Displacement of the Metatarsal Sesamoids in Relation to First Metatarsophalangeal Joint Extension.

Background: Quantifying normal sesamoid movement in relation to first metatarsophalangeal joint (MTPJ1) motion is essential to identifying aberrant kinematics and understanding how they may contribute to forefoot pain and dysfunction. The present study aims to report sesamoid displacement in relation to MTPJ1 extension and to compare sesamoid displacement with MTPJ1 range of motion (ROM) from several imaging modalities. Methods: Using 10 fresh frozen cadaveric feet, sesamoid displacement was evaluated during simulated MTPJ1 extension. The ability of 3 MTPJ1 measurement techniques (goniometry, fluoroscopy, and unloaded cone beam computed tomography [CBCT]) in predicting sesamoid displacement were compared. Kinematics were expressed in a coordinate frame based on the specimen-specific first metatarsal anatomy, and descriptive statistics are reported. Results: In the sagittal plane in both neutral and maximally extended positions, the tibial sesamoid was located on average more anteriorly than the fibular sesamoid. The angular displacement of the tibial and fibular sesamoids in the sagittal plane were 30.2 ± 14.3 degrees and 35.8 ± 10.6 degrees, respectively. In the transverse plane, both sesamoids trended toward the body midline from neutral to maximum extension. The intersesamoidal distance remained constant throughout ROM. Of the 3 measurement techniques, MTPJ1 ROM from CBCT correlated best (R 2 = 0.62 and 0.81 [P < .05] for the tibial and fibular sesamoid, respectively) with sagittal plane sesamoid ROM. Conclusion: The sesamoids were displaced anteriorly and medially in relation to increasing MTPJ1 extension. CBCT was the most correlated clinical imaging technique in relating MTPJ1 extension with sesamoid displacement. Clinical Significance: This study advances our understanding of the biomechanical function of the sesamoids, which is required for both MTPJ1 pathology interventions and implant design. These findings support the use of low-dose CBCT as the information gathered provides more accurate detail about bone position compared with other imaging methods.

Foot radiographic angle variation as a function of weightbearing magnitude.

Weightbearing radiographs are widely used to investigate foot disorders. However, it is unclear how imaging during partial weightbearing affects foot alignment measurements. This study aimed to determine a partial weightbearing threshold that yields consistent measurements of various radiographic angles. Eighteen normal fresh-frozen cadaveric foot specimens were dissected and prepared for mechanical testing using a custom-designed, computed tomography-compatible loading frame. Specimens were placed in a neutral ankle position and scanned in five axial loading conditions (0%, 12.5%, 25%, 37.5%, and 50% bodyweight) using weightbearing computed tomography. (Note 50% bodyweight per foot represents full bodyweight in quiet stance.) The lateral first talometatarsal and calcaneal pitch angles were measured on lateral radiographic projections, and the hallux valgus angle and first-second, fourth-fifth, and first-fifth intermetatarsal angles were measured on axial projection images. The lateral first talometatarsal angle decreased significantly with increased bodyweight loading (p < 0.01). Mean significant decreases in the lateral first talometatarsal angle compared to 0% were 6.6° for 12.5%, 7.6° for 25%, 8.8° for 37.5%, and 10.0° for 50% bodyweight loading; 12.5% to 50% was also significant. There was no significant differences between other loading condition pairings or with increased axial load at other angles. The medial longitudinal arch flattened with increasing axial load, resulting in a decreased lateral first talometatarsal angle. However, this radiographic parameter did not change between the 25% and 50% bodyweight conditions, indicating that partial weightbearing imaging (between 12.5% and 25% bodyweight) might be enough to reproduce the sagittal foot alignments observed under full weightbearing conditions in normal feet.

Evaluation of the Foot Arch in Partial Weightbearing Conditions.

BACKGROUND: Weightbearing plain radiography or computed tomography (CT) is used for diagnosis or treatment selection in foot disorders. This study compared foot alignment between full weightbearing (50% body weight [BW] per foot) plain radiography and nonweightbearing (0% BW) or partial weightbearing (10% BW per foot) CT scans. METHODS: Subjects had both full (50% BW per foot) weightbearing plain radiographs and either a nonweightbearing (0% BW) or a partial weightbearing (20% BW or 10% BW per foot) CT scan. Feet (n = 89) had been previously classified as pes cavus (n = 14/17 [subjects/feet]), neutrally aligned (NA; 20/30), asymptomatic pes planus (APP; 18/24), and symptomatic pes planus (SPP; 15/18). Lateral talometatarsal angle (LTMA) and calcaneal pitch angle were compared between weightbearing radiography and maximum-intensity projection images generated from CT. RESULTS: Significant differences in LTMA were found between nonweightbearing CT scans and full (50% BW per foot) weightbearing plain radiographs: the mean difference was 6.6 degrees in NA, 9.2 degrees in APP, and 11.3 degrees in SPP (P < .0001); no significant difference in LTMA was found for pes cavus. Although the interaction of foot type (P = .084) approached statistical significance, pairwise differences between 10% weightbearing and 50% weightbearing images by foot type were significant but small. The 50% weightbearing condition resulted in calcaneal pitch angles the same or slightly lower or higher than those of the 10% weightbearing and nonweightbearing images. LTMA and calcaneal pitch angle measurements made on full (50% BW per foot) weightbearing plain radiographs and non- (0%) or partial (10% BW per foot) weightbearing angles from CT scans were strongly correlated. CONCLUSION: Different foot types have similar 2-dimensional sagittal plane morphologies with partial weightbearing (10% BW per foot) CT scans and, to a lesser degree, nonweightbearing (0%) neutral-position CT scans when compared to full weightbearing (50% BW per foot) plain radiographs. LEVEL OF EVIDENCE: Level III, retrospective case control study.

Neuropathy, claw toes, intrinsic muscle volume, and plantar aponeurosis thickness in diabetic feet.

BACKGROUND: The objective of this study was to explore the relationships between claw toe deformity, peripheral neuropathy, intrinsic muscle volume, and plantar aponeurosis thickness using computed tomography (CT) images of diabetic feet in a cross-sectional analysis. METHODS: Forty randomly-selected subjects with type 2 diabetes were selected for each of the following four groups (n = 10 per group): 1) peripheral neuropathy with claw toes, 2) peripheral neuropathy without claw toes, 3) non-neuropathic with claw toes, and 4) non-neuropathic without claw toes. The intrinsic muscles of the foot were segmented from processed CT images. Plantar aponeurosis thickness was measured in the reformatted sagittal plane at 20% of the distance from the most inferior point of the calcaneus to the most inferior point of the second metatarsal. Five measurement sites in the medial-lateral direction were utilized to fully characterize the plantar aponeurosis thickness. A linear mixed-effects analysis on the effects of peripheral neuropathy and claw toe deformity on plantar aponeurosis thickness and intrinsic muscle volume was performed. RESULTS: Subjects with concurrent neuropathy and claw toes had thicker mean plantar aponeurosis (p < 0.006) and may have had less mean intrinsic muscle volume (p = 0.083) than the other 3 groups. The effects of neuropathy and claw toes on aponeurosis thickness were synergistic rather than additive. A similar pattern may exist for intrinsic muscle volume, but results were not as conclusive. A negative correlation was observed between plantar aponeurosis thickness and intrinsic muscle volume (R2 = 0.323, p < 0.001). CONCLUSIONS: Subjects with concurrent neuropathy and claw toe deformity were associated with the smallest intrinsic foot muscle volumes and the thickest plantar aponeuroses. Intrinsic muscle atrophy and plantar aponeurosis thickening may be related to the development of claw toes in the presence of neuropathy.

Altered tibiofemoral kinematics in the affected knee and compensatory changes in the contralateral knee after anterior cruciate ligament reconstruction.

BACKGROUND: Previous studies of knee kinematics after anterior cruciate ligament (ACL) reconstruction have generally employed low-effort tasks and typically not assessed changes in kinematics over time. HYPOTHESES: (1) During single-legged hop landing, ACL-reconstructed limbs will have altered kinematics compared with contralateral (ACL-intact) limbs 5 months after surgery. (2) Kinematic differences between limbs will decrease over time because of changes in both ACL-reconstructed and ACL-intact limbs. STUDY DESIGN: Controlled laboratory study. METHODS: In vivo kinematics of ACL-reconstructed and contralateral ACL-intact knees were evaluated for 14 subjects during single-legged forward-hop landings at 5 and 12 months after surgery on the basis of dynamic stereo x-ray imaging. Differences between limbs and changes over time were assessed via repeated-measures analysis of variance. RESULTS: Five months after surgery, ACL-reconstructed knees landed significantly less flexed compared with contralateral ACL-intact knees (20.9° vs 28.4°, respectively; P < .05). The ACL-reconstructed knees were significantly more externally rotated (12.2° vs 6.5°; P < .05) and medially translated (3.8 vs 2.3 mm; P < .009) compared with ACL-intact knees. Anterior-posterior translation was similar between limbs. From 5 to 12 months, knee flexion at landing increased in ACL-reconstructed knees (mean change, +3.4°; P < .05) and decreased in contralateral knees (mean change, -3.3°; P < .05). External tibial rotation also significantly decreased in ACL-reconstructed knees (-2.2°; P < .05) and increased in contralateral knees (+1.1°; P = .117) over time. Medial tibial translation decreased slightly over time only in ACL-reconstructed knees (-0.3 mm). CONCLUSION: Five months after ACL reconstruction, landing kinematics differed between ACL-reconstructed and contralateral ACL-intact knees during a dynamic high-loading activity. These differences decreased over time, owing to changes in both the ACL-reconstructed and contralateral ACL-intact limbs. CLINICAL RELEVANCE: This study identified kinematic changes over time in both the ACL-injured and contralateral ACL-intact knees after ACL reconstruction. These kinematic adaptations could have important implications for postoperative care, including evaluating the optimal timing of return to sports and the development of bilateral neuromuscular rehabilitation programs that may improve patient outcomes and reduce reinjuries in both the short and long terms.

Cervical spine bone mineral density as a function of vertebral level and anatomic location.

BACKGROUND CONTEXT: Bone mineral density (BMD) measurements acquired from quantitative computed tomography scans have been shown to correlate with bone mechanical properties such as strength, stiffness, and yield load. There are currently no reports of BMD as a function of anatomic location within each vertebra. PURPOSE: The overall objective of this study was to characterize BMD in the cervical spine as a function of level and anatomic location. STUDY DESIGN: Cervical spine BMD was evaluated in vivo using a clinically relevant age group. PATIENT SAMPLE: Twenty-two subjects (13 women and 9 men) were included with an average age of 48 ± 7 years (range, 35-61 years). Ten subjects were recently diagnosed with cervical radiculopathy (age 49 ± 8 years; six women and four men; and two smokers and eight nonsmokers), and 12 subjects were asymptomatic controls (age 46 ± 6 years; seven women and five men; and three smokers, three quit smoking, and six nonsmokers). OUTCOME MEASURES: Physiologic measures included overall BMD for C3-C7, average BMD within 11 anatomically defined regions of interest for each vertebra, and density distribution (by volume) within each anatomic region and vertebral level. METHODS: Subject-specific three-dimensional bone models were created from high-resolution computed tomography scans of the subaxial cervical spine (C3-C7). Custom software calculated the average BMD within 11 anatomically defined regions of interest for each three-dimensional bone model. Bone mineral density values for each voxel of bone tissue were binned into 50 mg/cc ranges to determine the density distribution by volume. Repeated-measures analysis of variance was used to test for differences within subjects by level (C3-C7) and anatomic location. The correlation between BMD in the central vertebral body and the pedicle and lateral mass regions was tested using Pearson correlation. RESULTS: Average BMDs by level were 476, 503, 507, 473, and 414 mg/cm(3) for C3-C7, respectively. C3 and C6 BMDs were significantly less than those of C4 and C5 (p<.007). C7 BMD was significantly less than those of all other levels (all p<.001). Control and female subjects showed a trend toward higher BMD than radiculopathy and male subjects across all levels (p value: .06-.17). Wide variation in BMD was observed over anatomical regions, with the pedicles having significantly higher BMD than all other anatomic locations and the anterior portion of the central vertebral body having significantly lower BMD than all other anatomic locations. There was a significant positive correlation between central vertebral body BMD and lateral mass BMD at each level. Bone mineral density distribution by volume plots revealed women had a higher volume of very high-density bone than men but only in the posterior elements. CONCLUSIONS: This study has characterized BMD in the cervical spine according to vertebral level and anatomic location within each vertebral level using live subjects from a clinically relevant age group. The results indicate significant differences in BMD according to vertebral level and among anatomical regions within each vertebra. The results suggest to the surgeon and device manufacturer that surgical procedures involving instrumentation attached to C7 may require a modification in instrumentation or in surgical technique to attain results equivalent to more superior levels. The results suggest to the basic scientist that computational models may be improved by taking into account the wide variation in BMD over different anatomical regions.

Medial portal drilling: effects on the femoral tunnel aperture morphology during anterior cruciate ligament reconstruction.

BACKGROUND: A goal of anatomic anterior cruciate ligament (ACL) reconstruction should be to create a femoral tunnel aperture that resembles the native attachment site in terms of size and orientation. Aperture morphology varies as a function of the drill-bit diameter, the angle in the horizontal plane at which the drilled tunnel intersects the lateral notch wall (transverse drill angle), and the angle of knee flexion in the vertical plane during drilling. METHODS: A literature search was conducted to determine population-based dimensions of the femoral ACL footprint. The tunnel aperture length, width, and area associated with the use of different drill-bit diameters and transverse drill angles were calculated. The effect of the knee flexion angle on the orientation (anteroposterior and proximodistal dimension) and size of the femoral tunnel aperture relative to the native femoral insertion of the ACL were calculated with use of geometric mathematical models. RESULTS: The literature search revealed an average femoral insertion site size of 8.9 mm for width, 16.3 mm for length, and 136.0 mm2 for area. The use of a 9-mm drill bit at a transverse drill angle of 40° resulted in a tunnel aperture area of 99.0 mm2 and a tunnel aperture length of 14.0 mm. Decreasing the transverse drill angle from 60° to 20° led to an increase of 152.9% in length and of 153.1% in tunnel aperture area. When a 9-mm drill bit and a transverse drill angle of 40° were used, the aperture seemed to best match the native ACL footprint when drilling was performed at a knee flexion angle of 102°; deviations from this angle in either direction resulted in increasing tunnel area mismatch compared with the baseline aperture. Increasing the knee flexion angle to 130° decreased the proximodistal dimension of the aperture by 2.78 mm and increased the anteroposterior distance by 0.65 mm, creating a mismatched area of 13.5%. CONCLUSIONS: The drill-bit diameter, transverse drill angle, and knee flexion angle can all affect femoral tunnel aperture morphology in medial portal drilling during ACL reconstruction. The relationship between drilling orientation and aperture morphology is critical knowledge for surgeons performing ACL reconstruction.