Back Pain Doctor
Patellar Instability (Unstable Kneecap)
Patellar instability is when the kneecap slips partly (subluxation) or completely (dislocation) out of the groove it normally glides in. It can follow a single twisting injury or a direct blow, and in some people it recurs, producing pain, swelling and a persistent sense that the knee is about to give way. Structural factors — a shallow groove, ligament (MPFL) damage, alignment and rotation of the leg, and where the patellar tendon attaches — all influence the risk.
Assessment covers how the episode happened, how the kneecap tracks, and whether alignment or muscle weakness predisposes to further dislocation. A dislocated kneecap that will not reduce, or a locked knee that cannot bear weight, needs same-day assessment. Imaging with X-ray, and often MRI, is used to look for loose fragments and to assess the ligaments and anatomy of the knee.
First-line care after a first dislocation is usually non-surgical — reduction if needed, a period of bracing, then a structured physiotherapy program to strengthen the quadriceps and hip and improve kneecap control, with a graded return to activity. Most first dislocations do well this way. Recurrent instability, high-risk first dislocations, or a severely maltracking kneecap are referred for an orthopaedic opinion, where soft-tissue reconstruction or bony realignment may be considered.
A knee that gives way is not always a patellar problem. Where the giving way occurs on pivoting rather than with the kneecap moving out of place, an ACL injury should be considered.
Common symptoms
- The kneecap slipping, partly dislocating or fully dislocating
- A feeling the kneecap is about to give way (apprehension)
- Pain and swelling at the front of the knee after an episode
- Reluctance to twist, pivot or bend the knee under load
Commonly seen in
Evidence for twelve treatment options in patellar instability (unstable kneecap)
This is not a fixed ladder or a package of treatments. Every option is assessed independently against this diagnosis, including treatments with limited direct research that may still be reasonable for a clearly defined tissue target. The evidence level, likely benefit, risks, cost and alternatives are weighed at consultation.
Foundation — diagnosis, education and rehabilitation
The part of care with the broadest relevance. For many people it is enough on its own; other options are judged against it, not automatically added after it.
Diagnosis, education and progressive rehabilitation Working out what is driving the pain, explaining what your imaging does and does not mean, and building a graded loading plan you can actually follow. Core care
What it involves
Assessment to identify the likely pain source, an explanation of what the diagnosis means, adjustment of the loads that aggravate it, and a progressive strength and conditioning plan — with weight management where that is clinically relevant.
What the evidence shows
For degenerative structural problems, exercise matches surgery. A trial of 321 patients found exercise-based physiotherapy non-inferior to arthroscopic partial meniscectomy for knee function at five years, with the same rate of radiographic osteoarthritis progression (Noorduyn, JAMA Netw Open 2022), confirming an earlier trial at two years that also found better thigh strength in the exercise group (Kise, Br J Sports Med 2016). Even in adults aged 18 to 40 with MRI-verified tears, traumatic or not, early surgery was no better than twelve weeks of exercise and education at one year (Damsted, J Orthop Sports Phys Ther 2024).
Pairing reviewed 2026-09-02.
Where it fits for you
A tear on a scan is not automatically the thing to fix. Rehabilitation comes first, with surgical review where the history, examination and imaging together point to a problem that loading will not solve — mechanical locking, instability, or a failure to progress despite doing the work.
Muscle and symptom-modifying options
Useful only when the examination identifies the tissue they target or when short-term pain control creates a useful rehabilitation window.
Wet needling and trigger point injection (trigger point injection) A fine needle into a tender band of muscle, with a small volume of dilute glucose solution injected through it. No trials in this condition
What it involves
The needle is placed into the tender muscle band and a small volume of 5% glucose with 0.02-0.08% lignocaine is injected. Often done in the same visit as your assessment, and usable where the tender area sits deeper. Dry needling — the same technique with nothing injected — is not offered here.
What the evidence shows
Searching patellar dislocation and patellar instability against dry needling, trigger point work and trigger point injection returned no study of needling in this condition. The records that matched sit at other knee structures - needling after cruciate reconstruction (Velázquez-Saornil, Medicine 2017) and a massage case report for kneecap pain after the same operation (Zalta, Int J Ther Massage Bodywork 2008). Needling has not been tested for an unstable kneecap.
Pairing reviewed 2026-09-19.
Where it fits for you
Does not address the tracking problem that drives the instability. Considered only where a tender band in the quadriceps or lateral thigh is adding to your pain.
Ultrasound-guided injections Guidance means we can see the needle reach the target. What goes into the needle depends on the diagnosis. Worth discussing
What it involves
The injection is performed under ultrasound so the needle can be watched into the target structure. What is injected is decided by the diagnosis — and corticosteroid is used sparingly, for the reasons set out below.
What the evidence shows
Ultrasound improves needle-placement accuracy, but guidance is not a treatment in itself: benefit depends on a valid injectable target and what is injected. Condition reviewed: patellar instability.
Evidence source: Oo et al., ultrasound-guided injection systematic review (2024)
Pairing reviewed 2026-08-30.
Where it fits for you
For patellar instability, an ultrasound-guided injection is considered only when there is a specific diagnostic question or a separate joint, bursa, sheath or nerve target. The injectate and purpose are stated before treatment.
V-ACTOR vibration therapy (vibration therapy) Low-frequency vibration applied over tender muscle. Not a shockwave, despite sharing the machine. Plausible — no studies
What it involves
A vibration handpiece is moved over the tender muscle and fascia for a few minutes. It runs from the same STORZ MASTERPULS icon console as radial shockwave but is a separate handpiece delivering a different, gentler form of energy. No needles, no anaesthetic, no downtime.
What the evidence shows
No published clinical trial of this device in this condition. It is a vibration handpiece delivered from the same console as radial shockwave, and the rationale is myofascial rather than tendon- or bone-directed.
Pairing reviewed 2026-08-30.
Where it fits for you
A comfort measure used within a session where muscular tightness is limiting movement. Never the reason for the appointment, and not a substitute for the treatments that do have evidence.
Energy-based treatment options
Radial pressure wave, focused shockwave and EMTT have different targets and different evidence. They are assessed separately rather than treated as one category.
Radial or focused shockwave? Read the overviewRadial shockwave (radial pressure wave) Broad treatment across tender muscle and fascia, close to the surface. Only if relevant
What it involves
A handpiece is moved over the tender tissue while ballistic pressure pulses are delivered, using a transmitter head chosen for the tissue — including heads shaped for fascia and for the muscle either side of the spine. The pulse is strongest at the skin and weakens with depth, so this is mainly a myofascial treatment, though it can reach deeper in some areas. No anaesthetic, no downtime, usually a course of sessions about a week apart.
What the evidence shows
Shockwave reviews in myofascial pain report a possible benefit but mix protocols and often mix radial pressure wave with focused shockwave; that evidence cannot be transferred to the underlying diagnosis. Condition reviewed: patellar instability.
Evidence source: Wu et al., shockwave for myofascial pain review (2022)
Pairing reviewed 2026-08-30.
Where it fits for you
For patellar instability, radial pressure wave may be considered for a distinct superficial muscle or fascial component. It is not used as evidence of benefit for the primary diagnosis.
Focused shockwave (ESWT) A true shock wave converging at depth — for tendon, joint, ligament and bone. Only if relevant
What it involves
A focused system generates an acoustic shock wave that converges at a focal point set at a defined depth, concentrating the energy where the target is. This is the form we use for tendon, joint, ligament and bone. Typically four to six sessions about a week apart, no anaesthetic and no formal downtime.
What the evidence shows
A tear or structural problem where the decision is a loading or surgical one. No trial evidence for shockwave in the structural lesion itself.
Pairing reviewed 2026-08-30.
Where it fits for you
Considered only for a coexisting tendinopathy, not for the tear.
EMTT (magnetotransduction therapy) High-energy magnetic pulses applied over the area. Painless, no contact. Plausible — no studies
What it involves
You sit with the applicator positioned over the area for a short session. Painless, no gel or contact required, and usually delivered as a course — commonly alongside shockwave.
What the evidence shows
There are no published randomised trials of EMTT in this condition, or in any musculoskeletal condition, that we can point to. The supporting work is laboratory work: EMTT increased tenocyte proliferation, migration and collagen expression in cultured human tendon cells (Mancini, Int J Mol Sci 2025). The nearest human evidence for a related electromagnetic therapy is negative — a randomised trial of pulsed electromagnetic field therapy added to eccentric exercise for Achilles tendinopathy found no improvement in outcome scores or tendon neovascularity over eccentric exercise alone (Ko, Orthop J Sports Med 2024).
Pairing reviewed 2026-08-30.
Where it fits for you
Offered only as an adjunct alongside treatment that does have evidence, never as the plan itself, and only after that gap is explained. Much of the EMTT literature is manufacturer-affiliated, which is part of why we describe it this way.
Biologic and joint injection options
Each injection is assessed independently for the named diagnosis. Cost, uncertainty, likely benefit, risks and alternatives are part of the decision.
Platelet-rich plasma (PRP) Your own blood, concentrated and injected under ultrasound guidance. Plausible — no studies
What it involves
Blood is taken from your arm, spun to concentrate the platelets, and injected into the target under ultrasound guidance in the same appointment.
What the evidence shows
No published randomised trial of platelet-rich plasma in patellar instability. The platelet-rich plasma literature is concentrated in tendon, joint and nerve-entrapment conditions, and a result at one site does not carry across to a different tissue and a different problem.
Pairing reviewed 2026-08-30.
Where it fits for you
Not offered for this. The problem is structural rather than a failure of tissue healing, which is what platelet-rich plasma is proposed to influence.
Prolotherapy (dextrose) A course of dextrose injections into and around the structure and its attachments. Plausible — no studies
What it involves
Hypertonic dextrose is injected at the tender ligament and tendon attachments, and into the joint where relevant, usually as a series of treatments a few weeks apart.
What the evidence shows
A PubMed search for prolotherapy or dextrose injection in patellar instability, patellar dislocation or the medial patellofemoral ligament returns no study of any design.
Pairing reviewed 2026-09-05.
Where it fits for you
Not offered. Instability after a dislocation is a matter of ligament competence, trochlear shape and quadriceps control; an injection changes none of them. Rehabilitation, and surgical reconstruction where it is warranted, are the options.
Viscosupplementation (hyaluronic acid) A gel-like injection into an arthritic joint. Widely used, and genuinely contested. Only if relevant
What it involves
One or a short series of hyaluronic acid injections into the joint under ultrasound guidance.
What the evidence shows
Hyaluronic acid evidence is concentrated in osteoarthritis—especially the knee—and remains contested; it cannot be extrapolated to a non-arthritic tissue or a different diagnosis. Condition reviewed: patellar instability.
Evidence source: Pereira et al., large-trial injection review (2024)
Pairing reviewed 2026-08-30.
Where it fits for you
For patellar instability, this is relevant only when a symptomatic arthritic peripheral joint is the actual target. It is not used for muscle, tendon, ligament, nerve, fracture or spinal pathology.
Nerve-targeted options
Relevant when examination identifies a superficial neuropathic pattern or a compressed peripheral nerve—not simply because pain is present.
Lyftogt perineural therapy (perineural injection therapy) A series of small dilute dextrose injections just under the skin, over tender superficial nerves. Only if relevant
What it involves
Small injections of low-concentration dextrose, usually 5%, placed just beneath the skin along tender superficial nerves. Given as a series of short sessions.
What the evidence shows
Perineural dextrose evidence is concentrated in diagnosed peripheral compression neuropathies, particularly the upper limb; no direct evidence was identified for this diagnosis itself. Condition reviewed: patellar instability.
Evidence source: Perineural dextrose for upper-limb entrapment neuropathy review (2025)
Pairing reviewed 2026-08-30.
Where it fits for you
For patellar instability, perineural treatment may be considered only if a separate superficial neuropathic pain pattern is found on examination. It is not treatment of the primary diagnosis.
Ultrasound-guided nerve hydrodissection Fluid placed around a nerve to free it from the surrounding tissue. Only if relevant
What it involves
Under ultrasound, fluid is placed in the plane around the nerve to separate it from the tissue that is tethering or compressing it.
What the evidence shows
Hydrodissection evidence is concentrated in ultrasound-confirmed peripheral nerve entrapment, especially carpal tunnel syndrome; no direct evidence was identified for this diagnosis itself. Condition reviewed: patellar instability.
Evidence source: Buntragulpoontawee et al., hydrodissection injectate review (2021)
Pairing reviewed 2026-08-30.
Where it fits for you
For patellar instability, hydrodissection may be considered only if ultrasound and examination identify a separate compressed or tethered peripheral nerve. It is not treatment of the primary diagnosis.
This is general information only and suitability is assessed individually. Treatments with limited or condition-dependent evidence may still be discussed, but only with clear explanation of the uncertainty, the expected benefit, risks, cost and alternatives. Red flags, progressive neurological symptoms or suspected serious pathology require a different pathway.
Every treatment above is described in full on the non-surgical treatments page, including what each one is used for and what the evidence supports. Ratings apply to the named diagnosis; an adjacent muscle, tendon, joint or nerve problem is assessed as a separate target.
Corticosteroid injection is reviewed separately for each diagnosis.
Cortisone reliably reduces pain in the short term, and that can be genuinely useful when pain is stopping you sleeping or moving enough to rehabilitate. Beyond that window the picture changes. A systematic review of 41 randomised trials and 2,672 participants found that corticosteroid injection reduced pain in the short term but that the effect reversed at intermediate and long term; in pooled analysis for lateral epicondylalgia the short-term effect was large (SMD 1.44, 95% CI 1.17 to 1.71) while no intervention was favoured at 26 weeks (-0.40, -0.67 to -0.14) and at 52 weeks (-0.31, -0.61 to -0.01) (Coombes, Lancet 2010). In a randomised trial in lateral epicondylalgia, 83 per cent of the corticosteroid group had completely recovered or much improved at one year against 96 per cent given a placebo injection, and recurrence ran at 54 per cent against 12 per cent; adding physiotherapy made no significant difference at one year (Coombes, JAMA 2013). In joints, repeated corticosteroid injections have been associated with cartilage loss. It does not repair anything.
So we do not build treatment plans around it. Where an injection is the right call, we review the specific diagnosis and target, discuss what is being injected and why, keep the number low, and pair it with the loading work that changes the longer-term course.
When we would still consider it
- Pain severe enough to block rehabilitation
- A clear inflammatory or bursal target on imaging
- A specific short-term goal — a trip, a procedure, a return to work
- Diagnostic use, where the response tells us where the pain is coming from
When a cortisone injection is worth doing, and when it is not
Other knee conditions
Pain in the same area can come from more than one source, and the label matters less than what the examination and history point to. These are the other guides for this region.
Frequently asked questions
How is patellar instability diagnosed?
What does treatment involve?
When should a dislocated kneecap be seen urgently?
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