Abstract
Background Calcaneal apophysitis (Sever disease) has been reported to be the most common cause of heel pain in athletic children.
Objective The study aim was to compare plantar pressure, plantar surface contact area, distribution of body weight across the lower extremities, and prevalence of gastrocnemius ankle equinus and gastrocnemius-soleus ankle equinus (which can cause decreases in ankle dorsiflexion range of motion) in children with and without Sever disease.
Design This was a case-control study.
Methods Participants were 56 male students enrolled in a soccer academy. Twenty-eight participants had Sever disease (Sever disease group), and 28 participants were healthy (control group). Dynamic and static peak plantar pressures, plantar surface contact area, and body weight distribution were assessed with pedobarography. A goniometer was used to assess gastrocnemius and gastrocnemius-soleus ankle dorsiflexion range of motion.
Results Both maximum and average peak pressures and percentages of body weight supported by each heel were significantly higher in the symptomatic feet of participants in the Sever disease group than in the control group. Twenty-six participants with Sever disease but only 8 participants in the control group exhibited bilateral gastrocnemius ankle equinus.
Limitations A limitation of the study is that measurements were obtained from participants who were symptomatic.
Conclusions Higher heel plantar pressures under dynamic and static conditions appear to be associated with Sever disease. It is unclear, however, whether these higher pressures are a predisposing factor contributing to the disease or a result of the condition. Gastrocnemius ankle equinus also may be a predisposing factor for Sever disease. Further research is needed to identify other biomechanical factors associated with the disease to enhance prevention and treatment strategies.
The calcaneal apophysis is a cartilaginous growth center into which the Achilles tendon inserts.1,2 Apophysitis, or inflammation of an apophysis, is caused by microavulsions at the bone-cartilage junction.3 It is commonly the result of repetitive motion and overuse during periods of rapid growth. Calcaneal apophysitis was first described in 1912 by Sever4 and was later given the name Sever disease. Kvist and Heinonen5 and Kim et al6 refined the definition of Sever disease to indicate traction epiphysitis. On the basis of this definition, it is a disease most commonly associated with prepubescent children who are active in sports that involve running and jumping.7–9 The commonality of sports participation was documented by McKenzie et al,10 who conducted a retrospective study of 20 children diagnosed with Sever disease. McKenzie et al10 reported that all of the children participated in sports, with the majority participating in track and field or soccer.
Sever disease has been reported to be the most common cause of heel pain in athletic children.8,11 Orava and Puranen12 and Orava and Virtanen13 found that Sever disease comprises 16.3% and 22.7% of exertion injuries in children, respectively. The heel pain limits physical activity and may interfere with activities of daily living in young athletes. The condition is self-limiting because the calcaneal cartilage disappears at 14 to 16 years of age to permit complete calcaneal ossification.5
The etiology of Sever disease is controversial.14 Potential contributing factors include participation in high-impact sports, improper footwear, running on hard surfaces, and excessive plantar heel pressures.15 The condition also is associated with radiographic changes, including variations in the normal ossification pattern.8 Currently, the cessation of high-impact activities, thus reducing mechanical overload at the affected heel, is a standard component of treatment.16–18 Further advancement in the treatment of Sever disease is predicated on a greater understanding of factors contributing to the pathology.
Although controlling mechanical loading is a treatment strategy, we are unaware of previous work evaluating dynamic plantar pressure in children diagnosed with Sever disease. Therefore, we sought to investigate the relationship between mechanical loading and calcaneal apophysitis by measuring dynamic and static plantar pressures in young athletes with and without Sever disease. We also evaluated the distribution of body weight and plantar surface contact area between the lower extremities to determine whether asymmetrical loading is associated with the disease.
Ankle dorsiflexion range of motion in children, measured with the knee in full extension, should be at least 10 degrees.19,20 Decreased ankle dorsiflexion range of motion, also called ankle equinus, differentiates the decreased ankle range of motion that is due to gastrocnemius ankle equinus from that due to gastrocnemius-soleus ankle equinus.21 The association of gastrocnemius ankle equinus, gastrocnemius-soleus ankle equinus, and Sever disease was evaluated on the basis of previous reports of a relationship between ankle equinus deformity and Achilles tendon thickening.22
Method
Participants
Participants in this study were male students who were enrolled in a soccer school and underwent an end-of-season health screening. A total of 131 students between 8 and 15 years of age were evaluated for study eligibility. Exclusion criteria included a recent history of ankle injury, such as sprain, tendinitis, or any pathology other than Sever disease, and the presence of a neurologic condition affecting either lower extremity.
All children in this study were from the same school (a soccer-focused program). Thus, all were exposed to the same amount of training hours per week. We studied children who never had heel pain under these training conditions and children who experienced heel pain under the same training conditions. Of the 56 participants included in the study, 28 had symptomatic Sever disease. The left heel was symptomatic in 15 participants, the right heel was symptomatic in 5 participants, and 8 participants had bilateral heel symptoms, resulting in a total of 36 affected heels. Evaluation for the presence of Sever disease was performed by a podiatrist (R.B.B.V.). For diagnostic purposes, Sever disease was defined as pain with compression of the mediolateral calcaneus in the growth plate region.23 The pain had to be of at least 2 months' duration, had to coincide with physical activity, and had to be severe enough to sufficiently interfere with normal physical activity, such as walking.11 Eight children were receiving treatment when they came to the school and were not allowed to play soccer because of their level of pain. Six children were receiving treatment and were still allowed to play, and 14 children reported pain at the end of the training sessions and during our evaluation.
Twenty-eight of the 56 participants were healthy and comprised a control group. These participants were selected from the total pool of eligible children by use of a random number generator program (Epidat 3.1, Pan American Health Organization, Washington, DC). There was no difference within or between groups for time spent in sports participation, including after-school or weekend training, or in competition.
Procedure
Before the initiation of data collection, written parental consent for study participation was obtained for each participant. The Silfverskiöld test was performed to assess the ankle range of motion and differentiate gastrocnemius ankle equinus (in which the gastrocnemius muscle limits ankle dorsiflexion range of motion) from gastrocnemius-soleus ankle equinus (in which the soleus muscle limits ankle dorsiflexion range of motion).19,24 Ankle joint dorsiflexion range of motion was determined for all participants by a clinician with extensive experience in foot and ankle physical examinations.
Ankle joint dorsiflexion range of motion was assessed by measurement with a standard clinical goniometer with the knee extended and with the knee flexed. The participant lay on his or her back with the knee flexed 90 degrees. Normal ankle dorsiflexion is approximately 10 degrees with the knee extended and 20 degrees with the knee flexed.19,25,26 Thus, the definition of gastrocnemius ankle equinus was the inability of the ankle to achieve dorsiflexion of 10 degrees with the knee extended and with the knee flexed. Gastrocnemius-soleus ankle equinus was defined as the inability of the ankle to achieve dorsiflexion beyond a neutral position with the knee extended (it remained <0°) or with the knee flexed (it remained <0°).21,27,28 The reported reliability of goniometric measurement of sagittal plane ankle motion in children29 suggests that ankle dorsiflexion measures are highly variable among examiners. Measurement of gastrocnemius ankle motion is more reliable than that of soleus ankle motion, and measurement of ankle dorsiflexion with the knee extended is more reliable than that with the knee flexed.29 During measurement of ankle dorsiflexion range of motion, care was taken to maintain the subtalar joint in a neutral position to ensure that talocrural motion, not midfoot dorsiflexion (rocker bottom), was evaluated.19
Dynamic plantar pressure was measured by an independent clinician using a digital portable pressure sensor platform (Medicapteurs, Balma, France) embedded in a 5-m walkway. The technical specifications of the pressure platform are shown in the eTable. Pressure sensor measurements from the platform were accurate to the nearest 0.001 kg/cm2. Before each use, autocalibration was performed in accordance with manufacturer specifications.
During practice and testing, participants were barefoot and walked at a steady, self-selected speed. Practice trials were performed to establish a preferred walking speed for each participant and to facilitate platform striking with the entire foot. After familiarization with testing procedures was complete, data collection was initiated. A trial was considered valid when a heel-strike–toe-off pattern was observed and the walking speed was consistent.30,31 Trials that did not meet each of these criteria were not used for subsequent analysis. A 2-step method in which plantar pressure data were obtained on the second step of each foot was used for each walking trial, and data for 6 steps with each foot were collected per session from each participant.20 The mean of 6 trials per foot was used for statistical testing. Plantar pressure data collected with the 2-step method were comparable to those collected with the midgait method; therefore, the former method may be preferred for examining children because of its ease and speed of data collection.28
Static plantar pressure measurements were collected with the same pressure sensor platform as that used during dynamic conditions. During testing, participants stood on the pressure sensor platform in a natural manner while barefoot. Participants were instructed to look straight ahead and keep their arms relaxed at the side. Plantar foot pressure measurements were collected simultaneously for both feet for 30 seconds. If the participant moved during testing, then the data were discarded and the trial was repeated. Testing continued until data were collected from 6 trials during which the participant remained stationary. The participant did not know when a trial was actually being recorded. The mean of 6 valid trials per foot was used for subsequent analysis.
Data Management
Data recording was performed with a personal computer linked to the pressure sensor platform. The commercially available software program S-plate (interactive rehabilitation software) for Windows (Medicapteurs) was used for all data collection and management. Software output included pressure maps, which provided the plantar pressure magnitude (kilopascals), contact area (square centimeters), and percent body weight (%BW) distribution through each limb. The dynamic plantar pressure outline for each participant was divided into 4 distinct regions (heel, midfoot, forefoot, and toes). The heel, midfoot, and forefoot regions were defined as equal thirds of the plantar pressure outline (omitting the toes).31,32
Variables of interest for dynamic plantar pressure included the surface contact area of the forefoot and heel and the maximum and average peak pressures of the forefoot and heel. Variables of interest for static plantar pressure included the total surface contact area, surface contact area of the forefoot and heel, maximum and average peak pressures of the forefoot and heel, %BW supported by each limb, and %BW supported in the forefoot and heel.
Data Analysis
Demographic characteristics, including participant height, weight, age, and body mass index, and each of the plantar measurements were summarized as mean±standard deviation; these data were compared in children with Sever disease and children who were healthy. The ratio of means was calculated to describe the change in 2 means. Independent Student t tests were performed to determine whether differences were statistically significant. The Kolmogorov-Smirnov test was used to confirm a normal distribution for each of the plantar measurements. Measurements that were not normally distributed were tested with a nonparametric method, the Wilcoxon test. The F test was used to confirm variance equality. If equal variance could not be confirmed, then Satterthwaite approximation was used in the t tests.
To make an overall comparison, we combined the heel with more severe symptoms for the 8 participants who had bilateral heel symptoms (6 right and 2 left feet) with the feet of the 20 participants who had unilateral heel symptoms, yielding a total of 28 symptomatic feet assessed (17 left and 11 right feet). We then randomly selected 28 feet of participants without Sever disease (control feet) and matched the numbers of left and right control feet to the symptomatic feet. Thus, the comparison involved 28 symptomatic feet and 28 control feet matched by side. The association between gastrocnemius ankle equinus or gastrocnemius-soleus ankle equinus and Sever disease was evaluated with a chi-square test. In all of the analyses, statistical significance was established by a P value of less than .05. All of the analyses were performed with commercially available software (SPSS 19.0, SPSS Inc, Chicago, Illinois).
Results
There was no difference between the groups in participant age, height, or body mass index (Tab. 1). There was a statistically significant difference between the groups in the prevalence of gastrocnemius ankle equinus, with 26 of 28 participants in the Sever disease group but only 8 of 28 participants in the control group exhibiting bilateral gastrocnemius ankle equinus (P=.019). There was no difference between the groups in the prevalence of gastrocnemius-soleus ankle equinus, with 3 of 28 participants in both groups exhibiting bilateral gastrocnemius-soleus ankle equinus (P=1.000).
Participant Characteristics
When we assessed dynamic plantar pressure measurements, we found that maximum and average peak pressures were significantly higher in the affected heel of participants in the Sever disease group than in the control group (Tab. 2, Fig. 1). Maximum and average forefoot pressures were also significantly higher on the side of the affected heel of participants in the Sever disease group than in the control group (Tab. 2, Fig. 1). There was no difference between groups in surface contact area (Tab. 2). The ratios of means were consistent with the P values. The lower bound of a confidence interval for a ratio of means was greater than 1 when the mean for the Sever disease group was significantly higher than that for the control group (P<.05).
Dynamic Plantar Pressures
Dynamic plantar pressure map of the heel and forefoot. Red indicates areas with the highest plantar pressures. (A) Increase in heel pressure in a participant with Sever disease and gastrocnemius ankle equinus. (B) Normal distribution in a participant from the control group with no gastrocnemius ankle equinus.
When we assessed static plantar pressures, we found that maximum and average peak pressures were higher in both the heel and the forefoot on the involved side of participants in the Sever disease group than in the control group (Tab. 3, Fig. 2). There was no difference between groups in total, heel, or forefoot surface contact area (Tab. 3). The %BW supported by the forefoot of each foot was significantly lower in participants in the Sever disease group than in the control group for both feet (Tab. 4). The %BW supported by the heel was significantly higher in participants in the Sever disease group than in the control group for both feet (P<.001) (Tab. 4), indicating a significant load for both heels of participants in the Sever disease group.
Static Plantar Pressures
Static plantar pressure map of the heel and forefoot. Red indicates areas with the highest plantar pressures. (A) Increase in pressure in both heels in a participant with Sever disease and gastrocnemius ankle equinus. (B) Normal distribution in a participant from the control group with no gastrocnemius ankle equinus.
Body Weight Distribution
Discussion
Many authors4,5,10,12,18,33–38 have noted that children with Sever disease are regular participants in sports activities. In the present investigation, we compared the dynamic and static plantar pressures in physically active children with symptomatic Sever disease. Our comparison involved children who spent the same amounts of time in physical activity. The higher plantar pressures found in participants with a symptomatic foot and Sever disease in the present study are consistent with the findings of a previous investigation.39 Higher maximum and average peak pressures and higher %BW supported by the symptomatic heel could translate to a secondary injury to the immature calcaneal cartilage. Overload in tissues may be associated with an inability to adequately attenuate forces during gait. Lower loading rates are widely regarded as less damaging than higher loading rates. Jahss et al40 postulated that if force or repetition of force is not attenuated to below a critical level, then tissue destruction can result; healing responses can lead to further structural changes and alterations in tissue mechanics, which can increase forces on the heel during gait and lead to repetitive microtrauma to the subcalcaneal tissues.41 This scenario supports the pathophysiologic concept most often presented in the literature of Sever disease as an overuse syndrome caused by repetitive microtrauma from increased traction on the apophysis.8,42–44
Our investigation identified an unequal distribution of body weight across the limbs in participants with Sever disease. The %BW in the symptomatic heel and in the forefoot of the involved foot of participants with Sever disease was significantly higher than that in the control group. In the absence of differences in surface contact area, these findings suggest that weight-bearing strategies may be a significant factor contributing to elevated plantar pressure in the involved foot of children with Sever disease. Similarly, in a previous case-control study in which static plantar pressures and distribution of body weight across the 2 lower extremities were evaluated in children with and without calcaneal apophysitis,39 participants in the control group (who had no history of heel pain) had a more equal distribution of body weight, with each foot supporting approximately half the load. Collectively, these findings suggest that balancing weight distribution between the sides, thus reducing weight bearing by the affected limb, can serve as an effective strategy for reducing plantar pressures and the symptoms associated with Sever disease. Studies that specifically test this clinical intervention strategy are needed to validate this hypothesis.
With the 2-step method used in the present investigation, 93% (26/28) of symptomatic participants exhibited bilateral gastrocnemius ankle equinus, whereas only 10% (3/28) exhibited bilateral gastrocnemius-soleus ankle equinus. The presence of a potential equinus deformity has been reported in patients with foot and ankle complaints.21 Furthermore, gastrocnemius ankle equinus and gastrocnemius-soleus ankle equinus are not uncommon among people who are asymptomatic.21 The exact mechanism by which ankle equinus may influence Sever disease is unknown.19 The presence of gastrocnemius ankle equinus may contribute to mechanical overloading in the symptomatic heel as a consequence of soft tissue tightness. This theory is supported by an investigation performed by Szames et al,22 who evaluated 79 cases of calcaneal apophysitis in 53 patients. They found that 82.3% of the cases had ankle equinus due to muscular retraction.22 They did not, however, distinguish between gastrocnemius ankle equinus contractures and gastrocnemius-soleus ankle equinus contractures.
The pathogenesis of Sever disease has been suggested to occur through repetitive microtrauma at the apophysis as a consequence of increased musculotendinous traction. The calcaneal growth plate and the apophysis are situated in an area subject to high stress from the plantar fascia and Achilles tendon.45 The theory that a tight triceps surae muscle causes excessive tension through the Achilles tendon and increases traction on the apophysis has been commonly cited as a mechanical factor contributing to Sever disease.3,7,8,17,18,22,46–54 The same musculotendinous tightness contributes to ankle equinus deformity. The strong relationship between calcaneal apophysitis and gastrocnemius ankle equinus may explain why treatments that include a heel lift to reduce Achilles tendon tension and limitation of strenuous activity are effective in relieving symptoms in patients with Sever disease.
An important limitation of the present study is that measures were obtained from participants who were symptomatic. We could not determine whether the elevated plantar pressures and unequal body weight distributions were causative factors in disease development or consequences of the disease. Furthermore, gastrocnemius-soleus ankle equinus tightness (limited ankle dorsiflexion with knee extended and with knee flexed) typically accompanies gastrocnemius ankle equinus tightness (limited ankle dorsiflexion with knee extended but not flexed), but there is no assessment for making a distinction. When ankle dorsiflexion is limited with the knee extended and with the knee flexed, one can be certain that the soleus muscle is tight. Alternatively, the soleus muscle is not tight when dorsiflexion occurs with the knee flexed. Unfortunately, there is no optimal assessment for clarifying whether the gastrocnemius muscle is tight when the soleus muscle is also tight. Prospective, longitudinal studies are needed to determine the exact etiology of Sever disease. Furthermore, in the present investigation we evaluated a limited number of physical and biomechanical variables that we believe may be related to Sever disease. Additional work is needed to identify other factors that may be associated with the disease.
In conclusion, children with Sever disease had higher maximum and average heel plantar pressures in the involved feet than children who were healthy. These findings indicate that high heel plantar pressures may be associated with symptoms that characterize this disease. Gastrocnemius ankle equinus may be a predisposing factor for the increased plantar pressure in the heel in patients with Sever disease. This clinical indication may serve as a screening tool for determining whether further assessments, including plantar pressure measurements, are warranted.
The Bottom Line
What do we already know about this topic?
Sever disease, one of the most common causes of heel pain in athletic children, is often associated with gastrocnemius ankle equinus.
What new information does this study offer?
The study defined dynamic and static plantar pressure maps of the heel and forefoot for physically active children with and without symptomatic Sever disease and demonstrated a significant pressure increase for patients with the disease.
If you're a patient, what might these findings mean for you?
The unequal distribution of body weight across the limbs of patients with Sever disease suggests that reducing weight bearing in the affected limb can reduce plantar pressures and associated symptoms. A diagnosis of gastrocnemius ankle equinus may predispose these patients to increased plantar pressure in the heel, providing a potential screening tool to determine the need for further assessments, such as plantar pressure mapping.
Footnotes
All authors provided concept/idea/research design, data collection and analysis, and study participants. Dr Losa-Iglesias and Dr Becerro-de-Bengoa-Vallejo provided writing, project management, and facilities/equipment. Dr Becerro-de-Bengoa-Vallejo provided consultation (including review of manuscript before submission).
All study procedures conformed to the guidelines set forth in the Declaration of Helsinki, with the Research Committee of the Complutense University of Madrid, Madrid, Spain, approving the study methods.
- Received April 7, 2012.
- Accepted January 22, 2014.
- © 2014 American Physical Therapy Association
References
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