Abstract
Background:
Deep medial collateral ligament (dMCL) injuries are a known cause of medial knee pain, which can result from either trauma or degenerative conditions. While conservative management, including bracing and physical therapy, remains the first-line treatment, persistent symptoms may necessitate additional interventions. Platelet-rich plasma (PRP) therapy has emerged as a promising treatment modality due to its ability to enhance ligament healing by promoting collagen synthesis and tissue regeneration. Recent studies highlight PRP's potential to improve pain and function in patients with medial collateral ligament injuries, particularly when guided by ultrasound for precise delivery.
Indications/Technique Description:
This study presents 2 cases of dMCL injury with different causes. The first case involves a 25-year-old male athlete with a traumatic valgus injury, while the second case is a 63-year-old man with nontraumatic medial knee pain and underlying degenerative changes. Both patients underwent ultrasound-guided PRP injections after not responding to conservative management. The PRP preparation involved centrifugation of autologous blood to obtain leukocyte-rich PRP, which was then injected into the meniscotibial ligament (MTL) under ultrasound guidance. The injection was performed using a high-frequency linear transducer to visualize the dMCL and guide the needle precisely into the injured area of the MTL. The in-plane approach ensured optimal placement, minimizing the risk of inadvertent tissue damage.
Results:
Both patients demonstrated significant pain reduction and functional improvement within 4 weeks postinjection. The athlete successfully returned to football, and the older patient resumed brisk walking without discomfort. Follow-up showed no recurrence of symptoms. Key considerations for PRP therapy include careful patient selection, individualization of PRP therapy, familiarity with the different PRP preparation systems, and proper patient education for managing expectations regarding treatment outcomes. Technical proficiency in ultrasound-guided injections is essential for accurate PRP delivery, minimizing procedural errors, and maximizing therapeutic benefits.
Discussion/Conclusion:
dMCL injuries can cause persistent medial knee pain that is unresponsive to conservative treatment. PRP therapy presents a promising option for promoting ligament healing, with ultrasound guidance improving precision and potentially optimizing outcomes. However, further research is needed to establish standardized protocols for PRP formulation, dosing, and long-term efficacy.
Patient Consent Disclosure Statement:
The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.
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Keywords
Video Transcript
This video journal discusses the clinical technique of ultrasound-guided platelet-rich plasma (PRP) injection for deep medial collateral ligament (dMCL) injury.
We have no disclosures.
Background
The medial collateral ligament (MCL) stabilizes the knee against valgus stress and external rotation during flexion.6,8 It consists of 3 layers, the deepest of which is the dMCL. The dMCL originates from the medial femoral epicondyle and inserts on the tibia just below the joint line. Its attachment to the medial meniscus divides it into the meniscofemoral ligament (MFL) and meniscotibial ligament (MTL). The dMCL is a part of the meniscocapsular complex, and its injury can cause anteromedial rotatory instability (AMRI). 7
Isolated dMCL injuries present with medial-sided knee pain, often after a sudden valgus stress. However, nontraumatic dMCL abnormalities can occur, particularly in knees with degenerative changes of the medial compartment.2,12
A retrospective review categorized MCL injuries into 3 groups based on trauma history and magnetic resonance imaging (MRI) findings. Group 1 (average age 35 years) included patients with traumatic valgus injuries and MRI findings of edema in all MCL layers, with fiber disruption. Group 2 (average age 47 years) had nontraumatic medial knee pain with a medial meniscus tear but no significant joint degeneration. Group 3 (average age 51 years) had nontraumatic pain with significant joint degeneration. MCL edema was likely due to friction from marginal osteophytes. 12
A key finding in dMCL injury on clinical examination is localized tenderness on the dMCL sulcus, corresponding to the proximal MFL or distal MTL. 8 This is distinct from joint line tenderness, which typically suggests meniscal pathology.
Assessment of MTL disruption includes palpation over the medial meniscus during valgus stress testing to detect peripheral meniscal subluxation. With MTL disruption, the anterior drawer test with the tibia in external rotation may produce anterior subluxation of the medial tibia, indicating AMRI. 7
MRI is the preferred imaging modality. In acute trauma, it may show edema in multiple MCL layers with or without fiber disruption. 12 In chronic cases, the key finding is thickened tissue with an intermediate signal, consistent with hypertrophic scarring. 8 However, MRI may not always reveal the full extent of medial knee injuries.6,8
Ultrasonography complements physical examination by providing real-time dynamic imaging. The MCL's superficial location allows high-resolution visualization. It is affordable and accessible, and it enhances the precision and safety of procedures, such as platelet-rich plasma (PRP) injections. 10
On ultrasound, an injured dMCL appears as a thickened, echogenic band from the medial femoral epicondyle to the anteromedial tibia, with neovascularization on color Doppler. 8
There is no standard treatment for dMCL injuries. Most isolated cases resolve with 5 to 8 weeks of bracing and physical therapy. Persistent symptoms may benefit from ultrasound-guided corticosteroid and PRP injections, as well as extracorporeal shock-wave therapy. 13 Surgery is typically considered for active individuals or athletes who do not respond to conservative treatment.
PRP therapy supports healing by stimulating fibroblast and tenocyte activity, increasing organized collagen production, and upregulating collagen type I gene expression, leading to improved tissue biomechanics. 3
Indications and Results
We will present 2 patients with medial knee pain but different demographic profiles and mechanisms of injury. Our first patient is a 25-year-old male competitive football player with right medial knee pain after a valgus injury. He had tenderness over the distal dMCL sulcus, with no laxity on the valgus stress test. Bedside ultrasonography revealed MTL tenderness on sonopalpation, intrasubstance hypoechogenicity, and neovascularization. The diagnosis was a right knee dMCL tear. After 2 months of knee bracing and physical therapy, pain persisted. Therefore, an ultrasound-guided PRP injection into the MTL was done. Immediate knee range of motion and weightbearing were permitted. After 2 weeks, strength exercises were gradually resumed. After 4 weeks, pain improved, and the patient resumed football. At the 4-year follow-up, there was no symptom recurrence.
Our second patient is a 63-year-old man who regularly brisk walks, with gradual-onset left medial knee pain for 2 months and no history of trauma. He had tenderness over the distal dMCL sulcus and pain on a valgus stress test without laxity. The MRI showed a stable degenerative medial meniscus posterior horn tear, with the MCL appearing normal. Bedside ultrasonography revealed tenderness on sonopalpation of the MTL over a marginal osteophyte, with MTL intrasubstance anechoic defect and neovascularization. The diagnosis was a left knee dMCL tear. As with the previous case, conservative management failed, and ultrasound-guided PRP injection into the MTL was planned.
Technique Description
Our preparation kit uses 8 to 10 mL of whole blood mixed with anticoagulant, then centrifuged for 9 minutes at 1500 ×g. This separates plasma and platelets from red and white blood cells. The yellow solution seen at the topmost layer contains plasma, and just above the thixotropic gel lie the platelets. Below the gel are the red and white blood cells.
Excess plasma is discarded, leaving about 1 mL above the platelet layer. The tube is gently inverted to suspend the platelets, forming the PRP, which is then drawn into a syringe. The final concentration was approximately 1.25 × 106/µL.
The patient was positioned supine with the left hip externally rotated and knee slightly flexed. The probe was placed in the coronal plane over the point of tenderness on the tibial MCL.
On ultrasound, the tibia and femur appeared as hyperechoic lines, with the medial meniscus between them and the superficial MCL above. An anechoic defect deep to the superficial MCL indicated an MTL tear, with increased Doppler signal. After prepping a sterile field, an in-plane approach was used to guide the needle to the defect, where PRP was injected under direct visualization.
The posttreatment rehabilitation was similar to the previous case. After 4 weeks, the pain resolved, and the patient resumed regular brisk walking. At 9 months, he remained symptom-free.
Discussion
The first clinical documentation of PRP therapy for acute MCL injury was in 2013. A professional football player who sustained an isolated superficial and deep MCL injury received 3 doses of PRP injections into the MCL. Within a month, the patient was able to return to competitive play with no residual symptoms. 5
In a randomized controlled trial in 2024, the effectiveness of ultrasound-guided PRP therapy was compared with pulsed ultrasound therapy in 32 athletes with MCL partial tears. Although both groups showed significant improvements in pain and knee function, ultrasound-guided PRP therapy offered superior short-term benefits, particularly up to the sixth week posttreatment. 4 These studies suggest that PRP therapy may expedite recovery in acute MCL injuries, enabling athletes to return to play sooner than traditional conservative treatments, as was the case with our first patient.
In a case series by Jones et al, 8 persistent medial knee pain after conservative management of low-grade MCL injuries may be attributed to pathology within the dMCL. Ultrasound-guided injections of local anesthetic and corticosteroid were administered into the dMCL. At an average follow-up of 20 months, 96% of patients had returned to their preinjury level of work. These findings support our assessment in our second patient, in whom persistent medial knee pain was ultimately attributed to a dMCL injury confirmed by ultrasonography.
PRP composition affects its therapeutic impact, primarily based on leukocyte concentration. Leukocyte-poor PRP (LP-PRP) with reduced inflammatory cytokines may help reduce chronic inflammation, such as in osteoarthritis. Leukocyte-rich PRP (LR-PRP) triggers a stronger inflammatory response, which may be beneficial in failed healing processes, such as those associated with chronic tendinopathy and ligament injuries. 1 This rationale guided our use of LR-PRP for treating chronic dMCL injury in our patient.
Successful PRP therapy for dMCL injuries begins with recognizing different patient profiles, traumatic and nontraumatic, as in our cases. Careful patient selection is important. Ideal candidates are those who have not responded to conservative treatment and in whom other causes of medial knee pain, like meniscal injury, have been ruled out. The patient's overall health should also be considered, as systemic conditions may affect the quality of the PRP harvested for treatment.
Individualizing PRP therapy is crucial. LP-PRP is preferred when minimizing inflammation, and LR-PRP is recommended for conditions with impaired healing. 1 Since different PRP devices yield varying concentrations, familiarity with the specific system used can help optimize treatment.
Managing patient expectations is essential. Patients should be informed of PRP's limitations, including the lack of standardized preparation and administration protocols, as well as the variability in long-term outcomes.
Proficiency in ultrasound is essential for accurate PRP delivery. For MCL assessment, position the leg in external rotation with 10° to 20° of knee flexion. Align the probe longitudinally over the medial femoral condyle, slide 4 to 5 mm posteriorly to visualize superficial and deep MCL layers, and then move distally to identify the MFL and MTL.
While PRP is generally considered safe, the potential adverse effects include (1) postinjection flare-ups, described as temporary pain, redness, and swelling, mainly linked to LR-PRP 6 ; (2) skin infection; (3) lack of response; (4) tendon rupture, reported in a case involving degenerative tendinopathy 11 ; and (5) diminished ligament healing, reported in a laboratory study on rabbits, in which high PRP concentrations, up to 4 times the baseline, negatively affected ligament strength and collagen organization. 9
Conclusion
Deep MCL injuries, whether traumatic or degenerative, can cause chronic medial knee pain unresponsive to conservative treatment. PRP therapy shows promise in promoting ligament healing, reducing pain, and improving function. As seen in our cases, ultrasound-guided PRP injection enhances delivery accuracy. However, more research is needed to confirm long-term efficacy and establish standardized protocols.
Footnotes
Submitted April 2, 2025; accepted April 28, 2025.
The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
