Andrew Shimmin

Metal-on-metal Hip Resurfacing Arthroplasty

The main advantage of hip resurfacing is bone conservation for patients likely to outlive a primary conventional hip replacement. Previous attempts at hip resurfacing failed predominantly because of the consequences of a high amount of wear of thin polyethylene acetabular components and poor femoral component fixation. With correct patient selection, surgeon education, and operative technique, survivorship at five years is comparable with that of traditional hip replacements. Hip resurfacing has its own unique set of complications, including a fractured neck of the femur. It is necessary to understand the risk factors prior to performing the procedure.

Metal Sensitivity as a Cause of Groin Pain in Metal-on-Metal Hip Resurfacing

We describe 4 patients pooled from our patient populations who presented with groin pain at different periods postoperatively after implantation of a metal-on-metal hip resurfacing. Each patient underwent exploratory surgery after radiographic imaging, hematologic testing, and microbiological assessment of joint aspirations failed to explain their symptoms. Samples of periprosthetic tissues revealed extensive amounts of lymphocytic infiltrates that were suggestive of an immunologic reaction. The patients obtained complete resolution of symptoms subsequent to revision surgery. The incidence of implant failures resulting from metal sensitivity is unknown owing to the difficulty in making a confirmed diagnosis. The possibility that this is the source of groin pain should be considered when other reasons for symptoms of pain and/or joint effusion in hips with metal-on-metal resurfacing arthroplasties have been discounted.

Use of bone morphogenetic proteins for musculoskeletal applications. An overview.

Since Marshall Urists original description, in 1965, of the potential of demineralized bone matrix to induce bone formation, the medical community has anticipated the development of osteogenic therapies1. Following this discovery, researchers sought to identify and isolate these growth factors, specifically bone morphogenetic proteins (BMPs). Reddi and Huggins first characterized these important molecules involved in bone formation in 1973, and, in 1982, Sampath and Reddi developed a rat subcutaneous assay for BMP activity that measures bone formation2. They found that BMPs initiate the bone-healing cascade through the recruitment of and interactions with mesenchymal stem cells found in surrounding tissues, including fascial planes, periosteum, peripheral blood, bone marrow, and cancellous bone. Several, but not all, of the fifteen human BMPs described to date have been found to bind to stem-cell receptors, triggering proliferation and differentiation, and to result in bone regeneration and repair. Once various BMPs were successfully isolated, a variety of animal models were used to test their efficacy in musculoskeletal applications. Early studies included bone-defect models as well as models of cartilage development, spinal fusion, and maxillofacial restoration. The healing of critical-sized defects in long bones was assessed in a variety of animal species, including rabbits, sheep, dogs, and primates3 (Figs. 1-A and 1-B). Fig. 1-A Canine model showing a surgically created 2-cm defect. Fig. 1-B New bone formation was noted across all BMP-treated defects. New insights into the nature of bone biology and the ability to manufacture proteins through recombinant gene technology have led to the commercialization of two BMPs: BMP-7 (OP-1; Stryker, Kalamazoo, Michigan) and BMP-2 (Infuse; Medtronic Sofamor Danek, Memphis, Tennessee). In addition, other BMPs or BMP-combination products are being evaluated clinically; these include various isolates of animal and human BMP implants, BMPx (Sulzer Biologics, Wheat Ridge, Colorado), BMP-9, and others. While current use …

Large diameter metal on metal articulations. Comparison of total hip arthroplasty and hip resurfacing arthroplasty.

The use of large diameter metal bearing total hip arthroplasty (THA) and hip resurfacing arthroplasty (HRA) increased in popularity in the last decade. More recent literature has highlighted the effect of head size in patient outcomes. Data was obtained from the Australian Orthopaedic Association National Joint Replacement Registry (AOA-NJRR) to evaluate the Birmingham (MoM) bearing surface when used with THA and HRA. There is no difference in the overall rate of revision between the THA and HRA but head size has a significant effect on revision rate. The data show that small diameter metal bearings in HRA (below 50mm) have a higher rate of revision than large diameter metal bearings in HRA (equal to and above 50mm) (P<.001). Conversely the large diameter metal bearings in THA have a higher rate of revision than the small diameter metal bearings in THA (P=.027). The revision rate for large diameter HRA compared to small diameter THA is not significantly different P=.670. We recommend caution when choosing either a large diameter (≥50mm) metal on metal THA or small diameter (<50mm) HRA.

Variation in functional pelvic tilt in patients undergoing total hip arthroplasty

Aims The pelvis rotates in the sagittal plane during daily activities. These rotations have a direct effect on the functional orientation of the acetabulum. The aim of this study was to quantify changes in pelvic tilt between different functional positions. Patients and Methods Pre‐operatively, pelvic tilt was measured in 1517 patients undergoing total hip arthroplasty (THA) in three functional positions ‐ supine, standing and flexed seated (the moment when patients initiate rising from a seated position). Supine pelvic tilt was measured from CT scans, standing and flexed seated pelvic tilts were measured from standardised lateral radiographs. Anterior pelvic tilt was assigned a positive value. Results The mean pelvic tilt was 4.2° (‐20.5° to 24.5°), ‐1.3° (‐30.2° to 27.9°) and 0.6° (‐42.0° to 41.3°) in the three positions, respectively. The mean sagittal pelvic rotation from supine to standing was ‐5.5° (‐21.8° to 8.4°), from supine to flexed seated was ‐3.7° (‐48.3° to 38.6°) and from standing to flexed seated was 1.8° (‐51.8° to 39.5°). In 259 patients (17%), the extent of sagittal pelvic rotation could lead to functional malorientation of the acetabular component. Factoring in an intra‐operative delivery error of ± 5° extends this risk to 51% of patients. Conclusion Planning and measurement of the intended position of the acetabular component in the supine position may fail to predict clinically significant changes in its orientation during functional activities, as a consequence of individual pelvic kinematics. Optimal orientation is patient‐specific and requires an evaluation of functional pelvic tilt pre‐operatively.

Functional orientation of the acetabular component in ceramic-on-ceramic total hip arthroplasty and its relevance to squeaking

AIMS Long-term clinical outcomes for ceramic-on-ceramic (CoC) bearings are encouraging. However, there is a risk of squeaking. Guidelines for the orientation of the acetabular component are defined from static imaging, but the position of the pelvis and thus the acetabular component during activities associated with edge-loading are likely to be very different from those measured when the patient is supine. We assessed the functional orientation of the acetabular component. PATIENTS AND METHODS A total of 18 patients with reproducible squeaking in their CoC hips during deep flexion were investigated with a control group of 36 non-squeaking CoC hips. The two groups were matched for the type of implant, the orientation of the acetabular component when supine, the size of the femoral head, ligament laxity, maximum hip flexion and body mass index. RESULTS The mean functional anteversion of the acetabular component at the point when patients initiated rising from a seated position was significantly less in the squeaking group than in the control group, 8.1° (-10.5° to 36.0°) and 21.1° (-1.9° to 38.4°) respectively (p = 0.002). CONCLUSION The functional orientation of the acetabular component during activities associated with posterior edge-loading are different from those measured when supine due to patient-specific pelvic kinematics. Individuals with a large anterior pelvic tilt during deep flexion might be more susceptible to posterior edge-loading and squeaking as a consequence of a significant decrease in the functional anteversion of the acetabular component. Cite this article: Bone Joint J 2016;98-B:910-16.

Osteogenic protein-1 (OP-1) in the repair of bone defects and fractures of long bones: clinical experience

The concept of osteoinductive or bone morphogenetic proteins (BMPs) was first introduced by Urist nearly 40 years ago [1], and by the late 1980’s the human cDNA for OP-1 (BMP-7) was cloned [2]. Utilizing recombinant technology, human OP-1 (rhOP-1) was produced and this molecule has demonstrated its capacity to induce bone formation [3, 4]. Subsequently, extensive preclinical and clinical research has confirmed the efficacy as well as safety of OP-1 in the process of bone repair and regeneration [5, 6, 7, 8]. This paper will focus on clinical experience with OP-1 in the treatment of nonunions of the appendicular skeleton.

Patient-specific instrumentation improves the accuracy of acetabular component placement in total hip arthroplasty

AIMS Accurate placement of the acetabular component during total hip arthroplasty (THA) is an important factor in the success of the procedure. However, the reported accuracy varies greatly and is dependent upon whether free hand or navigated techniques are used. The aim of this study was to assess the accuracy of an instrument system that incorporates 3D printed, patient-specific guides designed to optimise the placement of the acetabular component. PATIENTS AND METHODS A total of 100 consecutive patients were prospectively enrolled and the accuracy of placement of the acetabular component was measured using post-operative CT scans. PATIENTS AND METHODS A total of 100 consecutive patients were prospectively enrolled and the accuracy of placement of the acetabular component was measured using post-operative CT scans. CONCLUSION Accurate placement of the acetabular component can be achieved using patient-specific guides and is superior to free hand techniques and comparable to navigated and robotic techniques. Cite this article: Bone Joint J 2016;98-B:1342-6.

Risk factors for increased sagittal pelvic motion causing unfavourable orientation of the acetabular component in patients undergoing total hip arthroplasty

Aims It is important to consider sagittal pelvic rotation when introducing the acetabular component at total hip arthroplasty (THA). The purpose of this study was to identify patients who are at risk of unfavourable pelvic mobility, which could result in poor outcomes after THA. Patients and Methods A consecutive series of 4042 patients undergoing THA had lateral functional radiographs and a low‐dose CT scan to measure supine pelvic tilt, pelvic incidence, standing pelvic tilt, flexedseated pelvic tilt, standing lumbar lordotic angle, flexed‐seated lumbar lordotic angle, and lumbar flexion. Changes in pelvic tilt from supine‐to‐standing positions and supine‐to‐flexedseated positions were determined. A change in pelvic tilt of 13° between positions was deemed unfavourable as it alters functional anteversion by 10° and effectively places the acetabular component outside the safe zone of orientation. Results For both men and women, the degree of lumbar flexion was a significant predictor of risk in hip flexion (p < 0.0001) with increased odds of unfavourable pelvic mobility in those with lumbar flexion of < 20° (men, odds ratio (OR) 6.74, 95% confidence interval (CI) 3.83 to 11.89; women, OR 2.97, 95% CI 1.87 to 4.71). In women, age and standing pelvic tilt were significant predictors of risk in hip extension (p = 0.0082 and p < 0.0001, respectively). The risk of unfavourable pelvic mobility was higher in those aged > 75 years (OR 2.28, 95% CI 1.56 to 3.32) and those with standing pelvic tilt of <‐10° for extension risk (OR 7.10, 95% CI 4.10 to 10.29). In men, only standing pelvic tilt was significant (p < 0.0001) for hip extension with an increased risk of unfavourable pelvic mobility (OR 8.68, 95% CI 5.19 to 14.51). Conclusion Patients found to have unfavourable pelvic mobility had limited lumbar flexion and more posterior standing pelvic tilt in both men and women, as well as increasing age in women. We recommend that patients undergo preoperative functional radiographic screening to determine specific parameters that can affect the functional orientation of the acetabular component.