Pegs are often used in cementless total knee replacement (TKR) to improve fixation strength. Studies have demonstrated that interference fit, surface properties, bone mineral density (BMD) and viscoelasticity affect the performance of press-fit designs. These parameters also affect the insertion force and the bone damage occurring during insertion. We aimed to quantify the effect of the aforementioned parameters on the short-term fixation strength of cementless pegs. 6 mm holes were drilled in twenty-four human femora. BMD was measured using calibrated CT-scans, and randomly assigned to samples. Pegs were produced to investigate the effect of interference fit (diameters 6.5 and 7.6 mm), surface treatment (smooth and rough- porous-coating [friction coefficient: 1.4]) and bone relaxation (relaxation time 0 and 30 min) and interactions were studied using a DOE method. Two additional rough surfaced peg designs (diameters 6.2 and 7.3 mm) were included to scrutinize interference. Further, a peg based on the LCS Porocoat® (DePuy Synthes Joint Reconstruction, Leeds, UK) was added as a clinical baseline. In total seven designs were used (n = 10 for all groups). Pegs were inserted and extracted using an MTS machine (Figure 1), while recording force and displacement. Bone damage was defined as the difference between the cross-sectional hole area prior to and after the test. BMD and interference fit were significant factors for insertion force. BMD had a significant positive correlation with pull-out force and subsequent analyses were therefore normalised for BMD. . Pull-out force increased significantly with interference for both surface coatings at time 0 (p < 0.05). However, after 30 minutes the effect remained significant for rough pegs only (p < 0.05-Figure 2A). Pull-out force reduced significantly with roughness for both peg diameters at time 0 (p < 0.001). However, after 30 minutes the effect remained significant for small pegs only (p < 0.05-Figure 2A). The time dependant interaction was only significant for smooth pegs in both diameters (p < 0.05-Figure 2A). Additionally, the pull-out force increased with diameter in a non-linear manner for the rough pegs (Figure 2B). The two surface treatments were not significantly different to the clinical comparator. Interference fit was the only significant factor for bone damage. BMD was significant for insertion and pull-out forces, reinforcing the need to account for this factor in biomechanical studies and clinical practice. This study also highlights the importance of time in studying bone interactions, with surface treatment and interference showing different interaction effects with relaxation time. Although smooth pegs initially have a higher pull-out force, this effect reduces over time whereas the pullout force for rough pegs is maintained. Smooth pegs also show time sensitivity in relation to interference and the benefit of increased interference reduces over time, whereas it is maintained in rough pegs. This may be explained by different damage (compressive and abrasive) mechanisms associated with different surface treatments. In conclusion, BMD and interference fit are significant factors for initial fixation. Bone relaxation plays an important role as it reduces the initial differences between groups. Therefore, these findings should be strongly considered in the design development of cementless TKR

Most glenoid implants rely on centrally located large fixation features to avoid perforation of the glenoid vault in its peripheral regions [1]. Upon revision of such components there may not be enough bone left for the reinsertion of an anatomical prosthesis, resulting in a large cavity that resembles a sink hole. Multiple press-fit small pegs would allow for less bone resection and strong anchoring in the stiffer and denser peripheral subchondral bone [2], whilst producing a more uniform stress distribution and increased shear resistance per unit volume [3] and avoiding the complications from the use of bone cement. This study assessed the best combination of anchoring strength, assessed as the ratio between push in and pull out forces (Pin/Pout), and spring-back, measured as the elastic displacement immediately after insertion, for five different small press-fitted peg configurations (Figure 1, left) manufactured out of UHMWPE cylinders (5 mm diameter and length).

16 specimens for each configuration were tested in two types of Sawbones solid bone substitute: hard (40 PCF, 0.64 g/cm3, worst-case scenario of Pin) and soft (15 PCF, 0.24 g/cm3, worst-case scenario of spring-back and Pout). Two different interference-fits, Ø, were studied by drilling holes with 4.7 mm and 4.5 mm diameter (Ø 0.3 and Ø 0.5, respectively). A maximum Pin per peg of 50 N was defined, in order to avoid fracture of the glenoid bone during insertion of multiple pegs. The peg specimens were mounted into the single-axis screw-driven Instron through a threaded fixture. A schematic of the experimental set up is made available (Figure 1, centre). The peg was pushed in vertically for a maximum of 5 mm at a 1 mm/s rate, under displacement control, recording Pin. The spring-back effect was assessed by switching to load control and reducing the load to zero. The peg was then pulled out at a rate of 1 mm/s, recording Pout. The test profile is depicted in Figure 1 (right).

Average Pout/Pin, spring back (in mm) and force-displacement curves for all 80 specimens tested are shown in Figure 2. These were split into groups according to the type of bone substitute and interference-fit, with the right column showing the average values for the Pin. High repeatability among samples of the same configuration tested is noted. Configurations #1, #3 and #5 all exceed the maximum Pin per peg for at least one type of bone. Configuration #2 has the lowest Pin of all (best thread aspect ratio), followed by configuration #4 (thinner threads). The peg configurations #4 and #2 had the highest Pin/Pout. The peg configurations with lowest spring-back after insertion were configuration #2 and #4. Interference fit of Ø 0.3 mm was shown to reduce Pin below maximum limit of 50 N without great influence in spring-back.

Purpose: Outome after arthroscopic management of anterior instability of the shoulder has varied since the early series. The results proposed at the 1993 symposium of the French Society of Arthroscopy suggest we should be using this technique with prudence. We report here our experience with patients operated on between 1993 and 1997 who were selected on the basis of the 1993 conclusions that excluded patients with multiple recurrent instability and fractures of the anterior rim of the glenoid cavity.

Material and methods: Sixty-seven shoulders were operated on between 1993 and 1997. Mean follow-up for 58 of these shoulders (86%) was five years. These 58 patients constituted the study group. There were 31 men and 27 women, mean age 25 years, who had 30 recurrent shoulder dislocations, 12 shoulder subdislocations and 16 painful unstable shoulders. Forty-six percent of the patients participated in competition-level sports with forced shoulder movements in 39.6% of the cases. The surgical technique involved retightening the inferior glenohumeral ligament that was fixed with resorbable sutures. Immobilisation with elbow-to-body contention was strictly applied for three weeks at least followed by progressive rehabilitation exercises until renewed sports activities starting four months postoperatively.

Results: The mean overall Duplay score was 85.5 (sport 21/25; stability 18/25; mobility 24/25; pain 22/25). Outcome was good and very good in 82.7% of the patients, fair in 8.6%, and poor in 5 (recurrence). Subjectively, 55% of the patients were very satisfied, 27.5% were satisfied, 15.5% were disappointed and 1.7% were displeased. There were four complications (one infection cured with antibiotic therapy with a final score of 100 and three serious cases of capsulitis that recovered before one year). Gender, age, type and duration of instability, level of sports activity, and articular laxity appeared to affect outcome.

Discussion: The rate of failure (8.6%) is similar to that with open surgery (4.6% in the SOFCOT symposium 1999) and would be well below the rates observed in the 1993 arthroscopy series although the different patient selection does not allow valid comparison.

Conclusion: Arthroscopic stabilisation of the shoulder is a technically difficult procedure that has progressively shown its effectiveness after an appropriate learning curve and in carefully selected patients. Favourable elements include age over 20 years, competition level sports activity, recent instability, and absence of constitutional hyperlaxity.

Aims: To evaluate the effect of tapered pegs in reducing tibial tray tilt and subsidence in closed cell foam. Methods: 1. Foam validation was carried out using a load frame (Instron) to establish its static and fatigue behaviour. 2. Subsidence and tilt tests: Three brass peg sets of varying length and matching surface area were designed. Four identical pegs of each set were fixed with screws to an IBII tibial tray and testing was performed using the load frame and the closed cell foam. Results: Foam validation revealed an average strength of 0.65±0.01 MPa in compression and 1.53±0.02 MPa in tension and an average stiffness of 40.2±1.5 Mpa in compression and 50.4±1.06 Mpa in tension. Subsidence tests revealed a significant increase in the total load producing 0.2mm subsidence with pegs ( p< 0.0053) and no significant difference for 1 and 2mm (p> 0.1). Tilt tests revealed a significant increase in the total load producing 0.2mm tilt with the medium and short pegs ( p < 0.008 & < 0.042 respectively) and no significant difference for 1 and 2mm (p> 0.1). Conclusions: The foam analogue material shows similar behaviour to cancellous bone in both static and dynamic tests and suggests that polymer foams are a good analogue material to cancellous bone. The addition of tapered conical pegs to the tibial tray increases its resistance to initial subsidence while initial tilt resistance is increased only with the medium and short pegs. Combining tilt and subsidence resistance, the medium pegs perform most favourably.

Implant loosening is one of the primary mechanisms of failure for hip, knee, ankle and shoulder arthroplasty. Many established implant fixation surfaces exist to achieve implant stability and fixation. More recently, additive manufacturing technology has offered exciting new possibilities for implant design such as large, open, porous structures that could encourage bony ingrowth into the implant and improve long-term implant fixation. Indeed, many implant manufacturers are exploiting this technology for their latest hip or knee arthroplasty implants. The purpose of this research is to investigate if the design freedoms offered by additive manufacturing could also be used to improve initial implant stability – a precursor to successful long-term fixation. This would enable fixation equivalent to current technology, but with lower profile fixation features, thus being less invasive, bone conserving and easier to revise. 250 cylindrical specimens with different fixation features were built in Ti6Al4V alloy using a Renishaw AM250 additive manufacturing machine, along with 14 specimens with a surface roughness similar to a conventional titanium fixation surface. Pegs were then pushed into interference fit holes in a synthetic bone material using a dual-axis materials testing machine equipped with a load/torque-cell (figure 1). Specimens were then either pulled-out of the bone, or rotated about their cylindrical axis before being pulled out to quantify their ability to influence initial implant stability. It was found that additively manufactured fixation features could favourably influence push-in/pull-out stability in one of two-ways: firstly the fixation features could be used to increase the amount pull-out force required to remove the peg from the bone. It was found that the optimum fixation feature for maximising pull-out load required a pull-out load of 320 N which was 6× greater than the least optimum design (54 N) and nearly 3× the maximum achieved with the conventional surface (120 N). Secondly, fixation features could also be used to decrease the amount of force required to insert the implant into bone whilst improving fixation (figure 2). Indeed, for some designs the ratio of push-in to pull-out was as high as 2.5, which is a dramatic improvement on current fixation surface technology, which typically achieved a ratio between 0.3–0.6 depending on the level of interference fit. It was also found that the additively manufactured fixation features could influence the level of rotational stability with the optimum design resisting 3× more rotational torque compared to the least optimum design. It is concluded that additive manufacturing technology could be used to improve initial implant stability either by increasing the anchoring force in bone, or by reducing the force required to insert an implant whilst maintaining a fixed level of fixation. This defines a new set of rules for implant fixation using smaller low profile features, which are required for minimally invasive device design

Post operative stability is of paramount importance to obtain bone in growth and a tight interface in uncemented implants. Although hemispherical press fit cups are widely used different opinions exists according optimal fixation and a variety of principles are preferred. Lab studies show better stability if a cup is augmented by screws or pegs. However, cups with screws and holes increases penetration of joint fluid, pressure and particles to the interface with a risk for osteolyses. HA coating is in many studies favourable to obtain a quick in growth but is by many regarded unnecessary or even a risk for increased wear. This RSA studie was done to investigate stability and wear in cups with different fixation. Material: 80 hips in 75 patients with a mean age of 58 years (36–70) were operated with a cemented Spectron stem and a porous coated Reflection cup of titanium (Smith a Nephew) All cups were oversized 1–2 mm and fixed with press fit by experienced surgeons. Great care was taken to achieve a good rim fit. They hips were by randomisation allocated to one of four groups with different fixation methods. One group was done with only press fit technique, one with additional screws, one additional pegs and another with HA coating on the porous surface. Migration and wear was investigated with RSA at 2, 12 and 24 months and standard radiography was done post op and at 2 years. Mann-Whitneys U-test was used on signed values for evaluation of group differencies. Results: At 2 years the mean cup migration for the whole group was 0.2 mm longitudinally, 0.3 mm horizontally and 0.3 mm anterior-posteriorly. (SEM 0.03–0.05) The inclination changed 0.4 dgr and anteversion 0.4 dgr as well. Most cups moved laterally, proximally and anteriorly with increased anteversion and decreased inclination. No major differences in mean values were found between the groups according translations or rotations and no significant differences. Nor did we find differences between the press fit only and the augmented cups. Wear was 0.45 mm proximally and in total 0. 6 mm without any sign of differences between the HA and porous coated groups. HA coated cups had less radiolucent lines after 2 years. (p=0.01). Discussion: The Reflection cups were stable fixed ad we found no indication of inferior stability for cups without augmentation as might have been anticipated. The reason is probably the firm press fit fixation obtained with a stable cup, good bone and forceful impaction. Many use screws for safety but such cups are not sealed for leakage of joint fluid and pressure gradients and the risk for backside osteolyses is higher… Pegs are easier and safer to insert and tighten the holes better. A tight, no hole cup with HA is preferred by us in normal younger patients since HA gave a better interface. Such a solution should minimise the risk for penetration of particles and pressure gradients with less risk for lyses