It has been proposed that growth cones navigating through gradients adapt to baseline concentrations of guidance cues. This adaptation process is poorly understood. Using the collapse assay, we show that adaptation in Xenopus laevis retinal growth cones to the guidance cues Sema3A or netrin-1 involves two processes: a fast, ligand-specific desensitization that occurs within 2 min of exposure and is dependent on endocytosis, and a slower, ligand-specific resensitization, which occurs within 5 min and is dependent upon protein synthesis. These two phases of adaptation allow retinal axons to adjust their range of sensitivity to specific guidance cues.

Total Hip Replacement is one of the most common operations performed in the developed world today. An increasingly ageing population means that the numbers of people undergoing this operation is set to rise. There are a numerous number of prosthesis on the market and it is often difficult to choose between them. It is therefore necessary to have a good understanding of the basic scientific principles in Total Hip Replacement and the evidence base underpinning them. This paper reviews the relevant anatomical and biomechanical principles in THA. It goes on to elaborate on the structural properties of materials used in modern implants and looks at the evidence base for different types of fixation including cemented and uncemented components. Modern bearing surfaces are discussed in addition to the scientific basis of various surface engineering modifications in THA prostheses. The basic science considerations in component alignment and abductor tension are also discussed. A brief discussion on modular and custom designs of THR is also included. This article reviews basic science concepts and the rationale underpinning the use of the femoral and acetabular component in total hip replacement.

The incidence of obesity is rising worldwide. Obesity is a risk factor for developing osteoarthritis in the knee. Obesity and knee osteoarthritis are independently disabling conditions and in combination pose difficult therapeutic challenges. This review will discuss obesity, osteoarthritis, and the problems associated with knee osteoarthritis in an obese population. Treatment options including surgery and its success will be discussed.

Acetabular retroversion may lead to impingement and pain, which can be treated with an anteverting periacetabular osteotomy (aPAO). Pelvic tilt influences acetabular orientation; as pelvic tilt angle reduces, acetabular version reduces. Thus, acetabular retroversion may be a deformity secondary to abnormal pelvic tilt (functional retroversion) or an anatomic deformity of the acetabulum and the innominate bone (pelvic ring). To (1) measure the spinopelvic morphology in patients with acetabular retroversion and (2) assess whether pelvic tilt changes after successful anteverting PAO (aPAO), thus testing whether preoperative pelvic tilt was compensatory. Case series; Level of evidence, 4. A consecutive cohort of 48 hips (42 patients; 30 ± 7 years [mean ± SD]) with acetabular retroversion that underwent successful aPAO was studied. Spinopelvic morphology (pelvic tilt, pelvic incidence, anterior pelvic plane, and sacral slope) was measured from computed tomography scans including the sacral end plate in 21 patients, with adequate images. In addition, the change in pelvic tilt with aPAO was measured via the sacrofemoral-pubic angle with supine pelvic radiographs at an interval of 2.5 ± 2 years. The spinopelvic characteristics included a pelvic tilt of 4° ± 4°, a sacral slope of 39° ± 9°, an anterior pelvic plane angle of 11° ± 5°, and a pelvic incidence of 42° ± 10°. Preoperative pelvic tilt was 4° ± 4° and did not change postoperatively (4° ± 4°) (P = .676). Pelvic tilt in acetabular retroversion was within normal parameters, illustrating “normal” sagittal pelvic balance and values similar to those reported in the literature in healthy subjects. In addition, it did not change after aPAO. Thus, acetabular retroversion was not secondary to a maladaptive pelvic tilt (functional retroversion). Further work is required to assess whether retroversion is a reflection of a pelvic morphological abnormality rather than an isolated acetabular abnormality. Treatment of acetabular retroversion should focus on correcting the deformity rather than attempting to change the functional pelvic position.

This retrospective case series evaluates the technique of transverse debridement, acute shortening and subsequent distraction histogenesis in the management of open tibial fractures with bone and soft tissue loss, thereby avoiding the need for a soft tissue flap to cover the wound. Thirty-one patients with Gustilo grade III open tibial fractures between 2001 and 2011 were initially managed with transverse wound extensions, debridement and shortening to provide bony apposition and allowing primary wound closure without tension, or coverage with mobilization of soft tissue and split skin graft. Temporary monolateral external fixation was used to allow soft tissues resuscitation, followed by Ilizarov frame for definitive fracture stabilization. Leg length discrepancy was corrected by corticotomy and distraction histogenesis. Union was evaluated radiologically and clinically. Patients’ mean age was 37.3 years (18.3–59.3). Mean bone defect was 3.2 cm (1–8 cm). Mean time to union was 40.1 weeks (12.6–80.7 weeks), and median frame index was 75 days/cm. Median lengthening index (time in frame after corticotomy for lengthening) was 63 days/cm. Mean clinic follow-up was 79 weeks (23–174). Six patients had a total of seven complications. Four patients re-fractured after frame removal, one of whom required a second frame. Two patients required a second frame for correction of residual deformity, and one patient developed a stiff non-union which united following a second frame. There were no cases of deep infection. Acute shortening followed by distraction histogenesis is a safe method for the acute treatment of open tibial fractures with bone and soft tissue loss. This method also avoids the cost, logistical issues and morbidity associated with the use of local or free-tissue transfer flaps and has a low rate of serious complications despite the injury severity.