Background: A fracture is the most serious complication of surgical resection of the femoral head-neck junction in the treatment of cam-type femoroacetabular impingement (FAI). Purpose: To investigate the influence of resection length, width, and depth on postoperative fracture risk in activities of daily living. Study Design: Descriptive laboratory study. Methods: The femoral anatomy used for the finite element model was based upon a publicly available standardized model. For descriptive validation, the fracture location was compared with radiographs of patients who had suffered from a femoral neck fracture after surgical treatment of FAI in our institution. Additionally, a 2-part quantitative validation against previously published experimental data was performed. To simulate surgery, round resections were made in which length and width were varied at 10%, 20%, and 30%. The fracture loads were compared with published in vivo loads measured during activities of daily living with telemetric hip implants. Results: Validation showed that the model predicted fracture locations comparable with clinical cases and fracture loads within published experimental values. Femoral fracture loads were 325% more sensitive to resection deepening and 70% more sensitive to widening than lengthening. Conclusion: Although resection depth is the most important determinant of bone resistance, it should be considered in combination with resection length and width. Even a resection depth as low as 10% may lead to a fracture in case of stumbling. Clinical Relevance: We show that for resection depths of 20% or less and resection length of less than 35% of the femoral neck, normal activities of daily living are safe. Resection widths typically achieved in practice did not induce fractures during activities of daily living. Patients who have undergone surgical resection should be counseled on how to try to avoid stumbling.

Assessment of scaphoid fracture union on computed tomography scans is not currently standardized. We investigated the extent of scaphoid waist fracture union required to withstand physiological loads in a finite element model, based on a high-resolution CT scan of a cadaveric forearm. For simulations, the scaphoid waist was partially fused at the radial and ulnar sides. A physiological load of 100 N was transmitted to the scaphoid and the minimal amount of union to maintain biomechanical stability was recorded. The orientation of the fracture plane was varied to analyse the effect on biomechanical stability. The results indicate that the scaphoid is more prone to re-fracture when healing occurs on the ulnar side, where at least 60% union is required. Union occurring from the radial side can withstand loads with as little as 25% union. In fractures more parallel to the radial axis, the scaphoid seems less resistant on the radial side, as at least 50% union is required. A quantitative CT scan analysis with the proposed cut-off values and a consistently applied clinical examination will guide the clinician as to whether mid-waist scaphoid fractures can be considered as truly united.

Scaphoid fractures are the second most common wrist injury after distal radius fractures and primarily affect young individuals in their most productive working years. Some scaphoid fractures fail to heal, potentially resulting in chronic pain, functional impairment, and long-term osteoarthritis in the wrist, which may require salvage procedures and can have a significant impact on work capacity. Considerable debate exists around the biological and injury-related risk factors for scaphoid non-unions, as well as the criteria for surgical intervention. However, epidemiological data are still limited, often derived from small populations, and incidence reports about scaphoid non-unions remain inconsistent. In a retrospective analysis of over 9 Mio injuries, recorded by the Swiss National Accident Insurance (Suva) Statistical Service from 2008 to 2021, we identified 16,691 scaphoid fractures. The male-to-female ratio was 4:1 for both scaphoid fractures and non-unions. The rate of primary surgery was 1:3. Around 14% of scaphoid fractures progressed to non-union, and 3% developed posttraumatic arthritis. Patients with non-unions were three times more likely to be unable to work for more than 12 months. Blue-collar workers were particularly at risk for a non-union and for extended work absence. Notably, the type of treatment (surgical or non-surgical) had no significant effect on work absence-non-union itself was the key determinant.

The scaphoid is the most commonly fractured carpal bone. Headless compression screws became the gold standard for fixation, but the ideal screw diameter remains debated. This study investigates the relative benefit of using a larger screw diameter to improve stability in typical scaphoid fractures. It also examines the effects of preload and screw length on mechanical behaviour. A finite element (FE) model of a mid-waist scaphoid fracture was created. Screws from Medartis (1.7 mm, 2.2 mm, and 3.0 mm diameter; 23 mm length) were placed along the longitudinal axis. Boundary and loading conditions matched prior studies. Interfragmentary displacement (IFD) and von Mises stress were compared across screw sizes. The effects of screw length and preload were also evaluated. Maximum in-plane IFD was 2.08 mm (1.7 mm screw), 0.53 mm (2.2 mm), and 0.27 mm (3.0 mm). The 1.7 mm screw exceeded the scaphoid’s average ultimate stress (60.51 MPa). Increasing preload reduced IFD, especially above 60 N. Screws longer than 1.5 times the mid-waist diameter offered no added benefit. Larger screws provide better biomechanical fracture stability. However, the gain from 2.2 mm to 3.0 mm is minor, while 1.7 mm screws lack sufficient strength. The 2.2 mm screw offers a good balance of stability and bone preservation, making it the preferred choice.

We previously demonstrated that Homeobox (HOX) transcription factors are differentially expressed between joint locations and can accurately assign synovial fibroblasts (SFs) to their correct joint location. We show here that the expression of the 5’HOXD transcription factors HOXD10, HOXD11, and HOXD13 in SFs strikingly overlaps with predilection sites for the development of rheumatoid arthritis (RA). Changes in SFs gene expression after silencing 5’HOXDs aligned with joint-specific differences of RA SFs. In particular, we identify HOXD13 as regulator or primary cilia function in SFs modulating cell cycle, DNA damage and proteasome activity. Accordingly, we show joint specific differences in primary cilia morphology, DNA damage repair and proteasome activity. We thus propose that HOXD13 and primary cilia play a role in shaping joint-specific SFs functions that might underlie the pathognomic pattern of joint involvement in RA.