Aims

Plating displaced proximal humeral fractures is associated with a high rate of screw perforation. Dynamization of the proximal screws might prevent these complications. The aim of this study was to develop and evaluate a new gliding screw concept for plating proximal humeral fractures biomechanically.

Objectives

Osteosynthesis of anterior pubic ramus fractures using one large-diameter screw can be challenging in terms of both surgical procedure and fixation stability. Small-fragment screws have the advantage of following the pelvic cortex and being more flexible.

The aim of the present study was to biomechanically compare retrograde intramedullary fixation of the superior pubic ramus using either one large- or two small-diameter screws.

When inserting a lag-screw across an arthrodesis, stress is concentrated under the screw head risking asymmetrical force distribution and fracture of the cortical bone bridge. The IO FiX (Extremity Medical, NJ USA) is a new intraosseous device comprising an X-Post on one side of and parallel to the arthrodesis and a lag-screw inserted through the head of the X-Post which reinforces the cortical bone bridge. The X-Post behaves as an internal washer improving force distribution across the arthrodesis. Being intraosseous, near to the neutral axis of bend also means the device is fatigue-resistant and soft tissue irritation is reduced.

The IO FiX has not been independently verified and therefore we analysed its performance in a human cadaveric ankle model. Our null hypothesis was there is no difference in force generation and contact area in an ankle arthrodesis when the IO FiX is compared with partially-threaded lag-screws.

We used ten randomized cadaver ankles with a mean age of seventy-one years (44–84 years) prepared with flat arthrodesis cuts. A Tek-scan (Boston, USA) pressure transducer was used to measure force and contact area produced when the IO FiX was compared with a standard lag-screw and washer.

The median average force in the IO FiX group was 3.95 kg and 2.35 kg in the lag-screw group (p=<0.01 Wilcoxon signed-rank). The IO FiX was able to create a more uniform contact area within the arthrodesis with a median average of 3.41 cm² compared with 2.42 cm² in the lag-screw group (p=<0.03 Wilcoxon signed rank).

Our results suggest the IO FiX improves force generation and contact area across the arthrodesis. With the theoretical advantages of reduced soft tissue irritation and a lower risk of fatigue failure, the IO FiX offers a significant advantage compared with traditional fixation techniques.

The AO Foundation advocates the use of partially threaded lag screws in the fixation of fractures of the medial malleolus. However, their threads often bypass the radiodense physeal scar of the distal tibia, possibly failing to obtain more secure purchase and better compression of the fracture.

We therefore hypothesised that the partially threaded screws commonly used to fix a medial malleolar fracture often provide suboptimal compression as a result of bypassing the physeal scar, and proposed that better compression of the fracture may be achieved with shorter partially threaded screws or fully threaded screws whose threads engage the physeal scar.

We analysed compression at the fracture site in human cadaver medial malleoli treated with either 30 mm or 45 mm long partially threaded screws or 45 mm fully threaded screws. The median compression at the fracture site achieved with 30 mm partially threaded screws (0.95 kg/cm² (interquartile range (IQR) 0.8 to 1.2) and 45 mm fully threaded screws (1.0 kg/cm² (IQR 0.7 to 2.8)) was significantly higher than that achieved with 45 mm partially threaded screws (0.6 kg/cm² (IQR 0.2 to 0.9)) (p = 0.04 and p < 0.001, respectively). The fully threaded screws and the 30mm partially threaded screws were seen to engage the physeal scar under an image intensifier in each case.

The results support the use of 30 mm partially threaded or 45 mm fully threaded screws that engage the physeal scar rather than longer partially threaded screws that do not. A 45 mm fully threaded screw may in practice offer additional benefit over 30 mm partially threaded screws in increasing the thread count in the denser paraphyseal region.

Cite this article: Bone Joint J 2013;95-B:1662–6.

Introduction

Posterior malleolar fractures are present in up to 44% of all ankle fractures. Those involving > 25% of the articular surface have a higher rate of posterior ankle instability which may predispose to post traumatic arthritis. The posterolateral approach to the distal tibia allows direct reduction and stabilization of the posterior malleolus and concomitant lateral malleolus fractures. An anatomical study was performed to establish the safe zone of proximal dissection to avoid injury to the peroneal vessels in this uncommon approach.

Percutaneous plating of the distal tibia via a limited incision is an accepted technique of osteosynthesis for extra-articular and simple intra-articular distal tibia fractures. In this study we identify structures are risk during this approach.

Injection or aspiration of the ankle may be performed through either an anteromedial or an anterolateral approach for diagnostic or therapeutic reasons. We evaluated the success of an intra-articular puncture in relation to its site in 76 ankles from 38 cadavers. Two orthopaedic surgical trainees each injected methylene blue dye into 18 of 38 ankles through an anterolateral approach and into 20 of 38 through an anteromedial. An arthrotomy was then performed to confirm the placement of the dye within the joint.

Of the anteromedial injections 31 of 40 (77.5%, 95% confidence interval (CI) 64.6 to 90.4) were successful as were 31 of 36 (86.1%, 95% CI 74.8 to 97.4) anterolateral injections. In total 62 of 76 (81.6%, 95% CI 72.9 to 90.3) of the injections were intra-articular with a trend towards greater accuracy with the anterolateral approach, but this difference was not statistically significant (p = 0.25). In the case of trainee A, 16 of 20 anteromedial injections and 14 of 18 anterolateral punctures were intra-articular. Trainee B made successful intra-articular punctures in 15 of 20 anteromedial and 17 of 18 anterolateral approaches. There was no significant difference between them (p = 0.5 and p = 0.16 for the anteromedial and anterolateral approaches, respectively). These results were similar to those of other reported studies. Unintended peri-articular injection can cause complications and an unsuccessful aspiration can delay diagnosis. Placement of the needle may be aided by the use of ultrasonographic scanning or fluoroscopy which may be required in certain instances.

Intra-articular punctures and injections are performed routinely on patients with injuries to and chronic diseases of joints, to release an effusion or haemarthrosis, or to inject drugs. The purpose of this study was to investigate the accuracy of placement of the needle during this procedure.

A total of 76 cadaver acromioclavicular joints were injected with a solution containing methyl blue and subsequently dissected to distinguish intra- from peri-articular injection. In order to assess the importance of experience in achieving accurate placement, half of the injections were performed by an inexperienced resident and half by a skilled specialist. The specialist injected a further 20 cadaver acromioclavicular joints with the aid of an image intensifier. The overall frequency of peri-articular injection was much higher than expected at 43% (33 of 76) overall, with 42% (16 of 38) by the specialist and 45% (17 of 38) by the resident. The specialist entered the joint in all 20 cases when using the image intensifier.

Correct positioning of the needle in the joint should be facilitated by fluoroscopy, thereby guaranteeing an intra-articular injection.