Knee overuse disorders

Definition

Overuse injuries of the knee result from microtrauma associated with physical activity and exercise that exceeds the tissue tolerance of the affected structure. Each of these repetitive forces is applied to muscles, tendons, cartilage, or bone with less intensity than the acute injury threshold.¹ Common knee overuse injuries in adults include patellofemoral pain syndrome, iliotibial band syndrome, and quadricep/patellar tendinopathy.

Etiology

Most knee overuse injuries are of multifactorial etiology involving extrinsic factors (training errors) or intrinsic factors (anatomical and biomechanical variations). Training errors include excessive intensity or rapid increase of workload. Anatomical and biomechanical variations, including increased quadriceps angle, valgus deviation of the knee, and pronated feet, affect the forces that are applied to the knee joint.¹

Epidemiology including risk factors and primary prevention

A significant number of knee injuries can be classified as overuse, comprising 42% of all running injuries.¹ Overall prevalence of overuse injuries varies amongst sporting activities.²⁴

1. Patellofemoral pain syndrome (PFPS) is defined by peripatellar or retropatellar pain exacerbated by patellofemoral joint/knee extensor loading activities.^20,26  PFPS is a common condition amongst physically active individuals and young adults/adolescents with variability in prevalence across genders (female > males), and type of physical activity.^{34, 26, 27}  For example, PFPS constitutes 25% of knee injuries in runners, and has an incidence rate of 22/1000 person-years³⁴ in Naval Academy cadets.  Biomechanical risk factors include bony abnormalities (causing instability between the trochlea and patella), lower extremity functional malalignment, abnormal proximal and distal body mechanics (patellofemoral joint, hip/pelvis, foot/ankle), and muscle and soft tissue imbalances.^{2, 27, 30}
2. Iliotibial band friction syndrome (ITBS/ITBFS) is a primary cause of lateral knee pain.³³ It is a common running injury, with an incidence of 22% of reported lateral knee pain in runners.³ A 2002 retrospective study of running injuries identified ITBS frequencies of 38% in men and 62% in women.⁴⁰ Risk factors for ITBS vary, comprising both intrinsic and extrinsic factors. ³³ Intrinsic factors include joint biomechanics of the hip, knee and ankle, and proximal muscle weakness and endurance.³³ A systematic review of lower extremity running related injuries and hip abductor strength identified moderate to high quality evidence correlating hip abductor weakness to ITBS, with the greatest implication in younger participants.⁴⁴  Taunton et al. found the following biomechanical variabilities by percentage in patients with ITBS: varus knee 33%, valgus knee 15%, pes planus 15%, pes cavus 12%, patellar squinting 8%, high Q angle 2%, and large leg length discrepancy 10%.⁴⁰ Extrinsic factors identified include training patterns (i.e. abrupt increases in running mileage) and footwear.³³
3. Patellar tendinopathy (also identified as jumper’s knee) affects both elite and non-elite athletes, and is associated with repetitive knee flexion and extension, as seen with ballistic activities such as jumping, cutting, and running..  Prior studies have identified a prevalence of 40 to 50% in elite volleyball players⁴ and 2.8 to 4.8% in female runners.⁵ In a cross comparison of Norwegian athletes from 9 sporting events, the overall prevalence of jumper’s knee was 14.2% with vast variability between sporting events (volleyball 45%, cycling 0%).³⁸  Moreover, jumper’s knee was twice as common in elite male athletes.³⁸   A similar study performed by Zwerver et. al. compared non-elite recreational athletes and identified an overall prevalence of 8.5% (range 2.5 to 14.4%).³²  As in the elite athlete population, the prevalence was greater in males (males 10.2%, females 6.4%).³²  Sports with the highest reported prevalence included volleyball, basketball, and handball.³²

Patho-anatomy/physiology

The pathophysiology of knee overuse injuries will depend on the area and structures affected.

1. Overload forces increase stress in the patellofemoral joint by the transmission of abnormal loads through the articular cartilage and subchondral bone.
2. Repetitive eccentric overload on the extensor tendons while jumping is believed to be a cause of quadriceps/patellar tendinopathy.
3. Friction of the distal portion of the iliotibial band over the lateral femoral epicondyle with repeated flexion and extension of the knee is postulated to be one of two causes of ITBS.²⁹ The second suggests components of enthesopathy and fat compression under the iliotibial tract.^{36, 37, 22}

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Disease progression and interventional approaches vary based on the identified overuse injury and etiology, with multifaceted treatment approaches addressing both intrinsic and extrinsic factors underlying the injury. In the early stages of knee overuse disorders, the pain presents while performing the predisposing activity and improves with rest. A tendinopathy can progress from pain only after activity to pain during activity, which does not interfere with participation, pain both during and after participation, which interferes with competition, and finally to complete tendon disruption. When exercise resumes, following periods of rest, the pain may return if training, footwear, or biomechanical errors are not corrected.⁶

Specific secondary or associated conditions and complications

Understanding the long-term prognosis for knee overuse injuries is essential for patient management and education. Development of chronic pain, impairment in sports performance or daily activities, and degenerative changes of the knee joint can occur. PFPS, which has traditionally been considered a self-limited process, has a greater degree of chronicity than previously perceived.⁴⁵ Lankhorst et al., identified the persistence of PFPS during a 5-8 year follow-up period, with a longer baseline period of PFPS and lower Anterior Knee Pain Scores serving as potential indicators poorer outcomes.⁴⁶  A prospective study comparing athletes with jumper’s knee with nonsymptomatic control athletes over a fifteen-year period identified more knee pain and functional limitations. Over half of the athletes with jumper’s knee quit their athletic careers due to knee symptoms.⁴⁵Because of the transmission of forces from lower extremities to the spine and upper extremities, athletes can have subsequent injuries in other components of the kinetic chain caused by abnormal biomechanics. On rare occasions, some overuse injuries can lead to tendon rupture and may require surgical intervention.

History

History of the specific sport and player position should be elicited. Recent changes in training technique, training surfaces, shoes, road/track side, stage of current training cycle, and next important competition should always be evaluated in view that this will influence diagnosis, management, and prognosis at the moment of evaluation. Other areas should be also explored, such as the review of systems, history of medical comorbidities or previous injuries, and evaluation for endocrine disorders or nutrition deficits.

Physical examination

Evaluation includes inspection for identification of biomechanical factors, which predispose to the following specific conditions: femoral anteversion, knee valgus or varus, patellar malposition, excessive lateral insertion of the patellar tendon, foot pronation, decreased bulk of the vastus medialis muscle, and abnormal tracking of the patella (PFPS).⁷ Palpation for crepitus and pain at patellar facets (PFPS), distal iliotibial band and lateral femoral epicondyle (ITBS), and origin of the patellar tendon (patellar tendinopathy) are necessary for the diagnosis. Tightness of the patellar retinaculum, hamstring muscles, and iliotibial band should be evaluated. Functional and strength testing (single leg stance and squat) will provide information about control of hip, knee, and ankles and in the reproduction of symptoms (PFPS and patellar tendinopathy).

Test sensitivity and specificity must be considered in conjunction with the clinical picture, and poor diagnostic consistency has been demonstrated with many provocative tests for PFPS. While there is no definitive test for diagnosis, the best available test is anterior knee pain elicited during squatting. ^20,56  A study by Illett et al. found that the Ober & Modified Ober tests, which are commonly used assessing for ITBS, assessed proximal hip joint structures (i.e. gluteus medius and minimus), as opposed to ilitotibial tightness.²¹

Functional assessment

Functional tasks, such as bilateral and single leg squats, step down, and drop jump, are used in the evaluation for predisposing factors. These methods can identify hip/knee/ankle malalignment, hip and core muscle weakness, or valgus movements (knock-knees) during landing.^8,9 Excessive foot pronation, knee valgus, femoral internal rotation, lateral trunk deviation, and pelvic tilt/anteriorization can be identified and addressed.

Laboratory studies

Laboratory studies are not necessary for diagnosis of knee overuse conditions. However, they should be included if other conditions, such as infection, malignancy, or inflammatory arthritis, are suspected. These can include erythrocyte sedimentation rate, C-reactive protein, complete blood count, knee aspiration, and synovial fluid analysis for infection, if there is an intrarticular effusion.

Imaging

Plain films (weight-bearing anterior-posterior, lateral, and axial views) are not diagnostic; however, they can help rule out other causes of knee pain, such as bipartite patella, osteoarthritis, loose bodies, occult fractures, and tumors. They can also identify some risk factors, such as patella alta or patellar lateralization at the femoral groove (lateral and merchant view radiographs), in PFPS. Magnetic resonance imaging can provide information about degenerative changes, such as cartilage fissuring or thinning, subchondral bone marrow edema, and subchondral cysts. Musculoskeletal ultrasound can be an useful tool for identification of focal changes in tendon architecture and subtle changes in tendon vascularity (by using color/Doppler) in addition to its low cost, lack of radiation, and patient comfort when compared with other imaging modalities.^2,4

Supplemental assessment tools

Supplemental assessment tools include the following: instrumented gait analysis, anthropometric evaluation of hamstring/quadriceps flexibility, isokinetic testing, instrumented Q-angle measurement, and dynamic landing and dynamic electromyographic measurements.⁸ Additional functional assessment tools, such as the Kujala Anterior Knee Pain Scale, have been determined to be reliable and valid means of measuring outcomes of PFPS.⁴⁸  This scale consists of 13 weighted items addressing the following: 1) knee symptoms associated with the following: limp, support, stairs, squatting, running, jumping, and prolonged sitting with flexed knees and 2) Pain, swelling, abnormal painful kneecap movements, atrophy of the thigh, and flexion deficiency.⁴⁷

Early predictions of outcomes

Predictors of poor outcomes include reduced hamstring flexibility, high weekly running mileage, and the degree of activity. Patients with pain at rest or during daily activities may have slower response to treatment than patients with pain only during or after rigorous sports activity.^2,9  Patients with patellar tendinopathy and identifiable tendinous neovascularization on ultrasound tend to have more pain and lower functional scores as measured by Victorian Institute of Sport Assessment (VISA) Questionnaire than patients without neovascularization.³⁵  Lower scores on the Anterior Knee Pain Scale and baseline duration of PFP/knee pain serve as indicators for poor outcomes in PFPS regardless of age BMI, and gender.^46,50

Environmental

Environmental factors with predisposition to knee injuries include training surfaces and shoes. Hard or uneven surfaces produce greater stresses and loading forces on the knee. The use of appropriate shoes and orthotic devices for different body types and sport activities should also be evaluated because abnormal forces applied to the foot and ankle will translate to the knee.

Social role and social support system

The clinician must work in cooperation with the patient, family members, athletic trainers, and coaches to achieve a better outcome. It is important that all involved are aware of the nature of the disease process, treatment interventions, and probable outcomes expected.

Professional Issues

Return to play is an important issue when dealing with athletic injuries. Premature return to play may predispose an athlete to further injury of the affected knee area or to injury of other parts of the body because of abnormal mechanics in running or jumping. It is important to discuss this with the athlete and the multidisciplinary team, taking into consideration the athlete’s competitive priorities, and allowing for an informed decision to be made.