Table 2. Incidence.
| Study | Quality score | Study population | Sample Size | Case definition | Response rate | Results |
|---|---|---|---|---|---|---|
| Military | ||||||
| Boling (2010) [13] | 3/3 | United States Naval Academy (USNA) (39.8% female; mean age unknown, range 18–25*). | 1,525 | Retropatellar pain of any duration with two of the following activities: ascending/descending stairs, hopping/jogging, prolonged sitting with flexed knees, kneeling, and squatting. Plus one of the following: pain on palpation of medial or lateral patellar facets, or pain on palpation of the anterior portion of the medial or lateral femoral condyles. | 1,319/1,525 (86.5%) | 22/1,000 person-years (95% CI: 15/1,000, 29/1,000 person-years). Female incidence was 33/1,000 person-years (95% CI: 20/1,000, 45/1,000 person-years) and in males was 15/1,000 person-years (95% CI: 7/1,000, 22/1,000 person-years). |
| Coppack (2011) [79] | 2/3 | British Army recruits, United Kingdom (27.9% female, mean age 19.6). | 743 | Pain from at least 2 of the following: prolonged sitting, stair climbing, squatting, running, kneeling, and hopping/jumping; insidious onset of symptoms unrelated to a traumatic incident; and presence of pain on palpation of the patellar facets, on step down from a 25-cm step, or during a double-legged squat. | 743/743 (100%) | 14 week incidence 36 / 743 (4.8%; 95% CI, 3.5–6.7). 180/1,000 person-years (95% CI: 127.9/1,000, 246.5/1,000 person-years). |
| Kaufman (1999) [80] | 2/3 | United States Navy Recruits. (100% male; mean age 22.5 years) | 449 | Ill-defined ache of insidious onset localized to the peripatellar area, plus pain on palpation of patella and peripatellar soft tissues. | 449/449* (100%) | 25 week incidence 35/449 (7.8%). 162.1/1,000 person-years (95% CI: 114.7/1,000, 223.0/1,000 person-years). |
| Milgrom (1991) [17] | 1/3 | Infantry recruits, Israel (100% male; age unknown). | 390 | Subjective complaint of anterior knee pain, non-traumatic, with objective finding of pain on patellofemoral compression test and palpation of patella borders. | 390/390 (100%) | 14 week incidence 60/390 (15.4%). 571.4/1,000 person-years (95% CI: 439.9/1,000, 730.5/1,000 person-years). |
| Thijs (2007) [32] | 3/3 | Belgian Royal Military Academy recruits (22.6% female; mean age 19). | 84 | Two of the following: pain on direct compression of the patella with the knee in full extension, tenderness of the posterior surface of the patella on palpation, pain on resisted knee extension, or pain with isometric quadriceps muscle contraction. | 84/105 (80%) | 6 week incidence 36/84 (42.9%). 9.7/1,000 person-years (95% CI: 6.9/1,000, 13.3/1000 person-years). |
| Wills (2004) [81] | 3/3 | British Army Recruits (95.2% male; median age 19.4) | 1,008 | Pain around the anterior aspect of the knee, insidious onset and no evidence of trauma | 926/1,008 (91.9%) | 12 week incidence 81/926 (8.7%). 379.1/1,000 person-years (95% CI: 303.0/1,000, 468.7/1,000 person-years). |
| General Adult Population | ||||||
| Devan (2004) [26] | 2/3 | Female amateur collegiate hockey, basketball and athletic athletes, USA (mean age 19.4). | 63 | Pain in or under patella while running, going up or down stairs; with diffuse pain on palpation. | 53/63 (84.1%) | 1 athletic season incidence 1/53 (1.9%). |
| Thijs (2011) [82] | 2/3 | Female novice recreational runners on a 10 week start to run programme, Belgium (mean age 38.4) | 77 | Retropatellar pain during and/or after activities such as running, squatting, kneeling, going up and down stairs, cycling, prolonged sitting with the knee in flexion, or rising from a seated position. And 2 of the following: pain while compressing the patella, tenderness of patella on palpation, painful resisted knee extension and pain when isometrically contracting the quadriceps 15° flexion. | 77/77 (100%) | 10 week incidence 16/77 (20.8%). 1080.5/1,000 person-years (95% CI: 639.6/1,000, 1717.0/1,000 person-years). |
| General Adolescents Population | ||||||
| Finnoff (2011) [28] | 2/3 | High School runners aged 14–18, USA (45.9% female; mean age 16) | 98 | Anterior knee pain that was exacerbated by deep knee bending and/or climbing stairs plus pain on one of the following: (1) pressure over the subject’s distal quadriceps tendon combined with active contraction of his or her quadriceps muscle (patellar grind test) or (2) direct palpation of the medial or lateral patellar facets. | 98/1500 (6.5%) | 1 running season incidence 5/98 (5.1%). |
| Herbst (2015) [30] | 1/3 | Female adolescent basketball players in middle and high school, USA (mean age 12.7 years). | 255 | Anterior Knee Pain Scale score < 100; International Knee Documentation Committee (IKDC) form, standardized history and physician-administered physical examination. | 255/329 (77.5%) | 1 season incidence 38/255 (14.9%). 0.97 per 1,000 athletic exposures (1 game or training session). |
| Myer (2010) [16] | 2/3 | Female adolescent athletes in middle and high school, USA (mean age 13.4 years) | 152 | Anterior Knee Pain Scale score < 100; knee pain with or shortly following activity and also if anterior knee tenderness was recent. | 145/152 (95.4%) | 1 season incidence 14/145 (9.7%). 1.09 per 1,000 athletic exposures (1 game or training session). |
| Witvrouw (2000) [18] | 1/3 | Students taking physical education, aged 17–21 in Belgium (sex unknown; mean age 18.6) | 480 | Retropatellar pain > 6 weeks during physical activities such as jumping, running, squatting, and going up or down stairs. Plus two of the following; pain on direct compression of the patella, tenderness of the posterior surface of the patella, pain on resisted knee extension, and pain with isometric quadriceps contraction. | 282/480 (58.8%) | 2 year incidence 24/282 (8.5%). 42.6/1,000 person-years (95% CI: 27.9/1,000, 62.4/1,000 person-years). Female incidence was 13/131 (9.9%), 49.6/1,000 person-years (95% CI: 27.6/1,000, 82.7/1,000 person-years); male was 11/151 (7.3%), 36.4/1,000 person-years (96% CI: 19.2/1,000, 63.3/1,000 person-years). |
*Information not within publication, authors contacted for clarification.