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Human Subjects Committee approval given by the University of Kansas Medical Center #11903
We would like to thank Kevin Dodd, Kate Dillon and Tiffany Kramer for their help in data collection for this project.
Medial shin pain (MSP) is a common complaint that may stop an athlete from running. No previous study has identified deficits in pelvic, hip or knee motion as potential contributing factors to MSP. The purpose of this study was to investigate the differences in kinematics during running between uninjured athletes and those with MSP. Secondary analyses investigated differences in limbs between groups and differences between sexes.
This case-control study investigated fourteen runners aged 18–40 years old with a history of unilateral MSP and fourteen runner controls. Three dimensional lower quarter kinematics were captured as runners ran on a treadmill. Specifically, peak hip internal rotation (IR), frontal plane pelvic tilt (PT) excursion, and knee flexion were examined.
Groups were similar in age, mass, height, and training mileage. Subjects with a history of MSP demonstrated significantly greater frontal plane PT (P = 0.002, Effect size = 0.55) and peak hip IR (P = 0.004, Effect size = 0.51); and less knee flexion (P = 0.02, Effect size = 0.46) than the control group. No significant difference was found in kinematics of the MSP group during their involved side stance phase as compared to their non-involved side.
Runners with MSP displayed greater PT excursion, peak hip IR, and decreased knee flexion while running as compared to a control group. These results should help guide treatment for the running athlete that experiences MSP.
Over 38 million Americans choose running as their mode of exercise. Athletes that participate in running sports are commonly seen by a sports medicine specialist for overuse injuries involving the lower extremity.1 Medial shin pain (MSP) describes a specific overuse injury which produces pain along the posteromedial aspect of the distal two-thirds of the tibia. For purposes of this study, it excludes diagnoses of stress fracture or posterior compartment -syndrome.1,2 The sports in which athletes are most commonly afflicted are cross-country, track, basketball, and volleyball. The incidence of MSP in long distance runners can be as high as 16.8% and is more prevalent in female runners.3 In the military, the incidence has been reported to be as high as 35% with females being injured more commonly than males.3,4
Several risk factors have been suggested in the literature as causative of MSP.2,5,6 These factors are diverse and some are contradictory. These factors can be divided into three subsets of etiology including pathomechanics, training error, and body mass. The most widely studied subset is pathomechanics. Examples of all factors include pes cavus,7 pes planus,6 pronation velocity,1 time to maximum pronation,8 prolonged rearfoot pronation,8 limited ankle motion,2 sex,5 bone mineral density,9 menstrual dysfunction, previous injury10,11 and increased impact forces while running.12 Of all these factors, the only factor that is consistently linked to MSP is a previous injury.
Faulty biomechanics can be very detrimental to the running athlete when they result in pain. Biomechanics in the lower extremity hinge on the principle of the kinematic chain. The kinematic chain is composed of successively linked joint segments. Each segment transfers forces and motions to the neighboring joints in a predictable pattern.13 Therefore, in theory, when dysfunction occurs at a specific joint, the dysfunction will transfer to the following joint in sequence. For example, when decreased motion occurs at the ankle during weight-bearing activity, both the knee and hip will feel the effects of the dysfunction and attempt to balance out the lost motion by increasing their ranges of motion. Attempts to compensate for the faulty mechanics of the ankle will cause the knee and hip to function in a new pattern. This transfer of faulty forces and movement can lead to injuries. This principle holds true for any joint in the chain during weight-bearing; therefore pelvic and hip range of motion are possible contributors to injury in the lower extremity. Research on the biomechanical relationship of the pelvis and hip with respect to their influence on MSP is scarce to non-existent.
Specific to running and MSP, proximal mechanical faults will affect lower limb loading which may cause tissue breakdown.14 For example, if the stance limb femur internally rotates more than it should and the knee lands in limited flexion then the forces on the distal limb may be increased.15
Therefore, the primary purpose of this study was to investigate the differences in kinematics during running between uninjured athletes and those with a history of MSP. Secondary analyses investigated differences in limbs between groups and differences in females and males. The authors hypothesized that the MSP group would display more frontal plane pelvic tilt (PT) excursion and hip IR as compared to the control group. Determining the presence of specific hip impairments or faulty hip to lumbo-pelvic motion in athletes with lower leg pain could guide future research to determine the possible cause/s of these factors (e.g. muscle weakness, range of motion deficits, muscle timing).
Fourteen runners (8 females, 6 males) with a history of unilateral MSP and fourteen runner controls (8 females, 6 males) were recruited. The group with a history of MSP was recruited first, and then the control group was recruited to match the MSP group for age, sex, and training mileage. Groups were similar in age, mass, height, and training mileage (Table 1).
In order to participate in the study the subjects needed to be avid runners that ran at least 10 miles/week for the last six months or more. Inclusion criteria were 1) 18 to 40 years of age, 2) A history of medial shin pain in one lower extremity above the ankle that occurred with running and caused the runner to stop running, 3) Presently not experiencing pain greater than 1/10 with running so as not to interfere with running kinematics, 4) Duration of symptoms greater than four weeks, but not greater than one year and occurring within the last two years.
Subjects were excluded from the study if they 1) Had a history of a lower extremity stress fracture, compartments syndrome, distal nerve pain, 2) Recent (within one year) history of trauma or surgery to the lower extremity, 3) Knee pathology/surgery, 4) Paraesthesia in the lower leg, 5) Presented with excessive anteversion or retroversion as measured by the Craig's test, 6) Presently complained of low back pain, and 7) Had a history of hip or knee pain. Subjects were not excluded if they had received physical therapy for their medial shin pain. Individuals with anteversion/retroversion were excluded as the authors felt that this structural deviation would influence normal hip kinematics. Additionally, subjects were excluded if they had a neurological condition or cognitive or psychological disorder that might interfere with the testing. The screening process was two-staged. Initially a phone interview was conducted to screen for age, weekly mileage, injury location, present symptoms, and injury history. Once subjects passed the phone screen, they were invited to visit the testing laboratory where they were further screened for exact injury location and to rule-out any other exclusion criteria. The second screening was performed by an athletic trainer/physical therapist with over twenty-five years of sports medicine experience. The screening included palpation for location of symptoms, sensation testing, hip, knee, and ankle clearing, and a tibial percussion test. Besides the 14 runners that were included in the MSP group, five runners were excluded after the initial phone interview for not meeting study inclusion criteria. No runners were excluded once they were invited for the laboratory visit.
Ethical approval for this study was approved by the University of Kansas Medical Center's Internal Review Board. All subjects consented prior to the beginning of the study.
Preliminary Tests: The physical examination included measures of height, weight and the Craig test. The Craig test was performed16 to determine if subjects had a normal, anteverted or retroverted hip. For the Craig's test, subjects were placed in prone with the knee flexed to 90 degrees. The clinician palpated the greater trochanter of the subject and then passively rotated the limb until the tip of the trochanter was most prominent laterally. The angle that the limb measured relative to the vertical is the degree of anteversion. An angle less than 8 degrees is retroverted and an angle greater than 15 degrees is anteverted.16 Intra-tester reliability is high for the Craig test and is reported in the literature to range from 0.80–0.90.17,18
Hip kinematics during running: To acquire kinematic analysis of the pelvis, hip and knee during treadmill running, a six camera passive marker system (Vicon, Oxford Metrics LTD, Oxford, United Kingdom) at a sampling frequency of 250 Hz was used. Reflective markers (14 mm spheres) were placed bilaterally over the following anatomical landmarks: anterior superior iliac spine (ASIS), posterior iliac spine, lateral thigh, lateral shank, 2nd metatarsal heads, lateral malleoli, posterior calcaneus. The marker placement was based on the Plug-in Gait model (Oxford Metrics LTD, Oxford, United Kingdom) and depicted in Figure 1. The markers were held in place with double sided adhesive tape. All subjects wore their self-selected running shoes and were allowed to wear the orthotics that they normally wore with running. Prior to running, a standing calibration trial was performed to establish segment lengths, joint centers and joint coordinate systems.
The subjects were asked to run on a treadmill (Life Fitness, Schiller Park, IL, USA) at a zero percent grade. Subjects were instructed to run at a speed comparable to their five kilometer pace. Subjects completed a short warm up which consisted of walking for five minutes at 4.83 km/h followed by jogging for three to five minutes and then running at their self-selected test speed for five minutes. Five trials of five seconds of data were collected for each subject at 2.5 minutes into the self-selected speed trials.
Coordinate data were digitized in the Vicon Workstation software (Workstation, Oxford Metrics LTD, Oxford, England). The events of initial contact and toe-off were determined from the kinematic data using both the vertical displacement and vertical velocity of the markers at the lateral malleoli and the second metatarsal. Initial contact was determined as the point when the lateral malleoli markers began to move from a forward to backwards displacement. Toe-off was delineated as the point when the second metatarsal marker moved from a consistent horizontal position to a more vertical position, indicating that the foot was leaving the ground.
Coordinate data were filtered using a fourth-order zero-lag Butterworth low-pass filter with a cut-off frequency of 12Hz. Three-dimensional angular kinematics was calculated using the Plug-in-Gait lower limb model (version 1.8; Oxford Metrics LTD). Specific dependent variables that were calculated include the peak angles during stance phase for hip IR and knee flexion and total excursion of PT. Frontal plane pelvic tilt was defined as the angle between the two ASIS markers and the lab defined horizontal reference coordinate system. Hip IR was determined as the angle between the femur and pelvis around the vertical axis. Knee flexion angle was the angle between the femur and the tibia.
The kinematic data from Vicon was imported into a Microsoft Excel spreadsheet (Microsoft Corporation, Redmond, WA., USA) where the data could be managed for statistics. Peak values for hip IR and knee flexion was determined for each of five trials. The mean of the five peak values for hip IR and knee flexion was used for statistical analyses. The excursion of PT was calculated by subtracting the initial value from the peak dropped value that occurred during the stance phase. A positive value of PT indicates that the non-stance pelvis is positioned above the horizontal plane.
Group demographics were compared for age, mass, height, training miles, and testing treadmill speed using independent t-tests. Independent t-tests were calculated between extremities in the MSP and control groups for the variables PT excursion, peak hip IR and peak knee flexion. Independent t-tests were calculated between the involved limb of the MSP group and a randomly selected limb of the control group for the same variables. Level of significance was established at 0.05. Effect size was computed for differences between limbs in the MSP and control groups. A small effect is considered for values that are greater than or equal to 0.2 and less than 0.5, a moderate effect is greater than or equal to 0.5 and less than 0.8, and a large effect size is a value greater than 0.8.19 Secondary analyses were performed on the two limbs for females and males for each of the two groups. All statistical analyses were performed using SPSS, Version 17.0 (SPSS Inc, Chicago, IL,USA).
There were no differences in age, body mass, height, mileage run per week, or testing treadmill speed between groups (Table 1). Subjects in both groups displayed no significant difference between limbs with regards to the three variables studied (Table 2 and and3).3). Subjects with a history of MSP demonstrated significantly greater frontal plane PT (P = 0.002, Effect size = 0.55) and peak hip IR (P = 0.004, Effect size = 0.51); and less knee flexion (P = 0.02, Effect size = 0.46) than the control group (Table 4).
The variable data for females were compared to the data for males within each of the two groups. In the MSP group females had significantly greater PT compared to the males when analyzing the involved limb (P = 0.04). This difference was not seen on the uninvolved limb (Table 2). In the control group, no significant difference was found between females and males for either limb using the same variables.
The primary purpose of this study was to determine the relationship between select lower extremity kinematics and a history of MSP in the running athlete. Beyond the research regarding athletes with a diagnosis of tibial stress fracture18,19 no previous study has investigated whether or not such a relationship exists. First, it is necessary to recognize that MSP, much like other musculoskeletal dysfunctions, can have multiple and various etiologies. The inclusion/exclusion criteria used for the current study, as well as clinical screening, attempted to limit the variability of etiology. The majority of the subjects had complaints that were consistent with medial tibial stress syndrome but the authors did not use this term because there are no agreed diagnostic criteria for medial tibial stress syndrome.20 Still, it must be recognized that the subjects in the current study most likely were not a completely homogeneous group.
Differences between limbs: In the current study, the authors examined individuals with a history of unilateral shin pain in order to ascertain if there was a limb difference in runners with a history of MSP. These results are displayed in Table 2. Within the MSP group, none of the three variables that were measured were statistically different from the involved to the uninvolved limb. No differences were found between limbs in the control group (Table 3).
Symmetry of the lower extremity is expected in sports such as running that involves primarily sagittal plane and reciprocal movement between extremities. Shin pain is commonly bilateral and for this population with unilateral pain, limb asymmetry with regards to PT, hip IR, and knee flexion was not statistically different. Presently, to the authors' knowledge, no study has examined the same kinematic variables and differences between limbs in runners with a history of MSP. A study performed by Zifchock et al investigated side-to-side differences of kinetic and kinematic variable in overuse running injuries in twenty runners.21 These researchers found a significant difference in total passive IR motion between groups, with the injured runners having more total IR.21 Although, the measure was passive there is some suggestion that increased passive IR is associated with increased dynamic IR22 while others would state the contrary opinion, that static measures do not correlate with dynamic measures.23
Difference between groups: In comparing the MSP to the control group, statistically significant differences were observed for the variables PT, peak hip IR, and knee flexion (Table 4). The retrospective nature of the study design does not allow the authors to ascertain if the differences that were seen are due to the MSP or a result of the MSP. It can only be stated that there was a difference between groups.
In the current study, the subjects ran at an average speed of 3.08 meters/second, with the amount of PT being significantly greater (P = 0.002) for the involved limb of the MSP group (8.56 degrees) as compared to the average of 5.86 degrees for the control group. The IR value was less for the control group (6.25 degrees) and greater in the MSP group (11.48 degrees), a difference that was significantly different between groups (P = .004). The ROM values for IR varies in the literature from 8–10 degrees.24 Differences found in the current study compared to the Schache et al study are probably due to differences in running speed where runners in the current study averaged a slower running speed. Related to knee flexion, the MSP group averaged 37.11 degrees of flexion at foot contact whereas the control group had greater knee flexion at contact (42.12 degrees) and this difference was statistically different (P = 0.02). Differences between groups were relatively small: 2.70 degrees for PT, 5.23 degrees for peak hip IR, and 5.01 degrees for knee flexion. The moderate effect sizes associated with these differences support the results of the statistical analyzes. However, it is not clear if these values are clinically significant.
During running, each foot strikes the ground approximately 600 times per kilometer.25 With each heelstrike forces are transmitted from the foot up the lower extremity to the lumbar spine.26 Even minor malalignments and/or abnormal movement patterns can accumulate, resulting in an overuse injury.10,11,27 A greater amount of motion at the pelvis and hip would suggest a lack of stability in those joints in the selected planes of hypermobility. The authors theorize that excessive pelvic drop and hip rotation results in compensation distally that contributes to the development of MSP. The concept of proximal hip contributing to distal lower extremity pathology is further detailed in a conceptual model that is displayed in Figure 2. Increased frontal plane PT has been described to create a knee valgus moment at the knee as a result of the body's center of mass shifting medially.28 This increased valgus moment at the knee may result in compensation distally of increased subtalar joint pronation.14 In addition the MSP group had less knee flexion during stance which may affect the load dissipation of the ground reaction forces. Knee flexion during the initial phases of running gait is a key component for shock absorption throughout the lower quarter, without which the shock will be attenuated through the tibia and/or soft tissue.
Although there are not many investigations available for comparison with the current results, previous investigators have theorized regarding the biomechanical variables assessed in the current study. Hip IR, knee abduction and rearfoot eversion has been found to be associated with injuries in runners.8,14,29 Increased levels of hip IR have been previously found in runners with tibial stress fractures.30 Although the subjects in the current study did not have tibial stress fracture, shin pain is a precursor for tibial stress fracture. Hip motion does influence the way the foot hits the ground, stressing either the soft tissue or bone in the lower limb. In the current study, the three kinematic variables were examined independently, however, it is likely that these factors are inter-related and may combine to increase injury risk.
Difference between sexes: Women suffer disproportionately higher rates of exertional tibial pain in military32 and exercise related leg pain.5,10,31 Also, females demonstrate greater frontal and transverse plane motion than males during running.29,32,33 Specifically, females exhibit greater peak hip IR, hip adduction and greater peak knee valgus.
In this study, secondary analyses were performed between sexes within each group to establish if sex proved to be a distinguishing factor. Within the MSP group on the involved side (Table 2), PT was significantly greater in females as compared to males. Within the control group, there were no significantly different variables (in a randomly chosen limb) between sexes (Table 3). It is not clear how this variation may have affected the main findings of this study, but it appears that females may be at higher risk for MSP due to the tendency for greater pelvic and hip excursion during running. To further understand these differences, future studies should focus on one gender.
It is worth noting that all runners were able to perform the treadmill running without difficulty or reported symptoms. It could be argued that treadmill running does not simulate over-ground running, but the authors felt that for this study, treadmill running would allow the runners to achieve their normal running speed versus running on the short runway in the experimental lab. Additionally, the authors chose to have the subjects run at their self-selected speed to minimize kinematic variation in them running at a speed that was unnatural to them. Further, subjects wore their own shoes and orthotics to help minimize variation from their normal kinematics. The authors believe that using standardized shoes is artificial for the subject and may change their running pattern.
This study only investigated a few select variables that may distinguish between those with a history of MSP and those without. The authors acknowledge that they may excluded other variables that are important determinants of injury, such as muscle strength and delayed onset of muscle activation. Additionally, the data collected was retrospective; therefore it is impossible to discern if the potential differences between groups occurred prior to or after the onset of MSP.
Despite its high prevalence, little is known regarding the kinematic factors associated with MSP. There is a need to understand the risk factors associated with MSP so that effective prevention strategies can be developed and implemented. Individuals with a history of MSP demonstrated significantly greater frontal plane PT, peak hip IR, and less knee flexion as compared to a matched group of runners without pain. Normal loading in the presence of abnormal movement can contribute to increased injury risk. Valuable insight can be gained by considering the entire lower extremity.