Clinical Biomechanics 29 (2014) 283–288
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Retrocalcaneal bursitis but not Achilles tendinopathy is characterized by increased pressure in the retrocalcaneal bursa Heinz Lohrer a,b,⁎, Tanja Nauck a a b
Institute for Sports Medicine, Otto-Fleck-Schneise 10, D-60528 Frankfurt am Main, Germany Institute for Sports and Sports Science, Albert-Ludwigs-University Freiburg i.Brsg., Schwarzwaldstraße 175, D-79117 Freiburg, Germany
a r t i c l e
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Article history: Received 19 July 2013 Accepted 3 December 2013 Keywords: Achilles tendon insertion Haglund's disease Retrocalcaneal bursitis Achilles tendinopathy Heel pain
a b s t r a c t Background: We questioned whether different forms of Achilles tendon overuse injuries can be differentiated by retrocalcaneal bursa pressure measurement. Methods: Retrocalcaneal bursa pressure was determined by using invasive pressure measurement in patients suffering from retrocalcaneal bursitis (n = 13) or Achilles tendinopathy (n = 15), respectively. Standardized measurements were taken with the subject lying prone. Initially, the foot and ankle was in a spontaneous, unsupported position. Then passive dorsiflexion was induced by an increasing pressure which was applied in five defined steps against the plantar forefoot. Findings: Mean pressures found in unloaded position were 30.5 (SD 28.9) mmHg in retrocalcaneal bursitis and − 9.9 (SD 17.2) mmHg in Achilles tendinopathy (p b 0.001). A stepwise increase in passive ankle dorsiflexion was associated with increasing pressure values in both groups. The differences were p = 0.009 to 0.035 when dorsiflexion was initiated with 10, 20, 30, and 40 N, respectively. Dorsiflexion induced by 50 N load resulted in a mean pressure of 113.7 (SD 124.9) mmHg for retrocalcaneal bursitis and 32.5 (SD 48.9) mmHg for Achilles tendinopathy (p = 0,051). Interpretation: Higher retrocalcaneal bursa pressure values were found in patients suffering from chronic retrocalcaneal bursitis. This result supports the hypothesis that retrocalcaneal bursa hypertension leads to an impingement lesion of the corresponding anterior Achilles tendon. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Historically the term “Achilles tendinitis” has extensively been used to characterize any acute or chronic pain syndrome of the Achilles tendon and its surrounding structures (Leach et al., 1981; Schepsis et al., 1994). Later the suffix “-itis” was abandoned as inflammation was rarely found in histologic sections from specimens with Achilles tendon overuse injuries (Jozsa and Kannus, 1997; Khan and Cook, 2000). Further classifications were proposed with respect to specific clinical and histological findings. “Achilles tendinopathy” meanwhile has been adopted to describe the clinical findings of pain, swelling, and altered performance with respect to the noninsertional Achilles tendon area (Maffulli et al, 1998; van Dijk et al., 2011). Insertional and noninsertional tendinopathy have been differentiated, but the term “insertional” still remains unclear and some authors include Haglund's disease (DeOrio and Easley, 2008; Nicholson et al., 2007). Derived from different etiologic and surgical implications most authors differentiate retrocalcaneal bursitis (which is synonymous to Haglund's syndrome) from insertional Achilles tendinopathy which is anatomically ⁎ Corresponding author at: Institute of Sports Medicine Frankfurt am Main, Otto-FleckSchneise 10, 60528 Frankfurt/Main, Germany. E-mail address: [email protected] (H. Lohrer). 0268-0033/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinbiomech.2013.12.002
located more distally and is frequently associated with a calcified posterior heel spur (Heckman et al., 2009; Jerosch and Nasef, 2003; Lohrer and Arentz, 2003; McGarvey et al., 2002; Puddu et al., 1976; Schepsis et al., 1994, 2002; van Dijk et al, 2011). We propose to adopt this classification. It clearly differentiates between lesions originating from the Achilles tendon itself (midportion Achilles tendinopathy and insertional Achilles tendinopathy) and from adjacent structures (retrocalcaneal bursitis, Haglund's syndrome). Additionally, a third entity of Achilles tendinopathy exists anatomically corresponding with retrocalcaneal bursitis. This lesion is most probably induced by an “impingement” resulting from direct pressure of the chronically inflamed retrocalcaneal bursa against the anterior Achilles tendon (Lohrer, 2010; Lohrer and Arentz, 2003; van Dijk et al., 2011). The resulting Achilles tendon pathology (tendinosis and/or degenerative partial tears) may be clinically relevant in more advanced stages of retrocalcaneal bursitis (Heckman et al., 2009). We therefore propose to keep these lesions in mind when dealing with retrocalcaneal bursitis (Sella et al., 1998). About 15–50% of the patients suffering from chronic (more than 3 months) retrocalcaneal bursitis do not profit from conservative treatment and consequently undergo operation later on (Lohrer, 2010; Nicholson et al., 2007; Sammarco and Taylor, 1998). Resection of the retrocalcaneal bursa and Haglund's tuberosity is the main focus of operative treatment for retrocalcaneal bursitis (Lohrer et al., 2008) but
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impingement lesions of the anterior Achilles tendon column may require additional tendon repair (Leitze et al., 2003; Lohrer, 2010; Lohrer and Arentz, 2003). Authors agree that retrocalcaneal bursitis is the main feature in the pathogenic chain in Haglund's disease (Heckman et al., 2009; Jerosch and Nasef, 2003; Leitze et al., 2003; Lohrer and Arentz, 2003; Ortmann and McBryde, 2007; Sella et al., 1998; van Dijk et al., 2001). To confirm clinical suspicion and indicate operation of acute and chronic compartment syndromes intracompartmental pressure measurement is generally recommended (Styf, 2004). Analog to muscular compartments bursae are also closed compartments and pressure measurement in the retrocalcaneal bursa has been shown to be feasible in a pilot study (Lohrer et al., 2011). Derived from this we hypothesized that increased pressure inside the retrocalcaneal bursa should be present in patients suffering from retrocalcaneal bursitis but not in midportion Achilles tendinopathy patients (controls). Besides this, we speculated, that pressure inside the retrocalcaneal bursa might be increased by passive dorsiflexion of the foot in both Achilles tendinopathy and retrocalcaneal bursitis patients.
resection of anterior neovascularization, and scarification and/or longitudinal splitting with excision of degenerated tissue in the midportion of the Achilles tendon. Nine of the 37 measurements were excluded following the validation procedure. So, finally 13 retrocalcaneal bursitis (13 patients) and 15 Achilles tendinopathy measurements (15 patients) were considered eligible for further analyses (Fig. 1, Table 1). Inclusion criteria for patients to be eligible for this study were age over 18 years, legal capacity, indication for midportion Achilles tendinopathy or retrocalcaneal bursitis operation, and willingness to take part in the study. Exclusion criteria were previous operation at the relevant lower leg, reduced ankle dorsiflexion when compared with the opposite side, and systemic disorders like rheumatism, diabetes mellitus, generalized hypermobility with a Beighton score of four and more (Beighton et al., 2012), and idiopathic or posttraumatic axial misalignment of the lower extremity. 2.2. Diagnostic procedure
The local ethics committee approved the study and the patients gave their written informed consent.
In line with the current literature we diagnosed both midportion Achilles tendinopathy and retrocalcaneal bursitis based on the “anatomic location, symptoms, and clinical findings” (van Dijk et al., 2011). All patients were preoperatively investigated with radiographs. However, we were unable to detect morphologic differences in posterior calcaneal anatomy or any kind of deformity between the retrocalcaneal bursitis group and Achilles tendinopathy group (Table 1).
2.1. Patients
2.3. Retrocalcaneal bursa pressure measurement
In our center the overall relation between Achilles tendinopathy and retrocalcaneal bursitis patients is 60% to 40%. The ratio of the patients to be operatively treated for recalcitrant symptoms following ineffective conservative therapy for more than 3 months is about 15% for both conditions (Lohrer, 2010). Between October 2009 and January 2013 nineteen patients underwent operative treatment for retrocalcaneal bursitis (19 measurements) and 17 patients had their Achilles tendinopathy treated operatively (18 measurements). The operative procedure for retrocalcaneal bursitis is described elsewhere (Lohrer, 2010). Achilles tendinopathy operations included paratenon resection,
The retrocalcaneal bursa pressure measurements were performed in the operating room immediately prior to the operation for Achilles tendinopathy or retrocalcaneal bursitis. A commercially available single use pressure measurement system (Combitrans Monitoring-Set arteriell, B. Braun, Melsungen, Germany) was chosen. It is certified for monitoring arterial blood pressure and relies on a piezoresistive pressure transducer. The system is easy to use and has an accuracy of ± 1 to 3% in the expected pressure range. It has been validated in a previous pilot study and a nearly perfect relation was demonstrated between the inflated pressure and the registered values (R2 = 0.9992). Precision of
2. Methods
Fig. 1. CONSORT (Consolidated Standards of Reporting Trials) flow chart for the patients through the study.
H. Lohrer, T. Nauck / Clinical Biomechanics 29 (2014) 283–288 Table 1 Demographics and imaging findings of the study population. Demographics are presented as means, standard deviations () and ranges []. MRI = Magnetic Resonance Imaging. PPL = parallel pitch lines. The height of the Haglund's protuberance is measured as the distance of the most prominent point of the Haglund's protuberance to the upper parallel pitch line. Positive values represent a greater prominence. The angle of Fowler and Philip is measured as the included angle between a tangent to plantar and posterior aspect of the calcaneus. PPL and the angle of Fowler and Philip are determined on a lateral heel radiograph (Lohrer et al., 2006). The P value is provided where reasonable. * = the lateral heel radiographs from three Achilles tendinopathy patients were not available for retrospective analyses.
Gender Right/left Age [years] Body height [m] Body weight [kg] 2
Body mass index [m/kg ] Preoperative MRI • Partial tears o Distal/Impingement o Midportion • Haglund bone bruise Preoperative ultrasound • Hypoechoic area o Distal/Impingement o Midportion • Increased fluid in the retrocalcaneal bursa Preoperative lateral heel radiography • PPL (mm) • Fowler and Philip angle (°) • Posterosuperior calcaneal o erosions/cyst formations o spur • Intratendineous calcifications • Posterior heel spur
Retrocalcaneal bursitis (n = 13)
Achilles tendinopathy (n = 15)
5 female; 8 male 10/3 48.2 (6.3) [37.0 to 60.0] 1.76 (0,07) [1.61 to 1,90] 76 (13) [59 to 99] 24.2 (2.7) [20.7 to 28.9] 8
2 female; 13 male 9/6 48.9 (11.8) [33.0 to 73.0] 1.79 (0.08) [1.66 to 1.92] 83 (13) [52 to 104] 26.2 (4.1) [18.4 to 37.4] 7
4 0 3 13
0 6 0 15
12 0 9
0 14 0
13
12*
1.1 (3.3) [−2.6 to 10.0] 63.2 (5.9) [54 to 73]
−0.3 (2.7) [−4.8 to 5.5] 64.8 (4.2) [61 to 75]
4 4 0 5
0 0 0 4
P
0.849 0.400 0.140 0.146
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achieved incorrect placement of the cannula was assumed and the measurement was excluded from further analyses. 2.4. Statistical analysis We used the Kolmogorov–Smirnoff test to verify normal distribution of all variables. An unpaired t-test analyzed the difference between the two groups for the respective dorsiflexion loads. A Linear regression analysis was calculated to describe the relationship between the retrocalcaneal bursa pressures and the respectively applied dorsiflexion loads (spontaneous position, 10 N, 20 N, 30 N, 40 N, and 50 N). For either load condition overlap was defined as aggregated number of measurements ranging between the lowest retrocalcaneal bursitis value and the highest Achilles tendinopathy value. We expressed this overlap as percentage with respect to the whole 28 measurements. A receiver operating characteristic curve analysis (ROC) was performed to determine which dorsiflexion load was most suitable to discriminate between the control (Achilles tendinopathy) and the pathological (retrocalcaneal bursitis) condition. As a result of the ROC analysis, the sensitivity and specificity of the variable “spontaneous foot position” were calculated. A respective power analysis was made to underline the statistical result. Microsoft excel and SPSS version 20.0 (SPSS Inc., Chicago, IL) were used for statistical analyses. Tests were considered statistically significant at a level of P b 0.05. 3. Results
0.247 0.424
the measurements was 0.4 to 2.2% in a cadaver experiment (Lohrer et al., 2011). All procedures were performed by the same investigator. Therefore, within this study no inter- and intraobserver reliability tests were performed. Under general anesthesia (no nerve block or muscle relaxation was performed) the patient was lying prone and the distal part of the lower leg was supported by a cushion. So the knee was flexed about 15° and the foot and ankle were unsupported. A butterfly cannula (Venofix, 21 G, Braun, Melsungen, Germany) connected with the system was filled airbubble-free with saline solution using a threeway stopcock. Using a lateral approach via the palpable soft spot between the lateral Achilles tendon border and the posterior aspect of the Haglund's protuberance the cannula was inserted into the retrocalcaneal bursa. Then pressure measurements were taken first in the spontaneous (unloaded) position of the foot and ankle and then during stepwise passive dorsiflexion. Loads of 10, 20, 30, 40, and 50 N were incrementally applied rectangular over the third metatarsal head using a standardized spring driven device (Dolormeter, EMS-Electro Medical Systems, Nyon, Switzerland). Pressure data were continuously registered and stored for later analyses using Origin Pro 7.0 (Microcal, USA). Verification of the correct intrabursal placement of the butterfly cannula was performed at the end of the measurements by injecting sterile saline solution into the retrocalcaneal bursa using a separate approach. If the system's maximum value (415.5 mmHg) was not
In the spontaneous position (5 to 10° of plantarflexion) the mean pressure in the retrocalcaneal bursa of our Achilles tendinopathy patients (control) was negative (− 9.9 mmHg). It was 40.4 mmHg lower when compared with the retrocalcaneal bursitis group (P b 0.001; Table 2, Fig. 2). Both investigated groups presented increasing retrocalcaneal bursa pressures when the ankle was passively dorsiflexed with increasing loads. This increase was proportional to the applied dorsiflexion load (R2 = 0.99 for both the retrocalcaneal bursitis and for the midportion Achilles tendinopathy group, Fig. 2). Compared with the unloaded situation the five-step increase in dorsiflexion load resulted in a mean increase of 83.2 mmHg in the retrocalcaneal bursitis group and 42.4 mmHg in the midportion Achilles tendinopathy group. The differences between the groups were significant for the spontaneous position of the foot and ankle and for the 10, 20, 30, and 40 N load application (P = b0.00.1 to 0.035). For the 50 N load the difference between the groups was P = 0.051 (Table 2, Fig. 2). The individual pressure values overlapped between the tested groups in 42.9% (spontaneous position). We found 57.1%, 57.1%, 64.3%, 60.7%, and 60.7% overlaps, when 10, 20, 30, 40, and 50 N dorsiflexion loads were applied, respectively (Fig. 3). Table 2 Results of retrocalcaneal bursa pressure measurements presented as means, (standard deviations) and [ranges] in mmHg for the investigated groups. Power for the “spontaneous position” = 1-ß = 0.983 with α = 0.05.
Spontaneous position Level 1 (10 N dorsiflexion) Level 2 (20 N dorsiflexion) Level 3 (30 N dorsiflexion) Level 4 (40 N dorsiflexion) Level 5 (50 N dorsiflexion)
Retrocalcaneal bursitis [n = 13]
Achilles tendinopathy [n = 15]
P
30.5 (28.9) [−8.7 to 79.9] 53.0 (56.1) [−28.3 to 163.4] 69.0 (73.0) [−18.4 to 217.7] 85.8 (95.5) [−12.8 to 278.3] 95.7 (99.1) [1.5 to 318.0] 113.7 (124.9) [4.2 to 405.8]
−9.9 (17.2) [−42.5 to 17.8] 1.5 (21.1) [−37.7 to 32.9] 5.8 (25.2) [−37.6 to 56.0] 16.5 (34.2) [−37.0 to 74.9] 24.8 (41.4) [−36.0 to 103.8] 32.5 (48.9) [−36.0 to 130.2]
b0.001 0.009 0.012 0.031 0.035 0.051
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Fig. 2. Linear regression graphs. Means and standard deviations of the retrocalcaneal bursitis group and the midportion Achilles tendinopathy group plotted for each applied dorsiflexion load (0 N, 10 N, 20 N, 30 N, 40 N, and 50 N) against the resulting retrocalcaneal bursa pressure values [mmHg].
With an area of 0.86 (standard error 0.07; P = 0.001; 95% confidence interval from 0.729 to 0.999) under the ROC curve the spontaneous position of the foot was identified to discriminate best between the two conditions. The resulting sensitivity (true positive rate) of the measurements was 85% and the specificity was 67% (Fig. 4).
4. Discussion We conducted this study to verify the previously unproven hypothesis of an increased retrocalcaneal bursa pressure as a characteristic feature in retrocalcaneal bursitis. The results of our study clearly confirm this hypothesis and demonstrate increased retrocalcaneal bursa pressure in patients presenting with retrocalcaneal bursitis when compared with patients suffering from midportion Achilles tendinopathy (control condition). An unforced
Fig. 3. Distribution of the individual pressures of the retrocalcaneal bursitis group and the midportion Achilles tendinopathy group. Spontaneous (unloaded) foot position. The dotted line (1.05 mmHg) represents the best cut off value to discriminate midportion Achilles tendinopathy from retrocalcaneal bursitis with a sensitivity of 85% and a specificity of 67%. The area between the continuous lines indicates the overlap (uncertain diagnostic range) between the highest midportion Achilles tendinopathy and the lowest retrocalcaneal bursitis measure.
(spontaneous) foot and ankle position was associated with negative pressure values in 9/15 (60%) in the Achilles tendinopathy group but only in 2/13 (15%) in the retrocalcaneal bursitis group. Increasing dorsiflexion by introducing controlled load against the plantar forefoot resulted in increased retrocalcaneal bursa pressure in both groups but this increase was lower in the midportion Achilles tendinopathy group (Fig. 2). The retrocalcaneal bursa is generally thought “to decrease local pressure and friction” (Jozsa and Kannus, 1997; Theobald et al., 2006). The mode of action for this pressure reduction, however, is not clear from the published research. Previous anatomic (Theobald et al., 2006) and MRI (Magnetic Resonance Imaging) investigations (Canoso et al., 1988; Theobald et al., 2006) uniformly demonstrated a “sliding
Fig. 4. ROC curve. We plotted the true positive rate against the false positive rate for the different possible cut-off points. The spontaneous (unloaded) foot position is demonstrated.
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motion” of a wedge shaped fat pat into the retrocalcaneal bursa during plantarflexion. In principle three different mechanisms are assumed to explain this phenomenon: “(1) the movement is a passive consequence of an upward displacement of the calcaneus; (2) the fatty wedge is ‘sucked’ (i.e. pulled) into the bursa to minimize pressure changes; and (3) the fat is pushed into the bursa by muscle contraction, i.e. by the muscle belly of the Flexor hallucis longus” (Theobald et al., 2006). Our results demonstrate that in a physiologic situation this fat wedge most probably follows the decreasing bursa pressure during plantarflexion. This mechanism seems to be impaired when the retrocalcaneal bursa is inflamed and filled with increased fluid (Canoso et al., 1988). Our imaging (Table 1) and pressure measurement data confirm this hypothesis by demonstrating intrabursal hypertension in retrocalcaneal bursitis patients. Contrary to this an active, muscle generated mechanism pushing the fat pat inside the bursa is unlikely from the results of our experiments, because our subjects were under general anesthesia and exclusively passive forces were applied to the plantar forefoot. Direct imaging during the measurements with increasing dorsiflexion could further confirm this assumption. We did not expect to measure negative tissue pressures in the retrocalcaneal bursa. This finding is interesting, because both the involved anatomic structures and the physiologic course of action to produce negative pressure within the retrocalcaneal bursa remain unclear. In principle, negative pressures within a bursa make sense. Formation of an intermittent suction effect could prevent the overlaying tendon from local overload leading to impaired perfusion (capillary flow), malnutrition, and dysfunction (Theobald et al., 2006). Anatomic and MRI investigations have consistently demonstrated fibrous fascicles spanned over the retrocalcaneal bursa between the anterior Achilles tendon and the Haglund's tuberosity of the calcaneus and these fibers may have the potential to be involved in the “suction effect” (Lohrer et al., 2008; Theobald et al., 2006). Negative pressure values were already demonstrated in the area anterior to the midportion Achilles tendon and increasing isometric calf muscle exercise further reduced these values (Langberg et al., 1999). Until now, physical examination (Heckman et al., 2009), confirmed by diagnostic intrabursal local anesthesia are the mainstay in diagnosing retrocalcaneal bursitis (van Dijk et al., 2011). No information is available in the literature concerning the diagnostic accuracy of imaging (MRI, ultrasound, and radiography) and diagnostic local anesthesia injection into the retrocalcaneal bursa. Therefore we regard these modalities as useful to support clinical suspicion. In this study, all included cases with retrocalcaneal bursitis were confirmed by the intraoperative findings (inflamed retrocalcaneal bursa). Our study introduces an objective functional measure that may be clinically relevant in the future. The method is easy to perform, sensitive (85%), but its specificity is decent (67%). Additionally, it is invasive and therefore it cannot presently be recommended for use in clinical routine. Measuring the retrocalcaneal bursa pressure could be useful to investigate the leading pathology, when patients suffer from both retrocalcaneal bursitis and midportion Achilles tendinopathy. To validate the correct placement of the measurement cannula, we filled up the retrocalcaneal bursa with sterile saline using a separate approach. Consequently, we judged 24% (9/37) of our measurements as dropouts. We expect that an accidental insertion of the pressure measurement probe into soft tissue causes measurement errors. It is our experience from this study that application of the probe is easy in cases with an “unaltered” retrocalcaneal bursa. We typically find this condition in Achilles tendinopathy. It is also easy to insert the probe into a fluid filled chronically inflamed retrocalcaneal bursa. However, when the bursa is fluid free and intensive scar formation and mucous inflammation are present it is more demanding to place the cannula correctly inside the bursa lumen and this is the reason not to repeat these measurements on the same patient group postoperatively. One could argue that the used measurement system itself could be a matter of debate. Errors in measurement could emerge from an
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environment, where the retrocalcaneal bursa contains only little fluid like in our control group and a direct fluid-to-fluid contact to the measurement system is not necessarily to expect. However, this is unlikely because intramuscular pressure measurements were shown to be equally efficient when a fiber optic transducer-tipped catheter or a fluid filled Teflon catheter was used (Crenshaw et al., 1998). Additionally, we demonstrated the validity of our fluid filled measurement system in a previous pilot study (Lohrer et al., 2011). We recommend further investigations to clarify the role of individual retrocalcaneal bursa pressure for prognostic reasons. Prospective epidemiologic data will reveal the clinical importance of retrocalcaneal bursa pressure. Analog to the procedure in chronic compartment syndromes pressure measurements during or/and after specific functional tests (e.g. heel raises or defined running activity) may be more helpful than merely passive testing. In clinical practices, intracompartmental pressure measurements for compartment syndromes are not well reproducible and the literature reveals no clinical reliability studies. Nevertheless, it is considered useful in practice. inter- and intraobserver reliability and individual side to side difference testing was beyond the scope of this investigation but should be analyzed in future studies. In chronic compartment syndromes the measured intracompartmental pressure values of the symptomatic and normal individuals are reported to overlap at rest, during, and after activity. Therefore the reliability and consequently the diagnostic value of intracompartmental pressure measurements for chronic compartment syndromes are regarded to be “weak” (Aweid et al., 2012). Analog to this the present study demonstrates a substantial overlap between bursa pressure values from the retrocalcaneal bursitis and the Achilles tendinopathy patients. So, the diagnostic value of an individual retrocalcaneal bursa pressure measurement procedure is limited. The unphysiologic positioning of our subjects gives a weakness of our study. Probably the pressure obtained during an upright position is different. Additionally, active influences of the surrounding muscles cannot be determined in the anesthetized patient. We chose midportion Achilles tendinopathy as control condition and expected an unaltered retrocalcaneal bursa in these patients. However, occasionally both conditions are present within one patient. Therefore, minor bursa pathologies have to be considered in the Achilles tendinopathy group. Consequently, further research should focus also on normative values in subjects without any Achilles tendon related pathology. 5. Conclusions Our findings suggest that higher retrocalcaneal bursa pressure values specifically characterize patients suffering from chronic retrocalcaneal bursitis. We assume that this pressure is the main pathologic agent in the pathway to retrocalcaneal bursitis. This retrocalcaneal bursa hypertension may further lead to an impingement lesion affecting the corresponding anterior Achilles tendon. Acknowledgment The Hessian Ministry for Interior and Sports supported this project. This sponsor was not involved in the discharge or organization of the study. The authors thank Dr. H. Ackermann from the “Institut für Biostatistik und Mathematische Modellierung, Zentrum der Gesundheitswissenschaften, Klinikum und Fachbereich Medizin der Goethe-Universität Frankfurt am Main, Germany” for his statistical support. References Aweid, O., Del Buono, A., Malliaras, P., Iqbal, H., Morrissey, D., Maffulli, N., Padhiar, N., 2012. Systematic review and recommendations for intracompartmental pressure monitoring in diagnosing chronic exertional compartment syndrome of the leg. Clin. J. Sport Med. 22, 356–370.
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Lohrer, H., Raabe, T., Nauck, T., Arentz, S., 2011. Minimally invasive retrocalcaneal bursa pressure measurement: development and pilot application. Arch. Orthop. Trauma Surg. 131, 719–723. Maffulli, N., Khan, K.M., Puddu, G., 1998. Overuse tendon conditions: time to change a confusing terminology. Arthroscopy 14, 840–843. McGarvey, W.C., Palumbo, R.C., Baxter, D.E., Leibman, B.D., 2002. Insertional Achilles tendinosis: surgical treatment through a central tendon splitting approach. Foot Ankle Int. 23, 19–25. Nicholson, C.W., Berlet, G.C., Lee, T.H., 2007. Prediction of the success of nonoperative treatment of insertional Achilles tendinosis based on MRI. Foot Ankle Int. 28, 472–477. Ortmann, F.W., McBryde, A.M., 2007. Endoscopic bony and soft-tissue decompression of the retrocalcaneal space for the treatment of Haglund deformity and retrocalcaneal bursitis. Foot Ankle Int. 28, 149–153. Puddu, G., Ippolito, E., Postacchini, F., 1976. A classification of Achilles tendon disease. Am. J. Sports Med. 4, 145–150. Sammarco, G.J., Taylor, A.L., 1998. Operative management of Haglund's deformity in the nonathlete: a retrospective study. Foot Ankle Int. 19, 724–729. Schepsis, A.A., Wagner, C., Leach, R.E., 1994. Surgical management of Achilles tendon overuse injuries. A long-term follow-up study. Am. J. Sports Med. 22, 611–619. Schepsis, A.A., Jones, H., Haas, A.L., 2002. Achilles tendon disorders in athletes. Am. J. Sports Med. 30, 287–305. Sella, E.J., Caminear, D.S., McLarney, E.A., 1998. Haglund's syndrome. J. Foot Ankle Surg. 37, 110–114. Styf, J., 2004. Compartment Syndromes: Diagnosis, Treatment, and Complications. CRC press, Boca Raton. Theobald, P., Bydder, G., Dent, C., Nokes, L., Pugh, N., Benjamin, M., 2006. The functional anatomy of Kager's fat pad in relation to retrocalcaneal problems and other hindfoot disorders. J. Anat. 208, 91–97. van Dijk, C.N., van Dyk, G.E., Scholten, P.E., Kort, N.P., 2001. Endoscopic calcaneoplasty. Am. J. Sports Med. 29, 185–189. van Dijk, C.N., van Sterkenburg, M.N., Wiegerinck, J.I., Karlsson, J., Maffulli, N., 2011. Terminology for Achilles tendon related disorders. Knee Surg. Sports Traumatol. Arthrosc. 19, 835–841.
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Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech
Retrocalcaneal bursitis but not Achilles tendinopathy is characterized by increased pressure in the retrocalcaneal bursa Heinz Lohrer a,b,⁎, Tanja Nauck a a b
Institute for Sports Medicine, Otto-Fleck-Schneise 10, D-60528 Frankfurt am Main, Germany Institute for Sports and Sports Science, Albert-Ludwigs-University Freiburg i.Brsg., Schwarzwaldstraße 175, D-79117 Freiburg, Germany
a r t i c l e
i n f o
Article history: Received 19 July 2013 Accepted 3 December 2013 Keywords: Achilles tendon insertion Haglund's disease Retrocalcaneal bursitis Achilles tendinopathy Heel pain
a b s t r a c t Background: We questioned whether different forms of Achilles tendon overuse injuries can be differentiated by retrocalcaneal bursa pressure measurement. Methods: Retrocalcaneal bursa pressure was determined by using invasive pressure measurement in patients suffering from retrocalcaneal bursitis (n = 13) or Achilles tendinopathy (n = 15), respectively. Standardized measurements were taken with the subject lying prone. Initially, the foot and ankle was in a spontaneous, unsupported position. Then passive dorsiflexion was induced by an increasing pressure which was applied in five defined steps against the plantar forefoot. Findings: Mean pressures found in unloaded position were 30.5 (SD 28.9) mmHg in retrocalcaneal bursitis and − 9.9 (SD 17.2) mmHg in Achilles tendinopathy (p b 0.001). A stepwise increase in passive ankle dorsiflexion was associated with increasing pressure values in both groups. The differences were p = 0.009 to 0.035 when dorsiflexion was initiated with 10, 20, 30, and 40 N, respectively. Dorsiflexion induced by 50 N load resulted in a mean pressure of 113.7 (SD 124.9) mmHg for retrocalcaneal bursitis and 32.5 (SD 48.9) mmHg for Achilles tendinopathy (p = 0,051). Interpretation: Higher retrocalcaneal bursa pressure values were found in patients suffering from chronic retrocalcaneal bursitis. This result supports the hypothesis that retrocalcaneal bursa hypertension leads to an impingement lesion of the corresponding anterior Achilles tendon. © 2013 Elsevier Ltd. All rights reserved.
1. Introduction Historically the term “Achilles tendinitis” has extensively been used to characterize any acute or chronic pain syndrome of the Achilles tendon and its surrounding structures (Leach et al., 1981; Schepsis et al., 1994). Later the suffix “-itis” was abandoned as inflammation was rarely found in histologic sections from specimens with Achilles tendon overuse injuries (Jozsa and Kannus, 1997; Khan and Cook, 2000). Further classifications were proposed with respect to specific clinical and histological findings. “Achilles tendinopathy” meanwhile has been adopted to describe the clinical findings of pain, swelling, and altered performance with respect to the noninsertional Achilles tendon area (Maffulli et al, 1998; van Dijk et al., 2011). Insertional and noninsertional tendinopathy have been differentiated, but the term “insertional” still remains unclear and some authors include Haglund's disease (DeOrio and Easley, 2008; Nicholson et al., 2007). Derived from different etiologic and surgical implications most authors differentiate retrocalcaneal bursitis (which is synonymous to Haglund's syndrome) from insertional Achilles tendinopathy which is anatomically ⁎ Corresponding author at: Institute of Sports Medicine Frankfurt am Main, Otto-FleckSchneise 10, 60528 Frankfurt/Main, Germany. E-mail address: [email protected] (H. Lohrer). 0268-0033/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinbiomech.2013.12.002
located more distally and is frequently associated with a calcified posterior heel spur (Heckman et al., 2009; Jerosch and Nasef, 2003; Lohrer and Arentz, 2003; McGarvey et al., 2002; Puddu et al., 1976; Schepsis et al., 1994, 2002; van Dijk et al, 2011). We propose to adopt this classification. It clearly differentiates between lesions originating from the Achilles tendon itself (midportion Achilles tendinopathy and insertional Achilles tendinopathy) and from adjacent structures (retrocalcaneal bursitis, Haglund's syndrome). Additionally, a third entity of Achilles tendinopathy exists anatomically corresponding with retrocalcaneal bursitis. This lesion is most probably induced by an “impingement” resulting from direct pressure of the chronically inflamed retrocalcaneal bursa against the anterior Achilles tendon (Lohrer, 2010; Lohrer and Arentz, 2003; van Dijk et al., 2011). The resulting Achilles tendon pathology (tendinosis and/or degenerative partial tears) may be clinically relevant in more advanced stages of retrocalcaneal bursitis (Heckman et al., 2009). We therefore propose to keep these lesions in mind when dealing with retrocalcaneal bursitis (Sella et al., 1998). About 15–50% of the patients suffering from chronic (more than 3 months) retrocalcaneal bursitis do not profit from conservative treatment and consequently undergo operation later on (Lohrer, 2010; Nicholson et al., 2007; Sammarco and Taylor, 1998). Resection of the retrocalcaneal bursa and Haglund's tuberosity is the main focus of operative treatment for retrocalcaneal bursitis (Lohrer et al., 2008) but
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impingement lesions of the anterior Achilles tendon column may require additional tendon repair (Leitze et al., 2003; Lohrer, 2010; Lohrer and Arentz, 2003). Authors agree that retrocalcaneal bursitis is the main feature in the pathogenic chain in Haglund's disease (Heckman et al., 2009; Jerosch and Nasef, 2003; Leitze et al., 2003; Lohrer and Arentz, 2003; Ortmann and McBryde, 2007; Sella et al., 1998; van Dijk et al., 2001). To confirm clinical suspicion and indicate operation of acute and chronic compartment syndromes intracompartmental pressure measurement is generally recommended (Styf, 2004). Analog to muscular compartments bursae are also closed compartments and pressure measurement in the retrocalcaneal bursa has been shown to be feasible in a pilot study (Lohrer et al., 2011). Derived from this we hypothesized that increased pressure inside the retrocalcaneal bursa should be present in patients suffering from retrocalcaneal bursitis but not in midportion Achilles tendinopathy patients (controls). Besides this, we speculated, that pressure inside the retrocalcaneal bursa might be increased by passive dorsiflexion of the foot in both Achilles tendinopathy and retrocalcaneal bursitis patients.
resection of anterior neovascularization, and scarification and/or longitudinal splitting with excision of degenerated tissue in the midportion of the Achilles tendon. Nine of the 37 measurements were excluded following the validation procedure. So, finally 13 retrocalcaneal bursitis (13 patients) and 15 Achilles tendinopathy measurements (15 patients) were considered eligible for further analyses (Fig. 1, Table 1). Inclusion criteria for patients to be eligible for this study were age over 18 years, legal capacity, indication for midportion Achilles tendinopathy or retrocalcaneal bursitis operation, and willingness to take part in the study. Exclusion criteria were previous operation at the relevant lower leg, reduced ankle dorsiflexion when compared with the opposite side, and systemic disorders like rheumatism, diabetes mellitus, generalized hypermobility with a Beighton score of four and more (Beighton et al., 2012), and idiopathic or posttraumatic axial misalignment of the lower extremity. 2.2. Diagnostic procedure
The local ethics committee approved the study and the patients gave their written informed consent.
In line with the current literature we diagnosed both midportion Achilles tendinopathy and retrocalcaneal bursitis based on the “anatomic location, symptoms, and clinical findings” (van Dijk et al., 2011). All patients were preoperatively investigated with radiographs. However, we were unable to detect morphologic differences in posterior calcaneal anatomy or any kind of deformity between the retrocalcaneal bursitis group and Achilles tendinopathy group (Table 1).
2.1. Patients
2.3. Retrocalcaneal bursa pressure measurement
In our center the overall relation between Achilles tendinopathy and retrocalcaneal bursitis patients is 60% to 40%. The ratio of the patients to be operatively treated for recalcitrant symptoms following ineffective conservative therapy for more than 3 months is about 15% for both conditions (Lohrer, 2010). Between October 2009 and January 2013 nineteen patients underwent operative treatment for retrocalcaneal bursitis (19 measurements) and 17 patients had their Achilles tendinopathy treated operatively (18 measurements). The operative procedure for retrocalcaneal bursitis is described elsewhere (Lohrer, 2010). Achilles tendinopathy operations included paratenon resection,
The retrocalcaneal bursa pressure measurements were performed in the operating room immediately prior to the operation for Achilles tendinopathy or retrocalcaneal bursitis. A commercially available single use pressure measurement system (Combitrans Monitoring-Set arteriell, B. Braun, Melsungen, Germany) was chosen. It is certified for monitoring arterial blood pressure and relies on a piezoresistive pressure transducer. The system is easy to use and has an accuracy of ± 1 to 3% in the expected pressure range. It has been validated in a previous pilot study and a nearly perfect relation was demonstrated between the inflated pressure and the registered values (R2 = 0.9992). Precision of
2. Methods
Fig. 1. CONSORT (Consolidated Standards of Reporting Trials) flow chart for the patients through the study.
H. Lohrer, T. Nauck / Clinical Biomechanics 29 (2014) 283–288 Table 1 Demographics and imaging findings of the study population. Demographics are presented as means, standard deviations () and ranges []. MRI = Magnetic Resonance Imaging. PPL = parallel pitch lines. The height of the Haglund's protuberance is measured as the distance of the most prominent point of the Haglund's protuberance to the upper parallel pitch line. Positive values represent a greater prominence. The angle of Fowler and Philip is measured as the included angle between a tangent to plantar and posterior aspect of the calcaneus. PPL and the angle of Fowler and Philip are determined on a lateral heel radiograph (Lohrer et al., 2006). The P value is provided where reasonable. * = the lateral heel radiographs from three Achilles tendinopathy patients were not available for retrospective analyses.
Gender Right/left Age [years] Body height [m] Body weight [kg] 2
Body mass index [m/kg ] Preoperative MRI • Partial tears o Distal/Impingement o Midportion • Haglund bone bruise Preoperative ultrasound • Hypoechoic area o Distal/Impingement o Midportion • Increased fluid in the retrocalcaneal bursa Preoperative lateral heel radiography • PPL (mm) • Fowler and Philip angle (°) • Posterosuperior calcaneal o erosions/cyst formations o spur • Intratendineous calcifications • Posterior heel spur
Retrocalcaneal bursitis (n = 13)
Achilles tendinopathy (n = 15)
5 female; 8 male 10/3 48.2 (6.3) [37.0 to 60.0] 1.76 (0,07) [1.61 to 1,90] 76 (13) [59 to 99] 24.2 (2.7) [20.7 to 28.9] 8
2 female; 13 male 9/6 48.9 (11.8) [33.0 to 73.0] 1.79 (0.08) [1.66 to 1.92] 83 (13) [52 to 104] 26.2 (4.1) [18.4 to 37.4] 7
4 0 3 13
0 6 0 15
12 0 9
0 14 0
13
12*
1.1 (3.3) [−2.6 to 10.0] 63.2 (5.9) [54 to 73]
−0.3 (2.7) [−4.8 to 5.5] 64.8 (4.2) [61 to 75]
4 4 0 5
0 0 0 4
P
0.849 0.400 0.140 0.146
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achieved incorrect placement of the cannula was assumed and the measurement was excluded from further analyses. 2.4. Statistical analysis We used the Kolmogorov–Smirnoff test to verify normal distribution of all variables. An unpaired t-test analyzed the difference between the two groups for the respective dorsiflexion loads. A Linear regression analysis was calculated to describe the relationship between the retrocalcaneal bursa pressures and the respectively applied dorsiflexion loads (spontaneous position, 10 N, 20 N, 30 N, 40 N, and 50 N). For either load condition overlap was defined as aggregated number of measurements ranging between the lowest retrocalcaneal bursitis value and the highest Achilles tendinopathy value. We expressed this overlap as percentage with respect to the whole 28 measurements. A receiver operating characteristic curve analysis (ROC) was performed to determine which dorsiflexion load was most suitable to discriminate between the control (Achilles tendinopathy) and the pathological (retrocalcaneal bursitis) condition. As a result of the ROC analysis, the sensitivity and specificity of the variable “spontaneous foot position” were calculated. A respective power analysis was made to underline the statistical result. Microsoft excel and SPSS version 20.0 (SPSS Inc., Chicago, IL) were used for statistical analyses. Tests were considered statistically significant at a level of P b 0.05. 3. Results
0.247 0.424
the measurements was 0.4 to 2.2% in a cadaver experiment (Lohrer et al., 2011). All procedures were performed by the same investigator. Therefore, within this study no inter- and intraobserver reliability tests were performed. Under general anesthesia (no nerve block or muscle relaxation was performed) the patient was lying prone and the distal part of the lower leg was supported by a cushion. So the knee was flexed about 15° and the foot and ankle were unsupported. A butterfly cannula (Venofix, 21 G, Braun, Melsungen, Germany) connected with the system was filled airbubble-free with saline solution using a threeway stopcock. Using a lateral approach via the palpable soft spot between the lateral Achilles tendon border and the posterior aspect of the Haglund's protuberance the cannula was inserted into the retrocalcaneal bursa. Then pressure measurements were taken first in the spontaneous (unloaded) position of the foot and ankle and then during stepwise passive dorsiflexion. Loads of 10, 20, 30, 40, and 50 N were incrementally applied rectangular over the third metatarsal head using a standardized spring driven device (Dolormeter, EMS-Electro Medical Systems, Nyon, Switzerland). Pressure data were continuously registered and stored for later analyses using Origin Pro 7.0 (Microcal, USA). Verification of the correct intrabursal placement of the butterfly cannula was performed at the end of the measurements by injecting sterile saline solution into the retrocalcaneal bursa using a separate approach. If the system's maximum value (415.5 mmHg) was not
In the spontaneous position (5 to 10° of plantarflexion) the mean pressure in the retrocalcaneal bursa of our Achilles tendinopathy patients (control) was negative (− 9.9 mmHg). It was 40.4 mmHg lower when compared with the retrocalcaneal bursitis group (P b 0.001; Table 2, Fig. 2). Both investigated groups presented increasing retrocalcaneal bursa pressures when the ankle was passively dorsiflexed with increasing loads. This increase was proportional to the applied dorsiflexion load (R2 = 0.99 for both the retrocalcaneal bursitis and for the midportion Achilles tendinopathy group, Fig. 2). Compared with the unloaded situation the five-step increase in dorsiflexion load resulted in a mean increase of 83.2 mmHg in the retrocalcaneal bursitis group and 42.4 mmHg in the midportion Achilles tendinopathy group. The differences between the groups were significant for the spontaneous position of the foot and ankle and for the 10, 20, 30, and 40 N load application (P = b0.00.1 to 0.035). For the 50 N load the difference between the groups was P = 0.051 (Table 2, Fig. 2). The individual pressure values overlapped between the tested groups in 42.9% (spontaneous position). We found 57.1%, 57.1%, 64.3%, 60.7%, and 60.7% overlaps, when 10, 20, 30, 40, and 50 N dorsiflexion loads were applied, respectively (Fig. 3). Table 2 Results of retrocalcaneal bursa pressure measurements presented as means, (standard deviations) and [ranges] in mmHg for the investigated groups. Power for the “spontaneous position” = 1-ß = 0.983 with α = 0.05.
Spontaneous position Level 1 (10 N dorsiflexion) Level 2 (20 N dorsiflexion) Level 3 (30 N dorsiflexion) Level 4 (40 N dorsiflexion) Level 5 (50 N dorsiflexion)
Retrocalcaneal bursitis [n = 13]
Achilles tendinopathy [n = 15]
P
30.5 (28.9) [−8.7 to 79.9] 53.0 (56.1) [−28.3 to 163.4] 69.0 (73.0) [−18.4 to 217.7] 85.8 (95.5) [−12.8 to 278.3] 95.7 (99.1) [1.5 to 318.0] 113.7 (124.9) [4.2 to 405.8]
−9.9 (17.2) [−42.5 to 17.8] 1.5 (21.1) [−37.7 to 32.9] 5.8 (25.2) [−37.6 to 56.0] 16.5 (34.2) [−37.0 to 74.9] 24.8 (41.4) [−36.0 to 103.8] 32.5 (48.9) [−36.0 to 130.2]
b0.001 0.009 0.012 0.031 0.035 0.051
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Fig. 2. Linear regression graphs. Means and standard deviations of the retrocalcaneal bursitis group and the midportion Achilles tendinopathy group plotted for each applied dorsiflexion load (0 N, 10 N, 20 N, 30 N, 40 N, and 50 N) against the resulting retrocalcaneal bursa pressure values [mmHg].
With an area of 0.86 (standard error 0.07; P = 0.001; 95% confidence interval from 0.729 to 0.999) under the ROC curve the spontaneous position of the foot was identified to discriminate best between the two conditions. The resulting sensitivity (true positive rate) of the measurements was 85% and the specificity was 67% (Fig. 4).
4. Discussion We conducted this study to verify the previously unproven hypothesis of an increased retrocalcaneal bursa pressure as a characteristic feature in retrocalcaneal bursitis. The results of our study clearly confirm this hypothesis and demonstrate increased retrocalcaneal bursa pressure in patients presenting with retrocalcaneal bursitis when compared with patients suffering from midportion Achilles tendinopathy (control condition). An unforced
Fig. 3. Distribution of the individual pressures of the retrocalcaneal bursitis group and the midportion Achilles tendinopathy group. Spontaneous (unloaded) foot position. The dotted line (1.05 mmHg) represents the best cut off value to discriminate midportion Achilles tendinopathy from retrocalcaneal bursitis with a sensitivity of 85% and a specificity of 67%. The area between the continuous lines indicates the overlap (uncertain diagnostic range) between the highest midportion Achilles tendinopathy and the lowest retrocalcaneal bursitis measure.
(spontaneous) foot and ankle position was associated with negative pressure values in 9/15 (60%) in the Achilles tendinopathy group but only in 2/13 (15%) in the retrocalcaneal bursitis group. Increasing dorsiflexion by introducing controlled load against the plantar forefoot resulted in increased retrocalcaneal bursa pressure in both groups but this increase was lower in the midportion Achilles tendinopathy group (Fig. 2). The retrocalcaneal bursa is generally thought “to decrease local pressure and friction” (Jozsa and Kannus, 1997; Theobald et al., 2006). The mode of action for this pressure reduction, however, is not clear from the published research. Previous anatomic (Theobald et al., 2006) and MRI (Magnetic Resonance Imaging) investigations (Canoso et al., 1988; Theobald et al., 2006) uniformly demonstrated a “sliding
Fig. 4. ROC curve. We plotted the true positive rate against the false positive rate for the different possible cut-off points. The spontaneous (unloaded) foot position is demonstrated.
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motion” of a wedge shaped fat pat into the retrocalcaneal bursa during plantarflexion. In principle three different mechanisms are assumed to explain this phenomenon: “(1) the movement is a passive consequence of an upward displacement of the calcaneus; (2) the fatty wedge is ‘sucked’ (i.e. pulled) into the bursa to minimize pressure changes; and (3) the fat is pushed into the bursa by muscle contraction, i.e. by the muscle belly of the Flexor hallucis longus” (Theobald et al., 2006). Our results demonstrate that in a physiologic situation this fat wedge most probably follows the decreasing bursa pressure during plantarflexion. This mechanism seems to be impaired when the retrocalcaneal bursa is inflamed and filled with increased fluid (Canoso et al., 1988). Our imaging (Table 1) and pressure measurement data confirm this hypothesis by demonstrating intrabursal hypertension in retrocalcaneal bursitis patients. Contrary to this an active, muscle generated mechanism pushing the fat pat inside the bursa is unlikely from the results of our experiments, because our subjects were under general anesthesia and exclusively passive forces were applied to the plantar forefoot. Direct imaging during the measurements with increasing dorsiflexion could further confirm this assumption. We did not expect to measure negative tissue pressures in the retrocalcaneal bursa. This finding is interesting, because both the involved anatomic structures and the physiologic course of action to produce negative pressure within the retrocalcaneal bursa remain unclear. In principle, negative pressures within a bursa make sense. Formation of an intermittent suction effect could prevent the overlaying tendon from local overload leading to impaired perfusion (capillary flow), malnutrition, and dysfunction (Theobald et al., 2006). Anatomic and MRI investigations have consistently demonstrated fibrous fascicles spanned over the retrocalcaneal bursa between the anterior Achilles tendon and the Haglund's tuberosity of the calcaneus and these fibers may have the potential to be involved in the “suction effect” (Lohrer et al., 2008; Theobald et al., 2006). Negative pressure values were already demonstrated in the area anterior to the midportion Achilles tendon and increasing isometric calf muscle exercise further reduced these values (Langberg et al., 1999). Until now, physical examination (Heckman et al., 2009), confirmed by diagnostic intrabursal local anesthesia are the mainstay in diagnosing retrocalcaneal bursitis (van Dijk et al., 2011). No information is available in the literature concerning the diagnostic accuracy of imaging (MRI, ultrasound, and radiography) and diagnostic local anesthesia injection into the retrocalcaneal bursa. Therefore we regard these modalities as useful to support clinical suspicion. In this study, all included cases with retrocalcaneal bursitis were confirmed by the intraoperative findings (inflamed retrocalcaneal bursa). Our study introduces an objective functional measure that may be clinically relevant in the future. The method is easy to perform, sensitive (85%), but its specificity is decent (67%). Additionally, it is invasive and therefore it cannot presently be recommended for use in clinical routine. Measuring the retrocalcaneal bursa pressure could be useful to investigate the leading pathology, when patients suffer from both retrocalcaneal bursitis and midportion Achilles tendinopathy. To validate the correct placement of the measurement cannula, we filled up the retrocalcaneal bursa with sterile saline using a separate approach. Consequently, we judged 24% (9/37) of our measurements as dropouts. We expect that an accidental insertion of the pressure measurement probe into soft tissue causes measurement errors. It is our experience from this study that application of the probe is easy in cases with an “unaltered” retrocalcaneal bursa. We typically find this condition in Achilles tendinopathy. It is also easy to insert the probe into a fluid filled chronically inflamed retrocalcaneal bursa. However, when the bursa is fluid free and intensive scar formation and mucous inflammation are present it is more demanding to place the cannula correctly inside the bursa lumen and this is the reason not to repeat these measurements on the same patient group postoperatively. One could argue that the used measurement system itself could be a matter of debate. Errors in measurement could emerge from an
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environment, where the retrocalcaneal bursa contains only little fluid like in our control group and a direct fluid-to-fluid contact to the measurement system is not necessarily to expect. However, this is unlikely because intramuscular pressure measurements were shown to be equally efficient when a fiber optic transducer-tipped catheter or a fluid filled Teflon catheter was used (Crenshaw et al., 1998). Additionally, we demonstrated the validity of our fluid filled measurement system in a previous pilot study (Lohrer et al., 2011). We recommend further investigations to clarify the role of individual retrocalcaneal bursa pressure for prognostic reasons. Prospective epidemiologic data will reveal the clinical importance of retrocalcaneal bursa pressure. Analog to the procedure in chronic compartment syndromes pressure measurements during or/and after specific functional tests (e.g. heel raises or defined running activity) may be more helpful than merely passive testing. In clinical practices, intracompartmental pressure measurements for compartment syndromes are not well reproducible and the literature reveals no clinical reliability studies. Nevertheless, it is considered useful in practice. inter- and intraobserver reliability and individual side to side difference testing was beyond the scope of this investigation but should be analyzed in future studies. In chronic compartment syndromes the measured intracompartmental pressure values of the symptomatic and normal individuals are reported to overlap at rest, during, and after activity. Therefore the reliability and consequently the diagnostic value of intracompartmental pressure measurements for chronic compartment syndromes are regarded to be “weak” (Aweid et al., 2012). Analog to this the present study demonstrates a substantial overlap between bursa pressure values from the retrocalcaneal bursitis and the Achilles tendinopathy patients. So, the diagnostic value of an individual retrocalcaneal bursa pressure measurement procedure is limited. The unphysiologic positioning of our subjects gives a weakness of our study. Probably the pressure obtained during an upright position is different. Additionally, active influences of the surrounding muscles cannot be determined in the anesthetized patient. We chose midportion Achilles tendinopathy as control condition and expected an unaltered retrocalcaneal bursa in these patients. However, occasionally both conditions are present within one patient. Therefore, minor bursa pathologies have to be considered in the Achilles tendinopathy group. Consequently, further research should focus also on normative values in subjects without any Achilles tendon related pathology. 5. Conclusions Our findings suggest that higher retrocalcaneal bursa pressure values specifically characterize patients suffering from chronic retrocalcaneal bursitis. We assume that this pressure is the main pathologic agent in the pathway to retrocalcaneal bursitis. This retrocalcaneal bursa hypertension may further lead to an impingement lesion affecting the corresponding anterior Achilles tendon. Acknowledgment The Hessian Ministry for Interior and Sports supported this project. This sponsor was not involved in the discharge or organization of the study. The authors thank Dr. H. Ackermann from the “Institut für Biostatistik und Mathematische Modellierung, Zentrum der Gesundheitswissenschaften, Klinikum und Fachbereich Medizin der Goethe-Universität Frankfurt am Main, Germany” for his statistical support. References Aweid, O., Del Buono, A., Malliaras, P., Iqbal, H., Morrissey, D., Maffulli, N., Padhiar, N., 2012. Systematic review and recommendations for intracompartmental pressure monitoring in diagnosing chronic exertional compartment syndrome of the leg. Clin. J. Sport Med. 22, 356–370.
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