Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking

• Published in: Clinical orthopaedics and related research 2017-04, Vol.475 (4), p.998-1008
• Main Authors: Ng, K. C. Geoffrey, Mantovani, Giulia, Lamontagne, Mario, Labrosse, Michel R., Beaulé, Paul E.
• Format: Article
• Language: English
• Subjects: Adult; Asymptomatic Diseases; Biomechanical Phenomena; Case-Control Studies; Computer Simulation; Conservative Orthopedics; Disease Progression; Femoracetabular Impingement - complications; Femoracetabular Impingement - diagnostic imaging; Femoracetabular Impingement - physiopathology; Femur Neck - diagnostic imaging; Femur Neck - physiopathology; Finite Element Analysis; Hip; Hip Joint - diagnostic imaging; Hip Joint - physiopathology; Humans; Medicine; Medicine & Public Health; Models, Biological; Orthopedics; Sports Medicine; Stress, Mechanical; Surgery; Surgical Orthopedics; Symposium: 2016 Bernese Hip Symposium; Tomography, X-Ray Computed; Walking
• ISSN: 0009-921X; 1528-1132
• DOI: 10.1007/s11999-016-5038-2

Background It is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear. Questions/purposes We examined the effects of the cam morphology and femoral neck-shaft angle on hip stresses during walking by asking: (1) Are there differences in hip stress characteristics among symptomatic patients with cam morphology, asymptomatic individuals with cam morphology, and individuals without cam morphology? (2) What are the effects of high and low femoral neck-shaft angles on hip stresses? Methods Six participants were selected, from a larger cohort, and their cam morphology and femoral neck-shaft angle parameters were measured from CT data. Two participants were included in one of three groups: (1) symptomatic with cam morphology; (2) asymptomatic with a cam morphology; and (3) asymptomatic control with no cam morphology with one participant having the highest femoral neck-shaft angle and the other participant having the lowest in each subgroup. Subject-specific finite element models were reconstructed and simulated during the stance phase, near pushoff, to examine maximum shear stresses on the acetabular cartilage and labrum. Results The symptomatic group with cam morphology indicated high peak stresses (6.3–9.5 MPa) compared with the asymptomatic (5.9–7.0 MPa) and control groups (3.8–4.0 MPa). Differences in femoral neck-shaft angle influenced both symptomatic and asymptomatic groups; participants with the lowest femoral neck-shaft angles had higher peak stresses in their respective subgroups. There were no differences among control models. Conclusions Our study suggests that the hips of individuals with a cam morphology and varus femoral neck angle may be subjected to higher mechanical stresses than those with a normal femoral neck angle. Clinical Relevance Individuals with a cam morphology and decreased femoral neck-shaft angle are likely to experience severe hip stresses. Although asymptomatic participants with cam morphology had elevated stresses, a higher femoral neck-shaft angle was associated with lower stresses. Future research should examine larger amplitudes of motion to assess adverse subchondral bone stresses.