Abstract

Abstract

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.

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.

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.