Aim

Cementless prosthesis is one of the major bone-implant interface fixation methods in total joint replacement. Grit blasted surface, hydroxyapatite coated surface and plasma sprayed metallic porous coating have been popularly used. The latter has demonstrated higher bone implant mechanical stability in previous laboratory study in early and middle stages. However, question remains what the mechanism is to make it performing better and how to improve them further. This study is designed to examine the mode of failure in bone-implant interface in a sheep model.

This study was performed to compare the mechanism of bone-implant integration and mechanical stability among three popularly used cementless implant surfaces. Plasma sprayed porous surface (TiPL), grit-blasted rough surface (TiGB), and hydroxyapatite coated implant surface (HA) were tested in a sheep model at 4 and 12 weeks. The integration patterns were investigated using histology, histomorphometry, and mechanical strength by push-out test. All three groups demonstrated early bone ongrowth on their surfaces, with much of the ongrowth resembling contact osteogenesis. TiPL group showed bone anchorage into porous coating with new bone ingrowth into the pores. HA group revealed small cracks at its coating at 12 weeks time point. Plasma sprayed porous surface also demonstrated its superior mechanical stability maybe reinforced by its bone anchorage, whearas, HA surface exhibited higher osteoconductivity with highest ongrowth rate.

Animal studies examining tendon-bone healing have demonstrated that the overall structure, composition, and organization of direct type entheses are not regenerated following repair. We examined the effect of Low-Intensity Pulsed Ultrasound (LIPUS) on tendon-bone healing. LIPUS may accelerate and augment the tendon-bone healing process through alteration of critical molecular expressions.

Eight skeletally mature wethers, randomly allocated to either control group (n=4) or LIPUS group (n=4), underwent rotator cuff surgery following injury to the infraspinatus tendon. All animals were sacrificed 28 days post surgery to allow examination of early effects of LIPUS. Humeral head – infraspinatus tendon constructs were harvested and processed for histology and immunohistochemical staining for BMP2, Smad4, VEGF and RUNX2. All the growth factors were semiquantitative evaluated. T-tests were used to examine differences which were considered significant at p < 0.05. Levene's Test (p < 0.05) was used to confirm variance homogeneity of the populations.

The surgery and LIPUS treatment were well tolerated by all animals. Placement of LIPUS sensor did not unsettle the animals. Histologic appearance at the tendon-bone interface in LIPUS treated group demonstrated general improvement in appearance compared to controls. Generally a thicker region of newly formed woven bone, morphologically resembling trabecular bone, was noted at the tendon-bone interface in the LIPUS-treated group compared to the controls. Structurally, treatment group also showed evidence of a mature interface between tendon and bone as indicated by alignment of collagen fibres as visualized under polarized light. Immunohistochemistry revealed an increase in the protein expression patterns of VEGF (p = 0.038), RUNX2 (p = 0.02) and Smad4 (p = 0.05) in the treatment group. There was no statistical difference found in the expression patterns of BMP2. VEGF was positively stained within osteoblasts in newly formed bone, endothelial cells and some fibroblasts at the interface and focally within fibroblasts around the newly formed vessels. Expression patterns of RUNX2 were similar to that of BMP-2; the staining was noted in active fibroblasts found at the interface as well as in osteoblast-like cells and osteoprogenitor cells. Immunostaining of Smad4 was present in all cell types at the healing interface.

The results of this study indicate that LIPUS may aid in tendon to bone healing process in patients who have undergone rotator cuff repair. This treatment may also be beneficial following other types of reconstructive surgeries involving the tendon-bone interface.

The transosseous equivalent/Suture Bridge or TOE/SB repair has received much attention in recent years as more shoulder surgeons transition to all arthroscopic rotator cuff repairs. The purpose of this study was to compare the biomechanical behaviour of several variants of the Suture Bridge repair performed by the authors.

Four different Suture Bridge constructs were performed six times on 24 sheep infraspinatus tendon humerus constructs. The first group was a standard Suture Bridge with two medial mattress stitches with knots (KSSB4). The second group had four medial mattress stitches with knots and was called KDSB8. The third group had two medial mattress stitches without knots and was called USBFT4. These first three repairs used two medial 5.5 mm Bio-Corkscrew FT Anchors and two lateral 3.5 mm PushLock Anchors (Arthrex). The fourth repair had two medial mattress stitches without knots and used all Pushlocks and was called USBP4.

The repairs were then analysed for failure force, cyclic creep and stiffnessafter. Cycling was performed from 10 to 100 N at 1 Hz for 500 cycles. Following cyclic testing a single cycle pull to failure at 33 mm/sec was performed. The constructs were also observed for failure mechanism and gap formation using digital video recording.

The KDSB8 repair with a mean failure force of 456.9N was significantly stronger than the USBP4 repair at 299.7N (P=0.023), the KSSB4 repair at 295.4N (P=0.019) and lastly the USBFT4 repair at 284.0N (P=0.011). There was no statistical difference between the measured failure force for the two mattress stitch KSSB4 repair with knots and the knotless two mattress stitch repairs USBFT4 and USBP4. There was not a statistical difference between any of the repairs for measured stiffness and cyclic creep. However, the KDSB8 repair showed no discernable gap formation or movement at the footprint during cyclic testing. The KSSB4, USBFT4 and USBP4 repairs demonstrated bursal sided gap formation in the range of 1 to 3 mm.

Based on the results of this study the transosseous equivalent/Suture Bridge repair with four stitches tied in the medial row and maximal lateral suture strand utilization (KDSB8 TOE/SB) is the strongest. The KDSB8 also appeared to show less bursal sided gap formation and greater footprint stability than the other Suture Bridge constructs tested.

NICE published the guidelines ‘Selection of prostheses for primary hip replacement’ in 2000. Essentially these guidelines made two recommendations: firstly to use prostheses which had attained the ‘10 year benchmark’ of a revision rate of 10% or less at 10 years, or had a minimum of three years revision rate experience that was on target to reach this benchmark; and secondly to use cemented hip prostheses to the exclusion of uncemented and hybrid prostheses.

The information from the Trent Regional Arthroplasty Study (TRAS) has been used to retrospectively examine the types of hip prostheses used from 1990 – 2005, and assess the impact that the NICE guidelines have had on orthopaedic practice.

This study revealed that the percentage of prostheses used which attained the ‘ten year benchmark’ has increased since the guidelines were published. In 2001, of the ten cups, which constituted 80% of the acetabular components used, only three attained this NICE benchmark, but by 2005 this number had risen to eight. Similarly in 2001, of the eight stems, which constituted almost 80% of the femoral components used, only five attained this NICE benchmark. In 2005 seven out of these eight stems had attained the minimum standard.

However contrary to the recommendation made by NICE in 2000, to use cemented prostheses, the results indicate the use of uncemented prostheses has trebled (from 6.7% to 19.2%, n= 137 and 632 respectively), and the use of hybrid prostheses has more than doubled (from 8.8% to 22% of all prostheses, n= 181 and 722 respectively) since the guidelines were published.

Therefore the recommendations made by NICE are not being followed, which calls the value of NICE guidelines into question.