Tendon blood flow, angiogenesis, and tendinopathy pathogenesis

Widespread Vascularization and Correlation of Glycosaminoglycan Accumulation to Tendon Pain in Human Plantar Fascia Tendinopathy

BACKGROUND

Plantar fasciitis is a painful tendinous condition (tendinopathy) with a high prevalence in athletes. While a healthy tendon has limited blood flow, ultrasound has indicated elevated blood flow in tendinopathy, but it is unknown if this is related to a de facto increase in the tendon vasculature. Likewise, an accumulation of glycosaminoglycans (GAGs) is observed in tendinopathy, but its relationship to clinical pain is unknown.

PURPOSE

To explore to what extent vascularization, inflammation, and fat infiltration were present in patients with plantar fasciitis and if they were related to clinical symptoms.

STUDY DESIGN

Descriptive laboratory study.

METHODS

Biopsy specimens from tendinopathic plantar fascia tissue were obtained per-operatively from both the primary site of tendon pain and tissue swelling ("proximal") and a region that appeared macroscopically healthy at 1 to 2 cm away from the primary site ("distal") in 22 patients. Biopsy specimens were examined with immunofluorescence for markers of blood vessels, tissue cell density, fat infiltration, and macrophage level. In addition, pain during the first step in the morning (registered during an earlier study) was correlated with the content of collagen and GAGs in tissue.

RESULTS

High vascularization (and cellularity) was present in both the proximal (0.89%) and the distal (0.96%) plantar fascia samples, whereas inconsistent but not significantly different fat infiltration and macrophage levels were observed. The collagen content was similar in the 2 plantar fascia regions, whereas the GAG content was higher in the proximal region (3.2% in proximal and 2.8% in distal; P = .027). The GAG content in the proximal region was positively correlated with the subjective morning pain score in the patients with tendinopathy (n = 17).

CONCLUSION

In patients with plantar fasciitis, marked tissue vascularization was present in both the painful focal region and a neighboring nonsymptomatic area. In contrast, the accumulation of hydrophilic GAGs was greater in the symptomatic region and was positively correlated with increased clinical pain levels in daily life.

CLINICAL RELEVANCE

The accumulation of GAGs in tissue rather than the extent of vascularization appears to be linked with the clinical degree of pain symptoms of the disease.

Novel Insights Into the Intratendinous Pressure Behavior of the Achilles Tendon in Athletes

BACKGROUND

In contrast to other musculoskeletal tissues, the normal pressure behavior of the Achilles tendon is poorly understood. This study aimed to explore the normal intratendinous and perfusion pressures of the Achilles tendon at rest and during exercise, and investigate potential correlations with tendon load and morphology.

HYPOTHESIS

Intratendinous and perfusion pressures of the Achilles tendon exhibit similarities to other musculoskeletal tissues and depend on tendon load and morphology.

STUDY DESIGN

Observational study.

LEVEL OF EVIDENCE

Level 3.

METHODS

A total of 22 recreational athletes were enrolled. Demographics, activity level, and blood pressures were recorded. Achilles tendon thickness and echogenicity were assessed 25 mm proximal to the posterosuperior calcaneal border. In this region, intratendinous and perfusion pressures of the Achilles tendon were measured at rest and during isometric plantarflexion up to 50 N, using the microcapillary infusion technique. Linear mixed models were used to investigate the effects of plantarflexion force, tendon thickness, and echogenicity on intratendinous and perfusion pressures.

RESULTS

At rest, intratendinous and perfusion pressures of the Achilles tendon were 43.8 ± 15.2 and 48.7 ± 18.4 mmHg, respectively. Intratendinous pressure increased linearly with plantarflexion force, reaching 101.3 ± 25.5 mmHg at 50 N (P < 0.01). Perfusion pressure showed an inverse relationship, dropping below 0 mmHg at 50 N (P < 0.01). Neither intratendinous nor perfusion pressures of the Achilles tendon correlated with tendon thickness or echogenicity.

CONCLUSION

The normal intratendinous resting pressure of the Achilles tendon is higher than other musculoskeletal tissues, making it more susceptible to ischemia. During exercise, intratendinous pressure increases significantly to a level that lowers perfusion pressure, thereby compromising blood supply at already low plantarflexion forces.

CLINICAL RELEVANCE

Given the potential role of ischemia in Achilles tendinopathy, our findings caution against intratendinous injections, as they may exacerbate high intratendinous resting pressure, and against prolonged postexercise tendon stretching, as the associated rise in intratendinous pressure may impair the required hyperemic response.

Nearly half of patients with chronic tendinopathy may have a neuropathic pain component, with significant differences seen between different tendon sites: a prospective cohort of more than 300 patients

Objectives

Identifying the prevalence of neuropathic pain components in patients with chronic tendinopathy conditions using the Self-Administered Leeds Assessment of Neuropathic Symptoms and Signs (S-LANSS) questionnaire.

Methods

Patients with chronic tendinopathy and ‘tendon-like’ conditions treated within a single hospital outpatient clinic specialising in tendinopathy were identified. Pain scores, plus global function patient-reported outcome measures (5-Level version of EuroQol-5 Dimension and Musculoskeletal Health Questionnaire (MSK-HQ)), were completed and compared with the S-LANSS questionnaire

Results

341 suitable patients with chronic tendinopathy and potentially similar conditions were identified. Numbers: lateral elbow tendinopathy (39), greater trochanteric pain syndrome (GTPS; 112), patellar tendinopathy (11), non-insertional Achilles tendinopathy (40), insertional Achilles tendinopathy (39), plantar fasciopathy (100). 68% were female, with a mean age of 54.0±11.3 years and a mean symptom duration of 38.1±33.7 months.

There was a mean S-LANSS score of 11.4±6.4. Overall, 47% of patients scored 12 or greater points on S-LANSS, indicating the possible presence of neuropathic pain. The highest proportion was in patients with plantar fasciopathy (61%), the lowest in those with GTPS (33%). Weak correlations were found between the S-LANSS score and MSK-HQ score, the numerical rating scale (0–10) values for ‘average pain’ and for ‘worst pain’, but not with the MSK-HQ %health value.

Conclusion

S-LANSS identified nearly half of patients with chronic tendinopathy as possibly having a neuropathic pain component. This is of unclear clinical significance but worth further study to see if/how this may relate to treatment outcomes. These results are from a single hospital clinic dealing with patients with chronic tendinopathy, without a control group or those with shorter symptom duration. However, this reinforces the probability of neuropathic pain components in at least some patients with chronic tendinopathy.