Differences at the Achilles Insertion Between Adults with Insertional and Midportion Achilles Tendinopathy as Observed Using Ultrasound.

Abstract

Background:

The purpose of this study was to determine structural and pathological differences of Achilles tendon insertion between insertional Achilles tendinopathy (IAT) and midportion Achilles tendinopathy (MidAT) in both injured and uninjured sides.

METHODS:

Patients (n=34; 58.8% male) with unilateral Achilles tendinopathy (50% with IAT; 50% with MidAT) were recruited. Median age 52 years and Victorian Institute of Sport Assessment – Achilles (VISA-A) score mean 59, and 17 (12 male) had MidAT, median(range) age of 58(48)years, and VISA-A score mean(SD) 59.1(19.7). Ultrasound imaging was used to evaluate structural measurements at the insertion (insertional length, bone-to-insertion length, and tendon insertion angle), tendon length (calcaneus to soleus), tendon thickness at the calcaneal edge, and the presence of pathological changes (boney deformity and/or calcification). A 2×2 mixed Analysis of Variance (group by side) was used to compare IAT and MidAT groups and injured and uninjured sides.

RESULTS:

Tendon thickness at the calcaneus on the injured side was significantly greater than the uninjured side in the IAT group but not in the MidAT group (P=.001). VISA-A score was 59.9(18.7) in IAT group and 59.1(19.7) for MidAT group (P=.909). There were no significant group-by-side interactions for structural measurements at insertion site.

CONCLUSION:

Calcaneal edge tendon thickness was the only significant structural difference observed between involved and uninvolved sides in IAT, although this was not found in in MidAT.

Background

Achilles tendinopathy is a clinical diagnosis characterized by pain, swelling, and load-bearing impairment.(1) It can be categorized into two distinct diagnoses: insertional Achilles tendinopathy (tendon pathology less than 2 cm proximal to the calcaneus), or midportion Achilles tendinopathy (tendon pathology 2–7 cm proximal to the calcaneal insertion).(1) These disorders are considered different regarding their underlying pathophysiology, clinical features, and treatment response.(2–6) While it is clear that the mechanism of Achilles tendinopathy is mainly a result of overloading, the reason why someone develops insertional versus midportion tendinopathy, is poorly understood.

Patients with either of these disorders may present in the clinic with similar symptoms and performance impairments, but a simple way to differentiate between insertional and midportion Achilles tendinopathy is by physical examination.(7) Specifically, tendon palpation and subjective reporting are reliable and valid tests for diagnosing midportion Achilles tendinopathy.(8,9) Palpation reveals pain location, which is useful when distinguishing between insertional and midportion Achilles tendinopathies and other differential diagnoses.(7) Special tests, including the Royal London Hospital test and the arc sign are also helpful tests for confirming midportion Achilles tendinopathy.(10,11) In general, the capability of these clinical measures is more diagnostic than just screening.(12) Magnetic resonance imaging or ultrasonographic examinations are helpful to determine tendinosis presence and location and other pathological changes.(3,13) Pathological changes, such as insertion-site calcifications and boney deformity are associated with metabolic disorders and increased with age among individuals with insertional symptoms,(14,15) but their presence among those with midportion symptoms, has not been evaluated. Imaging of tendinopathy has also been suggested to be useful for monitoring clinical progress.(16–18)

The prognosis for patients with insertional Achilles tendinopathy is not as optimistic compared to midportion Achilles tendinopathy.(5,19) Insertional Achilles tendinopathy, is known as a recalcitrant injury, and responds poorly to nonsurgical treatments.(5,19–21) Patients with insertional Achilles tendinopathy have been reported to experience more symptoms, including pain, and more significant disability, compared to those with midportion injuries.(22) Nonsurgical treatments have also been found to be less successful for insertional Achilles tendinopathy compared to midportion Achilles tendinopathy.(5,19) For example, the success rate of using traditional eccentric exercise (without limiting dorsiflexion range of motion) was ~ 30% in patients with insertional Achilles tendinopathy.(5,23)

Insertion anatomical features might lead to a predisposition for insertional Achilles tendinopathy and affect treatment outcomes, since compression between the tendon and calcaneus is considered a mechanistic explanation of the injury itself.(21) Differences in insertional structural measurements between insertional Achilles tendinopathy and midportion Achilles tendinopathy groups on injured and/or uninjured sides may indicate that these differences are injury related. We have developed reliable ultrasound measurements for evaluating the Achilles tendon insertion(24) that can be used to compare the anatomical features between patients with insertional versus midportion Achilles tendinopathy. The size of the tendon attachment on the calcaneus may influence the load distribution and have effect on tendon injury location. Therefore, the purpose of this study was to evaluate for structural differences of the Achilles tendon insertion, tendon geometry, and pathological changes between insertional and midportion Achilles tendinopathy patient groups, on both the injured and uninjured sides. In both injured and uninjured sides, we hypothesized that bone-to-insertion length would be longer, and insertional length and length to soleus would be shorter among the insertional Achilles tendinopathy group when compared to the midportion Achilles tendinopathy group. We also hypothesized the tendon insertion angle would be smaller, and tendon thickness would be greater in the injured sides as compared to the uninjured sides in patients with insertional Achilles tendinopathy but not among those with midportion Achilles tendinopathy. Finally, we hypothesized that pathological changes (presence of boney deformity and/or calcification) in injured sides (but not in uninjured sides) would be present more frequently in individuals with insertional Achilles tendinopathy as compared to individuals with midportion Achilles tendinopathy.

Materials and Methods

Study Design and Participants Selection

This is a retrospective analysis of a cross-sectional study including 34 participants diagnosed with Achilles tendinopathy (n=17 insertional and n=17 midportion). The participants were included from two prospective studies of individuals with Achilles tendinopathy between November 2014 and June 2019. All participants were clinically-diagnosed by a physical therapist or physician prior to enrollment. We included participants who were at least 18 years-old and had a unilateral Achilles tendon injury. The criteria for clinical diagnosis of Achilles tendinopathy(25) are; 1) localized pain, swelling with palpation and sometimes stiffness at 2–7 cm proximal to the calcaneal insertion for midportion, and at the tendon-bone junction (but not extending more than 2cm proximal to calcaneus) for insertional Achilles tendinopathy; 2) increased symptoms with loading, and;3) impaired performance. Exclusion criteria included a history of Achilles tendon rupture, and/or foot and/or ankle surgery. Participants with symptoms on the uninjured side, as indicated by a scoring <90 on the VISA-A questionnaire, were excluded. The VISA-A consists of eight questions that are scored from 0 to 100, where 100 indicates symptom-free and physically active. The study was approved by the Institutional Review Board for Human Subjects Research at the University of Delaware and written consents were obtained from all participants prior to participation.

Patient-Reported Measures

Participants completed questionnaires regarding their demographics, past medical history, physical activity level, and injury severity. Current physical activity level was assessed with the Physical Activity Scale (PAS) questionnaire, which is a 6-level scale, where level-one indicate the person hardly participate in any physical activity; and level-6 person participate in very hard exercise regularly and several times a week.(26,27) While an index of the clinical severity of Achilles tendinopathy was determined using the Victorian Institute of Sports Assessment – Achilles (VISA-A) questionnaire, the VISA-A questionnaire is reliable and valid measurement tool.(28)

Measurement of Achilles Tendon Structure

Achilles tendon structure was measured using a LOGIQe ultrasound imaging system (GE Healthcare, Milwaukee, WI) using a wide-band linear transducer (10.0 MHz) with a depth setting of 3.5 cm. The first author, who has formal musculoskeletal ultrasound imaging training and has over 2 years of expertise with ultrasound imaging of the Achilles tendon, obtained and measured the ultrasound images. We followed a previously published protocol for imaging Achilles tendon structure bilaterally.(24,29) In brief, we used long-axis and extended field-of-view to obtain three images in prone where participants’ knees and hips were extended and feet were hanging freely over the edge of the bed. The images were exported to an external computer and measured by a single examiner(24) using OsiriX imaging software (Pixmeo SARL, Bernex, Switzerland). On each image the following measurements were taken: insertional measurements, including insertional length, bone-to-insertion, and tendon insertion angle(24); tendon length (i.e., calcaneus to soleus)(29), tendon thickness at the posterosuperior calcaneal edge, and presence of pathological changes [i.e., boney deformity and/or calcification; see Figure 1]. Mean value of three images per side were used in analyses.

Figure 1.

Ultrasound measurements for insertional length, bone to insertion tendon insertion angle, tendon length (calcaneus to soleus) and tendon thickness at the posterosuperior calcaneal edge for healthy Achilles tendon insertion.

Statistical Analysis

A priori power analysis was completed to estimate the sample size needed for this study. For the interaction effect in a 2 × 2 mixed Analysis of Variance (ANOVA), a sample size of 34 (n=17 per group) would be powered (power=.90), to detect a moderately large effect, (η_p²=.10) with nominal alpha, α=.05, and a moderately low correlation among repeated measures, r=.30. This effect size was chosen based on prior research hypothesized differences of insertional length, tendon insertion angle, and tendon thickness.

All statistical analysis were performed using SPSS version 26 (IBM Corp., Released 2019. IBM SPSS Statistics for Windows, Version 26.0. Armonk, NY: IBM Corp) of all data. Descriptive analysis of demographic and symptoms severity were reported. Independent t-test and Chi-square were used to compare patient demographics between groups (i.e., age, sex, BMI, symptom severity and physical activity level). Differences in insertional Achilles tendon measurements (insertional length, bone-to-insertion, and tendon insertion angle), tendon thickness and tendon length to soleus between insertional and midportion Achilles tendinopathy groups and injured and uninjured sides were analyzed using 2 × 2 mixed ANOVA. Bonferroni correction was applied to group and side comparisons. Differences in the ratio of the presence of calcification and/or boney deformity between groups and injured and uninjured sides were evaluated using z-test for dependent proportions. Partial eta-squared (η²_p) effect sizes are reported and interpreted as suggested by Cohen(30) as no effect (<0.01), small effect (≈0.06), medium effect (<0.14), and large effect (≥0.14). Also, the size of effect, Cohen’s H, was used for z-score test and interpreted as suggested by Cohen(30) as H near 0.2 is a small effect, an H near 0.5 is a medium effect, and an H near 0.8 is a large effect. The level of significance for all tests were set at p<0.05.

Results

Patients Characteristics

Overall, 34 participants with unilateral injury were included in the study (17 insertional, and 17 midportion Achilles tendinopathy). The results showed there were no significance differences between the groups for age, sex, height, weight, BMI, VISA-A injured side, VISA-A uninjured side, and PAS, see (Table 1).

Table 1.

Characteristics of patients with insertional and midportion Achilles tendinopathy.

	Insertional Achilles Tendinopathy n=17				Midportion Achilles Tendinopathy n=17
	Mean	SD	Median	Range	Mean	SD	Median	Range	p	Cohen’s d
Age (years)	48	14	49	46	50	16	58	48	0.610	0.091*
Sex (M:F)	8 Male : 9 Female				12 Male : 5 Female				0.300	NA
Height (cm)	174.8	11.6	173.9	39.9	175.5	8.5	176.5	31.8	0.832	−0.073
Weight (kg)	74.5	14.7	77.2	51.6	78.1	16.1	78.1	60.9	0.502	−0.233
BMI (kg/cm2)	24.2	3.7	23.7	15.2	25.2	3.9	25.2	14.3	0.503	−0.232
VISA-A injured	59.9	18.7	62.0	62.0	59.1	19.7	67.0	71.0	0.973	0.006*
VISA-A uninjured	96.5	3.0	97.0	10.0	94.8	3.9	94.0	10.0	0.205	0.227*
PAS	4.5	1.3	5.0	4.0	4.2	1.6	5.0	5.0	0.734	0.063*
Symptoms duration (month)	18.5	30.8	6.7	126.9	17.1	36.2	4.4	149.3	0.357	0.162*

^*Efffect size r was reported for non-parametric test.

Measurement outcomes

Tendon thickness at the calcaneus on the injured side was significantly greater than the uninjured side in within the insertional Achilles tendinopathy group but not within the midportion Achilles tendinopathy group F(1,32)= 14.53, p = .001, η²_p = 0.31 (see Figure 2). There were no significant group-by-side interactions for structural measurements for insertional length, F(1,32)= 1.68, p = .204, η²_p = 0.05, bone-to-insertion length, F(1,32)= 1.70, p = 0.202, η²_p = 0.5, insertion angle, F(1,32)= 0.91, p = 0.346, η²_p = 0.03, nor tendon length to soleus, F(1,32)= 1.73 p = 0.198, η²_p = 0.05. There were no significant main effects (side or group) for insertional length, bone-to-insertion length, insertion angle, nor length to soleus (see Figure 3).

Figure 2.

Mean (SD) tendon thickness at the calcaneus differences between groups and sides.

Figure 3.

Mean (SD) for anatomical features measurements differences between groups and sides.

On the injured sides, the insertional Achilles tendinopathy group had a significantly greater number of pathological changes (calcification/boney deformity) present than midportion Achilles tendinopathy group (difference sample proportion 0.48±0.51, z = 2.78, p = .006, Cohen’s H= 0.99); no significant between-group difference were found for uninjured sides (difference sample proportion 0.18±0.47, z=1.09, p = .28, Cohen’s H= 0.38) (see Figure 4).

Figure 4.

Between-group differences in side-to-side for the proportion of presence of pathological changes. IAT: insertional Achilles tendinopathy, MAT: midportion Achilles tendinopathy.

Discussion

The aim of this study was to evaluate Achilles tendon insertion using ultrasound imaging and compare the structural measurements of the injured and uninjured sides between patients with insertional and midportion Achilles tendinopathy. We hypothesized structural measurements at the calcaneal insertion (i.e., insertional length, bone-to-insertion length, and tendon insertion angle) would differ between tendinopathy groups and within sides. Our main findings showed differences in ultrasound-imaging obtained measurements of pathological changes (tendon thickness and presence/absence of calcification and/or boney deformity) but not for anatomical feature measurements at Achilles tendon insertion between the sides and groups. The injured side in the insertional Achilles tendinopathy group had significantly greater tendon thickness and more pathological insertional changes than the healthy side, and midportion tendinopathy group’s healthy and injured sides. Importantly, no significant differences were detected between sides or groups for measurements related to anatomical features (i.e., bone-to-insertion length, insertional length, tendon insertion angle, nor length to soleus) that may lead to developing insertional Achilles tendinopathy. In summary, measurement variables related to structural pathological changes but not anatomical features were different between groups.

Increased structural enlargement at the calcaneal insertion could be the cause of injury chronicity in the insertional Achilles tendinopathy group but not in the midportion Achilles tendinopathy group, according to the findings. Findings may explain why eccentric exercise(31) into full dorsiflexion is not beneficial for individuals with insertional Achilles tendinopathy, since at full dorsiflexion the distal tendon, and possibly the areas of pathological changes, are compressed. However, further evidence is required to understand if structural pathology at the calcaneal insertion contributes substantially to increased impingement and/or injury severity.

On the other hand, our results showed that anatomical features of the Achilles tendon and its insertion did not differ between tendinopathy groups, and thus, may not be of relevance in the development of insertional versus midportion Achilles tendinopathy. However, we did not include uninjured participants for this study, so we do not have normative values for comparison. In our reliability study, we presented typical average values of bone-to-insertion length and tendon insertion angle in healthy individuals, 9.34 mm and 15.33 degrees, respectively, but they were younger than the groups in this study.(24) These two values are lower than our results by few millimeters or degrees and may be related to the age(32) and not the injury development.

Different measurement methods have been applied in imaging studies of patients with insertional Achilles tendinopathy. Kang et al. compared radiographic measurements for Haglund’s deformity from patients with and without insertional Achilles tendinitis.(33) The radiographic measurements evaluated calcification size; between-group differences were not found(33), which is consistent with this study. Two other studies report calcification was present in 70%(33) and 65%(34) of patients with insertional Achilles tendinopathy (on the symptomatic side), which is consistent with our study results. The mechanism of calcium deposition at the insertion, however, is not clear but one theory suggests deposition as an adaptation to increased compression load.(35) Measuring the size of calcification/boney deformity is feasible on ultrasound images(34). While in our study we did not measure the size of calcification/bony deformity, insertional length may reflect the size of the deformity. Specifically, patients who showed presence of calcification/boney deformity usually exhibited smaller insertional length. The reason is that calcification/boney deformity is commonly located at the distal insertion, so a larger deformity effectively decreases the insertional length.

Another measurement method was addressed by Sella et al at the heel bone, where varying angle measurements at the calcaneus from plain radiographs (made with patient standing) in patients with different Achilles tendon disorders were obtained.(36) The radiographic measurements were used to identify calcaneal deformity before planning treatment. Our study, however, is the first, to our knowledge, to compare and evaluate tendon insertional angle obtained from ultrasound imaging with the ankle at rest; however, no differences between groups were found as this measurement did not show differences of the height of the superior aspect of the calcaneus. Future studies should consider measuring the insertion using a standardized ankle position, along with the resting angle, since the resting angle might vary between individuals.

We hypothesized that the direction of pull on the Achilles tendon insertion would depend on how far distally the soleus attached, such that a more distally attached soleus (resulting in a shorter free tendon) would cause more of an anterior pull on the Achilles tendon insertion helping to explain injury development; however, our hypothesis was not confirmed. The soleus length measurement was similar between groups. Perhaps individuals with insertional Achilles tendinopathy developed soleus muscle atrophy leading to an increase distance between the proximal Achilles tendon attachment and the soleus muscle as seen in patients with Achilles tendon rupture(37). It may be worth studying side-to-side differences of the length to soleus tendon in patients with acute versus chronic Achilles tendinopathy due to disuse atrophy of the soleus muscle to determine changes in tendon to soleus length. The majority of our sample had symptoms duration slightly greater than 6 months. Prolonged symptoms duration has been associated with musculoskeletal disuse(38), and soleus muscle is commonly impaired in Achilles tendon injuries.(39) Further evidence is needed to explore if tendon to soleus length increases are associated with prolonged symptom duration in patients with Achilles tendinopathy.

Medial pain and tenderness has been reported in about 50% of patients with chronic insertional Achilles tendinopathy as a result of plantaris tendon involvement.(40) The amount of compression at the calcaneal insertion may also be uneven as a result of the degree of twisting of the fascicles from the aponeuroses of gastrocnemius to the tendon insertion.(41) Unfortunately, our ultrasound imaging measurements were obtained at the tendon insertion midline, and therefore would not have detected any between-group differences of the medial or lateral tendon attachments.

Limitations

Additional study limitations include a heterogeneous sample in terms of age and symptom severity (which might reflect differing stages of injury recovery) and might have influenced the results. Given the cross-sectional study design, we cannot evaluate causation, i.e., understand the role of structure on injury characteristics (chronicity and symptom severity). While measurement procedures have established reliability, the measurements were taken in ankle resting position instead of a standardized position. It may be beneficial to perform the US measurements in various ankle positions to understand the influence of structure on possible compression at the insertion. Further, having a healthy comparison group could have aided with results interpretation as these results cannot be applied to those with bilateral Achilles tendinopathy. Finally, we did not evaluate other pathological features such as bursitis or neovascularization, and/or anatomical features such as the presence of a plantaris tendon.

Conclusions

We found greater tendon thickness on the posterior aspect of the calcaneus and more presence of pathological changes in patients with insertional Achilles tendinopathy compared to midportion Achilles tendinopathy on the injured sides. In addition, measurements of anatomical features were not different between groups or sides and may not be related to injury development.