Association Between Hip Translation and Hip Rotation and Anatomy: A Pilot Quasi-static MRI Study.

Background: There is little known about translation of the hip and the relationship with hip rotation and morphology in asymptomatic patients. Hypotheses: (1) Femoral head would exhibit significant translations in asymptomatic hips, (2) femoral head translations would correlate to femoral rotations, and (3) range of femoral head translations would correlate to hip morphology. Study Design: Cross-sectional study; Level of evidence, 3. Methods: A total of 11 individuals (age, 23-47 years; 64% female) with asymptomatic hips underwent hip magnetic resonance imaging (MRI) in the following postures: neutral (supine), midflexion, maximum-flexion, internal rotation, internal rotation + midflexion, internal rotation + maximum-flexion, adduction, flexion-abduction-external rotation (FABER), extension, and lateral abduction. All rotations were passive. MRI-generated 3-dimensional hip models were used to quantify femoral rotations and translations. Femoral head diameter, acetabular diameter, lateral center-edge angle, alpha angle, femoral anteversion, acetabular version and inclination, and neck-shaft angle were measured from MRI. A t test was used if measured translations were statistically significant. Linear regression was used to assess the associations between translation and rotation. Pearson correlation was used to assess the relationships between hip anatomy and range of femoral head translations. Results: In all tested positions, the femoral head translated anteriorly by 2 ± 1 mm (maximum 5 mm, P < .001), posteriorly by 1 ± 1 mm (maximum 6 mm, P < .001), superiorly by 2 ± 2 mm (maximum 7 mm, P < .001), inferiorly by 2 ± 2 mm (maximum 6 mm, P < .001), laterally by 1 ± 1 mm (maximum 4 mm, P < .001), and medially by 2 ± 1 mm (maximum 5 mm, P < .001), relative to the rested supine position. Femoral flexion was associated with posterior translation of the femoral head (P = .038). Femoral abduction was associated with medial translation of the femoral head (P = .042). Higher femoral anteversion and smaller alpha angle were associated with a higher total magnitude of femoral head translation in the anterior-posterior direction (P < .04). Smaller femoral anteversion, higher acetabular inclination, smaller lateral center-edge angle, and lower neck-shaft angle were associated with a higher total magnitude of femoral head translation in the superior-inferior direction (P ≤ .03). Conclusion: Our study demonstrated that, during passive physiologic movement, asymptomatic hips on average translated up to 2 mm (with up to 7 mm maximum translation in some positions), which is potentially related to hip rotations and morphology. Further investigations are warranted to understand the normal and pathologic hip translations and their impact on hip function (ie, instability and impingement).

Comparison of Size of Posterior Tibial Slope and Medial Tibial Depth in Patients With an Isolated Meniscal Tear Requiring Surgery and Matched Uninjured Controls.

BACKGROUND: Meniscal injuries are extremely common. Several anatomic features of the knee, including the tibial plateau morphology, have been shown to influence knee biomechanics and the risk of ligamentous injuries. Little is known, however, how these morphological features influence the risk of isolated meniscal injuries in the anterior cruciate ligament (ACL)-intact knee. HYPOTHESIS: There are differences in the slopes and concavity of the tibial plateau between patients with isolated meniscal tears and matched uninjured controls. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: In total, 89 patients with first-instance isolated medial (n = 37) or lateral (n = 52) meniscal injuries requiring surgical treatment (mean age, 16 ± 1 years; 35% female) were matched to 89 controls with uninjured knees and no previous injuries (mean age, 16 ± 2 years; 35% female) based on age and sex. Magnetic resonance imaging scans (preoperative for injured group) were used to measure the coronal slope of the tibial plateau, posterior slope of the medial and lateral tibial plateaus, and maximum depth of the medial tibial plateau. General linear models were used to evaluate the differences in tibial plateau morphology between the knees with and without meniscal injuries, with and without adjustment for age and sex. RESULTS: Compared with matched controls, patients with surgically treated isolated meniscal tears had a smaller lateral tibial slope (by 2.2° [medial meniscal injury] and 1.6° [lateral meniscal injury]; P < .02), a smaller medial tibial slope (by 2.3° [medial meniscal injury] and 2.4° [lateral meniscal injury]; P < .001) and a larger medial tibial depth (by 0.8 mm [medial meniscal injury] and 0.9 mm [lateral meniscal injury]; P < .001). There were no differences in coronal tibial slope between the injured and uninjured groups. There were no differences in quantified anatomic features between the isolated medial and lateral meniscal injury groups. The same trends were observed after adjusting for age and sex. CONCLUSION: This study suggests that patients with an isolated meniscal tear requiring surgery have a smaller posterior tibial slope and a larger medial tibial depth (more concave medial tibial plateau) than matched uninjured controls. This is contrary to what is known for ACL tears, in which a steeper posterior tibial slope and a shallower medial tibial depth have been associated with an increased risk of ACL tear.

Effects of joint loading on the development of capital femoral epiphysis morphology.

INTRODUCTION: The deleterious influence of increased mechanical forces on capital femoral epiphysis development is well established; however, the growth of the physis in the absence of such forces remains unclear. The hips of non-ambulatory cerebral palsy (CP) patients provide a weight-restricted (partial weightbearing) model which can elucidate the influence of decreased mechanical forces on the development of physis morphology, including features related to development of slipped capital femoral epiphysis (SCFE). Here we used 3D image analysis to compare the physis morphology of children with non-ambulatory CP, as a model for abnormal hip loading, with age-matched native hips. MATERIALS AND METHODS: CT images of 98 non-ambulatory CP hips (8-15 years) and 80 age-matched native control hips were used to measure height, width, and length of the tubercle, depth, width, and length of the metaphyseal fossa, and cupping height across different epiphyseal regions. The impact of age on morphology was assessed using Pearson correlations. Mixed linear model was used to compare the quantified morphological features between partial weightbearing hips and full weightbearing controls. RESULTS: In partial weightbearing hips, tubercle height and length along with fossa depth and length significantly decreased with age, while peripheral cupping height increased with age (r > 0.2, P < 0.04). Compared to normally loaded (full weightbearing) hips and across all age groups, partially weightbearing hips' epiphyseal tubercle height and length were smaller (P < .05), metaphyseal fossa depth was larger (P < .01), and posterior, inferior, and anterior peripheral cupping heights were smaller (P < .01). CONCLUSIONS: Smaller epiphyseal tubercle and peripheral cupping with greater metaphyseal fossa size in partial weightbearing hips suggests that the growing capital femoral epiphysis requires mechanical stimulus to adequately develop epiphyseal stabilizers. Deposit low prevalence and relevance of SCFE in CP, these findings highlight both the role of normal joint loading in proper physis development and how chronic abnormal loading may contribute to various pathomorphological changes of the proximal femur (i.e., capital femoral epiphysis).

Smaller epiphyseal tubercle in hips with slipped capital femoral epiphysis compared to the uninvolved contralateral hip.

Recent investigations suggest that physeal morphologic features have a major role in the capital femoral epiphysis stability and slipped capital femoral epiphysis (SCFE) pathology, with a smaller epiphyseal tubercle and larger peripheral cupping of the femoral epiphysis being present in hips with progressive SCFE compared to healthy controls. Yet, little is known on the causal versus remodeling nature of these associations. This study aimed to use preoperative magnetic resonance imaging (MRI) of patients with unilateral SCFE to perform a comparison of the morphology of the epiphyseal tubercle, metaphyseal fossa, and peripheral cupping in hips with SCFE versus the contralateral uninvolved hips. Preoperative MRIs from 22 unilateral SCFE patients were used to quantify the morphological features of the epiphyseal tubercle (height, width, and length), metaphyseal fossa (depth, width, and length), and peripheral cupping height in three dimension. The quantified anatomical features were compared between hips with SCFE and the contralateral uninvolved side across the whole cohort and within SCFE severity subgroups using paired t-test. We found significantly smaller epiphyseal tubercle heights (p < 0.001) across all severities of SCFE when compared to their uninvolved contralateral side. There was a marginally smaller metaphyseal fossa length (p = 0.05) in SCFE hips compared to their contralateral uninvolved hips, with mild SCFE hips specifically having smaller fossa and epiphyseal lengths (p < 0.05) than their contralateral uninvolved side. There were no side-to-side differences in any other features of the epiphyseal tubercle, metaphyseal fossa and peripheral cupping across all severities (p > 0.05). These findings suggest a potential causal role of epiphyseal tubercle in SCFE pathogenesis.