Patellar Instability in Adolescents: A Comprehensive Approach to Diagnosis and Management

Patellar instability, a common concern among adolescents, encompasses a spectrum of conditions ranging from subtle subluxation to complete dislocation of the kneecap. This article delves into the evaluation and management of a 16-year-old female presenting with recurrent patellar instability following a traumatic event, highlighting the importance of timely diagnosis and tailored treatment strategies.

Case Presentation

A 16-year-old female high school student with a history of recurrent patellar instability presented with left knee pain after a patellar dislocation. The injury occurred when stepping onto a slippery surface, causing internal rotation of the knee and lateral patellar dislocation. Spontaneous reduction occurred, but she was unable to ambulate due to pain, swelling and a sensation of instability. Prior conservative management included anti-inflammatory medications, bracing, activity modification, and physical therapy, without lasting relief. The patient is not an athlete.

Clinical Examination and Imaging

Physical examination revealed a large effusion, tenderness along the medial and lateral retinacula, and limited range of motion (0° to 20° flexion) due to pain. The patellar apprehension test was positive, indicating patellar instability. Ligamentous stability was confirmed with varus and valgus stress testing. Initial radiographs demonstrated an osteochondral injury at the median ridge of the patella. Magnetic Resonance Imaging (MRI) revealed a large effusion, a significant chondral defect in the medial facet, a loose body in the lateral recess, attenuation of the medial patellofemoral ligament (MPFL), and a normal tibial tubercle to trochlear groove (TT-TG) distance of 12.3 mm.

Management Strategy

Given the patient’s worsening instability refractory to conservative measures and the presence of a large loose osteochondral body, surgical intervention was recommended. Options discussed with the patient and her family included arthroscopic removal of the loose body, potential osteochondral fragment fixation, and MPFL repair, with consideration for a staged matrix-induced autologous chondrocyte implantation (MACI) procedure if the fragment was unsuitable for fixation.

Surgical Technique

The patient underwent arthroscopic surgery under general anesthesia with a tourniquet applied. Standard anterolateral and anteromedial portals were established. Diagnostic arthroscopy confirmed a large osteochondral defect involving most of the medial patellar facet. The trochlea, menisci, and cruciate ligaments were intact. A large osteochondral fragment was identified and removed from the lateral gutter. A medial parapatellar arthrotomy was performed, and the patella was everted to expose the osteochondral defect. The fragment, measuring 13.2 x 27 mm, was debrided and reduced into the defect, secured with three Kirschner wires, and then fixed with three resorbable compression screws and fibrin glue. The MPFL was imbricated and repaired with Vicryl suture. The capsule was closed, and a hinged knee brace was applied in extension.

Postoperative Course

Postoperative follow-up at 2 weeks, 6 weeks, 3 months, and 6 months revealed no recurrent instability or complications. The patient regained full, painless range of motion and adhered to her rehabilitation protocol. At 6 months, she achieved full extension and 140° of flexion, with a negative patellar apprehension test. Radiographs showed a congruent patellofemoral joint and stable osteochondral fragment reduction with evidence of reintegration.

Discussion

Adolescents with patellar instability are prone to osteochondral injuries due to their skeletal immaturity. Early recognition and advanced imaging, particularly MRI, are crucial for evaluating cartilage integrity, identifying loose bodies, and assessing MPFL injury. Surgical management should address both bony and soft-tissue contributors to instability. In this case, combining osteochondral fragment fixation with MPFL repair allowed for anatomic restoration of the patellofemoral joint and preserved the native cartilage surface. Successful fixation requires careful assessment of fragment viability and appropriate surgical technique, along with a dedicated rehabilitation program.

Key Takeaways

• Adolescents with patellar instability are susceptible to osteochondral injuries.
• Early imaging, especially MRI, is essential for accurate diagnosis and treatment planning.
• Combined osteochondral fragment fixation and MPFL repair can provide excellent functional outcomes.

For More Information

Kevin Credille, MD; Sanjiv Gopalkrishnan, MD, MBA; Robert Jack, MD; and Jennifer Liu, MD, can be reached at Houston Methodist Hospital in Houston, Texas. kcredille@houstonmethodist.org, svgopalkrishnan@houstonmethodist.org, jwliu@houstonmethodist.org, rajack@houstonmethodist.org.

Edited by Mitchell F. Bowers, MD, and Jennifer Liu, MD.