Changes in anteroposterior patellar tendon diameter support a continuum of pathological changes
- 1Centre for Sports and Exercise Medicine, Queen Mary, University of London, Mile End Hospital, London, UK
- 2School of Exercise and Nutrition Sciences, Deakin University, Burwood, Australia
- Correspondence to Peter Malliaras, Centre for Sports and Exercise Medicine, Queen Mary, University of London, Mile End Hospital, London E1 4DG, UK;
- Accepted 22 March 2011
- Published Online First 2 May 2011
Objectives A continuum of pathological ultrasound patellar tendon changes from normal tendons, followed by diffuse and then focal change in echogenicity has been proposed. The anteroposterior (AP) diameter of each pathological state and whether change in pathological state is accompanied by change in AP diameter are not known. The aims of this study were to (1) investigate the AP diameter of previously described patellar tendon ultrasound groups (normal, diffuse and focal change in echogenicity) and (2) investigate the change in AP diameter among active volleyball players during a season and whether this corresponds with change in ultrasound group.
Methods The grey-scale ultrasound pathological groups (normal, diffuse, focal) and AP diameter were measured among 102 volleyball players at the beginning of a season and 58 volleyball players at 6 one-monthly intervals during a 5-month indoor season.
Results There was a significant ordinal relationship (analysis of variance, Student–Neuman–Keuls post hoc test, p < 0.05) between AP diameter and normal tendons, diffuse and focally abnormal tendons among men (3.4 ± 0.4, 4.9 ± 0.4, 6.5 ± 1.8 mm) and women (3.2 ± 0.4, 4.2 ± 0.4, 4.6 ± 0.7 mm). Tendons that stayed in the same group tended to have a smaller mean change than tendons that changed group.
Conclusions These findings support the proposed continuum of tendon pathology. Mild patellar tendon thickening (>4.2 mm among men, >4 mm among women) may indicate pathology among active athletes.
Patellar tendinopathy is common among jumping and change of direction sports such as volleyball, badminton and football and can severely limit an athlete's ability to jump and run. Aside from decreasing function, the condition is prevalent; up to 40% of volleyball players may be affected.1 Incomplete knowledge of pathoaetiology contributes to difficulty in both preventing and managing this injury.2
A new continuum model of tendon pathology has recently been suggested including initial reactive phase of tendinopathy characterised by diffuse tendon thickening followed by increasing disruption of the extracellular matrix, termed dysrepair and degenerative tendinopathy.3 Tissue changes in degenerative tendinopathy include cell fatigue and apoptosis (programmed cell death), collagen deterioration and disorganisation, increased ground substance and neurovascular in-growth.4 Tissue changes in reactive tendinopathy need to be confirmed. Tenocyte stimulation and accumulation of ground substance5 6 have been shown in animal models but human studies needed to confirm these are ethically challenging. If confirmed, this model may influence management as tendons in each stage may respond to different interventions. We recently published temporal ultrasound changes in patellar tendinopathy that supports this pathology model. Normal patellar tendons developed diffuse changes in echogenicity (reactive) before focal areas of pathology (degenerative).7 The ultrasound categories and this research predate development of the pathology continuum minimising potential bias.
It is unclear whether these ultrasound groups (normal, diffuse and focal change in echogenicity) have a different AP tendon diameter. Pathological patellar and Achilles tendons are known to increase their AP diameter.8,–,10 This is likely to be explained by the accumulation of ground substance and vascular in-growth in tendon pathology. If the three ultrasound groups described in the patellar tendon display a different AP tendon diameter, this would provide further evidence that these groups represent different pathological stages and may provide clinical guidelines to categorise tendons. Further, a change in ultrasound group should correspond with change in AP diameter. We have previously shown that these ultrasound groups may change even within a month among active volleyball players7 but corresponding change in AP diameter has not been investigated.
The aims of this study were to (1) investigate the AP diameter of previously described patellar tendon ultrasound groups (normal, diffuse and focal change in echogenicity) and (2) investigate the change in AP diameter among active volleyball players during a season and whether this corresponds with change in ultrasound group. We hypothesised that both reactive and degenerative states would have an increased diameter and that degenerative would be greater.
Materials and methods
Volleyball players were recruited from the Victorian State League volleyball competition (elite to recreational) in Australia. Currently, active male or female volleyball players were included. Players under 18 years of age were excluded as they may have juvenile disorders, such as Sinding–Larsen–Johansson syndrome that are difficult to differentiate from patellar tendinopathy. The study was approved by a University Human Ethics Committee and participants provided informed consent before commencement of the study.
One hundred and two volleyball players were recruited into the study at the beginning of the season (59 men, 43 women). Complete monthly measurements were obtained from 58 players, including 36 men and 22 women (mean (SD) age 26.1 (5.3) years, height 181.6 (10) cm and bodyweight 80 (12.3) kg). There were only 58 players with complete records because some players were absent from some games due to reasons other than patellar tendon pain or players did not present for measurement. Fifty-eight players in the study were representative of the entire cohort with regard to age, height, weight or prevalence of patellar tendon pain and pathology.
Bilateral patellar tendon scans were performed with a high-resolution 13.5-MHz ultrasound machine (Siemens Acuson CV70, Medical Solutions Inc, Malvern, PA, USA) by a single experienced musculoskeletal ultrasonographer. The ultrasonographer was blind to the players' pain status and imaged tendons in the sagittal and axial planes monthly during the 5-month season. Tendons were categorised on grey-scale imaging in both planes as normal, diffuse thickening (thickened tendon with diffuse change in echogenicity) and hypoechoic (thickened tendon with focal change in echogenicity) (refer ref 7, figure 1). Tendons that contained with a focal hypoechoic region and diffuse thickening were categorised as focally hypoechoic. Measurement of AP patellar tendon diameter was performed at the proximal insertion of the patellar tendon. This measure has been shown to demonstrate acceptable reliability.11
Data were analysed with SPSS (version 17.0). AP diameter was compared between the ultrasound groups at the beginning of the season (analysis of variance, Student–Neuman–Keuls (SNK) post hoc tests). In a previous study, we have discussed the monthly change of tendons between discrete ultrasound groups so that will not be discussed in this paper. Change in AP diameter over the season was investigated among tendons that were normal throughout the season (paired samples t test). The proportion of tendons in each ultrasound group that experienced a change of 1 mm or more in AP diameter was reported (totalled over the five monthly changes: one to two, two to three, three to four, four to five, five to six). The mean (SD, minimum, maximum) change in AP diameter corresponding to each potential transition in ultrasound groups (three groups, nine potential transitions) was reported (totalled over the five monthly changes). The relationship between the grey-scale ultrasound groups, Doppler ultrasound and pain was reported in a previous study7 so was not included in the current study. The α level was set at 0.05 for all analyses.
There was an ordinal relationship between AP diameter and normal tendons, diffuse and focally abnormal tendons among men (3.4 ± 0.4, 4.9 ± 0.4, 6.5 ± 1.8 mm, respectively) and women (3.2 ± 0.4, 4.2 ± 0.4, 4.6 ± 0.7 mm, respectively) (figure 1). There was a significant difference in mean AP diameter between the three groups for both men (n = 146, F (2) = 107.6, p < 0.01) and women (n = 86, F (2) = 61.7, p < 0.01). Post hoc tests identified an ordinal relationship between AP diameter and the ultrasound groups among men and women (SNK, p < 0.05, figure 1). For each ultrasound group, men had a significantly greater AP diameter than women (t test, p < 0.05).
There were 19 patellar tendons that were normal throughout the season. There was a random pattern of increase and decrease in mean AP diameter in this group that is likely to reflect measurement error (figure 2). There was no significant change (t (18) = 0.8, p = 0.44) in mean AP diameter among normal tendons between the beginning (3.2 ± 0.4 mm) and end (3.1 ± 0.5 mm) of the season.
Tendons with diffuse or focal abnormality were more likely to have a change of 1 mm or more (χ (2) = 9.53, p < 0.01). Fewer normal tendons (14%) changed 1 mm or more (89% increased, 11% decreased diameter) compared with diffusely abnormal (25%, 20% increased, 80% decreased diameter) and focally abnormal tendons (21%, 45% increased, 55% decreased diameter).
Tendons that stayed in the same group tended to have a smaller mean change than tendons that changed group. Group change was associated with at least 1-mm change in AP diameter, except for a change from diffuse to focal abnormality that was associated with a mean increase of 0.5 mm (figure 3). A change from normal to focal abnormality or vice versa was associated with the greatest change in mean AP diameter (normal to focal = 1.42 mm, focal to normal = −1.78 mm).
This study demonstrated an ordinal relationship between AP diameter and the grey-scale groups among both men and women. Among men, tendons with diffuse abnormality were on average 44% thicker than normal tendons whereas focally abnormal tendons were 82% thicker. The difference in AP diameter between tendons with diffuse and focal abnormality was less pronounced among women (compared with normal, diffuse 31% thicker, focal 44% thicker). Men are known to be more susceptible to patellar tendon pathology than women.12 13 It appears that men are more likely to develop severe pathology when using AP diameter as an indicator, especially in the focally abnormal phase. Change in AP diameter among tendons that changed pathology groups also supports the three phases of tendon pathology. Normal tendons that developed focal abnormality (and vice versa) demonstrated greater mean change in AP diameter than tendons that only moved one group in the ordinal continuum. This study therefore provides further evidence that tendons with diffuse and focal abnormality represent different pathological phases and supports the proposed ordinal relationship between these phases (normal to diffuse then focal abnormality).3 7
Diffusely abnormal tendons may represent more acute or less tendon overload with ground substance accumulation but maintenance of a healthy collagen matrix.3 Tendons may then become focally abnormal and thicker in the degenerative stage with continued overload that is characterised by continued ground substance accumulation, a break down of the collagen matrix and neurovascular in-growth.3 This proposed sequence of pathological change needs to be confirmed histologically.
The findings of this study demonstrate that patellar tendons with an AP diameter greater than 4 mm among women and 4.2 mm among men may contain pathology (based on mean AP of normal tendons + 2 × SD). There was, however, considerable variability between the groups (figure 2) and some abnormal tendons had an AP diameter less than 4 mm. Group variability also makes it difficult to differentiate the pathological groups (diffuse and focal thickening) based on AP diameter, especially among women. el-Khoury et al8 investigated 11 tendons with patellar tendinopathy and 61 asymptomatic tendons and reported a cut-off of 7 mm for pathological tendons. In the current study, active volleyball players with abnormal patellar tendons tended to have a lower mean AP diameter than this. The discrepancy may be explained by improvements in ultrasound imaging or an ability to discern the spectrum of patellar tendon pathology among active athletes.
What is already known on this topic
The pathogenesis of tendon pathology remains obscure. Recently, a continuum of pathological ultrasound patellar tendon changes from normal tendons, followed by diffuse and then focal change in echogenicity has been proposed. This is thought to correspond to an initial reactive phase of tendinopathy characterised by diffuse tendon thickening followed by subsequent degenerative tendinopathy involving disruption of the extracellular matrix.
What this study adds
This study demonstrates that ultrasound categories of patellar tendons: normal, diffuse and focal thickening demonstrate an ordinal increase and decrease in AP diameter. Tendons that move two levels along this ordinal continuum (ie, normal to focal abnormality or vice versa) demonstrated a larger change in AP diameter than tendons that change by one level. This supports the proposed reactive and degenerative model of tendon pathology. Among active athletes, the cut-off in AP diameter for patellar tendon pathology may be lower than previously reported.
Nineteen per cent of monthly changes in AP diameter were greater than 1 mm and 3% were greater than or equal to 2 mm (figure 3). The greatest change in AP diameter over 1 month was more than a third of a centimetre (3.6; 3.2–6.8 mm) among a normal tendon that developed diffuse abnormality. Pathological increase in tendon AP diameter is likely to be associated with ground substance accumulation and less so to vascular in-growth.10 14 There is some evidence of a rapid upregulation (within minutes or days) of some ground substance molecules that are associated with tendinopathy in response to load.15 16
A limitation of the current study is that the error involved in measuring patellar tendon AP diameter is not known. A previous study reported a minimal detectable change (95% confidence) of 2.8 mm in measuring patellar tendon AP diameter when comparing results of two separate radiologists.11 In our study, the same radiologists performed all imaging so the measurement error is likely to be lower. In support of this, there was no significant change in AP diameter among tendons that were normal throughout the season. It is, however, unclear if the ultrasonographer was biased by patellar tendon AP diameter when determining the ultrasound category. For example, they may have expected a focal lesion among tendons that were extremely thick (ie, AP diameter >8 mm). This is unlikely as it was the practice of the ultrasonographer to categorise the tendon ultrasound groups before measuring tendon dimensions. As our study involved only volleyball players, it remains to be seen whether our findings are generalisable to other sports.
Competing interests None.
Ethical approval Ethical approval for this study was obtained from the La Trobe University Human Ethics Committee.
Provenance and peer review Not commissioned; externally peer reviewed.