Abstract

Abstract

Aims

The Oswestry-Bristol Classification (OBC) is an MRI-specific assessment tool to grade trochlear dysplasia. The aim of this study is to validate clinically the OBC by demonstrating its use in selecting treatments that are safe and effective.

Aims

We have previously demonstrated raised cobalt and chromium levels in patients with larger diameter femoral heads, following metal-on-polyethylene uncemented total hip arthroplasty. Further data have been collected, to see whether these associations have altered with time and to determine the long-term implications for these patients and our practice.

Aims

Trochlear dysplasia is a significant risk factor for patellofemoral instability. The Dejour classification is currently considered the standard for classifying trochlear dysplasia, but numerous studies have reported poor reliability on both plain radiography and MRI. The severity of trochlear dysplasia is important to establish in order to guide surgical management. We have developed an MRI-specific classification system to assess the severity of trochlear dysplasia, the Oswestry-Bristol Classification (OBC). This is a four-part classification system comprising normal, mild, moderate, and severe to represent a normal, shallow, flat, and convex trochlear, respectively. The purpose of this study was to assess the inter- and intraobserver reliability of the OBC and compare it with that of the Dejour classification.

Objectives

Wound complications are reported in up to 10% hip and knee arthroplasties and there is a proven association between wound complications and deep prosthetic infections. In this randomised controlled trial (RCT) we explore the potential benefits of a portable, single use, incisional negative pressure wound therapy dressing (iNPWTd) on wound exudate, length of stay (LOS), wound complications, dressing changes and cost-effectiveness following total hip and knee arthroplasties.

We undertook a randomised clinical trial to compare treatment times and failure rates between above- and below-knee Ponseti casting groups. Eligible children with idiopathic clubfoot, treated using the Ponseti method, were randomised to either below- or above-knee plaster of Paris casting. Outcome measures were total treatment time and the occurrence of failure, defined as two slippages or a treatment time above eight weeks.

A total of 26 children (33 feet) were entered into the trial. The above-knee group comprised 17 feet in 13 children (ten boys and three girls, median age 13 days (1 to 40)) and the below-knee group comprised 16 feet in 13 children (ten boys and three girls, median age 13 days (5 to 20)). Because of six failures (37.5%) in the below-knee group, the trial was stopped early for ethical reasons. The rate of failure was significantly higher in the below-knee group (p = 0.039). The median treatment times of six weeks in the below-knee and four weeks in the above-knee group differed significantly (p = 0.01).

This study demonstrates that the use of a below-knee plaster of Paris cast in conjunction with the Ponseti technique leads to unacceptably high failure rates and significantly longer treatment times. Therefore, this technique is not recommended.

Cite this article: Bone Joint J 2013;95-B:1570–4.

The revised Tokuhashi, Tomita and modified Bauer scores are commonly used to make difficult decisions in the management of patients presenting with spinal metastases. A prospective cohort study of 199 consecutive patients presenting with spinal metastases, treated with either surgery and/or radiotherapy, was used to compare the three systems. Cox regression, Nagelkerke’s R² and Harrell’s concordance were used to compare the systems and find their best predictive items. The three systems were equally good in terms of overall prognostic performance. Their most predictive items were used to develop the Oswestry Spinal Risk Index (OSRI), which has a similar concordance, but a larger coefficient of determination than any of these three scores. A bootstrap procedure was used to internally validate this score and determine its prediction optimism.

The OSRI is a simple summation of two elements: primary tumour pathology (PTP) and general condition (GC): OSRI = PTP + (2 – GC).

This simple score can predict life expectancy accurately in patients presenting with spinal metastases. It will be helpful in making difficult clinical decisions without the delay of extensive investigations.

Cite this article: Bone Joint J 2013;95-B:210–16.

Aim: To investigate whether cement mantle thickness influence early migration of the stem after impaction grafting.

Methods: Twelve artificial femora were prepared to mimic cavitary defects. After compacting morselized bone into the cavities, Exeter stems were cemented in place. By using all combinations of three sizes tamps and stems (0, 1 and 2), we created cement mantles of 0, 1, 2, 3 and 4 mm thickness. Bones with stems were placed in a testing machine and loaded cyclically to 2,500 N while measuring stem migration. Statistical analysis was by regression analysis. Outcomes were stem subsidence and retroversion, predictors were mantle thickness, tamp size and stem size.

Results: Average stem subsidence after 2500 cycles when using size 1 tamp and stem (2 mm mantle) was 0.94 mm. For a 0 mm mantle, subsidence was 0.59 mm and for a 4 mm mantle it was 2.54 mm. Cement mantle thickness significantly influenced stem subsidence (r=0.68, p=0.015). Cement mantle thickness also significantly influenced stem retroversion (r=0.62, p=0.031). Cement mantle thickness was a better predictor of stem stability than tamp or stem size.

Discussion: Concern exists that inadequate cement mantles may affect stability of impaction-grafted stems. In our study, larger difference between tamps and stems gave substantially more subsidence and rotation, whereas a smaller difference reduced them. Concerns over thin mantles may have been premature.

Introduction: This research aims to study the efficacy and effect of Bone Marrow Stromal Stem Cell (BMSSC) implantation on healing of refractory fracture non-union.

Methods: Approved by the local Ethics Committee, twelve patients (9M and 3F), age range 38 to 76 years (mean 49.9) with non-union resistant to multiple previous attempts of treatment (mean 3.75 procedures) were treated. Four tibial and eight femoral non-union.

The patients were admitted for harvesting of stromal stem cells by bone marrow aspiration from the iliac bone. BMSSC were expanded in tissue cultures for three weeks to an average of 5 x 10⁶ cells. After successful culture the non-union site underwent decortication and BMSSC added to synthetic bone substitute (different types) on one side of the fracture (medial or lateral) according to randomisation. The side of treatment was blinded to patient, surgeons and radiologist.

Standard radiographs were taken and evaluated independently by three experienced musculoskeletal radiologists. The extent of callus formation on each side was recorded. In equivocal cases computerized tomography (CT) was also obtained.

Results: No patient developed systemic complications related to the procedure. On follow-up callus formation was present in 9 of 12 patients. Callus was more marked on the cell implantation side in 6/12 patients (50%), control side in 1/12 (8.3%) and on both sides in 2 patients. 3 patients showed no change.

Discussion: These findings suggest that implantation of BMSSC can enhance bone formation in persistent non-union. A larger randomized controlled trial will follow to test this new treatment.

Introduction: Bio mechanical tests under realistic loading conditions of prostheses in bone can help to improve the design of joint implants. Cadaveric bones are most realistic but highly variable and difficult to obtain and conventional bone models have been used so far. Stereo lithography (SLA) techniques are used in industry to generate 3-D rapid prototypes. These techniques could serve to produce bones with complex geometries, but the material used is less stiff than cortical bone.

Aim: The purpose of the study was to answer the following two questions? 1. Does stability of and cortical strains around implants in SLA-made bones matched those of conventional artificial bones? 2. Whether increasing cortical wall thickness brings these variables closer?

Methods: Four artificial cortical shells of proximal tibiae were made from resin (SL5170, 3D systems Europe Ltd., Hemel Hempstead, UK) using SLA process. Two third generation large composite tibiae #3302 (Sawbones Europe AB, Malmö, Sweden) were chosen and the polyurethane foam that represents the cancellous bone was removed. All six cortices were filled with polyurethane foam (Tripor 224, ABL (STEVENS), Cheshire, UK) with an average compressive modulus of 53.9±7.2 SD MPa. The tibiae were prepared to receive a standard size cemented tibial tray for all models. The models were loaded with 100 cycles of 2000 N at 1 Hz along the longitudinal axis, separately on the lateral and on the medial condyle. Medial cortical strain and tray migration during load was determined.

Results: Cyclic loading gave a general pattern of cyclic movements, superimposed on a very small permanent movement. The first cycle gave most permanent displacement, after which further migration occurred at a decreasing rate. Permanent and cyclic migration of all four trays implanted in SLA-made tibiae fell within the range of those implanted in conventionally available tibiae. Strains at the proximal medial cortex were low and on the same order for all six tibiae. Strains more distally were approximately inversely proportional to the material stiffness and cortical thickness of the tibiae.

Conclusion: The study concludes that migration of tibial trays in all SLA models was with in the range of those in conventional models. Hence these models can be used to test early mechanical stability of joint implants despite their lower stiffness. The small difference may be related to load bearing mechanism of tibial trays which is largely through cancellous bone and not cortical bone. The low strains at the proximal cortex in this study also suggest that the cortex carried little direct load. The polyurethane foam representing cancellous bone in our study was identical for each tibia, which may explain that movements of the trays were comparable. Distal cortical strains reflected the stiffness of the tibiae and were directly influenced by cortical thickness.

The use of impaction bone grafting during revision arthroplasty of the hip in the presence of cortical defects has a high risk of post-operative fracture. Our laboratory study addressed the effect of extramedullary augmentation and length of femoral stem on the initial stability of the prosthesis and the risk of fracture.

Cortical defects in plastic femora were repaired using either surgical mesh without extramedullary augmentation, mesh with a strut graft or mesh with a plate. After bone impaction, standard or long-stem Exeter prostheses were inserted, which were tested by cyclical loading while measuring defect strain and migration of the stem.

Compared with standard stems without extramedullary augmentation, defect strains were 31% lower with longer stems, 43% lower with a plate and 50% lower with a strut graft. Combining extramedullary augmentation with a long stem showed little additional benefit (p = 0.67). The type of repair did not affect the initial stability. Our results support the use of impaction bone grafting and extramedullary augmentation of diaphyseal defects after mesh containment.

The role of bone-graft extenders in impaction revision surgery is becoming increasingly important. Tricalcium phosphate and hydroxyapatite have been shown to be both biocompatible and osteoconductive, yet many surgeons remain reluctant to use them. The difficulty in handling bone-graft extenders can be partly alleviated by using porous particles and adding clotted blood.

In an in vitro model we measured the cohesive properties of various impaction graft mixes. Several factors were evaluated including the use of pure bone graft compared with mixes with extender, washing the bone and the addition of clotted blood.

Our findings showed that pure allograft bone particles had significantly higher cohesion than when mixed with extender (p < 0.001). Washing had no effect on cohesion. The addition of clotted blood significantly increased the cohesion of both pure bone (p < 0.019) and mixes with pure bone and with porous graft extender (p < 0.044).

Introduction: Existing fatigue studies of ACL fixation have two disadvantages. There is no agreed standard protocol, making comparison of various studies difficult and average results are presented, disregarding data spread. This may be over-optimistic, because approximately half the fixations will not achieve the average level. The effect of data spread can be summarised using the one-sided 80/80 lower tolerance limit (LTL). This LTL indicates the strength that at least 80% of fixations will reach, with an 80% probability. It is commonly used in engineering.

We fatigue-tested a new resorbable composite screw (PLLA/tri-calcium phosphate) and a metal interference screw. We present average data and tolerance limits.

Methods: Porcine BPTB grafts (Ø=9mm) were fixed inside tibial tunnels (Ø=10mm) using composite or metal screws. Each screw was tested for static pull-out strength (n=6) and cyclic loading to failure at 330N and 415N (n=5 each level)

Means and standard deviations of pullout strength were compared. Log-log curves were fitted between force level and cycles to failure. LTLs were calculated.

Results: During static loading, all repairs failed by graft pullout or tissue failure. During cyclic loading, all except one graft fixed with composite screws failed by pullout. Grafts fixed with metal screws failed by bone fracture in 60% of the cases. A composite screw loaded at 300N would last on average 272 cycles or at least (LTL) 7 cycles. At 200N the average and LTL were 38,218 and 966 cycles. Corresponding values for the metal screw were 263 (mean) and 12 (LTL) at 300N; and 12,454 and 564 at 200N.

Discussion and Conclusions: Repairs with metal screw had higher pullout strength, but proved more prone to fatigue. Higher incidence of bone graft fracture in fatigue testing with metal screws suggests that their sharp threads act as stress risers. Fatigue testing of ACL reconstructions shows wide variation, due to several factors. Average levels are therefore over-optimistic and tolerance limits gives a better indication of screw performance. We suggest that tolerance limits should be reported in future studies.

Nomograms derived from mathematical analysis indicate that the level of malunion is the most important determinant of changes in the moment arm of the knee, the plane of the ankle and alterations in limb length. Testing in five patients undergoing reconstruction showed a mean error of postoperative limb length of 2.2 mm (sd 0.8 mm), knee moment arm of 4.7 mm (sd 3.3 mm) and ankle angle of 2.6° (sd 2.3°). These nomograms provide the information required when assessing whether a particular degree of angulation may be accepted.

We describe a technique for measuring the Stiffness of regenerate bone after leg lengthening. This allows early identification of slow healing by reference to normal patterns. We determined the time of removal of the fixator from clinical and radiological information independent of the stiffness result.

In a series of 30 leg lengthenings there were no refractures when the tibial stiffness had reached 15 Nm/° or the femoral stiffness 20 Nm/°. Three refractures occurred at lower stiffness values. The technique is simple to perform, will allow a reduction in plain radiography and is recommended for routine postoperative management.