Purpose

The measurement of radial head translation about the capitellum (in percent): the radio-capitellum ratio (RCR) has proven to have excellent inter- and intra-observer reliabilities when measuring the RCR on a lateral radiological view of elbows at 90° of flexion and in the neutral position of the forearm. However, in the clinical setting, radiographs may be taken with the elbow in different positions. However, the purpose was to validate the RCR measurement method on elbows in different positions in flexion-extension and in different positions of the forearm in pronation-supination.

Purpose: The literature contains little information on an objective method of measuring radiocapitellar joint translations, as would be seen with joint instability. The purpose of this study was to develop and validate a measurement method that was simple and that could be easily reproducible in a clinical setting or intra-operatively to assess radiocapitellar joint translations.

Method: We performed a radiological study on a synthetic elbow specimen in order to quantify radial head translations as related to the capitellum: the Radio-capitellum ratio (RCR). Thirty (30) lateral elbow x-rays were taken in different magnitude of subluxation of the radial head. The subluxation was created randomly by manipulation. X-rays where taken by fluoroscopy to obtain a perfect lateral view of the distal humerus. First, the evaluators determined the long axis of the radius and the center of the capitellum. The displacement of the radial head (in mm) was obtained by measuring the distance of the line perpendicular to the long axis of the radius passing through the center of the capitellum. Then, in order to adjust for variation of magnification, a ratio of the displacement of the radial head about the diameter of the capitellum was done. The RC ratio would be of zero because the long axis of the radius always crosses the center of the capitellum in a perfectly aligned joint. A five mm translation of the radial head and a capitellum diameter of twenty (20) mm would give a RCR of 25% and would be positive if anterior and negative if posterior. The measurements were done two times at one week intervals by three independent evaluators to test inter-observer agreement and intra-observer consistency. The radiological incidences were randomly ordered to minimize observer recall bias. Intra/inter-observer reliability was calculated using Intra-Class Correlation (ICC) and paired T-tests.

Results: The mean translation in the trial group was of 6,06% (SD 70.7%) from – 167% to 125%. A result over 100% means that it is a complete dislocation ie – the axis of the radius is outside of the capitellum. Negative values signify posterior translation and positive values an anterior translation. Intra-observer reliability was excellent for the Radio-capitellum ratio (ICC 0.988 and 0.995) and inter-observer reliability was excellent (ICC 0.984 in average). Paired T-test results confirm a high intra-observer repeatability (p=0.97 and p=0.99) as well as a large inter-observer reproducibility (p=0.98 in average).

Conclusion: The proposed measurement of radial head translation about the capitellum (in percent): radio-capitellum ratio (RCR) has excellent inter – and intra-observer reliability when using our measurement method.

Purpose: Greater trochanter reattachment is frequently accomplished using cable grip type systems. There is a relatively high failure rate for these systems, the mechanisms of which are unclear. One possible source of instability could be femoral neck cut location. Another concern is the effect of variability in cable tension. The objective is to create a femur implant model which allows for variation in cable tension, common muscle forces and the placement of the femoral neck cut in order to analyse trochanter fragment fixation.

Method: A finite element model (FEM) of a femur with simulated greater trochanter osteotomy (30°) was combined with the femoral component of a hip prosthesis and a greater trochanter reattachment system with 4 cables (Cable-Ready®, Zimmer). A total of 18 simulations were modeled in a full factorial design using three independent variables; cable tightening (178N, 356 N and 534 N), muscle forces (rest, walking and stair climbing) and femoral neck cut (10 mm and 15 mm above the lesser trochanter). Displacement of the fragment, in terms of both gap and shear components, as well, stress in the bone were investigated.

Results: The location of the femoral neck cut reduced contact surface area by 20% and had the largest influence on displacement (0.24 mm). Pivoting of the fragment was observed with a maximum gap (0.38 mm) and maximum total displacement (0.41 mm) at the bottom of the fragment. This was observed during stair climbing, while the cables were tightened to 177.9 N and with the femoral neck cut at 10 mm. Increased tightening of the cables provided no significant reduction in fragment displacement. However, higher cable tension significantly increased the stress in the bone (8 MPa and 26 MPa for cable tension of 178 N and 534 N respectively).

Conclusion: Placement of the femoral neck cut closer to the lesser trochanter significantly increased fragment displacement. Preservation of the contact surface area is recommended. Excessive cable tightening did not reduce fragment movement and only exacerbated bone stress. Caution must be used to not over tighten the cables. This model can be used to test and compare the performance of new implant designs.

Purpose: To determine the relationship between sacral morphology and developmental L5/S1 spondylolisthesis in children and adolescent.

Method: A radiographic study was conducted to investigate sacral morphology in developmental L5/S1 spondylolisthesis in a pediatric and adolescent population. The lateral standing radiographs of 131 subjects, aged 6 to 20 years old with developmental L5-S1 spondylolisthesis (91 low grade and 40 high grade) were analyzed with a dedicated software allowing to measure the following parameters, which were analyzed for each subject by the same individual and compared to an age and sex-matched cohort of 120 asymptomatic subjects: the sacral table index (STI), the sacral table angle (STA), the sacral kyphosis (SK), S1 superior angle, S2 inferior angle, and grade of spondylolisthesis. Student t tests were used to compare the parameters between the curve types.

Results: This study demonstrated that STA is significantly smaller (p< 0.01) in children and adolescents with L5-S1 spondylolisthesis compared to a similar control group. Furthermore, STA is significantly smaller in high grade spondylolisthesis when compared to subjects with low grade. There is also a significant difference in segmental sacral morphology (S1 and S2 anatomy) in the spondylolisthesis group. Increasing sacral kyphosis is also found to be significantly associated with spondylolisthesis.

Conclusion: The sagittal sacral morphology is a constant anatomic variable specific to each normal individual. The anatomy of the sacrum in children and aldolescentss with L5-S1 spondylolisthesis is particular and different from a control group. This study suggests that sacral anatomy may have a direct influence on the development of spondylolisthesis: a lower STA and higher sacral kyphosis may be two factors predisposing to vertebral slip in developmental spondylolisthesis.