Acetabular Migration of Lag Screw of Intramedullary Nail Used as Treatment for Intertrochanteric Fracture. Case Study

Most trochanteric fractures of the femur are classified as low-energy fractures as they are seen in people with decreased mechanical properties of bone tissue. The treatment is assumed to provide biomechanical fixation with the possibility of dynamization between bony fragments to stimulate the biological processes of bone union. The aim of the study was to analyze a complication presenting as migration of the cervical screw of an intra­medullary nail towards the hip joint acetabulum and present the therapeutic management of this complication. The case report concerned a 74-year-old patient with an AO/OTA type 31 A2.2 fracture of the trochanteric massif of the right femur treated with the Gamma3 intramedullary nail. An assessment of changes over time of the radiological appearances on A-P images after the surgery showed migration of the cervical screw towards the acetabulum and displacement of the major trochanter fracture. Extensive destruction of the acetabular fossa made biologic restorative treatment impossible. A total hip joint prosthesis with a modular stem and MDM articulation was implan­ted and the trochanter was fixed with a "hook" plate with a "cable system". The postoperative course was uneventful. Failure to perform axial radiographs in the preoperative and postoperative period made it impossible to objectively determine the type of fracture and the quality of screw insertion into the femoral neck, and assessment limited to A-P images turned out to be deceptive. The wandering of the screw towards the acetabulum led to extensive destruction of the acetabular fossa. The decision to stop biological treatment, which, if properly performed, stimulates bone union, and perform the mechanical procedure of endoprosthesoplasty was fully prognostically justified. The early and late postoperative course was not complicated.

Morphologic and Morphometric Study of Human Acetabulum and its Clinical Significance

Introduction: The acetabulum is a cup shaped hemispherical depression which is present on the hip bone, contributed by ilium, ischium and pubis. It has a central depressed non-articular part called acetabular fossa, surrounded by a curved lunate articular surface which articulates with the head of femur to form hip joint. The knowledge of acetabular dimensions assists the radiologists in diagnosing acetabular dysplasia and aids the surgeon to determine the correct size of the acetabular cup during total hip arthroplasty and to realign the acetabulum back to normal position. Aim: To measure and analyse the relationship between the depth and diameter of acetabulum and also to study the variations in the morphology of anterior acetabular ridge. Materials and Methods: A cross-sectional study was done on 104 unpaired dry human adult hip bones from February 2017 to September 2019 after obtaining ethical clearance. The diameter and depth of acetabulum was measured using vernier calliper and a metallic strip and correlation between them were analysed using Pearson’s test. Student’s t-test was used to test the significance between the variables. The p-value <0.05 were considered as statistically significant. The different shapes of anterior acetabular ridge were noted. All the recorded data were analysed using Statistical Package for the Social Sciences (SPSS version 16.0). Results: The average measurements of acetabular diameter and depth were 48.98±2.91 mm and 24.12±2.54 mm, respectively. A positive and a significant correlation was found between diameter and depth of the acetabulum (r=0.388, p<0.001). The mean values of diameter and depth of acetabulum in right side were 48.76±2.94 mm and 23.6±2.48 mm, respectively. The average values of diameter and depth in left side were 49.2±2.92 mm and 24.6±2.59 mm, respectively. Though the measurements of acetabular dimensions on left side were slightly greater than right side, they were not statistically significant (p>0.05). Four different shapes of anterior acetabular ridges were noted: angular (23.08%), curved (63.46%), straight (2.88%) and irregular (10.58%). Conclusion: The present study showed weakly positive correlation between diameter and depth of the acetabulum and morphological variations in the shape of anterior acetabular ridge.

Hip preservation surgery and the acetabular fossa

As our understanding of hip function and disease improves, it is evident that the acetabular fossa has received little attention, despite it comprising over half of the acetabulum’s surface area and showing the first signs of degeneration. The fossa’s function is expected to be more than augmenting static stability with the ligamentum teres and being a templating landmark in arthroplasty. Indeed, the fossa, which is almost mature at 16 weeks of intrauterine development, plays a key role in hip development, enabling its nutrition through vascularization and synovial fluid, as well as the influx of chondrogenic stem/progenitor cells that build articular cartilage. The pulvinar, a fibrofatty tissue in the fossa, has the same developmental origin as the synovium and articular cartilage and is a biologically active area. Its unique anatomy allows for homogeneous distribution of the axial loads into the joint. It is composed of intra-articular adipose tissue (IAAT), which has adipocytes, fibroblasts, leucocytes, and abundant mast cells, which participate in the inflammatory cascade after an insult to the joint. Hence, the fossa and pulvinar should be considered in decision-making and surgical outcomes in hip preservation surgery, not only for their size, shape, and extent, but also for their biological capacity as a source of cytokines, immune cells, and chondrogenic stem cells. Cite this article: Bone Joint Res 2020;9(12):857–869.

A Patient-specific Navigational Template for Precise Acetabular Placement in Unilateral Total Hip Arthroplasty: A Cadaveric Study

Background Total hip arthroplasty (THA) is a widely performed reconstructive surgical intervention. In this paper, we describe a novel patient-specific navigational template to assist in acetabular component implantation in unilateral THA. Methods The template was produced based on data preoperatively acquired with computed tomography (CT) scan. We used the mirror image of the healthy contralateral acetabular anatomical structure to ensure accurate acetabular component implantation in unilateral THA. The surface of the template was designed to conform to the unique contours of the cadaveric acetabular fossa by reverse engineering technology. The orientation of the navigation channel was defined by the acetabular central axis which was determined by the contralateral acetabular centre of rotation, anteversion angle and abduction angle. Each template was formed from acrylate resin by using rapid prototyping (RP) technique. Finally, the template was tested in 20 cadavers scheduled for unilateral THA and postoperative medical imaging was used to evaluate the accuracy and validity of the template. Results During the operation, the acetabular fossa template was easy to obtain in all cases. The abduction angle ( β ) of the cup was (49.9°±4.1°) versus (49.5°±4.7°) on the contralateral side. The anteversion angle (α) of the cup was (17.7° ± 3.1°) versus (18.3°±3.5°) on the contralateral side. In the operative hip, the height of the prosthesis centre(H)was (21.6 mm±2.8 mm) versus (21.9 mm±3.4 mm) in the contralateral side, and the horizontal location of the prosthesis centre(W) was (29.7 mm±3.1 mm) versus (30.90 mm±3.31 mm) in the contralateral side. There was no significant difference in the cup abduction (β) or anteversion (α) angle between the operative and contralateral sides (P=0.7531>0.05 for β and P=0.5996>0.05 for α); In addition, there was no significant difference in the height(H)or horizontal location(W) of the acetabular centre between the operative and contralateral sides (P=0.6494>0.05 for W and P=0.5143>0.05 for H). Conclusion The navigational template is a promising tool for facilitating preoperative planning and intraoperative techniques. With the aid of the template, an acetabular prosthesis can be precisely implanted to the expected position in unilateral THA.

Does Capsular Laxity Lead to Microinstability of the Native Hip?

Background: Hip “microinstability” is commonly cited as the cause of symptoms that occur in the presence of translation of the femoral head away from conformity with the acetabular fossa. However, there is still no consistent objective criteria defining its presence and biomechanical basis. One hypothesis is that abnormal motion of the articular surfaces occurs because of capsular laxity, ultimately leading to clinical symptoms. Purpose: To determine the relationship between capsular laxity and abnormal rotation and translation of the hip. Study Design: Controlled laboratory study. Methods: Eight cadaveric hips were dissected down to the capsule and mounted in a customized multiaxial hip activity simulator. Each specimen was loaded with 5 N·m of internal and external rotational torque in full extension and 0°, 30°, 60°, and 90° of flexion. During testing, the relative position and rotation of the femur and the pelvis were monitored in real time with a 6-camera motion analysis system. The testing was repeated after capsular laxity was generated by placing a regular array of incisions (“pie crusting”) in the iliofemoral, pubofemoral, and ischiofemoral ligaments. Joint rotation and femoral head translation were calculated with specimen-specific models. A hip microinstability index was defined as the ratio between the length of the locus of the femoral head center and the radius of the femoral head during rotation from extension to 90° of flexion. Results: In intact hips, the components of femoral head translation were within 0.5 mm in positions close to neutral (<30° of flexion). Capsular modification led to significant increases in internal and external rotation ( P < .01) and in the translation of the femoral head center at different positions ( P < .05). Compared with intact hips, the femoral head was inferiorly displaced during external rotation and anteroinferiorly during internal rotation. The length of the locus of the femoral head center increased from 3.61 ± 1.30 mm to 5.35 ± 1.83 mm for external rotation ( P < .05) and from 6.24 ± 1.48 mm to 8.21 ± 1.42 mm for internal rotation ( P < .01). The correlations between rotational laxity and the total translation of the femoral head were not significant, with coefficients of 0.093 and 0.006 in external and internal rotation, respectively. In addition, the hip microinstability index increased from 0.40 ± 0.08 for intact hips to 0.55 ± 0.09 for modified hips ( P < .01). Conclusion: The native hip approximates a concentric ball-and-socket joint within 30° of flexion; however, beyond 30° of flexion, the femoral head translation reached as high as 4 mm. Capsular laxity leads to microinstability of the hip, as indicated by significantly increased joint rotations and femoral head translations and an abnormal movement path of the femoral head center. However, there was no correlation between rotational laxity and the increase in femoral head translation. Clinical Relevance: Capsular laxity alters normal kinematics (joint rotation and femoral head translation) of the hip, potentially leading to abnormal femoral-acetabular contact and joint degeneration.