Musculoskeletal Intervention

General Principles

Introduction

The superficial location of many musculoskeletal structures makes them readily amenable to injection therapy and many unguided injections are carried out in the office or ward setting. Large superficial structures are easily targeted, although success will vary with the practitioner’s expertise. It is generally accepted that many of these unguided injections will miss their target, but, despite this, patients not infrequently report good responses. Good responses may be due to local diffusion (in a non-contained space even a small-volume injection will spread quite widely) or systemic absorption of the injected material. There is emerging evidence, however, that clinical outcome is improved by accurate injection, and image guidance, whether this is by X-ray fluoroscopy, CT ultrasound or MRI, plays an important role in ensuring that diagnostic and therapeutic injections reach their intended target. Accurate guidance of local anaesthetic into a presumed pain generator is an important part of the clinical workup in musculoskeletal practice, which cannot be replicated by systemic injection of therapeutic agents.

Key Point

Guidance is important when the target is small, difficult to feel clinically or landmarks are difficult to define. Accurate localization is important when surgical decisions are based on the patient’s response to local anaesthetic, when more complex intervention is being considered or where patients have failed to respond to unguided therapy.

Setup

In most cases, a complex setup is not required and most injections can be carried out as an adjunct to the basic ultrasound examination. Syringes and needles that are found in most departments and wards are sufficient. Simple sterilization measures have kept the incidence of infection very low. The routine use of a sterile probe cover is a matter of personal preference or local policy.

Key Point

More rigorous sterility is mandatory when an implanted joint is being injected, in the presence of infection, where significant bleeding is expected or when it is anticipated that the needle will lie very close to the probe and risk rubbing against it.

For many injections, a standard footprint probe can be used. If available, a smaller footprint probe, sometimes referred to as a ‘hockey stick’ probe, can be used to bring the puncture point closer to the target (Fig. 29.1). This is particularly helpful for very superficial structures such as interphalangeal joints.

Figure 29.1 Standard interventional set-up tray. In the bottom left corner, the two types of probe are visible. The hockey stick probe is useful for injecting superficial structures, particularly joints. The larger linear array probe is covered by a sterile sheath.

Treatment Rationale

Key Point

Broadly speaking, abnormalities of soft tissue commonly encountered in musculoskeletal practice can be divided into two main groups: inflammatory lesions and injuries that are the consequence of overuse or misuse.

Injection therapy in inflammatory lesions is aimed at reducing the inflammatory response and pain. The commonest combination of injection therapy used is a mixture of corticosteroid and local anaesthetic (Fig. 29.2). The purpose of the local anaesthetic is to make the injection more comfortable and to assess the diagnostic response. Resolution of symptoms, albeit temporarily, confirms that the area injected is the pain generator provided the injection has been contained. There is no specific cellular inflammatory response in most overuse injuries, although many other chemical components of the ‘inflammatory’ cascade are present. Mucoid degeneration possibly augmented by a mechanical predisposition leads to repetitive injury and maladaptive repair. Injection therapy in this group is aimed at inducing more organized repair and relieving pain. Rehabilitation is the most important component in managing overuse injuries. This includes physical therapy, as well as analysis and adjustment of technique and equipment if faulty. For patients who have undergone an unsuccessful rehabilitation programme, interventional options include techniques involving controlled breakdown and tissue repair with or without augmentation by growth factor stimulation and techniques to reduce pathological neovascularization. A variety of methods of controlled reinjury have been advocated and these will be discussed below. Although corticosteroids can sometimes be successful in this group of patients, the mechanism of action is less well understood. Their mechanism of action and rationale for use are better understood in the truly inflammatory conditions such as rheumatoid arthritis or tenosynovitis.

Figure 29.2 The typical injected agents are local anaesthetic, either long- or short-acting, and a corticosteroid preparation.

Corticosteroids and Their Side Effects

Corticosteroid Preparations

Corticosteroid preparations vary in their strength and efficacy. Some of these differences are due to solubility and composition, the latter related to chemical composition. The composition also results in different particle sizes, which in turn has an influence on side effects. Hydrocortisone is generally considered the weakest of the preparations in general use. Triamcinolone and methylprednisolone are intermediate in strength. The potency of dexamethasone and betamethasone is fivefold that of methylprednisolone or triamcinolone.

Steroid Flare

One of the most common complications occurring following steroid injection is steroid flare. This is an inflammatory type reaction that comes on relatively quickly after the injection and may last 2 to 3 days.

Practice Tip

The features of steroid flare are similar to infection; however, the relatively rapid onset occurring within hours usually differentiates these two conditions.

Steroid flare tends to occur in smaller joints rather than larger ones, and it has been suggested that the long-term response to injection is improved if steroid flare occurs. There is no particular method of preventing this side effect, although the prophylactic use of ice and analgesia may help to offset its effects.

Local Anaesthetic Preparations

Duration of Action

Lidocaine has a rapid onset of action and a duration of action of approximately 2–4 hours. Bupivacaine has a slower onset of action of approximately 10 to 15 min but is said to have a longer duration of action, but it may be no more than 6–8 hours. The relatively short duration of action of lidocaine means that the diagnostic effect may be obscured by the pain and anxiety related to the procedure itself. As previously outlined, an important role of the local anaesthetic component of the injectate is to assist with diagnosis and confirm that the patient’s symptoms do indeed emanate from the structure being anaesthetized. A longer-acting agent has obvious advantages. It is important to ensure that the patient understands that they need to test their symptoms following the injection, particularly in the initial several hours.

Key Point

A pain diary is a simple method of recording the response and should be kept for several weeks.

The diagnostic component of a local anaesthetic is less important in patients undergoing repeated injections following previous successful therapy, although it is still helpful to include some local anaesthetic to manage steroid flare.

Chondrotoxicity

Concern has been raised regarding toxic effects of intraarticular injections on articular cartilage. These have predominantly focused on local anaesthetics, particularly bupivacaine, although corticosteroids have also been implicated in the past. It does appear that repeated corticosteroid injections can result in cartilage loss, although this occurs in a very small proportion of patients over a long period of time. In vitro tests of bupivacaine have demonstrated a cytotoxic effect on cartilage. Concern has been expressed over the use of this agent for intraarticular injections, although its use as an intraarticular infusion following joint surgery is a greater risk. Lidocaine has been shown to be less toxic, although its duration of action is less than bupivacaine and may therefore not be as useful an agent as a diagnostic test. A suggested compromise is to use isomers of bupivacaine, ropivicaine or chirocaine, which are said to be less toxic and have durations of action only slightly shorter than bupivacaine.

General Principles of Ultrasound-Guided Injection

Most ultrasound-guided procedures can be kept relatively comfortable for the majority of patients. Unfortunately some are intrinsically painful, but even in these careful attention to detail can help minimize the trauma. Patients do not like to see needles and it is important that they are not flaunted. This is particularly important for children, where even the use of the word ‘needle’ should be avoided. Communication between the sonologist and assistant can be limited to describing the colour of the needle required. Once everything is made ready, the procedure should be carried out as quickly and as efficiently as possible.

The patient should be in as comfortable a position as possible, preferably one where they do not have to observe the procedure. It is also important that the operator is comfortable and machine and couch heights should be adjusted as appropriate. It is probably better to have the side being injected closest to the operator so as not to have to stretch over the patient, though of course this cannot be avoided if both sides are being treated simultaneously. To begin, a preliminary examination is carried out and a mark is placed on the skin when the best puncture point and approach to the lesion is found. It is sometimes helpful to use the blunt end of a needle sheath to make the mark, as marking with a pen can be difficult in the presence of ultrasound gel. Alternatively two marks can be made at right angles to each other away from the injection point out of any skin gel. This is more appropriate for injection of larger structures. In addition, it is sometimes helpful to draw a line next to the mark, giving the initial direction of approach for the needle (Fig. 29.3).

Figure 29.3 A small circular mark has been made on the patient’s skin by gentle compression with the open end of a plastic needle cover. This can be made through local anaesthetic gel where it is difficult to use skin markers. If necessary a line can also be drawn indicating the initial needle direction.

Practice Tip

Thought should be given to the choice of puncture point and needle track. In addition to the obvious desire to reach the target without transgressing important structures, particularly nerves, there is also an advantage in choosing a course that keeps the needle as parallel as possible to the ultrasound probe.

Visualization of the needle is best under these circumstances (Fig. 29.4). If a parallel approach is not possible, the closest alternative should be chosen. Beam steering or an asymmetrical gel layer can be employed to optimize the ‘probe to needle angle’ relationship.

Figure 29.4 Three needles have been inserted into gel. Needle a is inserted at a slight angle compared with needle b (arrow). The reflectivity of the latter is clearer. The discrepancy increases as depth increases. Needle c is specially formulated with a coating to increase ultrasound reflectivity. Although the needle is considerably more reflective, the additional expense in the majority of cases is not necessary.

Lidocaine is slightly acidic and may cause a stinging sensation that can be reduced by the addition of a small amount of sodium bicarbonate. If the target is very superficial, with experience, local anaesthetic is not required and can add to the discomfort of the procedure. If local anaesthetic is to be used, it is preferable to sterilize the skin and inject local anaesthetic before drawing up the other injection agents or preparing a sterile probe. This gives some time for the local anaesthetic to work before proceeding with the injection. A single puncture is recommended with local anaesthetic infiltrated using the same needle that will be used for the actual injection. Exceptions are where a large needle is to be used, such as for ganglion aspiration or in needle-phobic patients. In these cases the skin is anaesthetized with the smallest available needle.

It is important to have an agreed local policy for patients on anticoagulant therapy. For most superficial injections when small bore needles are being employed, stable international normalized ratio (INR) readings below 2.5 are often accepted. When larger needles are required, for biopsies or where the injection is in an area where occult bleeding could be problematic, alternative arrangements should be made. Generally this involves converting the patient to heparin and omitting a dose the evening before the procedure. Obviously the final decision depends on the patient’s overall medical condition and risks from stopping anticoagulation.

Needle Techniques

In most cases, needles that are in general use in the department suffice. Some manufacturers produce coated needles, which are undoubtedly easier to see; however, for most procedures the additional expense is debatable. For most procedures a 23 G needle is ample and it is useful to have a selection of lengths available. There are two approaches used to position needles under ultrasound guidance, depending on the size and depth of the target. For deeper lesions, small targets and biopsies, amongst others, the needle is kept in view at all times. This is the in-view approach. For superficial joint injections an out-of-view approach may be easier.

‘In View’ Method

For many procedures it is desirable to keep the needle in view at all times until it safely reaches its target. For an in view approach, the needle is aligned with the long axis of the probe. The skin is punctured in the middle of one of the short sides of the probe at an appropriate distance from it depending on the size and depth of the target. As the needle is advanced, it quickly comes into view on one side of the screen. The needle tip specifically must be identified and tracked until it reaches its intended target. The shape of the bevel must be visible to ensure that the tip and not another part of the needle is being followed. To protect the target, the bevel is kept upwards until the target is reached. Once within the target, the bevel is rotated to better position the opening of the needle within the target joint, bursa or sheath.

Key Point

During the procedure, the probe should remain on the target with the tip of the needle kept in view. If visualization of the needle tip is lost, it should not be advanced further until it has been relocated.

To relocate a ‘lost’ needle tip, the probe is moved away from the target towards where the needle tip is felt to be. Once the needle tip is located, the direction the probe had to be moved to find it is noted. The probe is returned to the target, the needle is retracted slightly and then moved in the opposite direction to bring it back into view. There is a tendency for needles to deflect away from the direction of the bevel, therefore for deep injections it is helpful to counter this tendency by rotating the needle.

‘Out of View’ Method

For superficial small joints, there is not necessarily a need to track the needle from skin to target. Instead, the probe is placed in the sagittal plane over the target joint such that its midpoint is directly over the joint or its most distended or effused part. The skin is punctured in the midpoint of the long side of the probe (as opposed to the short side for an in view approach), and directed deep and towards the probe. If the initial position of the probe is chosen carefully enough and no proximal or distal angulation is applied to the needle, its tip should suddenly appear in the ultrasound image within the joint. More recently, manufacturers have been placing marks on the midpoint of the probes to facilitate this. Short footprint probes also tend to be thinner, allowing the skin to be punctured closer to the target joint.

Soft Tissue Biopsy

Important Principles

A detailed discussion on the diagnosis of soft tissue masses will be found in Chapter 31. The principal role of the ultrasound of masses is to confirm the presence of a significant mass, to distinguish fluid from solid lesions, to identify tissue and compartment planes and to guide biopsy. Biopsy of musculoskeletal soft tissue masses follows similar principles to the biopsy of other organs; however, there are several aspects that are important when sarcoma is suspected.

Key Point

The prognosis of sarcoma is dependent on its local extent and in particular whether it is confined to a single anatomical compartment. It is therefore imperative that the biopsy approach to a soft tissue lesion takes account of the compartment within which it is located and ensures that the track does not transgress adjacent spaces.

It is mandatory to discuss the biopsy approach with the surgeon who will be carrying out the definitive surgery. This is to ensure that the track can be excised through the surgical approach to reduce the incidence of track recurrence and, equally importantly, to ensure the biopsy does not worsen the prognosis for the patient by spreading the tumour to another compartment. Some authors advocate the use of a soft tissue dye to help the surgeon identify the biopsy track.

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