Aims. Functional rehabilitation has become an increasingly popular treatment for Achilles tendon rupture (ATR), providing comparably low re-rupture rates to surgery, while avoiding risks of surgical complications. Limited evidence exists on whether gap size should affect patient selection for this treatment option. The aim of this study was to assess if size of gap between ruptured tendon ends affects patient-reported outcome following ATR treated with functional rehabilitation. Methods. Analysis of prospectively collected data on all 131 patients diagnosed with ATR at Royal Berkshire Hospital, UK, from August 2016 to January 2019 and managed non-operatively was performed. Diagnosis was confirmed on all patients by dynamic ultrasound scanning and gap size measured with ankle in full plantarflexion. Functional rehabilitation using an established protocol was the preferred treatment. All non-operatively treated patients with completed Achilles Tendon Rupture Scores (ATRS) at a minimum of 12 months following injury were included. Results. In all, 82 patients with completed ATRS were included in the analysis. Their mean age was 51 years (standard deviation (SD) 14). The mean ATRS was 76 (SD 19) at a mean follow-up of 20 months (SD 11) following injury. Gap inversely affected ATRS with a Pearson’s correlation of -0.30 (p = 0.008). Mean ATRS was lower with gaps > 5 mm compared with ≤ 5 mm (73 (SD 21) vs 82 (SD 16); p = 0.031). Mean ATRS was lowest (70 (SD 23)) with gaps > 10 mm, with significant differences in perceived strength and pain. The overall re-rupture rate was two out of 131 (1.5%). Conclusion. Increasing gap size predicts lower patient-reported outcome, as measured by ATRS. Tendon gap > 5 mm may be a useful predictor in physically demanding individuals, and tendon gap > 10 mm for those with low physical demand. Further studies that control for gap size when comparing non-operative and operative treatment are required to assess if these patients may benefit from surgery, particularly when balanced against the surgical risks. Cite this article: Bone Joint J 2020;102-B(11):1535–1541

Aims. To assess the characteristic clinical features, management, and outcome of patients who present to orthopaedic surgeons with functional dystonia affecting the foot and ankle. Methods. We carried out a retrospective search of our records from 2000 to 2019 of patients seen in our adult tertiary referral foot and ankle unit with a diagnosis of functional dystonia. Results. A total of 29 patients were seen. A majority were female (n = 25) and the mean age of onset of symptoms was 35.3 years (13 to 71). The mean delay between onset and diagnosis was 7.1 years (0.5 to 25.0). Onset was acute in 25 patients and insidious in four. Of the 29 patients, 26 had a fixed dystonia and three had a spasmodic dystonia. Pain was a major symptom in all patients, with a coexisting diagnosis of chronic regional pain syndrome (CRPS) made in nine patients. Of 20 patients treated with Botox, only one had a good response. None of the 12 patients who underwent a surgical intervention at our unit or elsewhere reported a subjective overall improvement. After a mean follow-up of 3.2 years (1 to 12), four patients had improved, 17 had remained the same, and eight reported a deterioration in their condition. Conclusion. Patients with functional dystonia typically presented with a rapid onset of fixed deformity after a minor injury/event and pain out of proportion to the deformity. Referral to a neurologist to rule out neurological pathology is advocated, and further management should be carried out in a movement disorder clinic. Response to treatment (including Botulinum toxin (Botox) injections) is generally poor. Surgery in this group of patients is not recommended and may worsen the condition. The overall prognosis remains poor. Cite this article: Bone Joint J 2021;103-B(6):1127–1132

Purpose. To explore the relationship in terms of time scale between pre-operative expectations and postoperative outcomes and satisfaction after Hallux valgus surgery. Methods. A patient derived questionnaire was developed and 30 patients aged 19 to 67 were included undergoing primary hallux valgus correction with a first metatarsal osteotomy and distal soft tissue release. Patients were asked pre-operatively to quantify their expected time scale for improvement in pain, ability to walk unaided, ability to drive, routine foot wear and foot feeling normal at 6 weeks, 3 and 6 months following surgery, and to indicate their confidence in achieving this result. Patients recorded postoperative outcomes achieved at number of weeks. Ordinal logistic regression multivariate modelling was used to examine predictors of postoperative satisfaction. Results. 90% of the patients were able to walk unaided and drive before or around the expected time scale at an average of five weeks' time. Persistent pain subsided at an average of two weeks post operatively which led to high satisfaction Although differences between patients' expectation and achievement were minimal at 6 weeks post-operatively, there was some discrepancy at 3 months, with patient expectations far exceeding achievement. The least satisfactory outcome was normal feeling of foot at six months follow up. There were significant correlations between failure to achieve expectations and the importance patients attached to recovery. Conclusions. This study underlines the importance of taking preoperative expectations into account to obtain an informed choice on the basis of the patient's preferences. Patients' pre-operative expectations of surgical outcome exceed their functional achievement but satisfaction remains high if pain control and ability to walk unaided is achieved early after hallux valgus corrective surgery

Background

Anatomical reduction of unstable Lisfranc injuries is crucial. Evidence as to the best methods of surgical stabilization remains sparse, with small patient numbers a particular issue. Dorsal bridge plating offers rigid stability and joint preservation.

The primary aim of this study was to assess the medium-term functional outcomes for patients treated with this technique at our centre. Additionally, we review for risk factors that influence outcomes.

Aim. To determine the influence of tendo achilles (TA) rupture gap distance and location on clinical outcome managed with accelerated functional rehabilitation. Methods. Twenty six patients with acute complete TA ruptures underwent ultrasound (US) within a week of injury. Measurements included the distance of the rupture from the enthesis and the gap distance between the tendon edges in three positions –. foot plantigrade,. maximum equinus and. maximum equinus with 90. o. knee flexion. All patients were managed non-operatively in functional weightbearing orthoses. Nineteen patients were followed up at a mean of 6.1 years (range 5.8–6.5). Outcomes included ultrasound confirmation of healing, Achilles Tendon Rupture Score (ATRS) and Modified Lepilahti score (MLS). Results. The mean distance of the rupture from the enthesis was 52mm (range: 40–76mm). The mean gap distance with the foot plantigrade was 11.4mm (95%CI: 9.9, 12.9) which reduced to 4.8mm (95%CI: 3.3, 6.4) in equinus and 1.5mm (95%CI: 0.8, 2.2) with 90° knee flexion. At follow up, no re-ruptures had occurred. US demonstrated continuity in all healed tendons. Mean ATRS was 86 (95%CI: 78.8, 93.9). There was a significant correlation between the distance of the rupture with the MLS (p=0.015) and the ATRS domains of strength (p=0.037) and fatigue (p=0.017). There was no significant correlation between the measured gap distance in the three positions with respect to the MTLS, ATRS or individual ATRS domain scores. There was no significant difference when comparing outcomes between left and right TAs or comparing gaps less than 1cm with those greater than 1 cm. Discussion. The distance of the gap from the enthesis may be more predictive of mid term clinical outcome in patients with TA rupture managed with accelerated functional rehabilitation compared with the magnitude of the gap and extent of closure with equinus and knee flexion

The incidence of periprosthetic fractures of the ankle is increasing. However, little is known about the outcome of treatment and their management remains controversial. The aim of this study was to assess the impact of periprosthetic fractures on the functional and radiological outcome of patients with a total ankle arthroplasty (TAA). A total of 505 TAAs (488 patients) who underwent TAA were retrospectively evaluated for periprosthetic ankle fracture: these were then classified according to a recent classification which is orientated towards treatment. The outcome was evaluated clinically using the American Orthopedic Foot and Ankle Society (AOFAS) score and a visual analogue scale for pain, and radiologically. . A total of 21 patients with a periprosthetic fracture of the ankle were identified. There were 13 women and eight men. The mean age of the patients was 63 years (48 to 74). Thus, the incidence of fracture was 4.17%. . There were 11 intra-operative and ten post-operative fractures, of which eight were stress fractures and two were traumatic. The prosthesis was stable in all patients. Five stress fractures were treated conservatively and the remaining three were treated operatively. . A total of 17 patients (81%) were examined clinically and radiologically at a mean follow-up of 53.5 months (12 to 112). The mean AOFAS score at follow-up was 79.5 (21 to 100). The mean AOFAS score in those with an intra-operative fracture was 87.6 (80 to 100) and for those with a stress fracture, which were mainly because of varus malpositioning, was 67.3 (21 to 93). Periprosthetic fractures of the ankle do not necessarily adversely affect the clinical outcome, provided that a treatment algorithm is implemented with the help of a new classification system. . Cite this article: Bone Joint J 2015;97-B:950–6

Metatarsal fractures are extremely common injuries accounting for 10% of all fractures seen in our accident and emergency departments (3). The vast majority can be treated conservatively. There is no standardised treatment, but it is commahplace to immobilise the foot and ankle joint in a below-knee back-slab, full cast or functional brace for a period of up to 6 weeks, weight-bearing the patient as pain allows. This practice is time-consuming and expensive, not to mention debilitating, and carries a morbidity risk to the patient. We describe a simple, effective and cheap treatment method for metatarsal fracture management using the functional forefoot-offloading shoe (FOS). This is clinically proven to offload pressure on the metatarsals and is commonly used in both elective forefoot surgery and in diabetic patients. Between January and September 2009, we identified 57 patients attending our fracture clinic with new metatarsal fractures. 28 met our inclusion criteria. All patients reported a significant improvement in their pain. At Injury – mean 8.21 out of 10 (range 4-10). After FOS fitting - mean 2.92 out of 10 (range 0-6). The forefoot-offloading shoe is an excellent alternative to plaster casting or functional boot immobilisation, offering high patient satisfaction, an excellent outcome and a considerable cost-saving to the hospital trust

Introduction:. The treatment of acute rupture of the tendo-achilles remains controversial. There is good evidence to suggest that outcomes are the same for both operative and non-operative treatment when a functional rehabilitation program is utilised. However, debate continues as to whether the radiological gap-size between the proximal and distal remnants of the tendon has an influence on the suitability for non-operative management. Methods:. All adult patients who attended the emergency department with a clinically suspected tendo-achilles rupture were place in a plantarflexed cast, and underwent MRI scanning to confirm the diagnosis. They were then counselled on the risks and benefits of operative versus non-operative treatment. Patients opting for non-operative treatment were asked to take part in the study and treated using a functional rehabilitation programme. Gap sizes were determined using a standardised protocol by a single musculoskeletal radiologist blinded to the clinical outcomes. Results:. A total of 69 patients have been recruited into the study, 40 have complete their one year review. There were two re-ruptures. The average age was 42.4 years (range 19–70). The average gap size recorded by MRI was 40.4mm (range 6–110). The average ATRS score was 80 (range 17–100) and the single limb heel raise percentage of contralateral side was 64.8% (range 4–115). The Spearman rank correlation coefficient comparing gap size and ATRS score was 0.272 (p=0.045) and for gap size and strength was 0.158 (p=0.165). Conclusion:. This study shows a weak positive correlation between MRI measured gap size of the ruptured tendo-achilles and the Achilles tendon Total Rupture Score at one year. No correlation could be demonstrated between gap size and strength at one year. These results suggest that the MRI measured gap size is unimportant in predicting outcome and hence suitability for non-operative treatment of tendo-achilles rupture using functional rehabilitation

Introduction. Isolated Weber B fractures usually heal uneventfully but traditionally require regular review due to the possibility of medial ligament injury allowing displacement. Following recent studies suggesting delayed talar shift is uncommon we introduced a functional treatment protocol and present the early results. Methods. 141 consecutive patients presenting acutely with Weber B fractures without talar shift between January and December 2015 were included. Patients were splinted in a removable boot and allowed to weight bear. ED notes and radiographs were reviewed by an Orthopaedic consultant. Patients without signs of medial injury were discharged with an information leaflet and advice. If signs of medial ligament injury were noted or the medial findings were not documented the patient was reviewed in fracture clinic at 4 weeks post-injury. If talar shift developed the patient was to be converted to operative treatment. Olerud and Molander scores were collected between 6 and 12 months post-injury. Results. 65 of 89 patients with signs of medial ligament injury or no documented medial findings attended fracture clinic. Of 51 patients without signs of medial ligament injury 23 were discharged according to protocol and 28 patients attended fracture clinic. One discharged patient re-accessed care. Of 93 patients reviewed in the fracture clinic none developed delayed talar shift. One underwent delayed ORIF for ongoing fibula discomfort and the remainder continued with non-operative treatment. 99 (70%) patients provided outcome scores. The mean score at a minimum of 6 months follow-up was 87 and the median score was 100. No significant difference was found between treatment arms. The scores were comparable to those in the published literature. Conclusion. We conclude the risk of delayed talar shift is low and satisfactory outcomes can be safely achieved with our functional protocol. Additional tests/imaging to establish the integrity of the medial ligament may be unnecessary

Introduction/Aim. Thromboembolism is a significant cause of patient morbidity and mortality, the risk of which increases in orthopaedic patients with lower limb immobilisation. It was therefore, our aim to identify a difference in symptomatic thromboembolism by treating acute Achilles tendon rupture patients with conventional non- weight bearing plaster versus functional weight bearing mobilisation. Methodology. The notes of 91 consecutive patients with acute Achilles tendon rupture were reviewed. The patients' demographics, treatment modality (non- weight bearing plaster versus weight bearing boot), and predisposing risk factors were analysed. From the 91 patients, 50 patients with acute Achilles tendon rupture were treated conservatively in a non- weight bearing immobilisation cast. From these 50 patients, 3 then underwent surgery and were therefore excluded from the results. 41 patients were treated with functional weight bearing mobilisation. Patients who did have a symptomatic thromboembolic event had an ultrasound scan to confirm a deep vein thrombosis of the lower limb, or a CT-scan to confirm pulmonary embolism. Results. Out of the 47 patients who were treated conservatively in a non-weight bearing plaster cast, 9 patients (19.1 %) had a thromboembolic event. Out of the 41 patients who were treated with functional weight bearing mobilisation, 2 patients (4.8%) had a thromboembolic event. Thus, patients who were treated in a non-weight bearing plaster had a significantly higher risk of developing thromboembolism (p value of <0.05) and an increased risk ratio of 24% compared to those who were treated with functional weight bearing mobilisation. Conclusion. There is a significant decrease in the clinical incidence of thromboembolic events in patients treated conservatively with early mobilisation in the functional weight bearing boot compared to those treated in a non- weight bearing cast

Aims

To evaluate the donor site morbidity and tendon morphology after harvesting whole length, full-thickness peroneus longus tendon (PLT) proximal to the lateral malleolus for ligament reconstructions or tendon transfer.

Background. Patients presenting with an acute tendoachilles (TA) rupture are managed in a dedicated clinic led by a Foot & Ankle Consultant and specialist physiotherapist. The diagnosis is made clinically and no ultrasound scan is performed. All management, rehabilitation and follow-up is undertaken within this clinic by the specialist physiotherapist, with Consultant support as required. Patients are offered a choice of conservative or surgical management (percutaneous TA repair). Both groups undergo a standardised functional rehabilitation regimen. Methods. All patients treated through our dedicated clinic between May 2010 and April 2016 were identified. Patient outcomes were reported using the validated Achilles Tendon Repair Score (ATRS). ATRS scores were collected at 3, 6 and 12 months post-injury. Re-rupture and complication rates were also documented. Results. 167 patients were identified. 79 patients underwent a percutaneous repair and 88 patients opted for conservative management. Mean age of patients undergoing percutaneous repair was 46 years (21–77 years) and 52 years (19–88 years) in the conservatively managed group. Male to female ratios were equal between both groups. Mean ATRS scores at 3, 6 and 12 months were 41.6, 69.5 and 85.3 respectively for the percutaneous repairs and 45.4, 69.0 and 77.1 respectively for the conservatively managed group. The re-rupture rate was 4.2% (3 patients) in the conservative group and 0% in our surgical group. In the surgical group, 1 patient developed a PE and 1 had a wound complication. Discussion. Our dedicated clinic for managing TA ruptures has proved popular with patients, with a patient satisfaction score of 98.7%. By standardising our rehabilitation regimen we believe our outcomes have improved. Our percutaneous repair group has an improved ATRS score compared to our conservative group at 12 months post injury. We believe that any fit active individual should be offered a percutaneous repair irrespective of age

Aims

Flexor hallucis longus (FHL) tendon transfer is a well-recognized technique in the treatment of the neglected tendo Achillis (TA) rupture.

Aim. Young patients with ankle arthritis that remains symptomatic in spite of conservative treatment and following arthroscopic debridement are usually offered either ankle fusion or ankle replacement. Both these options are far from ideal in this age group. The aim of this study was to evaluate functional outcomes following ankle distraction to determine whether it is a reliable alternative for the treatment of ankle arthritis in young adults. Material and methods. Data was collected prospectively for 15 patients (9 males and 6 females, mean age 31.9 years) with “stage 2” ankle arthritis who failed conservative treatment and continued to be symptomatic following arthroscopic ankle debridement. Distraction of 8 mm was done using a dynamic constrained ankle circular frame and all patients were allowed full weight bearing all through the distraction process. The subjective functional evaluation was based on the American Orthopaedic Foot and Ankle Score (AOFAS), the Foot Disability Index (FADI) and the Visual Analogue Score (VAS). In 10 patients the Manchester Oxford Foot questionnaire (MOXFQ) and the Short Form (SF) 12 patient satisfaction questionnaire were also filled preoperatively and at final follow up. Results. At a minimum follow-up of 24 months (mean 34.4) none of the patients required fusion or replacement. There was a significant improvement in all the functional outcome scores. There was also a significant improvement in the ankle joint space on weight bearing x-rays. Conclusion. Based on these results the use of ankle distraction can be considered a useful option for the treatment of symptomatic “stage 2” ankle arthritis in young adults. Longer-term follow-up and comparison with alternative techniques will be required to evaluate the true effectiveness of this treatment option

Freiberg's Infraction; osteonecrosis of the metatarsal head, is the fourth most common intra-articular osteonecrosis in the body. Surgical intervention is usually reserved for late stage of the disease process (III-V) or failure of conservative management. We evaluated the outcomes of patients treated with primary Interpositional Arthroplasty technique using periosteum and fat for adequate surfacing and as a spacer for Freiberg's Disease. Twenty-three cases (21 patients) were performed from February 2009 – March 2016 (18 women, 5 men). Mean age at surgery was 51.1 years (range 19 – 70.5 years) with 91% affecting the second metatarsal. Twenty-one cases were primary and two cases were revision. Five cases were stage III, 10 were in stage IV and 8 were stage V. All patients underwent Interpositional Arthroplasty using periosteum and fat graft from affected metatarsal inserted as joint spacer and secured with sutures. Patients were followed up by postal questionnaires using two validated questionnaires; MOXFQ and AOFAS. Mean follow-up was 3.7 years (0.6 – 7.6 years). Paired two-tailed student t tests were used to assess clinical significance. The left and right foot was affected in 12 and 11 cases respectively. There were no postoperative infections, non-unions or transfer metatarsalgia. Surgery allowed 8 patients to wear normal footwear, 9 wearing fashion shoes, 5 wearing dress shoes and 5 patients returned to sporting activities. Mean pre-operative and post-operative VAS pain scores were 6.7 (range 4–10) and 3.2 (range 0–0) (p< 0.05). Mean peri-operative AOFAS scores were 43.8 (range 14–14) and 71.3 (range 10–10) (p< 0.05). Mean peri-operative MOXFQ scores were 62.9 (range 23–23) and 31.8 (range 0–0) (p< 0.05). We recommend our novel Interpositional Arthroplasty using periosteum and fat spacer for late stage Freiberg's disease as it can result in significant improvement in pain, prevents donor site morbidity and produces significant functional improvement and patient satisfaction

It is recognised that as the severity of hallux valgus (HV) worsens, so do the clinical and radiological signs of arthritis in the first metatarsophalangeal joint.

However, few studies specifically document the degenerate changes. The purpose of this study is to determine if intraoperative mapping of articular erosive lesions of the first MTP joint can be correlated to clinical and/or radiographic parameters used during the preoperative assessment of the HV deformity.

Introduction

Longstanding complex muliplanar foot deformities represent a significant challenge. The traditional surgical techniques involve excessive dissection and excision of large bony wedges or modifications of the triple fusion to correct the deformity. The majority of the reports in the literature present collective data on different deformity patterns and also mix paediatric and adult patients, even with multiple correction techniques. The aim of this study was to evaluate the clinical, radiological and functional outcomes of the gradual correction of a single common deformity pattern of equino-cavo-varus using a single correction technique of the V-osteotomy and the Ilizarov frame.

Introduction. Ankle fractures represent approximately 10% of the fracture workload and are projected to increase due to ageing population. We present our 5 years outcome review post-surgical management of ankle fractures in a large UK Trauma unit. Methods. A total of 111 consecutive patients treated for an unstable ankle fracture were entered into a database and prospectively followed up. Baseline patient characteristics, complications, further intervention including additional surgery, functional status were recorded during five-year follow-up. Pre-injury and post-fixation functional outcome measures at 2-years were assessed using Olerud-Molander Ankle Scores (OMAS) and Lower Extremity Functional Scales (LEFS). A p value < 0.05 was considered significant. Results. The mean age was 46 with a male:female ratio of 1:1.1. The distribution of comorbidities was BMI >30 (25%), diabetes (5%), alcohol consumption >20U/week (15%) and smoking (26%). Higher BMI was predictive of worse post-op LEFS score (p = 0.02). Between pre-injury and post fixation functional scores at 2 years, there was a mean reduction of 26.8 (OMAS) and 20.5(LEFS). Using very strict radiological criteria, 31 (28%) had less than anatomical reduction of fracture fragments intra-operatively. This was, however, not predictive of patients' functional outcome in this cohort. Within 5-year period, 22 (20%) patients had removal of metalwork from their ankle, with majority 13 (59%) requiring syndesmotic screw removal. Further interventions included: joint injection (3), deltoid reconstruction (1), arthroscopic debridement (1), superficial sinus excision (2), and conversion to hindfoot nail due to failure of fixation (1). Reduction in OMAS was predictive of patients' ongoing symptoms (p=0.01). Conclusion. There is a significant reduction in functional outcome after ankle fracture fixation and patients should be counselled appropriately. Need for removal of metalwork is higher in patients who require syndesmosis stabilisation with screw(s)

Background. Patients who undergo either primary or revision total ankle replacement (TAR) expect improvements in pain, function and quality of life. The goal of this study was to measure the functional outcome improvements and the difference in patient-reported outcomes in patients undergoing primary total ankle replacements compared to revision TAR. Methods. A single-center prospective cohort study was undertaken between 2016 and 2022. All patients were followed up for a minimum of 6 months. Patients undertook the Manchester Oxford Foot Questionnaire (MoxFQ) and EQ-5D health quality questionnaires pre-operatively, at 6 months and yearly for life. The Mann Whitney test was undertaken for statistical analysis. Results. A total of 165 primary and 71 revision ankle replacements were performed between 2016 and 2022. The mean age was 71 years for primary replacements and 69 years for revisions. The INFINITY was utilized in the majority of primary total ankle replacements. Revision replacements were either the INBONE II or INVISION and they were most often revising the MOBILITY implant. The main indication for revision was aseptic loosening (83%). Other causes included infection, malalignment and insert wear. The overall MoxFQ improved by a mean of 46.5 for primaries and 40.2 for revisions. The EQ-5D score also showed overall improvements with the mean difference in mobility increasing by 1.6. Conclusion. Both primary and revision ankle replacements result in improved functional scores at 6 months, 1 year and 2 years. In this cohort with the implants used, both primary and revision ankle replacements demonstrate similar improvements in functional scores

Background. Total Ankle Replacement (TAR) is an established treatment option for end-stage ankle arthritis. We analysed at minimum, 10-year patient-reported and clinical outcomes of 156 TARs from a single centre. We specifically compared outcomes between patients under 60 and over 60 at time of surgery. Methods. Data was collected retrospectively from our departmental patient database. It included all patients who underwent a TAR by a single surgeon between 2006 and 2010 and patients were divided into those under 60 and those over 60 at the time of surgery. Patient reported outcomes (PROMs), including WOMAC, SF-36 and patient satisfaction scores and complications were analysed preoperatively and at one, two, five and over 10 years postoperatively. Results. There were 156 patients included in this analysis, 61 were under 60 (mean age 50.29) and 95 were over 60 (mean age 69.12). A total of 12 patients had revision surgery, (nine in the under 60 group) and 52 patients were deceased at the time of analysis (10 in the under 60 group). At one year the over 60 group had less pain and better functional scores (p=0.02, p=0.017). At two, five and ten years there was no statistical difference in pain and function between groups. At two years the over 60s reported less stiffness and quicker return to activities of daily living (p=0.007, p=0.001). However, at five and 10 years there was no statistical difference in any domain. Conclusions. This study demonstrates that age does not correlate with a significant difference in pain or functional outcomes in patients who have TAR, at over 10 years follow up. The higher revision rates in the younger group may correlate with higher functional demand and lower mortality rate