Purpose of the study: Anteversion of the cup during total hip arthroplasty (THA) is crucial for preventing the risk of dislocation. Interest has recently focused on an anatomic element often observed in the operative field during hip surgery: the transverse acetabular ligament (TAL). The TAL has become a landmark both for conventional procedures (Beverland) and for computed-assisted surgery. The purpose of this original research was to study the anteversion of the TAL in relation to the anterior pelvic plane in order to determine whether it could be a valid landmark for positioning the cup using the Lewinnek criteria (35±20° anteversion according to the Murray definition).

Material and methods: Eight laboratory cadavers (three male, five female, mean age 82±3.3 years) were dissected; the pelvis was removed. Fifteen fresh healthy hips (free of trauma or degenerative disease) were also used for the study. The orientation of the peri-acetabular structures was measured with the probe of the BrainLab^® navigation system and the Motion Analysis^® system (Santa Rosa. CA) at the laboratory of biomechanics and biomechanical shocks (INRETS, Bron). The Lewinnek reference plane (anterior pelvic plane) was defined from the anterosuperior iliac spines and the pubic tubercles.

Results: The anatomic version of the TAL varied from −8 to +13.3 (mean 1.9); the anatomic version of the horns of the semilunate surface from −12.2 to +14 (mean 3); for the labrum the figures were +17.4 to +41.8 (mean 26.63). Anteversion of the TAL and the horns were well correlated (r=0.8) significantly (p=0.001).

Discussion: There is no other study concerning the anatomic orientation of the TAL, the horns and the labrum. Archbold was the first to consider the TAL (1000 cases, posterolateral access, 28 mm head) as a reliable constant landmark for positioning the cup (0.6% dislocation). In our study, the anatomic version of the TAL was found outside the safety zone of Lewinnek. This is a supplementary argument for questioning the reliability of the Lewinnek criteria based solely on nine cases of dislocation and criticised by several authors (non-specific for each patient).

Conclusion: Anteversion of the labrum is situated within this safety zone. The TAL does not position the cup in the Lewinnek safety zone, which remains controversial.

Purpose of the study: To our knowledge, only qualitative data is available concerning the tension placed on the first carpometacarpal ligaments as a function of joint motion. The three articles published in the literature have provided discordant data. We conducted a quantitative study.

Material and methods:

Digitalized computed tomographies of the carpometacarpal joints magnified threefold were fed to a Stratasys® machine which created a rapid «polystyrene shock» prototype of the first and second metacarpals as well as the trapezium and the trapezoid.

Results: The anterior oblique ligament was under tension in the positions close to extension (positions L and D). The posterior oblique ligament was under tension in the position of ulnar finger opposition and in volar abduction (positions K and F). The inter-osseous ligament was under ension in volar abduction, opposition and flexion (positions F, K, J). A complex behavior was observed, best described by two portions, medial and lateral.

Discussion: This preliminary study on a model system depended on the interpretation of the ligament and joint surface anatomy. The method of creating joint motion described by Pieron enables comparison between two studies but does not correspond to the physiological position.

Conclusion: For a small-sized joint, magnification of the bony pieces and use of optical magnification facilitates apprehension of ligament lengthening during joint motion. This method can be used to better assess maximal range of motion according to ligament deformations observed in relation to joint solicitation.