Compartment syndrome, a devastating consequence of limb trauma, is characterised by severe tissue injury and microvascular perfusion deficits. We hypothesised that leucopenia might provide significant protection against microvascular dysfunction and preserve tissue viability. Using our clinically relevant rat model of compartment syndrome, microvascular perfusion and tissue injury were directly visualised by intravital video microscopy in leucopenic animals. We found that while the tissue perfusion was similar in both groups (38.8% (standard error of the mean (. sem). 7.1). , 36.4. % (. sem. 5.7), 32.0% (. sem. 1.7), and 30.5% (. sem. 5.35) continuously-perfused capillaries at 45, 90, 120 and 180 minutes compartment syndrome, respectively versus 39.2% (. sem. 8.6), 43.5% (. sem. 8.5). , . 36.6% (. sem. 1.4) and 50.8% (. sem. 4.8) at 45, 90, 120 and 180 minutes compartment syndrome, respectively in leucopenia), compartment syndrome-associated muscle injury was significantly decreased in leucopenic animals (7.0% (. sem. 2.0), 7.0%, (. sem. 1.0), 9.0% (. sem. 1.0) and 5.0% (. sem. 2.0) at 45, 90, 120 and 180 minutes of compartment syndrome, respectively in leucopenia group versus 18.0% (. sem. 4.0), 23.0% (. sem. 4.0), 32.0% (. sem. 7.0), and 20.0% (. sem. 5.0) at 45, 90, 120 and 180 minutes of compartment syndrome in control, p = 0.0005). This study demonstrates that the inflammatory process should be considered central to the understanding of the pathogenesis of cellular injury in compartment syndrome. Cite this article: Bone Joint J 2015;97-B:539–43

Introduction. Missile injuries are very serious injuries particularly in the cervical region. They are classified into high and low missile injuries when it involves the cervical spine. In modern guerrilla warfare, one must be aware of ballistic pathology with bullets as well as from explosives. In particular, improvised explosive devices commonly known as IED's play a new and important pathophysiology whether they are suicided vests or roadside bombs. They usually produce severe or lethal injuries and serious neurovascular deficit is frequent. We present the details of 40 patients with local experience on how to handle serious penetrating cervical missile injuries. Methods. All cases were collected from the record of Basrah University Hospital, Iraq. Healthy military gentlemen with ages ranging between 20–35 years were included. Results. 11 patients had bullet injuries and 29patients had fragments of shell injuries. The sites of injuries were 9: C2–C3, 12: C5–C6, 12: C4–C5 and 7: C7-T1. Bullet entrance was anterior in 23 patients, posterior in 7 patients and lateral in 10 patients. The cervical vertebrae were injured in 37 patients at body or lamina level while in 3 patients it was only neural tissue injuries. Missiles were retained in 13 patients. All injuries showed some degree of neurological deficit with quadriplegia in 26 patients. 9 patients presented with very serious injuries. No relation was found between the size of the missile and the extent of damage. Outcome of treatment in all patients was poor. Conclusion. Gunshot wounds only account for approximately one third of penetrating missile injuries in patients who survive and are well enough to receive medical treatment. 62% of patients' cohort were from explosive devices, consistent with data from 2010, where 58% of fatalities were from IED's occurring in foreign soldiers in Afghanistan. We discuss the importance of general supportive measures, generous wound excision, removal of the retained missiles and heavy cover of antibiotics

INTRODUCTION. Interest in tissue-preserving or minimally invasive total hip arthroplasty (THA) is increasing with focus toward decreased hospital stay, enhanced rehabilitation, and quicker recovery for patients. Two tissue-preserving techniques, the anterior and superior approaches to THA, have excellent clinical results, but little is known about their relative impact on soft tissue. The purpose of this study was to evaluate the type and extent of tissue damage after THA with each approach, focusing on abductors, short external rotators, and the hip capsule. METHODS. Total hip arthroplasty was performed on bilateral hips of eleven fresh-frozen cadavers (22 hips). They were randomized to anterior THA performed on one side and superior THA performed on the other, in the senior authors' standard technique. Two independent examiners graded the location and extent of tissue injury by performing postsurgical dissections. Muscle bellies, tendons, and capsular attachments were graded as intact, split, damaged (insignificant, minimal, moderate, or extensive damage), or detached based on direct visual inspection of each structure. Tissue injury was analyzed with either a chi-squared (≥5 qualifying structures) or Fisher's exact test (<5 qualifying structures). P values <0.05 were significant. RESULTS. The abductor muscles or tendons were intact or insignificantly damaged in 63.6% of anterior approach specimens compared with 84.1% of the superior specimens (p= 0.03). Specifically, the gluteus minimus tendon had moderate or extensive damage in 63.6% of anterior specimens compared with none of the superior specimens (p <0.01). Short external rotators (SERs) group, defined as both the muscle and tendon of the piriformis, conjoint, obturator externus, and quadratus, were intact or insignificantly damaged in 63.6% of anterior approach specimens compared with 80.5% of the SER group of superior specimens (p = 0.02). The femoral attachments of the anterior, posterior, and superior capsules were extensively damaged or detached in 90.9%, 81.8%, and 100% of anterior approach specimens respectively compared with 0%, 9.1% and 9.1% of superior approach specimens respectively (all p <0.01). CONCLUSION. In a cadaveric study examining superior and anterior approaches to THA, the superior approach demonstrated significantly less soft-tissue destruction than the anterior approach, specifically to the gluteus minimus tendon, short external rotators, and the hip capsule

Abstract. Objectives. The term heterotopic ossification (HO) describes lamellar bone formation within soft tissues following injury. A genome-wide scan of patients after hip arthroplasty has identified that variation within the lncRNA CASC20 is associated with HO susceptibility. Previous findings in our lab have demonstrated upregulation of CASC20 during BMP2-induced osteodifferentiation of adipose-derived stem cells (hMAD) alongside osteodifferentiation markers, RUNX2 and OSX. We hypothesize that CASC20 is a novel regulator of bone formation and aim to investigate CASC20 function in bone formation. Methods. 1) We used miRanda prediction algorithm and the ENCORI database to respectively predict which miRNAs CASC20 interacts with and to select for experimentally validated miRNAs. 2) We characterized the expression and functional role of CASC20-interacting miRNAs by respectively analyzing publicly available datasets (GSE107279 and pubmed.ncbi.nlm.nih.gov/26175215/) and by using Gene Ontology (GO) analysis. 3) We overexpressed CASC20 in hMAD using a lentiviral system and tested the effect of CASC20 overexpression in osteodifferentiation and expression of putative CASC20-interacting miRNAs. Results. 1) We identified 64 experimentally validated miRNAs that are predicted to interact with CASC20. 2) GO analysis revealed that the most frequently targeted molecular functions included SMADs, MAPKK and other kinase activities known to play a central role in osteo and chondrogenesis. We found 10 miRNAs including hsa-miR-485-3p that demonstrated down-regulation in both osteo- and chondrogenesis. 3) We found that CASC20-overexpression augmented the osteodifferentiation of hMAD measured in mineralization using Alizarin Red S. CASC20 overexpression increased the expression of osteogenic marker ALP and decreased the expression of hsa-miR-485-3p. Conclusion. Here we show how CASC20 may regulate bone formation by acting as a competitive endogenous RNA (ceRNA). We are currently using CASC20 overexpression model in osteo- and chondrogenesis, and testing CASC20-miRNA interaction to establish the underlying mechanism for the observed associations

Aims

The antidiabetic agent metformin inhibits fibrosis in various organs. This study aims to elucidate the effects of hyperglycaemia and metformin on knee joint capsule fibrosis in mice.

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It has been established that mechanical stimulation benefits tendon-bone (T-B) healing, and macrophage phenotype can be regulated by mechanical cues; moreover, the interaction between macrophages and mesenchymal stem cells (MSCs) plays a fundamental role in tissue repair. This study aimed to investigate the role of macrophage-mediated MSC chondrogenesis in load-induced T-B healing in depth.

Aims

CRP is an acute-phase protein that is used as a biomarker to follow severity and progression in infectious and inflammatory diseases. Its pathophysiological mechanisms of action are still poorly defined. CRP in its pentameric form exhibits weak anti-inflammatory activity. The monomeric isoform (mCRP) exerts potent proinflammatory properties in chondrocytes, endothelial cells, and leucocytes. No data exist regarding mCRP effects in human intervertebral disc (IVD) cells. This work aimed to verify the pathophysiological relevance of mCRP in the aetiology and/or progression of IVD degeneration.

Pathological assessment of periprosthetic tissues is important, not only for diagnosis, but also for understanding the pathobiology of implant failure. The host response to wear particle deposition in periprosthetic tissues is characterised by cell and tissue injury, and a reparative and inflammatory response in which there is an innate and adaptive immune response to the material components of implant wear. Physical and chemical characteristics of implant wear influence the nature of the response in periprosthetic tissues and account for the development of particular complications that lead to implant failure, such as osteolysis which leads to aseptic loosening, and soft-tissue necrosis/inflammation, which can result in pseudotumour formation. The innate response involves phagocytosis of implant-derived wear particles by macrophages; this is determined by pattern recognition receptors and results in expression of cytokines, chemokines and growth factors promoting inflammation and osteoclastogenesis; phagocytosed particles can also be cytotoxic and cause cell and tissue necrosis. The adaptive immune response to wear debris is characterised by the presence of lymphoid cells and most likely occurs as a result of a cell-mediated hypersensitivity reaction to cell and tissue components altered by interaction with the material components of particulate wear, particularly metal ions released from cobalt-chrome wear particles. Cite this article: Professor N. A. Athanasou. The pathobiology and pathology of aseptic implant failure. Bone Joint Res 2016;5:162–168. DOI: 10.1302/2046-3758.55.BJR-2016-0086

Objectives. Rotator cuff tears are among the most frequent upper extremity injuries. Current treatment strategies do not address the poor quality of the muscle and tendon following chronic rotator cuff tears. Hypoxia-inducible factor-1 alpha (HIF-1α) is a transcription factor that activates many genes that are important in skeletal muscle regeneration. HIF-1α is inhibited under normal physiological conditions by the HIF prolyl 4-hydroxylases (PHDs). In this study, we used a pharmacological PHD inhibitor, GSK1120360A, to enhance the activity of HIF-1α following the repair of a chronic cuff tear, and measured muscle fibre contractility, fibrosis, gene expression, and enthesis mechanics. Methods. Chronic supraspinatus tears were induced in adult rats, and repaired 28 days later. Rats received 0 mg/kg, 3 mg/kg, or 10 mg/kg GSK1120360A daily. Collagen content, contractility, fibre type distribution and size, the expression of genes involved in fibrosis, lipid accumulation, atrophy and inflammation, and the mechanical properties of the enthesis were then assessed two weeks following surgical repair. Results. At two weeks following repair, treatment groups showed increased muscle mass but there was a 15% decrease in force production in the 10 mg/kg group from controls, and no difference between the 0 mg/kg and the 3 mg/kg groups. There was a decrease in the expression of several gene transcripts related to matrix accumulation and fibrosis, and a 50% decrease in collagen content in both treated groups compared with controls. Additionally, the expression of inflammatory genes was reduced in the treated groups compared with controls. Finally, PHD inhibition improved the maximum stress and displacement to failure in repaired tendons. Conclusions. GSK1120360A resulted in improved enthesis mechanics with variable effects on muscle function. PHD inhibition may be beneficial for connective tissue injuries in which muscle atrophy has not occurred. Cite this article: J. P. Gumucio, M. D. Flood, A. Bedi, H. F. Kramer, A. J. Russell, C. L. Mendias. Inhibition of prolyl 4-hydroxylase decreases muscle fibrosis following chronic rotator cuff tear. Bone Joint Res 2017;6:57–65. DOI: 10.1302/2046-3758.61.BJR-2016-0232.R1

Purpose: Compartment syndrome is a limb-threatening complication of skeletal trauma. Both ischemia and inflammation may be responsible for tissue necrosis in compartment syndrome (CS). In this study, normal rodents were compared with neutropenic animals to determine the importance of inflammation as a mechanism of cellular damage using techniques of intravital videomicroscopy (IVVM) and histochemical staining. Method: Forty Wistar rats were randomised. Twenty animals served as a control (group C). Twenty rats were rendered neutropenic using cyclophosphamide (250mg/kg) (group N). Animals were anaesthetised with 5 % isoflurane. Elevated intracompartmental pressure was induced by saline infusion into the anterior hindlimb compartment and maintained at 30–40 mmHg for 0, 15, 45 or 90 minute time intervals. Following fasciotomy, the EDL muscle was analyzed using IVVM to quantify tissue injury, capillary perfusion, and inflammatory response. Results: The proportion of injured cells decreased in group N compared to group C at all time intervals of EICP (p< 0.05). The proportion of injured cells in group N was 8 % after 0 minutes EICP, and 12, 15, and 10 % at 15, 45, and 90 min of EICP. In group C injured cells increased from 8 % to 20, 22, and 21 % at 15, 45, and 90 minutes EICP respectively. Groups N and C both demonstrated a time-dependent reduction in capillary perfusion. In group N continuously-perfused capillaries decreased from 79±4/mm with 0 min of EICP, to 48±11/mm (15min), 36±7/mm (45min), and 24±10/mm (90min) (p < 0.05). Overall, There was no difference between groups N and C with regards to perfusion (p> 0.05). Conclusion: This study demonstrates the importance of inflammation as a cause of injury in compartment syndrome. There was a 50% decrease in injury in neutropenic animals compared to controls after 90 minutes of elevated intracompartmental pressure. Microvascular perfusion analysis demonstrated a time-dependent decrease in capillary perfusion in both neutropenic and control animals. Blocking of the inflammatory response via neutropenia was protective against tissue injury. These results provide evidence toward a potential therapeutic benefit for anti-inflammatory treatment of elevated intra-compartmental pressure

Background. Some reports have suggested that debris generated from the head neck taper junction is more destructive than equivalent doses from metal bearing surfaces. Methods. Part 1. We examined the relationship between the source (taper/bearing) and volume of metal debris on Cr and Co concentrations in corresponding blood and hip synovial fluid samples and the observed agglomerated particle sizes in excised tissues using regression analysis of prospectively collected data at a single revision unit. Part 2. We investigated variables most strongly associated with macroscopic soft tissue injury as documented at revision surgery using ordinal logistic regression. Independent variables included source and volume of CoCr exposure, Cr and Co joint fluid concentrations, joint fluid grade, ALVAL (Aseptic Lymphocytic Vasculitis Associated Lesion) grade, presence of vascular hyalinisation, agglomerated particle size, implant type, patient sex and age. Results. A total of 199 explanted MoM hips were analysed. Multiple regression statistical modelling suggested that a greater source contribution of metal debris from the taper junction was associated with smaller aggregated particle sizes in the local tissues and a relative reduction of Cr ion concentrations in the corresponding synovial fluid and blood samples. There was an association between increasing Co concentrations in the joint fluid and an increasing ALVAL score (p<0.001). In contrast, higher Cr concentrations were inversely related to ALVAL (p<0.001). The ALVAL response was itself strongly associated with larger fluid collections (p<0.001). Vascular hyalinisation and larger fluid collections were significantly associated with macroscopic tissue injury (coefficient 2.22, p<0.001 for fluid grade and 4.35, p<0.001 for hyalinisation). Discussion. Metal debris generated from taper junctions appears to be associated with a different biochemical environment than debris generated from bearing surfaces. We believe that this finding may provide some explanation as to the poor performance of MoM THRs compared to the equivalent resurfacing devices and the confusion surrounding the significance of blood metal testing. Conclusion. Chromium does seem to inhibit the development of ALVAL

Spinal cord injury (SCI) is a devastating disorder for which the identification of exacerbating factors is urgently needed. Although age, blood pressure and infection are each considered to be prognostic factors in patients with SCI, exacerbating factors that are amenable to treatment remain to be elucidated. Microglial cells, the resident immune cell in the CNS, form the first line of defense after being stimulated by exposure to invading pathogens or tissue injury. Immediately after SCI, activated microglia enhance and propagate the subsequent inflammatory response by expressing cytokines, such as TNF-α, IL-6 and IL-1β. Recently, we demonstrated that the activation of microglia is associated with the neuropathological outcomes of SCI. Although the precise mechanisms of microglial activation remain elusive, several basic research studies have reported that hyperglycemia is involved in the activation of resident monocytic cells, including microglia. Because microglial activation is associated with secondary injury after SCI, we hypothesized that hyperglycemia may also influence the pathophysiology of SCI by altering microglial responses. The mice were anesthetized with pentobarbital (75 mg/kg i.p.) and were subjected to a contusion injury (70 kdyn) at the 10th thoracic level using an Infinite Horizons Impactor (Precision Systems Instrumentation). For flow cytometry, the samples were stained with the antibodiesand analyzed using a FACS Aria II flow cytometer and the FACSDiva software program (BD Biosciences). We retrospectively identified 528 SCI patients admitted to the Department of Orthopaedic Surgery at the Spinal Injuries Center (Fukuoka, Japan) between June 2005 and May 2011. The patients' data were obtained from their charts. We demonstrate that transient hyperglycemia during acute SCI is a detrimental factor that impairs functional improvement in mice and human patients after acute SCI. Under hyperglycemic conditions, both in vivo and in vitro, inflammation was enhanced through promotion of the nuclear translocation of the nuclear factor kB (NF-kB) transcription factor in microglial cells. During acute SCI, hyperglycemic mice exhibited progressive neural damage, with more severe motor deficits than those observed in normoglycemic mice. Consistent with the animal study findings, a Pearson χ2 analysis of data for 528 patients with SCI indicated that hyperglycemia on admission (glucose concentration ≥126 mg/dl) was a significant risk predictor of poor functional outcome. Moreover, a multiple linear regression analysis showed hyperglycemia at admission to be a powerful independent risk factor for a poor motor outcome, even after excluding patients with diabetes mellitus with chronic hyperglycemia (regression coefficient, −1.37; 95% confidence interval, −2.65 to −0.10; P < 0.05). Manipulating blood glucose during acute SCI in hyperglycemic mice rescued the exacerbation of pathophysiology and improved motor functional outcomes. Our findings suggest that hyperglycemia during acute SCI may be a useful prognostic factor with a negative impact on motor function, highlighting the importance of achieving tight glycemic control after central nervous system injury

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To identify the prevalence of neuropathic pain after lower limb fracture surgery, assess associations with pain severity, quality of life and disability, and determine baseline predictors of chronic neuropathic pain at three and at six months post-injury.

Background: Neck pain is a growing problem which is linked to occupational factors that include work above shoulder height or sustained neck flexion. These activities may induce fatigue in the neck muscles impairing the muscles’ ability to provide reflex contractions that protect against tissue injury. The aim of this study was to investigate the effect of neck muscle fatigue on reflex activation of the neck muscles. Methods: Healthy volunteers were subjected to one of two loading protocols. Isometric contractions of neck extensors at 60% MVC were sustained to the endurance limit (n=30) to induce high level fatigue in these muscles. A similar protocol for neck flexors (n=21) was used to initiate low level contraction of the extensors which are co-activated to stabilise the cervical spine under such circumstances. Before and after each loading protocol, reflex activation of the trapezius muscle was assessed using skin surface electromyography (EMG) to measure the latency and amplitude of muscle activation in response to a sudden perturbation of the head. Results: Reflex latencies increased from 73±17ms to 93±27ms (p=0.0041), and from 72±12ms to 97±28ms (p< 0.0001) following low and high level extensor fatigue, respectively. Time to peak EMG also increased from 122±32ms to 148±39ms (p=0.0093), and from 113±15ms to 138±25ms (p< 0.0001), respectively, although no change in peak EMG amplitude was observed. Conclusions: Reflex activation of trapezius was substantially delayed following both loading protocols. These findings suggest that even low level postural loading in the workplace may impair neck muscle reflexes rendering the underlying tissues more vulnerable to strain injury. Conflicts of Interest: None. Source of Funding: BBSRC (Biotechnology and Biological Sciences Research Council, UK)

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Despite recent advances in arthroscopic rotator cuff repair, re-tear rates remain high. New methods to improve healing rates following rotator cuff repair must be sought. Our primary objective was to determine if adjunctive bone marrow stimulation with channelling five to seven days prior to arthroscopic cuff repair would lead to higher Western Ontario Rotator Cuff (WORC) scores at 24 months postoperatively compared with no channelling.

During two sequential deployments to Afghanistan, it was noticed that an inordinately high number of patients with bilateral lower limb injuries that resulted in amputations at Camp Bastion itself, had associated upper limb injuries. It was decided to study the incidence and distribution of the same. Permission was granted to conduct this study as it would throw a light on the pattern of injuries and allow a further study of the impact of this on rehabilitation. This was both a retrospective as well as a prospective study. Of the 221 cases, 68 were recorded and data collected prospectively whereas the data for the rest was gathered using the patients' scanned records from Camp Bastion, their radiology reports and clinical photographs (from the Joint Theatre Trauma Registry). A total of 221 patients were studied as described above. They included UK, NATO, US, ANA, ANP, EF and Afghan civilians (June 2009 - January 2011). There were 59 fatalities from these 221 cases. That data pertaining to these cases was discarded. Of the surviving 162 cases, 31 cases had no upper limb involvement. A number of these individuals were subjected to an IED attack when mounted, although dismounted injuries still accounted for the vast majority. 131 individuals had upper limb involvement of some sort or the other. The injuries were classified into anatomical distribution as well and the type of trauma (amputations, composite soft tissue, fractures, vascular, nerves etc). The predominance of the injuries was on the distal portion of the upper limb (i.e involving the digits, hands and forearm (digits and hands – 66 patients, wrist and forearm in 69 patients, elbow and arm in 42 patients). The most common form of involvement was a composite tissue injury (involving skin, muscle and vessels/nerves) in 85 patients. 27 patients ended up as triple amputees by the time they left the Camp Bastion Role 3 Hospital. From the pattern and severity of injuries it is obvious that dismounted individuals presented with a very severe spectrum of injuries. The predominance of the left upper limb being involved is in keeping with a dismounted right-handed soldier out on patrol with the left upper limb extended along the barrel of the rifle or his weapon. Using various cases (clinical photographs as well as radiographs) the spectrum of injuries is explained and a case is made for truly differentiating the debridement and radical treatment of upper limb versus lower limb trauma during initial surgery

Purpose of the study. We report septic shock as postoperative complication following an instrumented posterior spinal arthrodesis on a patient with multiple body piercings. The management of this potentially catastrophic complication and outcome of treatment is been discussed. Summary of Background Data. Body piercing has become increasingly more common due to change in culture or as a fashion statement. This has been associated with local or generalized ill effects including tissue injury, skin and systemic infections, and septic shock. There is no clear guideline pathway regarding removal and reinsertion of body piercings in patients who undergo major surgery. Complications following Orthopaedic or Spinal procedures associated with body piercing have not been reported. Methods. We reviewed the medical notes and radiographs of an adolescent patient with severe Scheuermann's kyphosis and multiple body piercings who underwent an uneventful posterior spinal arthrodesis with pedicle hook/screw/rod instrumentation and autologous iliac crest bone graft and developed septic shock. Results. Septic shock developed on postoperative day 2 after reinsertion of all piercings following patient's request. The patient became systemically very unwell and required intensive medical management, as well as a total course of antibiotics of 3 months. The piercings remained in situ. She did not develop a wound infection despite the presence of bacteraemia (coagulase-negative Staphylococci/Streptococci warneri) and spinal instrumentation. The patient had no new piercings subsequent to her deformity procedure. Two and a half years after spinal surgery she reported no medical problems, had a balanced spine with no loss of kyphosis correction and no evidence of nonunion or recurrence of deformity. Conclusion. The development of septic shock as a result of piercing reinsertion in the postoperative period has not been previously reported. This is an important consideration to prevent potentially life-threatening complications following major spinal surgery. Despite the wide array of complications associated to body art there are no clear guidelines for body piercing. There is growing public awareness and several countries are laying regulations which have not yet been internationally standardized. A clear practice guideline in the perioperative management of piercings is needed as the incidence of body piercing and associated complications is rising. There is need for surgeons to be aware of the hazards of body piercing and its implications. We propose that multiple piercings should not be reinserted after major surgery and appropriate counseling should be provided to the patients as part of the consent process

1. A study of the late results of 343 soundly united tibial shaft fractures was carried out. Limitation of ankle and/or foot movement occurred in twenty-one patients (6 per cent) and was found to be the most important cause of disability. Knee stiffness (2·3 per cent of cases) and shortening of up to three-quarters of an inch (5·5 per cent of cases) caused little functional impairment. 2. Stiffness of the foot and ankle was correlated with the severity of injury, occurring in 1 per cent of minor, 5 per cent of moderate and 22 per cent of major injuries. 3. One-third of the patients with limitation of foot and ankle movement had clinical evidence of ischaemic contracture. 4. It is argued that, in the absence of direct injury to the joint, persistent joint stiffness is caused by replacement fibrosis of soft tissues. This may result either from direct tissue injury or from associated vascular damage