MATERIALS AND METHODS

Study population

The study population consisted of 42 subjects (21 women, 21 men; age range 19–31; mean age 22.3 years), with no signs and symptoms of active knee pathology or recent trauma history. These symptomatic soccer players from seven teams (42 players) in major female professional and amateur soccer leagues were evaluated with bone SPECT during the playing season.

Bone scintigraphy and bone SPECT

Bone scintigraphy was performed three or four hours after the intravenous administration of 740 MBq (20 mCi) technetium-99m-methylene diphosphonate (^99mTc-MDP) using a large field of view gamma camera equipped with a high resolution collimator. Standard images including anterior planar spot images of the lower extremities, lateral images of the knee, and SPECT were obtained. A rotating gamma camera (GE Starcam 4000 CX/T) was used for image acquisition. Sixty four projections of 30 seconds each, with 64×64 matrix, in 360° circular rotation were acquired. All images were interpreted visually by two experienced nuclear medicine physicians.

Classifications of bone scan findings

Stress fracture lesions detected by bone scintigraphy were classified quantitatively into three groups according to the number of lesions and scintigraphic visualisation. Scintigraphic patterns of the stress fractures were classified into three grades of bone response according to dimension, bone extension, and tracer concentration in the lesions (fig 1).

Knee SPECT

Bone SPECT images were interpreted according to the following criteria: crescent shape of increased activity in the medial or lateral tibial plateau, posterior focal medial or lateral femoral condylar activity, and increased activity in the infrapatellar tendon insertion. Increased tracer accumulation in the lateral femoral condyle or posterolateral tibial plateau was considered an important bone SPECT finding related to ACL injury.^8,11

Figure 2 gives line drawings of the cross sectional anatomy showing the relevant sites of increased radionuclide uptake.

RESULTS

Table 1 summarises the localisation and grade of focal tracer uptake diagnosed as stress fracture. Increased tracer uptake was identified in the femur and tibia of 54 sites (62%). Most of the stress fractures were located in tibiae (62%). The diffuse tibial uptake was graded as A in 14 subjects, B in four subjects, and C in 10. Different grades of lesions were often found in the same subject.

Table 2 shows the results of bone SPECT of the asymptomatic soccer players. In the 42 subjects (84 legs), 35 sites (42%) showed abnormal uptake (fig 3), indicating rupture of the posterior horn of the lateral meniscus and bone bruising of the tibial plateau, 16 sites (19%) showed rupture of the anterior horn of the medial meniscus, eight sites (10%) showed bone bruising of the medial femoral condyle, 11 sites (13%) showed bone bruising of the lateral femoral condyle, and avulsion injury of the infrapatellar tendon insertion into the anterior tibia was detected in 34 sites (40%). Different localisations of the knee lesions were often found in the same patient. There were 11 ACL injuries.

DISCUSSION

Soccer injuries occur as a result of several factors: player factors (joint instability, muscle tightness, conditioning, and rehabilitation); equipment (type of shoe and shin guards); playing surface (grass versus artificial turf); rules (sportsmanship and adherence to rules); other miscellaneous factors.

In a group of older players (25–41 years old), the most severe types of knee injuries (ligament ruptures and meniscal tears) and muscle strains were recorded with approximately equal frequency (25%, 25%, and 26%).¹² We found approximately 30% of meniscal tears and 13% ACL injuries in our cohort. Previous studies on ACL injuries have shown that men have a higher incidence of ACL tears than women in a variety of sports. The results of our study are very similar (table 2). Intrinsic and extrinsic factors suggested for this discrepancy include hormonal effects, ligament size, body weight, experience, technique, and unequal access to adequate training facilities.¹³ A further factor may be that men play more aggressively than women. Also it may be related to the fact that, in some studies, injury incidence is defined as the number of injuries occurring during a study period. In adult male players, the incidence is 12–35 injuries per 1000 hours of outdoor games and 1.5–7.6 injuries per 1000 hours of practice, whereas in female players, the incidence seems to be lower.² In our study population, men had a higher incidence of ACL tears than women, which may be explained by this finding. Bjordal et al¹ suggested that it is difficult to perform a prospective study of the relatively rare ACL injury in soccer. Many ACL injuries are misdiagnosed at the first clinical examination. Lack of skilled medical examiners and the high cost of diagnostic tools such as MRI used in the initial evaluation may increase the cost of diagnosis. Therefore the ability of bone SPECT to detect meniscal tears early may have economic significance.

Scintigraphy detects stress fractures from the early pathological metabolic bone response that occurs in the periosteal-cortical region. Radiography detects stress fractures late in the bone reaction process (2–12 week after positive scintigraphy), is insensitive for diagnosing mild stress fractures, and remains negative during their resolution.⁴

Stress fractures result from excessive, repetitive loads on the bone which cause an imbalance between bone resorption and formation. The origins of stress fractures are probably site specific and depend on bone density and geometry, the direction of the load, the vascular supply to the bone, the surrounding muscular attachments, skeletal alignment, and the type of athletic activity. A high incidence of stress fractures has been reported in women runners.¹⁴ Our study shows a higher incidence of stress fractures of the tibia in female footballers than in male footballers (73% v 55%). We also found that most stress fractures were in the tibia (64%) and femur (5%), usually in the bone shaft.

A number of risk factors have been suggested for stress fractures in female athletes. Bone mass accretion is compromised in late maturing girls,^15,16 and low bone mineral density has been consistently reported in athletes with hypo-oestrogenic amenorrhoea.¹⁷ These athletes generally do not attain peak bone mass and may enter menopause with significantly lower bone density than normal women.¹⁸ Injuries commonly result from overuse of bone weakened by osteopenia.¹⁹ Numerous studies have shown a correlation between menstrual irregularities and incidence of stress fractures among athletes.¹⁷

Initial theories to explain the well documented association between hypo-oestrogenic amenorrhoea and bone loss focused on the role of oestrogen as a mediator of bone resorption.¹⁷ However, accumulating evidence suggests that metabolic factors associated with nutritional deprivation may be more important in regulating bone activity. Studies of bone turnover in amenorrhoeic distance runners have shown a pattern of bone remodelling characterised by reduced bone turnover and reduced bone formation rather than the increased bone turnover and increased bone resorption typical of hypo-oestrogenism.²⁰

In conclusion, the lower cost of bone SPECT compared with MRI suggests that it should be the preferred mode of investigation in some clinical situations. However, bone SPECT does not provide the anatomical detail that can be obtained with MRI. Our results suggest that bone SPECT may be valuable for detecting meniscal tears of the knee, especially when MRI is unavailable.