By Marc Darrow, MD, JD
A reader had knee surgery in 2005 and now has substantial pain with everyday walking and a feeling that the kneecap is unstable. A recent MRI describes persistent grade IV chondromalacia, congenital dysplasia of the anterior compartment, and acute-on-chronic changes of transient patellar dislocation. Their doctor and chiropractor have suggested PRP, but the reader is frightened of another operation.
PRP may be discussed as a possible way to reduce pain, but the mechanical instability needs its own assessment. An injection has not been shown to reshape a dysplastic groove or reliably prevent a kneecap from repeatedly slipping out of position.
That does not mean another operation is inevitable. It means the decision should address two related questions: what is causing the pain, and what is allowing the kneecap to sublux or dislocate? Treating pain alone may leave the second problem unresolved.
What do the MRI terms mean?
The report contains several findings that should be interpreted together with the images and examination.
| MRI wording | Plain-language meaning | What it does not establish by itself |
|---|---|---|
| Grade IV chondromalacia | Severe, full-thickness cartilage loss in the described area, generally exposing underlying bone | That every knee compartment is affected or that replacement is inevitable |
| Congenital dysplasia of the anterior compartment | A developmental difference in the shape of the front-of-knee joint structures | The precise abnormality or which treatment is appropriate without image review |
| Transient patellar dislocation | Evidence consistent with the kneecap having moved out of place and returned | That the kneecap is currently dislocated |
| Acute-on-chronic changes | Recent injury findings superimposed on longstanding changes | The exact date, cause, or clinical importance of each finding |
“Grade IV” is a local cartilage description. The size and location of the defect matter. A small full-thickness lesion and widespread joint-surface loss are different situations. “Persistent” suggests comparison with prior findings, but it does not establish that cartilage has been actively worsening at the same rate since 2005.
The wording “anterior compartment dysplasia” should also be clarified. It may refer to the patellofemoral anatomy, including the trochlear groove, but that cannot safely be assumed from a paraphrased report.
Subluxation and dislocation are different from ordinary giving way
Subluxation means partial displacement. Dislocation means the kneecap moves fully out of its normal relationship with the groove. A transient dislocation can reduce before the patient is examined while still leaving swelling, pain, and cartilage or soft-tissue injury.
The kneecap is guided by both bone shape and soft tissues. A shallow groove, abnormal limb alignment, the attachment position of the patellar tendon, or injury to the medial patellofemoral ligament can contribute to instability. The American Academy of Orthopaedic Surgeons describes these as distinct factors in recurrent patellar instability. (1)
A knee can also buckle because pain or swelling interferes with muscle control. That feels unstable but is not necessarily another patellar displacement. Examination helps distinguish the two, and they may coexist.
Our site’s patellar-instability article discusses the broader condition. In this reader’s situation, the new MRI findings and previous surgery make individual assessment particularly important.
The 2005 operation
The original procedure should be identified rather than presumed to have been a meniscus operation or a patellar stabilization. A lateral release, ligament reconstruction, cartilage procedure, and realignment operation leave different anatomy and different questions for current care.
The operative report, earlier imaging, and the period of improvement or continuing symptoms can help explain what has changed. A previous operation does not automatically mean that nonsurgical treatment cannot help. It also does not establish that repeating the old procedure would address the present problem.
The length of time since surgery is relevant, but time alone cannot identify which structure is responsible for today’s pain and instability.
Why recent dislocation changes deserve review before injection
A dislocation can injure cartilage and the bone beneath it, or produce a loose osteochondral fragment. A fragment may need a different approach from chronic cartilage wear.
The ESSKA consensus published in 2025 emphasizes examination and MRI assessment of predisposing anatomy and osteochondral injury after a first-time dislocation. This reader appears to have a recurrent, previously operated knee, so the consensus cannot be applied as a direct treatment algorithm. Its diagnostic principle remains useful: understand the injury and anatomy before selecting treatment. (2)
Substantial walking pain and an MRI suggesting a recent episode are reasons to have the images reviewed by an orthopedic clinician familiar with patellofemoral instability. That review does not commit the patient to another operation.
A currently displaced kneecap, a knee physically blocked from straightening, inability to bear weight after a new episode, or rapidly increasing swelling needs prompt assessment. Fever with a hot swollen joint, or a cold or numb foot, requires urgent evaluation.
What can rehabilitation and bracing offer?
Appropriate rehabilitation can address quadriceps and hip strength, movement control, balance, and walking confidence. The aim is to improve function and reduce aggravating loads, while respecting the recent injury and cartilage condition.
A stabilizing brace or taping may help selected patients feel more secure or tolerate activity. It cannot reshape the groove, and relief while wearing it does not establish long-term correction. The ESSKA treatment consensus supports rehabilitation but finds no clear long-term benefit from bracing after first-time dislocation. Its recommendations are based substantially on limited evidence and expert agreement. (3)
For an already unstable and painful knee, exercises should be selected according to assessment rather than prescribed solely from the MRI grade. Deep squats, forceful stretching, or repeated provocative testing are not automatically appropriate. A program that repeatedly triggers slipping or substantial swelling needs reassessment.
Temporary activity adjustments or walking support may help daily function. They are tools for managing the current problem, not an admission that recovery is impossible.
What does PRP research show for chondromalacia?
PRP is prepared from the patient’s blood and contains concentrated platelets and associated signaling substances. It is not a stem-cell preparation, and products and protocols vary.
A 2025 systematic review examined PRP for patellofemoral arthritis, chondromalacia, and anterior knee pain. It included five studies and 146 patients. Pain and function improved in the reported studies, but evidence of cartilage regeneration was limited and uncertain. The authors called for better randomized trials and more reliable imaging outcomes. (4)
These findings support interest in symptom relief. They do not establish that PRP rebuilds a grade IV defect, treats congenital dysplasia, or prevents another dislocation. Improvement from baseline also does not show how much improvement would have occurred with rehabilitation, time, or a control injection.
For the reader, a realistic question is whether PRP might reduce the painful component enough to improve walking and participation in rehabilitation. That goal is different from correcting the underlying instability.
New 2026 review: why certainty remains limited
A 2026 systematic review of randomized trials included six studies and 393 participants with knee chondromalacia. Most evaluated hyaluronic acid. One compared PRP with prolotherapy and another compared PRP with hyaluronic acid. None compared PRP or prolotherapy with placebo or no treatment, preventing firm conclusions about their effectiveness. (5)
A comparison between two active treatments can help assess relative outcomes, but it cannot automatically establish how much either adds beyond the natural course or other care. This is why a positive recommendation needs to acknowledge uncertainty rather than supply a confident success percentage.
Neither that review nor the 2025 review establishes a dependable response for a knee with this exact combination of prior surgery, grade IV damage, dysplasia, and recurrent displacement.
Does PRP research in other patients apply to this knee?
Patient selection matters. A 2024 cohort study reported better short-term outcomes with PRP plus hyaluronic acid than with physiotherapy alone in selected adults with chondromalacia. However, participants chose their treatment, the injectates were combined, and people with evident anatomical abnormalities were excluded. (6)
That is a particularly important limitation here because the reader’s MRI specifically describes congenital dysplasia. The study cannot establish that its findings apply to a mechanically unstable, dysplastic knee or that PRP alone produced the improvement.
Research about general knee osteoarthritis should likewise not be treated as proof of patellar stabilization. The diagnosis, anatomy, intervention, and outcome need to match the proposed claim.
What should be understood before trying PRP?
The proposed target and goal should be clear. An injection into the joint for pain is different from an intervention intended to treat a particular ligament. Image guidance may help placement, but it does not establish that the product will repair that structure.
Potential risks include temporary pain, swelling, bleeding, infection, and no meaningful benefit. Using the patient’s own blood does not make the procedure risk-free. The plan should also explain how pain, walking ability, swelling, and actual instability episodes will be reassessed.
Less pain should not be interpreted as permission to ignore repeated subluxations. A patient may feel better while the mechanical risk remains. Equally, lack of response does not automatically justify an escalating series of injections without reconsidering the diagnosis.
When might another surgical discussion be appropriate?
Surgery may be considered for recurrent symptomatic instability, a significant displaced osteochondral injury, or a mechanical problem that has not responded adequately to appropriate nonsurgical care. It should be selected according to the actual anatomy and prior operation.
Possible procedures address different problems. MPFL reconstruction addresses a medial soft-tissue restraint. A tibial tubercle osteotomy changes the position of the tendon attachment on the shinbone. Trochleoplasty changes the groove in carefully selected cases. Severe existing cartilage disease affects which options are appropriate, so none should be assumed suitable from a brief MRI description.
The ESSKA consensus discusses combining soft-tissue reconstruction with correction of relevant bony risk factors in selected patients, while acknowledging uncertainty about thresholds. It does not recommend treating everyone with the same operation. (3)
An isolated lateral release is not a universal answer to recurrent instability. Another operation, if proposed, should have a specific reason and realistic expectations for both pain and stability.
Fear after a previous operation is understandable. An independent patellofemoral specialist opinion can help clarify options without committing to surgery. The useful goal is to avoid an unnecessary procedure while recognizing situations in which an injection is unlikely to solve the mechanical problem.
For this reader, PRP may be a symptom-directed option to discuss after review of the recent injury and instability. It should not be promised to rebuild grade IV cartilage or correct congenital dysplasia. A careful assessment can establish what can reasonably be managed without surgery and what requires a different approach.
References
1 American Academy of Orthopaedic Surgeons. Patellar (Kneecap) Instability. OrthoInfo. Accessed October 29, 2026.
2 Blønd L, Askenberger M, Stephen J, Akmeşe R, Balcarek P, El Attal R, Chouliaras V, Ferrua P, Monart JM, Pagenstert G, Sillanpää P, Da Silva MV, Walawski J, Beaufils P, Dirisamer F. Management of first-time patellar dislocation: The ESSKA 2024 formal consensus-Part 1. Knee Surg Sports Traumatol Arthrosc. 2025;33(5):1925-1932. doi:10.1002/ksa.12620.
3 Balcarek P, Blønd L, Beaufils P, Askenberger M, Stephen JM, Akmeşe R, El Attal R, Chouliaras V, Ferrua P, Minguell Monart J, Pagenstert G, Sillanpää P, Vieira Da Silva M, Dirisamer F, Walawski J. Management of first-time patellar dislocation: The ESSKA 2024 formal consensus-Part 2. Knee Surg Sports Traumatol Arthrosc. 2025;33(12):4197-4206. doi:10.1002/ksa.12637.
4 Chalidis B, Pitsilos C, Davitis V. The Role of Platelet-Rich Plasma (PRP) in the Treatment of Patellofemoral Arthritis and Anterior Knee Pain: A Systematic Review. Int J Mol Sci. 2025;26(18):9006. doi:10.3390/ijms26189006.
5 De la Cerna-Luna R, Cabanillas-Lazo M, Arnillas Brigneti P, Rios-Garcia W, Taype-Rondan A. Intra-articular Injections for Knee Chondromalacia: A Systematic Review of Randomized Controlled Trials. Am J Phys Med Rehabil. 2026. Published online June 2026. doi:10.1097/phm.0000000000003058.
6 Ostojic M, Hakam HT, Lovrekovic B, Ramadanov N, Prill R. Treatment of anterior knee pain due to chondromalacia patellae with platelet-rich plasma and hyaluronic acid in young and middle-aged adults, a cohort study. Arch Orthop Trauma Surg. 2024;144(9):3969-3976. doi:10.1007/s00402-024-05363-w.