The influence of full-thickness supraspinatus tears on abduction moments: the importance of the central tendon.

BACKGROUND: Detachment of the central tendon of the supraspinatus from its insertion is considered to be crucial to functional deficit. The aim of the present study was to assess the function of the supraspinatus in terms of abduction moments by introducing different tear configurations to assess the functional effect of the central tendon insertion. METHODS: Ten fresh frozen shoulders from five cadavers were prepared for testing. A testing protocol was established to measure the abduction moment of the supraspinatus under physiological loading tailored to the anthropometrics of each specimen. Four conditions were tested: intact supraspinatus; complete detachment of portion of the supraspinatus tendon anterior to the main central tendon; detachment of the main central tendon; and detachment of the region of the supraspinatus posterior to the main central tendon. RESULTS: There was a significant and large reduction in abduction moment when the central tendon was sectioned (p < 0.05). A smaller reduction in abduction moment was found when the regions anterior and posterior to the main central tendon were sectioned (p < 0.05). CONCLUSIONS: The central tendon is vital in the role of functional arm abduction through force transmission through the intact rotator cuff. Reinsertion of the central tendon in the correct anatomical location is desirable to optimize functional outcome of surgery.

Design of a traumatic injury simulator for assessing lower limb response to high loading rates.

Current military conflicts are characterized by the use of the improvised explosive device. Improvements in personal protection, medical care, and evacuation logistics have resulted in increasing numbers of casualties surviving with complex musculoskeletal injuries, often leading to life-long disability. Thus, there exists an urgent requirement to investigate the mechanism of extremity injury caused by these devices in order to develop mitigation strategies. In addition, the wounds of war are no longer restricted to the battlefield; similar injuries can be witnessed in civilian centers following a terrorist attack. Key to understanding such mechanisms of injury is the ability to deconstruct the complexities of an explosive event into a controlled, laboratory-based environment. In this article, a traumatic injury simulator, designed to recreate in the laboratory the impulse that is transferred to the lower extremity from an anti-vehicle explosion, is presented and characterized experimentally and numerically. Tests with instrumented cadaveric limbs were then conducted to assess the simulator's ability to interact with the human in two mounting conditions, simulating typical seated and standing vehicle passengers. This experimental device will now allow us to (a) gain comprehensive understanding of the load-transfer mechanisms through the lower limb, (b) characterize the dissipating capacity of mitigation technologies, and (c) assess the bio-fidelity of surrogates.

Outcomes of IED foot and ankle blast injuries.

BACKGROUND: Improvements in protection and medical treatments have resulted in increasing numbers of modern-warfare casualties surviving with complex lower-extremity injuries. To our knowledge, there has been no prior analysis of foot and ankle blast injuries as a result of improvised explosive devices (IEDs). The aims of this study were to report the pattern of injury and determine which factors are associated with a poor clinical outcome. METHODS: U.K. service personnel who had sustained lower leg injuries following an under-vehicle explosion from January 2006 to December 2008 were identified with the use of a prospective trauma registry. Patient demographics, injury severity, the nature of the lower leg injury, and the type of clinical management were recorded. Clinical end points were determined by (1) the need for amputation and (2) ongoing clinical symptoms. RESULTS: Sixty-three U.K. service personnel (eighty-nine injured limbs) with lower leg injuries from an explosion were identified. Fifty-one percent of the casualties sustained multisegmental injuries to the foot and ankle. Twenty-six legs (29%) required amputation, with six of them amputated because of chronic pain eighteen months following injury. Regression analysis revealed that hindfoot injuries, open fractures, and vascular injuries were independent predictors of amputation. At the time of final follow-up, sixty-six (74%) of the injured limbs had persisting symptoms related to the injury, and only nine (14%) of the service members were fit to return to their preinjury duties. CONCLUSIONS: This study demonstrates that foot and ankle injuries from IEDs are associated with a high amputation rate and frequently with a poor clinical outcome. Although not life-threatening, they remain a source of long-term morbidity in an active population.

FASS is a better predictor of poor outcome in lower limb blast injury than AIS: implications for blast research.

OBJECTIVES: Due to the absence of clinical blast data, automotive injury data using the abbreviated injury score (AIS) has been extrapolated to define current North Atlantic Treaty Organisation (NATO) injury thresholds for anti-vehicle mine tests. We hypothesized that AIS, being a marker of fatality rather than disability, would be a worse predictor of poor clinical outcome compared with the lower limb-specific foot and ankle severity score (FASS). METHODS: Using a prospectively collected trauma database, we identified UK Service Personnel sustaining lower leg injuries from under-vehicle explosions from January 2006 to December 2008. A full review of all medical documentation was performed to determine patient demographics and the severity of lower leg injury, as assessed by AIS and FASS. Clinical endpoints were defined as (1) need for amputation or (2) poor clinical outcome (defined as amputation or ongoing clinical problems). Statistical models were developed to explore the relationship between the scoring systems and clinical endpoints. RESULTS: Sixty-three UK casualties (89 limbs) were identified with a lower limb injury after under-vehicle explosion. The mean age of the casualty was 26.0 years. At 33.6 months follow-up, 29.1% (26 of 89) required an amputation and 74.6% (67 of 89) having a poor clinical outcome. Only 9 (14%) casualties were deemed medically fit to return to full military duty. Receiver operating characteristic analysis revealed that both AIS = 2 and FASS = 4 could predict the risk of amputation, with FASS = 4 demonstrating greater specificity (43% vs. 20%) and greater positive predictive value (72% vs. 34%). In predicting poor clinical outcome, FASS was significantly superior to AIS. Probit analysis revealed that a relationship could not be developed between AIS and the probability of a poor clinical outcome. CONCLUSIONS: Our study clearly demonstrates that AIS is not a predictor of long-term clinical outcome and that FASS would be a better quantitative measure of lower limb injury severity.

The modern "deck-slap" injury--calcaneal blast fractures from vehicle explosions.

BACKGROUND: Anti-vehicle mines and improvised explosive devices remain the most prevalent threat to coalition troops operating in Iraq and Afghanistan. Detonation of these devices causes rapid deflection of the vehicle floor resulting in severe injuries to calcaneus. Anecdotally referred to as a "deck-slap" injury, there have been no studies evaluating the pattern of injury or the effect of these potentially devastating injuries since World War II. Therefore, the aim of this study is to determine the pattern of injury, medical management, and functional outcome of UK Service Personnel sustaining calcaneal injuries from under-vehicle explosions. METHOD: From January 2006 to December 2008, using a prospectively collected trauma registry (Joint Theater Trauma Registry), the records of all UK Service Personnel sustaining a fractured calcaneus from a vehicle explosion were identified for in-depth review. For each patient, demographic data, New Injury Severity Score, and associated injuries were recorded. In addition, the pattern of calcaneal fracture, the method of stabilization, local complications, and the need for amputation were noted. Functional recovery was related to the ability of the casualty to return to military duties. RESULTS: Forty calcaneal fractures (30 patients) were identified in this study. Mean follow-up was 33.2 months. The median New Injury Severity Score was 17, with the lower extremity the most severely injured body region in 90% of cases. Nine (30%) had an associated spinal injury. The overall amputation rate was 45% (18/40); 11 limbs (28%) were amputated primarily, with a further 3 amputated on return to the United Kingdom. Four (10%) casualties required a delayed amputation for chronic pain (mean, 19.5 months). Of the 29 calcaneal fractures salvaged at the field hospital, wound infection developed in 11 (38%). At final follow-up, only 2 (6%) were able to return to full military duty with 23 (76%) only fit for sedentary work or unfit for any military duty. CONCLUSION: Calcaneal injuries following under-vehicle explosions are commonly associated with significant multiple injuries including severe lower limb injury. The frequency of associated spinal injuries mandates radiologic evaluation of the spine in all such patients. The severity of the hindfoot injury is reflected by the high infection rate and amputation rate. Only a small proportion of casualties were able to return to preinjury military duties.

Evaluating the effect of vehicle modification in reducing injuries from landmine blasts. An analysis of 2212 incidents and its application for humanitarian purposes.

INTRODUCTION: Anti-vehicle (AV) mines have been laid indiscriminately in conflict areas for the past 100 years. With an indeterminate life-span they continue to pose a significant threat to the civilian population, as well as restrict the movement of people, aid and goods to vulnerable populations. The aim of this study was to analyse unique casualty data from 2212 mine incidents to determine if simple vehicle modifications can reduce fatality and injury rates from mine explosions. METHOD: We analysed casualty data from the Rhodesian War (1972-1980), to assess the effects of basic vehicle modifications (V-shaped hull, increased ground clearance, widened axles, heavy vehicles and blast deflectors) on injury rates. A multinomial regression statistical model was developed for vehicle modifications and number of alterations to explore these effects. RESULTS: Incident data was available on 2212 vehicle mine incidents involving 16,456 people. The overall fatality rate was 3.3% (544/16,456) and the overall injury rate was 22.7% (3741/16,456). Explosions against mine-protected vehicles resulted in a fatality rate of 1.2% (150/12,919); occupants in unprotected vehicles sustained a fatality rate of 11.4% (395/3537). The injury rate in mine protected vehicles was 22.2% (2868/12,919) compared to 24.7% in unprotected vehicles (873/3537). Utilising a multinomial logistical-regression model, we show that each design feature significantly reduced fatality rate (from 45% in unprotected vehicles to 0.8% in protected vehicles); each of these designs had a cumulative effect in fatality reduction. In isolation, blast deflectors, whilst reducing fatality rates, increased injury rates. CONCLUSIONS: Our data clearly demonstrates that simple vehicle modifications can have a significant effect on reducing fatality and injury rates from AV mine explosions. Given that the modifications described were produced using commercially available vehicles with basic engineering requirements, we believe that similar processes could be employed in post-conflict environments in a cost-effective manner.

Blast-related fracture patterns: a forensic biomechanical approach.

Improved protective measures and medical care has increased the survivability from battlefield injuries. In an attempt to reduce the debilitating consequences of blast injury, understanding and mitigating the effects of explosion on the extremities is key. In this study, forensic biomechanical analyses have been applied to determine mechanisms of injury after the traumatic event. The aims of this study were (i) to determine which effects of the explosion are responsible for combat casualty extremity bone injury in two distinct environments, namely open, free-field (open group), and in vehicle or in cover (enclosed group), and (ii) to determine whether patterns of combat casualty bone injury differed between environments. Medical records of casualties admitted to a military hospital in Afghanistan were reviewed over a six-month period. Explosive injuries have been sub-divided traditionally into primary, secondary and tertiary effects. All radiographs were independently reviewed by a military radiologist, a team of military orthopaedic surgeons and a team of academic biomechanists, in order to determine 'zones of injury' (ZoIs), and their related mechanisms. Sixty-two combat casualties with 115 ZoIs were identified. Thirty-four casualties in the open group sustained 56 ZoIs; 28 casualties in the enclosed group sustained 59 ZoIs. There was no statistical difference in mean ZoIs per casualty between groups (p = 0.54). There was a higher proportion of lower limb injuries in the enclosed group compared with the open group (p < 0.05). Of the casualties in the open group, 1 ZoI was owing to the primary effects of blast, 10 owing to a combination of primary and secondary blast effects, 23 owing to secondary blast effects and 24 owing to tertiary blast effects. In contrast, tertiary blast effects predominated in the enclosed group, accounting for 96 per cent of ZoIs. These data clearly demonstrate two distinct injury groups based upon the casualties' environment. The enclosed environment appears to attenuate the primary and secondary effects of the explosion. However, tertiary blast effects were the predominant mechanism of injury, with severe axial loading to the lower extremity being a characteristic of the fractures seen. The development of future mitigation strategies must focus on reducing all explosion-related injury mechanisms. Integral to this process is an urgent requirement to better understand the behaviour of bone in this unique environment.

In-vehicle extremity injuries from improvised explosive devices: current and future foci.

The conflicts in Iraq and Afghanistan have been epitomized by the insurgents' use of the improvised explosive device against vehicle-borne security forces. These weapons, capable of causing multiple severely injured casualties in a single incident, pose the most prevalent single threat to Coalition troops operating in the region. Improvements in personal protection and medical care have resulted in increasing numbers of casualties surviving with complex lower limb injuries, often leading to long-term disability. Thus, there exists an urgent requirement to investigate and mitigate against the mechanism of extremity injury caused by these devices. This will necessitate an ontological approach, linking molecular, cellular and tissue interaction to physiological dysfunction. This can only be achieved via a collaborative approach between clinicians, natural scientists and engineers, combining physical and numerical modelling tools with clinical data from the battlefield. In this article, we compile existing knowledge on the effects of explosions on skeletal injury, review and critique relevant experimental and computational research related to lower limb injury and damage and propose research foci required to drive the development of future mitigation technologies.

The compressive behavior of the human glenoid labrum may explain the common patterns of SLAP lesions.

PURPOSE: The aim of the study was to define the normalized compressive stiffness (modulus) of the glenoid labrum around its circumference and to characterize the difference in modulus between different areas. METHODS: Sixteen fresh-frozen cadaveric shoulders were harvested and dissected down to the glenoid labrum. Any specimens with significant degenerative changes were discarded, leaving 8 labra for testing. The labrum was divided into 8 segments, to allow comparison around its circumference. A uniform testing specimen was produced from each area by use of a microtome. Each specimen measured 3 x 1 mm in cross section and was 6 mm in length. Indentation testing was conducted in a controlled environment of 100% humidity at 37 degrees C +/- 1 degrees C. RESULTS: We obtained 52 test samples from 8 labra. The mean modulus of the glenoid labrum was 69.7 megapascal (standard deviation, 36.2 megapascal). The anterosuperior portion of the labrum had a higher modulus than the posteroinferior portion (P = .0075). CONCLUSIONS: This study has shown that the human glenoid labrum's compressive behavior varies around its circumference. The greater modulus of the anterosuperior portion of the labrum supports the theory that this area is anatomically different from the rest of the labrum and resists compressive loads. CLINICAL RELEVANCE: These results may explain why the common type of SLAP lesions seen show failure at the interface between the labrum and the glenoid rather than within the substance of the labrum itself.

The range of axial rotation of the glenohumeral joint.

There is a paucity of data in the literature on the restraining effects of the glenohumeral (GH) ligaments; cadaveric testing is one of the best methods for determining the function of these types of tissues. The aim of this work was to commission a custom-made six degrees of freedom (dof) joint loading apparatus and to establish a protocol for laxity testing of cadaveric shoulder specimens. Nine cadaveric shoulder specimens were used in this study and each specimen had all muscle resected leaving the scapula, humerus (transected at mid-shaft) and GH capsule. Specimens were mounted on the testing apparatus with the joint in the neutral position and at 30 degrees, 60 degrees and 90 degrees GH abduction in the coronal, scapula and 30 degrees forward flexion planes. For each orientation, 0-1 N m in 0.1 N m increments was applied in internal/external rotation and the angular displacement recorded. The toe-region of the moment-displacement curves ended at approximately +/-0.5 N m. The highest rotational range of motion for the joint was 140 degrees for +/-1.0 N m at 30 degrees GH abduction in the scapula plane. The range of motion shifted towards external rotation with increasing levels of abduction. The results provide the optimum loading regime to pre-condition shoulder specimens and minimise viscoelastic effects in the ligaments prior to laxity testing (>0.5 N m at 30 degrees GH abduction in any of the three planes). Knowledge of the mechanical properties of the GH capsuloligamentous complex has implications for modelling of the shoulder as well surgical planning and intervention.

Treatment of ligament laxity by electrothermal shrinkage or surgical plication: a morphologic and mechanical comparison.

Capsular plication or thermal shrinkage can be used to enhance surgical joint stabilization. We compared mechanical or morphologic properties of the medial collateral ligament of the rabbit knee treated by either bipolar radiofrequency electrothermal shrinkage or surgical plication. After 12 weeks, the medial collateral ligaments were procured from treated and contralateral knees to undergo viscoelastic (creep) testing, quantitative transmission electron microscopy, and immunohistochemistry. Creep strain in thermal (1.85% +/- 0.32%) and plicated (1.92% +/- 0.36%) ligaments was almost twice that of the control group (1.04% +/- 0.15%), although there was no difference between treatment modalities. The morphologic parameters of all 3 groups were significantly different (P < .001). The thermal ligaments demonstrated predominantly small fibrils, whereas the plicated group displayed an intermediate distribution of heterogeneous fibrils, suggesting a different pattern of remodeling. Viscoelastic properties are similar after thermal shrinkage or plication, though inferior to those of intact ligaments.

A biomechanical comparison of single and double-row fixation in arthroscopic rotator cuff repair.

BACKGROUND: The optimal method for arthroscopic rotator cuff repair is not yet known. The hypothesis of the present study was that a double-row repair would demonstrate superior static and cyclic mechanical behavior when compared with a single-row repair. The specific aims were to measure gap formation at the bone-tendon interface under static creep loading and the ultimate strength and mode of failure of both methods of repair under cyclic loading. METHODS: A standardized tear of the supraspinatus tendon was created in sixteen fresh cadaveric shoulders. Arthroscopic rotator cuff repairs were performed with use of either a double-row technique (eight specimens) or a single-row technique (eight specimens) with nonabsorbable sutures that were double-loaded on a titanium suture anchor. The repairs were loaded statically for one hour, and the gap formation was measured. Cyclic loading to failure was then performed. RESULTS: Gap formation during static loading was significantly greater in the single-row group than in the double-row group (mean and standard deviation, 5.0 +/- 1.2 mm compared with 3.8 +/- 1.4 mm; p < 0.05). Under cyclic loading, the double-row repairs failed at a mean of 320 +/- 96.9 N whereas the single-row repairs failed at a mean of 224 +/- 147.9 N (p = 0.058). Three single-row repairs and three double-row repairs failed as a result of suture cut-through. Four single-row repairs and one double-row repair failed as a result of anchor or suture failure. The remaining five repairs did not fail, and a midsubstance tear of the tendon occurred. CONCLUSIONS: Although more technically demanding, the double-row technique demonstrates superior resistance to gap formation under static loading as compared with the single-row technique. CLINICAL RELEVANCE: A double-row reconstruction of the supraspinatus tendon insertion may provide a more reliable construct than a single-row repair and could be used as an alternative to open reconstruction for the treatment of isolated tears.

Passive tension and gap formation of rotator cuff repairs.

The objectives of this study were to quantify the relationship between passive tension of rotator cuff repairs and arm position and to examine the effect of this tension on repair gap formation. Five patients undergoing open surgical rotator cuff repair of the supraspinatus tendon were recruited. Tendon tension was recorded as the supraspinatus was advanced into a bone trough and secured. The relationship between arm position and repair tension was then measured. Standardized rotator cuff tears were created in 3 cadaveric shoulders and repaired by use of the intraoperative technique. The difference in tension measured between 0 degrees and 30 degrees abduction was statically applied for 24 hours and the gap formation measured. Repair tension increased with advancement of the supraspinatus tendon into the bone trough. Abduction reduced the repair load. The mean reduction in load by 30 degrees abduction was 34 N. Twenty-four hours of 34-N loading caused gap formation of 9 mm in cadaveric rotator cuff repairs. Passive tension in surgically repaired rotator cuffs may contribute to repair failure and can be modified by arm positioning.