Marked differences in local bone remodelling in response to different marrow stimulation techniques in a large animal.

Marrow stimulation, including subchondral drilling and microfracture, is the most commonly performed cartilage repair strategy, whereby the subchondral bone plate is perforated to release marrow-derived cells into a cartilage defect to initiate repair. Novel scaffolds and therapeutics are being designed to enhance and extend the positive short-term outcomes of this marrow stimulation. However, the translation of these newer treatments is hindered by bony abnormalities, including bone resorption, intralesional osteophytes, and bone cysts, that can arise after marrow stimulation. In this study, three different marrow stimulation approaches - microfracture, subchondral drilling and needle-puncture - were evaluated in a translationally relevant large-animal model, the Yucatan minipig. The objective of the study was to determine which method of marrow access (malleted awl, drilled Kirschner wire or spring-loaded needle) best preserved the underlying subchondral bone. Fluorochrome labels were injected at the time of surgery and 2 weeks post-surgery to capture bone remodelling over the first 4 weeks. Comprehensive outcome measures included cartilage indentation testing, histological grading, microcomputed tomography and fluorochrome imaging. Findings indicated that needle-puncture devices best preserved the underlying subchondral bone relative to other marrow access approaches. This may relate to the degree of bony compaction occurring with marrow access, as the Kirschner wire approach, which consolidated bone the most, induced the most significant bone damage with marrow stimulation. This study provided basic scientific evidence in support of updated marrow stimulation techniques for preclinical and clinical practice.

Long term outcomes of biomaterial-mediated repair of focal cartilage defects in a large animal model.

The repair of focal cartilage defects remains one of the foremost issues in the field of orthopaedics. Chondral defects may arise from a variety of joint pathologies and left untreated, will likely progress to osteoarthritis. Current repair techniques, such as microfracture, result in short-term clinical improvements but have poor long-term outcomes. Emerging scaffold-based repair strategies have reported superior outcomes compared to microfracture and motivate the development of new biomaterials for this purpose. In this study, unique composite implants consisting of a base porous reinforcing component (woven poly(ε-caprolactone)) infiltrated with 1 of 2 hydrogels (self-assembling peptide or thermo-gelling hyaluronan) or bone marrow aspirate were evaluated. The objective was to evaluate cartilage repair with composite scaffold treatment compared to the current standard of care (microfracture) in a translationally relevant large animal model, the Yucatan minipig. While many cartilage-repair studies have shown some success in vivo, most are short term and not clinically relevant. Informed by promising 6-week findings, a 12-month study was carried out and those results are presented here. To aid in comparisons across platforms, several structural and functionally relevant outcome measures were performed. Despite positive early findings, the long-term results indicated less than optimal structural and mechanical results with respect to cartilage repair, with all treatment groups performing worse than the standard of care. This study is important in that it brings much needed attention to the importance of performing translationally relevant long-term studies in an appropriate animal model when developing new clinical cartilage repair approaches.

EBRA-FCA for measurement of migration of the femoral component in surface arthroplasty of the hip.

Studies on the migration of an implant may be the only way of monitoring the early performance of metal-on-metal prostheses. The Ein Bild Roentgen Analyse--femoral component analysis (EBRA-FCA) method was adapted to measure migration of the femoral component in a metal-on-metal surface arthroplasty of the hip using standard antero-posterior radiographs. In order to determine the accuracy and precision of this method a prosthesis was implanted into cadaver bones. Eleven series of radiographs were used to perform a zero-migration study. After adjustment of the femoral component to simulate migration of 3 mm the radiographs were repeated. All were measured independently by three different observers. The accuracy of the method was found to be +/- 1.6 mm for the x-direction and +/- 2 mm for the y-direction (95% percentile). The method was validated using 28 hips with a minimum follow-up of 3.5 years after arthroplasty. Seventeen were sound, but 11 had failed because of loosening of the femoral component. The normal (control) group had a different pattern of migration compared with that of the loose group. At 29.2 months, the control group showed a mean migration of 1.62 mm and 1.05 mm compared with 4.39 mm and 4.05 mm in the failed group, for the centre of the head and the tip of the stem, respectively (p = 0.001). In the failed group, the mean time to migration greater than 2 mm was earlier than the onset of clinical symptoms or radiological evidence of failure, 19.1 versus 32.2 months (p = 0.001) and 24.8 months (p = 0.012), respectively. EBRA-FCA is a reliable and valid tool for measuring migration of the femoral component after surface arthroplasty and can be used to predict early failure of the implant. It may be of value in determining the long-term performance of surface arthroplasty.

Radiographic evaluation of the Duraloc cup after 4 years.

We implanted 71 metal-backed, porous-coated, hemispheric, press-fit Duraloc-100 cups in 68 consecutive patients. In 61 patients, the femoral stem was a cementless Spotorno and in ten a cemented Lubinus SP II. A 28-mm Biolox ceramic head was used with both stems. After an average follow-up of 4 (3.7-5.9) years, we examined 67 hips. Radiolucencies were described in three zones according to DeLee and Charnley, and migration was measured on serial radiographs using the computer-assisted EBRA method. Total migration of more than 1 mm within the first 2 years occurred in 22/62 cups. Nine cups showed more than 1.5 mm total migration within the first 2 years and more than 2 mm within the whole period. The presence of post-operative radiolucencies correlated significantly with a total migration value of more than 2 mm within the first 2 years (p=0.02). Post-operative radiolucencies in zone 1 correlated with a total migration value of more than 2 mm within the first 2 years (p=0.027) and more than 2.5 mm within the whole period (p=0.051). These correlation values might reflect the quality of operative technique, particularly reaming, and implant selection.

Pelvic tilt in neuromuscular disorders.

The pelvic tilt is part of a complex deformity in which both the spine and the hip are involved. By viewing the different planes and analyzing the deforming forces, four different types of pelvic tilt in combination with spinal and hip deformities can be identified. In spina bifida patients congenital deformities of the spine may add to the progression of scoliosis. Analyzing our own patients we found that certain types of pelvic tilt can be related to certain neuromuscular diseases. Moreover our results show that the pelvic tilt can be effectively corrected by spinal surgery, whereas no effect of hip surgery could be demonstrated.