Arthroplasty has consistently shown ‘beneficial and often dramatic improvements in quality of life'. In developed healthcare systems arthroplasty has evolved to minimised complications through evidence-based implant selection, rigorous infection control and high volume training. The Children's Surgical Centre has performed 256 THAs since 2007, We aim to assess the outcome of arthroplasty in a LMIC. Our primary outcome was all cause of re-operation and our secondary outcome was any complications not requiring return to theatre.

A retrospective review of all consecutive THA since 2007 was conducted. Electronic and physical case notes were reviewed and basic demographics, indication for THA, risk factors for complications, implant combinations and complications were recorded. Statistical analysis was performed using MedCalc.

A total of 256 THA were identified in 225 patients. The mean age was 43, with a M2:1F ratio. The most common pathologies were (1)AVN (44%), (2)OA (11%) and (3)DDH (11%). Revision rate was 13%. The mean time from implantation to revision was 2.8 years (0–9). The most common reasons for revision were (1)stem fracture (5.8%), (2)aseptic loosening (4.8%) and (3)infection (2.7%). Six different stems have been use over the time period. The best surviving were the Zimmer ML Taper and the UMA Muller stems. The UMA C-Stem was the worst performing which suffered 100% stem fracture. 109 complications were identified in 85 patients (33.2%). The three most common complications were (1)aseptic loosening (10.5%) (2)stem fracture (5.8%) and (3)dislocation (5.8%). Previous surgery (n=44) was found to be a significant risk for complications but not infection. OHS initially improved but began to decline after year 3.

Patients present to CSC with neglected hip pathology, disability and significant pre-operative deformity. These patients benefit from THA and the initially high complication rates at CSC are declining suggesting the apex of the ‘learning curve' has passed. Cheap poorly manufactured implants continue to cause catastrophic failure.

Taper corrosion and fretting have been associated with oxide layer abrasion and fluid ingress that contributes to adverse local tissue reactions with potential failure of the hip joint replacement^[1,2]. Both mechanisms are considered to be affected by the precise nature of the taper design^[3]. Indeed relative motion at the taper interface that causes fretting damage and wear effects, such as pistoning and rocking, have been described following analysis of implants at retrieval^[4,5]. However, there is much less reported about the mechanisms that allow the fluid ingress/egress at the taper interface which would drive corrosion. Thus the aim of the present study was to investigate the effect of trunnion design on the gap opening and taper relative motions under different load scenarios and taper designs.

A 3-D finite element model of a 40mm CoCr modular femoral head and a Ti6Al4V trunnion was established in Abaqus CAE/2018. Femoral head and trunnion geometries were meshed with an element (C3D8) size of 0.17mm. Tapers were assembled by simulating a range of impact forces (AF); taper interface behaviour was evaluated under physiological forces and frictional moments simulated during walking activity^[6], assuming different coefficients of friction (CF), Figure 1. The output involved the total and normal relative motion of the surfaces at the taper interface.

The model predicted for a taper mismatch of 0.36° which, when combined with an assembly force of 2kN, generated the largest taper gap opening (59.2mm) during walking, Figure 2. In all trunnion designs the largest normal relative motion coincided with heel strike in the gait cycle (0–5%). The taper gap and normal relative motions were related to the initial taper lock area. Furthermore, the direction of the total motion was different in all three taper mismatches, with a shift in the direction towards the normal of the surface as the taper mismatch increased, Figure 3. By contrast, the direction of the normal relative motions did not change with different trunnion designs. Contact patterns were asymmetrical and contact areas varied throughout the walking activity; contact pressure and the largest taper gap were located on the same side of the taper, suggesting toggling of the trunnion.

The relationship between taper gap opening and initial taper lock contact area suggests that the taper contact area functions as a fulcrum in a lever mechanism. Large taper mismatches create larger relative motions that will not only create more wear and fretting damage but also larger normal relative motions. This may allow fluid ingress into the taper interface and/or the egress of fluid along with any metal wear particles into the body. This increased understanding of the taper motion will result in improved designs and ultimately taper performance.

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

Introduction

Wear debris and metal ions originating from metal on metal hip replacements have been widely shown to recruit and activate macrophages. These cells secrete chemokines and pro-inflammatory cytokines that lead to an adverse local tissue reaction (ALTR), frequently requiring early revision. The mechanism for this response is still poorly understood. It is well documented that cobalt gives rise to apoptosis, necrosis and reactive oxygen species generation. Additionally, cobalt stimulates T cell migration, although the effect on macrophage motility remains unknown. This study tests the hypothesis that cobalt ions and nanoparticles affect macrophage migration stimulating an ALTR.

Purpose

The decision to undertake prophylactic pinning to prevent contralateral slipped upper femoral epiphysis (SUFE) remains controversial; we hypothesised that the grade of initial SUFE could predict the grade of a second SUFE and risk of poor outcome.

There will be occasions when standards and guidelines stymie the development of new methods. For example, the majority of simulator studies utilized the international guideline specifying that cups will be positioned “Anatomically” (ISO-14242), i.e. acetabular liner is positioned above oscillating femoral head (Fig. 1). This can be disadvantageous for studies of “edge wear” in steeply inclined cups (Williams 2008, Leslie 2009, Angadji 2009). Importantly, such an “Anatomical” cup is fixed with respect to the resultant load-axis (Fig. 1d: R). This produces a constant edge-wear throughout the simulator's cycle. Our supposition was that it is more likely patients experience edge-wear intermittently, i.e. at extremes of motion. This intermittent effect can be best replicated with the cup mounted “Inverted” (Fig. 2), the rotating cam allowing precise selection of edge-wear at extreme of motion (Fig. 2c). An advantage of this method is that the wear-pattern in the orbiting cup is now much larger (Bowsher, 2009: x3.8 ratio), making edge-wear easier to achieve. Our hypotheses were that (1) the Inverted test would provide both “normal” and “edge wear” as defined (Clarke, 2015: steep-cup algorithm), (2) MOM wear rates under edge-wear condition would be greater than in standard simulator tests (Bowsher 2016) and (2) intermittent edge-wear of MOM cups (Inverted) would be less severe than in prior Anatomical tests (Williams 2008, Leslie 2009, Angadji 2009).

The 60mm MOM bearings (DJO, Austin TX) were selected on the basis of prior Anatomical study (Bowsher, 2009), were run with cups Inverted, using identical test methods as before, in the orbital simulator. Wear-rates in 60mm heads revealed both run-in and steady-state wear phases (Fig. 3a). The weight-loss method showed perturbations due to protein contaminants but these appeared of minor concern over 10-million cycles. One cup was damaged during set-up, did not recover, and was not included in the analysis (Fig. 3b). Cup wear rates over 10-million cycles appeared very stable with excellent consistency (Fig. 3c). By end of test, the edge-wearing cups averaged 3.7 times higher wear than mating heads. Overall MOM wear averaged 1.6mm³ per million cycles. Apart from the first 100,000 cycles of run-in, no lubricant changed color during entire test.

In this first study of its kind, we demonstrated both normal and edge-wear wear-patterns in accordance with predictions of the steep-cup algorithm (Clarke 2015), satisfying hypothesis #1. Wear rates with Inverted cups averaged 2.7 times greater wear than those in similar Anatomical study (Bowsher, 2009), satisfying hypothesis #2. The 60mm MOM wear rates Inverted were mid-range to those in the prior steep-cup Anatomical tests (range 1.3 – 1.9mm³ per 10⁶ cycles). This neither satisfied nor eliminated hypothesis #3, perhaps due to confounding effects, i.e. different designs, MOM diameters and methods. In conclusion, the Inverted test in the simulator appears to offer considerable merit, perhaps analogous to patients who experience edge-wear only intermittently. In contrast the Anatomical test mode appears analogous to patients with mal-positioned cups, who therefore walk on the cup rim constantly throughout their gait cycle.

Introduction

Revision of total hip replacements (THRS) is predominantly due to aseptic loosening, pain and infection [1]. The current method used to address the risk of infection is to administer antibiotics and to include antibacterial agents into bone cement (if used) and on implant coatings [2–4]. Currently, silver (Ag) coatings have only been applied to titanium hip stems [3]. Cobalt chromium alloy (CoCr) is a widely used orthopaedic alloy which is commonly used as a bearing surface; revisions of joints using this material often describe adverse reactions to the particulate wear debris [1]. This study considers an Ag containing CrN based coating on a CoCr substrate with the aim to reduce cobalt (Co) release and promote antibacterial silver release.

Introduction

Vitamin-E has been introduced into highly-crosslinked polyethylene liners to reduce the oxidation potential of the material while maintaining low wear rates. However, little has been reported on adverse testing of the material with one test on diffused vitamin-E polyethylene [1] and no adverse tests of vitamin-E blended polyethylene reported. Adverse testing of crosslinked polyethylene has focused on the use of large diameters, the incorporation of third body particles, roughening of the counterface or severe activity [2–4]. This investigation considers the wear of vitamin-E blended highly-crosslinked polyethylene under standard and adverse conditions articulating against uncoated and chromium nitride (CrN) coated metal heads.

Introduction

Only a few studies have assessed the outcome of ulnar nerve decompression, most comparing various forms of decompression. A review of the case notes of patients undergone ulnar nerve decompressions was undertaken looking at the pre-op symptoms, nerve conduction studies, the co-morbidities, operative procedures and the post-operative outcomes.

Aims: Replacing human cadaveric specimens with fresh frozen animal tissue in biomechanical studies has become increasingly more popular due to the scarcity of young human tissue. The aims of this study were to characterise and compare the biomechanical parameters of tailored strips of equine extensor tendon, with 4 strand young human semitendinosus and gracilis (STG) tendons as an alternative tendon model for testing anterior cruciate ligament (ACL) graft reconstruction techniques using the Soffix Polyester ACL fixation device.

Method: Common digital extensor tendons were harvested from normal equine forelimbs and tailored into 5 mm wide, 2 strand equine tendon strips. The doubled equine tendons were overlapped and braided around the buttonholes of a Soffix fixation device and secured with No 2 Ethibond sutures (Johnson & Johnson Ltd). The Soffix-4-strand young human STG tendon complex was prepared in an identical manner. Mechanical testing was performed measuring ultimate tensile load (UTL) and elongation to failure (EF), structural stiffness (SS) was calculated from load extension curves.

Results: The Soffix-STG and the equine tendon complexes produced a mean UTL of 1186 N +/− 113.89 and 1116 N +/− 208.5 respectively showing no statistically significant difference.

Conclusions: We conclude that a tailored 5mm wide 2-strand equine extensor tendon strip provides a comparable alternative for in vitro testing of young human four strand STG tendon graft using a Soffix polyester fixation device.

Background: The over the top technique was first described in 1974. The Mark II ACL reconstruction was a development on the ABC and the Mark I procedure and was introduced into clinical practice in March 1998. The soffix used is a polyester hamstring graft support device with three button holes at each end. Clinical observation showed progressive slackening of some initially successful reconstructions. Retightening restored stability. We studied the medium and long-term outcome of the procedure and tested the effects of preconditioning on its biomechanical properties.

Patients and methods: 90 patients underwent a prospective medium and long-term follow-up (3–5 years) in a dedicated research clinic. Standardised scores Lysholm, Tegner, and IKDC. were used. Biomechanical tests were performed in vitro using double equine extensor tendon-soffix model constructs. 18 experiments with an MTS Hydraulic testing machine, were carried out, preconditioning with 300, 400 and 500N. Constructs were then cyclically loaded 3000 times at 1 Hz and finally tested to failure.

Results Clinical follow-up showed good overall results. The mean Tegner score increased from 2.5 pre-operatively to 4.5. The majority had a Lysholm score of > 90(72%). The majority had an IKDC of B (75%). 10% had a side to side difference > 6mm. The mean stretch of 14mm after 3000 cycles was reduced to 4.2 mm by preconditioning with 500N. This had no adverse effect on the ultimate tensile strength.

Conclusion: The medium and long-term results of the MarK II ACL reconstruction are encouraging. Preconditioning the soffix tendon construct reduces the creep with no adverse effect on the ultimate tensile strength. A pre-conditioning device has been made to replicate this in theatre.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of 4 methods of fixation used for hamstring tendon ACL grafts. The fixation methods investigated included titanium round headed cannulated interference (RCI) screws, bioabsorbable RCI screws, Endobuttons and Bollard fixation. It has been previously shown that a 2 strand tailored equine tendon-Soffix graft has equivalent biomechanical properties to a 4 strand human hamstring tendon-Soffix graft [1,2], therefore this model was used for the graft in the study.

Materials and Method: 32 stifle joints were obtained from skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday Rhino horn jig to accurately position a guide wire. An 8 mm cannulated reamer was then used over the guide wire to create the final tibial tunnel. A back radiusing device was then placed into the tibial tunnel to chamfer the posterior margin of the tunnel exit to prevent abrasion and fretting of the graft. A 2 strand equine tendon-Soffix graft was then introduced into the tibial tunnel and secured with one of the four fixation methods. The proximal part of the graft was attached to the cross head of the materials testing machine using the Soffix. Five of each method of fixation were tested mechanically to failure and three of each method were cyclically loaded for 1000 cycles between 5 to 150 N, followed by 2000 cycles at 50 to 450 N.

Results: The mean ultimate tensile loads (UTL) were: titanium RCI screw = 444 N, bioabsorbable RCI screw = 668 N, Endobutton = 999 N and Bollard = 1153 N. The mode of failure for all RCI screws involved tendon slippage past the screw. Two Endobutton failures were encountered and one Bollard pull out occurred. Under cyclic loading conditions the titanium and bioabsorbable RCI screws failed rapidly after several hundred 5 to 150 N cycles due to tendon graft damage and progressive slippage. Both the Bollards and Endobuttons survived 1500 cycles at 50 to 450 N, with less tendon slippage occurring.

Conclusion: Titanium and bioabsorbable RCI screws provide poor initial fixation of tendon grafts used for ACL reconstruction, having significantly lower UTL’s than both Endobutton and Bollard fixation. Under cyclic loading titanium and bioabsorbable RCI screws fail rapidly due to progressive tendon slippage, whereas Bollards and Endobuttons survive cyclic loading. Both Bollard fixation and Endobuttons provide sufficiently high UTL’s and survive cyclic loading to allow early postoperative mobilisation and rehabilitation. Caution must be used in the early postoperative period when using interference screws to secure a hamstring tendon graft because progressive tendon slippage may result in excessive graft elongation and early clinical failure.

Metal ion release is a concern with all metal-on-metal (MOM) hip replacements. The Cormet Resurfacing Hip replacement, in use since 1997, has been validated in vivo and in vitro. In addition to clinical follow-up, extensive wear testing has been carried out under standard and severe conditions. A 6-year study on the serum metal ion levels in patients has also been done.

Between September 1997 and November 2003, 383 primary total hip resurfacings were performed in five centres. The mean age of the 196 men (23 bilateral procedures) and 146 women (18 bilateral procedures) was 55.4 years (24 to 73). Mean follow-up was 17 months (3 to 84). At the latest review the mean modified Harris hip score (truncated format) was 77.9 out of 91 (mean 86%), with a range of 49 to 91. The Kaplan Meier survivorship rate was 96% at 7 years.

Wear testing has shown that heat treatments do not affect the wear of cast high carbon cobalt chrome alloys and that larger bearings (56-mm and 40-mm diameter) have lower wear rates than conventional 28-mm bearings. Metal ion levels rose initially, then decreased over time.

Metal ion release does not appear to be a major long-term concern and medium-term clinical results are very encouraging.

Introduction and Aims: Metal-on-metal (MOM) hips offer an attractive solution for hip arthroplasty. However, concerns remain over the optimum metallurgical condition of the cobalt chrome alloy and also the optimum bearing diameter to produce to least possible wear.

Method: Hip bearings of 28, 40 and 56mm high carbon cobalt chrome diameter were tested, all were HIPed and Solution annealed, apart from four 40mm bearings were left ‘as cast’. Radial clearances were controlled at 110 microns, initial surface finish was Sa 0.05 microns, and the sphericity deviation was 4–8 microns. A multi-directional biaxial rocking hip joint simulator was used. All bearing couples were initially subjected to three million cycles of standard physiological walking (2450 N max, 1 Hz) followed by four million cycles of severe gait tests, i.e. slow walking (0.62 Hz) and fast jogging (4500 N max, 1.75 Hz).

Results: In the diameter study, the 56mm bearings produced the lowest wear rates for all patient activities simulated followed by the 40 and 28mm bearings. However, the running-in wear was greatest for the 56mm bearings followed by the 28 and 40mm bearings. All surface wear patterns showed very similar characteristics, suggesting similar wear processes. This would indicate that larger diameters are indeed better in terms of wear in the long term, but may produce slightly more wear initially, which has been reflected in increased ion release in short term studies.

Comparing the 40mm as cast and heat-treated bearings, running-in wear was observed for both material groups in the first million cycles, generating wear rates of 2.3 mm3/million cycles and 2.4 mm3/million cycles for the HIPed/solution heat treated and as cast components respectively, indicating no statistical difference (p > 0.9). Under steady-state wear conditions, the combined normal walking wear rate was also similar for both groups, showing 0.48 mm3/106 cycles (p > 0.2). Under simulated fast jogging cycles, the results again showed no statistical difference in wear performance between the two groups (p > 0.3), generating approximately a 10-fold increase in volumetric wear compared to normal walking, showing 4.4 mm3/106 cycles.

Conclusion: This wear testing program, which used both standard and adverse testing conditions, has shown that heat treatments (HIP and solution anneal) do not affect the wear rates of cast cobalt chrome alloy. Further, this testing has confirmed that larger diameter bearings do indeed produce less wear in the long term.

Aims: The aims of this study were to evaluate the biomechanical properties and mode of failure of four methods of fixation of hamstring anterior cruciate ligament (ACL) grafts. A 2-strand equine extensor tendon graft model was used because a previous study has shown it to have equivalent biomechanical properties to that of 4-strand human semitendinosus and gracilis tendon grafts. Method: Twenty stifle joints were obtained from 10 skeletally mature pigs, the soft tissues were removed and the ACL and PCL were sacrificed. Tibial tunnel preparation was standardised using the Mayday rhino horn jig to accurately position a guide wire over which an 8mm tunnel was drilled. A 2-strand equine tendon graft was then introduced into the tibial tunnel and secured with either a titanium round headed cannulated interference (RCI) screw, a bioabsorbable RCI screw, an Endobutton or an expansile Bollard. Five of each method of fixation were tested mechanically to ultimate failure and under cyclical loading. Results: The mean ultimate tensile loads (UTL) were: titanium RCI screw = 444 N, bioabsorbable RCI screw = 668 N, Endobutton = 999 N and Bollard = 1153 N. Under cyclic loading conditions the titanium and bioabsorbable RCI screws rapidly failed after several hundred 5 to 150 N cycles due to tendon damage and slippage. Both the Bollards and Endobuttons survived 1500 cycles at 50-450N, with less tendon slippage. Conclusion: Titanium and bioabsorbale RCI screws provide poor initial fixation of tendon grafts and fail rapidly under cyclic loading. Both Bollards and Endobuttons provide sufficiently high UTL’s and survive cyclic loading to allow early postoperative rehabilitation.

Aim: To demonstrate that a novel tricalcium phosphate bone cement (Biobon) could be effectively used to þll the dorsal metaphyseal defect after unstable distal radial fractures in the osteopenic wrist, and to conþrm with biomechanical studies that its mechanical properties were incompatible with its sole use. Methods: Compression and Biaxial ßexure testing was performed under both dry and wet conditions of physiological Saline and Ringers Lactate solutions at 37ûC. 9 female patients with a mean age of 65 years sustaining Frykman grade VIII fractures of the distal radius between 1999 and 2000 underwent open reduction and internal þxation with supplementation of the dorsal metaphyseal defect with Biobon. Results: Youngs Modulus (E) and the Ultimate compressive strength (UCS) for the two solutions were identical at 10 hours (406 MPa and 3.24 MPa respectively), reaching a maximum for Ringers Lactate solution. The Biaxial ßexure stress also reached a maximum value at 10 hours for Saline at 37û C (3.96 MPa). A signiþcant improvement of radiographic parameters were observed post-operatively (Mean volar tilt = + 1.1û; Mean radial length = 10.4mm: Mean radial inclination = 20.5û) and remained so at the time of assessment (Mean volar tilt = +2.5û; Mean radial length = 10.4 mm; Mean radial inclination = 21.8û).Conclusion: The use of a tri-calcium phosphate bone cement is an effective means of addressing the dorsal comminution sustained after unstable distal radial fractures. Its biomechanical properties precludes its sole use for the treatment of distal radial fractures.

Aim: The purpose of this paper was to describe the biological reaction imposed by a prosthetic ligament.

Materials-Methods: Polyester-carbon synthetic matrices were implanted into 29 rabbits. The implants were transected centrally and reconstructed with resorbable suture material. At regular intervals from 4th day to 29 weeks, tissue samples from the ingrown implants were obtained for histology and mechanical testing. Light microscopy, DNA cytometry, immunohistochemical analysis of the collagen types, transmission and scanning electron microscopy were carried out. Ultimate tensile strength (UTL), elongation to failure (EF) and structural stiffness (SS) were determined at intervals of 8, 16 and 29 weeks.

Results: The ingrowth of tissue into the scaffold provided a significant increase in tensile strength, which improved with time. The UTL significantly increased from 18.86 N ±14.69 at 8 weeks to 51.4 N ±14.64 at 29 weeks. Light microscopy showed no infl ammation or foreign body reaction. At 4th day the first fibroblast cells settled on the matrix. The DNA cytometry showed an increase of the number of the fibroblast cell mitoses up to 16 days. After 2 weeks a mesh of connective tissue was formed around the scaffold, but the number of fibroblast cells remained constant. At 4 weeks the connective tissue started to infiltrate in between the artificial fibres. Type I, III and V collagens were identified. Electron microscopically the collagen weave was irregular with a mean fibril diameter of 28.4 ± 5.2 nm of a monophasic distribution. Collagen type I accumulated progressively and more and more dense collagenous fascicles appeared in the mesh in the proximity of the artificial fibres.

Conclusion: The subcutaneous tissue may act as a bio-reactor and the skin fibroblast seeding of a synthetic matrix appears to be transformed a dense connective tissue during the first 4 weeks, providing tensile strength improvement to the tissue envelope with time.

Large diameter metal on metal hip bearings have been shown to display exceptionally low wear in vivo. However, as these components are often cast, they may be heat treated to improve homogeneity, although it has been suggested that this may adversely affect wear. Therefore a hip simulator study was commissioned to investigate this further.

Multi-station hip simulator testing was carried out on 40 mm diameter high carbon cast cobalt chrome alloy components, all having similar radial clearances (~100mm), surface finishes (0.01mm Ra) and sphericity deviations (< 10mm). Three bearing couples were hot isostatic pressed (HIPed) and solution heat treated, generating a fine carbide structure, and three bearing couples were left as cast, creating a coarse carbide structure. All sockets were mounted in an MTS hip simulator, inclined at 35° to the horizontal, and subjected to standard walking conditions (2450 N max) using 25% bovine serum as a test lubricant. Wear was calculated gravimetrically using temperature controls.

Running-in wear was observed for both groups generating a similar combined head and cup mean wear rate of 2.3 mm3/106 cycles. The mean steady-state wear rate (SE) for the as cast and HIPed components was 0.38 (0.13) and 0.57 (0.11) mm3/106 cycles respectively showing no statistical difference (p > 0.2). Wear was generally higher for the cups than the heads.

These wear rates are two orders of magnitude lower than published wear rates of metal-UHMWP E under similar conditions and one order of magnitude lower than lightly crosslinked UHMWPE articulating against CoCrMo under the same conditions.

In this test, the effect of HIPing and solution heat treatment on metal-metal wear would therefore appear to be insignificant. This is in contrast to the published influences of both bearing diameter and bearing tolerances, i.e. sphericity and radial clearance on the wear of metal-metal hip joints.