Many surgical decisions taken in the operating theatre are based on the experience and the expertise of the surgeon. Using biomechanical and computational data can provide additional information for the surgeon. By carrying out biomechanical trials pre-operatively as well as a full three dimensional analysis of the skeletal structure of the patient, it is possible to provide the surgeon with clinical data that can support the decision making with regards of fixation method, type of implant and size to name a few. In the presented project a description is provided of the pre-operative assessment of primary total hip patients in Iceland and how the analysis is helping to prevent periprosthetic fractures.

Over 70 patients undergoing primary total hip arthroplasty in Iceland were recruited for the study¹. Gait analysis was performed on the patients using a pressure plate in conjunction with two synchronised video cameras. In addition, EMG was recorded from three muscles: Rectus femoris, Vastus lateralis and Vastus medialis on both the healthy and the operated leg. Finally the patient was CT-scanned with an in-plane resolution of 0.5mm and slice thickness of 1mm. Three dimensional objects of both the femur and muscles were created based on the scans. The material properties were derived from the Hounsfield units. Finite element analysis was carried out on the femur and the fracture risk of press fitting procedure was calculated and areas of weak points in the bone identified. Analysis was carried out on the muscles and the volume distribution between fat, connective tissue and muscle tissue calculated.

The results showed that basing fixation method on age and sex may not necessarily be a good indicator. The three dimensional bone mineral density distribution and the relative volume of cortical bone provided a better indication of which patients should receive cemented implant. Using a strain based failure criteria on the finite element models showed increased number in failed elements with decreased volume of cortical bone. The results of the biomechanical assessment for each patient were finally collected using an automatic report which was presented to the clinician.

Using biomechanical assessment and modelling can help identify an optimal treatment method for total hip patients by giving surgeons quantitative data on which they can build their decision making in the operating theatre. This can eventually lead to reduction in revisions and increased quality of life for the patient.

Total Hip Replacement (THR) is one of the most successful operations in all of medicine, however surgeons just rely on their experience and expertise when choosing between cemented or cementless stem, without having any quantitative guidelines. The aim of this project is to provide clinicians with some tools to support in their decision making. A novel method based on bone mineral density (BMD) measurements and assessments was developed 1) to estimate the periprosthetic fracture risk (FR) while press-fitting cementless stem; 2) to evaluate post-operative bone remodeling in terms of BMD changes after primary THR.

Data for 5 out of over 70 patients (already involved in a previous study¹) that underwent primary THA in Iceland were selected for developing novel methods to assess intra-operative FR and bone mineral density (BMD) changes after the operation. For each patient three CT images were acquired (Philips Brilliance 64 Spiral-CT, 120 kVp, slice thickness: 1 mm, slice increment: 0.5 mm): pre-op, 24 hours and 1 year post-operative.

Pre-op CT scan was used to create 3D finite element model (Materialise Mimics) of the proximal femur.

The material properties were assigned based on Hounsfield Units. Different strategies were analyzed for simulating the press-fitting operation, developing what has already been done in prior study¹. In the finite element simulation (Ansys Workbench), a pressure (related to the implant hammering force of 9.25 kN²) was applied around the femur's hollow for the stem and the distribution of maximum principal elastic strain over the bone was calculated. Assuming a critical failure value³ of 7300 με, the percentage of fractured elements was calculated (i.e. FR).

Post 24 hours and Post 1 year CT images were co-registrated and compared (Materialise Mimics) in order to assess BMD changes. Successively, volumes of bone lost and bone gained were calculated and represented in a 3D model.

Age and gender should not be taken as unique indicators to choose between implants typologies, since also three dimensional BMD distribution along with volume of cortical bone influence the risk of periprosthetic fractures. Highest FR values were experienced in the calcar-femorale zone and in similar location on the posterior side.

BMD loss volume fractions after 1 year were usually higher than BMD gain ones. Consistently with prior studies⁴, BMD loss was mainly concentrated around the proximal end (lesser trochanter area, outer bone).

If present, BMD gain occurred at the distal end (below stem's tip) or proximally (lesser trochanter area, interface contact with the stem).

The use of clinical data for BMD assessments serves as an important tool to develop a quantitative method which will support surgeons in their decisions, guiding them to the optimal implant for the patient. Knowing the risk of fracture if choosing a cementless stem and being aware of how the bone will remodel around the stem in one year's time can eventually lead to reduction in revisions and increased quality of life for the patient. Further work will target analysis of a larger cohort of patients and validate FE models.

Wrist arthrodesis is a common surgical procedure that provides a high level of functional outcome and pain relief among patients.[1] Upon partial arthrodesis, the wrist experiences changes in load transmission that are influenced by the type of arthrodesis performed. Measuring the load through the wrist joint is difficult, however, combined with computational models [2], it is possible to obtain data regarding the load mechanics of the wrist joint. Although successful fusion rates among patients have been reported, it remains unclear what the biomechanical consequences are.

The aim of the study is to quantify pre and post operative load transmission through a cadaveric wrist which has undergone simulated arthrodesis of the radiolunate(RL) joint. An embalmed human wrist was dissected dorsally exposing distal radius, radiocarpal and carpometacarpal joints, and dorsal ligaments. The radioscaphoid(RS) ligament was sacrificed to accommodate insertion of a PPSEN-09375 force sensitive resistor (FSR) into the RS joint. The FSR was calibrated prior to measuring the contact force on the RS joint.

The wrist was aligned in the neutral position in cardboard piping, and secured proximally and distally with Dental Plaster (OthoBock Healthcare Plc, Surrey, UK). The midsection of piping was windowed to permit placement of the FSR in the RS joint, and fixation of the RL joint using 2 Kirschner wires. The window was completed circumferentially and the specimen was placed in the Instron where a graduated axial compression was applied at 20 N/min.

The results showed that when the radiolunate joint is fused, and a total axial load of 100N is applied, the load transmitted through the RS joint was approx 65N. i.e. 65% of the force. This is greater than the 56% measured experimentally by Blevens et al (1989) in an unfused specimen[3]. We plan to repeat our measurements and compare to an untreated cadaveric wrist.

Systemic inflammatory conditions frequently affect both the small joints of the hand and the eye. Uveitis and scleritis is common in this group and patients are required to apply regular eye drops. Ophthalmic conditions are also common in patients with Osteoarthritis of the thumb CMCJ who have weakness and pain on pinch grip. Poor compliance with therapy due to difficulties in administering eye drops can cause permanent ocular and visual morbidity.

A laboratory based biomechanical study was performed to replicate the pinch forces applied to the 20 most frequently used eye drops. The minimum force required to disperse a drop from a full bottle held in the inverted vertical position was assessed on three occasions by placing the eye drop bottles between a finger and thumb simulator attached to a load cell. Recordings of two bottle types were repeated using 2 different ergonomic ‘aids’ produced by the pharmaceutical companies.

The data was compared to published data for pinch strength of general ophthalmology patients and to collected data for patients with thumb base CMCJ osteoarthritis.

Compressive forces varied significantly between different eye drop types from 6.4 newtons (Systane) to 20.8 newtons (Minims). The highest values were found in minims which is the most frequently used eye drop. The use of the Xalatan aid appeared to increase the force required from 7.7(+/−0.64) to 12.9 (+/−3.93) but this difference did not reach significance, p=0.08, the results for Allegan aid showed no significant difference 11.3(+/−0.91) to 9.9 (+/−1.18)p=0.17. The forces required to disperse a drop increased as the bottles became less full.

Forces required to disperse eye drops from bottles varies considerably and can be greater than the maximum pinch pressure of some patient groups which may be a cause of poor compliance. Some ergonomic aids designed to help with the application of drops do not appear to reduce the forces required.