A novel hybrid design and modelling of a customised graded Ti-6Al-4V porous hip implant to reduce stress-shielding: An experimental and numerical analysis.

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of hip prostheses and exacerbates revision surgery rates. In order to minimise post-hip replacement stress variations, this investigation proposes a low-stiffness, porous Ti6Al4V hip prosthesis, developed through selective laser melting (SLM). The stress shielding effect and potential bone resorption properties of the porous hip implant were investigated through both in vitro quasi-physiological experimental assays, together with finite element analysis. A solid hip implant was incorporated in this investigation for contrast, as a control group. The stiffness and fatigue properties of both the solid and the porous hip implants were measured through compression tests. The safety factor of the porous hip stem under both static and dynamic loading patterns was obtained through simulation. The porous hip implant was inserted into Sawbone/PMMA cement and was loaded to 2,300 N (compression). The proposed porous hip implant demonstrated a more natural stress distribution, with reduced stress shielding (by 70%) and loss in bone mass (by 60%), when compared to a fully solid hip implant. Solid and porous hip stems had a stiffness of 2.76 kN/mm and 2.15 kN/mm respectively. Considering all daily activities, the porous hip stem had a factor of safety greater than 2. At the 2,300 N load, maximum von Mises stresses on the hip stem were observed as 112 MPa on the medial neck and 290 MPa on the distal restriction point, whereby such values remained below the endurance limit of 3D printed Ti6Al4V (375 MPa). Overall, through the strut thickness optimisation process for a Ti6Al4V porous hip stem, stress shielding and bone resorption can be reduced, therefore proposing a potential replacement for the generic solid implant.

Idiopathic Capital Femoral Chondrolysis: A Case Report.

Idiopathic capital femoral chondrolysis is a rare condition most commonly seen in African-American pre-adolescent females. The primary symptoms are hip stiffness and pain, which are accompanied by limping. Physical examinations typically reveal an external rotation contracture, flexion contracture, and abduction contracture. There is also immobility at the hip secondary to muscle spasms. Here, we present and discuss the follow-up case of a 10-year-old female patient who was diagnosed with idiopathic chondrolysis of capital femoral epiphysis, right side, and underwent right hip arthroscopic evaluation and lavage. At follow-up two months after the right hip arthroscopic evaluation, she presented with painless limping on the right side. The patient underwent soft tissue release right hip under general anaesthesia and was discharged in stable condition.

Stress Shielding and Bone Resorption of Press-Fit Polyether-Ether-Ketone (PEEK) Hip Prosthesis: A Sawbone Model Study.

Stress shielding secondary to bone resorption is one of the main causes of aseptic loosening, which limits the lifespan of the hip prostheses and increases the rates of revision surgery. This study proposes a low stiffness polyether-ether-ketone (PEEK) hip prostheses, produced by fused deposition modelling to minimize the stress difference after the hip replacement. The stress shielding effect and the potential bone resorption of the PEEK implant was investigated through both experimental tests and FE simulation. A generic Ti6Al4V implant was incorporated in this study to allow fair comparison as control group. Attributed to the low stiffness, the proposed PEEK implant showed a more natural stress distribution, less stress shielding (by 104%), and loss in bone mass (by 72%) compared with the Ti6Al4V implant. The stiffness of the Ti6Al4V and the PEEK implant were measured through compression tests to be 2.76 kN/mm and 0.276 kN/mm. The factor of safety for the PEEK implant in both static and dynamic loading scenarios were obtained through simulation. Most of the regions in the PEEK implant were tested to be safe (FoS larger than 1) in terms of representing daily activities (2300 N), while the medial neck and distal restriction point of the implant attracts large von Mises stress 82 MPa and 76 MPa, respectively, and, thus, may possibly fail during intensive activities by yield and fatigue. Overall, considering the reduction in stress shielding and bone resorption in cortical bone, PEEK could be a promising material for the patient-specific femoral implants.

Patient-Specific Parameters Associated With Traction in Primary and Revision Hip Arthroscopic Surgery.

BACKGROUND: Distraction of the hip joint is a necessary step during hip arthroscopic surgery. The force of traction needed to distract the hip is not routinely measured, and little is known about which patient factors may influence this force. PURPOSE: To quantify the force of traction required for adequate distraction of the hip during arthroscopic surgery and explore the relationship between hip joint stiffness and patient-specific demographics, flexibility, and anatomy. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: A total of 101 patients (61 female) undergoing primary hip arthroscopic surgery were prospectively enrolled. A load cell attached to the traction boot continuously measured traction force. Fluoroscopic images were obtained before and after traction to measure joint displacement. The stiffness coefficient was calculated as the force of traction divided by joint displacement. Relationships between the stiffness coefficient and patient demographics and clinical parameters were investigated using a univariable regression model. The regression analysis was repeated separately by patient sex. Variables significant at P < .05 were included in a multivariable regression model. RESULTS: The instantaneous peak force averaged 80 ± 18 kilogram-force (kgf), after which the force required to maintain distraction decreased to 57 ± 13 kgf. In univariable regression analysis, patient sex, alpha angle, hamstring flexibility, and Beighton hypermobility score were each correlated to stiffness. However, patient sex was the only significant variable in the multivariable regression model. Intrasex analysis demonstrated that increased hamstring flexibility correlated with decreased final holding stiffness in male patients and that higher Beighton scores correlated with decreased maximal stiffness in female patients. CONCLUSION: Male patients undergoing primary arthroscopic surgery have greater stiffness to hip distraction during arthroscopic surgery compared with female patients. In male patients, stiffness increased with decreasing hamstring flexibility. In female patients, increased Beighton scores corresponded to decreased stiffness. The presence of a labral tear was not correlated with stiffness to distraction. These data may be used to identify patients in whom a specific focus on capsular repair and/or plication may be warranted.

Idiopathic hypertonicity as a cause of stiffness after surgery for developmental dysplasia of the hip.

INTRODUCTION: There are various complications reported with surgical treatment of DDH. Most studied complication is avascular necrosis of the femoral head and hip stiffness. The purpose of this report was to describe a case with severe stiffness of the hip due to hypertonicity in periarticular muscles after it was treated for developmental dysplasia of the hip (DDH). PRESENTATION OF CASE: Three-year-old patient referred to our institution with bilateral DDH. Two hips were operated separately in one year with anterior open reduction, femoral shortening osteotomy. Third month after last surgery, limited right hip range of motion and limb length discrepency identified. Clinical examination revealed that patient had limited range of motion (ROM) in the right hip and compensated this with pelvis obliquity. Gluteus medius, sartorius and iliofemoral band release performed after examination under general anesthesia. Symptoms were persisted at 3rd week control and examination of the patient in general anesthesia revealed full ROM without increased tension. For the identified hypertonicity, ultrasound guided 100IU botulinum toxin A injection performed to abductor group and iliopsoas muscles. Fifth month later, no flexor or abductor tension observed, and there was no pelvic obliquity. DISCUSSION: Stiffness as a complication is rare and is usually resolved without treatment or simple physical therapy. Usually it is related with immobilization or surgery associated joint contracture, and spontaneous recovery reported. Presented case is diagnosed as hip stiffness due to underlying local hypertonicity. That is resolved with anesthesia and it was treated after using botulinum toxin A injection. CONCLUSION: Hypertonicity with hip stiffness after surgical treatment of DDH differ from spontaneous recovering hip range of motion limitation and treatment can only be achieved by reduction of the muscle hypertonicity by neuromuscular junction blockage.