What is a hydrodistension injection?

Ultrasound-guided steroid injections for frozen shoulder have been used for many years. There is good evidence that they are beneficial when used for frozen shoulders.
A Systematic Review and Meta-analysis of Randomized Controlled Trials by Sun et al (2016) demonstrated the benefit of steroid injections versus no injection or placebo injections.
In the last 10 years or so, hydrodistension procedures for frozen shoulders have become more and more popular. They have mainly been touted as an effective way of treating frozen shoulder. But what is the evidence for its effectiveness?

What is hydrodistension?

Hydrodilatation, or hydrodistension, is an injection performed under ultrasound (or X-ray) guidance that aims to stretch the tightened joint capsule. Local anaesthetic and steroid, as well as saline, are injected into the shoulder under pressure in an attempt to stretch the capsule and allow movement.
Hydrodistension was first described by Andren and Lundberg (1965) who described the injection into the glenohumeral joint under X-ray guidance.

Evidence for efficacy and safety of hydrodistension injections

Three systematic reviews on the efficacy of hydrodistention injections vs normal steroid injections have been published in the last two years.
Catapano (2017) et al in their systemic review concluded that combining hydrodilatation with corticosteroid injection potentially expedites recovery of pain-free ROM. The most significant benefit is experienced within the first 3 months of intervention.
Meng-Ting Lin et al (2018) in their systematic review concluded that intra articular steroid injection was as effective as distension in shoulder function improvement, pain reduction, and increasing ER of the shoulder. Distension yielded better ER improvement in the medium term but to a minor extent in the long term. For patients with predominant ER limitation, early distension could be considered the primary choice of treatment.
Wei-Ting Wu (2017) in their systematic review concluded that distension of the glenohumeral joint provides a similar long-term efficacy to all reference treatments. A single dose of a corticosteroid-contained regimen introduced through the ultrasound-guided posterior approach is preferable practice of capsular distension for the management of frozen shoulder.

Capsule rupture vs capsule preservation

Currently, in many clinics it is an established standard of care to distend the joint capsule with saline solution and corticosteroid until rupture (Koh et al. 2012). Many researchers and clinicians believed that increasing intra-articular pressure could lead to capsular rupture at the tightest point.
However capsular rupture mostly occurs at the weakest and thinnest areas of the joint capsule such as the subacromial bursa, subscapularis recess or the long biceps tendon sheath (Rizk et al,1994) rather then the stronger and thicker parts of the capsule which are the main dysfunctional areas in adhesive capsulitis.
Capsular preservation provides continual dilatation whilst ensuring that injected corticosteroid stays within the joint capsule, where  the thinking is that it can provide maximal anti-inflammatory effects. With capsular rupture fluid will leak into the surrounding soft tissues carrying away the corticosteroid from the joint capsule which is its intended target.
One RCT (Kim et al 2011) found that in a head to head comparision of those those in whom the joint capsule was preserved (n=20) vs those injected until capsular rupture (n=26) the capsule preserved group showed a significant better range of movement and pain reduction in the short term (3  days post procedure and at 1 month post procedure). This study also monitored intra-articular pressures throughout the procedures which  is likely to have ensured the accuracy of the procedures.
A recent slide share from Mr. Lennard Funk (Shoulder Doc) (McBride) shows a retrospective analysis of hydrodistension (n=58) for capsular rupture and seemed to indicate that whether there had been capsular rupture or not it made no difference to clinical outcomes.

Biomechanical properties of joint capsules and changes due to repeat hydrodistension injections:

A very interesting study by Koh et al (2010) showed that repeated (3) Capsule-preserving hydrodistension injections changed the biomechanical properties of the glenohumeral joint capsule, lessening the stiffness and enlarging the volume capacity. these changes were accompanied by improved range of motion and relief of pain. Three hydrodistension distensions with saline solution and corticosteroid were performed with 1-month intervals.
This study would suggest that the pressure effect is responsible for the increase in range of motion and reduction in pain and that these improvements were accumulative.

Summary of the evidence:

At least in terms of increase in range of movement hydrodistension appears better than steroid injection alone in the short and medium term. Despite the trend demonstrated in the literature, there remains a lack of robust data on the effect of hydrodilatation with corti-costeroid injection via this optimized technique, as only a few studies have combined these factors.

Capsule preserved vs capsule rupturing hydrodistension injections

Kim et al 2011 showed a significant better range of movement and pain reduction in the short term with capsule preserved hydrodistension when compared with capsule rupturing hydrodistension.
Koh et al (2010) showed that there is evidence suggesting that repeat hydrodistension injections (3) up to maximum pressure without capsular rupture can lead to reduced capsular stiffness and enlarged volume capacity resulting in improved range of movement and reduced pain levels. However In clinical practice without pressure monitoring equipment it might not be possible to avoid capsular rupture in every case.
What is now required is a large RCT to evaluate capsular preserved hydrodistension vs capsular rupturing hydrodistension. In the clinical situation it will remain a challenge to achieve maximum capsular distension whilst avoiding capsular rupture without using pressure monitoring equipment.

REFERENCES:

Andrén, L. and Lundberg, B.J., 1965. Treatment of rigid shoulders by joint distension during arthrography. Acta Orthopaedica Scandinavica, 36(1), pp.45-53.
Catapano, M., Mittal, N., Adamich, J., Kumbhare, D. and Sangha, H., 2017. Hydrodilatation With Corticosteroid for the Treatment of Adhesive Capsulitis: A Systematic Review. PM&R.
Kim, K., Lee, K.J., Kim, H.C., Lee, K.J., Kim, D.K. and Chung, S.G., 2011. Capsule preservation improves short‐term outcome of hydraulic distension in painful stiff shoulder. Journal of Orthopaedic Research, 29(11), pp.1688-1694.
Lin, M.T., Hsiao, M.Y., Tu, Y.K. and Wang, T.G., 2018. Comparative efficacy of intra-articular steroid injection and distension in patients with frozen shoulder: a systematic review and network meta-analysis. Archives of physical medicine and rehabilitation, 99(7), pp.1383-1394.
Sun, Y., Zhang, P., Liu, S., Li, H., Jiang, J., Chen, S. and Chen, J., 2017. Intra-articular steroid injection for frozen shoulder: a systematic review and meta-analysis of randomized controlled trials with trial sequential analysis. The American journal of sports medicine, 45(9), pp.2171-2179.
Wu, W.T., Chang, K.V., Han, D.S., Chang, C.H., Yang, F.S. and Lin, C.P., 2017. Effectiveness of glenohumeral joint dilatation for treatment of frozen shoulder: a systematic review and meta-analysis of randomized controlled trials. Scientific reports, 7(1), p.10507.
Koh, E.S., Chung, S.G., Kim, T.U. and Kim, H.C., 2012. Changes in biomechanical properties of glenohumeral joint capsules with adhesive capsulitis by repeated capsule-preserving hydraulic distensions with saline solution and corticosteroid. PM&R, 4(12), pp.976-984.