Extracorporeal shockwave therapy (ESWT) is a technology that uses shock waves to treat chronic painful conditions of the musculoskeletal system, and in the knee this mostly relates to the patellar tendon.
What is patellar tendinopathy?
Patellar tendinopathy is a common problem associated with sporting and overuse activities, especially involving running and jumping, and it most frequently affects the lower pole of the patella. Diagnosis of chronic patellar tendinopathy is based on clinical evaluation alone. Further imaging studies play a role only in confirming the diagnosis and excluding other pathologies.
There is an estimated overall incidence of patellar tendinopathy of 14% in the general population, but a much greater incidence among higher level athletes. Patellar tendinopathy can, however, also affect sedentary patients with other lower limb abnormality resulting in increasing mechanical stress through the knee extensor mechanism with normal daily activities. The patellar tendon has to cope with the largest tensional load forces, the largest muscle groups, the longest bones and the largest sesamoid bone in the human body. Although the exact pathological mechanism is not fully understood, patellar tendinopathy is associated with sustained mechanical load on the patellar tendon with resulting stress-induced inflammation and subsequent degeneration. The changes in affected tendons demonstrate abnormal arrangement of the collagen fibres and a decrease in the cellularity. Microscopic studies have in fact shown there is an absence of inflammatory cells, normal levels of prostaglandin and a lack of vascularity, so it cannot be defined as a tendinitis (which implied 'inflammation') but as a chronic avascular tendinopathy (which implies a disorder of blood supply rather than of inflammation).
How has patellar tendinopathy conventionally been managed?
Several treatment strategies exist in dealing with patellar tendinopathy. The most accepted treatment has been physical therapy with a particular focus on eccentric loading exercises and heavy load isometric resistance exercises. Injections of corticosteroids has shown good short-term results, but has dose-related complications such as crystallisation of the tendon matrix and a risk of tendon rupture. Biological therapeutic options such as injection with platelet rich plasma (PRP), bone marrow aspirates and autologous growth factors are still at an experimental level. Surgery has always been a last resort treatment with the aim of inducing tendon regeneration following surgical debridement.
The use of mechano-transductional impulses (extracorporeal shock waves therapy) to stimulate breakdown of degenerative tissue and healing to normal connective tissue has gained popularity over the last two decades. Mechano-transduction refers to the processes through which cells are aware of and respond to mechanical stimuli by then converting them to biochemical signals which themselves stimulate specific cellular responses.
New options in the management of tendinopathy. Maffulli N, Longo UG, Loppini M, Spiezia F and Denaro V. Open Access J Sports Med. 2010; 1: 29–37.
What is extracorporeal shockwave therapy?
A shock wave is an intense but short energy wave travelling faster than the speed of sound which is passed through the skin at the injured area and works by stimulating certain components within the body which accelerates the healing process. In addition to stimulating the healing process the shock wave therapy seems to have a direct effect on the nerves and reduces pain. The shock waves are mechanical, not electric and are generated outside of the body. Extracorporeal means outside the body. It is a very low-risk procedure.
In the patellar tendon the mechanical stimulus provided by the shock waves can aid tendon remodelling in tendinopathy by promoting inflammatory and tendon remodelling processes, although physical training, and particularly eccentric training, remains the treatment of choice for patients suffering from patellar tendinopathy.
When may ESWT be offered for patellar tendinopathy?
ESWT is offered to patients struggling with patellar tendinopathy who have not responded as anticipated to other conservative treatments such as painkillers, rest, ice therapy, physiotherapy or steroid injections. The benefit of the ESWT is that it can offer relief from pain and other symptoms and combined with physiotherapy allow return to function. Studies have shown the treatment to be associated with 60-80% improvement in symptoms.
The underpinning theory has been mechano-transduction induced modulation of neovascularization, migration and differentiation of mesenchymal stem cells, as well as local angiogenic stimulation. Several studies examining the biological response have proven that ESWT decreases tendon matrix metalloproteinases and interleukins.
Current concepts of shockwave therapy in chronic patellar tendinopathy. Leal C, Ramon S, Furia J, Fernandez A, Romero L and Hernandez-Sierra L. Int J Surg. 2015;24(Pt B):160-164.
Are there any risks to ESWT?
Shockwave treatment for chronic patellar tendinopathy that has not responded to conservative measures and physical therapy is an effective and safe procedure. It cannot be recommend it for acute conditions, since more than 80% of cases improve with conventional therapy, and only an estimated 20% develop a dysplastic insertional tendinopathy.
Most patients do experience some discomfort during the treatment but it should be easily tolerated. It is advisable to take mild painkillers (paracetamol and/or codeine) approximately half an hour before the procedure to counteract this. Following the treatment a patient may experience redness, bruising, swelling and numbness to the area but these effects are rare and should resolve within a week. There is a very small risk of tendon or ligament rupture and damage to the soft tissue.
Paatients must not have ESWT if they:
- are pregnant
- are taking antiplatelet medication (e.g. aspirin or clopidogrel) or anticoagulants (e.g. warfarin or rivaroxaban)
- have a blood clotting disorder
- are under the age of 18
- have been diagnosed with bone cancer
- have a cardiac pacemaker or other cardiac device
- have an infection in the knee
- have a history of previous tendon or ligament rupture
- have had steroid injections in the previous 12 weeks
Is shockwave therapy painful?
The treatment is generally carried out in an orthopaedic outpatient department where the patient is asked to lie on a couch or sit on a chair. The leg is placed in a flexed position. Some ultrasound gel is placed on the skin over the injured area and the handpiece of the ESWT device is placed in contact with the gel. The shock wave is then delivered via the hand-held transducer using the gel as a conductive medium. The gel enables a tight bond between the skin and the device allowing the waves to transmit to the tissues beneath. The waves are audible. If a patient experiences severe discomfort during the treatment they should inform the health professional performing the procedure, as the technician will be able to adjust the energy level to manage this. Any discomfort will stop at the end of the procedure. Each treatment takes approximately five minutes to perform but the appointment time is generally slightly longer to allow time for information giving, questions and consent process. In the research carried out on this treatment some patients - one in six - experienced a short-lived patch area of numbness on the front part of the knee where the treatment was applied.
How effective is ESWT?
What happens if there is no improvement following ESWT?
Certain patients can experience a short-lived improvement or no improvement in symptoms at the end of the prescribed treatment protocol and subsequent rehabilitation phase. If that is the case they often need a follow-up consultation within their orthopaedic clinic for further clinical evaluation, and further investigations which may include an MRI scan of the knee. In the extremely refractory case the specialist knee surgeon may consider alternative treatment options, which may include surgery such as arthroscopic debridement/decompression, or high frequency cold ablation (with Smith&Nephew's Topaz device).