44, 51].

Upon operative repair, a complete tear can show a “bald patella” where the tendon has torn completely off of the proximal patella. A firm and secure repair of the torn tendon to its bony attachment via suture anchors or sutures placed into the bone and tendons should be performed (Fig. 5.5). Ideally a firm and secure repair which allows for early knee range of motion is desired [28, 29].

Fig. 5.5
figure 5

Anteroposterior (a) and lateral (b) radiographs of a left knee showing a repaired quadriceps tendon tear with suture anchors (yellow arrows) in the proximal pole of the patella

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5.4.2.3 Quadriceps Muscle Tears

Operative findings for quadriceps muscle tears typically show damage to the muscle body (Fig. 5.6). On histological examination, Temple et al. in 1998 reported finding patients with large areas of chronic inflammation mixed in with normal muscle, degenerating muscle, and reactive fibrous tissue. They also noted areas of small focal hemorrhage and neovascularity. Normal-appearing muscle was also seen, and they postulated that the time frame between repair and the initial injury could account for operative findings [49, 51].

Fig. 5.6
figure 6

Intraoperative photograph showing a chronic mid-substance tear of the left rectus femoris muscle (yellow arrow)

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5.4.2.4 Quadriceps Tendinopathy

Surgery should only be considered for patients suffering from quadriceps tendinopathy once conservative measures have failed or a tendon rupture has occurred. Typical findings upon surgical repair are macroscopically normal tendon tissue, but degeneration is seen occasionally, especially with a previous history of steroid injections. On pathological and histological examination, tendon samples from surgically repaired quadriceps tendons demonstrate abnormalities at the junction of the muscle and bone. These include pseudocystic cavities between the mineralized fibrocartilage and the bone. Cavities are filled with necrotic or areolar tissue with signs of neovascularization. Areas of pseudocysts will demonstrate a loss of the so-called blue line, the borderline which separates fibrocartilage from mineralized fibrocartilage. Increased thickness of fibrocartilage at the insertion of the tendon can also be seen due to increased production of myxomatous tissue or hyaline cartilage [50].

5.4.2.5 Quadriceps Muscle Hernia

The fascia overlying the quadriceps muscles is not easily torn. Operative repair of herniation through the fascia typically reveals a small defect in the fascia which has allowed a portion of the muscle to bulge out and cause symptoms or become strangulated. The accepted treatment for such defects is a fasciotomy with extension of the fascial defect to a length of 7–10 cm. This will usually alleviate symptoms. Fascial repair was an option previously thought to hold merit, but as it has been known to cause compartment syndrome, it is no longer performed. MRI can provide valuable preoperative information for the surgeon regarding the size and location of the fascial defect, as well as being useful if postoperative complications are a concern [34, 47].

5. Conclusion

Injuries involving the quadriceps musculature including muscle contusions, strains, tears, tendinopathy, and herniations are among the most common muscle injuries. A review of the mechanism of injury, combined with physical examination and imaging studies, when indicated, can help to define the type of injury to the quadriceps musculature. Proper diagnosis and classification of injury patterns and grades can assist with selecting nonoperative or operative treatment regimens in the majority of cases.