Tendinopathy is the most frequent musculoskeletal disease that requires medical attention. Mechanical overload has been considered as a key driver of its pathology. However, the underline mechanism on how overload induces tendinopathy and inflammation is unclear. Extracellular mitochondria (EM) are newly identified as cell-to-cell communicators. The aim of this study is to elucidate the role of mitochondria in overload-induced inflammation.

We performed three-dimensional uniaxial stretching to mouse tendon organoid in bioreactors. Cyclic strain of uniaxial loadings included underload, normal load, and overload, according to previous work. We then harvested microvesicles including EM, from the bioreactor by differential centrifugation and evaluated their characteristics by flow cytometry and super-resolution confocal microscopy. Raw 264.7 mouse macrophage cell line was used for chemotaxis assay in a Boyden Chamber System with Magnetic-Activated Cell Sorting Technology. EM induced cytokines secretion by macrophages was analyzed by a bead-based multiplex assay panel. N-Acetyl-L-cysteine (NAC) was used as the antioxidant to tendon organoid to regulate mitochondrial fitness.

We showed mechanical load induced tendon organoid to release microvesicles including mitochondria. The size of microvesicles is mainly in the range from 220nm to 880nm. More than 75% of microvesicles could be stained by PKH26, confirming they were with lipophilic membrane. Super-resolution confocal microscopy identified two forms of mitochondria, including mitochondria encapsulated in vesicles and free mitochondria. Overload led to the degeneration of the organoid and induced microvesicles release containing most EM. Chemotaxis assay showed that EM from overloaded tendon organoid induced macrophages chemotaxis. In addition, microvesicles extracted from overloaded tendon organoid induced the production of proinflammatory cytokines including IL-6, KC (Keratinocyte-Derived Chemokine) and IL-18. NAC treatment to tendon cells could attenuate overload-induced macrophage chemotaxis.

Overload induces EM releasing from tendon cells, which leads to chemotaxis of macrophages toward tendon, resulting in induction of inflammation.

Distal interphalangeal joint (DIPJ) fusion using a k-wire has been the gold standard treatment for DIPJ arthritis. Recent studies have shown similar patient outcomes with the headless compression screws (HCS), however there has been no cost analysis to compare the two. Therefore, this study aims to 1) review the cost of DIPJ fusion between k-wire and HCS 2) compare functional outcome and patient satisfaction between the two groups.

A retrospective review was performed over a nine-year period from 2012-2021 in Counties Manukau. Cost analysis was performed between patients who underwent DIPJ fusion with either HCS or k-wire. Costs included were surgical cost, repeat operations and follow-up clinic costs. The difference in pre-operative and post-operative functional and pain scores were also compared using the patient rate wrist/hand evaluation (PRWHE).

Of the 85 eligible patients, 49 underwent fusion with k-wires and 36 had HCS. The overall cost was significantly lower in the HCS group which was 6554 New Zealand Dollars (NZD), whereas this was 10408 NZD in the k-wire group (p<0.0001). The adjusted relative risk of 1.3 indicate that the cost of k-wires is 1.3 times more than HCS (P=0.0053). The patients’ post-operative PRWHE pain (−22 vs −18, p<0.0001) and functional scores (−38 vs −36, p<0.0001) improved significantly in HCS group compared to the k-wire group.

Literatures have shown similar DIPJ fusion outcomes between k-wire and HCS. K-wires often need to be removed post-operatively due to the metalware irritation. This leads to more surgical procedures and clinic follow-ups, which overall increases the cost of DIPJ fusion with k-wires.

DIPJ fusion with HCS is a more cost-effective with a lower surgical and follow-up costs compared to the k-wiring technique. Patients with HCS also tend to have a significant improvement in post-operative pain and functional scores.

Interstitial supraspinatus tears can cause persistent subacromial impingement symptoms despite non operative treatment. Autologous tendon cell injection (ATI) is a non-surgical treatment for tendinopathies and tear. We report a randomised controlled study of ATI compared to corticosteroid injection (CS) as treatment for interstitial supraspinatus tears and tendinopathy.

Inclusion criteria were patients with symptom duration > 6 months, MRI confirmed intrasubstance supraspinatus tear, and prior treatment with physiotherapy and ≥ one CS or PRP injection. Participants were randomised to receive ATI to the interstitial tear or corticosteroid injection to the subacromial bursa in a 2:1 ratio, under ultrasound guidance. Assessments of pain (VAS) and function (ASES) were performed at baseline, and 1, 3, 6 and 12 months post treatment.

30 participants (19 randomised to ATI) with a mean age of 50.5 years (10 females) and a mean duration of symptoms of 23.5 months. Baseline VAS pain and ASES scores were comparable between groups. While mean VAS pain scores improved in both groups at 3 months after treatment, pain scores were superior with ATI at 6 months (p=0.01). Mean ASES scores in the ATI group were superior to the CS group at 3 months (p=0.026) and 6 months (p=0.012). Seven participants in the CS group withdrew prior to 12 months due to lack of improvement. At 12 months, mean VAS pain in the ATI group was 1.6 ± 1.3. The improvements in mean ASES scores in the ATI group at 6 and 12 months were greater than the MCID (12.0 points). At 12 months, 95% of ATI participants had an ASES score > the PASS (patient acceptable symptom state).

This is the first level one study using ATI to treat interstitial supraspinatus tear. ATI results in a significant reduction in pain and improvement in shoulder function.

Progressive collapsing foot deformity (PCFD) is a common condition with an estimated prevalence of 3.3% in women greater than 40 years. Progressive in nature, symptomatic flatfoot deformity can be a debilitating condition due to pain and limited physical function; it has been shown to have one of the poorest preoperative patient reported outcome scores in foot and ankle pathologies, second to ankle arthritis. Operative reconstruction of PCFD can be performed in a single-stage manner or through multiple stages. The purpose of this study is to compare costs for non-staged (NS) flatfoot reconstructions, which typically require longer hospital stays, with costs for staged (S) reconstructions, where patients usually do not require hospital admission. To our knowledge, the comparison between single-staged and multi-staged flatfoot reconstructions has not been previously done. This study will run in conjunction with one that compares rates of complications and reoperation, as well as patient reported outcomes on function and pain associated with S and NS flatfoot reconstruction. Overall, the goal is to optimize surgical management of PCFD, by addressing healthcare costs and patient outcomes.

At our academic centre with foot and ankle specialists, we selected one surgeon who primarily performs NS flatfoot reconstruction and another who primarily performs S procedures. Retrospective chart reviews of patients who have undergone either S or NS flatfoot reconstruction were performed from November 2011 to August 2021. Length of operating time, number of primary surgeries, length of hospital admission, and number of reoperations were recorded. Cost analysis was performed using local health authority patient rates for non residents as a proxy for health system costs. Rates of operating room per hour and hospital ward stay per diem in Canadian dollars were used. The analysis is currently ongoing.

72 feet from 66 patients were analyzed in the S group while 78 feet from 70 patients were analyzed in the NS group. The average age in the S and NS group are 49.64 +/− 1.76 and 57.23 +/− 1.68 years, respectively. The percentage of female patients in the S and NS group are 63.89% and 57.69%, respectively. All NS patients stayed in hospital post-operatively and the average length of stay for NS patients is 3.65 +/− 0.37 days. Only 10 patients from S group required hospital admission.

The average total operating room cost including all stages for S patients was $12,303.12 +/− $582.20. When including in-patient ward costs for patients who required admission from S group, the average cost for operating room and in-patient ward admission was $14,196.00 +/− $1,070.01 after flatfoot reconstruction.

The average in-patient ward admission cost for NS patients was $14,518.83 +/− $1,476.94 after flatfoot reconstruction. The cost analysis for total operating room costs for NS patients are currently ongoing. Statistical analysis comparing S to NS flatfoot reconstruction costs are pending.

Preliminary cost analysis suggests that multi-staged flatfoot reconstruction costs less than single-staged flatfoot reconstruction. Once full assessment is complete with statistical analysis, correlation with patient reported outcomes and complication rate can guide future PCFD surgical management.

Progressive collapsing foot deformity (PCFD) is a complex foot deformity with varying degrees of hindfoot valgus, forefoot abduction, forefoot varus, and collapse or hypermobility of the medial column. In its management, muscle and tendon balancing are important to address the deformity. Peroneus brevis is the primary evertor of the foot, and the strongest antagonist to the tibialis posterior. Moreover, peroneus longus is an important stabilizer of the medial column. To our knowledge, the role of peroneus brevis to peroneus longus tendon transfer in cases of PCFD has not been reported.

This study evaluates patient reported outcomes including pain scores and any associated surgical complications for patients with PCFD undergoing isolated peroneus brevis to longus tendon transfer and gastrocnemius recession.

Patients with symptomatic PCFD who had failed non-operative treatment, and underwent isolated soft tissue correction with peroneus brevis to longus tendon transfer and gastrocnemius recession were included. Procedures were performed by a single surgeon at a large University affiliated teaching hospital between January 1 2016 to March 31 2021. Patients younger than 18 years old, or undergoing surgical correction for PCFD which included osseous correction were excluded.

Patient demographics, medical comorbidities, procedures performed, and pre and post-operative patient related outcomes were collected via medical chart review and using the appropriate questionnaires.

Outcomes assessed included Visual Analogue Scale (VAS) for foot and ankle pain as well as sinus tarsi pain (0-10), patient reported outcomes on EQ-5D, and documented complications.

Statistical analysis was utilized to report change in VAS and EQ-5D outcomes using a paired t-test. Statistical significance was noted with p<0.05.

We analysed 43 feet in 39 adults who fulfilled the inclusion criteria. Mean age was 55.4 ± 14.5 years old. The patient reported outcome mean results and statistical analysis are shown in Table one below. Mean pre and post-operative foot and ankle VAS pain was 6.73, and 3.13 respectively with a mean difference of 3.6 (p<0.001, 95% CI 2.6, 4.6). Mean pre and post-operative sinus tarsi VAS pain was 6.03 and 3.88, respectively with a mean difference of 2.1 (p<0.001, 95% CI 0.9, 3.4). Mean pre and post-operative EQ-5D Pain scores were 2.19 and 1.83 respectively with a mean difference of 0.4 (p=0.008, 95% CI 0.1, 0.6). Mean follow up time was 18.8 ± 18.4 months.

Peroneus brevis to longus tendon transfer and gastrocnemius recession in the management of symptomatic progressive collapsing foot deformity significantly improved sinus tarsi and overall foot and ankle pain. Most EQ-5D scores improved, but did not reach statistically significant values with the exception of the pain score. This may have been limited by our cohort size. To our knowledge, this is the first report in the literature describing clinical results in the form of patient reported outcomes following treatment with this combination of isolated soft tissue procedures for the treatment of PCFD.

For any figures or tables, please contact the authors directly.

Abstract

Objectives

The incidence of acute Achilles tendon rupture appears to be increasing. The aim of this study was to summarize various therapies for acute Achilles tendon rupture and discuss their relative merits.

Introduction

One of the objectives of total hip arthroplasty is to restore femoral and acetabular combined anteversion. It is desirable to reproduce both femoral and acetabular antevesions to maximize the acetabular cup fixation coverage and hip joint stability. Studies investigated the resultant of implanted femoral stem anteversion in western populations showed that the implanted femoral stems had only a small portion can meet the desirable femoral anteversion angle¹, and anteversion angle increases after the implantation of an anatomical femoral stem with anteverted stem neck comparing to anatomical femoral neck². The purpose of this study was to anatomically measure the anteversion angular difference between metaphyseal long axis and femoral neck in normal Chinese population. The metaphyseal long axis represents the coronal fixation plane of modern cementless medial-lateral cortical fitting taper stem. This angular difference or torsion Δ angle provides the estimation of how much the neck antevertion angle of femoral stem would be needed to match for desirable anatomical femoral neck version.

Introduction

Self tapping bone screw has been widely used in the fixation of Arthroplasty implants and bone graft. But the unwanted screw or driver breakage can be a direct result of excessive driving torque due to the thread cutting resistance. Previous studies showed that bone drill bit cutting rake angle was a critical factor and was inversely related to the bone cutting efficiency.^{1, 2, 3, 4} (Figure 1) However to date there was no data for how the rake angle could influence the performance of self tapping bone screw. The purpose of this study was to investigate the torque generated by the self tapping cortical screw in simulated bone insertion as a function of the screw tip cutting flute rake angle.

Objective

The purpose of this study was to investigate how rim poly locking scallop cutting depth could affect the rigidity of acetabular cup.

Introduction

Mechanical properties of irradiated Ultra High Molecular Weight Polyethylene (UHMWPE) after aging have been well documented. However there was no sufficient data for the dimensional change due to irradiation and aging. This change may have adverse effects to the implant modular locking mechanism. The purpose of this study was to characterize the dimensional change of UHMWPE after irradiation and aging.

Objective

The purpose of this study was to compare the proximal femoral morphology between normal Chinese and Caucasian populations by 3D analysis derived from CT data.

Blood tests including liver function tests (LFTs), C-reactive protein (CRP), coagulation screens and international normalising ratios (INR) are frequently requested investigations that complement the surgical and anaesthetic pre-operative assessment of patients. The paucity of guidance available for blood requesting in acute trauma and orthopaedic admissions can lead to inappropriate requesting practices and over investigation. Unnecessary tests place an economic burden on a hospital and repeated venepuncture is unpleasant for patients.

We audited blood requesting practices and with multidisciplinary input developed guidelines to improve practice which were subsequently implemented.

Admissions over a period of one month to Ninewells Hospital and Perth Royal Infirmary were audited retrospectively. The frequency and clinical indications for LFTs, coagulation screens/INR and CRP for the duration of the patient's admission were recorded. Re-audit was carried out for one month after the introduction of the guidelines.

216 patients were included in January and 236 patients in September 2014. Total no. of LFTs requested: January 895, September 336 (−62.5%). Total no of coagulation screens/INR requested: January 307, September 210 (−31.6%). Total number of CRPs requested: January 894, September 317 (−64.5%). No. of blood requests per patient: January (M=4.81, SD 4.75), September (M=3.60, SD = 4.70). A significant decrease was observed in admission requesting and subsequent monitoring (p<0.01) for LFTs, coagulation screens/INR, CRP when the guidance was introduced.

The implementation of the bloods guidance resulted in a large reduction in admission requesting and subsequent monitoring without incident. The cost of investigation was significantly reduced, as were venepuncture rates.

Multi-directional motion at the ball-socket interface of a hip replacement joint has been discovered as a fundamental feature that determines the magnitude of wear for ultra-high molecular weight polyethylene (UHMWPE). The present study considers the wear of UHMWPE moving along a circular path with a uniform angular change rate of the velocity vector defined by the curvature of the sliding circle. It is apparent the as the sliding circle radius increases the motion is approaching more towards linear tracking. Therefore, wear rate per unit sliding distance would decrease with increasing the slidng circle radius. However, the sliding distance per cycle increases linearly with the radius of the circle, which would cause a proportional increase in the wear rate per cycle. We hypothesize that these two opposing effects on wear with respect to the changing radius of the sliding circle would cancel out each other leading to wear rate per cycle being independent of sliding distance.

Experiments were conducted on a hip simulator with a biaxial rocking motion that results in a circular sliding path at the polar region of the acetabular cup that experiences the highest contact stresses and wear. The radius of the sliding circle, r, depends solely on the radius of the femoral ball, R, and the biaxial rocking angle, a, such that r=Rsina. Two tests were conducted. The first test was run under standard conditions with a constant biaxial rocking angle of +/−23 and head diameters ranging between 28 mm and 44 mm. Acetabular components were machined from virgin non-crosslinked UHMWPE with inner diameters matching those of the femoral heads. For the 28 mm bearing, the cups were of standard hemispherical geometry. The larger cups were truncated by various degrees so that the nominal contact area remained exactly the same as that of the standard 28 mm hemispherical components. The second test was run with the standard 28 mm components and various biaxial rocking angles: +/−10, +/−15, +/−20 and +/−23. Both tests were run for a total duration of 2 million cycles with diluted alpha-serum as a lubricant and physiologic loading (peak load: 2450N) as described by Paul.

Volumetric wear at 2 million cycles for both tests are summarized in Figure 1. Fig. 2 shows a graphic representation of the total volumetric wear (DV) as a function of the sliding circle radius (r). Total volumetric wear is independent of the head diameter (2R), the biaxial-rocking angle (a) and the sliding circle radius (r). The total volumetric wear is proportional to the number of cycles and independent of the sliding distance per cycle. The clinically observed wear rate-ball diameter relationship, therefore, is not attributed to variations in sliding distance per walking step with differing ball head sizes.

For the same nominal contact area between a ball and a socket, the total volumetric wear of UHMWPE is independent of the ball diameter, the biaxial rocking angle and the sliding circle radius. In other words, the total volumetric wear is proportional to the number of cycles and independent of the sliding distance per cycle.

Pin-on-disk studies have demonstrated the role that cross-shear plays in polyethylene wear. It has been found that applying shear stresses on the polyethylene surface in multiple directions will increase wear rates significantly compared to linear sliding. Hip and knee joint replacements utilize polyethylene as a bearing surface and are subjected to cross-shear motions to various degrees. This is the mechanism that produces wear particles in hip and knee arthroplasty bearings and if excessive may lead to osteolysis, implant loosening, and failure. The amount of cross-shear is dependent on the bearing diameter and the angular motion exerted onto the bearing due to the gait of the patient. This study will determine the effect of sliding curvature (angular change per linear sliding distance) on the wear rate of polyethylene. Virgin polyethylene blocks were machined with a 28mm diameter bearing surface and against 28mm cobalt chromium femoral heads in a hip simulator. Dynamic loading was applied simulating walking gait but the motion differed between testing groups. Typical walking gait testing utilizes 23° biaxial rocking motion, in this study, 10°, 15°, 20°, and 23° biaxial rocking motions resulting in various sliding curvatures. Sliding motion path is described in Figure 1 and is a function of the bearing radius and the rocking angle. With increased rocking angle, the sliding distance reduces per cycle and the sliding path becomes more curved (more angular change per linear distance of sliding). Despite a significant increase in sliding distance at higher rocking angles, wear rates were relatively unchanged and ranged from 57mm3/mc to 62mm3/mc. Wear rates per millimeter increased exponentially with reduced sliding arc radius (smaller rocking angle) as shown in Figure 2. This study suggests that wear of polyethylene is highly dependent on sliding path curvature. The sliding path is largely a function of the bearing diameter and the patient activity. Large bearing diameter implants have been recently introduced to increase joint stability. Sliding distance increases proportional to the bearing radius which has led to some concerns regarding increased wear in larger bearings. However, in vitro wear studies have not shown this trend. Increased bearing diameter also increases the sliding path curvature which this study has shown to cause a reduction in wear roughly proportional to the radius of the bearing. Therefore, the increase in wear due to sliding distance is offset by the reduction in wear caused by the sliding curvature resulting in no significant change in wear with increased bearing diameter. Curved sliding path causes a change in surface shear direction which has been shown to increase wear of polyethylene. This study confirms that increased cross-shear in the form of more angular change per linear sliding distance can increase wear of polyethylene exponentially

Studies have indicated that the shallow Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular socket or the socket with no head center inset can significantly increase the risk of hip joint dislocation. A previous study suggested the rim loading model in UHMWPE socket and metal femoral head can generate an intrinsic dislocating force component pushing head out of socket. Recently there has been renewed interest in dual mobility articulations due to the excellent stability. The outer bearing couple of the dual mobility articulations are comprised of the UHMWPE femoral head and metal acetabular socket while inner bearing is the locked conventional metal-poly construct. The acetabular socket is also featured by an anatomically shaped head inset wall. The purpose of this study was to theoretically compare the intrinsic dislocating force between conventional metal head on UHMWPE socket articulations and the poly head on metal socket articulations used in the dual mobility cup under direct loading.

The 3-D finite element analysis (FEA) models were same as previous study but with different material combinations. Sixty FEA model assemblies were consisted of CoCr or UHMWPE femoral heads and their corresponding 10mm thick generic UHMWPE or CoCr acetabular sockets. There were five different head center insets of 0, 0.5, 1, 1.5 and 2mm for each of six bearing diameters of 22, 28, 32, 36, 40 and 44mm for either sockets. The joint load of 2,446N was applied through the femoral head center as the same fashion as previous study. The dislocating force generated by the joint loading force intrinsically pushed femoral head out of socket. FEA results were verified with two data points of physical testing of actual UHMWPE 28mm ID liners with 0 and 1.5mm head center insets.

The highest dislocating force was 1,269N per 2,446N of rim loading force for the 0mm head center inset in poly cup with 22mm CoCr femoral head or the case of easiest to dislocate. The lowest dislocating force was 17.7N per 2,446N force for the 2mm inset in CoCr socket with 44mm poly head which therefore was the least likely to dislocate. The average dislocating force decreased by 78% from metal head- poly cup couple to poly head - metal cup couple. The dislocating force decreased as the head center inset and head size increased in all material cases.

The study suggests that not only the head center inset and head size but also the bearing material combinations can affect the intrinsic dislocating force component. The dual mobility poly head and metal socket couple generates less intrinsic dislocating force in all comparable conditions for conventional metal head and poly socket couple. During the hip separation and vertical placement of the cup, all variables found in this study may play the important rules to maintain joint stability. The stiffened cup rim reduces the deformation and thus reduces the potential cup wedge effect to generate dislocating force. The result of this study should provide the guidance to improve acetabular cup design for better joint stability.

Previous studies suggested that the shallow Ultra High Molecular Weight Polyethylene (UHMWPE) acetabular socket liner or the liner with no head centre inset can significantly increase the risk of hip joint dislocation. Independent to the traditional neck impingement models, the purpose of this study was to investigate an additional dislocation force pushing the femoral head out of UHMWPE acetabular liner bearing under direct hip joint loading and the factors including the head centre inset affecting the magnitude of this force. The 3 D Finite Element Analysis (FEA) models were constructed by (30) 10 mm thick UHMWPE liners with six inner bearing diameters ranging from 22 mm to 44 mm and five head centre insets in each bearing size from 0 mm to 2 mm. A load of 2 446 N was applied through the corresponding CoCr femoral head to the rim of the liner. The DF was recorded as a function of head centre inset and head diameter. The results were verified by the physical tests of two 28 mm head bearing liners with 0 and 1.5 mm head centre insets respectively.

The results showed that the highest DF was 1 269N in 0 mm head centre inset and 22 mm head. The lowest DF was 171 N in 2 mm head centre inset and 44 mm head. The DF decreased as the head centre inset and head size increased. When head centre inset increased from 0 mm to 1 mm, the DF was reduced more than 50%. Two experimental data points were consistent with the trend of DF curve found in the FEA.

We concluded that the new intrinsic dislocating force DF can be induced by the rim directed joint loading force alone and can reach as high as 51% of the femoral loading force. This can be the addition to the dislocating moment generated by the neck impingement. A head inset above 1mm can effectively reduce DF to less than 25% of the joint force. Furthermore, the larger head diameter generates less DF. The DF is likely caused by the wedge effect between the deformed polyethylene bearing and the femoral head. The inset allows the femoral head to be separated from the spherical bearing surface, thus reducing the wedge effect. Our observation of the stabilizing effect trend of the head centre inset was consistent with reported clinical data. However, the increased height of the capture wall also reduces the range of motion. It is therefore necessary to minimize the inset height with the maximum benefit of the stabilize effect. This study suggested the larger femoral head has the advantage of reducing the DF and the stabilizing effect is more effective when combining with the inset wall. The result of this study should provide the guidance to improve acetabular poly liner design for better joint stability.

Previous studies suggested the lack of capture wall of acetabular Ultra High Molecular Weight Polyethylene (UHMWPE) liner can significantly increase the risk of hip joint dislocation. To date, the dislocation studies have been focused on the femoral neck impingement models. The purpose of this study was to identify a new Dislocating Force (DF) generated by rim directed joint force alone and investigate the factors to affect the magnitudes of the DF. The 3 D Finite Element Analysis (FEA) models were constructed by (30) 10 mm thick UHMWPE liners with six inner bearing diameters ranging from 22 mm to 44 mm and five capture wall heights in each bearing size from 0 mm to 2 mm. A load of 2 446 N was applied through the corresponding CoCr femoral head to the rim of the liner. The DF was recorded as a function of capture wall height and head diameter. The results were verified by the physical tests of two 28 mm head bearing liners with 0 and 1.5 mm capture wall heights respectively.

The results showed that the highest DF was 1 269N in 0 mm capture wall and 22 mm head. The lowest DF was 171 N in 2 mm capture wall and 44 mm head. The DF decreased as the capture wall and head size increased. When capture wall increased from 0 mm to 1 mm, the DF was reduced more than 50%. Two experimental data points were consistent with the trend of DF curve found in the FEA.

We concluded that the new intrinsic dislocating force DF can be induced by the rim directed joint loading force alone and can reach as high as 51% of the femoral loading force. A capture wall height above 1mm can effectively reduce DF to less than 25% of the joint force. In addition, the larger head diameter also resulted in less DF generation.

Acetabular rim damge due to rim impingement is frequently found on retrievals and may be associated with increased wear and contact stresses, instability, and implant loosening of total hip replacement devices. Large X3 bearings (> 36mm) from Stryker have increased implant range of motion and improved polyethylene material (sequentially crosslinked and annealed). A hip simulator wear study was performed with and without femoral neck to acetabular rim impingement to determine the wear performance of these new bearings under aggressive impingement conditions. Two sizes of these new components were tested (36mm with 3.9mm thickness and 40mm with 3.8mm thickness) with two standard sized controls (28mm with 7.9mm thickness in X3 and conventional polyethylene. The 36mm component was chosen to be the largest component utilizing the same shell as the standard 28mm size components while the 40mm component was chosen to be the thinnest bearing currently offered.

Impingement significantly increased wear for all bearings (p< 0.05) but no cracking or failures of the rim occurred. Wear rates for all X3 bearings were statistically indifferent under each testing condition despite bearing size and thickness. Average wear rates for X3 bearings were 0.3mm3/million cycles (mc) under standard conditions and 3.5mm3/mc under impingement conditions. Average wear rates for conventional bearings were 19.5mm3/mc under standard conditions and 48.3mm3/mc under impingement conditions. Overall the X3 bearings exhibited a 93% reduction in wear under impingement conditions and 99% reduction in wear under standard conditions.

Increased bearing range of motion reduces the chance of impingement. This study shows the simulated outcome even if these larger bearings were to impinge. We conclude that these larger X3 bearings exhibits the same wear performance as standard X3 bearings and significantly superior wear performance compared to conventional polyethylene bearings under standard and impingement conditions.

Femoral head roughening is a clinically observed phenomenon that is suspected to cause increased wear of acetabular inserts. Two approaches have been taken to reduce hip bearing wear. Improved femoral head materials may decrease the impact of roughening and reduce the effect of abrasion. Additionally, improved polyethylene materials may be utilized to reduce wear against smooth or roughened femoral heads. This study looks at these two approaches in the form of a toughened alumina femoral head (Biolox Delta) and a sequentially crosslinked and annealed polyethylene (X3). A wear study was performed with new and artificially scratched ceramic femoral heads (28mm Biolox Delta) as compared to new and artificially scratched Cobalt Chromium femoral heads. These femoral heads were articulated against both conventional (N2\Vac) and highly crosslinked (X3) polyethylene acetabular cups. Artificial scratching utilized a Rockwell C indentor loaded at 30N to scratch a multidirectional scratch pattern on the articulating surface of the femoral head to simulate in vivo roughening.

Delta femoral heads exhibited superior resistance to scratching. Peak to valley roughness for CoCr heads was 7.1um while Delta heads only roughened to 0.4um. Head material under standard conditions (no scratch) had no effect on PE wear (p=0.31 and p=0.53). Under abrasive conditions, the Delta femoral head exhibited a clear advantage over CoCr heads (65–97% reduction in wear rate; p< 0.007). X3 polyethylene also showed a clear advantage over conventional PE against either CoCr or Delta heads and under both conditions (all p < 0.012).

This study clearly demonstrates that X3 polyethylene has a clear wear advantage over conventional polyethylene despite head material or abrasive conditions. Secondary to the polyethylene choice, the use of a ceramic femoral head leads to superior performance under abrasive conditions.