Kathryn L. Bohnert

Excessive Adipose Tissue Infiltration in Skeletal Muscle in Individuals With Obesity, Diabetes Mellitus, and Peripheral Neuropathy: Association With Performance and Function

Background and Purpose: The primary purpose of this study was to report differences in calf intermuscular adipose tissue (IMAT), muscle strength (peak torque), power, and physical function in individuals with obesity, diabetes mellitus (DM), and peripheral neuropathy (PN) compared with those without these impairments. A secondary purpose was to assess the relationship between IMAT and muscle strength, power, and physical function. Subjects and Methods: Six participants with obesity, DM, and PN (2 women, 4 men; mean age=58 years, SD=10; mean body mass index=36.3, SD=5; mean modified Physical Performance Test [PPT] score=22, SD=3) and 6 age- and sex-matched control subjects without these impairments were assessed and compared in muscle strength, muscle power, physical functioning, and muscle and fat volume, including IMAT in the calf muscles. Muscle, adipose tissue, and IMAT volumes of each calf were quantified by noninvasive magnetic resonance imaging. Muscle strength and power of the plantar-flexor and dorsiflexor muscles were quantified using isokinetic dynamometry. The modified PPT was used to assess physical function. Results: Leg muscle and fat volumes were similar between groups, although IMAT volumes were 2.2-fold higher in the subjects with obesity, DM, and PN (X̄=120 cm3, SD=47) than in the control subjects (X̄=54 cm3, SD=41). Muscle strength, muscle power, ratio of leg muscle power to leg muscle volume, and modified PPT scores were lower in subjects with obesity, DM, and PN compared with the control subjects. Discussion and Conclusion: The data indicate that excess fat infiltration in leg skeletal muscles is associated with low calf muscle strength, low calf muscle power, and impaired physical function in individuals who are obese with DM and PN.

Plantar Stresses on the Neuropathic Foot During Barefoot Walking

Background and Purpose: Patients with diabetes mellitus and peripheral neuropathy are at high risk for plantar skin breakdown due to unnoticed plantar stresses during walking. The purpose of this study was to determine differences in stress variables (peak plantar pressure, peak pressure gradient, peak maximal subsurface shear stress, and depth of peak maximal subsurface shear stress) between the forefoot (where most ulcers occur) and the rear foot in subjects with and without diabetes mellitus, peripheral neuropathy, and a plantar ulcer measured during barefoot walking. Subjects: Twenty-four subjects participated: 12 with diabetes mellitus, peripheral neuropathy, and a plantar ulcer (DM+PN group) and 12 with no history of diabetes mellitus or peripheral neuropathy (control group). The subjects (11 men, 13 women) had a mean age (±SD) of 54±8 years. Methods: Plantar pressures were measured during barefoot walking using a pressure platform. Stress variables were estimated at the forefoot and the rear foot for all subjects. Results: All stress variables were higher (127%–871%) in the forefoot than in the rear foot, and the peak pressure gradient showed the greatest difference (538%–871%). All stress variables were higher in the forefoot in the DM+PN group compared with the control group (34%–85%), and the peak pressure gradient showed the greatest difference (85%). The depth (X̄±SD) of peak maximum subsurface shear stress in the forefoot in the DM+PN group was half that in the control group (3.8±2.0 versus 8.0±4.3 mm, respectively). Discussion and Conclusions: These results indicate that stresses are relatively higher and located closer to the skin surface in locations where skin breakdown is most likely to occur. These stress variables may have additional value in predicting skin injury over the traditionally measured peak plantar pressure, but prospective studies using these variables to predict ulcer risk are needed to test this hypothesis.

Training-Induced Strength and Functional Adaptations After Hip Fracture

Background and Purpose At 3 months after hip fracture, most people are discharged from physical therapy despite residual muscle weakness and overall decreased functional capabilities. The purposes of this study were: (1) to determine, in frail elderly adults after hip fracture and repair, whether a supervised 6-month exercise program would result in strength gains in the fractured limb equivalent to the level of strength in the nonfractured limb; (2) to determine whether the principle of specificity of training would apply to this population of adults; and (3) to determine the relationship between progressive resistance exercise training (PRT) intensity and changes in measures of strength and physical function. Subjects The study participants were 31 older adults (9 men and 22 women; age [X̄±SD], 79±6 years) who had surgical repair of a hip fracture that was completed less than 16 weeks before study enrollment and who completed at least 30 sessions of a supervised exercise intervention. Methods Participants completed 3 months of light resistance and flexibility exercises followed by 3 months of PRT. Tests of strength and function were completed at baseline, before PRT, and after PRT. Results After PRT, the subjects increased knee extension and leg press 1-repetition maximum by 72%±56% and 37%±30%, respectively. After 3 and 6 months of training, lower-extremity peak torques all increased. Specificity of training appeared to apply only to the nonfractured limb after PRT. Strong correlations were observed between training intensity and lower-extremity strength gains as well as improvements in measures of physical function. Discussion and Conclusion Frail elderly adults after hip fracture can benefit by extending their rehabilitation in a supervised exercise setting, working at high intensities in order to optimize gains in strength and physical function.

Inflammatory Osteolysis in Diabetic Neuropathic (Charcot) Arthropathies of the Foot

Objective: Osteolysis and low bone mineral density (BMD) are underappreciated consequences of several chronic diseases that may elevate the risk for fracture. The purpose of this study was to assess tarsal BMD associated with acute inflammation (ie, inflammatory osteolysis) in individuals with chronic diabetes mellitus (DM), peripheral neuropathy (PN), and recent-onset neuropathic (Charcot) arthropathy (NCA) of the foot. Research Design and Methods: This was a case-control study of 32 people (11 men, 21 women) with DM, PN, and NCA of the foot or ankle. The subjects with DM, PN, and NCA were compared with 64 age-, sex-, and race-matched control subjects (24 men, 40 women) without DM, PN or NCA. Within the first 3 weeks of cast immobilization, BMD was estimated in both calcanei using quantitative ultrasonometry. Acute inflammation was confirmed by comparing skin temperature differences between the feet of the subjects with DM, PN, and NCA and the feet of the control subjects. Results: Skin temperature differences averaged 6.7°F (SD=4.0°F) (involved foot minus noninvolved foot) in the feet of the subjects with DM, PN, and NCA compared with 0.0°F (SD=1.3°F) in the feet of the control subjects. Calcaneal BMD averaged 384 mg/cm2 (SD=110) in the involved feet and 467 mg/cm2 (SD=123) in the noninvolved feet of the subjects with DM, PN, and NCA and 545 mg/cm2 (SD=121) in combined right and left feet of the control subjects. Conclusions: Inflammation in individuals with DM, PN, and NCA may contribute to or exacerbate a rapid loss of BMD. Inflammatory osteolysis may be a prominent factor responsible for both the spontaneous onset of neuropathic fracture and the insidious and progressive foot deformity that is the hallmark of the chronic Charcot foot.

Progression of Foot Deformity in Charcot Neuropathic Osteoarthropathy

BACKGROUND Charcot neuropathic osteoarthropathy associated foot deformity can result in joint instability, ulceration, and even amputation. The purpose of the present study was to follow patients with and without active Charcot osteoarthropathy for as long as two years to examine the magnitude and timing of foot alignment changes. METHODS We studied fifteen subjects with Charcot osteoarthropathy and nineteen subjects with diabetes mellitus and peripheral neuropathy without Charcot osteoarthropathy for one year; eight of the subjects with osteoarthropathy and five of the subjects with diabetes and peripheral neuropathy were followed for two years. Bilateral weight-bearing radiographs of the foot were made at baseline for all subjects, with repeat radiographs being made at six months for the osteoarthropathy group and at one and two years for both groups. Radiographic measurements included the Meary angle, cuboid height, calcaneal pitch, and hindfoot-forefoot angle. RESULTS The Meary angle, cuboid height, and calcaneal pitch worsened in feet with Charcot osteoarthropathy over one year as compared with the contralateral, uninvolved feet and feet in patients with diabetes and peripheral neuropathy. Cuboid height continued to worsen over the two-year follow-up in the feet with Charcot osteoarthropathy. These feet also had a greater change in the hindfoot-forefoot angle at one year as compared with the feet in patients with diabetes and peripheral neuropathy and at two years as compared with the contralateral, uninvolved feet. CONCLUSIONS In patients with Charcot neuropathic osteoarthropathy, radiographic alignment measurements demonstrate the presence of foot deformity at the time of the initial clinical presentation and evidence of progressive changes over the first and second years. The six-month data suggest worsening of medial column alignment prior to lateral column worsening. This radiographic evidence of worsening foot alignment over time supports the need for aggressive intervention (conservative bracing or surgical fixation) to attempt to prevent limb-threatening complications.

Foot progression angle and medial loading in individuals with diabetes mellitus, peripheral neuropathy, and a foot ulcer

Foot progression angle (FPA) and duration of foot medial column loading during walking were studied in individuals with diabetes mellitus (DM), peripheral neuropathy (PN), and a forefoot ulcer (DMPN), and in age-matched control subjects. FPA was calculated from EMED-ST P-2 pressure maps as the angle formed between the longitudinal axis of the foot and the forward line of progression during walking. The medial loading duration was calculated as the amount of time the center of pressure line spent in the medial side of the foot pressure map. FPA was increased in the DMPN group, on the involved and uninvolved sides [15(9) degrees and 13(4) degrees respectively] compared the control group [9(4) degrees ]. FPA and medial loading duration were significantly correlated in the DMPN group on the involved and uninvolved sides (r>0.54, p<0.036), but were not significantly correlated in the control group (r<|0.07|, p>0.82). This study provides evidence that FPA is an important biomechanical contributor to the pattern of foot loading in individuals with DM, PN, and a forefoot ulcer.

Kinetics and kinematics after the Bridle procedure for treatment of traumatic foot drop.

BACKGROUND The Bridle procedure restores active ankle dorsiflexion through a tri-tendon anastomosis of the tibialis posterior, transferred to the dorsum of the foot, with the peroneus longus and tibialis anterior tendon. Inter-segmental foot motion after the Bridle procedure has not been measured. The purpose of this study is to report kinetic and kinematic variables during walking and heel rise in patients after the Bridle procedure. METHODS 18 Bridle and 10 control participants were studied. Walking and heel rise kinetic and kinematic variables were collected and compared using an ANOVA. FINDINGS During walking the Bridle group, compared with controls, had reduced ankle power at push-off [2.3 (SD 0.7) W/kg, 3.4 (SD 0.6) W/kg, respectively, P<.01], less hallux extension during swing [-13 (SD 7)°, 15 (SD 6)°, respectively, P<.01] and slightly less ankle dorsiflexion during swing [6 (SD 4)°, 9 (SD 2)°, respectively, P=.03]. During heel rise the Bridle group had 4 (SD 6)° of forefoot on hindfoot dorsiflexion compared to 8 (SD 3)° of plantarflexion in the controls (P<.01). INTERPRETATION This study provides evidence that the Bridle procedure restores the majority of dorsiflexion motion during swing. However, plantarflexor function during push-off and hallux extension during swing were reduced during walking in the Bridle group. Abnormal mid-tarsal joint motion, forefoot on hindfoot dorsiflexion instead of plantarflexion, was identified in the Bridle group during the more challenging heel rise task. Intervention after the Bridle procedure must maximize ankle plantarflexor function and midfoot motion should be examined during challenging tasks.

Neuropathic midfoot deformity: associations with ankle and subtalar joint motion

BackgroundNeuropathic deformities impair foot and ankle joint mobility, often leading to abnormal stresses and impact forces. The purpose of our study was to determine differences in radiographic measures of hind foot alignment and ankle joint and subtalar joint motion in participants with and without neuropathic midfoot deformities and to determine the relationships between radiographic measures of hind foot alignment to ankle and subtalar joint motion in participants with and without neuropathic midfoot deformities.MethodsSixty participants were studied in three groups. Forty participants had diabetes mellitus (DM) and peripheral neuropathy (PN) with 20 participants having neuropathic midfoot deformity due to Charcot neuroarthropathy (CN), while 20 participants did not have deformity. Participants with diabetes and neuropathy with and without deformity were compared to 20 young control participants without DM, PN or deformity. Talar declination and calcaneal inclination angles were assessed on lateral view weight bearing radiograph. Ankle dorsiflexion, plantar flexion and subtalar inversion and eversion were assessed by goniometry.ResultsTalar declination angle averaged 34±9, 26±4 and 23±3 degrees in participants with deformity, without deformity and young control participants, respectively (p< 0.010). Calcaneal inclination angle averaged 11±10, 18±9 and 21±4 degrees, respectively (p< 0.010). Ankle plantar flexion motion averaged 23±11, 38±10 and 47±7 degrees (p<0.010). The association between talar declination and calcaneal inclination angles with ankle plantar flexion range of motion is strongest in participants with neuropathic midfoot deformity. Participants with talonavicular and calcaneocuboid dislocations result in the most severe restrictions in ankle joint plantar flexion and subtalar joint inversion motions.ConclusionsAn increasing talar declination angle and decreasing calcaneal inclination angle is associated with decreases in ankle joint plantar flexion motion in individuals with neuropathic midfoot deformity due to CN that may contribute to excessive stresses and ultimately plantar ulceration of the midfoot.

Impaired cardiac and skeletal muscle bioenergetics in children, adolescents, and young adults with Barth syndrome

Barth syndrome (BTHS) is an X‐linked condition characterized by altered cardiolipin metabolism and cardioskeletal myopathy. We sought to compare cardiac and skeletal muscle bioenergetics in children, adolescents, and young adults with BTHS and unaffected controls and examine their relationships with cardiac function and exercise capacity. Children/adolescents and young adults with BTHS (n = 20) and children/adolescent and young adult control participants (n = 23, total n = 43) underwent 31P magnetic resonance spectroscopy (31P‐MRS) of the lower extremity (calf) and heart for estimation of skeletal muscle and cardiac bioenergetics. Peak exercise testing (VO2peak) and resting echocardiography were also performed on all participants. Cardiac PCr/ATP ratio was significantly lower in children/adolescents (BTHS: 1.5 ± 0.2 vs. Control: 2.0 ± 0.3, P < 0.01) and adults (BTHS: 1.9 ± 0.2 vs. Control: 2.3 ± 0.2, P < 0.01) with BTHS compared to Control groups. Adults (BTHS: 76.4 ± 31.6 vs. Control: 35.0 ± 7.4 sec, P < 0.01) and children/adolescents (BTHS: 71.5 ± 21.3 vs. Control: 31.4 ± 7.4 sec, P < 0.01) with BTHS had significantly longer calf PCr recovery (τPCr) postexercise compared to controls. Maximal calf ATP production through oxidative phosphorylation (Qmax‐lin) was significantly lower in children/adolescents (BTHS: 0.5 ± 0.1 vs. Control: 1.1 ± 0.3 mmol/L per sec, P < 0.01) and adults (BTHS: 0.5 ± 0.2 vs. Control: 1.0 ± 0.2 mmol/L sec, P < 0.01) with BTHS compared to controls. Blunted cardiac and skeletal muscle bioenergetics were associated with lower VO2peak but not resting cardiac function. Cardiac and skeletal muscle bioenergetics are impaired and appear to contribute to exercise intolerance in BTHS.

Impact of Charcot neuroarthropathy on metatarsal bone mineral density and geometric strength indices

Charcot neuroarthropathy (CN), an inflammatory condition characterized by rapid and progressive destruction of pedal bones and joints, often leads to deformity and ulceration in individuals with diabetes mellitus (DM) and peripheral neuropathy (PN). Repetitive, unperceived joint trauma may trigger initial CN damage, causing a proinflammatory cascade that can result in osteolysis and contribute to subsequent neuropathic fracture. We aimed to characterize osteolytic changes related to development and progression of CN by measuring bone mineral density (BMD) and geometric strength indices using volumetric quantitative computed tomography. Twenty individuals with DM+PN were compared to twenty age-, sex-, and race-matched individuals with DM+PN and acute CN. We hypothesized that individuals with acute CN would have decreased BMD and decreased total area, cortical area, minimum section modulus, and cortical thickness in the diaphysis of the second and fifth metatarsals. Results showed BMD was lower in both involved and uninvolved feet of CN participants compared to DM+PN participants, with greater reductions in involved CN feet compared to uninvolved CN feet. There was a non-significant increase in total area and cortical area in the CN metatarsals, which helps explain the finding of similar minimum section modulus in DM+PN and CN subjects despite the CN groups significantly lower BMD. Larger cortical area and section modulus are typically considered signs of greater bone strength due to higher resistance to compressive and bending loads, respectively. In CN metatarsals, however, these findings may reflect periosteal woven bone apposition, i.e., a hypertrophic response to injury rather than increased fracture resistance. Future research using these techniques will aid further understanding of the inflammation-mediated bony changes associated with development and progression of CN and other diseases.