Working Diagnosis:
Fibular hemimelia with congenitally absent ACL. New cause of pain was suspected to be the acute meniscal tear.

Treatment:
Given improvement of pain and function upon follow-up, non-operative treatment was opted with patient education on permanent laxity of her knee.

Outcome:
Given improvement of pain and swelling, the patient opted conservative management, followed by a formal course of physical therapy. She was able to gradually increase her mileage in hiking over the next four weeks without any mechanical instability.

Editor's Comments:
Fibular hemimelia is the most common lower limb congenital long bone deficiency, which occurs in approximately 5.7-20 cases per 1 million births (1). In unilateral cases, the right side is more commonly involved with frequent tibial bowing and absent or deficient foot rays/toes (1). ACL aplasia or hypoplasia is very commonly associated with fibular hemimelia (2). In addition, PCL hypoplasia and meniscus anomalies such as tears of the posterior horn of the medial meniscus are also found in patients with ACL aplasia (3). This case highlights how commonly associated asymptomatic congenital deficiencies (i.e. fibula, ALC, and PCL) may present as a red herring to true pathology (meniscus tear). It is important to differentiate between pathology and asymptomatic congenital deficiencies for optimal management and return to activity in such patients. While imaging may indicate certain abnormalities, treatment decisions should be based patient presentation in terms of pain and function. In a patient with minimal pain and limited mechanical symptoms, conservative treatment can be pursued.

References:
1 Monteagudo A, Dong R, Timor-Tritsch IE (2006). "Fetal Fibular Hemimelia
Case Report and Review of the Literature." J Ultrasound Med 2006 25: 533-537.


2. Walker JL et al. (2019). "Classification of Cruciate Ligament Dysplasia and the
Severity of Congenital Fibular Deficiency." J Pediatr Orthop 39: 136-140.


3. Kambhampati SBS et al. (2022). "Management of Anterior Cruciate Ligament Aplasia
for the Arthroscopy Surgeons: A Systematic Review." Indian Journal of Orthopaedics 56: 1123-1138.

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